bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Structure of Silica Glasses by Molecular Dynamics Simulations
Authors: Levine S. M. , Garofalini S. H.
Published: March 2011

Molecular dynamics computer simulations were used to study surfaces of pure silica glass. The potentials used here were those previously established to model bulk silica and have been extended to study surface relaxation in a perfect vacuum. A large number of surfaces were made using different starting configurations; system sizes, and cooling procedures. Following “fracture”, many broken bonds rearranged in response to the changes in the net forces in the surface region. After this reconstruction, the simulations showed the expected general features observed experimentally, such as a prevalence of oxygen atoms at the outermost surface, non-bridging oxygens, and strained siloxane bonds. Three fold silicons (similar to e’ centers) were initially present in the “fractured” surfaces but most often were incorporated into the network tetrahedrally after reconstruction. Other defects produced during the reconstruction were five coordinated silicons and more importantly, edge sharing tetrahedra, forming the strained siloxane bonds. Bond angles and bond lengths for each defect were determined, showing good agreement with previously published results as well as providing new information. Finally, estimations for silanol concentrations were made which compare well with experimentally determined coverages. The computer simulation technique used here adequately reproduces many of the structural and dynamic characteristics of silica glass surfaces.
Time Resolved Fluorescence Line Narrowing in Ytterbium-Doped Inorganic Glasses
Authors: Brundage R. T. , Yen W. M.
Published: March 2011

We have used time resolved fluorescence line narrowing to study optical dephasing and energy transfer among Yb3+ ions doped in inorganic glasses. We observe for the first time in any rare earth doped glass system a change in the power of the temperature dependence of the homogeneous linewidth of the 2F5/2(1)-2F7/2(1) transition of Yb, 3+ as well as an efficient one-phonon assisted energy transfer process occuring among Yb3+ ions at higher concentration due to a quadrupole-quadrupole coupling of the ions. In this paper we review past studies in rare earth doped gla s systems of these topics and compare them to our observations of Yb3+ in silicate and phesphate glasses.
Color Centers in Glass Optical Fiber Waveguides
Authors: Friebele E. J. , Griscom D. L.
Published: March 2011

Color centers formed in the core and cladding of optical fiber waveguides by exposure to nuclear radiation can greatly increase the attenuation in the infrared spectral region of interest for optical communications. The radiation-induced paramagnetic defect centers in pure silica, silica doped with Ge, P, or B, and heavy metal fluoride glasses have been identified and thoroughly characterized by electron spin resonance (ESR) techniques. This paper will review the results of recent studies of color centers in optical fiber waveguide materials and their Identification via correlations of the radiation-induced optical absorptions and defect centers elucidated by ESR.
Topological Origin of the Surface Singularities in Glasses
Authors: Kerner Richard
Published: March 2011

A model of CRN in two dimensions is presented, composed of equilateral but not equiangular polygons with a constant coordination number = 3; in a simplified version only pentagons, hexagons and heptagons are present in the network. We introduce the mean potential energy per atom averaged over a typical cell containing three adjacent polygons; we assume that although the thermal equilibrium is not attained for single atoms, it is attained on the level of these cells, so that we can apply the virial theorem for the cells. Then we minimize the free energy which contains the configuration entropy contribution. In terms of two variables P and δ (hexagon frequency and mean bond angle deviation) we get the surfaces of constant energy. Under stress the energy configurations cease to be one-connected, and the 0-th homotopy group is no more trivial. This can give rise to surface singularities (cracks).
The Structure of SiO2-Sol-Gel Glasses Produced from Gels with Various Mole-Water per Mole-TEOS Ratios
Authors: Kordas George
Published: March 2011

SiO2-gels produced with 4,8, and 16 mol water per mol TEOS were densified up to 1000°C and then exposed to gamma-ray irradiation in order to produce paramagnetic defect centers. Various paramagnetic states were detected during densification of these gels, the formation of which depends on the mol water per mol TEOS ratio. In the gels O−2 ions were detected. The paramagnetic centers detected in the n = 16 gel with TH = 900°C were attributed to a non-bridging oxygen and an E'1-center. Three different O−2 ions, probably in interstitial positions, were detected in the n = 16-gel with TH = 1000°C. The CO−2 center was observed in the n = 8 gel with TH = 900°C. A variety of new components occur at TH = 1000°C in the n = 8 gel, the origin of which remains unresolved at present. The CH3, CO−2, and E1′-centers were detected in the n = 4 gel with TH = 700°C. The CO−2 and E′1 centers were preserved after heat treating the n = 4 gel at TH = 1000°C.
Materials by Design – a Hierarchical Approach to the Design of New Materials
Authors: Eberhardt James J. , Hay P. Jeffrey , Carpenter Joseph A.
Published: March 2011

