bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural and chemical effects of low energy ion bombardment of PMDA-ODA surfaces
Authors: Sengupta Kabul S. , Birnbaum Howard K.
Published: July 2002

The effects of ion irradiation on polyimide surfaces have been studied using x-ray photoemission techniques. Ion bombardment with energies in the range 0.5–2.0 keV and doses between 8×1013 and 1×1015 ions/cm2 were carried out in situ in the x-ray photoelectron spectrometer and the chemistry of the modified surface was monitored using core level spectral changes. At low doses and energies, carbonyl groups were preferentially sputtered keeping the rest of the monomer intact. Loss of nitrogen was insignificant compared to losses of carbon and oxygen. At higher energies and doses, the polymer undergoes extensive bond scission, restructuring of various functional groups and species, together with radical and anion formation. High resolution spectra indicated a binding energy scale shift to a lower value, which increased with ion energy and dose, and which was related to the creation of a surface negative charge. The effects of exposure to moisture in the ambient on the surface charge, on the surface structure, and on the surface chemistry was studied.
Characterization of the resolving power of a double multilayer monochromator in the energy range of 600–900 eV
Authors: Puik E. J. , van Dorssen G. E. , van der Wiel M. J. , Verhoeven J. , van der Laan G. , Padmore H. A.
Published: July 2002

Two different pairs of x-ray reflecting multilayer coatings have been tested in a double crystal monochromator configuration. The two pairs consisted of Ni (0.4 nm)–C (1.85 nm) and NiSi (0.4 nm)–C (1.85 nm), both with 225 periods. In order to determine the resolution in the energy range of 600–900 eV, the photoelectron yield of several 3d transition metal compounds was recorded as well as the throughput around the Ni L lines. We found for both pairs a resolving power of 220. Simulations taking into account the angular divergence of the x-ray beam yield a resolution of 250. The difference with the observed value can be due to the nonhomogeneity of the multilayer coating.
Compact electron cyclotron resonance ion source with high density plasma
Authors: Shimada Masaru , Watanabe Iwao , Torii Yasuhiro
Published: July 2002

A compact electron cyclotron resonance (ECR) ion source has been developed that has an outer diameter of 11 cm and generates a high-density plasma (1×1013 cm−3, O2 gas) at low microwave power (200 W). The source incorporates a plasma chamber with a 5-cm diam., which is smaller than the cutoff size (7.2 cm) as determined by the microwave frequency (2.45 GHz). To accommodate this chamber size, the waveguide for coupling microwaves into the chamber through a vacuum window was miniaturized by filling it with dielectric material. A plasma density of 4×1011 cm−3 was obtained by using a BN plate as the microwave window. Moreover, the coupling efficiency of the microwaves to high-density plasma was enhanced by choosing alumina with a high dielectric constant as the window. With this window, a much higher plasma density of 1×1013 cm−3 was achieved at a low microwave power of 200 W. A coaxial cable can be utilized at this power for easily adapting this compact ECR source to vacuum systems.
Surface x-ray diffraction study of the Au(111) electrode in 0.01 M NaCl: Electrochemically induced surface reconstruction
Authors: Ocko B. M. , Gibaud Alan , Wang Jia
Published: July 2002

The structure of the Au(111) electrode surface in a 0.01 M NaCl electrolyte has been investigated using grazing incident angle x-ray diffraction. The top layer of gold atoms undergoes a reversible phase transition between the (1×1) bulk termination and a (p×√3) uniaxial discommensuration (striped) phase on changing the electrode potential. Below a critical potential the stripe separation, p=23, is identical to vacuum measurements. At sufficiently positive potentials the surface forms an ideally terminated, (1×1), Au(111) surface. Cycling the potential in the reconstructed region improves the reconstructed surface order.
Theoretical studies of clean and hydrogenated diamond (100) by molecular mechanics
Authors: Yang Yuemei L. , D’Evelyn Mark P.
Published: July 2002

The atomic structure and energetics of the clean (100)-(2×1), (100)-(2×1):H monohydride, (100)-(1×1):2H full dihydride, (100)-(3×1):1.33H intermediate dihydride, and other intermediate hydride surfaces obtained by local removal of H atoms from or addition of H atoms to the (2×1) monohydride, are investigated by molecular mechanics (MM3). The monohydride phase is found to be the most stable thermodynamically and is predicted to be the dominant phase under chemical vapor deposition conditions. Gas-surface reactions relevant to diamond chemical vapor deposition involving hydrogen and the diamond (100)-(2×1):H surface are discussed in light of the derived energetics.
X-ray photoelectron spectroscopy study on the electrical double layer at an Al2O3–Al interface
Authors: Sambe Hideo , Ramaker David E.
Published: July 2002

Upon oxidation of a clean Al surface, an electrical double layer (EDL) is formed at the Al–Al2O3 interface. This EDL is investigated using x-ray photoelectron spectroscopy data available in the literature. The EDL strength, measured as a potential difference across the EDL, depends on the Al surface and the oxidation process. The polarity of the EDL is however invariably the same: the Al2O3 side of the Al–Al2O3 interface is always positively charged. The reduction of the Al work function upon oxidation is attributed to this EDL. The asymmetry in the potential barrier shape formed in Al–Al2O3–Al sandwiches is also attributed to a strong EDL at the electrode-film interface and a weaker EDL at the interface between the counter electrode and the film.
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u growth of YBa2Cu3Ox thin films by reactive cosputtering
Authors: Hahn M. R. , Hylton T. L. , Char K. , Beasley M. R. , Kapitulnik A.
Published: July 2002

