bluuebunny/crossref_metadata_2025 huggingface dataset:
Probing the Interfacial Adhesion Strength in Compositional Libraries of Epoxy Films
Authors: Stafford Christopher M , Kim Jae Hyun , Kawaguchi Daisuke , Royston Gareth , Chiang Martin Y.M.
Published: April 2011

We are developing a measurement platform, based on the edge delamination test geometry, geared towards combinatorial and high-throughput (C&HT) assessment of interfacial adhesion and reliability of epoxy films bonded to a rigid substrate. A critical parameter space to be explored is composition of the epoxy formulation. We have constructed an automated mixing and deposition system for creating discrete and continuous gradients in composition of viscous epoxy formulations. By dicing the combinatorial library into a contiguous discrete sample array, the interfacial adhesion strength can be deduced from the critical stress required to debond each film cell from the substrate. These results can be used to predict the adhesion reliability of epoxy formulations as a function of composition and applied stress.
Combinatorial Fabrication and Study of Luminescent Nanocrystalline Si Particles Embedded in a SiO2 Matrix
Authors: Fonseca Luis F , Resto Oscar , Weisz S. Zvi , Shinar Joseph
Published: April 2011

The combinatorial fabrication of nanocrystalline Si particles embedded in a SiO2 matrix (nc-Si:SiO2) by RF co-sputtering of Si and SiO2 targets is described. The peak of the photoluminescence (PL) spectra of the films varies systematically from 760 to 600 nm, consistent with the presumed systematic variation in the size distribution of the embedded Si particles. The correlation between the optical properties of the samples and the formation parameters is also analyzed.
Model silica pores with controllable surface chemistry for molecular dynamics simulatinos
Authors: Gulmen Tolga S. , Thompson Ward
Published: April 2011

Model amorphous silica pores have been developed for use in molecular dynamics simulations. Specifically, roughly cylindrical pores have been constructed with hydrophilic, hydroxyl-terminated surfaces. The approach is designed to allow systematic variation of the pore radius and surface functionality. Thus, these pores are suitable for studying the variability in solvent structure, energy transfer and reaction dynamics occurring inside the pore due to surface modification. The method is described and the properties of the generated pores are discussed.
Surface-Passivant Dependence of Dynamic Charging Effect in Alkanethiolate-Passivated Au Nanoparticles on Graphite Substrates Studied by Photoelectron Spectroscopy
Authors: Tanaka Akinori , Imamura Masaki , Yasuda Hidehiro
Published: April 2011

We have performed a photoemission study of various alkanethiolate- (AT-) passivated Au nanoparticles with diameter of 4 nm on the highly oriented pyrolytic graphite (HOPG) substrates. It is found that the photoemission spectra in the vicinity of Fermi level of all the present AT-passivated Au nanoparticles on the HOPG substrates do not exhibit the usual metallic Fermi edge, with the steep slope being away from the Fermi level. Moreover, it is found that these spectral features depend on the surface-passivant molecules. We attribute the unusual spectral features in the vicinity of Fermi level to the dynamic charging effect in photoemission final-state, indicative of the interaction between the nanoparticle and substrate through the surface-passivants on a femtosecond time scale.
Ballistic and diffusive random walks in confinement
Authors: Levitz Pierre , Grebenkov D. , Petit D. , Vigouroux C.
Published: April 2011

Porous materials, concentrated colloidal suspensions are example of confining systems developing large specific surface and presenting a rich variety of shapes. Such an interfacial confinement strongly influences the molecular dynamics of embedded fluids and the diffusive motion of entrapped Brownian particles. An individual trajectory near the interface can be described as an alternate succession of adsorption steps and random flights in the bulk. Statistical properties of these random flights in various interfacial confining systems are determinant to understand the full transport process. Related to first passage processes, these properties play a central role in numerous problems such as the mean first exit time in a bounded domain, heterogeneous catalytic reactivity and nuclear magnetic relaxation in complex and biological fluids. In the present work, we first consider the various possibilities to connect two points of a smooth interface by a random flight in the bulk. Second, we analyze at the theoretical and experimental points of view a way to probe Brownian flights statistics. Implications concerning diffusive transport in disordered porous materials are discussed.
Surface Plasmon Excitation in Three-dimensional, Ordered, Gold Nanocrystal Arrays Using a Prism Coupler
Authors: Yang Kai , Fan Hongyou , O'Brien Michael J. , Malloy Kevin J. , Lopez Gabriel P. , Brinker Jeffrey C. , Sheik-Bahae Mansor , Sigmon Thomas W.
Published: April 2011

We report plasmon excitation in 3-dimensional, ordered, gold nanocrystal(NC) arrays using a prism coupler. The gold NCs are arranged in the silica host matrix in a face-centered cubic lattice with the mono-dispersion gold core size of ∼3 nm. We observed the collective optical behavior of the gold NC array and found a blue shift in the plasmon absorption peak with increasing gold volume fraction (Au loading). Plasmon resonance bands centered at 536, 530 and 520 nm are measured for gold NC arrays with gold loading factors of 0.25, 0.5 and 1.0, respectively. The corresponding angular spectra of the gold NC arrays show resonance angles at 60.3, 63.3 and 66.4 degree.
Simple Estimation of Nanoparticle Diameter Produced in a Flow Tube Reactor
Authors: Kuwana Kazunori , Saito Kozo
Published: April 2011

