bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Polysilicon Processing on the Quality of Thin RTP/Furnace Gate Oxides
Authors: Haase J. , Ferretti R. , Prasad S.
Published: March 2011

Thin layers of oxides (10–11nm) were fabricated by rapid thermal (RTP) or furnace oxidation. The RTP oxides were grown at different temperatures and were exposed to a two step post oxidation anneal (POA). The furnace oxides were grown at one temperature and received different POA/s. As gate metallization, in-situ phosphorus-doped polysilicon was used. Post poly anneal (PPA) is carried out in the RTP system using a set of temperatures. After having defined MOS structures by photolithography oxide charges, breakdown voltages and breakdown charges were determined. For different current densities, FN-voltage shift during constant current injection was monitored to make lifetime predictions. Received data were correlated to the different process parameters.
High Performance Thin Film Transistors for Scanner Applications
Authors: Hseih B.-C. , Hawkins G.A. , Ashok S.
Published: March 2011

We report on the characteristics of polycrystalline silicon (polysilicon) thin film transistors (TFTs) fabricated with low temperature crystallized LPCVD amorphous silicon film as an active layer and plasma enhanced chemical vapor deposition (PECVD) SiO2 as a gate insulator. High performance transistor characteristics are achieved, even though no process temperature exceeds 600°C. No threshold drift has been observed. As a result, these devices are highly suitable for application to image scanners as well as flat panel displays.
Cmos Polysilicon Thin Film Transistors with Simultaneously Deposited Layers for Source-Drain and Gate
Authors: Huang T. Y. , Tsai C. C. , Wu I. W. , Lewis A. G. , Chiang A. , Bruce R. H.
Published: March 2011

A new process architecture for fabricating CMOS thin film transistors (TFTs) using in-situ-doped polysilicon source-drain layers is proposed. In the new architecture, a top-gate n-channel TFT and a bottom-gate p-channel TFT, or vice versa, form a CMOS pair. This allows an n+ - doped polysilicon bottom (or top) layer to serve simultaneously as the source-drain layer of the n-channel TFTs and the gate layer of the p-channel TFTs; while a p+ - doped polysilicon top (or bottom) layer serves as the source-drain layer of the p-channel TFT and the gate layer of the n-channel TFT. It thus eliminates the deposition of a separate doped gate layer normally required in the conventional process flow. In addition, a thin tri-layer stack, consisting of undoped-poly / gate dielectric / undoped-poly, separates the two doped polysilicon layers, thus allowing the use of a single island mask to define the channel regions for both the n- and p-channel TFTs. As a result, the photolithographic steps are also reduced by one mask. Working n- and p-channel TFTs with both top- and bottomgate structures, obtained by reversing the dopant types of the top and the bottom layers, have been successfully demonstrated using low-temperature (< 600 °C) polysilicon technology.
Geometrical Effects and Disintegration of Narrow TiSi2/Poly-Si Lines
Authors: Norström H. , Maex K. , Vandenabeele P.
Published: March 2011

The geometrical shape and the thermal stability of the TiSi2/poly-Si interface on narrow lines has been studied. The examined line-widths varied between 0.8 μm and 1.5 μm. The thermal stability was found to strongly correlate to theactual line-width of the structures. At the onset of degradation, at and above 900 ºC, narrow lines were observed to disintegrate at a much faster rate than wider ones. Cross-sectional microscopy (TEM and SEM) revealed the TiSi2/poly-Si interface to be curved inwards. The interface bowing was found to be more pronounced on narrow lines. It is suggested that the interface bowing results from a mechanical pinning of the TiSi2/poly-Si interface by the side-wall spacers.
Interface Oxide Free Poly Silicon Deposition Using in-Situ HF Cleaning Process
Authors: Huang C.K. , Feygenson A.
Published: March 2011

A LPCVD polysilicon deposition with in-situ anhydrous HF cleaning process has been developed. The deposited polysilicon and interface properties have been characterized using SIMS, XTEM, RBS, and Auger analysis. The results indicate that an interface oxide free polysilicon deposition using conventional LPCVD furnace can be achieved by careful design of in-situ anhydrous HF cleaning process. After short time rapid thermal annealing, random and channel RBS studies show that most of the deposited polysilicon is epitaxially aligned with silicon substrate and there is no oxide ball up phenomenon. Twinning structure was observed under TEM. No impurity segregation at the poly-mono silicon interface confirms that the interface is oxide free. Possible applications of this polysilicon process include polysilicon emitter contact for high speed bipolar technology and source/drain contacts for MOS devices.
From Point Defects to Amorphous Structures: Atomic Resolution Studies of Semiconductor Surfaces by Scanning Tunneling Microscopy (STM)
Authors: Wiesendanger R. , Tarrach G. , Buergler D. , Scandella L. , Guentherodt H.-J.
Published: March 2011

We have studied point defects, linear defects as well as spatial transitions between ordered and disordered structures on silicon surfaces with atomic resolution by using scanning tunneling microscopy (STM). Point defects in the vicinity of multiple step edges as well as surface reconstructions at multiple step edges as high as 3 nm have been characterized by STM. STM images of partially disordered silicon surfaces prepared by laser and thermal annealing demonstrate the potential of STM for characterizing non-periodic surfaces on the atomic scale.
Electron Microscopy of Interfaces in Silicon Carbide Whisker-Reinforced Alumina Composites
Authors: Alexander K. B. , Angelini P. , Becher P. F.
Published: March 2011

