bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative Secondary Ion Mass Spectrometry (SIMS) of III-V Materials
Authors: Lierde P. Van , Tian C. , Rothman B. , Hockett R. A. 
Published: April 2011

AbstractSecondary ion mass spectrometry (SIMS) provides direct methods to characterize the chemical composition of III-V materials at major, minor and trace level concentrations as a function of layer depth. SIMS employs keV primary ions to sputter the surface and sensitive mass spectrometry techniques to mass analyze and detect sputtered secondary ions which are characteristic of the sample composition. In-depth compositional analysis of these materials by SIMS relies on a number of its unique features including: (1) keV primary ion sputtering yielding nanometer depth resolutions, (2) the use of MCs+ detection techniques for quantifying major and minor constituents, and (3) ion implant standards for quantifying trace constituents like dopants and impurities. Nanometer depth resolution in SIMS sputtering provides accurate detection of diffusion of dopants, impurities and major constituents. MCs+ refers to the detection of “molecular” ions of an element (M) and the Cs+ primary beam. MCs+ minimizes SIMS matrix effects in analysis for major and minor constituents, thus providing good quantification. This paper presents a SIMS study of AlxGa1−xAs structures with three different x values. MCs+ (M=Al or Ga) data are presented for the accurate determination of major and minor components. Rutherford backscattering spectrometry (RBS) and x-ray diffraction (XRD) data were crosscorrelated with the MCs+ results. Three specimens with different x values were ion implanted with H, C, O, Mg, Si, Zn and Se to study quantification of trace levels. SIMS data acquired on a double focusing instrument (CAMECA IMS-4f) and a quadrupole instrument (PHI ADEPT 1010) are also compared. Lastly, we discuss our efforts to improve the analysis precision for pand n-type dopants in AlGaAs which currently is ± 3% (1 sigma).
Passive components on AlN for application in AlGaN/GaN power amplifiers
Authors: Jacobs B. , Straaten B. Van , Kramer M. , Karouta F. , Hek P. De , Suijker E. , Dijk R. Van 
Published: April 2011

AbstractWe have investigated Coplanar Waveguide (CPW) elements on AlN for use in future AlGaN/GaN based power amplifiers. This technology becomes crucial if a via-hole technology is not available. Lines, discontinuities, metal-insulator-metal (MIM) capacitors and resistors were measured and modelled. These elements are embedded between two adaptors for RF probing. A technique was developed to de-embed the adaptors from the overall measurement and hence correctly determine the properties of the element itself. Measurements on elements containing multiple ports with right angles can best be carried out using standard calibration techniques followed by carefully reorienting the probes. It is shown that for accurate design of matching networks operating at 10 GHz each element has to be carefully modelled. The method presented in this paper can be a useful contribution tackling some of the problems related to the design of these networks.
Palladium and Aluminum Gate Metals/Aluminum Nitride/Silicon Balanced Capacitors for Selective Hydrogen Sensing
Authors: Prakasam H. E. , Serina F. , Huang C. , Auner G. W. , Rimai L. , Ng S. , Naik R. 
Published: April 2011

AbstractAn alternate array of Pd/AlN/Si and Al/AlN/Si metal-insulator-semiconductor (MIS) devices has been developed using plasma source molecular beam epitaxy (PSMBE) method for deposition of AlN on Si and magnetron sputtering for deposition of Pd and Al electrodes (via mask) on AlN. Both devices show essentially identical capacitance (C) versus voltage (V) characteristics of the typical MIS capacitor. However, the C-V characteristic of a Pd-device shows a clear shift in the presence hydrogen, while that of an Al-device shows no shift. These sensors were characterized using C(V) and C(time) measurements under varying hydrogen concentration. The effects of oxygen and hydrocarbon gases on the sensors were also studied. The Pd-device responds selectively to hydrogen. These results suggest the possibility of fabricating a balanced sensor structure, which might have significant practical importance, as it would cancel all thermal and material sources of drift in the electrical component of the sensor response.
Apriori Process-Property Relationships of GaN Epitaxial Growth in Ga/N/H/C/O Systems
Authors: Loukeris Constantine , Khan Shumaila , Takoudis Christos G. 
Published: April 2011

