bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of molecular-beam epitaxially grown CdTe surfaces by high-energy electron diffraction and synchrotron radiation photoemission spectroscopy
Authors: Hernández-Calderón Isaac , Niles David W. , Höchst Hartmut
Published: July 2002

The homoepitaxial growth of CdTe films on CdTe(110) substrates was studied by reflection high-energy electron diffraction (RHEED) and synchrotron radiation photoemission spectroscopy. Deposition of 50 to 100 monolayer thick CdTe films at room temperature and subsequent annealing to 350 °C produced high structural quality surfaces. The RHEED pattern was well defined with sharp streaks and distinctly visible Kikuchi lines. The valence-band photoemission spectra developed sharp features characteristic for direct transitions from a highly ordered surface. We obtained similar high structural quality for the homoepitaxial growth of CdTe on a substrate held at 250 °C. The evolution of the RHEED pattern, the Cd 4d core level emission, and the Fermi level pinning position for growth temperatures ranging from 25 to 350 °C provide detailed information about homoepitaxial growth characteristics. We discuss the appearance of these spectral features in terms of the structural properties of the CdTe(110) surface.
Structure of Si/SiO2 thin multilayers sputtered in argon–hydrogen mixtures
Authors: Yachi T.
Published: July 2002

A technique is described for preparing Si/SiO2 thin multilayers by performing sputtering from two independent sources in argon–hydrogen mixtures. Structural studies carried out by x-ray diffraction and Auger electron spectroscopy indicate a well-defined multilayer structure. The x-ray reflection peaks of the Si/SiO2 multilayer structure are found to intensify as a result of (i) inclusion of hydrogen in the sputtering gas and (ii) lowering of the sputtering pressure. Studies of the infrared spectra reveal that samples produced by sputtering in argon–hydrogen mixtures have absorption bands at ∼880 and 630 cm−1.
Plasma-enhanced photoemission in argon discharges: Signal characterization and silicon doping effects
Authors: Selwyn Gary S. , Singh J.
Published: July 2002

The recently reported technique of plasma-enhanced photoemission (PEP) provides capability for in situ, noncontact and rapid monitoring of the surface of a wafer during plasma processing. In this work the technique is characterized as a function of laser power, rf power, laser synchronization with the rf cycle, and wafer doping. At higher laser power the signal is observed to be space-charge limited. Synchronization of the laser pulse with the 13.6-MHz rf plasma shows a strong dependence on the rf phase. The PEP signal is seen to be influenced by the type and density of the wafer dopant. Results are compared for low and high laser powers. These trends are interpreted in terms of the photoemissive properties of the semiconductor surface.
Optical emission characterization of a divergent magnetic field electron cyclotron resonance source
Authors: McKillop John S. , Forster John C. , Holber William M.
Published: July 2002

High-resolution optical emission experiments have been performed to investigate the application of this technique to the characterization of electron cyclotron resonance (ECR) sources. Preliminary experiments have used Ar and O2 discharges operating between 0.5 and 1.5 mTorr, with 700–2300 W of microwave power, and two distinct magnetic field configurations. Results of these measurements indicate that ECR discharges are optically thick for transitions which terminate on long-lived (metastable) energy levels, producing significant self-absorption. Measurements of emission intensity for Ar and Ar+ lines which are not self-absorbed show that selected transitions can be used to reliably monitor the relative concentrations of these species.
High-efficiency solar cells fabricated from direct-current magnetron sputtered n-indium tin oxide onto p-InP grown by atmospheric pressure metalorganic vapor phase epitaxy
Authors: Li X. , Wanlass M. W. , Gessert T. A. , Emery K. A. , Coutts T. J.
Published: July 2002

Solar cells based on dc magnetron sputtered indium tin oxide onto epitaxially grown films of p-InP have been fabricated and analyzed. The best cells had a global efficiency of 18.4% and an air mass zero (AMO) efficiency of 16.0%. The principal fabrication variable considered was the constituency of the sputtering gas and both argon/hydrogen and argon/oxygen mixtures have been used. The former cells have the higher efficiencies, are apparently stable, and exhibit almost ideal junction characteristics. The latter cells are relatively unstable and exhibit much higher ideality factors and reverse saturation current densities. The temperature dependence of the reverse saturation current indicates totally different charge transfer mechanisms in the two cases.
Schottky barrier formation by silicon deposition on unreactive and reactive metal substrates
Authors: Chang Y. , Hanson J. , Hwu Y. , Zanini F. , Margaritondo G.
Published: July 2002

We compare the interface Fermi-level positions in the Si gap, obtained from photoemission studies of Si overlayers on Al(110) and Cu(111), and of Al overlayers on Si(111). These positions are similar to each other, and consistent with the predictions of a corrected midgap-energy approach.
Light-induced defects in hydrogenated amorphous carbon films
Authors: Reyes-Mena A. , González-Hernández J. , Asomoza R. , Contreras G.
Published: July 2002