Knowledge about the nature of interfaces between SiC whiskers and alumina matrices is critical to understanding the mechanical behavior of these types of composites. The fracture toughness, in particular, is strongly influenced by the bond characteristics of this interface. Previous results have shown that oxidizing the whiskers in air prior to composite fabrication by vacuum hot-pressing results in composites which have lower toughness compared to those made with whiskers in the as-received condition. This investigation focusses on the effects of oxidizing and reducing surface treatments on the whiskers themselves and on the whisker-matrix interface. High resolution electron microscopy (HREM) was used to characterize the morphology and the amount of amorphous phase at the whisker-matrix interface, as well as the crystallography and topography of the interface. The present results indicate that the characteristics of the whisker/matrix interface may not be directly related to the initial whisker surface chemistry. Surprisingly, the thickest thermally-grown oxide layer resulted in the thinnest amorphous film at the SiC/Al2O3 interface.
Surface Structures and Rearrangements in Oxides
Authors: Mccartney M. R. , Smith David J.
Published: March 2011

Electron-beam-induced surface reactions and rearrangements have been observed for a number of oxides including MgO, TiO2, SrTiO3 and SnO2 using conventional and ultra-high-vacuum high-resolution electron microscopes. Electron irradiation of TiO2 resulted in a variety of effects including reduction, re-oxidation and amorphization. SnO2 was observed to form facets readily during high-resolution imaging but it was stable against reduction except when exposed to extreme current densities which caused the formation of metallic tin crystals. Electron irradiation of MgO under UHV conditions resulted in the formation of facetted pits. The surfaces of SrTiO3 were stable for moderate electron dose rates but rapidly amorphized when irradiated at extreme current densities.
Defects and Metal Particles in Zeolites Studied with High Resolution Electron Microscopy
Authors: Zandbergen H. W. , van Dyck D.
Published: March 2011

A number of examples of high resolution electron microscopy on defects and metal particles in zeolites is given: defects in Zeolite Y and Zeolite β, metal particles in ZSM-5, and structural changes due to reactions in Zeolite L and Zeolite Y.
Atomic Structure of Ag/Ni Interfaces
Authors: Gao Y. , Merkle K. L.
Published: March 2011

While in heterophase systems of small lattice parameter differences, misfit dislocations are often formed at the interface, it is not known, whether and in which form, misfit localization occurs when the misfit is very large. The atomic structure of Ag/Ni interfaces (misfit 14%) was studied by high-resolution electron microscopy (HREM). A special technique was developed to prepare interface specimens suitable for HREM observations.

Lattice statics calculations, using embedded-atom potentials, were performed to determine the structure and energies of Ag/Ni interfaces. The lowest interfacial energy was found for the cube-on-cube orientation and (111) interfaces. This is in agreement with the experimental observation, that all interfaces are strongly faceted with (111)Ag/(111)Ni facets.

Misfit localization was found by HREM and computer simulation. The HREM observations will be compared to images derived from image simulations, based on model structures obtained from embedded atom calculations.
Applications of Strained Layer Superlattices
Authors: Smith D. L. , Laurich B. K. , Mailhiot C.
Published: March 2011

Because of different band-edge lineups, strain conditions, and growth orientations, various strained-layer superlattice (SLS) materials can exhibit qualitatively new physical behavior in their optical properties. We describe two examples of new physical behavior in SLS: strain-generated electric fields in polar growth axis superlattices and strained type II superlattices. In SLS, large electric fields can be generated by the piezoelectric effect. The fields are largest for SLS with a [111] growth axis; they vanish for SLS with a [100] growth axis. The strain-generated electric fields strongly modify the optical properties of the superlattice. Photogenerated electron-hole pairs screen the fields leading to a large nonlinear optical response. Application of an external electric field leads to a large linear electrooptical response. The absorption edge can be either red or blue shifted. Optical studies of [100], [111], and [211] oriented GaInAs/GaAs superlattices confirm the existence of the strain-generated electric fields. Small band-gap semiconductors are useful for making intrinsic long wavelength infrared detectors. Arbitrarily small band gaps can be reached in the type II superlattice InAs/GaSb. However, for band gaps less than 0.1 eV, the layer thicknesses are large and the overlap of electron and hole wavefunctions are small. Thus, the absorption coefficient is too small for useful infrared (IR) detection. Including In in the GaSb introduces strain in the InAs/GaInSb superlattice, which shifts the band edges so that small band gaps can be reached in thin-layer superlattices. Good absorption at long IR wavelengths is thus achieved.
Role of Interface-States in the Reverse Bias Aging of GaAs Schottky Barriers
Authors: Christianson K. A.
Published: March 2011

Forward bias capacitance has been used to examine the Au/W/GaAs and Au/Pt/Ti/GaAs Schottky barriers present in power microwave MESFET devices to see if interface-state generation plays any role in the previously reported reverse bias barrier height aging process. If a constant carrier capture cross-section is assumed, forward bias capacitance has shown that for samples strongly susceptible to aging (i.e. the Au/W/GaAs samples in this study) interface-state generation is taking place during the aging process. The validity of the constant capture cross section assumption has been tested by examining the I–V properties. For those samples whose reverse I–V properties were not dominated by thermionic-field emission, similar increases in interface-state densities were evaluated from the I–V characteristics for the degraded samples.
Thermal Stability of A1-Pt Thin Films/GaAs for Self-Aligning Gate Contacts
Authors: Wilk G. D. , Blanpain B. , Olowolafe J. O. , Mayer J. W. , Zheng L. R.
Published: March 2011

