bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoluminescence study of deep-level defects in undoped GaN
Authors: Reshchikov M. A. , Morkoç H. , Park S. S. , Lee K. Y. 
Published: April 2011

AbstractWe studied photoluminescence (PL) and PL excitation (PLE) spectra in a large number of undoped GaN layers grown on sapphire by molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD) and hydride vapor phase epitaxy (HVPE). The HVPE-grown GaN layers with thickness of ~200 m m were separated from the sapphire substrate by laser lift-off and represented bulk freestanding templates of very high quality. Identical position and shape of the YL band were reproduced in many samples grown by MBE and MOCVD: maximum at ~2.23 eV and full width at half maximum (FWHM) of about 460 meV at room temperature. However, in some samples the band maximum was observed at about 2.0 eV. The freestanding templates reveal a broad band (FWHM=530-680 meV) whose position depends on excitation energy and intensity, varying from 2.22 eV to 2.47 eV. PLE spectra taken from various samples represented a broad band with apparent maximum at about 3.3 eV. For below-gap excitation, the intensity of the YL band was independent of temperature except for the one in the freestanding template. The latter was temperature independent above 60 K, however at lower temperatures the PL intensity decreased by 5 times. An activation energy of 15 meV has been determined that is related to a barrier in the adiabatic potential in the excited state of the defect.
Exciton Spectra of AlN Epitaxial Films
Authors: Onuma T. , Chichibu S. F. , Sota T. , Asai K. , Sumiya S. , Shibata T. , Tanaka M. 
Published: April 2011

AbstractExcitonic resonance energies in a C-plane AlN epilayer on the (0001) sapphire substrate grown by low-pressure metalorganic vapor phase epitaxy were determined as a function of temperature by means of optical reflectance (OR) and cathodoluminescence (CL) measurements. The OR spectra exhibited distinct reflectance anomalies at the photon energies just above the multiple internal reflection fringes, and the spectral lineshape was fitted considering A (???u7v7c) and BC (???9v,???17v7c) exciton transitions. The energies of them at 0 K were obtained to be 6.211 and 6.266 eV, giving the crystal field splitting (Δcr) of approximately 55 meV. The AlNfilm exhibited an excitonic emission even at 300 K, which is due to the small Bohr radius of excitons and large longitudinal optical phonon energies. The Einstein characteristic temperature Q E was estimated to be 580 K.
Growth of AlN bulk crystals from the vapor phase
Authors: Schlesser Raoul , Dalmau Rafael , Yakimova Rositza , Sitar Zlatko 
Published: April 2011

AbstractAlN single crystals were grown by two different vapor phase processes: by vaporization of metallic Al in a nitrogen atmosphere, or by sublimation of an AlN source. Growth experiments were carried out under quasi-stagnant flow conditions, with typical flow rates of 100 sccm at reactor pressures ranging from 300 to 700 Torr. Growth temperatures ranged from 1800 to 2300°C. In Al vaporization experiments, the crystal shape and fastest growth direction was found to strongly depend on the growth temperature: at relatively low temperatures (1800-1900°C) long needles were grown, temperatures around 1900-2000°C yielded twinned platelets, while c-platelets were formed at temperatures above 2100°C. These c-plates grew at a rate of 5 mm/hr in the c-plane. When using AlN as a source material, growth rates were considerably slower, however, long-term stability of the Al flux was greatly improved. Seeded growth was demonstrated under these conditions. All grown single crystals were transparent and virtually colorless. Analytical results indicated very high crystalline quality and dislocation densities lower than 104cm-3.
Properties of 2D and 3D Dielectric Structures Fabricated by Electrochemical Dissolution of III-V Compounds
Authors: Tiginyanu I.M. , Langa S. , Christophersen M. , Carstensen J. , Sergentu V. , Foca E. , Rios O. , Föll H. 
Published: April 2011

AbstractPorous layers and membranes representing 2D and 3D dielectric structures were fabricated on different III-V compounds (GaAs, InP, GaP) by electrochemical etching techniques. Nonlithographically fabricated ordered nanopore arrays in InP are reported for the first time. We show that the reflectance from nanostructured InP is lower than that from bulk InP in the spectral interval 1.5-2.2 eV. The artificial anisotropy induced by nanotexturization was studied in porous GaP membranes and the refractive indices for ordinary and extraordinary beams were evaluated.
Transmission Characterization of Drilled Alternating-Layer Three-Dimensional Photonic Crystals
Authors: Kuramochi Eiichi , Notomi Masaya , Yokohama Itaru , Takahashi Jun-ichi , Takahashi Chiharu , Kawashima Takayuki , Kawakami Shojiro 
Published: April 2011

