bluuebunny/crossref_metadata_2025 huggingface dataset:
Low Temperature Silicon Nitride Films Deposited on 3D Topography by Hot Wire Chemical Vapor Deposition (HWCVD)
Authors: Warnat Stephan , Hoefer Markus , Schaefer Lothar , Foell Helmut , Lange Peter
Published: April 2011

Silicon nitride films were deposited by hot-wire chemical vapor deposition processes (HW-CVD). The films reveal a morphological structure very similar to nitrides formed in low pressure CVD (LP-CVD) or plasma enhanced CVD (PE-CVD) processes. The electrical breakdown voltages, however, are much smaller for HW- than PE- or LPCVD films. The deposition in holes for isolation purpose in “through silicon vias” (TSV) technologies in combination with optical devices, which require very low temperatures (<200 °C), have been investigated. They reveal sufficiently good properties for the planned applications.
Direct production of the Ti-Zr-Ni-Cu icosahedral phase for hydrogen-storage applications by rapid quenching from the melt
Authors: Kocjan Andraz , McGuiness Paul J. , Recnik Aleksander , Kobe Spomenka
Published: April 2011

Our study focused on the formation of Ti40Zr40Ni20 and Ti45Zr35Ni17Cu3 icosahedral (i-phase) quasicrystals directly from the melt and their subsequent characterization and high-pressure hydrogenation. The samples were produced in an inert-gas melt-spinning device from a series of arc-melted precursors. By varying the wheel speeds we were able to produce a range of crystallographic structures, from amorphous, through quasicrystalline, to crystalline. The ribbon thickness showed the expected reduction with wheel speed, from 120 microns to 30 microns, while the Ms exhibited a surprisingly modest change with wheel speed. The XRD analysis showed that depending on the cooling rate it was possible to freeze the icosahedral phase directly from the melt, without any subsequent heat-treatment. Using the same procedure to test the range of formation wheel speeds for a comparable system we also produced samples containing up to 3 atomic % copper. Using transmission electron microscopy we have confirmed that the ribbons contain nanosized particles of Ti40Zr40Ni20 icosahedral phase imbedded in an amorphous matrix with the same composition. The average particle size of the i-phase was approximately 20 nm. The 5-fold symmetry was confirmed by selected-area electron diffraction and high-resolution TEM having the crystallite oriented close to the symmetry axis. Both our X-ray diffraction measurements and the TEM observations have provided direct evidence for the quasicrystalline ordering of Ti40Zr40Ni20 by rapid quenching from the melt. To test the hydrogen-absorption properties of the icosahedral phase we crushed ribbons into finer particles to provide fresh, new surfaces to aid hydrogen dissociation at the metal surface. The uptake of hydrogen was found to be critically dependent on the surface state of the Ni–Ti–Zr ribbons; even modest exposure to the atmosphere produced a protective layer of oxide on the surface that practically prevented any hydrogen being taken up by the icosahedral phase. The concentration of hydrogen in the i-phase was determined from the shift in the XRD peaks. The calculated expansion of aq was 6% and the corresponding [H]/[M] value was 1.5.
Investigation of Hydrogen Storage Using Combinatorial Thin Films and IR Imaging
Authors: Oguchi Hiroyuki , Takeuchi Ichiro , Josell Daniel , Heilweil Edwin J , Bendersky Leonid A
Published: April 2011

Three 100 nm-thick Mgx(TM)1-x (TM = Ni and Ti) composition spread thin films having compositional variation 0.4<x<0.95 and capped with a 5 nm-thick Pd layer were deposited in combinatorial electron-beam (e-beam) deposition chamber. Crystallinity of the films was characterized by scanning x-ray diffraction (XRD) and cross-sectional transmission electron microscopy (TEM). Hydrogen absorption and desorption of the films were monitored with an infrared (IR) camera that could image a full area of the films. The observed changes in IR intensity due to hydrogen absorption/desorption demonstrated sensitivity of the method to the differences in compostion, microstructure and type of TM.
The Effect of Initial Activation on Microstructures of Mg/Cu Super-laminates and Hydrogen Absorption Properties
Authors: Tanaka Koji , Takeichi Nobuhiko , Tanaka Hideaki , Kuriyama Nobuhiro , Ueda Tamotsu T , Tsukahara Makoto , Miyamura Hiroshi , Kikuchi Shiomi
Published: April 2011

Microstructures and hydrogen storage properties of Mg/Cu super-laminates were compared to clarify the effect of initial activation. The initial activation change micro/nano-structures of Mg/Cu super-laminates into Mg2Cu with layered structure in fine grain size of about 1μm and pores highly dispersed between layers in sub-micrometer size. Large surface area, dense defects and short diffusion distance for the reaction enable Mg/Cu super-laminates to absorb hydrogen very quickly.
Mechanical response of a single and released InP membrane
Authors: Le Bourhis Eric , Patriarche Gilles
Published: April 2011

InP membranes have been microfabricated and released on top of an InP substrate. The release process comprises membrane photolithography, interlayer sacrificial etching of a InP/InGaAs/InP substructure and drying with CO2 at critical point. The mechanical response of the obtained small (40 µm) and thin (0.4 µm) membranes could be tested by nanoindentation. While keeping their epitaxial orientation through the fabrication process, delamination of the membrane was observed to occur before the indenting load reached 10 mN. Then cracking of the membrane was detected as a pop-in on the loading curves for loads larger than 10 mN.
Mapping of the Initial Volume at the Onset of Plasticity in Nanoindentation
Authors: Zhu Tingting , P'ng K.M.Y. , Hopkinson M. , Bushby A.J. , Dunstan D.J.
Published: April 2011

