bluuebunny/crossref_metadata_2025 huggingface dataset:
Photodesorption from copper-plated stainless steel at liquid-helium temperature and at room temperature
Authors: Bintinger D. , Limon P. , Rosenberg R. A.
Published: July 2002

Photodesorption yields have been measured from copper-plated stainless steel at liquid-helium temperature and at room temperature using synchrotron radiation. The copper-plated surface is a proposed inner surface for the liquid-helium temperature beam pipe of the Superconducting Super Collider (SSC). The inner surface of the SSC beam pipe will be illuminated by synchrotron radiation from 20-TeV protons. The number of H2 molecules desorbed per incident photon (ηH2) from the liquid-helium temperature surface has been measured as ∼0.018 for an accumulated photon dose of 1016 photons/cm2 and as ∼0.004 for an accumulated dose of 1018 photons/cm2. The ratio of ηH2 for the liquid-helium temperature surface to ηH2 for the room-temperature surface is ∼1.1 for an accumulated dose of 1016 photons/cm2 and is ∼2.0 for an accumulated dose of 1018 photons/cm2. Estimates of η for H2O, CO, and CO2 are also given.
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u x-ray photoelectron spectroscopy/Auger electron spectroscopy studies of 302 stainless steel annealed in humidified H2/N2 atmospheres
Authors: Cabrera A. L.
Published: July 2002

Surface characterization of 302 stainless steel samples, annealed in situ at 1040 °C in humidified atmospheres of 30% H2–70% N2, confirmed our previous surprising discovery that a nondulling Si-containing film is formed on the surface. We found that partial inhibition of N2 uptake is always observed when Si is detected on the surface and that the Si concentration is proportional to the PH2O/PH2 ratios in the annealing atmosphere. The Si film is produced when bulk Si segregates to the surface during annealing and, upon reaction with oxygen, forms SiO2. The thickness of the SiO2 film varies between 50 and 300 Å depending on the annealing time (0.5–1.3 h).
Study of direct-current, pulsed, and temperature–field emission from LaB6/tungsten field emitter
Authors: Khairnar Rajendra S. , Dharmadhikari C. V. , Joag Dilip S. , Kanitkar P. L. , Nigavekar A. S.
Published: July 2002

This paper reports dc, temperature–field (T–F), and pulsed emission from a lanthanum hexaboride (LaB6)–tungsten (W) field emitter. Various parameters are drived from the Fowler–Nordheim plots for the three configurations of the emitter, viz., clean tungsten, LaB6 overgrowth on W(111) plane (‘‘two spot’’), and LaB6 equilibrated W surface (‘‘well spread’’). The current stability is observed at 300, 730, and 850 K, (and 1065 K for well spread) under T–F operation. A comparison is made with various types of field emitting cathodes and the results are discussed from the point of view of LaB6/W field emitting cathodes.
Reflectance–difference studies of organometallic chemical vapor deposition growth transients on (001) GaAs
Authors: Aspnes D. E. , Bhat R. , Colas E. , Keramidas V. G. , Koza M. A. , Studna A. A.
Published: July 2002

Using reflectance–difference spectroscopy to follow surface coverage on a submonolayer scale, alternating trimethylgallium (TMG) and arsine flows to separate their surface-chemical effects and to eliminate gas-phase interactions, and low (330–430 °C) temperatures to eliminate gas-phase pyrolysis, we isolate and identify the different factors that kinetically limit organometallic chemical vapor deposition (OMCVD) growth on (001) GaAs by their time, pressure, and temperature dependences. When an AsH3-stabilized surface is exposed to TMG, the relative coverage by Ga-containing reacted species increases linearly in time to 80% coverage and exponentially thereafter, and exhibits a pressure dependence of classic Langmuir adsorption-isotherm form. We derive a model that quantitatively describes these features in terms of reversible excluded-volume chemisorption and subsequent irreversible decomposition of TMG at (001) surface lattice sites. Analysis of the data yields −26 and 39 kcal/mol for the chemisorption enthalpy and decomposition barrier, respectively. This model describes kinetically limited atmospheric- and near-atmospheric-pressure GaAs OMCVD growth rates not only for alternating-flow OMCVD below 450 °C but, unexpectedly, also for conventional OMCVD to temperatures at least as high as 650 °C. We show that the wide range of OMCVD activation energies reported for (001) GaAs in the literature, 13–32 kcal/mol, does not represent unusually large scatter but is a result of the actual TMG decomposition rate being determined by a combination of fractional-occupancy and decomposition-probability effects. The surprising success of this model raises serious questions about the importance of gas-phase reactions in GaAs growth by OMCVD.
An experimental study of the factors that effect ion desorption yields
Authors: Wen C.-R. , Rosenberg R. A.
Published: July 2002

Many models of photon-stimulated desorption (PSD) predict that the desorption yields resulting from the formation of two-hole or two-hole, one-electron states will increase as the effective hole–hole interaction Ueff increases and the covalent interaction V decreases. In order to investigate this effect in a systematic manner, we have studied PSD of H+, CH+3, and F+ ions from solid Si(CH3)4−nFn (n=0–4) using synchrotron radiation in the energy range 15–40 eV. The trends of the PSD desorption yields of H+, CH+3, and F+ as a function of n were determined. There is a dramatic increase in the H+ and CH+3 PSD yields as n becomes larger, while the F+ yield increases slowly as a function of n. In order to explain the results, we propose a model which considers the manner in which Ueff and V depend on the number of –CH3 and –F ligands.
Effect of carburization on diffusion and desorption properties of a La–Mo system
Authors: Sreenivasa Rao G. , Dharmadhikari C. V. , Nigavekar A. S.
Published: July 2002