We have synthesized superconducting YBa2Cu3Ox thin films in situ using magnetron cosputtering with three metallic targets (Y, Ba, Cu). We present details of the sputtering chamber, as well as the growth conditions necessary to obtain superconducting films. We discuss the effects of oxygen and ozone partial pressure, differential pumping, O2–Ar plasma deposition and Ba–Cu alloy targets. We elaborate on our ozone condensing and delivery system. Finally, we describe the difficulties encountered with the deposition system and provide details of possible improvements.
Characterization of sputter deposited tungsten films for x-ray multilayers
Authors: Aouadi M. S. , Parsons R. R. , Wong P. C. , Mitchell K. A. R.
Published: July 2002

The microstructural and optical properties of tungsten thin films prepared by dc magnetron sputtering were investigated as a function of the argon pressure. The films were characterized by x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), x-ray diffraction (XRD), grazing x-ray reflectometry (GXR), and spectroscopic ellipsometry (SE). From the analysis of the XPS data, the films were found to consist of a base tungsten layer, a graded oxide transition layer, and a surface oxide layer. Also, the thickness of the oxide layers were determined. XRD indicated that the films were either amorphous or composed of crystallites with grain size <100 Å. STM and GXR have revealed that the films grown at low pressures were the smoothest. Finally, SE measurements allowed the determination of the dielectric function of a compact tungsten layer. Further SE analysis of the films indicated that with increasing argon pressure, the films developed into a more voided columnar structure.
Formation of cBN films by ion beam assisted deposition
Authors: Wada Tetsuyoshi , Yamashita Nobuki
Published: July 2002

Boron nitride films were deposited by using ion beams of nitrogen mixed with argon and simultaneous evaporation of boron. The effect of deposition conditions on the formation of the cBN phase were also studied. The acceleration voltage of ions was in the range of 0.3–7 kV. The deposited films were analyzed by infrared absorption spectra, x-ray diffraction, and transmission electron diffraction. The infrared absorption spectra showed a strong absorption at 1080 cm−1, indicating a formation of the cBN film. It seemed that the amount of the cBN phase in deposited films largely increases with decreases in acceleration voltage, and that the use of ion beams of nitrogen mixed with argon is effective for the formation of the cBN phase. Deposited films exhibited electron diffraction rings with interplanar spacings that agreed well with the values of cBN having a zinc blende structure. Deposited films also exhibited x-ray diffraction patterns that agreed with the (111) plane of cBN. The micro Vickers hardness of the obtained film was 4500–5500.
Kinetic model for the chemical vapor deposition of tungsten in the silane reduction process
Authors: Hsieh Julian J.
Published: July 2002

The kinetics involved in the chemical vapor disposition of tungsten, using the silane reduction chemistry, is modeled by a triple Eley–Rideal mechanism, which includes three competitive surface reaction pathways: (1) silane reduction of surface adsorbed WF6, (2) surface dissociation of silane and silicon reduction of WF6, and (3) (residual) hydrogen reduction of surface adsorbed WF6. The last two reaction pathways have not been properly considered in the past, and will be shown to be of critical importance to the understanding the complex Arrhenius behavior exhibited by the silane reduction process. A quantitative deposition rate expression, with no fitting parameters, is derived from the kinetic model using kinetic constants in the literature. The model can predict the deposition rate obtained experimentally, after taking into account the effect of reactant depletion in the reactor.
Fabrication of quantum dot structures using aerosol deposition and plasma etching techniques
Authors: Maximov I. , Gustafsson A. , Hansson H.-C. , Samuelson L. , Seifert W. , Wiedensohler A.
Published: July 2002

We present a novel technology for the fabrication of quantum dot structures using the deposition of ultrafine aerosol Ag particles onto the surface of GaInAs/InP quantum well structures grown by metal-organic vapor-phase epitaxy. The particles, ranging in size between 30 and 40 nm, are subsequently used as an etching mask. The aerosol particles are produced by homogeneous nucleation and have a diameter in the range of 2–100 nm. After size selection, the monodisperse particles with a very narrow size distribution are deposited onto the semiconductor surface at a density of about 109 cm−2. Optimized CH4/H2/Ar electron cyclotron resonance plasma etching at low energy (about 100 eV) results in the formation of free-standing columns 50–80 nm in diameter and 120–280 nm in height. Their size and stability were found to be dependent on the etching conditions (e.g., methane concentration and ion energy) and the diameter of the particles. Low-temperature cathodoluminescence was used to evaluate the optical quality of the quantum dot structures fabricated by this technique.
Reactive sputtering of Ta under gradient oxygen pressure
Authors: Niwa T. , Saito T. , Kinbara A.
Published: July 2002

