Yongfeng Lu University of Nebraska-Lincoln
CraigB. Arnold Princeton University
CostasP. Grigoropoulos University of California-Berkeley
Michael Stuke Max-Planck-Institute for Biophysical Chemistry
StevenM. Yalisove University of Michigan
TT2: Ultra-fast Laser Processing II
Tuesday PM, April 26, 2011
Nob Hill AB (Marriott)
2:30 PM - **TT2.1
Effect of Temporal Pulse Shaping and Coherent Excitation on Laser Micorfabrication.
Xianfan Xu 1 Show Abstract
1 , Purdue University, West Lafayette, Indiana, United States
In this work, we investigate femtosecond temporal pulse shaping and coherent phonon excitation on laser micro fabrication and surface modification. Femtosecond laser micromachining process is determined by the ultrafast laser-matter interaction and energy transfer dynamics. By controlling the temporal shapes of the laser pulses and therefore the energy coupling process between ultrafast laser pulses and the target, it is possible to influence energy transfer and phase change processes. Experiments were carried out using femtosecond pulses with various temporal distributions. There were clear differences in the machining of different materials when different pulse shapes were used. The role of non-thermal melting caused by phonon vibration at the ultrafast time scale is also explored.
3:00 PM - **TT2.2
Real-Time Structural Dynamics of Polar Solids Studied by Femtosecond X-Ray Powder Diffraction.
Thomas Elsaesser 1 , Flavio Zamponi 1 , Philip Rothhardt 1 , Michael Woerner 1 Show Abstract
1 , Max-Born-Institute, Berlin Germany
The study of structural dynamics on an atomic length and ultrafast time scale has developed into an important area of solid state research. X-ray diffraction with a femtosecond time resolution allows for probing such processes most directly by determining transient atomic positions and deriving transient charge density maps from the diffraction patterns . Recent progress in the generation of ultrashort hard x-ray pulses in laser-driven plasma sources has allowed for performing highly sensitive Bragg and powder diffraction studies of (poly)crystalline materials [2,3]. In this contribution, we report new results on ultrafast structural dynamics in molecular ferroelectrics with an ionic hydrogen-bonded crystal structure. After photoexcitation of the materials, up to 20 Debye Scherrer rings are recorded simultaneously by diffracting a hard x-ray pulse (wavelength 0.154 nm) from the excited powder sample. The combined spatial and temporal resolution is 30 pm and 100 fs. A first series of experiments gives evidence of a so far unknown concerted transfer of electrons and protons in ammonium sulfate, a structure displaying inversion symmetry. Charge transfer from the sulfate groups results in the sub-100 fs generation of a highly confined electron channel along the c-axis of the unit cell which is stabilized by transferring protons from the adjacent ammonium groups into the channel. Time-dependent charge density maps derived from the diffraction data display a periodic modulation of charge density in the channel mediated by low-frequency lattice motions with a concerted electron and proton motion between the channel and the initial proton binding site. A second study addresses atomic rearrangements and charge dislocations in potassium dihydrogen phosphate, a structure without inversion symmetry. The time-resolved powder diffraction data demonstrate an ultrafast transfer of electronic charge from the phosphorus atoms to hydrogen bonded protons, resulting in the formation of hydrogen atoms. Such hydrogens are localized at initially unpopulated sites in the unit cell close to oxygen atoms of the phosphate groups, in this way generating local defect sites. We will present a novel projection method to derive transient charge density maps in the non-centrosymmetric material. For an overview, see: Special issue on 'Dynamical Structure Science' Acta Cryst. A 66, 133-280 (2010). C. von Korff Schmising, M. Bargheer, M. Kiel, N. Zhavoronkov, M. Woerner, T. Elsaesser, I. Vrejoiu, D. Hesse, M. Alexe, Phys. Rev. Lett. 98, 257601 (2007). F. Zamponi, Z. Ansari, M. Woerner, T. Elsaesser, Opt. Express 18, 947 (2010). M. Woerner, F. Zamponi, Z. Ansari, J. Dreyer, B. Freyer, M. Prémont-Schwarz, T. Elsaesser, J. Chem. Phys. 133, 064509 (2010).
3:30 PM - TT2.3
Ultrafast Laser Patterning of Carbon Nanotube Structures.
Ryan Murphy 1 3 , Huanan Zhang 2 , Haiping Sun 3 , Ben Torralva 3 , Nicholas Kotov 2 , Steven Yalisove 3 1 Show Abstract
1 Applied Physics, University of Michigan, Ann Arbor, Michigan, United States, 3 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Chemical Engineering, University of Michigan, Ann Arbor, Michigan, United States
Nanostructures of single-walled carbon nanotubes (SWCNT) are formed after irradiation of a monolayer of randomly aligned SWCNT by a Ti:Sapphire 800 nm laser with a 150 fs pulse at fluences near 0.1 J/cm2. At varying peak fluences morphology is seen where the tubes are ejected from the substrate or formed into “nanohair” structures. Nanohair has been created on both glass substrates and carbon grids. These structures can form a 3-D “foam” from the monolayer or smaller structures in the plane that are 400 nm long and 5 nm wide and are arranged such that they are aligned towards the middle of the crater. Transmission Electron Microscopy analysis of the nanotubes and a possibility of using the foam as a conductor in photovoltaics will be presented.
3:45 PM - TT2.4
Direct Fabrication of Waveguide Amplifiers Inside Er-Yb Doped Zinc Polyphosphate Glass Using Femtosecond Laser Pulses.
Luke Fletcher 1 , Jon Witcher 1 , Neil Troy 1 , Richard Brow 2 , Denise Krol 1 Show Abstract
1 Applied Science, University of California Davis, Davis, California, United States, 2 Materials Science and Engineering, Missouri University of Science and Technology, Rolla, Missouri, United States
Permanent modification to the glass structure induced by femtosecond laser pulses can be used inside a variety of active glasses to fabricate waveguide lasers and amplifiers, with applications in three-dimensional photonic circuits. Zinc phosphate glasses, are excellent glass systems for achieving high rare-earth oxide concentrations with low luminescence quenching effects, and are ideal for fabricating compact high gain waveguide lasers that operate over the entire C-band. Previous research with zinc polyphosphate glasses has demonstrated important relationships between the initial composition of simple phosphate glasses and the structural changes that result from fs-laser modification. In particular, waveguides fabricated in glasses with the [O]/[P] ratio near 3.25 demonstrate local densification of the glass that occurs inside the irradiated area, which can be used to fabricate single mode waveguides fabricated under a wide range of laser processing conditions. In this study we have investigated the direct fabrication of sub-surface waveguide amplifiers in Er-Yb zinc polyphosphate glasses by utilizing this relationship between the glass composition and the resulting changes to the network structure after modification by fs-laser pulses. Such laser-induced structural changes in the glass were characterized using confocal fluorescence and Raman microscopy. In this study, waveguides inside Er-Yb doped zinc polyphosphate glass have been fabricated using a regenerative amplified Ti:sapphire 1 kHz, 180 fs-laser system. Fs-laser writing parameters such as the laser fluence, the beam focusing, and the writing geometry have been studied. Near field guiding profiles and white light images as well as insertion losses and internal gain were measured after waveguides were written.
4:00 PM - TT2: Ultra-fast
4:30 PM - **TT2.5
Nonlinear Micro-processing of Silicon by Ultrafast Fiber Laser at 1552 nm.
Yoshiro Ito 1 , Rie Tanabe 1 , Kozo Tada 2 Show Abstract
1 Mechanical Engineering, Nagaoka University of Technology, Nagaoka, Niigata, Japan, 2 , Citizen Finetech Miyota, Tomi, Nagano, Japan
Processing of transparent materials by non-linear absorption processes induced by short pulse lasers has been applied in many fields. Silicon (Si) is widely used materials in microelectronics, MEMS and photonics. It is, however, not transparent for commonly used processing lasers in near ir to uv spectral range and is not targeted for the non-linear processing by lasers so far. In this paper, possibilities and capabilities of non-linear processing of Si by transparent 1552nm laser radiations are described with special emphasis on application to frequency adjustment of crystal oscillators in packages made from Si [1, 2]. A fiber-based ultrashort laser which delivered 900 fs, 1552.5 nm pulses at 10 to 500 kHz was used. Machining at different positions, from the front surface of the first substrate to rear surface of the second substrate placed at the back of the first, was carried out in air. Focused outputs of the laser make trenches on the front surface of the Si substrate. Sharp and deep grooves are machined with some deposition on the edges on the front surface. When it is focused on the second substrate placed at the back of the first Si substrate, trenches are made on the surface of the second with no detectable change on the first. When the focus is placed at the rear surface, quite different machined features are observed on the rare surface. A wide stripe of fine grained structure without any deep trench is formed on the rare. Highly position selective machining of surfaces has been achieved by adjusting the focus to each surface with no detectable change on the other surfaces. Gold film on the second substrate can be ablated without any change on front and rear surfaces of the first substrate. Frequency adjustment of the crystal oscillator sealed in silicon package is tried and up-conversion of the frequency is achieved by removing small amount of thin gold film on the crystal with irradiation of the laser through the silicon package. During the research, we have found that infrared laser light come through the silicon substrate is accompanied by green light, the wavelength of which is 517 nm, exactly the one third of the laser wavelength 1552.5 nm. This phenomenon is considered as the third harmonics generation (THG) in bulk Si and will be described to some extent. 1. Yoshiro Ito, Fumiya Sato, Yuuki Shinohe, Rie Tanabe, Kozo Tada, Proc. SPIE Vol. 7584, 75840M (Feb. 17, 2010)2. Rie TANABE, Fumiya SATO, Yuki SHINOHE, Kozo TADA and Yoshiro ITO, Proc of LPM2010, http://www.jlps.gr.jp/en/proc/lpm/10/ #10-25 (2010)
5:00 PM - TT2.6
Ultrafast Laser Processing of Hybrid Micro- and Nano-structures in Silicate Glasses.
