bluuebunny/crossref_metadata_2025 huggingface dataset:
Experiments on eliminating spherical aberration in electron guns using aspherical mesh lenses
Authors: van Gorkum A. A. , Beirens L. C. M.
Published: July 2002

Experiments on electron lenses incorporating aspherical meshes are described. Two guns with adjustable position of the aspherical mesh were constructed. In the first, the gap between the mesh and the focus electrode was variable; in the second, the gap was fixed and the mesh could be positioned relative to this gap. It was possible to change the spherical aberration from the usually positive value to zero or even to a negative value. This was verified by calculations. Spot size reductions by a factor of 3 were observed at the highest currents around 5 mA. The minimum spot sizes were obtained for a negative spherical aberration of the lens, which compensates the positive aberration of the object.
Thin-film formation using single-grid ion-beam sputtering
Authors: Nishimura Chikara , Yanagisawa Keiichi , Tago Akio , Toshima Tomoyuki
Published: July 2002

This paper discusses fundamental characteristics of a single-grid ion-beam sputtering system as well as indicating the optimum aperture dimensions and transparency of a grid. With an optimum thickness and aperture size, a high deposition rate of over 90 nm/min and a grid lifetime of over 10 h were obtained at an accelerator voltage of <600 V. The effect of the accelerator voltage or the beam current on the thin-film properties were investigated and it was clarified that films prepared with a lower accelerator voltage or lower beam current are likely to become amorphous.
Outgassing tests on thick plasma-sprayed TiC coatings for fusion applications
Authors: Terreault B. , Boucher C. , Andrew P. L. , Haasz A. A. , Brunet C. , Dallaire S.
Published: July 2002

TiC coatings of 300-μm thickness produced by plasma spraying have been tested for their outgassing properties from room temperature to 1000 °C, to assess their suitability as high-heat/particle flux protective surfaces in tokamaks. The coatings were found to contain the following approximate amounts of gas (in mol %): H2, 0.9; H2O, 0.7; CO, 0.05; Ar, 0.01; CO2, 0.03, and lesser amounts of N2 and hydrocarbons. The experimental uncertainties are estimated to be ±25%. Whereas argon outgasses totally at room temperature and water vapor mostly below 100 °C, the other gases require much higher temperatures. This material, baked only at ≤100 °C, would be acceptable with respect to the base vacuum of a tokamak; however high-temperature baking is recommended from the viewpoint of recycling and impurity control.
Isothermal desorption spectroscopy of CO from epitaxial (111) Pd/mica films
Authors: Gotoh Y. , Vook R. W. , Morales De La Garza L. , Pan Y.
Published: July 2002

An isothermal desorption spectroscopy study of carbon monoxide adsorbed on clean, vapor deposited, epitaxial (111) Pd films grown on mica was carried out using Auger electron spectroscopy (AES) techniques. Saturation CO coverages were obtained at room temperature and followed by AES peak-to-peak height measurements as a function of time at elevated temperatures ranging from 90 to 130 °C. Data analysis was carried out using first-order kinetics that yielded an activation energy for desorption Ed =24.0±0.3 kcal/mol. This value was found to apply to surface coverages ranging from saturation down to a few percent of saturation at the higher temperatures used. Previous studies by others on (111) Pd surfaces using flash desorption and contact potential methods have shown that at low coverage the desorption energy is ∼34 kcal/mol; but that as saturation coverage is approached, the desorption energy drops sharply to 22–24 kcal/mol. The present isothermal annealing results on epitaxial thin films are thus in agreement with previous near saturation coverage results using different methods. However, the present work indicates a constant desorption energy as the coverage decreases to values that are small fractions of saturation.
Organic films containing metal prepared by plasma polymerization
Authors: Kashiwagi K. , Yoshida Y. , Murayama Y.
Published: July 2002

The organic films containing metal particles were prepared by rf ion plating system. The metal was evaporated during plasma polymerization of organic monomer, in order to make polymer–metal composite materials. The organic films containing metal obtained was observed by transmission electron microscopy to study the structures, and measured by x-ray photoelectron spectroscopy to find the ratio of components. These films were found to have mixed metal and metal carbide. Moreover, these films showed the characteristics of semiconductorlike electrical properties.
Near-surface disorder studied with slow positrons
Authors: Vehanen A. , Huttunen P. , Mäkinen J. , Hautojärvi P.
Published: July 2002

We report on measurements of the distribution of open-volume defects in regions close to solid surfaces. Data are obtained by analyzing the fraction of implanted positrons which diffuse back to the entrance surface as a function of the incident positron energy. The method is applied to detect damage profiles of clean metal surfaces in ultrahigh vacuum, sputtered with keV Ar+ and N+2 ions. The extracted vacancy-type defect distributions have a surface peak typically 10–30 Å wide, with a tail extending down to ∼100 Å. The dependence of defects on various sputtering parameters and annealing treatment is discussed, and we also observe strong interaction between defects and sputtering particles. The results are compared with molecular dynamics and binary collision simulations. Furthermore, we have grown epitaxial Ag/Cu(111), Ag/Ag(111), Cu/Ag(111), and Cu/Cu(111) structures in situ. Defects at the interface and in the overlayer are studied in different growth conditions. Significant open-volume defect concentrations were recorded only in the Cu/Ag(111) system at Cu thicknesses 10–1000 Å. Evaporation on sputtered surfaces resulted in a partial loss of defects, and we also observed an enhanced level of interdiffusion.
Experimental studies of the electronic structure of I–II and I–III intermetallic compounds with B32 (Zintl) structure
Authors: Curelaru I. M. , Din K.-S. , Jang G.-E. , Chen L.-G. , Wall E. , Susman S. , Brun T. O. , Volin K. J. , Koch E.-E. , Horn K. , Ghijsen J. , Johnson R. L.
Published: July 2002

