bluuebunny/crossref_metadata_2025 huggingface dataset:
Loading Effects During Low-Temperature Seg Of Si And SiGe
Authors: De Boer W. B. , Terpstra D. , Dekker R.
Published: April 2011

Selective Epitaxial Growth (SEG) of Si and SiGe suffers from pattern sensitivity. The growth rate and layer composition change with the pattern and the window size. In relation to growth at atmospheric pressure, the sensitivity to the window size is suppressed at reduced pressure, whereas some growth rate effects of a more global nature become more visible. The Si growth rate decreases when the area of exposed silicon on the wafer and the susceptor decreases. SiGe shows the opposite behavior: its growth rate increases with decreasing silicon area. Another difference between Si and SiGe is the range over which the loading effects are active. The influence of a large silicon area on the Si growth rate can be felt inches away, whereas the SiGe growth rate is affected over a much shorter distance. In common epi reactors the wafer rests on a susceptor, which extends beyond the wafer, exposing a large Si-coated surface area around the circumference of the wafer. Consequently, the Si growth rate varies unacceptably across the wafer. A sacrificial polysilicon layer has been successfully applied to improve the growth rate uniformity across the wafer.
A Selective/Non-Selective Epitaxy Process For A Novel Sige Hbt Architecture
Authors: Schiz J. , Bonar J. M. , Shburn P
Published: April 2011

A selective/non-selective epitaxy process for a novel self-aligned SiGe HBT structure is described. It is shown that damage in the silicon substrate induced by reactive ion etching can be effectively removed and that this allows the growth of high quality selective and nonselective epitaxy. Control of the base thickness and doping can be maintained during selective and non-selective epitaxy, thereby demonstrating the feasability of producing the self-aligned HBT structure.
Photoluminescence Of Sisnc Alloys Grown On (100) Si Substrates
Authors: Wright N. , Khan A.T. , Berger P.R. , Guarin F.J. , Iyer S.S.
Published: April 2011

Photoluminescence (PL) of SiSnC alloys grown on Si (100) substrate by molecular beam epitaxy (MBE) has been investigated. The following epitaxial layers were investigated. The samples were similar in structure, and consisted of a 200 Å Si buffer layer grown on a (100) Si substrate followed by the respective alloy layer; a 4500 Å Si0.955Sn0.03C0.015, a 1500 Å Si0.9Sn0.04, or a 1500 Å Si0.985C0.015. The layer composition was measured by Rutherford back scattering spectrometry (RBS) and confirmed by x-ray diffraction analysis (XRD). X-ray diffraction measurements of the layers confirmed the Sn and C were substitutional and the layers were pseudomorphic and coherently strained. The Si0.955Sn0.03C0.015 alloy layer was found to be strain compensated. PL spectra of all the layers revealed band edge luminescence as well as a very sharp peak at 0.767 eV superimposed on a very broad peak that exhibited excitonic behavior. The addition of C to the alloys resulted in a reduction of the bandgap, contrary to what is predicted by Vegard's Law. However, the addition of Sn results in a reduction in the bandgap, which was attributed to the bulk alloy effect and residual strain. The luminescence feature at 0.767 eV was found to be much more intense in alloys that contain carbon. We have observed quite similar deep-level well resolved PL spectra for SiGe, SiC, SiSn, SiGeC, SiSnC, and SiGeSnC alloy layers grown by MBE on Si (100) substrates. Previous studies on PL of silicon have reported a peak at 0.767 eV to be associated with oxygen (P line) and the broad peak to carbon/oxygen complexes.
Growth and Characterization of Epitaxially Stabilized Pseudomorphic α-Sn/Si Heterostructures
Authors: Min Kyu Sung , Atwater Harry A.
Published: April 2011

Growth and structural characterization of ultrathin, coherently strained oc-Sn/Si quantum well heterostructures have been performed. Severe Sn segregation to the surface during growth, which prevents growth of these structures at ordinary Si epitaxy temperatures, has been minimized by substrate temperature and growth rate modulations during molecular beam epitaxy. Single Sn/Si quantum wells grown with Sn coverage up to 1.4 ML have been verified to be pseudomorphic by transmission electron microscopy and X-ray rocking curve analysis. Similarly, pseudomorphic superlattices with up to 10 periods of 1 ML Sn/7.7 nm Si have been verified to be free of extended defects.
Single Crystal Gd203 Films Epitaxially Grown on GaAs - A New Dielectric for GaAs Passivation
Authors: Hong M. , Kwo J. , Kortan A. R. , Mannaerts J. P. , Wu M. C. , Lay T. S. , Sergent A. M.
Published: April 2011

Single crystal Gd2O3 dielectric thin films were epitaxially grown on GaAs. The Gd2O3 film has a cubic structure isomorphic to Mn2O3, and is (110) oriented in single domain on the (100) GaAs surface. The oxide film has low leakage current densities ˜ 10–9 – 10–10 A/cmT2 at zero bias. Typical breakdown field is 4 MV/cm for an oxide film 185 Å thick, and >10 MV/cm for an oxide less than 50 Å thick. Both accumulation and inversion layers were observed in the Gd2O3-GaAs metal oxide semiconductor (MOS) diodes using capacitance-voltage (C-V) measurements, with an interfacial density of states around 1011 cm–2 eV–1.
Lattice Engineering Using Lateral Oxidation of Alas: an Approach to Generate Substrates With New Lattice Constants
Authors: Chavarkar P.M. , Zhao L. , Keller S. , Black K.A. , Hu E. , Speck J. , Mishra U.
Published: April 2011