Pavel Mardilovich 1 , Luke Fletcher 2 , Neil Troy 2 , Subhash Risbud 1 , Denise Krol 2 Show Abstract
1 Chemical Engineering and Materials Science, UC Davis, Davis, California, United States, 2 Department of Applied Science, University of California, Davis, Davis, California, United States
This study focuses on application of ultrafast laser in processing of semiconductor doped glasses. A specific aim is the fabrication of hybrid micro-/nanostructures of semiconductor nanocrystals precipitated in micrometer scale domains defined by laser exposure. Ultrafast laser processing had been used to induce structural modifications in the bulk of transparent dielectric materials, such as glass. This has enabled a creation of several optoelectronic device-oriented structures, such as waveguides, splitters and couplers, Bragg gratings, amplifiers etc. So far most of these structures have been homogeneous on a nanometer scale. Manufacturing heterogeneous structures of micro-scale domains with nano-scale inclusions will greatly expand the toolbox available for optoelectronic device design.In certain doped glasses it is possible to nucleate and grow semiconductor nanocrystals under certain thermal conditions. Determining factors in the nucleation and growth dynamics of these crystallites are the mobility of the semiconductor in the glass network, and the degree of supersaturation of the semiconductor in a glass.It has been established that ultrafast laser processing of multi-oxide glasses can lead to structural changes in the glass matrix that favor local nucleation and growth of nanocrystals upon subsequent heat treatment. In this study we used ultrafast laser processing to introduce local structural modifications in glasses doped with Cd, S and Se. This processing produced micron-sized regions in the glass, which displayed markedly different properties and behavior from the surrounding bulk. The resultant structures were investigated using optical and electron microscopy, as well as confocal fluorescence and Raman microscopy to elucidate the underlying structural changes, both before and after subsequent heat treatment.We will discuss the results of this study, addressing how laser processing parameters affect structural changes in the irradiated glass, and how these changes subsequently influence the semiconductor precipitation dynamics on a local scale.
5:15 PM - TT2.7
Ultrafast Laser Interactions with Interfaces and Micro-fluidics Fabrication.
Ryan Murphy 1 2 , Ben Torralva 2 , Steven Yalisove 2 1 Show Abstract
1 Applied Physics Program, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Interfaces have been found to play an important role in material removal after irradiation by ultrafast light. Only 10 nm of nickel sputter coated onto a silicon substrate changes the morphology of craters in the nickel after irradiation by 150 fs pulses at a wavelength of 780 nm causing material removal to occur at fluences below the bulk removal threshold. This capping layer also affects the response of the substrate to the incident laser light. Varying amounts of nickel deposited between layers of glass can produce buckling (blistering) of the glass at fluences which are an order of magnitude below those required to induce buckling at a glass-glass interface. By lowering the minimum amount of nickel required to induce blistering, there is strong promise for the production of stacked (3-D), transparent micro-fluidics by the overlap and layering of multiple blisters. A general model involving the heterogeneous nucleation and growth of voids at defects present at the interface will be presented and applied to several different systems where buckling and material removal of interfaces with varying film thickness and composition were observed.
Yongfeng Lu University of Nebraska-Lincoln
CraigB. Arnold Princeton University
CostasP. Grigoropoulos University of California-Berkeley
Michael Stuke Max-Planck-Institute for Biophysical Chemistry
StevenM. Yalisove University of Michigan
TT3: Laser Ablation and Deposition
Wednesday AM, April 27, 2011
Nob Hill AB (Marriott)
9:30 AM - **TT3.1
Laser Forward Transfer of Freestanding Microstructures.
Alberto Pique 1 , Ray Auyeung 1 , Andrew Birnbaum 1 , Heungsoo Kim 1 , Nicholas Charipar 1 , Kristin Metkus 1 , Scott Mathews 1 Show Abstract
1 Materials Science & Technology Division, Naval Research Laboratory, Washington, District of Columbia, United States
Laser forward transfer processes are capable of directly generating patterns and structures of functional materials for the rapid prototyping of electronic, optical and sensor devices. These processes, also known as laser induced forward transfer or LIFT, offer unique advantages and capabilities for digital microfabrication. A key advantage of laser forward transfer techniques is their compatibility with a wide range of materials, surface chemistries and surface morphologies. These processes have been demonstrated in the fabrication of a variety of microelectronic elements such as interconnects, passives, antennas, sensors, power sources and embedded circuits. Overall, laser forward transfer is perhaps the most flexible digital microfabrication process available in terms of materials versatility, substrate compatibility and range of speed, scale and resolution. Recently, laser forward transfer of thin film-like structures with excellent lateral resolution and thickness uniformity using metallic nanoinks has been shown at NRL using a technique named laser decal transfer. The high degree of control in size and shape achievable with laser decal transfer has been applied to the digital microfabrication of 3-dimensional stacked assemblies and freestanding structures for MEMS applications. This talk will describe the unique advantages and capabilities of laser decal transfer of electronic nanoinks, discuss its applications and explore its role in the future of digital microfabrication.This work was sponsored by the Office of Naval Research.
10:00 AM - TT3.2
Metal and Metal-oxide Nanoparticle Synthesis by Laser Ablation of Aqueous Aerosols.
Kristofer Gleason 1 , John Keto 2 , Desiderio Kovar 3 , Michael Becker 1 Show Abstract
1 Department of Electrical and Computer Engineering, University of Texas at Austin, Austin, Texas, United States, 2 Department of Physics, University of Texas at Austin, Austin, Texas, United States, 3 Department of Mechanical Engineering, University of Texas at Austin, Austin, Texas, United States
We present a scalable, continuous manufacturing method of nanoparticle production based on laser ablation of an aerosol generated from an aqueous precursor solution. A Collison nebulizer is used to generate a mist of ~10 μm diameter water droplets containing dissolved transition metal salts, suspended in 1 atmosphere of buffer gas. Water from the droplets quickly evaporates, leaving solid particles ~2 μm in diameter for a typical solution concentration. These microparticles are then ablated by a pulsed KrF excimer laser (10 ns, λ = 248 nm, 2 J/cm2 at focus). Ablation results in plasma breakdown of the microparticle and photothermal decomposition of the precursor material. Following ablation, nanoparticles 5-20 nm in diameter are formed and collected. For AgNO3 ablated in He gas, metal Ag nanoparticles were produced. For Cu(NO3)2 ablated in He, crystalline Cu2O nanoparticles were produced. For Ni(NO3)2 ablated in He, crystalline NiO nanoparticles were produced. A combination of AgNO3 and Cu(NO3)2 ablated in a reducing atmosphere of 10% H2 and 90% He yielded Ag-Cu alloy nanoparticles. In contrast to conventional wet-chemical synthesis processes, our nanoparticles are formed ‘bare,’ without surfactants or organic material contaminating the surface. Owing to their small size and high free surface area, nanoparticles produced by this process are ideally suited for applications that include catalysis and facilitated transport membranes.
10:15 AM - TT3.3
In Situ Spectroscopic Diagnostics of SnO2 Nanowire Growth Pulsed Laser Vapor Deposition.
Alex Puretzky 1 , Junsoo Shin 1 , Chris Rouleau 1 , Jason Readle 1 , Norbert Thonnard 1 , Amit Goyal 1 , Gerd Duscher 1 , Karren More 1 , David Geohegan 1 Show Abstract
1 , ORNL, Oak Ridge, Tennessee, United States
SnO2 nanowires exhibit n-type semiconductor properties with the band gap of 3.6 eV and are very attractive nanomaterial for many important applications, including flexible electrical and optoelectronic devices, photovoltaic cells, and gas sensors. Therefore it is important to develop different approaches to control the growth of these nanowires and understand their growth mechanism. Here we demonstrate a laser ablation approach to grow tin oxide nanowires on different substrates (Si, SrTiO3, etc.) covered with a thin layer of gold (1-10 nm). Au nanoparticles formed by roughening of the film are typically used as catalysts for the VLS growth of oxide nanowires. In the laser vaporization approach described here, material ablated from a SnO2 target at 700°C by a KrF-laser (248 nm, 4J/cm2, 5Hz) inside a quartz tube reactor supplied reactants to grow the SnO2 nanowires at relatively high pressures (100-200 Torr) of flowing Ar gas (100 sccm). Under these conditions, relatively long (~5 μm) and thin (~ 20 nm) tin oxide nanowires are formed with preferential vertical orientations on the substrate. The nature of the reactants was investigated using fast gated ICCD imaging and spectroscopy. To understand if the nanowires grow from tin oxide nanoparticles formed during laser ablation into the high pressure background gas or from tin atoms generated by laser ablation of gas suspended nanoparticles on subsequent laser shots, laser induced fluorescence and Rayleigh scattering were employed. The dynamics of nanoparticle formation were studied in a pulsed laser deposition (PLD) chamber at room temperature as well as in a high temperature window furnace using a second laser at 355 nm. The possible growth mechanisms will be discussed.Research sponsored by the Materials Science and Engineering Division, U.S. Department of Energy. A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, U.S. Department of Energy.
10:30 AM - TT3.4
Two-beam Studies of Nanoparticle Ejection and Transport Dynamics Resulting from Femtosecond Laser Ablation.