In many carbon nanotube synthesis methods, catalyst nanoparticles are formed via pyrolysis of a precursor such as ferrocene. Since the diameter of a carbon nanotube is usually determined by the diameter of the catalyst nanoparticle, it is of great importance to control the size of nanoparticles. To do so, it is necessary to identify the key reaction parameters that influence nanoparticle size. For engineering purposes, a simple analytical model offers a convenient first estimation of particle diameter. It also clarifies the dependence of nanoparticle diameter on each reaction parameter and enhances our understanding of the formation mechanism of nanoparticles. This paper presents a simplified model that can calculate the diameter of particles and the model's analytical solutions.
Structural evolution of La0.9Sr0.1Cr0.9Co0.1O3 thin films for SOFCs and catalysis
Authors: Coratolo Anthony Mario , Orlovskaya Nina , Johnson Christopher , Gemmen Randal
Published: April 2011

The deposition of La0.9Sr0.1Cr0.9Co0.1O3 thin films by RF magnetron sputtering and annealing leads to the formation of a conducting perovskite film for the protection of metallic interconnects in SOFCs. The nanoporous structure, formed by a two-step phase transition, may also be a promising candidate for catalytic applications.
Optical Gas Sensor Using Cobalt Oxide Thin Film Prepared by Pulsed Laser Ablation
Authors: Nam Hyun-Jeong , Sasaki Takeshi , Koshizaki Naoto
Published: April 2011

Gas sensors based on optical absorption changes in thin films are of interest for detection of various gases such as CO, NO, H2. Optical gas sensors have several advantages over conventional electronic gas sensors, including the potential for higher sensitivity, reduced signal noise, and compatibility with combustible gases. Pulsed laser deposition (PLD) is an excellent method to prepare thin films with controllable thickness, composition and microstructures. Recently, our group reported that films of cobalt oxide prepared by PLD exhibit remarkably high sensitivity), showing an absorbance change in CO gas 70 times greater than those prepared by sputtering methods). Here we examine the effect of film microstructure and composition on CO gas sensing properties in order to identify the origin of the high sensitivity. Cobalt oxide films were prepared by PLD from a CoO target in an inert argon gas at various pressures. Films prepared near vacuum were smooth and continuous while the porosity and grain size increased linearly with pressure. In addition the pressure affected the composition and the thickness of the films. Data on the detection of CO gas suggests a direct relationship between sensitivity to CO gas and the effective surface area of films. We will discuss how the ablation plume can be used to tune the surface area for optimal sensitivity, and will demonstrate origin of the high detection sensitivity based on the structural changes with detecting gas.
First-Principles Study of Helical Silver Single-Wall Nanotubes and Nanowires
Authors: Elizondo Shelly L. , Mintmire John W.
Published: April 2011

We investigate the electronic structures of extended helical silver single-wall nanotubes (AgSWNTs). Because these helical nanotubes are essentially comprised of n-atom strands winding about the nanotube's axis, we systematically examine, strand by strand, the electronic properties and the number of conduction channels associated with these structures. Herein, we study a special case of high-symmetry nanotubes. Nanotubes with sufficiently large radii were also calculated with a silver atomic chain inserted along the nanotube's axis. The analysis is carried out within a first-principles, all-electron self-consistent local density functional approach (LDF) adapted for helical symmetry. Modeling helical silver (or gold) single-wall nanotubes entails rolling up a sheet of atoms and mapping the atoms onto the surface of a cylinder, comparable to rolling up a graphite sheet for a carbon nanotube. It is well known that controlling the size and shape of silver and gold nanostructures results in the ability to tailor the optical and catalytic properties of these materials. In this preliminary study, we consider changes in the electronic structures of these materials as each nanotube is built strand by strand.
Synthesis and Properties of Barium Titanate Thin Films Deposited on Copper Foil Substrates
Authors: Ihlefeld Jon , Borland William , Maria Jon-Paul
Published: April 2011

Barium titanate thin films have been deposited on copper foils in the absence of interfacial layers via a chemical solution process. The dielectric – base metal stacks have been processed in reductive atmospheres such that substrate oxidation is avoided while allowing the perovskite film phase to crystallize. This accomplishment has facilitated the pursuit of a new embedded capacitor technology offering compatibility with polymer printed wiring boards and capacitance densities in excess of 2.5 µF/cm2. This represents a distinct improvement beyond conventional foil-based capacitor strategies. Finally, two critical phenomena will be discussed: (1) the effect of grain size on the dielectric properties of barium titanate thin films and (2) the effect of the B-site substituent Zr on the lattice, microstructure, and dielectric properties. Most importantly, high processing temperatures have allowed for microstructural and dielectric properties similar to well-prepared bulk ceramics, including average grain diameters greater than 0.1 µm, relative permittivities in excess of 2000, and coercive fields below 10 kV/cm. These properties will be discussed in the context of bulk ceramic and thin film reference data and with regard to integration into printed wiring boards.
The Properties of Ferroelectric Domain of PLT Thin Films Prepared by RF Magnetron Sputtering
Authors: Liu Hong , Pu Zhaohui , Wang Zhihong , Huang Huidong , Li Yanrong , Xiao Dingquan , Zhu Jianguo
Published: April 2011

