bluuebunny/crossref_metadata_2025 huggingface dataset:
Si3 N4/SiO2 Multi-Layer Reflecting Stacks for Photonic Switching Applications
Authors: Stephens D.J. , He S.S. , Lucovsky G. , Mikkelsen H. , Leo K.
Published: March 2011

We have fabricated stacked-structures comprised of i) fused silica substrates, and ii) near-periodic Si3N4/SiO2 bi-layers by low-temperature, 250°C, remote plasmaenhanced chemical-vapor deposition. Comparing the reflectance of these structures with model calculations, we have been able to identify the effects on the reflectance spectra of departures from i) exact periodicity, ii) not having the constituent dielectric layers each posses an ideal optical path length, OPL, exactly equal to λcentral/4, and iii) the intrinsic dispersion in the dielectric functions of the oxide and nitride materials. We have prepared quasi-periodic structures in which the OPL of the higher index Si3N4 layer was > λcentral/4, and in which the OPL of the lower index SiO2 layer was < λcentral/4. This promotes a second strong reflectance band at an energy that is approximately two times that of the primary band. Calculations have shown that the reflectance values in this band, and near a reflectance minimum on the high energy side of the band, are both very sensitive to changes in the optical properties of the nitride film. We present calculations that demonstrate the effects on the reflectance of this band by a temperature-induced modulation of the optical properties of the oxide and nitride layers.
The Effects of Halogen Exposure on the Photoluminescence of Porous Silicon
Authors: Lauerhaas Jeffrey M. , Sailor Michael J.
Published: March 2011

Interaction of I2 vapor with luminescent porous silicon (PS) results in a mixed hydrogen/iodine terminated surface. The photoluminescence (PL) of PS is completely quenched upon I2 exposure. Excess iodine can be removed by pumping on the PS for several hours, resulting in partial recovery of the original PL spectrum. Exposing the hydrogen/iodine terminated PS to air results in the accelerated growth of an oxide layer and increased PL. The adsorption of iodine is postulated to induce surface traps that are responsible for the luminescence quenching observed.
Optical Properties of Free-Standing Porous Si Films
Authors: Kanemitsu Y. , Uto H. , Masumoto Y. , Matsumoto T. , Futagi T. , Mimura H.
Published: March 2011

We have studied optical properties of free-standing porous Si thin films fabricated by electrochemical anodization. The average diameter of Si crystallite spheres is evaluated by Raman spectroscopy and transmission electron microscopy. The blueshift of optical absorption spectrum is observed with a decrease in the average diameter of Si crystallites. However, there is no clear size dependence of the peak energy of broad photoluminescence spectrum. Spectroscopic analysis strongly suggests that the photogeneration of carriers occurs in the c-Si core whose band gap is modified by the quantum confinement effect, whereas the radiative recombination of carriers occurs in the near-surface region of small crystallites.
Porous Silicon Nanostructure Revealed By Electron Spin Resonance
Authors: Xiao Y. , McMahon T.J. , Pankove J.I. , Tsuo Y.S.
Published: March 2011

Electron spin resonance (ESR) study of annealed porous Si (PS) samples shows the existence of 20% to 30% of oxygen related Pbl (.Si-Si2O) centers, in addition to the Pb0 (·Si-Si3) centers already reported by other groups. The 29Si hyperfine and superhyperfine lines are well-defined at room temperature. We find that the nanostructure of PS, although twisted as appeared in scanning electron microscopy images, is well aligned with the underlying crystal lattice, and the ESR line broadening is mainly due to the local strain around the dangling bonds and not to the nanoscale column or particle misalignment.
Effect of Preparation Conditions on the Silicon L-Edge In Electrochemically Prepared Porous Silicon
Authors: Buuren T. Van , Tiedje T. , Weydanz W.
Published: March 2011

High resolution measurements of the silicon L-edge absorption in electrochemically prepared porous silicon show that the absorption threshold is shifted to higher energy relative to bulk silicon, and that the shift is dependent on how the porous silicon is prepared. When the porous silicon is made from n-type material with light exposure, the blue shift increases logarithmically with the anodizing current. Porous silicon prepared by anodizing p-type silicon exhibits a blue shift in the L-edge which increases with the time spent in the HF solution after the anodizing potential is turned off. The data are consistent with the quantum confinement model for the electronic structure of porous silicon.
Two-Dimensional Excitons in Siloxene
Authors: Brandt M. S. , Rosenbauer M. , Stutzmann M.
Published: March 2011

The luminescence properties of two different modifications of siloxene are studied with photoluminescence excitation spectroscopy (PLE) und optically detected magnetic resonance (ODMR). The luminescence of as prepared siloxene, which consists of isolated silicon planes, is resonantly excited at the bandgap, indicating a direct bandstructure. The observation of Δm = ±2 transitions in ODMR shows that triplet excitons contribute to the luminescence process. In contrast, annealed siloxene consisting primarily of six-membered silicon rings shows a PLE typical of a material with an indirect bandgap. The ODMR signal of annealed siloxene and of porous silicon show the same Gaussian line with a typical width of 400 G, which can arise from strong dipolar coupling of an electron and a hole ≈ 5Å apart.
Variations in the Photoluminescence Intensity of Chemically and Anodically Etched Silicon Films
Authors: Williams P.S , Kidder J.N. , Yun H. , Crain D. , Pearsall T.P.
Published: March 2011