In this work, we have studied the effects of intense illumination on the photoluminescence (PL) spectrum of hydrogenated amorphous carbon films prepared by glow discharge decomposition of CH4 at a rf power density of  0.8  W/cm2. The changes in the PL spectra of the as-prepared samples were measured as a function of both the sample temperature in the range 13–300 K and the illumination time. Similar to hydrogenated amorphous silicon, light soaking of carbon samples reduces their integrated PL intensity and changes the PL band shape; both of these effects depend on the energy of the excitation as well as on the sample temperature. The degraded a-C:H films can be restored to their original nondegraded state by annealing, but in contrast to amorphous silicon, the annealing temperature that recovers the original state in a-C:H films is below room temperature. Previous studies in similar samples suggest that the PL fatigue may occur as a result of an increase in the nonradiative recombination centers associated with dangling bonds which are created by illumination.
Determination of the adsorption site of C, N, and O on Ni(100) and Cu(100) using photoelectron diffraction
Authors: Kilcoyne A. L. D. , Woodruff D. P. , Lindner Th. , Somers J. , Bradshaw A. M.
Published: July 2002

Scanned energy mode photoelectron diffraction spectra, collected at normal emission over an energy range typically in excess of 300 eV, are presented for 1s photoemission from O on Cu(100) and from O, N, and C in ordered structures on Ni(100). Double-scattering curved wave cluster calculations are used to analyze these data. In all cases adsorption in a hollow site is favored, but the only simple case of chemisorption appears to be Ni(100)c(2×2)O. All the other structures appear to involve adsorbate-induced substrate reconstruction, in which important ingredients appear to be expansion of the top metal layer, and lateral movements within this layer.
Adsorption of NO and H,O/NO coadsorption at Ni(110) surfaces
Authors: Schenk A. , Hock M. , Küppers J.
Published: July 2002

Adsorption of NO and H,O/NO coadsorption at Ni(110) surfaces has been studied using thermal desorption spectroscopy, low-energy electron diffraction, Auger electron spectroscopy, and high-resolution electron energy-loss spectroscopy. At 110 K up to Θ=0.2 NO adsorbs dissociatively. Further uptake occurs at top (1875 cm−1 at Θ=0.5) and bridge (1675 cm−1 at Θ=0.5) sites, initially predominantly at bridge sites. No vibration due to inclined NO is observed, nor a Ni–N vibration loss. At saturation coverage, Θ=0.5, the ratio of the site population is top/bridge=1.7 as deduced from the HREELS intensities. Decomposition of bridge bonded NO starts around 190 K. Simultaneously, bridge bonded NO is shifted to top sites due to a blocking effect of the decomposition product oxygen. Above 340 K the top site NO starts to decompose (predominantly) and desorb, leaving a N and O covered surface. Activation energies for desorption and decomposition are ∼20 kcal/mol. Of the decomposition products oxygen diffuses into the bulk, T>550 K, and nitrogen desorbs recombinatively around 850 K. After preadsorption of hydrogen at the Ni(110) surface NO top site adsorption decreases and is suppressed after 0.5-L H2 exposure. Bridge bonded NO with coadsorbed H present exhibits an enhanced stability with respect to dissociation and starts to decompose only after hydrogen is desorbed. Conversely, hydrogen bonding to the Ni surface is destabilized and the H induced surface reconstruction suppressed. After preadsorption of oxygen NO can be postadsorbed even if the substrate is oxidized, however, in slightly reduced quantity only. Coadsorbed oxygen favors NO adsorption at top sites; at oxygen saturation postadsorbed NO only occupies top sites.
Periodic forcing of the oscillatory CO oxidation on Pt single-crystal surfaces
Authors: Eiswirth M. , Möller P. , Ertl G.
Published: July 2002

The kinetic oscillations occurring in the oxidation of carbon monoxide on Pt(110) and Pt(100) single-crystal surfaces at low pressure under isothermal conditions exhibit, despite a similar underlying mechanism, some pronounced differences in phenomenology between the two surfaces, which become most clearly evident in studies of the system response to external periodic perturbations. These differences can be rationalized in terms of different types of spatial self-organization on the two surfaces in question, namely, reaction–diffusion coupling on Pt(100) and feedback through the gas phase for Pt(110).
Oxygen induced reconstruction on Cu(100)
Authors: Wuttig M. , Franchy R. , Ibach H.
Published: July 2002

The adsorption of oxygen on Cu(100) has been studied by low-energy electron diffraction, Auger spectroscopy, and electron energy-loss spectroscopy (EELS). Using an electron spectrometer for an intensity analysis of the diffracted beams we show that with increasing coverage a first-order phase transition from a disordered (1×1) phase into a long-range ordered ((2)1/2×2(2)1/2)R45 structure takes place. Contrary to most previous studies no evidence is found for a c(2×2) structure. High-resolution EELS spectra (ΔE=16–20 cm−1) change significantly upon the transition, establishing that the ((2)1/2×2(2)1/2)R45 structure involves a reconstruction of the substrate. Both the perpendicular in-phase and out-of-phase vibration of the oxygen atoms are detected. Their observation is consistent with a reconstruction model where second nearest-neighbor rows in the [100] direction show a row pairing. We interpret this reconstruction mechanism as a cooperative Jahn–Teller effect.
Photoemission study of uranium compounds with MgAgAs structure
Authors: Höchst H. , Tan K. , Buschow K. H. J.
Published: July 2002

Synchrotron radiation photoemission spectroscopy has been used to investigate the electronic structure of the intermetallic compounds UNiSn, URhSb, and UPtSn. All compounds show the same typical valence-band structure. Transition-metal d-like density of states (DOS) is removed from the Fermi-level region deeper into the valence band with maxima at ∼2 eV for UNiSn and at ∼2.8 and ∼4.6 eV for URhSb and UPtSn. Resonant photoemission at the U 5d threshold energy around hν≂98 eV has been used to project the U 5 f valence-band DOS. In all compounds the 5 f states are close to the Fermi energy with a full width at half-maximum ranging from 1.1 eV for UNiSn to 1.6 eV for UPtSn. Our results for UNiSn are in good agreement with recent partial valence-band DOS calculations.
Determination of overlayer growth by angle-resolved Auger electron spectroscopy
Authors: Idzerda Y. U. , Lind D. M. , Prinz G. A.
Published: July 2002