Lanthanum-modified lead titanate (PLT) ferroelectric thin films were fabricated by the RF magnetron sputtering system on Pt/Ti/SiO2/Si(100) substrates. The x-ray diffraction (XRD) patterns of the PLT films showed that the pure perovskite structure was formed in the PLT thin films. The Piezoresponse Force Microscopy (PFM) was used for determining the domain structure of these films. It was found that the 90 degree domain was the main domain structure of PLT thin films. It was found that the PLT films prepared by RF sputtering have relatively large pyroelectric coefficient γ=2.20×10-8C·(cm2·K)-1 and relatively high figures of merit for current responsivity, voltage responsivity and specific detectivity.
Initial Growth Behavior of Ultra-Thin c-Axis-Oriented Epitaxial SrBi2Ta2O9 films on SrTuO3
Authors: Takahashi Kenji , Suzuki Muneyasu , Yoshimoto Mamoru , Funakubo Hiroshi
Published: April 2011

c-axis-oriented epitaxial SrBi2Ta2O9 ultra-thin films were grown by pulse-gas-introduced metalorganic chemical vapor deposition (pulsed-MOCVD) on (100)SrTiO3 single crystal substrates with atomic scale step structure and their growth behavior was investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Minimum growth unit was found to be “ghalf-unit-cell” of SrBi2Ta2O9. Height of steps and width of terraces observed at SrBi2Ta2O9 film surface were in good agreement with those at SrTiO3 substrate surface. This shape transfer was induced by lattice displacement of SrBi2Ta2O9 along c-direction formed at atomic step on SrTiO3 substrate. In-plane growth of half-unit-cell SrBi2Ta2O9 2D-islands striding across the step walls was observed. It was considered to be a special phenomenon for c-axis-oriented films of layer-structured compounds due to their large crystal anisotropy and/or several times larger half-unit-cell height than single step one of SrTiO3.
Microwave Phase Shifters: Epitaxial Growth by Pulsed Laser Deposition of Dielectric Ba0.5Sr0.5TiO3 Thin Films on MgO
Authors: Tse YauYau , Suherman P. S. , Jackson T. J. , Jones I. P.
Published: April 2011

Ba0.5Sr0.5TiO3 (BSTO) thin films were grown on (001) MgO using pulsed-laser deposition (PLD). The microstructures of in-situ and ex-situ annealed BSTO films were studied by X-ray diffraction and transmission electron microscopy (TEM). The films showed a cube on cube epitaxial relationship with <100> BSTO // <100> MgO. They were essentially single crystals with a columnar structure and possessed smooth surfaces. The interfaces of the BSTO films and substrates were atomically sharp, with misfit dislocations. Better crystallinity and full strain relaxation was obtained in films grown in 10-1 mbar oxygen and annealed ex-situ. A 30% increase in dielectric tuneability was achieved compared with in-situ annealing and deposition at 10-4 mbar. Threading dislocations are the dominant defects in the films grown in 10-1 mbar oxygen and annealed ex-situ, while the films with in-situ annealing show columnar structures with low angle boundaries.
Trap Charge Density at Interfaces of MOCVD Pt(Ir)/PZT/Ir(Ti/SiO2/Si) Structures
Authors: Delimova Lyuba A. , Grekhov I. V. , Mashovets D. V. , Shin Sangmin , Koo June-Mo , Kim Suk-Pil , Park Youngsoo , Afanasjev V. P. , Afanasjev P. V. , Petrov A. A.
Published: April 2011

A method providing estimation of the trap density at metal/ferroelectric interfaces of a depleted ferroelectric film located between back-to-back Schottky barriers has been developed. The method is based on the recharge of interface traps induced by external bias pulse applied to the metal/ferroelectric/metal structure. It is shown that the transient current under bias pulse can be controlled by the traps recharge on the reverse-biased interface. Using the method, the trap charge density on interfaces of MOCVD Pt/PZT/Ir(Ti/SiO2/Si) and Ir/PZT/Ir(Ti/SiO2/Si) capacitors were found from transient current measurements.
Intrinsic defects in high purity semi-insulating 6H SiC
Authors: Savchenko D. V. , Kalabukhova E. N. , Lukin S. N. , Sudarshan Tangali S. , Khlebnikov Yuri I. , Mitchel William C. , Greulich-Weber S.
Published: April 2011

Electron paramagnetic resonance (EPR) and photo EPR measurements were performed on undoped semi-insulating (SI) 6H SiC material grown by the physical vapor transport (PVT) method. EPR lines from a carbon-related surface defect, two photosensitive high temperature stable intrinsic defects with S=1/2 and shallow nitrogen and boron were observed. The EPR spectrum of the intrinsic defect labeled XX was observed in the dark and consists of three single lines XX1, XX2, XX3 due to three inequivalent sites in the 6H SiC. The second defect labeled PP appeared in EPR spectrum during photo-excitation of the SI 6H SiC and consisted of a single EPR line. The photo EPR data placed the energy level of the defects in the region EV + 1.24 ÷ 1.29 eV. The EPR parameters and symmetry behavior of XX agree well with those of the carbon vacancy-related Ky center observed in p-type electron irradiated 6H SiC and we tentatively identify the XX defect with VC+. The electronic processes occurring in undoped SI 6H SiC under photo-excitation are also described.
High Quality Uniform Thick Epitaxy of 4H-SiC for High Power Device Applications
Authors: Zhang Jie , Mazzola Janice , Romano Esteban , Hoff Carl , Mazzola Mike , Casady Janna , Casady Jeff
Published: April 2011

Growth of thick SiC epilayers has been investigated in a horizontal hot-wall CVD reactor capable of growing 3x2-in wafers or single wafer with a diameter up to 100mm. Good uniformity of lower than 3% for thickness and lower than 20% for doping has been obtained on 2-in or 3-in epi wafers with thickness of 60 - 120 μm. Low intentional nitrogen doping of 5.8x1014 cm-3 was achieved on a 3-in epi wafer with a thickness of 120 μm. A higher growth rate of 10 μm/h was achieved while good uniformity was maintained. Surface morphology of the thick epilayers was carefully examined and smooth surface was observed for epilayers thicker than 100 μm. The defect density of the thick epilayers was also discussed and the high purity of the thick epi was verified by low temperature PL measurement.
High Power SiC MESFETs
Authors: Harris Christopher , Konstantinov Andrei O , Svedberg Jan-Olov , Ray Ian , Hallin Christer
Published: April 2011