We are studying the effects of etch conditions on the surface morphology, chemistry, and luminescent properties of porous silicon (PS) films. Luminescent silicon films are produced by chemical etching using solutions of HNO3 in HF and by anodic etching using aqueous HF electrolytes. Films produced by both methods are analyzed and compared using photoluminescence (PL), vibrational, and X-ray photoelectron (XPS) spectroscopies. The initial characterization of PS is performed immediately following the etching process, resulting in oxide-free films (as confirmed by XPS). In chemically etched PS films, the luminescent intensity decreases as the vol. % HNO3 in etch solution increases. Spectral features evolve in the PL spectrum of chemically etched films as the result of aging under ambient conditions and when the films are cooled under illumination. Moreover, we have also found that increased electrolyte convection results in a decrease in photoluminescence intensity of PS films formed anodically. The role of electrolyte flow in modifying the luminescent properties of PS is being evaluated in an etch cell with well-characterized hydrodynamics.
Ion Exchange Effects in Porous Silicon
Authors: Matvienko B. , Basmaji P. , Grivickas V. , Bernussi A.
Published: March 2011

We report an effect of alkaline metal ion incorporation into porous silicon (PS) structure from the electrolyte during anodic etching. Blue shift of the whole luminescence spectrum was obtained as a consequence of ion incorporation. We suggest the presence of zeolite-type structures in PS, as an explanation to the observed properties.
Energy Localisation and Surface Interactions in the Luminescence of Porous Silicon
Authors: Gardelis S. , Dawson P. , Hamilton B.
Published: March 2011

The fundamental mechanisms controlling the light emission from porous Si remain unresolved. In this paper we report attempts to modify the luminescence using a variety of surface processing steps, such as vacuum annealing with subsequent anneals in nitrogen and oxygen, exposure to hydrofluoric acid (HF) and rapid thermal oxidation. Luminescence, infrared absorption, and electron spin resonance (ESR) have all been used to gain more information on the link between the optical emission and the localisation of the electrons in this material system. We present evidence that the silicon dangling bond is the key component in the non-radiative recombination. This is based on measurements shown that hydrogen coverage of the surface is significant because of saturation of the dangling bonds and a subsequent reduction in the competing non-radiative paths rather than as an active component in the radiative transition. Finally, we focus our attention upon the lower energy band which appears in the luminescence spectrum of porous Si (∼0.9eV) by examining its behavior under the surface treatments mentioned above. We found that this luminescence band originates from the surface of the porous layer and its intensity correlates well with increasing oxidation of the porous layer.
The Role of Silicon in Optoelectronics
Authors: Hall Dennis G.
Published: March 2011

This invited paper reviews some of the ways in which silicon technology has been applied in integrated optics and optoelectronics.
Electroluminescence From μc-SiC / Porous Si PN Junctions
Authors: Mimura H. , Futagi T. , Matsumoto T. , Ohta Y. , Kitamura K. , Kanemitsu Y.
Published: March 2011

We have measured electrical properties and electroluminescence (EL) characteristics of the light-emitting diode (LED) based on a pn junction of n-type microcrystalline silicon carbide (μc-SiC) and porous silicon (PS). The μc-SiC/PS pn junctions showed rectification behavior, and a uniform red EL was observed at a forward voltage larger than 15V. From the relationship between the EL intensity and the forward current, the EL mechanism is interpreted as the recombination of electron-hole pairs doubly injected into the PS layer. No degradation was observed in the EL intensity during the measurements over 8 hours. These results means that μc-SiC serves well as a electron injector to the PS.
Monocrystam Disiocationless Si:Ge, Grown from the Helt Wits Gd Impurity
Authors: V.V. Borschensky , D.I. Brinkevich , V.V. Petrov , V.S. Prosolovch
Published: March 2011

The properties of Si grown from the melt having impurities of germanium and gadolinium have been studied by IR-absorption and Hall effect methods.It was stated that Ge and Gd are effective getters for technological impurities of oxygen and carbon in silicon melt. It has been shown that the combined doping by rare earth and isovalent impurities allows to increase the thermostability of dislocationless monocrystals of silicon.
Epitaxial Layers Si: (Sn,Yb) Produced by the Crystallization From the Melt-Solution on the Basis of Sn.
Authors: Brinkevich D.I. , Kazuchits N.M. , Petrov V.V.
Published: March 2011

Epitaxial layers (EL) Si:Sn doped with Yb in the process of liquid phase epitaxy were studied by optical microscopy and photoluminescence (PL) methods.At low concentration of lanthanoid (0,01 < Nyb > 0,1 weight %) the good planarity of the interface and high quality of the surface are detected. At NYb > 0,1 weight % microirregularities are presented.

In EL Si:(Sn, Yb) irradiated by 4,5 MeV-electrons the suppression of the generation of radiaton defects, responsible for G– and C-lines of PL, has been found. This effect has been explainedwithin the score of the model takeng into the consideration gettering propering ofYb in reference to the impurities of 0 and C as deformation fields, attributed to the presence of Sn atoms.
High Concentrations of Erbium in Crystal Silicon by Thermal or Ion-Beam-Induced Epitaxy of Erbium-Implanted Amorphous Silicon
Authors: Custer J. S. , Polman A. , Snoeks E. , Hoven G. N. van den
Published: March 2011

