bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermomechanical and chemical properties of SiC–C functionally gradient coatings on graphite
Authors: Richards M. R. , Richards A. C. , Taya M. , Ohuchi F. S.
Published: July 2002

Functionally gradient coatings (FGC) represent a new class of composite materials in which the chemical composition and/or structure have been intentionally graded to overcome interfacial discontinuities. When depositing FGCs for applications requiring a homogeneous coating over the entire surface of the material, conventional chemical vapor deposition (CVD) techniques produce discontinuities that compromise the coating’s integrity. We have developed an innovative cold wall CVD apparatus specifically designed to overcome these problems. The key feature of the design is to employ electromagnetic fields that simultaneously heat and levitate the substrate. This technique has been applied to the fabrication of SiC–C functionally gradient coatings on graphite and C/C composites. By controlling the flow rates of the reactant gases (SiCl4, C3H8, and H2), a gradient coating can be grown to a tailored compositional profile and thickness. Thermomechanical, chemical, and oxidation properties of the SiC–C FGCs are characterized in order to assess the coatings reliability for use in high temperature oxidizing environments.
Ion deposition by inductively coupled plasma mass spectrometry
Authors: Hu Ke , Houk R. S.
Published: July 2002

An atmospheric pressure inductively coupled plasma (ICP) is used with a quadrupole mass spectrometer (MS) for ion deposition. The deposited element is introduced as a nebulized aqueous solution. Modifications to the ICP-MS device allow generation and deposition of a mass-resolved beam of 165Ho+ at 5×1012 ions s−1. The ICP is a universal, multielement ion source that can potentially be used for applications such as deposition of mixtures of widely varying stoichiometry or of alternating layers of different elements.
In situ Fourier transform infrared-attenuated total reflection spectroscopy monitoring of polyaniline synthesis mechanism on the p-type silicon electrode
Authors: Fan Qinbai , Ng Lily M.
Published: July 2002

The polymerization of aniline on the p-Si electrode was investigated by in situ Fourier transform infrared-attenuated total reflection spectroscopy. Results show that the N–H vibrational mode of aniline, in the 3490–3050 cm−1 range, shifts to lower wave number when the applied electrode potential becomes more positive. There is no benzidine intermediate in this polymerization process. The IR adsorption spectrum of the polyaniline spectrum obtained by the in situ method is similar to that obtained by ex situ IR transmission detection. The mechanism of polyaniline synthesis on the p-Si electrode is discussed.
Molecular beam epitaxial growth and characterization of mixed (Ti,Nb)O2 rutile films on TiO2(100)
Authors: Chambers S. A. , Gao Y. , Thevuthasan S. , Liang Y. , Shivaparan N. R. , Smith R. J.
Published: July 2002

Epitaxial films of mixed (Nb,Ti)O2 rutile have been grown on TiO2(100) rutile at 600 °C by molecular beam epitaxy. These films grow in a laminar fashion for Nb mole fractions up to ∼0.10. In addition, reflection high-energy and low-energy electron diffraction, along with x-ray photoelectron diffraction and Rutherford backscattering reveal that the overlayers possess excellent long- and short-range structure order up to 10 at. %. However, strain-induced disorder becomes prevalent for higher Nb mole fractions, and the surfaces roughen and become defected accordingly. X-ray photoelectron diffraction and Rutherford backscattering reveal that Nb atoms substitutionally incorporate at cation sites in the rutile lattice for all Nb mole fractions investigated, leading to a mixed rutile NbxTi1−xO2 phase. Analysis of Nb 3d and Ti 2p core-level binding energies reveals that the oxidation state of both Ti and Nb is +4.
Ultrafine silicon quantum wires fabricated by selective chemical etching and thermal oxidation
Authors: Shi Y. , Liu J. L. , Wang F. , Lu Y. , Zhang R. , Gu S. L. , Han P. , Hu L. Q. , Zheng Y. D. , Lin C. Y. , Du D. A.
Published: July 2002

Combining SiGe/Si heteroepitaxy, selective chemical etching, and subsequent thermal oxidation, we have successfully fabricated ultrafine silicon quantum wires (SQWRs) with Si/SiO2 interfaces. Experimental result shows that the present method provides a very controllable way to fabricate ultrafine SQWRs, that is completely compatible with silicon microelectronic technology. As one of the key processes of controlling the lateral dimensions of SQWRs, wet oxidation of silicon wires have been investigated. It is found that a self-limiting oxidation phenomenon of silicon wires occurs for wet oxidation. This oxidation retardation characteristic of silicon wires is discussed.
Controlled bias ramping for scanning tunneling microscopy of molecular adsorbates
Authors: Roach J. S. , Musselman I. H. , Honeyman J.
Published: July 2002

This work details a systematic approach to finding optimum instrumental conditions for obtaining scanning tunneling microscope (STM) images from weakly bound adsorbates. In our laboratory, controlled bias ramping has been implemented on a modified Nanoscope III STM (Digital Instruments, Inc.) using a modified version of Digital’s Electrochemistry STM Software. The tip-to-sample bias is ramped under computer control over a specified voltage range at a programed rate. Simultaneously, the tunneling current is manually altered until the best image quality is obtained. The bias and setpoint, recorded as a function of total imaging time, are stored within the files of the captured images. The effect of these parameters on image quality can then be assessed off-line or postimaging. Controlled bias ramping has proved to be useful in studying molecular adsorbates, including linear alcohols and liquid crystals, deposited onto highly oriented pyrolytic graphite.
Study of station flow dynamics in a sequential multiwafer chemical vapor deposition batch reactor using reactor modeling
Authors: McInerney E. J.
Published: July 2002