AbstractWe propose a new three-dimensional photonic crystal structure or drilled alternating-layer photonic crystal (DALPC), which can be fabricated by a combination of the deposition of alternating layers of dielectric films and one-time dry etching. Our band calculation predicts that the DALPC has a photonic band gap (PBG) in all directions. We fabricated a Si/SiO2 DALPC by electron beam lithography, bias sputtering, and fluoride-gas electron cyclotron resonance etching. We measured the light transmission of the DALPC sample in both the in-plane and vertical directions. We observed a transmission minimum around the 1.4-µm-wavelength for all measured directions and TE/TM polarizations, which demonstrated a potential of the DALPC as a three-dimensional PBG material.
Interference lithography for 3D photonic band gap crystal layer by layer fabrication.
Authors: Feigel A , Kotler Z. , Sfez B. , Arsh A. , Klebanov M. , Lyubin V. 
Published: April 2011

AbstractWe present fabrication of 3D photonic band gap woodpile crystals from photosensitive chalcogenide glass with the help of interference lithography and layer by layer construction. The alignment method is described, which is scalable to extremely small feature sizes required for photonic crystals in the visible region.
Selective Deposition of Two-Dimensional Colloidal Arrays on Patterned Polyelectrolyte Multilayer Templates
Authors: Zheng Haipeng , Lee Ilsoon , Rubner Michael F. , Hammond Paula T. 
Published: April 2011

AbstractA new method for the patterning of colloidal particles on polymer templates is presented. A polyelectrolyte multilayer film is deposited onto a chemically patterned monolayer surface, which is further used as a functional template to direct the deposition of charged particles through electrostatic and secondary interactions. After modified by an opposite charged surfactant, the particles change their deposition selectivity from the polyelectrolyte surface to a neutral ethylene glycol monolayer surface. Based on the different selectivity, we have first demonstrated a new approach to direct two component colloidal arrays onto a patterned polyelectrolyte multilayer template.
Direction Dependent Grain-Interaction Models for the Diffraction Stress Analysis of Thin Films
Authors: Welzel Udo , Leoni Matteo , Mittemeijer Eric J. 
Published: April 2011

ABSTRACTThe well-known grain-interaction models for the description of the macroscopic elastic behaviour of polycrystalline specimens, for example the models due to Voigt and Reuss, may be applied to bulk specimens, but they are generally not suitable for thin films because they imply macroscopic elastic isotropy of the body. A thin film is usually at most transversely elastically isotropic, even in the absence of texture. A recently elaborated, alternative model for grain-interaction in thin films, adopting grain-interaction assumptions first given by Vook and Witt (J. Appl. Phys. 7, 2169 (1965)), is able to predict the transversely isotropic elastic behaviour. Although this model is more appropriate for thin films than traditional models, it still imposes extreme grain-interaction assumptions, which are in general not compatible with the true elastic behaviour of real specimens. In this paper a more general approach to grain-interaction in thin films is proposed.
Adaptive Protocol for Robust Estimates of Coatings Properties by Nanoindentation
Authors: Jennett Nigel M. , Bushby Andrew J. 
Published: April 2011

ABSTRACTThe determination of the elastic modulus and hardness of a wide range of coating systems has been studied recently in the EC project INDICOAT. This paper describes a protocol for determining the coating properties, which has been developed and tested in that project. The procedure contains simple to implement strategies to evaluate the response of the coating and design a suitable series of indentation experiments that enable a reasonable estimation of ‘coating-only’ properties. The protocol directs how the experimental design adapts the experimental parameters to each sample. An adaptive protocol is essential to cope adequately with the different indentation responses. Indentation response depends, for example, on coating thickness and the relative properties of coating and substrate and creep response. The protocol also has to adapt itself so that it can reliably target the range of indentation depth with respect to the coating thickness necessary to obtain the coating properties from the composite indentation response. Results presented show that the parameters and approach for measurement of hard coatings are very different to those required for soft or ductile coatings. The systems studied are DLC on tool steel, Au on Ni, aluminium oxide on Ni and aluminium on optical glass (BK7).
Nanoindentation and Magneto-Optical Study of Oxidized Co Thin Films
Authors: Mishra S. R. , Rho J. , Sherfy G. , Roy M. , Buckner T. 
Published: April 2011

