bluuebunny/crossref_metadata_2025 huggingface dataset:
Propagation of Multiple Short-Length-Scale Stall Cells in an Axial Compressor Rotor
Authors: Inoue M. , Kuroumaru M. , Tanino T. , Furukawa M.
Published: July 2002

Evolution and structure of multiple stall cells with short-length-scale in an axial compressor rotor have been investigated experimentally. In a low-speed research compressor rotor tested, a short-length-scale stall cell appeared at first, but did not grow rapidly in size, unlike a so-called “spike-type stall inception” observed in many multistage compressors. Alternatively, the number of cells increased to a certain stable state (a mild stall state) under a fixed throttle condition. In the mild stall state the multiple stall cells, the size of which was on the same order of the inception cell (a few blade spacings), were rotating at 72 percent of rotor speed and at intervals of 4.8 blade spacings. With further throttling, a long-length-scale wave appeared overlapping the multiple short-length-scale waves, then developed to a deep stall state with a large cell. In order to capture the short-length-scale cells in the mild stall state, a so-called “double phase-locked averaging technique” has been developed, by which the flow field can be measured phase locked to both the rotor and the stall cell rotation. Then, time-dependent ensemble averages of the three-dimensional velocity components upstream and downstream of the rotor have been obtained with a slanted hot-wire, and the pressure distributions on the casing wall with high-response pressure transducers. By a physically plausible explanation for the experimental results, a model for the flow mechanism of the short-length-scale stall cell has been presented. The distinctive feature of the stall cell structure is on the separation vortex bubble with a leg traveling ahead of the rotor, with changing the blade in turn on which the vortex leg stands. [S0889-504X(00)00701-7]
Exact Solutions for Longitudinal Vibration of Multi-Step Bars with Varying Cross-Section
Authors: Li Q. S.
Published: July 2002

Using appropriate transformations, the equation of motion for free longitudinal vibration of a nonuniform one-step bar is reduced to an analytically solvable equation by selecting suitable expressions, such as power functions and exponential functions, for the area variation. Exact analytical solutions to determine the longitudinal natural frequencies and mode shapes for a one step nonuniform bar are derived and used to obtain the frequency equation of multi-step bars. The new exact approach is presented which combines the transfer matrix method and closed form solutions of one step bars. A numerical example demonstrates that the calculated natural frequencies and mode shapes of a television transmission tower are in good agreement with the corresponding experimental data, and the selected expressions are suitable for describing the area variation of typical high-rise structures. [S0739-3717(00)00302-0]
Stoichiometric and Non-Stoichiometric SnO2(110) Surfaces
Authors: Christiaen Anne-Claire , Abee Mark W. , Cox David F.
Published: July 2002

XPS spectra are presented for two different preparations of an SnO2(110) single crystal surface. A highly oxygen-deficient surface is prepared by ion-bombardment and annealing to 1000 K in ultrahigh vacuum. In situ oxidation with N2O is used to produce a nearly stoichiometric surface. Both surfaces exhibit (1×1) LEED periodicities. In spite of the known variations in composition between these two surfaces, normal emission XPS shows only a 5% variation in the apparent compositions.
Diaspore (β-AlOOH) by XPS
Authors: Rotole John A. , Sherwood Peter M. A.
Published: July 2002

The XPS spectra of diaspore were collected with a VSW HA150 using monochromatic Al Kα x-radiation. Monochromatic radiation provides a distinct clarity to the peak structure in the valence band of diaspore due to the absence of interfering x-ray satellites from the intense O 2s region. Variations in the intensities and peak separation of the two-peak structure in the valence bands of the oxides, hydroxides, and oxyhydroxides of aluminum allow one to distinguish between these compounds. The valence band, survey, and the Al 2s, Al 2p, O 1s, and C 1s core levels are reported.
Cu(OH)2 by XPS
Authors: Vasquez R. P.
Published: July 2002

X-ray photoemission measurements of Cu(OH)2 are presented.
Study of the double layer CeO2/Nb2O5 thin film
Authors: Zhang Zaoli , Du Xinhua , Wang Wendong
Published: July 2002

A double layer CeO2/Nb2O5 thin film by magnetron sputtering was prepared. The property and microstructure of the thin film were carefully characterized by x-ray photoelectron spectroscopy (XPS), transmission electron microscopy, and high resolution transmission electron microscopy. XPS measurement clearly demonstrated that the Nb2O5 layer underlying CeO2 as a electrical-conductive layer could greatly improve the reduction ability of CeO2 thin film compared with that of a single layer CeO2 thin film. Fitting to the XPS experimental data and deconvoluting the spectra showed the increase of Ce3+ concentration in the double layer CeO2/Nb2O5 thin film. The microstructure of the double layer thin film was composed of three distinguishable layers, which are a polycrystalline CeO2 layer, an amorphous Nb2O5 layer, and an intermediate amorphous layer with regard to the silicon substrate. The interface between CeO2 and Nb2O5 was rough and indistinct. A detailed analysis was given from the viewpoint of interdiffusion at the CeO2/Nb2O5 interface.
Carbon Monoxide Adsorption on Ni(110)
Authors: Taylor T. N. , Estrup P. J.
Published: July 2002