AbstractA comprehensive thermodynamic analysis has been performed for the Ga/N/H/C/O system. Apriori process-property relationships of the metal organic chemical vapor deposition (MOCVD) of Gallium Nitride (GaN) are thus obtained. The parameter space for pure GaN growth is studied for system water vapor levels of 0.1 ppb – 10 ppm, system pressure between 10-6- 106 Torr, N/Ga feed ratios of 1 - 100,000, C/Ga feed ratios of 0 – 100, and H2/Ga feed ratios of 100 – 10,000. Higher growth temperatures for pure GaN are predicted at high operating pressures (for pressures greater than 0.1 Torr), low C/Ga feed ratios, high carrier gas flow rates, and mostly at low N/Ga feed ratios. Because relative C/Ga, N/Ga and H2/Ga feed ratios have been considered, the predictions in this study are applicable to any multiple and single precursor systems. Such analyses can be easily extended to the molecular beam epitaxy of GaN, when the feed ratio C/Ga = 0. Experimental data reported on the growth of GaN are found to be in good agreement with our theoretical predictions, for many systems that have included different source species.
Double pendeo-epitaxial growth of GaN films with low density of threading dislocation
Authors: Hong Y. K. , Jung H. S. , Hong C-H. , Kim M.H. , Leem S-J. 
Published: April 2011

AbstractA double pendeo-epitaxy technique for growing uniformly GaN films with low defect density over the entire surface of a substrate has been achieved by metalorganic chemical vapor deposition(MOCVD). The structural properties of the first pendeo-epitaxial layers were optimized with the ratio of the lateral to the vertical growth rate, which is strongly affected by the growth temperature and the TMGa flow rate. The second pendeo-epitaxial growth was performed on the first regrown layers after removing a high defective region originating from underlying GaN seed layer. From the analysis of atomic force microscopy(AFM) images, the termination of surface steps by threading dislocations were not observed at the second regrown GaN layers. This result implies that a very low density of threading dislocation exists on the GaN surface. Cathodoluminescence(CL) results showed a strong band-edge emission from the all regrown regions.
Effect of Additional HCl on the Surface Morphology of High Quality GaN on Sapphire by HVPE
Authors: Xiu X.Q. , Zhang R. , Lu D.Q. , Gu L. , Shen B. , Shi Y. , Zheng Y.D. 
Published: April 2011

AbstractThe effect of introduction of additional HCl on the surface morphology and structural properties of hydride vapor phase epitaxy grown GaN during growth is investigated, and high quality GaN with smooth surface on sapphire is obtained by adding the additional HCl into the HVPE reactor. The result is attributed to the control of polarity of GaN films during growth. The additional HCl altered the equilibrium at the GaN growth front, and the reversible reaction decreased the nucleation density or growth rate. Further, lower growth rate promote the surface diffusion and the coalescence over (0001) plane. Additional HCl may improve the surface morphology by suppressing the (000-1) polarity growth in the initial stage of the growth.
Growth of GaN:Sb MBE-Layers
Authors: Cristea P. , Ebling D.G. , Benz K.W. 
Published: April 2011

AbstractThe single crystalline growth of the GaNxSb1-x system is difficult due to the miscibility gap expected for nearly the whole composition range under thermodynamic equilibrium conditions. The gap is determined by the differences of the atomic radii and of the electro negativities for N and Sb. To overcome this problem crystal growth has to be performed under non-equilibrium conditions with kinetically controlled growth, as it is observed for molecular beam epitaxy (MBE) growth. A single crystalline MBE-growth within the miscibility gap has been demonstrated already in the GaAsxN1-x system exhibiting a similar large miscibility gap. GaN:Sb-layers were grown on Si(111)-substrates by MBE using NH3 as a N-source and solid element sources for Ga and Sb. The parameter window for growth was limited due to side reactions like the decomposition of NH3, the desorption of (at high temperature volatile) compounds like Sb and GaSb or the reaction of Sb with NH3. The composition of the layers was analyzed by XRD and RBS. Antimony bulk concentrations of up to 1.6 % could be obtained in GaN. Optical characterization of the samples was performed by CL-measurements and indicate Sb-induced transitions in the 2.2 eV and 1.42 eV range.
Prepare of ZnAl2O4/-Al2O3 complex substrates and growth of GaN films
Authors: Bi Z.X. , Zhang R. , Li W. P. , Wang X.S. , Gu S.L. , Shen B. , Shi Y. , Liu Z.G. , Zheng Y.D. 
Published: April 2011