ABSTRACTWe have studied the mechanical and magneto-optical properties of postdeposition oxidized Co thin films. Oxidization process leads to the formation of double-layered structure of cobalt oxide on top of metallic cobalt. The nanoindentation measurements show decrease in hardness and Young's modulus at low annealing temperature and are related to increasing porosity of the film. The magneto-optical Kerr effect (MOKE) reveals dependence of the MOKE spectra on annealing temperature. The increased coercivity of the annealed films has been observed by MOKE and is related to the structure of the film.
Nanoindentation and Nanowear Studies of Sputter-Deposited Ultrathin Tin Oxide Films on Glass Substrates
Authors: Wang J. G. , Stahley M. E. , Pantano C. G. , Yang D. H. , Anderson T. , Kuhn L. 
Published: April 2011

ABSTRACTTin oxide thin films on glass are used in a variety of applications ranging from transparent conductors to coupling layers to wear resistant coatings. The mechanical properties and wear resistance are crucial to most applications of tin oxide films. In the present study, ultrathin tin oxide films were sputter-deposited on the two different glass substrates. Nanoindentation, nanoscratch and nanowear experiments were performed on the tin oxide films with different thickness using a Hysitron TriboScope at different loads. Hardness and Young's modulus of elasticity were determined from the depth sensing load-displacement data. A lower friction coefficient was observed on the thinner film using the ramping load scratch test. Critical loads were determined by the ramping load scratch test and multi-slide nanowear tests on the tin oxide film deposited on the alkali contained commercial float glass (LOF-P16) glass. Discussion on the effect of surface chemistry on the mechanical properties was made.
Infrared Photoelastic Study of Thin-Film-Edge-Induced Stresses in Silicon Substrates
Authors: Peng H. J. , Wong S.P. , Zhao Shounan 
Published: April 2011

ABSTRACTThe stress distribution in silicon substrates under a silicon dioxide thin film edge, long oxide thin film stripes and long oxide window structures have been studied using the infrared photoelastic (IRPE) method. The experimental IRPE stress fringe patterns were compared with the simulated patterns based on an analytic solution we obtained recently for the stress distribution under a thin film edge in isotropic substrates. Dependence of the stress distribution in these structures on the geometrical parameters such as the stripe width, window width, and substrate thickness were also studied. The implication of a slight discrepancy between the experimental and simulated IRPE patterns on the singular behavior of stress field in the substrate at the film edge and the concentrated force assumption are discussed.
Residual Stress Measurement in a Pt-Aluminide Bond Coat
Authors: Watanabe Makoto , Mumm Daniel R. , Chiras Stefanie , Evans Anthony G. 
Published: April 2011

ABSTRACTThe residual stress induced in a Pt-aluminide bond coat formed on a single-crystal superalloy has been measured. The stresses arise because of the thermal expansion misfit with the substrate on cooling from the manufacturing temperature. Since the lattice parameters are unknown, the interpretation of diffraction measurements is problematic, and the “wafer” curvature method has been applied. This method required that the substrate thickness be systematically reduced by mechanical thinning. It was also required that curvature measurements be made with the bond coat present as well as after it had been removed by thinning. This approach revealed that the bond coat is in residual tension, 140MPa, consistent with its thermal expansion coefficient, relative to that for the substrate.
Mechanical Properties and Porosity of Organo-Silicate Glass (OSG) Low-k Dielectric Films
Authors: Vella J. B. , Xie Q. , Edwards N. V. , Kulik J. , Junker K. H. 
Published: April 2011