The development of high power, high efficiency silicon carbide RF MESFETs is reported. High power densities of over 3W/mm have been measured for devices with total power output in excess of 25W. The devices have been fabricated using a novel lateral epitaxy technique. The MESFET employs a buried p-type depletion stopper in order to suppress short channel effects and increase the operation voltage. The use of the depletion stopper also allows high RF signal gain, while maintaining high voltage operation capability. Single-cell components measured on-wafer demonstrate an Ft of 10 GHz and a high unilateral gain.

Packaged 6-mm RF transistors have been evaluated using amplifier circuits designed for operation in classes A, AB or C. Operation in class AB demonstrated a saturated power of 20 W and a P1dB of 15W with a linear gain of over 16 dB at Vdd of 60 V for 2.25 GHz operation. Maximum drain efficiency is 56% for class AB operation, 48% at 1 dB compression point and 72% for class C at 2.25 GHz.
950V, 8.7mohm-cm2 High Speed 4H-SiC Power DMOSFETs
Authors: Ryu Sei-Hyung , Jonas Charlotte , Heath Bradley , Richmond James , Agarwal Anant , Palmour John
Published: April 2011

Fabrication and characteristics of high voltage, high speed DMOSFETs in 4H-SiC are presented. The devices were built on 1.2×1016 cm-3 doped, 6 mm thick n-type epilayer grown on a n+ 4H-SiC substrate. A specific on-resistance of 8.7 mW-cm2 and a blocking voltage of 950 V were measured. Device characteristics were measured for temperatures up to 300oC. An increase of specific on-resistance by 35% observed at 300oC, when compared to the value at room temperature. This is due to a negative shift in MOS threshold voltage, which decreases the MOS channel resistance at elevated temperatures. This effect cancels out the increase in drift layer resistance due to a decrease in bulk electron mobility at elevated temperature, resulting in a temperature stable on-resistance. The device operation at temperatures up to 300 oC and high speed switching results are also reported in this paper.
Electron-beam Directed Layer-by-Layer Assembly of Dendrimer Scaffold for Biomolecule Patterning
Authors: Bhatnagar Parijat , Mark Sonny S , Kim Il , Chen Hongyu , Schmidt Brad , Lipson Michal , Batt Carl A
Published: April 2011

A method for patterning biomolecules using electron beam (e-beam) lithography has been developed. First, a non-biofouling poly (ethylene glycol) terminated self-assembled monolayer (SAM) was deposited on a silicon oxide substrate. This SAM was then ablated by e-beam to create patterns aligned with the pre-existing features on the wafer. Aldehyde-terminated polyamidoamine (PAMAM) dendrimers were assembled in a layer-by-layer fashion in the ablated patterns to allow the covalent immobilization of oligonucleotide probes. The aminated oligonucleotides were attached using Schiff base chemistry followed by reductive amination. The functionality of the attached oligonucleotides was demonstrated by the hybridization of fluorescently labeled complementary target oligonucleotides. The hybridized target oligonucleotides could be stripped and the regenerated surface bound probe oligonucleotides could be rehybridized with complementary target oligonucleotide.
A Novel Mechanical Method to Measure Shear Strength in Specimens Under Pressure
Authors: Escobedo Juan Pablo , Field David , Lassila David , Leblanc Mary
Published: April 2011

A new experimental apparatus has been developed for performing shear tests on specimens held under moderately high hydrostatic pressures (on the order of 4 GPa). This testing procedure experimentally determines the pressure-dependent shear strength of thin foil specimens. The experiments provide calibration data for models of materials subjected to extreme pressures such as the Steinberg-Guinan hardening model and can assist in model validation for discrete dislocation dynamics simulations, among others. This paper reports the development of the experimental procedures and the results of initial experiments on thin foils of polycrystalline Ta performed under hydrostatic pressures ranging from 1 to 4 GPa. Both yielding and hardening behavior of Ta are observed to be sensitive to the imposed pressure.
Chemical, Mechanical and Electrical Properties of Glassy Polymeric Carbon
Authors: Muntele Iulia , Muntele Claudiu I. , Minamisawa Renato , Chhay Bopha , Ila Daryush
Published: April 2011

Glassy Polymeric Carbon (GPC) is obtained by a molding technique, in various shapes, from a phenolic resin precursor. The heat treatment of the precursor is achieved in three stages up to 1000 °C. Similar GPC materials produced in our laboratory displayed large strain to failure ratio, small thermal expansion coefficient and low density. Like all carbon forms, is attacked by oxygen, especially atomic oxygen. Nevertheless the kinetics for reaction with atmospheric oxygen is very slow. We investigated the composition and structural changes of the phenolic precursor as a function of temperature and evaluated materials stability when exposed to high temperatures in presence of hydrogen or oxygen.
Improvement on Thermoelectric Characteristics of Layered Nanostructure by Ion Beam Bombardment
Authors: Zheng Bangke , Budak S. , Muntele C. , Xiao Z. , Celaschi S. , Mutele I. , Chhay B. , Zimmerman R. L. , Holland L. R. , Ila D.
Published: April 2011