AbstractWith the solid phase reaction between the ZnO film and -Al2O3 substrate, the ZnAl2O4/-Al2O3 complex substrate have been prepared. GaN films were then directly grown on this new kind of substrate using light-radiation heating low-pressure metalorganic chemical vapor deposition (LRH-LP-MOCVD) without any nitride buffer layer. The structure and surface morphology of the ZnAl2O4/-Al2O3 substrates and GaN epilayers have been characterized by employing X-ray diffraction (XRD) and scanning electron microscope (SEM). The result show that as the thickness of ZnAl2O4 layer is increased, the film changes from a (111)-oriented single crystal to a poly-crystal, together with the surface morphology transforms from uniform islandsa a to the bulgy-line structure, leading to GaN films grown on ZnAl2O4/ -Al2O3 substrates varying from c-axis oriented single-crystal to poly-crystal.
In-Situ Rheed Observation of Mocvd-Gan Film Growth
Authors: Sumiya Masatomo , Ogusu Noritaka , Osada Kouhei , Fuke Shunro 
Published: April 2011

AbstractWe developed the MOCVD apparatus equipped with RHEED system, which enable us to observe in-situ and real time RHEED for GaN film growth in ~100mTorr of pressure. We attempted to grow GaN film with this MOCVD chamber in 100mTorr. The in-situ RHEED was subsequently observed along the film deposition process in order to understand both the role of buffer layer and the mechanism of GaN film growth by MOCVD on highly lattice-mismatched substrate like sapphire. The results indicate that oxygen removed from the sapphire surface was observed during its cleaning in H2 flow at 1100°C. The dependence of re-crystallization and evaporation of the buffer layer on the annealing ambient was also detected. Although the nitrogen was slightly deficient, HT-GaN film with smooth surface was obtained in 100mTorr by adding H2 gas and reducing total flow rate. In preliminary deposition, the RHEED oscillation-like was observed in MOCVD-GaN growth. Thus, our developing deposition system has a potential to understand the growth mechanism with atomic level.
Modification of Stress in CVD Tungsten Silicide (Polycide) Film by SiO2Capping
Authors: Pelleg Joshua , Elish E. 
Published: April 2011

ABSTRACTStresses in chemical vapor deposited polycide tungsten silicide (poly-Si/WSi2) wereevaluated at each stage of fabrication. The individual layers of the Si/SiO2/Poly-Si/WSi2/Poly-Si multilayer structure were deposited sequentially on separate wafers and subjected to x-ray diffraction analysis in the as deposited and annealed conditions to determine the changes in strain occurring in WSi2. Samples cut from wafers containing all the layers were capped with a 25nm thermal oxide and the strain in the WSi2film was also analyzed by XRD. The change in strain of the WSi2layer, following each step of the fabrication process, was evaluated by the lattice parameter variation of the c axis. The layers of the multilayered film affect the stress in the WSi2. A poly-Si layer on top of WSi2reduces its stress, since it introduces a compressive component, which further decreases upon annealing. It also maintains a Si supply at the poly- Si/SiO2interface, thus, eliminating Si outdiffusion during heat treatment in an oxygen containingambient. Capping the system by a thin oxide layer modifies the stress pattern of the WSi2, which becomes compressive.
Mechanical Properties and Stresses in Thin Gold Films on a Silicon Substrate
Authors: Xie Changjin , Emery Richard D. , Yang Seung-Yong , Tong Wei 
Published: April 2011