Several compositions of A1-Pt thin films have been co-evaporated on GaAs substrates to study the stability of the alloys at high-temperature anneals. The A1 concentration in the alloys ranges from 45 at.% to 70 at.%, and we show that the films meet thermal stability requirements imposed by GaAs selfaligning gate technology for compositions between AIPt and Al2Pt.
Electronic Stimulation of Acceptor Reactivation IN p - Type Hydrogenated GaAs
Authors: Szafranek I. , Stillman G. E.
Published: March 2011

The mechanism of light-induced reactivation (LIR) of shallow substitutional acceptors in high-purity p-type hydrogenated GaAs has been investigated. Photoluminescence was used to determine the dependence of the rate and extent of this effect on photon energy, illumination intensity, as well as on sample temperature and chemical composition. At a sample temperature of 1.7 K a sharp threshold in the photon energy, Et, has been observed at about 7.5 meV below the bandgap energy of GaAs. This energy corresponds approximately to the onset of acceptorbound exciton absorption in the material. For photon energy E < Et, only a weak reactivation effect is observed. The efficiency of reactivation increases dramatically for E > Et, and for sufficiently large values of (light intensity).(illumination time) product the LIR process saturates. Both the extent of the subthreshold effect and the saturation level that is attainable with E > Et are independent of the photon energy, excitation power and exposure time in the investigated range of these quantities. For E > Et the initial LIR rate depends on the square of the light intensity, indicating a bimolecular reaction in terms of the photo-generated carrier densities. The observed strong dependence of the saturation level on the sample temperature during LIR is found to be consistent with the relative binding energies of different acceptor-hydrogen passivating complexes in GaAs. Based on these results, it is proposed that LIR of acceptors is electronically stimulated via recombination-enhanced vibrational excitation of acceptor-hydrogen complexes.
Photoemission from Ordered and Disordered Cu3Au
Authors: Jordan R.G. , Ginatempo B.
Published: March 2011

We report angle-resolved uv photoemission measurements from ordered and disordered Cu3Au. We observe considerable changes in the photoemission spectra across the order-disorder transition which we attempt to correlate with recent electronic structure calculations. Overall, we find reasonable agreement between theory and experiment although we note some important discrepancies.
A Study of the Phase Decomposition of Fe-Ni-Al-Mo Alloys
Authors: Miller M.K. , Hetherington M.G. , Weertman J.R. , Calderon H.A.
Published: March 2011

The aging of β′ NiAl precipitates in ferritic Fe-Ni-Al alloys has been studied by transmission electron microscopy (TEM) and atom-probe field-ion microscopy (APFIM). The addition of Mo alters the lattice parameter of the phases and segregation of Mo to the interface between the matrix and the particles may alter the interfacial energy. The compositions of the matrix, precipitates and interfaces have been measured by TEM and APFIM. The results are compared.
Mechanical Properties and Microstructure of Certain Niaico(Hf) Alloys
Authors: Russell S. M. , Law C. C , Lin L. S. , Levan G. W.
Published: March 2011

Cobalt-modified NiAl alloys are being studied for their potential for room temperature ductility and toughness. An alloy of Ni - 29.3 a/o Al - 36.7 a/o Co has shown improved toughness and ductility with respect to binary NiAl alloys due in part to a stress-induced martensitic transformation. Furthermore, the cobalt additions have altered the slip behavior to {110}<111> type from {110} <001> for binary NiAl alloys. Hafnium was added to improve the alloy's relatively poor creep resistance and high temperature strength. Hf was found to be insoluble in the NiAlCo alloy and formed precipitates with a hexagonal structure. The Hfmodified alloy had improved high temperature strength. In addition, the Hf apparently changed the creep mechanism resulting in poorer creep resistance at low temperatures, but improved creep resistance at higher stresses and temperatures.
Deformation and Dislocation Structure of Ti3AI Single Crystals
Authors: Minonishi Y.
Published: March 2011

Deformation characteristics of Ti3A1 single crystals has been examined as a function of orientation and temperature. This paper mainly describes the result of compression along the c axis. In this orientation, the yield stress increases from 300 to 1100K, decreasing rapidly thereafter. The slip system activated are {1121}<1126> and dislocations observed are nearly of edge character. The anomaly is discussed in comparison with the behavior of other intermetallics and pure metals. An important role this pyramidal slip plays in polycrystalline ductility of Ti3Al is shown in the light of the briefly described results of the prism slip.
Alloy Design of Ordered Intermetallics
Authors: George E. P. , Liu C. T.
Published: March 2011

