bluuebunny/crossref_metadata_2025_split huggingface dataset:
Annealing Effects on Interfacial Fracture of Gold-Chromium Films in Hybrid Microcircuits
Authors: Moody N. R. , Adams D. P. , Volinsky A. A. , Kriese M. D. , Gerberich W. W. 
Published: April 2011

ABSTRACTIn this study, stressed overlayers and nanoindentation were used to study the effect of elevated temperature on the resistance to interfacial fracture of gold-chromium films in hybrid microcircuits. The samples were prepared by sputter deposition of gold films and chromium adhesive layers onto sapphire substrates. Some films were left in the as-deposited condition for testing. Others were annealed until either most or all the chromium adhesive layer had diffused from the substrate interface. Stressed overlayers and nanoindentation were then used to drive interfacial delamination and blister formation. From these blisters, interfacial fracture energies were determined using mechanics-based models modified for multilayer film effects. The results clearly showed that the chromium interlayers increased interfacial fracture energy. However, they showed an even greater increase in fracture energy after diffusion had reduced the continuous chromium adhesion layer to a solid solution of gold and chromium, suggesting two different mechanisms act to control resistance to interfacial fracture in these films.
Interface Properties of Ceramic Composites at High Temperature
Authors: Zhou X.-F. , Marston C. , Nutt S. R. 
Published: April 2011

ABSTRACTFor high-temperature performance of ceramic composites, interfaces are designed to provide toughness through debonding while resisting thermal oxidation in aggressive environments. Thus, the evaluation of interfacial properties at high temperatures is of critical importance. In recent work at USC, interfacial properties were measured at high temperatures by single fiber pushout tests. Six advanced ceramic composites were selected to perform pushout testing at 20–1000°C. Variation in interface designs and effects of thermal history were evaluated with respect to interface failure strength. At higher temperatures, the average interfacial bond strength was often higher. SEM observations were correlated with pushout measurements to evaluate the interfacial behavior.
Effect of Self-Assembling Monolayers (SAMs) on Ice Adhesion to Metals
Authors: Peng S. L. , Petrenko V. F. , Arakawa M. 
Published: April 2011

ABSTRACTIn this research we used an original method to study the role of hydrogen bonding in ice adhesion and to minimize the effect of this mechanism on ice adhesion. We coated metals (Au and Pt) with a mono-molecular layer of specific organic molecules that had either strong hydrophobic properties (CH3(CH2)11SH) or strong hydrophilic properties (OH(CH2)11SH). To determine the contribution of hydrogen bonding to ice adhesion, self-assembling monolayers (SAMs) of varying degrees of hydrophobicity/hydrophilicity were created by mixing the hydrophobic and hydrophilic components. All of the SAMs were composed of similar molecules that differed only in their outermost groups, OH- and CH3-. Thus, when the SAMs were grown on the same substrate (almost atomically smooth metal coatings), any differences in their adhesion to ice were due to differences in the hydrogen bonding between the ice and SAMs. The SAMs structure and quality were examined with scanning force microscopy (SFM) and the degree of the SAM's hydrophobicity/hydrophilicity was characterized by the contact angle of water on the monolayers. We then froze water on the SAMs and measured the shear strength of the ice/SAM/metal interfaces. Possible damage to the interfaces was examined with SFM after the ice had melted. We found a good correlation between the contact angle of water and the ice adhesion strength and determined the fraction of ice adhesion caused by hydrogen bonding.
Ultrathin Alumina Films on Metallic Substrates: Structure and Metal Adsorption
Authors: Jennison Dwight R. , Bogicevic Alexander 
Published: April 2011

ABSTRACTFirst principles density functional calculations are used to study the structure and properties of ultrathin films of alumina on Al(111) and Ru(0001) substrates. We focus on ∼5 Å two O-layer films, naturally produced by oxidizing NiAl, Ni3Al, and Al deposited on Ru(0001). The interface consists of chemisorbed l×1 oxygen on the underlying metal [1], with a nearly coplanar layer of Al2O3 above. The lowest energy structure of the Al-sublattice is found to consist of zig-zag rows of octahedral and tetrahedral Al ions, resembling the bulk κ-phase. Eleven different adsorbed metals, spanning the periodic table, have been studied [2]. At low coverage the bond is purely ionic; at high coverage most metals bind principally by polarization. Contrary to speculations, isolated vacancies are found on MgO(100) not to directly promote metal nucleation [3], and we suggest this behavior is general. However, ad-OH is found not only to promote island nucleation, but can also, in high concentrations, produce wetting of alumina by Cu [4].
Wetting Transitions of Grain Boundaries
Authors: Blendell John 
Published: April 2011