Photoemission and electron energy-loss data are reported for a series of I–II and I–III intermetallic compounds with B32 (Zintl) structure (LiAl, LiGa, LiIn, and LiZn). The structure of the valence band of LiAl, LiGa, and LiIn agrees well with theoretical relativistic augmented plane-wave (RAPW) band-structure calculations, while LiZn deviates appreciably from theory. Binding in Zintl phases is confirmed to be achieved through s-to-p charge promotion at both Li and the second metal, rather than by Li–Me(II, III) charge transfer. The rich near-edge x-ray absorption fine structure at the Li-1s absorption edge, and an interband transition observed in electron-energy loss spectra also support the RAPW predictions for the structure of the empty band. The plasmon energy in LiAl is equal to that calculated for free electrons, and its value is insignificantly affected by the defect structure of the LiAl lattice.
How CO guides surface reactions
Authors: Akhter S. , White J. M.
Published: July 2002

The role of CO in guiding surface processes in coadsorbed layers is discussed. Structural control and site blocking are two important mechanisms through which CO influences surface processes. Representative examples from CO oxidation, CO+H coadsorption, CO+NO reaction, and CO+hydrocarbon coadsorption are used to illustrate the two mechanisms.
Electronic structure of Pd thin films on the Al(110) surface
Authors: Xu Mingde , Smith R. J.
Published: July 2002

The electronic structure of thin epitaxial Pd films on Al(110) was studied as part of an investigation of the role of the substrate in modifying the electronic structure of supported thin metallic films. Ultraviolet photoemission spectroscopy was used to monitor the development of the Pd d bands as a function of overlayer thickness. Auger electron spectroscopy and low-energy electron diffraction were used to characterize the structure of the overlayer. For submonolayer coverage of Pd a narrow band of Pd-derived d states is observed 4.8 eV below the Fermi level EF. This band shifts to lower binding energy and broadens into a bulklike Pd density of states with increasing Pd coverage. A model for the electronic origin of this behavior is discussed. In some respects the Pd monolayer on Al(110) resembles the theoretical ideal of a free, unsupported monolayer, in contrast with the case for Pd on various noble and transition-metal substrates, and thus provides a means of further probing the nature of substrate–overlayer interactions in bimetallic thin-film interfaces.
The change in Si–Al bonding with metal coverage at the Si(111)√3×√3–Al interface
Authors: Nelson J. S. , Batra Inder P. , Fong C. Y.
Published: July 2002

The self-consistent pseudopotential method is used to study the change in the bonding properties of the Si(111)(3)1/2×(3)1/2–Al interface as a function of Al coverage. For Al coverages of (1)/(3) , (2)/(3) , and 1 monolayer total energies, total charge densities and work functions are reported. We find, with the Al atom absorbed in a threefold site, that as the metal coverage increases the Si–Al chemisorption bond weakens, due to an outward relaxation of the Al overlayer, with a corresponding increase in the metallic character of the Al overlayer. We also find that at monolayer coverage the Al atom favors the less coordinated on-top site over the threefold site.
Laser enhanced adhesion of copper films to sapphire substrates
Authors: Pedraza Antonio J. , Godbole Mukund J. , Kenik Edward A. , Lowndes Douglas H. , Thompson James R.
Published: July 2002

Strongly adherent films of copper on sapphire can be grown by discrete and sequential sputter depositions alternating with pulsed laser treatment (PLT). In this work the influence of various processing parameters on the film adhesion and morphology are analyzed. Ultraviolet excimer lasers produce less damage to metallic films than do other visible or infrared pulsed lasers. However, the laser energy density must be carefully controlled in order to prevent excessive evaporation or film damage. Film damage and separation from the substrate are likely to occur during PLT if the initial copper films are thicker than 80 nm. Transmission electron microscopy reveals the formation of an intermediate copper/alumina compound in a 30-nm-thick film grown in two steps (10 nm+PLT+20 nm+PLT). The regions of strong copper–sapphire bonding and good thermal contact that are established in the early stages of the sequential deposition process, and that are maintained during the subsequent process of building up a thick, adherent copper film, most probably consist of this intermediate compound.
Diode and hollow cathode etching in CF4
Authors: Davies K. E. , Horwitz C. M.
Published: July 2002

The voltage and power input requirements of some hollow cathode and single-target (diode) systems are compared, using CF4 etch gas. Hollow cathodes can be confined more effectively than diode systems, with an etch rate improvement of a factor of 15 over the diode being obtained at a fixed target voltage and 1 Pa pressure. In addition, the hollow cathode is roughly three times more power efficient than the diode. Etch rate results between 0.5 and 30 Pa CF4 pressure, and at various target voltages, are presented. Pressure probe measurements taken over the active discharge area show similar behavior to our etch rate results, with large pressure gradients being observed in the guard-confined hollow cathode.
Surface phonon dispersion curves via thermal energy atom scattering: He atoms on RbCl(001) surface
Authors: Chern G. , Brug W. P. , Safron S. A. , Skofronick J. G.
Published: July 2002