Major developments in materials characterization instrumentation over the past decade have helped significantly to elucidate complex processes and phenomena connected with the microstructure of materials and interfacial interactions. Equally remarkable advances in theoretical models and computer technology also have been taking place during this period. These latter now permit, for example, in selected cases the computation of material structures and bonding and the prediction of some material properties. Two assessments of the state of the art of instrumental techniques and theoretical methods for the study of material structures and properties have recently been conducted. This paper will discuss aspects from these assessments of computational theoretical methods applied to materials. In addition, an approach will be presented which uses advanced instrumentation and complementary theoretical computational techniques in tandem in an effort to construct and verify hierarchies of models to translate engineering materials performance requirements into microscopic-level and atomic-level materials specifications (composition, structure, and bonding). Areas of practical interest include catalysis, tribology (contacting surfaces in relative motion), protective coatings, and metallurgical grain boundaries. A first attempt involving modeling of grain boundary adhesion in Ni3Al with and without boron additions will be discussed.
Microstructural Dynamic Study of Grain Growth
Authors: Anderson M. P. , Grest G. S. , Srolovitz D. J.
Published: March 2011

The complete prediction of microstructural development in polycrystalline solids as a function of time and temperature is a major objective in materials science, but has not yet been possible primarily due to the complexity of the grain interactions. The evolution of the polycrystalline structure depends upon the precise specification of the coordinates of the grain boundary network, the crystallographic orientations of the grains, and the postulated microscopic mechanisms by which elements of the boundaries are assumed to move. Therefore, a general analytical solution to this multivariate problem has not yet been developed. Recently, we have been able to successfully incorporate these aspects of the grain interactions, and have developed a computer model which predicts the main features of the microstructure from first principles [1,2]., The polycrystal is mapped onto a discrete lattice by dividing the material into small area (2d) or volume (3d) elements, and placing the centers of these elements on lattice points. Interactions and dynamics are then defined for the individual elements which are analagous to those postulated in continuous systems. This discrete model preserves the topological features of real materials, and can be studied by computer simulation using Monte Carlo techniques. In this paper we report the application of the Monte Carlo method to the metallurgical phenomenon of grain growth with isothermal annealing. Extension of the model to treat primary recrystallization is presented elsewhere [3,4].
Computer Simulation of Sputtering from Two Component Liquid Metal Targets
Authors: Shapiro M. H. , Lo D. Y. , Tombrello T. A.
Published: March 2011

The sputtering of In and Ga atoms from a “liquid” target composedof gallium coveredby a surface monolayer of indium by incident 5 keV Ar+ ions was simulated using the multiple interaction molecular dynamics technique. Yields, energy distributions, and angular distributions of sputtered atoms were obtained at a temperature above the melting point for the eutectic alloy. Similar information was obtained for a pure gallium and a pure indium target. Our results for layer yield ratios and angular distributions are in good qualitative agreement with Dumke's experimental data for the Ar+, In-Ga system. Absolute yields, however, were found to be sensitive to the detailed nature of the two-body potentials used to describe the atom-atom interactions.
Dynamics of Compressed and Stretched Liquid SiO2, and the Glass Transition
Authors: Angell C. A. , Cheeseman P. A. , Phifer C. C.
Published: March 2011

Ion dynamics simulations are presented to model the system SiO2over wide ranges of temperature and density as it passes from liquid into glassy states. Essential features of the diffusive mechanism by means of which the system configuration space is explored are examined in relation to density and structure. The presence of a water-like density maximum in the liquid state of this system is established by using the negative pressure regime to stretch the system and thereby sharpen the phenomenon.
Crystal. Liquid and Glass in 2 Dimensions. Analysis of the glass Transition
Authors: Lançon Frédéric , Chaudhari Praveen
Published: March 2011

A molecular dynamics technique has been used to simulate the melting of a 2-dimensional diatomic crystal and to quench the liquid phase to a solid phase. We demonstrate that a 2-dimensional dense amorphous structure can be obtained and that a 2-dimensional glass transition does exist. Furthermore, atomic vibrations in the liquid can be separated from motion produced by diffusion. The relaxation time during which atoms have a vibratory motion but do not diffuse, diverges to infinity near the observed glass transition. Because of the 2-dimensionality. we are able to display the microscopic processes associated with the glass transition.
Three Dimensional Characterization of Interfaces in Semiconductors by Scanning Electron Microscopy
Authors: Joy David C. , Maher D. M. , Farrow R C
Published: March 2011

In many semiconductor materials problems, structural characterizations must be achieved in both the lateral and vertical dimensions. Although a combination of cross-sectional and planar transmission electron microscopy can provide this information, the sample preparation time is demanding and only relatively small volumes of material are examined. We describe here an alternative approach in which the charge collection (‘CCM’) imaging mode of the scanning electron microscope (SEM) is used. It is shown that, by varying the incident electron beam energy, electricallly active defects at different positions beneath the entrance surface of the material can be imaged and their depth estimated.
Raman Scattering Study of Mixing of GaAs/AlAs Superlattices by Ion Implantation and Rapid Thermal Annealing
Authors: Kirillov D. , Ho P. , Davis G. A.
Published: March 2011

Raman scattering was applied to study mixing of GaAs/AlAs superlattices. Different implantation ions and doses were used. The evolution from partially amorphous to completely amorphous and from partially mixed to completely mixed structures was observed. Rapid thermal annealing caused recrystallization of the damaged material. Different types of structures were obtained, depending on the implantation doses and species of ions. Completely mixed crystalline alloys could be obtained only for high implantation doses.
Characterization of Recoiling Oxygen in Silicon by Double-Crystal X-Ray Diffraction, Tem and Monte Carlo Simulation
Authors: Cembali F. , Mazzone A. M. , Servidori M.
Published: March 2011