The effect of carburization on diffusion properties of a La–Mo system has been investigated using Auger electron spectroscopy in conjunction with Ar+ ion sputtering. Both bulk and grain boundary diffusion is investigated: The former increases by one or two orders of magnitude after carburization, depending on the temperature, whereas the latter shows decrease by the same order. The grain boundary diffusion coefficients of La in Mo–C are approximately only two orders of magnitude higher than the corresponding bulk values in contrast to five orders of magnitude in the case of La in Mo. The results suggest that the carburization causes drastic changes in defect and morphological structures both in the grain and at the grain boundaries of molybdenum. The isothermal desorption of La from polycrystalline Mo–C is also investigated and yields values 2.56 eV and 3.0×108 s−1 of activation energy and pre-exponential factors, respectively. Comparison of the present results with that of clean La–Mo system is used to elucidate the role of carbon in the performance of a La–Mo cathode.
A multipurpose quadrupole mass spectrometer detector for surface kinetic and absolute surface coverage measurements
Authors: Smentkowski V. S. , Yates J. T.
Published: July 2002

A multipurpose mass spectrometer detector has been constructed for studies of adsorption and desorption from single-crystal surfaces in an ultrahigh vacuum system. The detector may be used for studies of the kinetics of adsorption on single crystals using collimated and calibrated molecular-beam dosers, as well as the direct measurement of the absolute sticking probability as a function of the absolute surface coverage. In addition, using a small sampling aperture for line-of-sight desorption procedures, it is possible to achieve high sensitivity for the detection of gaseous desorption products as well as condensible products. In the direct line-of-sight detection mode of operation, a desorbing free radical species has been detected. Normally, mass spectrometers used in ultrahigh vacuum systems are not able to be employed for the combination of purposes addressed by this instrument.
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u spectroscopic measurements of erosion behavior of Tokamak Fusion Test Reactor-redeposited carbon materials under high-flux plasma bombardment in PISCES-A (Plasma Interactive Surface Component Experimental Station-A)
Authors: Hirooka Y. , Pospieszcyk A. , Conn R. W. , Mills B. , Nygren R. E. , Ra Y.
Published: July 2002

The chemical erosion behavior of graphite materials preexposed in the Tokamak Fusion Test Reactor (TFTR) as the bumper limiter has been investigated spectroscopically under deuterium plasma bombardment in the Plasma Interactive Surface Component Experimental Station-A (PISCES-A) facility. The deuterium plasma bombardment conditions are ion bombarding energy of 300 eV, ion flux of 1.7×1018 ions s−1 cm−2, plasma density of 1.4×1012 cm−3, electron temperature of 11 eV, and neutral pressure of 3×10−4 Torr. The chemical erosion yield is measured with calibrated CD-band spectroscopy during the temperaure ramp from 100 to 900 °C at an average rate of ∼5 K/s. The materials used include virgin POCO graphite and graphite tile pieces from the redeposited and eroded areas of the bumper limiter of TFTR. The deuterocarbon formation rate from TFTR redeposits maximizes at ∼500 °C. Essentially the same chemical erosion behavior is observed for TFTR-eroded and virgin graphites and is characterized by the compound peak, indicative of two erosion yield maxima at around 575 and 700 °C. The maximum erosion yield for TFTR redeposits is found to be ∼15% higher than those of TFTR-eroded and virgin POCO graphites which is attributed to deuterium incorporated in the redeposited material. In addition, the removal behavior of redeposits by helium plasma bombardment has been studied. The removal rate is evaluated to be similar to the physical sputtering yield of carbon by helium. The surface morphology and surface composition have been analyzed with scanning electron microscopy and electron microprobe analysis along with these erosion yield measurements.
Calibration of an argon in germanium standard using Rutherford backscattering spectrometry for energy dispersive x-ray spectroscopy
Authors: Skulina K. M. , van der Leeden G. A. , Vincent D. H.
Published: July 2002

An argon standard for energy dispersive x-ray spectroscopy (EDS) has been made by bias sputtering hydrogenated amorphous germanium (a-Ge:H) films and determining the concentration of argon with Rutherford backscattering spectrometry. Varying concentrations of argon in hydrogenated amorphous germanium were achieved by changing the dc bias on the substrate holder and the gas pressure during rf magnetron sputtering onto a silicon substrate. It was found that standardless EDS analysis underestimates the argon concentration by about a factor of 2.
Ion-assisted laser deposition of CaF2 thin films at low temperatures
Authors: Gluck N. S. , Sankur H. , Gunning W. J.
Published: July 2002

Thin CaF2 films have been grown at low temperatures (20 °C) using an ion-beam-assisted laser evaporation method. Smooth, dense, environmentally stable coatings with bulk refractive indices were produced. This technique was applied to deposit mid-wave IR dichroic filters using CaF2 and Ge layers onto cold substrates.
Carbon vacancies at a V6C5(100) surface
Authors: Miura K. , Souda R. , Aizawa T. , Oshima C. , Otani S. , Ishizawa Y.
Published: July 2002