Understanding the finite volume throughout which plastic deformation begins is necessary to understand the mechanics of small-scale deformation. In indentation using spherical indenters, conventional yield criteria predict that yield starts at a point on the axis and at a depth of half the contact radius. However, Jayaweera et al (Proc. Roy. Soc. 2003)[4] concluded that yield occurs over a finite volume at least 100 nm thick. Semiconductor superlattice structures, in which the stress and thickness of individual layers can be varied and in which known internal stresses can be incorporated, open up new possibilities for investigation that cannot be achieved by varying external stresses on a homogenous specimen. We have designed samples with bands of highly strained InGaAs superlattice, which are essentially bands of low yield-stress material devoid of other metallurgical artifacts. These bands are placed at different depths in a series of samples. Spherical indenters with a range of radii were used to determine the elastic-plastic transition. The stress field from different sized indenters interacts with the low yield-stress material at different depths below the surface to map out the size of the initial yield volume.
New Experimental Approach for Measuring Electrical Contact Resistance with an Accurate Mechanical Actuation, Evaluation of the Performances of Gold Micro-switches
Authors: Seguineau Cedric , Broue Adrien , Pennec Fabienne , Dhennin Jérémie , Desmarres Jean-Michel , Pothier Arnaud , Lafontan Xavier , Ignat Michel
Published: April 2011

A specific experimental setup combining nanoindentation and electrical inputs has been developed in order to determine the reliability and the performances of Micro-ElectroMechanical Systems (MEMS) which include thin free-standing elements like micro-switches applications. The evolution of the electrical resistance with respect to a mechanical solicitation applied on the contact, are henceforth available. The description of the set-up goes with a brief overview of the tests performed on a gold ohmic switch. A discussion is developed considering the mechanisms involved in the contact response. This is based on a confrontation among the experimental results, the analytical modeling and also finite-element analysis.
Analysis and Measurement of Forces in an Electrowetting-Driven Oscillator
Authors: Crane Nathan Brad , Volinsky Alex A , Ramadoss Vivek , Nellis Michael , Mishra Pradeep , Pang Xiaolu
Published: April 2011

Electrowetting is a promising method for manipulating small volumes of liquid on a solid surface. This complex phenomenon couples electrical and fluid properties and offers many potential surprises. The complex electrical and capillary interactions in electrowetting are illustrated by an analysis of an electrowetting configuration that produces an oscillating droplet motion from a steady DC voltage input. The paper presents an analysis of the electrowetting forces to explain the oscillation and presents a new method for measuring electrowetting forces using a Hysitron Triboindenter. Initial results are compared with predictions from numerical models and simplified analytical solutions.
Perovskite and Composite Materials for Intermediate Temperatures Solid Oxide Fuel Cells
Authors: Kharlamova T. , Pavlova S. , Sadykov V. , Krieger T. , Mezentseva N. , Muzykantov V. , Alikina G. , Boronin A. , Zaikovskii V. , Ishchenko A. , Rogov V. , Uvarov N. , Frade J. , Argirusis Chr.
Published: April 2011

La0.8Sr0.2Fe0.6Ni0.4O2.9 (LSFN) and LSFN-La9.83Si4.5Fe1.5O26 (LSiF) nanocomposite were synthesized and investigated as cathode materials for intermediate temperature (IT) solid oxide fuel cells (SOFC). Phase and structure evolution with sample sintering temperature as well as their transport properties and catalytic activity in oxygen reduction were studied.
Synergistic Physical Properties of Multiphase Nanocomposites with Carbon Nanotubes and Inorganic Particles
Authors: Sumfleth Jan , Sriyai Montira , Prado Luis , Wichmann Malte H.G. , Schulte Karl
Published: April 2011

Multiphase epoxy-nanocomposites based on multi-wall carbon nanotubes (MWCNT) and inorganic nanoparticles (TiO2) were produced. The rheological, electrical and thermo-mechanical properties were investigated in order to reveal informations about the interparticle interactions between the different types of nanoparticles. TEM-investigations reveal altered microstructures for the multiphase nanocomposites (MWCNT plus TiO2). TiO2 causes changes in the state of dispersion of MWCNT which can lead to an increase of the rheological parameters (e.g. G'). Due to changes in the formation of the percolated MWCNT network during curing, the electrical conductivity is decreased if the concentration of the non-conductive fillers exceeds a critical value. Additional synergistic effects could be found for the glass transition temperature. The presence of nanoparticles leads to a chemical inactivation of reactive groups of the matrix. Thus, the generated interphase between matrix and nanoparticles exhibits a lower curing degree which results in lower thermo-mechanical properties. For the multiphase systems the glass transition temperature is decreased less, due to an inactivation of the surface of the different types of nanoparticles by a self assembly which leads to a higher curing degree of the interphase.
Use of Sonication and Influence of Clay Type on the Enhancement in Physical Properties of Poly(methyl methacrylate) Nanocomposites
Authors: Ingram Sharon , Dennis Hugh , Hunter Ian , Liggat John J , McAdam Craig , Pethrick Richard A , Schaschke Carl , Staszczak Sylwia K , Thomson David
Published: April 2011

