bluuebunny/crossref_metadata_2025_split huggingface dataset:
Silver Nanoparticle Films as Sulfide Gas Sensors in Oddy Tests
Authors: Chen Rui , Moussa Laura , Morris Hannah R. , Whitmore Paul M. 
Published: April 2011

AbstractThe preparation and performance of a silver nanoparticle-based sensor for use in Oddy tests are reported. A suspension of spherical silver nanoparticles (Ag NPs) (mean diameter of 30 nm, absorption of surface plasmon resonance (SPR) at 428 nm) in methanol was synthesized and the Ag NPs were self-assembled into monolayer films on glass slides, using polyethylenimine as a linking agent. UV-vis spectrophotometry was employed to measure the SPR intensity of the Ag NP films in order to evaluate the extent of reaction. It was observed that the Ag NP films were quite stable under Oddy test conditions in a blank test, after a brief alteration of the spectrum due to particle dispersal, with no significant decrease in the SPR intensity after 1.5 months at 60°C and 100% RH. The sensitivity of Ag NP films to sulfide gases emitted from a test wool fabric in the Oddy test was investigated. UV-vis spectra taken after the Oddy tests showed the disappearance of the Ag NP SPR peak and the growth of the UV absorption due to Ag2S. Elemental analysis with energy dispersive x-ray spectroscopy confirmed that sulfur had been incorporated into the Ag NP film. Ag NP assemblies of lower NP density were created that indicated the presence of sulfide gases prior to significant tarnishing of a Ag foil. The results demonstrate that the Ag NP films can be used as sensitive, quantitative optical sensors to replace Ag foils in the Oddy test system.
General Elasticity Theory for Graphene Membranes Based on Molecular Dynamics
Authors: Samadikhah Kaveh , Atalaya Juan , Huldt Caroline , Isacsson Andreas , Kinaret Jari 
Published: April 2011

ABSTRACTWe have studied the mechanical properties of suspended graphene membranes using molecular dynamics (MD) and generalized continuum elasticity theory (GE) in order to develop and assess a continuum description for graphene. The MD simulations are based on a valence force field model which is used to determine the deformation and the elastic energy of the membrane (EMD) as a function of external forces. For the continuum description, we use the expression Econt = Estretching + Ebending for the elastic energy functional. The elastic parameters (tensile rigidity and Poisson ratio) entering Econt are determined by requiring that Econt = EMD for a set of deformations.Comparisons with the MD results show excellent agreement. We find that the elastic energy of a supported graphene sheets is typically dominated by the nonlinear stretching terms whereas a linear description is valid only for very small deflections. This implies that in some applications, i.e. NEMS, a linear description is of limited applicability.
Carbon Nanotube Dispersion in Epoxy Nanocomposites with Clay
Authors: Liu Lei , Grunlan Jaime 
Published: April 2011

ABSTRACTClay particles were used to facilitate the dispersion and network formation of single-walled carbon nanotubes (SWNTs) in an epoxy matrix. In the presence of clay, electrical conductivity increase and percolation threshold reduction for SWNT/epoxy composites were achieved simultaneously. These improvements are due to better SWNT dispersion, as evidenced by optical microscopy and scanning electron microscopy. Dynamic mechanical analysis (DMA) shows that mechanical properties of the composites without clay could be improved by clay addition. SWNTs appear to have an affinity for clay that causes them to become more exfoliated and better networked.
Effect of Graded AlxGa1-xN Interlayer Buffer on the Strain of GaN Grown on Si (111) Using MOCVD Method
Authors: Lin KungLiang , Chang Edward-Yi , Li Tingkai , Huang Wei-Ching , Hsiao Yu-Lin , Tweet Douglas , Maa Jer-shen , Hsu Sheng-Teng 
Published: April 2011