A thermal energy atom scattering instrument, employing a time-of-flight technique to observe inelastically scattered He atoms, has been used to measure the surface phonon dispersion curves of the RbCl(001) surface. Data were collected over the entire Brillouin zone for a target temperature of 115 K and incident He wave vector of ki ≊7 Å−1. The results for the 〈100〉 and 〈110〉 high-symmetry directions are in good agreement with theoretical predictions based on a slab dynamics model calculation. Relaxation effects of the surface are negligible for this crystal.
Laser irradiation of polyethylene oxide
Authors: Yang M. , Fang S. J. , Salovey R. , Allen S. D.
Published: July 2002

The temperature profiles in polyethlene oxide (PEO) films on a soda lime glass substrate heated by scanning a continuous wave (cw) CO2 laser beam are calculated by finite element methods. The volumetric heating rate in the irradiated film depends on the total power of the laser, the radius of the illuminated spot and the scan rate, as well as film parameters such as absorption depth, density, heat capacity, and thermal conductivity (Ref. 1). The absorption depth in PEO at a wavelength of 10.6 μm is less than, but comparable to the thickness of the the PEO film (40 μm). Therefore, heat loss from the bottom surface of the polymer film cannot be neglected. The thickness of the glass substrate

is much greater than that of the PEO, so that heat loss from the bottom surface of the glass may be neglected. We use a coordinate system fixed in the material. The beam is parallel to the z axis and scans continuously along the x direction with velocity v (Fig. 1). A time dependent temperature profile on the surface, along the trajectory of the beam center, is shown in Fig. 2. Comparison of calculated temperature profiles and the shapes of PEO spherulites in the zone refined polymer enable us to elucidate melting, nucleation, and recrystallization under laser irradiation (Refs. 2 and 3).
A bolt-on deposition source for ultrahigh vacuum growth of intermetallic compound films
Authors: Shuh David K. , Kim Young K. , Williams R. Stanley
Published: July 2002

An 8-in. ConFlat■ flange assembly with both an electron beam evaporator and a Knudsen cell has been constructed to deposit intermetallic compounds containing transition and group-III metals with specific phase composition. Initial depositions of thin films using this design have shown excellent epitaxy with the desired compound stoichiometry.
On the multiple fracture of low-elongation thin films deposited on high-elongation substrates
Authors: Wojciechowski P. H. , Mendolia M. S.
Published: July 2002

The multiple fracture of brittle, low-elongation thin films adhering to high-elongation plastic substrates subject to uniaxial strain is addressed. Results are presented for Permalloy on Kapton. It is observed that crack density in the film increases dramatically immediately after crack onset and subsequently approaches an asymptotic value with substrate strain. Thicker films experience crack onset earlier, and their asymptotic crack densities are lower than with thinner films. To provide some theoretical basis for the observed phenomena, the relevant literature is summarized. An empirical model is developed that fits the data obtained in this study and agrees with the results obtained by others as well. An attempt is made to mechanistically model the problem using a modified shear-lag theory developed initially for bulk composite materials. It is shown that the shear-lag model has potential application to this problem and needs further investigation.
Scanning tunneling microscopy observation of MoS2 surface and gold clusters deposited on MoS2 surface
Authors: Ichinokawa T. , Ichinose T. , Tohyama M. , Itoh H.
Published: July 2002

Gold islands deposited on MoS2 surface were studied many years ago by transmission electron microscopy connected with the surface defects. The present experiment has been carried out for confirmation of these results by scanning tunneling microscopy with atomic resolution. The samples of MoS2 cleaved surface and gold clusters decorated on MoS2 were investigated at a vacuum pressure of 10−6 Torr by a scanning tunneling microscope (STM) combined with a scanning electron microscope (SEM). As results, a point defect on the MoS2 surface, an effect of the surface step on island nucleation, a correlation of atomic structures between a gold thin crystal and the substrate and movement of gold clusters on the MoS2 surface during STM observation are demonstrated. Some discussions on these results are presented in reference to the previous reports by transmission electron microscopy.
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u, real-time monitoring of electrode surfaces by scanning tunneling microscopy. III. Surface structure of Pt and Pd electrodes
Authors: Uosaki Kohei , Kita Hideaki
Published: July 2002

Pt and Pd electrodes were monitored by STM in situ in real time. In the case of Cu deposition on Pd, small domains of Cu were first formed and they gradually merged to form terraces. The surface finally became relatively smooth. Surface structure change of Pt electrode during oxide formation/reduction was also investigated. Growth of parallel ridge and domelike structures was observed.
Modeling of the SiC chemical vapor deposition process and comparison with experimental results
Authors: Annen K. D. , Stinespring C. D. , Kuczmarski M. A. , Powell J. A.
Published: July 2002