The nature of the dispersion of a clay platelet in a resin composite will play an important role in the process of enhancement of the physical properties of that material. This paper describes studies of ultrasonically and mechanically mixed dispersion of various clays in methyl methacrylate (MMA) and reports the effects of organic surface modification on the rheology, suppression of settlement of filled systems, cure characteristics and final mechanical properties.
Mechanical Properties of PDMS/CNTs Nanocomposites
Authors: Wu Chung-Lin , Lin Hsueh-Chu , Huang Chien-Hsin , Yip Ming-Chuen , Fang Weileun
Published: April 2011

This study presents the mechanical and electrical properties (including elastic modulus, yield strength and electrical resistance) of PDMS/CNTs nanocomposites. The elastic modulus and yield strength were determined from tensile tests. In addition, a high resistance meter was used to measure the electrical resistances of the PDMS/CNTs nanocomposites. The test specimens of nanocomposites were manufactured using the thermoforming method. There were two recipes used during the thermoforming process: 100 °C for 1 hour, and 150 °C for 15 minutes. The mixtures of PDMS and CNTs were stirred by ultrasonic instrument to prevent polymerization. A feeler gap was used to define the thickness of the specimens. Therefore, the thickness could be controlled within the range of ∼100 μm. Four different kinds of specimens were investigated, including pure PDMS, 1.0 wt%, 2.0 wt% and 4.0 wt% CNTs polymeric composites. As for the l00°C recipe, the elastic modulus of pure PDMS, 1.0 wt%, 2.0 wt%, and 4.0 wt% CNTs were 1.05MPa, 1.17MPa, 1.10MPa and 1.35MPa, respectively. A for the l50°C recipe, the elastic modulus of pure PDMS, 1.0 wt%, 2.0 wt% and 4.0 wt% CNTs were 1.32MPa, 1.42MPa, 1.43MPa, and 1.54MPa. The differences of electrical resistance of PDMS/CNTs nanocomposites at two different conditions and the microstructures composed of the mixtures are also described in this article.
Silicon Carbide Nanowire Heterostructures Constructed from Released Iron Catalysis
Authors: Liu Zhenyu , Srot Vesna , van Aken Peter A. , Rühle Manfred , Yang Judith C.
Published: April 2011

Herein, we present the capability of creating silicon carbide (SiC) nanowires and branched nanostructures via a released cataltic process. Core-shell structured carbon-encapsulated iron nanoparticles were used as catalysts for SiC nanostructures formations by vapor-solid reaction. Various SiC nanostructures, including SiC nanocones, biaxial SiC-SiC composite nanowires, SiC-Fe-SiC junctions, Y, T branched SiC nanowires, and other complex heterostructures were observed from this process. It was demonstrated that the encapsulated iron could gradually migrate out of the carbon shell, and the released iron nanoparticles catalyzes the SiC nanostructures formation. Their morphologies and microstructures were investigated by different techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM), and their formation mechanisms are proposed.
Synthesis and Characterization of High Quality InN Nanowires and Nano-networks
Authors: Cai Zhihua , Garzon Samir , Webb Richard A. , Koley Goutam
Published: April 2011

High quality InN nanowires have been synthesized in a horizontal quartz-tube furnace through direct reaction between metallic Indium and Ammonia using Nitrogen as the carrier gas. Thin film of Au on SiO2/Si substrate has been used as the catalyst layer, facilitating vapor-liquid-solid growth of the nanostructures. The nanowires were grown at a very fast rate of up to 30 μm/hr. Smooth and horizontal nanowire growth was achieved only with nanoscale catalyst patterns, while large area catalyst coverage resulted in uncontrolled and three-dimensional growth. The InN nanowires, which were usually covered with a thin shell layer of In2O3, grew along [110] direction, with overall diameters 20 - 60 nm and lengths 5 - 15 μm. The synthesized nanowires bent spontaneously or got deflected from other nanowires at multiples of 30 degrees forming nano-networks. The catalyst particles for the NWs were found mostly at the sides of the NW apex which helped them to bend spontaneously or get deflected from other NWs at angles which were multiples of 30 degrees. The NW based FETs with a back-gated configuration have already been investigated. The gate-bias dependent mobility of the NWs ranged from 55 cm2/Vs to 220 cm2/Vs, and their carrier concentration was ∼1018 cm−3.
Large-Scale Hierarchical Self-Assembly Structures from Gold Nanoparticles
Authors: Kim Nam-Jung , Li Hao
Published: April 2011

Metallic nanoparticles may form hierarchical dendrites in the presence of ionic surfactant through self-assembly upon solvent drying at room temperature. With nanoparticle density varying in the drying area on the supporting solid substrate, the morphology and relevant size of the dendrites evolve in different structures. At the region where the nanoparticle density is high, the large dendrite can develop with manifest crystal symmetry. At the low density region, many small sizes of compact crystals can be found, indicating that particle nucleation dominates over the long-range crystal growth. SEM image reveals the ordered stacking of gold nanoplates over the long dendrite branches, resembling the liquid crystal array. We present the possible physical origins to explain the various structures of the assembled dendrites during the solvent evaporation at the interface of solid and air.
A Cell's Perspective of its Culture Surface
Authors: Yongsunthon Ruchirej , Baker David E. , Baker Wendy A. , Chang Theresa , Walczak Wanda J. , Senaratne Wageesha , Petzold Odessa N. , Youngman Randall E.
Published: April 2011