We made p-type nanoscale super lattice thermoelectric cooling devices which consist of multiple periodic layers of Si1−x Gex / Si, The thickness of each layer ranges between 10 and 50 nm. The super lattice was bombarded by 5 MeV Si ion with different fluencies aiming to form nano-cluster quantum dot structures. We estimated the thermo-electric efficiency of the so fabricated devices, measuring the thin film cross plane thermal conductivity by the 3rd harmonic method, measuring the cross plane Seebeck coefficient, and finally measuring the cross plane electric conductivity before and after ion bombardment. As predicted, the thermo-electric Figure of Merit of the films increases with increasing Si ion fluencies. In addition to the effect of quantum well confinement of the phonon transmission, the nano-scale crystal quantum dots produced by the incident Si beam further adversely affects the thermal conductivity by absorbing and dissipating phonon along the lattice, and therefore further reduces the cross plane thermal conductivity, This process increases the electron density of state therefore increasing Seebeck coefficient, and the electric conductivity.
A Novel Method For The Diffusion Of Boron In 60-80 Micron Size Natural Diamond Type II/A Powder
Authors: Mendez Adrian E. , Prelas Mark A , Glascock Michael , Ghosh Tushar K
Published: April 2011

The purpose of this paper is to report the experimental results of boron doping on 60-80 micron size diamond particles using Field Enhanced Diffusion with Optical activation (FEDOA) [1-5]. Diamond is a wide band gap material with unique combinations of optical, thermal, mechanical and electronic properties that can be useful for a number of applications including optoelectronic applications and micro sensor technology. The incorporation of boron into diamond has been proven to change its electrical properties and convert the diamond from insulator to a p-type semiconductor [3]. A promising technique for incorporation of impurities into diamond is FEDOA. FEDOA drives impurities into single crystalline diamond material and we have used this method in this study [5-7]. FEDOA uses a combination of thermal diffusion with bias plus thermal ionization and optical ionization I simultaneously. A modified version of FEDOA was implemented for the diffusion of boron in natural diamond type II/a powder of size 60-80 microns (Figure 1). The diamond powder was obtained from Microdiamant and has 99.9% purity. The boron powder used in the experiment was amorphous, 325 mesh 90 %(Assay), Mg (5%) nominal obtained from AESAR. A ratio of 3:1 Boron-Diamond mixture was used for the doping process. A heating element and a diamond-boron powder mixture holder were designed and incorporated in the FEDOA system. Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS) were used to study the diamond-doped morphology and identify impurities. Boron and hydrogen concentration results in the doped samples were studied using Prompt Gamma Neutron Activation Analysis (PGNAA) at the University of Missouri Research Reactor (MURR). Raman analysis of the treated samples was done as part of this work. The experimental results and analysis show that the samples were doped with boron. It was also found that samples with high boron concentration exhibited a high electrical conductivity. This work presents additional evidence that boron can be diffused into natural diamond powders. It also demonstrates that the FEDOA diffusion process is not only a powerful technique for the diffusion of impurities into wide band-gap materials in the form of single crystal plates, polycrystalline plate but also in a powder form with the modified FEDOA process.
Compression Testing and Microstructure of Heat-Treatable Aluminum Periodic Cellular Metal
Authors: Bouwhuis B. A. , Hibbard G. D.
Published: April 2011

Periodic cellular metals (PCMs) can offer higher specific strengths and stiffnesses than conventional (i.e. stochastic) metallic foams. This study examines the effects of PCM microstructure and loading conditions on the mechanical performance.

PCM cores with 95% open porosity were constructed from perforated 6061 aluminium alloy sheets using a perforation-stretching method. This method places planar, periodically-perforated sheet metal in an alternating-pin jig. The pins apply force out-of-plane, plastically deforming the sheet metal into a truss-like array of struts (i.e. metal supports) and nodal peaks (i.e. strut intersections). Micro-hardness profiles were taken in the PCM struts to investigate microstructural evolution during fabrication and after heat treatment.

Truss cores were tested in two limiting uniaxial compression conditions. In the first, the PCM cores are placed between smooth compression platens where the nodes are laterally free and compressive forces are resisted through PCM node-bending (i.e. free compression). In the second, the PCM cores were placed between plates where the nodes are laterally confined and compressive forces are resisted through PCM beam-buckling (i.e. confined compression). Compression response was analyzed in terms of peak compressive strength, elastic modulus, and energy density absorbed upon densification; response values were used to illustrate the effect of compression test conditions. In addition, PCM cores were tested in the age-hardened state and annealed state to determine microstructural effects on compressive response.

Analysis of PCM response in free- and confined-compression conditions indicates a greater force resistance in beam-buckling over node-bending resistance mechanisms. The compressive strength, elastic modulus, and energy density of heat-treatable AA6061 PCMs are be found to respond: 1) over a wide range of value, dependent on the microstructure; 2) over a wide range of value, dependent on the PCM compression conditions; and 3) equally, if not more repeatable and with higher compressive strength-to-weight ratio than conventional metal foams.
Effects of Extreme Radiation Environment on Composite Materials
Authors: Zhou J. , Moore Jerrel , Calvin Vernon , Wilkins Richard , Vilarino Sofia Martinez , Zhong Yang , Gersey Brad , Thibeault Sheila
Published: April 2011

Future manned space travel will go beyond the Lower Earth Orbit into deep space exploration and providing protection from space radiation is a major challenge. It is essential to study the effects of the space environment on materials to ensure safe and successful missions.

