bluuebunny/crossref_metadata_2025 huggingface dataset:
Carrier mobilities and process stability of strained Si n- and p-MOSFETs on SiGe virtual substrates
Authors: Currie M. T. , Leitz C. W. , Langdo T. A. , Taraschi G. , Fitzgerald E. A. , Antoniadis D. A.
Published: July 2002

Surface channel strained Si metal–oxide–semiconductor field-effect transistors (MOSFETs) are a leading contender for future high performance complementary metal–oxide–semiconductor (CMOS) applications. The carrier mobility enhancement of these devices is studied as a function of channel strain, and the saturation behavior for n- and p-channel devices is compared. Carrier mobility enhancements of up to 1.8 and 1.6 are achieved for n- and p-channel devices, respectively. The process stability of strained Si MOSFETs is also studied, and carrier mobility enhancement is shown to be robust after well implantation and virtual substrate planarization steps. The effects of high-temperature implant activation anneals are also studied. While no misfit dislocation introduction or strain relaxation is observed in these devices, increased interface state densities or alloy scattering due to Ge interdiffusion are shown to decrease mobility enhancements. Channel thickness effects are also examined for strained Si n-MOSFETs. Loss of carrier confinement severely limits the mobility of devices with the thinnest channels. Overall, surface channel strained Si MOSFETs are found to exhibit large carrier mobility enhancements over coprocessed bulk Si devices. This, combined with the high process stability exhibited by these devices, makes them superb candidates for future CMOS applications.
Oxidation of deuterium-, acetylene-, and ethylene-terminated Si(100) by atomic oxygen
Authors: Litorja Maritoni , Buntin Steven A.
Published: July 2002

The oxidation of deuterium-, acetylene-, and ethylene-terminated Si(100) by gas-phase atomic oxygen is evaluated using Auger electron spectroscopy (AES). The atomic oxygen is generated by the 157 nm laser photolysis of O2, which results in nominally a 50/50 mix of the ground (3P) and electronically excited (1D) state species. O atom adsorption probabilities for oxygen coverages in the 1–3 ML regime are estimated to be on the order of 0.1 for these adlayer systems. For both C2H2 and C2H4 adlayers no effective loss of surface carbon is observed, indicating that there first must be extensive oxidation of the near-surface region of silicon (greater than about 3 ML) prior to the removal of chemisorbed carbon on Si(100). The O/Si AES ratio for the O atom oxidation for oxygen coverages of about 1–3 ML in the near-surface regime is found to be linear with O atom exposure for all three adlayers, with the propensity for reaction being given by the relative slopes of 1.0:1.4:2.0 for D-, C2H2-, and C2H4-terminated Si(100), respectively. The relatively low rate for O atom oxidation of D-terminated Si(100) suggests that the presence of defects facilitates the oxidation. While the difference in the oxidation rates for the C2H2 and C2H4 adlayers is statistically significant, this is most likely not due to initial adlayer coverage effects; the specific cause(s) of this difference, however, is not established.
Ti diffusion in ion prebombarded MgO(100). II. Effects of the irradiation spectrum
Authors: Lu M. , Lupu C. , Lee S. M. , Rabalais J. W.
Published: July 2002

Ti diffusion in MgO(100) has been studied for MgO that was prebombarded with the inert ions Ne+, Ar+, and Kr+ in the keV energy range using various ion doses, energies, momenta, and penetration ranges. Diffusion was induced by annealing to 1000 °C for 6 min following the prebombardment and Ti evaporation. This type of radiation enhanced diffusion (RED) is called non-steady-state RED, or NSRED. The diffusion penetration profiles were analyzed by using secondary ion mass spectrometry depth profiling techniques and TRIM ion trajectory simulations. The observed diffusion behaviors were treated with our previously developed model for NSRED. A figure of merit, Σ, has been introduced to assess the density of extended vacancy defects (EVDs) responsible for NSRED and to compare NSRED effects for the different ion bombardment parameters. The trends observed in Σ are in agreement with the experimentally observed RED effects and provide a quantitative measure of their magnitudes. The results show that the NSRED effects and vacancy densities responsible for NSRED correlate with the degree of vacancy production from TRIM simulations. It is found that NSRED of Ti in MgO and the density of EVDs responsible for NSRED reach a saturation level after a dose of ∼1016 ions/cm2 for 7 keV Ar+ prebombardment. A threshold value of the vacancy production for the formation of EVDs for NSRED at this dose is in the range of 94–111 vacancies/ion from TRIM simulations.
Synthesis and mechanical properties of boron suboxide thin films
Authors: Music Denis , Schneider Jochen M. , Kugler Veronika , Nakao Setsuo , Jin Ping , Östblom Mattias , Hultman Lars , Helmersson Ulf
Published: July 2002

Boron suboxide thin films have been deposited on Si(100) and graphite substrates by reactive rf magnetron sputtering of a sintered B target in an Ar/O2 atmosphere. X-ray photoelectron spectroscopy, elastic recoil detection analysis, Fourier transform infrared spectroscopy, x-ray diffraction, and transmission electron microscopy were applied to study the influence of the O2 partial pressure on the film composition and microstructure. BOx thin films with x=[0.02–0.21] and a C impurity of approximately 0.3 at. % were formed by varying the O2 partial pressure from 7.2×10−7 to 3.3×10−2 Pa. All films were amorphous and the films with x⩾0.15 contained boric acid on the surface due to a probable chemical reaction with water in laboratory atmosphere. Mechanical properties were evaluated by nanoindentation. As x was increased from 0.02 to 0.21, the elastic modulus decreased from 272 to 109 GPa. The change in the elastic modulus was attributed to the O concentration variations.
Field emission from chemical vapor deposition diamond surface with graphitic patches
Authors: Cui J. B. , Robertson J.
Published: July 2002