A model of the NASA Lewis SiC-chemical vapor deposition (CVD) process is described and the results presented. A key feature of the model is the direct coupling of gas phase chemical kinetics with diffusion. A deposition chemistry model using reactive sticking coefficients for each gas phase species provides the diffusion boundary conditions. Chemical characteristics of the SiC CVD process are discussed and a comparison between predicted and experimentally observed deposition rates is made. SiC deposition rates predicted by the model agree reasonably well with the observed rates. Qualitative agreement for deposition rate dependence on velocity is obtained, although lack of agreement on details of the behavior indicate that improvements in the fluid dynamic model are needed.
Surface phonon modes of the NaI(001) crystal surface by inelastic He atom scattering
Authors: Brug W. P. , Chern G. , Duan J. , Safron S. A. , Skofronick J. G. , Benedek G.
Published: July 2002

The present theoretical treatment of the surface dynamics of ionic insulators employs the shell model with parameters obtained from bulk materials. The approach has been generally very successful in comparisons with experiment. However, most of the experimental surface dynamics work has been on the low-mass alkali halides with very little effort on higher energy modes or on the heavier alkali halides, where effects from relaxation might be important. The work of this paper explores these latter two conditions. Inelastic scattering of He atoms from the 〈110〉NaI(001) surface has been used to obtain the acoustic S1 Rayleigh mode, the S6 longitudinal mode, and the S8 crossing mode, however, no gap S4 optical mode was seen. The results compare favorably with reported theoretical models employing both slab calculations and the Green’s function method thus indicating that bulk parameters and the shell model go a long way in explaining most of the observations.
Tunneling spectroscopy on an organic superconductor (BEDT-TTF)2Cu(NCS)2
Authors: Bando H. , Kashiwaya S. , Tokumoto H. , Anzai H. , Kinoshita N. , Kajimura K.
Published: July 2002

We have constructed a scanning tunneling microscope that is capable of operation at low temperatures. Spectroscopic measurements were performed on single crystals of an organic superconductor, κ-(BEDT-TTF)2Cu(NCS)2, at temperatures between 1.8 and 12 K. Current-voltage characteristics measured well below the superconducting critical temperature Tc=11 K clearly showed superconducting energy gap, though the tip was supposed to be in contact with the sample surface. Its magnitude and temperature dependence were comparable to the value according to the Bardeen–Cooper–Schrieffer theory. Line shape of differential conductance dI/dV, however, tended to deviate from the shape according to the theory. Current-voltage characteristics typical of charging effect were also observed.
Trimethylgallium dissociative chemisorption on gallium-rich GaAs(100) surfaces
Authors: Creighton J. Randall
Published: July 2002

Trimethylgallium (TMGa) chemisorption on the gallium-rich ‘‘(4×6)’’ and (1×6) GaAs(100) surfaces has been studied with temperature programmed desorption (TPD) and static secondary ion mass spectroscopy (SSIMS). Low coverages of TMGa irreversibly dissociate on GaAs(100) and methyl radicals are the main gas-phase product observed around 700 K during TPD. At higher TMGa coverages some recombinative desorption of molecular TMGa occurs from 250–650 K. On the Ga-rich surface reconstructions the desorbing methyl radicals are kinetically indistinguishable, strongly suggesting that they evolve from a single type of binding site. We believe this binding site corresponds to surface MMGa, which is formed by stepwise methyl group transfer from chemisorbed TMGa to neighboring surface gallium atoms. The presence of MMGa is supported by SSIMS results at ∼650 K. Temperature-programmed SSIMS was used to follow the dissociation of adsorbed TMGa from 120 to 700 K.
Synthesis of Pd–Te intermetallic compound films on 2H–MoS2(0001) by molecular beam epitaxy
Authors: Yata Masanori , Nakamura Keikichi , Ogawa Keiichi
Published: July 2002

A successful attempt to grow the Pd–Te intermetallic compounds on 2H–MoS2(0001) surfaces by molecular beam epitaxy will be reported. When a Te2 molecular beam alone impinges onto the 2H–MoS2(0001) substrate, the sticking coefficient is found to decrease with increasing substrate temperature (Ts) and to become zero at Ts≥470 K. The sticking coefficient of the Te2 molecules impinging simultaneously with a Pd beam, however, is finite even at temperatures above 470 K. Under the simultaneous impinging condition, three kinds of intermetallic compounds: PdTe2(001), PdTe(001), Pd9Te4(010) are found to grow heteroepitaxially. The phase formed in the film depends on the flux ratio and the substrate temperature. The resultant phase diagram is explained quantitatively by considering a capture rate of Te molecules by the arriving Pd atoms.
Chemical vapor deposition TiN coating on silicon carbide coated boron fibers
Authors: Tan Beng Jit , Hwan Luchen , Suib Steven L. , Galasso Francis S.
Published: July 2002

TiN was deposited as a coating onto SiC coated B fiber from TiCl4 and NH3 by chemical vapor deposition technique at 650 °C. Several analytical techniques such as scanning electron microscopy (SEM), x-ray photoelectron spectroscopy, and x-ray diffraction were employed to study the TiN coating and the coating-fiber interface. The bulk of the coating is TiN with small amounts of titanium oxynitride. Depth profile by Auger electron spectroscopy showed that the diffusion zone of the TiN coating into the fiber is narrow, which indicates weak interfacial bonding. The structural morphology, as revealed by SEM, shows a globular structure transforming into a star-shaped morphology down the length of the fiber. Finally, the TiN coated fibers showed higher tensile strength than the as-received fiber.
Coverage dependent surface photovoltage induced by synchrotron radiation at metal/GaAs interfaces
Authors: Mao D. , Kahn A. , Marsi M. , Margaritondo G.
Published: July 2002