Single-scattering cluster theory, augmented by the inclusion of spherical wave effects, is used to model the substrate and overlayer angle-resolved electron emission intensity to determine the mode of growth of the overlayer. For large inelastic mean-free-path (IMFP) electrons, a new method for identifying first- and second-layer completion is described which will have wide application to intermediate and high-energy electron emission. Calculations for azimuthally integrated data (cylindrical mirror analyzer based measurements) finds that the standard determination of the IMFP is too large by ∼20%.
Effects of the film thickness on the interfacial reaction of Pt/(111)Si
Authors: Chen Jiann-Ruey , Chang Li-Di , Yeh Fon-Shan
Published: July 2002

Pt thin films 50–300 Å thick were deposited onto the p-type, (111)-oriented Si substrate with the substrate kept at 450 °C during film deposition, while silicide formations and their microstructures were investigated by transmission electron diffraction and x-ray diffraction analysis. It was found that for different thicknesses of the deposited Pt films, the silicides were formed in different phases and different microstructures in the as-deposited sample. β-Pt2Si was observed in the samples of 50- and 200-Å-thick deposited Pt films, but with different orientations. And if the thickness of the Pt deposited layer was increased to 300 Å, the as-deposited sample will present the formation of the PtSi epitaxial layer, Pt polycrystalline, and the texture polycrystalline of α-Pt2Si. This film thickness effect is believed to be due to the grain growth and/or grain transformation of various grain orientations at different film thickness depositions.
Electron energy-loss spectroscopy analysis of low-temperature plasma-enhanced chemically vapor deposited a-C:H films
Authors: Nelson A. J. , Benson D. K. , Tracy C. E. , Kazmerski L. L. , Wager J. F.
Published: July 2002

Electron energy-loss spectroscopy (EELS) has been applied to the analysis of a-C:H films grown on various substrates by a unique low-temperature (<100 °C) plasma-enhanced chemical vapor deposition (PECVD) process using ethylene and hydrogen gases. EELS data are used to characterize the relative amounts of fourfold coordinated sp3 carbon bonding to threefold coordinated sp2 carbon bonding as well as the relative order/disorder due to substrate effects. Ellipsometric and transmission measurements provide optical constants for the PECVD a-C:H films.
Composition distribution and magnetic characteristics of sputtered Permalloy films with substrate angle
Authors: Nakagawa Y. , Ohshita Y. , Narishige S. , Setoyama E.
Published: July 2002

Permalloy sputtered films for a thin magnetic head are deposited under precisely controlled conditions. The head pattern on a substrate shows not only a flat portion but also an inclined portion. The film characteristics on the inclined portions are important for a good thin-film head. Using a rf magnetron sputtering device with an 8-in. target, the angular distributions of sputtered Permalloy atoms (Ni and Fe), composition profile, and the magnetic characteristics were investigated. The results showed that the angular distributions of the Ni–Fe atoms depended on the rf power and were different from those of the cosine rule. A comparison of the film characteristics between the flat and inclined portions was carried out using a special substrate holder, in which nine glass substrates were fixed. The film thickness of the inclined portion differed, depending on the positions where the substrates were fixed. The coercive forces decreased with decreasing sputtering gas pressures, and those of thin films deposited on the inclined substrates were 20–50 A/m.
An accurate and simple method of measuring relative mass spectrometric sensitivities
Authors: Sun Y.-K. , Weinberg W. H.
Published: July 2002

We describe an accurate and convenient method of determining the relative mass spectrometric sensitivities of various species by using surface decomposition reactions to generate these species in known stoichiometric ratios in situ in vacuum systems. In particular, we have used the decomposition reactions of formaldehyde and formic acid on Ru(001) to determine the relative mass spectrometric sensitivities of H2, HD, D2, and CO.
A compact scanning tunneling microscopy control and data acquisition system based on a Macintosh II workstation
Authors: Grafström S. , Kowalski J. , Neumann R. , Probst O. , Wörtge M.
Published: July 2002

A compact system based on a Macintosh II workstation for scanning tunneling microscopy (STM) control, data acquisition, and image display and processing is presented. To access the versatile analog electronics and the piezo scanner of our STM, a multifunction board (MacAdios II) is employed as an interface. The on-board timer/counter permits well defined time intervals between each tip movement and subsequent data acquisition. For on-line control and image display of scanning processes an efficient code was written in Pascal and C. To achieve simple and user-friendly operation, the program takes advantage of so-called mouse–window–desktop techniques supported by the Macintosh operating system. The entire code has a modular structure and therefore facilitates easy replacement of existing modules or implementation of additional ones.
Application of infrared spectroscopy in vacuum
Authors: Yi-Peng Yuan
Published: July 2002

This paper describes the application of infrared spectroscopy in precise measurements of residual substances and oil contamination in a vacuum system, such as the measurement of ultralow backstreaming rate of diffusion pump and the measurement of ultramicro quantities of oil contamination in vacuum systems and equipment. We will also discuss the possibility of other applications of infrared spectroscopy in a vacuum system.
Properties of insulator interfaces with p-HgCdTe
Authors: Schacham S. E. , Finkman E.
Published: July 2002