ABSTRACTGaN film grown on Si substrate with AlN/AlxGa1−xN buffer is studied by low pressure metal organic chemical vapor deposition (MOCVD) method. The AlxGa1−xN film with Al composition varying from 0∼ 0.66 was used. The correlation of the Al composition in the AlxGa1−xN film with the stress of the GaN film grown was studied using high resolution X-ray diffraction including symmetrical and asymmetrical ω/2θscans and reciprocal space maps. It is found that with proper design of the Al composition in the AlxGa1−xN buffer layer, crack-free GaN films can be successfully grown on Si (111) substrates using AlN and AlxGa1−xN buffer layers.
InGaN Thin Films Grown by ENABLE and MBE Techniques on Silicon Substrates
Authors: Reichertz Lothar A. , Yu Kin Man , Cui Yi , Hawkridge Michael E , Beeman Jeffrey W , Liliental-Weber Zuzanna , Ager III Joel W , Walukiewicz Wladyslaw , Schaff William J , Williamson Todd L , Hoffbauer Mark A. 
Published: April 2011

ABSTRACTThe prospect of developing electronic and optoelectronic devices, including solar cells, that utilize the wide range of energy gaps of InGaN has led to a considerable research interest in the electronic and optical properties of InN and In-rich nitride alloys. Recently, significant progress has been achieved in the growth and doping of InGaN over the entire composition range. In this paper we present structural, optical, and electrical characterization results from InGaN films grown on Si (111) wafers. The films were grown over a large composition range by both molecular beam epitaxy (MBE) and the newly developed “energetic neutral atomic-beam lithography & epitaxy” (ENABLE) techniques. ENABLE utilizes a collimated beam of ∼2 eV nitrogen atoms as the active species which are reacted with thermally evaporated Ga and In metals. The technique provides a larger N atom flux compared to MBE and reduces the need for high substrate temperatures, making isothermal growth over the entire InGaN alloy composition range possible. Electrical characteristics of the junctions between n- and p-type InGaN films and n- and p-type Si substrates were measured and compared with theoretical predictions based on the band edge alignment between those two materials. The predicted existence of a low resistance tunnel junction between p-type Si and n-type InGaN was experimentally confirmed.
A Comprehensive Study of Growth Techniques & Characterization of Epitaxial Ge1−xCx (111) Layers Grown Directly on Si (111) for MOS Applications
Authors: Jamil Mustafa , Donnelly Joseph P , Lee Se-Hoon , Shahrjerdi Davood , Akyol Tarik , Tutuc Emanuel , Banerjee Sanjay K 
Published: April 2011

ABSTRACTWe report the growth and characterization of thin germanium-carbon layers grown directly on Si (111) by ultra high-vacuum chemical vapor deposition. The thickness of the films studied is 8-20 nm. The incorporation of small amount (less than 0.5%) of carbon facilitates 2D growth of high quality Ge crystals grown directly on Si (111) without the need of a buffer layer. The Ge1−xCx layers were grown in ultra high vacuum chemical vapor deposition chamber, at a typical pressure of 50 mTorr and at a growth temperature of 440 °C. CH3GeH3 and GeH4 gases were used as the precursors for the epitaxial growth. The Ge1−xCx films were characterized by atomic force microscopy (AFM), secondary ion mass spectroscopy, x-ray diffraction, cross-sectional transmission electron microscopy and Raman spectroscopy. The AFM rms roughness of Ge1−xCx grown directly on Si (111) is only 0.34 nm, which is by far the lowest rms roughness of Ge films grown directly on Si (111). The dependence of growth rate and rms roughness of the films on temperature, C incorporation and deposition pressure was studied. In Ge, (111) surface orientation has the highest electron mobility; however, compressive strain in Ge degrades electron mobility. The technique of C incorporation leads to a low defect density Ge layer on Si (111), well above the critical thickness. Hence high quality crystalline layer of Ge directly on Si (111) can be achieved without compressive strain. The fabricated MOS capacitors exhibit well-behaved electrical characteristics. Thus demonstrate the feasibility of Ge1−xCx layers on Si (111) for future high-carrier-mobility MOS devices that take advantage of high electron mobility in Ge (111).
Concentric Metallic-Piezoelectric Microtube Arrays
Authors: Fan Hongjin , Kawasaki S. , Gregg J. M. , Langner A. , Leedham T. , Scott J. F. 
Published: April 2011