Atomic Force Microscopy (AFM) was employed to probe the internal structure of living HepG2/C3A cells grown on various commercially-available substrates. In order to understand the driving mechanisms behind the different cell morphologies, the surface properties of these substrates was characterized with AFM and related techniques. The roughness of a 10μm×10μm region of a series of substrates was determined and found to be independent of both coating and culture media, with the exception of thick hydrogel-like coatings. Probing with functionalized tips could not distinguish relative degrees of hydrophobicity under cell culture media, presumably because Debye shielding masks the substrate surfaces. Force spectroscopy was performed on the surfaces to determine exposed surface proteins/polymers intrinsic to the substrate and adsorbed from culture media. Preliminary investigation of cell-mediated substrate reconstruction suggests that the cells secrete large (1000kDa) polymeric molecules at the substrate interface.
3-Mercaptopropionic Acid modified Porous Silicon Substrate used in Hyperammonemia
Authors: Yun Dong-hwa , Chang Jun-Hyoung , Lee Woo-Jin , Hong Suk-In
Published: April 2011

Amperometric urea sensor is more suitable than optical and potentiometric urea sensor to diagnose hyperammonemia. However, because sensitivity in low concentration decreases remarkably, despite amperometric urea sensor has been studied for a long time it has not been applied for clinical diagnosis. In this paper, a new structure for an amperometric urea sensor was fabricated by MEMS, electrochemical etching, and electrostatic covalent binding techniques. Until now most amperometric urea sensors have had a membrane fixed on top of the transducer. That method often leads to malfunction of the sensor, arising from problems such as inadequate membrane adhesion, insufficient mechanical stability, and low sensitivity. To solve these kinds of problems, urease (Urs) was immobilized by electrostatic covalent binding method on the porous silicon (PSi) substrate coated self-assembled monolayer (SAM). Electrostatic covalent binding method was used to keep anisotropic orientation of urease on SAM.
Characterization of Gap Defect States in Hydrogenated Amorphous Silicon Materials
Authors: Jiao Lihong , Wronski C. R.
Published: April 2011

An enhanced simulation model based on the carrier recombination through these states was developed to characterize the gap defect states in hydrogenated amorphous silicon materials (a-Si:H). The energy dependent density of electron occupied gap states, kN(E), was derived directly from Dual Beam Photoconductivity (DBP) measurements at different bias currents. Through Gaussian de-convolution of kN(E), the energy peaks of the multiple defect states, including both neutral and charged states, were obtained. These energy levels, together with the information on the capture cross sections, were used as known input parameters to self-consistently fit the subgap absorption spectra, the electron mobility-lifetime products over a wide range of generation rates, as well as the energy dependent density of electron occupied gap state spectra. Accurate gap state information was obtained and the nature of the defect states was studied. Simulation results on light degraded hydrogen diluted, protocrystalline a-Si:H show that the density of charged states is 2.3 times that of neutral states. The two states close to the midgap act as effective recombination centers at low generation rates and play key roles in photoconductivity studies.
Nanocrystalline Silicon Diodes for Rectifiers on Flexible RFID Tags
Authors: Kwong Ian Chi Yan , Lee Hyun Jung , Sazonov Andrei
Published: April 2011

There has been an on-going effort to produce low cost radio frequency identification (RFID) tags as a replacement for traditional barcodes. One method to achieve low cost production is to integrate the manufacturing of the substrate, antenna and active devices into one single continuous process. Hydrogenated nanocrystalline silicon (nc-Si:H) is a suitable material for manufacturing the active devices in such a process.

We present a nc-Si:H diode suitable for use in rectifiers on RFID tags. It consists of a Cr bottom contact, an undoped layer of nc-Si:H, an n-doped nc-Si:H and an Al top contact. We demonstrate the current-voltage characteristics of the nc-Si:H diode are much improved over a-Si:H diodes. Current density of 10 A/cm2 and ON/OFF ratio greater than 106 was measured at 2 V forward bias. Output DC voltage of 2.6 V was achieved using four nc-Si:H diodes in a full-wave bridge rectifier. The input AC signal was a sine wave at 14 MHz and 2 VRMS amplitude.
Microstructure Effects in Hot-wire Deposited Undoped Microcrystalline Silicon Films
Authors: Beyer Wolfhard , Carius Reinhard , Lennartz Dorothea , Niessen Lars , Pennartz Frank
Published: April 2011

The microstructure of hot-wire microcrystalline silicon films prepared at a wide range of deposition conditions was characterized by both the microstructure parameter from infrared absorption data (analyzing the Si-H stretching modes) and the effusion spectra of (low dose) implanted He and Ne. Parameter ranges leading to the growth of a dense material are identified. A (relatively) high silane flow at rather high filament temperature is found to result in a dense material at high deposition rate. The microstructure data obtained by the two microstructure characterization methods are found to be largely correlated.
Structural and Opto-Electronic Properties of a-Si:H/a-SiNx:H Superlattices
Authors: Luxembourg Stefan L. , Tichelaar Frans D. , Kúš Peter , Zeman Miro
Published: April 2011

A series of multilayer structures consisting of alternating layers of hydrogenated amorphous silicon (a-Si:H) and amorphous silicon nitride (a-SiNx:H) was fabricated using plasma enhanced chemical vapor deposition. The overall thickness and a-Si:H-to-a-SiNx:H ratio was kept constant for the different multilayer samples fabricated. A blue shift of the optical bandgap was observed with decreasing a-Si:H well layer thickness. High-Resolution Transmission Electron Microscopy was used to estimate the abruptness of the layer-to-layer transitions. The thickness of the interface mixing layer for transitions from a-Si:H to a-SiNx:H was estimated to be 0.5 − 1 nm, while for the reverse transition a thickness of 2-2.5 nm was found. Results from Fourier Transform Infrared Spectroscopy support the found thickness range.
Characterization and light emission properties of osmium silicides synthesized by low energy ion implantation
Authors: Poudel Prakash R. , Hossain K. , Li J. , Gorman B. , Neogi A. , Rout B. , Duggan J. L. , McDaniel F. D.
Published: April 2011

