Symposium Organizers
Apparao Rao, Clemson University
Paola Ayala, University of Vienna
Yang-Yaun Chen, Academia Sinica
Nai-Chang Yeh, California Institute of Technology
NM08.01: Synthesis and Defect Characterization
Session Chairs
Mei-Yin Chou
Thomas Pichler
Monday PM, November 27, 2017
Hynes, Level 3, Room 309
8:15 AM - NM08.01.01
Doped Amorphous TiO2 as a Photocatalyst for Water Splitting
Kulbir Ghuman 1
1 , International Institute for Carbon-Neutral Energy Research, Kyushu University, Fukuoka Japan
Show AbstractVisible light photocatalysts based on doped crystalline forms of titanium dioxide (TiO2) have attracted significant scientific attention in recent decades. On the other hand, amorphous TiO2 (aTiO2), despite many merits over crystalline phases, has not been studied as thoroughly. This motivated us to investigate aTiO2 for its potential application in photocatalysis using leading edge computational techniques. First, we analyzed the electronic and structural properties of pristine aTiO2 models, which suggested that even though aTiO2 is cheaper and more abundant, it is somewhat less efficient as compared to crystalline TiO2 [1]. Since doping induces incremental structural distortion, there could be a tendency for large polarons and excitons to form in the doped aTiO2 than pristine aTiO2, which can act as trapping centers instead of recombination centers and enhance the catalytic activity. Therefore, we further modified aTiO2 by doping it with Fe having different oxidation states (Fe(II), Fe(III), and Fe(IV)) and provided insights into the synergetic role that intrinsic and extrinsic defects play in enhancing the photoactivity of doped aTiO2. This investigation revealed that among all the Fe-doped aTiO2 models which showed highly localized states at mid-gap and band edges, doping with Fe(II) led to maximum visible light absorption. This distinct behavior of Fe(II)-doped aTiO2 is attributed to the unique position of its mid-gap states, high self-trap energy, low mobility, and weak chemical bonds [2]. Finally, mechanistic properties of water-splitting over Fe(II)-doped aTiO2 surface were investigated [3], which will also be discussed in this presentation.
Acknowledgements: This work was supported by Compute Canada, University of Toronto, Okazaki computational resources and JSPS Core-to-Core Program, A. Advanced Research Networks.
[1] Kulbir Kaur Ghuman, and Chandra Veer Singh, Effect of Doping on Electronic Structure and Photocatalytic Behavior of Amorphous TiO2, Journal of Physics: Condensed Matter, 25, 475501 (2013).
[2] Kulbir Kaur Ghuman, and Chandra Veer Singh, Self-Trapped Charge Carriers in Defected Amorphous TiO2, The Journal of Physical Chemistry C, 120, 27910 (2016).
[3] Kulbir Kaur Ghuman, Water Activation on amorphous Titanium dioxide, Science and technology of advanced materials, (2017) (Submitted).
8:30 AM - *NM08.01.02
Discovery of Q-Carbon and Q-BN and Direct Conversion of Carbon into Diamond and h-BN into c-BN
Jagdish Narayan 1 2
1 , North Carolina State University, Raleigh, North Carolina, United States, 2 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractWe present the discovery of a new phase of carbon (Q-carbon) and BN (Q-BN) and direct conversion of carbon into diamond and h-BN into c-BN.at ambient temperatures and pressures in air. Amorphous carbon or nanocrystalline h-BN films are melted in a super undercooled state by nanosecond laser irradiation, and quenched into diamond (or Q-carbon) and h-BN into c-BN (or Q-BN), depending upon the degree of undercooling. By this process diamond and c-BN can be formed as nanodots, microdiamonds, nanoneedles and microneedles, and large-area single-crystal films. These phases can be doped with both n- and p-type dopants, opening a new frontier in diamond and c-BN electronics. We discuss atomic structure and bonding characteristics of Q-carbon and correlations with unique properties: harder than diamond, RTFM and extraordinary Hall effect with Curie temperature over 500K, negative electron affinity, and high-temperature superconductivity Tc>37K in B-doped Q-carbon. We have also created epitaxial <111> NV nanodiamonds of uniform size (4-10nm), which can be driven electronically and photonically, for applications ranging from biosensors to quantum computing. Similar results are presented for Q-BN and c-BN with a strong synergy between carbon and BN.
9:00 AM - NM08.01.03
Defect-Mediated Nanopore Formation in Single-Layer Transition Metal Dichalcogenides
Jian-An Ke 1 , Akshay Singh 1 , Slaven Garaj 2 3 , Silvija Gradecak 1
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Physics, National University of Singapore, Singapore Singapore, 3 Centre of Advanced 2D Materials, National University of Singapore, Singapore Singapore
Show AbstractNanopores in single-layer transition metal dichalcogenides (TMDs) have been demonstrated in applications including energy (reverse electrodialysis), sensing (DNA translocation), or filtration and desalination. The ultimate functionality of these nanopores will depend on their controlled formation where the pore size, areal density, and edge structure are modulated through high-throughput and scalable methods. On an example of a single-layer MoS2, we show that the pore formation in TMDs can be controlled through defect-engineering, either via synthesis or post-processing using electron-beams.
A scalable method to generate nanopores in single-layer MoS2 is by heating a membrane in air at temperatures higher than 200°C. The nanopores have been postulated to nucleate at structural defects in the chemical vapor deposition grown or mechanically exfoliated samples. However, nature of the defects and the role of process parameters during the oxidation have yet to be established. We show that nanopores in single-layer MoS2 during oxidation adopt non-random distribution, which can be directly related to the intrinsic structure of dislocation arrays in the starting material. Furthermore, we demonstrate that the areal density and growth rate of oxidation-formed nanopores can be controlled by irradiating a single layer MoS2 with a low-energy electron beam prior to the oxidation step. We use high resolution scanning and transmission electron microscopy to quantify effects of the electron beam exposure on nanopore formation and properties. Enhanced nanopore growth rate and nanopore nucleation in electron-beam exposed areas of the MoS2 film indicate that the defect levels and/or surface adsorption can be controlled by exposing MoS2 with electron beam energies < 2kV. The proposed scalable technique can be applied to tune the membrane performance in nano-power osmotic devices and for nano-patterning of nanopore arrays.
9:15 AM - NM08.01.04
Dislocations in 2D—Mechanisms of Mismatch Strain Relief and Strengthening
Pascal Pochet 1 2 , Brian McGuigan 3 , Anastasia Tyurnina 1 4 , Hanako Okuno 1 2 , Jean Dijon 1 4 , Harley Johnson 3
1 , Univ Grenoble Alpes, Grenoble France, 2 INAC, CEA, Grenoble France, 3 MechSE, University of Illinois at Urbana-Champaign, Urbana-Champaign, Illinois, United States, 4 Liten, CEA, Grenoble France
Show AbstractThe presence of crystalline dislocation can affect many important properties of 2D materials like graphene, h-BN, and transition metal dichalcogenides, and in some cases key potential applications may be affected. Indeed dislocations are always present in materials, and may be desirable or undesirable depending upon the application. For example, dislocations are often undesirable because they can alter the electronic properties of the host material. One classic approach to dislocations in 3D heterostructures is found in semiconductor science, where the presence of misfit dislocations can be avoided using the critical thickness framework introduce by Matthews and Blakeslee [1]. Here we recast this classic framework to consider interface misfit dislocation formation in lateral or in-plane heterostructures of 2D materials [2]. We consider graphene/h-BN interfaces with various dislocation core reconstructions. This makes it possible to identify a design space where defect-free heterostructures can be grown. In a different example, the presence of dislocations can be beneficial, as they are building blocks for strengthening of materials through pile-ups that form grain boundaries. In this case we show, in the context of recrystallization, a way to tailor the properties of graphene. Experimentally, the method can be achieved using a modified hot-filament-assisted Chemical Vapor Deposition setup, which does not require any control of crystal nucleation and orientation. We propose an original growth mechanism [3] that includes a stage of structural evolution from nanocrystalline to microcrystalline graphene film, opening a new route to control the electrical properties of large-scale uniform graphene film.
References
[1] «Defects in epitaxial multilayers: I. Misfit dislocations»; J. W. Matthews and A. E. Blakeslee ; J. Cryst. Growth 27, 118 (1974).
[2] «Critical thickness for interface misfit dislocation formation in two-dimensional materials»; B. McGuigan, P. Pochet and H. T. Johnson ; Phys. Rev. B 93, 214103 (2016).
[3] «CVD graphene recrystallization as a new route to tune graphene structure and properties»; A. V Tyurnina, H. Okuno, P. Pochet and J. Dijon ; Carbon 102, 499-505 (2016).
[4] «Toward Moiré engineering in 2D materials via dislocation theory»; P. Pochet, B. McGuigan, J. Coraux and H. T. Johnson ; Applied Materials Today 9, 240-250 (2017)
9:30 AM - NM08.01.05
Synthesis and Characterization of Nanocarbon-Infused Metal Alloys
Beihai Ma 1 , Balu Balachandran 1 , Stephen Dorris 1 , Tae Lee 1 , Jie Wang 1 , Jianguo Wen 1 , Adam Rondinone 2
1 , Argonne National Laboratory, Lemont, Illinois, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractNanophase-carbon infused base-metal conductors, such as copper and aluminum, exhibit enhanced electrical and thermophysical properties. This new class of materials, known as covetics, have attracted increased research interest because of their superior performance. Covetic materials are prepared by incorporating large amount of nanophase-carbon into metal matrixes using a unique melting and electrical infusion process. The enhanced electrical and thermal conductivities of covetics originate from carbon nanostructures dispersed in the metal. Understanding the nature of interaction between the carbon nanostructures and their host metal matrix is critical to elucidate the mechanism for superior performance. Nano-carbon structures in covetic copper and aluminum alloys were examined by electron and helium ion microscopy and correlated to their physical performance. Details of microstructural characterization, electrical and thermophysical performance of copper and aluminum covetics will be presented in this talk.
This work was supported by the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, Advanced Manufacturing Office, under Contract DE-AC02-06CH11357. This work was performed, in part, at the Center for Nanoscale Materials, a DOE Office of Science User Facility. Helium Ion Microscopy was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.