The reactive deposition process of TaOx thin films onto a substrate surface under a gradient of oxygen pressure in dc magnetron sputtering was studied. By assuming that Ta and O2 react on the Ta target and the glass substrate surface, the dependence of film characteristics on target current and the position on the substrate surface was explained. Transparent films were obtained under the condition: average total pressure PAr+O2=5×10−3 Torr, average oxygen pressure PO2=6×10−4 Torr, target current density <0.042 A/cm2, deposition rate <830 Å/min. For these conditions, about 73% of Ta atoms deposited on the substrate were oxidized on the target surface and the rest, on the substrate surface. The oxygen flux onto the substrate should be 40 times larger than the tantalum flux to obtain stoichiometric tantalum oxide films.
Characteristics of oxygen implanted indium phosphide
Authors: He L. , Anderson W. A.
Published: July 2002

Oxygen implantation was performed on n-type (undoped and Sn doped) and p-type (Zn doped) InP. Ion implantation was done at ion energy of 50 and 100 keV with implantation doses of 1010, 1011, and 1012/cm2. Carrier compensation was observed in p-InP and some n-InP samples as confirmed by current–voltage (I–V) and capacitance–voltage (C–V) measurements. Deep level transient spectroscopy was used to characterize defect levels and their relation to carrier compensation. The compensation comes from free carrier trapping in damage induced defect levels. In p-InP, the dominant trap levels were located deep in the band gap with activation energy of 0.57–0.61 eV below the conduction band. This may be the reason that p-InP can be made highly resistive. For n-InP, observed damage induced trap levels located in the upper half of the band gap, with activation energies of 0.28 or 0.35 to 0.47 eV below the conduction band, caused the difficulty in making n-InP highly resistive. Carrier creation was observed in n-InP which may come from certain shallow donor type defect levels.
Metal ion implantation for large scale surface modification
Authors: Brown Ian G.
Published: July 2002

Intense energetic beams of metal ions can be produced by using a metal vapor vacuum arc as the plasma discharge from which the ion beam is formed. We have developed a number of ion sources of this kind and have built a metal ion implantation facility which can produce repetitively pulsed ion beams with mean energy up to several hundred kilo electron volts, pulsed beam current of more than an ampere, and time averaged current of several tens of milliamperes delivered onto a downstream target. We have also done some preliminary work on scaling up this technology to very large size. For example a 50-cm diam (2000 cm2) set of beam formation electrodes was used to produce a pulsed titanium beam with ion current over 7 A at a mean ion energy of 100 keV. Separately, a dc embodiment has been used to produce a dc titanium ion beam with current over 600 mA, power supply limited in this work, and up to 6 A of dc plasma ion current was maintained for over an hour. We present here a review and summary of this metal ion implantation research program and describe some of the surface modification research that we have done with it.
Preparation and characterization of crystalline ZrC films
Authors: Tessner T. C. , Davis P. R.
Published: July 2002

The characterization of the surface properties of ZrC films grown by thermally evaporating ZrC onto room temperature W(100)and W(110) and then annealing, are reported. These films as deposited have no long range order as determined by low energy electron diffraction, but heating to above 1800 K produces well-ordered layers. During annealing the ZrC(100) face forms on W(100), and the ZrC(111) face forms on W(110). Work functions as low as 2.75 eV have been measured on these films after initial heating, but final values are 3.85 eV for ZrC(100), and from 4.40 to 4.80 eV for ZrC(111), depending on the C contamination of the W(110) substrate. From thermal desorption spectra desorption energies were also calculated. Possible mechanisms for the ZrC crystalline ordering during annealing are discussed.
Stable and reproducible Bayard–Alpert ionization gauge
Authors: Arnold P. C. , Bills D. G. , Borenstein M. D. , Borichevsky S. C.
Published: July 2002

This is the third in a series of related reports on (1) nonstable behavior of widely used ionization gauges, (2) causes of nonstability and nonreproducibility in widely used Bayard–Alpert (BA) gauges, and (3) a stable and reproducible BA gauge design with approximately a tenfold improvement in both stability of gauge calibration after thousands of hours of operation and reproducibility gauge-to-gauge compared to older design BA gauges and inverted magnetron gauges. Computer simulation of electron and ion trajectories utilizing a program named simion was used to optimize the design. A grounded conducting shield of closely controlled dimensions completely surrounds the cathodes and anode. The anode has partial end caps on both ends. Dual, independently tensioned, thoria coated iridium ribbon cathodes are precisely positioned so that the flat emitting surfaces face imaginary axes laterally displaced from the anode axis by a small amount. The cathodes are relatively short compared to the anode. A 0.040 in. diam ion collector and an emission current of 100 μA help extend the upper pressure measuring limit to above 1×10−2 Torr and provide an x-ray limit of 1.6×10−10 Torr. With a 0.005 in. diam ion collector and an emission current of 4 mA, the x-ray limit is 1.4×10−11 Torr and the upper pressure measuring limit is above 1×10−3 Torr. This new technology, called Stabil-Ion technology, provides sufficient stability and reproducibility to justify storing accurate calibration data for a specific Stabil-Ion system or averaged data from a set of nominally identical systems in electronic memory. Thus, the typical nonlinearities in sensitivity and purposeful changes in emission current or gas type do not significantly affect the accuracy of pressure indication. Consequently, accurate real time readout of pressure and stable process control are provided by the new design.
Photodissociation of SF6 near the F 1s absorption edge
Authors: Mochiji K. , Lee K. , Ma C.-I. , Kim D. Y. , Mahalingam M. , Hanson D. M.
Published: July 2002