ABSTRACTThin gold films with a thickness of 2mm were deposited on a silicon substrate by electron-beam evaporation. The material microstructure and internal stresses of the as-deposited gold films were characterized by scanning ion microscopy, orientation imaging microscopy, and X-ray diffraction. Microtensile tests of free-standing gold film samples were carried out to establish their intrinsic mechanical properties (in connection with a finite element analysis using crystal plasticity). Nanoindentation tests of the thin gold films attached to the silicon substrate were also carried out. Finite element analyses incorporating the crystal plasticity model were used to evaluate the effects of thin film textures, constraints due to the elastic substrate, and internal stresses on the plastic deformation behavior of the thin gold films under indentation at a direction normal to the film surfaces. Results of the combined experimental and numerical investigation indicate that the internal stresses have a strong effect on the uniaxial compression stress-strain behavior of the gold films and it may contribute to the relatively large hardness numbers obtained from the nanoindentation tests.
Constitutive Response of Passivated Copper Films: Experiments and Analyses
Authors: Shen Y.-L. , Ramamurty U. 
Published: April 2011

ABSTRACTThe constitutive behavior of passivated copper films is studied. Stresses in copper films of thickness ranging from 1000 nm to 40 nm, passivated with silicon oxide on a quartz or silicon substrate, were measured using the curvature method. The thermal cycling spans a temperature range from - 196 to 600°C. It is seen that the strong relaxation at high temperatures normally found in unpassivated films is nonexistent for passivated films. The copper film did not show any rate-dependent effect over a range of heating/cooling rate from 5 to 25°C/min. Further analyses showed that significant strain hardening exists during the course of thermal loading. In particular, the measured stress- temperature response can only be fitted with a kinematic hardening model, if a simple constitutive law within the continuum plasticity framework is to be used. The analytic procedures for extracting the film properties are presented. Implications to stress modeling of copper interconnects in actual devices are discussed.
Real-Time in Situ Imaging of the Delamination of thin Ta Films on Si(100) Substrates Via a Synchrotron Radiation Technique
Authors: French B. L. , Bilello J. C. 
Published: April 2011

ABSTRACTThe thermal stress-induced delamination of 500nm polycrystalline Ta coatings on Si(100) substrates was studied via a recently developed real-time in situ imaging technique. This method used white beam synchrotron (on SSRL station 2-2) Laue transmission diffraction topography coupled with simultaneous direct radiography to record the thermomechanical failure modes of the Ta films as a function of temperature. The observations were made using a novel experimental apparatus, consisting of a 600°C hot stage and a portable CCD x-ray imaging/storage system with ~20m m resolution. The system is capable of recording 30 images/sec; hence, at moderate strain rates not only was the morphology of failure evident, but detailed study of the dynamics of delamination was also possible. The mode of failure and the adhesion strength are correlated with the physiochemical nature of the coating-substrate interface, and also with the degree of in-plane/out-of-plane texture of the Ta films. These observations should be capable of extension to the study of a variety of adhesion and cyclic failure issues in thin coatings.
Atomic Force Microscopy and Transmission Electron Microscopy Study of Self-Organized Ordering in Vertically Aligned PbSe Quantum Dot Superlattices
Authors: Raab A. , Springholz G. , Lechner R. T. , Vavra I. , Kang H. H. , Salamanca-Riba L. 
Published: April 2011

AbstractSelf-organized lateral ordering is studied for PbSe/Pb1-xEuxTe quantum dot superlattices as a function of spacer thickness using atomic force microscopy and transmission electron microscopy. It is found that a pronounced hexagonal lateral ordering tendency exist not only for fcc-stacked superlattices but also for those with vertical dot alignment. For the latter case, a best in-plane ordering is observed for Pb1-xEuxTe spacer thicknesses around 160 Å. This is accompanied by a pronounced narrowing of the size distribution to values as low as ±8%. The resulting in-plane dot separations and dot densities are tunable by changes in spacer thickness. Similar marked changes are also found for PbSe dot shape as well as the dot sizes. This provides additional means for the tuning of the optical and electronic properties of the dots.
The influence of many body interactions in the stress-velocity relation of a single dislocation in a 2D lattice
Authors: Robles M. , Mustonen V. , Kaski K. , Patriarca M. 
Published: April 2011