Ordered intermetallics based on aluminides and silicides constitute a unique class of metallic materials possessing promising high-temperature properties. However, brittle fracture and poor ductility have limited their use as engineering materials in most cases. During the past ten years extensive research has been conducted on ordered intermetallics. As a result, significant progress has been made in identifying various causes of brittle fracture, and their relative importance in different ordered alloys. In some cases this understanding has helped achieve dramatic improvements in ductility. We review here three different classes of brittle fracture in ordered intermetallics and discuss the results in terms of model alloy systems chosen from each class. Ni3A1 and NiAl are discussed as prototypical ordered alloys prone to intrinsic intergranular brittleness. They are used to review our current understanding of intrinsically weak grain boundaries and the mechanisms by which boron is thought to suppress intergranular fracture. Next, FeAl and Fe3A1 are discussed as examples of ordered intermetallics that are susceptible to environmental embrittlement at ambient temperatures. Recent discoveries in these two alloy systems are reviewed with special emphasis on some of the rather interesting but subtle effects of test environment. Finally, A13X type intermetallics (A13Sc, Al3Ti-base, and Al3Zr-base alloys) are discussed as examples of ordered alloys that have high symmetry (L12structure), are relatively soft, yet cleave transgranularly with very little ductility. In all these cases, experimental results are compared with theoretical calculations.
Does Σ Control Intergranular Cracking in Ni3Al?
Authors: Lin Hui , Pope David P.
Published: March 2011

The relation between intergranular fracture and grain boundary character was studied in Ni3Al using the electron backscattering pattern (EBSP) technique. Using specimens of small grain size, we are able to index the orientation of a large number of grains, thus improving the statistical quality of the data compared to previous results. Furthermore, we are able to characterize the boundary planes using the EBSP method because of the special specimen geometry used. It was found that Σ3 boundaries do have a substantially lower propensity for cracking as compared to other boundaries, but there is no correlation between grain boundary Σ value and the propensity for cracking for low Σ and low angle boundaries. These results are in general agreement with recent theoretical predictions of grain boundary structure.
Sulfide Stability, Void Nucleation and the Toughness of Ultra High Strength Steels
Authors: Garrison W. M. , Maloney J. L.
Published: March 2011

The upper shelf fracture toughness of ultra high strength steels is dependent on both the microstructure, which is determined by composition and heat treatment, and on the inclusions present in the steel. The inclusions In ultra high strength steels are typically oxides and sulfides [1]. In most ultra high strength steels the sulfides are manganese sulfides, although depending on the composition of the steel and the melt practice used, other sulfides are found, such as chromium sulfide, calcium sulfide and lanthanum oxy-sulfide [2]. If the inclusions can be regarded as pre-existing voids then the inclusion volume fraction and spacing appear to be sufficient to characterize the inclusion population from the standpoint of fracture toughness [3,4]. The purpose of this paper is to discuss results which show sulfur can be gettered as particles which are much more resistant to void nucleation than manganese sulfides and that this increased resistance to void nucleation can result in vastly improved upper shelf fracture toughness. In particular, when HY180 steel contains manganese sulfides the fracture toughness is about 250 MPa but when the sulfur is gettered as particles containing titanium, carbon and sulfur the fracture toughness of HY180 steel will approach 550 MPa . These particles, believed to be titanium carbosulfides, are much more resistant to void nucleation than manganese sulfides and this increased resistance to void nucleation appears to be the reason for the improved fracture toughness.
On the Structure-Property Relationship of Rapidly Solidified High Temperature Application Aluminium Alloys
Authors: Chowdhury A.J.S. , Sheppard T.
Published: March 2011

The phases responsible for high temperature strength and ductility of Al-Fe based alloys, specifically Al-Fe-Mo alloys, have yet to be unambiguously identified. The phases appear to vary slightly under different experimental and processing conditions. This poses some queries concerning the reproducibility of mechanical properties of these alloys. In this paper an attempt is made to address these points and focus on the structure-property relationships of Al-Fe-Mo and Al-Fe-V rapidly solidified powder alloys.
Development of Microstructures with Improved Cryogenic Toughness Through Local Variations in Stress State: Aluminum-Lithium Alloys
Authors: Rao K. T. Venkateswara , Ritchie R. O.
Published: March 2011

Microstructurally-induced changes in the local stress state (triaxial constraint) and their effect on fracture-toughness behavior are examined at ambient and cryogenic temperatures in an Al-Li-Cu-Zr alloy, processed in the form of 12.7 mm-thick "naturally laminated" plate containing aligned-weak interfaces and 1.6 mm-thin unlaminated sheet. It is shown that marked improvements in long-transverse (L-T) toughness can be achieved in the plate material at cryogenic temperatures by promoting through-thickness delamination along these interfaces, which relaxes local constraint and promotes a fracture-mode transition from global plane strain to local plane stress. Conversely, in thin sheet material, the absence of such interface delamination leads to a reduction in toughness with decrease in temperature, consistent with the greater degree of crack-tip constraint.
Phase Stability in the Al(6−x)CuxZr2 System for 0 < × < 1.
Authors: Desch P. B. , Schwarz R. B. , Nash P.
Published: March 2011

We have determined the structures and thermal stability of AI(6-x) CuxZr2 (0≤ × ≤ 1) powders prepared by mechanically alloying elemental powder mixtures. In the as mechanically alloyed condition the structure is L12 for all ×. After heating to 750°C the alloy is single phase D023 for 0 < × < 0.2, is a two-phase mixture of D023 and L12 for 0.2 < × < 0.6, and remains in the Ll2 phase for 0.6 < × < 1. Al5CuZr2 is stable in the Ll2 structure up to 1300°C. The lattice parameter of the annealed L12 phase is Independent of ×.
On the Effects of Magnetic Bonding in Rare Earth Transition Metal Interxmetallics
Authors: Kumar R. , Bentley J. , Yelon W. B.
Published: March 2011

Neutron diffraction experiments on rare-earth transition metal magnetic alloys Er2Fe14B and Er2Fe17 have been carried out at temperatures above and below the ordering temperature (Tc). An anomalously large magnetic moment is observed at the crystallographic j2 site in Er2Fe14 B which is the intersection point of the major ligand lines in the crystal structure. The interatomic Fe-Fe distances are in the range of strong ferromagnetic bonds (≥2.66 Å). The analogous f site in Er2Fe17 does not develop as large a magnetic moment. In addition, the same sites show strong preference for Fe atoms in the respective substituted compounds. Due to poor phase stability of Er2 (CoxFe1-x)14 B compounds, iron substitution has been studied in detail in Er2(CoxFe1-x)17 alloys for site specific order and lattice distortion effects. However, a nonlinear change in the c lattice parameter observed in the neutron diffraction results cannot be explained on the basis of site preference alone.

