bluuebunny/crossref_metadata_2025 huggingface dataset:
Abstract: Interaction of ion beams with solids
Authors: Davies J. A.
Published: July 2002

Ion implantation is now a widely used technique for modifying the chemical and physical properties of a shallow surface region of a solid. In principle, almost any combination of ion (Z1) and target (Z2) can be used over a wide concentration range, and with independent and precise control of the number and the depth distribution of the implanted ions. Furthermore, with modern vacuum techniques, ion implantation is an ideal ’’clean room’’ process, an advantage which has not yet been fully exploited. We will review briefly the major physical processes involved in implantation: viz., (i) the number and depth distribution (range) of the implanted ions, with particular emphasis on some of the complicating factors, such as ion reflection, charge exchange (in the beam), channeling, enhanced diffusion effects, and trapping at interfaces, which must be either eliminated or taken into account; (ii) the depth and nature of the radiation damage produced by the implantation; and (iii) the ultimate lattice location of the implanted ions within the crystal structure of the host lattice.

The radiation damage problem will then be considered in more detail, as this is generally the most important and also the most complicated aspect of ion bombardment. In particular, some recent work on the role of molecular ion beams will be presented in which equal atom−dose implants of various diatomic and monatomic ions were injected into Si and Ge at room temperature. In each case, the molecular ion implant had the same energy per atom and the same atomic flux and fluence as the corresponding monatomic implant. Yet, the molecular beam (As+2, Sb+2, Bi+2) produced ∠50% more damage than the monatomic beam, indicating that damage production depends not only on the total amount but also on the localized concentration of deposited energy. For the highest density cascades studied, the observed amount (Nd) of damage per ion corresponds to almost 100% of the predicted cascade volume; furthermore, there is no evidence of the molecular effect levelling off as the damage approaches this 100% limit. Also, the Nd values in semiconductor crystals are all considerably greater than the upper limit of 0.8 ν (E)/2Ed predicted by the Kinchin−Pease equation, 1 and the discrepancy becomes even worse for similar implants at low (30 K) temperature. These results provide strong experimental evidence for a breakdown of the generally accepted linear−cascade model, and suggest that at fairly low energies some sort of energy−spike model (as recently proposed by Sigmund 2) may indeed be more appropriate.
The dc sputter coating of solar-selective surfaces onto tubes
Authors: Harding G. L. , McKenzie D. R. , Window B.
Published: July 2002

A device for coating tubes using reactive or nonreactive dc sputtering is described. The coating of glass tubes with a solar selective surface consisting of a layer of metallic carbides on copper is used as an example. Uniformity of thickness and composition are demonstrated. The cylindrical design of the coating equipment and low manufacturing tolerances make this a low-cost system.
Some limitations on electron beam lithography
Authors: Crewe A. V.
Published: July 2002

Since there is a considerable interest in improving the performance of electron probe systems it is important to know what, if any, are the ultimate limitations. In this paper we examine some potentially limiting factors. Specifically we look at those due to the resist material itself, spherical aberration, the electron source, the deflection system and finally some concerns about the properties of small conductors. Our conclusion is that it should be possible to obtain currents of 500 nÅ in probes 200 Å or so in radius.
Double epitaxy and the growth of polymorphic films of thallium iodide (TlI) on potassium chloride (KCl)
Authors: Moravec T. J. , Skogman R. A. , Boord W. T.
Published: July 2002

Thermally evaporated thin films of TlI have been found to grow epitaxially on KCl(100) surfaces equally with two mutually perpendicular orientations. We present x-ray and optical data to show that the TlI(004) plane grows with its bo axis parallel to each of the two KCl 〈110〉 directions that lie on the (100) surface. This unusual double epitaxial microstructure with mutually perpendicular orientations results in optical scattering by the diffraction of light passing from one biaxially birefringent orientation to another. Due to the highly desirable properties of TlI as an optical coating material for high powered infrared laser components, several techniques have been devised to minimize the optical scattering and improve film homogeneity. Data are presented on the use of a thin buffer layer which severely reduces the epitaxial growth of TlI resulting in homogeneous films similar to those deposited on glass. Epitaxial TlI films may also be made with no visible light scattering by alternating thin layers of TlI with those of another material. This alternating layer method takes advantage of the polymorphism of TlI in thin layers to produce films in the cubic phase. We show by x-ray and optical measurements that each TlI layer possesses the CsCl structure at room temperature.
Interdiffusion of Al and Cr thin films
Authors: Chamberlain M. B.
Published: July 2002

The interdiffusion of Al and Cr thin films from 659–726 K was investigated by measurements employing Auger electron spectroscopy (AES) and Ar ion beam sputtering. The only intermetallic phase observed at the Al–Cr interface of isothermally annealed couples was Al7Cr. The rate constant measured for the parabolic-growth model dx/dt=K/x of the Al7Cr-layer thickness was K=1.3×106 exp[−(262 kJ mol−1)/RT] cm2 s−1. The chemical interdiffusion coefficient ? was calculated from compositional profiles of unannealed and annealed specimens by the Boltzmann–Matano solution to the interdiffusion of bimetallic, semiinfinite couples that form three phases. The interdiffusion coefficient was ?=1.3×106 exp [−240 kJ mol−1)/RT] cm2 s−1 at 6 at. % Cr.
Effects of sputter etching and process techniqes on the properties of sputtered aluminum films
Authors: McLeod Paul S. , Hughes John L.
Published: July 2002