The chemisorption of CO on Ni(110) has been studied at temperatures down to −145 °C, by means of LEED, Auger and work function measurements, and flash desorption. Since electron impact caused dissociation of the adsorbed molecules, precautions had to be taken to minimize spurious effects. The LEED patterns showed considerable disorder but could be described approximately by the sequence c(2×2)→(4×2)→c(2×1). These structures suggest that both linear and bridged bonding of CO occurs on Ni(110), and flash desorption revealed two bindings states separated by ∼0.2 eV. The isosteric heat of adsorption for the lower energy state was found to be 1.1 eV. The maximum work function change was 1.6 eV.
Holographic Measurements of the Plasmas in a High-Current Field Emission Diode
Authors: Mix L. P. , Kelly J. G. , Kuswa G. W. , Swain D. W. , Olsen J. N.
Published: July 2002

Two-exposure holographic interferometry has been employed to obtain the first quantitative measurements of the plasma densities in an intense electron beam diode. Several diode configurations which produce an intense pinch of the electron beam at the anode plane have been investigated. Holograms indicating the temporal and spatial evolution of the plasmas in these diodes are presented. Two types of plasmas are observed in these diodes: a lower density plasma (< 1018/cm2) with a velocity of 5–10 cm/μsec and a higher density plasma (> 1018/cm3) with a velocity of about 2 cm/μsec. Preliminary analysis indicates that the lower density plasma plays a dominant role in determining the primary beam dynamics.
The crystallographic distribution of field-desorbed species
Authors: Panitz J. A.
Published: July 2002

The complete crystallographic distribution of field-evaporated W3+ and W4+ as well as field-desorbed hydrogen has been observed by using a new technique called field desorption spectrometry. The distributions are obtained during a single evaporation event in a modified field-ion microscope by recording the desorption image displayed on a spherical CEMA detector time gated with the arrival of an ion species of preselected mass-to-charge ratio. Preliminary observations show no unique crystallographic origin for W3+ or W4+ at 78 or 27 K during field evaporation in vacuum or imaging gas. Hydrogen appears to originate at random insterstitial locations at the surface and is not uniquely associated with the protruding atoms imaged in a conventional ion micrograph. The general lack of a one-to-one correspondence between gated desorption and ion micrograph images suggests that using the atom probe to identify individual preselected ion micrograph image spots may be much more difficult than originally anticipated.
Optimization of microcolumn electron optics for high-current applications
Authors: Mankos M. , Lee K. Y. , Muray L. , Spallas J. , Hsu Y. , Stebler C. , DeVore W. , Bullock E. , Chang T. H. P.
Published: July 2002

The optimization of electron-optical properties of a microcolumn for high-current, high-resolution applications in microcolumn arrays is discussed. The goal of the optimization is to increase the current available in the microcolumn to approximately 10–50 nA while maintaining a spot size sufficiently small for sub-100 nm technology (not larger than approximately 20–50 nm). To achieve this goal, it is necessary to operate the microcolumn as a two-lens electron-optical system. The electron-optical performance of the single-lens and two-lens microcolumn operational modes is compared at 1 keV beam energy, angular intensity of 100 μA/sr, and a working distance of 1 mm. The two-lens mode can achieve spot sizes from 25 to 50 nm for a wide range of beam currents, up to 50 nA. A two-lens microcolumn has been built and evaluated, and the experimental data is presented.
Scaling of Tg and reaction rate with film thickness in photoresist: A thermal probe study
Authors: Fryer David S. , Nealey Paul F. , de Pablo Juan J.
Published: July 2002

A thermal probe technique, local thermal analysis, was used to measure the glass transition temperature (Tg) and reaction rate as a function of film thickness in chemically amplified photoresists. Using this technique, heat loss into a resist film was monitored as the temperature of the probe was ramped from ambient to temperatures as high as 200 °C. The thermal events, glass transition temperature or heat evolved during reaction, were recorded as a function of the probe temperature. The Tg of the photoresists UVN 30, UV6, UV3, KRS, and KRS-XE was measured for thick films and for ultrathin films approximately 50 nm thick. The measured Tg in ultrathin resist films was 4–22 °C higher relative to that measured in thick films. We also investigated the behavior of polyhydroxystyrene films, and found that crosslinking to the substrate can increase Tg by a large amount. The photoresist films were then exposed with x-ray radiation at the same dose (950 mJ/cm2) for both thick and ultrathin films to ensure a constant photogenerated acid concentration with thickness. The exposed areas of the films were heated with the thermal probe, and an increase in heat flow into the exposure area, attributed to the heat of reaction, prior to the glass transition temperature was measured. Kinetic rate constants were estimated with data from the power supplied to the probe as a function of temperature using a first order reaction model. The results indicate that the rate of reaction in ultrathin resist films is smaller than in thicker films for resists processed at the same postexposure bake temperature. We find that Tg and reaction rate depend on film thickness in ultrathin photoresist films; the differences in these properties are expected to lead to large changes in the processing conditions used for ultrathin films relative to thick films.
Thermally oxidized GaN film for use as gate insulators
Authors: Kim Hyunsoo , Park Seong-Ju , Hwang Hyunsang
Published: July 2002

The structural and electrical characteristics of a thermally grown gallium oxide on GaN films were investigated. A furnace oxidation at 850 °C for 12 h resulted in the formation of monoclinic β-Ga2O3, 88 nm in thickness. From the I–V measurements of the metal–oxide–semiconductor (MOS) structure, the breakdown field strength (EBD) was found to be 3.85±0.32 MV cm−1. Under gate voltage sweep, C–V hysteresis was observed due to the oxide charge trap. By comparing the ideal and experimental C–V curves, the oxide charge density (Nf) was calculated to be 6.77×1011 cm−2. These results suggest that the thermally grown Ga2O3 is suitable for gate dielectric applications of power MOS field-effect transistors.
High density plasma via hole etching in SiC
Authors: Cho H. , Lee K. P. , Leerungnawarat P. , Chu S. N. G. , Ren F. , Pearton S. J. , Zetterling C.-M.
Published: July 2002