Solid phase epitaxy and ion-beam-induced epitaxial crystallization of Er-doped amorphous Si are used to incorporate high concentrations of Er in crystal Si. During solid phase epitaxy, substantial segregation and trapping of Er is observed, with maximum Er concentrations trapped in single crystal Si of up to 2 x 1020 /cm3. Ion-beam-induced regrowth results in very little segregation, with Er concentrations of more than 5 X 1020 /cm3 achievable. Photoluminescence from the incorporated Er is observed.
Optical Direct and Indirect Excitation of Er3+ Ions in Silicon
Authors: Majima A. , Uekusa S. , Ootake K. , Abe K. , Kumagai M.
Published: March 2011

Optical direct and indirect excitation of erbium (Er) ions in silicon substrates was performed in order to investigate the high efficiency of Er3+− related 1.54μm emission (4I13/2→4I15/2) for direct excitation that is not concerned with the indirect band gap and low quantum efficiency of a Si host. The samples were prepared by ion-implantation or thermal diffusion methods. In each sample, photoluminescence (PL) showed the peaks originating from 4I13/2→4I15/2 of Er3+ ions.

In Er thermally diffused samples, optical excitation for energy level 4I11/2 of Er3+ ions was successfully effected by photoluminescence excitation spectroscopy (PLE). The PLE spectra consisted six peaks (963.1nm, 965.0nm, 976.lnm, 978.9nm and 980.9nm) which were caused by direct excitation (4I15/2→4I11/2) of Er3+ ions. The emission directly excited is about 2 times more intense than the indirectly excited emission. The six peaks originating from the splitting of the 4I11/2 levels meant that Er3+ ions were in the sites of noncubic symmetry. The samples prepared by Er ion-implantation did not show the effect.
Effect of the Er3+ Concentration on the Luminescence of Ca1-xErxF2+x Thin Films Epitaxially Grown on Si(100)
Authors: Barriere A.S. , Raoux S. , Favennec P.N. , L'haridon H. , Moutonnet D.
Published: March 2011

Ca1-xErxF2+x thin films, with a substitution rate, x, varying from 1 to 20%, were deposited on Si(100) substrates by sublimation of high purity solid solution powders under ultra-high-vacuum. Rutherford backscattering studies have shown that the films have the composition of the initial solid solution powders, are quite homogeneous and are epitaxially grown on the substrates.

The optical properties of these films were studied by means of cathodoluminescence and photoluminescence. At room temperature, the emissions due to the de-excitations from the 4S3/2, 4F9/2, 4I11/2 and 4I13/2 excited levels to the 4I15/2 ground state of Er3+ (4f11) ions are easily detected (λ = 0.548, 0.66, 0.98 and 1.53 μm)

The strong 1.53 μm infrared luminescence, which presents evident potential applications for optical communications, is maximum for an erbium substitution rate included between 15 and 17%. These Er concentrations are three or four orders of magnitude greater than the optimum ones in the case of Er-doped semiconductors, which are close to 1018 cm-3. In the visible range, the luminescences are also important.They allow us to detect high energy ion or electron beams. However their maximum efficiencies were observed for a relatively low erbium concentration, close to 1%. These different behaviours are explained by the cross relaxation phenomena, which depopulate the higher levels to the benefit of the 4I13/2 → 4I15/2 transition.

The energy distribution of the Stark sublevels of the 4I15/2 state, which results from crystal field splitting, was deduced from a photoluminescence study at 2K. The obtained results show that the environment of the luminescent centres does not change with the erbium concentration.

At last, it must be noted that the refractive index of the layers increases with the erbium concentration, leading to the realization of optical guides. Consequently opto-electronic components could be developed from such erbium doped heterostructures.
Reduction of Misfit Dislocation Density in Finite Lateral Size Sil-xGex Films Grown by Selective Epitaxy
Authors: Vescan L. , Stoica T. , Dieker C. , LÜth H.
Published: March 2011

In Si0.88Ge0.12/Si strained layers misfit dislocations formed during growth in small pads are generated at a significantly higher critical thickness than on extended areas, while pads of lateral size of 10 μm or smaller show no evidence of misfit dislocations at all. The SiGe layers investigated were selectively grown on patterned substrates with pad sizes from 2 μm to 1 cm. An elastic relaxation model was used to calculate the pad size dependence of the critical thickness. The main hypothesis of the model is that the density of misfit dislocations is solely affected by the elastic relaxation at the edges of small epitaxial areas. This equilibrium model is able to explain the observed absence of misfit dislocations on small pads, however it predicts a critical thickness for finite sizes much lower than the observed one.
Intrasubband 1.55 μm Electrooptical Modulation in SiGe Asymmetric Quantum Well Structures
Authors: Friedman Lionel R. , Soref Richard A.
Published: March 2011

A new, fast, intrasubband 1.55 μm electrooptic modulator in the SiGe/Si/CaF2-on-Si steppedquantum- well system is proposed and analyzed. At electric fields of ±8 V/μm, resonant 1-3 conduction intrasubband absorption is predicted to give 18 dB of optical extinction for narrow-linewidth transitions. We expect this field effect modulator to have microwave response, plus compatibility with Si-based optoelectronic integration.
Photoluminescence Investigations of High Purity Mbe-Grown Sil−xGex/Si Single Quantum Wells
Authors: Wachter M. , Schdffler F. , Thonke K. , Sauer R. , Herzog H.-J. , Kasper E.
Published: March 2011