9:45 AM - NM08.01.06
Superhard Q-Carbon Nanostructures Formed via Nanosecond Laser Melting and Ultrafast Quenching
Siddharth Gupta 1 , Ritesh Sachan 1 2 , Anagh Bhaumik 1 , Punam Pant 1 , Jagdish Narayan 1
1 , North Carolina State University, Raleigh, North Carolina, United States, 2 , Materials Science Division, Army Research Office, Raleigh, North Carolina, United States
Show AbstractIn the present study, the mechanical and magnetic properties of various Q- carbon nanostructures formed by quenching of amorphous carbon thin films at ambient temperature and atmospheric pressure in the air are studied. On irradiating with a single nanosecond laser pulse, carbon melts and depending on the extent of undercooling it leads to the formation of diamonds or densely-packed amorphous Q-carbon phase. This undercooling is a function of sp3 content in the parent diamond-like-carbon and laser irradiation energy density. On increasing the sp3 content in the parent film, we achieved maximum undercooling which led to ultrafast regrowth rates and formation of Q-carbon nanocomposite. Finite element heat flow calculations have been performed, quantifying regrowth velocities which substantiate the claim that super undercooling varies monotonically with sp3 content. The directional nature of solidification at melt interface creates instability. This instability results in lateral segregation, which increases on enhancing regrowth velocity, leading to a decrease in the wavelength of instability. The cell size and wavelength at the onset of instability dependence on sp3 content has been modeled based on the perturbation theory. The resulting Q-carbon nanostructures have a cellular size of 1-4 μm providing a conformal coverage throughout the substrate. The composite has improved mechanical hardness of 67 GPa, Young’s Modulus ~843 GPa in comparison to 24 GPa hardness and 325 GPa Young’s Modulus of as-deposited DLC thin film. The nanocomposite has 0.16 coefficient of energy dispersion in comparison to 0.65 for DLC thin film resulting from the high hardness and elastic constants for Q-Carbon. The soft sp2 rich α phase provides the film with lubrication which reduces friction coefficient to 0.09 and wear rate to 1.55x 10-5 mm3/Nm. The field-dependent magnetization analysis confirmed room-temperature ferromagnetism in the composite structure with 150 Oe coercively and 22.31 emu g-1 saturation magnetization. The Curie temperature was estimated to be ~500 K. The mechanical and magnetic properties of these novel nanostructures have been correlated with the regrowth velocity during structural evolution, determined via simulation of laser solid interaction in materials (SLIM) software. The superhard behavior of nanocomposite coupled with conformal coverage throughout the sapphire wafer make it an ideal candidate for hard coatings and diamond precursors.
10:30 AM - NM08.01.07
Novel Q-Carbon Coatings on Tool Steel and WC
Alexander Niebroski 1 , Anagh Bhaumik 1 , Punam Pant 1 , Jagdish Narayan 1 , Adele Moatti 1
1 , North Carolina State University, Raleigh, North Carolina, United States
Show AbstractThin films for tribological applications require high hardness, toughness, and good adhesion to the substrate material. High hardness creates the cutting edge, toughness prevents fracture, while adhesion prevents peeling of the film from the tool. Though high hardness and toughness have historically been relatively easy to achieve in a material system, e.g. in diamond-like carbon (DLC) films deposited on steel, obtaining adhesion along with the first two has presented great difficulties for cutting tool coatings. This has led to increased wear rates and the necessity of replacing the cutting surface frequently, often at great cost and leading to significant downtime. Current state of the art tools often use polycrystalline diamond films grown by the chemical vapor deposition (CVD) technique, yet this process also yields poor adhesion due to a layer of graphite at the film-substrate interface. Recently, our discovery of Q-carbon led to an alternative pathway which can achieve the required hardness, toughness, and adhesion. In this process, a 20 nanosecond pulsed ArF laser is focused and directed at a DLC thin film. The film heats up to several thousands of degrees, and then rapidly quenches from the super undercooled state, forming diamond or a superhard amorphous material (Q-carbon), depending on the amount of undercooling. We present in this work the formation of diamond and Q-carbon on tool steel and tungsten carbide substrates using the pulsed laser annealing technique. We evaluate the wear rates of diamond and Q-carbon samples formed through pulsed laser annealing. We also compare the wear performance of these thin film coatings to those grown by the CVD process. Results are complemented with Raman spectroscopy, high-resolution SEM/HRTEM imaging, electron backscatter diffraction (EBSD), and electron energy-loss spectroscopy (EELS). In this study, we show that because the diamond or Q-carbon is formed directly as a result of ultrafast melt quenching, adhesion of the diamond or Q-carbon layer is improved compared to traditional growth methods. This technique therefore has great potential in high-speed machining, deep-sea drilling, and other applications related to oil and gas exploration, and can be further adopted for usage in diamond electronics. Furthermore, the knowledge gained from this process can be used to create similar superhard materials, such as quenched boron nitride coatings for advanced ferrous machining.
10:45 AM - NM08.01.08
Investigation of Self-Assembled Nanostructure in ZnSnN2 and ZnGeN2, and Their Alloys with GaN
Paul Quayle 1 2
1 , Kyma Technologies, Inc., Raleigh, North Carolina, United States, 2 , Case Western Reserve University, Cleveland, Ohio, United States
Show AbstractRecent research into ZnSnN2 and ZnGeN2 has revealed lattice disorder phenomena that may apply to the broad class of heterovalent ternary compounds. ZnSnN2 and ZnGeN2 fall into the wurtzite-based subclass of the ternaries, and are closely related to the binary nitrides in both crystal structure and electronic band structure. ZnGeN2 and GaN have nearly the same atomic positions, lattice parameters and band gaps. Investigations of the lattice structure of ZnSnN2 and ZnGeN2 by Raman and X-ray diffraction spectroscopy have revealed pronounced, and potentially tunable, disorder properties. Measurements of the photoluminescence properties of these materials however have shown that the lattice disorder likely has only a moderate effect on their electronic structures. Theoretical studies of the defect physics in ZnSnN2 and ZnGeN2 have provided insight into the apparent electron-crystal/phonon-glass properties, and suggest that the lattice disorder may result from a self-assembled nanostructure phenomenon, and reveal the potential for order-disorder phase transitions in these materials. The well-characterized zincblende-based heterovalent ternary semiconductor AgSbTe2 is referenced in analogy to ZnSnN2 and ZnGeN2. The analogy between the wurtzite-based and zincblende-based systems is extended to the ZnGeN2 and GaN alloy system which, like the AgSbTe2 and PbTe alloys, may form self-assembled quantum dot structure as a result of phase separation.
11:00 AM - NM08.01.10
Mobile Nanoparticles for Autonomous Exploration of Surface Structural Defects on Nano- and Micro-Scales
Irina Zvonkina 1 , Alamgir Karim 1 , Matthew Becker 1
1 , University of Akron, Akron, Ohio, United States
Show AbstractDefect-free functional surfaces are a goal and a challenge in several technologies. A novel approach to exploring the surface topography at the micro- and nano-scale, based on selective adsorption of smart mobile and fluorescent polymer nanoparticles with surface functionalization is demonstrated. Such smart nanoparticles can autonomously detect the location of a micro- or nano-scratch, rendering the defects visible, and, in particular systems, heal them. This new defects detection and healing method was investigated and successfully applied to surface defects in a variety of categories. These include surface defects in polymer thin films including pin-holes and line scratches. We also demonstrated the indirect detection of defects on hard polar substrates, including scratches and defects in patterns such as silicon wafer or metals by applying a thin conformal polymer layer that reduces the surface polarity, enabling for selective detection capability. Exposure of the substrates to nanoparticle dispersions results in evaporation-induced self-assembly of the nanoparticles, promoted by capillary and intermolecular forces, chemical affinity, and by a difference in the surface energy of defect sites in polymer films. Depending on the size scale of the defect, Individual nanoparticles as well as interlocked nanoparticle clusters formed on the surface defects that can easily be observed by fluorescence microscopy. Application of the mobile nanoparticles of different chemical compositions and structures for revealing hidden surface heterogeneities and confinements will expectedly have a broader impact on development of new surface characterization techniques, visualizing invisible and advancing intelligent technologies.
NM08.02: Electron and Ion Beam Induced Defects—Imaging and Dynamics
Session Chairs
Monday PM, November 27, 2017
Hynes, Level 3, Room 309
1:30 PM - *NM08.02.01
Atomic-Scale Defect-Engineering of 2D Materials with Electron and Ion Beams
Jani Kotakoski 1
1 , University of Vienna, Vienna Austria
Show AbstractDespite the great promise of two-dimensional materials due to their exciting properties, they are not always directly suitable for applications. One way to tune the material properties is to manipulate the atomic structure using particle irradiation. However, as one might expect, this is challenging to do in the case of extremely thin materials, where careful control over the irradiation energy and solid understanding of the underlying atomic-scale phenomena are required.
Despite the challenges, electron and ion irradiation have recently evolved into powerful techniques to manipulation the atomic structure of two-dimensional materials. At the same time, the recent advancements in aberration-corrected transmission electron microscopy both provide means to directly image the manipulated structures but also to fine tune them by inducing local structural changes and even to move defects and impurity atoms.
In this presentation, I will describe the advances in manipulating graphene with electron irradiation (e.g., Ref. [1]) and overview our latest progress in using ion irradiation at a large energy scale to implant foreign atoms into graphene [2], moving impurity atoms and defects at will (e.g., Refs. [3,4]), creating nanopores into graphene [5] and MoS2, patterning graphene with gratings and two-dimensional amorphized areas [6,7] as well as other recent results.
I will also describe our new experimental setup (to be finished in 2017) combining low-energy ion irradiation line in the same vacuum as a state-of-the-art aberration-corrected scanning transmission electron miroscope fitted for in situ manipulation during imaging.
[1] Susi et al., Nat. Commun. 7 (2016) 13040.
[2] Susi et al., 2D Materials 4 (2017) 021013.
[3] Kotakoski et al., Nat. Commun. 5 (2014) 4991.
[4] Susi, Meyer, Kotakoski, Ultramicroscopy (2017) doi: 10.1016/j.ultramic.2017.03.005.
[5] Emmrich et al., Appl. Phys. Lett. 108 (2016) 163103.