Heat treatment at 70 °C of low carrier concentration p-type HgCdTe samples (p0=8×1014 cm−3) generates an inverted surface layer. A two day anneal process below 95 °C did not affect the Hall coefficient, whereas an almost complete recovery was obtained by annealing at 120 °C. While bulk electron mobility, obtained from PEM data, remained high (about 9×104 cm2/V s at 77 K), surface mobility is lower by more than an order of magnitude. Surface recombination velocity indicates a continuous improvement with increased temperature, and the activation energy remains equal to the vacancies energy level. The proposed mechanism is that of positive charges in the sulfide migrating towards the interface and generating an image inversion layer.
Ion current density and its uniformity at the electron cyclotron resonance position in electron cyclotron resonance plasma
Authors: Samukawa Seiji , Mori Sumio , Sasaki Masami
Published: July 2002

Extremely high and uniform ion current density is achieved at the electron cyclotron resonance (ECR) position in a microwave cavity resonator with a 260 mm diam. Microwave power is most efficiently absorbed at the ECR position in the ECR plasma. The uniformity of the ion current density at the ECR position is 15±0.75 mA/cm2 in a 200 mm diam area. This high and uniform ion current density is accomplished with a large quartz window size with a 170 mm diam for microwave introduction and a flat profile of the 875 G equimagnetic field position. The ECR plasma etching system equipped with this microwave cavity resonator that is 260 mm in diameter has a high potential for uniform and high rate pattern fabrication in a ULSI circuit on a more than 6 in. diam substrate.
On the transport and heating of particulate contamination entrapped in an intense cylindrical ion beam
Authors: Brown D. A. , Sferlazzo P. , O’Hanlon J. F.
Published: July 2002

Utilizing a previously developed entrapment model, the equations of motion for a particle confined within an intense cylindrical ion beam are derived. Energy transfer from the beam to the particle is then calculated and an expression for the time rate of change of the particle’s temperature determined. From the resulting model, trajectories and temperatures are calculated for micron and submicron-sized aluminum and tungsten particles placed in a 100 keV, 10 mA, 3-cm-diam BF2 ion beam. It is predicted that the Al particles undergo a phase transition in a time ∼1 ms, during which they acquire a center-of-mass velocity ∼1 m/s, and traverse an axial distance ∼1 mm, ultimately reaching the vaporization temperature. In contrast, during a 50 ms flight, the denser W particles are expected to follow precessing orbits, travel axial distances ∼0.1–1 m, and possess final axial velocities ∼10–100 m/s, never attaining their vaporization temperature. Along trajectories crossing a beam of radially varying ion density (a Gaussian profile is assumed), heat transfer to the particle varies as a function of radial position. Thus, as the particle’s radial position fluctuates, particle temperatures are predicted to oscillate about an equilibrium value that is independent of particle properties, varying solely with beam parameters.
Thermomechanically induced voiding of Al–Cu thin films
Authors: Whitman Charles S. , Chung Yip-Wah
Published: July 2002

It is now recognized that voiding failures in Al–Cu interconnects in integrated circuits are due to the high residual stresses developed as a result of thermal expansion mismatch between Al and Si or SiO2. In this paper, we review some of the current theoretical developments in calculating times to failure for these interconnects. Thermal cycling experiments were performed to determine times to failure under different testing conditions. These results were then compared with the recent theory developed here at Northwestern. It is based on consideration of grain-boundary and surface diffusion and fracture mechanics. The theory appears to give predictions that agree very well with experiments.
Chemical effects of annealing ZnS capped anodic fluoride films on Hg1−xCdxTe (x∼0.2)
Authors: Weiss Eliezer , Helms C. R.
Published: July 2002

The chemical effects of annealing a three-phase structure: ZnS–anodic fluoride–Hg1−xCdxTe used in infrared detector devices were studied using Auger electron spectroscopy (AES). The ZnS cap prevents the oxidation of the anodic fluoride upon annealing. The anodic fluoride is unstable in contact with the ZnS and a reaction takes place at their interface forming the stable ZnF2 compound and Te or HgTe. Nevertheless, the annealing does not affect the film–substrate interface as long as the fluoride has not reacted completely. This explains the relative thermal stability of electrical devices fabricated using this passivation scheme.
Optical emission spectroscopy for plasma-assisted epitaxial growth of (In, Ga) (As, Sb)
Authors: Fang S. F. , Hariu T. , Ono S.
Published: July 2002

Optical emission spectroscopy (OES) has been applied to detect the excited species in plasma-assisted epitaxial growth of (In, Ga) (As, Sb) compound semiconductors. The plasma cracking of evaporated group V molecules into atoms, which is an important advantage in plasma-assisted epitaxy (PAE), and the excitation of all the source elements were confirmed both in hydrogen plasma and argon plasma. The effect of V/III supply ratio on the growth behaviors observed in PAE can be well explained by the change of group V atomic densities caused by this plasma cracking. OES is also useful for detecting and monitoring residual impurities such as moisture in the growth atmosphere.
Infrared absorption and x-ray photoelectron spectroscopy studies of the anodic oxidation of plasma silicon nitride
Authors: Montero I. , Galán L. , Pivin J. C. , Sánchez O. , Albella J. M.
Published: July 2002