Sil-xGex/Si(100) single quantum well samples were grown by MBE with x varying from 18.5% to 36%, well widths Lz from 1.1 nm to 175 nm, and growth temperatures To in the range from 350°C to 750°C. We studied the photoluminescence (PL) properties in detail using Fourier transform spectroscopy. In most of the samples, the dominant and phononresolved SiGe band edge PL exhibits exclusively free exciton luminescence even at sample temperatures as low as 2 K. From the absence of bound excitons we conclude that the background concentration of shallow impurities is low in our SiGe layers. Variation of the growth temperature of the Si cap layer strongly influences the efficiency of the SiGe band edge PL at higher temperatures, whereas the PL efficiency is less affected at T=4 K. This indicates a reduction of the concentration of non-radiative defects in the cap layer when it is grown at higher temperatures. A broad PL band 150 meV below the SiGe bandgap, supposed to be typical for MBE-grown material, is weakly observed in only a few samples. The strength of the broad PL band does not unambiguously depend on the strain energy density in the SiGe layer as recently suggested.
Separation of Nucleation and Crystallization in the Solution-Phase Synthesis of Group IV Quantum Structures
Authors: Heath James R. , Seidler Paul F.
Published: March 2011

Solution-phase chemical syntheses are presented for the fabrication of Ge quantum structures, including 0-dimensional dots, 1-dimensional wires, and 2-dimensional platelets. The syntheses, which are based on the reduction of chlorogermanes and organochlorogermanes, are carried out in two steps. Step I, the nucleation step, is done at ambient temperature with a liquid metal reducing agent (NaK) and under the influence of sonication. Step 2, crystallization, is carried out at elevated temperatures and pressures in a sealed bomb. Separation of these two steps is shown to be critical for obtaining size and shape control over the product crystallite.
Mechanical Parameter Extraction Using Resonant Structures
Authors: Elders J. , Tilmans H.A.C. , Bouwstra S. , Elwenspoek M.
Published: March 2011

In order to model and design micromechanical sensors and actuators, it is of crucial importance that thin film mechanical parameters, such as the Young's modulus and the residual stress, are known. In this paper, the parameter extraction method using resonant structures has been used to obtain these data and has been compared with the bulge test. Circular aluminum diaphragms have been used as samples.
Study of Bulk and Film-Substrate Composite Materials Behaviour Under Vickers Indentation By Three-Dimensional Finite Element Simulation
Authors: Wang Haifeng , Bangert Herwig
Published: March 2011

Three-dimensional finite element simulation is employed to investigate the general indentation behaviour of bulk materials and corresponding film-substrate systems in Vickers hardness test. MARC™, a routine finite element software package was used on the following samples: bulk aluminium, bulk steel and their respective film-substrate systems, i.e., aluminium on steel as soft film on hard substrate and steel on aluminium as reverse situation. The results are given in two different cross-sectional planes, i.e., through opposite pyramidal edges and perpendicular to pyramidal side faces. In all cases the calculation provides a general view of the deformation characteristics, but also values for material displacement and the extension and shape of the stress fields as well as the plastically deformed zone under load or after load release. The indenter load versus indentation depth relation during loading and unloading are also calculated for all the examples.
The Calibration of the Nanoindenter
Authors: Mccormick N J , Gee M G , Hall D J
Published: March 2011

The nanoindenter has a tremendous potential for the measurement of mechanical properties of thin films and coatings. Information can be obtained about plastic, elastic and time dependent deformation behaviour. In some cases fracture behaviour of the coatings and the adhesion of the coating to the substrate can also be investigated.

Before accurate and reproducible measurements can be made the nanoindenter needs to be suitably calibrated. The magnitude of the uncertainties associated with calibration and their relevance to measurements are also required. Additionally it is important that a thorough understanding of the effect of thermal drift on the measurement process is developed. Traceability of calibration is also an important consideration.

The primary areas where calibration is essential are displacement, load and shape of the indenter.
Microstructure Based Modelling of Stress Migration and Electromigration Induced Failure Distributions
Authors: Børgesen P. , Korhonen M. A. , Brown D. D. , Li C.-Y.
Published: March 2011

Stress and current induced degradation of the interconnects may well define the ultimate limits on device density and total on-chip power in microelectronic circuits. The two damage mechanisms are found to be mutually interdependent in a fashion determined by the line microstructure, as well as by design features such as W-studs and refractory metal back up layers. We have developed a comprehensive model for the synergistic effects of stress migration and electromigration, taking such factors into account. The present work reviews the modelling of the statistical failure distributions, with emphasis on the temperature and current density dependencies, for the case of 'near-bamboo' sub-micron lines.
Mechanical Stress Effects on Electromigration Voiding in a Meandering Test Stripe
Authors: Lowry Lynn E. , Tai Beverly H. , Mattila J. , Walsh LH.
Published: March 2011

Earlier experimental findings concluded that electromigration voids in these meandering stripe test structures were not randomly distributed and that void nucleation frequently occurred sub-surface at the metal/thermal oxide interface. The data showed a strong correlation between void area, void growth rate and stripe segment length [1]. The influence of mechanical stress on electromigration damage in these test structures has been examined by applying tensile stresses to both passivated and unpassivated samples. The stress distributions are calculated using finite element analysis for each of the test conditions. The resulting impact on electromigration voiding, as well as mechanical stress voiding, and lateral hillock formation is discussed.
Non-Destructive Evaluation of Strains and Voiding in Passgvated Copper Metallizations
Authors: Vinci Richard P. , Marieb Thomas N. , Bravman John C.
Published: March 2011