Contact potential difference measurements of synchrotron radiation-induced surface photovoltage (SPV) are performed on GaAs(110) as a function of metal coverage and temperature. On low doped n-samples, the low temperature SPV (0.55 eV) is almost equal to the total band bending at submonolayer coverage and discharges with a time constant of hours. Above a monolayer, the rate of discharging increases dramatically, emphasizing the role of charge leakage through the overlayer. The room temperature SPV is considerably smaller (0.2 eV) and its coverage dependence does not correlate with that of band bending. A metal-dependent enhancement of SPV is found. No significant SPV is detected on highly doped p-GaAs.
Rutile-type TiO2 formation by ion beam dynamic mixing
Authors: Miyake S. , Honda K. , Kohno T. , Setsuhara Y. , Satou M. , Chayahara A.
Published: July 2002

A compact dynamic mixing system with a bucket type electron cyclotron resonance (ECR) ion source is used for the formation of oxide films. The oxygen ion energy can be varied between 1 and 25 keV with sufficient current density for the oxide film formation. Titanium oxide films were prepared by Ti evaporation and O2+/O+ ion beam bombardment onto Si wafers and quartz plates. X-ray diffraction (XRD) of films prepared at about 3×10−3 Pa presents polycrystal rutile structure of TiO2 alone and the crystallization is influenced by ion energy and its arrival rate. Rutherford backscattering spectroscopy of these films indicates that the film composition has stoichiometry of TiO2 with or without ion bombardment. The composition is greatly affected by the background cold O2 flow onto samples and at about 3×10−4 Pa the film shows the structure of TiO by ion bombardment.
Molecular beam deposition of Dy1Ba2Cu3O7−δ(001) high-temperature superconductor thin films
Authors: Bae J. , Seshadri P. , Choudhary K. M.
Published: July 2002

Epitaxial Dy1Ba2Cu3O7−δ(001) high-temperature superconductor thin films on LaAlO3 substrates have been prepared by coevaporation of Dy, BaF2, and Cu and postannealing. The vapors in desired ratio were evaporated from effusion cells in a miniature molecular beam deposition system. The films show critical transition temperature (Tc,0) of 89.5±0.5 K. During process development it was found that single phase Dy1+xBa2−xCu3Oy(001) thin films can be grown (x=0 to 0.3). Their electrical properties were useful in calibration of quartz crystal thin film thickness monitor (FTM) for determination of relationships between the actual vapor arrival rate (flux) and FTM reading.
Plasma assisted chemical vapor deposition on ‘‘three-dimensional’’ substrates
Authors: Halverson Ward , Vakerlis George D. , Garg Diwakar , Dyer Paul N.
Published: July 2002

A novel plasma assisted chemical vapor deposition reactor forms ceramic coatings on ‘‘three-dimensional’’ surfaces of complicated parts such as cutting tools and bearing surfaces. The reactor chamber features a unique rf-driven electrode configuration to establish uniform, large volume, low temperature plasmas from which the coatings are deposited. Highly adherent silicon nitride coatings formed from silane/ammonia/argon plasmas have hardness values up to 30 GPa. Variations of methane/silane feed gas ratios produce microcrystalline silicon carbide films with C/Si atomic ratios ranging from 0.4 to 3; the coatings consist of free Si and stoichiometric SiC; SiC, free Si and diamond-like carbon (DLC); or SiC and DLC, depending on the methane/silane fraction. Hardness varies monotonically between about 10 and 60 GPa as the carbon fraction increases. SiC coatings significantly reduced wear rates in abrasive wear tests; Si–SiC coatings effectively protected molybdenum samples during a 180 h oxidation test in 650 °C air.
Deposition temperature dependence of the deep defect density for a-Si:H films grown by electron cyclotron resonance microwave plasma
Authors: Essick J. M. , Pool F. S. , Shing Y. H.
Published: July 2002

The dependence on deposition temperature of the mobility gap density of states has been determined for hydrogenated amorphous silicon (a-Si:H) films grown by electron cyclotron resonance (ECR) microwave plasma chemical vapor deposition (CVD). A minimum in the integrated deep defect density of 1×1016 cm−3 was found to occur at a temperature of approximately 250 °C, while an Urbach slope minimum of 52 meV was observed at 175 °C under our deposition conditions. Based on these measurements the ECR-grown films were found to be of excellent device quality and comparable to a-Si:H films grown by rf plasma-enhanced CVD.
Direct current bias as an ion current monitor in the transformer coupled plasma etcher
Authors: Ra Yunju , Chen Ching-Hwa
Published: July 2002

Independent of plasma generation, ion energy can be controlled by applying rf power to a substrate in the transformer coupled plasma etcher. Due to high plasma density of the plasma source, most of rf power to the substrate is confined within the sheath region and used in accelerating ions. This enables development of a simple equation correlating dc bias and ion current density. Based on this equation, ion current densities for different plasma conditions have been measured. The results show good agreement with Langmuir probe measurements.
Computer solution to chamber-gas fractionation during pumpdown
Authors: Santeler Donald , Warren David
Published: July 2002