We demonstrate a new approach to the growth of dislocation free lattice-mismatched materials on GaAs substrates using Al2O3 interlayers obtained by lateral oxidation of AlAs. This is achieved by generating relaxed low threading dislocation density InGaAs templates which are mechanically supported but epitaxially decoupled from the host GaAs substrate. This process uses the phenomena of relaxation of strained coherent hypercritical thickness (h > hcritical,) layer in direct contact with an oxidizing Al-containing semiconductor (i.e. AlAs or AlGaAs). 5000 Å In0.11Ga0.89As layers were then grown on the In0.2 Ga0.8As/Al2O3/GaAs template which acts as a pseudo-substrate (lattice-engineered substrate). The epitaxial layers are partially relaxed and have extremely smooth surface morphology. Further TEM micrographs of these epitaxial layers show no misfit dislocations or related localized strain fields at the In0.2Ga0.8As/Al2O3 interface. The absence of misfit dislocations or local strain contrast at the In0.2Ga0.8As/Al2O3 interface is attributed to both reactive material removal during the oxidation process and the porous nature of the oxide itself. We propose that the strain relaxation in In0.3Ga0.7As is enhanced due to the absence of misfit dislocations at the In0.2Ga0.8As/A12O3 interface.
Growth of Improved GaAs/Si: Suppression of Volmer-Weber Nucleation for Reduced Threading Dislocation Density
Authors: Taylor P. J. , Jesser W.A. , Simonis G. , Chang W. , Lara-Taysing M. , Bradshaw J. , Clark W. , Martinka M. , Benson J.D. , Dinàn J.H.
Published: April 2011

The growth of reduced dislocation density GaAs/Si is performed by a novel two-step technique where the first epitaxy step takes place at 75° C and the second is performed at 580° C. The initial deposition is single crystal, continuous, and planar such that there is no contribution to the dislocation density from Volmer-Weber island coalescence and no trapping of dislocations in pinholes. Using this new growth technique, a reduced dislocation density the order of 106/cm2 was obtained. The improved crystallinity is indicated by the more narrow x-ray full-width-at-half-maximum (FWHM) value of 110 arcseconds. GaAs p-i-n diodes were grown on the reduced dislocation density GaAs/Si and it was found that the resistivity of the intrinsic region for the heteroepitaxial diodes was similar to homoepitaxial ones for small mesa sizes.
Strain Relaxation During Heteroepitaxy on Twist-Bonded Thin Gallium Arsenide Substrates
Authors: Kopperschmidt P. , Senz S T. , Scholz R. , Kästner G. , Gösele U. , Velling P. , Prost W. , Tegude F.-J. , Gottschalch V. , Wada K.
Published: April 2011

We realized “compliant” substrates in the square centimeter range by twist-wafer bonding of an (100) GaAs handle wafer to another (100) GaAs wafer with a several nm thick epitaxially grown GaAs layer followed by an appropriate back-etch procedure. The twist angle between the two GaAs wafers was chosen between 4 and 15 degrees. The twisted layers were characterized by area scanned X-ray diffraction, optical and electron microscopy and atomic force microscopy. Occasionally we observed regions showing pinholes in the transferred thin twistbonded GaAs layer.

After epitaxial deposition of 300 nm InP and InGaAs films with different degrees of mismatch on these substrates, transmission electron microscopy revealed grains which are epitaxially oriented to either the substrate or the twist-bonded layer. The grain boundaries between the twisted and untwisted grains probably collect threading dislocations, thus reducing their density in the areas free of boundaries.
Deep Level Defect Studies in Mocvd-Grown InxGa1−sAs1−yNy Films Lattice-Matched to GaAs
Authors: Kwon Daewon , Kaplar R. J. , Boeckl J. J. , Ringel S. A. , Allerman A. A. , Kurtz Steven R. , Jones E. D.
Published: April 2011

Deep level defects in MOCVD-grown, unintentionally doped p-type InGaAsN films lattice matched to GaAs were investigated using deep level transient spectroscopy (DLTS) measurements. As-grown p-InGaAsN showed broad DLTS spectra suggesting that there exists a broad distribution of defect states within the band-gap. Moreover, the trap densities exceeded 1015 cm−3. Cross sectional transmission electron microscopy (TEM) measurements showed no evidence for threading dislocations within the TEM resolution limit of 107 cm−2. A set of samples was annealed after growth for 1800 seconds at 650 °C to investigate the thermal stability of the traps. The DLTS spectra of the annealed samples simplified considerably, revealing three distinct hole trap levels with energy levels of 0.10 eV, 0.23 eV, and 0.48 eV above the valence band edge with trap concentrations of 3.5 × 1014 cm−3, 3.8 × 1014 cm−3, and 8.2 × 1014 cm−3, respectively. Comparison of as-grown and annealed DLTS spectra showed that post-growth annealing effectively reduced the total trap concentration by an order of magnitude across the bandgap. However, the concentration of a trap with an energy level of 0.48 eV was not affected by annealing indicating a higher thermal stability for this trap as compared with the overall distribution of shallow and deep traps.
Spatial Distribution of Luminescent Centers in Organometallic Vapor Phase Epitaxy Grown ZnxCdl−xSe/InP (001)
Authors: Zhang X. B. , Hark S. K.
Published: April 2011