[6] Kotakoski et al., Nano Lett. 15 (2016) 5944.
[7] Brand et al., Nat. Nanotech. 10 (2015) 845.
2:00 PM - NM08.02.02
Engineering Nanoscale Functionalities in Ceramics Using Energetic Ions
William Weber 1 2 , Ritesh Sachan 3 , Eva Zarkadoula 2 , Dilpuneet Aidhy 4 , Christina Trautmann 5 , Yanwen Zhang 2
1 , University of Tennessee, Knoxville, Tennessee, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , North Carolina State University, Raleigh, North Carolina, United States, 4 , University of Wyoming, Laramie, Wyoming, United States, 5 , GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt Germany
Show AbstractThe interaction of energetic ions with solids is well known to result in inelastic energy loss to electrons and elastic energy loss to atomic nuclei in the solid. The coupled effects of these energy loss pathways on defect production, nanostructure evolution and phase transformations in ionic and covalent materials are complex and not well understood. Using experimental and computational approaches, we have investigated the separate and combined effects induced by nuclear and electronic energy loss on the response of ceramics to ion irradiation over a range of energies. Experimentally, ion mass and energy are used to control the amount of energy deposition and the ratio of electronic to nuclear energy loss. Large scale molecular dynamics simulations, which include atomic collision processes and inelastic thermal spikes, are used to model these effects. High angle annular dark field imaging, complemented with molecular dynamics simulations, have been employed to characterize the formation, structure and properties of nanoscale ion tracks created by energetic ions in complex oxides. In Gd2Ti2O7, swift heavy ions lead to a cylindrical ion track with a core-shell structure. The atoms in the shell structure surrounding the amorphous core are disordered and have relatively larger cation-cation interspacing, suggesting the presence of tensile strain. Static pair-potential calculations show that planar tensile strain lowers the barriers for oxygen vacancy migration, leading to enhanced oxygen ion conductivity in the strained shell structure. Amorphous ion tracks in Yb2Ti2O7 and Gd2TiZrO7 can be restructured to the defect fluorite structure, which is ionic conducting. In SrTiO3 and KTaO3, nanoscale amorphous ion tracks are formed only where pre-existing defects are created, revealing a synergy between the pre-existing defects and the electronic energy loss by ions. The cylindrical interfaces along the ion tracks in these oxides are highly strained, which greatly affects electronic, ferroelectric, transport and magnetic properties. This work advances the understanding on the role of defects in electronic energy dissipation and electron-phonon coupling. The knowledge gained provides insights for creating novel interfaces and nanostructures with controlled morphologies, multiple phases and local strain, which can be employed to engineer functionalized thin film structures with tunable electronic, ionic, magnetic and optical properties on the nanoscale.
This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division.
2:15 PM - NM08.02.03
Controlled Crystallization and Amorphization of Silicon Using Electron Beams with Atomic Layer Precision
Ondrej Dyck 1 , Eva Zarkadoula 1 , Panchapakesan Ganesh 1 , Miguel Fuentes-Cabrera 1 , Andrew Lupini 1 , Bethany Hudack 1 , Artem Maksov 2 , Sergei Kalinin 1 , Stephen Jesse 1
1 , Oak Ridge National Lab, Knoxville, Tennessee, United States, 2 , University of Tennessee, Knoxville, Knoxville, Tennessee, United States
Show AbstractWith the advent of aberration corrected scanning transmission electron microscopes (ac-STEM) sub-angstrom probes are now routinely formed, resolving single atoms with great clarity. Another feature of such probes is the ability to direct electron beam currents of ~10,000 A/cm^2 onto single atomic columns. Beam damage from electron irradiation is well known and has historically been seen as a nuisance. However, instead of fighting nature, one may take advantage of the beam-induced changes, understand the beam-sample interactions and view them as tools to be used for material manipulation at the atomic scale. In this presentation, we demonstrate the ability to control a focused electron beam in an ac-STEM with a real-time automated feed-back loop. By analyzing the output of the various detectors (i.e. HAADF, MAADF etc.) as the beam interacts with the sample, we are able to control beam exposure to subatomic areas of the sample (we can actually miss all the atoms in a crystal entirely) until a specific, predefined result is obtained. The automated system then quickly moves or blanks the beam to preserve the material structure formed. As an example system, an a-Si/x-Si interface is used. We control the crystal growth at the interface with atomic layer precision and demonstrate that under the same beam conditions the crystal may be either grown or amorphized based on triggers used in the feed-back loop. This suggests that, with appropriate automation, even unlikely structures may be engineered and quickly frozen in place. Such exquisite beam control necessitates the use of automation and real-time data analysis for decision making. These topics will be discussed with a view to future possibilities and opportunities.
This research was conducted at and partially supported OD, GP, MF, SVK, and SJ at the Center for Nanophase Materials Sciences, which is a US DOE Office of Science User Facility. This research partially supported (EZ, ARL, BH) and is sponsored by the Division of Materials Sciences and Engineering, BES, DOE. A.M. acknowledges fellowship support from the UT/ORNL Bredesen Center for Interdisciplinary Research and Graduate Education.
2:30 PM - NM08.02.04
Single Atom Spectroscopy and the Dynamics of Phosphorous Dopant in Graphene
Cong Su 1 , Ju Li 1 , Juan-Carlos Idrobo 2
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractElectron energy loss spectroscopy (EELS) in aberration corrected scanning transmission electron microscopy (STEM) has the capability of chemical identify single impurities[1], as well as the single atom species. In the case of two-dimensional materials, EELS has been able to identify the bonding characteristics of individual Si impurities in monolayer [2,3].
Here we have successfully synthesized the P doped graphene using chemical vapor deposition (CVD) with a high dopant atomic percentage. The three-coordinated, four-coordinated, and the double layer scnarios are found with EELS data acquied. The EELS data in each of the case is simulated with multiple scattering methods using FEFF, and the main features of peaks are identified successfully. The dynamics of P dopant is also observed with explanations from ab-initio simulations.
The experiments were performed in an aberration-corrected Nion UltraSTEMTM 100, equipped with a cold field emission electron source and a corrector of third and fifth order aberrations, operating at an accelerating voltage of 60 kV [4]. EEL spectra were collected using a Gatan Enfina spectrometer, with 0.3 eV/channel dispersion, giving an energy resolution of 0.9 eV. The convergence semi-angle for the incident probe and the EELS collection semi-angle were 30 mrad and 48 mrad, respectively. The EELS simulation is done in FEFF using multiple scattering method performed under real space. The ab-initio simulation is completed using VASP.
References:
[1] Varela, M., et al. Physical Review Letters 92.9 (2004): 095502.
[2] Zhou, Wu, et al. Physical review letters 109.20 (2012): 206803.
[3] Ramasse, Quentin M., et al. Nano letters 13.10 (2013): 4989-4995.
[4] O. L. Krivanek, et al.,Ultramicroscopy 108, (2008). p. 179-195.
3:15 PM - *NM08.02.05
Defects and Interface Engineered Electrodes for High Energy and High Power Li and Al Ion Batteries
Ramakrishna Podila 1
1 , Clemson University, Clemson, South Carolina, United States
Show AbstractNotwithstanding the success of batteries in portable electronic applications, new strides are imperative for radically improving their energy and power densities, safety, and cycle life. Achieving higher energy and power in lightweight systems demands volatile and toxic cathodes. Contrary to the notion that defects and interfaces are performance limiters, we found defect and interface engineering of nanocarbon (NC) electrodes could avoid such environmentally unfriendly battery chemistries. This talk will summarize our recent breakthroughs in manufacturing aqueous solvent-based Li and Al ion batteries (LIBs and AIBs) with defect and interface engineered NC electrodes. Fundamental spectroscopic insights into the interactions between defects/interfaces in NC electrodes and the ionic liquid electrolytes, which are key for realizing the full potential of LIBs and AIBs, will be presented.
3:45 PM - NM08.02.06
Defective Graphene and Graphene Allotropes as High-Capacity Anode Materials for Mg Ion Batteries
Dequan Er 1 , Eric Detsi 1 , Hemant Kumar 1 , Vivek Shenoy 1
1 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractAlthough rechargeable Mg ion batteries have recently received renewed interest as a promising alternative to Li ion batteries, the Mg metal used for anodes in state-of-the-art Mg ion batteries is not compatible with conventional battery electrolyte solvents. On the other hand, graphite electrode materials function well with common battery electrolyte solvents, but Mg intercalation into graphite is very difficult. In the case of two-dimensional (2D) carbon-based materials, pristine graphene, the most well-studied 2D material, is known to have no capacity for Li or Mg. Here we demonstrate the potential of defective 2D carbon-based structures to be used as high-capacity anode materials for Mg ion batteries. Adsorption of divalent Mg ions on defective graphene and graphene allotropes is predicted by first-principles density functional theory. Our results show enhanced Mg adsorption on both defective graphene and graphene allotropes. Moreover, we show that Mg storage capacity can be improved by increasing the defect concentration or changing the local arrangement of carbon rings. A Mg storage capacity as high as 1042 mAh/g can be achieved in graphene with 25% divacancy defects. These new insights, together with the fact that carbon-based materials are very compatible with a wide range of battery electrolyte solvents, will pave the way for developing carbon-based anode materials for practical Mg ion batteries.
4:00 PM - NM08.02.07
Ionic Transport and Structural Evolution in One-Dimensional Manganese Oxide Nanorods
Jianping Huang 1 , Xiaobing Hu 2 , Alexander Brady 1 , Lijun Wu 2 , Yimei Zhu 2 , Amy Marschilok 1 , Kenneth Takeuchi 1 , Esther Takeuchi 1 2
1 , Stony Brook University, Stony Brook, New York, United States, 2 , Brookhaven National Laboratory, Upton, New York, United States
Show AbstractCathode materials which can provide facile ion and electron transport are crucial to high power Li batteries. Here, we investigate the ionic transport in a silver ion containing α-MnO2 (AgxMn8O16) with a one-dimensional tunneled structure. We find that oxygen defects on the surface of α-MnO2 nanorods facilitate Li+ ion transport through the tunnel walls, therefore enabling two- or three-dimensional Li+ ion diffusion in the nanorods. Ag1.36Mn8O15.6 with a high degree of surface oxygen vacancy delivers 2-fold larger capacity than Ag1.36Mn8O15.9. The improved electrochemical behavior in Ag1.36Mn8O15.6 is attributed to the facile Li+ ion diffusion in the radial direction of nanorods. In addition, the impacts of Li+ ion and Na+ ion insertion on Ag+ ion reduction are compared. The Na+ ion transport in AgxMn8O16 facilitates silver metal formation, which contributes to a significant resistance drop in the initial discharge process.