Throughwafer vias up to 100 μm deep were formed in 4H-SiC substrates by inductively coupled plasma etching with SF6/O2 at a controlled rate of ∼0.6 μm min−1 and use of Al masks. Selectivities of >50 for SiC over Al were achieved. Electrical (capacitance–voltage: current–voltage) and chemical (Auger electron spectroscopy) analysis techniques showed that the etching produced only minor changes in reverse breakdown voltage, Schottky barrier height, and near surface stoichiometry of the SiC and had high selectivity over common frontside metallization. The SiC etch rate was a strong function of the incident ion energy during plasma exposure. This process is attractive for power SiC transistors intended for high current, high temperature applications and also for SiC micromachining.
Effect of surface treatment on the γ-WO3(001) surface: A comprehensive study of oxidation and reduction by scanning tunneling microscopy and low-energy electron diffraction
Authors: Tanner Robert E. , Altman Eric I.
Published: July 2002

The structure of the (001) surface of monoclinic γ-WO3 was characterized using scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED). The surface structure depended strongly on preparation conditions. Oxidizing by heating in O2 removed carbonaceous impurities and resulted in large atomically rough terraces. Subsequent heating in lower O2 pressures led to metastable superstructures and c(2×2) terraces. Continued heating progressively reduced the surface, resulting in a series of reconstructions. Each could be explained in terms of ordered oxygen vacancies. First, regions of a c(2×2) reconstruction grew. This structure corresponds to a WO2 plane in which half the W6+ sites are covered by terminal O. Since all the W atoms are in a 6+ oxidation state, this surface is considered “fully oxidized.” Certain STM images of the c(2×2) terraces revealed a pseudo-primitive-(2×2) periodicity that can be related to the monoclinic distortion from cubic symmetry. It is shown that the distortion is always present but the ability to detect it depends on the tip. The distortion also caused twinning that lead to spot splitting in LEED patterns. The splitting disappeared on heating to 785 K when the bulk converted to orthorhombic symmetry. Continued reduction produced areas with (2×2), (6×2), and c(4×2) periodicities. These reconstructions are formed when further terminal O is removed, and half the total W sites are reduced to W5+. Sputtering and ultrahigh vacuum annealing also reduced the surface, ultimately leading to “fully reduced” (1×1) terraces with no terminal oxygen and only W5+ surface cations. These structural transformations were reversible: at any stage during reduction, heating in ⩾10−4 Torr of O2 reoxidized the surface, regenerating the original rough morphology.
Photoinduced outgassing from the resist for extreme ultraviolet lithography by the analysis of mass spectroscopy
Authors: Watanabe Takeo , Kinoshita Hiroo , Nii Hajime , Hamamoto Kazuhiro , Tsubakino Harushige , Hada Hideo , Komano Hiroshi , Irie Shigeo
Published: July 2002

Extreme ultraviolet lithography (EUVL) requires the vacuum environment for exposing the resist. The contamination in the vacuum environment decreases the reflectivity of the reflective mask and that of the imaging optics. The photoinduced outgassing from the resist becomes the contamination in the vacuum environment. Therefore, the outgassing detection investigation is very important. The outgassing from the chemically amplified (CA) resists EUV001 for EUVL, EUV006N for EUVL, UV5 for KrF lithography and the nonchemically amplified resists OEBR2000 and ZEP520 for electron beam lithography were investigated. Based on the photoinduced reactions of the resist, the fragment ions species that were measured by the quadrupole mass spectrometer were identified. It is found that the amount of the photoinduced outgassing such as hydrocarbons from the DQN resist and annealing-type CA positive-tone resist is small.
Solid particle production in fluorocarbon plasmas. I. Correlation with polymer film deposition
Authors: Takahashi Kazuo , Tachibana Kunihide
Published: July 2002

Solid particles and agglomerates of the particles were found to be produced in octafluorocyclobutane (c-C4F8) plasmas used for reactive ion etching of SiO2 and chemical vapor deposition of low dielectric constant fluorocarbon films. Analyses of the solid products elucidated a part of the chemical reactions related to the polymerization process in gas phase. The particle production depended strongly on the feed gas pressure in the plasma. A marked increase of the production was observed as the pressure became higher than 50 mTorr. The production accompanied the pressure depression at the steady state in the discharge, indicating the depletion of the gas species owing to polymerization. Furthermore, the partial pressure of stable molecules such as CF4 and C2F6 produced in the plasma and the film deposition rate on surfaces changed drastically at the critical pressure. These pressure dependencies suggest that polymerization reactions between reactive species and source molecules in gas phase lead to the particle production.
Study of Cerium Dioxide Thin Films by X-ray Photoelectron Spectroscopy
Authors: Barreca Davide , Battiston Giovanni A. , Gerbasi Rosalba , Tondello Eugenio
Published: July 2002