Low energy (55 KeV) Osmium ( Os− ) negative ion beam was used to implant (5×1016 atoms/cm2 ) into p-type-Si (100). The implantation was performed with the ion source of a National Electrostatic Corp. 3 MV Tandem accelerator. The implanted sample was subsequently annealed at 650 °C in a gas mixture that was 4% H2 + 96% Ar. Rutherford Backscattering spectrometry (RBS) analysis with 1.5 MeV Alpha particles was used to monitor the precipitate formation. Photoluminescence (PL) measurements were also performed to study possible applications of silicides in light emission. Cross-sectional Scanning Electron Microscopy (X-SEM) was performed for topographic image of the implanted region. RBS along with PL measurements indicate that the presence of osmium silicide (Os2Si3) phase for light emission in the implanted region of the sample.
High Performance Bottom Gate μc-Si TFT Fabricated by Microwave Plasma CVD
Authors: Hiroe Akihiko , Teramoto Akinobu , Ohmi Tadahiro
Published: April 2011

Deposition trend of μc-Si was investigated using microwave (2.45GHz) plasma enhanced CVD. μc-Si films with the preferential orientation of (111) and (220) were deposited and compared. Raman scattering results show that the (111) preferentially oriented film has higher crystallinity while ESR measurements result in the fact that the (220) preferentially oriented film has smaller dangling bond density. Bottom gate thin film transistors (TFT's) were fabricated using these μc-Si films as channel layer and evaluated. H2 plasma post-treatment has been found to be effective to improve the TFT characteristics. Mobility of about 1.4cm2/Vsec and on/off ratio of more than 105 have been achieved.
Hydrogenated Nanocrystalline Silicon Thin Film Transistor Array for X-ray Detector Application
Authors: Shin Kyung-Wook , Esmaeili-Rad Mohammad R. , Sazonov Andrei , Nathan Arokia
Published: April 2011

Hydrogenated nanocrystalline silicon (nc-Si:H) has strong potential to replace the hydrogenated amorphous silicon (a-Si:H) in thin film transistors (TFTs) due to its compatibility with the current industrial a-Si:H processes, and its better threshold voltage stability [1]. In this paper, we present an experimental TFT array backplane for direct conversion X-ray detector, using inverted staggered bottom gate nc-Si:H TFT as switching element. The TFTs employed a nc-Si:H/a-Si:H bilayer as the channel layer and hydrogenated amorphous silicon nitride (a-SiNx) as the gate dielectric; both layers deposited by plasma enhanced chemical vapor deposition (PECVD) at 280°C. Each pixel consists of a switching TFT, a charge storage capacitor (Cpx), and a mushroom electrode which serves as the bottom contact for X-ray detector such as amorphous selenium photoconductor. The chemical composition of the a-SiNx was studied by Fourier transform infrared spectroscopy. Current-voltage measurements of the a-SiNx film demonstrate that a breakdown field of 4.3 MV/cm.. TFTs in the array exhibits a field effect mobility (μEF) of 0.15 cm2/V·s, a threshold voltage (VTh) of 5.71 V, and a subthreshold leakage current (Isub) of 10−10 A. The fabrication sequence and TFT characteristics will be discussed in details.
Laser Fabrication of Sharp Conical Microstructures on Si Thin Films by Nd:YAG Laser Single Pulse Irradiation
Authors: Georgiev Daniel , Georgiev Daniel
Published: April 2011

Conical microstructures with nanoscale sharpness form on silicon films as a result of single-pulse, localized UV irradiation using a solid-state, Q-switched Nd:YAG laser. Projection imaging of pinhole apertures was employed to obtain micron-sized irradiation spots on the surface of silicon-on-insulator samples. The formation of these structures requires melting of the silicon film and was followed at different laser fluence levels and irradiation spot sizes. Atomic force microscopy (AFM) was used to characterize the structures. After fabricating small arrays of such micro-cones, the silicon top layer was selectively etched away in order to understand the role of the underlying silicon oxide. AFM images of such etched samples revealed that the topography of the oxide material below the cones had been significantly modified: bumps with heights that represent a significant fraction of the original Si cone height have formed. This suggests that substrate melting plays an important role in the mechanism of formation of the silicon cones.
Optimization of Flash Annealing Parameters to Achieve Ultra-Shallow Junctions for sub-45nm CMOS
Authors: Kalra Pankaj , Majhi Prashant , Tseng Hsing-Huang , Jammy Raj , King Liu Tsu-Jae
Published: April 2011

The use of millisecond annealing to meet ultra-shallow junction requirements for sub-45nm CMOS technologies is imperative. In this study, the effect of flash anneal parameters is presented. Reduced dopant diffusion and lower sheet resistance Rs is achieved for intermediate temperature Tint = 700°C (vs. 800°C). Significantly lower Rs is achieved with peak temperature Tpeak = 1300°C (vs. 1250°C). Multiple shots provide for lower Rs, albeit at the expense of increased dopant diffusion. Based on a simple quantitative model, an optimal flash anneal can achieve 82% dopant activation efficiency.
Dopant Condensation beyond Solubility Limit in the Vicinity of Silicon/Silicide Interface Based on First-Principles Calculations
Authors: Yamauchi Takashi , Nishi Yoshifumi , Kinoshita Atsuhiro , Tsuchiya Yoshinori , Koga Junji , Kato Koichi
Published: April 2011