Aluminum and aluminum–silicon alloys are frequently used for silicon wafer metallization using dc magnetron high rate sputtering sources. Processes using these sputtering sources have been investigated with special emphasis on the coating properties of film resistivity, surface reflectivity, and step coverage. The major thrust of this work has been to improve these coating properties in the production processes of high rate, fully automatic coating systems, using sputter etching prior to wafer coating. This paper presents the results of these investigations. Coating reflectivity was found to be highly dependent on the release of adsorbed residual gases during deposition. Similarly, film resistivity was affected by the same phenomenon. The increase of pumping speed for water vapor significantly improved coating cycle times and the reflectivity and resistivity of the coatings. An effect of sputter etching on desorption is indicated after reducing the effects of residual gas and temperature rise of the substrate. Step coverage was also dramatically improved by limiting the number of coating passes in front of a sputtering target. Film resistivity improved to within 90% of bulk values and step coverage was better than 50% on a 90° step.
High-resolution L
M
M Auger spectra from argon implanted in Be and Si
Authors: Zehner D. M. , Madden H. H.
Published: July 2002

The L2,3M2,3M2,3 and L2,3M1M2,3 Auger electron spectra from argon implanted by 1-keV ion bombardment in Be and Si crystals, have been obtained using a double-pass CMA operated in both the nonretard and retard modes. Background subtraction and loss-deconvolution were subsequently applied to obtain the final results. The argon-in-Be spectrum consists of a series of narrow peaks (FWHM less than 2 eV) which are sharper than those previously reported for the L2,3M2,3M2,3 spectrum from solid argon. Associating the major peak in our spectrum with the L3M2,3M2,3(1D2) peak in the gas-phase spectrum leads to an identification in terms of energy separations of our peak structure with the principal peaks of the gas-phase spectrum to within 0.5 eV. We conclude that the transitions responsible for the Auger spectrum can be characterized as quasiatomic, although the multitude of gas-phase satellite peaks is not seen in our results. Peaks in the argon-in-Si spectrum are slightly broader than those in the argon-in-Be spectrum. As a result of screening by the conduction electrons in the host material, our argon Auger emission energies are higher than those in the gas-phase spectrum.
UPS Studies of H2, O2, and CO adsorption on ordered carbon overlayers on W(100)
Authors: Stefan P. M. , Helms C. R. , Perino S. C. , Spicer W. E.
Published: July 2002

An ordered carbon overlayer which is prepared by carburization of a W(100) surface and exhibits a (5×1) LEED pattern, is used as a model of bulk WC. UPS studies at hν=21.2 eV were performed on this surface with adsorbed H2, O2, or CO. No evidence for H2 adsorption was seen. Oxygen is easily adsorbed and probably bonds in a manner different from oxygen in dissociated CO on W(100). CO adsorbs molecularly, as evidenced by emission from CO 5σ–1π molecular orbitals.
Chemisorption of Cl in surface vacancies on Si(111) 1×1
Authors: Schlüter M. , Rowe J. E. , Weeks S. P. , Christman S. B.
Published: July 2002

Chemisorption of atomic chlorine on Si(111) surfaces has been investigated theoretically for a threefold substitutional geometry corresponding to adsorption into an initial surface vacancy site. Comparison with photoemission data indicates that this adsorption geometry is achieved by room-temperature Cl exposure of clean Si(111) 1×1 surfaces prepared by quenching from ∠950 °C.
Reliability of surface structure determinations by LEED
Authors: Jona F. , Shih H. D.
Published: July 2002

The search for a solution in the problem of surface structure determination by analysis of low-energy electron diffraction (LEED) intensities is made by comparing a number of calculated and observed intensity spectra with one another. The test for the correctness of a given structural model consists often in the subjective judgment of the quality of the fit between calculated and observed curves, a judgment based merely on visual comparison between the two sets of data. The subjectivity and arbitrariness of this procedure have long been deplored, and have often led to controversies, inaccurate reports, and sometimes blunders. The subsequent need for an objective criterion of evaluation seem to be filled by the reliability factor proposed by Zanazzi and Jona. Definition and properties of this r factor are reviewed, and examples and suggestions of its use for both the evaluation and the refinement of surface structural models are given.
Bulk interpretation of the angle-resolved photoemission spectra from GaAs(110)
Authors: Colbert J. , Shevchik N. J.
Published: July 2002

The theory developed in previous papers of this series is used to calculate the angle resolved photoemission spectra of the (110) surface of GaAs, a material for which the final electron state is expected to be far from free electronlike. The good agreement of the calculated spectra with the experimental results of Knapp and Lapeyre confirms the predictions made in the previous papers that the simple theory ought to work for materials having strong atomic pseudopotentials. In addition, we find that features in the experimental spectra attributed previously to surface states can be explained by emisions from the bulk bands.
Hartree–Fock formalism for the calculation of total energies and charge densities of thin films
Authors: Harris Frank E. , Monkhorst Hendrik J. , Schwalm William A.
Published: July 2002