The widespread use of through-oxide implants in Si-MOS technology has prompted many studies to characterize the behaviour of oxygen recoiling from the passivating SiO2 layer into the Si substrate. These studies have given support for the idea that an anomalous formation of defects, which alter the profile of the implanted impurity and the mobility of the free carriers, is connected with the oxygen recoils.
Micro-Tomography Using Synchrotron Radiation
Authors: Johnson Quintin C. , Kinney John H. , Bonse Ulrich , Nichols Monte C. , Nusshardt Rudolf , Brase James M.
Published: March 2011

This paper discusses the results of recent experiments at Stanford Synchrotron Radiation Laboratory (SSRL) and Hamburger Synchrotronstrahlungslabor (HASYLAB) which were designed to explore the feasibility of using synchrotron radiation in high-resolution, computerized, critical-absorption tomography. The results demonstrate that it is possible, using absorption-edge differencing, to identify adjacent elements in the periodic table with high sensitivity. Furthermore, by using the fine structure in the absorption spectra, it is possible to distinguish between regions of different chemical states. Methods of using synchrotron radiation for high-resolution, three-dimensional chemical-state mapping in small samples are discussed.
Analysis and Comparison of EL2 Concentration and Stress Distribution in Undoped LEC-Grown Semi-Insulating GaAs Ingots
Authors: Dobrilla P. , Blakemore J. S.
Published: March 2011

Near-IR absorption mapping has been used for polished GaAs wafers (0.5 mm thick) cut at intervals along the seed-to-tail length of (100)-oriented LEC-grown semi-insulating (SI) ingots. Some 2000 points are measured, point by point, over a wafer's area, usually near 1.0 μm for EL2 mapping, and near 1.4 μm for observation of stress interferograms. For the results presented here (high pressure LEC crystals from a major commercial supplier), stress maps display the fourfold symmetry predicted in thermoelastic models. The EL2 maps do not necessarily display the same symmetry, especially for wafers from near the tail end of an ingot.
Raman Spectroscopy for Semiconductor Thin Film Analysis
Authors: Nemanich R. J.
Published: March 2011

The application of Raman spectroscopy to various semiconductor thin film, interface and surface problems will be presented. Specific focus will be on the vibrational excitations of the materials systems which are probed by the Raman measurements. Experimental configurations are described which are optimized for general thin film analysis, microprobe analysis, and in situ UHV surface/interface analysis. The vibrational properties can be used for phase and composition identification, crystal/amorphous structure, strain, impurity configurations, and superlattice properties. Specific examples will include thermal processing of CVD Si films, microprobe of laser annealed films, MOCVD AlxGa1−xAs films, silicide formation and identification, amorphous superlattices, and hydrogen impurities in crystalline Si.
Optimizing the Depth Resolution of Rutherford Backscattering Through Modeling of Noise Sources
Authors: Abelson John R. , Sigmon T. W.
Published: March 2011

Grazing angle configurations improve the depth resolution of Rutherford Backscattering Spectrometry (RBS) because the path length of scattered particles is geometrically increased. But in the limit of very grazing angles the resolution degrades due to the finite detector acceptance angle and low angle forward scattering of the beam, considerations which are not present in near-normal incidence geometries. The forward scattering, for example, worsens the depth resolution approximately as the square of the depth, rather than the familiar square root dependence of energy straggling. We present a simple computational scheme which predicts the depth resolution in any target as a function of scattering depth, beam energy, and the grazing angle. The calculations are simpler than previous studies because we use analytic expressions in place of numerical inputs without loss of accuracy. The results lead directly to an optimum depth resolution. We find good agreement between the predicted resolution and measurements on thin silicon dioxide and amorphous silicon films. Finally, we calculate the resolution expected with the use of ion beams heavier than He+, and find improved near surface depth resolution if a low noise detector is used.
Investigation of Metal/GaAs Reactions by Heavy Ion Rutherford Backscattering Spectrometry(HIRBS)
Authors: Yu Kin Man , Jaklevic J. M. , Haller E. E.
Published: March 2011

Thermally activated metallurgical reactions between GaAs and various metals of potential importance in contact structures were studied using Heavy Ion Rutherford Backscattering Spectrometry (HIRBS). The improved mass resolution obtained with heavy ions (160) as projectiles for backscattering measurements facilitated the identification of the various intermetallic compounds formed on GaAs. The metal/GaAs systems investigated in this study included Pt/GaAs, Pd/GaAs, and Ni/GaAs. Three different binary compounds were formed in the Pt/GaAs system during annealing. Complete reaction between 1200Å of Pt and GaAs was observed after annealing at 500°C for 20 min. Reactions in Pd/GaAs and Ni/GaAs systems were, however, very different from that of Pt/GaAs. Both Pd and Ni formed ternary compounds with GaAs. Detailed information on the various compound compositions of the three systems as measured by HIRBS is presented. Comparisons of results on similar systems obtained by using other analytical techniques are discussed.
Deviations from Bragg's Rule for the Stopping Cross Sections of Deuterium in Titanium and Zirconium Deuteride Films
Authors: Borders J. A.
Published: March 2011