The neutron refinement results indicate iron rich compositions in Er2(CoxFe1-x)17 materials, which is related to random substitution of Fe dumbbell pairs on the rare earth sites in the lattice. However, extensive electron microscopy (selected area electron diffraction and high resolution imaging) of Er2Fe17 and Er2 (Co .40Fe.60)17 failed to reveal any microscopic inhomogeneity. At this stage, the concept of direct negative exchange interaction between dumbbell Fe atom pairs at very short distances of −2.38 A is invoked and its effect is correlated with phase stability. We further suggest that the addition of boron in Er2Fe14B suppresses the substitution of dumbbell Fe pairs as a result of which Tc is raised significantly.
Quantum-Mechanical Origins Of complex Structures in Al-Transition Metal Compounds
Authors: Carlsson A. E.
Published: March 2011

The energetic factors leading to the stability of complex structures in Al-rich transition-metal compounds are analyzed via ab-initio band-theoretic total-energy calculations comparing the Al12W and Cu3Au structures. For nearly half-filled d-bands, the Al12W structure is preferred by 1 eV per transition-metal atom or more. The preference for complex structures results from effects related to the shape of the d-projected electronic density of states, which are found to be more important than atomic-size effects, and are directly related to the complexity of the structure.
Theoretical Investigation of Phase Stability in Non-Magnetic Copper-Nickel Alloys
Authors: Sluiter M. , Turchi P.E.A.
Published: March 2011

The phase stability of non magnetic Cu-Ni alloys is studied within a tight binding framework. Densities of states, enthalpies of mixing and ultimately the phase diagram are computed and compared to experimental data.
Investigations of CuInSe2 Thin Films and Contact
Authors: Raud S. , Vu Quat T. , Nicolet M-A. , Pollock G. A. , Mitchell K. W. , Leavitt J. A. , Ashbaugh M. D. , Mcintyre L. C.
Published: March 2011

We study the properties of CuInSe2 thin films grown on glass and on Mo substrates. The investigation is carried out with X-ray diffraction, RBS, XTEM and SEM.

CuInSe2/Mo contact stability is investigated after annealing at 600°C. RBS reveals that this treatment induces an interdiffusion between the metal and the chalcopyrite. To clarify this reaction, we have investigated the individual thin-film couples upon annealing. RBS and X-ray diffraction reveal insignificant interaction between Mo/Cu and Mo/In, but Se reacts with Mo.
Computer Simulation Study of Thin Film Formation Process
Authors: Sasajima Yasushi , Ozawa Satoru , Yamamoto Ryoichi
Published: March 2011

The thin film formation process was studied by the molecular dynamics(MD) method and by the hybrid method which combined the MD method with the Monte Carlo(MC) simulation technique. The Morse potential was assumed as the atomic interaction model. The substrate temperature was changed to see its effect on the film structure. The MD simulation found that the reconstruction process of the deposited nuclei was essential to determine the metastable film structure and that the relaxed atomic arrangements were strongly dependent on the depth of the interaction potentials. The hybrid method simulated the high rate deposition process and confirmed the results of the MD simulation.
Magnetic Ordering of Tb Overlayers on Ni(111)
Authors: Lagraffe D. , Miller A. , Dowben P.A. , Onellion M.
Published: March 2011

The 5p3/2 to 5p1/2 shallow core level branching ratios in different photoemission geometries provide a measure of the magnetic ordering in rare earth overlayers as a result of final state effects in photoemission. This 5p level anisotropy can be used to probe magnetic ordering across the Tb Curie temperature as well as magnetic ordering induced by a ferromagnetic substrate in a paramagnetic overlayer. Results are shown for paramagnetic Tb overlayers on Ni(111). The Ginzberg-Landau theory can be used to accurately model terbium thin films for T>Tc.
Structural and Electronic Changes in the Growth of Mercury Overlayers on Cu(001): A Helium Beam Scattering, Leed and Arpes Study
Authors: Vidali G. , Li W. , Dowben P. A. , Karimi M. , Hutchings C.W. , Lin J. , Moses C. , Ila D. , Dalins I.
Published: March 2011

We used atom beam scattering (ABS), LEED and angle-resolved photo-electron spectroscopy (ARPES) to study bilayer films of Hg on Cu(001). In the surface temperature range of 180 to 330 K, the first Hg layer forms two ordered phases, a c(2×2) (with coverage=0.5 of Cu(001)) and a high density (partially commensurate) c(4×4) (coverage=0.62 ). ARPES data show that there is little or no dispersion of the 5d band of Hg. ABS data show that this layer is not flat, with in-registry Hg atoms lying about 0.15 below the not-in-registry Hg atoms. From ABS we find that the second layer forms a completely registered c(4times;4) phase. From ARPES we obtain that the second layer has an electronic structure, particularly the 5d levels, characteristic of bulk mercury.