The evacuation process of a gas mixture in the molecular flow range is characterized by the fact that each gas type is separately pumped at its own respective pumping speed. Since the pumping speeds for most high-vacuum pumps depend on the individual gas type and, further, since the molecular gas-flow conductance is dependent on the inverse square-root-of-mass behavior, gas fractionation occurs. This merely means that the gases which have higher pumping speed are removed faster leaving the gases with lower speed as the predominant residuals. By far, the most common occurrence of gas fractionation is during the evacuation of almost every high-vacuum system. While gas fractionation is most predominant in the molecular flow range, it also occurs in the transition range where the gas-flow behavior is mathematically more complex. The net result of gas fractionation is that the relative composition of the residual gas in the vacuum system steadily changes with time during pumpdown. Since the mathematical aspects of gas fractionation are well established, it seems reasonable that this phenomenon should be simulated in modern computer programs which otherwise simulate the normal vacuum system behavior of gas flow as a function of pressure and of system pressure as a function of time. This article discusses some of the complex interacting problems as well as a final solution which was applied to a specific commercial vacuum-system-design computer program, VSD-II.
Surface and interface effects in WSi2 formation
Authors: Duchateau J. P. W. B. , Kuiper A. E. T. , Lathouwers E. G. C. , Reader A. H.
Published: July 2002

We studied the influence of a thin Fe interface layer between W and the substrate Si and of a surface W–oxide on the formation kinetics of WSi2. Auger depth profiling, Rutherford backscattering spectrometry and x-ray diffraction have been used to investigate the reaction between the layers and the Si substrate. W layers with a thickness of 20 nm were deposited by electron beam evaporation on HF dipped Si(100) samples. If deposition and subsequent annealing are performed in ultrahigh vacuum, the complete conversion of a W layer into tetragonal WSi2 occurs within 1 h at 800 °C. The intercalation of a 5 nm-thick Fe layer between the W layer and the substrate reduces the conversion temperature to 650 °C. Ironsilicide is formed at a relatively low temperature. This silicide acts as a medium through which Si can easily diffuse towards the surface, thus maintaining a fast Si supply to the W layer. This experiment indicates that reactions at the metal/Si interface are rate determining in the formation of WSi2. Both with and without an Fe intermediate layer, the reaction proceeds via the migration of Si to the film surface followed by the formation of WSi2 at the surface. Continuation of the reaction occurs from the surface to the substrate. Furthermore, we found that the presence of a native oxide layer at the W surface retards the reaction between W and Si. Oxygen migrates via the open structure of the W film to the interface where it probably forms a thin SiO2 layer that hampers the transport of Si into the W film.
Effect of surface re-emission on the surface roughness of film growth in low pressure chemical vapor deposition
Authors: Singh Vivek K. , Shaqfeh Eric S. G.
Published: July 2002

For films deposited by low pressure chemical vapor deposition (LPCVD) the effect of roughness in the underlying substrate on film microstructure is investigated by computer simulation. Previous workers have assumed a normal surface velocity related to the local surface curvature; however, transport in many LPCVD systems has been shown to be governed by surface re-emission of the deposition precursors with a single sticking coefficient. In this article, the dependence of film profile evolution on both the sticking coefficient of the precursors, as well as the wave number of the underlying roughness is demonstrated. All wave numbers are shown to grow in the small time regime, for all values of the sticking coefficient except zero. At longer times, the mechanism of cusp formation is shown to arrest this growth for small but finite values of the sticking coefficient. In the limit that the sticking coefficient approaches zero, a simple geometric model for profile evolution is developed to accurately predict both the time required for cusp formation, as well as the maximum rate of decay of roughness. All wave numbers grow for large values of the sticking coefficient, eventually leading to the formation of a columnar microstructure with voids. For the sticking coefficient equal to unity, small geometric perturbations on the starting surface are shown to grow into asymptotic columns. Pair interactions between adjacent, unequal perturbations are studied, and larger columns are found to ‘‘shadow’’ smaller columns. For low values of the sticking coefficient, these interactions result in slowing down the decay of surface roughness by an effective halving of the wave number. The conclusions obtained from simulating deposition on periodic, sinusoidal surfaces are shown to be useful in understanding deposition on statistically rough surfaces.
Chlorine-enhanced F-atom etching of silicon
Authors: Coburn J. W.
Published: July 2002

Reactive ion etching processes, currently in use in microstructure fabrication, often use more than one feed gas and more than one reactive etching specie. An example is the use of gases containing both chlorine and fluorine. These processes have been developed empirically with little understanding of the detailed surface science. Directed beam measurements have been carried out using mixed chlorine-fluorine chemistries and an unexpected enhancement of the F-atom etching of Si by molecular chlorine has been observed.
Miniature cryosorption vacuum pump for portable instruments
Authors: Piltingsrud Harley V.
Published: July 2002