The carbon vacancies at a V6 C5 (100) surface and their chemical activity for oxygen have been investigated by low-energy ion scattering spectroscopy (ISS) and x-ray photoelectron spectroscopy (XPS). The concentration of carbon vacancies increases with increasing flashing temperature of the sample: 10% and 20% at flashing temperatures of ∼1200 and ∼1600 °C, respectively. The adsorption of oxygen at a V6 C5 (100) surface is saturated with oxygen exposure of ∼10 L, and the oxidation occurs only at the V6 C5 (100) surface.
Behavior of phosphorus doped in microcrystalline Si:H films
Authors: Hirasaka Masao , Hashiba Masao , Yamashina Toshiro
Published: July 2002

For phosphorus(P)-doped hydrogen silicon(Si:H) films produced by glow discharge decomposition with a mixture of SiH4 and PH3 gases diluted by H2 , the phosphorus concentration was measured by Auger electron spectroscopy(AES). The P concentration, doped in Si:H films which were prepared with high-power glow discharge decomposition, was lower than that in the films prepared with low-power discharge decomposition. This P concentration in Si:H films decreased with increasing in the microcrystalline phase in Si:H films. By means of this correlation, microcrystallinity of films and growth of a microcrystalline mechanism were discussed. P concentration in layers formed in very early stages of deposition was already low. Therefore, it was considered in the growth of microcrystalline process, that a core of the crystal forms on a substrate surface at first and then grows to 100 Å in a latter period. Then, segregation of P doped in an amorphous layer was observed at a top surface while the P segregation in a microcrystalline layer was not observed. This could be explained by the speculation that many free P atoms exist in an amorphous layer and segregate with ease, compared with P atoms bonded to Si atoms.
Inversely operated aluminum alloy distributed ion pump
Authors: Momose T. , Kanazawa K. , Hisamatsu H. , Ishimaru H.
Published: July 2002

The distributed ion pump (DIP) for the accumulation ring (AR) for TRISTAN is described. The elements of the DIP are newly designed and fabricated. The cathode consists of titanium (Ti) rods and the anode is five aluminum (Al) plates with punched holes 12 mm in diameter. The unit of the DIP is 50 cm long and 5.3 cm wide. There are 62 holes in the unit. Five units are connected and installed in a bending magnet (B) chamber. Both the cathode and the anode are insulated from the chamber. The insulation makes it possible to measure only the current between the anode and the cathode. Therefore, the insulation enables us to use the DIP as an ultrahigh vacuum gauge. The initial pumping curve shows that the ultimate pressure is 9×10−11 Torr at 2000-h operation after several conditioning processes were applied. The processes are a higher magnetic field application (4–11 kG), bakings, a higher voltage application (5–12 kV), and argon glow discharge (dc, ac). Pressure improvement of one order was obtained after baking (140 °C, 64 h). Pressure improvement of a factor of 2 was obtained by the higher magnetic or electric field application. However, pressure deterioration was observed after the argon discharge. The DIP was operated for different magnetic fields simulating beam injection and acceleration. By changing the polarity of the power supply, pumping speed was measured for two cases: Ti cathode and Al anode, and Ti anode and Al cathode. For the latter, a different discharge pattern was observed. Before baking, the pumping speed for nitrogen was 150 l/s at 10−7 Torr and 5 kG and after baking, 310 l/s at 10−8 Torr at a field higher than 3 kG. The DIP of the AR has been operated successfully for more than five years. While the DIP was in operation, pressure in the AR was reduced by about one order. The base pressure is ∼1×10−9 Torr without baking.
A new distributed ion pump made of aluminum alloy with an aluminum or a titanium cathode in the transposable ring intersecting storage accelerators in Nippon e+e− colliding ring
Authors: Momose T. , Chen J. R. , Kanazawa K. , Hisamatsu H. , Ishimaru H.
Published: July 2002

The characteristics of the distributed ion pump (DIP) for TRISTAN (TMR) which has Al cathodes (Al-DIP) are described. The test of the Al-DIP showed a comparable initial pumping curve and pumping speeds (1/2–1/3) to the DIP which has a Ti cathode (Ti-DIP). But the Al-DIP in TMR showed a deteriorated pumping action. The reasons for this action were: (i) The surface of Al cathode was covered with a thicker oxide layer than those of the original cathode and of the tested DIP. (ii) The oxide layer was possibly grown in polyethelene envelopes with no desiccant, while the Al-DIP’s were transported and stocked before DIP assembly. (iii) The residual gases during a test evacuation of the deteriorated DIP in a TMR B chamber were H2 and H2O. (iv) A burst of H2 was observed after the DIP was turned on. An exponential increase of H2 was observed during the operation of DIP alone (before baking). (v) H2 decreased by about two orders after baking. These facts suggest that the H2 decomposed from the water contained in the thicker oxide on the cathode surface brought about the deteriorated action which was aided by the smaller pumping capacity rather than that of the Al-DIP test system.
Adaptation of dependex fittings to International Standards Organization fittings
Authors: Stockli Martin P. , Hill Dave
Published: July 2002

Dependex flanges are widespread in traditional nuclear research laboratories equipped with an HVEC accelerator, but are not common elsewhere because the modern vacuum community adapted the ISO and the ASA norms for standard O−ring sealed high−vacuum joints. Therefore, many traditional nuclear research laboratories have a frequent need for adapters in order to attach equipment with new standards to their systems. We show in this note the close match between the dependex and the ISO standards, which allows one to join the flanges with a minimum of adapting hardware.  (AIP)
Plasma enhanced chemical vapor deposition of HgTe–CdTe superlattices
Authors: Williams L. M. , Lu P.-Y. , Chu S. N. G. , Ross M. H.
Published: July 2002