X-ray photoelectron spectroscopy measurements of cerium dioxide thin films have been performed. The samples were prepared by chemical vapor deposition (CVD) using Ce(dpm)4 (Hdpm = 2,2,6,6-tetramethyl-3,5-heptanedione) as precursor on alumina and glass substrates. In this work, the spectra of the principal core levels for a CeO2 film on glass are presented. The Ce 3d photopeak has the typical structure of Ce(IV) compounds. By deconvolution of the O 1s signal, the presence of –OH groups and adsorbed water are evidenced. Sputtering treatments confirm that carbon contamination is limited to the outermost layers, while resulting hydrated species are bonded tenaciously to the oxide network.
Focus latitude enhancement of symmetrical phase mask design for deep submicron contact hole patterning
Authors: Chou Shuo-Yen , Lou Jen-Chung , Chen Li-Jui , Shiu Lin-Hung , Liu Ru-Gun , Wang Chien-Ming , Gau Tsai-Sheng
Published: July 2002

The mechanism of focus latitude enhancement for contact/via hole printing is explained by approximating the axis intensity distribution of an image as a series of cosine functions to characterize the interference between each pair of diffraction beams. It is found that a phase-shifting mask (PSM) with symmetrical assist features improves the depth of focus (DOF) by introducing destructive interference to counterbalance the intensity fluctuation from constructive interference as defocus. A simple formula was derived to represent the capability of focus latitude enlargement. It shows that the extent of enhancement depends on the exposure wavelength and numerical aperture of a projection lens only. Increasing the degree of partial coherence degrades the focal range enlargement because a larger illumination angle elongates the destructive interference pattern in the optical-axis direction to weaken its ability for intensity compensation. On the other hand, the lack of constructive interference in dense hole imaging fails the mask pattern transfer, which limits the application of the phase-shifting method to pattern pitch greater than 2λ/NA. A tiny amount of spherical aberration results in prominent asymmetrical defocus behavior because the wave deformation in the projection lens shifts the distribution of constructive and destructive interference patterns to opposite defocus directions. The printing characteristics of 0.17 μm contact using an 18% transmission, rim-type attenuated phase-shifting mask are investigated to corroborate our analysis of defocus behavior. The dependence of depth of focus on pattern duty is stressed to elucidate the difference in mechanisms of focus latitude improvements for a sparse hole and periodic dense hole.
Demonstration of two-photon lithography
Authors: Schwarz Ch. J. , Nampoothiri A. V. V. , Jasapara J. C. , Rudolph W. , Brueck S. R. J.
Published: July 2002

Two-photon exposure is demonstrated using ∼12 fs duration pulses at a center wavelength of 800 nm and a standard I-line photoresist. Using direct-writing with a focused Gaussian beam, developed resist features as small as 300 nm, compared with the ∼1 μm focal spot diameter, have been achieved. The experiments reveal substantial differences (∼104) in the two-photon absorption coefficient for multiple pulse trains (100 MHz) and for single pulses. A simple model involving photoexcitation of an intermediate conformation of the photoactive compound and relaxation back to the ground state can explain this observation. The resolution enhancement of √ resulting from the two-photon absorption is demonstrated by writing two lines as close as possible to each other with both one- and two-photon absorption mechanisms.
Reduction in surface roughness during secondary ion mass spectrometry depth profiling with an ion-milling method
Authors: Jiang Z. X. , Backer S. , Chen S. , Lerma J. , Guenther T. , Lee J. J. , Sieloff D.
Published: July 2002

Depth resolution for secondary ion mass spectrometry (SIMS) profiling of poly Si/SiO2/Si gate stacks is often hindered by roughness of poly Si surfaces. In order to maintain the high depth resolving power of low-energy SIMS for the gate stacks, an ion-milling method was developed to smoothen and thin poly Si films by O2+ beam bombardment at normal incidence. The ion milling has led to a remarkable smoothening in the sputtered area: the rms roughness in poly Si was reduced from 4.5 to 0.6 nm, after removal of 120 nm poly Si by 5 keV O2+ bombardment at normal incidence. SIMS profile analyses with the ion milling provided detailed in-depth distributions of As and Si in a gate stack, showing vividly the pile up of As at the poly Si/SiO2 interface and the difference in the beam-induced diffusion of As in Si and SiO2.
Nondestructive via in-hole profile characterization using atomic force microscopy metrology
Authors: Ali Abbas , Ukraintsev Vladimir , Sabri Hasan , Yang Ming
Published: July 2002

An advanced, nondestructive via in-hole characterization method is described in this article. Via profiling can be very beneficial as technology node shrinks with more back end of the line processing schemes. This method of real time, nondestructive 3D via imaging was used to characterize via bottom anti-reflection coating fill process for dual-damascene formation used extensively in Cu metallization. The results showed that atomic force microscopy (AFM) can profile deep vias with very good accuracy and can help in real-time process loop feedback. The AFM measurements reported in this article have been done using Veeco’s metrology AFM SXM-320. This tool provides a patented “deep trench” mode of operation. The mode is specifically designed to use tips with very high aspect ratios. It is shown that AFM can measure via profiles, depth, sidewall roughness and critical dimensions.
Chlorine dissociation fraction in an inductively coupled plasma measured by ultraviolet absorption spectroscopy
Authors: Neuilly François , Booth Jean-Paul , Vallier Laurent
Published: July 2002

Broadband ultraviolet absorption spectroscopy of the weak Cl2 continuum between 250 and 400 nm was used to measure the molecular Cl2 density in pure chlorine inductively coupled plasmas at pressures of 15–100 mTorr and radio-frequency (rf) power up to 800 W. The depletion of the Cl2 density was greatest at high-rf power and low pressure, and reached 80% at 15 mTorr 800 W. A simple global model was developed to explain the variation of the Cl2 dissociation rate as a function of source power and total gas pressure, and was in excellent agreement with the observations.
High direct energy band gaps determination in InxAl1−xAs coherently grown on InP
Authors: Convertino Annalisa , Padeletti Giuseppina , Cerri Luciana , Viticoli Sesto
Published: July 2002