Structural evolution upon lithiation/de-lithiation of AgxMn8O16 is investigated using multiple characterization techniques, including transmission electron microscopy (TEM), synchrotron-based X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). The Ag1.2Mn8O16 material shows small increases in lattice a (or b) and Mn-Mn atomic distances when the lithiation level is <2 electron equivalents. Amorphization and structural deformation are observed at higher levels of lithiation, Li4Ag1.2Mn8O16, where Mn-Mn distances in the ab plane increase. Thus, cycle stability of Ag1.2Mn8O16 material is investigated under controlled reduction conditions (2 and 4 electron equivalents). The terminal voltage shows minor change under 2 electron equivalents after 40 cycles, with a more significant change observed under 4 electron equivalents of cycling. XAS data after 40 cycles indicate a reversible structural change at 2 electron equivalents while a retention of structural deformation at 4 electron equivalents. This study experimentally demonstrates structural changes of α-MnO2 type materials during lithiation/de-lithiation processes, providing guidelines to achieve long-term cycle stability in Li-based batteries.
4:15 PM - NM08.02.08
Dislocation Density Prediction Model for GaN-Based Electronic Devices
Dhaneshwar Mishra 1 , Youjoung Seo 1 , Y. Eugene Pak 1
1 Multiscale CAE Lab, Advanced Institutes of Convergence Technology, Suwon-si, Gyeonggi-do, Korea (the Republic of)
Show AbstractGallium nitride (GaN)-based electronic devices are fabricated by depositing multilayers of thin films on thick foreign substrates such as sapphire/silicon at elevated temperatures. High lattice and thermal expansion coefficient mismatch between the multi quantum well thin film layers and the substrate material generates high misfit/thermal strain. High magnitude of the inplane strains in the multi quantum well films are released by formation of defects such as dislocations. GaN-based devices such as LEDs, HEMTs have large number of threading and misfit dislocations (in the order of 108 - 1010cm-2). It is important to understand the strain relaxation mechanisms and thereby quantify the defect density in these devices to correctly predict the device performance as well as to take necessary measures to reduce defects. In this work, we have developed analytical model to understand the strain relaxation mechanism in these highly strained devices and developed a theoretical model to predict the dislocation density. Internal energy due to dislocation interaction has also been evaluated for edge-edge, edge-screw and screw-screw dislocations at the interface of two layers. Finite element modeling and analysis has been carried out to verify the interaction model developed analytically. The dislocation density prediction model has been developed by evaluating the strain energy available in the multi quantum well layers and the energy required to form the dislocation. Energy due to interactions among the dislocations has also been appropriately considered for better prediction. Gallium nitride and other nitride film layers are piezoelectric; therefore, the piezoelectric constitutive relations have been used. This work can shed light on the interaction mechanism of dislocations in high defect density region so that a better prediction of dislocation density can be made.
4:30 PM - *NM08.02.09
Nanoscale Thermal Imaging of Dissipation in Encapsulated Graphene
Dorri Halbertal 1 , Moshe Ben Shalom 2 3 , Aviram Uri 1 , Kousik Bagani 1 , Alexander Meltzer 1 , Ido Marcus 1 , Yuri Myasoedov 1 , John Birkbeck 2 3 , Leonid Levitov 4 , Andre Geim 2 3 , Eli Zeldov 1
1 , Weizmann Institute of Science, Rehovot Israel, 2 , National Graphene Institute, The University of Manchester, Manchester United Kingdom, 3 The School of Physics and Astronomy, The University of Manchester, Manchester United Kingdom, 4 Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractEnergy dissipation is a fundamental process governing the dynamics of physical systems. In condensed matter physics, in particular, scattering mechanisms, loss of quantum information, or breakdown of topological protection are deeply rooted in the intricate details of how and where the dissipation occurs. More specifically, conversion of electric current into heat involves microscopic processes that operate on nanometer length scales and release minute amounts of power. While central to our understanding of the electrical properties of materials, individual mediators of energy dissipation have so far eluded direct examination.
We recently developed a superconducting quantum interference nano thermometer device with sub 50 nm diameter that resides at the apex of a sharp pipette and provides scanning cryogenic thermal sensing with four orders of magnitude improved thermal sensitivity of below 1 uK/sqrtHz at 4.2 K [1]. We applied this novel thermal imaging technique to study dissipation processes in hBN encapsulated graphene heterostructures. We reveal local heat released through resonant inelastic electron scattering from individual defects along the edges of graphene that from localized states near the Dirac point. The defects act as switchable phonon emitters providing energy sinks for electrons when brought into resonance with defects’ energy levels.
[1] D. Halbertal, J. Cuppens, M. Ben Shalom, L. Embon, N. Shadmi, Y. Anahory, H. R. Naren, J. Sarkar, A. Uri, Y. Ronen, Y. Myasoedov, L. S. Levitov, E. Joselevich, A. K. Geim & E. Zeldov, Nature 539, 407–410 (2016), http://dx.doi.org/10.1038/nature19843
NM08.03: Poster Session
Session Chairs
Tuesday AM, November 28, 2017
Hynes, Level 1, Hall B
8:00 PM - NM08.03.01
Tailoring the Silver Content within the Tunnels and on the Exposed Surfaces of Manganese Oxide Nanowires—Impact on Impedance and Electrochemistry
Bingjie Zhang 1 , Paul Smith 1 , Seung-Yong Lee 2 , Lijun Wu 2 , Yimei Zhu 2 , Esther Takeuchi 1 2 , Amy Marschilok 1 , Kenneth Takeuchi 1
1 , Stony Brook University, Stony Brook, New York, United States, 2 , Brookhaven National Laboratory, Upton, New York, United States
Show AbstractDesign and development of the structure and morphology of materials can have a profound effect on electrochemical properties of lithium ion batteries, which can lead to the efficient conduction of both electrons and cations. Our results demonstrate material design strategies which can significantly increase electronic and ionic conductivities. Within this study, a coprecipitation method has been applied with the ability to change the silver ion content within (intra-tunnel) and on the surface (inter-tunnel) of α-MnO2 tunneled materials AgxMn8O16-y ● aAg2O. Specifically, pure AgxMn8O16-y materials with low (x = 1.13) and high (x = 1.54) intra-tunnel silver content were coated with various amounts of Ag2O (a = 0.25, 0.63, 1.43), and the resulting composites were characterized using x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), inductively coupled plasma-optical emission spectroscopy (ICP-OES) and transmission electron microscopy (TEM), followed by a comparison of their impedance and electrochemistry. Electrochemical measurements under intermittent galvanostatic discharge and AC impedance indicate a higher functional capacity and lower impedance with moderate amounts of Ag2O coating.
8:00 PM - NM08.03.03
A Novel Approach to Study of the Conductivity Behaviour of CaCu3Ti4O12 Using Scanning Probe Microscopy Technique
Maxim Ivanov 1 , Filipe Amaral 2 , Vladimir Khomchenko 1 , José Paixão 1 , Luís Costa 3
1 , Universidade de Coimbra, Coimbra Portugal, 2 , Polytechnic Institute of Coimbra, Coimbra Portugal, 3 , University of Aveiro, Aveiro Portugal
Show AbstractHigh-k dielectrics with colossal dielectric constant (CDC) (ε’ > 103) are a matter of great interest since they provide an improvement in the efficiency of electronic devices through the miniaturization of capacitive electronic components. Calcium copper titanate (CaCu3Ti4O12), a non-ferroelectric material, whose exceptional dielectric properties have been reported in 2000 [1], attracts the attention of scientific community because of its CDC (ε’ >105), observed for ceramics and single crystals.
Despite the efforts of the scientific community, a conclusive explanation about the polarization mechanisms that justify the exhibition of CDC is still missing. Discarding the existence of any ferroelectric transition, the experimental data, collected during the last decade, point to an extrinsic barrier mechanism(s) as the origin of the main dielectric polarization. Recently, in a theoretical work, Bueno et al. [2], have indicated a polaronic stacking fault defect model as the origin of the high dielectric constant in CaCu3Ti4O12 (CCTO) materials. In this work, we present the experimental confirmation for the inhomogeneous conductivity in CCTO ceramics, at the nanometric scale, which can support the polaronic stacking fault defect model as the origin of CDC. Using the Scanning Probe Microscopy technique implemented in the contact Spreading Resistance mode, we have confirmed an insulating behavior of the grain boundaries and, for the first time, revealed a dual behavior of the grain microstructure with a clear coexistence of conductive and insulating nanoscale-patterned in-plane features.
References
[1] M. A. Subramanian, L. Dong, N. Duan, B. A. Reisner, and A. W. Sleight, J. Solid State Chem. 151, 323 (2000).
[2] P. R. Bueno, R. Tararan, R. Parra, E. Joanni, M. A Ramírez, W. C. Ribeiro, E. Longo and J. A Varela, J. Phys. D: App. Phys., 42, 5 (2009).