A formalism has been developed by which the Hartree–Fock self-consistent equations for thin films and surfaces are solved in an essentially exact way from first principles. The Fourier transform method, which was developed and used very successfully for the calculation of bulk properties, has now been extended to permit the study of the surfaces of crystals of a wide variety of materials. The development is sufficiently general to permit the treatment of any surface of any crystal geometry together with relaxations and reconstructions. A basis set of Slater-type, layer orbitals is used to compute a self-consistent density matrix for electrons in the field of bare nuclei in a slab geometry. The basis functions are handled in the Fourier representation which reduced many of the integrals to sums of one-dimensional ones which are computed in closed form. The use of the Fourier integral representation also permits an analytical treatment of the cancellation of the Coulomb singularities in the classical potential.
Abstract: Total reflection x-ray diffraction studies of the formation and the geometrical structure of Al–Ge(100) interfaces
Authors: Weng Shang-Lin , Cho A. Y. , Eisenberger P.
Published: July 2002

Total reflection x-ray diffraction studies of Al−Ge(100) interfaces are made.(AIP)
Some basic problems with copper vacuum gaskets
Authors: Moore Richard L.
Published: July 2002

Problems with copper gaskets are evaluated. (AIP)
Coating laser microspheres with homogeneous low density foams
Authors: Coudeville A. , Eyharts P. , Perrine J. P. , Rey L. , Rouillard R.
Published: July 2002

We describe both a method to produce a low density foam and a small mechanical apparatus used to embed a microsphere in the foam. Freeze-drying techniques offer an efficient way to create low density foams. Good results are obtained with 3%–5% of dextran in water. The density measured on samples of a few cubic millimeters is in the range of 5×10−2 g cm−3 with cell size of the order of 1 μm. The conditions which greatly enhance homogeneity and uniformity of the foam will be described. The method is well suited to a mold cavity assembly in which microspheres of 80–100 μm have been coated with foam thicknesses of 200–300 μm.
Electron microscope study of very thin mixed Cu/CuO films
Authors: Paoletti L. , Rosa P. A. , Picozzi P. , Santucci S.
Published: July 2002

The oxidation kinetics and morphology of very thin (<10 nm) mixed Cu/CuO films obtained by exposing very thin discontinuous Cu films to atomic oxygen plasma were investigated by electron diffraction and dark field electron microscopy. The oxidation process is characterized by an initial stage of oxide logarithmic growth which goes on until about 50% of the initial Cu is oxidized. The morphology of the films during the oxidation evolves from a situation characterized by discontinuous metallic islands covered with an oxide layer to another one in which metallic grains are embedded in a continuous oxide film.
Thermal and sputtered aluminum oxide coatings for high temperature electrical insulation
Authors: Kreider Kenneth G. , Semancik Stephen
Published: July 2002

Aluminum oxide coatings have been investigated as electrically insulating layers for mounting thin film Pt–Pt/Rh thermocouples on gas turbine blade and vane alloys (MAR M200 + Hf and MAR M509). Thermal oxides were grown directly onto NiCoCrAlY and FeCrAlY coatings on these alloys at temperature between 1300 and 1400 K in oxygen partial pressures 10−7 to 2×104 Pa. Although these thermal oxides exhibited good adherence, analytical characterizations using electron and optical microscopy, as well as x-ray photoelectron spectroscopy (XPS) showed that they had defects and impurities which limited their insulating ability. The insulating quality of the coating was greatly improved however by reactively sputtering an aluminum oxide film over the thermal oxide. Results are presented on the electrical performance of the 2–5 μm thick composite layers for temperatures up to 1300 K.
Structure-thermal properties—relationship in plasma sprayed zirconia coatings
Authors: Pawlowski Lech , Lombard Didier , Fauchais Pierre
Published: July 2002

Plasma sprayed coatings of zirconia stabilized with 7, 8, and 20 wt.% of yttria were investigated. The microstructure of the coatings was characterized by optical microscopy and x-ray diffraction. The thermal properties of the coatings, i.e., thermal diffusivity, thermal dilatation, specific heat, and resulting thermal conductivity were determined for each zirconia coating and the results were correlated with the microstructure.
Design of an ultralow coverage metal evaporator based on a geometric factor
Authors: Chin K. K. , McKernan P. , Lindau I.
Published: July 2002

An ultralow coverage eight-metal evaporator has been designed, built, tested, and put into use. Based on a geometric factor of 1:200, a metal coverage as low as 10−4 monolayer is reproducibly obtained with an error in coverage less than 20%. Various considerations during the design of the evaporator are discussed.
Control of the surface composition of isothermal vapor phase epitaxial mercury cadmium telluride
Authors: Fleming J. G. , Stevenson D. A.
Published: July 2002

A method is described for controlling the surface composition of mercury cadmium telluride during isothermal vapor phase epitaxy of mercury cadmium telluride. The method employs a three-phase solid–liquid–vapor source in equilibrium with the desired composition. The thermodynamic and kinetic basis of the method is outlined.
Effect of chemisorbed sulfur on the electrochemical hydrogen adsorption and recombination reactions on Pt (111)
Authors: Protopopoff E. , Marcus P.
Published: July 2002