ABSTRACTIt has been shown that the concepts used to determine the equilibrium shape of crystals can be extended to determine the conditions under which grain boundaries will be fully wetted, partially wetted, or not wetted by a second phase. Recent experimental observations on the equilibrated morphologies of solid or fluid wetting phases along grain boundaries, reveal features that are predicted, and in some cases required, by this construction. Theory distinguishes between cases where surfaces are smoothly curved or where there are facets, edges and corners. In the latter case the conventional comparison of the energy of the original grain boundary with the sum of the surface energy of the two surfaces of the wetting layer leads to erroneous predictions. The correct predictions are obtained by comparing the Wulff shape of the grain boundary (the interfacial energy minimizing shape for a fixed volume of material) with a carefully defined sum of Wulff shapes of the surfaces of the wetting layer. Where orientations that are wetted join with those that are not, there is almost always an abrupt change of orientation. Faceting on two hierarchical levels can occur. Microscopic morphology changes along macroscopically curved surfaces follow well defined rules predicted by theory. The analogy between the thermodynamics of interface faceting and phase transformations allows the well known concepts of phase equilibria to be used to understand the predicted structures. The predictions of the model will be used to identify the nature of the faceting observed in alumina in the presence of a second phase.
Enhancing Oxidation Performance by Control of Interfacial Segregation and Microstructural Design
Authors: Alexander Kathleen B. , Pint Bruce A. , Tortorelli Peter F. 
Published: April 2011

ABSTRACTThermally-grown oxide scales on high temperature alloys can provide oxidation protection if they are slow-growing, dense and adherent to the substrate. The factors affecting the integrity of the metal/oxide interface during dynamic oxidation processes are complex and include interfacial segregation, interface morphology, near-interface substrate properties, as well as the development of stresses in the growing oxide scale. Minor additions of reactive elements (RE) to the base metal have been shown to improve the oxidation performance of many high temperature materials. Studies on a variety of alloys have shown that the presence of reactive elements in the alloy affects segregation processes at both the metal/oxide and oxide/oxide interfaces. Whereas segregation to the metal/oxide interface can affect the scale adherence, segregation to the oxide/oxide interfaces in RE-containing systems has been proposed to result in changes in transport mechanisms as well as changes in the scale microstructure itself. High spatial resolution analytical electron microscopy techniques have been used to provide information on the microstructure and microchemistry of the scale and the metal/oxide and oxide/oxide interfaces. In general, in systems which exhibit improved oxidation performance, a consistent set of interfacial segregation phenomena and microstructural features were observed. Examples will be shown from a variety of nickel- and iron-based alumina formers. These kinds of studies, combined with traditional scanning electron microscopy studies of oxide scales can lead to the development of a more complete link between RE doping, interfacial segregation, interfacial/scale microstructure, and oxidation performance.
Ab-Initio Study of the Local Bonding at Metal-Ceramic Heterophase Boundaries
Authors: Köstlmeier S. , Elsässer C. 
Published: April 2011

ABSTRACTThe adhesion geometries of the (100) heterophase boundaries between the metals Al or Ag and spinel (MgAl2O4) were determined by density-functional calculations employing a mixed-basis pseudopotential method. The results compare well with high-resolution transmission-electronmicroscopy studies which were carried out in parallel. An analysis of the calculated electronic structures shows that the strong adhesion of Al on spinel is mediated by directional bonding. The comparatively weak interaction of spinel with Ag is dominated by polarization effects which can be classified as originating from an image-charge interaction. Additionally, the effects of changes in stoichiometry and of segregated substitutional atoms at the interface were analyzed in terms of the excess of the corresponding component at the interface. The implications for the geometric structure and the related mechanical properties at the metal-ceramic junctions are discussed.
Molecular Simulations of Tilted Chain Crystal - Amorphous Interfaces in Polymers
Authors: Gautam S. , Balijepalli S. , Rutledge G. C. 
Published: April 2011