Zincblende ZnxCdl−xSe alloys were grown on (001) InP by organometallic vapor phase epitaxy (OMVPE) using various VI / H precursor flow ratios, ranging from 0.95 to 12, at a temperature of 420°C. Spatial distribution of luminescent centers in the epilayer was characterized by cathodoluminescence (CL) spectroscopy and imaging. Both near band-gap (NBE) and deep level (DLE) emissions were observed in the spectra, with the width of the NBE peak increases with the VI / II flow ratio. Monochromatic CL images showed that the broadening of the NBE peak has its origin in the spatial inhomogeneity of the luminescent centers of the epilayer. Extended defects responsible for the DLE was only found in pyramidal hillocks seen in the CL images. The density of these defects was found to increase with the VI / I1 flow ratio.
A Peierls-Nabarro Model for Kink-Pair Generation in Screw Dislocations at Low Temperatures
Authors: Ngan A.H.W.
Published: April 2011

Kink-pair generation in three-fold screw dislocations in the bcc lattice is investigated within the framework of the generalised Peierls-Nabarro model. Using a piece-wise plane strain approximation, the apparent activation energy is predicted to vary with stress in a parabolic manner which is in good agreement with experimental findings.
From Molecular Dynamics to Kinetic Rate Theory: A Simple Example of Multiscale Modeling
Authors: Stoller Roger E. , Greenwood Lawrence R.
Published: April 2011

Radiation damage formation in iron has been investigated using the method of molecular dynamics simulation. The MD simulations have been used to determine primary defect production parameters for cascade energies up to 50 keV at temperatures from 100 to 900K. The energy dependence of these parameters has been used to determine appropriate neutron-energy-spectrum averaged damage production cross sections for various irradiation environments. Two applications of these effective cross sections are discussed. The first is an evaluation of neutron energy spectrum effects in commercial fission reactor pressure vessels. The second example deals with the use of these cross sections in the source term of a kinetic model used to predict void swelling and microstructural evolution. The simulation of the primary damage event by MD involves times less than 100 ps and a size scale of a few tens of nm, while the kinetic simulation encompasses several years and macroscopic sizes. This use of the MD results to develop an improved source term for rate theory modeling provides a simple example of multiscale modeling.
A Study of Grain Growth and Microstructure Control in Silicon Nitride by Computer Simulation
Authors: Okamoto Y. , Hirosaki N. , Matsubara H.
Published: April 2011

A grain growth simulation technique is developed for microstructure design of ceramic materials by extending the Potts model. The simulation model has successfully reproduced the self-reinforced microstructure which is peculiar to silicon nitride, consists of large elongated grains and small equiaxed grains.

To control the microstructure of silicon nitride further, a seeding technique is effective and often employed. Grain growth behavior of seed particles in the simulation is studied. It is found that the seed grains grow with a relatively high growth rate during the early stage of grain growth. In contrast in the later stage, the difference between microstructures with and without seed particles decreases. This behavior agrees well with that of actual silicon nitride. These results demonstrate the consistency of the simulation.
A Unified Computational Approach to Oxide Aging Processes
Authors: Hjalmarson Harold P. , Schultz Peter A. , Bowman Duane J. , Fleetwood Daniel M.
Published: April 2011

In this paper we describe a unified, hierarchical computational approach to aging and reliability problems caused by materials changes in the oxide layers of Si-based microelectronic devices. We apply this method to a particular low-dose-rate radiation effects problem.
Linking ab initio Energetics to Experiment: Kinetic Monte Carlo Simulation of Transient Enhanced Diffusion of B in Si
Authors: Theiss Silva K. , Caturla M.-J. , Rubia T. Diaz de la , Johnson M.C. , Uralt Ant , Griffin P.B.
Published: April 2011

We have developed a kinetic Monte Carlo (kMC) simulator that links atomic migration and binding energies determined primarily from first principles calculations to macroscopic phenomena and laboratory time scales. Input for the kMC simulation is obtained from a combination of ab initio planewave pseudopotential calculations, molecular dynamics simulations, and experimental data. The simulator is validated against an extensive series of experimental studies of the diffusion of B spikes in self-implanted Si. The implant energy, dose, and dose rate, as well as the detailed thermal history of the sample, are included. Good agreement is obtained with the experimental data for temperatures between 750 and 950°C and times from 15 to 255 s. At 1050°C we predict too little diffusion after 105 s compared to experiment: apparently, some mechanism which is not adequately represented by our model becomes important at this temperature. Below 1050°C, the kMC simulation produces a complete description over macroscopic time scales of the atomic level diffusion and defect reaction phenomena that operate during the anneals. This simulator provides a practical method for predicting technologically interesting phenomena, such as transient enhanced diffusion of B, over a wide range of conditions, using energetics determined from first-principles approaches.
Dislocations and Plasticity in Silicon Crystals by 3-D Mesoscopic Simulations
Authors: Kubin L.P. , Moulin A. , Pirouz P.
Published: April 2011

Several problems related to the dynamics of dislocation sources and the plasticity of silicon crystals are investigated with the help of a mesoscopic simulation. The questions successively examined are the dynamics of a source of perfect dislocations and the conditions under which perfect or partial dislocations are emitted by a source. This leads to a discussion of the initial steps of the model proposed by Pirouz for mechanical twinning and, further, to the suggestion that a relation may exist between several transitions experimentally observed at low temperatures in elemental or compound semi-conductors: a change in the slope of the yield stress vs. temperature curves, a brittle-to-ductile transition and a change in the nature of the mobile dislocations. Finally, simulations are presented of the yield point phenomenon that is a well-known feature of Si and Ge crystals. The results are discussed in terms of evolutionary laws for the total dislocation density during straining.
Measurement of Planar Fault Energies in Ni3Ge-Fe3Ge Intermetallic Alloys
Authors: Kumar Mukul , Balk T. J. , Hemker K. J.
Published: April 2011