Silicon oxide films have been grown by anodic oxidation of plasma enhanced chemically vapor deposited silicon nitride films onto silicon substrates. Infrared absorption and nuclear reaction analysis (NRA) of the films reveals that during the anodic oxidation the nitrogen of the silicon nitride films is lost to electrolyte/oxide interface. These analyses combined with x-ray photoelectron spectroscopy analysis show that the final oxide structure is formed by an outer silicon dioxide layer followed by the inner layer of the previously deposited silicon nitride. In the case of thicker oxides the silicon dioxide layer is followed by a region made of a mixture of SiO2 and SiNx molecules. The elementary reactions as well as the ionic transport through the interface is discussed.
Photoemission study of the SiO2/Si interface structure of thin oxide films on Si(100), (111), and (110) surfaces
Authors: Niwano Michio , Katakura Hitoshi , Takeda Yuki , Takakuwa Yuji , Miyamoto Nobuo , Hiraiwa Atsushi , Yagi Kunihiro
Published: July 2002

The SiO2/Si interface structure of thin oxide films thermally grown on Si(100), (111), and (110) surfaces under device processing conditions has been investigated using high-resolution photoemission spectroscopy with synchrotron radiation. The intensity distribution of the so-called suboxides, Si1+, Si2+, Si3+, displays a strong dependence on the crystallographic orientation of the substrate over the oxidation temperature range from 600 to 900 °C; Si1+ is enhanced in intensity on Si(111) and (110), while the Si2+ intensity is larger than the Si1+ one on Si(100). This orientation dependence is explained in terms of the bond topology of the substrate surface. A Si(110) surface exhibits a rather large Si3+ intensity as compared to Si(100), (111) surfaces, suggesting that Si–Si bonds on the outermost layer of a Si(110) surface are easily broken by oxygen atoms to generate the bridge bond Si–O–Si. The presence of an interfacial Si atom to which hydrogen is bonded is clearly observed. The total suboxide intensity, i.e., the sum of the suboxide intensities depends on both oxidation temperature and substrate orientation, which is interpreted by means of the interfacial roughness and the surface Si atom density of the substrate. It is shown that an ordered crystalline phase of SiO2 is present at the interfacial region. The generation of this phase has a Si(111)-preferred orientation.
Interfaces in composites: Relations between structure and properties
Authors: Mayer J. , Rühle M.
Published: July 2002

The toughness of ceramic composites is mainly governed by the mechanical behavior of the interfaces between the ceramic matrix and the ductile particle or the strong fiber/whisker reinforcements. The toughening can be described by a bridging zone mechanism. In the crack bridging models, debonding of the reinforcement at the interface plays an important role. The status of present understanding is reviewed. Transmission electron microscopy has been used to study the interfacial structure and behavior of ductile particles and fiber/whisker reinforced composites. Furthermore, model systems of ceramic/ceramic and metal/ceramic interfaces have been investigated. The atomic structure of such interfaces can be determined by a quantitative analysis of high resolution micrographs. Chemical reaction products and structural defects at the interface can be identified by analytical electron microscopy. The results of such studies will help to tailor the interfaces in composites.
Large, all-metal-sealed, vacuum gate valve for fusion application
Authors: Batzer Thomas H. , Lang Dwight D. , Moir Ralph W.
Published: July 2002

Two large (30 cm and 1 m in diameter), innovative, fusion-reactor-compatible, vacuum gate valves have been developed which should contribute significantly to the vacuum hardware needs of the next-generation, tritium-burning fusion devices. Because no organic materials are used, the valves are tritium-compatible and radiation-hardened as well as compatible with toxic gases. These valves should also find applications in semiconductor manufacturing and in similar industries that have requirements for large, all-metal vacuum valves. We have designed, built, and successfully tested a 30-cm-diam valve, and we have designed and are fabricating a 1-m-diam valve that we plan to assemble and test in 1992. This work makes use of the all-metal-sealed, radially directed, fluid-pressure-loaded seal design that was developed under a Department of Energy contract at the Lawrence Livermore National Laboratory. This seal, due to its radially directed loading, is easily scaled to larger diameters, and scales with the atmospheric loading of the gates, rather than with the seal loading. The valves are designed for high reliability: the 30-cm-diam valve utilizes double gates to provide two seals, and differential pumping; the 1-m-diam valve has a single gate with a double metal seal, and differential pumping. These valves are relatively light weight due to the unique radial seal. Typically, leak-tight closures are obtained on every operation without differential pumping at pressures of 500–1000 psi applied to the radially sealing diaphragm. The seal components are fabricated from 304 stainless steel, but can also be made from aluminum.
Photoemission of adsorbed xenon study of surface defects generated by ion bombardment of Ni(111)
Authors: Malafsky Geoffrey P. , Fu Sabrina S. , Hsu David S. Y.
Published: July 2002