A series of InxAl1−xAs samples (0.50<x<0.56) coherently grown on InP substrates has been investigated in order to study the dependence of the two dimensional excitonic energies associated with the E1 and E1+Δ1 energy gaps and the spin–orbit splitting parameter Δ1 on InAs molar composition x. The samples have been fabricated by means of molecular beam epitaxy and the energy gaps have been determined by performing normal–incidence reflectivity measurements at room temperature.
Formation and oxidation properties of (Ti1−xAlx)N thin films prepared by dc reactive sputtering
Authors: Matsui Y. , Hiratani M. , Nakamura Y. , Asano I. , Yano F.
Published: July 2002

We prepared (Ti1−xAlx)N thin films by dc reactive sputtering using alloy targets and investigated their oxidation properties. The oxidation rate of the (Ti1−xAlx)N film decreases with increasing aluminum content because Al2O3, with a low oxygen diffusion coefficient, is segregated at the film surface. In particular, the phase separation into a double layer of Al2O3 and TiO2 is more noticeable at high temperature. On the other hand, at an initial stage of oxidation, a mixed oxide of titanium and aluminum (>5 nm thick) is formed after oxidation at 550 °C for 1 min. This mixed-oxide formation is a result of insufficient growth of the Al2O3 layer, which causes fast oxygen diffusion and hence high oxidation rate. We thus conclude that (Ti1−xAlx)N is difficult to use as a barrier metal for metal-insulator-metal capacitors as long as the oxidation resistance is based on the growth of a protective Al2O3 layer on the film surface.
Atomistic simulations of deep submicron interconnect metallization
Authors: Yang Y. G. , Zhou X. W. , Johnson R. A. , Wadley H. N. G.
Published: July 2002

Damascene approaches are widely used for creating microelectronic interconnects. Successful implementation of the process is reliant upon the deposition of a refractory metal or metal nitride liner coating. It functions as a diffusion barrier layer to suppress transport of subsequently deposited interconnect metals into the surrounding dielectric. The development of vapor-phase processes for the deposition of uniform thickness liner layers has been problematic. Flux collimation and energetic deposition approaches have been attempted with mixed results as the feature size is decreased. Here, a modified kinetic Monte Carlo (KMC) method has been used to explore the physical vapor deposition of liner coatings. To incorporate the many effects associated with energetic metal fluxes, the results of molecular dynamics calculations of incident atom reflection, resputtering, surface biased diffusion, and athermal relaxations have been introduced into the KMC algorithm. The method has been applied to investigate the effects of the incidence flux’s angular distribution and kinetic energy upon the liner coating coverage. It has been found that trench step coverage uniformity increases with increasing atom kinetic energy above a threshold energy value of 20 eV. Atom resputtering/reflection are found to be the most important mechanisms responsible for improvements in the step coverage. Sputtering of already deposited material is found to be the most important mechanism for transporting the flux to the most difficult to coat lower sidewall region of a trench. Energetic deposition processes that activate these mechanisms are therefore preferred. The simulations reveal the existence of an optimal incident angular distribution to maximize coverage uniformity. For a flux with a kinetic energy of 70 eV, a cosine angular distribution within the collimation angle of ±15°–25° provided the best balance of direct and resputtered/reflected fluxes to maximize coating uniformity.
Present Trends in Condensation and Evaporation Theories
Authors: Rutner Emile
Published: July 2002

A review is given of theories of nucleation and condensation based on quasi-equilibrium models. Relations between a kinetic theory for nucleation, such as the path-probability method, and the quasi-equilibrium theories are also noted. Theories of condensation and vaporization based on the defect structure of the surface as the site for the processes are also reviewed. The application of absolute-reaction-rate theory to these phenomena is discussed.
Adhesion Mechanism of Gold-Underlayer Film Combinations to Oxide Substrates
Authors: Haq K. E. , Behrndt K. H. , Kobin Ilse
Published: July 2002

The adhesion between glass or oxidized Si substrates and evaporated gold films in combination with an adherent intermediate layer of Ta, Si, Ge, or Cr has been investigated. The experimental results regarding changes of adhesion as a function of the relative thickness of the Au and underlayer films as well as time, environment, and treatment after deposition are described in detail. They can be explained in terms of the thermodynamic properties of the respective Au-underlayer systems: In the case of Au–Si and Au–Ge, alloying and diffusion processes play the dominant role while, for Au–Ta, oxidation of Ta is responsible for adhesion changes. Most importantly, in the Au–Cr system, none of the above processes are effective, at least up to 450 °C. Consequently, no loss of adhesion was observed for periods of one month and thicknesses of the Cr layer of only about 10 Å.
Microstructure of Sputter-Deposited 304L Stainless Steel
Authors: Dahlgren S. D. , McClanahan E. D. , Johnston J. W. , Graybeal A. G.
Published: July 2002