The effect of preadsorbed sulfur on the cathodic hydrogen adsorption and recombination reactions was quantitatively studied on a platinum (111) surface in acid aqueous medium. The sulfur coverage was measured by a radiotracer technique. In the presence of sulfur the rate of the overall hydrogen evolution reaction (HER) is strongly lowered. This effect is attributed to a poisoning by sulfur of the sites of adsorption of hydrogen. The weakly bonded hydrogen species involved in the HER is not adsorbed in the same sites as the strongly bonded hydrogen species adsorbed at underpotential. Different poisoning effects by sulfur are observed on the two kinds of sites. The measurements are well fitted by a model in which one isolated sulfur atom blocks three adsorption sites of weakly bonded hydrogen.
Direct E0 energy gaps of bismuth-containing III–V alloys predicted using quantum dielectric theory
Authors: Barnett S. A.
Published: July 2002

Quantum dielectric theory has been used to predict the direct E0 energy gaps of ternary and quaternary III–V semiconductor alloys containing up to ∼10 mol % InBi. The calculated composition dependence of E0 for InSb1−xBix is in good agreement with experimental results with a predicted semiconductor–semimetal transition (77 K) at x=0.124. E0 (77 K) values corresponding to infrared wavelengths of 8 to 12 μm are obtained at x=0.043–0.070, respectively, corresponding to lattice mismatches with InSb substrates in the range from 0.11% to 0.17%. The quaternary alloys InAs1−x−ySbxBiy and In1−xGaxSb1−yBiy also yield E0 values in this range with similar InBi contents while maintaining exact lattice match to InSb substrates. InAs1−xBix is proposed as a new alloy for spanning the wavelength range from 3 to 5 μm. The required x values range from 0 to 0.079 (measuring E0 at 77 K) and the maximum lattice mismatch with either InAs or GaSb substrates for these compositions is <0.31%. The related quaternary alloy In1−xGaxAs1−yBiy also spans the 3–5 μm wavelength range while maintaining lattice match with InAs or GaSb substrates.
Study of the structure and performance of a new type of molecular pump
Authors: Yang Naiheng , Yu Luguang , Pang Shijing , Zhu Yue
Published: July 2002

A relationship between the pumping performance of a new type of molecular pump and its structure was studied in this paper. The pumping performance of the pump was calculated with the three-dimensional model and the simplified transmission probability matrix method. In order to verify the theory and compare the pumping performance of the pumps, two pumps with different structures were designed. The measured values agree with the calculated results.
Thermal limitations of the pumping speed of refrigerator cooled cryosurfaces ≥− 90 °C
Authors: Schwarz W.
Published: July 2002

Refrigerator cooled cryosurfaces are often used as pumps for water vapor and solvents in industrial vacuum systems in the pressure range between 10−3 and 0.5 mbar. Due to the high condensation rate at these pressures large thermal loads have to be removed from the cryosurfaces. The associated increase in surface temperature limits the pumping speed of the cryosurface. Model calculations of the water vapor pumping speed have been performed for pressures between 10−3 and 1 mbar for water and coolant temperatures Tliq≥−90 °C. We discuss the influence of the heat transfer coefficient between cryosurface and coolant, the influence of the cooling power of the refrigerator, and the reduction of the pumping speed due to ice layers on the surface. It is shown that the pumping speed of cryosurfaces is limited by these thermal parameters. The results yield layout criteria for cryosurfaces and their refrigerators.
Infrared reflection–absorption spectroscopy of surface modified polyester films
Authors: Dunn D. S. , McClure D. J.
Published: July 2002

Infrared reflection–absorption spectroscopy (IRRAS) has been used to study the chemical and morphological changes which occur during oxygen sputter etching of poly(ethylene terephthalate) (PET). The IRRAS results show that the PET in immediate contact with the oxygen plasma is oxidized to a depth of about 3 nm and is of low molecular weight; about one-third of it is soluble in water. Beneath this layer is a region of chemically unmodified, but crosslinked, amorphous PET. This layer is of variable thickness with an equivalent thickness in the range of 2–20 nm.
Rotational dynamics and electronic energy partitioning in the electron-stimulated desorption of NO from Pt(111)
Authors: Burns A. R. , Stechel E. B. , Jennison D. R.
Published: July 2002

Using laser resonance ionization, we have examined the rotational dynamics of neutral NO molecules desorbed by electron impact from a cold (80 K) Pt(111) surface. Previously [A. R. Burns, E. B. Stechel, and D. R. Jennison, Phys. Rev. Lett. 58, 250 (1987)], we observed ‘‘hot’’ rotational temperatures in the range 481–642 K for the ν=0, 1, 2, and 3 vibrational levels. We now present more detailed data which do not reveal shifts or broadening in the rotationally selected NO velocity distributions as a function of rotational level J in the range J=2.5–29.5. The rotationally independent velocity distributions, peaked at 0.05 eV, as well as the rotational temperature can be understood within the framework of ‘‘electronically stimulated adsorbate rotation’’ (Burns et al., above). The model also predicts complete rotational alignment in a plane normal to the surface. In the laboratory, no alignment is observed, but this is most likely due to the presence of stray magnetic fields. We will also discuss our measurements which show an equal partitioning between the two lowest NO electronic states (2Π1/2 and 2Π3/2), and a preference for the π level which is perpendicular (antisymmetric) to the plane of rotation.
Ceramic coating as an ultrahigh vacuum compatible protective surface treatment for aluminum alloys against reactive species
Authors: Suemitsu Maki , Kaneko Tetsuya , Miyamoto Nobuo
Published: July 2002