AbstractTrilayer concentric metallic-piezoelectric-metallic microtubes are fabricated by infiltrating porous Si templates with sol precursors. LaNiO3(LNO) is used as the inner and outer electrode material and PbZrTiO3(PZT) is the middle piezoelectric layer. Structure of the microtubes is characterized in details using scanning and transmission electron microscopy which are equipped with energy dispersive X-ray spectroscopy for elemental mapping. The hysteresis of a trilayered thin film structure of LNO-PZT-LNO is shown. This trilayered tubes might find applications in inkjet printing.
Fused Heterocyclic Aromatics as Potential Organic Semiconductors: a Theoretical Study
Authors: Tal Faleh Al , Pham Phuong-T T. , Al-Maadeed Mariam Ali , Bader Mamoun M. 
Published: April 2011

AbstractWe report herein the results of density functional theory calculations of the geometric and electronic structure for a series of fused heterocyclic compounds. These molecules were compared with the corresponding carbocyclic oligoacenes, which are currently being experimentally investigated for use as organic semiconductors. The impact of various structural modifications on this class of compounds on the calculated structures is examined. The results of our calculations reveal that such materials hold exceptional promise as organic semiconductors.
Variable Temperature Measurement on Operating Pentacene-Based OTFT
Authors: Chen Hung-Keng , Liu Po-Tsun , Chang Ting-Chang , Shy S.-L. 
Published: April 2011

AbstractVariable temperature electrical measurement is well-established and used for determining the conduction mechanism in semiconductors. There is a Meyer¡VNeldel relationship between the activation energy and the prefactor with a Meyer¡VNeldel energy of 30.03 meV, which corresponds well with the isokinetic temperature of about 350 K. Therefore, the multiple trapping and release model is properly used to explain the thermally activated phenomenon. By the method, an exponential distribution of traps is assumed to be a better representation of trap states in band tail. Samples with higher temperature during measurement are observed to show better mobility, higher on-current and lower resistance, which agree well with the multiple trapping and release model proposed to explain the conduction mechanism in pentacene-based OTFTs.
Inter Laboratory Comparison and Analysis on Mechanical Properties by Nanoindentation
Authors: Alvarado-Orozco J. M. , Cárdenas-Jaramillo C. , Torres-Torres D. , Herrera-Basurto R. , Hurtado-Macias A. , Muñoz-Saldaña J. , Trápaga-Martinez G. 
Published: April 2011

ABSTRACTThis contribution presents the results obtained by a Mexican laboratory in the Asia-Pacific Economy Cooperation Interlaboratory Comparison (IC) on mechanical properties by nanoindentation from 2008 using fused silica and polycarbonate as samples. Reduced modulus and indentation hardness are the parameters asked to be measured and compared. The aim for this paper is to show and to discuss the so called “indentation size effect” (ISE) on the indentation hardness of fused silica. Using the spherical formulation of the ISE model for crystalline materials, the macroscopic hardness and material length scale of fused silica are determined as (7.34 ± 0.085) GPa and (166.36 ± 14) nm, respectively.
Synthesis and Mechanical Characterization of Aluminum Based Composites Prepared by Powder Metallurgy
Authors: Estrada-Guel I. , Cardoso J. L. , Careño-Gallardo C. , Herrera-Ramírez J. M. , Martínez-Sánchez R. 
Published: April 2011

ABSTRACTAluminum-based composites prepared from pure Al powder and previously Cu metallized graphite are fabricated by a solid state route and are characterized by X-ray diffraction and scanning electron microscopy in order to follow their microstructural evolution. Composites are processed using powder metallurgy technique in order to obtain cylindrical samples to carry out mechanical testing. Microstructural and mechanical characterizations reveal that, by milling, a homogeneous dispersion of insoluble particles into the Al matrix is obtained; this produces an important improvement in hardness and strength with respect to an un-milled sample. Milling intensity and particle concentration have an important effect on the mechanical properties of the synthesized composites.
High-Temperature Oxidation Resistant Nanocoatings on Austenitic Stainless Steels
Authors: Lopez Hugo F. 
Published: April 2011