Christopher Rouleau 1 , Jason Readle 1 , Alex Puretzky 1 , Norbert Thonnard 2 , David Geohegan 1 Show Abstract
1 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , University of Tennessee, Knoxville, Tennessee, United States
The processes which occur during ultrashort (fs) pulse laser ablation have recently been shown to lead to three distinct components of the laser-induced plume, namely an atomic component; a nanoparticle component; and micron-sized droplets. In the majority of cases, nanoparticles have been shown to comprise a significant fraction of the ejecta, thereby making fs laser ablation a viable and efficient method for nanomaterial synthesis. Work to date has concentrated upon imaging the plasma emission from the atomic component, and the nascent blackbody radiation from the heated nanoparticle and microparticle components. Here we use a time-delayed sheet of light from a second laser to illuminate the plume for gated-ICCD imaging of Rayleigh scattering and laser induced luminescence from nanoparticles ejected from the target or generated during transport or confinement in background gases.These techniques are used to understand the spatiotemporal distribution of nanoparticles of single element metal and semiconductor targets, as well as electron-beam deposited nm-thick metal multilayer thin films. Ejecta are collected on witness plates and TEM grids at various locations within the deposition environment to understand size distributions, for example, and in the case of multicomponent films, the extent of intermixing of the constituents. These and similar experiments are valuable both for in situ diagnostics as well as a means of directing gas phase nanoparticle synthesis during fs laser ablation. Research sponsored by the Materials Science and Engineering Division, U.S. Department of Energy. A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, U.S. Department of Energy.
10:45 AM - TT3: Ablation
11:15 AM - **TT3.5
Thin Oxide Films Applied as Models Systems for Energy Applications.
Thomas Lippert 1 Show Abstract
1 ENE, Paul Scherrer Institut, Villigen Switzerland
Pulsed laser deposition (PLD) is a highly flexible technique which is well suited for the deposition of thin oxide films. These films can be either applied as model systems for energy applications or can be utilized in microdevices.Thin films of dense, particulate-free, ion conducting materials (solid electrolyte) e.g. yttria-stabilized ZrO2, are a requirement to build micro solid oxide fuel cells (µ-SOFC) operating at low temperatures (≤ 500 °C). These thin films can be deposited by various techniques, e.g. PLD, sputtering, or spray pyrolysis, etc., but the necessity to form dense films makes PLD an attractive method. The design of a µ-SOFC, where the thin solid electrolyte layer must be deposited on a membrane is rather challenging, and a “soft” processing approach is needed. PLD can be applied to deposit x-ray amorphous YSZ films at room temperature, which crystallize at surprisingly low temperatures (~250 °C). As a result the strain in these YSZ film is considerably reduced which is important for the assembly of fragile µ-SOFCs. The low crystallization temperature for the x-ray amorphous PLD films is especially remarkable as amorphous films prepared by sputtering require crystallization temperatures of > 800 °C. The µ-SOFC containing films deposited by PLD are functional and produce electricity at temperatures ≤ 500 °C. Li-metal oxides are used as electrode materials in re-chargeable Li-ion batteries and are one example where thin films deposited by PLD serve as model systems for fundamental electrochemical studies. These oxides show exemplary the limitations of PLD thereby emphasizing the need and importance of a careful process control and material analysis. A congruent transfer of the Li manganite oxide seems to be impossible, i.e. all films are Li deficient and targets with an excess of Li must be applied. The thin films can be used to study the formation of the so-called solid electrolyte interphase, which is a layer that may inhibit the Li-diffusion upon charge/discharge cycles. The influence of the cycling parameters, such as electrolyte, can be studied in detail with the thin model films.
11:45 AM - TT3.6
Microstructure and Electrical Properties of p-type Ag-doped ZnO Thin Films.
Michelle Myers 1 , Joon Hwan Lee 2 , Zhenxing Bi 1 , Haiyan Wang 1 2 Show Abstract
1 Electrical Engineering, Texas A&M University, College Station , Texas, United States, 2 Materials Science and Engineering, Texas A&M University, College Station, Texas, United States
P-type ZnO thin films have attracted a wide research interest for enabling ZnO based optoelectronic devices. As one type of the p-type dopants in ZnO, group Ib elements have been proposed however not yet been well explored in literature. In this paper, we report the successful growth of p-type Ag-doped ZnO films on sapphire (0001) substrates by pulsed laser deposition (PLD). 1 at% Ag2O was introduced in the target as the dopant. Optimization of electrical properties of the p-type films was conducted by control of deposition parameters including substrate temperature, laser energy, oxygen pressure and post-deposition process. Electrical resistivity and Hall measurements were conducted using a physical property measurement system (PPMS). Detailed microstructure characterizations including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were conducted to correlate with the electrical properties of the samples under various depositions.
12:00 PM - TT3.7
Formation of Foamy Coatings by Laser Ablation of Glass-ceramic Substrates in the Nanosecond Regime Substrate - Temperature and Wavelength Dependence.
Daniel Sola 1 , Andres Escartin 1 , Jose Ignacio Pena 1 Show Abstract
1 , Universidad de Zaragoza, Zaragoza Spain
In this paper a study of the formation mechanisms of foamy coatings on the surface of glass-ceramic substrates produced by laser ablation is presented. Three laser systems emitting at 1064, 532 and 355 nm with pulsewidths in the nanosecond range were used. In the NIR range the formation of the coating is only possible when the temperature of the surface is higher than 300 C. In this case, the generation is related to an increase of the layer in liquid-phase produced in the interaction zone. However, when the sample is machined at 532 or 355 nm, it is not necessary to heat the whole surface to be processed. In this case, the local temperature and the pressure exerted over the interaction zone produce the generation of this coating, obtaining the layer at room temperature. Furthermore, the coating can be produced at higher speeds. In this way, it is possible to reduce the energetic cost improving the efficiency of the process. Morphology, composition, microstructure and thermal properties of the layer are described.
12:15 PM - TT3.8
Ablation and Deposition of Polymeric Barrier Materials by Infrared Pulsed Laser Irradiation.
Ken Schriver 1 , Sergey Avanesyan 1 , Senthilraja Singaravelu 3 4 , Michael Klopf 4 , Hee Park 5 , Michael Kelley 2 4 , Richard Haglund 1 Show Abstract
1 Physics and Astronomy, Vanderbilt University, Nashville, Tennessee, United States, 3 Physics, Old Dominion University, Norfolk, Virginia, United States, 4 , Thomas Jefferson National Accelerator Facility, Newport News, Virginia, United States, 5 , AppliFlex LLC, Sunnyvale, California, United States, 2 Applied Physics, College of William and Mary, Williamsburg, Virginia, United States
Barrier materials are a critical element in electronic and opto-electronic devices made from small-molecule organics and polymers. However, many of these materials are insoluble, making it difficult to deposit them by conventional solution-phase coating techniques. In this paper, we describe experiments to test the feasibility of infrared pulsed laser deposition (IR-PLD) to synthesize thin films of cyclic olefin copolymers, using laser deposition of polystyrene to connect to previous mechanistic studies. We have employed both resonant (R) and non-resonant infrared pulsed laser deposition on cyclic olefin copolymers (COC) and polystyrene. RIR-PLD has been shown to be a relatively low-temperature process leading to evaporation and deposition of intact molecules. In this paper, we focus on deposition of barrier and protective materials that are potentially useful in the fabrication of organic light emitting diodes, displays, photovoltaics and other optoelectronic devices. We compared the characteristics of the ablation craters, the ablation plume and films deposited by Nd:YAG and Er:YAG lasers, picosecond and nanosecond optical parametric oscillators, and two different infrared free-electron lasers. The films were characterized by profilometry, digital optical microscopy, scanning electron microscopy, and Fourier-transform infrared spectroscopy. We will discuss the constraints that these results will impose on the selection and design of efficient, cost-effective lasers that can lead to a commercial future for RIR-PLD.
TT4: Process Control and Nanomaterials
Wednesday PM, April 27, 2011
Nob Hill AB (Marriott)
2:30 PM - **TT4.1
What Can Lasers Do In the Nano-fabrication of Carbon-nanotube-based Devices?
Yunshen Zhou 1 , Wei Xiong 1 , Masoud Mahjouri-Samani 1 , Matt Mitchell 1 , Yongfeng Lu 1 Show Abstract
1 , University of Nebraska, Lincoln, Nebraska, United States
Development of carbon nanotubes (CNTs) is at a critical point. Enormous accomplishments have been achieved and profound experience has been accumulated after twenty-year extensive and intensive investigations. A large number of potential applications based on CNTs have been suggested and developed in laboratorial environments. However, successful implementation of CNT-based potentials requires nano-fabrication of CNT-based devices, which requires precise control in the growth and integration of CNTs into pre-designed micro/nano-architectures. Numerous investigations have been made carried on this field. However, high-performance-on-demand solution packages are still absent. In this study, we investigated applications of lasers in the controlled growth and integration of CNTs, and developed laser-based strategies trying to achieve nano-fabrication of CNT-based devices. By making use of unique features of lasers, including optical near-field effect, polarization, localized heating, intense energy delivery, a wide spectrum of photons, etc., we achieved 1) Parallel integration of CNTs into pre-designed micro/nano-architectures in a single-step laser-assisted chemical vapor deposition (LCVD) process, 2) Selective removal of metallic CNTs in open air, 3) Growth of controlled-alignment CNTs, and 4) Diameter modulation in individual CNTs. The laser-based strategies developed in this study suggest a laser-based solution-package to meet the challenges for the nano-fabrication of CNT-based devices and promises a reliable and scalable approach to achieve CNT-integrated devices.
3:00 PM - TT4.2
Laser-induced Plasmonic Catalysis for Synthesis of Carbon-based Nanostructures.