This paper summarized the studies of two materials, in-site regolith composites and LTM 45 composites, for potential applications in space radiation environments. The effects of radiation on the mechanical and thermal properties of the composites were investigated. The radiation shielding effectiveness of in-situ composites and low temperature molding materials was analyzed. The work was part of the efforts in study and development of the multifunctiaonal materials for long-term radiation exposures to ensure effective radiation shielding and maintaining integrity of materials' mechanical and thermal properties for future space missions.
Investigation of Spreading and Traction of Human Osteosarcoma Cells on Microgrooved Polydimethylsilaxone Surfaces
Authors: Cao Yifang , Chen Jianbo , Soboyejo Winston O.
Published: April 2011

The paper presents the recent results of the spreading and traction of human osteosarcoma cells on soft polydimethylsiloxane (PDMS) microgrooved surfaces. The results show that the cell tractions resulted in significant deformation of the microgrooves. The tractions were calculated, and found to be in good agreement with the results from other studies. The results suggest that the cell spreading-induced soft substrate deformation needs to be considered in the design of implantable bioMEMS structures.
Biocompatible Silver-containing a-C:H and a-C coatings: A Comparative Study
Authors: Endrino Jose Luis , Allen Matthew , Galindo Ramon Escobar , Zhang Hanshen , Anders Andre , Albella Jose Maria
Published: April 2011

Hydrogenated diamond-like-carbon (a-C:H) and hydrogen-free amorphous carbon (a-C) coatings are known to be biocompatible and have good chemical inertness. For this reason, both of these materials are strong candidates to be used as a matrix that embeds metallic elements with antimicrobial effect. In this comparative study, we have incorporated silver into standard diamond-like carbon (DLC) coatings by plasma ion implantation and deposition (PIII&D) using methane (CH4) plasma and simultaneously depositing Ag from a pulsed cathodic arc source. In addition, we have grown amorphous carbon – silver composite coatings using a dual-cathode pulsed filtered cathodic-arc (FCA) source. The silver atomic content of the deposited samples was analyzed using glow discharge optical spectroscopy (GDOES). In both cases, the arc pulse frequency of the silver cathode was adjusted in order to obtain samples with approximately 5 at.% of Ag. Surface hardness of the deposited films was analyzed using the nanoindentation technique. Cell viability for both a-C:H/Ag and a-C:/Ag samples deposited on 24-well tissue culture plates has been evaluated.
Ordering and shape tuning of Ge islands on metal-patterned Si
Authors: Robinson Jeremy T. , Cao Yifan , Walko Donald , Arms Dohn , Liddle J. Alexander , Dubon Oscar D.
Published: April 2011

In semiconductor epitaxy, a central challenge for the formation of ordered arrays of nanostructures, such as quantum dot islands, is the realization of processing routes to control surface-mediated growth mechanisms with high spatial precision and reproducibility across macroscopic lengths. To this end we have recently demonstrated a simple route for the directed assembly of heteroepitaxial islands based on rudimentary metal patterning. Here we show that the same metal patterns on the silicon surface that lead to island ordering radically modify island morphology resulting in shapes such as nanorods and truncated pyramids that are set by the choices of metal species and substrate orientation. These effects reflect a remarkable combination of metal-mediated growth phenomena that may be exploited to tailor the functionality of island arrays.
Reliable Local Strain Characterization on Si/SiGe Structures in Biaxial Tension
Authors: Zhao Wenjun , Duscher Gerd , Zikry Mohammed A. , Rozgonyi George
Published: April 2011

The strain in the strained Si layer on a blanket strained Si/SiGe structure could not be determined with only convergent beam electron diffraction to high order Laue zone (HOLZ) line splitting. Combined with CBED and finite element calculations, we quantified the deformation field from HOLZ line splitting and demonstrated a procedure to determine the initial strain in the strained Si layer. Our results also gave us insights in strain relaxation in a TEM sample. The CBED technique combined with FE modeling has the potential for initial strain measurements on new generation short channel CMOS technology nodes.
Optical Properties of Multiple, Delta-doped Si:B/Si Layers
Authors: Chang Han-Yun , Lee Eun-Kyu , Kamenev Boris V. , Baribeau Jean-Marc , Lockwood David J. , Tsybeskov Leonid
Published: April 2011

Reliable fabrication of high-speed, delta-doped transistors and better understanding of two-dimensional metal-insulator transitions can be achieved using silicon molecular beam epitaxy (MBE). However, this fabrication technique should be performed with care, avoiding dopant segregation on epitaxial Si surfaces and improving the doping efficiency. Here we report comprehensive structural and optical investigations of MBE-grown Si/delta-doped Si:B multilayer structures. Measurements of Auger electron spectroscopy, Raman scattering, optical reflection and photoluminescence are performed. Our results indicate nearly metallic conductivity at room temperature with metal-insulator phase transition near T ∼100 K. In contrast to recently reported data, no enhancement of photoluminescence at room temperature is found. Occasionally, a few samples in specific areas exhibit strong photoluminescence at 1.4-1.6 micron attributed to structural defects, most likely due to B segregation.
Characterization of Coherent Si1−xGex Island Superlattices on (100) Si
Authors: Baribeau Jean-Marc , Wu Xiaohua , Picard Marie-Josée , Lockwood David J.
Published: April 2011