ABSTRACTLow-k material integration issues that plague the microelectronics industry include the compromise in mechanical properties that one incurs in abandoning fully dense silica dieletrics. Typical elastic moduli of OSG low-k dieletric films are 2-10 GPa with corresponding hardnesses of 0.5 to 1.5 GPa. In the present study, the hardness and elastic modulus properties measured by nanoindentation of porous silica based low-k films are correlated with in initial estimates of density using a novel technique of spectroscopic ellispsometry. Transmission electron microscopy and X-ray photoelectron spectroscopy show the structural and chemical similarity of the films. Nanoindentation and spectroscopic ellipsometry results reflect significant deviations in material behavior from that expected from a simple model of silica (SiO2) with included voids or porosity, suggesting that the methyl groups are actively participating in the mechanical and optical properties of the material.
Viscous Creep in Metallic Wires at Elevated Temperatures and Low Stresses.
Authors: Fiala Jaroslav , Kloc Lubos , Sklenicka Vaclav 
Published: April 2011

ABSTRACTViscous creep behaviour of several metals and alloys was investigated at the temperatures close to one half of the absolute melting point and at very low stresses using the technique of helicoid specimens. Due to extremely high sensitivity the technique represents a unique tool for measurement of very low creep strains in reasonable time. Helicoid spring specimens were made of wires of either circular or square cross section. The stress distribution along the wire radius (caused by shear stress loading) and threshold stresses were taken into account, as well as the influence of the surface layer loaded by maximum stress.The experimental results were interpreted as Coble diffusional creep and/or Harper-Dorn dislocation creep. Some data are in a very good agreement with Coble theory especially those obtained on some fine grained materials. For the coarse grained materials is this dependence replaced by large data scattering. Some authors dispute about the role or even the very existence of diffusional creep and offer other explanations. There are many theories trying to describe Harper-Dorn creep mechanism, but none of them is capable to explain all observed properties.The observed effects which cannot be explained by the current theories are discussed (large scatter of creep rates obtained for coarse grain materials, creep rates much higher than those predicted by the diffusional creep theory in some materials, transition stage duration independent of stress but dependent on temperature.Despite the problems in theoretical description, the experiment shows clearly that the viscous creep regime must be considered as an important behaviour of structural materials at conditions of engineering practice.
A Study on the Behavior of Water Absorption of SiOf Thin Films Deposited by Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition Method
Authors: Kim S. P. , Choi S. K. , Park Youngsoo , Chung Ilsub 
Published: April 2011

ABSTRACTFluorinated silicon oxide (SiOF) films were deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECRPECVD). The behavior of residual stress w as studied with water absorption. SiOF film showed compressive stress after deposition. The compressive stress increased after the exposure to room air. Fourier transformed infrared (FTI R) spectroscopy analysis was carried after the water absorption. However, the change of chemical bonding structure was not observed during the water absorption in this study. After the exposu re to room air, the films were kept in dry air. The residual stress returns to the initial value after 1 week. Considering the results of the residual stress and FTIR analysis, it is supposed that the water absorption in this study occurs entirely by physical adsorption of H2O molecules to Si-F bonds on the surface.
A New Force-Displacement Model for Continuous Indentation of Bilayer Materials
Authors: Nayebi A. , El Abdi R. , Mauvoisin G. , Bartier O. 
Published: April 2011

ABSTRACTA new relationship between indentation load and depth in relation to flow stress and strain hardening exponents of film and substrate of bilayers is given. The comparison between the numerical results and those experimentally obtained from known materials, confirms the interest of the proposed model for film characterization of these materials.
Metal Adhesion to <100> Si Substrates with Varying Surface Conditions
Authors: Barbosa Nicholas , Ridley Rodney S. , Strate Christopher H. , Dwyer Robert S. , Grebs Thomas , Vinci Richard P. 
Published: April 2011

ABSTRACTAdhesion in multi-layer thin film structures was measured using the four-point bend technique. The investigation primarily focused on layers found in the backside metalization processes of Power MOSFETs (typically in a DMOSFET or U-MOSFET structure). Variation in metal layer and substrate condition produced changes in the adhesion behavior of the systems of interest. Pt, Cu, and Ti metals were applied to Si and SiO2 surfaces with various roughnesses in order to establish the relative contributions of surface chemistry and roughness variation. G values ranging from 2 – 100 J/m2 were measured and it was found that variation in surface chemistry has a larger impact than roughness on the adhesion strength of the systems investigated. The four-point bend adhesion test was determined to be adequate for the measurement of weak to intermediate adhesion of metals on Si wafers with RMS roughness values on the order of the metal film thickness.
Fracture Behavior of Micro-Sized Specimens Prepared From an Amorphous Alloy Thin Film at Ambient and Elevated Temperatures
Authors: Takashima K. , Tarumi R. , Higo Y. 
Published: April 2011