This article describes the design, construction, and laboratory testing of a low power, low-weight, and compact cryosorption vacuum pump for backing, roughing, or other intermediate pressure applications. Novel features of this pump include a high-temperature, low-pressure desorption cycle allowing useful pumping capacities of many gases at 77 K, and the use of a miniature cryorefrigerator. The laboratory test pump used a cold finger cooled by a single stage helium Stirling cycle refrigerator having a 1 W capacity at 70 K, weighing between 1.6 and 2.0 kg, and consuming less than 45 W of electrical power. Calculations show that pumping rates for N2 at 1×10−4 Torr could be up to 10 Torr ℓ s−1 short-term, and approximately 0.5 Torr ℓ s−1 continuously. Our laboratory working model showed that it was possible to pump at pressures down to approximately 2×10−5 Torr using a type 5A molecular sieve. Pumping rates for air of up to 5 Torr ℓ min−1 were achieved. Using desorption at 363 K and 2×10−1 Torr, the capacity of type 5A molecular sieve was determined to be approximately 16 Torr ℓ g−1 at 1×10−4 Torr. It is anticipated that such a pump would be useful in certain portable instruments such as portable gas chromatograph-mass spectrometers used for occupational health applications, or other applications where weight, available power, and pumping requirements were compatible.
CO2 laser chemical vapor deposition of silica films in a parallel configuration: A study of gas phase phenomena
Authors: Fernández D. , González P. , Pou J. , García E. , Serra J. , León B. , Pérez-Amor M. , Garrido C.
Published: July 2002

Low-temperature silicon oxide films were successfully grown using SiH4–N2O mixtures by a continuous wave-CO2 laser tuned at 10.6 μm in a parallel configuration. The reaction was initiated by high gas temperatures obtained as a result of multiple successive absorption of photons by silane molecules, followed by energy redistribution through intermolecular collisions. The study of film growth rate and properties as influenced by both total gas pressure and substrate temperature for a gas mole ratio φ=PN2O/PSiH4=30 demonstrated that peak gas temperature controls the deposition rate, revealing that the process is driven by gas phase reactions. For the process, apparent activation energy was determined to be 45 kcal/mol, and apparent overall order of the reaction m=−1.5. The gas temperature distribution was calculated by means of a steady-state energy balance in the gas volume, explaining very well the experimental growth rates and the properties of the obtained films.
Application of dynamic in situ ellipsometry to the deposition of tin-doped indium oxide films by reactive direct-current magnetron sputtering
Authors: Fukarek W. , Kersten H.
Published: July 2002

The application of dynamic in situ ellipsometry to the monitoring of the deposition of transparent indium tin oxide layers by reactive direct-current magnetron sputtering in Ar/O2 gas mixtures is described. The dependence of the refractive index and the deposition rate on the discharge power and on the oxidation state of the target show that the state of the target is the essential parameter for the production of indium tin oxide films with the desired properties. The sputter yield of the pure In:Sn alloy exceeds that of the oxide by a factor of about 6. The film growth species in the case of an oxidized target are In2O molecules or oxide clusters rather than metal atoms.
Electron beam effects on (CH2)17 self-assembled monolayer SiO2/Si specimens
Authors: Baer D. R. , Engelhard M. H. , Schulte D. W. , Guenther D. E. , Wang Li-Qiong , Rieke P. C.
Published: July 2002

This paper examines the damage created by an electron beam on layered specimens consisting of a (CH2)17 self-assembled monolayer (SAM) deposited on an oxidized Si wafer. Beam effects on both the SAM and substrate were observed. X-ray photoelectron spectroscopy (XPS) measurements indicate that less than 20% of the carbon from the film is lost during the beam damage, ion analysis shows hydrogen emission from the films, and residual gas analysis suggest loss of some CHx (x=2–4) molecules. Consistent with the conversion of some (CH)n chains to ‘‘graphite,’’ the C 1s photopeak is broadened by the electron beam. In addition to the effects on the SAM layer, there are shifts for the O 1s and oxidized-Si2p binding energies due to the electron beam exposure. Studies on SiO2 films formed in a wide variety of ways, without the SAM, show similar effects. These shifts are attributed to changes in potential at the Si–SiO2 interface.
Comparative study of Ni ultrathin film grown on Pt(110)-(1×1) and -(1×2) at 130 K
Authors: Tsay J. S. , Fu Tsu-yi , Tsai P. S. , Shern C. S.
Published: July 2002

The growth mode of a nickel thin film on Pt(110)-(1×1) and Pt(110)-(1×2) surfaces was studied by low-energy electron diffraction (LEED) and Auger electron spectroscopy at a temperature of 130 K. From the results of Auger uptake curves and the intensity profiles of LEED spots, we conclude that the growth of Ni on the Pt(110)-(1×1) surface follows the Volmer–Weber mode, while the Pt(110)-(1×2) surface follows the Stranski–Krastanov mode. The mechanism of the different growth behaviors is discussed.
Study of the structure of the Rh/Ag surface using positron annihilation induced Auger electron spectroscopy
Authors: Yang G. , Yang S. , Kim J. H. , Lee K. H. , Koymen A. R. , Mulhollan G. A. , Weiss A. H.
Published: July 2002