A combination of transmission electron microscopy (TEM) and image simulations has facilitated a highly quantitative measure of superdislocation dissociations. The experimental observations have been corrected for image shifts within the framework of anisotropic elasticity by comparison with simulated images. This allows experimental quantification of planar fault energies, thus providing a benchmark for first principles and atomistic simulations and fundamental insight towards alloy modeling and design. Such measurements of superdislocation dissociations on the order of 1-15 nm have been recorded for the pseudobinary Ni3Ge-Fe3Ge alloy system. These detailed measurements of fault widths obtained by weak-beam TEM observations of deformation structures will be presented and discussed as a function of alloy composition. The transition from anomalous to normal temperature dependence of yielding behavior in these alloys will also be discussed in terms of observed dislocation structures and planar fault energies calculated using the above measurements.
A Study of Vacancies in Pure Aluminium and Their Role in the Diffusion of Lithium in a Dilute Al-Li Alloy Using the Embedded Atom Model
Authors: Derlet P. M. , Hoier R. , Holmestad R. , Marthinsen K. , Ryum N.
Published: April 2011

Constant temperature and pressure molecular dynamics are employed to study bulk Al and the substitutional Al-Li alloy using the embedded atom model. The appropriate embedding energy functionals and pair potentials have been determined using known experimental data of bulk Al and Li, together with the results of density functional theory studies of small Aln-Lim clusters and the ordered Al3Li crystallographic phase. The primary goal is to study the role vacancies play in the early stages of the nucleation and growth of the Al3Li crystallographic phase. To this end we present the preliminary results of a study of vacancy diffusion in Al, and Li diffusion through the Al matrix via a vacancy mechanism. In the present work the results of vacancy diffusion are analysed using a modified inverse Laplace transform, producing a continuous distribution of vacancy hopping times which reproduces the characteristic times for both the single and double vacancy hopping events.
Substitution Behavior in NiAl-A First Principle Prediction Considering Lattice Relaxation
Authors: Xu D. S. , Li D. , Hu Z. Q.
Published: April 2011

The substitution behavior of alloying elements in NiAl is investigated on the basis of electronic structure calculation using the discrete variational Xα cluster method. The method proposed by the authors to predict the substitution behavior is extended to considering lattice relaxation around an alloying atom. A diagram is drawn using the binding energy of clusters when each alloying element occupies either Ni or Al sites as parameters. Two straight lines on the diagram with slope of unity and passing the point of Ni or Al separate the alloying elements into three groups. The elements above the upper line will take Al sites and those below the lower line will take Ni sites regardless of the composition. The substitution behavior of elements in between the two lines will be affected by the alloy composition. The driving force for an element to order on one sublattice is related to its position on the diagram. The effects of temperature, composition and multi-element alloying are discussed. The concepts of site competition and stepped ordering are put forward.
The Influence of Heat Excitations, Vacancies and Impurities on the Energy Electronic Band-Structure of Metallic Lithium
Authors: Popov V. A.
Published: April 2011

The Korringa-Kohn-Rostoker method with Green's function averaged over the atomic configurations in a complex Ising lattice and a muffin-tin potential was used to calculate the electronic-band structure in lithium containing vacancies and s, p, and d impurities. It is shown that substantial changes in the profile of the Fermi surface do not lead to necking, as was postulated previously, but cause splitting of the electronic states at the face of the Brillouin zone. This is attributed to the reduced symmetry of the crystal lattice with impurity excitation of the electronic-subsystem.
Microscopic Description of Plasticity in Computer Generated Metallic Nanophase Samples
Authors: Spaczér M. , Swygenhoven H. Van , Caro A.
Published: April 2011

We report simulations on the plastic behaviour of nanocrystalline Ni and Cu with grain sizes in the range of 3-12 nm. We observe a change in deformation mechanism in both materials: at the smallest grain sizes all deformation is accommodated in the grain boundaries, while at higher grain sizes we observe intragrain deformation. Analysis of the atomic configurations shows that stacking faults are produced by the passage of partial dislocations generated and absorbed in opposite grain boundaries. In Cu, we observe the stacking faults at smaller grain sizes than in Ni (8 and 12nm, respectively), which is attributed to the lower stacking fault energy of copper. Dislocations appear on slip systems that are not necessarily those favoured by the Schmid factor. Atomic displacement analysis shows deformation starts at triple points, with grain boundary sliding followed by the creation of intragrain partial dislocations.
Atomistic Aspects of Fracture Modelling in the Framework of Continuum Mechanics
Authors: Cleri F.
Published: April 2011

The validity and predictive capability of continuum models of fracture rests on basic informations whose origin lies at the atomic scale. Examples of such crucial informations are, e.g., the explicit form of the cohesive law in the Barenblatt model and the shear-displacement relation in the Rice-Peierls-Nabarro model. Modem approaches to incorporate atomic-level information into fracture modelling require to increase the size of atomic-scale models up to millions of atoms and more; or to connect directly atomistic and macroscopic, e.g. finite-elements, models; or to pass information from atomistic to continuum models in the form of constitutive relations. A main drawback of the atomistic methods is the complexity of the simulation results, which can be rather difficult to rationalize in the framework of classical, continuum fracture mechanics. We critically discuss the main issues in the atomistic simulation of fracture problems (and dislocations, to some extent); our objective is to indicate how to set up atomistic simulations which represent well-posed problems also from the point of view of continuum mechanics, so as to ease the connection between atomistic information and macroscopic models of fracture.
Self Consistent-Charge Density-Functional Tight-Binding Method for Simulations of Biological Molecules
Authors: Elstner M. , Porezag D. , Seifert G. , Frauenheim Th. , Suhai S.
Published: April 2011

