Symposium Organizers
David Gracias Johns Hopkins University
Ritesh Agarwal University of Pennsylvania
Pavle Radovanovic University of Waterloo
Joerg Ackermann Universite de la Mediterranee
JJ1: Nanowire Growth
Session Chairs
Monday PM, November 26, 2007
Room 306 (Hynes)
9:30 AM - **JJ1.1
Epitaxial Silicon and Silicon/Germanium Nanowires.
Ulrich Goesele 1 , Stefan Senz 1 , Volker Schmidt 1 , Peter Werner 1 , Alexeij Milenin 1 , Yewu Wang 1 , Tomohiru Shimizu 1
1 , Max Planck Institure of Microstructure Physics, Halle Germany
Show AbstractVarious methods of fabricating epitaxial silicon nanowires and silicon/germanium heterostructure nanowires will be described and compared including VLS and VSS growth and various kinds of plasma and chemical etching. The use of various templates such as nanoporous alumina to grow nanowires in <100> direction will be discussed as well as the use of a solid catalyst such as aluminum to grow silicon nanowires. Varous promising approaches to grow epitaxial heterostructure Si/Ge nanowires with sharp interfaces will be presented.
10:00 AM - JJ1.2
Using pn Junction Depletion Regions to Position Epitaxial Nanowires.
Nate Quitoriano 1 , Ted Kamins 1
1 , HP Laboratories, Palo Alto, California, United States
Show AbstractSemiconductor nanowires have promising properties to possibly augment or replace top-down, lithographically defined Si MOSFET (metal oxide semiconductor field effect transistor) channels because of their small, bottom-up-defined diameters. [1,2] One major difficulty in using nano-scale structures is controlling their location. It is possible to demonstrate ten, or even 100, devices by individually manipulating and connecting them, a technique which has demonstrated the promising device properties of nano structures. [3,4,5] However, to utilize nano structures to their full capability, thousands or millions of individual nano structures must be used in each system. To this end, we present a technique that shows promising results for controlling the location of nanowires by controlling the location of Au catalyst nanoparticles, which are necessary for nanowire formation using the vapor-liquid-solid (VLS) method.In this work, we use the negative charge on citrate stabilized Au nanoparticles to aid in placing them along a specific line. The line is defined close to the metallurgical junction between a lightly-doped, p-type Si substrate and a heavily doped, n-type region. Near the metallurgical pn junction, an electric field is formed by the positive and negative charge of the depletion region. Since the Au nanoparticles have a negative charge, they are attracted to the positively charged depletion region of the n-type material and repelled by the depletion region of the negatively charged, p-type material. We study the effects of different structures and applied voltages in positioning Au nanoparticles along this junction and then use these nanoparticles as catalysts for Si nanowire growth. Vertical {111} surfaces were formed by etching a (110) Si substrate covered with an epitaxial layer of the opposite conductivity type and catalyst nanoparticles were positioned as described above. We find that highly-doped, n-type material forming a junction with lightly-doped, p-type material is the best structure to use to focus the Au particles. Also, applying a reverse bias across the junction increases the positive charge in the n-type material’s depletion region, thereby enhancing the electric field and better focusing the nanoparticles along the line on the vertical surface.Si nanowires were then grown horizontally from the vertical {111} surfaces using these catalyst nanoparticles and the VLS method. Substantial alignment of the nanowires was achieved.[1] V. Schmidt, H. Riel, S. Senz, S. Karg, W. Riess, and U. Gosele, Small 2, (2006).[2] J. Goldberger, A. I. Hochbaum, R. Fan, and P. Yang, Nano Letters 6, (2006).[3] X. Duan, Y. Huang, Y. Cui, J. Wang, and C. M. Lieber, Nature 409, 681 (2001).[4] Y. Huang, X. Duan, Q. Wei, and C. M. Lieber, Science 291, 550 (2001).[5] Y. Cui, L. J. Lauhon, M. S. Gudiksen, J. Wang, and C. M. Lieber, Appl. Phys. Lett. 78, 1 (2001).
10:15 AM - JJ1.3
Fabrication of Oriented and Ordered GaAs Nanowire Arrays on GaAs(111)B and Si(111) Substrates Using Metal-organic Chemical Vapor Deposition.
Jeff Cederberg 1 , A. Talin 2 , Doug Nelson 1 , Karen Cross 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , Sandia National Laboratories, Livermore, California, United States
Show AbstractSemiconductor nanowires are being investigated intensively, motivated by a desire to discover and manipulate physics at nanometer dimensions. The result of these investigations may be electronics and optoelectronics with characteristics superior to what is currently available. These fundamental and applied interests drive the materials research and development of nanowires for all types of materials. An issue that remains under investigation is the formation of dense arrays of nanowires with uniform dimensions. We are investigating the formation of ordered GaAs nanowire arrays. Our approach utilizes the controversial vapor liquid solid/vapor solid solid (VLS/VSS) technique using Au to “catalyze” nanowire growth. The first technique forms a template by having Au films, 0.5 to 3.0 nm in thickness, deposited on GaAs(111)B and Si(111) substrates. The template was then annealed under AsH3 at 650°C to disperse the Au prior to cooling to 450°C. A metal-organic chemical vapor deposition system was used to control the growth. Our work has been able to compare trimethylgallium to triethylgallium as group III sources. Growth was performed for times ranging from 10 to 50 minutes. This technique forms a large distribution of diameters, but generates large (5 cm) arrays that are preferentially oriented normal to the growth surface. We have discovered that a small thickness of Au (1 nm and under) leads to a higher fraction of oriented nanowires. As the nanowires get longer than 2 µm, a larger fraction of them kink and deviate from the (111) orientation. Oriented nanowires are only part of the picture. Techniques to control the diameter and placement of these structures are needed. To address this need, we are investigating nano-imprint lithography to form arrays of nanowires. Nano-imprint lithography allows features that are tens of nanometers to be generated in a fixed pattern. Au seeds with a 200 nm diameter on a 600 nm pitch were deposited by metal lift-off. Square arrays approximately 2.5 cm on a side were fabricated. Using the conditions established from planar Au film experiments, we have shown it is possible to form localized nanowires with high fidelity. This result indicates that patterned-substrates represent a route to controlled density and placement of nanowires. Nano-imprint lithography is especially well suited to fabrication of large nanowire arrays with the desired geometrical control. Sandia is a multiprogram laboratory operated by Sandia Corporation , a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.
10:30 AM - JJ1.4
Ion Implanted GaAs Nanowire Pn-junctions.
Gutsche Christoph 2 , Werner Prost 2 , Franz-Josef Tegude 2 , Daniel Stichtenoth 1 , Carsten Ronning 1
2 Institute of Semiconductor Technology, University of Duisburg-Essen, Duisburg Germany, 1 II. Institute of Physics, University of Goettingen, Goettingen Germany
Show AbstractIon beam doping of materials offers advantages in comparison to doping during growth or by diffusion. First, the impurity concentrations as well as the lateral and depth distribution of the dopants are precisely controllable, and secondly, almost all elements can be implanted with sufficient high purity even beyond any solubility limit. However, doping by ion implantation is hampered by the created radiation damage, but this can be removed by thermal treatment.Here, we will report on studies in order to fabricate GaAs nanowires pn-junctions. Nominal undoped GaAs nanowires were grown according to the VLS mechanism using Au nanoparticles on top of Si(100) substrates. Zinc as an acceptor was implanted with different ion energies in such samples in order to create a box-like implantation profile matching the diameter of the GaAs nanowires. Subsequently, the samples were re-insert into the MOCVD system and the growth of the nanowires was continued, but with the addition of Si donors. This growth at high temperatures not only resulted into n-type material, but also also in annealing of the implantation defects of the first section of the nanowires. Finally, the pn nanowires were cut of the growth substrate, and processed with contacts on top of new insulating substrates. First results on the electrical characterization will be presented and discussed in this presentation.
10:45 AM - JJ1.5
Silicon / Nickel-silicide Axial Nanowire Heterostructures for High Performance Electronics.
Walter Weber 1 2 , Lutz Geelhaar 1 , Eugen Unger 3 , Caroline Cheze 1 , Franz Kreupl 3 , Henning Riechert 1 , Paolo Lugli 2
1 , Qimonda Dresden and NaMLab, Dresden Germany, 2 Institute for Nanoelectronics, Technische Universitaet Muenchen, Munich Germany, 3 , Qimonda AG, Munich Germany
Show AbstractSemiconducting and metallic nanowires (NW) are widely investigated as potential building blocks for future electronic devices. Silicon and nickel silicide NWs are particularly interesting, because these materials are currently used as bulk materials in the volume production of highly integrated circuits. In this work, intrinsic Si and NiSi2 NWs as well as NiSi2/Si/NiSi2 axial NW heterostructures are fabricated and investigated electrically. Si NWs are grown by Au-catalyzed chemical vapor deposition. Axial segments of the Si-NWs are transformed into metallic ones by a longitudinal silicidation process. To this end, Si-NWs are contacted with a Ni reservoir at one of their ends. Annealing leads to longitudinal Ni diffusion inside the NWs for lengths of up to several micrometers. Along the diffusion path, single crystalline NiSi2 NW segments are formed in a solid-state reaction [1]. The interface between the NiSi2 and the pristine Si segment has a sharpness on the nanometer scale. This axial silicidation reaction is different from previous NW silicidation findings, since those ones only observed radial Ni diffusion [2]. Fully Ni-silicided NWs have an ohmic behavior and a resistivity of at most 98 μΩ-cm as determined by two point IV measurements. Moreover, NiSi2 NWs conduct current densities of up to 205 MA/cm2 before breakdown. This high value is within the same order of magnitude as that of metallic carbon nanotubes and higher than that of Cu nano-interconnects. Schottky barrier (SB) field effect transistors (FET) are fabricated by a controlled NiSi2 formation from both NW-ends, leaving a pristine Si segment in the middle which constitutes the active region. Gate control is performed by a common back gate stack. The NiSi2 NW-segments extend the source and drain contacts, reducing the length of the active region, e.g. from 1 µm to 20 nm. Hence, this method gives simple access to fabricate nanoscale Si regions by only employing a single and coarse optical lithography step to structure the Ni reservoirs. Although undoped, the FETs exhibit unipolar p-type behaviour if the NW diameter is below 30 nm. For thicker NWs, the behavior is increasingly ambipolar. Such a NW heterostructure SB-FET has the advantage over a common SB-FET contacted by a large pad; that for geometrical reasons the gate field is enhanced at the needle-like Schottky contacts. Therefore, gate control over SB-width and carrier transmission is optimized as shown by electrostatic calculations. Consequently, modulation of over 10^7 and subthreshold slopes as low as 110 mV/dec are achieved. Moreover, these SB-FETs exhibit the highest current densities in the on-state reported up to date for intrinsic Si-NW FETs, amounting to 0.8 MA/cm2 at 1 V bias. These results reflect the performance improvement of one dimensional metal to semiconductor heterostructures in comparison to bulk devices. [1] W. M. Weber et al. Nano Lett. 6, 2660 (2006)[2] Y. Wu, et al. Nature 430, 61 (2004)
11:30 AM - **JJ1.6
Abstract Not Available
Charles Lieber 1
1 Department of Chemistry & Chemical Biology, Harvard University, Cambridge, Massachusetts, United States
Show Abstract12:00 PM - JJ1.7
Using Real Time Microscopy to Quantitatively Determine NucleationMechanisms and Kinetics during the Growth of Si Nanowires on Si3N4Substrates.
Bong Joong Kim 1 , Jerry Tersoff 2 , Suneel Kodambaka 3 , Frances Ross 2 , Eric Stach 1
1 School of Materials Engineering & BIrck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 2 , IBM T.J. Watson Research Center, Yorktown Heights, New York, United States, 3 Department of Materials Science & Engineering, University of California, Los Angeles, Los Angeles, California, United States
Show AbstractA comprehensive understanding of vapor-liquid-solid (VLS) nanowiregrowth mechanisms and kinetics is of considerable importance for structuraloptimization of nanoscale wires with desired properties. Despite over 40years of research, little has been reported on nanowire nucleation. Here, wereport, for the first time, real time transmission electron microscopy (TEM)measurements of the nucleation kinetics of Au-catalyzed Si nanowires. Ourdirect observations of Au mediated Si nanowire nucleation span from initialobservations of the pure solid Au catalyst to final nanowire nucleation. Ourmeasurements show that the nucleation time is linearly proportional to thediameter of the AuSi alloy drop – contrary to behavior expected from theGibbs-Thomson effect – and that the nucleation rate linearly increases withdisilane pressure. These two observations indicate that the rate limiting stepthroughout the processs is the thermally activated dissociative adsorptionof disilane on the catalyst surface. Furthermore, we classify the subsequentnucleus growth process of Si nanowires into three regimes: an initial rapidgrowth of the nucleus, a subsequent slow growth of the nucleus, followedby axial growth of the nanowires away from the AuSi drop. We show thatfor the initial growth, the growth rate (dr/dt) is simply proportional to thecritical supersaturation required to nucleate the nanowire. Additionally,during the slow growth regime and final nanowire growth, the growth rate isproportional to the ratio between the surface area of the AuSi alloy and the Sinucleus. These observations are in an excellent agreement with a theoreticalmodel we have proposed for nanowire nucleation kinetics. Finally, using thismodel we are working to extract the critical supersaturation of Si at which nanowire nucleation occurs, leading to the determination of an effective, kinetically controlled liquidus line in the binary phase diagram. These quantiative measurements yield critical data needed for controlling nanowire nucleation during the fabrication of high performance nano-electronic devices based on these structures.
12:15 PM - JJ1.8
Synthesis of Epitaxially-Aligned Ge/Si Core-Shell Nanowires.
Irene Goldthorpe 1 , Paul McIntyre 1
1 Department of Materials Science, Stanford University, Stanford, California, United States
Show AbstractDepositing a Si or SiGe film around a Ge nanowire (NW) creates a structure which may have additional advantageous properties beyond that of a single-element Si or Ge NW. A heteroepitaxially grown shell may allow for engineering of strain in both the shell and the inner core. Moreover, the valence band offset may allow confinement of holes to the core, reducing the influence of surface defects on carrier scattering in p-type NWs. The Ge-core/Si or SiGe-shell arrangement is desirable for the higher carrier mobilities of Ge and the superior properties of SiO2 passivation.In this work, vertically aligned arrays of Ge/Si and Ge/SiGe core-shell NWs have been synthesized by CVD. First, <111> Ge NWs were heteroepitaxially grown on Si (111) substrates; the NW diameter was controlled through the use of monodisperse Au nanoparticles as the catalysts. Silane, with or without germane, was then used to deposit the shell. The Au remaining on the Ge NW tips is problematic since (i) the Au can catalyze unwanted Si NW growth and (ii) the Au particles at the NW tips diffuse into the structure at the temperatures required to obtain single crystalline shells. We have found that Ge NWs dissolve in commercially available wet chemical Au etchants. We will present a KI/I2-based wet etching procedure for Au removal from Ge NWs that does not significantly etch the Ge so that a heteroepitaxial Si or SiGe shell can subsequently be deposited. The resulting core-shell NWs were characterized with transmission electron microscopy to determine their defect and stress states.
12:30 PM - JJ1.9
Failure and Formation of Axial Nanowire Heterostructures in Vapor-Liquid-Solid Growth.
Mohanchand Paladugu 1 , Jin Zou 1 2 , Ya-Nan Guo 1 , Graeme J. Auchterlonie 2 , Hannah J. Joyce 3 , Qiang Gao 3 , H. Hoe Tan 3 , Chennupati Jagadish 3 , Yong Kim 4
1 School of Engineering, The University of Queensland, Brisbane, Queensland, Australia, 2 Centre for Microscopy and Microanalysis, The University of Queensland, Brisbane, Queensland, Australia, 3 Department of Electronic Material Engineering, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, Australian Capital Territory, Australia, 4 Department of Physics, Dong-A University, Busan Korea (the Republic of)
Show AbstractSemiconductor nanowires and their associated heterostructures have many potential applications in nanoelectronic and nano-optoelectronic devices owing to their unique physical properties, which have drawn extensive research attention in the past decade. The vapor-liquid-solid (VLS) mechanism has been a widely used mechanism for the growth of semiconductor nanowires and their heterostructures. In typical VLS growth, metal nanoparticles are deposited on a substrate surface and heated to the growth temperature under the vapor species of growing material. Nano-sized metal liquid droplets form and then catalyze nanowires growth, so that the nanowires have metal particles at their growth fronts. Au nanoparticles have been widely used to catalyze the nanowires and nanowire heterostructures growth. Axial nanowire heterostructures can be grown by altering the chemical composition of vapor species during the nanowires growth and subsequent achievement of respective compositional alteration along the nanowire growth axis.Successful axial growth of GaAs on InAs nanowires using Au nanoparticles have been reported in the literature. In this work, InAs nanowire sections were grown on GaAs nanowire sections through VLS mechanism using Au nanoparticles. Axial growth failure of InAs on GaAs nanowires was observed through transmission electron microscopy (TEM) characterizations with a sequence of : (i) the initial InAs clustering at an edge of the Au/GaAs interface displaces the Au droplet with respect to its underlying GaAs nanowire; (ii) the Au droplets move sidewards and then downwards with further growth of InAs by preserving an interface with the GaAs sidewalls. The fundamental reason for this failure of InAs axial growth on GaAs nanowires and feasibility of GaAs axial growth on InAs nanowires has been determined by quantifying the interfacial energies between Au-InAs, Au-GaAs and InAs-GaAs at equilibrium. This quantification is done by adopting the model proposed for description of heterogeneous nucleation of a solid from liquid metal along a solid wall of a mold. We use this model because, in our case, the Au particles are in the liquid form during the nanowire growth and GaAs and InAs can act as the wall of the mold and nucleated solid, respectively. Through this quantification, we found that the axial growth failure of InAs on GaAs nanowires is due to higher interfacial energy between Au-InAs than that between Au-GaAs.Thermodynamically, following conclusion can be drawn from this work. When a nanowire axial heterostructure is to be grown with two materials combination “A” and “B” using catalyst particle “C”, and if the interfacial energy between A and C-droplet is higher than that between B and C-droplet, the axial growth of A on B fails, whereas axial growth of B on A is feasible.
12:45 PM - JJ1.10
InAs/InP Radial Nanowire Heterostructures: Rational Design, Controlled Synthesis and High Performance Devices.
Xiaocheng Jiang 1 , Qihua Xiong 1 , Sungwoo Nam 2 , Fang Qian 1 , Yat Li 1 , Charles Lieber 1 2
1 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 2 School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts, United States
Show AbstractRadial core/shell nanowire heterostructures represent important one-dimensional building blocks with substantial potential for tuning materials electronic and photonic properties. Specifically, it is possible to create structures with novel properties through the rational choice of core/shell materials coupled with highly-controlled synthesis. Here, we report the rational design, synthesis and properties of InAs/InP core/shell nanowires as a new one-dimensional electron gas (1DEG) system. Transmission electron microscopy studies revealed uniform, crystalline InP shell growth and clean, epitaxial interfaces between InAs core and InP shell. In addition, energy-dispersive X-ray spectroscopy analysis further confirmed the composition of the designed core/shell nanowire heterostructure. Room-temperature electrical measurements on InAs/InP nanowire field-effect transistors (FETs) showed significant improvement of the on-current and transconductance compared with InAs nanowire FETs fabricated in parallel. Notably, analysis of these transport data yield an electron mobility of 11,500 cm2/V-s that exceeds substantially values previously reported for n-channel nanowire and nanotube devices. In addition, high-performance FET devices were fabricated by incorporating a high-κ dielectric and top-gate geometry. Studies of these top-gated InAs/InP nanowire FET structures yielded a scaled on-current value of 3.2 mA/μm at a bias of 0.5 V, which is larger than any other n-channel electronic devices up to date. The designed 1DEG in InAs/InP core/shell nanowires opens up opportunities for exploring our fundamental knowledge of nanoscale building blocks, and also the development of quantum coherent transport devices and high-speed, low-power nanoelectronic circuits.
JJ2: Nanowire Device Integration
Session Chairs
Monday PM, November 26, 2007
Room 306 (Hynes)
2:30 PM - **JJ2.1
CMOL: A Challenge For Nanowire Technology.
Konstantin Likharev 1
1 , Stony Brook University, Stony Brook, New York, United States
Show AbstractI will review the recent work on devices, circuits and architectures for possible hybrid semiconductor/nanodevice integrated circuits based on nanowire crossbars, with similar, simple, two-terminal devices (with the functionality of programmable diodes) formed at each crosspoint [1-5]. Special attention will be given to the d “CMOL" variety of the hybrids, in which the crossbar is connected to the underlying CMOS circuit with an area-distributed interface [3-5]. Such interface allows the CMOS subsystem to address each and every of the crosspoint devices, even with no nanoscale alignment between the CMOS and crossbar subsystems. Recent detailed studies have shown CMOL may enable (at least) the following applications:(i) terabit-scale memories with access time below 100 ns and defect tolerance up to 10% [6],(ii) FPGA-like reconfigurable logic circuits with the area-by-delay product at least two orders of magnitude lower than that of CMOS FPGAs [5, 7, 8], and(iii) mixed-signal neuromorphic networks (“CrossNets”) [9] which may provide unparalleled performance for some important information processing tasks including pattern classification [10], and in future may become the first hardware basis for challenging the human cerebral cortex. Recently, the hybrid circuit concept has received a strong boost from the announcement of reproducible fabrication of the necessary crosspoint devices (programmable diodes) using copper oxide [11] and the demonstrations of nanowire crossbars with 15-nm-scale half-pitch [12, 13].In order to fight with advanced nanolithography for their application in CMOL circuits, nanowire technologies face tough challenges including low specific and interface resistances, tight chirality control, and (most importantly) a nm-scale placement accuracy. The work has been supported in part by AFOSR, MARCO via FENA Center, and NSF.[1] K. K. Likharev, in: Nano and Giga Challenges for Microelectronics, Springer, Berlin, 2003, pp. 27-68.[2] P. J. Kuekes, G. S. Snider, and R. S. Williams, Sci. American., vol. 293, pp. 72-76, Nov. 2005.[3] K. K. Likharev and D. B. Strukov, in: Introducing Molecular Electronics, Springer, Berlin, 2005, pp. 447-477.[4] G. Snider, and R. S. Williams, Nanotechnology, vol. 18, art. 035204, Jan. 2007.[5] D. Tu et al., preprint, Feb. 2007.[6] D. B. Strukov and K. K. Likharev, J. of Nanoscience and Nanotechnology, vol. 7, pp. 151-167 , Jan. 2007. [7] D. B. Strukov and K. K. Likharev, Nanotechnology, vol. 16, pp. 888-900, June 2005.[8] D. B. Strukov and K. K. Likharev, in: Proc. FPGA’06, pp. 131-140.[9] Ö. Türel et al., Int. J. of Circ. Theor. Appl., vol. 32, pp. 277-302, Sep./Oct. 2004.[10] J. H. Lee and K. K. Likharev, Int. J. of Circuit Theory and Applications, vol. 35, pp. 239-264, Jan. 2007.[11] A. Chen et al., in IEDM’05 Tech. Digest, Report 31.3. [12] G. Y. Jung et al., Nano Letters, vol. 6, pp. 351-356, Jan. 2006.[13] J. E. Green et al., Nature, vol. 445, pp. 414-418, Jan. 2007.
3:00 PM - **JJ2.2
Nanowire-based Architectures for High-Density Memory and Logic.
Andre DeHon 1
1 Electrical and System Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractHow can we exploit the new capabilities offered by nanowires to build large-scale, high-density electronic systems, and how can we cope with the high rates of variation, defects, and faults expected for these components?Nanowires are emerging as powerful nanoscale building blocks which can be synthesized using bottom-up self-assembly techniques and which offer engineering control over material properties and access to nanometer-scalefeatures. Device structures can be integrated into nanowires along with low-resistance interconnect. In this talk, we describe architectures for memory and logic constructed from these nanowire building blocks,highlighting the nanowire properties and features which make these architectures feasible as well as the challenges they raise. We show how our architectures can exploit statistical assembly to differentiate nanowires and post-fabrication configuration to avoid defects, mitigatevariation effects, and allow deterministic construction of reliable memory and logic. We further estimate system-level characteristics (e.g. memory and logic density, performance, and energy) from lower-level nanowireproperties (e.g. resistivity, junction defect rates, variation).
3:30 PM - JJ2.3
Titanium Nanowires Interspersed With Tens of Zeptofarad Tunnel Junctions for High Density Single Electron Circuit Fabrication.