The field emission properties of a polycrystalline diamond film with hydrogenated and hydrogen free surfaces have been investigated by monitoring both the emission current–voltage curve and emission site density. A very low turn-on field of electron emission was found to be 0.5 V/μm for the hydrogenated surface and 4 V/μm for the hydrogen free surface. The emission site densities were significantly reduced from 3×103 to 2×102 cm−2 at 5 V/μm after the surface hydrogen desorption. The low turn-on field and high emission site density on the hydrogenated surface are explained by the low work function of diamond combined with graphitic patches on the surface.
Developments in ultrashallow spreading resistance analysis
Authors: Dickey David H.
Published: July 2002

Spreading resistance analysis on ultrashallow structures is complicated by the interaction of bevel rounding with geometric effects associated with lateral boundaries. When a spreading resistance probe is stepped from the original sample surface, across the rounded region at the bevel edge and onto the bevel, the resistance increases. Some of the increase is the result of approaching the lateral boundary represented by the bevel, and some is the result of increasing local sheet resistance as the probes begin to move below the original surface. We remove the geometric effect by solving the boundary value problem involving a sheet resistance which varies with distance along the direction of probe travel. Having obtained the local sheet resistance, we assign a depth for each point from profilometer data, and the usual depth-dependent analysis is used to obtain the resistivity profile.
Experimental Studies of a Low-Pressure Air-Water Vapor-Ice System
Authors: Martin D. H.
Published: July 2002

A series of temperature and pressure measurements are described which were made on a low pressure system in which water vapor leaves ice samples and passes through air to a vacuum pump in a cylindrical geometry. Evidence of a Gaede-type pumping of the air is noted. Saturation vapor pressures associated with the steady-state ice temperatures are found to have a linear relationship with the air pressures maintained by the pump, allowing the use of ice as a pressure “gauge.” A heat flow balance equation is used to confirm the applicability of diffusion theory to the water vapor flow (at a sufficient distance from the ice), and arguments based on this equation are used to explain the linearity described above. A kinetic theory treatment by Takaishi is compared with the present measurements, and the possibility of a more complete description of the system is discussed.
LEED intensity−averaging experiments for surface−layer structure determination
Authors: Lagally M. G. , Buchholz J. C. , Wang G.−C.
Published: July 2002

Constant−momentum−transfer averaging of LEED intensities for surface crystallography is reviewed. It is shown that a range of structural information on both the clean surface and adsorbed layers can be obtained. The method is illustrated with experimental results for clean and oxygen−covered W(110). The status of some parameters relevant to all techniques of surface structure analysis is briefly reviewed.
Binding of carbon atoms at a stepped−Ni surface
Authors: Isett L. C. , Blakely J. M.
Published: July 2002

We have studied the equilibrium segregation of carbon to a stepped surface of nickel, Ni[S] [7(100) × (1̄33)] using Auger electron spectroscopy and LEED. At temperatures below 640 K diffuse p (2×2) structures were observed to form and progressively sharpen as the temperature was lowered. The p (2×2) spots were split, indicating ordering between terraces. The surface coverage of carbon vs temperature was well described by a Langmuir model, but with three distinct heats of segregation ΔEseg = −0.82 eV for ϑ?1/3, ΔEseg = −0.51 eV for 1/3 <ϑ<2/3, and ΔEseg = −0.37 eV for 2/3?ϑ≲1. The ratio of integrated Auger current to the peak−peak value on the derivative spectrum changes abruptly at ϑ?1/3, 2/3, indicating a change in chemical bonding. These results are interpreted in terms of terrace dimensions, and provide information to complement experiments performed on Ni(100) surfaces in the same temperature and doping range.
Optical properties of ultrathin Ag films
Authors: McCarthy S. L.
Published: July 2002

Reflection and transmission measurements from 1.8 to 4.4 eV have been made on evaporated Ag films with mass thicknesses less than 8 nm on fused silica substrates. The data were analyzed using approximative techniques. The results are discussed in terms of both the Maxwell–Garnett theory and the two-dimensional sphere model. Results indicate that the properties of specially heat-treated films are predicted very closely by the Maxwell–Garnett theory.
Thermal aging of Al thin films on GaAs
Authors: Johnson N. M. , Magee T. J. , Peng J.
Published: July 2002

Electrical and structural properties of annealed Al films on GaAs were evaluated for the purpose of identifying reactions at the Al–GaAs interface. After annealing at 400° or 500°C (1 h, in vacuo), Al films on GaAs are covered with an array of erosion centers that expose the substrate. The Schottky barrier height increases with annealing temperature from 0.73 eV, with the ideality parameter n?1.03 in as-prepared contacts, to 0.82 eV, with n? 1.07, for contacts annealed at 500°C (1 h, in vacuo). Data from both selected-area transmission electron diffraction (TED) and dark-field transmission electron microscopy reveal the presence of Al precipitates in the near surface region of the GaAs in samples annealed at 500°C (2 h, in vacuo). Selected-area TED patterns obtained from alloyed Al films on (310) -oriented GaAs indicate the formation of AlAs crystallites at the interface. Chemical depth profiles obtained with the use of Auger electron spectroscopy provide further indication of thermally induced interdiffusion in Al–GaAs structures.
Thin film deposition using low-energy ion beams. I. System specification and design
Authors: Amano J. , Bryce P. , Lawson R. P. W.
Published: July 2002