AbstractThe stress-velocity relation of a single dislocation moving in a 2-D lattice has been studied using interactive molecular dynamic simulations. A hybrid interatomic model potential which couples Lennard-Jones(LJ) potential and the Embedded Atom Model (EAM) potential, is used to include radial and many body interactions. Both parts are assembled by a parameter so that the potential can be changed to describe a pure radial interaction to a strong many body interaction in a continuous way. Setting up a constant-stress scenario, the movement of a single dislocation is tracked from zero velocity state, up to a terminal velocity state. The external stress vs. terminal velocity curves have been obtained in the subsonic regime for different values of the coupling parameter. Non-linear relations are found velocity regime 0.1ct to 0.6ct, where Ct is the transverse speed of sound. Results have been analyzed using an augmented Peierls model to seek the connection between atomic scale, continuum variables and the limiting speed of dislocations
Determination of Total Energy Tight Binding Parameters from First Principles Calculations Using Adaptive Simulated Annealing
Authors: Froseth Anders G. , Derlet Peter , Hoier Ragnvald 
Published: April 2011

AbstractEmpirical Total Energy Tight Binding (TETB) has proven to be a fast and accurate method for calculating materials properties for various system, including bulk, surface and amorphous structures. The determination of the tight binding parameters from first-principles results is a multivariate, non-linear optimization problem with multiple local minima. Simulated annealing is an optimization method which is flexible and “guaranteed” to find a global minimum, opposed to classical methods like non-linear least squares algorithms. As an example results are presented for a nonorthogonal s,p parameterization for Silicon based on the NRL tight binding formalism.
Salt-Induced Block Copolymer Micelles as Nanoreactors for the Formation of CdS Nanoparticles
Authors: Zhao Hanying , Douglas Elliot P. 
Published: April 2011

ABSTRACTA novel preparation method of CdS nanoparticles in the core or corona of micelles is presented. Poly(styrene-block-2-vinylpyridine) (PS-b-P2VP) and cadmium ions form aggregates of single micelles, called compound micelles, upon addition of the cadmium acetate salt into a solution of the block copolymer in tetrahydrofuran. The growth of CdS nanoparticles is confined to the core of single micelles after introduction of hydrogen sulfide gas into the solution. UV-visible spectroscopy, fluorescence spectroscopy, and transmission electron microscopy were employed to characterize the prepared core-embedded CdS nanoparticles. Corona-embedded CdS nanoparticles were prepared by dropping the core-embedded CdS nanoparticles into water with a low pH value. The location change of the CdS nanoparticles was accompanied by a structural change of the micelles, a change from compound micelles to single micelles. In a single micelle, CdS nanoparticles distribute randomly in the corona. The size of the nanoparticles increases slightly after the transition.
Nanostructuring of Multilayers by a Thermally Driven Self Assembling Process
Authors: Herweg C. , Dreyer S. , Troche P. , Hoffmann J. , Sievers S. , Lang C. , Freyhardt H. C. 
Published: April 2011

AbstractMultilayers consisting of two immiscible components (e.g. Fe/Ag Fe/Au or Ni/NiO) could by transformed by an annealing process into a nanostructured system of non statistically distributed nearly spherical particles in a surrounding matrix of the complementary component. The non statistical arrangement of the particles and the dynamics of the disintegration process strongly depend on the initial interface energy, i.e. the local interface curvature and the local interfacial stress. Detailed microstructure investigations of the different systems are used to interpret the measured transport properties.
Hydrogen Storage Capacity Improvement of Nanostructured Materials
Authors: Lawrence Jeremy , Xu Gu 
Published: April 2011

AbstractSafe, lightweight, and cost-effective materials are required to practically store hydrogen for use in portable fuel cell applications. Compressed hydrogen and on-board hydrocarbon reforming present certain advantages, but their limitations must ultimately render them insufficient. Storage in hydrides and adsorption systems show promise in models and experimentation, but a practical medium remains unavailable. To study hydrogen storage properties a new volumetric testing apparatus was designed and constructed. Adsorption conditions are evaluated up to pressures exceeding 250 bar and a broad range of temperatures. RF sputtering was used to introduce metals to carbon nanotubes with the aim to enhance hydrogen storage. Here we show a significant improvement in the gravimetric storage density over that of as-prepared single-wall nanotube samples that may be due to the unique interface introduced.