Wei Hsuan Hung 1 , I-Kai Hsu 1 , Wenbo Hu 1 , Jesse Theiss 1 , Mehmet Aykol 1 , Stephen Cronin 1 Show Abstract
1 , University of Southern California, Los Angeles, California, United States
Abstract The growth of a variety of carbonaceous materials is achieved by taking advantage of the strong plasmon resonance of gold nanoparticles. When gold nanoparticles are irradiated by a laser near the plasmon resonant frequency, a localized high temperature and strong electric field are induced at the metal surface, which is known as a hot spot. This plasmonic heating triggers the formation of iron oxide nanocrystals and enhances the synthesis of graphitic carbon and carbon nanotubes.1 The resulting materials are characterized by Raman spectroscopy, transmission/scanning electron microscopy, and energy-dispersive X-ray spectroscopy. We also monitor the in situ temperature and byproducts produced during the reaction by infrared spectroscopy and mass spectroscopy.2 Pre-defined microstructure geometries of crystalline iron oxide and carbon nanotubes are achieved by controllably rastering the focused laser spot during the growth process. This plasmon-enhanced process can also be extended to improve photochemistry studies. 1.Wei Hsuan Hung, I-Kai Hsu, Adam Bushmaker, Rajay Kumar, Jesse Theiss, and Stephen B. Cronin, “Laser Directed Growth of Carbon-Based Nanostructures by Plasmon Resonant Chemical Vapor Deposition,” Nano Lett., Vol. 8, p. 3278 (2008).2.Wei Hsuan Hung, Mehmet Aykol, David Valley, Wenbo Hou, and Stephen B. Cronin, “Plasmon Resonant Enhancement of Carbon Monoxide Catalysis,” Nano Lett., Vol. 10(4), p. 1314–1318 (2010)
3:15 PM - TT4.3
Plasmon Assisted Upconversion with Core-shell Nanorods.
Vladan Jankovic 1 , Abhijeet Joshi 2 , Jane Chang 1 Show Abstract
1 Chemical Engineering, UCLA, Los Angeles, California, United States, 2 Electrical Engineering, UCLA, Los Angeles, California, United States
Rare-earth (RE) oxides are an important class of photonic materials due to their nonlinear optical and upconversion (UC) properties which find application in high power lasers, remote sensing, optical communications and photovoltaics (PV). In the context of solar cells, these materials could increase cell efficiencies by upconverting photons with energies below and near the silicon bandgap (1.1eV), which are poorly absorbed by the indirect band-gap semiconductor, to higher energy photons that can be absorbed more efficiently. Unfortunately, up-conversion efficiencies in rare-earth ions are usually low due to non-radiative processes such as concentration quenching. One strategy to address this problem is to control the spatial distribution of the RE ions while the other is to couple the UC of RE-oxides with plasmonic modes of metal nano-structures. Noble metal nanostructures have been shown to exhibit localized surface plasmon resonances which can readily be tuned to a particular spectral range of interest by means of size, shape and local dielectric environment. By coupling metal nanoparticles’ plasmon resonances to RE ion energy transitions, the UC rates of rare earth ions can be significantly improved (theoretically by 2 orders of magnitude) to have an impact on improving solar cell efficiencies. In this work, we designed and synthesized Au|SiO2|Yb:Er:Y2O3 core|shell nanorods as a potential route to improve solar cell efficiencies in the near infrared regime. Au nanorods were chosen because their plasmon resonance can be tuned by adjusting the rod aspect ratio and were synthesized using a surfactant-mediated growth technique, in which cetyltrimethylammoniumbromide (CTAB) micelles are used to direct the growth of Au nanoparticles in the  direction while blocking growth on  and  crystal faces. Au nanorod aspect ratios from 2 to 8 were achieved by varying the concentration of the reducing agent, ascorbic acid, and the plasmon resonance was shown to range from 600nm to 1000nm, ideal for coupling with RE ion based UC. A 4-5nm silica spacer layer was deposited through a controlled TEOS hydrolyzation reaction and was shown to be effective in preventing quenching yet enabling energy coupling between the Au nanorod and the RE-ion doped oxides. Spatially and compositionally controlled Yb:Er:Y2O3 outer shells were deposited using both wet chemistry methods and radical enhanced atomic layer deposition (RE-ALD). Upconversion (UC) and radiative lifetime measurements with 980 nm excitation were used to assess the effect of Au nanorod aspect ratio and spacer layer thickness on the optical properties of the core|shell nanorods. The preliminary optical measurements showed a 5X increase in upconversion rates compared to SiO2|Yb:Er:Y2O3 core|shell nanoparticles (without the Au core) and a 2X lower UC threshold incident power, thus making this a promising material system to be integrated with silicon based solar cells.
3:30 PM - TT4.4
Non-planar Nanopatterning by Array-based Optically Trapped Micro-spheres.
Yu-Cheng Tsai 1 , Romain Fardel 1 , Craig Arnold 1 Show Abstract
1 Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States
While several probe-based techniques offer the possibility of direct writing parallel features at the nanometer scale, there is an increasing demand for parallel patterning on non-planar substrates. However, for most techniques, this ability requires simultaneous control of the probe-surface distance for each individual tip, which still remains very difficult. In this work, we experimentally show the use of parallelized optical trap assisted nano-patterning (OTAN) for creating arrays of nano-features over non-planar polyimide substrates. In this technique, a dielectric micro-sphere is used as a near-field objective to focus an ultraviolet laser pulse with sub-micrometer resolution. If a substrate is present below the sphere, the near-field intensity enhancement that takes place beneath the sphere will locally modify the substrate. Arrays of continuous lines are created across pre-existing trenches 1.5 μm deep without feedback control. We achieved both nano-feature uniformity and relative positioning accuracy better than 15 nm. The relative insensitivity to surface roughness enables the future use of adaptive optical system such as spatial light modulator (SLM) to massively parallelize the technique by positioning multiple micro-spheres above rough surfaces. These results suggest OTAN processing as a viable approach for high-throughput nano-patterning on non-planar surfaces.
3:45 PM - TT4: Nano
4:15 PM - **TT4.5
Laser-assisted Nanoscale Material Processing and In-situ Diagnostics.
David Hwang 1 , Costas Grigoropoulos 1 2 Show Abstract
1 Department of Mechanical Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Advanced Energy Technologies Department, EETD, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Lasers have proven to be efficient tools in a variety of micro/nanoscale material processing and diagnostics. As a possible route to the laser-based nanoscale processing and diagnotics, the optical near-field based technique has been extensively examined in recent years. However, an advanced in-situ monitoring method has been highly desired for real-time inspection of sharp probe geometry in close proximity of the processing spot and the nanoscale features under dynamic change. To this end, the optical near-field has been coupled into the electron microscopes, providing useful means to inspect in-situ the interaction of laser with nanomaterials at unprecedented spatial resolution.Due to the direct-writing nature of the optical near-field processing, the issues on the processing throughput should be addressed. Recent progress on the improved throughput will be reported based on the probe array scheme and further strategies on the scalable nanomanufacturing will be discussed.Lastly, recent results on the direct synthesis of nanomaterial systems assisted by laser will be presented as a versatile means to fabricate high quality optoelectronic devices.
4:45 PM - TT4.6
Interaction between Pulsed Laser and Silicon Carbide in Different Polytypes and Surface Terminations.
Sangwon Lee 1 , Alberto Salleo 1 Show Abstract
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Silicon carbide (SiC) has a range of useful physical, mechanical and electronic properties that make it a promising material for high-power and high-frequency electronic devices requiring high-temperature operation. These properties include a large indirect bandgap (~3 eV), large breakdown electric field (~2×106 V/cm), large dielectric constant (~10) and high electron mobility (~900 cm2/Vs). In addition, SiC wafers have attracted much re-newed attention as an effective vehicle for realizing large-area epitaxial graphene (EG) films that may find application in terahertz devices and next-generation microprocessors. These interests have become the source of motivation to study this material which exists in more than 200 stacking modifications (polytypes) and to develop rapid and convenient formation techniques for obtaining highly crystallized EG films on this material. For the thermal annealing process, although various methods have been proposed, high temperature and long residence time are inevitable to grow EG. It is well known that laser treatment has various advantages in comparison with conventional heat treatments. Radiation by a laser beam allows the treatment of the surface only, with very little damage to the bulk. Also, it is possible to heat treat a very small and localized region. Such a process is compatible with traditional semiconductor manufacturing and is amenable to large-scale integration. In this talk, we describe the interaction between KrF pulsed excimer laser (λ = 248 nm, τ ~ 25 ns) and the surface of 4H-SiC (Si-terminated and C-terminated) and 3C-SiC in the extension of our previous work (Laser-assisted Synthesis of Epitaxial Graphene on SiC) in spring 2010. Surface treatment by means of laser-beam radiation is a relatively new technology in the field of surface heat treatment. KrF laser radiation is well above the SiC bandgap (EKrF = 5 eV; ESiC ~ 3 eV). Absorption therefore generates excited carriers that thermally relax to the bottom of the band. Also, the thermal diffusion length in SiC during the laser pulse (LT~ 4.1 µm) is much larger than the optical absorption length (α-1 ~ 76 nm): the laser can thus be considered as a surface heating source on SiC. As a result, the substrate is held essentially at room temperature except for the thin SiC surface layer that absorbs the laser light. The surface morphologies of different polytype and surface terminated SiC after laser radiation are analyzed and compared with thermally grown EG by various characterization methods such as AFM, SEM, TEM, Raman and Synchrotron X-ray.
5:00 PM - TT4.7
Laser Direct Writing of Graphene Patterns.