Design criteria for a clean thin film deposition facility are discussed. A low-energy ion beam film deposition system satisfying the design requirements has been constructed. Initial performance data are given for gaseous ion beams and for several ion beam-deposited elemental metallic films. The facility has numerous features built in to allow a wide range of diagnostic tests to be carried out on films produced within the system, both in situ and in external equipment such as electron microscopes and Rutherford backscattering analysis. A deposition energy between 70 and 75 eV is suggested as an optimum energy range for deposition of Pb+ and Mg+ onto carbon substrates.
Tight-binding study of the electronic structure of the InAs–GaSb (001) superlattice
Authors: Nucho R. N. , Madhukar A.
Published: July 2002

We present tight-binding model calculations for the InAs–GaSb (001) superlattice including second nearest-neighbor interactions. The tight-binding parameters used were obtained by fitting to the bulk band structure of InAs, GaSb, InSb, and GaAs. The parameters were required to be consistent with each other, to yield accurate energy values at the symmetry points, and to reproduce well the overall dispersion. Results for the behavior of the energy gap of the superlattice as a funcion of layer thickness, and of the conduction-band–valence-band edge discontinuity at the Γ point have been obtained. With increasing magnitude of the discontinuity, the nature of the superlattice changes from a direct gap semiconductor to an indirect gap semiconductor, to a semimetal. These results are compared with recent experimental studies.
Theoretical studies of nickel clusters and chemisorption of hydrogen
Authors: Upton Thomas H. , Goddard III William A. , Melius Carl F.
Published: July 2002

First principles calculations of high- and low-symmetry clusters (up to Ni87) are reported. Macroscopic properties [ionization potential (IP), electron affinity (EA), and bandwidth] are not sensitive to cluster symmetry and, except for EA, are converged to bulk values by Ni87. Even for Ni87 the EA is over 2.5 eV smaller than the IP; the origin of this effect is discussed. The chemisorption of hydrogen is considered on the low-symmetry clusters, where it is found that threefold and fourfold sites are most favored with bond energies of ∠3 eV for both types of sites. Geometries are not cluster sensitive with R (NiH) values of 1.57, 1.62, and 1.78 Å for twofold, threefold, and fourfold sites, respectively. Vibrational frequencies for these sites are 1420, 1212, and 592 cm−1, respectively.
Structure determination for the (110) surface of zincblende structure compound semiconductors
Authors: Duke C. B. , Meyer R. J. , Paton A. , Mark P. , Kahn A. , So E. , Yeh J. L.
Published: July 2002

A survey is presented of determinations of the atomic geometries of the (110) surfaces of zincblende-structure III–V and II–VI compounds via analyses of elastic low-energy electron diffraction intensities, of both integrated and angle-resolved ultraviolet photoemission spectra, and of electron paramagnetic resonance signals associated with adsorbed O−2 complexes. Comparison of the proposed model geometries for GaAs(110) reveals that they are compatible both with each other to within the accuracy of the analytical methodologies and with energy-minimization calculated structures. Results for other materials are fragmentary, but suggest incompatibilities between spectroscopically-determined and energy-minimized structures for ZnTe(110) and InSb(110). All of the model surface structures embody large movements of species in the uppermost atomic layer, with the cation moving inward by Δd⊥?0.4 A and the anion outward either less or not at all. The reconstructions penetrate to the second and perhaps third atomic layer for covalently bonded materials like GaAs and InSb. Spectroscopic evidence for the penetration of the reconstructions beneath the top layer is weak, however, for more ionic compounds like ZnTe.
High resolution electron energy loss spectrometer for vibrational surface studies
Authors: Sexton Brett A.
Published: July 2002

A high resolution energy loss spectrometer for general surface studies is described. Based on the 127° sector design, it utilizes a fixed analyzer and monochromator geometry, and a plug-in compatibility with a LEED–Auger UHV system. With an energy resolution of 8–10 meV and 1–3×10−10 A incident current at 5 eV energy, the performance is comparable to existing instruments. The main advantage of this design is that it allows a rapid interconversion between EELS and other surface techniques in the same chamber. The performance is illustrated with reference to scattering from a Cu(100) surface, and after adsorption of oxygen, carbon monoxide, and water.
X-ray zone plates fabricated using electron-beam and x-ray lithography
Authors: Shaver D. C. , Flanders D. C. , Ceglio N. M. , Smith Henry I.
Published: July 2002

Fresnel zone plate patterns, free of spherical aberration, with diameters of up to 0.63 mm and linewidths as small as 1000 Å were fabricated on polyimide membrane x-ray masks using scanning electron beam lithography. Distortion of the electron beam scan raster was reduced to ?2500 Å over a 2×2 mm field by applying deflection corrections, while viewing the distortion using a Moiré method. CK x-ray lithography was used to replicate the zone plate pattern in thick PMMA over a 100 Å thick plating base on a glass substrate. Zones plates in 1.3 μm thick gold were fabricated by plating, and made free-standing by removal of the plating base and the supporting glass substrate. Zone plates were tested as imaging elements with visible light and soft x-rays.
Spatial period division—A new technique for exposing submicrometer-linewidth periodic and quasiperiodic patterns
Authors: Flanders D. D. , Hawryluk A. M. , Smith Henry I.
Published: July 2002