From its extremely low outgassing rate, the aluminum-alloy UHV system possesses substantial advantages in the fabrication processes of next-generation semiconductor devices. In order to realize the advantages, however, its vacuum properties must be tested under actual fabrication circumstances where the inner surface of the chamber is continuously irradiated with chemically reactive species or energetic ions and photons. In this study, the effects of reactive gas (dichlorosilane: SiH2 Cl2 ) on the outgassing rates of aluminum-alloy surfaces were examined for three different surface treatments: the ethanol lathing (EL), the special extrusion (EX), and the ceramic coating (CC). Without exposures to the reactive gas, all three surfaces, after having been baked, resulted in extremely low outgassing rates below the experimental limit of 10−12 Torr l/s cm2 to prove their usefulness as UHV materials. After an exposure to the reactive gas, however, the outgassing rates of EL and EX increased by about a factor of 50, while that of CC remained basically of the same order. Changes in the surface morphology and the surface layer compositions were also examined by scanning electron microscopy and energy dispersive x-ray analyzer, respectively, which revealed the extent of their corrosions to be in the order EX>EL≫CC. Ceramic coating technique will provide us with a promising surface treatment for aluminum alloy used in reactive semiconductor processes.
Quantitative secondary ion mass spectrometry analysis of contaminants in TaSi2 thin films
Authors: Stevie F. A. , Kahora P. M. , Cochran G. W.
Published: July 2002

Secondary ion mass spectrometry has been used to identify and quantify contaminants in TaSi2 thin films. Quantification was established for 31 elements by the analysis of ion implants into TaSi2 layers. The results are tabulated in terms of useful yield and relative sensitivity factor. The data follow the same useful yield versus ionization potential relationship noted for a Si matrix. Contamination, in films deposited by cosputtering from pure Ta and Si targets in a multiwafer rotating hemisphere system, was correlated to metallic machine components. Analysis of films from more than 75 targets used in a composite target single-wafer system showed that the metallic contamination was caused by the presence of impurities within the target. The mobility of the detected elements was investigated by analyzing samples as deposited and after anneal. Al and B showed significant redistribution after anneal, but most elements, including Fe, remained stationary in the TaSi2. The contamination and diffusion results were useful in analysis of product problems and in the determination of specifications for TaSi2 targets.
CO adsorption on stepped Ni(111) surfaces
Authors: Benndorf Carsten , Meyer Lutz
Published: July 2002

The CO adsorption on Ni(331) and Ni(221) [referred to as Ni(s)(111)] was studied with low-energy electron diffraction (LEED), thermal desorption spectroscopy (TDS), and work function change measurements. LEED from the clean Ni(s)(111) crystals give evidence for nonreconstructed surfaces with atomic arrangements as expected from the ideal (331) and (221) orientations; these surfaces can be interpreted as stepped Ni(111) surfaces with (111) terraces and (111) steps. CO desorption shows on both surfaces several desorption states, which are sequentially filled with increasing CO exposure. The desorption state with the highest peak temperature [Tm=455 K for Θ(CO)≊0] is identified on both surfaces and related to CO desorption from (111) terraces. For higher coverages, due to the presence of steps, new desorption states fill in with lower desorption temperature in the range of 200–350 K. These desorption states are not present on flat Ni(111). With LEED in a definite regime of CO coverages half and one fourth-order streaks in [1̄10] directions of Ni(s)(111) are observed and related to a one-dimensional ordering of CO in directions parallel to the step directions. Ordered LEED overlayers with c(4×2) [Ni(331) and Ni(221)] and (2×1) [Ni(221)] are established on both surfaces near the CO saturation coverage at 120 K. These overlayers demonstrate that the barrier for lateral interaction introduced by the steps is overcome at higher coverages.
Study of x-ray emissions from cold deuterium–tritium fuel inside glass targets for inertial confinement fusion
Authors: Mruzek M. T. , Felmlee W. J.
Published: July 2002

We have remotely monitored the thermodynamic phase of deuterium–tritium (DT) fuel inside glass shells used for inertial confinement fusion (ICF) research by observing the x-ray emissions from the shell. These studies are an adjunct to our beta heating experimental program. [M. T. Mruzek, D. L. Musinski, and J. S. Ankey, J. Appl. Phys. 63, 2217 (1988)]. By monitoring the production of low-energy x rays (< 18.6 keV) from the interaction of the beta decay with the shell walls, we are able to track phase changes between gas and solid. We incorporated the mature x-ray detection technology of scintillators and photomultiplier tubes onto the experimental apparatus we use to study the beta heating effect. [M. T. Mruzek, J. S. Ankey, and D. N. Decker, J. Vac. Sci. Technol. A 6, 1889 (1988)]. Restrictive space limitations were a major hardware consideration in the retrofit. We review the scientific basis for the technique, the proof of principle experiment that encouraged us to pursue it, and the final experimental configuration the x-ray probe has assumed. We suggest that a refinement of the measurement technique may provide information about the rate of DT fuel redistribution in beta heating targets.
Studies of the reactive ion etching of SiGe alloys
Authors: Oehrlein G. S. , Kroesen G. M. W. , de Frésart E. , Zhang Y. , Bestwick T. D.
Published: July 2002