8:00 PM - NM08.03.04
Tuning Both Bandedge Exciton Dynamics and Energy Transfer Dynamics in Mn-Doped QDs via Doping of Ag Co-Dopants
Wonseok Lee 1 , Sungjee Kim 1
1 Department of Chemistry, POSTECH, Pohang Korea (the Republic of)
Show AbstractIn quantum confined regime, dopant ions interact intimately with each other and show stronger dopant effects than that of bulk. Introduction of transition metal ions into semiconductor nanocrystals is important for various applications that include optoelectronics, spintronics and biological labeling. Mn-doped quantum dots (QDs) has been extensively studied as a model system, in which energy transfer process has been known to be a competitive process of charge carrier trapping. Rapid dynamics and sensitized phosphorescence of localized excitons in [MnS4] can reduce nonradiative loss of excitons and improve QD emission yield. However, while there have already been considerable number of reports on these nimble energy transfer dynamics in Mn-doped QDs, only limited cases have been studied especially on the interactions between two different types of dopants in co-doped quantum confined systems due to physical complexity of themselves. We investigated on the oxidation number of Ag co-dopants and how Ag co-dopants in Mn-doped QDs affect the exciton dynamics carefully following the doping concentration of them. Through conducting both steady state and time-resolved spectroscopy, we found that Ag dopants affect the intensity of both bandedge photoluminescence (PL) and Mn dopant sensitized phosphorescence. We also figured out that the trend of those variations dramatically changes with incorporated concentration of Ag dopants and their doping depth in nanocrystals. After that, for further inspection, lifetime study of both bandedge emission and forbidden d-d transition at [MnS4] impurity center were conducted. Through these experiments we figured out how silver ions affect the optical properties of Mn doped QDs, which showed two different behaviors upon the Ag concentration. Few (~one or two) Ag ions in CdS/ZnS QDs occupied interstitial site of the QDs and behaved as positive ion center which pulls electrons from the interface of QD which resulted in suppression of non-radiative Auger recombination. As more Ag ions were introduced, Ag ions repelled each other to high energy core/shell interface that resulted in interstitial to substitutional replacement accompanied by the possible oxidation number change. Substitutional Ag ions in QDs seems to have created charge traps that altered QD and dopant PL. The charge traps quenched the bandedge exciton recombination and at the same time enhanced the luminescence of Mn d-d transition. Through transient absorption analyses, we concluded that Ag ions may change their oxidation number while substitution reaction took place, and localized excitons at [AgS4] center acted as an energy transfer intermediate state which enhanced energy transfer rate from bandedge exciton to Mn d-d transition state.
8:00 PM - NM08.03.06
Device Instability Behaviors on MoTe2 Thin-Film Transistors under Bias Temperature Stress
Seung Jae Yu 1 , Jae Hyun Ryu 1 , Geun Woo Baek 1 , Sung Hun Jin 1
1 , Incheon National University, Incheon Korea (the Republic of)
Show AbstractRecently transition metal dichalchogenides (TMDCs) have attracted considerable attention toward various electronic applications due to their novel electrical, optical, and chemical properties along with ideal two dimensional structure. Among various TMDCs, many research activities have been predominantly focused on MoS2 TFTs because of its abundance, nontoxicity, easy preparation of MoS2 films through exfoliation or/and CVD. However, MoTe2, as one of promising candidates, has just begun to be explored for the application of logic circuits and optical sensing application, particularly due to its smaller semiconducting energy band gap (Eg~0.8 or 1.24 eV in a single layer form), suitable for near infrared wavelength and ambipolar electronic behaviors. However, most of research activities for MoTe2 field effect transistors have been focused on high performance device implementation, understanding on gas (or chemical) adsorption effects, along with transport behaviors in ultra-low temperature.
Interestingly there have been few reports on investigation of device reliability of MoTe2 FETs even though understanding on device instability mechanisms associated with defect generation (or charge trapping in insulators) are indispensable to application of reliable emerging application such as nanoscale logic circuits and sensors beyond Si technology.
In this study, we implemented MoTe2 FETs with various number of layers from a few layer to multiple layers larger than 20 and improved electrical stability of devices accompanied by novel passivation technology. For understanding on intrinsic instability behaviors for MoTe2 FETs with (or without passivation), we investigated implemented devices in vacuum independently with various substrate temperature ranging from 100 K to 373 K. Furthermore, low temperature characterization for each device before and after bias temperature stress (by DC or pulse mode stress) lead to extraction of activation energy and trap characteristics such as characteristic time constant (τ) and stretched –exponential fitting parameters (β) which induce the device instabilities. In parallel, nanoscale device instability for MoTe2 FETs were systematically tested and modelled by DC and pulse mode characterization.
8:00 PM - NM08.03.07
Layer Thickness Dependent Thermal Stability in Metallic Multilayers at Nanoscale
Zhenhua Cao 1
1 , Nanjing University, Nanjing China
Show AbstractIn this work, we have investigated grain growth and heterogeneous interface evolution of Cu/Ag multilayers with individual layer thickness (h) varying from 5 to 50 nm during annealing. It was found that the thermal stability of Cu/Ag multilayers exhibits strong length scale dependence. With the increment of h, the temperature for stable layered structure increases from 200 °C to 300 °C. For smaller h, the existence of a large number of grain boundaries (GBs) will decrease the stability of multilayers, resulting in grain growth easily. Meanwhile, there are more heterogeneous interfaces contributing to resisting atomic diffusion, then inhibiting grain growth. In comparison, less GBs and interface in multilayers with larger h will enhance the energy barrier of grain growth. The equilibrium is achieved by a competitive process between GBs diffusion and heterogeneous interfaces resistance. Moreover, the formation of annealing twins in multilayer also significantly improve the microstructural stability.
8:00 PM - NM08.03.09
Exploring Substitutional Doping in Nickel Oxide Employing Ab Initio Models
Janakiraman Balachandran 1 , Hyeondeok Shin 2 , Ye Luo 2 , Anouar Benali 2 , Friederike Wrobel 2 , Anand Bhattacharya 2 , Paul Kent 1 , Panchapakesan Ganesh 2 , Olle Heinonen 2
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , Argonne National Laboratory, Lemont, Illinois, United States
Show AbstractDoping complex oxides with large bandgaps through intrinsic defects or extrinsic dopants have important technological consequences. However, many of these oxides show fundamental asymmetry in doping. For example, NiO can be readily doped with holes, whereas it is difficult to dope them with electrons. This is generally attributed to the asymmetry in non-stoichiometry, wherein it is easier to form Ni vacancies (VNi) compared to oxygen vacancies (VO). However, introducing extrinsic substitutional dopants (such as Li and K) can change these vacancy formation energies, in particular VO that can suppress holes, which in turn influences the substitutional doping limits in NiO [1].
In this work by employing ab initio models to systematically explore the various defect formation (VNi, VO, LiNi, KNi) and defect interaction energies (LiNi -VO, KNi-VO) in NiO. Such a comparison enables us to compare and contrast the influence of different substitutional dopants. However, density functional theory based models are known to be notoriously bad in predicting electronic structure of Mott insulators like NiO. To overcome these limitations, we employ ab initio models that incorporate Hubbard corrections (DFT+U), where the U-value is variationally obtained from correlated electronic-structure methods such as Quantum Monte Carlo (QMC). The resulting electronic structure and defect energies are compared with the corresponding QMC results. This comparison enables us to quantify the errors in defect energies, and also identify the most stable defects that will form in a given growth environment, along with its effects on the underlying electronic and magnetic structure.
Acknowledgement
This work was supported by the Center for Predictive Simulation of Functional Materials, through U.S. Department of Energy, Office of Science, Basic Energy Sciences, Computational Materials Sciences Program. This research used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725.
References
1. Stephan Lany, Jorge Osorio-Guillén, and Alex Zunger, "Origins of the doping asymmetry in oxides: Hole doping in NiO versus electron doping in ZnO", Phys. Rev. B 75, 241203�R� �2007
Symposium Organizers
Apparao Rao, Clemson University
Paola Ayala, University of Vienna
Yang-Yaun Chen, Academia Sinica
Nai-Chang Yeh, California Institute of Technology
NM08.04: Electronic Properties of 1D and 2D Materials
Session Chairs
Jani Kotakoski
Nai-Chang Yeh
Tuesday AM, November 28, 2017
Hynes, Level 3, Room 309
8:30 AM - NM08.04.00
Revealing the Charge Carrier Trapping Process in Silicon Nanowire Photoconductors by Hall Effect Measurements
Kaixiang Chen 1 , Yaping Dan 1
1 , Shanghai Jiao Tong University, Shanghai China
Show AbstractNanoscale devices may find applications in flexible electronics and biophotonics. However, nanoscale photodetectors often suffer from weak absorption of light due to the ultrascaled volume, resulting in low external quantum efficiency and photosensitivity [1, 2]. Nano-scale photoconductors are reported to have extraordinarily high photoresponsivities, which is believed to originate from the charge carrier trapping effect of surface trap states, surface gating effects and others [3, 4]. In this work, we use the Hall effect measurements to investigate the trapping process of photogenerated charge carriers in a single silicon nanowire (SiNW) photoconductor. The results reveal that the surface states dominantly contribute to the photo gain by trapping photogenerated minority charge carriers, leaving the majority photogenerated counterparts to accumulate in the energy band. It is the accumulation of photogenerated majority charge carriers that lead to the observed high photogain. What’s more, by the effect of surface states, nanowire with small size and low doping level can be fully depleted. In our experiments, the SiNWs with different size (range from 200nm to 800nm) were fabricated on a silicon-on-insulator (SOI) wafer by electron beam lithography (EBL). Following EBL, the SiNWs with a wide range of doping levels (8×1016/cm3 and 2×1018/cm3) were formed through ion implantation. Overall, the experimental results support the hypotheses about the surface states effect on the nanoscale photoconductor, and help the researchers better understand the gain mechanism of photoconductors.
Reference:
[1] Tang, L.; Kocabas, S. E.; Latif, S.; Okyay, A. K.; Ly-Gagnon, D.-S.; Saraswat, K. C.; Miller, D. A. B., Nanometre-scale germanium photodetector enhanced by a near-infrared dipole antenna. Nature Photonics 2008, 2 (4), 226-229.
[2] Felic, G. K.; Al-Dirini, F.; Hossain, F. M.; Thanh Cong, N.; Skafidas, E., Silicon nanowire photodetector enhanced by a bow-tie antenna. Applied Physics a-Materials Science & Processing 2014, 115 (2), 491-493.
[3] Soci C, Zhang A, Xiang B, et al. Nano letters, 2007, 7(4): 1003-1009.
[4] Li Y, Della Valle F, Simonnet M, et al. Applied Physics Letters, 2009, 94(2): 023110.