We describe a technique for exposing patterns of spatial period p/n using near-field diffraction from masks of spatial period p. The technique, which we propose to call ’’spatial-period-division’’, can be used with visible, UV, or x-ray radiation. With soft x rays, it is possible to produce gratings of much finer spatial period than can be achieved by current laser holographic methods. A simple model predicts that a mask pattern of period p, with an opening or slit of width ?p/2n, will give rise to an intensity pattern of period p/n at a distance from the mask, S=p2/nλ, where λ is the wavelength of the incident radiation and l≪p. The model was confirmed at visible wavelengths using a scaled simulation of a laboratory x-ray lithography unit. The feasibility of the technique was demonstrated at the 4.5 nm carbon K x-ray wavelength by ’’doubling’’ a 196.8 nm period grating-pattern x-ray mask to produce a 98.4 nm period pattern in PMMA. Exposure of higher spatial-frequency-multiples appears feasible, especially with a synchrotron source. If the mask introduces a phase shift, such that the zero-order diffracted beam is cancelled, and if p<2λ, only the second spatial-frequency-multiple will be present. This should enable quasiperiodic patterns such as variable-period gratings and Fresnel zone plates to be ’’doubled’’.
Structure of the clean Re(101̄0) surface
Authors: Davis H. L. , Zehner D. M.
Published: July 2002

Existing LEED data from the clean Re(101̄0) surface have been analyzed by comparing with the results of fully dynamical calculations for numerous models. The analysis indicates that this surface has the second layer atoms located directly below the centers of the geometric rectangles of the first layer. This geometry is one of the two possible terminations of the truncated bulk crystal. Further, the analysis indicates that the interlayer spacing between the 1st and 2nd atomic layers is contracted by about 17% from its bulk value, while the spacing beteeen the 2nd and 3rd layers may be slightly expanded. Since the data employed in the analysis consisted of only two diffracted beams, the above conclusions should be considered as tentative and accepted with reasonable caution. However, this is the first reported LEED analysis for the (101̄0) surface of an hcp metal. So it is of interest to determine whether our conclusions will be verified for Re and/or similar results found for other hcp metals.
Surface atomic geometry of covalently bonded semiconductors: InSb(110) and its comparison with GaAs(110) and ZnTe(110)
Authors: Duke C. B. , Meyer R. J. , Paton A. , Yeh J. L. , Tsang J. C. , Kahn A. , Mark P.
Published: July 2002

The first determination of the atomic geometry of the (110) surface of InSb is reported. The structure is determined by comparing dynamical calculations of elastic low-energy electron diffraction (ELEED) intensities with those measured at T=150 K. Initial candidate structures were obtained from an energy-minimization calculation and from a kinematic analysis of room-temperature ELEED intensities. Neither candidate proved fully compatible with the measured intensities so another search for the correct structure was performed using dynamical calculations. This procedure yields as the most probable surface structure for InSb(110) one in which the top layer undergoes both a rigid rotation of 28.8° and a 0.05 Å contraction toward the substrate. The Sb atoms move outward and the In atoms inward, giving a relative vertical shear of 0.78 Å in this uppermost layer. In the second layer, the In moves outward 0.09 Å and the Sb inward 0.09 Å. The resulting structure is analogous to that of covalently bonded GaAs(110) but different from that of ZnTe(110) which exhibits a more ionic bonding. We infer that highly covalent zincblende-structure compound semiconductors exhibit reconstructions of their (110) surfaces characterized by (1) large bond rotations in the uppermost layer, with the anion moving outward and cation inward, (2) small bond-length alterations (i.e., a few percent or less), and (3) distortions from the bulk geometry which penetrate at least two atomic layers in from the surface.
Effect of three-body interactions on the structure of small clusters
Authors: Halicioglu Timur , White Patrick J.
Published: July 2002

Minimum energy configurations of microclusters (up to six atoms) have been calculated using two- and three-body interactions. Structural changes were parametrically analyzed as a function of the intensity of three-body forces. The results are qualitative in nature; they indicate, however, that three-body interactions play an important role in the equilibrium structure of microclusters. The effect of the intensity of the three-body interactions on the structure of small clusters is not manifested in a continuous manner. Rather, changes in the energetically most stable structure occur abruptly. The results are in qualitative agreement with experimental observations as well as other calculations.
Electronic states and atomic structure at the Pd2Si–Si interface
Authors: Schmid P. E. , Ho P. S. , Föll H. , Rubloff G. W.
Published: July 2002

Electronic states and atomic structure at the Pd2Si–Si interface have been investigated using AES and UPS in conjunction with transmission electron microscopy (TEM). By following the core and valence spectra from submonolayer to several atomic layers of Pd coverages, the changes in the partial state density of the Pd and Si atoms during interface formation have been observed. Stoichiometry calibration based on relative variation of Auger intensities reveals extra Si states existing within a few Å of the interface. Analysis of the spectral shapes and peak shifts shows that these Si states are derived from a Si-rich environment at the interface and are located mostly near the Si bandgap region. TEM lattice images reveal a structurally sharp Pd2Si–Si (111) interface with misfit dislocations and atomic steps present within several Å of the interface. Combining the spectroscopy and TEM results, we infer that the interface states originate from chemical bonds associated with the atomic defect structures produced by silicide formation.
A 1013/s 14 MeV neutron generator for cancer therapy
Authors: Walko R. J. , Bacon F. M. , Bickes R. W. , Cowgill D. F. , Boers J. E. , Riedel A. A. , O’Hagan J. B.
Published: July 2002