Arnaud Beaumont 1 , Christian Dubuc 1 , Jacques Beauvais 1 , Dominique Drouin 1
1 Department of Computer and Electrical Engineering, Universite de Sherbrooke, Sherbrooke, Quebec, Canada
Show AbstractIn the late 80’s, the Coulomb blockade (CB) theory of electron tunnelling has been favourably evaluated to provide highly integrated logic devices. Many processes have since been proposed to take advantage of this theory but most do not operate above cryogenic temperatures. This limitation is directly related to the CB principle, involving an “island” (i.e. conductive particle) isolated between two electrodes. If the bias does not enable electrons to overcome the charging energy of the island (Ec) no current flows. In analogy with CMOS transistors, a third electrode may lift the blockade but thermal fluctuations may wash this effect if Ec is not widely superior to kT, with k Boltzmann’s constant and T temperature. Recently, a “nanodamascene” process showing CB up to 130°Cwas reported [1]. This process enables one to build metallic nano-wires interspersed with low-capacitance tunnel junctions. The high temperature operation is related to the capacitance of the tunnel junctions, which is as low as 60-80zF (1zf=1E-21 F), i.e. two orders of magnitude below typical values reported in the literature. We present here the steps we took to demonstrate the feasibility of single electron circuits (SEC) by the nanodamascene process. First, individual control gates were patterned next to the double tunnel junctions. Their presence increases the total capacitance of the islands, decreasing in turn Ec and thus the temperature of operation. However, we successfully fabricated single electron transistors (SETs) with room temperature operation by developing the process to achieve sub-50zF tunnel junctions. These ultra-low-capacitance junctions increased the voltage gain (Gv) of the SETs. Indeed, Gv is given by the ratio Cg/Cd, where Cg and Cd are the gate and the drain capacitances. For a given Cg, low values of Cd increase Gv and this explains that we were able to obtain values of Gv reproducibly superior to unity from electrical characteristics. This is very important, since the Gv>1 criterion is a sine qua non condition for SETs to be combined in circuits, and is rarely met in the literature. We also compared the characteristics of unique devices with those of SETs placed at few tens of nm from each other. Indeed, since CB is an electrostatic effect, the coupling between adjacent devices is of high concern for high density SECs. In these conditions, the bias of the gates influenced the surrounding SETs, depending not only on the inter-SET distance but also on the spatial arrangement of SETs. The impact of these two parameters was also successfully modelled by a finite element analysis of the electric field distribution, which was used to determine the best architectures for low-coupling integration of SETs. We conclude that the nanodamascene process is in good position to become the standard technique for the fabrication of high density room temperature SECs.[1] C. Dubuc, J. Beauvais, D. Drouin, Appl. Phys. Lett., vol. 90, p. 113104 (2007).
3:45 PM - JJ2.4
Infiltration of Microstructured Optical Fibers with Crystalline Semiconductors and Metals: A Novel Integration of Optics and Electronics.
Neil Baril 1 , John Badding 1 , Jacob Calkins 1 , Venkatraman Gopalan 2 , Pier Sazio 3 , Anna Peacock 3 , Adrian Amezcua-Correa 3 , Dong-Jin Won 2
1 Chemistry, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 3 Optoelectronics Research Centre, University of Southampton, Highfield, Southampton, United Kingdom
Show AbstractThe infiltration of a platform designed to transmit light, such as microstructured optical fibers (MOFs), with optoelectronic materials would open the door to numerous new and exciting devices and device architectures. We have developed a high pressure chemical vapor deposition (CVD) technique capable of introducing metals, semiconductors, and insulators into the capillaries of MOFs. MOFs are versatile templates capable of producing high density arrays of capillaries with diameters ranging from tens of microns down to tens of nanometers. Pressures of 20-35 MPa are used to force precursors through the capillaries of the MOFs enabling deposition within nanoscale capillaries. Greater complexity can be introduced by sequential deposition, in this manner radial heterojunctions can be fabricated within the capillaries. The ability to utilize the present knowledge base of CVD chemistry and adapt it to high pressure will further enable the introduction of structural complexity within each capillary. There is tremendous potential within this integrated platform for the development of in-fiber optoelectronic devices with potential applications including light modulation, generation, and amplification.
4:30 PM - **JJ2.5
Integration of Semiconductor and Metal Nanowires.
Ted Kamins 1
1 Quantum Science Research, Hewlett-Packard, Palo Alto, California, United States
Show AbstractNanowires of many different semiconductors and metals have been grown over the past decade, following earlier work as much as 4 decades ago, and interest has continued to increase. However, using nanowires requires that they be positioned to interface with other components of an electrical, optical, sensing, or other system. The nanowires can either be grown in the location where they are to be used, or they can be positioned after growth. Each technique has advantages and drawbacks. Growing the nanowires in place allows the position of the nanowire and its ends to be accurately known. Advanced techniques, such as nanoimprint lithography, can be used to position a catalyst nanoparticle and, consequently, determine where the nanowire will be subsequently grown. Electric fields can also be used to position the catalyst nanoparticle. Some examples will be discussed. On the other hand, decoupling the nanowire growth from the substrate where it is to be used allows a wider range of deposition conditions for nanowire growth without being limited by the devices already formed in the substrate.Semiconductor device and sensing applications have been discussed in most detail, and the needed characteristics of the nanowires are known. However, forming a useful device from the nanowire requires attention to electrical contacts and connections to the remainder of the system. For some applications, such as field-effect sensors, forming a number of nanowires in a specific region provides the needed large surface area with a small volume, but the exact number of nanowires is not critical. In other applications, such as electronic devices, the number of nanowires (generally one) and its properties must be well controlled. Metal nanowires are being discussed as potential interconnections and vias in advanced CMOS, and are likely to be included in the 2007 edition of the International Technology Roadmap for Semiconductors (ITRS). Some of the requirements for this application will be discussed, along with related data from the literature. The importance of specular (elastic) scattering from the sides of the nanowires will be considered.
5:00 PM - JJ2.6
Selective Barrier Layer Perforation in Nanoporous Anodic Alumina for Templated Growth of Electrically Connected Nanowires.
Jihun Oh 1 , Carl Thompson 1
1 Materials Science and Technology, MIT, Cambridge, Massachusetts, United States
Show AbstractOrdered Porous Alumina (OPA) is a nano-structured material that self-orders with domains and can be templated for pore ordering over arbitrarily large areas [1]. Thin films of OPA have been used as templates for growth of metallic and semi-conducting nano-dots, and as both templates and scaffolds for growth of nano-wires and nano-tubes. To incorporate these nanostructures in electrically active devices and systems, it is necessary to have two electrodes at top and bottom of each nanowire. However, OPA has thin insulating barrier oxide and it is desirable to remove the thin barrier oxide at the base of the pores. This barrier oxide is normally removed by chemical etching, by barrier thinning technique, or by reverse bias techniques [2-3]. However, these methods have side effects such as pore widening and difficult implementation for OPA on substrates, with difficulties increasing for small-diameter pores and pores with small spacings.A new method for perforation of the OPA barrier layer has been developed, based on anodization of Al/W multilayer films on substrates. When Al/W multilayer films are anodized and pores approach the Al/W interface, tungsten oxide forms and penetrates the alumina barrier oxide. By selectively etching the tungsten oxide, the barrier oxide can be removed and the base of the pores opened, without etching of the OPA. Using this technique, we demonstrate that it is possible to perforate OPA barrier layers for porous structures with small-diameter pores at small spacings. We also demonstrate use of this approach for templated growth of nanodots and for growth of nanowires in an OPA scaffold but electrically connected to conducting underlayers.[1] R. Krishnan and C. V. Thompson, Adv. Mater 19, 998 (2007).[2] K. Nielsch et al, Advanced Materials 12, 582 (2000).[3] M. Tian et al., Nano Letters 5, 697 (2005)
5:15 PM - JJ2.7
Arrays of Dense sub-10 nm Gold Nanowires for Electronics.
Vaida Auzelyte 1 , Harun Solak 1 , Yasin Ekinci 1 , Robert MacKenzie 2 , Janos Voros 2 , Sven Olliges 3 , Ralph Spolenak 3
1 Laboratory for Micro and Nanotechnology, Paul Scherrer Institut, Villigen Switzerland, 2 Laboratory of Biosensors and Bioelectronics,Institute for Biomedical Engineering, ETH, Zürich Switzerland, 3 Laboratory for Nanometallurgy, Department of Materials, ETH, Zürich Switzerland
Show AbstractLarge arrays of extremely small metal nanowires have tremendous potential for use in nanotechnology applications. Regular nanowire arrays can serve as nanoelectrodes to apply electronic control to address and functionalize selected nanowires with receptor molecules for biosensing applications or for computing and storage in a cross-bar geometry arrangement. Fabrication of the required periodic nanostructures for these and other applications with the required resolution, quality and quantity is a challenge for conventional fabrication techniques. We present novel nanowire fabrication processes that utilize Extreme Ultraviolet Interference Lithography (EUV-IL), shadow evaporation and lift-off techniques. EUV-IL provides large area, dense and uniform resist patterns with periodicity down to 25 nm and high throughput [1]. The line patterns were first created in a photoresist. Perpendicular thermal evaporation of gold and a liftoff process were used to create the nanowire arrays. We obtained lines with widths in the 20-70 nm range through this method. In a modified process, additional shadow evaporation of another metal on top of the resist lines was used to modify the width and profile of the resist lines in order to decrease the spacing between the lines. A lift-off process using these modified line patterns led to the creation of 7 nm wide gold lines with a period of 35 nm. The grain size of evaporated gold defines the roughness of nanowires when the linewidth goes below 10-15 nm. The roughness of these extremely thin gold nanowires becomes a limiting factor in achieving even narrower lines. As many as 5000 regular 1 mm long gold nanowires were fabricated. EUV-IL technique in combination with novel processing techniques has enabled the production of large area nanowire arrays with high throughput. Experimental results on characterization of the electrical and mechanical properties of the nanowires with various linewidth and thicknesses will be presented. 1. H. H. Solak, J.Phys.D: Appl.Phys. 39 (2006) R171
5:30 PM - JJ2.8
A First Step Toward a New Architecture for Li-ion Batteries.
Timothy Arthur 1 , James Mosby 1 , Amy Prieto 1
1 Chemistry, Colorado State University, Fort Collins, Colorado, United States
Show AbstractSecondary lithium-ion batteries are the current power source of choice for portable electronics. However, there are two main limitations to the rate of charging and discharging in these batteries: slow diffusion of Li+ into the anode and the cathode, as well as slow diffusion between the two electrodes. The fabrication of nanowire arrays of both carbon based anodes and several common cathode materials has been shown to dramatically enhance electrode performance because reducing the particle size of the electrode materials, while maintaining electrical contact from grain to grain, reduces the distance the Li+ ions have to diffuse. We will show preliminary results on a battery architecture designed to reduce the Li+ diffusion length from cathode to anode. This architecture is based on a geometry predicted by Long et al. and is designed around a nanowire array of anodes, electrochemically coated with a polymer electrolyte, then surrounded by a cathode matrix. Preliminary electrical measurements on this architecture will be discussed.
5:45 PM - JJ2.9
Vertical Si Nanowire Crossbar Arrays for Electronic-Based Sensing.
E. Akhadov 1 , S. Chikkannanavar 1 , S. Choi 1 , K. Cha 1 , S. Picraux 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractWe report on the fabrication and characterization of crossbar arrays containing vertical Si nanowires (NWs) that can be individually addressed electrically. Semiconductor NW arrays with the acuity of a dog’s nose for chemical and biomolecular sensing have the potential for revolutionary impact on detection technology in both commercial and national security applications. However, a roadblock to development of such electronic-based sensors systems has been the realization of practical methods to fabricate electrically connected NW arrays. In our approach we integrate top-down and bottom-up processing to create crossbar arrays of electrically connected, addressable, vertical Si NWs with lateral access for gas/liquid sensing. The bottom layer of the crossbar consists of patterned SOI. Au seeds for subsequent Si NW growth are deposited in patterned arrays (both smaller EBL and larger optical patterned openings are used). Intermediate steps to protect the Au seeds and introduce Si oxide support bars and pads for the top crossbar will be discussed. The Si NWs are grown by the vapor-liquid-solid method (400-600C, silane in an LPCVD system) with NW densities ranging from 1 to several 10’s of NWs in each discrete element. The top metal crossbar (Ni) is then deposited after polymer fill, chemical-mechanical polishing and light plasma etching to planarize the structure and expose the NWs. The polymer fill is subsequently removed to expose the Si NWs. Processing issues include seeded vertical NW growth, control of the number and uniformity of NW density in each element, and formation of the top electrical contact with the NWs. We will report on the processing issues and on preliminary electrical characterization results for 25 element (5 x 5) undoped and p-doped NW arrays.
JJ3: Poster Session I
Session Chairs
Tuesday AM, November 27, 2007
Exhibition Hall D (Hynes)
9:00 PM - JJ3.1
Homoepitaxial Growth of Vertical Si Nanowires on Si(100) Substrate using Anodic Aluminum Oxide Template.
Tomohiro Shimizu 1 , Tian Xie 1 , Volker Schmidt 1 , Jo Nishikawa 2 , Shoso Shingubara 2 , Stephan Senz 1 , Ulrich Goesele 1
1 Microstructure physics, Max Planck Institute, Halle, Weinberg 2, Germany, 2 Graduate Scool of Engineering, Kansai University, Osaka Japan
Show AbstractHomo-epitaxial growth of Si nanowires on Si (100) substrate was accomplished using a combination of anodic aluminum oxide (AAO) template and Vapor-Liquid-Solid (VLS) growth. At first an AAO template was formed on Si substrates, and the alumina barrier layer that existed at the bottom of nanoholes and native oxide on Si substrate was removed by chemical etching without loosing the connection between the AAO template and the Si substrate. Subsequently, catalytic gold nanoparticles for VLS growth of Si nanowires were deposited directly onto the Si substrate at the bottom of AAO nanopores by electrolerss plating. The Si nanowires were synthesized by an ultra high vacuum chemical vapor deposition (UHV-CVD) facility using silane gas as a precursor. Morphology and crystallographic analysis for the nanowires were carried out by scanning electron microscope (SEM) and transmission electron microscopy (TEM). We observed vertically grown epitaxial Si (100) nanowires in the AAO template. In addition, after leaving filled pores, Si nanowires changed their growth direction from [100] to <111>. This result shows that the walls of the pores forced the growth direction of Si nanowires parallel to the direction of the pores, and after filling, the growth direction changes to that of the Si nanowires on an unpatterned Si substrate. This method allows preparing various diameters of nanowires by changing the pore diameter of the AAO templates and synthesizing various crystal orientations of nanowires by changing the crystal orientation of the substrate.
9:00 PM - JJ3.10
Synthesis and Characterization of GaSb/GaAs Heterostructured Nanowires.
Yanan Guo 1 2 , Jin Zou 1 2 , Mohanchand Paladugu 1 2 , Qiang Gao 3 , Hoe Tan 3 , Chennupati Jagadish 3
1 School of Engineering, University of Queensland, Brisbane, Queensland, Australia, 2 Center for Microscopy and Microanalysis, University of Queensland, Brisbane, Queensland, Australia, 3 Department of Electronic Materials Engineering, Australian National University, Canberra, Australian Capital Territory, Australia
Show AbstractTo extend potential applications of semiconductor nanowires (NWs), axial heterostructured NWs have shown their advantages. In fact, the fabrication of heterostructured semiconductor NWs suitable for device applications has been a current challenge. This is particularly true for fabricating lattice mismatched heterostructured NWs, such as GaAs NWs on Si. GaSb-based III-V semiconductors are of great interest for near- and mid-infrared optoelectronic devices. However, it is very challenging to grow high quality GaSb epilayer on large areas, especially on GaAs due to the large lattice mismatch (~7.8%). In our work, all GaAs/GaSb heterostructured NWs were grown on {111}B GaAs substrates with Au particles as nucleation sites with sizes of 10 - 50 nm in a horizontal flow MOCVD reactor at a pressure of 76 Torrs. The substrate coated with Au particles was firstly annealed at 600°C under AsH3 flow for 10 min to desorb surface contaminants and form the eutectic alloy between Au and Ga from the substrate. After cooling down to 450°C, Ga source, trimethylgallium (TMG), was switched on to initiate GaAs NW growth. After 15 mins, TMG was switched off and the reactor cell was cooled down to 425°C under the AsH3 flow. AsH3 was then switched off, and, simultaneously, Sb source (trimethylantimony) and TMG were switched on to initiate the GaSb NW growth. The growth time for GaSb was 120 mins. The molar flow rate of TMG remains the same for both growths. SEM images show that the GaAs/GaSb heterostructured NWs are all well aligned, and each individual NW has a tapered body with a thick column shaped head. In terms of TEM investigation, HRTEM and SAED were employed. SAED patterns were taken from the interfacial regions of the heterostructure. Two sets of <110> diffraction patterns can be clearly distinguished with one set being GaAs and the other being GaSb. By delicate measurements of corresponding atomic planes for GaAs and GaSb, a 7.5±0.3% lattice mismatch was determined, which is consistent with the lattice mismatch between GaAs and GaSb (~7.8%). To understand the fundamental mechanism of the growth of GaSb on the GaAs NW, we noticed the fact that The growth of GaSb is significantly slow. The growth rate for GaSb NWs is about 2% of that for GaAs NWs. Additionally, in all the NWs being investigated, GaSb regions are defect-free. It has been suggested that the planar defects such as twins can cost energy (although very small). This indicates that the growth of GaSb part is governed by thermodynamics, in which case, each growth step requires the system to reach a minimum energy state. Each building atoms (Ga and Sb atoms from the decomposed precursors) finally adopted the most energetically preferable sites. For this reason, the slow nature of the GaSb NW growth is the fundamental mechanism for achieving thermodynamically grown defect-free GaSb NWs.
9:00 PM - JJ3.11
Hyperbranched and Complex Heterostructured Nanowires of PbS and PbSe.
Song Jin 1 , Matthew Bierman 1 , Y. K. Albert Lau 1
1 , University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractThe discovery of multiple exciton generation in nanocrystals of semiconducting PbS and PbSe promises a 800% quantum efficiency limit and 65% theoretical photovoltaic conversion efficiency. We report a chemical vapor deposition synthesis and the structural characterization of hyperbranched single-crystal nanowires of PbS and PbSe. Multiple levels of nanowires grow perpendicularly from the previous generation of nanowires in an epitaxial fashion to produce a dense cluster structure of a complex nanowire network. The flow rate and duration of the hydrogen co-flow in the argon carrier gas during the CVD reactions are found to have significant effect on the morphology of PbS/PbSe grown, from hyperbranched nanowires to micron-sized cubes. No intentional catalyst was employed for the nanowire synthesis, but it is suggested that lead itself might serve as a vapor-liquid-solid (VLS) catalysts for the anisotropic growth of PbS/PbSe. We also discuss the formation of other complex heterostructured nanowires of these materials and conclusively explain the formation mechanism of these intricate and exotic PbS/PbSe network or other complex nanostructures. We will explore these nanostructures in high performance photovoltaic applications and as integrated device architectures.
9:00 PM - JJ3.12
Three-Dimensional Gold Nanobridge Based on Au Nanoparticles.
Shih-Hsien Chao 1 , Chia-Ling Chen 1 , Selvapraba Selvarasah 1 , Mehmet Dokmeci 1
1 , Northeastern University, Boston, Massachusetts, United States
Show AbstractNanoscale materials with their attractive properties such as large surface to volume ratio, high packaging density and long-range order are the building blocks of the burgeoning field of nanotechnology. Moreover, approaches to control the precise location of these materials and to be able to integrate them on to microscale devices are needed to fully exploit the attractive properties of these materials. Several nanoscale manipulation techniques, such as the use of nanomanipulators, nanorobotic systems and pick and place tools have various limitations to serve as high rate large scale assembly methods. In this paper, we present an approach using alternating electric field for the fabrication of three-dimensional (3D) gold nanobridges. Utilizing a micromachined platform built using a 2 mask process and dielectrophoretic (DEP) force, we assemble gold nanoparticles (~10nm) to form 3D nanoscale structures. During assembly, conductive nanostructures can easily be damaged due to high current passing through nanobridges. To prevent this damage, we have designed and incorporated a resistance (1-2K Ohms) in series and hence avoided melting. In addition, the height of the micromachined platform can be adjusted by varying the height of the insulator layer (parylene) and hence can be engineered for other nanomaterials. The assembly process is achieved at room temperature and is compatible with conventional semiconductor fabrication and large scale nanoassembly. Due to the attractive properties of gold nanoparticles, this 3D nanobridge can find potential applications in nanomedicine, nanobiosensors and for in-line characterization of manufactured conductive nanoelements.
9:00 PM - JJ3.13
Synthesis and Characterization of Silver Nanowires Mediated by DNA.
Enrique Samano 1 , Mariana Oviedo 1
1 , CCMC-UNAM, San Ysidro, California, United States
Show AbstractThere is an increase interest in nanotechnology in looking for alternatives for the conventional top-down methods used nowadays in electronics devices, like lithography. One of these bottom-up approaches for designing devices in the micrometer and nanometer scale is based on organic molecules like DNA. The first living cells emerged 3.5 billion years ago. Cells house nanoscale biomachis that perform such specific task as manipulating genetic material by means of DNA. The building block of a nanodevice is a semi-conducting and/or conducting nanowire. This work shows a scheme based on sequence-specific molecular lithography on a DNA substrate to synthesize a wire with a diameter similar to the DNA itself. The method is supported by homologous recombination by RecA protein harnessed on lambda-DNA. The lambda-DNA is digested by the Hind III enzyme. They are purified with a kit of invitrogen to obtain the band corresponding to 2027bp and 2322bp. The homologues recombination with RecA and a dsDNA forms a nucleoprotein. The nucleoprotein is incubated with the dsDNA in a solution of AgNO3 to grow metallic islands which coalesce along of specifics sites of the dsDNA created by the protein to form a continuos silver nanowire. One metallization processing on Si wafers is performed to fabricate nanowires, in contrast to recent published results. The morphology of the nanowire is observed by AFM and SEM. Elementary chemical analysis is done by EDS.
9:00 PM - JJ3.14
Si Nanowires with Diamond Cubic / Diamond Hexagonal Heterostructures Using Cu as Catalyst.
Jordi Arbiol 1 2 , Sonia Estrade 2 , Francesca Peiro 2 , Joan Ramon Morante 2 , Anna Fontcuberta i Morral 3
1 TEM-MAT, Serveis Cientificotecnics, Universitat de Barcelona, Barcelona, CAT, Spain, 2 EME/CeRMAE/IN2UB, Dept. d'Electronica, Universitat de Barcelona, Barcelona, CAT, Spain, 3 Walter Schottky Institute, Technical University of Munich, Garching Germany
Show AbstractOne of most common method for the synthesis of nanowires is the Vapor-Liquid-Solid method (VLS), in which a metal seed catalyst is required to nucleate the growth of nanowires. Different metals have been proposed in literature, and it has been found that silicon crystallization is strongly influenced by which metal is used. Al, In and Au have been claimed to form eutectics with Si, whereas Pd and Ni are accepted to form various silicides with Si which enhance the incorporated Si atoms in a crystallized structure. Many efforts have been centered to find other appropriate metal catalyst compatible with device processing. Among different candidates, copper has been reported to interact in a different way with silicon atoms than those other metals catalysts forming eutectics (gold) and silicides (nickel). As during the process of metal-induced recrystallization of amorphous silicon, the metal atoms appear to enhance crystallization of amorphous silicon. It is believed that the metal atoms are repelled by the c-Si whereas Si atoms from the a-Si migrate into the c-Si side resulting in crystallization. When using Cu as a metal, higher crystallization rates are obtained, in comparison to other commonly used metals, such as Ni and Au. Within this logic, we have recently successfully synthesized silicon nanowires by using Cu as catalyst.In the present work we present a detailed study on the structural defects that silicon nanowires present when synthesized with Cu as a catalyst and discuss the relation with the growth mechanism. Initially, High Resolution Transmission Electron Microscopy measurements that indicate the presence of lamellar twinning along the growth direction are presented. Secondly, the experimental results are analyzed showing that the multiplicity of <111> twinning can generate local changes in the stacking sequence of the diamond structure, leading to a Si diamond cubic / hexagonal heterostructure, which is a complete new result in the case of Si NWs. Finally, a detailed study of the structural properties between both semiconductor phases (cubic and hexagonal) and nanowire morphology are reported and plausible growth models discussed.
9:00 PM - JJ3.15
Synthesis of the Bi doped ZnO Nanowires and its Electrical Properties.
JungHwan Chun 1 , DongEon Kim 1
1 physics, POSTECH, Pohang, kyungbuk, Korea (the Republic of)
Show AbstractBi doped ZnO nanowires were obtained through a vapor transport route at temperatures as low as around 250 °C. The electrical transport of Bi-ZnO nanowires shows n-type semiconducting behavior with a carrier concentration of ~3.5 × 108 cm-1 and an electron mobility of 1.5 cm2/V s. The carrier concentration is one order of magnitude larger than that of undoped ZnO nanowires, indicating that Bi acts as donor rather than the usual acceptor in ZnO films. Near band edge emission in photoluminescence spectrum of Bi-ZnO nanowires is redshifted relative to undoped ZnO nanorods as a result of enhanced carrier concentration. The donor-acceptor pair transition associated with Bi was also observed at 3.241 eV.
9:00 PM - JJ3.16
Preparation and Characterization of Highly Ordered Defect-free Nanowire-inorganic Salt Composites.