In the trend of scaling down metal-oxide-semiconductor field effect transistors (MOSFETs), reduction of contact resistance at the silicide/silicon (Si) interface will be essential for higher performance. Nickel silicide (NiSi) is considered as a substi-tute for a present electrode material in MOSFETs, cobalt silicide (CoSi2), because silicidation temperature can be reduced as compared with the case of the conventional CoSi2. Hence, we have focused on the NiSi/Si Schottky interface. An ordinary method to increase the dopant concentration at the interface is ion implantation before silicidation process. The dopant atoms are consequently condensed around the interface by snowplow effect, leading to the effective lowering of the Schottky bar-rier height (SBH) because of the band bending enhancement of the Si layer. However, this band bending technique does not reduce the SBH in further scaled MOSFETs. In this context, we studied another possibility of SBH modulation technique, based on the first-principles calculations. Throughout our calculations, we found that a large atomic-scale dipole between impurity and silicide atoms is generated across the interface. Impurity atoms are expected to be condensed because of a large energy gain at the interfaces, leading to the dramatic reduction of the SBH. Based on these results, we proposed a novel di-pole comforting Schottky (DCS) junction. We have also found that the thickness of the Si layer interfacing with the NiSi layer can be 1nm or less. In the present work, we applied this idea to the actual process through experimental techniques. The calculated results suggest that B implantation after silicidation leads to larger B concentration at the interface than that before silicidation, and thereby larger SBH modulation due to interface dipoles can be produced. Then, the NiSi/Si Schottky diodes were formed by ion implantation after silicidation process for dopants (As, B). We evaluated the interface dipoles contribution to the measured SBH reduction. As a result, the dopant atoms were found to be condensed beyond solubility limits on the interface Si side and we confirmed the generated interface dipoles actually reduces the SBT. Furthermore, we explored the other possibility of another type of impurity atoms applicable to the DCS junction. Among some other impurity atoms (Al, In, Mg), the calculated SBH modulation due to dipoles generated around these impurity atoms were found to be further enhanced in some cases. Based on these understandings, we propose a principle for choosing dopants towards ulti-mate lowering of the contact resistance in ultimately scaled MOSFETs.
Strategies for CMOS Low Equivalent Oxide Thickness Achievement with High-κ Oxides Grown on Si(001) by MBE
Authors: Becerra Loic , Merckling Clément , Baboux Nicolas , El-Kazzi Mario , Saint-Girons Guillaume , Vilquin Bertrand , Plossu Carole , Hollinger Guy
Published: April 2011

Amorphous LaAlO3 high-k oxide was grown in a molecular beam epitaxy reactor on p-Si(001) using a thin γ-Al2O3 epitaxied buffer layer. Interfaces were free of SiO2 or silicates and remained abrupt despite the high temperature used for annealing, as X-ray photoelectron spectroscopy showed. Electrical measurements performed on as-deposited samples revealed a dielectric constant value close to that of the bulk, small equivalent oxide thickness and low density of interface states. But some negative charges were present, leading to a flat band voltage shift. Post deposition annealing with forming gas can correct this effect.
Real-Time Spectroscopic Ellipsometry Studies of Zinc Oxide Deposition
Authors: Fesenmaier Christian Carl , Li Xiaonan S. , To Bobby , Levi Dean H.
Published: April 2011

Zinc oxide is increasingly being studied as an eventual replacement for indium tin oxide as a transparent conducting oxide (TCO) for thin film solar cells. In order to better understand the growth process of ZnO, as well as provide for accurate control on the National Renewable Energy Laboratory's TCO deposition system, undoped RF-magnetron sputtered ZnO films on silicon were analyzed in situ using real-time spectroscopic ellipsometry (RTSE). A large wavelength range (245-994 nm) was measured in order to derive information about optical properties both below and above the bandgap. Atomic force microscopy (AFM) measurements were also taken to confirm ellipsometry surface roughness results and provide additional insight into the surface morphology.

In light of observed poor fit of typical two-layer optical models to in situ ellipsometry data, we propose a model film structure consisting of two layers: a bulk ZnO layer of graded density that increases in thickness as the growth proceeds and a growth zone at the top of the film of approximately constant thickness with a slightly larger bandgap, lower density, and decreased excitonic absorption. Unfortunately, this model is insufficient to explain the evolution of the film during the early growth period, corresponding to film thicknesses less than 100 nm. Nevertheless, the presence of a growth zone for films above a certain thickness should provide some insight into the growth process of RF-magnetron sputtered ZnO.
Preparation and Properties of Silica-Coated AgI Nanoparticles with a Modified Stober Method
Authors: Kobayashi Yoshio , Misawa Kiyoto , Takeda Motohiro , Ohuchi Noriaki , Kasuya Atsuo , Konno Mikio
Published: April 2011

Iodine compounds have been used as X-ray contrast agents in the field of medicine, because of their low transmittance property for X-ray. The iodine compounds may provoke adverse events as allergic reactions in patients, so that they can not be administered to such people. Core-shell nanoparticles are good candidates for prevention of allergic reactions, because the shell materials can keep the contrast agents from living systems. We have proposed a method for silica-coating of iodine compounds as AgI nanoparticles. In the present work, properties of the silica-coated AgI nanoparticles such as colloidal stability, X-ray absorption and X-ray CT imaging were examined.