ABSTRACTSemi-crystalline polymeric materials exhibit metastable interfaces which must simultaneously feature molecular connectivity through chain bonding and disorder across the interface. To address this, off lattice molecular simulations have been constructed to capture the structure and properties of crystal-amorphous interfaces in polyethylene with freely rotating chains. Monte-Carlo simulations were performed on systems having {001 }, {201} and {502} interfaces (polymer chains tilted to the lamella normal by 0°, 34.4° and 41° respectively.)Results of the simulations reveal changes in interfacial structure with variation in the chain-tilt angle. The degree of tight folding decreases with increasing tilt, from predominantly [110] loops in the {001} interface to [200] and [310] loops on the other interfaces. The topology shifts towards an increase in loosely folded loops along with longer bridges and tails. The results also compare well with a Gaussian chain length distribution model. The {201} interface exhibits the lowest interfacial energy, in apparent agreement with experimental data.
Atmoic-Scale Control of Oxide Substrate Surface/Termination and Novel Heteroepitaxial Growth
Authors: Yoshimoto Mamoru , Mizuno Keisuke , Miyahara Takafumi 
Published: April 2011

AbstractAtomic-scale surface/termination of single-crystal oxide substrates were examined by coaxial impact collision ion scattering spectroscopy (CAICISS) and atomic force microscopy (AFM). CAICISS enabled us to determine the terminating atomic species and their arrangements of single crystal oxide substrates and epitaxial oxide films. Through thermal-annealing of the single crystal oxide substrates, atomically flat terrace and stepped structures were developed on the surface. The molecular layer-by-layer growth was verified by in situ monitoring of reflection high energy electron diffraction (RHEED) intensity oscillation. The atomic-scale substrate engineering made it possible to attain the novel heteroepitaxial growth such as step-decoration epitaxy resulting in the nanowire structures and diamond epitaxy on the ultrasmooth sapphire substrate. The diamond films could be grown epitaxially only on the atomically flat sapphire substrates by pulsed laser ablation of graphite. The novel application of the ultrasmooth sapphire substrate to the AFM observation stage for DNA molecules was also presented.
Si/SiC UHV Direct Wafer Bonded Interface Structure
Authors: Kim M.J. , Xu Hong , Liu R.-J. , Cox M.J. , Carpenter R.W. 
Published: April 2011

AbstractPlanar (001)Si/(0001) Si-terminated 6H-SiC interfaces were synthesized by UHV diffusion bonding of cleaned, on-axis and vicinal wafers at 1100°C for 5 hours, at MPa pressure. The interfaces were crystalline up to their defining plane, without nanospectroscopically detectable impurities. The crack opening tests showed the interfaces were stronger than the Si substrates. Oxygen on the substrate surfaces resulted in silicon carbide on insulator (SiCOI) interface formation.
Low-Pressure Chemical Vapor Deposition of Borosilicate Glasses and their Application to Wafer Bonding
Authors: Hansen Darren M. , Moran Peter D. , Kuech T. F. 
Published: April 2011

AbstractThe essential features of the deposition process and the film properties of borosilicate glasses are presented here as an alternative to pure SiO2in wafer bonding and compliant substrates. While the deposition of SiO2 is a well-studied system, the deposition of boron-doped films is less understood. The deposition rate of the SiO2 mole fraction in the films was accelerated by the presence of trimethylborate and oxygen and this is associated with an increased adsorption of the tetraethylorthosilicate related precursor in the presence of boranols. Typical deposition conditions result in borosilicate glass films with an r.m.s. roughness of ∼0.5 nm as measured by atomic force microscopy. Annealing the films at temperatures above 550°C reduces the film roughness via glass reflow. Room temperature bonding of these films was achieved after a 250 WO2 plasma surface treatment. Fourier-transform infrared investigations of the bonded interface revealed the importance of the role of surface OH and H2O groups in the bonding of these films.
The Effect of Stress in the PdGe Mediated Solid Phase Epitaxial Growth of Ge on GaAs
Authors: Radulescu Fabian , McCarthy John M. 
Published: April 2011