Jongbok Park 1 , Yongfeng Lu 1 Show Abstract
1 , University of Nebraska, Lincoln, Nebraska, United States
Rapid growth of few-layer graphene using laser-induced chemical vapor deposition (LCVD) with visible CW laser (λ = 532 nm) irradiation at room temperature was investigated. In this study, an diode-pumped solid-state laser with a wavelength of 532 nm irradiates a thin nickel foil to induce a local temperature rise, thereby allowing the direct writing of graphene patterns about ~20 um in width with high growth rate on precisely controlled positions.It is demonstrated that the fabrication of graphene patterns can be achieved with a single scan for each graphene pattern using LCVD with no annealing or preprocessing of the substrate. The scan speed reaches to about ~40 um/s, which indicates that the graphene pattern with 1:1 aspect ratio (x:y) can be grown in 0.5 sec. The patterned graphene on nickel was transferred to SiO2/Si substrate for fabrication of electrical circuits and sensor devices.
5:15 PM - TT4.8
In situ Diagnostic-controlled Laser-driven Growth of Graphene.
David Geohegan 1 , Murari Regmi 2 , Alex Puretzky 1 , Jason Readle 1 , Norbert Thonnard 4 , Gyula Eres 2 , Christopher Rouleau 1 , Mina Yoon 2 , Gerd Duscher 3 , Matthew Chisholm 2 Show Abstract
1 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 , University of Tennessee, Knoxville, Tennessee, United States, 3 Materials Science and Engineering Dept., University of Tennessee, Knoxville, Tennessee, United States
Lasers hold unique advantages to explore nonequilibrium synthesis conditions of thin films and nanomaterials, including the ability to induce rapid heating, deliver pulsed fluxes with variable composition and high kinetic energies, and provide in situ real-time imaging and spectroscopic diagnostics. Here, nonequilibrium, pulsed laser vaporization and heating approaches for the synthesis of graphene are explored and compared with lower-temperature, chemical vapor deposition methods. The high-temperature plasma conditions from the high-power laser vaporization of pure C into inert background gases at 1000°C is shown to provide sufficient energy and time to permit the self-assembly of single-wall carbon nanohorns in high yields. This synthesis process can be shifted toward that of planar graphene sheets through the addition of hydrogen, which can be understood by energy calculations. HRTEM analyses reveal that co-vaporization and co-condensation of metals, including traditional catalysts (Ni, Co, Fe, etc.) or those with lower carbon solubility (Cu, Ir, Pt, etc.), perturbs the carbon self-assembly process to form a variety of new nanostructures, including single- and multi-layer graphene. Laser vaporization is also used to directly provide C for the growth of graphene by pulsed laser deposition. PLD of graphene was performed in background hydrogen onto heated metal substrates (Cu, Ni, etc.) under conditions similar to those used for the chemical vapor deposition of graphene from methane/hydrogen mixtures. In order to understand the conditions for graphene growth, the dynamics of the plasma plume and gas-phase processes during pulsed laser deposition are characterized by time-resolved, gated-ICCD imaging, ion probe, and spectroscopy utilizing a second, time-delayed probe laser sheet. The properties of the films grown under different kinetic energies and plume compositions are compared with graphene growth by CVD in a hot-wall reactor, and within the same cold-wall conditions of the PLD chamber. Films are characterized by Raman spectroscopy, SEM, TEM, and EELS. Research sponsored by the Materials Science and Engineering Division, U.S. Department of Energy. A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, U.S. Department of Energy.
Yongfeng Lu University of Nebraska-Lincoln
CraigB. Arnold Princeton University
CostasP. Grigoropoulos University of California-Berkeley
Michael Stuke Max-Planck-Institute for Biophysical Chemistry
StevenM. Yalisove University of Michigan
TT9: Poster Session: Laser-Material Interactions at Micro/Nanoscales
Thursday PM, April 28, 2011
Salons 7-9 (Marriott)
Thursday PM, April 28, 2011
Nob Hill AB (Marriott)
4:15 PM - **TT8.1
A New Femtosecond Laser-aided Tomography Technique for Multiphase Materials.
Tresa Pollock 1 2 , Naji Husseni 2 , McLean Echlin 1 2 , John Nees 2 , Alessandro Mottura 1 Show Abstract
1 Materials Dept., Univ California Santa Barbara, Santa Barbara, California, United States, 2 , University of Michigan, Ann Arbor, Michigan, United States
Three-dimensional (3D) information on the distribution of elements or phases within inorganic and organic materials is often essential when material features are anisotropic or heterogeneously distributed. Such information is critical for developing predictive models for material properties and for optimizing processes for materials synthesis. We have developed a new tomography technique using the unique characteristics of femtosecond laser ablation for rapid serial sectioning and assembly of mm3-scale 3D datasets. A protocol for controlled, cumulative deposition of millions of low-damage femtosecond laser pulses on the sample surface permits rapid layer-by-layer material ablation at precisely controllable rates. This fully automated technique provides new capabilities for imaging of multiphase materials with sectioning rates orders of magnitude faster than current mechanical or focused ion beam type techniques. An example is presented where 3D information on the mm-scale is captured for widely-dispersed nm-scale TiN particles in a iron alloy. We also demonstrate that chemical and microstructural information can be gathered simultaneously by incorporating laser-induced breakdown spectroscopy. Finally, a new approach that integrates the ultrafast laser with ion and electron beams in a FIB chamber will be described.
4:45 PM - TT8.2
Laser-induced Breathing Modes in Metallic Nanoparticles: A Symmetric Molecular Dynamics Study.
Ming-Yaw Ng 1 , Yia-Chung Chang 1 Show Abstract
1 Research Center fro Applied Sciences, Academia Sinica, Taipei Taiwan
The laser-induced acoustic oscillation of metallic nanomaterials has been studied extensively by several experimental methods. Undeniably, a numerical method with a full-atom treatment is needed to have a detailed understanding of the mechanism of the laser-induced phonon oscillation of metallic nanomaterials. A symmetric molecular dynamics (SMD) approach is applied to study the laser-induced breathing oscillation of gold and silver nanospheres. According to previous experimental results, the heating time of laser light is faster than the oscillation period of nanospheres; therefore the effect due to laser-induced heating is modeled as a symmetric sudden expansion of the nanospheres by increasing the interatomic distances uniformly. Under second-moment approximation, a long-range empirical potential model which is capable of describing the phonon-dispersion curves of fcc metals in the full frequency range is established. In order to simulate large-scale nanospheres, group theory is employed to reduce the computation time significantly. Only the motion of atoms in the irreducible segment is calculated in the molecular dynamics (MD) simulation, and the oscillation behavior of nanospheres of over 3 x 106 atoms can be simulated efficiently. Oscillation frequencies of nanospheres are obtained by calculating the Fourier transform of the velocity autocorrelation function. The breathing modes of nanospheres are identified as the A1g modes with in-phase radial displacement of atoms in the nanospheres. The resulting oscillation frequencies are in very good agreement with experimental data. Our simulated results indicate that the excitation of the breathing modes in nanospheres strongly depends on the initial condition of the MD simulations or experiments.
5:00 PM - TT8.3
Coherent Vibrational Oscillations of Hollow Gold Nanospheres.
Rebecca Newhouse 1 , Damon Wheeler 1 , Shengli Zou 2 , Jin Zhang 1 Show Abstract
1 Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, California, United States, 2 Chemistry, University of Central Florida, Orlando, Florida, United States
Ultrafast pump-probe spectroscopy was used to characterize coherent vibrational oscillations of hollow gold nanospheres (HGNs). The period of oscillation for HGNs which had an SPR absorption maximum at 580 nm was measured to be 40 ps. This period is ~2.6 times longer than the oscillation period measured for solid Au nanoparticles of the same outer diameter. The oscillation period was measured for HGN samples with different shell thicknesses and core diameters. When the shell thickness and outer diameter are both increased, the plasmon absorption is shifted to an absorption maximum of 600 nm. For these particles, the oscillation period was observed to decrease to 35 ps. The oscillation period of these nanomaterials is shown to be sensitive to the specific HGN structure however the precise relationship between the two structural parameters of HGNs (shell thickness and particle diameter) and the associated vibrational oscillation period must be examined in more detail. Fundamental understanding of the electron relaxation processes in HGNs including lattice heating and subsequent phonon oscillation could help direct the synthesis of structures that function more efficiently in applications which utilize metal nanoparticle electronic relaxation such as photothermal imaging and ablation.
5:15 PM - TT8.4
Ultra-fast Photoluminescence in Fused Silica Surface Flaws Susceptible to Laser Damage.
Ted Laurence 1 , Jeff Bude 1 , Nan Shen 1 Show Abstract
1 , Lawrence Livermore National Laboratory, Livermore, California, United States
Using high-sensitivity confocal time-resolved photoluminescence (PL) techniques, we found an ultrafast PL (40 ps-5 ns) from impurity-free surface flaws on fused silica, including polished, indented, or fractured surfaces of fused silica, and from laser-heated evaporation pits. This PL is excited by the single-photon absorption of sub-band gap light, and is especially bright in fractures. Regions which exhibit this PL are strongly absorptive well below the band gap, as evidenced by a propensity to damage with 3.5 eV nanosecond-scale laser pulses. For such high defect densities, significant interactions between defects may strongly affect the temporal and spectral characteristics of both excitation and emission of electronic excitations. We propose that the distribution in lifetimes observed is not simply due to a large variety of defect states, but due to a variety of energy transfer interactions between defect states. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
TT9: Poster Session: Laser-Material Interactions at Micro/Nanoscales
Friday AM, April 29, 2011
Salons 7-9 (Marriott)
9:00 PM - TT9.1
Closed-loop Control of a Laser Assisted Carbon Nanotube Growth Process for Interconnects In Flexible Electronics.