Positron annihilation induced Auger electron spectroscopy (PAES), electron induced Auger electron spectroscopy (EAES), and low-energy electron diffraction have been used to study the temperature dependent composition of vapor-deposited of Rh on Ag(100). Earlier work using AES, ion scattering spectroscopy, and TDS has shown that a Ag layer diffuses to the Rh surface upon annealing to form a structure in which Rh is sandwiched between a Ag cap layer and the Ag substrate. In this work, the top layer selectivity of PAES was utilized to study the diffusion of Ag to the surface as Rh films deposited at 173 K were heated to 573 K. Analysis of the PAES spectra indicates that Rh remains in the top layer during the ∼3 h required to take PAES data when the sample is maintained at the 173 K temperature of deposition. There is a clear indication that significant migration of Ag to the surface takes place by 373 K. The Ag content of the top layer increases to approximately 100% above 473 K.
In situ electron cyclotron resonance plasma surface cleaning of silicon
Authors: Hu Y. Z. , Buaud P. P. , Spanos L. , Wang Y. Q. , Li M. , Irene E. A.
Published: July 2002

An argon electron cyclotron resonance plasma has been applied to the SiO2/Si system, in order to investigate the SiO2 film etching reaction and the Si surface damage using in situ spectroscopic ellipsometry (SE) and single wavelength ellipsometry. Ex situ atomic force microscopy was used to characterize the surface morphology and compare with SE results. Experiments included a range of ion dose rates from 3×1015–2×1016 ions/cm2 s, at substrate temperatures of floating temperature (<100 °C) and 700 °C, and doses from 1016–1019 ions/cm2 at low ion energies from 0 to 100 V dc bias. Etch rates of about 20 nm/min for SiO2 have been achieved at −50 V bias. At floating temperature a critical minimum ion energy for removal of the oxide is about −25 V bias, and the damage includes a roughness layer and an interface amorphous layer which increased with ion energy. At 700 °C no amorphous layer was observed and the Si roughness layer varied with the ion dose from 0.4 to 30 nm for 1017 and 1019 ions/cm2, respectively after SiO2 removal. The determination of the optimum cleaning end point was achieved using real time ellipsometry.
Performance characteristics of an oxygen radical beam radio-frequency source
Authors: Imai Fumikazu , Kunimori Kimio , Nozoye Hisakazu
Published: July 2002

An oxygen radical beam source discharged by radio frequency was newly designed and constructed. Effects of wall materials on the optical emission intensity of the oxygen plasma and the atomic oxygen flux were measured. The optical emission intensity correlated well with the intensity of the atomic oxygen flux. An atomic oxygen flux as high as 1.4×1016 atoms/(cm2 s) was achieved at 50 mm away from an end plate, with nine orifices, of the radical beam source by using a sleeve made of pyrolytic boron nitride in the beam source.
Reactivity of Ni on oxygen-covered W(110) surfaces
Authors: Whitten J. E. , Gomer R.
Published: July 2002

The adsorption at 90 K of hydrogen, carbon monoxide, and benzene on Nin/O0.5/W(110) (with n=1–10) has been studied by thermal desorption, x-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, low-energy electron diffraction, and work function measurements. The surfaces are relatively inert to hydrogen adsorption, with estimated quasisaturation uptake being H/W=0.18 for n=1 and increasing to 0.36 for n=10. In contrast, CO and C6H6 adsorb readily on Ni1/O0.5/W(110), with saturation coverages of CO/W=0.85±0.09 and C6H6/W=0.18±0.03, respectively. These values are comparable to coverages obtainable on clean W(110), namely, CO/W=0.70 and C6H6/W=0.18. Coadsorption of Ni and O on W(110) and subsequent annealing to 500–1000 K leads to segregation of Ni and O, with the formation of Ni crystallites largely 〈111〉 oriented along the surface normal. The heights of these Ni ‘‘towers’’ can be adjusted by varying the amounts of coadsorbed oxygen and Ni. The Ni crystallites resist sintering, even when annealed at 1000 K for 3600 s. Adsorption of H2 and CO on them at 90 K was also investigated, and found to be less than expected from the estimated overall Ni surface area.
Multibounce direct scattering of N2 from Cu(110): Experiment and trajectory simulations
Authors: Siders Jennifer L. W. , Sitz Greg O.
Published: July 2002

Rotational state distributions of N2 scattered from Cu(110) were studied as a function of incident energy and surface temperature. State-selective and time resolved molecular beam techniques were used. The dependence on incident energy was found to be similar to previously studied systems while the dependence on surface temperature was found to be strong at low incident energy, becoming weaker as the incident energy is increased. Classical trajectory simulations show excellent agreement with the experimental results. In both the experiment and simulation, multiple collision trajectories play a large role in the dynamics at low incident energy and low surface temperature.
Boron nitride thin film deposition from solid borane ammonia using an electron cyclotron resonance microwave plasma source
Authors: Eddy C. R. , Sartwell B. D.
Published: July 2002

An electron cyclotron resonance (ECR) microwave plasma source has been used to deposit boron nitride thin films onto silicon substrates. Borane-ammonia (BH3⋅NH3) vapor was introduced in a controlled fashion by congruent thermal sublimation of the non-toxic white crystalline solid and resulted in the deposition of stoichiometric films without the need for additional nitrogen-bearing precursors. Deposition parameters involved a constant microwave power, substrate bias (effective ion energy) ranging from −10 to −100 V dc, and substrate temperatures ranging from 350 °C to 575 °C. The films were characterized with respect to their crystal structure, composition and nature of bonding using a variety of techniques. The crystalline structure and bonding type were weak functions of substrate bias and temperature. At modest bias (−100 V) there was evidence for the existence of the wurtzitic and/or cubic phase, but in general the films were predominantly sp2 bonded and amorphous.