Preliminary results of calculations of the structure of the bilayer are given.
Scanning Tunneling Microscopy of Platinum Clusters on Hop-Graphite
Authors: Sattler Klaus , Mueller Ulrich , Xhie Jie , Venkateswaran Narayana , Raina Gargi
Published: March 2011

We report on recent studies of small platinum clusters supported on highly-oriented pyrolytic graphite, using a scanning tunneling microscope (STM). The clusters are generated by vapor deposition of single atoms with subsequent diffusion and growth processes occurring on large, flat and ordered substrates. Single adatoms, small clusters and larger islands are imaged with atomic resolution and their atomic structures are determined by direct observation. We find different isomeric structures for clusters of one size. Taking the substrate lattice as reference we determine bond lengths and angles for the clusters. We investigate the effect of the substrate on the adsorbed particles.
Epitaxial Grain Growth and Orientation Metastability in Heteroepitaxial Thin Films
Authors: Floro J. A. , Thompson C. V.
Published: March 2011

Conventional heteroepitaxial thin film growth may result in a film whose epitaxial orientation is metastable. One method of probing the relative energies of various film orientations is epitaxial grain growth. Epitaxial grain growth selects the orientation having lowest total free energy, including the free energy of both the film-substrate interface and the free surface of the film. Experimental examples of epitaxial grain growth in metal films on insulating substrates will be discussed.
Solid Phase Epitaxy of Strained Si1−xGex Alloys Formed by Highdose Ion Implantation into <001> Silicon
Authors: Howard D. J. , Paine D. C. , Stoffel N. G.
Published: March 2011

In this paper we propose a new method for the synthesis of Si1−xGex strained-layer alloys using high-dose ion implantation of 74Ge at 200 keV into a preamorphized <001> Si wafer followed by solid phase epitaxy (SPE). Cross-sectional TEM was performed on samples at various stages of regrowth which revealed the evolution of the amorphous/crystalline interface and the development of strain relieving defects during SPE. We report that stacking faults are kinetically favored during SPE of Si1−xGex but are energetically feasible only above a critical strain energy. We propose a model that is based on the well known Matthews and Blakeslee approach which predicts the onset of stacking faults during SPE of high-dose ion implant-synthesized Si1−xGex/Si.
On Geometric Models for Interphase Boundaries
Authors: Fecht Hans J.
Published: March 2011

The energy interphase boundaries can be described as a function of the lattice matching at the interface between two adjacent crystals, the chemical interaction and the interfacial entropy of the boundaries. Geometric models relating the energy of interphase boundaries (metal/metal and metal/non-metal) to their atomic structure can be based on the static distortion wave concept. This approach constitutes the physical basis for the lock-in model and the planar CSL-model proposed previously to describe the low energy configurations of such interfaces.
Structural and Elastic Properties of HF/ZR Multilayer Thin Films
Authors: Meng W. J. , Eesley G. L. , Svinarich K. , Meisner G. P.
Published: March 2011

We have investigated structural and elastic properties of Hf/Zr multilayer thin films by x-ray diffraction and transient piezoreflectance measurements. Similar structural and elastic behaviors have been observed in two series of samples grown at different deposition rates (1 – 10Å/sec). Our measurements suggest different (˜ 10%) effective elastic constants between multilayers with coherent and incoherent interfaces.
Cu-Cr Multilayers and Metastable Alloy Films
Authors: Payne A.P. , Clemens B.M.
Published: March 2011

A notable aspect of the copper-chromium phase diagram is the strong chemical aversion between the two elements. At room temperature, the solubility of chromium in copper is limited to .02%, while that of copper in chromium is believed to be even less [1]. The elements are even immiscible in the liquid state, exhibiting a miscibility gap which persists to an undetermined temperature. Cu-Cr alloys are of technological interest in applications ranging from electrical switches [2] to catalysis [3]. Fabrication of Cu-Cr alloys is hindered, however, by the large positive heat of mixing exhibited by the system. Cu-Cr multilayers are also of technological interest for application as soft x-ray mirrors [4]. Here the limited mutual solubility of the constituents is advantageous since interfacial mixing is reduced. In this study, we show that vapor deposition can be used to achieve complete solubility in the Cu-Cr system. On the other hand we present evidence suggesting that Cu-Cr multilayers possess sharp composition modulations with little interface mixing.
Molecular Dynamics Computer Simulation of the Rupture of the two - Dimensional Lennard - Jones Film
Authors: Maguire John F. , Leung Chun- Pok
Published: March 2011

We have conducted a molecular dynamics computer simulation of the rupture of a small, two-dimensional film. The film was composed of two hundred atoms arranged on a close-packed triangular lattice and was thermally equilibrated at a reduced temperature of 0.05. Following equilibration, the rupture characteristics of the film were investigated under tensile loading, and the atomistic dynamical response was followed throughout the rupture process. An estimate of the internal stress field was made by performing a time average over the random forces. In tensile failure, the system undergoes an initial elastic deformation followed by plastic flow. The fundamental mechanisms of defect nucleation are briefly discussed.
Mechanisms and Kinetics of Misfit Dislocation Formation in Heteroepitaxial Thin Films
Authors: Nix W. D. , Noble D. B. , Turlo J. F.
Published: March 2011

The mechanisms and kinetics of forming misfit dislocations in heteroepitaxial films are studied. The critical thickness for misfit dislocation formation can be found by considering the incremental extension of a misfit dislocation by the movement of a “threading” dislocation segment that extends from the film/substrate interface to the free surface of the film. This same mechanism allows one to examine the kinetics of dislocation motion and to illuminate the importance of dislocation nucleation and multiplication in strain relaxation. The effects of unstrained epitaxial capping layers on these processes are also considered. The major effects of such capping layers are to inhibit dislocation nucleation and multiplication. The effect of the capping layer on the velocity of the “threading” dislocation is shown to be small by comparison.