Stress induced voiding in passivated Cu lines was investigated by x-ray strain analysis and in-situ high voltage scanning electron microscope (HVSEM) techniques. Cu lines on a Ta underlayer and Cu lines on an Al underlayer were patterned by a trilayer liftoff technique and passivated with Si3N4. For direct observation of stress voiding, specimens were heated to 350ºC in the HVSEM and then cooled and held at 150ºC. Identical samples were subjected to the same thermal cycle for strain state determination using x-ray techniques. The hydrostatic stress state at each temperature was calculated from the measured strains. Few initial voids were observed after passivation in either sample. After heating to 350ºC and cooling to the dwell temperature, no new voiding was seen in the Ta/Cu lines. Measured hydrostatic strains were half those measured in the Al/Cu lines. Heavy voiding was observed in the Al/Cu lines after cooling to the dwell temperature.
Stress Gradient and Relaxation Measurements in AL and Oxygen-Implanted AL Films.
Authors: Besser Paul R. , Bader Stefan , Venkatraman Ramnath , Bravman John C.
Published: March 2011

Synchrotron radiation has been used in the grazing incidence geometry to determine the stress gradients and stress relaxation in 0.6 μm thick Al uniform films. We have examined both pure Al and Al implanted with 3 at % oxygen. The films were cycled between 23°C and 400°C. The surface of the pure Al films was more highly stressed, on average, than the film as a whole, both in tension and in compression. In contrast, the surface of the oxygen-implanted film was relaxed relative to the average film stress in compression but was more stressed in tension. The larger gradient in stress in the implanted films reduces during subsequent thermal cycling. These differences are attributed to the microstructures of the films. The O-implanted film develops a small, non-columnar grain structure and forms small Al2O3 particles during annealing. The small grain size allows diffusional relaxation to occur in compression, relieving the stress in areas close to the film surface.
The Transformation Characteristics in Thin Film SMA Heterostructures— The Importance of Interfacial Stress Accommodation
Authors: Hua Susan Z. , Su C. M. , Wuttig M.
Published: March 2011

Shape memory alloy (SMA) thin films have attracted attention due to their potential application as actuators in micromechanical systems. The stress development in Ni50Ti50 films has been measured using a cantilever beam method. It is of interest to study their transformation characteristics. We have investigated a striking change of the stress during the B2-B19 transformation. The magnitude of this stress depends on the film thickness and reflects the interface constraint. In order to obtain direct information about the interface, in situ cross-section TEM observations of NiTi/SiO2/Si heterostructures were performed at various temperatures. A layer of parent phase at the film/substrate interface was found to buffer the transformation induced stress. The origin and effect of this buffer layer was analysed based on the TEM cross-sectional observations of the formation history of the layer.
Theoretical Considerations on Growing Uniformly Thick Films of Perfect Crystallinity
Authors: Van Der Merwe Jan H.
Published: March 2011

Theoretical considerations that facilitate the design of procedures to grow epilayers of uniform thickness and perfect crystallinity are briefly reviewed. The attainment of uniformity and crystallinity are respectively best served by growing in the monolayer-by-monolayer mode and below a critical thickness. Equilibrium and non-equilibrium criteria developed to accomplish these goals are briefly dealt with.
Reorientation of Misfit Dislocations During Annealing in InGaAs/GaAs(001) Interfaces
Authors: Chen Y. , Liliental-Weber Z. , Washburn J. , Klem J.F. , Tsao J.Y.
Published: March 2011

Transmission electron microscopy is applied to investigate the effect of post-annealing on misfit dislocations in an In0.2Ga0.8As/GaAs(001) heterostructure. An orthogonal array of 60º dislocations along [110] and [110] directions was observed in the interfaces of the samples grown by MBE at 520 ºC. When the as-grown samples were annealed at temperatures ranging from 600 to 800 ºC, the 60º dislocations were gradually reoriented by dislocation reactions occurring at the 90º intersections followed by nonconservative motion driven by dislocation line tension and the residual elastic misfit strain. The final result of this process was a dislocation array lying along [100] and [010] directions. The reoriented u=<100> dislocation has a Burgers vector , which is the same as that of 60º dislocation, but the edge component of its Burgers vector in the (001) interfacial plane is larger than that of 60º dislocation by a factor of , resulting in a greater contribution to elastic strain relaxation. This nonconservative reorientation of 60º dislocations to form the u=<100> dislocations represents a new strain relaxation mechanism in diamond or zinc blende semiconductor heterostructures.
Threading Dislocation Densities in GaAs Grown on Reduced Area Si Substrates
Authors: Knall J. , Romano L.T. , Biegelsen D.K. , Bringans R.D.
Published: March 2011

We have studied the possibilities of reducing the threading dislocation (TD) density in GaAs on Si using free side wall growth on patterned Si substrates and/or using a soft ZnSe interlayer in combination with post growth annealing procedures. TD densities were accurately determined using large area plan view TEM and were found to be unaffected by proximity to free side walls and by the ZnSe interlayer. Post growth heat treatments led to a factor of ∼2 reduction in TD density and to bunching of dislocations throughout the thickness of the film.
Diffusion-Induced Dislocations in Silicon
Authors: Ning X. J. , Pirouz P.
Published: March 2011