We examine the nanostructural properties of Si/Si1−xGex island superlattices with 0.37 < x < 0.56 grown at 620-640 °C by molecular beam epitaxy. Analytical transmission electron microscopy (TEM) shows that during growth Ge atoms migrate towards the center of the large islands to maintain epitaxial growth and that the most regular structures are obtained at higher Ge composition when the built-in strain is also higher. High-resolution x-ray reciprocal space mapping shows that these heterostructures remain pseudomorphic and that the undulations are aligned along [010] directions and exhibit a long-range coherence and vertical correlation as revealed by the presence of strong satellites in a wave vector direction parallel to the surface. Raman spectra of these samples exhibit the usual Ge-Ge, Si-Ge and Si-Si vibrational modes. When compared with planar Si/Si1−xGex superlattices the Ge-Ge and Si-Ge Raman peaks are shifted to lower frequencies indicating an average alloy composition that is approximately x = 0.1 less than the nominal values, which is in general agreement with analytical TEM.
Bright Contrast Imaging of Carbon Nanofiber-Substrate Interface using Scanning Electron Microscopy
Authors: Suzuki Makoto , Ominami Yusuke , Ngo Quoc , Yamada Toshishige , Roth Bill , Betts Mark , Cassell Alan M. , Li Jun , Yang Cary Y.
Published: April 2011

Scanning electron microscopy (SEM) for imaging the interface between carbon nanofibers (CNFs) and the underlying substrate is presented. By irradiating the electron beam perpendicular to the substrate, bright contrast is observed at the region where a small gap exists between the CNF and substrate. The energy-diameter diagram for the observation of the bright contrast is derived, which can be understood by using the theory of electron penetration into solid. Monte Carlo simulation is performed to reproduce the experimental observation based on our model, and the contrast sensitivity to the gap height is discussed.
Carrier Doping of Silicon Nanowires Synthesized by Laser Ablation
Authors: Fukata Naoki , Okada Naoya , Matsushita Satoshi , Tsurui Takao , Ito Shun , Chen Jun , Sekiguchi Takashi , Uchida Noriyuki , Murakami Kouichi
Published: April 2011

Boron (B) doped silicon nanowires (SiNWs) were synthesized by laser ablation. Local vibrational modes of B in SiNWs were observed by micro-Raman scattering measurements at room temperature. Broadening due to a coupling between the discrete optical phonon and a continuum of interband hole excitations was also observed in the Si optical phonon peak. This is called Fano broadening. These results prove that B atoms were doped in substitutional sites of crystalline Si core of SiNWs during laser ablation.
Influence of Chemical Dopant Technique to Reduce Schottky Barriers of Pd-Contacted CNTFETs
Authors: Casterman Damien , De Souza Merlyne Maria
Published: April 2011

The role of the p-type chemical dopant, SbCl6, on Palladium (Pd)-contacted carbon nanotube field effect transistors (CNTFETs) is investigated using ab initio calculations. The interaction of SbCl6 with Pd leads to the chemisorption of one chlorine atom (Cl) which separates off from the rest of the molecule leaving behind a rehybridized SbCl5 molecule. This interaction increases the local workfunction by 0.08 eV. The interaction of the molecule with the carbon nanotube (CNT) itself results in the physisorption of SbCl6 onto CNT. The SbCl6 is found to degenerately dope CNT p-type and shifts the local potential by 0.29 eV. These barriers are useful for modelling of transport of Schottky barrier CNTFETs.
SiC Nanowires by Silicon Carburization
Authors: Tsakalakos Loucas , Fronheiser Jody , Rowland Larry , Rahmane Mohamed , Larsen Michael , Gao Yan
Published: April 2011

Polycrystalline SiC nanowires and composite Si nanowire-SiC nanograin structures have been synthesized using a combined catalytic chemical vapor deposition and carburization method. Si nanowires are grown at low temperature (550-650 C) and subsequently carburized at 1100-1200 C in a methane/hydrogen or propane/hydrogen environment. Thermochemical calculations showed that the Si carburization is thermodynamically favorable over a wide tempareture range, whereas our studies showed that the Si nanowire carburization is kinetically limited below ∼1100 °C. Partially carburized nanowires contained distinct SiC nanosized grains on the Si nanowire surface, whereas fully carburized nanowires were polycrystalline 3C SiC with grain sizes of ∼ 50-100 nm.
Nonaqueous Viscous Electrolytes for Growth of Anodic Titania Nanotubes
Authors: Macak Jan M. , Albu Sergiu P. , Schmuki Patrik
Published: April 2011

The present work compares two different organic electrolytes (glycerol and ethylene glycol) for the growth of self-organized TiO2 nanotubes by anodic oxidation of Ti. In both electrolytes these self-organized layers of TiO2 nanotubes can be grown to considerable thickness (several 10 μm). It is found that except for the detailed electrochemical conditions also the water content has a dramatic influence on the tube dimensions, mainly length and tube morphology. The best result in terms of length is achieved in “water-free” electrolytes.
Effects of Metal Nanocrystals and Traps in Tunneling Rate Measurements in Metal Nanocrystal Based Carbon Nanotube Memory
Authors: Ganguly Udayan , Hou Tuo-Hung , Kan Edwin
Published: April 2011