Plasma enhanced chemical vapor deposition was used to grow epitaxial layers of cadmium telluride and mercury telluride from metalorganic compounds. High deposition rates were obtainable for both of the materials, and the plasma allowed epitaxial growth to occur at temperatures that were markedly lower than those required for the standard metalorganic deposition processes. Properties of the mercury telluride and cadmium telluride will be presented. Superlattices were grown at 150 °C that had 70 Å thick mercury telluride layers.
Blazed grating formation in a hollow cathode etcher
Authors: Gross M. , Wu Y. , Horwitz C. M.
Published: July 2002

Blazed gratings with well-defined facet angles can be etched in a modified hollow cathode reactive sputtering system. Electric field distortion and metal compound deposition are combined to give asymmetrically etched, controlled-angle structures. The grating blank is scanned past the active discharge area to form a large-area sample with uniform properties. Computer models of the etch and deposition processes agree with our experimental data in showing that blaze angles of ∼25° with apex angles of <90° are possible using this method.
Dependence of oxygen redistribution on titanium film thickness during titanium silicide formation by rapid thermal annealing
Authors: Kang S. W. , Chun John S. , Park S. C.
Published: July 2002

Silicidation of titanium (Ti) thin films sputter-deposited onto (100) oriented single-crystal silicon (Si) was performed by rapid thermal annealing (RTA) at temperatures of 500–800 °C. Auger depth profiling shows that, when exposed to air, the Ti films take in oxygen atoms independently of Ti thickness. During RTA the oxygen tends to be redistributed uniformly throughout the Ti film near the onset of silicide formation. As silicide formation progresses, the redistributed oxygen is expelled by the advancing silicide front. For 50 nm Ti thickness, the oxygen driven from the TiSi2 is confined at the surface of Ti film and the silicide growth is almost stopped even though there remains unreacted Ti. For 100 and 200 nm Ti thicknesses, before the oxygen driven from the TiSi2 is confined at the surface a second silicide layer starts growing at the surface. The oxygen driven from the both silicides is buried where the two silicide fronts meet. The depth of the buried oxygen peak was found to be dependent on the annealing temperature and on the Ti thickness: The peak tends to penetrate deeper for higher temperatures and for thicker Ti films. Also, it was found that amorphous silicon (a-Si), which is sputter-deposited sequentially on Ti film without breaking the vacuum, is quite effective in forming oxygen free and homogeneous TiSi2 by preventing oxygen infiltration into Ti film.
The role of sputter redeposition in the growth of cones and filaments on carbon surfaces during ion bombardment
Authors: Solberg W. A. , Spain I. L.
Published: July 2002

Cones topped by filaments with submicron diameters grow on carbon surfaces when they are bombarded with energetic (e.g., 1 keV) argon ions. It is shown that sputter redeposition is an important process by which cone growth occurs. The possible role of hydrogen in poisoning growth sites and increasing the density of cones at higher temperature is discussed. Several experiments are proposed to clarify growth mechanisms.
Ion energy measurements at the surface of an ion cyclotron range of frequencies antenna Faraday shield
Authors: Caughman J. B. O. , Ruzic D. N. , Hoffman D. J. , Langley R. A. , Lewis M. B.
Published: July 2002

The effects of rf fields on the energy of ions hitting the surface of an ion cyclotron range of frequencies (ICFR) antenna exposed to a plasma must be investigated to provide an understanding of the impurity generation from the antenna. A resonant loop antenna with a two-tier Faraday shield, installed on the Radio Frequency Test Facility at Oak Ridge National Laboratory, was used to study these effects. Samples of silicon were placed below the antenna and on the Faraday shield surface, facing the plasma, to measure incident ion energy. The samples were exposed to electron cyclotron heated plasmas without rf power and with 22 kW of rf power at antenna currents of up to 400 A. The fluence of ∼5×1017 D/cm2 from deuterium plasmas was near the saturation level of the samples. The energy of the incident ions was estimated by measuring the amount of deuterium trapped in the samples with D(3He,p)4 He nuclear reaction analysis. The results obtained from the trapped deuterium measurements are compared with ion energies measured directly with a gridded energy analyzer located near the antenna. They show that the rf-enhanced ion energy distribution measured in the plasma is proportional to the impact energies on the surface of the Faraday shield and increases with antenna current.
Auger electron spectroscopy depth profile study in fracture surfaces of sinterized YBa2Cu3O7−x
Authors: Colino J. , Sacedon J. L. , Del Olmo L. , Vincent J. L.
Published: July 2002

Auger electron spectroscopy depth profiles from different surfaces of the YBa2Cu3O7−x polycristalline compound, such as fracture and polished fracture surface of sintered ceramics, fracture of isostatically pressed powder and powder surface, have been measured. For the first time in this material, a study of the apparent enrichments in the Auger profiles compared with a preferential sputtering model in nonsimple oxides, recently tested in other perovskite oxide compound, is reported. These data show an oxygen surface release and an intergrain copper enrichment as consequence of thermal processing of the material. Thus, the existence of different stoichiometry in the grain boundaries as an additional contribution to the formation of weak links appears confirmed.
Comment on ‘‘Influences of noble gases (Ne, Ar, and Kr) on magnetic properties of ion-beam sputtered Fe/SiO2 multilayer films’’
Authors: Paparazzo E.
Published: July 2002