Deposits of 304L stainless steel from 0.002–0.064 in. thick were produced at rates from 0.002–0.00075 in./h by triode sputtering techniques. Substrates were maintained at temperatures from 1 °–800 °C. The 304L, alloy was found to be removed by krypton atoms at a rate of 4.6 g/A-h (22 atoms/ion) with the target at 1509 V. The 0.064-in-thick sample produced on a substrate held at 1 °C showed a variation in columnar grain microstructure through the deposit thickness. Chemical analysis showed that the alloy composition of the deposits was nearly the same as the target. The data indicated that the deposits had slightly more chromium, but less nitrogen and carbon than the target. Electron microprobe data indicated the deposits were uniform in chromium and nickel concentrations. The deposit appearance, microstructure, and crystal structure were strongly dependent on substrate temperature. The deposits had dull surfaces, columnar grain microstructures, and body-centered cubic (bcc) crystal structure for substrate temperatures below about 360 °C. Between 360 ° and 500 °C the surfaces had mirror finishes, the grains were equiaxed, and the deposits consisted of a mixture of face-centered cubic (fcc) and bcc phases; at 500 °C the deposit was essentially all fcc. At 800 °C the deposit had a mirror finish, the grains were columnar, and the crystal structure was fcc.
High-rate physical vapor deposition of refractory metals
Authors: Sherman Max A. , Bunshah Rointan F. , Beale Harry A.
Published: July 2002

Molybdenum, niobium, and vanadium bulk deposits produced by high-rate physical vapor depostion techniques (HRPVD) were analyzed for impurity content, grain size and morphology, yield strength, hardness, and bend ductility. Yield strengths of Mo and Nb were comparable to those of wrought material having equivalent grain sizes, while the yield strength of vapor-deposited V was superior to that of wrought V because of its ultrafine (0.7 μm) grain size. Ultrafine-grained refractory metals, such as the V deposits produced in this study, may greatly reduce void formation and growth, which causes dimensional changes and degradation of mechanical properties in reactor structural components. It is suggested that HRPVD techniques may be used to prepare fine-grained materials having superior resistance to swelling induced by fast-neutron irradiation.
Bonding of flame-sprayed Ni–Al
Authors: Ingham H. S.
Published: July 2002

Several composite flame-spray materials of nickel and aluminum have been in extensive use because of their unusual ability to bond to substrates. Generally, it has been presumed that this property is related to the exothermic reaction that occurs when these two metals are melted together. The question has arisen, however, as to whether the heat of oxidation of the constituents in the flame-spray stream may be responsible for the bonding. A series of experiments was run in order to distinguish between the two mechanisms. The evidence leads strongly to the conclusion that oxidation does not enhance the bonding, and that the reaction between the Ni and Al is the predominant factor.
Quantitative analysis of thin oxide films using x-ray photoelectron spectroscopy and rastered ion bombardment
Authors: McIntyre N. S. , Zetaruk D. G.
Published: July 2002

Using x-ray photoelectron spectroscopy (XPS or ESCA), it is possible to construct a quantitative profile of the composition of a surface film as a function of depth into that film. The factors contributing to distortion of the profile are considered with reference to an oxidized Inconel 600 alloy surface containing metallic and oxidized iron, chromium, and nickel. The ability of XPS to differentiate clearly between metal and oxide components is important since the photoelectron yield can differ for each of these species. Differentiation of oxide from metal is accomplished by automated analysis of the XPS peak shapes together with application of the appropriate, experimentally derived photoelectron yields. Ion bombardment can distort the quantitative information in a depth profile by preferential sputtering of some components and by beam-induced chemical decomposition of the surface. For the oxide mixtures under study, preferential sputtering was not detected. Moreover, ion bombardment of these oxide surfaces did not result in significant reduction of oxide to metal. The appearance of metallic components, observed in some systems during the sputtering of oxides, is attributed to the redeposition of sputtered components on the edge of a sputtered region, and their absence in this work is due to the use of a rastering ion beam to remove the entire analysis region evenly. Thus, the component ratios obtained in profile experiments on Inconel films can be expected to reflect the real concentrations.
Planar magnetron sputtering
Authors: Waits Robert K.
Published: July 2002

The technology is reviewed with emphasis on implementation. PM sputtering is characterized by cathode potentials of 300–700 V and sputtering gas pressures of 1-15 mTorr (0.1–2 Pa). Deposition rates are proportional to power density, which in turn is primarily limited by the thermal conductivity and cooling efficiency of the target. rf operating characteristics are similar to dc, but plasma plus target impedance is somewhat higher. For both rf and dc PM sputtering higher power (or current) densities are achievable at lower target potentials than for conventional sputtering. Permanent magnets and electro-magnets have been used to produce closed electron-trapping field patterns adjacent to the surface of both circular and rectangular planar targets. Plasma intensity and target erosion is a maximum where the magnetic field lines are parallel to the cathode surface. Deposition uniformity can be achieved by substrate motion combined with optimized magnet geometry. For a given material at equivalent deposition rates PM sputtering results in less substrate heating due to reduced bombardment by dark-space-accelerated electrons.
Cryopump measurements relating to safety, pumping speed, and radiation outgassing
Authors: Graham William G. , Ruby Lawrence
Published: July 2002

A test cryopump has been constructed to investigate operation in close proximity to a neutral beam, to determine static and dynamic pumping speeds, and to study outgassing such as might be produced by a pulse of nuclear radiation. No difficulty was encountered in operating the cryopump close to a deuterium neutral beam source suitable for a fusion-reactor injector. Static and dynamic pumping-speed measurements agreed well, but were somewhat lower than expectations, probably due to the unusual method chosen to supply liquid helium. Safety tests showed that hydrogen could not be ignited at any subatmospheric pressure resulting from a leak-up-to-air accident. The possible hazard of liquid-oxygen condensation in such accidents was not explored. Tests made with pulses of neutrons and gamma rays produced by a TRIGA reactor showed that the cryopump could be partially outgassed by radiation pulses of sufficient intensity. However, the effect is ascribed to the gamma-ray component of the TRIGA pulse which is about 103 times that expected from a fusion reactor such as TFTR.
I
n s
i
t
u vaporization of very low molecular weight resists using 1/2 nm diameter electron beams
Authors: Isaacson M. , Muray A.
Published: July 2002