Core-excited fragmentation of SF6 is analyzed by using monochromatic synchrotron radiation and time-of-flight mass spectroscopy. Excitation of fluorine K and sulfur L levels yields highly dissociated and multiply charged ions such as SF2+, S2+, and S3+ that are not seen with valence level excitation. Excitation of sulfur L levels is found to be more dissociative than that of fluorine K levels in the sense that more atomic ions and more multiply charged sulfur ions are produced. In addition to the above results, the generation mechanism for these ions is discussed by considering the multistep Auger cascade decay of core holes.
Development of artificial neural networks for in situ ellipsometry of films growing on unknown substrates
Authors: Urban F. K. , Tabet M. F.
Published: July 2002

An in situ ellipsometry method has recently been developed by the authors in which the refractive index and thickness of a growing film can be computed without knowledge of the underlying interface layers and the substrate. The method makes use of five in situ measurements through windows in a deposition system. A ‘‘virtual interface’’ is defined by the first measurement made after the growth has settled down following the initial interfacial microstructure such as island formation and interface reactions. A variably damped least squares algorithm computes the optical properties of the growing overlayer film, four thicknesses (of growth past the virtual interface), and the complex reflection coefficients of the virtual interface. However, this algorithm alone is slow and requires initial estimates within a few percent of the solution. Artificial neural networks have been developed to provide very quickly (sub millisecond) initial estimates of sufficient accuracy to improve overall solution speed with the goal of real time operation. Results using several different multilayer perceptron architectures will be presented. Performance using existing in situ data recorded for Ni and Au grown on BK7 substrates are presented.
Construction and commissioning of the Synchrotron Radiation Research Center vacuum system
Authors: Hsiung G. Y. , Huang J. R. , Shyy J. G. , Wang D. J. , Chen J. R. , Liu Y. C.
Published: July 2002

The installation of the vacuum system of the Synchrotron Radiation Research Center 1.3 GeV electron storage ring was completed in January 1993. Both the straight (S-) chambers and bending (B-) chambers are made of aluminum alloy. Oil-less machining processes were adopted in the fabrication of the B-chambers and some components of the S-chambers. Stringent welding processes were performed in a clean room in order to get a good welding quality and a clean chamber surface. The pumping system is a combination of several kinds of oil-free pumps. In the commissioning phase, the photon induced desorption phenomenon was clearly observed. The major desorbed gases are H2, CH4, CO, and CO2. The desorption yields of these gases are described in this paper. An interlock system for the purpose of vacuum safety is also built in the system in order to increase the reliability of the vacuum operation. In the early stage of the commissioning, the malfunction of some ion gauges and quadrupole mass spectrometers were observed due to the beam interference. A solution has been found to reduce the interference.
Emitted current instability from silicon field emission emitters due to sputtering by residual gas ions
Authors: Karain W. I. , Knight Larry V. , Allred David. D. , Reyes-Mena A.
Published: July 2002

We have fabricated arrays of silicon field emitters using semiconductor lithography techniques. The density of the tips was 105/cm2. The maximum current that can be extracted from each emitter is limited by resistive heating. We have investigated how the electron current emitted changes under constant applied voltage. We found that the current is very sensitive to the vacuum conditions. We attribute this to sputtering of the emitters due to ionized residual gas molecules. The poorer the vacuum, the higher the instability in the current. We studied this phenomenon at 10−6 and 10−8 Torr. The model of two concentric spherical shells is used to obtain the ion energy distribution. This is then used to calculate the rate of ion bombardment and the rate of atoms sputtered. A lifetime of the tip can be deduced from these calculations.
Surface roughness formation in Si during Cs+ ion bombardment
Authors: Matsuura Y. , Shichi H. , Mitsui Y.
Published: July 2002

The dependence of the formation of surface roughness in Si on the incident angle of the Cs+ primary ion in secondary ion mass spectrometry is reported. No ripples formed in the analytical crater bottom when the primary ion incident angle was from 0° to 30° for sputtered depths of less than 4 μm, but ripples were observed when the incident angle was from 45° to 75°. The depth of ripple formation became shallower with the incident angle increasing. Cross sections of ripples observed by a scanning electron microscope and a transmission electron microscope suggest that ripples grow by forming facets from those plane faces with the largest sputtering rates so that the shapes of the facets remain constant during sputtering.
Existence of structural inhomogeneity in ion-beam-modified polyimide films
Authors: Xu X. L. , Xu D. , Xu H. L. , Wang R. , Zou S. C. , Du G. D. , Xia G. Q.
Published: July 2002