ABSTRACTIn recent years, the increasing energy costs have lead to power utility industries to seek/develop high efficiency systems of production and of energy utilization. In addition, environmental concerns regarding greenhouse gas emissions are playing a major role in the development of clean energy systems. The development of metallic materials that can withstand elevated temperatures is among the viable alternatives to increase energy efficiency. Nevertheless, for this to happen, the corrosion and oxidation resistance of Fe- and Ni-based alloys needs to be significantly improved. Among the possible ways to enhance the life of high temperature alloys is the application of protective ceramic coatings. Conventional coatings are expensive and the protective effects controversial at times. An alternative which offers a great potential is the application of nano-ceramic coatings. Hence, in this work nanocrystalline coatings based on nano-CeO2 are applied to an austenitic stainless steel 304L and then exposed to elevated temperatures. Weight changes are monitored as a function of time and the results are compared with uncoated alloys tested under similar conditions. In addition, computer simulations of possible rate limiting diffusion mechanisms are carried out. It is found that the nanocoatings provided remarkable high-temperature oxidation resistance and improved scale adhesion. In particular, it is found that the smaller the nanoparticles are, the more effective the nanocoatings in providing oxidation resistance.
A Thermal Stage for Nanoscale Structure Studies with the Scanning Force Microscope
Authors: Kulnis W. J. , Unertl W. N. 
Published: April 2011

ABSTRACTWe have constructed an inexpensive sample mounting stage for studies of temperature dependent processes in a surface force microscope (SFM). The stage is constructed from a Peltier thermoelectric heater secured to a standard SFM mounting stage with silver paint. The sample temperature can be varied from room temperature to about 100°C thus making it possible to use the SFM to observe thermally activated processes at lateral spatial resolutions of 10-20 nm. Approximately 10 minutes is required to reach thermal equilibrium following a 5°C temperature change. The lateral magnification must be calibrated at each temperature. We illustrate the capabilities of the stage with images of polystyrene spheres just below their glass transition temperature of 100°C.
Stm Studies at Electrochemically Controlled Interfaces
Authors: Lindsay S.M. , Pan J. , Jing T.W. 
Published: April 2011

ABSTRACTWe use electrochemical methods to control the adsorption of molecules onto an electrode for imagingin-situby scanning tunneling microscopy. Measurements of the barrier for electron tunneling show that the mechanism of electron transfer differs from vacuum tunneling. Barriers depend upon the direction of electron tunneling, indicating the presence of permanently aligned dipoles in the tunnel gap. We attribute a sharp dip in the barrier near zero field to induced polarization. We propose a ‘tunneling’ process consisting of two parts: One is delocalization of quantum-coherent states in parts of the molecular adlayer that hybridize strongly (interaction ≥kT) with Bloch states in the metal. This gives rise to a quantum-point-contact conductance,Gc≤ 2e2/hat a height zo. The other part comes from the exponential decay of the tails of localized states, G =Gcexp{−2K(z − z0)}. Because measured decay lengths, (2K‘)−1, are small (≈ 1 Å), STM contrast is dominated by the contour along which G[z0(x,y)] = Gc. Measured changes in z0are used to calculate images which are in reasonable agreement with observations. We illustrate this with images of synthetic DNA oligomers.
Nanometer Scale Structures Resulting from Graphite Oxidation
Authors: Nowakowski Marilyn J. , Vohs John M. , Bonnell Dawn A. 
Published: April 2011

ABSTRACTScanning tunneling microscopy (STM) and spectroscopy (STS) were used to characterize highly oriented pyrolytic graphite (HOPG) which was oxidized by two different methods, furnace heating in atmosphere and immersion in oxygen plasma. The character of the surfaces was found to be dissimilar on a micron scale but comparable on a nanometer scale, at which both appear to be comprised of sharp step edges. Variations in local electronic structure near a step edge were compared.
Cross-Sectional Scanning Tunneling Microscopy of III-V Quantum Structures
Authors: Johnson M.B. , Pfister M. , Alvarado S.F. , Salemink H.W.M. 
Published: April 2011

ABSTRACTIn this paper, we report on the use of cross-sectional scanning tunneling microscopy (XSTM) to analyze several aspects of MBE-grown III-V quantum structures on an atomic scale. In particular, we discuss our recent work to identify various atomic species within the same chemical group (e.g. Al and Ga within the group Ill sublattice of AlGaAs) thereby allowing the determination of atomic roughness at GaAs/A1GaAs interfaces and alloy clustering in AlGaAs. We demonstrate and discuss the sensitivity of the STM to individual dopants in the near surface layers, as well as to the local carrier concentration. Lastly, we use XSTM to obtain images of cross-sectioned GaAs/AIGaAs quantum well wires with atomic detail.
An Analysis by Scanning Acoustic Microscopy of the Mechanical Stability of PSG and Si3N4 Passivation Films
Authors: Scafidi P. , Ignat M. , Mortini P. , Marty M. 
Published: April 2011