Silica-coated AgI nanoparticles were prepared with Stöber method, which was performed with 2.3×10-5 M MPS, 11 M water, 0.01 M DMA and 0.01 M tetraethyl orthosilicate in the presence of 5×10-4 M AgI nanoparticles that were prepared from AgClO4 and KI. The particles had an AgI core size of ca. 15 nm and a silica shell thickness of ca. 20 nm.

Since high iodine concentration in sample solution is desired for practical use as X-ray contrast agents, the colloid of as-prepared coated particles was concentrated with centrifugation. The particle colloid that was concentrated up to an AgI concentration as high as 0.4 M was colloidally stable in saline, and exhibited properties of X-ray absorption and X-ray contrasting comparable to a commercial X-ray contrast agent. Accordingly, the silica-coated AgI nanoparticles prepared in the present work are expected to be applied to a novel X-ray contrast agent.
Electrochemical Fabrication of InSb Nanowires using Porous Alumina Membrane and their Characterization
Authors: Khan Muhammad Ibrahim , Wang Xu , Bozhilov Krassimir N. , Ozkan Cengiz S.
Published: April 2011

Among various ways to produce nanowires; anodic alumina membrane (AAM) based synthesis has constantly received much attention because AAM possess a uniform and parallel porous structure which makes them an ideal template material for creating highly ordered nanostructures. In this paper we report fabrication of InSb nanowire arrays with diameter of 200 nm and 30 nm by direct current electrodeposition inside the nanochannels of anodic alumina membranes without subsequent annealing. The nanowires have four major growth direction, [220] being the most dominant with structure defects such as twins. The transmission electron microscopy (TEM) and scanning electron microscopy (SEM) results demonstrate that these InSb nanowires are uniform with diameters about 200 nm and 30 nm, corresponding to the pore diameter of the AAMs. The nanowires also conduct almost no current in the dark, but when hit with light, they conduct 10,000 times more current. This photoconduction property could lead to a variety of tiny optoelectronic devices potentially useful in future generations of nanoelectronics and chemical sensors. The light-induced conductivity increase and the temperature dependent behavior of the nanowires are also reported.
C60 Fulleride Molecular Nanowire Crystals
Authors: Moriyama Hiroshi , Sugiura Takahito , Mori Hatsumi
Published: April 2011

The novel low-dimensional nanostructural self-alignment of molecular nanowire composed of a C60 anion radical moiety (fulleride) formed by electrocrystallization was revealed by single crystal structure analysis of C60 fulleride salts stabilized by triphenylmethane dye cations. The structure should be noted as molecular nanowire and anticipated to be an organic novel semiconductor from the preliminary four-probe conductance measurement. C60 fulleride has drawn much attention because of its interesting physical properties, such as superconducting of alkali-metal doped C60(A3C60) and unique ferromagnetic behavior of tetrakis(dimethylamino)ethane salts of C60 fulleride, (TDAE)C60.[20]. These intriguing solid-state properties of C60 fulleride should arise from electronic cooperative interactions, mainly due to electron-accepting ability of C60 and the ball-to-ball van der Waals interaction. However, there have been rather a limited number of well-characterized C60 anion radical salts, in particular, molecular discrete fulleride, predominantly because of their sensitivity to air.

We have succeeded in obtaining highly ordered single crystals of C60 anion radical salts stabilized by cationic triphenylmethane dyes, some of which were found to give rise to an intriguing nanostructural columnar alignment like molecular nanowire of C60 fullerides. The single-crystal structure of [Crystal Violet]+C60−. C6H5Cl, reveals that the C60 fulleride aligns like molecular nanowire with the columnar structure along the a axis (crystal growth direction), as well as a zigzag structure along the b axis, with contacts of almost van der Waals magnitude (ca. 10 Å, distance of the C60–C60 center of mass), stabilized by mutual interactions of C60−. and dye, due to such as CH-π, π-π, and face-to-face mutual interactions.

Magnetic susceptibility measurements for crystal violet salts demonstrate antiferromagnetic behavior, which can be fitted fairly by one-dimensional Heisenberg model (uniform chain), associated with the one-dimensional columnar crystal structure of the C60 fulleride molecular nanowire. These results also account for the semiconducting properties of the corresponding salts.
CO Coverage Effects on Pt(111) from First-Principles Calculations
Authors: Shan Bin , Wang Ligen , Hyun Jangsuk , Sang Yang , Zhao Yujun , Nicholas John B
Published: April 2011

CO saturation coverage on Pt(111) is crucially important in diesel oxidation catalysis. We systematically studied high coverage CO adsorption on the Pt(111) surface using density functional theory (DFT) calculations and classical Monte Carlo (MC) simulations. The zero-coverage limit CO adsorption energy at different binding sites is almost degenerate at the revised Perdew–Burke–Erzernhof functional (RPBE) level. As CO populates the surface, strong through-space repulsion and substrate-mediated metal sharing tends to dominate the stability of adsorbates and alter their binding preferences. The calculated differential binding energy curve and adsorption patterns compare well with experiments.
Dissociative Adsorption of O2 on Clean and CO-Precovered Pt Surfaces
Authors: Shan Bin , Wang Ligen , Hyun Jangsuk , Sang Yang , Zhao Yujun , Nicholas John B
Published: April 2011