Vladimir Novikov 1 , Stanislav Khomich 2 , Alla Stetsik 1 , Sveta Filipovich 1
1 , Joined Institute of Solid State and Semiconductor Physics, National Academy of Sciences of Belarus, Minsk Belarus, 2 , Belarus State Medicine University, Minsk Belarus
Show AbstractNanowires (NWs) are among the key objects in nanotechnology. It was reported that various NWs have been used as components in composite materials and as elements of matrices for electron emitters, catalysts and electrodes for biophysical investigations. In view of broad prospects for the technological application of NWs, methods for the synthesis of NWs and related structures are extensively developed. A novel method of ordered metal nanowire–inorganic salt composites formation was proposed in this work. The method is based on a new phenomenon accompanying the electrolysis of salts, whereby an ordered composite is formed under certain conditions. NWs/salt composite have been synthesized using nonaqueous solutions and under galvanostatic regime of electrolysis. Using this method we obtained the following types of composite: Cu / Cu4 P2O7; Fe / FeCl2; FexCoy / FeCl2* Co Cl2 and Ag/Ca3(PO4)2 Scanning electron microscopy (SEM ) and X-ray diffraction (XRD) were used to characterize the topography and crystalloid structure of these materials .The diameter of nanowires in such types of composites was ranged of 50-500 nm and practically unlimited length (in our experiments the length of wires was abut 10 mm). It is worth to notice that the diameter of wires decrease with current density of deposition process and concentration of surfactant as well . The formation of a spatial order in this system can be explained by minimization of the total interfacial energy of elastic stresses in the growing composite and the surface energy of this structure. We successfully tested these composites as materials for supercapacitors (Fe / FeCl2; FexCoy / FeCl2* Co Cl2 ) and also as material for implanted ceramics - Ag/Ca3(PO4)2
9:00 PM - JJ3.17
Measurement of Silicon Nanorod Carrier Concentrations and Diffusion Lengths.
Michael Kelzenberg 1 , Michael Filler 2 , Brendan Kayes 2 , Morgan Putnam 3 , Harry Atwater 2
1 Electrical Engineering, California Institute of Technology, Pasadena, California, United States, 2 Applied Physics, California Institute of Technology, Pasadena, California, United States, 3 Chemical Engineering, California Institute of Technology, Pasadena, California, United States
Show AbstractSilicon nanowire arrays have the potential to enable low-cost, high efficiency solar cells via efficient radial minority carrier collection in an optically thick layer of vertically-oriented nanowires [1]. Optimal photovoltaic performance enhancement for low-minority carrier-lifetime materials is predicted to occur when nanowire diameter is less than or equal to minority carrier diffusion length, and when surfaces and junctions are well passivated.Silicon nanowires for photovoltaic applications were grown on silicon substrates by a vapor-liquid-solid (VLS) chemical vapor deposition (CVD) process from SiCl4 or SiH4 diluted in argon using gold catalyst particles. Straight, single-crystalline silicon nanowires were grown with diameters of 300 nm to 1.2 μm and lengths of 1 to 100 μm. Individual nanowires were deposited onto an insulating substrate and contacted using optical lithography and metal evaporation. Ohmic contacts, verified by four-probe measurements, were obtained using annealed Al contacts. Scanning photocurrent microscopy (SPCM) was performed on unintentionally-doped single nanowires using confocal and near-field optical microscopy (NSOM) laser excitation at 488 and 650 nm.Current-voltage measurements performed in a four point probe configuration on individual nanowires indicate that bulk resistivities from 0.04 Ω-cm to 7 kΩ-cm can be obtained by the introduction or omission of dopant gasses during nanowire growth, or by conventional dopant deposition and diffusion following growth. These correspond to electrically-active doping concentrations from approximately 1012 cm-3 to 1018 cm-3. Back-gated measurements were performed to determine the carrier type for unintentionally doped nanowires. Photocurrent collection was found to be influenced by photovoltaic carrier collection due to band bending at either contact. A one-dimensional charge transport model of drift, diffusion, and single-τ recombination is fit to the measured photocurrent profiles to extract effective carrier diffusion lengths, which are on the order of microns, corresponding to effective carrier lifetimes of a few nanoseconds. Effective diffusion lengths are approximately equal to nanowire diameter, indicating that carrier lifetimes are dominated by surface recombination. This result is supported by photoluminescence (PL) data, in which silicon band-edge emission is observed only following surface passivation by HF etch and dry thermal oxidation, and where carrier lifetimes are less than 10 ns.[1] Kayes, Atwater, and Lewis, J. Appl. Phys., 97, 114302 (2005).
9:00 PM - JJ3.18
Colloidal Synthesis of In/InP Nanoneedles and Their Use as Schottky Diodes.
Christian Klinke 1 , Tim Strupeit 1 , Andreas Kornowski 1 , Horst Weller 1
1 Institute of Physical Chemistry, University of Hamburg, Hamburg Germany
Show AbstractSemiconducting nanostructures are promising candidates for future electronic devices, not least due to their ability to accommodate whole device structures in one nano-object. Additionally, the electronic properties of those nanostructures can be tailored by means of size and dimensionality due to quantum confinement effects. The evolution of the confinement has been demonstrated by means of optical spectroscopy for colloidal zero- and one-dimensional CdSe quantum structures. The one-dimensionality of nanorods affords new properties like the polarized emission under photoexitation and electroluminescence. Their non-linear properties, their bandgap in the visible range, their easy integratability into device structures make InP nanowires ideal candidates as building blocks for novel types of nanowire-based photodevices.In II-VI semiconductor nanowire syntheses (e.g. CdSe) the growth is controlled by the amount and type of added ligand molecules - the proper choice allows the synthesis of rods, dots, or tetrapots. Unlike the preferential growth in wurtzite-like nanoparticles III-V semiconductors, however, possess a cubic zincblende lattice structure, i.e. the required chemically different surfaces are not given. Instead, another growth mechanism, the solution-liquid-solid (SLS) mechanism, can be exploited. A liquid metal droplet acts as seed and catalyst for the crystal growth. This mechanism was found for a few systems establishing III-V semiconductor rods and wires. The used seeds are gold, bismuth, silver or indium. Usually such methods are two-step syntheses. In a first step the metal seeds are produced by decomposing an organometallic precusor. The second step is a dehalosylation reaction of a metal salt (InCl3, InAc3) with tristrimethylsillyl phosphine in presence of the metal seeds in a high-boiling coordinating solvent like trioctyl phosphine (TOP) or trioctylphosphin oxide (TOPO). With this reaction it is possible to synthesize nanowires and nanorods of some microns in length. Recent publications focused on the control of the diameter of the metal seeds, since the diameter of the semiconductor nanowires is determined by the diameter of the metal seeds. Thus, the optical properties of InP nanowires can be adjusted by manipulating the seed size allowing the growth of InP with dimensions in a size range below the exciton Bohr radius.In the presented work we demonstrate a new reaction route for the synthesis of InP nanowires of several micrometers in length. We discuss two different growth mechanisms which depend on the reaction temperature. The length of the wires is tunable by the reaction time. We characterize the items by electron-microscopical and spectroscopical means. Their specific design with an In head and an InP tail represents a ready-made electrical device and allowed using them as Schottky diodes. The electrical analysis rendered the typical asymmetric diode characteristic.
9:00 PM - JJ3.19
Horizontal Porous Alumina Finger Arrays as Growth Templates for Large Area Single Nanowire Devices.
Ying Xiang 1 , Woo Lee 2 , Kornelius Nielsch 2 , Gerhard Abstreiter 1 , Anna Fontcuberta i Morral 1
1 , Walter Schottky Institut, Garching Germany, 2 , Max-Planck-Institut für Mikrostrukturphysik, Halle Germany
Show Abstract1D nanostructures have the potential to revolutionize broad areas of nanotechnology, such as electronics, sensing, and information technology. As building blocks for future applications, however, one of the biggest challenges in the study of these 1D nanostructures is their controlled synthesis and organization on a substrate. An elegant way to perform this is the membrane-based synthesis, also called template growth. Template growth of nanowires has been extensively studied over the past few years, since it provides compactness and uniformity which are necessary for reproducible device fabrication based on arrays of individual nanoobjects. Especially porous anodic alumina (PAA) film has attracted much interest due to the high aspect ratio, high level of ordering, high pore density, uniformity and low cost. PAA templates are commonly obtained with the pores oriented vertically on a substrate [MAS, LEE]. Unfortunately this method is hardly compatible with the mainstream Si planar processing technology.Here, we present a novel approach to synthesize PAA parallel to the substrate surface [COJ]. Using our sample design and fabrication method horizontally aligned PAAs with few nanopores or single nanopore can be fabricated, enabling the application for single or few nanowire devices. The horizontally aligned, well-defined nanopores are fabricated by anodic oxidation of aluminum stripes and aluminum fingers using two-step anodization. Using different electrolytes and different anodization voltage, pore diameters between 15 nm and 130 nm, and interpore distances between 45 nm and 250 nm have been obtained. The pore diameter is linearly dependent on the anodization voltage, but slightly differently from that of typical vertical anodization. Due to the anisotropy of our material system, the geometry is slightly changed from the typical honeycomb structure. By decreasing the finger widths down to 750 nm, the pore diameter and the interpore distances remains constant, proving that our fabrication approach enables the fabrication of single and few wire devices. Using these templates, metal wires are grown via pulsed electro-deposition. Electrical transport measurements at room temperature are presented. As a result of horizontal alignment and separation of the individual nanowires, our approach is promising for nanoelectronics and sensing.Reference:[LEE] W. Lee, R. Ji, U. Gösele and K. Nielsch, Nature Materials 5, 741-747 (2006)[MAS] H. Masuda and F. Fukuta, Science 268, 1466 (1995)[COJ] C.S. Cojocaru, J.M. Padovani, T. Wade, C. Mandoli, G. Jaskierowicz, J.E. Wegrowe, A. Fontcuberta i Morral and D. Pribat, Nano Letters 5(4), 675-680 (2005)
9:00 PM - JJ3.2
Enhancing the Electrical and Optoelectronic Performance of Nanobelt-Devices by Molecular Surface Functionalization.
Chang Shi Lao 1 , Yi Li 1 , C. Wong 1 , Zhong Wang 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractEnhancing the Electrical and Optoelectronic Performance of Nanobelt-Devices by Molecular Surface FunctionalizationChangshi Lao, Yi Li, C.P. Wong, Z.L. WangSchool of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0245Self-assembled thin molecular-layer has demonstrated the effectiveness in modifying surface physics and properties of metal and metal oxide materials. It has been used as a functional group in different nanowire based devices for chemical and biological sensing. In this presented work, we have explored a novel approach of using self-assembled thin monomolecular-layer on nanowire surface for improving the electrical and optoelectronic performances of nanowires (NWs) and nanobelts (NBs). A few kinds of molecules with different terminal groups (stearic acid, lysine, dodecanedioic acid, mercapto-acetic acid and perfluorotetradecanoic acid) were tested as functional layers and their performances were compared. For ZnO NBs with molecular coating, the contact properties and the carrier mobility were greatly enhanced. More importantly, the optical and gas sensing performance of these small organic molecule functionalized ZnO were also greatly enhanced. Details of achievements with coating of the molecular layers are listed as follows. First, due to energy band tuning and surface modification, coating molecule layer has changed a Schottky contact into an Ohmic contact without sophisticated deposition of multilayered metals the conductance. This enhanced magnitude of the transport current (i.e. conductivity) by six orders of magnitude; Secondly, a functionalized NB showed negative differential resistance which is a useful electron transport phenomenon in molecular devices; Thirdly, these functional layers huge improved photoconductivity and gas sensing response; Lastly, the functionalized molecular also greatly reduced the etching rate of the ZnO NBs by buffer solution, largely extended their life time for biomedical applications. This study demonstrates a new approach for improving the physical properties of oxide NBs and nanowires for device applications and also is a simple and cost-effective method for improving the performance of oxide nanowire/nanobelt based devices.[1] Chang Shi Lao, Yi Li, C.P. Wong, Z.L. Wang “Enhancing the Electrical and Optoelectronic Performance of Nanobelt-Devices by Self-Assembled Monolayer Surface Functionalization”, Nano Letters, 7 (2007) 1323-1328.[2] for more details: http://www.nanoscience.gatech.edu/zlwang/
9:00 PM - JJ3.20
Investigation of the Structural Properties of Li+{Mo3Se3}- Nanowires, Nanowire Networks and Ion Exchanged X+{Mo3Se3}- Networks by High Resolution TEM and Solution Characterisation Techniques.
John Sheridan 1 , A. Heidelberg 1 , D. Brougham 2 , P. Nellist 3 , D. Ozkaya 4 , John Boland 1
1 CRANN and School of Chemistry, Trinity College Dublin, Dublin Ireland, 2 School of Chemical Sciences, Dublin City University, Dublin Ireland, 3 Dept of Materials Science, Oxford University, Oxford United Kingdom, 4 , Johnson Matthey, Sonning Common, Reading United Kingdom
Show AbstractWith the limits of current silicon processing techniques drawing nearer, the “bottom up” approach for future technologies has become a focus of major research worldwide. This requires detailed studies of possible replacement materials for interconnects and the active components of nanoscale devices. To this end we present results for the inorganic nanowire system, Li+{Mo3Se3}- and of its ion exchanged network counterparts, X+{Mo3Se3}-, by a variety of techniques, including high resolution TEM and its associated spectroscopies, AFM, rheology and dynamic light scattering of solutions.Li+{Mo3Se3}- forms quasi-1D crystals that can be dissolved in polar solvents such as DMSO. Dispersing these solutions on surfaces via drop casting or spin coating yields single wires (0.6nm), bundles of nanowires and nanowire networks. Rheometry solution data is consistent with highly anisotropic particles or wires and light scattering measurements indicate a polydispersed size distribution. HR-TEM shows that networks of this material are continuous and not comprised of assemblies of individual wires. The mechanism of network formation is discussed based on cryogenic TEM imaging of nanowire solutions.By replacing the Li+ counter ion with a fluorinated organic ligand, dense networks of X+{Mo3Se3}- can be obtained. HR-TEM reveals the inter-wire spacing to be ligand dependent and that individual nanowires within these networks persist over large length scales. Electrical measurements of these networks show that their susceptibility to corrosion in moist air is much less than that of uncoated wire networks, and resistance vs. temperature measurements show a semiconducting like behaviour with a phase transition noted at low temperatures.
9:00 PM - JJ3.21
Bridged ZnO Nanowires Across Trenched Electrodes.
Pu-Xian Gao 1 3 , Jin Liu 3 , J. Lee 2 , Zhong Wang 3
1 Institute of Materials Science & Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States, 3 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 , Sandia National Laboratories, Livermore, California, United States
Show AbstractUsing a hydrothermal synthesis approach, large scale and laterally bridged nanowires (NWs) have been successfully grown across trenched Au/Si, Au/SiO2/Si, and ZnO/Si electrodes. This technique shows a low temperature (80oC) approach for growing ZnO nanowires on a pre-patterned substrate, showing its potential for integrating with silicon based technology. The I-V characteristics of the nanowires have been measured and their non-linear behavior has been analyzed. The bridged nanowire arrays could be useful for fabricating gas, chemical, or biochemical nanosensor arrays.
9:00 PM - JJ3.22
Nanowire Self-Assembly and Integration.
Zhiyong Gu 2 , David Gracias 1
2 Chemical Engineering, University of Massachusetts , Lowell, Massachusetts, United States, 1 Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractWe describe the fabrication and assembly of multisegmented nanostructures using electrodeposition in nanoporous templates. We have focused on structures that can be assembled into 3D integrated structures for electronics, sensing and fluidic applications. We have utilized several forces to direct assembly of the nanowires including surface tension, magnetic and dielectrophoretic. We also demonstrate a new strategy to bond nanowires (NWs) using fluidic interfacial diffusion bonding of gold (Au), The strategy was used to form very large scale, electrically interconnected three dimensional, NW networks, composed of both homogeneous and heterogeneous (multisegmented) NWs. The size of the networks ranged from tens micrometers to millimeters. We have measured the electrical characteristics of the networks and explored one application of the networks in 3D spatial chemical sensing.
9:00 PM - JJ3.23
Controlled, Highly Aligned Growth of Vertical GaN Nanowires on Sapphire.
George Wang 1 , Qiming Li 1 , J. Randall Creighton 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractWe report the Ni-catalyzed growth of very high-density (up to 150 per square micron) and highly aligned vertical GaN nanowires on unpatterned r-plane sapphire substrates. The degree of alignment and density was found to be highly sensitive to the growth temperature and Ni catalyst film thickness, particularly as the thickness was decreased below 1 nm, down to submonolayer thicknesses. The growth is highly controllable and uniform over very large areas. Interestingly, an investigation of the initial stage growth of the nanowires indicates a significant number of tilted nanowires in addition to the vertical nanowires, the density of which sharply decreases with growth time. We propose and present a collision-based model to explain the sharp decay in the density of tilted nanowires due to collisions with vertical nanowires during growth. The results show that at high nanowire densities, tilted nanowires can be rapidly selected out via this mechanism.
9:00 PM - JJ3.24
Single Potential Electrodeposition of Cu2Sb: Toward the Fabrication of Nanowire Arrays of a Promising Anode Material.
James Mosby 1 , Amy Prieto 1
1 Department of Chemistry, Colorado State University, Fort Collins, Colorado, United States
Show AbstractSecondary lithium-ion batteries are the current power source of choice for portable electronics and account for approximately 63% of the portable battery sales world wide. Improvements in the energy capacity, rate capabilities, and cycle life of secondary lithium-ion batteries have been pursued by investigating new materials and material morphologies. We are focused on nanowires of anode materials, in particular in developing synthetic methods for materials with strong structural relationships between the lithiated and delithiated compounds. One such example is Cu2Sb, which has been shown to exhibit smaller volume changes upon cycling and hence a longer cycle life. We have developed a single potential electrodeposition of Cu2Sb thin films and nanowires from aqueous citrate solutions at room temperature. This facile synthesis produces polycrystalline Cu2Sb (without annealing) directly on a copper current collector, which is then ready for battery testing. We have electrodeposited Cu2Sb into porous alumina templates, resulting in ordered arrays of nanowires. The increased surface area of the nanowires relative to bulk films is expected to further improve the cycle life and improve the rate capability of this promising anode material. We are in the process of applying this single potential deposition procedure to other intermetallics of interest as anode materials. The mechanism of electrodeposition and subsequent material characterization will be presented.
9:00 PM - JJ3.25
Synthesis of Si Nanowires Using Pt Catalyst and Structural and Compositional Modulation.
Han Nah Jeong 1 , Tae Eon Park 1 , Ungkil Kim 1 , Myoung Ha Kim 1 , Ryong Ha 1 , Han Kyu Seong 1 , Heon Jin Choi 1
1 , Yonsei University , Seoul Korea (the Republic of)
Show AbstractSilicon nanowires have novel properties such as high aspect ratio, single crystallinity and CMOS compatibility. As a result of these properties, Si nanowires are one of the most outstanding materials which may serve as the building blocks for the next generation of electronic devices. In most case, Si nanowires are grown by a vapor-liquid-solid (VLS) mechanism with Au as a catalyst. However, Au has limitations in some aspects of structural and compositional modulation of Si nanowires. We explored synthesis of Si nanowires with the use of Pt as a catalyst. The growth was performed in a CVD furnace. Small pieces of Si wafer coated with Pt with thickness of several nanometers were located in a horizontal furnace. With SiCl4 as precursor gas, Si naowires were grown at 1000 degrees Celsius with various range of holding time. The lengths of nanowires were controlled by holding time. In case of 10-hour holding, up to centimeter-scaled Si nanowires were fabricated. The growth rate of Si nanowires using both Au and Pt catalyst were measured at 1000 degrees Celsius with 5~30 minutes of holding time. According to our experiment, the growth rate of Si nanowires using Pt catalyst was 2~3 times faster than those using Au catalyst. Interestingly, single crystalline Si nanoribbons could be fabricated with assistance of Pt. They had a few μm long and nm scaled width. In addition to structural modulation, compositional modulation could be carried out with Ge alloying in Si nanowires. In our experiments, Si nanowires can be homogeneously alloyed with Ge up to 30 %. This indicates that Pt forms an alloy with both Si and Ge and simultaneously acts as a catalyst for these two components. In summary, we confirmed that Pt works on growth and engineering of Si nanowires as a catalyst.
9:00 PM - JJ3.26
Fabrication and Electrical Properties of the ZnO Single Nanowire Device.
Seung Eon Moon 1 , Eun Kyoung Kim 1 , Hong-Yeol Lee 1 , Jonghyurk Park 1 , So-Jeong Park 1 , Jun-Hyuk Kwak 1 , Sunglyul Maeng 1 , Kang-Ho Park 1 , Sang Woo Kim 2 , Hyun-Jin Ji 3 , Gyu-Tae Kim 3
1 , ETRI, Daejeon Korea (the Republic of), 2 , Kumoh National Institute of Technology, Gumi Korea (the Republic of), 3 , Korea University, Seoul Korea (the Republic of)
Show AbstractA single ZnO nanowire device was fabricated by electron beam lithography and its current-voltage characteristics were recorded with varying the atmospheric pressure to test the possible applications as a chemical gas sensor. Vertically well-aligned ZnO nanowires were grown on GaN epilayer on c-plane sapphire via a vapor-liquid-solid (VLS) process by introducing an Au thin film (3 nm) as a catalyst. Semiconducting nanowire devices were fabricated using photolithography and e-beam lithography, and their electrical properties were studied. To realize the reliable device operation which is a key factor for a chemical sensor, the contact resistance should be optimized. Here, we studied the contact resistance problem using scanning probe microscopic tool to characterize surface potential behaviors. To overcome contact resistance problem, post thermal process was adapted to the nanowire device. And atmospheric pressure and other environmental gas dependent electrical properties of the ZnO nanowire device were studied for chemical sensor application.
9:00 PM - JJ3.27
Portable Environmental Gas Sensor using Metal-Oxide Nanowires.
Eun-Kyoung Kim 1 , Seung Eon Moon 1 , Hong-Yeol Lee 1 , Jonghyurk Park 1 , So-Jeong Park 1 , Jun-Hyuk Kwak 1 , Sunglyul Maeng 1 , Kang-Ho Park 1 , Sang-Woo Kim 2 , Tak-Hee Lee 3
1 , ETRI, Daejeon Korea (the Republic of), 2 , Kumoh National Institute of Technology, Gumi Korea (the Republic of), 3 , Gwangju Institute Science and Technology, Gwangju Korea (the Republic of)
Show Abstract9:00 PM - JJ3.28
Solution Based Synthesis and Optical Characterization of CdS Nanowires.
James Puthussery 1 , Aidong Lan 1 , Thomas Kosel 2 , Masaru Kuno 1
1 Dept of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana, United States, 2 Electrical Engineering, University of Notre Dame, Notre Dame, Indiana, United States
Show Abstract One dimensional systems such as nanowires and nanotubes have attracted considerable attention due to their unique charge transport properties which make them potential candidates in nanoelectronics. The synthesis of nanowires using solution-liquid-solid (SLS) synthesis offers improved control over nucleation and their subsequent growth. We carried out the synthesis of cadmium sulfide (II-VI) nanowires using SLS, which employs au/Bi core shell nanoparticles as catalyst and temperatures below 300 °C. The resulting nanowires have diameters around 10 nm and length of the wires varied from 1 to 25 μm. X-ray diffraction measurements and high resolution TEM images clearly show that the wires are highly crystalline and both wurtzite and zinc blende phases are present along the wires. It is also observed that although the diameter of the wires is greater than the exciton Bohr radius of CdS (aB=2.9 nm), the absorption measurements show a significant blue shift of 200 meV, compared to the band edge absorption of bulk material. Interestingly, CdS nanowires exhibit band edge emission at room temperature with the peak centered at 487 nm and the quantum yield of emission is measured to be of 1%. The NW emission, as opposed to quantum dot emission is further confirmed by polarization anisotropy measurement and the anisotropy value is calculated to be 0.76(σ=0.06). The high anisotropy value confirms the one dimensional origin of the optical signal consistent with large aspect ration of CdS nanowires. The transient absorption of CdS NWs is recorded using femtoseond transient absorption spectrometer and the bleaching at 482 nm is in good agreement with the spectral position of the first transition in the linear absorption spectrum. The rate of recovery of bleaching can be fit to biexponential curve with lifetimes 34 ps and 100 ps.
9:00 PM - JJ3.29
Pressure Dependent Electrical Properties of Vanadium Pentoxide Nanowires.
Han Young Yu 1 , Byung Hoon Kim 1
1 Nano-bio electronic device team, ETRI, Daejeon Korea (the Republic of)
Show AbstractTime-dependent current characteristics of V2O5 (VO) have been investigated as a function of pressure with the various gases: air, nitrogen, oxygen, helium, and argon. The main mechanism adsorption of gases is physisorption, which is related to the layer structure of VO. The electrical detection of the pressure-dependent structural deformations of the vanadium pentoxide nanowire was done using the conventional field effect transistor configuration composed of the source and drain electrodes of normal metals, the conductance channel of vanandium pentoxide nanowire, and the gate oxide of silicon dioxide with increase of the injected gas pressure to a chamber. For the applied voltage the current paths are generated through the nanowires and the interstitial layer of water, and the conducting channel is modified with the transition from nanowire to water or vice versa by not only the injection of the gases, but the increase of the ambient pressure. The mechanism of the conductance variation is ascribed to the modulation of distance between the layers of vanandium pentoxide crystal, substitutional packing of the interstitial area by injected gases, and the switching of the conducting paths by the gases. The adsorption of gases is related to physisortption and the structural properties of the VO layer. Furthermore, using the intrinsic properties originated from the structural modification by the injection of the gases, the vanadium pentoxide nanowire device can be used as a good pressure gauge for various gases.