The ratios of the stopping cross sections of deuterium ions in titanium and zirconium deuteride films to those in the pure metals have been determined at incident deuteron energies from 300 keV to 2.0 MeV. These ratios are evaluated from measurements of the yields of deuteron elastic scattering in the deuteride films and in films of the pure metals. Although the absolute stopping cross sections cannot be evaluated from the measurements, use of the Brice yield equation allows the ratios of the cross sections in the deuterides to those in the pure metals to be determined. Significant deviations from Bragg's rule are found and these results are in general agreement with recent measurements at lower deuteron energies (40–200 keV). These measurements represent some of the largest deviations from strict additivity of stopping powers yet observed.
Numerical Analysis of Transient Capacitance Data Obtained from Titanium Induced Levels in Silicon
Authors: Courcelle E. , Mesli A. , Siffert P.
Published: March 2011

Using electrical and optical DLTS analysis based on the capacitance transient measurements and taking into account the spatially dependent capture and the competition between emission and capture, parameters of Titanium levels in silicon are derived. By curve fitting the calculation to trap-filling data, the electron capture cross section of the first donor level (Ec - .284 eV) is found to be 5.8 10-15 exp (.013/kT)cm2 at ξ= 5 104 V/cm. The hole trap capture cross section of the second donor level (Ev + .260 eV) is found to be 1.97 10-17exp (-.017/kT)cm2 at zero electric field.
Material Characterization by Contactless Photoconductivity Measurements
Authors: Kunst M. , Werner A.
Published: March 2011

Transient photoconductivity measurements with the time-resolved microwave conductivity (TRMC) method have been applied to three different types of semiconductors: hydrogenated amorphous silicon, single crystalline silicon and GaAs/GaAlAs multiple quantum well structures. Analysis of the signals in terms of charge carrier-lattice interaction points to an intimate relation between TRMC signals and intrinsic material properties. It is shown that the TRMC-technique is an excellent tool to characterize photosensitive materials.
Determination of the Dislocation Network Density in GaAs Using Thermal Wave Microscopy
Authors: Brandes Anita G. , Tang Chwan , Fillmore Charles
Published: March 2011

The pattern and density of dislocations in GaAs is thought to affect the ultimate performance of finished devices. Previous studies of dislocation networks have usually involved molten KOK etching of GaAs wafers or X-ray topography. A relatively new technique, Thermal Wave Microscopy (TWM), offers an alternative method of analysis. High frequency blanking of the scanning electron beam in an SEM produces thermal waves that propagate approximately 1–2 wavelength through a sample, are then carried by thermoacoustic waves and detected by a piezoelectric transducer. Dislocations, microcracks, and voids will disturb this wave and the resulting image will show a change in contrast (bright or dark) at the defect site. Resolution is dependent on the thermal properties of the material being analyzed as well as on the accelerating voltage, beam current, beam blanking frequency and phase of the electron beam. TWMim ages of dislocation networks in as-received GaAs are very similar in appearance to the results of molten KOH etching. TWM is a relatively new technique for microanalysis. Its full range of applications are still being explored. For determination of dislocation networks it is a faster, less cumbersome method of analysis. TWM is a basically nondestructive technique involving none of the uncertainties of molten KOH etching (etch time, etch uniformity). For this reason TWM is recommended as an alternative analytical technique.
The Elastic Properties of LaNbO4
Authors: Nevitt M. V. , Chan S.-K. , Grimsditch M. H. , Fisher E. S.
Published: March 2011

The measurement of single-crystal elastic properties is an important method of materials characterization. Elastic properties define intrinsically bulk behavior, but they also provide a microscopic insight into the dynamical behavior of the crystal lattice in relation to crystal structure and bonding. Moreover, they are particularly informative probes into the onset and the nature of a lattice instability and its role in inducing a phase transformation. On a macroscopic scale, stress-strain relationships, particularly those of an anisotropic kind, can be better understood and described in terms of the single-crystal elastic constants.
Neutron-Induced Particle Track Mapping of Elemental Distributions
Authors: Bild R. W.
Published: March 2011

Thermal neutrons are captured by several elements which emit charged particles as reaction products. These particles leave etchable damage tracks in detector materials placed against a sample, creating a map of the distribution and concentration of the target element. The most common applications are for trace U using fission fragment tracks and B using alpha tracks. Li, N and possibly S and O can also be determined. We have applied the technique to B in metals and coatings, Li in Al, N in glass and U in O-ring seals. Dectection limits are better than 10−11g/g for U, 10−9g/g for B, 10−6g/g for Li and 0.1 wt % for N. Spatial resolution for mapping is about 25 μm.
Spatially-Resolved Non-Contact Methods for the Investigation of Transport and Defects in Semiconductors
Authors: Amer Nabil M.
Published: March 2011

Photothermal spectroscopy employs the small rise in temperature associated with the absorption of electromagnetic radiation to probe optical and transport properties of materials. A review of the various photothermal detection schemes is given, and examples which illustrate the power of this technique are reviewed.
Deep Level Transient Spectroscopy: Defect Characterization in Semiconductor Devices
Authors: Johnson N. M.
Published: March 2011

The use of deep-level transient spectroscopy for electronic defect characterization in semiconductors is reviewed with emphasis on the underlying principles and concepts.
Nanomechanics of Thin Films
Authors: Hoffman R. V.
Published: March 2011

Recognition of the importance of the mechanical properties of thin deposited films has received increasing attention over the past decade. The film or near surface region must be treated as a material to understand its particular mechanical properties in terms of the unique microstructure present. A vapor condensed film often has an extremely small grain size and gives brittle behavior. It is not uncommon to form an impurity stabilized amorphous film during growth.