A high output D-T neutron generator is being developed at Sandia National Laboratories as a cancer therapy tool. Preliminary results have been obtained with a high vacuum deuterium accelerator consisting of a duopigatron ion source, single stage accelerator, and a scandium occluder target. The ion source and accelerating system have been optimized to reliably focus a 200 mA, 200 kV deuterium ion beam onto the scandium target 1.5 m away with a beam spot size of 10−3m2. The scandium target degrades due to implantation of impurities from the unbaked vacuum system. A UHV accelerator is being fabricated which will permit a 450 °C bakeout to alleviate the impurity problem. This system will also be compatible with the use of tritium, a necessary component of the therapy machine.
Spatial separation of carriers in InAs–GaSb superlattices
Authors: Chang L. L. , Sai-Halasz G. A. , Esaki L. , Aggarwal R. L.
Published: July 2002

Optical absorption measurements have been performed in InAs–GaSb superlattices to demonstrate the effect of spatial separation of carriers. From these and additional magneto-absorption measurements, the absorption edge is shown to arise from transition involving ground sub-bands of electrons and heavy holes. Fine structures in the spectra are identified with transitions from the excited sub-bands of both heavy and light holes to the sub-bands of electrons, which are governed by the spatial overlap of their associated wavefunctions.
A novel approach to o-nitrobenzyl photochemistry for resists
Authors: Reichmanis E. , Wilkins C. W. , Chandross E. A.
Published: July 2002

We have developed a two-component (resin-solution inhibitor) resist system having good photosensitivity in the 230–300 nm range. The resin is an optically transparent methyl methacrylate-methacrylic acid copolymer that is soluble in aqueous alkali. The second component is one of a family of o-nitrobenzyl carboxylates that are initially insoluble in the alkaline developer but are cleaved to soluble components upon irradiation. A number of o-nitrobenzyl alcohol esters have been prepared and examined for use in this two-component system. They have proven useful in the development of sensitive high-resolution short-wavelength photoresists which are described.
Auger signal intensity dependence on surface area (roughness)
Authors: Wu O. K. T. , Butler E. M.
Published: July 2002

The effects of surface roughness on Auger electron spectroscopy (AES) and electron spectroscopy for chemical analysis (ESCA) have been a problem in surface analysis. In this study, the quantitative relationship between surface area and Auger signal intensity was studied using a variety of electrodeposited Cu foils. The foil surfaces studied here can be classified into two categories: Type A is cone shaped (diameter about 5 μ, height about 5 μ), and Type B is cone shaped with small nodules (diameter about 1 μ) on the surface. The surface area of foil samples was measured by the Brunauer, Emmett, and Teller (BET) gas adsorption technique. In addition, the foil samples were characterized by scanning electron microscopy and light scattering experiments. The Auger signal intensities of foils were studied after thin film (gold or zinc oxide) deposition. The results indicate that (1) there are strong correlations between surface area data, Auger signal intensities, and light reflectance data for both Type A and Type B foils; and (2) this kind of Auger signal intensity dependence on surface area (roughness) is independent of the energy for the range studied (up to 1000 eV) here.
Localized Auger final states in linear alkanes and polyethylene
Authors: Kelber J. A. , Jennison D. R.
Published: July 2002

The energies and Auger lineshapes of the linear alkanes and polyethylene strongly suggest the presence of highly correlated (localized) two-hole excitations in these materials. This conclusion is supported by a comparison of the polyethylene spectrum to the predictions of independent particle theory. A semiempirical configuration–interaction formalism which explicitly considers final-state hole screening in the static limit is applied to the alkane spectra. The calculations show that while the ethane Auger spectrum is independent, particle-like correlation effects are present in longer alkane chains and become more pronounced with increasing chain length. The dominant central peak in the alkane spectra is assigned to transitions to localized states while the higher valence region is assigned to delocalized states.
Ion beam sputter deposition onto levitated and stalk mounted laser fusion targets
Authors: Glocker D. A. , Drumheller J. P. , Miller J. R.
Published: July 2002

Ion beam sputter deposition has been used to coat both levitated and stalk mounted hollow glass microballoon (GMB) laser fusion targets. GMBs levitated with a focused molecular beam were coated with Cu at pressures which ranged from 0.020 Pa (0.15 mTorr) to 0.13 Pa (1.0 mTorr). Stalk mounted GMBs were coated with Cu, Fe, Ta, or Mo at pressures from 0.0050 Pa (0.038 mTorr) to 0.10 Pa (0.75 mTorr). Beam energies of 300–1000 eV and beam current densities of 4–8 mA/cm2 were used. Scanning electron micrographs of fractured cross sections of the coatings were examined for film structure and surface smoothness. As the deposition pressure was reduced, both Cu and Fe exhibited a transition from zone 1 to zone T growth, in agreement with Thornton’s Structure Zone Model. The Ta and Mo coatings were dense and had surface roughness less than 100 nm at all beam powers and pressures studied.
Developments in broad-beam, ion-source technology and applications
Authors: Kaufman H. R. , Harper J. M. E. , Cuomo J. J.
Published: July 2002