9:00 PM - JJ3.3
Polymer Functionalized Piezoelectric-FET as Humidity/Chemical Nanosensors.
Chang Shi Lao 1 , Qin Kuang 1 , Myung-Chul Park 2 , Yulin Deng 2 , Zhong L. Wang 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractPolymer Functionalized Piezoelectric-FET as Humidity/Chemical NanosensorsChang Shi Lao, Qin Kuang, Myung-Chul Park, Yulin Deng and Zhong L. WangSchool of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0245 USAMost recently, a new research direction termed of nanopiezotronics has been coined based on the piezoelectric-semiconducting coupled properties of ZnO NWs and NBs for fabricating novel and unique electronic components. [1,2] Prototype devices such as piezoelectric nanogenerator, piezoelectric field-effect transistors (PE-FET) and diodes are demonstrated. In this presented work, we report the first demonstration of humidity/chemical sensor based on PE-FET, which also contributes as a new component of nanopiezotronics. The devices were based on a single-side coated ZnO NB functionalized with multi-layers of polymers. The functionalization process was realized with electrostatic self-assembly method. By dipping the substrate into cationically charged PDADMAC solution and anionically charged PNIPAM solution with different cycles, we can coat polymers onto ZnO NB with control of different layers. Upon exposure of high humidity moisture, the as-functionalized polymers swell and produce an asymmetric strain across the ZnO NB, which bends the ZnO NB. In return, the deformation of ZnO NB generates a piezoelectric field across the NB which serves as a gate for controlling the flow of current along the NB. This is the working principle of the polymer functionalized PE-FET. It is a brand-new way in fabrication of nanopiezotronic devices and might bring a broad future of potential applications. Here, in this paper, we also demonstrated the possible application of use this polymer functionalized PE-FET as a chemical sensor to monitor the phase transition of PNIPAM upon temperature increase in aqueous solution. PNIPAM undergoes hydration and dehydration in aqueous solution when temperature is increased. By monitoring the current changed across NB, we can observe the phase transition of the polymer in situ. With the increase precise in polymer functionalization control and device fabrication, this polymer functionalized PE-FET might bring an alternative option in nanodevice fabrications to generate and convert energies between two different formats, which adds an attracting and promising component to the family of nanopiezotronics. [1]Z.L. Wang “The new field of Nanopiezotronics”, Materials Today, 10 (No. 5) (2007) 20-28.[2]Z.L. Wang “Nano-piezotronics”, Adv. Mater., 19 (2007) 889-992.[3] for more details: http://www.nanoscience.gatech.edu/zlwang/
9:00 PM - JJ3.30
Pulsed PECVD Growth of Silicon Nanowires on Various Substrates.
David Parlevliet 2 , John Cornish 2
2 Physics & Energy Studies, Murdoch University, Perth, Western Australia, Australia
Show AbstractSilicon nanowires of high density and high aspect ratio similar to those shown in the literature (Hofmann, Ducati et al. 2003; Niu, Sha et al. 2004) have been grown using a variation of Plasma Enhanced Chemical Deposition (PECVD) known as Pulsed PPECVD (PPECVD). A number of different materials have been trialled as substrates for the growth of silicon nanowires by this technique. This paper details the differences in nanowire morphology and density with the use of different materials as substrates. The nanowires grown in this work were produced via the VLS mechanism using gold as a catalyst.Deposition was carried out in a parallel plate PECVD chamber at temperatures up to 350°C, in an atmosphere of semiconductor grade silane. A square wave was used to modulate the 13.56MHz RF power. A 100nm gold catalyst layer was used for all samples. Substrate materials included polished n-type Si substrates with various orientations, stainless steel, copper, glass and ITO coated glass which was either clean or pre-coated with a thin layer of amorphous silicon. Some crystalline substrates were given an HF etch after the gold deposition (3nm) and immediately before the growth of silicon nanowires to remove the silicon oxide over layer as recommended by Jagannathan, Nishi and co-workers (2006) to aid epitaxial growth (Jagannathan, Nishi et al. 2006). Scanning electron microscopy was used to compare the growth and morphology of silicon nanowires on these substrates.Due to the thickness of the gold catalyst layer used there was little evidence of aligned or epitaxial growth upon the crystalline silicon substrates despite HF etching. Copper and stainless steel substrate were found to be unsuitable substrates for the growth of silicon nanowires at the deposition temperature used, with only a few nanowires being observed. The nanowires observed on these substrates were of an unusual morphology compared to those grown on crystalline silicon or glass.Of the glass samples it was found that nanowires grew with higher density on the ITO coated glass substrates. The reason for this was proposed to be the presence of a conductive layer immediately preceding the gold catalyst layer. Samples where a poorly conducting amorphous silicon layer was interposed between the ITO and Au layers were found to have a lower density of nanowires. Of all the substrates trialled, ITO coated aluminosilicate glass was found to be the most effective substrate to produce high density silicon nanowires.Hofmann, S., C. Ducati, et al. (2003). "Gold catalyzed growth of silicon nanowires by plasma enhanced chemical vapor deposition." Journal of Applied Physics 94(9): 6005-6012.Jagannathan, H., Y. Nishi, et al. (2006). "Effect of oxide overlayer formation on the growth of gold catalyzed epitaxial silicon nanowires." Applied Physics Letters 88(10): 103113-1.Niu, J., J. Sha, et al. (2004). "Tiny silicon nano-wires synthesis on silicon wafers." Physica E 24(3-4): 328-32.
9:00 PM - JJ3.32
Growth of SnO2-In2O3 Hetero Nanostructures.
S. Joon Kwon 1 , Dong-Wan Kim 1 , In-Sung Hwang 1 , Kyoung-Soo Park 1 , Jae-Gwan Park 1
1 Nano Science and Technology Division, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractWe report on the growth of hetero nanostructures composed of SnO2 and In2O3. The single-crystalline hetero nanostructures were formed by thermal evaporation accompanied by vapor-liquid-solid (VLS) process catalyzed by Au. The difference between the transport properties of the precursors of SnO2 and In2O3 led to the formation of the hetero structures. We observed that there exists a distinguished structural evolution of the hetero nanostructures. In the initial stages, nanowires were formed, and the core was SnO2 covered by a thin SnO2-In2O3 alloy layer. In the final stages, periodic array of In2O3 nuclei were formed on the surface of the SnO2 core, and the formation of SnO2-In2O3 core-shell nanowires, subsequently. The structural evolution of the hetero nanostructruers were thoroughly analyzed and electronic properties were also examined.
9:00 PM - JJ3.33
Memory Characteristics of Top-gate ZnO Nanowire Field-effect Transistors with Floating Gate Nodes of Au Nanoparticles.
Donghyuk Yeom 1 , Jeongmin Kang 1 , Changjoon Yoon 1 , Byoungjun Park 1 , Kihyun Keem 1 , Dong-Young Jeong 1 , Mihyun Kim 1 2 , Eui Kwan Koh 2 , Sangsig Kim 1
1 , Department of Electrical Engineering and Institute for Nano Science, Korea University, Seoul Korea (the Republic of), 2 , Nano Bio System Research Team, Seoul Center, Korea Basic Science Institute, Seoul Korea (the Republic of)
Show AbstractNanowire-based field-effect transistors (FETs) with floating gate nodes of nanoparticles have been greatly paid attention as nonvolatile memory devices of next generation due to both their excellent transportation of charge carriers in the nanowire channels and outstanding capability of charge trapping in the nanoparticles. In this work, top-gate single ZnO nanowire-based FETs were fabricated and characterized, after the formation of Au nanoparticles on Al2O3-coated ZnO nanowire channels using thermal evaporation and rapid thermal annealing processes. I-V curves taken from the top-gate single ZnO nanowire-based FETs with the Au nanoparticles embedded in the Al2O3 gate layers show clockwise hysterisis loops with ΔVth = 1.9 V, resulting from the tunneling of the charge carriers from the nanowire channels into the nanoparticles. On the other hand, the device without nanoparticles shows a negligible countclockwise hysterisis loop. The observation reveals that the influence of oxide trap charges or mobile ions is negligible and that the charge storage effect mainly comes from the nanoparticles present on the surface of the Al2O3–coated nanowire. Our experimental results demonstrate that the top-gate single ZnO nanowire-based FETs decorated with Au nanoparticles are one of promising devices for the application in the nonvolatile memory devices of next generation.
9:00 PM - JJ3.34
Charge Transfer Mechanism in Hybrid Systems Composed of Semiconductor Nanoparticles and Single Nanowires.
Hojun Seong 1 , Changjoon Yoon 1 , Donghyuk Yeom 1 , Kyoungah Cho 1 , Kihyun Keem 1 , Miyoung Park 2 , Dongmok Whang 2 , Sangsig Kim 1
1 Department of Electrical Engineering and Institute for Nano Science, Korea University, Seoul Korea (the Republic of), 2 Department of Advanced Materials Science and Engineering. SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractCharge transfer mechanism from nanoparticles to nanowires in hybrid systems composed of semiconductor nanoparticles and single nanowires were investigated by photocurrent and photocurrent spectra. Two different hybrid systems were prepared in this work; a single ZnO nanowire channel attached with ZnO nanoparticles and a single Si nanowire channel attached with CdTe nanoparticles. The photocurrent measured in these hybrid system excited by the 325 nm wavelength light from a HeCd laser is larger by several hundred times in intensity, compared with single nanowires without nanoparticles. In contrast, any photocurrent was not observed for systems composed of only nanoparticles, indicating that photo-excited charge carriers are not able to transport in these systems. In the photocurrent spectra taken from the two different hybrid systems, excitonic absorption bands originating from the nanoparticles were observed. The observation reveals that charge charriers in the nanoparticles excited by light are transferred efficiently to the nanowire channels. Charge transfer mechanism will be discussed in detail on the basis of band diagrams of the hybrid systems.
9:00 PM - JJ3.35
Heterostructures of Transition Metal Oxide Nanowires.
Takeshi Yanagida 1 , Kazuki Nagashima 1 , Aurelian Marcu 1 , Hidekazu Tanaka 1 , Tomoji Kawai 1
1 ISIR-Sanken, Osaka University, Osaka Japan
Show AbstractOne-dimensional nanowires have gained attention recently because of their potential applications in nanoscale devices and sensors [1]. Transition metal oxides exhibit the rich variation of the physical properties, such as superconductivity, ferromagnetism and ferroelectricity. Such rich functionalities might expand the application range of nanowire devices. Principally, there is a limitation to create diverse transition metal oxide nanowires. “Oxide-Heterostructures in Nanowires” would be one of ways to overcome such difficulties since many oxide heterostructures in thin film forms have been realized and proved to be useful and powerful [2-8]. Here we report heterostructures of transition metal oxide nanowires via controlling precisely “core” magnesium oxide nanowire morphologies as “nanoscale substrate” [9-11] and depositing “shell” iron-, and/or titanium- oxides onto the core nanowires. The oxide heterostructures in nanowires were fabricated by in-situ pulsed laser deposition (PLD) technique. Magnesium oxide “core” nanowires were synthesized on MgO (001) single crystal by Au catalyst-assisted PLD. Controlling appropriately the growth atmosphere, including temperature, pressure, catalysts, and others, was found to be crucial to determine the morphologies of “core” nanowires [9-11]. Especially, the diffusion of catalyst on the tip must be controlled by varying the ambient pressure and temperature. This essentially allows the fabrication of long-untapered core oxide nanowires. When the formation of “shell” oxides onto the core nanowire formation, macroscopically controlling the ablated particle flux is important to achieve the homogeneity of shell layer. When the ablated particle flux was too high, selective shell layer formation near the tip was observed. Microscopically, controlling the ambient temperature was a key factor. In addition, the diffusion of core nanowire into the shell layer was also observed, which was confirmed by HRTEM, transport and magnetic measurements. Thus well-defined “Oxide-Heterostructures in Nanowires” can be realized by precise control using in-situ PLD technique.[1] F.Patolsky et al., Scinece, 313, 1100 (2006)[2] T.Yanagida et al., Phys. Rev. B, 70, 184437 (2004)[3] T.Kanki, T.Yanagida et al., Phys. Rev. B, 71, 012403 (2005)[4] T.Yanagida et al., Phys. Rev. B, 73, 132503 (2006)[5] K.Nagashima, T.Yanagida et al., J. Appl. Phys., 100, 063714 (2006) [6] K.Nagashima, T.Yanagida et al., Phys. Rev. B, 74, 172106 (2006) [7] K.Nagashima, T.Yanagida et al., J. Appl. Phys., 101, 026103 (2007)[8] A.Marcu, T.Yanagida et al., J. Appl. Phys., 102, (2007) in press [9] K.Nagashima, T.Yanagida et al., Appl. Phys. Lett., 90, 233103 (2007)[10] K.Nagashima, T.Yanagida et al., J. Appl. Phys., 101, (2007) in press[11] A.Marcu, T.Yanagida et al., J. Appl. Phys., 102, (2007) in press
9:00 PM - JJ3.4
Tailoring of Structural Morphology of Silver Nanowires in Electrochemical Growth.
Amrita Singh 1 , Arindam Ghosh 1
1 Physics Department, Indian Institute of Science, Bangalore, karnataka, India
Show AbstractNoble metal such as Ag normally exists in an fcc crystal structure. However as the size of the material is decreased to nanometer lengthscales, a structural transformation from that of its bulk state can be expected with new atomic arrangements due to competition between internal packing and minimization of surface energy. In many previous studies, it has been shown that silver nanowires (AGNWs) grown inside anodic alumina (AAO) templates by ac or dc electrochemical deposition from silver salts or complexes, adopt fcc structure and below some critical diameter ~ 20 nm they may acquire hcp structure at low temperature. This is, however, critically dependant on the nature of confinement, as AgNWs grown inside nanotube confinement with subnanometer diameter have been reported to have fcc structure. Hence the question of the crystal structure of metal nanowires under combined influence of confinement, temperature and deposition condition remains open.In this abstract we show that the alternative crystal structures of AGNWs at room temperature can be achieved with electrochemical growth processes under specific conditions determined by the deposition parameters and nature of confinement. We fabricated AgNWs of 4H hexagonal structure with diameters 30 – 80 nm inside polycarbonate (PC) templates with a modified dc electrodeposition technique, where the nanowires were grown at deposition potentials as low as 10 mV in 2 M silver nitrate solution. We call this low-potential electrodeposition (LPED) since the electrodeposition process occurs at potential much less than the standard Nernst potential (770 mV) of silver.Two types of electrodes were used – stainless steel and sputtered thin Pt film, neither of which had any influence on the crystal structure of the nanowires. EDS elemental analysis showed the nanowires to consist only of silver. Although the precise atomic dynamics during the LPED process is unclear at present, we investigated this with HRTEM (high-resolution transmission electron microscopy) characterization of nanowires grown over various deposition times, as well as electrical conductivity measurements. These experiments indicate that nanowire growth does not occur through a three-dimensional diffusion controlled process, as proposed for conventional over-potential deposition, but follow a novel instantaneous linear growth mechanism. Further experiments showed that, (a) conventional electrochemical growth at a small over-potential in a 2 mM AgNO3 solution yields nanowires with expected fcc structure inside the same PC templates, and (2) no nanowire was observed under the LPED conditions inside hard AAO templates, indicating that LPED-growth process, and hcp structure of the corresponding nanowires depend on deposition parameters, as well as nature of confinement.
9:00 PM - JJ3.5
Vertical Germanium Nanowires Arrays Studied for Bio-molecule Sensing.
Makoto Koto 1 , Paul Leu 1 , Paul McIntyre 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractSemiconductor nanowires (NWs) are attractive components for electronic and photonic devices which can be integrated with Si circuitry to achieve novel functions. We propose a reproducible and CMOS compatible fabrication process and report sensor function for vertical free-standing germanium nanowire devices.As FET-channel structure, germanium nanowires were grown vertically on low resistivity Si(111) substrates by a VLS (vapor-liquid-solid) growth method within a 1 um high microfluidic channel formed by patterning silicon nitride. Vertically grown nanowires were covered comformally by high-k dielectric material deposited by ALD (atomic-layer-deposition). After sacrificial layer deposition and CMP (chemical-mechanical-polishing), nanowire cross-sections were exposed. This was followed by metal deposition to make top electrode contacts. By removing the trench-filling sacrificial layer, vertically free-standing nanowire device arrays were obtained inside the microfluid channel.We have demonstrated pH sensing with these nanowire devices, and we will discuss approaches for other chemical and biomolecular sensing applications using such arrays.
9:00 PM - JJ3.6
Novel Planer Microwave Circuit Applications and Characterization of Ni Nanowires.
Ryan Marson 1 , Bijoy Kunar 2 , Sanjay Mishra 1 , Robert Camley 2 , Zbigniew Celinski 2
1 Department of Physics, The University of Memphis, Memphis, Tennessee, United States, 2 Department of Physics, University of Colorado, Colorado Springs, Colorado, United States
Show Abstract9:00 PM - JJ3.7
The Role of Surface in the Transport Properties of Si Nanowires Prepared by Chemical Etching.
Jiansheng Jie 1 2 , Wenjun Zhang 1 , Kuiqing Peng 1 , Zhenhua Chen 1 , Chun-Sing Lee 1 , Shuit-Tong Lee 1
1 Physics and Materials Science, City University of Hong Kong, Hong Kong China, 2 School of Science, Hefei University of Technology, Hefei, Anhui, China
Show AbstractLarger-area oriented p-type Silicon nanowire (SiNW) arrays were synthesized by chemical etching and their transport properties were investigated by fabricating the field-effect transistors (FETs) from individual nanowires (NWs). In ambient air, four-probe measurements demonstrate that the etched SiNWs have much lower resistivity (~2.2 Ωcm for a NW with a diameter of 255 nm) than that of the initial Si wafer (8-13Ωcm); and thinner NWs show higher conductivity. The SiNW FETs made via photolithography show hole mobilities up to 44±22 cm2/Vs, carrier concentrations higher than 1×1017 cm-3, and on-off current ratios up to 104 in air. In vacuum, the conductivity of the SiNWs at zero gate bias has dramatically decreased, but the hole mobility increases on the contrary. The distinct results in air and in vacuum demonstrate the performance characteristics of the SiNW FETs are intimately tied to the presence and nature of adsorbed surface species, and the surface states can dominate the transport properties of the SiNWs. Further improvements on the device performances were achieved by embedding the SiNW FETs with 250 nm SiO2, which can isolate the devices from atmosphere as well as passivate the surface defects of the NWs. A model that involves surface band bending and surface carrier scattering caused by the adsorption of oxygen gas and humidity in atmosphere is proposed to interpret the experimental results. Moreover, it is found the conductivity of Si NWs is proportional to the reciprocal of their diameter. As a result, the density of surface charges can be estimated to be about 8.5×1011 cm-2.
9:00 PM - JJ3.8
Highly Organized Single-Walled Carbon Nanotube-PDMS Hybrid System for Electromechanical Flexible Devices.
Laila Jaber Ansari 1 , Xugang Xiong 1 , Myung Hahm 1 , Sivasubramanian Somu 1 , Ahmed Busnaina 1 , Sinan Muftu 1 , Yung Jung 1
1 Mechanical and Industrial, Northeastern university, Boston, Massachusetts, United States
Show AbstractThe interest in hybrid nanocomposite structures is growing rapidly due to their unique electronic, optical and mechanical properties that have many potential applications towards flexible functional devices. In this presentation, we will discuss composite structures consisting of highly organized single-walled carbon nanotube (SWNT) micro and nanoscale networks on the flexible insulating polydimethylsiloxane (PDMS) matrix and their characterization using several techniques such as Raman spectroscopy, AFM, and 4 points I-V measurement. The synthesis method combines lithographically patterned template guided fluidic self-assembly of SWNTs on the silicon substrate through SWNT solution evaporation with controlled dip coating. Then, with a high pressure PDMS based transfer-printing technique, conductive carbon nanotube architectures in a large scale can be transferred on the PDMS film. In our experiment, the PDMS matrix undergoes excellent conformal filling within the dense nanotube network, giving rise to extremely flexible conducting structures with unique electromechanical properties. This level of mechanical robustness, good electrical performance and optical transparency make transferred SWNT networks an attractive type of electronic material for applications in electro-mechanics, sensors, and other systems such as thin-film transistors (TFTs) in future flexible electronic devices.
9:00 PM - JJ3.9
Novel Synthesis of Metal Nano-whiskers: High-temperature Glancing Angle Deposition.
Motofumi Suzuki 1 , Kenji Hamachi 1 , Koji Nagai 1 , Kaoru Nakajima 1 , Kenji Kimura 1
1 Department of Micro Engineering, Kyoto University, Kyoto, Kyoto, Japan
Show AbstractIt is well known that the so-called Ehrlich-Schwoebel (ES) barrier plays an important role to form islands or mounds at early stages of the thin film growth. An adatom diffusing on an upper atomic layer will likely encounter an additional potential energy barrier, called the ES barrier, when descending to a lower layer at the edge of its residing terrace. The nanostructures taller than the conventional islands or quantum dots may grow if the adatoms are supplied preferentially on the upper layers with strong ES barrier. This situation can be achieved in the glancing angle deposition on a high temperature substrate (HT-GLAD), during which the incident atoms are deposited preferentially on the higher part of the surface due to the self-shadowing effect. In this study, Al, Ag, Au, and Fe were deposited at the deposition angle of 58° - 85° on the substrate of glass or surface oxidized Si held at a temperature of 180°C – 560 °C. For all the metals, nano-whiskers with a thickness of 30-500 nm and a length up to about 10 μm grew on the samples deposited at the very glancing deposition angle larger than 80° and at a high substrate temperature, which is higher than approximately a half of the melting point of the deposited metal. In the case of Al, for example, the critical temperature of formation of the Al whisker at a deposition angle of 85° was found to be between 180 °C and 290 °C. The similar results were obtained for Ag, Au and Fe, though the critical temperatures depended on the metals. These results provide the two crucial concepts to control the growth of nano-whiskers. The first is that the growth cites and direction of nano-whiskers can be controlled by the geometrical conditions, e.g., the nano-whiskers can be grown on the sidewall of the trench pattern fabricated on the Si wafers. This is quite useful to integrate the nano-whiskers with the electrical and/or optical device elements. The second is that the robustness in the selection of materials not only gets nano-whiskers to possess useful properties such as plasmonic, magnetic, catalytic etc. but also enables the synthesis of heterogeneous nano-whiskers. The HT-GLAD enhances richness for growth manipulation and control of nano-whiskers.
Symposium Organizers
David Gracias Johns Hopkins University
Ritesh Agarwal University of Pennsylvania
Pavle Radovanovic University of Waterloo
Joerg Ackermann Universite de la Mediterranee
JJ4: Hierarchical Growth
Session Chairs
Tuesday AM, November 27, 2007
Room 306 (Hynes)
9:30 AM - **JJ4.1
Guided Self-assembly of Epitaxially Nucleated III-V Nanowires for Device Applications.
Lars Samuelson 1
1 Solid State Physics, Lund University, Lund Sweden
Show AbstractWe use epitaxial control of the nucleation and direction of III-V nanowires, grown either on a III-V substrate or on a silicon substrate. The lateral position and extension of the nanowire is governed by the definition of the metal particle from which growth is initiated. In special cases, we use the first formed vertical trunks as “substrates” to nucleate nanowire branches, by which nano-tree-like structures can be formed as monolithic complex 3D-structures. These structures may in the future allow new architectures, such as the self-assembly of neural-net-like complex network of inter-connected nanotrees.One of the key-issues is the use of lithographic techniques as a top-down patterning method to control the sites at which nanowires are to grow in a bottom-up fashion. Among the methods that can be used are deep-UV optical lithography, holographic interferometric methods, electron-beam lithography and nanoimprint lithography, each with different merits and limitations. Special attention has been paid to ways to form heterostructures between semiconductors of different compositions, in the axial direction as well as radially. The axial heterostructure are used to define short segments acting as quantum dots and also to form tunnel-barriers, while the radial heterostructures are used primarily to passivate and to surround the inner core nanowire with a shell of a larger bandgap semiconductor. I will present structural investigations as well as optical and transport studies of different kinds of heterostructure systems and will discuss how some materials combinations make possible the formation of ultra-abrupt hetero-interfaces while other cases of materials exchange across a heterostructure interface may either form an more diffuse interface of may simply not form in a controlled fashion. Finally I will describe ways in which we process and fabricate nanowire devices, with an emphasis on the realization of vertical, wrap-around gate transistors, called WIG-FETs (wrapped insulator-gate field-effect transistors). I will present recent results from enhancement-mode as well as depletion-mode WIG-FETs, with gate-lengths down to sub-50 nm. Finally I will discuss how the incorporation of heterostructures in the gated region of the nanowire transistors may lead to performance advantages compared to homogeneous transistor regions.I want to acknowledge the contributions to this research from colleagues and students, and the support from the Swedish Research Council (VR), the Swedish Foundation for Strategic Research (SSF), the Office of Naval Research (ONR) and the European Union via the project NODE 015783.