Reactive-ion etching (RIE) of epitaxial, strained Si1−xGex alloys, x≤0.20, in fluorine-chlorine-, and bromine-based low-pressure plasmas has been investigated. The reactive-ion etch rates of the Si1−xGex alloys increase with the Ge content of the alloy for most etching gases. This effect is most pronounced for fluorine (CF4 and SF6) plasmas where the etch rate of a Si80Ge20 alloy is increased by a factor of ≂2 over that of Si. The etch rate enhancement is of reduced importance for chlorine (CF2Cl2) and bromine (HBr) plasmas, where the etch rate increases by less than 50% for a Si80Ge20 alloy relative to that of elemental Si. Analysis shows that the etch rate increase is not accounted for by the greater rate of gasification of Ge atoms alone but that the presence of Ge atoms in the SiGe alloy increases the Si etch product formation rate. Directional SiGe profiles are observed for CF2Cl2 and HBr plasmas which are identical to those obtained with Si. After etching in CF4 or SF6 plasmas the Ge surface concentration of the SiGe alloy is increased relative to its bulk value and both fluorinated Si and Ge are observed by in situ x-ray photoemission spectroscopy. On the other hand, for CF2Cl2 and HBr plasmas the SiGe surface is Si rich. The effect of band-gap narrowing, strain and plasma-induced surface modifications on the etching of the SiGe alloys is discussed.
Ion spectroscopy gauge: Total pressure measurements down to 10−12 Pa with discrimination against electron-stimulated-desorption ions
Authors: Watanabe Fumio
Published: July 2002

The hot-cathode magnetron gauge by Lafferty (which presently holds the possibility of making the lowest-pressure measurements, 10−15 Pa) and the improved Helmer gauge by Benvenuti and Hauer (which carried out the lowest-pressure measurements to date, 2.5×10−12 Pa) have been examined regarding the measurement limit due to electron-stimulated-desorption (ESD) ions. On the basis of this examination, a new hot-cathode total pressure gauge, called an ion spectroscopy gauge, which substantially avoids errors caused by ESD ions down to 10−12 Pa, has been developed. Discrimination against ESD ions is accomplished by combining three technical elements: (i) a spherical grid ion source; (ii) a spherical 180° ion energy analyzer; and (iii) burying the ion source in an aluminum alloy flange. The ion source plays an important role in the generation of a large kinetic energy difference between gas-phase ions and ESD ions, by using electron space charge. The 180° analyzer, which has a high energy resolution, promotes ion focusing and tends to reduce the x-ray limit. The burying technique reduces the outgassing rate of the hot-cathode gauge. Performance measurements of the new gauge have been carried out in a new aluminum extreme high vacuum system. The effective separation of gas-phase ions from ESD ions for two variants of the gauge, one with a molybdenum grid and one with a platinum grid, was demonstrated using oxygen dosing. The performance of the platinum-grid gauge was confirmed down to 2×10−11 Pa, essentially free from errors caused by ESD ions. The x-ray limits and sensitivities of the new gauges were: below 2×10−12 Pa with a sensitivity of 4.5×10−4 A/Pa for the molybdenum grid and 5.6×10−12 Pa with a sensitivity of 1.8×10−4 A/Pa for the platinum grid.
Mass spectrometry of fusion-plasma gases
Authors: Dobrozemsky R. , Schwarzinger G. W.
Published: July 2002

In a D–T fusion plasma, not only the components of primary interest (D2, T2, 4He), but also H2 and reaction products like HD, HT, and DT have to be considered. Even traces of 3He may be found in the system. For mass-spectrometric analyses of these eight gas species, at most six data are usable out of the mass range 1 to 6. Moreover, also taking into account water and hydrocarbon molecules, the unknowns outnumber by far the available data, making the underlying equation system unsolvable. This problem is overcome by repeatedly measuring the spectrum, but with stepwise changes in the settings of selected parameters of the instrument. Of particular interest are parameters like electron energy E (offering chemical separation of helium and hydrogen) and−in case of quadrupoles−field axis potential V (allowing to distinguish between molecular ions and fragment ions). By choosing 2 parameters each of E and V, we can get up to 24 linear independent equations out of the mass range 1 to 6, good enough for spectrum decomposition by means of established fit procedures. Details of this method and results from analyzing typical gas mixtures are presented.
Spectroscopic immersion ellipsometry study of the mechanism of Si/SiO2 interface annealing
Authors: Yakovlev V. A. , Liu Q. , Irene E. A.
Published: July 2002

In this study we apply an interface sensitive ellipsometry technique to study the evolution of the Si–SiO2 interface as a function of high temperature annealing (750–1100 °C). Essentially, the ellipsometry technique embodies the use of liquids that refractive index match with the bulk film thereby removing the optical response of the overlayer and greatly enhancing sensitivity to the interface. According to both time and temperature of anneal, distinct modes of behavior are observed for the evolution of the interface. For short anneal times a rapid change in the interface is observed that correlates with the disappearance of protrusions, followed by a slower change that correlates with the disappearance of the suboxide. At high temperatures viscous relaxation dominates, while at low temperatures the suboxide reduction is apparent. A model for the interface in terms of chemical and physical interface processes is proposed and model parameters are compared with literature results.
Adatom location on the Si(111) 7×7 and Si(111) √3×√3–In surfaces by the x-ray standing wave and photoemission techniques
Authors: Woicik J. C. , Kendelewicz T. , Herrera-Gomez A. , Andrews A. B. , Kim Boong Soo , Cowan P. L. , Miyano K. E. , Bouldin C. E. , Karlin B. A. , Herman G. S. , Erskine J. L. , Pianetta P. , Spicer W. E.
Published: July 2002