AbstractThe residual stress and the microstructure associated with it were studied in connection with the Pd-Ge ohmic contact formation on GaAs. Evaporated Pd (20 nm) / Ge (150 nm) / Pd (50 nm) thin film stacks on GaAs were annealed at various temperatures and the resulting microstructures were investigated by transmission electron microscopy (TEM). Micro-cantilever beam structures were fabricated with a focused ion beam (FIB) workstation and the residual stress present was calculated from the deflection magnitude. It was found that Ge solid phase epitaxial (SPE) growth on GaAs is associated with a stress relaxation of the thin film system. A new model that suggests the tensile stress induced by the intermediate layer may play an important role in the SPE growth mechanism is proposed. Other cases of solid phase heteroepitaxial growth with an intermediate medium, such as Ge/Au/Si, Co/Ti/Si (the TIME method) and Co/SiOx/Si (the OME method) are discussed in light of this newly proposed model. Also, the possibility of using controlled stress to engineer new methods for growing SPE based heterostructures will be presented.
MBE Growth and Ultrahigh Temperature Processing of High-Quality AlN Films
Authors: Fan Z.Y. , Rong G. , Newman N. , Smith David J. , Chandrasekhar D. 
Published: April 2011

AbstractMolecular beam epitaxial growth of AlN on sapphire and 6H-SiC has been performed utilizing mono-energetic activated nitrogen ion beams (2-80 eV kinetic energies). The growth temperature of AlN in MBE is found to be limited by the sticking coefficient of incident reactants. The combination of elevated growth temperatures (1050-1150°C), high kinetic-energy reactive nitrogen (>40 eV) and post-growth thermal processing (1150-1350°C) produces high-quality AlN thin-f ilms with narrow rocking curve widths (<2 arcmin) and low dislocation densities (<∼3×108cm−2). In contrast, the use of in-situ step anneals during synthesis did not achieve similar quality materials.
The Use of AlN Interlayers to Improve GaN Growth on A-Plane Sapphire
Authors: Koleske D.D. , Twigg M.E. , Wickenden A.E. , Henry R.L. , Gorman R.J. , Freitas J.A. , Fatemi M. 
Published: April 2011

AbstractThe lack of a suitable, lattice matched substrate for the growth of the group III nitrides typically restricts GaN film growth to substrates such as sapphire or SiC, despite the large lattice and thermal mismatch. With the use of AlN or GaN nucleation layers (NL), GaN films of sufficient quality have been produced for blue LEDs. However, for laser and large-area microwave device applications, the large number of dislocations (> 108 cm−2) limit device performance, and techniques are desired to reduce dislocation density during the growth process. Here, we demonstrate how low temperature AlN interlayers (IL) sandwiched between high temperature (HT) GaN layers can be used to improve the electrical, optical, and structural properties of Si doped GaN films. A nearly two-fold increase in mobility is observed in Si doped GaN grown using 5 AlN IL compared to GaN grown on a single AlN NL. For GaN films grown on multiple AlN IL, cross-sectional transmission electron microscopy images reveal a significant reduction in the screw dislocation density and photoluminescence spectra reveal a reduction in yellow band intensity. An analysis of the electrical data based on a single donor/single acceptor model suggests that the improved electron mobility is the result of a reduced acceptor concentration in the top GaN film. The reduction in the calculated acceptor concentration may be associated with the reduction of the screw dislocation density.
Photoluminescence and Photoluminescence Excitation Mechanisms for Porous Silicon and Silicon Oxynitride
Authors: Liu Xingsheng , Calata Jesus Noel , Liang Houyun , Shi Wangzhou , Lin Xuanyin , Lin Kuixun , Qin G. G. 
Published: April 2011

AbstractThrough a comparative study of the light emission and light excitation property of porous silicon (PS) and Si oxide, photoluminescence (PL) and photoluminescence excitation (PLE) mechanisms for blue-light-emitting PS are analyzed. Strong blue light (445nm) and ultraviolet light (365nm) emission from silicon-rich silicon oxynitride films at room temperature were observed. An analysis of the PL and PLE spectra of PS and Si oxide indicated that for blue-light emission from PS, there are two types of photoexcitation processes: photo-excitation occurring in nanometer Si particles (NSP's) and in the Si oxide layers covering NSPs, and radiative recombination of electron-hole pairs taking place in luminescence centers (LCs) located on the interfaces between NSP's and Si oxide and those inside Si oxide layers. The PL spectra of silicon-rich silicon oxynitride films implies that the PL originated from some LCs in SiOx and SiOxNy:H, while PLE spectra indicates that photoexcitation occurs in NSPs, SiOx and SiOxNy:H. The 365 nm band is attributed to the former two photoexcitation processes and the 445 nm one to the third process. As such, the quantum confinement/luminescence center model appears to be a satisfactory model in explaining the experimental results.
Study of Raman Scattering on InP/InGaAs/InP HEMTs
Authors: Radhakrishnan K. , Patrick T.H.K. , Zheng H.Q. , Yoon S.F. 
Published: April 2011