8:45 AM - *NM08.04.01
Experimental Analysis of the Properties of Graphene, Carbon Nanotubes and Carbon Chains as Function of Their Local Structure
Thomas Pichler 1
1 , University of Vienna, Vienna Austria
Show AbstractThe physical properties of single quantum objects are governed by its precise atomic arrangement. The direct correlation of localized electronic transport, vibronic structure and optical properties with the atomic structures has been therefore strongly desired.In this presentation I ll review recent progress in experimental understanding the influence of the local structure on the electronic/optical properties of individual SWCNT [1] and carbyne and other carbon chain filled DWCNT [2] as well as on graphene with controlled and high functionalization degree [3]. As methods we combine analysis of high-resolution EELS inside a high-resolution TEM concomitant with multi-frequency and near field Raman as well as photoluminescence spectroscopy.
For individual SWCNT well separated EELS peaks are obtained from a single freestanding pristine and carbon chain filled nanotube with the local chiral index and unambiguously related to the van Hove singularities. They clearly vary upon the different areas even in the individual carbon nanotube. Hence, these variations in interband transitions, plasmonic behaviors, and unoccupied electronic structures are clearly attributed to the local irregular atomic arrangement such as topological defect and/or elastic bond stretching as well as the dielectric environment. The resulting energy dependent dielectric function in the optical range will be directly compared to complementary optical absorption measurements [1].
For confined carbyne I will also show recent progress on unraveling the influence of charge transfer, local strain and hybridization on their electronic transport properties [2]. Then I will proof how stabilized carbyne chains with more than 6000 carbon atoms length exhibit novel electronic and optical properties such as a huge resonance Raman signal as well as the energy gap and act as functional elements enhancing the photoluminescence of inner tubes [2].
For graphene I ll show how in-situ Raman spectroscopy allows revealing the unique fingerprint of covalent sp3 defects in the Raman spectra of highly functionalized graphene which allows to monitor and control the relative functionalization degree of these tailored gaphenes [3].
Work supported by FWF and the EU.
[1] DOI:10.1021/acs.nanolett.6b00825, Nano Letters 16, 3661 (2016)
[2] DOI: 10.1038/NMAT4617, Nature Materials, 15, 634 (2016);
DOI: https://doi.org/10.1103/PhysRevB.94.195422, Phys. Rev. B, 94, 195422 (2016);
DOI: 10.1002/adfm.201505502, Advanced Functional Materials 26, 4874 (2016);
arXiv:1705.02259,
[3] DOI: 10.1038/ncomms15192; Nature Communications 8, 15192 (2017).
9:15 AM - *NM08.04.02
Electronic Transport through Atomic Carbon Chains
Jean-Christophe Charlier 1
1 Institute of Condensed Matter and Nanosciences, University of Louvain, Louvain-la-Neuve Belgium
Show AbstractCarbyne, the sp1-hybridized phase of carbon, is still a missing link in the family of carbon allotropes. Recently, detailed electrical measurements and first-principles electronic transport calculations have been performed on monoatomic carbon chains [1]. When the 1D system is under strain, the current-voltage curves exhibit a semiconducting behavior, which corresponds to the polyyne structure of the atomic chain with alternating single and triple bonds. Conversely, when the chain is unstrained, the ohmic behavior is observed in agreement with the metallic cumulene structure with double bonds. These measurements confirm recent theoretical predictions, namely that a metal-insulator transition can be induced by adjusting the strain in carbyne [2]. The key role of the contacting leads is also scrutinized by ab initio quantum conductance calculations, explaining the rectifying behavior measured in monoatomic carbon chains in a non-symmetric contact configuration [3].
[1] Electrical transport measured in atomic carbon chains, O. Cretu, A. R. Botello-Mendez, I. Janowska, C. Pham-Huu, J.-C. Charlier, and F. Banhart, Nano Letters 13, 3487-3493 (2013).
[2] Strain-induced metal-semiconductor transition observed in atomic carbon chains, A. La Torre, A. R. Botello-Mendez, W. Baaziz, J.-C. Charlier, and F. Banhart, Nature Communications 6, 6636 (2015).
[3] Electronic transport through atomic carbon chains : the role of contacts, F. Ben Romdhane, J.-J. Adjizian, J.-C. Charlier, and F. Banhart, submitted for publication (2017).
9:45 AM - NM08.04.03
Dopant Morphology as the Factor Limiting Graphene Conductivity
Mario Hofmann 1 , Ya-Ping Hsieh 2 , Kai-Wen Chang 3
1 , National Taiwan University, Taipei Taiwan, 2 , Academia Sinica, Taipei Taiwan, 3 , National Cheng Kung University, Tainan Taiwan
Show AbstractGraphene’s low intrinsic carrier concentration necessitates extrinsic doping to enhance its conductivity and improve its performance for application as electrodes or transparent conductors. Despite this importance limited knowledge of the doping process at application-relevant conditions exists.
Employing in-situ carrier transport and Raman characterization of different dopants, we here explore the fundamental mechanisms limiting the effectiveness of doping at different doping levels. Three distinct transport regimes for increasing dopant concentration could be identified. First the agglomeration of dopants into clusters provides a route to increase the graphene conductivity through formation of ordered scatterers. As the cluster grows, the charge transfer efficiency between graphene and additional dopants decreases due to emerging polarization effects. Finally, large dopant clusters hinder the carrier motion and cause percolative transport that leads to an unexpected change of the Hall effect. The presented results help identifying the range of beneficial doping density and guide the choice of suitable dopants for graphene’s future applications.
10:30 AM - *NM08.04.04
Tunable Electronic and Topological Properties of BN-Embedded Monolayer Graphene
Chih-Piao Chuu 1 , Ching-Ming Wei 1 , Mei-Yin Chou 1 2
1 IAMS, Academia Sinica, Taipei Taiwan, 2 Physics, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractFinding an effective and controllable way to create a sizable energy gap in graphene-based systems has been a challenging topic of intensive research. We propose that the hybrid of boron nitride and graphene (h-BNC) at low BN doping serves as an ideal platform for band-gap engineering and valleytronic applications. We report a systematic first-principles study of the atomic configurations and band gap opening for energetically favorable BN domains embedded in graphene. The calculations find a linear dependence of the band gap on the BN concentration at low doping, arising from an induced effective on-site energy difference at the two C sublattices as they are substituted by B and N dopants alternately. The significant and tunable band gap of a few hundred meVs, with preserved topological properties of graphene and feasible sample preparation in the laboratory, presents great opportunities to realize valley physics applications in graphene systems at room temperature.
11:00 AM - NM08.04.05
Effect of Carbon-Doping on Electrical Properties of Cubic Boron Nitride Grown by Pulsed Laser Annealing Technique
Ariful Haque 1 , Jagdish Narayan 1
1 , North Carolina State University, Raleigh, North Carolina, United States
Show AbstractPhase pure crystalline cubic boron nitride (c-BN) thin film is of immense interest because of its highly desirable electrical, optical, thermal and mechanical properties. We present the discovery of single step conversion of pulsed laser deposition (PLD) grown hexagonal boron nitride (h-BN) into phase pure cubic boron nitride (c-BN) by pulsed laser annealing (PLA) technique using a pulsed ArF nanosecond excimer laser with 193 nm wavelength. This discovery of the conversion of h-BN to quenched boron nitride (Q-BN) and single crystal c-BN by rapid heating and ultrafast quenching has been successfully implemented to fabricate carbon-doped c-BN thin films with doping concentration far beyond the retrograde solubility limit. These films were characterized by Raman spectroscopy, X-ray diffraction (XRD), high resolution SEM, EBSD, and electrical transport measurements. Raman spectroscopy confirmed the complete conversion of h-BN into phase pure c-BN and identified the crystallinity of the c-BN films. XRD analysis confirmed the presence of the cubic phase and a particular (111) epitaxy with the (0001) sapphire substrate. We controlled the dopant concentration from 0.03 at. % to 5.4 at. % of C atoms, uniformity, and growth orientation by controlling the process parameters in this liquid-phase mediated growth of C-doped c-BN films. Depending on the concentration of C, a clear change in the electrical properties such as the carrier concentration, Hall mobility, resistivity, etc. was observed while retaining the pure cubic phase in BN, which indicates a successful electrical doping effect. Hall measurements established n-type conductivity and the resistivity vs temperature measurements confirmed semiconducting nature of the doped c-BN thin films. The maximum electron mobility in the C-doped c-BN films was determined to be ~ 4.6 cm2V-1s-1 at room temperature. From the fitting profile of resistivity vs temperature plot, a shift in the dominant conduction mechanism was observed from one impurity ionization with activation energy in the range between 0.012 eV - 0.076 eV in a high-temperature region to another between 0.0024 eV- 0.0086 eV in a low-temperature region. The change in activation energy at various doping level was due to the band broadening effect and can be explained by Lee-McGill model. This work proves that C can be used as an n-type dopant for c-BN semiconductor, which opens new possibilities for this material to be used in practical devices such as deep ultraviolet photo detectors and high frequency power-electronic devices.
11:15 AM - NM08.04.06
High-Temperature Carbon-Based Superconductors—B-Doped Q-Carbon
Anagh Bhaumik 1 , Ritesh Sachan 1 2 , Siddharth Gupta 1 , Jagdish Narayan 1
1 , North Carolina State University, Raleigh, North Carolina, United States, 2 Materials Science Division, Army Research Office, Research Triangle Park, Raleigh, North Carolina, United States
Show AbstractThe versatility in the arrangements of C atoms to form various allotropes and phases has led to the discovery of several carbon-based superconducting materials. In the present study, B-doped Q-carbon thin films are formed on sapphire substrates by employing pulsed laser annealing using a nanosecond excimer ArF laser. This process involves the rapid quenching of highly undercooled melt of homogenously mixed B and C. Nanosecond laser melting of carbon in a super undercooled state and rapid quenching result in strongly bonded unique superconducting phase of B-doped Q-carbon. As a result of rapid melting and quenching, we can achieve 17.0±1.0 or higher atomic % of B in the electrically active sites of Q-carbon which leads to the formation of shallow electronic states near the valence band maximum. The temperature-dependent magnetic susceptibility measurements demonstrate a type II superconductivity in this material with a transition temperature of 36.0±0.5 K and upper critical field of 5.4 T at 0 K. It has also been shown that in B-doped Q-carbon, the upper critical magnetic field (Hc2(T)) follows Hc2(0) [1-(T/Tc)2.11] temperature dependence and is consistent with the Bardeen-Cooper-Schrieffer formalism. Through the structure-property correlation measurements in B-doped Q-carbon, we estimate a higher electronic density of states near the Fermi energy level. Higher density of states near the Fermi-level along with higher Debye temperature and phonon frequency are responsible for enhanced Tc. From the critical current density versus magnetic field plots, the value of critical current density (Jc (2T)) in B-doped Q-carbon at 21 K is calculated as 4.3×107 A cm-2, which indicates that this novel material can be used for the persistent mode of operation in MRI and NMR applications. This discovery of high-temperature superconductivity in B-doped amorphous Q-carbon shows that non-equilibrium synthesis technique using super undercooling process can be used to fabricate materials with greatly enhanced physical properties.[1]
[1] Bhaumik, A; Sachan, R; Narayan, ACS Nano 2017, DOI: 10.1021/acsnano.7b01294.