The stresses in a silicon wafer which has undergone diffusion by a high concentration of boron are partially relaxed by the generation of dislocations in the boron-diffused regions of Si. It is found that these dislocations nucleate at the Si surface as dissociated half-loops lying on {111} planes inclined to the surface. Expansion of the half-loops to the diffused/virgin Si interface produce segments of misfit dislocations which are of the dissociated 60º type. These misfit dislocations move deeper into the crystal as the diffusion front moves further in the wafer and often intersect other misfit dislocations on intersecting glide planes. In this paper, the misfit dislocations and the reactions between them are characterized and discussed.
Slipline Offset of In.25Ga.75As/GaAs (100) Imaged by Atomic Force Microscopy
Authors: Harvey S.E. , Angelo J.E. , Gerberich W.W.
Published: March 2011

We have discovered a surface instability in In.25GaAs.75/GaAs (100) grown by molecular beam epitaxy (MBE) by direct comparison of atomic force microscopy (AFM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) investigations. While slipline spacings measured by AFM correspond fairly well with those measured by TEM and SEM, the height displacement measured by AFM was seven times greater than that inferred from dislocations observed with TEM; the number of dislocations are insufficient to produce such dramatic heights. The difference in height measured by AFM with respect to the theoretical height calculated by strain relaxation and TEM dislocation number measurement can be attributed to a surface instability.
Mechanical Properties of the GaAs/Si [001] Interface by X-rays Hybrid Multiple Diffraction
Authors: Morelhão S. L. , Cardoso L.P. , de Carvalho M.M.G.
Published: March 2011

In this work, the directions of the secondary beams which are scattered by each mosaic block within an epitaxial layer allow to explain the position and profile of the LS hybrid multiple diffraction peak in the substrate Renninger Scan (RS). Furthermore, by choosing a secondary beam diffracted almost parallel to the interface, the LS peak is able to provide information even for thin (500Å) layers. The position of the LS peak in the substrate RS of the GaAs layers grown by VCE on Si(001) provides the a║ values necessary to analize the layer stress state. As an external bending moment is applied on the sample to compensate the stress steming from the difference in thermal expansion coefficients a split of both epilayer and buffer layer LS peaks can be observed. This split also indicates the degree of cohesion between these two layers.
Effect of Stress on the Carrier Contribution to Elastic Constants in Thin Films of Small Gap Compounds
Authors: Ghatak Kamakhya P. , Nath Biswas Sambhu
Published: March 2011

In this paper we have investigated the carrier contribution to elastic constants in very thin films of stressed small gap compounds within the domain of theory. It is found, taking stressed ultrathin films Hg1-xCdxTe and In1-xGaxAsyP1-y lattice matched to InP as examples, that the elastic constants increase with increasing electron concentration and decreasing film thickness respectively in oscillatory manners. Besides the stress enhances the numerical values of such contribution to the elastic constants. In addition, the theoretical formulation is in agreement with the suggested experimental method of determining such constants in materials having arbitary dispersion laws.
Ti-W-N Deposition Stress as a Function of Microstructure
Authors: Witvrouw A. , De Bosscher W. , Deweerdt B. , Verbeeck R. , Loosen F. , Roussel Ph. , Maex K.
Published: March 2011

160 nm Ti-W-N layers were sputtered on Si/SiO2/Al-Si-Cu substrates with the thickness of the Al-Si-Cu layer varying between 0 and 1000 nm. As a result the apparent grain size of the Ti-W-N increased from 40 to 130 nm and the compressive deposition stress of the Ti-W-N decreased from 1.77 to 0.34 GPa. The relation between stress and the inverse grain size was found to be linear for grain sizes smaller than 130 nm. Assuming a simple model, the excess volume per unit area of grain boundary can be estimated from the slope of the fit and was found to be 0.17 nm.

Light scattering measurements can be used as a quick and non-destructive method for evaluating the microstructure of these layers.
Nanoidentation Study of the Mechanical Properties of Granular Metal Thin Films
Authors: Scanlon M. R. , Ferber M. K. , Cammarata R. C.
Published: March 2011

Nanoindenter techniques have been used to investigate the mechanical properties of Ag-Al2O3 and Fe-SiO2 granular metal films. A discontinuity in the rate of change of hardness as a function of metal volume fraction p was observed. The discontinuity occurs at the percolation threshold pc of the metal, and appears to result from a change in the deformation mechanism at pc. A large peak in compliance (inverse modulus) as measured during indentation unloading was observed in the Ag-Al2O3 films near pc, but was not observed for the Fe-SiO2 films. The compliance peak displayed by Ag-Al2O3 is believed to result from debonding at the metal-ceramic interface and subsequent interfacial sliding, and is not an intrinsic materials property.
Compressive Stress Increase With Repeated Thermal Cycling in Tantalum(Oxygen) Thin Films
Authors: Cabral C. , Clevenger L.A. , Schad R.G.
Published: March 2011

Stresses which build up in thin films, such as tantalum, during thermal processing, can cause major reliability problems in x-ray optics and electronic applications. We have demonstrated that 50 nm to 200 nm thick sputtered beta tantalum thin films undergo repeated compressive stress increases when thermally cycled from room temperature to 400°C (at 10°C/min) and back in a purified He ambient because of low levels of oxygen gettered by the tantalum. The oxygen contamination is a result of the poor quality of the quartz annealing chamber atmospheric seal. As-deposited stress in the sputter deposited tantalum films ranges from -1 to -4 GPa. The compressive stress build up was monitored in situ and was shown to increase -0.5 GPa on average after each thermal cycle for a final value of -6 to -7 GPa after seven cycles. After being cycled thermally seven times any perturbation of the film such as a four point probe resistivity measurement can cause the film to instantaneously crack in a serpentine pattern relieving the large compressive stress. Auger electron spectroscopy depth profiling analysis indicated that the as-deposited films contained one atomic percent oxygen which increased to eight to twelve percent after seven thermal cycles accompanied by an approximate doubling in resistivity. In conclusion, the increase in oxygen concentration in tantalum thin films which occurs upon thermal cycling leads to a repetitive increase in compressive stress which could be detrimental when the films are used in x-ray or electronic applications.
Mechanical Properties of Pyrolytic "SiOCN" Thin Coatings
Authors: Bec Sandrine , Tonck André , Loubet Jean-Luc
Published: March 2011