AbstractRaman scattering studies have been recently used to relate the strain in the semiconductor layer structure with the line shape of allowed modes. It can yield important information about the nature of the solid on a scale of the order of a few lattice constants. It can also provide an evaluation on the carrier concentration in the channel layer of high electron mobility transistors (HEMTs). In this investigation, Raman scattering was used to study the effect of varying the In mole fraction (x) from 0.53 to 0.81 in the InxGa1−xAs channel layer of InGaAs/InP heterostructures. The effect of varying the doping concentration in the donor layer from 6×1017/cm3 to 2.5×1018/cm3, and the effect of varying the In0.75Ga0.25As channel thickness from 140 Å to 260 Å are also reported.A two-mode Raman characteristic for all InxGa1−xAs/InP HEMTs is clearly seen, with the two LO modes (InAs-like LO and GaAs-like LO) located at 229cm−1 and 268.6cm−1, respectively. At a Raman frequency of 347cm−1, a small peak is observed due to InP LO mode. As the In composition increases from 0.53 to 0.81, the InAs-like LO mode peak intensity increases while that of GaAs-like LO mode decreases. The peak intensity ratio of InAs-like LO mode and GaAs-like LO mode increases from 0.78 to 1.10. By increasing the doping concentration in the donor layer (ND), there is also an increase in the carrier concentration in the InGaAs channel assuming that the donors are fully ionised. The coupled mode between the InGaAs longitudinal optical phonons and electrons in the InGaAs channel shifts continuously to a low wave number with the increasing ND in the InP donor layer. The increase in the lnGaAs channel thickness from 140Å to 260Å causes the InAs-like LO mode peak to shift to a lower wave number from 235.5 to 228.5cm−1. There is no change in the GaAs-like LO peak position located at 268.4cm−1.
Microstructural Characterization of Antimonide Based III-V Compounds and their Effect On Electro-Optical Properties of Substrate Materials and Devices
Authors: Dutta P.S. , Gutmann R.J. , Charache G.W. , Wang C.A. 
Published: April 2011

AbstractThis paper presents some of the widely used characterization tools for antimonide based III-V compounds, focusing on characterization of defects that limit device operation. The effect of microstructure on the electro-optical properties of GaSb and GaInAsSb important in devices is emphasized.
Cathodoluminescence from Inx Ga1−x as Layers Grown on GaAs Using a Transmission Electron Microscope
Authors: Yamamoto N. , Mita T. , Heun S. , Franciosi A. , Bonard J.-M. 
Published: April 2011

AbstractInxGa1−xAs epilayers grown on GaAs(100) were studied by cathodoluminescence (CL) spectroscopy and imaging technique with 0.8 nm spectral resolution, using a transmission electron microscope. Linear features appear in the monochromatic CL image taken by the emission from the InxGa1−x.As layers, and do not appear in those from the GaAs layers. There is no direct correlation between the dark-line contrast in the panchromatic CL image (due to misfit dislocations) and the strong line contrast in the monochromatic CL images of the InxGa1−xAs layers. A peak wavelength shift in the CL spectrum was observed as the electron probe was moved across the linear features. The linear features also appear in a thin sample where the misfit dislocations are removed by ion milling, which clearly reveals that the strong line contrast is not directly due to the misfit dislocation. From those results the linear features in the monochromatic CL image are considered to be due to compositional fluctuations of the In concentration in the InxGa1−xAs layer.
Optically Induced Condensation of Impurity Excitations in Transparent Solids
Authors: Manykin E. A. , Ojovan M. I. , Poluektov P. P. 
Published: April 2011

AbstractThe interaction of electromagnetic radiation with impurities in transparent solids is studied for the case when interactions between excitations become significant. It is shown that intense optical radiation leads to condensation of the excitations of impurities. The condensed excited state, consisting of excited impurities, is an energetically favourable phase, which minimises the energy of the system. Nevertheless, condensation, as a rule, causes mechanical stresses, in some cases followed by either redistribution of impurities or even breaches of solids.