Pyromellitic dianhydride and oxydianiline polyimide films turn electrically conductive upon irradiation with energetic ions. Raman spectroscopy shows an initial dissociation of the molecular structure at low irradiation doses ranging from 1×1014 to 1×1015 B+/cm2, followed by the appearance, at a high dose of 1×1016 B+/cm2, of structures similar to those observed in amorphous graphite. Comparing the reduced Raman spectra of materials irradiated up to a dose as high as 1×1016 B+/cm2 with the one-phonon density of states of amorphous graphite, one finds that this structural similarity to graphite only exists within a short range. Meanwhile, an ion-beam-induced aggregation of aromatic rings in irradiated polyimide films is indicated by ultraviolet-visible spectroscopy. In view of the structural information from resonant Raman spectroscopy, the existence of structural inhomogeneity is proposed for the high-dose irradiated polyimide. From perspectives of the model of heterogeneous media, the structural similarity to graphite within a short range is attributed to the existence of the second phase composed of broken functionalities of irradiated polyimide and the sp3-bonded carbon atoms.
Instrument for the measurement of adhesion forces in ultrahigh vacuum surface analysis apparatuses
Authors: Takahashi Kunio , Iiyama Takashi , Katoh Noboru , Onzawa Tadao
Published: July 2002

An instrument for direct measurement of the adhesion forces in the ultrahigh vacuum (UHV) chamber of surface analysis apparatus [Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy, low-energy electron diffraction, etc.] was developed. It is attachable to any UHV chamber which has a open flange, a manipulator, and a specimen introduction system. It was attached to an AES apparatus (Perkin-Elmer PHI model 650) and tested. The adhesion force between the Au ball and Si wafers was examined.
Electron cyclotron resonance plasma and thermal oxidation mechanisms of germanium
Authors: Wang Y. , Hu Y. Z. , Irene E. A.
Published: July 2002

The electron cyclotron resonance (ECR) plasma oxidation and thermal oxidation mechanisms for germanium were investigated using in situ spectroscopic and single wavelength ellipsometry. ECR plasma oxidation was performed at substrate temperatures of 80–400 °C while thermal oxidations were performed between 400 and 600 °C. Optical modeling shows that there is an interface between the oxide film and the substrate that is composed of germanium oxide and amorphous germanium. Fourier transform infrared and x-ray photoelectron spectroscopy data confirm that the oxides resulting from thermal and ECR plasma oxidation are GeO2. The real time oxidation analysis shows that both kinds of oxidation of Ge follow linear-parabolic kinetics, and yield temperature activated transport. The activation energy for ECR plasma oxidation is about one order smaller than that of thermal oxidation. This indicates different oxidation species. Less charge was formed at the interface for ECR plasma oxides.
Study of ion-beam-sputtered ZnO films as a function of deposition temperature
Authors: Qu Y. , Gessert T. A. , Coutts T. J. , Noufi R.
Published: July 2002

In this investigation, undoped, ion-beam-sputtered ZnO thin films have been studied as a function of deposition temperature from room temperature to ∼350 °C. Analysis techniques include x-ray diffraction (XRD), scanning tunneling microscopy, Hall measurement, and spectrophotometry. Hall measurements show that the electrical resistivity of the film decreases with increasing deposition temperature, due to increasing carrier mobility. Additionally, temperature-dependent Hall measurements show that the potential barrier height at the grain boundaries decreases with increasing deposition temperature. By combining data from XRD and Hall measurements, the potential effects of scattering by grain boundaries and ionized oxygen vacancies have been numerically modeled. This analysis indicates that the electron mobility observed in these films is not readily attributed to these scattering mechanisms alone, and other mechanisms, such as point defects within grains, may be present. Optical analysis indicates that transmission in the visible range improves with increasing substrate temperature. Presently, it is speculated that this improved transmission is mainly due to reduced defect levels both within the grains and at the grain boundaries.
Interaction of H2O and Cl2 on iron oxide surfaces
Authors: Murray E. , Kelber J. A.
Published: July 2002

We have used temperature programmed desorption (TPD) and Auger electron spectroscopy to study H2O–Cl2 interactions on an iron oxide surface under ultrahigh vacuum conditions over the temperature range 90–900 K. On the clean Fe oxide, the TPD spectra of H2O show two desorption peaks at 175 and at 250 K. No H2 desorption is observed. This is in contrast to other studies of H2O on a sputtered α-Fe2O3 (001) plane that indicate the complete dissociation of H2O, leading to H atoms, which then recombine resulting in H2 desorption (220–750 K). The Fe oxychloride [Fe(OCl)x] formation that occurs at low temperatures (240 K) at the Fe polycrystalline surface as a result of H2O–Cl2 interactions does not occur on the Fe oxide surface. FeCl2 desorption is observed at temperatures significantly higher (695 K) than the temperature for the desorption of FeCl2 from metallic Fe (585 K). On the Fe oxide surface, FeCl2 desorption is independent of H2O precoverage, in contrast to results on the Fe surface that show inhibition of FeCl2 formation with increasing H2O preexposure. These results indicate the presence of different sites on the oxide surface for the preferential adsorption of Cl2 and H2O, in agreement with our previously reported x-ray photoelectron studies.
Resolution in sputter depth profiling assessed by AlAs/GaAs superlattices
Authors: Kajiwara K. , Shimizu R.
Published: July 2002