10:00 AM - JJ4.2
Hierarchical Silicon Carbide Nanowire Heterostructures Constructed from Released Iron Catalysis.
Zhenyu Liu 1 , V. Srot 2 , Peter Aken 2 , Judith Yang 1 , Manfred Ruehle 2
1 Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 , Max-Planck-Institute for Metals Research, Stuttgart Germany
Show AbstractNanowires are attractive building blocks for functional nanoscale electronics, optoelectronic, electrochemical, and electromechanical devices. Nowadays many individual semiconductor nanowires have already been configured into device structures with novel properties. In particular, the construction of nanowire junctions is needed for large-area integrated nanoscale devices. Herein, we present the capability of creating branched and hyperbranched silicon carbide (SiC) nanostructures via a released catalytic process. Our previous results demonstrate that conical SiC nanowires can be formed by Fe catalyzed vapor-solid reaction between carbon and silicon monoxide, where the Fe nanoparticle is originally encapsulated in a graphitic carbon shell. At high temperature, the Fe nanoparticles leave the C-shell, migrate and combine with other Fe to form larger Fe nanoclusters. The increasing cross-sectional diameter of the SiC is due to the increasing diameter of the exposed Fe surface, that catalyzes the SiC growth, which could be caused by the release of the nanocluster from the C-shell and/or the coalescence with other Fe particles. Furthermore, the released Fe can migrate onto an existing SiC nanowire, which catalyzes the nucleation and growth of a secondary SiC nanowire. Consequently, different Y and T branched structures and more complex hierarchical SiC nanostructures can be realized from this unique catalytic process. The migration of iron nanocrystal from the graphitic carbon shell is visualized by in situ transmission electron microscopy (TEM). The resultant SiC hierarchical structures are analyzed systematically by different electron microscopy techniques, including Z-contrast imaging, energy dispersive X-ray emission (EDX) and electron energy-loss spectroscopy (EELS) techniques, electron diffraction and high-resolution electron microscopy (HREM). These hierarchical nanostructures are the building blocks needed for three-dimensional nanoelectronics, such as multi-terminal nanoscale transistors.
10:15 AM - JJ4.3
Self-branching in GaN Nanowires Induced by a Novel Vapor-Liquid-Solid Mechanism.
Chang-Yong Nam 1 2 , John Fischer 1
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractNanowires have great potential as building blocks for nanoscale electrical and optoelectronic devices. The difficulty in achieving functional and hierarchical nanowire structures poses an obstacle to realization of practical applications. While post-growth techniques such as fluidic alignment might be one solution, self-assembled structures during growth such as branches are promising for functional nanowire junction formation. In this study, we report vapor-liquid-solid (VLS) self-branching of GaN nanowires during AuPd-catalyzed chemical vapor deposition (CVD). This is distinct from branches grown by sequential catalyst seeding or vapor-solid (VS) mode. We present evidence for a VLS growth mechanism of GaN nanowires different from the well-established VLS growth of elemental wires. Here, Ga solubility in AuPd catalyst is limitless as suggested by a hypothetical pseudo-binary phase diagram, and the direct reaction between NH3 vapor and Ga in the liquid catalyst induce the nucleation and growth. The self-branching can be explained in the context of the proposed VLS scheme and migration of Ga-enriched AuPd liquid on Ga-stabilized polar surface of mother nanowires
10:30 AM - JJ4.4
Ion-Enhanced VLS Growth of Aligned and Shape-Controlled Silicon and Silicon Oxide Nanowhisker Arrays.
Martin Bettge 1 , Daniel Abraham 2 , Steve Burdin 1 , Scott MacLaren 1 , Ivan Petrov 1 , Ernest Sammann 1
1 Dept. of Materials Science & Engineering , Univ. of Illinois at Urbana/Champaign, Frederick Seitz Materials Research Lab, Urbana, Illinois, United States, 2 Chemical Technology Division, Argonne National Laboratory, Chicago, Illinois, United States
Show AbstractVertically aligned silicon oxide nanowhiskers were synthesized over a large area by an ion-enhanced Vapor-Liquid-Solid (VLS) method at low temperatures. Growth of nanowhiskers was initiated by a self-organized molten indium seed layer predeposited on a Si or SiO2 surface. In contrast to conventional VLS growth that uses Si-containing gaseous precursors, atomic Si was in this case supplied to the metal seed layer by magnetron sputtering. Concurrent vigorous ion bombardment aligned the whiskers vertically and expedited a state of supersaturation within the seeds due to enhanced mixing of the two insoluble phases, indium and silicon.Whisker growth occurred normal to the substrate surface at rates up to 200 nm/min in an ambient containing argon, hydrogen, and traces of water vapor at about 190 °C. Whisker diameters were on the order of 10-100 nm and the whisker aerial density was found to be between 109 and 1010 cm-2. Ion-enhanced VLS growth offers a promising route for growth of high aspect-ratio semiconducting nanostructure arrays. However, careful control of the ion bombardment is essential due to physical sputtering of the elevated metal seed. One seed material of choice is indium, due to its low eutectic temperature with silicon, its common use as p-type dopant for silicon, and the low solubility of silicon in indium. It is expected that the growth process also applies to other potential seed materials. The use of an atomic Si source offers technological advantages due to replacement of the gaseous precursors normally required. Concurrent and subsequent ion-assisted silicon deposition has been shown to offer a great deal of choice over the size, shape, and coverage of the final nanostructures. Technological application of shape-controlled nanostructures, for instance in electrodes for Li-ion batteries, is currently under investigation and will be discussed briefly.
11:15 AM - **JJ4.5
Synergetic Nanowire Growth.
Magnus Borgstrom 1 , George Immink 1 , Bas Ketelaars 1 , Rienk Algra 1 , Marcel Verheijen 1 , Erik Bakkers 1
1 , Philips research laboratories, Eindhoven Netherlands
Show AbstractFor vertical architecture design relying on closely-spaced nanowire-based devices, absolute control of growth rates and wire (device) dimensions is required. For instance for a modulation doped vertical transistor the gate alignment to a segment of a certain length and position is crucial. Heterostructured nanowires with predefined segment lengths for novel devices based on new physics were synthesized, where the segment dimensions critically determines quantization effects and thus the (opto) electronic properties of the wires.By systematically studying the effect of seed particle size and wire-to-wire spacing on the nanowire growth rate, we reveal a counterintuitive ‘synergetic’ effect which influences the nanowire growth rates in a way strongly contradicting existing literature: the growth rate increases for decreasing wire-to-wire distance, within our range of parameters used by a factor of four. By evaluating the nanowire growth rate in the pre-defined arrays as a function of growth temperature and precursor molar fractions, we find that the growth rate is proportional to the catalyst area fraction. The effect has its origin in the catalytic decomposition of precursors on the Au based alloy particle and is applicable to a variety of nanowire materials and growth techniques.
11:45 AM - JJ4.6
InN Nanorods and Nanowires; their Tapering, Bending and Branching.
Zuzanna Liliental-Weber 1 , M. Hawkridge 1 , J. Mangum 2 , O. Kryliouk 2
1 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Dept. of Chemical Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractTransmission electron microscopy was applied to study InN nanorods grown on different planes of GaN/Al2O3 and (001) Si substrates by non catalytic, template-free hydride metal-organic vapor phase epitaxy (H-MOVPE). Trimethyl Indium TMIn (which first reacts with HCl to form InCl) and NH3 were used as In and N sources, respectively. Single crystal nanorod growth was obtained on all substrates. The majority of them are of a high structural perfection and exhibit abrupt sidewalls. Cross-section TEM studies of the interface between the GaN/Al2O3 substrate and nanorods show first the formation of a thin amorphous layer followed by a GaN corrugated crystalline layer with differently oriented grains. These GaN grains provide an origin for differently oriented InN nanorods. It was noticed that depending on the substrate used for growth, their size, shape and tip morphologies vary. For example, nanorods grown on (001) Si and r-plane sapphire have sharp, pencil-like tips. In contrast, growth on the other substrates results in flat tips with clear facets on their sides. Differences in facet length on the sides of the tips are observed that may be related either to growth polarity.In addition to nanorods, InN nanowires grown on (001) Si and (0002) GaN/ Al2O3 were also studied. InN nanowires were grown in a RF heated, horizontal cold-wall MOVPE reactor using TMIn and NH3 source materials. A vapor-liquid-solid growth (VLS) mechanism occurs due to the formation of In droplets on the substrate surface (at low V/III ratios), which act as catalytic sites for 1D growth. The VLS growth mechanism allows these nanowires to achieve lengths greater than the nanorods grown by H-MOVPE, which grow via a solid-vapor (SV) mechanism. Nanowires grown on GaN/ Al2O3 differ drastically from the nanorods. Controlling the inlet group III flow ratio and the flow velocity inside the reactor varied the relative V/ III ratio at the substrate surface. The length of nanowires were in a range of 8-14 μm. A two-step growth method was also applied (which featured nucleation at a low and followed by a high V/III ratio). This growth procedure gave the longest nanowires (some as long as 100 μm), their diameters were about 500 nm and tips approximately flat. However, a substantial roughening and the presence of amorphous material was noticed on all nanowires. A substantial branching and bending of the nanowires was observed. This phenomenon was never observed for the nanorods studied. Understanding of the mechanism of branch formation is important for the assembly of nano-elements for devices. High-resolution electron microscopy shows that in most cases the formation of a branch is related to defects formed between the main nanowire and branch. In most cases, a twinning or formation of basal stacking faults starting from the interface with a nanowire is observed. This study shows that a branch is much more defective than a main nanowire.
12:00 PM - JJ4.7
Highly Ordered, Free Standing Nanowire and Heterostructure Arrays via Electrodeposition in Controlled, Perfectly Ordered, Supported AAO Templates.
Adam Robinson 1 , Kevin Musselman 1 , Lukas Schmidt-Mende 1 , Gavin Burnell 2 , J. MacManus-Driscoll 1
1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 School of Physics and Astronomy, University of Leeds, Leeds United Kingdom
Show AbstractAnodic aluminium oxide (AAO) templates form an ideal route to the production of arrays of nanostructures by electrodeposition; they are robust, insulating and can be produced with a range of geometries. If the template is used as a mask over a conducting substrate, deposition will take place from the base of the pore up, forming nanowires with the same dimensions as the pores. The majority of the work on AAO templates has however focused on thick foils, which prohibits the fabrication of nanowire devices from the materials deposited in the pores. Here we present work on the production of thin (<1um) disordered and perfectly ordered AAO templates on supporting substrates such as Si and ITO, by focussed ion beam (FIB) pre-patterning, and their filling by electrodeposition to produce nanowire and heterostructure arrays. Pre-patterning allows for production of perfectly ordered templates with controlled pitch (between 100 and 200 nm), pore size (50 to 70 nm) and geometry (hexagonal or square arrays) over a 15 x 15 µm area. Filling of the templates was facilitated by an underlying metal electrode and a computer controlled electrodeposition set up. This allowed for fabrication of highly ordered arrays of single material, such as Cu2O for solar cell applications, and heterostructure nanowires, such as Co/Cu multilayers and pseudo spin valves, from a single electrolyte with control of layer thicknesses on the nanoscale. A freeze drying technique was employed to produce free standing nanowire arrays after etching of the template.
12:15 PM - JJ4.8
Synthesis of Multifunctional Co-Au Heterostructured Nanorods.
Fabienne Wetz 1 , Katerina Soulantica 2 , Andrea Falqui 2 , Marc Respaud 2 , Etienne Snoeck 3 , Bruno Chaudret 1
1 LCC, CNRS, Toulouse France, 2 DGP, INSA, Toulouse France, 3 CEMES, CNRS, Toulouse France
Show AbstractThe combination of different materials on the same nanoparticle, offers many additional opportunities for various applications. We present the synthesis, the structural and some magnetic properties of hybrid magnetic nanorods composed of a cobalt main body and Au nanoparticles. In a first step, metallic Co nanorods are synthesized by the decomposition of an organometallic compound in the presence of a mixture of long chain amine and long chain acid. In a second step, by proper choice of the gold precursor we can switch from a galvanic displacement mechanism, which destroys the Co structure, to a heterogeneous growth mechanism, which permits the growth of Au nanoparticles strictly on the Co, which in this case serves as a seed. The location of gold is controllable by changing the reaction conditions. The Au nanoparticles can grow either epitaxially on the lateral sides or non-epitaxially on the tips of the Co nanorods. The most important factor that dictates the outcome of the reaction is the surface chemistry and the mobility of the ligands that serve as stabilisers of the nanorods. Au tipped Co nanorods are interesting materials thanks to the magnetic properties of Co nanorods. Indeed each nano-object posses a high magnetic moment and a large anisotropy controlled by the magnetocrystalline and the shape anisotropy. The use of the Au tips as anchor points after its selective functionalisation, opens new perspectives for the implementation of the magnetic nanorods in different applications such as high density magnetic recording devices or nanomedecine.
JJ5: Strategies for Directed Assembly of Nanowires
Session Chairs
Tuesday PM, November 27, 2007
Room 306 (Hynes)
2:30 PM - **JJ5.1
Electric-field Directed Assembly of Nanowires for Heterogeneous Integration of On-chip Electronic Systems.
Theresa Mayer 1 , Mingwei Li 1 , Jaekyun Kim 1 , Thomas Morrow 1 , Christine Keating 1
1 Electrical Engineering, Pennsylvania State University, University Park , Pennsylvania, United States
Show AbstractRealizing the potential of nanowires and nanotubes as active devices in integrated micro/nano-systems requires the development of assembly strategies for producing individually addressable arrays of these nanostructures. Long-range forces induced by spatially localized, nonuniform AC electric fields have been used previously to assemble nanowires from suspension between pairs of prepatterned electrodes on a silicon chip. In this presentation, we will summarize the results of an experimental and theoretical study conducted to investigate the factors that influence nanowire alignment density, placement position, and assembly yield. By understanding the balance of forces exerted on the nanowires during assembly, we were able to optimize the assembly conditions and align large-area nanowire arrays (> 2 x 2 cm2) with densities exceeding 106/cm2 and individual nanowire placement yields greater than 90%. We will also show that this electric-field directed assembly technique can be used to integrate nanowires onto fully processed multiplexed CMOS circuits, and to position different types of chemically-functionalized nanowires in different locations of the chip. This will enable bottom-up integration of on-chip multi-analyte chemical and biological sensor arrays.
3:00 PM - JJ5.2
Controlled, Accurate Dielectrophoretic Assembly of Metallic Nanowires into Ordered Arrays.
Stergios Papadakis 1 , Zhiyong Gu 2 , Trupti Maddanimath 2 , David Gracias 2
1 , Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, United States, 2 Chemical and Biomolecular Engineering, Johns Hopkins University, Laurel, Maryland, United States
Show AbstractWe demonstrate controlled dielectrophoretic assembly of metallic nanowires into parallel arrays which bridge two electrodes. This is done by tuning the adhesion of the nanowires to the substrate and by controlling the depth of the dielectrophoretic potential well. Initially, the nanowires are suspended in water or a water/ethanol mixture such that they do not adhere well to the substrate. Thus, they undergo Brownian motion due to thermal randomness. The dielectrophoretic potential is tuned such that the nanowires are weakly attracted to the region between the electrodes. Under the influence of Brownian motion, the dielectrophoretic potential, and the inter-nanowire interactions, the nanowires arrange themselves into their minimum energy configuration. For a pair of parallel electrodes, the nanowires assemble such that each nanowire spans the gap between the electrodes, and the nanowires are parallel to each other and uniformly spaced laterally. Once the nanowires achieve this minimum-energy configuration, they can be permanently fixed in place either by changing the water/ethanol mixture ratio or by significantly increasing the dielectrophoretic force. This technique shows promise for incorporating nanowire devices into lithographically patterned integrated electronics. For example, nanowires with device junctions in their centers could be used. They can be assembled accurately enough that the junction falls between the electrodes for all of the nanowires. We also discuss a surprising effect of changes in the water/ethanol mixture ratio on the adhesion of the nanowires to the substrate.
3:15 PM - JJ5.3
Electric Field Directed Growth of Molecular Wires of Charge Transfer Molecules on Prefabricated Metal Electrodes.
T. Sai 1 , A. Raychaudhuri 1 2
1 Physics Department, Indian Institute of Science, Bangalore, Karnataka, India, 2 Unit for Nanoscience, S.N.Bose National Center for Basic Sciences, Kolkata, West Bengal, India
Show AbstractConducting organic micro and nanowires are useful for constructing efficient all organic electronic devices. Charge transfer molecules are for long considered as promising candidates for organic molecular conductors. Most well studied charge transfer molecules are complexes of TCNQ-TTF in single crystalline form and thin film form, where they show metallic conduction. TCNQ-TTF belongs to quasi one-dimensional conductors having high electronic conduction along ‘b axis’. The complex consists of segregated stack of donor (TTF) and acceptor (TCNQ) molecules. Recent studies have shown that TTF-TCNQ charge transfer molecular electrodes can be used to replace the regular metal source-drain electrodes for pentacene thin film transistor with almost same contact resistance as the metal electrodes. Organic nano-channel FET has been recently fabricated using TTF-TCNQ molecular wires. We have used co-evaporation technique to simultaneously evaporate the donor and acceptor charge transfer molecules form two different crucibles whose temperatures were controlled by PID controller in a vacuum chamber. The substrate is also maintained at a constant temperature during evaporation. An electric field is applied between anode and cathode to enhance the growth of the molecular wires.. We have used TMTTF or TTF as donors and TCNQ as acceptor molecules. We have used Ti/Au contact pads grown on mica as substrate. We used varied the dimension of the contact pads ranging from tens of mm to 1mm. For larger dimensions of contact pads and the gaps (~20μm) a number of wires grow on the electrodes. The application of electric field directs the growth and few wires bridge the gap. These wires on subsequent imaging by FEG-SEM were found to be bundles that have dimensions of ~200nm -~50nm depending on the material. Single wires of diameter ~200nm and length 1μm were grown on e-beam fabricated electrodes that have a dimension of 1μm and have gaps of the same dimensions. These single wires grow by bridging the 1μm gap.The wires so grown are single crystalline and show semi-conducting behavior in resistivity in the temperature range 100K-300K. The molecular wires are supposed to be conducting nature. This particular behavior may arise from contact resistance or from intrinsic inhomogenity.
3:30 PM - JJ5.4
Precision Transport and Positioning of Nanowires by Electric Fields.
Donglei Fan 1 2 , Robert Cammarata 1 , C. Chien 2 1
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractWe report a method for transporting and positioning of nanowires in suspension with controlled orientations using a combination of dielectrophoretic (DEP) force and electrophoretic (EP) force generated by electric fields from patterned electrodes. We show that charged nanowires (e.g., Au, Ni, multi-wall carbon nanotubes) can be transported by the EP force, while their orientations are aligned by the DEP force. By using multiple electrodes, the transport of nanowires can be made to follow prescribed and arbitrary trajectories (e.g. zigzags or rectangles). The transport is sufficiently precise such that two individual nanowires with a separation over 100 μm can been made to join end to end. Using this technique, we have also determined the Stokes coefficient for nano-entities with high aspect ratios in a low Reynolds number regime ( < 10-5 ). Nanowires may be important building blocks for nano-electromechanical system (NEMS) based devices. This will be illustrated with a resonator assembled from two nanowires in a liquid that is sent into oscillations with a controlled frequency.
3:45 PM - JJ5.5
A Bottom-up Approach of Ultra-thin Nanosheet Fabrication from Ultra-narrow PbS Nanowires.
Somobrata Acharya 1 , Katsuhiko Ariga 1
1 International Center for Young Scientists, National Institute for Materials Science, Tsukuba Japan
Show AbstractA nanosheet can be thought as a two-dimensional (2D) system where the charge carriers are constrained to move in a plane of negligible thickness. The nanosheets are expected to achieve advanced functions in unidirectional energy transfer, improved photocatalysis activity, higher photovolataic efficiency due to reduced electron-hole recombination rates and could find applications in energy storage and memory devices. Langmuir Blodgett (LB) technique is an established technique for inducing such large scale 2D assemblies of the surfactant coated nanowires in a single step. Recently, we have reported on the ultra narrow (1.8 nm) lead sulphide (PbS) nanowires with tight side-by-side registry and on an one step 2D patterning technique below the conventional lithographic limit to yield an aligned area over ca 15 square micron using LB technique. Here we introduce a new easy bottom-up approach of making ultra-thin 2D nanosheet by the coalescence of individual ultra narrow PbS nanowires as building blocks at ambient temperature. The nanosheets of ~20 micron in length and ~500 nm in width are grown as single crystals in a one step process with the aid of 2D surface pressure retaining the same core thickness of 1.8 nm of the wires. The ultra-thin nanosheets generate dark current of the order of ~mA, which could be enhanced by illuminating suitable light window. This semiconductor nanosheet could be an ideal system for understanding dimensionality dependent transport phenomena and building advanced functional devices.
4:30 PM - **JJ5.6
Multifunctional Metallic Nanowires.
Peter Searson 1
1 , JHU, Baltimore, Maryland, United States
Show AbstractNanometer size particles, such as nanorods or nanowires exhibit many unique properties associated with their inherent shape anisotropy. The introduction of multiple segments along the length of a nanowire can lead to further degrees of freedom associated with the shape of each segment and the coupling between the layers. The unique properties of multisegment metallic nanowires can also be exploited in suspensions where the manipulation and assembly of nanometer scale particles has become an important tool in nanotechnology. Examples to be discussed include manipulation of magnetic nanowires, nanoporous nanowire sensors, directed end-to-end assembly, and drug delivery.
5:00 PM - JJ5.7
Dispersion Behavior and Assembly of Inorganic Nanorods, Nanowires, and Nanowhiskers.
Virginia Davis 1 , Bennett Marshall 1 , Shanthi Murali 1 , Dhriti Nepal 1 , Khristine Pizarro 1 , Doh Lee 2 , Brian Korgel 2
1 Dept. of Chemical Eng., Auburn University, Auburn, Alabama, United States, 2 Dept. of Chemical Eng., University of Texas at Austin, Austin, Texas, United States
Show AbstractThe recent development of facile routes for the production of inorganic nanorods, nanowires, and nanowhiskers has resulted in an array of materials with intriguing optical, electronic, magnetic and structural properties. However, the production of functional materials from these nanoscale building blocks often requires aligning the nanorods on the micro- to macro- scales. The theoretical foundation for self-assembly of anisotropic rigid materials in solution dates back to Onsager (1949), but understanding the liquid crystalline phase behavior of nanorod dispersions is a nascent field formed by the intersection of nanotechnology, liquid crystalline science and colloid science. We report results on the Brownian behavior and orientational alignment of model dispersions of anisotropic nanomaterials including germanium nanowires, silver nanorods, and silicon nitride nanowhiskers. We further demonstrate the promise of liquid crystalline assembly of these materials into aligned films. This work represents a step forward in developing a fundamental understanding about the impacts of nanorod concentration, nanorod aspect ratio, and nanorod-nanorod and nanorod-solvent interactions on liquid crystalline phase behavior as well as the potential for liquid crystalline dispersions of nanorods to be processed into highly aligned macroscale coatings, films and fibers.
5:15 PM - JJ5.8
PMMA Blown Bubble Films for Direct Fabrication of Nanowire and Nanotube Device Arrays.
Guihua Yu 1 , Anyuan Cao 3 , Charles Lieber 1 2
1 Chemistry & Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 3 Mechanical Engineering, University of Hawaii, Honolulu, Hawaii, United States, 2 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractPhotoresist materials are central to lithographic patterning and fabrication of micro- and nano-scale devices. Here we report a simple and scalable method for fabrication of nanowires (NWs) and carbon nanotubes (NTs) devices, using recently reported blown bubble films (BBFs) approach based on photoresist polymer, poly(methyl methacrylate) (PMMA). The PMMA based BBFs could be directly photo/ebeam processed to make patterned devices on embedded aligned NWs and carbon NTs over large areas. Centimeter-scale arrays containing thousands of silicon nanowire field-effect transistors were efficiently fabricated on these PMMA based BBFs (with yield over 75%) and shown to exhibit high device performance with high reproducibility and uniformity. In addition, large arrays of multi-walled nanotube (MWNT) interconnects were also successfully fabricated using MWNT-BBFs. The PMMA based BBF approach allows unique integration of large scale assembly of aligned nanostructures and fabrication of nanoelectronic devices.
5:30 PM - JJ5.9
Electrostatic Deposition of Carbon Nanotubes and C60 Fullerenes from Aqueous Suspension onto Locally Charged Substrates.