Yoeri van de Burgt 1 2 , Yves Bellouard 1 , Rajesh Mandamparambil 2 , Andreas Dietzel 1 2 Show Abstract
1 Mechanical Engineering, Eindhoven University of Technology, Eindhoven Netherlands, 2 , Holst Centre/TNO – Netherlands Organization for Applied Scientific Research, Eindhoven Netherlands
In recent years, flexible electronics have gained significant importance in the development of flexible displays, wearable devices, intelligent clothes or ambient intelligence. To mass produce these flexible devices, roll-to-roll manufacturing process involving lamination of various functional multilayer device stacks is used. These functional layers need eventually to be electrically interconnected. Conventional interconnects are made out of metals, pastes or inks filled with metal particles. The use of these materials poses numerous performance issues: both mechanical (due to the high stiffness difference between the polymer matrix and the metal causing interfacial stress-mismatch); and process related (thermal expansion mismatch, low thermal resistance of the polymeric substrate, process incompatibility, etc.).We propose to use carbon nanotubes (CNTs) embedded in the polymer matrix as interconnects for flexible electronics. This is motivated by the excellent electrical properties of CNTs (~10.000 cm2 V-1s-1 and ~4e9 A cm-2). In this research, a laser assisted chemical vapor deposition method (LACVD) is used to locally grow the CNT forests on a silicon substrate in a carbonaceous environment. Laser assisted CVD has the advantage that the growth is localized and opens up a range of possibilities for different materials and geometries that are sensitive to heat. For CNTs as interconnects, the length, width and density of the CNT forests need to be controlled. For example, the CNTs need to be as long as the thickness of the interconnecting layer between the functional layers. The structure, geometry and characteristics of CNTs forests are known to be strongly dependant from the heating profile applied during the growth process. A current limitation of LACVD set up is the lack of an accurate temperature control at the laser spot.To address this issue, here we present a feedback control mechanism based on infrared radiation monitoring from the CNT growth region. Since the emitted infrared radiation is mainly depending on temperature, by this method we can indirectly control the temperature. In addition to IR radiation, we also monitor additional parameters such as the laser-reflected light from the growth site as well as the spectrum emitted by the CNTs. With this technique, we successfully demonstrate that substrate overheating, eventually leading to amorphous carbon deposits, can be avoided and that good process reproducibility is achieved over repetitive experiments.
9:00 PM - TT9.10
Laser Interference Patterning as a Tool for Microstructural Design and Enhancement of Tribo-mechanical Behavior of Metallic Materials.
Rodolphe Catrin 1 , Carsten Gachot 1 , Peter Leibenguth 1 , Frank Muecklich 1 Show Abstract
1 Materials Science and Engineering, Saarland University, Saarbruecken, Saarland, Germany
Giving a function and tailoring the microstructure of materials are key competences in surface engineering and processing. Materials properties are so strongly related to the microstructure and their spatial distribution. By irradiating metallic surfaces with a high power ns-laser source working at 355 nm, a variety of physical processes can be induced. The spectrum ranges from melting, annealing and (re)-crystallization to diffusion and formation of other phases, far from thermodynamic equilibrium. Therefore several laser beams are used here to create a one-step interference pattern, arranged in a periodic manner of intensity maxima and minima. It produced a precise redesigning of surface microstructures in terms of local periodic melting and resolidification at the constructive interference regions. In this study, we highlighted the laser-induced grain growth in the form of super-lateral-growth regime, the local formation of intermetallic phases and the tribo-mechanical behavior of treated metallic thin films. The morphology and phase/grain formation were characterized by Scanning Electron Microscopy and Electron Backscatter Diffraction with regard to orientation distribution and texture formation, respectively. The mechanical properties of the tailored films have been determined through nanoindentation experiments. Finally, the tribological behavior has been characterized by evaluating the friction coefficient and wear in a nano-tribometer facility.
9:00 PM - TT9.11
Micro-structuring of Metal Films by Localized Single-pulse Laser Irradiation.
Chandraprakash Gaddam 1 , Joseph Moening 2 , Nanke Jiang 1 , Daniel Georgiev 1 Show Abstract
1 Electrical Engineering and Computer Science, University of Toledo, Toledo, Ohio, United States, 2 Electrical Engineering, Lake Superior State University, Sault Ste. Marie, Michigan, United States
Micro-structuring the surface of metals and metal films is of interest to various sensor, vacuum microelectronics and biomedical applications. The main advantages of laser microstructuring include local processing down to the sub-micrometer range, lack of thermal damage to the substrate and neighboring regions, the non-contact nature and the possibility of combining it with other types of processing such as surface chemical treatment and/or film deposition steps. In this work, we present data on micrometer-scale localized single-pulse laser irradiation of Au, Cu, Al, or Ti films on borosilicate glass or silicon substrates. These metals represent a range of thermal properties, chemical reactivity levels and relevance to specific applications. The laser source was a Q-switched Nd:YAG laser, capable of producing 8ns pulses with energies of up to 200mJ at a wavelength of 266nm (4th harmonic). A diffraction-limited lens was used to image pinhole masks, at a demagnification factor of 10, onto micrometer-sized circular spots on the sample surface. The metal films, deposited by RF-sputtering, had thicknesses ranging from several hundred nanometers to more than one micrometer. Laser irradiation was performed in either vacuum or ambient air at fluence levels ranging between 0.05 – 1.5 J/cm2. The resulting microstructures were examined via scanning electron and/or atomic force microscopy. This project is still ongoing and represents a continuation of earlier work on the irradiation of Au or Si films [1, 2]. This previous work has shown the controllable formation of conical micro-tips of silicon, as well as high-aspect ratio nano-protrusions of gold to be possible within certain fluence ranges and under specific irradiation geometry conditions. Our current research focuses on exploring the possibility of fabricating similar micro-structures on other metals of interest. We are also interested in learning more about the nature of the laser-material interactions under this specific type of irradiation, as well as understanding the mechanism responsible for the formation of these structures. Our preliminary work has indicated that irradiation of Cu films can result in the formation of sharp cones or protrusions. However, the controllability of these structures in Cu films seems to be more limited than those formed in Au or Si. Irradiation of Ti films on the other hand, have thus far only resulted in melting related surface roughening or the formation of ablation openings, regardless of the conditions of irradiation, film thickness, substrate or ambient gas. J.P. Moening, S.S. Thanawala, D.G. Georgiev, Appl.Phys. A, 95 (2009) 635 J.P. Moening, D.G. Georgiev, J. Appl. Phys., 107 (2010) #014307
9:00 PM - TT9.12
Assembly of Carbon Nanotube Devices by Tip-induced Optical Trapping.
Wei Xiong 1 , Yunshen Zhou 1 , Matt Mitchell 1 , Jongbok Park 1 , Masoud Mahjouri-Samani 1 , Yang Gao 1 , Yongfeng Lu 1 Show Abstract
1 , University of Nebraska, Lincoln, Nebraska, United States
Fabrication of nanoscale devices by assembling individual carbon nanotubes (CNTs) remains challenging despite enormous effort made in this field. Fulfilling the promise of CNTs requires more efficient assembly techniques. In this study, we have developed an in-situ assembly method for precise and cost-effective integration of CNTs using a laser-assisted chemical vapor deposition (LCVD) technique. Results show that CNTs can be trapped between sharp metallic tips due to the optical gradient forces around the tip apexes generated by CO2 laser irradiation. This technique enables the scalable assembly of nanoscale devices with integrated CNTs bridging pre-patterned electrodes and paves the way for the successful implementation of the CNT-based nanoelectronics.
9:00 PM - TT9.13
Targetted Optoporation of HEK Cells with GFP Using Femtosecond Laser Optoporation.
Pranav Soman 1 , Wande Zhang 1 , Aiko Umeda 2 , Zhiwen Zhang 2 , Shaochen Chen 1 Show Abstract
1 Nanoengineering/Bioengineering, University of California, San Diego, La Jolla, California, United States, 2 , University of Texas, Austin, Austin, Texas, United States
Targeted and reversible permeabilization of the plasma membrane is of paramount interest in today’s biology and biotechnology. In conventional methods, cells are treated as a population and the produced data only represents the average of the whole group. Single-cell manipulation and analyses has been drawing attention recently since analyses of individual cells could often provide a wealth of information. Optical-poration using femtosecond laser has recently been receiving much attention as a promising method for easy and efficient delivery of extrinsic compounds into single live cells. Laser can produce a tiny, submicrometer-sized pore, which lasts for a fraction of a second, at a defined location on the plasma membrane of a target cell to facilitate introduction of membrane impermeable substances such as foreign DNA. Lack of standardization of various experimental parameters seems to be the reason for discrepancies among various labs. In this work, we present a detailed experimental study on standardization of the protocol for the femtosecond laser-assisted optoporation using human embryonic kidney (HEK) cells. We optimized the parameters for cellular optoporation by monitoring the influx of a membrane impermeable fluorescent dye SYTOX into the targeted cells. Upon entering the cells, the dye binds to nucleic acids and produce fluorescence signal. The optimal and most reproducible results were obtained from the laser exposures at 60 mV for 35 ms. An increase of fluorescence inside the cell was observed as a function of time, indicating successful perforation of the plasma membrane. The SYTOX dye mainly accumulated in the nucleus as expected. As control, no sign of dye uptake was observed by the adjacent non-treated cells, indicating that the laser exposure on the plasma membrane is required to change the membrane permeability. Also, no change was observed when the laser focus was in the vicinity of the cell but not on the cell. The cells were negative to the Trypan blue stain which verifies the integrity of the cell-membrane after laser treatment. Cells when exposed to higher values of laser parameters were permanently damaged. We used the optimized laser paremeter (laser power = 60 mW; exposure time = 35 ms; location= protruding edge of cells) to perform DNA transfection experiments with HEK cells. Cells were irradiated in the presence of plasmid DNA pEGFP-N1 in the culture medium and then returned to the incubator. Positive expression of GFP in the irradiated cells and their daughter cells after cell division indicates that the plasmid DNA was successfully introduced into the cell interior by optoporation treatment. No fluorescence was observed in the surrounding cells not exposed to the laser. Using simulations, we also demonstrate that the transient perforation created by the laser can even be smaller than the size of the laser focal volume.