Recent advances in broad-beam, ion-source technology are summarized, including low-energy ion optics, improved extraction grid fabrication, a compact ion-source design and a gridless ion-source design. Recent applications have emphasized concepts such as stress modification of vapor deposited films, very low energy ion beams to minimize the physical sputtering portion in reactive etching, and the use of multiple sources and targets to sputter deposit alloys and compounds. A comprehensive critical review by the same authors appears concurrently, describing in detail the developments in broad-beam, ion-source technology1 and the applications of these sources.2
Measurement of plasma density using nuclear techniques
Authors: Strachan J. D. , Chrien R. E. , Heidbrink W. W.
Published: July 2002

The magnitude of a fusion reaction rate in a plasma depends strongly on the relative energy of the reacting plasma ions and less strongly on the ion number density. The ratio of two reaction rates, however, is less dependent on the relative velocities while retaining the linear dependence on the relative densities of the plasma ion species. In this manner, the ratio of t(d,n)α to d(d,n) 3He fusion reactions depends only on the ratio nt/nd, so that tritium levels in a deuterium plasma can be determined from the d–t/d–d reaction ratio (nd ≂ne). Similarly, the density of 3He can be determined in a deuterium plasma from the ratio of 3He (d, p)α to d(d,n) 3He fusion reactions. Such measurements of the 3He density are of interest since they relate to the alpha ash removal problem expected on a tokamak reactor.
Photography of impurity injection into PLT plasmas
Authors: Timberlake J. , Cohen S. , Daughney C. , Manos D.
Published: July 2002

Using still color photography with submillisecond time resolution, observations of impurities injected into the PLT tokamak by laser blowoff have been made. These clearly show the existence of atomic vapor and particulates with abundances depending on laser fluence, material, and film thickness. Velocity determinations for each component have been made: for atomic vapor v≂2×105 cm/s; and for particulates v≂5×104 cm/s. Their penetration depths into plasmas of different electron densities have also been measured. Models of penetration are compared with the data.
Electrical, optical, and structural properties of semitransparent metallic layers
Authors: Kar S. , Varghese R. , Bhattacharya S.
Published: July 2002

Electrical, optical, and structural properties of ultrathin films of Ag, Au, and Al were investigated. MOS solar cells were fabricated with Ag, and Au barrier metals on n-type and with Al barrier metal on p-type silicon. The short-circuit current density Jsc was measured as a function of the average metal layer thickness tm. The film structure was examined under a transmission electron miscroscope. The optical transmittance T was measured as a function of the wavelength λ with tm as a parameter. The transmission electromicrographs indicated that, in the Ag and Au case, the film network structure attained electrical continuity at a lower value of tm than in the case of Al. Also, in the Ag and Au case, surface covered by the film was lower. Largely due to this, optical transmittance was higher in the Ag and Au case than in the case of Al. The T(λ) characteristics exhibited strong features in the Ag and Au case but not in the Al case. The profiles of Jsc(tm) were found to be peaked with the maximum occuring around 55 Å for Ag and Au and around 70 Å for Al. Furthermore, the peaks were sharp in the Al case, but were broad in the Ag and Au case. Also, the peak values were larger in the Ag and Au case. The higher rate of degradation of Ag and Au MOS cells than Al MOS cells can be related to the presence of large discontinuity in Ag and Au films.
Initial stages of oxidation of the Pt3Ti(111) and (100) single crystal surfaces
Authors: Bardi U. , Ross P. N.
Published: July 2002

The process of segregation of titanium oxides onto the surface of Pt3Ti upon the exposure to oxygen at different pressures and temperatures was studied by LEED and AES. Oriented [111] and [100] monocrystals as well as polycrystals were synthesized for study. Qualitatively similar behavior was observed with all three types of surfaces, with three stages of oxidation observed on each surface. A layer of stoichiometry close to TiO segregated onto the surface in the initial stage of oxidation, depleting the subsurface region of the alloy in Ti. The TiO formed a compact, epitaxial monolayer which completely blocked the metallic surface for chemisorption by carbon monoxide. Further oxidation caused formation of a multilayer of TiO1.2, an oxide with an orthorhombic structure derived from TiO by removing Ti atoms to form an ordered vacancy lattice. Finally, oxidation at the relatively extreme conditions of atmosphere pressure at high (>1000 K) temperature caused formation of thick TiO2 (rutile) overlayers.
Development of boron liquid–metal–ion source
Authors: Ishitani T. , Umemura K. , Hosoki S. , Takayama S. , Tamura H.
Published: July 2002

A boron liquid–metal–ion source is described that uses a combination of a glassy carbon or carbide emitter and a Ni–B base alloy as its source material. The B+ ion emission current is 25%–35% of the total emission current, and the energy spread for B+ ions is 12 eV at a total current of 30 μA. A source lifetime of more than 250 h was achieved with a total current of 30–50 μA. This source mounted on a mass-separated focusing column has led to B+ submicron beams with maximum energies of 20 keV for preliminary experiments on maskless implantation.
Inertial fusion target fabrication using polystyrene mandrels
Authors: Kim Hyo-gun , Powers Thomas F. , Mason James F.
Published: July 2002

Large-aspect-ratio, plastic-coated, metal shells are useful targets for obtaining valuable information on thermal transport in laser implosion experiments. We have found that by using polystyrene as a leachable mandrel, it is possible to fabricate such complex, inertial-fusion targets. The present fabrication technique offers advantages over previous techniques, including the hemispherical-shell approach, the leachable-metal-mandrel approach, and the coating of a prefabricated metal shell. For fabrication of such diagnostic targets, comprised of a high-aspect-ratio, plastic-coated, metal shell, a polystyrene sphere is mounted on a stalk, then coated with metal and parylene layers. A hole of 5–10 μm is drilled with a laser pulse through the layers and the polystyrene is then leached out by immersing the system in toluene. The concept of the present technique presents a number of possibilities for the fabrication of complex targets not possible previously.
Surface characterization by photoemission of adsorbed xenon (PAX)
Authors: Wandelt K.
Published: July 2002