Livia Seemann 1 , Nicola Naujoks 1 , Andreas Stemmer 1
1 Nanotechnology Group, ETH Zurich, Zurich Switzerland
Show AbstractNanowires and carbon nanotubes (CNTs) have attracted much attention as potential key components in future nanotechnological devices. However, to integrate individual wires and tubes into devices, it is essential to have concepts for their precise placement and alignment. Likewise, the controlled assembly of C60 molecules on surfaces still represents a challenging issue.One way to guide self-assembly processes is to use electrostatic fields that allow for the deposition of a large number of objects in parallel. In this work, we show how electrostatic fields can help in positioning carbon nanotubes and fullerenes with nanometer resolution. Patterns of local surface charges are created by atomic force microscopy (AFM)-based charge writing. To this end, voltage pulses are applied to a conductive AFM tip scanning over a thin electret layer. These charge patterns act as templates for the deposition of the nanotubes and fullerenes in the subsequent development step.So far, various kinds of particles and molecules, ranging from dielectric microspheres [1], over gold nanoparticles [2], to biomolecules [3] have been successfully attached using this AFM-assisted assembly method. In these assays, water-in-oil emulsions were used as the development medium. However, since the resolution is limited by the emulsion droplet size, smaller structures can only be fabricated when depositing the particles directly from suspension. This way, polymer beads and multi-walled carbon nanotubes [4] have been deposited from alcohol-based suspensions.Here we demonstrate the selective deposition of single-walled carbon nanotubes (SWCNTs) and C60 molecules from aqueous suspensions containing non-ionic surfactants such as Synperonic NP10 or Triton X-100. These surfactants bind reversibly, expose their polar head group to water, and can be washed away later on. Coulomb attraction guides the charged particles onto the previously charged locations. Both carbon nanotubes and C60 molecules reproduce the charge patterns with high precision, yielding structures with a lateral resolution down to the particle diameter. We show that the magnitude of the local surface potential strongly influences the deposition behavior, offering control over pattern resolution. Since a certain surface potential can induce alignment of single CNTs on charge lines, we will further demonstrate the creation of small CNT networks by this method. We are confident that this surfactant-based assembly process can be extended to a wide variety of nano objects.[1] P. Mesquida, A. Stemmer, Adv. Mater. 13 (2001) 1395.[2]P. Mesquida, A. Stemmer, Microelectron. Eng. 61 (2002) 671. [3]N. Naujoks, A. Stemmer, J. Nanosci. Nanotechnol. 6 (2006) 2445.[4] L. Seemann, A. Stemmer, N. Naujoks, Microelectron. Eng. 84 (2007) 1423.
JJ6: Posters Session II
Session Chairs
Wednesday AM, November 28, 2007
Exhibition Hall D (Hynes)
9:00 PM - JJ6.1
Growth, Characterization and Device Applications of One-dimensional Oxide Nanostructures.
Sven Barth 2 1 , Sanjay Mathur 2 1 , Francisco Hernandez-Ramirez 3 , Albert Romano-Rodriguez 3
2 Dept. of Nanocrystalline Materials and Thin Film Systems, Leibniz Institute of New Materials, Saarbruecken Germany, 1 Department of Chemistry, University of Wuerzburg, Wuerzburg Germany, 3 Department of Electronics, University of Barcelona, Barcelona Spain
Show AbstractDue to their unique structural features and interesting functional properties one dimensional (1D) inorganic materials are gaining high attention. These nanostructures show promising application potential in vacuum and oxidizing atmospheres, which makes them competitive for device fabrication. We have developed a generic approach for size-selective and site-specific growth of nanowires by combination of chemical precursor design and a catalyst assisted growth mechanism. For instance, high-yield synthesis of NWs of tin, vanadium and iron oxides was performed by the chemical vapor deposition of appropriate metal-organic precursors. Axial and radial dimensions of the NWs were varied in the ranges 20-1000 nm and 1-50 µm, respectively by adjusting the precursor feedstock, deposition temperature, and catalyst size. We have investigated the device potential of these 1D building blocks as photo- and gas sensors and obtained electrical characterisation of materials is performed. Magnetic properties of obtained magnetite nanostructures were investigated dependent on shape and chemical history of the samples. In addition, pure tin oxide NWs partially reduced composite wires were grown on sensor platforms and their response towards different gaseous species was recorded. Besides these multiwire devices, individual SnO2 and Fe3O4 nanowires were contacted by FIB nanolithography and the intrinsic properties were investigated to obtain precise informations of electrical and sensing behaviour in different atmospheres. We could show that the sensitivity against CO showed diameter dependence, where a remarkable enhancement of sensor performance was observed with dimishing wire thickness. Moreover, metal oxide heterostructures were synthesized influencing the material properties of the host structures by structural doping with oxides owning different work functions, such as band gap.A brief account of the generic features of our approach for the synthesis of oxide nanowires of various compositions and the results obtained on device applications will be presented.
9:00 PM - JJ6.10
Directed Assembly of Gold Nanoparticle Nanowires for Nanodevices.
Xugang Xiong 1 , Ming Wei 2 , Selvapraba Selvarasah 1 , Sivasubramanian Somu 1 , Ahmed Busnaina 1 , Mehmet Dokmeci 1 , Joey Mead 2
1 NSF Nanoscale Science and Engineering Center for High- rate Nanomanufacturing, Northeastern University, Boston, Massachusetts, United States, 2 NSF Nanoscale Science and Engineering Center for High- rate Nanomanufacturing, University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractWe used alternating electric field assisted approach to assemble gold nanoparticle nanowires from aqueous solution. The effects of electrode geometry and the dielectrophoresis force on the chaining and branching of nanowire formation are investigated. The assembly processes are studied at different time steps both experimentally and numerically using multiphysics software to yield an insightful understanding of the assembly mechanism. Assembly of nanoparticle nanowires with 10 nm resolution has been achieved. The nanostructures of the nanoparticle wires can be controlled by using different electrode designs and assembly parameters. This work provides an approach towards rapid assembly and organization of nanoparticle networks without relying on chemical functionalization of particles or substrates.
9:00 PM - JJ6.11
Nanowire Arrays for Neural Recording Applications.
Sucharita Saha 2 , Donald O'Malley 2 , Latika Menon 1
2 Biology, Northeastern University, Boston, Massachusetts, United States, 1 Physics, Northeastern University, Boston, Massachusetts, United States
Show AbstractHigh density gold nanowire arrays are prepared by meansof electrodeposition inside nanoporous alumina templates.Neuron cells are cultured at the surface of the nanowiresafter coating the Au array with appropriate biomoleculessuited for cell growth. We report our preliminary resultson the nanowire-neural interfaces and cell viability onsuch nanowire arrays. Such structures will eventually beused to record and stimulate neuronal activity.
9:00 PM - JJ6.13
Synthesis of High Quality InN Nanowires and Nano-networks.
Zhihua Cai 1 , Samir Garzon 2 , Richard Webb 2 , Goutam Koley 1
1 Electrical Engineering and USC Nanocenter, University of South Carolina, Columbia, South Carolina, United States, 2 Physics and Astronomy and USC Nanocenter, University of South Carolina, Columbia, South Carolina, United States
Show AbstractHigh quality InN nanowires have been synthesized in a horizontal quartz-tube furnace through direct reaction between metallic Indium and Ammonia using Nitrogen as the carrier gas. Thin film of Au on SiO2/Si substrate has been used as the catalyst layer, facilitating vapor-liquid-solid growth of the nanostructures. The nanowires were grown at a very fast rate of up to 30 μm/hr. Smooth and horizontal nanowire growth was achieved only with nanoscale catalyst patterns, while large area catalyst coverage resulted in uncontrolled and three-dimensional growth. The InN nanowires, which were usually covered with a thin layer of In2O3, grew along [110] direction, with overall diameters 20 – 60 nm and lengths 5 – 15 μm. The synthesized nanowires bent spontaneously or got deflected from other nanowires at multiples of 30 degrees forming nano-networks. The catalyst particles for the NWs were found mostly at the sides of the NW apex which helped them to bend spontaneously or get deflected from other NWs at angles which were multiples of 30 degrees. The bending occasionally resulted in the formation of nanobelts which is probably caused by significant growth rates along both [110] and [1-10] directions. Evidence of NW polarization was also observed from formation of multiple loops during NW growth. The NW based FETs with a back-gated configuration have already been investigated. The gate-bias dependent mobility of the NWs ranged from 50 cm^2/Vs to 250 cm^2/Vs, and their carrier concentration was ~10^18 cm^-3.
9:00 PM - JJ6.15
Catalyst-free Synthesis of Multi-component Nanowires.
Romaneh Jalilian 1 2 , Zhiqiang Chen 3 , Gamini Sumanasekera 2 1
1 Department of Electrical and Computer engineering, University of Louisville, Louisville, Kentucky, United States, 2 Department of Physics, University of Louisville, Louisville, Kentucky, United States, 3 Institute for Advanced Material and Renewable Energy, University of Louisville, Louisville, Kentucky, United States
Show Abstract9:00 PM - JJ6.16
Optimum Control over the Vapor-liquid-solid Nanowire Morphology Through Surface Kinetics.
Shadi Dayeh 1 , Edward Yu 1 , Deli Wang 1
1 Electrical and Computer Engineering Department, University of California-San Diego, La Jolla, California, United States
Show AbstractSemiconductor nanowires (NWs) have been studied intensively over the past decade for a variety of electronic and photonic applications. Understanding the underlying growth mechanism and achieving control over the NW morphology are necessary for widespread practical use of NWs. In this paper, we experimentally distinguish, for the first time, two NW growth regimes defined by the direction of adatom exchange between the NW (InAs) and the substrate (InAs(111)B) in Au-nanoparticle assisted Vapor-Liquid-Solid (VLS) InAs NW growth using metal organic chemical vapor deposition. In the case of NW to substrate adatom diffusion at low tri-methyl-indium flow rate (1µmol/min), uniform diameter NWs are obtained through the VLS growth mechanism with an exponential axial growth with time. As the NW length exceeds the indium surface diffusion length on the NW sidewalls (λNW), linear (14nm/s) axial VLS growth is obtained as well as linear (0.13nm/s) Vapor-Solid (VS) growth along the NW radial direction. This occurs only at distances larger than λNW from the substrate and the NW tip indicating that both the Au-In alloy and the InAs(111)B substrate act as material sinks in this case. The faceted hexagonal NW base was found as a continuum of the NW (110) hexagonal facets and grows with time post nucleation and elongation of the InAs NW in contrast to previous beliefs that the base forms prior to NW growth. For the case of substrate to NW adatom diffusion at high TMIn flow rate (6µmol/min), tapering in the NW, even for NW lengths less than λNW, is obtained. Here, logarithmic axial VLS growth with time is observed for short growth times followed by linear growth (18.6nm/s). The VS radial growth rate at the center of the NW starts in this case at very short growth time (20s) at a rate of 1.6nm/s, more than one order of magnitude higher than the case of NW to substrate surface diffusion. A λNW of ~1µm along the (110) InAs surface and at a growth temperature of 500°C was obtained utilizing solutions of the diffusion equation for NW growth. The results discussed above not only improve our understanding of the fundamentals of NW growth but also set a limit for the lengths of NWs only over which optimum control over NW morphology is possible.
9:00 PM - JJ6.17
Effect of Boundaries on Superconductivity in Single-Crystal Nanowires.
Haidong Liu 1 , Zhiping Luo 2 , Zuxin Ye 1 , Hong Zhang 1 , Wenhao Wu 1 , K. Rathnayaka 1 , Donald Naugle 1
1 Physics, Texas A&M University, College Station, Texas, United States, 2 Microscopy and Imaging Center, Texas A&M University, College Station, Texas, United States
Show Abstract It has been observed recently that carbon nanotubes, semiconductor nanowires, and metallic nanowires of length 100 nm to 1μm can be superconducting if they are in good contact with superconducting leads. Such systems can work as magnetic field sensors, photon detection devices and building blocks for quantum computing units. In this paper, we report experimental studies of the effect of boundaries on superconductivity in much longer single-crystal nanowires with lengths up to 60 μm, whose both ends are in contact with pairs of macroscopic electrodes that are either superconducting (Sn or Pb) or non-superconducting (Au). Our Sn, Pb, and Zn nanowires are fabricated using a template-based electrochemical deposition method. Electric contacts to the nanowires are formed in situ during electrochemical growth as described earlier (Applied Physics Letters 84, 6996 (2004)). This method produces high transparency contacts between a pair of macroscopic electrodes and a single nanowire, avoiding the generation of oxidation and other poor conducting interface layers between a nanowire and electrodes. We will present extensive analyses of the structure and the composition of the nanowires by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which have concluded that (1) the nanowires are single crystalline and (2) the nanowires are clean without any mixing of the materials from the electrodes. We have observed that in relatively short (~6 μm) Sn and Zn nanowires, robust superconductivity is induced at the superconducting transition temperatures of the electrode with which they are in contact. When Sn and Pb nanowires are in contact with a pair of Au electrodes, superconductivity is suppressed completely. In longer nanowires, at least as long as 60 μm, although the suppression of superconductivity by Au electrodes is only partial, the induced superconductivity at a higher transition temperature by superconducting electrodes remains full and robust. Therefore, we have observed an anomalous superconducting proximity effect with a length scale that can not be explained by existing theories. The length scale of our nanowires is significantly longer than that of the other system with which electrode-induced superconductivity has been previously investigated. We will also present the measured current-voltage characteristic in our nanowires which reveal more details of the superconductor-electrode interfaces. The behavior of the nanowires in the applied magnetic field will also be presented. Possible physical mechanisms such as Andreev reflection will also be discussed. We believe this effect should be significantly considered for designing superconducting devices.
9:00 PM - JJ6.18
High-Performance Sub-100 nm Channel Length Ge/Si Nanowire Transistors.
Yongjie Hu 1 , Jie Xiang 1 , Hao Yan 1 , Gengchiau Liang 2 , Mark Lundstrom 3 , Charles Lieber 1 4
1 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 2 Department of Electronic and Computer Engineering, National University of Singapore, Singapore Singapore, 3 School of Electrical and Computer Engineering and Network for Computational Nanotechnology, Purdue University, West Lafayette, Indiana, United States, 4 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractGe/Si core/shell nanowire represents a promising alternative to conventional metal-oxide-semiconductor field-effect transistor (MOSFET) based on Si, due to its unique and clean electronic structure. To explore the size-dependent limits of Ge/Si nanowire field-effect transistor (NWFET) performance, we develop a novel method to fabricate sub-100 nm channel device that overcomes short channel effects by converting Ge/Si in a controlled manner to metallic NiSixGey nanoscale electrodes. Electrical transport measurements demonstrate high-performance with scaled transconductance value of 5.1 mS/µm and scaled on-current of 2.7 mA/µm, which exceed the best reported in p-MOSFETs and NWFETs. In addition, analysis of the intrinsic switching delay benchmark, τ = CV/I, shows that terahertz (THz) intrinsic operation speed is possible when channel length is reduced to 70nm, and that ~2 THz is achieved in our 40 nm device. Comparison of the experiment data with simulations based on semi-classical, ballistic transport model suggests that the NWFET with integrated high-kappa gate dielectric is operating near the ballistic regime. The implications of these results and potential applications will be discussed.
9:00 PM - JJ6.19
Designing for Large Strain in Dislocation Free Si/Ge Nanowire Heterostructures.
J Swadener 1 , Sukgeun Choi 1 , Samuel Picraux 1
1 MPA-CINT, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractWe report on computational and experimental studies of the onset of dislocations in highly strained Si/Ge nanowire heterostructures. Strain is widely used to modify the bandstructure of semiconductors in quantum well devices for improved performance, but the amount of strain that can be imposed in thin films is limited by dislocation nucleation at the interface. For example, for epitaxially grown Ge films on Si (4.2% lattice mismatch) misfit dislocations are introduced for films as thin as 10 nm. In contrast, significantly larger strains without defect introduction should be attainable in nanowire heterostructures due to strain sharing, a lack of lateral confinement, and the changes in dislocation nucleation conditions. For example, the nanowire lateral free surfaces reduce the stress on the Si/Ge interface – particularly at the edge where dislocations could nucleate from heterogeneities. The greatest stress occurs at the center of the nanowire where any dislocation would have to nucleate homogeneously. Our analysis predicts that homogenous nucleation will not occur for Si/Ge axial nanowire heterostructures for diameters of 60 nm or less. At this size, a thin Ge layer sandwiched between two relatively thick Si layers would have a compressive strain of ~4% and a bandgap of less than half the value for bulk Ge. Molecular dynamics (MD) simulations using MEAM potentials show that a perfect dislocation free interface is a stable structure for diameters less than ~25 nm and a metastable structure for nanowire diameters from 25 to 60 nm. Dislocation free Si/Ge nanowires of this size or greater have been grown experimentally and comparisons with the simulations will be discussed. In the experiments, the interfaces are probably not atomically sharp, which reduces the interface strain and the driving force for dislocation nucleation. MD results for these effects will also be compared with the experiments. Our results will be summarized in terms of the maximum strain vs. nanowire diameter for dislocation free heterostructures and additional heterostructures designed to achieve highly strained, dislocation free structures will also be discussed.
9:00 PM - JJ6.2
Nanoscale Chemical Characterization of Vapor-liquid-solid Grown Silicon Wires by Secondary Ion Mass Spectrometry.
Morgan Putnam 1 , Michael Filler 1 , Brendan Kayes 1 , Michael Kelzenberg 1 , Harry Atwater 1
1 Thomas J. Watson Laboratories of Applied Physics, California Institute of Technology, Pasadena, California, United States
Show AbstractVapor-liquid-solid (VLS) growth is a widely employed method for the fabrication of nanowire-based devices. The fundamental understanding and reproducibility of nanowire synthesis would be greatly advanced by nanoscale chemical mapping of catalyst and dopant concentrations. Secondary ion mass spectrometry (SIMS) has high mass and chemical sensitivity but traditionally has high spatial resolution only in the direction of the depth profile. The lateral spatial resolution is on the order of the beam size, normally ~ 1 μm, which would be insufficient for nanoscale chemical characterization. We report here use of a new generation SIMS instrument with ~ 30 nm beam diameter to obtain chemical profiles of catalyst impurity distributions in VLS-grown silicon wires. Silicon wires for SIMS analysis were grown from lithographically patterned gold catalysts by chemical vapor deposition. Wire growth was completed at atmospheric pressure using SiCl4 diluted in H2 at T = 900-1000 oC. Prior to SIMS analysis, the gold catalyst tip was removed. The Cs+ primary ion beam of a Cameca NanoSIMS 50 was configured to depth profile a 4 μm2 area, from which the center 1 μm2 was analyzed. A distinct depth profile was obtained for residual gold trapped in the silicon wires by the VLS growth process. Near the tip of the wire a gold rich region was observed with concentrations > 1018 atoms/cm3, while further into the wire the gold concentration was ~ 1017 atoms/cm3. These gold concentrations are greater than the equilibrium concentration of gold in silicon, 1016 atoms/cm3 at the growth temperature. In addition to a depth profile of gold in the silicon wire, two-dimensional images of the cross-sectional composition of the wire were produced with 100 nm spatial resolution, thus providing three-dimensional mapping of the catalyst concentration in a silicon wire. Lastly, the measurement of both p-type and n-type dopant concentrations at pn-junctions in silicon wires will be discussed.
9:00 PM - JJ6.20
Horizontally Aligned SiC Nanowires on Sapphire.
Jian Shi 1 , Qingkai Yu 2 , Shin-Shem Pei 2 , Hao Li 1
1 , University of Missouri-Columbia, Columbia, Missouri, United States, 2 , University of Houston, Houston, Texas, United States
Show AbstractPrecise directional and positional control of one-dimensional (1-D) nanostructures, especially in horizontal directions, are critical to 1-D nanostructure based nanodevices. In the present study, horizontally aligned SiC nanowires were achieved on a-plane, c-plane and r-plane sapphire substrates in a hot-wall chemical vapor deposition system using SiO vapor and solid carbon as the precursors. Au nanoparticles (NPs), Ni NPs and Fe-Mo NPs were used as the catalysts. Scanning electron microscope (SEM), transmission electron microscope (TEM), and X-Ray diffraction were used to characterize the as-received SiC nanowires on sapphire substrate. It was observed that catalysts play a very important role in determining the alignment of SiC nanowires on substrates. In general, Au nanoparticles (NPs) and Fe-Mo NPs tends to yield horizontally aligned SiC nanowires on the substrates, while Ni NPs tends to yield curled SiC nanowires, which do not stick to the substrates. It was also found that the growth directions of the horizontally aligned SiC nanowires match certain crystal directions of the sapphire substrate and small lattice mismatch was also found between the SiC nanowires and the sapphire substrate in the matching crystal directions. This may indicate epitaxial growth, but further investigation is needed. The influence of other experimental conditions on the growth of SiC nanowires will also be discussed.
9:00 PM - JJ6.23
Field Emitting Properties of Self-assembled Ni Silicide Nanowires.
Joondong Kim 1 , Youngjin Kang 2 , Dojin Kim 2 , Wayne Anderson 3 , Chang-Soo Han 1
1 Nano-Mechanical Systems Research Center, Korea Institute of Machinery and Materials, Daejeon Korea (the Republic of), 2 Micro-Electronic Technology Lab, Chungnam National University , Daejeon Korea (the Republic of), 3 Electrical Engineering, University at Buffalo, State University of New York, Buffalo, New York, United States
Show AbstractNanowire or nanotube has been attracted as an effective cold cathode due to the high aspect ratio. Moreover, an excellent electrical conductive nanowire would enhance the electron emission performance. Silicides have been utilized to be contact materials in Si technology due to the compatibility to Si and low resistance property, which drives interests in the silicide nanowire growth and applications [1-3] to be a nanoscale interconnection, a microscopy tip, or a emitting entity. Ni silicide nanowires were spontaneously grown by physical vapor deposition (PVD) in a dc magnetron system. The deposited thin Ni film was formed a silicide layer by reacting to Si. The further Si supply provides Ni diffusion resulting to growth of Ni silicide nanowire above the silicide layer. Field emission measurement was performed in a vacuum condition of 10-6 Torr at room temperature providing a high current density at a reduced electric field. The emitting current density of 10 μA/cm2 was reached at 750 V. It is worthy to note that the silicide layer was used as an electrode due to the high conducting properties. This self-assembled Ni silicide nanowires grown above a silicide layer may provide a feasible scheme of the one-dimensional structured display application. [1] J. Kim, D. Shin, E.-S. Lee, and C.-S. Han Appl. Phys. Lett. 90, 253103 (2007) [2] J. Kim and W. A. Anderson, Nano Lett. 6, 1356 (2006). [3] J. Kim and W. A. Anderson, Appl. Phys. Lett. 86, 253101 (2005).
9:00 PM - JJ6.24
Microstructure of SnO2 Nanowire and Field-effect Transistor based on SnO2 Nanowire.
Yanbin Chen 1 , Xiaoqing Pan 1 , Qing Wan 2 , Eric Dattoli 2 , Wei Lu 2
1 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, 48109, Michigan, United States, 2 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, 48109, Michigan, United States
Show Abstract9:00 PM - JJ6.25
Synthesis and Properties of GaAs/AlGaAs Nanowire Heterostructures for Nanoscale Electronics.
Michael Tambe 1 , Sung-Keun Lim 1 , Megan Brewster 1 , Silvija Gradecak 1
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show Abstract9:00 PM - JJ6.26
Polymer Composites with Oriented Magnetic Nanowires as Fillers.
Kusuma Keshoju 1 , Li Sun 1
1 Mechanical Engineering, University of Houston, Houston, Texas, United States
Show AbstractMetallic nanowires with excellent mechanical and electrical/thermal conductivity have been introduced into polymer matrix to form composites. Here we report on the mechanical property investigation of polydimethylsiloxane (PDMS) based composite with nickel nanowires as fillers. The nickel nanowires are first fabricated by template-assisted electrochemical deposition and then collected after the selective dissolution of template matrices. The use of ferromagnetic nanowires allows us to use external magnetic field to control the alignment and distribution of nanowires in liquids. Different form dielectrophoresis and synchronous electrorotation, magnetic manipulation provides a cost effective, non-contact, and versatile approach to control nanostructured materials in fluids over large space. Composites with longitudinal, transverse, oriented and random oriented nanowires were studied. Tensile tests showed that the composites with longitudinal arrangement have high elastic modulus and strength compared to other samples. Elastic moduli from tensile tests were compared with classical Halpin-Tsai theoretical mode. The interfacial shear strength between nanowires and PDMS has been studied by pull-out measurements. Scanning electron micrographs revealed the fiber surfaces were coated with thin layers of polymer to provide good interfacial load transfer.
9:00 PM - JJ6.27
Assembly, Patterning, and Alignment of Metallic Nanowires and One-Dimensional Metal/Single-Wall Carbon Nanotube and Metal/Semiconductor Nanowire Heterojunctions Directly on Surfaces.
Francis Zamborini 1 , Aneta Mieszawska 1 , Greg Slawinski 1
1 , University of Louisville, Louisville, Kentucky, United States
Show Abstract9:00 PM - JJ6.28
Electron Transport Properties in InAs Nanowires.