ABSTRACTTwo types of mechanical tests associated with acoustic microscopy characterizations were performed to investigate the mechanical stability of PSG and Si3N4 passivation films. An in situ tensile test micro-device was installed under a scanning acoustic microscope to study the damage development in the passivation films deposited on A1,1%Si substrates. The analysis of the attenuation of the acoustic signature of the film/substrate systems and the variations of the leaky surface acoustic wave velocity permitted detection of the cracking and decohesion of the passivation films. The four-point bending test was used to submit passivated aluminum multilayers deposited on silicon substrates to cyclic compression. Then subsurface acoustic images revealed decohered zones in the passivation.
Plasticity, Microstructure and the Thermal Dependence of Flow Stresses in Aluminum Thin Film Interconnects
Authors: Venkatraman Ramnath 
Published: April 2011

ABSTRACTA study was conducted towards fundamentally understanding the nature and magnitude of thermal stresses in aluminum thin films on silicon and correlating them with deformation mechanisms that serve to relax the stresses imposed by the thermal strain. A number of experiments and theoretical considerations are described in order to describe the sources of strengthening and stress relaxation in such films. It is shown that the flow stress of an aluminum film corresponds to the critical stress required to drive dislocation glide events. This mechanism entails an inverse flow stress dependence on the film thickness and grain size. A novel set of experiments in which the effects of strengthening due to finite film thickness and the grain size were separated and quantified is described. The variation of these strengthening components with temperature during heating and cooling were noted. Theoretical considerations of diffusional relaxation combined with the results of grazing incidence X-ray scattering (GIXS) experiments suggest that grain boundary diffusion is much less effective in limiting film flow stress than would be expected from the strain rate relation derived for a free-standing film. Line broadening observations in the GIXS experiments suggested large changes in dislocation density in the tested films during thermal cycling. The nature of these variations are qualitatively consistent with those of the film flow stress, suggesting that strain hardening could be an additional strengthening mechanism in Al films during thermal cycling.
Stress Relaxation and Electromigration Kinetics in Short Metal Lines: Transition to Creep Controlled Regime
Authors: Glickman E. , Klinger L. , Katsman A. , Levin L. 
Published: April 2011

ABSTRACTAn analysis of transition from the electrotransport controlled to the creep controlled electromigration (EM) is made for the Blech test geometry. The analysis rests on the approach developed by the authors with relaxation of electromigration induced stress by diffusional creep and non-linear stress distribution along the line. The derived solution confirms the idea of Glickman and Vilenkin that for high current density as the length of the line decreases the transition from the electrotransport controlled to the creep controlled electromigration kinetics must occur. The value of introduced parameter r that relates electromigration behavior to the creep viscosity is estimated by the comparison with experimental observations for aluminum stripes and discussed in terms of the Coble creep mechanisms.
The Roles of Several E′ Variants in Thermal Gate Oxide Reliability
Authors: Conley John F. , Lenahan P.M. , Evans H.L. , Lowry R.K. , Morthorst T.J. 
Published: April 2011

ABSTRACTWe combine electron spin resonance measurements with vacuum ultraviolet, ultraviolet, and corona bias charge injection schemes to examine the properties and charge trapping roles of three E′ variants in conventionally processed thermally grown thin film SiO2 on Si.
Early Failure Sites and Electromigration
Authors: Ramseyer George O. , Beasock Joseph V. , Renz Thomas E. , Walsh Lois H. 
Published: April 2011

ABSTRACTBy definition, half of all interconnects fail before the measured mean time to failure (t50) is reached. To predict early failures the basic reactions occurring in the metallization and its environment must be understood. To this end, fatal interconnect failure sites were characterized by Auger electron spectroscopy, atomic force microscopy and backscattered scanning electron microscopy. CVD silicon dioxide passivation layer/fatal void interfaces of typical early failure voids were characterized and compared to a typical late failure void interface. The topographies of these fatal voids were also quantitatively compared to increase our understanding of early failure sites and electromigration.