The photoemission derived electron binding energies (with respect to the Fermi level) of xenon atoms adsorbed on nonuniform metal surfaces are found to be sensitive to the local work function of the respective adsorption site. As a consequence separated photoemission lines can be resolved corresponding to xenon atoms coexisting on differing surface patches. This effect makes photoemission of adsorbed xenon (PAX) a powerful tool to characterize heterogeneous surfaces on an atomic scale. Various examples are discussed to demonstrate the capability as well as the limits of this technique, such as the ‘‘titration’’ of surface defects and the determination of the surface topography of coldly deposited Ag films.
Time-resolved electron energy loss spectroscopy of surface kinetics
Authors: Ho W.
Published: July 2002

The study of adsorbate kinetics on single crystal surfaces by time-resolved electron energy loss spectroscopy with resolution as fast as a few milliseconds is described. Rapid temperature and pressure jumps are used to perturb the system out of equilibrium, and the subsequent relaxation is followed in real time by a parallel data acquisition scheme achieved by incorporating a multichannel detector into the electron energy analyzer. Chemical transformations and structural transitions on surfaces are probed directly by recording as a function of time vibrational spectra of absorbed molecules. Surface kinetics problems that can be uniquely studied by this technique are identified. In addition, the potentials as well as the limitations set by the present capabilities of the instrument are also addressed.
The behavior of oxygen in HgCdTe
Authors: Yoshikawa M. , Ueda S. , Maruyama K. , Takigawa H.
Published: July 2002

The behavior of oxygen in HgCdTe has been studied using a liquid phase epitaxial growth technique. The oxygen has been found to act as a donor impurity in Hg0.7Cd0.3Te. High-purity Hg0.7Cd0.3Te crystals with carrier concentration of less than 5×1013 cm−3 can be obtained reproducibly by complete deoxidization of the growth solution. As a result, carrier concentration can be controlled accurately within ±1×1014 cm−3.
Auger and core level electron energy loss studies of (Y2O3)m(ZrO2)1−m single crystal surfaces
Authors: Solomon J. S. , Grant J. T.
Published: July 2002

Core level electron energy loss spectroscopy (EELS) and Auger electron spectroscopy (AES) were used to study yttria stabilized cubic zirconia (YSCZ) substrate surfaces subjected to various treatments before Si epitaxy for silicon-on-insulator (SOI) applications. The Y and Zr M4,5 EELS peaks are shown to be quite sensitive to chemical state differences. In the case of YSCZ these peaks exhibit subtle differences with varying yttria content. These differences are thought to be related to oxygen vacancy concentration and its effect on local density of states. Because of Y and Zr AES peak overlap problems, no changes in peak shape with yttria content were observed in corresponding AES specta. Both AES and EELS data were used to quantify the yttria concentration at YSCZ surfaces and to identify the elements remaining on YSCZ surfaces following various chemical treatments.
Polymers as electronic materials
Authors: Duke C. B.
Published: July 2002

In this reviw the scope of modern applications of polymers as electronic materials is noted and the status of theoretical models of their electrical properties is indicated. Emphasis is placed on the role of disorder in localizing injected charges and excitons. Because of the rudimentary state of the quantitative characterization of the structure of polymer films, direct measurements (e.g., via valence electron photoemission spectroscopy) of the energy distributions of localized charges are utilized to characterize the effects of composition and processing on electrical properties as well as to test theoretical models. The triboelectric charging of polymers is examined as an illustration of the application of current models to describe a subtle electrical phenomenon of practical interest in electrophotography and the fabrication of microelectronic devices.
Total energy all-electron theory of surface structural, electronic, and magnetic properties
Authors: Freeman A. J. , Fu C. L. , Wimmer E.
Published: July 2002

In the last decade, intense experimental efforts using advanced techniques for sample preparation and characterization have provided a vast quantity of data. These developments have challenged present theoretical understanding and have encouraged the development of theoretical methods interpreting the phenomena observed. Our total energy all-electron local density theoretical approach, implemented as the full potential linearized augmented plane wave (FLAPW) method, is described and shown to have high precision (to 10−9 in the total energy) and stability for describing the structural, electronic, and magnetic properties of (i) free surfaces [including surface relaxation and reconstruction, e.g., W(001)], (ii) interface phenomena in Au/Cr/Au(001) sandwiches [e.g., prediction of the enhanced magnetic moment on the interface Cr site], (iii) catalytic promotion and poisoning of molecular dissociation on surfaces [e.g., CO + K or S/Ni(001)]. The three examples just cited illustrate the present predictive power and sophistication of total energy all-electron calculations in elucidating properties of direct interest to experimentalists.
Hydrogen pellet acceleration with a two-stage system consisting of a gas gun and a fuseless electromagnetic railgun
Authors: Honig J. , Kim K. , Wedge S. W.
Published: July 2002