9:00 PM - TT9.14
High Photosensitivity Two-photon Photoresists for Large Area Surface Microstructuring.
Robert DeVoe 1 , Tzu Lee 1 , Jeremy Larsen 1 , David Ender 1 , Jennifer Sahlin 1 , Craig Sykora 2 , Cheryl Patnaude 1 , Matthew Atkinson 1 , Michael Griffin 1 , Brian Gates 1 , David Redinger 1 Show Abstract
1 Corporate Research Labs, 3M Co., St Paul, Minnesota, United States, 2 Electronic Markets and Materials Division, 3M Company, St. Paul, Minnesota, United States
Two-Photon initiated polymerization (TPIP) has shown great promise for fabrication of complex micro- and nano-structures. The method has been limited to surface microstructuring over relatively small areas (< 1 mm^2) because of slow fabrication speeds and resulting long fabrication times. In order for TPIP to reach practical application in a commercial setting fabrication times need to be reduced by orders of magnitude. We report results on a highly photosensitive photoinitiation system for photoresists based on free radical and cationic polymerization, where photosensitivity is increased 10^2 to 10^3 fold compared to previously reported photoinitiation systems. Threshold writing speeds are determined for critical exposure conditions, including laser power, type and concentration of photoinitiation system, and photoresist type. Surface roughness of microstructures, a critical parameter in applications such as optics and microfluidics, for example, is also used to determine threshold writing speed. The utility of the approach is demonstrated by making a cellphone keypad lightguide from a 20 cm^2 master microreplication tool fabricated in a commercially viable timeframe using the highly photosensitive photoresist.
9:00 PM - TT9.16
Ultrafast Optical Properties of CdSe Nanocrystals.
Jessica Freeman 1 , Jasmine Austin 1 , Maria Rigo 1 , Bagher Tabibi 1 , Jaetae Seo 1 Show Abstract
1 , Hampton University, Hampton, Virginia, United States
Ultrafast third-order nonlinear dynamics in quantum dots at room temperature have been investigated. The intensity-dependent photon-echo relaxation time in nanocrystals at room temperature was investigated using femtosecond time resolved forward degenerate four-wave mixing (F-DFWM) at 775 nm. This technique was used to characterize the third-order nonlinear optical properties of CdSe quantum dots (with size of 3 nm and lowest absorption peak at 560 nm) in toluene at 775 nm. Our studies show that as the intensity of the excitation pulse increased the dephasing time of metal nanocrystals decreased. We also show that the copolarization Χ(3) at 775 nm was found to be about -0.164X10-21 m2/V2 and the dephase time was shorter than the resolution limitation of our system at room temperature. The third-order nonlinear susceptibility of the sample was also measured and will be discussed. In addition, theoretical analysis for the dephasing time of cadmium chalcogenide (Te, Se, and S) quantum dots within Bohr radius will be presented at the conference.This work at Hampton University was supported by the National Science Foundation (HRD-0734635 and HRD-063037
9:00 PM - TT9.17
Dephasing Time of Plasmonic Gold Nanoparticles.
Jasmine Austin 1 , Jessica Freeman 1 , Maria Rigo 1 , Wanjoong Kim 2 , Sungsoo Jung 2 , Jaetae Seo 1 Show Abstract
1 , Hampton University, Hampton, Virginia, United States, 2 , Electronics and Telecommunications Research Institute, Daejeon Korea (the Republic of)
We present a simple experimental to measure the dephase time, T2 of gold nanoparticles in solution. The dephasing time is useful for photonic applications as well as optics and their role in communications. The dephase time for gold (Au) nanoparticles happens within a few femtoseconds and so modern measurement methods are limited. The dephase time is the measure of the lifetime of polarization of the electrons in the valence band. The electrons are in an excited state leading to resonance on the surface of the particles. The resonance determines the optical properties of the nanoparticles. The experiment performed uses the Plasmon absorption bands of the Au nanoparticles in order to find the intraband transitions or the localized surface plasmon resonance. The measurements give the absorbance wavelengths of the Au nanoparticles by passing a light source through the sample and measuring the intensity of the light that is returned through the sample. The resultant intensity is from the polarization of the electrons and their return to ground state. The absorption wavelength is then analyzed to determine the dephase time through the analysis of the energy change of the free electrons and the wavelength they transmit. This work at Hampton University was supported by the National Science Foundation (HRD-0734635 and HRD-0630372).
9:00 PM - TT9.18
Probing Dynamic Generation of Hot-spots in Self-assembled Chains of Gold Nanorods by SERS.
Anna Lee 1 , Gustavo Andrade 2 , Aftab Ahmed 2 , Michele Souza 2 , Ethan Tumarkin 1 , Reuven Gordon 2 , Alexandre Brolo 2 , Eugenia Kumacheva 1 Show Abstract
1 , University of Toronto, Toronto, Ontario, Canada, 2 , University of Victoria, Victoria, British Columbia, Canada
The focus of research in self-assembly of nanoparticles (NPs) is evolving from the fabrication of nanostructures to exploring their properties and functions. Furher progress in the applications of self-assembled nanostructures depends on improving our fundamental understanding of the relation between properties of NP ensembles and their geometry, degree of aggregation and dynamic behavior. Here we report a direct correlation between ordered gold nanorod assembly and optical properties of extinction and surface-enhanced Raman scattering resulting from controlled plasmonic, electromagnetic hot-spot generation in solution. Comprehensive electromagnetic simulations using finite-difference time-domain (3D-FDTD)) are in good agreement with experimental results. Our work provides the basis for creating dynamic, solution-based, plasmonic platforms that can be utilized in applications from sensing to nanoelectronics.
9:00 PM - TT9.2
Nonlinear Absorption in Cr2+:ZnSe Crystal in Strong Pump Intensity Region.
Qiguang Yang 1 , Thoth Gunter 1 , EiEi Brown 1 , Uwe Hommerich 1 , Doyle Temple 2 Show Abstract
1 Department of Physics, Hampton University, Hampton, Virginia, United States, 2 Center for Materials Research, Norfolk State University, Norfolk, Virginia, United States
The transition-metal-doped zinc chalcogenides, especially Cr:ZnSe, have attracted great attention in the last 10 years for development of compact and tunable mid-infrared laser, which may operate at room temperature. Negligible excited-state absorption is preferred to minimize losses and maximize the output of a laser. Precise measurement of the excited-state cross section of a laser crystal at the excitation wavelength is critical for a complete characterization. In this work, the excited-state cross section of Cr:ZnSe crystals at 1900 nm was measured using a CW fiber laser. Both Z-scan and I-scan techniques were used to precisely measure the excited-state cross section of Cr:ZnSe crystal. The measurements were carried out in a relatively large intensity range and the influence of the excitation intensity on the accurate determination of the excited-state cross section will be discussed. Acknowledgment: This work at Hampton University was supported by the National Science Foundation (HRD-0630372).
9:00 PM - TT9.3
Pulsed Laser Deposition of Organic Multilayers for High Performance Thin Film Transistor.
Antonio Pereira 1 , Stephan Guy 1 , Ludovic Rapp 2 , Patricia Alloncle 2 , Philippe Delaporte 2 Show Abstract
1 , LPCML - Universite Lyon 1 / CNRS, Villeurbanne France, 2 , LP3 - Université de la Mediterannée / CNRS, Marseille France
The fabrication of n- and p-type organic thin film transistors (OTFTs) by laser-induced forward transfer (LIFT) process has been the subject of extensive study, since this process allows the transfer from a donor substrate of pixels with micrometer sizes of organic and inorganic materials with a submicronic resolution. However, the final device performance remains directly correlated to the quality of interfaces, i.e semiconductor-dielectric. It is then necessary to optimize the preparation of donor substrates, including the realization of multilayers films where critical interfaces are formed under vacuumIn this study, we investigate the preparation of multilayer thin films under vacuum by pulsed laser deposition (PLD). This technique guarantees a high quality of the interfaces and prevents any reactivity of lowers layers with ambient atmosphere. We study the deposition of pentacene and PMMA thin films. The main objective is to control i) their molecular degradation that can occur during the deposition, and ii) their structural and morphological properties which influence the device performance. Among all the experimental parameters that can influence the film properties, the focus is put on the laser fluence and on the substrate temperature. We show that by tuning these two critical parameters, it is possible to obtain high-quality (high crystallinity and low surface roughness) thin films without chemical degradation. In situ spectroscopy during the deposition process and conventional analysis techniques are used to control the film quality and their properties.Finally, functional OTFTs have been fabricated by LIFT and have been characterized by current-voltage measurements.
9:00 PM - TT9.4
Optimization of Cavity Length to Obtain Low Threshold Solid-state Dye Laser.