11:30 AM - NM08.04.07
Opening Electronic Properties in Graphene by Exploiting Defects
Dingyi Sun 1 , David Funes Rojas 2 , Mauricio Ponga 2
1 , Brown University, Providence, Rhode Island, United States, 2 , University of British Columbia, Vancouver, British Columbia, Canada
Show Abstract2D materials - particularly graphene - have factored heavily into the design of lightweight, flexible electronic devices. In the pursuit to control the electronic properties of these materials, a paramount interest has been the manipulation of the band gaps in these materials. Unfortunately, most band gaps in these materials have been primarily dictated by interfaces such as grain boundaries, which are not very well-controlled in the manufacturing process. As an alternative to this, we propose the exploitation of twins - a symmetric reorientation of the material lattice about a planar discontinuity - in these materials. We use a newly-developed twin framework to kinematically predict novel twin modes in graphene. We then perform a series of density functional theory and molecular dynamics simulations in order to study the energetics of these twin modes, along with their effects on the material band gap and transmission coefficients. In particular, by showing that several of these newly-predicted twin modes open up promising band gaps in these materials, our work opens an avenue to systematically generate novel twin modes in graphene as a means for controlling electronic properties for the advancement of the design of 2D materials, including possible development of phononic metamaterials through twinning.
11:45 AM - NM08.04.08
Length Scale and Dimensionality of Defects in Epitaxial SnTe Topological Crystalline Insulator Films
Omur Dagdeviren 1 , Subhasish Mandal 1 , Ke Zou 1 , Chao Zhou 1 , Georg Simon 1 , Stephen Albright 1 , M.D. Morales-Acosta 1 , Xiaodong Zhu 1 , Sohrab Ismail-Beigi 1 , Fred Walker 1 , Charles Ahn 1 , Udo Schwarz 1 , Eric Altman 1
1 , Yale Univ, New Haven, Connecticut, United States
Show AbstractRevealing the local electronic properties of surfaces and their link to structural properties is an important problem for topological crystalline insulators (TCI) in which metallic surface states are protected by crystal symmetry. Here, we characterized the structure and electronic properties of TCI SnTe film surfaces grown by molecular beam epitaxy using scanning probe microscopy. The results reveal the influence of various defects on the electronic properties, including screw dislocations, point defects, and tilt boundaries that lead to dislocation arrays that serve as periodic nucleation sites for pit growth. These features manifest on multiple length scales, thereby inducing variations in the electronic structure of the surface. Mapped in scanning tunneling microscopy images as standing waves superimposed on atomic scale images, their exact appearance is shaped by the details of the surface topography such as surface steps and point defects. Since any symmetry-breaking defect affects the formation of topological states, we propose that by patterning the surface with the scanning probe tip, custom electronic structures could be created that may enable the fabrication of topological devices.
NM08.05: Spectroscopic and Magnetic Properties
Session Chairs
Sriparna Bhattacharya
Jagdish Narayan
Tuesday PM, November 28, 2017
Hynes, Level 3, Room 309
1:30 PM - *NM08.05.01
Defect Engineering in 1D and 2D Materials—In Situ Spectroscopy
Rahul Rao 1 2
1 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson AFB, Ohio, United States, 2 , UES, Inc., Dayton, Ohio, United States
Show AbstractStructural defects are ubiquitous in crystalline materials, and owing the reduced dimensionality of nanomaterials, they affect material properties significantly. Lattice defects in 1D and 2D materials exist in various forms, including vacancies, dislocations, grain boundaries and substitutional dopants. While the majority of these defects have an adverse effect on the optical, electrical and mechanical properties, they can also be advantageous, for example for sensors. In order to engineer defects in a nanomaterial, it is necessary to understand their origin and their influence on the electronic and phononic structure. We use in situ Raman and photoluminescence spectroscopy during and after synthesis to measure the evolution of lattice defects in 1D and 2D materials. In particular, we will discuss structure-dependent defect formation in single-walled carbon nanotubes, as well as oxidation and healing dynamics in monolayer graphene and MoS2.
2:00 PM - *NM08.05.02
The Influence of Defect Dimensionality in the Raman Scattering from Graphene
Ado Jorio 1 , Mateus Gomes da Silva 1 , Erlon Ferreira 2 , Ferdinant Hof 3 , Katerina Kampioti 3 , Kai Huang 3 , Alain Pénicaud 3 , Carlos Achete 2 , Rodrigo Capaz 4 , Luiz Cançado 1
1 ICEx, Dep. de Física, Universidade Federal de Minas Gerais, Belo Horizonte Brazil, 2 Divisão de Metrologia de Materiais-DIMAT, Instituto Nacional de Metrologia, Qualidade e Tecnologia-INMETRO, Duque de Caxias Brazil, 3 Centre de Recherche Paul Pascal—CNRS, Université Bordeaux, Pessac France, 4 Instituto de Física, Universidade Federal do Rio de Janeiro, Rio de Janeiro Brazil
Show AbstractFrom the dimensionality standpoint, defects in two-dimensional systems can be either one- (1D) or zero-dimensional (0D). In graphene, both types of defects produce changes in the Raman spectrum, but identifying separately the contribution from each defect-type has not yet been achieved. Here we show that a diagram can be built for disentangling contributions of point-like and line-like defects to the Raman spectra of graphene-related materials embracing, from the topology point of view, all possible structures from perfect to fully disordered sp2 bonded carbons. Two sets of graphene-related samples, produced by well-established protocols that generate either 0D or 1D defects in a controlled way, are analyzed with our model and used to parameterize the limiting values of the phase space. We then discuss the limitations and apply our new methodology to analyze the structure of two-dimensional nanocarbons generated from renewable gas, used to produce inks and conducting coatings.
2:30 PM - NM08.05.03
Unraveling Electronic Structures of Confined Linear Carbon Chains by Resonance Raman Scattering
Lei Shi 1 , Philip Rohringer 1 , Sofie Cambre 2 , Wim Wenseleers 2 , Sören Waßerroth 3 , Stephanie Reich 3 , Marius Wanko 4 , Angel Rubio 4 5 , Paola Ayala 1 6 , Hans kuzmany 1 , Thomas Pichler 1
1 Faculty of Physics, University of Vienna, Wien Austria, 2 Experimental Condensed Matter Physics Laboratory, University of Antwerp, Antwerp Belgium, 3 Department of Physics, Freie Universität Berlin, Berlin Germany, 4 Nano-Bio Spectroscopy Group and European Theoretical Spectroscopy Facility (ETSF), Universidad del País Vasco, CFM CSIC-UPV/EHU-MPC \& DIPC, San Sebastián Spain, 5 , Max Planck Institute for the Structure and Dynamics of Matter, Hamburg Germany, 6 School of Physical Sciences and Nanotechnology, Yachay Tech University, Urcuqui Ecuador
Show AbstractResonance Raman scattering (RRS) is an excellent analytical tool to unravel electronic structures of systems where direct access is difficult, because the electronic structures are directly linked to the vibrational frequencies.
Recently we demonstrated synthesis of confined carbyne inside double-walled carbon nanotubes (DWCNTs) with a record length of more than 6000 carbon atoms [1]. This opens a trail into uncharted territory, which will now allow for the first time unraveling intrinsic properties of such confined polyyne and carbyne. For example, the electronic energy gap of confined carbon chains with different length was explored by the RRS and the band gap of infinite chains can be accurately analyzed [2]. Furthermore, the interaction and charge transfer between the carbon chains and their host CNTs lead to an increase of the photoluminescence signal of the inner tubes of DWCNTs [3,4]. Very recently excitations of the confined carbon chains from polyyne to carbyne reveal additional resonances, revealing the RRS diversity of confined polyynes and carbyne from molecules to solid [5].
This work was supported by the FWF (P27769-N20) and EU projects (2D-Ink FA726006).
1. Nat. Mater. 15, 634, 2016
2. arXiv:1705.02259, 2017
3. Phys. Rev. B 94, 195422, 2016
4. Adv. Funct. Mater. 26, 4874, 2016
5. In preparation.
2:45 PM - NM08.05.04
Defect-Induced Multiferroics with Atomic Dimensions in Nonmagnetic Ferroelectrics
Takahiro Shimada 1 , Tao Xu 1 , Jie Wang 2 , Takayuki Kitamura 1
1 , Kyoto University, Kyoto Japan, 2 , Zhejiang University, Hangzhou China
Show AbstractMultiferroics in nanoscale dimensions are promising for novel functional device paradigms, such as magnetoelectric memory, due to intriguing cross-coupling between coexisting ferroelectric and (anti-)ferromagnetic order parameters. However, the ferroic order is inevitably destroyed below the critical dimension of several nanometers. Here, we demonstrate a new path toward realization of ultimately-small multiferroics while resolving the controversial origin of dilute ferromagnetism that unexpectedly emerges in nanoparticles of nonmagnetic ferroelectric PbTiO3. Systematic exploration using state-of-the-art hybrid Hartree-Fock density functional calculations as well as the DFT+U calculations with a theoretical Hubbard U derived from the constrained random phase approximation (cRPA) successfully identifies that oxygen vacancies formed at surfaces/grain boundaries induce ferromagnetism due to local non-stoichiometry and orbital symmetry breaking. The localized character of emerged magnetization allows an individual oxygen vacancy to act as an atomic-scale multiferroic element with a nonlinear magnetoelectric effect that involves rich FM-AFM-NM phase transitions in response to switching spontaneous polarization. Moreover, we also demonstrate that the local (anti-)ferromagnetism can emerge at dislocations as a line defect. Therefore, defects in ferroelectric oxides can behaver as atomic-scale low-dimensional multiferroics. Engineering these multiferroic features opens a new avenue to the design of ultrahigh-density integration for atomic-scale multiferroics.