Pyrolysis of polymer precursors (polysilazane) is a technologically and economically interesting way to produce thin ceramic coatings. However, many cracks appear and decohesion occurs during pyrolysis when the ceramic coatings (SiOCN) are thicker than 0.5 micrometers. In order to understand these cracking phenomena, the coatings are mechanically characterized by nanoindentation at different stages of the pyrolysis heat treatment.

During pyrolysis, the cracking temperature is detected by in-situ optical observation. The thickness of the coatings varies during pyrolysis from 3 micrometers at the polymeric state to 1 micrometer at the ceramic state. The coatings' properties, hardness and Young's modulus are evaluated after heat treatment, taking into account the substrate's influence. A large variation of these properties occurs at the cracking temperature. Both the hardness and the Young's modulus are multiplied by a factor of 10. By analysing these results, we show that cracking is correlated with the evolution of the coatings' mechanical properties during the transformation.
Influence of the structure on the mechanical properties of electrodeposited metallic thin films
Authors: Delplancke J.-L. , Winand R. , Dille J. , Charlier J.
Published: March 2011

Production of thin (10 to 200 microns thick) metallic (Cu, Co and Ni-P) foils is performed by electrodeposition on various substrates. A competition between substrate-induced and electroplating-induced inhibition of crystal growth appears. Film structures observed by SEM, TEM and X-Ray diffraction are related to the mechanical properties of the films (stress-strain curves, microhardness and work hardening bend test).

In some cases, copper thin films with a large number of submicron crystals are obtained. These films recrystallize at room temperature and their mechanical properties are completely modified by this ageing process.
Tribomechanical Properties of Ion-Beam-Densified Sol-Gel Zirconia Thin Films on Cubic Zirconia
Authors: Levine Timothy E. , Revesz Peter , Mayer James W. , Giannelis Emmanuel P.
Published: March 2011

We have investigated the tribomechanical properties of ion-beam-densified sol-gel zirconia overlayers on bulk zirconia. Ion irradiation of the sol-gel films leads to hydrogen, oxygen, and carbon losses as indicated by Rutherford backscattering spectrometry and forward recoil energy spectroscopy. Ellipsometry measurements show that the film thickness decreases with increasing dose. The microhardness exhibits an increase and subsequent decrease with dose. Friction measurements along with profilometry measurements indicate that severe abrasive wear of the film takes place in the first 1000 cycles after which point the substrate is in direct contact with the pin.
Micromechanical Behaviour of Amorphous Hydrogenated Silicon Carbide Films
Authors: Meneve J. , Jacobs R. , Lostak F. , Eersels L. , Dekempeneer E. , Smeets J.
Published: March 2011

Amorphous hydrogenated silicon carbide (a-Si1-xCx:H) films (x = 0.65 to 1) were deposited by radio frequency plasma assisted chemical vapour deposition (RF-PACVD). Their friction and wear properties were investigated by means of a conventional ball-on-disk apparatus. The results were correlated with film mechanical properties. It was found that adding silicon to a-C:H (also called diamond-like carbon (DLC)) films reduces the hardness, elastic modulus and internal stress values by 15 to 30 %. Scratch testing induces film spallation from stainless steel substrates at low loads (1 N). In the low normal load (1 N) ball-on-disk tests under humid N2 conditions, a-Si1-xCx:H films (0.7 < x < 0.9) combine a very low wear rate of both the film and the counterbody with a steady state low friction coefficient below 0.1. For higher loads (5 and 10 N), however, this low friction coefficient only lasts for a relatively short time. In this case, the harder diamond-like carbon films perform tribologically better because of their higher wear resistance, low wear rate of the counterbody and generally low friction coefficients between 0.15 and 0.35 in a humid ambient atmosphere. In a dry N2 atmosphere, pure DLC films perform tribologically better than a-S1-xCx:H films in all respects.
Stress in Thin Layers Applied by Substrate Bending; Calibration and Potentialities
Authors: Chroboczek J.A. , Stöhr M. , Whall T.E.
Published: March 2011

Uniaxial stresses up to 0.3GPa, both compressive and tensile, can be generated in thin epitaxial layers by substrate bending. We demonstrate the feasibility of the method and calibrate the stress, measuring piezoresistance at temperatures below the impurity freeze-out, on lightly B-doped silicon MBE layers, using the known expression for a surface stress in a bent cantilever beam. The ground state energy displacement of B in Si thus obtained can vary by ±5meV, suggesting potential applications of the technique in tunable devices, involving doped semiconductors or heterostructures.
Evaluation of Adhesion Strength in a Ti/Al2O3 Composite
Authors: Wang Hsin-Fu , Nelson John C. , Lin Chien-Li , Gerberich William W. , Skowronek Charles J. , Deve Herve E.
Published: March 2011