It is generally accepted that CO oxidation on transition metals follows a Langmuir-Hinshelwood mechanism. The oxidation reaction takes place in two sequential steps where the oxygen molecule first dissociates into atomic oxygen and then reacts with an adsorbed CO to form CO2. One critical question concerning the reaction kinetics under high pressure is the probability of oxygen dissociation on a highly CO covered surface. On bare transition metal surfaces, molecularly adsorbed oxygen readily dissociates with little or no apparent activation barrier. In industrial diesel engine catalysis, the metal surface is initially packed with CO. Subsequent reactions such as oxygen dissociation must take place on a CO covered surface. In this paper, we performed density functional theory (DFT) calculations for O2 dissociation on Pt(111) in the presence of different CO adsorption environments. While several stable O2 molecular precursor states (top-bridge-top, top-fcc-bridge, and top-hcp-bridge) exist on a clean Pt(111) surface, these precursors become endothermic beyond a critical CO coverage of ∼0.44 ML. Furthermore, the reaction path for CO oxidation via dissociated atomic oxygen becomes less favorable at higher CO coverage, primarily due to competitive adsorption and lateral repulsion. It was found that the oxygen dissociation barrier and the binding energies of atomic oxygen are well correlated via the Evans-Polanyi relationship.
QMC Assessments of Weak-interaction Described by DFT within various XC approximations / Effects of Carbon Nanotube Oxidation on Molecular Interactions
Authors: Kanai Yosuke , Grossman Jeffrey C.
Published: April 2011

This paper first presents the fixed-node diffusion and reptation quantum Monte Carlo (QMC) assessment of density functional theory (DFT) description of weak molecular interactions within several exchange-correlation (XC) approximations. The case of Benzene-molecule complex was studied with a number of small molecules. We found that the binding energy for the set of complexes depend significantly on XC approximation employed although its trend appears rather consistent. Analysis of the reduced density gradient revealed that the binding energy trend among different XC approximation is highly correlated with the exchange enhancement factor behaviors at large reduced density gradients. Our findings point to the importance of accurate exchange energy functional in describing the weak interactions, in addition to the more obvious correlation part in DFT description.

We then present DFT investigation on molecular interaction of NO3 toward a single-wall carbon nanotube (CNT). We aim to explain the atomistic processes that are responsible for the recently observed CNT conductance changes in the redox process. We found that molecular physisorption and chemisorption to be energetically stable states, and the chemisorbed configuration becomes less endothermic with an increased oxidation state of the CNT. Our results also show that the dissociative incorporation of the molecule can become highly favored energetically in the process. This chemical state may play an important role of the occasionally-observed CNT conductance irreversibility in the experiment.
Additivity of Hardening by Nanolamellar Structure and Antiphase Domain in Ti-39at%Al Single Crystals
Authors: Koizumi Yuichiro , Minamino Yoritoshi , Tanaka Takayuki , Iwamoto Kazuki
Published: April 2011

A mixed microstructure of antiphase domains (APD) and fine lamellar structure were introduced in a Ti-39at%Al single crystal and it was examined whether the APD hardening works even in nano-scaled lamellar structures. The hardness increases with decreasing APD size even where the L is smaller than 100 nm below which the hardening by lamellar refining saturates. The mechanism of the additivity of strengthening by APD and lamellar structure is discussed in the context of the geometries of slip direction, lamellar boundaries and APD boundaries (APDBs). For {1100}<1120> prism slip (the easiest slip system of α2-Ti3Al), the lamellar boundaries are parallel to the slip direction, and therefore they interrupt the motion of screw dislocations effectively. On the other hand, APDBs inclined from lamellar boundaries can effectively obstruct the dislocation motion regardless of the dislocation character because the shear of such APDBs results in the formation of step-like APDBs on the slip-plane and requires additional stress for dislocation motion whereas APDBs parallel to the slip direction can be sheared without forming such a step-like APDB. Accordingly, APDs and lamellar structure can contribute to the strengthening complementarily.
DNA - Directed Synthesis of ZnO Nanowires
Authors: Jost Micha , Atanasova Petia , Gerstel Peter , Sigle Wilfried , van Aken Peter A. , Bill Joachim
Published: April 2011

In this paper, a new and simple method for the synthesis of ZnO nanowires under very mild conditions is presented. The nanowire preparation is based on mineralization from alkaline aqueous zinc nitrate solution in the presence of fish sperm DNA as a structure-directing agent. The morphological features of the obtained structures were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), while the structural characterization of ZnO was done by X-ray diffraction.
Microstructure Characterization Of Calcified Tissues By Xrd Using An Area Detector
Authors: Rodriguez-Navarro Alejandro , Checa Antonio G.
Published: April 2011

Organisms can precipitate a wide array of minerals which they use to build calcified tissues (i.e., bone, mollusk shell, eggshell, coccolith) having highly sophisticated microstructures. The disposition of organic and mineral components building these materials is highly organized from the nano- to the millimeter scale. Their ordered assembly implies self-organization processes accorded in space and time, giving rise to highly sophisticated textured materials. The objective of our work is the study of fundamental processes in biomineralization such as self-organization processes and texture control in biomineral crystal aggregates. To study the order in the arrangement of shell making crystals we used area detectors available today in modern X-ray diffractometers. The 2D diffraction patterns, collected using such detectors, contain detailed information not only about the mineralogy but also about the microstructure characteristics of polycrystalline materials – crystal size, stress, crystallinity and crystallographic-texture. For instance, to understand microstructure development in mollusk shells, we use this type of detector to do microdiffraction analyses combined with high resolution SEM in order to follow the ordering mechanisms of crystals making these biomaterials.