In this paper emphasis is placed on concepts and recent instrumentation for measurements of the stress during film deposition. This growth stress and its distribution results from the microstructure plus the mechanical constraints of the underlying material, and may be modified by the processing. Both elastic and plastic components are present and local deformation maps allow a reasonable level of modelling. Lacking in this approach are experimental material parameters for the film, near surface, or interfacial material. New data for the tensile properties of cast polystyrene and SiO films is presented.
On The Melting of Amorphous Ge and Si
Authors: Turnbull David
Published: March 2011

The amorphous semiconducting phase (a-sc) of Si or Ge is so resistant to crystallization that rapid heating may bring it into a temperature regime in which it melts. Such melting might occur in one or the other of two ways, either homogeneously, by the reverse of the glass transition, to a viscous semi-conducting melt (ℓ-sc) or by transition, probably by nucleation and growth, to the molten metallic state (ℓm). Using the self-diffusion constant of the crystalline elements in conjunction with the Stokes-Einstein equation, upper limiting values of the glass transition (a-sc→ℓ-sc) temperatures of Si and Ge were calculated. These were of the order 0.6 to 0.65 Tcℓ for slow and 1.1 Tcℓ for ultra rapid heating, where Tcℓ is the equilibrium melting temperature of the crystal. Arguments are given that superheating to a temperature 1.15 to 1.25 Taℓ (a-sc↔ℓm in equilibrium at temperature T = Taℓ< Tcℓ) may be required for copious internal nucleation of im in a-sc. At lesser superheating the transition must be initiated at internal flaws (e.g. voids) or at the external surface of the a-sc film. Therefore the superheating at perceptible onset of the transition during rapid heating can vary widely from specimen to specimen, depending on the flaw concentration and how the external surface of a-sc was treated.
Metastable Solid Solutions of Impurities in Silicon
Authors: Williams J. S. , Short K. T.
Published: March 2011

High resolution Rutherford backscattering and channeling techniques have been used to investigate the formation and stability of supersaturated solid solutions of As, Sb, In, Pb, Tℓ and Bi implants in (100) silicon. In all cases nearsubstitutional solid solubilities far exceeding maximum equilibrium solubility limits can be achieved by furnace annealing at temperatures ≤ 600°C. Details of the recrystallisation process indicate that the maximum impurity concentration which can be incorporated onto silicon lattice sites may be controlled by impurity size and associated strain effects at the amorphous-crystal boundary during epitaxial regrowth.
Precipitation Phenomena in Implanted Ionic Oxide MgO
Authors: Perez A. , Treilleux M. , Thevenard P. , Abouchacra G. , Marest G. , Fritsch L. , Serughetti J.
Published: March 2011

MgO single crystals implanted with alkali ions (Li+, Na+, K+ and Rb+),Fe+, In+ and Au+ ions have been studied after implantation with doses up to 1017 ions.cm−2 and after annealing at temperatures up to 1100°C.In order to characterize defects and precipitated phases, several techniques have been associated depending on the implanted ions : optical absorption, transmission electron microscopy, Rutherford backscattering spectrometry, conversion electron Mössbauer spectroscopy and X-ray diffraction at oblique incidence. Directly after implantation the intrinsic defects in the anionic sublattice (F, F+, F2-centers) and in the cationic sublattice (V−-centers) are observed. As to the implanted species, two precipitation processes are observed : (i) the implanted ions precipitate independently of the matrix elements. This is the case of alkali ions which form alkali metal precipitates. (ii) the implanted species precipitate with those of the matrix to form compounds. This is observed with iron which forms oxide precipitates and spinel ferrite. In the case of indium and gold, the precipitation process occurs with the cations of the matrix to form binary alloys : Mg3In and Au3Mg.
Electrical Properties of Ion Implanted Poly (P-Phenylene Sulfide)
Authors: Abel J.S. , Mazurek H. , Day D.R. , Maby E.W. , Senturia S.D. , Dresselhaus G. , Dresselhaus M.S.
Published: March 2011

Ion-implantation can increase the electrical conductivity of the polymer poly (p-phenylene sulfide) (PPS) by ~ 14 orders of magnitude. This conductivity increase, which is stable under ambient conditions, is studied as a function of temperature, ion energy, fluence and species, using a novel technique, based on microelectronics processing, capable of accurately measuring conductivities as low as 10−10 (Ω-cm)−1. Mechanisms for the enhanced conductivity of PPS are discussed in relation to our measurements.
Crystalline to Amorphous Transformation of Fe3B By 1 MeV Electron Irradiation
Authors: Mogro-Campero A. , Hall E.L. , Walter J.L. , Ratkowski A.J.
Published: March 2011

Specimens of amorphous Fe75B25 produced by rapid quenching from the melt were annealed to complete crystallization and subjected to 1 MeV electron irradiation in a transmission electron microscope at room temperature and at 130 K. The irradiation was interrupted at various intervals in order to obtain bright field images and diffraction patterns. The Fe3B crystals did not become amorphous at room temperature, even after damage levels of several dpa, whereas at 130 K the crystalline to amorphous transformation was observed to be complete at damage levels below 1 dpa. The results are combined with those of ion irradiation work on Fe3B; qualitative agreement is found between Fe3B and previous work on the Zr3Al alloy concerning their response to displacement damage by electron and ion irradiation.
Radiation Induced Amorphous Transformation in Intermetallic Compounds
Authors: Brimhall J. L. , Kissinger H. E. , Charlot L. A.
Published: March 2011