The surface defect density generated by 1.0 keV Ar+ ion bombardment of a Ni(111) crystal at 88 K is studied with photoemission of adsorbed xenon (PAX). The defect sites are distinguished by the position of the Xe 3d5/2 peak. The peak position reflects the local electrostatic potential at the Xe adsorption site that is modified at a defect site from the terrace sites by the electron-density smoothing process. The PAX spectra of the ion bombarded surfaces have peaks at 669.3 eV from Xe adsorbed at terrace sites, 670.0 eV from Xe at step sites, and 671.0 eV. We ascribe the latter peak to Xe adsorbed at small vacancy islands or kink sites where the Xe atom can experience a larger electrostatic potential perturbation compared to Xe adsorbed at a step site producing the additional 1 eV shift to higher binding energy. The PAX spectra are acquired with two ambient Xe pressures, 7×10−10 and 5×10−6 Torr. At low Xe pressure, the total Xe coverage and step peak intensity rapidly increase with low ion fluence with initial rates of 3 Xe atoms/ion for the total Xe coverage and 1.5 Xe atoms/ion for the step sites in the first 2.9×1013 ions/cm2 fluence. In contrast, at high Xe pressure, the total Xe coverage, and the terrace peak intensity decrease rapidly in the same region of ion fluence with initial rates of −3 Xe atoms/ion for the total Xe coverage and −5 Xe atoms/ion for the terrace peak. The rate of decrease of the terrace peak intensity corresponds to 15 Ni terrace atoms uncovered per incident ion since the large Xe atom covers three terrace atoms. The loss of Xe coverage on terrace sites likely results from the destruction of the long-range order in the Xe two-dimensional solid on the ion bombardment roughened surface.
Structural properties of Y2O3 stabilized ZrO2 films deposited by reactive thermal coevaporation
Authors: Chéron J. P. , Tcheliebou F. , Boyer A.
Published: July 2002

Films of Y2O3 stabilized ZrO2 were obtained by reactive thermal coevaporation using an electron gun. These films were deposited on nickel substrates at substrate temperature to 500 °C, while the oxygen pressure was held to 4×10−5 Torr. The film structure was characterized by x-ray diffraction, the film composition has been determined by electron probe microanalysis. Postdeposition x-ray analysis showed the cubic phase of ZrO2. The cubic phase’s lattice parameter presented a monotonic increase with increased Y2O3; the mole fraction of Y2O3 was varied from 0.6% to 18.5%.
Thin films from energetic cluster impact: A feasibility study
Authors: Haberland Hellmut , Karrais Martin , Mall Martin , Thurner Yonca
Published: July 2002

An intense, continuous beam of metal clusters and cluster ions is produced by combining a magnetron sputter discharge with a gas aggregation source. The average cluster size can be varied between 50 and more than 106 atoms per cluster. The sputter discharge is also used to ionize the clusters; between 30% and 80% of them carry a charge without further electron-impact ionization. Mon− clusters with n≊1200 were separated from the neutral clusters, accelerated, and deposited on a polished Cu substrate. Above a kinetic energy of 6 keV, highly reflecting, strongly adhering thin films are formed on room-temperature substrates. The films can be mechanically polished, which increases the reflectivity from 95% to 97% at 10.6 μm. Rutherford backscattering spectroscopy data reveal that less than 0.5% argon is incorporated into the films. The standard structure zone model of Movchan, Demchishin, and Thornton [in B. Chapman, Glow Discharge Processes (Wiley, New York, 1982)] is not applicable. The impact of an energetic cluster leads locally to a sudden increase of pressure and temperature. A tiny, high-temperature spot is formed at each impact of an energetic cluster. The high local temperature present for several picoseconds leads to the observed film properties. The main advantage of the method seems to be that excellent thin films can be produced on room-temperature substrates. The name ‘‘energetic cluster impact’’ is proposed for this new deposition method.
Study on direct current reactive sputtering deposition of aluminum nitride thin films
Authors: Stedile F. C. , Baumvol I. J. R. , Schreiner W. H. , Freire F. L.
Published: July 2002

Aluminum nitride thin films were deposited by dc magnetron reactive sputtering. The deposition parameters (cathode voltage, incident power, total pressure, and N2 partial pressure) were correlated and their influences on the compositional properties of the films were determined. The analytical tools used to characterize the aluminum nitride thin films were Rutherford backscattering spectrometry and the (d,p) and (p,γ) nuclear reactions. From these techniques the thickness and stoichiometric ratio N/Al of the films, the N and Al depth profiles, and the contamination levels of O and C were obtained.
Microwave plasma enhanced chemical vapor deposition in magnetic fields below electron cyclotron resonance
Authors: Popov Oleg A. , Shapoval Sergej Y. , Yoder Merle D.
Published: July 2002

Microwave plasmas ( f=2.45 GHz, 200–1000 W) at magnetic fields below electron cyclotron resonance (ECR), Bce = 875 G, were used for room temperature chemical vapor deposition of silicon nitride films. Plasmas were maintained in a nonresonant (with respect to any microwave mode) cavity at magnetic fields of 200–600 G, and were ‘‘extracted’’ with the divergent magnetic field into the process chamber. Silicon wafers of 10–20 cm diameters were positioned at 25 cm downstream in the process chamber. The total gas pressure was 0.7–2 mTorr and silane/nitrogen partial pressure ratio varied from 0.1 to 0.8. The film growth rate was 100–200 Å/min at a microwave power of 100–300 W and was found to be 15%–25% lower than in electron-cyclotron-resonance plasma streams. The index of refraction grew with silane partial pressure and was essentially the same as in ECR plasma films.
Study of W/Ti triode plasma etching
Authors: Coulon J. F. , Turban G. , Rabinzohn P. , Jeannerot L.
Published: July 2002

Real microelectronic structures made of W/Ti layers and patterned with a photoresist mask have been etched successively in SF6/N2 and SiCl4/Cl2 plasmas with a triode etching system. The etched samples have been analyzed after different steps of the process with scanning electron microscopy and x-ray photoelectron spectroscopy (XPS). Angular XPS carried out on such structures supplies spatially resolved analysis by the geometrical shadowing effect of specific photoelectrons. The tungsten etching process has been optimized after study of the analysis results with a statistical experimental design. The photoresist fluorination has been spatially characterized by XPS and discussed. At the end of the tungsten etching, TiFx films are observed as trench sidewalls and cannot be removed during titanium etching. By characterization of these films and then by detection of their presence, angular XPS has been successful in developing a new etching process.
High temperature air-annealing behavior of sputter deposited amorphous yttria films on fused silica
Authors: Mukherjee S. N. , Aita C. R.
Published: July 2002