This paper reports some comments on the x-ray photoelectron spectra of ion beam sputtered Fe/SiO2 multilayer films which were discussed in a recent work by Senda and Nagai [J. Vac. Sci. Technol. A 8, 13 (1990)]. The area of major disagreement regards the interpretation that the two authors gave to explain the Si2p and O1s spectra. It is pointed out that great care should be exercized in order to account for the Ar ion reductive effects in iron–silicon oxide systems, and that a careful analysis should be done of the complex O1s spectra in order to assess which oxidized species are present in the films.
The effect of cathodic hydrogen charging of substoichiometric Ni3Al on Auger electron spectroscopy measured intergranular boron segregation
Authors: Choudhury Ashok , White C. L. , Brooks C. R.
Published: July 2002

A cathodic hydrogen charging procedure is described which allows intergranular fracture in boron-doped Ni3 Al samples which are normally ductile and do not fracture intergranularly. This has allowed determination of the boron content of the grain boundaries. It is shown that the hydrogen charging has no influence on the measured boron content.
Compact scanning tunneling microscope with easy-to-construct X–Z inertial sample translation
Authors: Meepagala S. C. , Real F. , Reyes C. B. , Novoselskaya A. , Rong Z. , Wolf E. L.
Published: July 2002

A new compact scanning tunneling microscope (STM) with easy-to-construct X–Z inertial sample translation has been developed. A key feature of this design is that a single piezoelectric tube performs inertial sample translation, X–Y scan, and the Z feedback control. The performance of the STM is tested by imaging a highly oriented pyrolytic graphite sample. The ability of this STM to translate the sample laterally is demonstrated using a gold sample. The design is stable against the thermal drifts in the X–Y plane.
Growth and morphology kinetics of adsorbate structures on silicon
Authors: Feldman L. C. , Zinke-Allmang M.
Published: July 2002

The approach to thermodynamic equilibrium is the ultimate driving force in determining the configuration of surface structures. In adsorbate and thin film structures such macroscopic thermodynamic concepts may be used to predict the kinetics of islanding, clustering and other fundamental surface processes. In this paper we describe experimental and theoretical studies of cluster growth mechanisms which involve surface diffusion, adsorbate/adsorbate interactions, and surface energy concepts. We show that the time and temperature dependence of growth can be described in terms of a cluster ripening mechanism, the mass transport of material driven by surface concentration gradients. Since the limiting process for the mass transport is surface diffusion, we consider the influence of surface structure and surface energy on the clustering rate. Examples of structures studied include, Ga, Sn, and Ge on Si and As terminated Si surfaces.
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u infrared diagnostics of particle forming etch plasmas
Authors: O’Neill James A. , Singh Jyothi , Gifford George G.
Published: July 2002

I n situ Fourier transform infrared absorption techniques are employed to characterize the gas-phase plasma species and etch products present in halocarbon containing plasmas which produce particles. A correlation is demonstrated between the distribution of these species and the extent of particle formation as measured by laser light scattering. The effects of the presence of silicon and the addition of oxygen on both the plasma species distribution and the degree of light scattering are also characterized. Additionally, x-ray photoelectron spectroscopy (XPS) and infrared (IR) microscopic techniques are employed to determine the chemical composition of the particulate material which is found on the silicon wafer after etching.
Depth profile analysis of Pt, Cu, and Au overlayers on p-Hg1−xCdxTe
Authors: Storm W. , Altebockwinkel M. , Wiedmann L. , Benninghoven A. , Ziegler J. , Bauer A.
Published: July 2002

Metallic overlayers of platinum, copper, and gold on a p-doped mercury cadmium telluride substrate have been depth profiled by 5 keV Ar+ sputtering and analyzed with Auger and photoelectron spectroscopy, secondary ion, and secondary neutral mass spectroscopy. The dependence of the composition, diffusion behavior, and chemical state of the systems on different annealing conditions and substrate pretreatment procedures has been investigated. Depending on the metal, these features can differ very strongly, thus yielding different electronic properties of the metal–semiconductor contacts.
Combined chemical and surface analytical investigation of the calcium catalyzed coal gasification process
Authors: Schwar J. , Jahn P. W. , Wiedmann L. , Benninghoven A.
Published: July 2002

The calcium catalyzed steam gasification of coal has been studied by a combination of a chemical microreactor working under technical conditions and surface analytical characterization (Auger and photoelectron spectroscopy, secondary ion and thermal desorption mass spectrometry) under ultra high vacuum conditions. The reaction model proposed by McKee was confirmed, and reaction products like calcium oxide, hydroxide and carbonate were detected after exposure to gasification conditions. The catalyst dispersion was studied as a function of reaction temperature and carbon conversion. The lowering of the CaCO3 decomposition temperature and the decreasing sample charging at higher temperatures indicate the good contact between the catalyst and the substrate at reaction conditions. Deactivation of the catalyst is due to two processes: the inevitable sintering of calcium to CaO and catalyst poisoning by sulfur by forming calcium sulfide.
Surface chemistry and thickness-dependent optical properties of films of oxidized Ni/Cr on polyimide
Authors: Draeger Norman A.
Published: July 2002