Shadi Dayeh 1 , Edward Yu 1 , Deli Wang 1
1 Electrical and Computer Engineering, UC San Diego, La Jolla, California, United States
Show Abstract9:00 PM - JJ6.29
Multisegment Nanowires for Nanoelectronics and Biosensors.
Cengiz Ozkan 1
1 Mechanical Engineering, University of California at Riverside, Riverside, California, United States
Show Abstract9:00 PM - JJ6.3
Guided Growth of GaN nanowires using Porous Templates.
Zhen Wu 1 , Yung Jung 2 , Latika Menon 1
1 Physics, Northeastern University, Boston, Massachusetts, United States, 2 Mechanical Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractWe describe our results on the growth of single crystal GaN nanowires on Ni-patterned sapphire wafers. We show a strong dependence of morphology and orientation of nanowires on the catalyst parameters, such as deposition mode of the catalyst and also the dimensions of the catalyst. For example for very large catalyst dimensions, several nanowires are seen to grow from a single catalyst. On the other hand for very small dimensions of the catalyst, the GaN orientation is seen to follow step-edge patterns on the cleaved sapphire surface. Detailed analysis of these results by means of high resolution scanning electron microscopy and atomic force microscopy will be presented
9:00 PM - JJ6.30
GeSb Nanowire Based Phase Change Memory.
Keith Chan 1 , Xin-Yu Bao 2 , Yong Ding 3 , Zhong-Lin Wang 3 , Brian Maple 1 4 , Deli Wang 2
1 Physics Department, UC San Diego, La Jolla, California, United States, 2 Electrical and Computer Engineering, UC San Diego, La Jolla, California, United States, 3 School of Materials Science and Engineering, , Georgia Institute of Technology, Atlanta , Georgia, United States, 4 Institute for Pure and Applied Physical Sciences, UC San Diego, La Jolla, California, United States
Show Abstract9:00 PM - JJ6.32
Kinetics Controlled Ge2Sb2Te5 Nanostructures for PRAM Application by Pulse Induced Evaporation System.
Hyunjung Kim 1 , Junhyuck Jeon 1 , Sikyung Choi 1
1 Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of)
Show AbstractRecently, wireless communication systems such as the ubiquitous mobile phone have grown in popularity. These systems require new memory devices with features that include low power consumption, non-volatility, and a high density. These requirements are a driving force in the development of a universal memory that combines all of the advantages of SRAM, DRAM, and flash RAM. Phase-change random access memory (PRAM) is widely regarded as the most feasible candidate as next-generation memory due to its feasible programming characteristics, even with programmable resistor elements of in the nanometer size range. However, it is essential to reduce the size of phase-change materials to the sub-lithographic length scale in order to enable high-density operations. This is a major bottleneck that limits the true potential of these materials. As top-down fabrication technologies are approaching the physical limits and because they incur cost constraints, bottom-up strategies have gained considerable momentum. In many reports, GST nanowires have been synthesized using the Vapor-Liquid-Solid (VLS) mechanism with a gold nanoparticles catalyst in a horizontal tube furnace. Although research efforts focused primarily on the synthesis of nanostructures (NSs), assembly remains a significant hurdle that stunts the development of nanodevices. Moreover, aligning cell arrays using the VLS mechanism is limited.In this study, a new method for fabricating GST nanowires termed the Electrical Pulse Induced Evaporation System is introduced. It is believed that this method has the important merit of being able to array GST nanostructure very rapidly. Krätschmer and Ijima produced NSs by passing electric current between two electrodes while controlling their distance. With this in mind, GST NSs were synthesized in this study. The substrate used to fabricate the GST nanowires was Pt/Ti/SiO2 deposited onto a Si wafer. For GST NSs, nominally Ge2Sb2Te5 film targets were heated to several hundred degrees and then biased with a positive voltage pulse for the short time (tens to hundreds nano-seconds) to support the evaporation of the Ge2Sb2Te5 film. The diameters of the nanowires ranged from several tens of nm to several μm. Quantitative analysis using X-ray spectroscopy (EDS) point scanning confirmed that Ge, Sb, and Te were present at an atomic ratio of 2:2:5. High-resolution TEM (HRTEM) imaging revealed that the as-synthesized GST NSs were single crystalline. The reciprocal lattice peak obtained by a two-dimensional Fourier transform of HRTEM was indexed to a hexagonal close-packed (hcp) Ge2Sb2Te5 structure with six (01-10) plane surfaces. SPM topography images of GST NS were utilized to estimate the growth mechanism. I-V curves of the NS using a nanoprobe appeared differently in accordance with the NS shape, showing low resistance in the crystalline state. Additionally, the NSs could switch reversibly between reset and set states over many cycles.
9:00 PM - JJ6.33
Radial Periodic Instability in Vertically Aligned Sub-30nm ZnO Nanowires.
D. Baptista 1 , S. Dalal 2 , R. Papaleo 3 , K. Teo 2 , W. Milne 2 , F. Zawislak 1
1 Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil, 2 Engineering Department, University of Cambridge, Cambridge United Kingdom, 3 Faculdade de Física, Universidade Católica do Rio Grande do Sul, Porto Alegre Brazil
Show AbstractThe control of the sizes and shapes of nanostructures is crucial for the development of novel devices involving self-organized growth. Several structures such as wires, belts, tetrapods, helix and others have been fabricated through different growth conditions. Some of them are grown in non-equilibrium conditions where the growth kinetic plays important role. One interesting example is the chain and helical-like growth of whiskers that involves instabilities with self-oscillating character. This self-oscillation is directly connected to the processes governing the vapor-liquid-solid (VLS) mechanism of growth. Periodic changes of the diameter of Si whiskers have been reported early and were attributed to fluctuations in the supersaturation during the VLS mechanism, according to the Gibbs-Thomson effect. These instabilities are very dependent to the growth conditions as well as the size of the catalytic particles. A systematic work reporting on the experimental conditions for radial periodic instability in thin nanowires is still missing.In this contribution we report on the radial periodic instability in sub-30 nm vertically aligned ZnO nanowires grown using single-ion nanolithography. The ZnO nanowires are grown in a tube furnace by evaporation of a ZnO:graphite mixture onto sapphire substrates patterned with Au catalyst. The deposition temperature and pressure varied from 600 to 890 °C and 1 to 9 mbar respectively. Each wire grows from isolated sub-30 nm Au islands formed after lithography. The radial periodic instability is strongly dependent to the growth conditions (temperature, pressure, catalyst size) and appears only in special growth conditions. It is typically observed as a row of knots and necks with respective diameters of 28 and 60 nm in a frequency of 1/150 nm-1. A map indicating the regions for smooth surface or instable growth is presented. The wires were characterized using scanning electron microscopy (SEM), high-resolution transmission electron (HRTEM) and X-ray diffraction (XRD).
9:00 PM - JJ6.4
Electrical Characterization of Silicon Nanowires and Crossed Nanowires Fabricated by a Top-down Approach.
Francois Vaurette 1 , Bruno Grandidier 1 , Dominique Deresmes 1 , Jean-Philippe Nys 1 , Didier Stievenard 1
1 Dpt ISEN, Institut d'Electronique, de Microelectronique et de Nanotechnologie, Villeneuve d'Ascq France
Show AbstractBottom-up elaboration of semiconductor nanowires (NWs) has reached a great interest since the pioneering works of Lieber et al., showing the possibilities to obtain new electrical and optical devices integrated in novel architectures, using low cost microfluidic based manipulation or more recently, Langmuir-Blodgett derived technique. However, in spite of the great technological interested associated with these one-dimensional structures, there is only few direct electrical measurements of the doping level. Moreover, due to the high surface-volume ratio of the nanowires, the surface states play an important role on the electrical behaviour of the nanowire. Depending on their electrical activity, the measured conductance can vary on a few orders of magnitudes and theoretical calculations have recently confirmed their importance on the nanowire conductance. We propose an original approach which allows determining the density of nanowires surface states both with their resistivity.For this, we need a set of nanowires with different lengths and various widths. At the moment, it is difficult to routinely obtain calibrated nanowires in length and diameter from bottom-up approach. So, we have used a top-down one. Silicon nanowires were fabricated using e-beam lithography and RIE etching on SOI substrate (thickness of silicon : 20 nm N and P-type intentionally doped at a few 1e19cm-3, thickness of silicon dioxide : 145 nm, substrate of 700 μm). Using HSQ resist (Hydrogen Silsesquioxane), we can obtain nanowire widths from 100 nm down to 10 nm, and an RIE etching with a SF6/N2/O2 plasma is used to fabricate the nanowires. Then, structures are connected with evaporated metallic contacts, and lateral gates are made along the nanowires.Thanks to the different lengths for each nanowires width, we can extract the intrinsic resistance of the nanowires, excluding the contacts resistances and the electrodes resistances. Measurements were made on both N and P doped types and we found resistances superior to theoretical resistances. We explain these higher resistances by surface defects on nanowires naturally oxidized. The widths of the nanowires are determined by Scanning Electron Microscopy and by Atomic Force Microscopy, and using a simple model, we are able to determine the depletion width due to surface defects, and to deduce the doping level and the density of surface states. We found a reasonable value of 1e13 to 2e13 defects/cm2, associated with a doping value of 4e19 to 8e19 cm-3. Hydrogen surface passivations are in progress in order to decrease this surface states density.Finally, 10 nm-crossbar nanowires with lateral gates were analyzed and we show the possibility of realizing nanoswitches by applying opposite voltages on two gates, leading to the depletion of one branch whereas the current can go through the other branch.We would like to thank Jacques Gautier (CEA Grenoble) for the SOI substrates.
9:00 PM - JJ6.7
One Dimensional Electron Gas in InAs/InP Radial Nanowire Heterostructures
Qihua Xiong 1 , Xiaocheng Jiang 1 , Charles Lieber 1 2
1 Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 2 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractElectrons or holes confined in one-dimensional (1D) nanotube or nanowire heterostructures represent important systems for quantum coherent transport studies. Here, we demonstrate the rational design and synthesis of InAs/InP core/shell nanowires as a novel 1D electron gas (1DEG) system. Transport measurements on individual nanowires show clearly electron accumulation in the quantum confined InAs/InP nanowires, and yield the highest room-temperature electron mobility of 11,500 cm2/V-s among 1D nanostructures. As temperature is lowered, the zero-bias conductance was found to exhibit a series of plateaus versus back gate voltage that correspond to electron transport through discrete 1D subbands. The measured subband spacing extracted from these measurements is in good agreement with calculations for a cylindrical confinement potential. The potential of this nanowire 1DEG system for quantum electronics and other areas will be discussed.
9:00 PM - JJ6.8
Nanoscale One-Dimensional Materials and Devices.
Darren Lee 1 , Anna Drury 1 , Shweta Chaure 2 , Werner Blau 1
1 School of Physics, Trinity College Dublin, Dublin Ireland, 2 The Centre for Materials Research, Queen Mary, University of London, London United Kingdom
Show AbstractPorous anodic alumina membranes are readily synthesised by anodisation of aluminium in weak acidic electrolytes. The size and density of the pores are controlled by the choice of electrolyte and by the anodising voltage. These porous alumina substrates are then used to synthesise high density ordered arrays of one dimensional nanostructures. Arrays of conductive polymer nanowires are formed using electrodeposition techniques. Nano-Schottky diodes are formed between polypyrrole nanowires and thermally evaporated aluminium and the electrical characteristics of the metal / semiconductor junctions measured. The values of the diode characteristics are found to be comparable to those found in literature for similar metal / conducting polymer Schottky junctions. The nanowires are also characterised using Raman spectroscopy and scanning electron microscopy techniques and it is found that the diameters of the nanowires are dependant on the size of the pores in the alumina membrane.Hybrid nanostructures are also synthesised using electrodeposited metals and polymers. Cobalt and nickel metal, both of which are used as catalysts for thermal chemical vapour deposition (CVD) growth of carbon nanotubes, are deposited in the pores of porous alumina using electrochemical deposition techniques. These substrates are then placed in the CVD apparatus and subsequently, carbon nanotubes are grown in the pores.
9:00 PM - JJ6.9
Modified Tin Oxide Nanofibers for Gas Sensor Applications.
Kathy Sahner 1 , Il-Doo Kim 2 , Harry Tuller 1
1 Materials Science and Engineering Department, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Center for Energy Materials, KIST, Seoul Korea (the Republic of)
Show AbstractDue to their ability to detect trace concentrations of various gases, typically in the ppm levels and above, semiconducting metal oxides such as SnO2, TiO2, and WO3 have received considerable attention. Inspired by the exceptional sensing properties of carbon nanotubes and silicon nanowires, new types of one dimensional metal oxide architectures were recently introduced. For example, TiO2 nanofiber mats were obtained by electrospinning followed by hot-pressing and calcination. This nanowire network exhibited exceptional sensitivity towards NO2 in dry air with a detection limit estimated to be below 1 ppb [1].In the present study, SnO2 fiber mats, prepared in a similar manner, were investigated. Using a poly vinylacetate–SnO2 composite precursor, the sensor fibers were electrospun on different substrate materials prepared with Au and Pt interdigitated electrodes, hot-pressed, and annealed. As observed by electron microscopy, this leads to very fine surface sub-structures and an enhanced surface-to-volume ratio. The resistances of specimens were measured at temperatures between 200 °C and 400 °C in response to exposure to controlled levels of respectively, NO2, CO, and methane admixed with dry air. An attractive feature of the SnO2-based sensors compared to TiO2 was its much lower overall resistance by 4 or more orders of magnitude. NO2 detection, well below the ppm level, was achieved. Cross interference of CO was found to be more pronounced, yielding for example a response R0/R of 7 at 50 ppm CO compared to 1.33 in the case of TiO2. Reasonably fast response towards the reducing gases CO and methane was obtained even at a reduced temperature of 200 °C attributed to the unique surface structure of the nanofibers. The mechanisms for NO2 sensitivity will be discussed with respect to adsorption characteristics in relation to the unique microstructure. [1] Kim, Il-Doo, Rothschild, Avner, et al., Nano Lett.; 2006; 6 (9) 2009-2013.
Symposium Organizers
David Gracias Johns Hopkins University
Ritesh Agarwal University of Pennsylvania
Pavle Radovanovic University of Waterloo
Joerg Ackermann Universite de la Mediterranee
JJ7: Integrated Nanowire Devices
Session Chairs
Wednesday AM, November 28, 2007
Room 306 (Hynes)
9:30 AM - **JJ7.1
Chemical and Sensing Applications of Silicon Nanowires.
Lee Shuit-Tong 1
1 Center Of Super-Diamond and Advanced Films (COSDAF), & Department of Physics & Materials Science, City University of Hong Kong, Hong Kong China
Show AbstractSilicon nanowires (SiNWs) are excellent candidates for sensing, chemical, and catalysis applications, because they not only have a large fraction of surfaces, but also their surfaces can be easily modified or functionalized. Further, Si nanowires can serve both as anchors/concentrators for adsorbates, and transducers and carrier transporters. These unique properties are exploited in various sensing, chemical and catalysis applications. In this talk, we report the unusual sensitivity of electrical properties of Si nanowires towards gas molecules. H-SiNWs are extraordinarily reactive; they can reduce metallic ions to metals and hydrocarbons to carbon nanostructures. SiNWs are also excellent substrates for ultrasensitive surface-enhanced Raman spectroscopy (SERS) detection. We further describe the use of SiNWs as both the electron-transfer mediator and immobilization matrix to construct amperometric biosensors. The surfaces are shown to play a dominant role in determining the transport and sensing properties of SiNWs. Si nanowires offer exciting opportunities for sensing, chemical and catalytic applications.
10:00 AM - JJ7.2
Highly-scalable, Ultra-low Power Nonvolatile Phase-change Nanowire Memory Device.
Yeonwoong Jung 1 , Se-Ho Lee 1 , Ritesh Agarwal 1
1 Materials Science & Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractIn this work, we present novel nanowire-memory devices operating based on fast and reversible crystalline to amporphous phase-transition in nanowires. Nanowires assembled from chalcogenide materials (Ge-Sb-Te alloys) are shown to undergo crystalline-amorphous transition via electric field-induced Joule heating. Each structural phase displays distinct electronic states accompanied by large differences in electrical resistances, which represents a two-bit data storage process. We incorporate a combination of bottom-up and top-down approaches in nanowire synthesis and nanowire-based device integration, respectively. Phase change nanowires were synthesized via conventional Vapor-Liquid-Solid (VLS) process and Focused Ion Beam (FIB) assisted-direct Pt writing was applied to fabricate the memory devices. By assembling composition controlled Ge2Sb2Te5 nanowires, we have investigated detailed nanowire size-scaling effects on critical device parameters, such as, switching currents, cyclability endurance, switching speed, and data retention properties. Highly-efficient memory switching scaled-down to 30 nm was observed with dramatic reduction in switching currents (160 μA), thereby demonstrating low power consumption (<1 mW). The phase-transition nanowire devices reliably switch between the two states for over >105 cycles under alternating write/read/erase/read pulses, while the large margin (>100 times) of resistance differences is not compromised by high switching speed (~ 50 ns). Moreover, size-dependent spontaneous recrystallization dynamics is systematically studied as a function of nanowire size through electrical measurements at elevated temperatures. The analysis determines recrystallization activation energies and data retention times, which shows non-volatile data storage achieved down to 20 nm. In-situ TEM studies clearly reveal that memory switching is indeed due to thermally-activated crystallization occurring via nucleation-dominant mechanism, while the observed nanowire size-dependent behavior is attributed to the enhanced heterogeneous-nucleation owing to the increased surface-to-volume ratio at smaller diameters. Our results demonstrate that phase-transition nanowires satisfy attributes of ideal memory-devices and hold great promise toward non-volatile and ultra-high memory density in highly-integrated device architectures. In addition, this study suggests the ultimate limit in exploring fundamental size-dependent phase transitions in nanoscale systems, which is not hindered from etching-induced structural damages involved in conventional top-down technologies. Results from multiply aligned-nanowires and large-scale epitaxially grown nanowire-devices will also be presented.
10:15 AM - JJ7.3
Crystalline/Amorphous Core/Shell Nanowire-Based Nonvolatile Memory.
Yajie Dong 1 , Guihua Yu 1 , Wei Lu 1 2 , Michael McAlpine 1 , Charles Lieber 1 3
1 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 2 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States, 3 Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractCrossbar structures have been a central part of many proposed nanoelectronic architectures because of their simplicity of fabrication, potential for three-dimensional scaling and inherent redundancy, which supports defect tolerance. Research has led to considerable success in development of novel approaches for crossbar array fabrication, however, the development of nonvolatile memory (NVM) devices with fast switching speed, long retention time, and intrinsic addressability in arrays remains an area of active research. In this talk we report work towards high performance NVM based on a crystalline/amorphous silicon (c-Si/a-Si) core/shell nanowire crossed metal nanowire structure. Electrical transport studies of single crossed devices demonstrate reproducible bistable switching behavior with an ON/OFF ratio exceeding 10^6, endurance longer than 10^4 cycles, writing time less than 100 ns, retention time in excess of two weeks, and notably, an intrinsic rectification ratio ca. 10^6. The origin of the unique rectification behavior has been addressed through variations in the metal nanowire and temperature-dependent transport studies. In addition, one- and two-dimensional crossed c-Si/a-Si nanowire – metal nanowire arrays have been fabricated and characterized. The results from these array studies and prospects for future applications will be discussed.
10:30 AM - JJ7.4
Direct Current Nanogenerator Driven by Ultrasonic Wave.
Xudong Wang 1 , Jinhui Song 1 , Jin Liu 1 , Zhong Lin Wang 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractThe operation of nanodevices fabricated with one-dimensional nanostructures usually requires very low power, which is provided by an external source, such as a battery. The reliance on an external power source that may have to be replaced or recharged regularly presents a limitation for these systems. Various approaches have been developed for energy scavenging with applications in wireless electronics, such as thermoelectric, piezoelectric thin-film, and vibrational cantilevers. We have recently demonstrated an innovative approach for converting nanoscale mechanical energy into electric energy by piezoelectric zinc oxide (ZnO) nanowire (NW) arrays with the help of Atomic Force Microscope (AFM) [1]. To improve the power generation capabilities of the system, it is necessary to replace the AFM tip with a simpler source of mechanical energy that can actuate all the NWs simultaneously and continuously. We solved these problems by using ultrasonic waves to drive the motion of the NWs, leading to the production of a continuous current [2]. The nanogenerator was fabricated with vertically aligned zinc oxide nanowire arrays that were placed beneath a zigzag metal electrode with a small gap. The wave drives the electrode up and down to bend and/or vibrate the nanowires. A piezoelectric semiconducting coupling process converts mechanical energy into electricity. The zigzag electrode acts as an array of parallel integrated metal tips that simultaneously and continuously create, collect, and output electricity from all of the nanowires. The approach presents an adaptable, mobile, and cost-effective technology for harvesting energy from the environment, and it offers a potential solution for powering nanodevices and nanosystems. This prototype has also been improved for generating electricity inside bio-fluid when stimulated by ultrasonic waves. The potential of increasing output current and voltage has also been revealed by connecting multiple NGs in parallel and serial, respectively, clearly demonstrating the possibility of raising output power by three-dimensional integration and architecture. The output current was increased by 20-30 times and reached as high as 35 nA when a 2 mm2 size NG was placed at a region where the ultrasonic waves were focused. This work unambiguously shows the feasibility of NG for power conversion inside bio-fluid. It sets a solid foundation for self-powering implantable and wireless nanodevices and nanosystems in bio-fluid and any other type of liquid.[1] Z.L. Wang and J.H. Song “Piezoelectric Nanogenerators Based on Zinc Oxide Nanowire Arrays”, Science, 312 (2006) 242-246.[2] X.D. Wang, J.H. Song, J. Liu, and Z.L. Wang “Direct current nanogenerator driven by ultrasonic wave”, Science, 316 (2007) 102-105.
10:45 AM - JJ7.5
Nanowire-nanoparticle Assemblies with Novel Optical Properties: Exciton-plasmon Resonance, Eenergy Transfer, and Light-harvesting.
Alexander Govorov 1 , Pedro Hernandez 1 , Jaebeom Lee 2 , Nicholas Kotov 2
1 , Ohio University, Athens, Ohio, United States, 2 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractWe explore the systems assembled from one-dimensional nanowires (NWs) and zero-dimensional spherical nanoparticles. Optical responses of NP-NW system become enhanced due to energy transfer between the components of assembly and plasmon enhancement of photonic fields. In the case of semiconductor NPs and NWs (CdTe), we describe the effect of energy channeling from NPs toward a NW [1]. To model Foerster transfer in the NP-NW system, we employ the rate equations and fluctuation-dissipation theorem. The NP-NW energy transfer rate for this system behaves as 1/d^5, where d is the NP-NW distance. Using metal NPs as plasmon resonators, one can enhance optical absorption or emission [2]. For the enhancement effect, it is essential to bring the system into the plasmon-photon or plasmon-exciton resonances. This can be realized, for example, with Au-CdTe and Ag-CdTe material systems [2]. If a NP-NW linker is sensitive to environmental parameters, such as temperature or protein concentration, the assembly has sensor properties. We model two types of structures with sensor properties realized in recent experiments [2,3]. The first structure incorporating polymer linkers is sensitive to the temperature. The second structure is a CdTe-NW conjugated with Au-NPs; the position of exciton peak in such structure is sensitive to the protein concentration [3]. We found two important features of NP-NW assemblies: (1) Large plasmon enhancement factor due to the collective action of many metal NPs conjugated with a NW, (2) One-dimensional diffusion and drift of excitons along a NW. The second effect leads to the wavelength shift effect used for bio-sensing in ref. [3]. Potentially, NW-NP assemblies can be integrated into electrical circuits as light-harvesting/photo-voltaic elements. Another potential application is in fluid sensors. [1] J. Lee, A. O. Govorov, and N. A. Kotov, Nano Letters 5, 2063 (2005). [2] J. Lee, A. O. Govorov, and N. A. Kotov, Angewandte Chemie, 117, 7605 (2005); Nano Letters, 4, 2323 (2004). [3] J. Lee, P. Hernandez, J. Lee, A. O. Govorov, and N. A. Kotov, Nature Materials 6, 291 (2007).
11:30 AM - JJ7.6
Transparent Electronics Based on SnO2 Nanowires.
Eric Dattoli 1 , Qing Wan 1 , Wei Guo 2 , Yanbin Chen 2 , Xiaoqing Pan 2 , Wei Lu 1
1 Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractWe report fully-transparent electronic devices fabricated on glass and plastic substrates using lightly doped SnO2 nanowires. The nanowires were grown using a simple, low-cost vapor transport method and exhibit excellent optical transmittance and electrical mobility. After growth, a physical transfer technique was employed to transfer the nanowires to diverse substrates and form thin-film structures. Nanowire-based transparent thin-film transistor (TFT) device arrays were fabricated using conventional photo-lithography, sputtering and annealing processes. Our electrostatic simulations verify that the nanowire TFTs with even relatively low surface-coverage can perform effectively as devices with a continuous single-crystalline thin-film channel. Key performance metrics obtained on the transparent nanowire TFTs such as mobility (> 100 cm^2/V-s), on-off ratio (> 10^3), operation voltage (2.5 V) are encouraging. Studies on the high-frequency properties and simple integrated-circuits based on the nanowire-TFTs will also be discussed.