This article addresses the response of amorphous yttria films grown on fused silica substrates to high temperature (900 °C) cyclic annealing in air for up to 145.5 h. Surface science and bulk analytical techniques were applied to determine and correlate changes in microstructure, crystallization, optical behavior, and chemistry (atomic concentration and bonding) concurrent with annealing. Limited crystallization occurred after short-term annealing, resulting in regions of nanocrystallinity in an amorphous matrix. X-ray photoelectron spectroscopy data showed an accompanying loss of resolution of Y 3d5/2 − 3d3/2 spin states, but no change in the fundamental optical absorption edge was observed. Long-term annealing resulted in granularization of the matrix itself, with a large increase in optical absorption in the 3–5 eV range. X-ray photoelectron spectroscopy data showed a broadening of the O 1s peak. No evidence of Si diffusion from the interfacial region into the yttria film was seen, even after long-term annealing, demonstrating amorphous yttria’s potential use as a high temperature diffusion barrier for metal-on-Si-based ceramic applications.
Surface analysis of an alumina based supported catalyst by means of dynamic secondary ion mass spectrometry
Authors: Nagase S. , Martin J. R.
Published: July 2002

The process of dynamic secondary ion mass spectrometry has been used to examine the disposition of Cs in the surface region of a set of samples of an Al based Ag supported catalyst both before and after a heat treatment process which serves to change the effects of the additive and to improve the catalyst stability. Depth profiles of the bulk pellet material of these catalytic samples demonstrate that there is no significant migration of Cs away from the surface region and into the bulk of the material due to the high temperature treatment. Comparison with untreated samples of this nature and with the results of other analysis methods such as x-ray photoelectron spectroscopy also support this conclusion. A surface model for depth profiling of these materials is discussed in order to account for topographical effects due to their granular nature.
Electron emission holography of small clusters and surfaces
Authors: Thevuthasan S. , Herman G. S. , Kaduwela A. P. , Tran T. T. , Kim Y. J. , Saiki R. S. , Fadley C. S. , Van Hove M. A.
Published: July 2002

We consider the three-dimensional imaging of near-surface structures by holographic transformations of large-solid-angle electron emission data sets. Results are presented for both single and multiple scattering theoretical simulations and experimental data which have been obtained for both the c(2×2) structure of S on Ni(001) and clean Si(111). Although features associated with near-neighbor atoms are seen in Fourier-transform images for all of the cases studied, these peaks show shifts of 0.30–1.5 Å, as well as broadening and artifacts, that are primarily due to strong forward peaking and phase shifts in the electron-atom scattering. We further discuss correcting these image aberrations by several methods such as eliminating the forward peaking by a reduction of the data set or multiplication by a suitable Gaussian function, using the scattered-wave-included Fourier transform method, and taking a phased summation of several transforms at different energies. All of these correction methods are found to improve image quality in one or more aspects, and thus to show promise for future studies.
Historical perspective of vacuum system application at the Nevada Test Site
Authors: Wilson Norman G. , Still Gary J. , Ward Charles O.
Published: July 2002

From the beginning of nuclear-device testing at the Nevada Test Site (NTS) in 1951 to the present, the U. S. Nuclear weapons laboratories have used high-vacuum environment in a wide range of applications. Nuclear measurement and diagnostic devices used in the test procedures require vacuum levels from 10−1 to less than 10−7 Torr. Researchers also need these vacuum levels to control the experimental environment when they study the effects of nuclear weapons on materials, devices, structures, or weapon system components. To produce the required vacuum environments in volumes up to 107 ℓ, researchers have used the following pumping systems: simple pumping apparatus, such as oil-sealed, rotary-vane mechanical pumps (pumping speeds as low as 2 ℓ/s); conventional, multistage, cascade pumping arrangements of oil diffusion, Roots blowers, and high-speed mechanical pumps (pumping speeds greater than 100 000 ℓ/s); and state-of-the-art, high-speed cryogenic, sputter-ion, turbomolecular, and evaporable or nonevaporable getter pumps (pumping speeds from 10 to more than 30 000 ℓ/s). More often, these pumping systems are remote from their operational control points. This paper describes these high-reliability vacuum systems and their engineering, design, and fabrication.
Decomposition pathway for model fluorinated ethers on the clean iron surface
Authors: Napier Mary E. , Stair Peter C.
Published: July 2002

Polymeric perfluoroalkylethers (PFAE) are being considered for use as lubricants in high temperature applications, but in the presence of certain metals these molecules show enhanced decomposition. X-ray photoelectron spectroscopy (XPS) was used to explore the pathways for decomposition of three model fluorinated ethers on clean iron surfaces. The decomposition reaction, in vacuum, was observed to proceed at remarkably low temperatures, 155 K and below, via defluorination of the carbon–oxygen backbone, with formation of iron fluoride. The reactivity of iron toward perfluoroalkylether decomposition, when compared to other metals, is due to the strength of the iron fluoride bond. The remarkably low temperature threshold for the decomposition reflects a low activation barrier for C–F scission due to the strong electron donating ability of metallic iron.
Dispersionless vibrational mode of a chemisorbed adsorbate observed with inelastic helium scattering: Hg on Cu(001)
Authors: Moses C. , Zeng Hong , Lin J. S. , Li Wei , Karimi M. , Vidali G.
Published: July 2002