The x-ray standing wave technique has been used to determine the adatom positions on the Si(111) 7×7 and Si(111) √3×√3–In surfaces. By monitoring the intensity of the surface sensitive Si 1s photopeak as a function of photon energy around the Si(111) Bragg backreflection condition, we determine the Si adatoms of the clean 7×7 surface to reside 1.69±0.1 Å above the extrapolated Si(111) bulk plane. In contrast, the In adatoms on the 1/3 monolayer √3×√3–In surface are found to remove the Si displacements and lie at a position of 2.11±0.05 Å. High-resolution Si 2p core-level measurements support the T4 geometry for the In adatom location.
Quantitative analysis of InxGa1−xAs by Auger electron spectroscopy
Authors: Chen W. D. , Cui Y. D.
Published: July 2002

Quantitative Auger electron spectroscopy analysis for the ternary system InxGa1−xAs grown by molecular-beam epitaxy has been studied. The relative sensitivity factors are determined by with an internal reference element. The matrix correction factor for In relative to Ga was shown to be 1.08. No preferential sputtering of As for the ternary compounds was found, and the sputter correction factor, KInGas is 0.75. The results are compared with that measured by the x-ray double-crystal diffraction analysis, electron probe microanalysis, and Auger analysis without matrix and sputter corrections.
Reactions between backstreaming perfluorinated polyether pump oil and various metals in an oxygen plasma
Authors: Chaug Yi-Shung , Adams Richard
Published: July 2002

Deposition of backstreaming oil vapor onto work pieces in a vacuum chamber can be a serious source of contamination. In addition to the contamination due to the backstreaming oil, a possibly more serious problem might be caused by breakdown or decomposition of the oil and the reaction of the decomposition products with the work pieces. Low vapor pressure vacuum pump oils made from perfluorinated polyether (PFPE) are commonly used in vacuum deposition systems. Reactions of backstreamed PFPE with gold films, stainless-steel foils, nickel/iron alloy films, aluminum foils, and silicon wafers when exposed to an oxygen plasma were studied using x-ray photoelectron spectroscopy. The PFPE appeared to decompose and the decomposition products reacted with some of the substrates studied to form metal fluorides. Indications of preferential reactions controlled by the heats of reaction were found.
Electron trapping mechanisms in an irradiated single crystal of quartz
Authors: Carroll D. L. , Doering D. L. , Xiong-Skiba P.
Published: July 2002

Electron trapping states in the near surface region of electron irradiated single crystal quartz have been studied using thermionic and photon simulated electron emission. Electron bombardment at energies between 1 and 4 keV causes oxygen desorption and produces defects and electron trapping states in the material which remain populated for long times. After irradiation the sample is heated and the electron emission is measured as a function of temperature. Five thermionic emission peaks were identified two of which only occur when the sample temperature is below 175 K during irradiation. These peaks occur at temperatures related to the binding energies of the traps. The highest binding energy peaks correlate with oxygen depletion of the surface and we associated these with vacancies both at bulk and surface sites. By measuring the photoelectron emission intensity as a function of incident photon energy, five corresponding photoemission thresholds were identified which are related to electron traps with binding energies ranging from 2.3 to 4.6 eV. Overall, the thermionic emission peaks and corresponding photoemission thresholds provide a direct measure of the trap energies for both intrinsic and radiation induced defects in SiO2.
Influence of the xenon induced work function change on the xenon binding energy in photoemission of adsorbed xenon
Authors: Malafsky Geoffrey P.
Published: July 2002

Photoemission of adsorbed xenon has been shown to probe the local atomic work function. The Xe binding energy has a constant value relative to the vacuum level causing the measured binding energy relative to the Fermi level to vary with the work function of the adsorption site. The alignment of the Xe core level to the vacuum level should result in peak shifts with the work function change caused by the adsorbed Xe since the substrate vacuum level shifts with this work function change. However, the Xe peak positions are invariant to the work function changes and remain aligned to the work function of the clean substrate. It is shown in this article how this invariance creates a paradox for the model of the Xe core levels aligned to the vacuum level. The paradox arises from the simultaneous invariance of the Xe and the substrate core level binding energies to the work function change along with the modified threshold for secondary electron emission. The work function change is typically described by a dipole field created by the adsorbed atom. However, this dipole field would alter the kinetic energy of the substrate photoelectrons as well as the secondary electron threshold. A compensating change in the contact potential difference could make the measured substrate levels constant but this would require the Xe level to shift which they do not. This is the basis of the paradox which cannot be resolved by ascribing the work function change to an electrostatic field such as an adsorbed dipole or screening of the image charge. It is proposed that the work function change originates from the perturbation of the conduction electron wave function by the Xe adatom as described for the effect of Xe in scanning tunneling microscopy.
Temperature and composition dependent structures of SixGe1−x/Si and SixGe1−x/Ge superlattices
Authors: Carter Lawrence E. , Weakliem Paul C. , Carter Emily A.
Published: July 2002