Hydrogen pellets are successfully accelerated for the first time using a two-stage system consisting of a pneumatic gun and an electromagnetic railgun. The pneumatic gun preaccelerator forms cylindrical hydrogen ice pellets (1.6-mm diam×2.15-mm long) and accelerates them with high-pressure helium gas to velocities in excess of 500 m/s. The booster accelerator, which is a fuseless, circular-bore electromagnetic railgun, derives its propulsive force from a plasma arc armature. The plasma arc armature is formed by electrically breaking down the propellant gas which follows the pellet from the gas gun into the railgun. The diagnostics are for the monitoring of the main capacitor bank and rail currents, for the pellet detection and velocity measurements at the breech and muzzle ends of the railgun, for the recording of the plasma-arc-armature movement inside the railgun bore, and for the photographing of the hydrogen pellet exiting the railgun. Using the system, which is a 60-cm long proof-of-principle machine for refueling magnetic fusion devices, hyrogen pellet velocities exceeding 1 km/s have been achieved for pellets exiting the gas gun at velocities of ∼500 m/s.
Operation of a repeating pneumatic hydrogen pellet injector on the Tokamak Fusion Test Reactor
Authors: Combs S. K. , Milora S. L. , Foust C. R. , Schmidt G. L. , McBride T. P.
Published: July 2002

The repeating pneumatic hydrogen pellet injector, which was developed at the Oak Ridge National Laboratory (ORNL), has been installed and operated on the Tokamak Fusion Test Reactor (TFTR). The injector combines high-speed extruder and pneumatic acceleration technologies to propel frozen hydrogen isotope pellets repetitively at high speeds. The pellets are transported to the plasma in an injection line that also serves to minimize the gas loading on the torus; the injection line incorporates a fast shutter valve and two stages of guide tubes with intermediate vacuum pumping stations. A remote, stand-alone control and data acquisition system is used for injector and vacuum system operation. In early pellet fueling experiments on TFTR, the injector has been used to deliver deuterium pellets at speeds ranging from 1.0 to 1.5 km/s into plasma discharges. First, single large (nominal 4 mm diam) pellets provided high densities in TFTR (1.8×1014 cm−3 on axis); after conversion to smaller (nominal 2.7 mm diam) pellets, up to five pellets were injected at 0.25 s intervals into a plasma discharge, giving a line-averaged density of 1×1014 cm−3. Operating characteristics and performance of the injector in initial tests on TFTR are presented.
Ablation layer coating of mechanically nonsupported inertial fusion targets
Authors: Gram R. Q. , Kim H. , Mason J. F. , Wittman M.
Published: July 2002

Ablation layers are deposited on DT-filled glass microballoon targets by a parylene coating scheme while the targets are bounced on the surface of a mechanical resonator. Optimum bouncing is achieved with the resonator surface moving with a peak vertical velocity of ∼3 cm/s at a frequency much greater than the bounce frequency of the targets. The resonator, a solid cylinder of high-Q material, uses a longitudinal mode of vibration to achieve vertical motion, which is uniform over its surface. A flexural mode of the cylinder is used for dislodging targets which have become stuck. In their natural state, the targets become charged triboelectrically and by the beta emission from the tritium decay. The adhesion of these charged targets is eliminated by creating a low power plasma in the bouncing region. Real time monitoring and control of coating thickness are achieved by use of a laser reflectometer. Coatings are examined with electron microscopy and x-ray radiography.
Carbonaceous overlayers on Ru(001)
Authors: Hrbek Jan
Published: July 2002

Binding energies of carbonaceous overlayers on ruthenium were measured using angle-resolved XPS data and curve fitting procedures. A carbonaceous overlayer prepared by dehydrogenation of adsorbed ethylene at 750 K was disordered and had a binding energy of 285.0 eV. After annealing to 1300 K islands of azimuthally ordered graphite were formed with binding energy shifted to 285.6 eV.
The β-SiC(100) surface studied by low energy electron diffraction, Auger electron spectroscopy, and electron energy loss spectra
Authors: Dayan Moshe
Published: July 2002

The β-SiC(100) surface has been studied by low energy electron diffraction (LEED), Auger electron spectroscopy (AES), high resolution electron energy loss spectra (HREELS), and core level excitation EELS. Two new Si-terminated phases have been discovered, one with (3×2) symmetry, and the other with (2×1) symmetry. Models are presented to describe these phases. New results, for the C-rich surface, are presented and discussed. In addition, core level excitation EELS results are given and compared with theory.
Pulsed laser-induced desorption studies of the kinetics of ethylene dehydrogenation on Ni(100)
Authors: Hall R. B. , Bares S. J. , DeSantolo A. M. , Zaera F.
Published: July 2002

Pulsed laser-induced desorption is used to study the initial C–H bond cleavage of ethylene on Ni(100) in real time. The dependence of the rate of bond breaking on surface coverage, surface temperature, and isotopic substitution is measured. For coverages below 0.4 monolayer, dehydrogenation of C2H4 is unimolecular with kinetic parameters: log ν=9.8±0.5 s−1 and Ea=8.4±0.4 kcal mol−1. At higher coverages the reaction rate is slower. There is a pronounced kinetic isotope effect (KIE). The rate of C2H4 dehydrogenation is roughly 60 times the rate of C2D4 dehydrogenation at 170 K. A secondary KIE is also observed for 1,1- and 1,2-C2D2H2. Although the bond broken in both cases is a C–H bond, the rate for C2D2H2 is 1/3 that for C2H4. The magnitudes of the KIE’s indicate that a C–H stretching vibration is probably the dominant mode involved in the bond breaking but that other modes contribute significantly.