Dispersionless single phonon creation and annihilation features have been observed across the entire Brillouin zone for the low density Hg monolayer adsorbed on Cu(001). This uncorrelated vibration of Hg atoms perpendicular to the surface contrasts sharply with the vibrational activity of most other chemisorbed metal atoms on metal substrates which exhibit correlated vibrations between groups of adsorbate atoms. The measured phonon energy has been used to build an interaction potential which incorporates both dynamical as well as static structural and thermodynamic properties of this system.
Growth parameters affecting the formation of buried CoSi2 by endotaxy of Co on Si(111)
Authors: Fathauer R. W. , George T.
Published: July 2002

At growth temperatures of ≊800 °C, Co deposited on Si(111) diffuses through a Si capping layer and exhibits oriented growth on buried CoSi2 seeds, a process referred to as endotaxy. This occurs preferentially to surface nucleation of CoSi2 under certain growth conditions. High-quality continuous single-crystal buried silicide layers have been obtained by endotaxy. This requires very low densities of attractive nucleation sites other than the buried seeds. For this reason, use of a silicon buffer layer and a low base pressure in the molecular-beam epitaxy system are found to be essential. Growth conditions required for high-quality layers and problems which result from growth outside these limits are discussed.
Effects of hydrogen adsorption on the performance of the W(001) spin-polarized low-energy electron diffraction electron polarimeter
Authors: Sawler J. , Venus D.
Published: July 2002

Since hydrogen is the main residual gas in a metal ultrahigh vacuum chamber, the effect of hydrogen adsorption on the performance of an electron polarimeter based on spin-polarized low-energy electron diffraction (SPLEED) from the W(001) surface, has been investigated experimentally. The experiments involved both dosing the analyzer crystal to calibrated coverages of hydrogen, and allowing residual gas in the vacuum chamber to adsorb on the analyzer crystal surface. The sensitivity (Sherman function, S) and efficiency (figure of merit, F) were monitored using SPLEED rotation curves. The W(001) SPLEED polarimeter is found to be resiliant to hydrogen adsorption. The sensitivity and efficiency require only a small scaling, which is linear in hydrogen coverage up to about 0.5 of saturation coverage. In a residual hydrogen partial pressure of 1 × 10−10 Torr, the analyzer crystal need be cleaned only every 2 h. The polarimeter may also be operated with a saturation coverage of hydrogen on the analyzer crystal. Under these conditions, the sensitivity falls to S=−0.19±0.02 and the efficiency to F = 4 × 10−5.
Atomic structure of the LaB6(100) surface as observed with scanning tunneling microscopy
Authors: Ozcomert John S. , Trenary Michael
Published: July 2002

We have studied the LaB6(100) surface using scanning tunneling microscopy and low-energy electron diffraction. We observe a surface with a square lattice of La atoms having a 4 Å spacing with approximately 10% of the La surface sites vacant. As indicated by a weak atomic corrugation of only 0.2 Å, the electronic states at the surface near the Fermi level display a degree of delocalization typical of a metal. On a larger scale, the surface is observed to consist of (100) terraces with an average width of 125 Å separated by steps one unit cell high.
Ar-pumping characteristics of diode-type sputter ion pumps with various shapes of ‘‘Ta/Ti’’ cathode pairs
Authors: Yoshimura Nagamitsu , Ohara Kenji , Ando Ichiro , Hirano Haruo
Published: July 2002

Ar-pumping characteristics of diode-type sputter ion pumps (30 anode cells, 0.15 T of magnetic flux density at the center of the discharge area) with various shapes of ‘‘Ta/Ti’’ cathode pairs were measured by an orifice method. The Ar-pumping speed of the pump of a ‘‘flat Ta/flat Ti’’ cathode pair was about 13 ℓ/s in the 10−5 Pa range. On the other hand, the Ar-pumping speeds of the pumps of a ‘‘holed Ta on flat Ti/flat Ti’’ pair and of a ‘‘slotted Ta on flat Ti/flat Ti’’ pair and that of the pump of a ‘‘slotted Ta on flat Ti/slotted Ti on flat Ti’’ pair were about 23 ℓ/s and 24–25 ℓ/s, respectively, in the 10−5 Pa range. The N2-pumping speed of the pump of the slotted Ta on flat Ti/flat Ti pair was measured as about 55 ℓ/s in the 10−5 Pa range. Therefore, the Ar-pumping speed was as large as 42% of the corresponding N2-pumping speed for the pump of the slotted Ta on flat Ti/flat Ti cathode pair.
A permanent, retractable screen for charge neutralization of insulating specimens during x-ray photoelectron spectroscopy analysis
Authors: Davis G. D. , Anderson C. R. , Clearfield H. M.
Published: July 2002

Differential charging that occurs during x-ray photoelectron spectroscopy analysis of insulating specimens is especially problematic in systems incorporating a focused, monochromatic x-ray source. Often, a grounded charge compensation screen is used in conjunction with an electron flood gun to alleviate this problem. Because the use of such a screen can be inconvenient or impossible in some experiments, we have developed a method by which it can be permanently incorporated into the analysis chamber and retracted when not in use. We describe two such applications. In one, we also incorporate a phosphor screen and analysis standards. The use of a retractable screen allows cyclic surface modification/film deposition/characterization studies to be achieved conveniently on insulating specimens.