11:45 AM - JJ7.7
Transparent Electronics Based on Metal Oxide Nanowires and Aligned Carbon Nanotubes.
Fumiaki Ishikawa 1 , Sanghun Ju 2 , Tobin Marks 3 , David Janes 2 , Chongwu Zhou 1
1 Department of Electrical Engineering, University of Southern California, Los Angeles, California, United States, 2 School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana, United States, 3 Department of Chemistry and the Materials Research Center, Northwestern University, Evanston, Illinois, United States
Show AbstractNext generation display technologies are seeking for a replacement of poly-silicon thin-film transistors (TFTs) and amorphous silicon thin-film transistors that are currently used in commercial displays, due to the limitation of transparency. Oxide nanowires (e.g., In2O3 and SnO2) and carbon nanotubes are promising candidates for future see-through display electronics with excellent transparency and mechanical flexibility. In this talk, we will present fully transparent transistors based on metal oxide nanowires and aligned carbon nanotubes. N-type In2O3 nanowire transistors were fabricated by depositing nanowires on a glass substrate with prefabricated indium-zinc oxide gate electrodes and Al2O3 dielectric. Indium-tin oxide (ITO) was subsequently sputter coated to contact the nanowires and work as source and drain electrodes. The resulting devices exhibited good transistor characteristics with subthreshold swings ~ 160 mV/dec, on/off ratios of 106, and effective mobilities ~ 514 to 300 cm^2/Vs. In addition, these transistors are highly transparent with optical transmittance ~ 82% in the 350 - 1350 nm wavelength range. Furthermore, we have demonstrated fully transparent p-type transistors based on aligned nanotubes to complement the n-type nanowire transistors. We first grew massively aligned single-walled carbon nanotubes on quartz substrates, and then a transfer printing technique was developed to transfer the aligned nanotubes from the original substrate to a glass substrate with prefabricated ITO gate electrodes and polymer dielectric layer. ITO source and drain were then defined using photolithography. Notably, based on the aligned carbon nanotubes, we achieved 100% electrical connection between source and drain except fabrication failures. These devices exhibited on/off ratios ~ 103 - 104. The transmittance of the devices was over 80% within the 400 - 1100 nm wavelength range. We have further demonstrated transparent n-type nanotube transistors by coating the nanotubes with polyethyleneimine without hurting the transparency of the device (>80% after coating).
12:00 PM - JJ7.8
Covalently Modified Nanowire Arrays on Plastic Substrates for Sensitive, Flexible, and Selective Chemical Sensors.
Michael McAlpine 1 , James Heath 1
1 Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, United States
Show AbstractIntegrating high performance electronics on biocompatible plastic substrates could enable exciting avenues in fundamental research and novel medical devices. However, the temperature restrictions imposed by these substrates limit their use to low mobility semiconductors such as amorphous silicon and organic semiconductors. The development of novel materials processes for overcoming this restriction could impact a broad spectrum of applications. One area of vital relevance is chemical and biological sensing, which if implemented on biocompatible substrates, could yield breakthroughs in implantable or wearable monitoring systems. Semiconducting nanowires (and nanotubes) are particularly sensitive chemical sensors because of their high surface-to-volume ratios.
Here we present a scalable and parallel process for transferring hundreds of pre-aligned silicon nanowires onto plastic to yield highly ordered films for low power sensor chips. A superlattice pattern transfer process is utilized to produce a film of perfectly aligned 17-nm nanowires at a regular 34-nm pitch on silicon-on-insulator wafers. Elastomeric stamps are subsequently used to peel the wires from the host wafer and comprehensively transfer them to a flexible plastic substrate. Significantly, this transfer process does not disrupt the pristine nano-morphology of the aligned wires. The nanowires are excellent field-effect transistors, and, as sensors, exhibit parts-per-billion sensitivity to NO2, a hazardous pollutant.
Unique to silicon nanowires is the well established silicon surface chemistry, and the assortment of commercially available reagents for modifying the chemical functionality of the native oxide. We exploit these SiO2 surface chemistries to construct a "nano-electronic nose" library, which can distinguish acetone and hexane vapours via distributed responses. Furthermore, we demonstrate that amide coupling of distinctively tailored peptide sequences to the arrays allows for selective discrimination of chemicals often found in the breath of sick patients. This excellent sensing performance coupled with bendable plastic could open up tremendous opportunities in portable, wearable, or even implantable sensors.
12:15 PM - JJ7.9
Gas Sensing with Subwavelength Optical Waveguides.
Donald Sirbuly 1 , Timothy Ratto 1 , Aleksandr Noy 1
1 , Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractHere we demonstrate an optical gas sensing platform that utilizes the evanescent field of a subwavelength semiconductor nanowire waveguide to detect gas vapors. To promote portability, multiplex sensing, and reusability, the optical cavities are integrated into polymeric flow cells. Gas concentration is quantitatively determined by submersing high dielectric nanoparticles within the propagating evanescent field and sensing changes in the shape, density, and/or optical properties of the nanoparticles. The signal from the waveguide can be read-out by monitoring the optical transmission through the waveguide or by collecting photons elastically scattered by the nanoparticles. With sub-femtoliter probe volumes, reusability, and the ability to perform optical spectroscopy, these evanescent field sensors offer a unique design for portable all-optical detection systems. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.
12:30 PM - JJ7.10
Nano and Microwire Arrays from Earth-abundant Catalyst Metals for Photovoltaic Applications.
Michael Filler 1 , Brendan Kayes 1 , Morgan Putnam 2 , Michael Kelzenberg 3 , Harry Atwater 1
1 Applied Physics, California Institute of Technology, Pasadena, California, United States, 2 Chemical Engineering, California Institute of Technology, Pasadena, California, United States, 3 Electrical Engineering, California Institute of Technology, Pasadena, California, United States
Show AbstractSilicon nano and microwire arrays have the potential to enable low-cost, high-efficiency solar cells via efficient radial minority carrier collection in materials with low minority carrier diffusion lengths [1]. As materials selection is a key component of the overall cost for photovoltaics due to their large areas, it is desirable to replace the Au catalyst currently employed during the vapor-liquid-solid (VLS) growth of semiconducting nano and microwires with a material that is inexpensive, earth-abundant, and ideally not a deep-level trap.Arrays of silicon nano and microwires for photovoltaic applications have been grown by VLS chemical vapor deposition (CVD) process with Cu and Ni catalysts. While Cu meets cost requirements, Ni is both inexpensive and not a deep-level trap in silicon. Catalyst arrays were fabricated by photolithographic patterning and etching of a thermally grown oxide, evaporation of catalyst metal, and resist lift-off. Wire growth was carried out at atmospheric pressure near 1000oC on Si(111) substrates with SiCl4/H2 precursor gases. Arrays with nearly 100% vertically aligned wires, exceeding 50 μm in length can be achieved over areas of at least 1 cm2. Transmission electron microscopy (TEM) indicates that wires are single crystalline and grow along the <111> direction. A comparison of wires grown from Cu evaporated films with those grown from Cu/oxide patterns reveals that the oxide serves as a surface diffusion barrier for Cu atoms during the growth process and prevents wire tapering. Photoluminescence (PL) measurements near the silicon band edge of native and passivated wires show that surface recombination dominates bulk recombination in these VLS grown wires. Minority carrier lifetime, diffusion length, and catalyst concentration of Cu and Ni-catalyzed wires will also be discussed.[1] B. M. Kayes, H. A. Atwater, and N. S. Lewis, J. Appl. Phys., 97, 114302 (2005).
12:45 PM - JJ7.11
One-dimensional Nanophotonic Switch Using ZnO Double-quantum-well Structures.
Takashi Yatsui 1 , Suguru Sangu 2 , Tadashi Kawazoe 3 , Motoichi Ohtsu 3 1 , Sung Jin An 4 , Jinkyoung Yoo 4 , Gyu-Chul Yi 4
1 SORST, JST, Bunkyo-ku, Japan, 2 Advanced Technology R&D Center, Ricoh Co. Ltd., Yokohama Japan, 3 Department of Electronics Engineering, University of Tokyo, Bunkyo-ku Japan, 4 Department of Materials Science and Engineering, POSTECH, Pohang Korea (the Republic of)
Show AbstractZnO is a promising material for realizing room-temperature nanophotonic devices, owing to its large exciton binding energy. We report the near-field time-resolved spectroscopy of ZnO nanorod double-quantum-well structures (DQWs). We demonstrated switching dynamics via an optical energy transfer among resonant exciton levels.Two QWs, QW1 and QW2, were used as the input/output and control ports of the switch. Assuming well widths, Lw, 3.2 (QW1) and 3.8 (QW2) nm with Zn0.8Mg0.2O barrier layers, the ground exciton energy level in QW1 (EA1) and the first excited energy level in QW2 (EB2) resonate. In the OFF operation, all the exciton energy in QW1 is transferred to the ground energy level in the neighboring QW2. Therefore, no optical output signals are generated from QW1. In the ON state, the escape route to QW2 is blocked due to state filling in QW2 by applying the control signal; thus, an output signal is generated from QW1.To confirm the switching dynamics, using metalorganic vapor phase epitaxy (MOVPE), we fabricated ZnO/ZnMgO DQWs with Lw = 3.2 and 3.8 nm with 3 nm separation on the ends of ZnO nanorods. To observe the optical properties of individual ZnO DQWs, we used near-field optical microscopy at 15K, with an apertured (D=30nm) fiber probe.The near-field PL with continuous input light excitation from a He-Cd laser (3.814 eV) resulted in a single emission peak from the exciton ground level of QW2 (EB1) at a photon energy of 3.425 eV. This indicates that the excited energy in QW1 was transferred to the excited level of QW2. Furthermore, the excited level of QW2 is a dipole-forbidden level. In contrast, both input and control (3.425 eV with a pulse duration of 10 ps) light excitation resulted in an output signal with an emission peak at 3.435 eV in addition to the emission peak at 3.425 eV, which corresponds to the ground level of QW2. Since the excited level of QW2 is dipole-forbidden, the emission at 3.435 eV indicates that the excitation of the ground level of QW2 blocked the energy transfer from the ground level of QW1 to the excited level of QW2. In other words, we directly confirmed the dipole-forbidden optical energy transfer among resonant energy levels in ZnO QWs via an optical near field.Next, we evaluated the dynamic properties of the nanophotonic switch. We observed time-resolved near-field PL at 3.435 eV with both input and control lasers excitation. The decay time constant was found to be 483 ps.For room-temperature operation, since the spectral width is broadened with thermal energy (26 meV), a higher Mg concentration in the barrier layers and thinner well width are required so that the spectral peaks of the first excited (E2) and ground (E1) levels do not overlap. This criterion can be met using two QWs with 1.5 nm (QW1) and 2 nm (QW2) well widths with an Mg concentration of 50 %, in which the energy difference (E2-E1) in QW2 is about 50 meV.
JJ8: Novel Nanowires and Assembly
Session Chairs
Wednesday PM, November 28, 2007
Room 306 (Hynes)
2:30 PM - **JJ8.1
Programmable DNA Self-Assembly for Functional Electronic and Photonic Nanostructures.
Thom LaBean 1 2 , Anne Lazarides 3 , Gleb Finkelstein 4
1 Computer Science, Duke University, Durham, North Carolina, United States, 2 Chemistry, Duke University, Durham, North Carolina, United States, 3 Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina, United States, 4 Physics, Duke University, Durham, North Carolina, United States
Show AbstractSelf-organization and self-assembly are used repeatedly on multiple length scales in the construction of biological systems. Recently, we have made major advances in the design and control of self-assembly in artificial biomolecular systems at the critical nanometer scale [1,2]. Nucleic acids and proteins have been used successfully to create organized materials with increasingly complex nano-scale patterns, shapes, and dynamics [3,4]. These novel biomolecular assemblies are being employed as scaffolds, templates and actuators for the directed-assembly of additional nano-materials such as metal particles and wires, quantum dots, and carbon nanotubes [5,6]. These promising nano-fabrication techniques can be thought of as programmable, artificial biomineralization processes and will result not only in multicomponent nanowires but also in smart molecular agents for detection and imaging applications. [1] H. Yan, S-H. Park, G. Finkelstein, J.H. Reif, T.H. LaBean Science 301 (2003)1884. [2] T. LaBean, H. Li, Nano Today 2 (2007) 26. [3] S-H. Park, C. Pistol, S.- J. Ahn, J. H. Reif, A. Lebeck, C. Dwyer, T.H. LaBean. Angew. Chem, Int. Ed. 45 (2006) 735. [4] D. Sebba, T.H. LaBean, A.A. Lazarides. submitted (2007). [5] S-H. Park, H. Yan, J.H. Reif, T.H. LaBean, G. Finkelstein. Nanotech. 15 (2004) S525. [6] S-H. Park, M.W. Prior, T.H. LaBean, G. Finkelstein. Appl. Phys. Lett. 89 (2006) 033901.
3:00 PM - JJ8.2
Bionanofabrication of Semiconducting Nanowires using Bacterial Surface Layer Protein/nanoparticles Templates.
Yajaira Sierra-Sastre 1 5 , Sukgeun Choi 5 , Sofia Sotiropoulou 2 , Tyson Moyer 3 , Cameron Bardliving 4 , S. Tom Picraux 5 , Carl Batt 2
1 Chemistry, Cornell University, Ithaca , New York, United States, 5 Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Food Science, Cornell University, Ithaca, New York, United States, 3 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 4 Biomedical Engineering, Cornell University, Ithaca, New York, United States
Show AbstractIn recent years, one-dimensional nanostructures, such as semiconducting nanowires (SCNWs), have been the focus of extensive research due to their potential applications in novel electronic, photonic, and sensing devices. However, to realize the potential of SCNWs in such applications, high density SCNWs arrays with monodispersed diameters and spacing must be created and integrated into various device architectures. Bionanofabrication —a process that takes advantage of the structural specificity of biological systems to create various types of micro/nanostructures— allows parallel fabrication of extremely small feature sizes (<50nm) with controlled diameters and without the slow throughput of conventional ion/e-beam lithography and the high cost of X-ray lithography. Two dimensional surface layer (S-layer) protein lattices from Deinococcus radiodurans were employed in the fabrication of gold nanoparticles (AuNPs) arrays for the spatially controlled growth of SCNWs. S-layer proteins were immobilized on Si(100) and further used to create hexagonal arrays of 5nm citrate-stabilized AuNPs catalysts (~18nm interparticle spacing). SCNWs of germanium and germanium/silicon alloys were successfully grown via a vapor-liquid-solid mechanism. Under the vapor deposition conditions used for NWs growth, neither the AuNP diameter, nor the protein organic layer and native oxide were limiting factors for nucleation. A density of 0.14 NW/μm2 GeNWs with an average diameter of ~153nm was achieved for NWs grown on non-patterned AuNPs substrates. On the other hand, GeNWs grown from biotemplated AuNPs exhibited higher densities (25±4 NWs/μm2) and smaller diameters (<21nm). Different CVD parameters and crystallographic substrate orientations are being explored to faithfully transfer the highly-ordered array structure of the S-layer-patterned catalysts into that of the synthesized NW arrays. We envision that vertical growth will allow the three dimensional integration of more complex structures such as room temperature ultraviolet NW nanolasers and vertical field-effect-transistors arrays.
3:15 PM - JJ8.3
Biomediated Organization, Templating, and Integration of Nanowire Assemblies.
Erik Spoerke 1 , Chris Orendorff 1 , Andrew Boal 1 , George Bachand 1 , Bruce Bunker 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractLiving systems are capable of organizing extremely complex nanomaterial configurations. Microtubules and motor proteins are key agents used to direct this organization. We have developed a novel approach that adapts these biological tools to assemble and integrate nanowire structures onto lithgraphic platforms. Utilizing the bioselective interactions between microtubules and their molecular motor counterparts, we can direct the organization of microtubules to form protein-based nanowire templates between lithographic structures. These biological, chemically-functional templates can then either be sacrificed to form metallic, semiconducting, or insulating nanowire interconnects, or they may be preserved as biological templates to direct the nanomaniupulation of other nanowires made of materials such as gold or zinc oxide. In this second, more bioactive approach, combinations of bioselective agents and molecular motors are used to position nanowire cargo onto the organized microtubule assemblies. Combining these approaches, complex, hybrid nanowire materials may also be created. In addition, as solution-based techniques, these two templating approaches can be readily adapted to produce large-scale assemblies of functionally-integrated nanowires. The use of cooperative biological agents to position and integrate nanowires into functional architectures is a novel and promising approach to nanoscale manipulation.
3:30 PM - JJ8.4
Hydrodynamic Stretching Of Single Molecules Of Dna Bound To An Individual Nanowire.
Andrea Carbonaro 1 , Nathan Sanford 1 , Lydia Sohn 1
1 Mechanical Engineering, UC Berkeley, Berkeley, California, United States
Show AbstractA key requirement for the fast hybridization of DNA is stretching the molecule, itself. Most methods that have been developed for DNA stretching are involved and require trapping single molecules of fluorescently-labeled DNA for optical screening. Here, we describe a straightforward approach based on stretching hydrodynamically lambda-phage (λ) DNA bound to a gold nanowire in the vertical channel of a microfludic T-junction. Our approach provides opportunities for both optical and electronic screening.Our device consists of a microfluidic T-junction embedded in a polydimethylsiloxane (PDMS) slab that is permanently bonded to a glass coverslip. The vertical channel of the T-junction is 5000 µm x 200 µm x 30 µm (L x W x H) and the horizontal channel is 10000 µm x 200 µm x 30 µm (L x W x H). A gold nanowire is initially deposited on the substrate and then connected to lithographically-defined platinum (Pt) electrodes. Gold is used so that functionalization, through a biotin-streptavidin bond, with DNA is possible. The PDMS slab is aligned on top of the substrate such that the nanowire is located in the middle of the T-junction and is permanently bonded. Two access holes on either end of the horizontal channel, punched through the PDMS slab before sealing, are used to inject TT buffer (pH 8) at a rate of 0.1–1 µL/min. An access hole at the far end of the vertical channel serves as an outlet. We have performed measurements to confirm that flow is laminar and diffusion between streamlines is negligible. These conditions are necessary for successful DNA stretching.In this talk, we will describe the fabrication of our T-junction device and demonstrate the functionalization of a gold nanowire with λ-phage DNA in the device. Further, we will show preliminary DNA stretching measurements. As well, we will discuss the various parameters necessary for hydrodynamic stretching of DNA bound to an individual nanowire.This work is partially supported by NSF and NIH.
4:15 PM - JJ8.5
Fabrication, Characterization and Application of Polymer-Based Nanowire Arrays.
Jingjiao Guan 1 , Oludurotimi Adetunji 2 , Nan-Rong Chiou 2 , Bo Yu 3 1 , Chung-Hsun Lin 4 , Shiu Wu Chau 4 , Arthur Epstein 2 , L. Lee 3 1
1 Nanoscale Science and Engineering Center, The Ohio State University, Columbus, Ohio, United States, 2 Department of Physics , The Ohio State University, Columbus, Ohio, United States, 3 Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, Ohio, United States, 4 , Chung Yuan Christian University, Chungli Taiwan
Show AbstractCentral to the development of many nanowire-based devices is patterning the nanowires into well-defined arrays. Polymers as natural and inexpensive one-dimensional nanostructures hold great potential to build future nanodevices. We have developed a novel approach to create large and high-ordered arrays of polymer nanowires through a surface pattern-mediated dewetting process. This technique is simple, robust and inexpensive. DNA has been the major material used in this method. Functionalization of the DNA nanowires has been realized by either metallization by vapor deposition or incorporation of nanoparticles into stretched DNA strands. We have also studied the dewetting process by computer simulation and used this method to fabricate novel hybrid nanowire-nanoparticle arrays and nanowire-nanofiber arrays. In addition, we are studying the optical properties of metallized nanowire arrays based on which we are trying to develop novel optical devices.
4:30 PM - JJ8.6
Well-Aligned Ultra-High Density Array of Conducting Polymer Nanowires using Block Copolymer Nanoporous Templates.
Jeong In Lee 1 , Jin Kon Kim 1 , Jae Woong Yu 2 , Thomas P. Russell 3
1 Chemical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of), 2 Optoelectronic Materials Research Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 3 Department of Polymer Science and Engineering, University of Massachusetts at Amherst, Amherst, Massachusetts, United States
Show AbstractConducting polymer nanowires with high density have attracted much attention, due to their various applications including electrochromic devices, organic photovoltaic devices, polymer nano actuator and drug delivery. Here, we proposed a new template-based synthesis method using polystyrene-block-poly(methyl methacrylate) copolymers (PS-b-PMMA) nanoporous template to fabricate conducting polymer nanowires. Nanoporous templates have been used for the fabrication of nanostructured materials that have their potential applications in electronics, optics, magnetism, and energy storage. Among many different types of self-assembled materials, block copolymers with well-defined nanoscopic structures have recently gained much attention for their potential uses as functional nanostructures. Well-aligned ultra high density arrays of polypyrrole (Ppy) or poly(3,4-ethlenedioxythiophene) (PEDOT) nanowires were prepared on the ITO glasses by electropolymerization inside holes of the nanoporous templates. These nanowires grown inside nanoporous templates have much higher conductivity compare to films, higher conductivity was observed using CS-AFM (Current Sensing AFM). We find out that high conductivity results from the well-aligned chain orientation of nanowires because they were grown inside confined holes. So, ‘confinement effect’ is very important for higher conductivity and well-aligned structure of conducting polymer nanowires. Chain orientation of nanowires is characterized by HR-TEM, XRD and IR spectroscopy. Also, these conducting polymer nanowires which have higher conductivity can be used for electronic device. Especially, in the case of organic photovoltaic device, this geometry will be allowed us to obtain large contact area of P-N heterojunction, which allows a high efficiency of the current conversion from the light.
4:45 PM - JJ8.7
High-yield Integration of Conducting Polymer Nanowire Sensors onto CMOS Chips using Electric-field Assisted Assembly.
Jaekyun Kim 1 , Yanyan Cao 2 , Thomas Mallouk 2 , Theresa Mayer 1
1 Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractChemoresistive conducting polymer (CP) nanowires (NW) are emerging as promising building blocks for high-density cross-reactive nanosensor arrays because of their potential to deliver massive redundancy, high-sensitivity, low cost, and low power consumption. For practical systems to be realized, it is necessary to develop high-yield approaches to position nanosensors in multi-element arrays that are integrated with silicon (Si) circuits. Here we will discuss a scalable technique for assembling individual CP NWs synthesized off-chip at predefined locations on electrically-multiplexed Si CMOS cross-point transistor arrays. The NWs were synthesized by electrochemical deposition of polyethylenedioxythiophene (PEDOT), polyaniline (PANI), and polypyrole (PPY) CPs within 250 nm diameter pores of anodic aluminum oxide (AAO) membranes, and suspended in isopropanol following selective chemical etching of the membrane. Electric-fields assisted assembly was used to introduce spatially-confined long-range dielectrophoretic forces and short-range capacitive forces that orient and align the NWs relative to the transistor source and ground electrodes that are lithographically patterned in the top level metal of a CMOS process. This is achieved by coupling a kHz-frequency AC voltage to the top electrodes using electrically-isolated buried electrodes. Control experiments conducted using 8μm long, 300 nm diameter rhodium (Rh) NWs resulted in single NW assembly yields exceeding 90% across 16×32 arrays, with NWs centered in the gap between electrodes and a measured circuit resistance of ~100 Ω (transistor drain to ground). This confirms that a low resistance electrical contact is formed between the NW and the metal electrodes during assembly. This approach was also used to assembly CP NWs with a 10 μm long CP layer incorporated between 1 μm long Au segments deposited at the two ends of the NW. The current is nonlinear with voltage indicating that a Schottky contact is formed between the Au metal and the CP segment. The resistance measured at a 0.5 V bias ranged from 0.1 ΜΩ to 1 ΜΩ for the different CPs NWs, which are many orders of magnitude smaller than the open circuit resistance of each site in the array. We will report the measured response of these integrated CP NW sensors to different gas mixtures.
5:00 PM - JJ8.8
Electrospun Light-Emitting nano-Fibers.
Jose Moran-Mirabal 1 , Jason Slinker 2 , Hector Abruna 3 , George Malliaras 2 , Harold Craighead 1
1 Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 2 Materials Science and, Cornell University, Ithaca, New York, United States, 3 Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States
Show AbstractWe will present the fabrication of novel sub-wavelength light sources based on electrospun nanofibers. We have electrospun nanofibers from ruthenium(II) tris(bipyridine)/polymer mixtures. The fibers were deposited on gold interdigitated electrodes and lit up as a voltage was applied across the electrodes in a nitrogen atmosphere. The fibers showed light emission at low operating voltages, with turn-on voltages approaching the band gap limit of the organic semiconductor. Because of the fiber diameter, emission from electrospun light-emitting nanofibers in the transverse direction is confined to sub-wavelength dimensions. Confinement in the fiber axis is provided by the operation mechanism of the transition metal complexes. The small size of such light emitters is an attractive feature for sensing applications and lab-on-a-chip integration where highly localized excitation of molecules is required.