The metal nanocrystal (NC) based carbon nanotube (CNT) memory device has been probed with tunneling rate measurements. Firstly, tunneling behavior at two temperatures (300K and 10K) is reported here to demonstrate the distinct charge tunneling behavior for traps versus NCs and understand their relative contributions to program operations. Low temperature measurements show clear differentiation for two regimes of quantum transport. The FN tunneling regime exhibits strong bias dependence and dominates at high electric fields producing larger tunneling rates than the direct tunneling regime. In comparison to traps, the metal NCs repel potential contours and hence produce higher electric fields that enhance tunneling. The FN tunneling diminishes when the charging of the nanocrystal or traps decreases (relaxes) the electric field in the tunnel dielectric (TD) enough for the low field direct tunneling to dominate. The direct tunneling occurs at low fields, and is less sensitive to electric fields. The NCs demonstrate faster tunneling which can be ascribed to their large tunneling cross-section compared to traps. This is despite the relative proximity of traps to the channel in our structure. Secondly, the tunneling rates for two different TDs of similar EOT (under linear approximation) have been characterized and compared. They are a homogenous evaporated SiO2 and layered dielectric consisting of an evaporated SiO2 and ALD Al2O3 stack. While the evaporated SiO2 based TD demonstrates the distinct NC versus trap tunnel rate performance, the layered TD demonstrates stronger resistance to tunneling to the NCs. This result is consistent with the low tunneling rates demonstrated in Al2O3 elsewhere. Finally, the program performance of the NC-CNT memory device is evaluated as 0.5 V threshold voltage (VT) shift for a charging pulse of 9V and 100 μs. Combining with previous results, this indicates that NC-CNT memory is a promising candidate for low voltage, fast, multi-level cell (MLC) operation with sub-lithographic (self-assembled) features for sub 30 nm FLASH memory node. From the device physics perspective, these measurements may serve as the calibration and validation for advanced tunneling calculations and device modeling for promising nanoscale charge-based non-volatile memories.
Self-Assembled Conductive Network of Carbon Nanotubes in Polyaniline Forming Potential Nanocomposites
Authors: Gupta Sanju , Kandagor V , Hauge R. , Ding Y , Patel R. J.
Published: April 2011

Carbon nanotubes (CNTs) are of great interest because of several unsurpassable physical (mechanical, electrical, thermal, and chemical) properties. Especially their large elastic modulus and breaking strength make them highly attractive for their use as reinforced agents in forming a new class of multifunctional advanced materials - onanocomposites, in addition to high conductivity (either in semiconducting or metallic regimes) achieved through lower percolation thresholds for several electronic applications. Among the known conducting polymers, polyaniline (PANI) has a high potential due to its ease of synthesis, excellent environmental, and thermal stability and reversible control of its electrical/electronic properties. In this work, PANI-single-/multiwalled NTs composites films containing different nanotube content of both kinds were synthesized by spin-cast preceded by ultrasonic mixing of the constituents. They were characterized using complementary techniques including scanning electron microscopy, X-ray diffraction, infrared and Raman spectroscopy, and conductivity revealing their microscopic structure and physical properties thus helping in establishing process-structure-property correlations. The present work will discuss some of these findings in terms of a) self-alignment of nanotubes in conducting polymer b) their optical and electrical properties, and c) their design with a view to electronic and sensor applications, all ascribed due to long range π-π interaction between the constituents.
Study on the Synthesis of CNTs and the Fabrication of CNTs-Based MEA for DMFC Application
Authors: Su Chun-Hsi , Lin Chii-Ruey , Hung Hsin-Chin
Published: April 2011

A fuel cell (FC) generates electricity by chemical reactions. The catalyst dispersion in membrane electrode assembly (MEA) of FC is a crucial factor to affect the performance of the cell. A novel grafting method is adopted in this study to grow secondary carbon nano-tubes (CNTs) on a substrate comprised of primary CNTs, in order to form branchy CNTs with higher specific surface area (SSA). The as-obtained branchy CNTs are then used as catalyst, Pt, carriers in the MEA of direct methanol fuel cell (DMFC). A self-assembled DMFC of air-breathing type with active MEA area of 2 × 2 cm2 is used in this study as the standard FC for the electrical performance test. The peak power of DMFC comprised of an MEA with sole primary CNTs is 0.002 watts at 0.15 V. Such peak power can be increased up to 0.01 watts at 0.4 V for the replaced MEA with new branchy CNTs. The open circuit voltages (OCVs) are 0.4 V and 0.6 V for DMFCs with MEAs of sole primary CNTs and branchy CNTs, respectively. Furthermore, the patterns of CNTs was designed to provide micro-channels of fuel. The pattern growth of CNTs have been fabricated by selective area growth method in this research.
Carbon Nanotube-Based Fluid Flow/Shear Sensors
Authors: Ni Chi-Nung , Deck Christian P. , Vecchio Kenneth S , Bandaru Prabhakar R
Published: April 2011

The response of vertically oriented multi-walled nanotubes (MWNTs) to fluid flows forms a basis for monitoring shear forces at the nanoscale. We report on the modulation of polarized light transmission through a MWNT mat, as a function of the nanotube axis relative to the laser polarization. Nanotubes are deflected under fluid flow, with fluid pressures corresponding to pico-Newton range forces. This deflection is measured as a function of transmitted laser light intensity. While the response of the CNTs to the flows could be modeled through standard elastic beam deflection theory, their recovery, after the force removal, invokes viscoelastic behavior due to CNT disentanglement. The fluid flow direction, as well as its pressure, can also be determined by monitoring the change in transmitted laser polarization.
O2 Plasma Treatment of Al Layer on Metal Anode to Improve the Performance of Organic Light-Emitting Devices
Authors: Lee Su Hwan , Shin Dong-Won , Kim Sung-Jun , Kang Yoon Ho , Lee Gon-Sub , Park Jea-gun
Published: April 2011

A gold and aluminum layer was investigated as an anode for organic light-emitting devices (OLEDs). By pretreating the ultrathin aluminum layer in an oxygen (O2) plasma, the hole injection from the metal anode to the organic layer was greatly enhanced. The fabricated OLEDs demonstrated improved current density and luminance characteristics as compared with other devices using a gold anode and an aluminum layer not treated with an oxygen plasma.