ABSTRACTFracture behavior of micro-sized cantilever beam type specimens prepared from an electroless deposited Ni-P amorphous alloy thin film has been investigated at ambient and elevated temperatures. Cantilever beam type specimens with dimensions of 10 x 12 x 50 μm3were prepared from an electroless deposited Ni-P amorphous alloy thin film and notches were introduced by focused ion beam machining. Fatigue pre-cracks were introduced ahead of the notches. The introduction of fatigue pre-crack and fracture toughness tests were carried out using a mechanical testing machine for micro-sized specimens. The temperature of the specimen was controlled from room temperature to 473 K using a newly developed heating system. Compared with room temperature, fracture toughness increased approximately 40 % at 373 K but decreased 19 % at 473 K. The increase of fracture toughness at 373 K is considered to be related with the formation of nano-sized crystals and the decrease of fracture toughness at 473 K is considered to be due to the growth of crystals. It is required to consider the fracture behavior obtained in this investigation when designing actual MEMS devices using electroless deposited amorphous films.
In-Situ Mechanical Characterization of a Freestanding 100 Nanometer Thick Aluminum Film in SEM Using MEMS Sensors
Authors: Haque Aman , Saif Taher 
Published: April 2011

ABSTRACTWe present the uniaxial stress-strain response of a freestanding 100 nanometer thick 99.99% pure sputtered Aluminum film with grain size about 60 nanometers, tested in-situ inside a SEM chamber. The specimen is cofabricated with MEMS force and displacement sensors to minimize the experimental setup size, allowing both quantitative and in-situ tests to be performed in SEM and TEM chambers. The experimental results strongly suggest that at this size scale, a) Elastic modulus remains same as the bulk Aluminum, b) Yielding starts at about 625 MPa, and c) Strain hardening effect is absent, which indirectly suggests the deformation at this size scale is not dislocation mechanism based.
Spontaneous Pattern Formation from Focused and Unfocused Ion Beam Irradiation
Authors: Cuenat Alexandre , Aziz Michael J. 
Published: April 2011

AbstractWe study the formation and self-organization of “ripples” and “dots” spontaneously appearing during uniform irradiation of Si, Ge, and GaSb with energetic ion beams. Features have been produced both with sub-keV unfocused Ar+ ions and with a 30 keV Ga+ Focused Ion Beam. We follow the evolution of features from small amplitude to “nanospikes” with increasing ion dose. It appears that the edge of the sputtered region influences the patterns formed, an effect that may make it possible to guide the self-organization by the imposition of lateral boundary conditions on the sputter instability.
Strain Relaxation of He+ Implanted, Pseudomorphic Si1−xGex Layers on Si(100)
Authors: Holländer B. , Mantl S. , Lenk St. , Trinkaus H. , Kirch D. , Luysberg M. , Hackbarth Th. , Herzog H.-J. , Fichtner P.F.P. 
Published: April 2011

AbstractStrain relaxed Si1−xGex buffer layers are of great importance as virtual substrates for Si1−xGex/Si quantum well structures and devices. We apply He+ ion implantation and subsequent annealing on pseudomorphic, MBE-grown Si1−xGex/Si(100) heterostructures with an implantation depth of about 100 nm below the Si1−xGex/Si interface. A narrow defect band is generated inducing the formation of strain relieving misfit dislocations during subsequent thermal annealing. Efficient strain relaxation was demonstrated for Si1−xGex layers with Ge fractions up to 30 at. %. The variation of the implantation dose and the annealing conditions changes the dislocation configuration and the He bubble structure. At a dose of 2×1016 cm−2 a high degree of relaxation is accompanied by a low density of threading dislocations of about 107 cm−2 for a Ge content of 30%. An additional increase of the Ge content can be achieved by annealing in oxygen. The oxidation of Si1−xGex leads to the formation of SiO2 while the Ge atoms are rejected from the oxide leading to a pile-up of Ge below the oxidation front. The heterostructures were analyzed using X-ray diffraction, Rutherford backscattering/channeling spectrometry and transmission electron microscopy.