Shi Lanting 1 2 , Jin Feng 1 , Chen Weiqiang 1 , Zhao Zhensheng 1 , Duan Xuanming 1 Show Abstract
1 , Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing China, 2 , Graduate School of the Chinese Academy of Sciences, Beijing China
Polymeric solid-state dye lasers (SSDLs) show great promise for the advantages of compact, low-cost, tunable, hazard-less, efficient laser sources and have been expected to be applied in the numerous fields such as communication, biomedical devises and lab-on-chip systems. Basically, the SSDLs are constructed with a resonator cavity to provide optical feedback and an active medium to acquire high optical gain. The gain media within the laser resonator are of critical importance for performing high quality lasing oscillation with low threshold. In a Fabry-Perot optically pumped solid-state laser cavity, the thickness of active layer is corresponding to the cavity length, which is a significant parameter to fabricate high-efficient low threshold laser. For the future study on the photonic crystals (PCs) based lasers, research on optimizing the thickness of active layer is needed at the technological front to enable the design and optimization of PCs lasers. In this paper, we present a novel approach of preparing active layer with doping tert-butyl Rhodamine (t-RhB) into polymer and demonstrate the properties of the polymer gain media in the cavity constructed by PCs. Owing to the isomerization between the lactone and zwitterion forms of t-RhB, we successfully improved the solubility of t-RhB in polymer materials and avoided the photobleaching in the polymerization process of preparing active layer. The concentration of t-Rh B in the polymer material is 3 wt%. With changing the stress on cover glass, t-Bu RhB-doped polymer films with different thicknesses were prepared. The film thickness varied from 5.6micrometer to 18.6micrometer. We fabricated resonator cavity consisted of self-assembly polystyrene (PS) PCs with designed bandgap and t-Bu RhB doped PMMA films with different film thickness. When excited by a Nd:YAG laser beam (532nm, 10Hz, 8ns), single-mode laser emissions were observed from the cavities with active layer thickness of 5.6, 7.3, 9.4, 11.3, 15.2 micrometer. The lasing thresholds is 5.63, 1.92, 1.13, 1.82, 4.15 microJoule/pulse, respectively. The FWHM of resonator cavities with different active layer thickness were around 1.0nm. The lasing thresholds as functions of thickness for t-Bu RhB doped PMMA films at the fixed dye concentration of 3 wt% was evaluated. As is indicated in the threshold trend, with increasing active layer thickness, resonator cavities exhibit a minimum threshold of 1.13 microJoule/pulse when the active layer thickness is 9.4 micrometer, then the lasing thresholds of the sample gradually increase with the film thickness enhancing. Therefore, if the thickness of active layer has been optimized, we can obtain an approving polymeric SSDL with low lasing threshold. This approach presented here provides a potential methodology which is simple and sufficiently effective for the development of practical organic SSDLs.
9:00 PM - TT9.5
Investigation of Microstructure in Silicon due to Sub- damage-threshold Ablation.
Maarij Syed 1 , Jessica Wittig 1 , Galen Duree 1 , Elaine Kirkpatrick 1 , Scott Kirkpatrick 1 Show Abstract
1 Physics & Optical Engineering, Rose-Hulman Institute of Technology, Terre Haute , Indiana, United States
Ultrashort pulse lasers (USPL) have been used to create randomly oriented structures with nanometer scales on the surfaces of many different materials . These structures have several novel properties. In this paper we report on the formation of structures on the surfaces of silicon with varying oxide thickness irradiated by USPL. We used an amplified Ti:sapphire system producing femtosecond pulses with a variable repetition rate to form nanostructures and microstructures on the surfaces of gold and silicon. All intensities used are below the ablation threshold for the respective materials. With these conditions, material is not ejected from the surface, but turned into a low-temperature plasma that allows the atoms to assemble in low energy configurations and reattach to the surface. The laser parameters are varied and the characteristics of the structures are measured.The modified surface structure thus created is investigated using spectroscopic ellipsometry (SE) along with other complementary measurements such as AFM and X-ray diffraction. We present results obtained from spectroscopic ellipsometry (SE) that allow us to extract the modified dielectric function of silicon samples with very thin oxide layers (less than 5 nm) and much thicker oxide layers (> 500 nm). We will discuss various theoretical models that can be used to model the dielectric environment of the modified surface of the samples. In particular, we will employ General Oscillator Models  approach to track the changes in various parameters (resonance energy, broadening parameter, etc.) that are used to describe the dielectric functions of the unexposed samples and relate them to the ablation conditions (pulse energy, repetition rate, and pulse duration). Additionally, we will present analysis that shows how X-ray diffraction methods can help establish certain key features of the microstructure that characterizes the surface profile. Our analysis will help narrow down the range of valid dielectric functions that can be considered representative of the modified sample surface. We also hope to relate our results to various other techniques that have been employed recently to investigate these microstructures . F. Costache, S. Kouteva-Arguirova, and J. Reif, Appl. Phys A, 79 (2004) J. Leng, J. Opsal, H. Chu, M. Senko, and D. E. Aspnes, Thin Solid Films, 132 (1998) T. H. Crawford, J. Yamanaka, and E. M. Hsu, Appl. Phys A, 91 (2008)
9:00 PM - TT9.7
Laser-assisted Micropatterning of Zinc Oxide Nanowires.
Sukjoon Hong 1 , Junyeob Yeo 1 , Hyun Wook Kang 1 , Jin Hwan Lee 1 , Seung Hwan Ko 1 Show Abstract
1 Applied Nano Tech & Science Lab, KAIST, Daejeon Korea (the Republic of)
Zinc oxide, being a piezoelectric transparent semiconductor with high electron mobility and a direct band gap of 3.37eV, has been extensively studied for various applications such as light emitting diode, UV laser, UV sensor, solar cell and nanogenerator. In consequence, diverse techniques to pattern ZnO nanostructures on substrates also have been developed so as to produce aforementioned devices in a controllable way. The preceding patterning methods include standard photolithography/etching processes, templating, patterned catalyst, functionalized polymer surfaces and numerous others, yet ZnO nanostructure patterning of a non-periodic or completely arbitrary shape requires a pre-made mask which complexes the overall patterning process. In this study, we demonstrate a maskless and facile method of patterning ZnO nanowires at a micron-scale by means of direct laser writing. It has been reported earlier that the zinc acetate solution can be transformed into ZnO seed layer through a simple thermal decomposition process. In our scheme, a ND:YAG laser operating at 532nm is tightly focused on a gold film which is covered with zinc acetate solution(5mM in EtOH) in order to raise the temperature and activate the ZnO seed layer locally. For the patterning, focused laser spot is scanned via a telecentric f-theta lens with two galvano mirrors at various scanning speeds. After the scanning process, the substrate, now covered with patterned ZnO seed layer, is immersed in ZnO precursor solution (25mM Zinc nitrate hexahydrate, 25mM Hexamethylenetetramine and 1mM Polyethylenimine in water) in which the reaction continues for 7 hours at 95 degree C to induce localized growth of ZnO nanowires. Typical diameter and length of ZnO nanowires grown on the irradiated region are around ~100nm and ~2micron respectively and these geometric parameters can be further controlled by changing growing conditions such as the growth time, precursor concentration and solution composition. Unwanted ZnO nanostructures grow on the non-irradiated region at the same time, but they can be eliminated easily through a short ultra-sonication procedure. It has been confirmed that the film of zinc acetate crystallites starts to transform into the ZnO seed layer at the laser fluence of <100mW while higher power and multiple scanning primarily change the verticality of ZnO nanowires and the feature size of ZnO nanostructure pattern. In summary, we successfully fabricated ~2micron long ZnO nanowires of ~100nm diameter on an arbitrary pattern with the minimum feature size of ~10 micron by exploiting the laser as a localized heat source. This method enables a facile patterning of ZnO nanostructures on a metallic film without a mask even for a non-periodic arbitrary pattern.
9:00 PM - TT9.9
Direct Metal Nano-patterning by Selective Femtosecond Laser Sintering of Metal Nanoparticles.
Yong Son 1 , Junyeob Yeo 1 , Hanul Moon 2 , Seung Hwan Ko 1 , Dong-Yol Yang 1 , Seunghyup Yoo 2 Show Abstract
1 Department of Mechanical Engineering, KAIST, Daejeon Korea (the Republic of), 2 Department of Electrical Engineering, KAIST, Daejeon Korea (the Republic of)
For various applications in the electronic and photonic industries, fabrication of metal nanopatterns on various substrates, such as a glass and flexible polymers has become important. In recent years, advances in the synthesis of metal nanoparticles have enabled the direct patterning of microscale metal patterns on transparent and flexible substrates. This progress has been made primarily in screen printing, nanoimprinting, micro-contact printing, inkjet printing and selective continuous wave (CW) laser sintering processes. Further enhancements in direct metal patterning technology can be realized if more versatile methods for the patterning of nanoscale metal patterns become available. In this study, we introduce a low-temperature, ultra-high-resolution direct metal patterning process where the metal nanoparticles are sintered by applying a femtosecond laser beam for the fabrication of precise metal nanopatterns. To achieve homogeneous dispersion of the silver nanoparticles, the nanoparticles are encapsulated by a functional self-assembled monolayer. The key advantage of the femtosecond laser sintering process is to reduce the heat-affected zone during the sintering as the femtosecond (10-15s) laser pulse which is shorter than the heat diffusion time (picosecond: 10-12s). Therefore, sintering of metal nanoparticles will be limited to the laser focal spot and thermal diffusion effect will be suppressed to enable the sub-wavelength feature fabrication. Through this process, metal conductors with nanometer features and high conductivity were successfully fabricated. The smallest pattern size fabricated was 380 nm and the minimum measured resistivity was 1.8 x 10-7 Ωm. The proposed process also enabled the fabrication of organic field effect transistors which featured high-performance characteristics. These results indicates that the femtosecond laser sintering of metal nanoparticles is a novel process which offers low-temperature, single-step, ultra-high-resolution results, and which has numerous further applications in electronics and photonics.