AlAs/GaAs superlattices are proposed as a potential reference material for sputter depth profiling since, at present, AlxGa1−xAs/GaAs superlattices are grown in a defect-free single crystalline state with atomically flat and abrupt interfaces by metalorganic chemical vapor deposition. It is anticipated that such superlattices should have wide applicability for the assessment of resolution in sputter depth profiling. A preliminary round-robin test was performed by the International Organization for Standardization (ISO)/Technical Committee (TC) 201 on Depth Profiling in Japan. It is clear that in all the Auger electron spectroscopy (AES) and secondary ion mass spectrometry (SIMS) data obtained on these superlattices, the depth resolution is a constant unrelated to the sputtered depth. In the x-ray photoelectron spectroscopy data, which have a larger analyzed area, the depth resolution deteriorates with the sputtered depth, confirming that the depth resolution is affected by the analyzed area owing to the crater edge effects. Furthermore, in the SIMS data the resolution of the leading and trailing edges depends strongly on primary reactive ion species (O+2, Cs+). This is in contrast to AES data using inert gaseous ions (e.g., Ar+). Consequently, the present round-robin test demonstrated preparatorily that these superlattices are useful for work in order to understand why different techniques and sputtering conditions result in different determinations of resolution.
Heteroepitaxial growth of C70 films on MoS2(0001) and their characterization by low energy electron diffraction and photoelectron spectroscopy
Authors: Han Bo-ying , Hevesi K. , Yu Li-ming , Gensterblum G. , Pireaux J.-J. , Thiry P. A. , Caudano R.
Published: July 2002

Heteroepitaxial growth of C70 films (up to 1000 Å in thickness) has been obtained on the MoS2(0001) lamellar substrate. Photoelectron spectroscopies were used to study the C70/MoS2(0001) interface interaction. The geometry of the epitaxy and the lattice parameters of the deposited C70 overlayer were determined by low energy electron diffraction. The C70 film growth mode was shown by x-ray photoelectron spectroscopy to be layer-by-layer (Franck–van der Merwe mode); a small upward band bending (∼90 meV) of the substrate was observed, indicating a slight charge delocalization from the substrate toward the C70 overlayer in the interface region.
Reactive ion etching-induced damage in GaAs/AlGaAs quantum well structures and recovery by rapid thermal annealing and hydrogen passivation
Authors: Yoo Byueng-Su , Park Seong-Ju , Park Kyung-Ho
Published: July 2002

Reactive ion etching (RIE)-induced damage in a GaAs/AlGaAs quantum well structure, consisting of four GaAs quantum wells with different thicknesses, has been investigated by photoluminescence (PL). RIE was performed using a mixture of He and CCl2F2 gases under a variety of etching conditions. The PL intensities from the quantum wells damaged under an etching condition of physical sputtering decrease uniformly across the depth through the sample. The reduced PL intensities from the damaged quantum wells are restored by rapid thermal annealing and hydrogen plasma treatment. In particular, PL intensities from the quantum wells situated at the deep region from the surface are more drastically recovered than those from the near surface region. This result suggests that the decreases in the PL intensities created in the deep region have different recovery efficiencies from those at the near surface region. It is indicated also that the defects in the deep region are closely related to the vacancies of sublattice, particularly when light ions are involved in the etching process.
Modeling of a multistage claw rotor vacuum pump
Authors: Ioffe I. V. , Koss V. A. , Gray M. , Livesey R. G.
Published: July 2002

Claw rotor compressors are used in a wide variety of vacuum pumping applications. However, the published literature on these machines offers little guidance on the physical processes which occur during pump operation, their effect on pump performance, or the influence of design and operating parameters. In the present work, a model based on algebraic and differential equations describing pressure and temperature time dependence for a multistage pump is developed. The equations are based on the laws of conservation of mass and energy and use a lumped-parameter approximation. The model includes volume variation, gas flow between stages, leakage within and between stages, gas mixing, and heat exchange. Expressions for the pumping speed and power consumption are also presented. Predictions based on the model are compared with experimental data.
Investigations of the surface chemistry of pathogenic silicates
Authors: Seal Sudipta , Krezoski Susan , Hardcastle Steven E. , Barr Tery L. , Petering David H. , Cheng Chi-Feng , Klinowski Jacek , Evans Peter H.
Published: July 2002

The following is a continuation of our extensive investigations of the chemistry of complex silicate systems employing a combination of electron spectroscopy for chemical analysis and magic angle spinning nuclear magnetic resonance. In this case, we are beginning to provide unique chemical information that may have implications in the field of silicate-induced pathogenesis (e.g., asbestosis). Select silicate materials (such as amphiboles) have been investigated both before and following alterations of their physical conditions (e.g., crushing) and also before and after contact with certain in vitro cell cultures. In our studies to date, we have been able to track the ‘‘in-lattice’’ chemistry of the constituents of these, and related, silicates, determining such features as the simultaneous presence of aluminum in tetrahedral and octahedral sites of amphiboles, as well as the iron in M(4), as opposed to M(3) or M(1) octahedral positions of these amphiboles. We are comparing results for fibrous silicates with those achieved with related nonfibrous forms to try to confirm (or deny) the views of the biomedical community regarding the structural and chemical features of the fibrous silicates that are suspected to be primarily responsible for the pathogenic silicate behavior.
Visualization of a buried organic interface by imaging time-of-flight secondary ion mass spectrometry and scanning Auger microprobe of an ion-beam crater edge
Authors: Schamberger Patrick C. , Jones Gary L. , Gardella Joseph A. , McKeown Patrick J. , Davis Larry E.
Published: July 2002