The mechanical properties of interfaces in Ti/Al2O3 composites were characterized by four point bending and fiber pushout tests. To determine the bi-material fracture toughness with four point bending tests, planar interfaces were evaluated as sandwich composites. By changing the processing temperature from 700°C to 1000°C, the interfacial fracture energy was found to increase ug to 950°C. It then decreases when the processing temperature is further increased to 1000°C. This is because of the formation of the intermetallic compound (Ti3Al). Interfacial shear strength and interfacial frictional stress of 323MPa and 312 MPa were obtained, respectively, by performing pushout tests of the Al2O3 fiber reinforced Ti matrix composites. These values are smaller than the shear yielding strength of the Ti matrix which is 525 MPa.
Stress-Corrosion Cracking at Ceramic-Metal Interfaces
Authors: Card J. C. , Cannon R. M. , Dauskardt R. H. , Ritchie R. O.
Published: March 2011

It is known that the fracture resistance of glass-copper interfaces depends strongly on the water content in ambient gaseous environments. In the present study, subcritical crack growth stimulated by water and other environmental species is investigated for such interfaces. Tests were conducted in various liquids, namely water, N-methylformamide, and n-butanol. All were found to accelerate fracture with the greatest effects from liquid water. Results are considered in the context of current models for stress-corrosion crack growth.
High Speed Joining of Aluminum Metal Matrix Composites Using Continuous Wave and Pulsed Lasers
Authors: Khan Parwaiz A. A. , Paul Anand J.
Published: March 2011

Due to their superior mechanical properties and high strength to weight ratio, metal matrix composite materials are increasingly being used in aerospace, automotive and defense industries. The use of a fusion related conventional joining technique, such as arc welding, leads to the formation of undesirable non-equilibrium phases in the weld zone, where as diffusion and adhesive joining techniques are rather slow. Non contact multi-kilowatt laser joining, though fully developed for high speed autogenous joining of different alloys, is not yet adequate for joining of metal matrix composites. Efforts have been made by several researchers to control the composition and microstructure of laser joined aluminum metal matrix composites by controlling the energy input and by the use of filler wires. In view of the current industry trend to use more light weight structural composite materials, and greater use of high energy density beams for a variety of metalworking applications, the authors have reviewed the current status of high speed laser joining of metal matrix composites. Emphasis is placed on problems and various techniques which can be used to achieve a better control on composition and microstructure during high energy laser joining of aluminum metal matrix composites.
CD Weld Interfacial Structure for Al-Fe Based Couples
Authors: Dogan C. P. , Wilson R. D. , Hawk J. A.
Published: March 2011

The U.S. Bureau of Mines has studied the capacitive discharge weld interface between Al and Fe using optical and transmission electron microscopy (TEM). Capacitive discharge welding (CDW) is a rapid solidification process in which the amount of molten metal at the interface is small compared to the sample size. As a result, high cooling rates (106 K/s) can be achieved, providing a weldment made up of small grains. Large magnetic fields produced by the process tend to mix the molten metals at the interface to form a complex alloy, the nature of which depends upon the starting electrode materials. This effect is characterized by a marblecake pattern in optical micrographs. The amount of mixing is related to the melting temperature of the cathode with respect to the anode. Increased mixing occurs when the melting temperature of the cathode is higher than the melting temperature of the anode. TEM has revealed that when aluminum is the anode material, the iron grains of the cathode are surrounded by a layer of aluminum. When the iron is the anode, a thin layer of iron surrounds the aluminum grains.
Fundamentals of The Shs Joining Process
Authors: Messler Robert W. , Orling Timothy T.
Published: March 2011

The process of self-propagating high-temperature synthesis offers potential for joining similar or dissimilar combinations of heat-resisting or refractory metals and refractory or corrosion resistant oxide or nonoxide ceramics or intermetallics by using the exothermy inherent in the synthesis reaction. The process offers unique capability for producing functionally gradient material joints between dissimilar materials to overcome mismatches in chemical, mechanical and physical properties, facility for incorporating reinforcing phases in the filler, and exceptional efficiency given that the energy for joining is largely internally generated. A systematic study of the fundamentals of the process critical for joining in either a primary or a secondary mode is being undertaken. Specialized fixtures are being employed to study the role of substrate temperature in bond formation and strength, and the role of precompaction density and applied pressure on joint density. A Gleeble thermomechanical simulator is being used to study the role of reactant composition, reactant particle size, heating rate and reaction mode, precompaction and applied pressure, and atmosphere. Ultimately, a model of the SHS process for joining will be developed to facilitate joint design, predict joint properties, and enable intelligent control.
Reaction Processing and Properties of Sic-To-Sic Joints
Authors: Rabin B. H. , Moore G. A.
Published: March 2011

Reaction processing methods have been developed for fabricating SiC-to-SiC joints that can be used in elevated temperature applications. Processing steps include tape casting thin sheet SiC+C interlayer precursors, clamping the tape between the ceramic parts, providing a source of Si adjacent to the joint, and heating above the melting point of Si in argon. Molten Si infiltrates the tape via capillary action forming a reaction bonded silicon carbide (RBSC) interlayer and simultaneously joining the ceramic parts. Four-point bending strength and fracture toughness of joined pressureless sintered α-SiC test specimens have been evaluated at room and elevated temperatures. At low temperatures the joint mechanical properties were comparable to those reported for bulk SiC, while at elevated temperatures the joint properties were characteristic of the RBSC interlayer.