We apply a self-consistent charge tight-binding scheme to biomolecules. This method has been shown to give a reliable description of reaction energies, geometries and vibrational frequencies of small organic molecules. We discuss the performance of this method for model peptides and non-bonding interactions in biologically relevant molecular complexes. A comparison with semi-empirical methods and ab initio calculations will be given for DNA base pair H-bonding and stacking interactions.
Structural Characteristics and Quantum Chemistry Calculation of Si-Doped Boron Carbides
Authors: Xinmin Min , Cewen Nan , Kefeng Cai
Published: April 2011

Structural characteristics, chemical bonds and thermoelectric properties of Si-doped boron carbides are studied through calculations of various structural unit models by using a self-consistent-field discrete variation Xα method. The calculations show that Si atom doped in boron carbide is in preference to substituting B or C atoms on the end of boron carbide chain, and then may occupy interstitial sites, but it is difficult for Si to substitute B or C atom in the centers of chain or in the icosahedra. A representative structural unit containing a Si atom is [C-B-Si]ε+ [B11C]ε-, while the structural unit without Si is [C-B-B(C)]δ--[B11C]δ+, and the coexistence of these two different structural units makes the electrical conductivity increases. As the covalent bond of Si-B or Si-C is weaker than that of B-B or B-C, the thermal conductivity decreases when Si is added into boron carbides. With the electrical conductivity increases and the thermal conductivity decreases, Si doping has significant effect on thermoelectric properties of boron carbides.
Atomistic Simulations of Cross-Slip Processes in Model FCC Structures and L10 TiAl
Authors: Rao S.
Published: April 2011

Three dimensional (3D) cross-slipped core structures of a/2[110] screw dislocations in model FCC structures are simulated using lattice statics within the Embedded Atom Method (EAM) formalism using potentials fitted to the elastic and structural properties of FCC Ni as well as L10TiAl. 2 and 3-D Green's function (GF) techniques are used to relax the boundary forces in the simulations. The core structure of the constrictions are diffuse. At large separation distances between Shockley partials in the unconstricted configuration, the two constrictions formed by cross-slip onto a cross {111} plane have significantly different energy profiles suggesting that self-stress forces dominate the energetics of the cross-slip process. The variation in cross-slip energy with stacking-fault energy is in reasonable agreement with continuum predictions, excepting at high fault energy values as in L10TiAl. Cross-slip energies estimated for Cu, Ni and γ-TiAl from these calculations show reasonable agreement with experimental data. The cross-slip energy shows a significantly weaker dependence on Escaig stress as compared to elasticity calculations, with the activation volume for the cross-slip process being approximately 20b3 at an applied Escaig stress of 10-3μ in Cu.
Temperature Effects and Fast-Moving Screw Dislocations at High Strain Rate Deformations
Authors: Roos A. , Metselaar E.D. , Hosson J.TH.M. De , Cleveringa H.H.M. , Giessen E. Van Der
Published: April 2011

In this paper, shear deformation at high strain rates is modeled within the framework of discrete dislocation plasticity. The method of discrete dislocation plasticity is extended to incorporate the temperature rise induced by moving dislocations. Also, the stress and displacement fields of a screw dislocation on inclined planes in a periodic structure are developed. The influence on the temperature rise on various micro-mechanical processes is discussed.
A Dlts Investigation of The Effect of Ion Mass, Fluence and Energy on the Introduction of a Higher-Order Vacancy Cluster in Noble Gas Ion Bombarded n-Si
Authors: Deenapanray P.N.K. , Williams J.S.
Published: April 2011

We have recently reported the annealing and electrical properties of three new families (N1, N2 and N3) of vacancy complexes introduced in 1 keV He-, Ne- and Ar-ion bombarded nSi. In this paper we have employed deep level transient spectroscopy to investigate the ion mass, fluence and energy dependence of the introduction of N1 -defects. We observed an increase in the intensity of Ni -defects with increasing mass of bombarding ions for a fluence of 1×1012cm−2and flux of 1×1011cm−2s−1, which we have correlated with the mass dependence of nuclear energy deposition. The ratio of the intensities of Ni-defects to VO-center, [N1]/[VO], increased by ∼5 when bombarding with Ar- compared to He-ions. Increasing the Ar-ion fluence from 1×1012cm−2to l×1014cm−2for a flux of 5×1010 cm−2s−;1increased the intensity of N1-defects by ∼20 times, while [N1]/[VO] increased by a factor ∼2.3. N1-defects were not created by 5.4 MeV alpha-particle irradiation, but were present in varying relative concentrations in 1 to 150 keV He-ion bombarded n-Si.
Radiation Effects in Nonmetals: Amorphization, Phase Decomposition, and Nanoparticles
Authors: Meldrum A. , Boatner L.A. , White C.W. , Henderson D.O.
Published: April 2011