A new substrate curvature technique for measuring the strain and studying the kinetics of strain relaxation in heteroepitaxial films is also briefly described.
The Low Temperature Phases of 3He
Authors: Richardson Robert C.
Published: March 2011

In the temperature range between 1 mK and 3 mK and in magnetic fields between 0 T and 1 T, there are four distinct phases of liquid 3He and three distinct phases of solid 3He. The liquid becomes a triplet superfluid and the solid becomes a nuclear antiferromagnet. Despite the great differences which exist between a superfluid and an antiferromagnet, there are remarkable similarities between phase diagrams of the two systems.
Effect of Concentration Gradient on Phase Stability
Authors: Tu K.N. , GöSele U.
Published: March 2011

A feature of thin film reaction that is different from the reaction in bulk samples is the tendency to form a single intermetallic compound rather than all of them which are allowed according to the equilibrium phase diagram. For example, in thin film silicide formation, Pd2Si has been found to form alone and to grow as a layer between Pd and Si. The silicide is stable over a wide temperature range of 100 to 700°C. The phenomenon of single intermetallic compound growth is not unique to silicide formation between transition metal films and silicon, but is also commonly observed in reactions between bimetallic thin films. The phenomenon indicates phase stability.
Phase Equilibria in the Ni–Rich Region of the Ni–Al–Zr System
Authors: Jayanth C.S. , Nash P.
Published: March 2011

Alloys from the Ni–rich corner of the Ni–Al–Zr system have potential for use in high temperature, high strength applications. Such applications require a detailed knowledge of the high temperature phase equilibria.

In the case of the Ni–Al–Zr system no isothermal sections have been published although the existence of a monovariant eutectic valley between Ni3Al and Ni7Zr2 has been established. An experimental determination of the phase equilibria in this system is being carried out using quantitative electron microprobe analysis (JEOL JSM–U3), xray diffraction and optical metallography. Partial isothermal sections are being determined for 1373K (1100°C) and 1273K (1000°C) and the resulting phase equilibria compared to that in the Ni–Al–Hf system determined previously.
Semiconductor Epitaxy and Bandgap Engineering by Pulsed Laser Ablation
Authors: Cheung Jeff T. , Sankur H.
Published: March 2011

Introduction

Recently, Pulsed Laser Ablation [1] has been receiving much attention as a viable thin film deposition technique due to its success in demonstrating excellent high Tc superconducting thin films, although the use of laser radiation as an external energy source to vaporize materials for vacuum deposition was first carried out more than twenty five years ago [2].Most of the early work was focused on dielectric films, a few sporadic reports on III-V compounds [3], some investigations on II-V compounds [4] and elemental semiconductors [5]. Since material qualities were inferior to those grown by Molecular Beam Epitaxy (MBE) at that time, this area of work was largely ignored. After further refinement, the quality of semiconductor films grown by Pulsed Laser Ablation is now comparable to those by MBE, most notably in HgCdTe, CdTe, their superlattices [6] as well as Ge epitaxy [7].
Thin Films of Uniform Thickness by Pulsed Laser Deposition
Authors: Erington K. B. , Ianno N. J.
Published: March 2011

In order to enhance the utility of Pulsed Laser Deposition (PLD), a method to deposit uniform films has been devised. This method employs the deposition profile produced by PLD and the discrete nature of the process. We have simulated this process using experimentally determined deposition profiles and have used the results to design a system that produces films of uniform thickness to within a few percent across a substrate of 1 inch diameter and have obtained excellent agreement between theory and experiment.
Regularities of Laser-Stimulated Desorption from Oxide Semiconductors and Insulators
Authors: Moiseenko I. F. , Lisachenko A. A.
Published: March 2011

The time–of–flight method was used to study the laser stimulated desorption of atoms and molecules from the surfaces of Cr2O3, ZnO, TiO2, MgO, A12O3 under the influence of radiation of four harmonics of a pulsed neodymium laser. For the oxides studied, the kinetic energy distributions of desorbed oxygen molecules are characterized by the presence of two forms: “fast” with kinetic temperature Tk˜2500–3500 K, and “slow” with Tk˜350–550 K. The first one is typical for desorption excitation in the self-absorption region (hv > Eg), and the second one in the transparent region. “Fast” O2 desorption is accompanied by emission of single oxygen and metal atoms. Two non-thermal mechanisms of desorption are suggested, associated with the nature of the initial state of atoms and molecules on the surface and of the mechanism of the laser excitation of this states. The “slow” molecular oxygen desorption results from the excitation and subsequent neutralization of adsorbed molecular ions. The “fast” O2 emission is the result of recombination of oxygen atoms, after neutralization of the surface lattice ions by photoexcited carriers.
Fe Substituted, Laser Ablated YBa2Cu3O7 films using Off-Stoichiometric Targets
Authors: Bridges Frank , Truher J. , Fork D. K. , Boyce J. B. , Fenner D. B. , Connell G. A. N. , Geballe T. H. , Johnson S. , Liu L.
Published: March 2011