A method has been developed for chemically imaging a buried organic interface of thickness similar to that of a biological conditioning film. Using an ion beam to form a sputter crater, elemental analysis of the edge of the crater is performed using Auger electron spectroscopy and chemical imaging of the edge is performed by time-of-flight secondary ion mass spectrometry. The crater edge that is formed due to the shape of the ion beam and geometry of the spectrometer has the ability to magnify the interfaces by 1000×. Samples mimicking titanium bone implant protheses were analyzed to demonstrate the feasibility of the method.
New ultrahigh-frequency plasma discharge for overcoming the limitations of etching processes
Authors: Samukawa Seiji , Nakano Toshiki
Published: July 2002

Electron, ion, and neutral temperatures are measured in an ultrahigh-frequency (UHF) plasma by Langmuir probe and Doppler-shifted laser-induced fluorescence. The electron, ion, and neutral temperatures are found to be 1.5–2.0 eV (Ar plasma), 0.066 eV for Ar+, and 0.036 eV for Ne, respectively, and are lower than those reported for electron cyclotron resonance and helicon wave plasmas. The low temperatures cause lower dissociations of CHF3 gas even in the plasma production region of the UHF plasma source. The plasma is expected to dramatically improve the selectivity of SiO2 to the underlying Si. Additionally, the plasma can be used to accomplish a notch-free poly-Si etching profile and microloading-free Si trench etching with a high etching rate and high anisotropy with a narrow space pattern of less than 0.3 μm. It is suggested that the charge accumulation with the narrow space pattern is eliminated because of the low electron temperature in the UHF plasma.
Chemical bonding and electronic properties of Se-rich ZnSe–GaAs(001) interfaces
Authors: Bratina G. , Ozzello T. , Franciosi A.
Published: July 2002

We report synchrotron radiation, soft-x-ray photoemission spectroscopy studies of ZnSe–GaAs heterojunctions fabricated by molecular beam epitaxy in situ on GaAs(001)2×4 substrates. Measurements of the band offsets confirm that interfaces grown in Se-rich conditions exhibit relatively low valence band offsets (as low as 0.5 eV), while interfaces grown in Zn-rich conditions show relatively high valence band offsets (as high as 1.3 eV). In the Se-rich case, the improved surface sensitivity of the technique revealed previously unreported contributions to the As 3d and Ga 3d core lineshapes, with substantial (0.8–2 eV) chemical shifts. The shifts, as well as the coverage and escape-depth dependence of the results suggest enhanced atomic intermixing across Se-rich interfaces, with the formation of both Se–As and Se–Ga chemical bonds.
Adsorption of CO on Pd/Al2O3/Ta(110) model catalysts
Authors: Rainer D. R. , Wu M.-C. , Mahon D. I. , Goodman D. W.
Published: July 2002

The adsorption of CO on Pd/Al2O3/Ta(110) model catalysts was studied using infrared reflection adsorption spectroscopy (IRAS) for two different Pd coverages, corresponding to 25–30 and 60–70 Å average particle sizes. Striking similarities between the IRAS data for the larger particles and Pd single crystals indicate that the particles are comprised predominantly of 〈111〉 and 〈100〉 facets. The isosteric heat of adsorption of CO extrapolated to zero coverage was determined to be 38.9 kcal/mol on the 60–70 Å particles. IRAS and Auger results provide evidence of CO dissociation on the smaller particles.
High rate vacuum deposition of polymer electrolytes
Authors: Affinito J. D. , Gross M. E. , Coronado C. A. , Dunham G. C. , Martin P. M.
Published: July 2002

Two new, high rate, vacuum processes have been developed for the deposition of polymer electrolyte layers on wide web substrates. One method involves the vacuum extrusion of monomer salt solutions followed by e-beam or ultraviolet (UV) curing. The second method involves the vacuum flash evaporation of the monomer salt solution followed by e-beam or UV curing. Each method is compatible with simultaneous, in-line, deposition by conventional processes like sputtering or evaporation in a wide web system. Optically clear polymer electrolyte layers may be deposited at line speeds in excess of 100 meters per minute with these new techniques. Ionic conductivity measurements will be presented for vacuum deposited, evaporated and extruded, polymer electrolyte layers. Films were deposited with thicknesses ranging from 2 to 50 μm. Application of these methods to ongoing electrochromic and battery work at the Pacific Northwest Laboratory will be discussed.
Optimization of selective TiSi2 chemical vapor deposition by mechanistic chemical kinetics
Authors: Southwell R. P. , Mendicino M. A. , Seebauer E. G.
Published: July 2002

The a priori kinetic optimization sometimes needed for process development has generally proven difficult for reactions governed by surface chemistry. The difficulty usually results from the considerable detail with which the component steps of the overall reaction must be understood. In the present work, we summarize advances in kinetic methodology that were required for fully modeling the chemical vapor deposition of titanium disilicide from TiCl4 and SiH4. Modifications of the ultrahigh vacuum (UHV) technique of temperature programmed desorption (TPD) proved invaluable in measuring useful rate constants for polycrystalline surfaces and for products not normally visible in TPD. New methodology for sample transfer into UHV also provided the data required for development of a silicide process having 100% selectivity on Si vs SiO2. This work represents to our knowledge the first time UHV-based kinetic models have successfully guided the a priori development of a process governed by surface reactions in which optimization has not already been accomplished by enlightened trial and error.
Evaluation of low cost residual gas analyzers for ultrahigh vacuum applications
Authors: Rao M. G. , Dong C.
Published: July 2002