3:30 PM - NM08.05.05
Large Thermal Hysteresis in Verwey Transition of Mono-Domain Fe3O4 Nanoparticles
Taehun Kim 1 2 , Sumin Lim 3 , Jaeyoung Hong 4 5 , Soon Gu Kwon 4 5 , Jun Okamoto 6 , Zhi Ying Chen 7 , Jaehong Jeong 1 2 , Soonmin Kang 1 2 , Jonathan Leiner 1 2 , Di Jing Huang 6 7 , Taeghwan Hyeon 4 5 , Soonchil Lee 3 , Je-Geun Park 1 2
1 Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of), 2 Center for Correlated Electron Systems, Institute for Basic Science, Seoul Korea (the Republic of), 3 Physics, KAIST, Daejeon Korea (the Republic of), 4 Chemical and Biological Engineering, Seoul National University, Seoul Korea (the Republic of), 5 Center for Nanoparticle Research, Institute for Basic Science, Seoul Korea (the Republic of), 6 , National Synchrotron Radiation Research Center, Hsinchu Taiwan, 7 Physics, National Tsing Hua University, Hsinchu Taiwan
Show AbstractWe discovered that high stoichiometric Fe3O4 nanoparticles (NPs) have large thermal hysteresis of Verwey transition, which is more than three times compared to bulk case. According to several experiments such as magnetization, nuclear magnetic resonance (NMR) spectra and X-ray diffraction (XRD), we could deduce that the width of hysteresis have a clear size dependence as same as the size dependence on coercivity of typical ferromagnetic materials. The ratio between remanent magnetization (Mr) and saturated magnetization (Ms) suggests that the thermal hysteresis is related to mono-domain behavior in smaller particles with critical size of 120 nm. We also carried out resonant inelastic X-ray scattering (RIXS) experiments on several samples to conclude that there is a gradual suppression of polaronic excitations near the Fermi level with reducing size, which indicates the intrinsic size effect of magnetite in nm scale. Based on all data, we concluded that our Fe3O4 nanoparticles have mono domain, which have larger thermal hysteresis in Verwey transition, and our findings might come from the correlation effect of spin and charge ordering in single domain of magnetite.
3:45 PM - NM08.05.06
Extraordinary Hall Effect, Electrochromic Effect and Room-Temperature Ferromagnetism in Q-Carbon
Anagh Bhaumik 1 , Ritesh Sachan 1 2 , Sudhakar Nori 1 , Siddharth Gupta 1 , Jagdish Narayan 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 , U.S. Army Research Office—Materials Science Division, Raleigh, North Carolina, United States
Show AbstractThe outer 2s and 2p shells in a carbon atom can hybridize in three different ways to form sp, sp2 and sp3 orbital wave functions. For the carbon materials comprising a mixture of sp2 and sp3 bonding types, a dominant factor in determining their physical properties is the sp2/sp3 ratio. In the present study, we report extraordinary Hall effect, electrochromic effect and room-temperature ferromagnetism in undoped Q-carbon, which is formed by nanosecond pulsed laser melting and subsequent quenching process. The analysis of the extraordinary Hall effect in Q-carbon follows non-classical “side-jump” electronic scattering mechanism. We have also found n-type electrical conductivity in Q-carbon in the entire temperature range from 10 - 300 K based on the extraordinary Hall coefficient versus magnetic induction experiments. The isothermal field-dependent magnetization plots confirm room-temperature ferromagnetism in Q-carbon with a finite coercivity at 300 K and a Curie temperature of 570 K. Through detailed structure-property correlations in Q-carbon thin films, we show the excess amount of unpaired electrons near the Fermi energy level, which give rise to interesting magnetic and electrical properties. This gives rise to a 48% increase in optical absorption at 275 nm with an applied electric field of 10 V. High-resolution scanning electron microscopy and transmission electron microscopy clearly illustrate the formation of Q-carbon and its subsequent conversion to single crystalline diamond. Magnetic force microscopy and Kelvin probe force microscopy also indicate room-temperature ferromagnetism and electrochromism, respectively. This discovery of interesting magnetic and electron transport properties of Q-carbon show that non-equilibrium synthesis technique using super undercooling process can be used to fabricate new materials with greatly enhanced physical properties and functionalities.
4:00 PM - NM08.05.07
Nitrogen Vacancy Induced Room-Temperature Ferromagnetism in TiN Epitaxial Thin Films via Ultrafast Laser Melting
Siddharth Gupta 1 , Ritesh Sachan 1 2 , Adele Moatti 1 , Jagdish Narayan 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Materials Science Division, U.S. Army Research Office—Materials Science Division, Raleigh , North Carolina, United States
Show AbstractAmong the metal nitrides, Titanium Nitride(TiN) is unique due to its properties such as thermal insulation, metal-like electrical conductivity, and high melting point. In the present study, nitrogen vacancies were generated in as-deposited TiN thin films by performing nanosecond laser irradiation. The out-of-plane and in-plane epitaxial relationships between TiN and c- Sapphire are determined to be (111)TiN|| (0001)Sapphire and (-110)TiN|| (10-10)Sapphire respectively. With the lattice matching of 1/3 d(10-10) of sapphire with d(-110) of TiN, the in-plane strain was calculated as 13.32%. As TiN/c-Al2O3 is a large misfit system, the lattice relaxes completely following domain matching epitaxy (DME) paradigm. Based on DME framework, 8 domains of the sapphire match with 9 domains of TiN lead to a residual misfit strain of 0.7%. The thin film then gets relaxed via the principle of domain variation, where the 8/9 and 9/10 domains alternate to achieve close to zero (0.028%) residual strain. The strain along the {200} planes of TiN was measured to be -0.624%, which matched with the calculated thermal strain in the thin film signifying complete misfit relaxation. Interestingly, on performing laser irradiation, both out of plane lattice and thermal strain gets annihilated along the {200} planes of TiN and the thin film completely relaxes. The field-dependent magnetization analysis confirmed the room-temperature ferromagnetism in TiN thin films with the magnetic moment of 0.54 emu g-1 at 300 K for the as-deposited film in the vacuum, which got enhanced to 1.28 emu g-1 with finite coercivity on laser irradiation with a single pulse at 0.8 J cm-2. On annealing the deposited thin film under the pure N2 pressure of 10 Torr, the magnetic moment drastically reduced to 0.02 emu g-1. The nitrogen vacancies in the deposited thin films were quantified via TO/TA peak ratio in the Raman spectra. This ratio was much lower for vacuum deposited thin film in comparison to pure N2 annealed film and monotonically decreased on performing subsequent laser irradiation, signifying an increase in Nitrogen vacancies in TiN lattice. The nitrogen bonding states probed via X-Ray photoelectronic spectroscopy reveal that Ti interstitials and O-N bonds start forming after subsequent laser-irradiated thin film due to lattice overlayer breakdown. The systematic increase in the magnetic moment by progressive laser irradiation and the decrease in the magnetic moment on annealing thin films in pure nitrogen, experimentally prove that nitrogen vacancies induce pinning centers which generate ferromagnetism in the TiN thin films.
4:15 PM - NM08.05.08
Role of Electronic Structure on Superconductivity and Ferromagnetism of Q-Carbon
Ritesh Sachan 1 2 , Anagh Bhaumik 2 , Siddharth Gupta 2 , Jagdish Narayan 2
1 , Army Research Office, Raleigh, North Carolina, United States, 2 , North Carolina State University, Raleigh, North Carolina, United States
Show AbstractThe discovery of Q-carbon has drawn a lot of attention in the past two years due to its interesting physical properties. Q-carbon is synthesized by rapid quenching (~1010 K/s) of highly undercooled carbon melt and is constituted of ~80% sp3 and ~20% sp2 hybridized carbon. In the present study, we present a correlation of electronic structure of Q-carbon with the ferromagnetism and superconductivity properties. In contrast to the other diamagnetic derivatives of carbon, such as graphite, it is shown that Q-carbon nanostructures exhibit room temperature ferromagnetism with finite coercivity. Using electron energy-loss spectroscopy (EELS), we demonstrate that the C K-edge of Q-carbon consists of a sharp π* peak and a broad σ* peak. On comparing the C K-edge of amorphous Q-carbon with various diamond-like-carbon (DLC) films having a different sp3-sp2 ratio, it is found that π* peak intensity is exceptionally high in spite of having just ~20% sp2 content. This increase in the intensity corresponds to the increased unpaired spin electron density in Q-carbon due to the highly non-equilibrium synthesis route and gives rise to the room temperature ferromagnetism. Q-carbon, due to this dramatic increase in unpaired spin electron density, also exhibits the extraordinary Hall Effect characteristics.
Using EELS, we also demonstrate the correlation between superconductivity and the role of B doping in Q-carbon. We show that the nanosecond laser melting and rapid quenching of C results in strongly bonded unique superconducting phase of B-doped Q-carbon. This results into a type II superconductivity in B-doped Q-carbon with a transition temperature of 36.0±0.5 K. The EELS results show that we can achieve a homogeneously distributed B doping in Q-carbon as high as 17.0±1.0 at% with the employed synthesis process.[1] An essential conduction for superconductivity in B-doped C is that B stays in sp3 hybridized state with carbon. We quantify that ~60% B atoms bond with sp3 hybridized C and contribute in the superconducting state of B-doped Q-carbon. With monochromated low-loss EELS and Raman spectroscopy, we demonstrate a higher electronic density of states near the Fermi energy level, which leads us to achieve remarkably high superconductivity transition temperature in B-doped Q-carbon. With this study, we present an insight on the role of electronic structure in achieving high-temperature superconductivity.
[1] Bhaumik, A; Sachan, R; Narayan, J. High-Temperature Superconductivity in Boron-Doped Q Carbon. ACS Nano 2017. DOI: 10.1021/acsnano.7b01294