A technique is presented for in situ measurements of contrast curves for electron beam vaporizable resists. Using a 1/2 nm diam beam of 100 keV electrons, we have etched lines, holes and patterns in NaCl crystals at the 2 nm size scale. Troughs about 1.5 nm wide on 4.5 nm centers and 2 nm diam holes have been etched completely through NaCl crystals more than 30 nm thick.
Ion-beam sensitivity of polymer resists
Authors: Ryssel H. , Haberger K. , Kranz H.
Published: July 2002

The ion-beam sensitivity of polymer resists, mainly PMMA, was investigated for argon, gallium, helium, and hydrogen ions. The resists were exposed in a standard ion accelerator at energies of 40 to 120 keV. The samples were irradiated with doses varying between 5×1010 and 5×1014 cm−2. It was found that the resists are about a factor of 100 more sensitive for hydrogen ions than for electrons of 20 keV; whereas for helium, up to a factor of 150, and for argon and gallium a factor of more than 300 were found for positive resists. Using an energy of 120 keV, layers of more than 1.3 μm thickness can be exposed by hydrogen ions, 1.0 μm thickness by helium ions and 0.25 μm thickness by argon ions. The effective sensitivity is energy-dependent, and within the region of 40 to 120 keV between a factor of 1.4 and 2.0, with the higher sensitivity at lower energies. The achievable resolution of structures using ion beams is very high. Resists with a sensitivity of 5×10−7 C/cm2 easily yield a resolution of 0.25 μm wide and 1.3 μm thick lines.
Hydrogen-induced features in the Auger spectra from amorphous silicon
Authors: Madden H. H.
Published: July 2002

Si-L23VV spectra have been measured for hydrogenated amorphous silicon (a-Si:H) surfaces produced by direct ion bombardment (IB) with mixed hydrogen/argon ion beams. Interpretation of the hydrogen-induced features in the loss-corrected, integral spectra could be made by comparisons of the a-Si:H spectra with corresponding spectra from clean ordered Si surfaces, from an ordered dihydride surface system, from amorphous surfaces produced by argon IB, and by comparisons with theoretical density-of-states calculations for a-Si:H. As is the case with the ordered, chemisorbed hydrogen system, hydrogen causes a decrease in intensity on the high energy side of the Auger signal. This decrease indicates a tying off of ‘‘dangling bonds.’’ In the a-Si:H system, however, this effect is in competition with the effects of surface damage produced by the IB which can result in a net increase in high energy signal intensity. At lower energies the a-Si:H signals exhibit both of the two broad Si–H bonding features noted for the ordered dihydride surface and a third, weaker feature at still lower energies.
Comparison of the atomic geometries of GaSb(110) and ZnTe(110): Failure of ionicity-structure correlations
Authors: Duke C. B. , Paton A. , Kahn A.
Published: July 2002

The atomic geometries of the (110) surfaces of GaSb and ZnTe are determined by comparing calculated elastic low energy electron diffraction (ELEED) intensities with those measured at T=125 K. The quality of the model description of the observed intensities is measured by the x ray R factor Rx. Using the minimization of Rx as the structure determination criterion, the atomic geometries of these two surfaces are shown to be very similar, in fact, nearly identical to within the uncertainties inherent in the analysis. GaSb(110) is reconstructed via a bond-length conserving rotation in its uppermost atomic layer characterized by ω1=30±2°, and the Sb relaxed outward from the substrate. ZnTe(110) exhibits an analogous bond-length conserving rotation of ω1=28±2° in its uppermost layer. In addition, however, this layer is relaxed by 0.05±0.05 Å toward the substrate, and the second layer exhibits a counter relaxation of the Zn outward by 0.025±0.05 Å and the Te inward by 0.025±0.05 Å. The spectroscopic ionicity of GaSb is fi=0.26, whereas the difference in Pauling electronegativities of Sb and Ga is ΔX=0.3. For ZnTe the values are fi=0.55 and ΔX=0.5. The absence of second-layer relaxations for GaSb(110) reveals that such relaxations are not characteristic of all highly covalent compound semiconductors (i.e., fi<0.5, ΔX<0.7). Moreover, their suggested presence for ZnTe(110) reveals that their absence is not characteristic of materials with fi>0.5. Thus, this characteristic feature of the surface atomic geometries of the (110) surfaces of zinc-blende-structure compound semiconductors does not correlate simply with either the spectroscopic or Pauling ionicities.
Reactive sputtered copper indium diselenide films for photovoltaic applications
Authors: Thornton John A. , Cornog David G. , Hall R. B. , Shea S. P. , Meakin J. D.
Published: July 2002