Intermetallic compounds and ordered phases in the Ti-Ni, Ti-Fe, Re-Ta, and Mo-Ni systems became amorphous after high energy, ion irradiation. Compounds in the Ni-Al and Fe-Al systems remained crystalline and formed dislocation networks after similar irradiation. The ease of amorphous formation correlated best with the lack of solubility within the phase field. The high internal energy of the defect state in these limited solubility alloys is believed responsible for the tendency to transform to an amorphous state. A correlation with other properties such as atom size ratio or outer electron concentration was not found.
Structural Analysis of A–15 Nb3Al Substrates Implanted With Heavy Doses of Boron ions
Authors: Treuil Clapp Mireille
Published: March 2011

Very heavy doses of B ions, up to 22 At%, were implanted into Nb3Al substrates depleted of Al. Energies as high as 1 MeV were used. The surface composition was Nb3Al1−xBx where x varied from 0 to 1 over a distance of 20,000Å. Auger analysis was done to determine composition depth profiles. Structure was analyzed with a diffractometer using Cr radiation. The x-rays sampled primarily the implanted layer. Phase analysis was carried out as a function of incremental heat treatments up to 1000 C. The A–15 phase was always present although its composition was uncertain. The tetragonal Nb3B2 phase appeared after annealing at 95OC. Superconducting transition temperatures were measured at all stages; no increase in Tc above that of the substrate was observed.
Principles of Ion Mixing
Authors: Matteson S. , Nicolet M.-A.
Published: March 2011

Several mechanisms can cause atomic relocation as a result of ion irradiation. Experiments are reviewed that provide information on the atomic redistribution within a solid. Predictions of different models, when compared with these results, shed light on the dominant processes. Sucesses and problem areas are discussed and possible practical applications of the results are explored.
Intermixing of Chromium and Copper by Argon Ion Recoil Implantation
Authors: Baron N. , Greggi J. , Schreurs J
Published: March 2011

Argon ions at 150 keV and fluences ranging from 5 × 1015 to 4.8 × 1017 ions/cm2 were used to bombard 60 nm chromium layers deposited on copper. The resulting concentration profiles were determined by AES and thin film microstructural analyses were performed using an STEM equipped with an energy dispersive X-ray spectrometer (EDS). The concentration profiles are in qualitative agreement with the theory of radiation induced mixing. At fluences up to 2.4 × 1017 Ar+/cm2, metastable solid solutions of increasing copper content in BCC chromium are formed. At the highest fluence (4.8 × 1017 Ar+/cm2 ), chromium rich precipitates form in the copper matrix.
The Surface Behavior of a Binary Alloy During Production by Ion Implantation
Authors: Reynolds G. W. , Vozzo F. R. , Alias R. G. , Knudson A. R. , Lambert J. M. , Treado P. A.
Published: March 2011

Thin surface copper-nickel alloys were prepared by ion implantation at 90 keV. During the implantation of one pure element by the other the sputtered products were collected on catcher foils at different stages from the beginning of the implant through to the steady state configuration of the target surface. The collector foils and targets were analyzed to determine the behavior of the sputtering yields during implantation and for the change in surface composition at the selected fluence. The total sputtering yield for the target and the effective elemental sputtering yields for each component appear to be functions of the changing surface fractions, the self ion sputtering yield of the implanted species, and the elemental sputtering yield of the initial target species. A model relating these parameters is presented.
Electronic Structure of Divalent Defects in Tetrahedrally Bonded Amorphous Materials
Authors: Lin S. Y. , Lucovsky G. , Guha S. , Payson J. S.
Published: March 2011

This paper describes a calculation of twofold-coordinated (or divalent) intrinsic bonding defects in a-SiSn:H alloy films. The motivation for this study comes from experimental studies of the electronic and optical properties of a- Si, Sn:H alloys which indicate dramatic changes in the electronic and photoelectronic properties for small concentrations of Sn (approximately 1–2 at. %). We have used a cluster Bethe lattice structural model and an empirical tight-binding Hamiltonian to investigate the electronic properties of tetrahedrally bonded Sn atoms and neutral Sn defect centers (T2o and T3o) and in an a-Si host. We find that: (C) fourfoldcoordinated Sn atoms simply promote a reduction in the optical bandgap, with the energy gap disappearing for Sn concentrations of about 20 to 30 at. %; (2) neutral dangling bonds (T2o) or threefold-coordinated Sn atoms generate a localized state in the gap that is iower in energy than the corresponding neutral Si atom dangling bond; and (3) divalent (T2o) or twofold-coordinated Sn atoms give rise to two states in the gap, an occupied state that is lower in energy that either the Sn or Si dangling bond, and an empty state that is just below the conduction band edge. We show that the electronic and optical properties of the a-SiSn:H alloys can be understood in terms of a model in which there are relatively high densities of unhydrogenated Sn divalent sites and/or Sn dangling bonds.
Study of Trapping and Recombination In a-Si:H By Means of Infrared Enhancement Spectra of Photoconductivity
Authors: Wenhao Wu , Changhua Qiu , Shifu Zhao , Daxing Han
Published: March 2011