Films were sputter deposited from a Ni/Cr target (4:1 weight ratio) in an oxygen plasma onto polyimide substrates. The films are black in color, and show excellent adhesion and flexibility. Comparison of x-ray photoelectron spectra of 1.7 μm- and 3.5 μm-thick coatings of oxidized Ni/Cr with a control coating of oxidized Ni (i.e., presumably NiO) suggests that the presence of the Cr correlates with the formation of at least one nickel species other than NiO. As the oxidized Ni/Cr film thickness varies from 0.13 to 3.5 μm, the absorptance and emittance vary from 0.78 to 0.89, and from 0.27 to 0.62, respectively. Using a model proposed by Thakur, it is calculated that for the thicker films the emitted radiation has a wavelength of approximately 7 or 8 μm.
New x-ray limit measurements for extractor gauges
Authors: Watanabe Fumio
Published: July 2002

A new x-ray limit measurement method for extractor gauges has been developed using modulation of the hemispherical ion reflector. The measurement is possible from pressures as high as the 10−8 mbar range. X-ray limits for commercial extractor gauges have been examined for various emission currents and different gauge port geometries. The scatter in the x-ray limits measured is about 30% and the effect of gauge port geometry is more than 70%.
Analysis of TiC and TiN films prepared by an arc-induced ion plating
Authors: Jeong J. I. , Hong J. H. , Kang J. S. , Shin H. J. , Lee Y. P.
Published: July 2002

A new ion-plating system has been devised through a simple and cost-effective modification of the ordinary thermal evaporator. We characterized the system itself through evaporation of the various metallic elements such as Zn, Al, and Ti, first of all. The ionization efficiency for the evaporants was so enhanced without any introduction of inert gases that the bias voltage for, and temperature of substrate were reduced in the preparation of the films. The practical performance of the system was recognized in terms of the preparation of the TiN and TiC films which are widely employed for decoration and tools. The overall and layer-by-layer compositions, surface and cross-sectional morphology, and textures of the films have been analyzed by scanning Auger multiprobe (including inert-gas depth profiling), X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and x-ray diffraction. The process parameters such as nitrogen pressure have been established for five typical groups of colors of TiNx. In case of gold color, the atomic ratio of N to Ti was 0.95 and the main texture was developed along the (200) direction. The surface of film was smooth and dense. The relationship between microhardness, stoichiometry, and texture was investigated for the TiC films which were prepared with the various combination of the process parameters. Higher atomic ratio of C to Ti and Vicker’s hardness number were obtained at higher C2H2 pressure with two distinct preferred orientations, (111) and (200).
Hydroxyl desorption from platinum in the catalytic formation and decomposition of water
Authors: Fridell E. , Hellsing B. , Kasemo B. , Ljungström S. , Rosén A. , Wahnström T.
Published: July 2002

The water formation and decomposition reactions on Pt and the presence of intermediate OH were investigated by simultaneously measuring the OH desorption rate (by laser-induced fluorescence) and the overall H2O formation rate at different H2/O2 and H2O/O2 mixtures. These measurements were combined with computer modeling of the reactions to yield information about the reaction kinetics, e.g., about the relative importance of two different H2O formation steps (H+OH and OH+OH, respectively) in different reaction parameter regimes. A numerical value for the OH bond strength to the Pt surface was obtained from the observed temperature dependence of the OH desorption.
Sandwich holography modeling study of solid deuterium–tritium layers
Authors: Bittner D. N. , Shane M. D. , Musinski D. L.
Published: July 2002

We have conducted ray trace modeling calculations to determine the sensitivity of holographic interferometry as a tool for the study of cryogenic deuterium-tritium layers. This effort was initially designed to model experiments we had conducted in which a reference hologram of a gas phase target is ‘‘sandwiched’’ with a hologram of the identically oriented condensed layer target to form an interference image. We have extended the refractive ray trace modeling study to include reference holograms other than gas phase. We have used empty, gas filled, uniform solid layer, and 180° rotated slumped solid layer holograms as references to sandwich with a slumped solid layer. The highest sensitivity is achieved when a rotational shear of 180° is applied between two identical holograms of the slumped solid layer.
A general method for the stability analysis of a uniform liquid fuel layer inside a spherical shell inertial confinement fusion target
Authors: Todd R. D. , Simpson E. M. , Kim K. , Bernat T. P.
Published: July 2002

The formulation of a general method is presented for the stability analysis of the spherically shaped surface of a gas bubble inside a thin, finite, incompressible liquid layer of a ternary D–T mixture as found in a spherical cryogenic inertial confinement fusion target. A force balance on the liquid–vapor interface is performed to find the initial surface-tension gradient required to hold the liquid layer uniform. A node centered, finite volume, central difference formulation is then used to solve numerically the transient continuity, Navier–Stokes, and energy equations in the presence of a variety of nonaxisymmetric perturbations. The approach used in establishing the appropriate numerical procedures is described.
Real-time optical diagnostics for epitaxial growth
Authors: Aspnes D. E. , Quinn W. E. , Gregory S.
Published: July 2002