Single phase chalcopyrite CuInSe2 coatings have been deposited by reactive cosputtering from Cu and In planar magnetron sources operated in an Ar+H2Se working gas. Effective sputtering yields from the conditioned Cu and In targets were approximately 0.7 and 0.5 atoms/unit charge, respectively. Sputtering rate, H2Se injection rate, and H2Se and H2 partial pressure measurements were consistent with the overall reaction Cu+In+2H2Se→CuInSe2+2H2. The formation of near-stoichiometric coatings appears to be aided at elevated temperatures by a reemission mechanism which removes excess In. Photovoltaic devices formed by evaporating CdS onto the sputtered CuInSe2 yielded short circuit currents of about 33 mA/cm2 and efficiencies of about 4%.
Causes of unstable and nonreproducible sensitivities in Bayard–Alpert ionization gauges
Authors: Arnold P. C. , Bills D. G.
Published: July 2002

The fundamental ionization gauge equation p=i+/(Si−) can be rigorously derived. However, the values of the two currents i+ and i− can only be inferred from measurements of the ion collector current Ic and electron emission current Ie. Measurements are reported in which some physical parameters upon which i+ and i− are dependent were varied under closely controlled conditions. Experimental evidence is presented to show that the sensitivity S of Bayard–Alpert (BA) gauges varies with changes in the electron emission density pattern along the length of the hot cathode. Because the grid intercepts an appreciable fraction of the electron current on each pass through the grid, small changes in the emission density pattern can cause the fraction intercepted to vary widely. Therefore, the amount of ionizing current i− in the ion collection volume varies causing sizable changes in the rate of ion production and in the gauge sensitivity. It is concluded that these causes of changes in sensitivity in BA gauges are inherent in all ionization gauges in which a change in the emission density pattern can effect the rate of ion production.
Hot corrosion behavior of low pressure plasma sprayed NiCoCrAlY+Ta coatings on nickel base superalloys
Authors: Frances M. , Steinmetz P. , Steinmetz J. , Duret C. , Mevrel R.
Published: July 2002

The hot corrosion behavior of NiCoCrAlY+Ta coatings obtained by low-pressure plasma spraying has been investigated (type I hot corrosion with T=850 °C). These coatings have been deposited on two nickel-base superalloys and on a cast alloy of the same composition as the coating. Comparison of the cyclic oxidation behavior at 850 °C between the sprayed coating and the cast alloy shows that the sprayed material exhibits a satisfactory and higher resistance than the cast alloy. In the latter case, repeated spalling of the oxide scale results from fractures often associated with Y-rich oxide protrusions. Hot corrosion experiments (salt-spraying test with T=850 °C and thermal cycling in air every hour) have been conducted on two cast alloys, NiCoCrAl+Ta and NiCoCrAlY+Ta. The Y-containing alloy has a better corrosion resistance than the other alloy which is subject to extensive oxide spallation. In both cases, morphologies typical of basic fluxing processes, involving Cr, Al, Y, and Ta can be observed in highly attacked zones. Finally, tests on plasma sprayed coatings show a high resistance to hot corrosion of these coatings, regardless of the substrate used: a fine adherent alumina layer is formed, and only a limited fluxing of Cr, Al, and Y takes place. The quite different results obtained on cast and sprayed alloys imply that data relative to cast alloys can be unreliable when one wants to predict high temperature behavior and especially lifetimes of overlay coatings.
Auger electron spectroscopic study of the etching of cadmium telluride and cadmium manganese telluride
Authors: Feldman R. D. , Opila R. L. , Bridenbaugh P. M.
Published: July 2002

The surface compositions of Cd1−xMnxTe and CdTe that result from various chemical treatments have been studied by Auger electron spectroscopy. The depths of nonstoichiometric surface layers have been determined by sputter profiling. Bromine methanol and mineral acids leave surfaces depleted in Cd and Mn. The depth and degree of depletion is generally more severe for Mn than for Cd. Nearly stoichiometric surfaces result from soaking Cd1−xMnxTe and CdTe in water solutions with KOH. The depletion of Mn from the surface after bromine methanol etching can be reduced by dissolving Mn in the etch solution.
Temperature dependent formation of surface undulations in explosively crystallized films
Authors: Wickersham C. E. , Bajor G. , Greene J. E.
Published: July 2002

Van Saarloos and Weeks have recently proposed an instability theory which predicts that self-sustained explosive crystallization can result in a thermal instability which leads to the formation of periodic surface undulations in the transformed film. We have obtained experimental results which verify the essential features of this model. That is, large scale undulations with amplitudes of the order of micrometers are observed when amorphous In1−xGaxSb alloys are explosively crystallized at temperatures Tt near the critical minimum transformation temperature T*. The thermal instability vanishes at higher values of ΔT=(Tt−T*) and the films exhibit only a uniform small scale roughness. For intermediate ΔT values, the amplitude of the undulations decreases with increasing ΔT. Transmission electron microscopy results indicate that the surface undulations are due to density differences in alternating regions of polycrystalline material with an average grain size of the order of 100 nm and regions of amorphous or very fine grained polycrystalline material. The uniform small scale surface roughness obtained at large ΔT was produced by complete surface melting followed by rapid quenching.
A differential pressure-rise method for measuring the net outgassing rates of a solid material and for estimating its characteristic values as a gas source
Authors: Yoshimura Nagamitsu
Published: July 2002

A differential pressure-rise method for measuring net outgassing rates of solid materials is introduced, which has an outstanding advantage in that the error due to chamber walls and the vacuum gauge is much reduced. The differential method was successfully applied to measuring net rates of solid materials. The net rate K per unit surface area of a solid material at a pressure P could be practically expressed as K=K0(1−P/Px), where the characteristic values Px and K0 are estimated by measuring two net rates at two different pressures.