We have investigated the equilibrium structures of thin-layer SixGe1−x/Si and SixGe1−x/Ge superlattices as a function of composition and temperature using a Monte Carlo simulation technique combined with a many-body empirical potential. In general, the alloy layers are found to adopt an overall random structure at equilibrium. Some segregation of Ge to the interface is found to occur at room temperature in superlattices containing pure Si layers and high Ge content in the alloy. The alloy lattice is highly sensitive to the degree of strain imposed by the Si or Ge substrate: We observe a significant expansion or compression of the alloy lattice perpendicular to the interface as a means of relieving the imposed strain.
Laser induced desorption of small alcohols from Ag(111) by resonant vibrational excitation
Authors: Chan K.-C. , Donsig H. A. , Ranier D. , Brown L. S.
Published: July 2002

Laser induced photodesorption of methanol, ethanol, and 1-propanol from films condensed on a Ag(111) crystal by resonant excitation of the O–H stretching vibration has been examined, and preliminary results are presented. The desorption yield depends exponentially on the laser pulse energy. For a particular pulse energy, the desorption yield decreased with increasing molecular weight of the alcohol, which is consistent with the variation of the heats of adsorption for these molecules. For methanol, a strong dependence of the desorption yield on the film morphology was observed as well, with crystalline films producing desorption signals as much as an order of magnitude greater than amorphous films of the same thickness. Time-of-flight measurements have been used to determine the kinetic energy of the desorbed molecules, and it was found that this energy also depends on the laser pulse energy. For a fixed pulse energy, the observed kinetic energy increased with increasing molecular weight of the alcohol. All of these results are at least qualitatively consistent with a resonant heating mechanism for the photodesorption process.
Fabrication and x-ray photoelectron spectroscopy of granular Ge in Al and Al2O3 matrices
Authors: Waite M. M. , Shah S. Ismat , Doele B. A. , Unruh K. M.
Published: July 2002

Granular Ge films consisting of Ge grains uniformly dispersed in Al and Al2O3 matrices were prepared by magnetron sputtering. Films were deposited by either cosputtering a Ge target and an appropriate matrix target or, as in the case of Al2O3, by sputtering composite targets pressed from mixtures of Ge and Al2O3 powders. Films containing 10%–90% Ge were fabricated in both the cases. Transmission electron microscopy analyses of the Ge–Al films indicate a granular to nongranular microstructure transition with composition. In the Ge–Al2O3 system similar granular microstructure is obtained at low Ge concentrations; but high Ge concentration films, although phase separated, did not have microstructure typical of the granular films. The granular films have grain size ranging between 20 and 100 nm. X-ray photoelectron spectroscopy analyses of Ge–Al films indicate the presence of small amounts of oxygen in the films, perhaps from the residual gases in the system or from the targets. This oxygen, however, was found to be preferentially associated with Al. Ge existed primarily in the elemental form. In the case of Ge–Al2O3, various oxides of Ge form depending on the composition.
Plasma enhanced chemical vapor deposition silicon oxides as studied by x-ray photoelectron spectroscopy, Rutherford backscattering, electron recoil detection analysis, infrared spectroscopy, and electron spin resonance
Authors: Sindzingre T. , Ermolieff A. , Marthon S. , Martin P. , Pierre F. , Peccoud L.
Published: July 2002

SiO2 thin films were obtained by microwave plasma enhanced chemical vapor deposition. Plasma with two different gas mixtures were studied: Ar/O2/SiH4 and O2/SiH4, the gas ratio R=O2/SiH4 varying from 0.5 to 10 with two radio frequency bias powers (0 W and 100 W). Seventeen dielectric layers with a thickness of around 500 nm were studied to determine their chemical composition by x-ray photoelectron spectroscopy and valence band studies, Rutherford backscattering spectroscopy and elastic recoil detection analysis, infrared spectroscopy, and electronic spin resonance. These samples could then be classified into three groups corresponding to different SiOH and SiH or only SiOH concentrations. Their stoichiometries were also determined. An explanation of the valence band shift and its modifications is proposed.
Control of As diffusion using ultrathin metal passivating layers at GaAs(100) surfaces
Authors: Raisanen A. , Vitomirov I. M. , Brillson L. J. , Kirchner P. D. , Pettit G. D. , Woodall J. M.
Published: July 2002

We have performed low-energy cathodoluminescence spectroscopy (CLS) and synchrotron radiation photoemission (SXPS) measurements of Sb-passivated, clean and ordered molecular-beam epitaxy-grown GaAs(100) surfaces. SXPS measurements show an effective stabilization of the surface As/Ga atomic ratio under annealing for Sb-passivated surfaces, in contrast to the variations in the surface stoichiometry observed for unpassivated GaAs(100) surfaces. Our CLS data provide evidence for the generation of deep level states during annealing to 550 °C in the GaAs(100) subsurface region. Fabrication of a passivating layer by annealing a 2 ML Sb layer on the GaAs(100) surface has been found to dramatically reduce the formation of this subsurface defective layer by inhibiting As desorption from the surface. Studies of Al Schottky barrier formation on Sb-passivated layers demonstrate that the Schottky barrier value becomes independent of the details of processing, in contrast to the surface-dependent variations in barrier height observed for Al/GaAs(100) junctions without Sb passivating layers.