A variety of optical methods is now available for studying surface processes and for monitoring layer thicknesses and compositions during semiconductor crystal growth by molecular beam epitaxy, organometallic chemical vapor deposition, and related techniques. New capabilities for surface analysis are provided by new techniques such as reflectance-difference spectroscopy, which use intrinsic symmetries to suppress ordinarily dominant bulk contributions. Bulk and microstructural properties such as compositions and layer thicknesses can be determined directly by techniques such as spectroellipsometry, which return information integrated over the penetration depth of light. Proven capabilities suggest new applications to interrupted growth and to metastable materials systems involving self-ordering and strain relaxation. The first closed-loop system for controlling semiconductor crystal growth, which uses a spectroellipsometer as the monitoring element, is briefly described.
Comparative study of the oxide growth mode on GaAs(111) and (1̄1̄1̄) surfaces: Implications for direct oxide electron beam writing
Authors: Alonso M. , Soria F. , González M. L.
Published: July 2002

The growth mode of oxide films (<3 nm thick) obtained by electron beam oxidation is investigated on a wide range of polar GaAs{111} surfaces. Information is derived from a quantitative analysis of the Auger intensities for different oxidation models. Oxidation is always found to progress by a layer-by-layer mechanism with separate Ga and As oxide phases. The Ga-oxide growth is nearly insensitive to the starting surface, whereas a clear dependence is observed in the evolution of the As signal. Only a small fraction of the As atoms initially contained in each monolayer (ML) of GaAs{111} remains embedded in the Ga oxide; this fraction is zero, one-sixth or one-third of 1 As ML, for each oxide layer depending on the perfection of the initial surface. Therefore, this oxidation model supports previous indications that the elemental As often detected at the oxide/GaAs interface could not be formed during the oxidation process, but rather it is due to anion inclusions in the bulk which segregate at the interface.
Chemical release of implanted deuterium in graphite
Authors: Chiu S. , Haasz A. A.
Published: July 2002

Graphite is extensively being used in present-day fusion devices and has been selected as the reference material for plasma-facing components in the international thermonuclear experimental reactor, ITER. Graphite’s major advantages are associated with its low Z and excellent thermomechanical properties. Its drawbacks include susceptibility to erosion and large capacity for H retention under hydrogen plasma exposure. H-retention affects fuel recycling and also presents a potential environmental risk when operating with tritium, during vacuum vessel maintenance and accidental vacuum loss. The objective of the present study was to investigate the removal of energetically implanted deuterium from pyrolytic graphite via chemical reaction with atmospheric gases (N2, O2, and H2O) for different graphite temperatures. N2 exposure at 300–570 K appeared to be ineffective for the removal of implanted D. Oxygen exposure, on the other hand, was most effective in removing the implanted D from graphite, most likely by the erosion of carbon through O2+C reactions. For example, 10 h O2 or air exposure at 570 K resulted in an order of magnitude reduction in D content. At ∼770 K, three orders of magnitude reductions were observed in less than an hour of O2 or air exposure. While H2O was also effective in reducing the implanted D concentration, the corresponding D-removal rates were observed to be lower than those for the case with O2. Comparisons of D-removal rates for ion-implanted D and chemisorbed thermal D0 atoms on graphite surfaces are also discussed.
Effect of deposition parameters on the optical properties and microstructure of radio frequency magnetron sputtered ZnSe films
Authors: Caneve L. , Scaglione S. , Martelli S. , Emiliani G.
Published: July 2002

rf sputtering process complexity causes the influence of deposition parameters on the coating properties to be the subject of many papers. Zinc selenide thin films have been deposited by a rf sputtering system on employing different targets and sputtering conditions. The correlation between the thin-film composition and the target stoichiometry has been analyzed by Rutherford backscattering spectrometry. X-ray diffraction analysis has been applied to the samples in order to investigate the deposition parameters effect on the film microstructure. The optical properties of coatings realized with different sputtering conditions have been examined in the 5–11 μm wavelength region.
Modeling bias sputter planarization of metal films using a ballistic deposition simulation
Authors: Dew S. K. , Smy T. , Tait R. N. , Brett M. J.
Published: July 2002

A simulation by ballistic deposition model (SIMBAD) has been developed to predict thin-film microstructures of films deposited over topography. In order to study the radio frequency (rf) bias planarization process, this model has been extended to include film resputtering, redeposition, ion reflection, and ion-induced diffusion. To test the resulting SIMBAD simulations, tungsten was bias sputter deposited over high aspect ratio grooves. The resulting films exhibited increased sidewall coverage and planarity. Ion milling effects were also observed. These features were qualitatively matched by SIMBAD predictions as were microstructural details, such as column orientations and void locations. This preliminary success shows that such SIMBAD simulations can be useful in understanding and optimizing the rf bias planarization process.
Structure modification of radio frequency sputtered LaB6 thin films by internal stress
Authors: Nakano T. , Baba S. , Kobayashi A. , Kinbara A. , Kajiwara T. , Watanabe K.
Published: July 2002

Thin films of LaB6 are prepared by a radio frequency (rf) magnetron sputtering technique. The effect of sputtering conditions on the film properties of internal stress and crystalline orientation are investigated. The film deposited at low pressures (<1 Pa) has a strong compressive stress as high as 109 Pa. As the pressure of Ar discharge gas decreases, the internal stress becomes greater and the preferred orientation is transformed in the sequence: (100)→(110)→(111). This behavior can be explained as an energetically favorable structure of LaB6 film by taking both the surface energy and the strain energy into account. An application of a negative bias (−20 V) to substrates results in a greater stress, so that the (110) and (111) orientation becomes more preferential.
An electron energy-loss spectroscopy study analysis of the surface species formed during ethylene hydrogenation on Pt(111)
Authors: Backman A. L. , Masel R. I.
Published: July 2002