IR re-excitation of non-equilibrium carriers in undoped a-Si:H has been used to probe the profile of the distribution of deep traps. In a dualbeam experiment, after turning off a pump light, the trapped carriers are re-excited by an IR probe light which causes the photoconductivity(PC) to pass through a maximum, σmax, before settling down towards its steady state value, σs. σmax depends on the time interval td between turning off the pump light and turning on the probe light in a manner Δσ=σmax-σs∞td-α(T) Based on the multiple trapping (MT) model, the distribution of deep traps has been deduced from the temperature dependences of α(T).
The Photoconductivity Exponent For Recombination At Dangling Bonds In a-Si:H
Authors: Vaillant F. , Jousse D.
Published: March 2011

A theoretical model has been developed for recombination at dangling bonds which explains the γ variations between 0.5 and 1 depending on the Fermi level position. The occupation probabilities of the T3+, T3° and T3- states under illumination have been calculated using the statistics of correlated levels. The γ exponent is derived through a parametric representation of the equations of detailed balance and charge conservation. A good agreement with experiment is obtained with a dangling bond density of 5×1015 cm-3, a placing of the T3° level at 0.95 eV below Ec, an effective correlation energy of 0.4 eV and a charged to neutral capture cross section ratio of 50.
Novel Properties of a-SI:H Prepared by Dual Ion Beam Sputtering
Authors: Windischmann H. , Collins R. W. , Cavese J. M.
Published: March 2011

Films of a-Si:H were deposited by dual ion beam sputtering using a new configuration in which both the argon and hydrogen beam sources are directed at the silicon target. This geometry also permits independent control of the hydrogen and argon energy and particle flux. Infrared absorption mealurents show that even for high hydrogen concentrations, the 2000 cm-1 Si-H stretching band is dominant. This result is in contrast with the more conventional configuration in which the H soyrce is directed at the substrate, resulting in films with dominant 2100 cm-1 mode. This suggests that the precursors resulting in H-incorporation are different for the two configurations. In fact, IR reflectance and SIMS analysis of the silicon sputtering target reveal hydrogen is incorporated, peaking at about 30 Å below the target surface. A strong increase in the photo and dark dc conductivity occurs as the hydrogen ion enery is reduced below 30 eV, suggesting the importance of preventing high energy back-scattered H ion bombardment of thS film. At a H ion energy of 8eV, the values are 2x10-5 (AM1) and 2x10-9 (ohm-cm-1), respectively. Spectroscopic ellipsometry measurements of films reveal a Si-Si bond packing greater than that of low Hcontent a-Si prepared by LPCVD even up to H contents as high as 24%. Above 25% a microstructural transition is observed, verified by SEM, resulting in an increase in the density of voids, (which appears to be responsible for a sudden drop in the hydrogen-induced compressive stress) and accompanied by a shift in the dominant stretching mode energy.
Dopant Incorporation and Doping Efficiency in a-Si:H and a-Ge:H
Authors: Stutzmann Martin
Published: March 2011

Doping of hydrogenated amorphous silicon and germanium with boron, phosphorus, and arsenic is investigated. The incorporation of the dopants from the gas phase into the solid film is found to differ strongly for the various dopant-host systems. The doping efficiency is calculated from measurements of the density of dangling bond defects and of shallow band-tail states as a function of the doping level. A common square root dependence of the efficiency on dopant gas concentration is obtained.
Measurements of Light-Induced Degradation in A-Si, Ge:H, F Alloys,
Authors: Kolodzey J. , Aljishi S. , Smith Z E. , Chu V. , Schwarz R. , Wagner S.
Published: March 2011

The effects of illumination on the optical and electronic properties of narrow gap hydrogenated and fluorinated amorphous Si-Ge (a-Si1-xGex:H, F) alloys have been evaluated. A series of alloys with optical gaps ranging from 1.30 eV to 1.64 eV has been light soaked at ∼1 sun intensity for 354 hours. Measurements of sub-gap absorption, photo- and dark conductivities and dark conductivity activation energy were made on alloys in the annealed and the light-soaked states. The results indicate that samples with optical gaps ≳ 1.4 eV degrade significantly. The 1.3 eV sample shows no degradation in its optical or electronic properties except for a factor of 5 increase in the dark conductivity.
Control of a-Si:H Film Properties by Phoyo-Assisted Plasma CVD
Authors: Fkuda Nobuhiro , Miyachi Kenji , Tanaka Hirofumi , Igarashi Takashi , Yamamyto Sadaaki
Published: March 2011

CO2 laser irradiation onto growing a-Si:H surface caused a decrease of the optical bandgap down to 1.63 eV and a significant increase of the photosensivity. Primary effect of the laser irradiation was a conventional substrate heating, while the optical bandgap narrowing could not be explained by heating effect alone.
Status of Amorphous Silicon and Related Alloys Prepared by Photochemical Vapor Deposition
Authors: Konagai Makoto
Published: March 2011

A review is given of the current status of amorphous Si(a-Si) and related alloys prepared by photo-CVD. Preparation techniques and film quality of the following materials will be reviewed;

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undoped a-Si films,

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highly conductive n-type and p-type μc-Si films, a-SiGe films.