Radiation effects in nonmetals have been studied for well over a century by geologists, mineralogists, physicists, and materials scientists. The present work focuses on recent results of investigations of the ion-beam-induced amorphization of the ABO4 compounds – including the orthophosphates (LnPO4; Ln = lanthanides) and the orthosilicates: zircon (ZrSiO4), hafnon (HfSiO4), and thorite (ThSiO4). In the case of the orthosilicates, heavy-ion irradiation at elevated temperatures causes the precipitation of a nanocrystalline metal oxide. Electron irradiation effects in these amorphized insulating ceramics can produce localized recrystallization on a nanometer scale. Similar electron irradiation techniques were used to nucleate monodispersed compound semiconductor nanocrystals formed by ion implantation of the elemental components into fused silica. Methods for the formation of novel structural relationships between embedded nanocrystals and their hosts have been developed and the results presented here demonstrate the general flexibility of ion implantation and irradiation techniques for producing unique near-surface microstructures in ion-implanted host materials.
Interaction of Deuterium with Cavities In Crystalline Si and Mgo
Authors: Fedorov A. V. , Veen A. Van , Schut H.
Published: April 2011

To create cavities a Si (100) single crystal and a MgO (100) single crystal were subjected to 30 keV 3 He implantation and a subsequent annealing at 1100 K. In both materials the formation of cavities takes place during the annealing stage when the implanted gas is released. The presence of cavities was detected by positron beam analysis. After the creation of cavities was established the samples were re-filled with deuterium by means of 15 keV D+ implantation with a dose of 1015 cm−2. During the subsequent annealing at 1000 K D escaped from the cavities. In the case of MgO further growth of cavities was observed.
The Structure of Ion-Implanted Amorphous Silicon
Authors: Gibson J. M. , Cheng J-Y. , Voyles P. , TREACY M.M.J. , Jacobson D.C.
Published: April 2011

Using fluctuation microscopy, we show that ion-implanted amorphous silicon has more medium-range order than is expected from the continuous random network model. From our previous work on evaporated and sputtered amorphous silicon, we conclude that the structure is paracrystalline, i.e. it possesses crystalline-like order which decays with distance from any point. The observation might pose an explanation for the large heat of relaxation that is evolved by ion-implanted amorphous semiconductors.
Irradiated Microstructures of Magnesium Aluminate Spinel and their Controlling Factors
Authors: Kinoshita C. , Matsumura S. , Yasuda K. , Soeda T. , Noujima M.
Published: April 2011

This paper reviews our recent progress in study on the strong resistance of magnesium aluminate spinel to void swelling during irradiation, along with the related characteristic features of its radiation damage. Comparative experimental results on irradiated microstructures and mechanical properties in magnesium aluminate spinel and alpha-alumina are shown in terms of controlling factors of radiation resistance of the former crystal. It is experimentally shown that structural vacancies due to non-stoichiometry provide effective recombination sites for displaced cations to suppress the formation of interstitial loops. Decreased formation of interstitial loops enhances the further recombination of interstitials and vacancies and thereby the formation of voids.
A Comparative Study of Mechanical Properties in Ion-Irradiated A12O3 and MgO·nAl203
Authors: Yasuda K. , Kinoshita C. , Izumi K.
Published: April 2011

We have investigated radiation hardening in alumina (A1203), stoichiometric and nonstoichiometric spinel (MgO·nA1203: n= 1, 2.4) crystals at 300 K irradiated with 100 keV He+ ions by using a ultra-microhardness technique. Al203 shows a remarkable radiation hardening (35% increase in hardness) at a fluence of 5×1019 He+/m2 and saturates at 60 % of the maximum value at fluences higher than 8×1019 He+/m2. In spinel crystals, hardness increases monotonically with fluence, reaching to a saturation at a fluence of 1×1020He+/m2. Analyses of load- displacement curves indicate that both plastic and elastic hardening are responsible for the radiation hardening in A1203, and that plastic hardening is the main cause in MgO'nAl2O3. Microstructure observations and lattice constant measurements showed that point defects are mainly responsible for the radiation hardening in both A1203 and MgO·nAl2O3. The difference in the radiation hardening response is discussed in terms of the difference in recombination rate of point defects among the MgO-A1203 system ceramics.
The Search for Interstitial Dislocation Loops Produced in Displacement Cascades at 20K in Copper
Authors: Kirk M. A. , Jenkins M. L. , Fukushima H.
Published: April 2011

A low-temperature in situ ion-irradiation and annealing experiment has been performed by TEM in copper. Most defect clusters which persisted through an anneal to 120 K showed no size changes within the resolution (0.5 nm) of a new weak-beam sizing technique. Of 55 defects measured under a range of weakly diffracting conditions, 7 showed measurable size decreases while 3 showed size increases. We argue that these clusters are likely to be of vacancy and interstitial nature, respectively. Also on annealing to 120 K a fraction of about 25% of the clusters formed by irradiation with 600 kV Cu+ ions at 20 K disappeared, while a similar number of clusters appeared in different locations.
Formation of Voids in Pure Copper and FE-CR-NI Alloys Irradiated by Simultaneous Multi-Ion Beam of Hydrogen, Helium and Ni Ions
Authors: Mukouda I. , Shimomura Y. , Iiyama T. , Katano Y. , Yamaki D. , Nakazawa T. , Noda K.
Published: April 2011