We present data on thin films of YBa2Cu3O7 (YBCO) and YBa2(Cu1−xFex)3O7 prepared by laser ablation using a sequence of targets, including Cu-deficient YBa2Cu2.4O7, CuO, and (CuO)1−y(FeO)y. This technique achieves mixing on an atomic scale. We find that stochiometric films, made using a combination of the Cudeficient target and CuO, have a sharp transition (width < 1K) near 90K although the Cu-deficient material alone has a broad transition at a lower Tc. We have achieved substitution of Fe on the Cu sites, using a sequence of the three targets for a range of Fe concentrations. Tc decreases nearly linearly with concentration and Tc → 0 near 15% Fe. The Tc suppression for the films is slightly less than the corresponding value obtained for bulk samples.
Nd: Yag Laser Ablation of BaTiO3 Thin Films
Authors: Gibson Ursula J. , Ruffner J. A. , Mcnally J. J. , Peterson G.
Published: March 2011

We have deposited thin films of barium titanate onto a variety of substrates, using picosecond and nanosecond pulsed Nd: YAG lasers. The films were deposited from a hot-pressed target onto substrates that were heated by either CO2 laser or conventional means, in a partial pressure of oxygen. Highly oriented films resulted from depositions onto MgO and LiF substrates held at temperatures greater than 600C.
Post-Deposition Patterning of Laser Deposited YBa2Cu3O7−δ Films
Authors: Dye R. C. , Foltyn S. , Martin J. A. , Nogar N. S. , Estler R. C. , Muenchausen R. E. , Mukherjree A. , Brueck S. R. J. , Carim A. H.
Published: March 2011

We report here on two aspects of non-chemical, post-deposition processing of laser-deposited superconducting Yba2Cu3O7-δthin films. One patterning process consists of placing a contact mask over the film and removes the surrounding material by excimer laser ablation. Good edge definition for 30–100 μm etch features is obtained. However, some redeposition of material is observed. In separate patterning experiments, oxygen-deficient films were re-oxygenated by a direct-write laser heating method. This process produces very smooth edges between the superconducting patterns and the surrounding material.
Pulsed Laser Ablation as a Source of Energetic Reactants: Synthesis of Superconducting High to Thin Films
Authors: Lynds L. , Weinberger B. R.
Published: March 2011

Pulsed KrF (248 nm) excimer laser ablation of targets can provide a source of atomic particles with energies in the range of 40 – 850 eV with beam-like characteristics. Optical intensities above about 109 W/cm2 lead mainly to single and multiply charged ground state positive atomic ions plus electrons with a pronounced angular energy dependence, the highest energies peaked in the direction normal to the target. A wide mass range of metallic and non-metallic targets were studied to determine the effects of atomic weights and other physical properties on the distribution of ion energies. Analysis of the energetics indicates that ablation mechanisms are non-equilibrium in nature. We have explored the use of very energetic (200–400 eV) Y, Ba and Cu ions to form very thin YBa2Cu3O7-x superconducting films grown on flat gold surfaces. SQUID magnetometry is used to study the temperature and field dependence of magnetization in these materials.
Growth of TiO2 Thin Films by Pulsed Laser Evaporation
Authors: Chen Ming Y. , Murray P. Terrence
Published: March 2011

Thin films of TiO2 have been grown by pulsed laser evaporation. The films were analyzed by in-situ Auger and x-ray photoelectron spectroscopy as well as by ex-situ grazing incidence xray diffraction. Films grown at room temperature and at a pressure of 5×10minus; 3 Torr were oxygen deficient. Films grown at 500°C and higher were found to be stoichiometric TiO2.The effect of substrate temperature and evaporation conditions on film properties will be discussed.
SiC Film Deposited by Pulsed Excimer Laser Ablation
Authors: Tench R. J. , Balooch M. , Connor A. L. , Bernardez L. , Olson B. , Allen M. J. , Siekhaus W. J. , Olander D. R.
Published: March 2011

Thin films of β- SiC were grown on Si substrates by excimer laser pulse ablation of bulk SiC. The films were examined by Auger electron, X-ray, and photoelectron spectroscopies. The film was smooth as monitored by scanning electron microscopy. Scanning electron and scanning tunneling microscopy showed inclusions in the deposited SiC film and laser ionization mass analysis detected SiC dimers in the vapor plume emitted from the target.
Surface Composition Changes and Ablation Dynamics in Excimer Laser Irradiated CdTe
Authors: Brewer P. D. , Zinck J. J. , Olson G. L.
Published: March 2011

We have investigated the dynamics of KrF excimer laser ablation of CdTe and the fluence dependent changes in surface stoichiometry that accompany the laser ablation process. The composition of the CdTe surface was reversibly controlled between stoichiometric and a Te-rich condition by varying the laser fluence over the range from 15–65 mJ/cm2. The primary species ejected from the irradiated surface were Cd atoms and Te2 molecules. Their velocity distributions as measured by time-of-flight mass spectrometry were found to be Maxwellian. From the analysis of the velocity distributions, the preferential desorption of surface atoms, and the reversible nature of the process, we conclude that the desorption is due to a photo-thermal mechanism which mediates the competition between Te2 formation and desorption and the desorption of Cd atoms.