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a-SiC films, superlattice structures.

Finally, the present status of a-Si solar cell performance prepared by photo-CVD will be introduced and the merit of photo-CVD will be discussed.
Electronic Transport and the Density of States Distribution in a-(Si, Ge):H, F Alloys
Authors: Aljishi S. , Smith Z E. , Slobodin D. , Kolodzey J. , Chu V. , Schwarz R. , Wagner S.
Published: March 2011

The electronic and optical properties of amorphous silicon-germanium alloys produced by d.c. and r.f. glow discharge are reported. Data on the sub-gap absorption, dark and photo conductivities, drift mobilities and drift mobility-lifetime products are used to propose a density of states model.
a-(Si, Ge):H, F Alloys Prepared from SiH4 and GeF4
Authors: Slobodin D. , Aljishi S. , Okada Y. , Shen D.-S. , Chu V. , Wagner S.
Published: March 2011

The properties of a-(Si, Ge):H, F alloys prepared by glow discharge deposition from SiH4 and GeF4 are described. The measured IR absorption spectra, sub-gap absorption spectra, dark conduction activation energies, carrier drift mobilities and deep trapping lifetimes of these alloys are similar to those of alloys prepared from SiF4, GeF4, and H2. However, they have over an order of magnitude lower photoconductivity over most of the composition range. Infrared absorption measurements indicate that these alloys have a fluorine content less than 1.5 at.% and a Si-H2 content that increases with germanium concentration.
NMR and ESR Studies on a-Si1-x Gex:H Films Prepared by Glow Discharge and Magnetron Sputtering
Authors: Shimizu T. , Kumeda M. , Morimoto A. , Tsujimura Y. , Kobayashi I.
Published: March 2011

Properties of a-Si1-xGex:H films prepared by magnetron sputtering (MG) and glow discharge decomposition (GD) were compared by means of NMR, ESR, IR and hydrogen-evolution measurements. For MG films, the content of dispersed H is roughly independent of x while the content of clustered H decreases with x. For GD films, both the contents of dispersed and clustered H decrease with x. ESR results reveal that most defects in the films are Ge dangling bonds and that the number of dangling bonds per Ge atom is roughly independent of x for MG films whereas it increases largely with x for GD films. Therefore the content of dispersed H has a good correlation with the number of Ge dangling bonds per Ge atom in a-Si1-xGex:H films. The ratio of the intensity of the IR peak at 2100 cm-1 to that at 2000 cm-1 decreases and increases with x, respectively, for MG and GD films, and the ratio of the intensity of the low temperature H evolution peak to that of the high temperature H evolution peak decreases and increases with x, respectively for MG and GD films.
Effective p+-Doping of a-Si:H and a-Sic:H Layers by Plasma Assisted Boron Diffusion
Authors: Mohring H.-D. , Bauer G. H. , Bilger G. , Nebel C. E.
Published: March 2011

Doping of a-Si:H and a-SiC:H has been performed by plasma enhanced boron migration from thin (5–30 nm) Si0.2B0.8 layers on top of the substrate into the growing i-film. Transport coefficients for this plasma assisted diffusion (PAD) evaluated from SIMS profiles (D* = 10−15 … 10 cm2/s for a-Si:H, 10−15 cm2/s for a:SiC:H) by far exceed those for thermal diffusion after film deposition (10−21 cm2/s). Boron profiles are strongly governed by deposition parameters like substrate temperature, types and energies of radicals growing the film. Boron migration can be modelled assuming particle extraction from the network to the surface by bombardment of ions and atoms and high surface mobility of BHx radicals as a result from interaction with the plasma. Temperature dependent dark conductivity measurements show doping efficiencies comparable to B2H6 gas phase doping, but leaving plasma parameters optimized for i-film Leposition unchanged. Thin a-SiC:H layers are effectively p+-doped without affecting transmission, as no layer is optically detectable after PAD.
Properties of the Interface Between Amorphous Silicon and Nitride
Authors: Tsai C. C. , Street R. A. , Ponce F. A. , Anderson G. B.
Published: March 2011

The structural, compositional and electronic properties of the a-Si:H/a-SiNx:H interface are reported. High resolution TEM and light/dark ESR studies conclude that the interface has a finite width of the order of 10 Å. In addition, there is a high density of charges residing near the interface. Band bendings occur in both a-Si:H and a-SiNx:H, resulting in few neutral dangling bonds in the a-Si:H/a-SiNx:H multilayer structure. The depletion width in the nitride is of the order of 100 Å. The slow decay of the LESR in multilayers with thin sublayers is attributed to charges trapped in the slow states in the nitride.
The Origin of Slow States at the Interface of a-Si:H and Silicon Nitride
Authors: Street R. A. , Tsai C. C.
Published: March 2011

Transient photoconductivity is used to investigate the origin of slow states near the interface of a-Si:H and silicon nitride. A graded composition of the nitride layer near the interface greatly increases the density of slow states. We deduce that slow states are bulk nitride traps and that the magnitude of charge storage is largely determined by the composition dependence of the localization radius of electrons within these traps. The kinetics of charge storage and release are found to be very different and are interpreted in terms of an activation step at the interface.