Pure copper and Fe-15Cr-2ONi alloy were irradiated at 500°C by 5 MeV Ni ions (single beam), Ni ions plus gas atoms (H and He) (dual beam irradiation) or triple beam of Ni, He and H ions (triple beam irradiation) simultaneously. Irradiation was carried out with accelerators TIARA at Takasaki-establishment of JAERI. Thin specimens were prepared with the combined technique of FIB (Focus Ion Beam) and electro-polishing. Damage structure versus the depth from surface was examined by TEM. In Fe-15Cr-20Ni alloy, voids were formed in the range of Ni ion irradiated specimens. In Fe-Cr-Ni alloy which is irradiated by a dual beam of Ni ion and He ion, the number density of voids increased significantly at the stopping range of He atoms. Remarkable results are void formation in specimens irradiated with dual beam of Ni and H ions, only voids of very small size were observed through the range of specimen. In irradiated specimen with triple beam, the size of voids was suppressed to be smaller than that of irradiated specimens with Ni and He ions. In pure copper which is irradiated with dual beam of helium and Ni ions, number density of voids were increased significantly. While in copper irradiated with hydrogen and Ni ions, number density of voids were not so large. Experimental results show that helium atoms have strong effect for void formation, while hydrogen atoms suppress void formation because the remarkable degradation of movement of small vacancy clusters can be induced by trapping hydrogen atoms.
Ion Irradiation of GeSi/Si Strained-Layer Heterostructures
Authors: Glaskol J.M. , Elliman R. G. , Zou J. , Cockayne D.J.H. , Gerald J. D. Fitz
Published: April 2011

The strain in GeSi/Si strained layer heterostructures is studied as a function of ion-irradiation and thermal annealing conditions and correlated with the defect microstructure in the GeSi alloy layer. For room temperature irradiation, compressive strain within the alloy layer increases with increasing ion fluence for both low (projected range of ions within the alloy layer) and high energy (projected range of the ions greater than alloy thickness) irradiation. In contrast, elevated temperature irradiation results in an increase in strain for low-energy irradiation, but a decrease for high-energy irradiation. For example, strain relaxation is observed in layers irradiated with I MeV 28Si+ at 253 °C. During subsequent annealing to 750 °C, the strain is partially recovered but relaxes again at temperatures > 750°C. This behavior is shown to be consistent with the evolution of intrinsic (vacancy-type) defects within the alloy layer.
Atomistic Simulation of Mobile Defect Clusters in Metals
Authors: Osetsky Yu.N. , Bacon D.J. , Serra A.
Published: April 2011

The structure, stability and thermally-activated motion of interstitial and vacancy clusters in Fe and Cu have been studied using atomic scale computer simulation. All studied interstitial clusters and perfect interstitial loops (PILs) in Fe are mobile whereas their mobility in Cu can be suppressed at large sizes (bigger than 49–61 self-interstitials depending on the temperature) due to dissociation. A comparative study of relaxed configurations has shown that the structure of small perfect dislocation loops of vacancy and self-interstitial nature is very similar. Molecular dynamics simulation has demonstrated that small perfect vacancy loops (PVLs) in Fe consisting of more than 37 vacancies are stable over a wide temperature range and produce atomic displacements by a thermally-activated movement in the direction of the Burgers vector. The mechanism is qualitatively similar to that of SIA clusters studied earlier. Motion of vacancy loops in Cu does not occur because they transform into sessile configurations similar to stacking fault tetrahedra. These results point to the possibly important contribution of vacancy loop mobility to the difference in radiation damage between bcc and fcc metals, and between fcc metals with different stacking fault energy.
Annealing Kinetics of Single Displacement Cascades in Ni: An Atomic Scale Computer Simulation
Authors: Almazouzi A. , Caturla M. J. , Rubia T. Diaz de la , Victoria M.
Published: April 2011

In order to describe the long term evolution of the defects produced by a displacement cascade, Molecular dynamics (MD) and Kinetic Monte Carlo (KMC) methods are employed. Using an empirical Ni interatomic potential in MD, the damage resulting from primary knock-on atom (PKA) energies up to 30 keV has been simulated. The annealing kinetics and the fraction of freely migrating defects (FMD) are determined for each single displacement cascade, by a KMC code which is based on a set of parameters extracted mainly from MD simulations. It allows an atomistic study of the evolution of the initial damage over a time scale up to lOOs and the determination of the fraction of the defects that escape the KMC box, compared to those obtained by MD, as function of temperature and PKA energy. It has been found that this fraction depends strongly on the temperature but reaches a saturation value above stage V.
Mechanical Properties of Feedstock Material for Fused Deposition of Ceramics
Authors: Venkataraman N. , McNulty T. , Rangarajan S. , Vidaic M. , Matthewson M. J. , Langrana N. , Safari A. , Danforth S. C.
Published: April 2011

A scientific methodology to characterize the critical mechanical properties of feedstock material for fused deposition of ceramics has been developed. A detailed discussion of the methodology of mechanical characterization and results for lead zirconate titanate (PZT) fused deposition of ceramics (FDC) feedstock is presented. The effect of storage time, temperature and crosshead displacement rates on the mechanical properties of the PZT FDC feedstock was studied. The modulus and the failure stress increase with displacement rate. The modulus and failure stress decrease with temperature indicating the necessity for cooling filaments prior to entrance to liquefier. The modulus also decreases with storage time in 50% RH while failure strain increases with storage time in 50% RH.
Direct-Write Precision Resistors for Ceramic Packages
Authors: Yang P. , Dimos D. , Rodriguez M. A. , Huang R. F. , Dai S. , Wilcox D.
Published: April 2011

A direct-write approach to fabricate high precision resistors is reported. Special attention is paid to the effect of print thickness on the resistance value of buried resistors after a low temperature co-firing process. The results show that the direct-write approach provides a superior line definition and thickness control over a traditional screen printing process. Microstructural analysis indicates that there is an interdiffused layer developed between the resistor material and the low temperature co-fired ceramic substrate. These observations are consistent with electrical measurements which show that resistance increases as the effective cross-sectional area is reduced. The resistance data show that the standard deviations for resistors printed on a 6” × 6” area are 5% and 15% for the direct-write and the screen-printed patterns, respectively.
Freeform Fabrication of High Performance Titanium Components via SLS/HIP
Authors: Das S. , Beaman J. J. , Wohlert M. , Bourell D. L.
Published: April 2011