Electron energy-loss spectroscopy is used to examine the surface intermediates formed during ethylene hydrogenation on platinum at 298 K. We find that during the reaction the surface is covered with a mixture of ethyl radicals and ethylidyne. The ethyl radicals can be easily hydrogenated off the surface suggesting that they may be reactive intermediates. However, the ethylidynes are stable suggesting that they are spectators in the reaction.
Scanning tunneling microscopy of collagen molecules
Authors: Zhu X.-Y. , Poirier G. E. , White J. M.
Published: July 2002

Calf skin collagen molecules adsorbed on a graphite substrate were directly imaged by scanning tunneling microscopy in air. The right-handed helical structures were observed and the average periodicity was quantitatively measured to be 31 Å, in good agreement with the value of about 28 Å estimated from biochemical studies. The intermolecular distance in a collagen bundle was 23 Å.
A study of secondary ionization mechanism for LiF on Au by time-of-flight secondary ion mass spectrometry and direct recoil measurements
Authors: Moon Dae Won , Kim Yang Sun , Kim Jong Ho , Kang Hee Jae
Published: July 2002

We have studied the change of Li+ and F− secondary ion intensiters with the matrix transition from submonolayer LiF on gold to thick LiF by time-of-flight secondary ion mass spectrometry. Based on direct recoil particle measurements and Monte Carlo simulations, we estimated that the ratio of Li+/F− secondary ion yields did not change significantly with the matrix. From the results, it is suggested that the bond breaking model can be applied for submonolayer LiF on gold as well as for thick LiF.
Photon-stimulated desorption study of a SiO2 film surface
Authors: Niwano M. , Takakuwa Y. , Katakura H. , Miyamoto N.
Published: July 2002

Photon-stimulated desorption (PSD) experiments on thermal oxide films on Si have been performed using synchrotron radiation with photon energies in the Si 2p core-level excitation region, to investigate the chemical nature of the film surface. Mass analysis of the PSD ions is performed using a time-of-flight technique. H+ is found to be the dominant ion species that desorbs from the film surface. It is observed that the H+ PSD ion yield decreases exponentially with increasing the irradiation time of incident photons. The H+ PSD ion yield as a function of photon energy exhibits a close similarity in spectral shape to the photoabsorption spectrum of SiO2. The present experimental results confirm us that hydrogen atoms exists on the outermost layer of SiO2 film, and provide direct evidence for Si–OH and Si–H termination of SiO2 films.
X-ray characterization of (Zn,Cd)Te/CdTe strained layer superlattices
Authors: Qadri Syed B.
Published: July 2002

The structural properties of molecular beam epitaxially (MBE) grown (Zn,Cd)Te/CdTe superlattices on InSb substrates have been investigated using x-ray double crystal rocking curves and topographs. The value of unit cell parameters a⊥ and a∥ have been obtained for (Zn,Cd)Te layers from the θ/2θ scans of (004) and (444) reflections and their relaxed parameters calculated. Rocking curve measurements show that for (004) reflection the full-width at half-maximum (FWHM) of the superlattice is significantly reduced when compared with that for ZnCdTe layer of comparable Zn composition. The narrow rocking curves for the central and the satellite peaks suggest that the interfaces are very sharp and the superlattice periods do not fluctuate.
Process optimization and scale-up of a rapid thermal processing system using design of experiments
Authors: Rastogi Rajiv
Published: July 2002

Process optimization and scale-up of a rapid thermal processing system was done for TiSi2 films using design of experiments. The conventional two-step TiSi2 process was studied and an experimental design conducted with ten process variables. The screening experiment used to test process variables for main effects, indicated that only three of the ten process variables—low temperature anneal, time of anneal, and Ti film thickness—affected the measured film properties with greater than 95% significance. A second D-optimal design experiment was used to study the affect of three process variables on the film properties of TiSi2. This design studied the main effects as well as quadratic interactions of the process variables on the measured responses of the TiSi2 film. The experimental results predicted an optimized TiSi2 film with 0.60% uniformity and 0.96 Ω/sq sheet resistance. These predicted results were confirmed by device lots. The process capability index of the transferred process is 3.12.
Effect of step edge transition rates and anisotropy in simulations of epitaxial growth
Authors: Chason E. , Dodson B. W.
Published: July 2002

The results of a hybrid rate equation/Monte Carlo simulation of epitaxial growth on vicinal surfaces is presented. The effect on surface morphology of changing transition rates at step edges, of changing detachment rates from step edges and clusters, and of adding anisotropy to the diffusion and incorporation kinetics at step edges and islands was studied. The effect of the transition rates on surface morphology are discussed in terms of a balance between growth by nucleation and coalescence of islands and by the propagation of steps.
Effects of target microstructure on aluminum alloy sputtered thin film properties
Authors: Bailey R. S.
Published: July 2002

Target microstructure influences the properties of sputter deposited films. In this article, we report the effect of target microstructure on aluminum alloy sputtering from conical targets. We have controlled the fabrication of Al–Si and Al–Si–Cu targets to produce differing amounts of Al2Cu and Si second phase precipitates and grain sizes. Films, 1 μm thick, were sputter deposited onto oxidized silicon wafers at several different substrate temperatures. The characterization of these films is presented both as sputtered, and after annealing. The thin film properties studied include: resistivity, resistance ratio, reflectivity, and silicon nodule formation. The amount of second phase in a target was found to impact film properties, while target grain size had no effect on film properties.