In recent years several low cost computer controlled residual gas analyzers (RGAs) have been introduced into the market place. It would be very useful to know the performance character- istics of these RGAs in order to make an informed selection for UHV applications. The UHV applications include extreme sensitivity helium leak detection and monitoring of the residual gas spectra in UHV systems. In this article, the sensitivity and linearity data for nitrogen, hydro-gen, and helium are presented in the pressure range 10−8–10−1 Pa. Further, the relationships between focus voltage and ion currents, relative sensitivity, and fragmentation factor are also included. A direct comparison method is used in obtaining this data. Spinning rotor and extractor gauges are the transfer standard gauges used in Jefferson Lab’s vacuum calibration facility, with which all the reported measurements here were carried out.
Analysis of the growth processes of plasma-enhanced chemical vapor deposited diamond films from CO/H2 and CH4/H2 mixtures using real-time spectroellipsometry
Authors: Lee Joungchel , Collins R. W. , Hong Byungyou , Messier R. , Strausser Y. E.
Published: July 2002

Real-time spectroscopic ellipsometry (RTSE) has been applied to study the growth of nanocrystalline diamond thin films by microwave plasma-enhanced chemical vapor deposition on silicon substrates. The goal of this research is to characterize the diamond film growth process as a function of the gas source and substrate temperature, comparing the results obtained using various mixtures of CO and H2 with those obtained from a standard mixture of CH4 highly diluted in H2. The capabilities of RTSE have been exploited to establish the true near-surface substrate temperature under the specific diamond film growth conditions, as well as the deposition rates for a succession of films prepared on the same substrate under different conditions. The latter capability allows large regions of parameter space to be scanned expeditiously. As a result of this study, a low-temperature growth process has been identified that yields high deposition rates (up to 2.5 μm/h) at relatively low microwave plasma powers (0.5 kW). In contrast to the commonly-used H2-rich mixtures of CH4 or CO and H2 that exhibit monotonic reductions in the growth rate with decreasing substrate temperature from 800 to 400 °C, CO-rich mixtures of CO and H2 exhibit an increase and a well-defined maximum as the temperature is reduced over this range. At a CO/H2 gas flow ratio of 18, for example, the growth rate peaks near 450 °C and is a factor of ∼20 higher than that obtained with the standard H2-rich mixtures of CH4/H2 and CO/H2. These observations suggest a different diamond growth mechanism from the CO-rich mixtures of CO/H2 with potentially important applications for low-temperature substrate materials.
Observations of standing waves on an inductive plasma coil modeled as a uniform transmission line
Authors: Lamm Albert J.
Published: July 2002

As previously reported by the author at the 47th Annual GEC in paper AA-5 (1994) voltage and current standing waves have been observed along two-and four-turn inductive coils operated at 13.56 MHz. Inductive rf power was used to generate a CHF3 plasma at 4 mTorr. Data from voltage and current probes installed on each end of the coil were used to derive spatial variations of V and I by using the standard formalism of a uniform transmission line. The variation of the effective distributed plasma inductance is presented as well as deviations from transverse electromagnetic modes. The ability to describe the spatial variation of V and I along the coil is useful in the design of inductive plasma etching systems, since both radial and azimuthal variations can potentially affect uniformity of etch and selectivity. The applicability of standard transmission line theory to these coils makes this information readily available via the transmission matrix.
Determining the optical properties of a mixed-metal oxide film, Co3−x−yCrxFeyO4, with spectroscopic ellipsometry and atomic force microscopy
Authors: Ruzakowski Athey P. , Tabet M. F. , Urban F. K.
Published: July 2002

The optical properties of a mixed-metal oxide thin film from the Co3−x−yCrxFeyO4 family has been determined from combined analysis of ellipsometry, atomic force microscopy, and transmittance measurements. These types of films are useful as solar absorbing films on a variety of float glass substrates to lower the solar heat gain admitted through a glass pane in a window, skylight, or door. A commercial product with a film composition in this family is sold under its registered trademark SOLARCOOL® glass. Each constituent metal oxide film was analyzed with variable angle of incidence spectroscopic ellipsometry and transmittance (T) measurements to determine their optical constants and film thickness. Surface roughness was measured with atomic force microscopy and included in the optical model as a known variable. The oxide films were optically modeled with a bulk layer and a known surface roughness layer. The mixed-metal oxide film was optically modeled with an effective medium approximation layer consisting of each constituent metal oxide Fe2O3, Cr2O3, and Co3O4. Best fits between measured and calculated data were obtained by allowing both the film thickness and the optical constants of each constituent oxide phase to vary in the model. Each metal oxide phase (Fe2O3,Cr2O3, Co3O4, and Co3−x−yCrxFeyO4) deposited onto heated soda-lime-silica float glass was identified with thin film x-ray diffraction analysis. The ratio of the metals in the mixed-metal oxide film was determined with x-ray fluorescence analysis. The film thickness was independently measured from in lens cross-sectional field emission scanning electron microscopy images to constrain the modeled film thickness. Spectra for the optical constants of each metal oxide and the mixed-metal oxide are presented and discussed.