This paper presents the development of Selective Laser Sintering/Hot Isostatic Pressing (SLS/HIP) technology for production of functional high performance components in the titanium alloy Ti-6AI-4V. SLS/HIP is a net shape manufacturing technique that combines and exploits the freeform shaping capability of selective laser sintering and the full densification capability of hot isostatic pressing. The advantages of SLS combined with in situ HIP encapsulation include single step net shape canning, full densification by containerless HIP, no container-powder adverse interactions, reduced pre-processing time, and minimal post-process machining compared to conventional HIP of canned powders. Microstructure and mechanical properties of SLS processed and HIP post-processed Ti-6A1-4V are consistent with conventionally processed material. The potential of SLS/HIP technology was demonstrated by net shape fabricating a component to specification, namely the titanium guidance section housing base for the AIM-9 Sidewinder missile.
Direct Materials Deposition: Designed Macro and Microstructure
Authors: Mazumder J. , Schifferer A. , Choi J.
Published: April 2011

Rapid Fabrication of three-dimensional shapes of engineering materials such as H 13 tool steel and Nickel super alloys are now possible using Direct Materials Deposition (DMD) technique. H 13 tool steel is one of the difficult alloys for deposition due to residual stress accumulation from martensitic transformation. However, it is the material of choice for the die and tool industry. DMD offers Copper chill blocks and water cooling channels as the integral part of the tool. On the other hand ZrO2 was co-deposited with nickel superalloys using DMD. This process thus is amenable to produce both macro and microstructure to a designed specification. This paper briefly reviews the state of the art of DMD and describes the microstructure and mechanical properties of selected engineering alloy systems deposited by DMD.
Processing of Novel Electroceramic Components by SFF Techniques
Authors: Safari A. , Danforth S. C. , Kholkin A. L. , Cornejo I. A. , Mohammadi F. , McNulty T. , Panda R.
Published: April 2011

Novel piezoelectric ceramic and ceramic/polymer composite structures were fabricated by solid freeform fabrication (SFF) for sensor and actuator applications. SFF techniques including fused deposition of ceramics (FDC) and Sanders prototyping (SP) were utilized to fabricate a variety of complex structures directly from a computer aided design (CAD) file. Novel composite structures including volume fraction gradients (VFG) and staggered rods, as well as actuator designs such as tubes, spirals and telescopes were made using the flexibility provided by the above processes. VFG composites were made by SP technique with the ceramic content decreasing from the center towards the edges. This resulted in a reduction of side lobe intensity in the acoustic beam pattern. The FDC technique was used to manufacture high authority actuators utilizing novel designs for the amplification of strain under applied electric field. The design, fabrication and electromechanical properties of these composite and actuator structures are discussed in this paper.
Homogeneity, Anisotropy, and Texture In Si3n4 Ceramics made by Fused Deposition
Authors: Rangarajan S. , Pozsgai I. , McIntosh J. , McCuiston R. , Harper B. L. , Langrana N. , Safari A. , Danforth S. C. , Clancy R. B. , Gasdaska C. , Whalen P. J.
Published: April 2011

The Fused Deposition of Ceramics (FDC) process is an extrusion based layered manufacturing technique. In this study, the microstructural and property homogeneity of GS44-Si3N4 parts made by FDC is examined. The feedstock, green, and sintered parts were examined using characterization techniques such as optical and scanning electron microscopy, x-ray radiography, and x-ray diffraction. In addition, mechanical properties (σf, and Klc), shrinkage, and warpage results were used to characterize the FDC parts. It was found that by using proper build parameters and tool paths, dense, homogenous, near-net-shape GS44-Si3N4 parts can be fabricated. While the mechanical properties of these parts are shown to be isotropic, there is some degree of texturing detected with XRD. Si3N4 filament feedstock intentionally textured with 5.5 vol% of β-seed particles has also been made.
Thermoelectric Properties of AgBiTe2-Ag2Te Composite
Authors: Takigawa Y. , Imoto T. , Sakakibara T. , Kurosawa K.
Published: April 2011

We prepared composite materials of AgBiTe2 with several contents of Ag2Te small-size grains for applications to thermoelectric devices. By enhancing long-wavelength phonon scattering at the grain boundaries, lattice thermal conductivity (thermal conductivity due to lattice vibrations) decreased 30% and thus the thermoelectric characteristics were significantly improved.
Experimental Study of Phonon-Folding in Si/Ge and Si/Sige Structures Designed for Thermoelectric Applications
Authors: Liu J. , Balandin A. , Borca-Tascjuc T. , Tang Y. S. , Wang K. L. , Chen G.
Published: April 2011

We report data of Raman study of Si/Ge and Si/SiGe superlattices designed for thermoelectric applications. The obtained Raman spectra clearly indicate the presence of folded doublets from longitudinal acoustic phonons. Due to the significant difference in the sound velocities for Si and Ge the position of the doublets strongly depends on the superlattice layer thickness and ordering. Comparison of the Raman data for different samples with measured thermal and thermoelectric properties allows us to determine a correlation between the strength of the phonon confinement in these structures and their thermoelectric properties. Our experimental results are consistent with recent theoretical prediction of increased thermoelectric figure of merit in semiconductor quantum wells.