Commercial chemical vapor deposition (CVD) equipment is generally designed around either a single-wafer architecture or a multiwafer architecture. Single-wafer systems are touted as giving more control over the deposition process (and thus higher quality films), while multistation systems have higher throughput. In this article, computational fluid dynamics modeling of both configurations is used to better understand their strengths and limitations for the case of CVD TiN films. It is found that the multistation design does result in substantial changes to the flow field at each deposition station in comparison to the single-wafer reactor. However, these flow changes have minimal effect on the actual film deposition profile. This is because the deposition characteristics depend primarily on the z component of velocity, which is not altered. Additionally, the crosstalk between adjacent stations is found to be negligible for gas flows typical of CVD processes.
Fast photoreactions of oxygenates on tropospheric fly ash particles
Authors: Idriss H. , Seebauer E. G.
Published: July 2002

Ethanol and methyl tert-butyl ether (MTBE) are finding increasing use as fuel additives in the U.S. because of governmental mandates, and the relative merits of each have therefore become the focus of intense debate. The ultimate fate of fugitive emissions of these species forms one aspect of this controversy, because ethanol has been implicated in reductions in air quality, while MTBE has been linked to human illness. Both species are known to react homogeneously with photogenerated OH radicals. Here we show that both can also photoreact on fly ash and related particulates present ubiquitously in urban tropospheres. The heterogeneous reactions involving MTBE ultimately form formaldehyde and acetone at rates comparable to purely homogeneous pathways, demonstrating for the first time the existence of a significant catalytic process on tropospheric particulates having widespread spatial distribution. Oxides of Ti and Fe drive the reaction.
A multilevel approach to the control of a chemical–mechanical planarization process
Authors: Telfeyan Roland , Moyne James , Chaudhry Nauman , Pugmire James , Shellman Scott , Boning Duane , Moyne William , Hurwitz Arnon , Taylor John
Published: July 2002

A multilevel hierarchical control system has been designed and is being applied to chemical–mechanical planarization (CMP) process control. The current implementation of the control system incorporates closed-loop run-to-run (R2R) control and open-loop real-time monitoring, and can accommodate inter-cell control. The R2R control element is enabled via a generic cell controller (GCC) implementation that provides flexible automated control of the process and equipment, multiple control algorithm branches and fuzzy logic decision capability among the branches, simulation capabilities, hardware and software independence, and extensive GUI support for control and data analysis. The R2R element utilizes a linear approximation multivariate control algorithm (branch) that supports individual exponential weighted moving average (EWMA) modeling of advices (outputs), weighting of inputs, granularity, and input bounding. The real-time element of the control system utilizes a partial least squares (PLS) algorithm to identify real-time equipment input trace patterns and relate these patterns to alarming conditions. The entire control system is designed to provide multivariate control of CMP process removal rate and uniformity. As a result of extensive design of experiments and testing, the R2R control level has been demonstrated to achieve good control of removal rate and fair control of uniformity. The addition of the real-time element is expected to improve process control and reduce R2R process noise, thus leading to a more effective R2R control element.
Hydrogen adsorption on GaAs (001) surfaces observed by surface photoabsorption and reflectance difference spectroscopy
Authors: Uwai Kunihiko , Kobayashi Naoki
Published: July 2002

Surface reflectance spectra are observed for H-adsorbed GaAs (001) surfaces. Atomic hydrogen produced with a hot tungsten filament is adsorbed on the (2×4) surface, converting it to (1×1). Reflectance difference (anisotropy) spectra show an enhanced peak at 2.8 eV upon H adsorption at room temperature, which is not consistent with the notion that this peak originates from As dimers. Analysis of surface photoabsorption spectra show that surface dielectric changes along [1̄10] for H adsorption and for Ga deposition can be represented by a superposition of a change at the bulk critical points E1,E2,E0′ of GaAs and a broad feature centering at 2.5–2.7 eV.
Evidence of aging effects in sputtered ZrN films from positron annihilation
Authors: Brunner J. , Perry A. J.
Published: July 2002

The lifetime of positrons in a lattice is strongly affected by structural defects even if the concentration of the latter is well beyond the limit of detection by classical methods. The lack of a repulsive center in a vacancy acts as a trap for the positron which then annihilates itself with reduced probability due to the lower electron density at this site. The existence of a component longer than the bulk annihilation thus reflects the presence of vacancies. The behavior of this long-lived component in ZrN films sputtered onto stainless steel substrates was monitored over a period of 18 months. During this time, its value decreased steadily by a factor of 2–3 depending on the negative bias used during the sputtering. No significant changes in the color were observed during the measurements. A consistent explanation is the breakup of polyvacancies or voids leading to a higher concentration of monovacancies.
Atom manipulation on Si(111)-7×7 surface by contact formation of biased scanning tunneling microscope tip: Surface structures and tip current variation with atom removal
Authors: Hasunuma R. , Komeda T. , Mukaida H. , Tokumoto H.
Published: July 2002

A novel technique of Si atom removal by approaching biased scanning tunneling microscopy tip to the surface to the point contact region followed by retraction to the tunneling region was applied to Si(111)-7×7 surface to reveal (i) the atomic structures on the newly exposed surfaces, (ii) tip-substrate current variation in relation with the Si atom removal. When the adatoms were removed, the second layer of the diameter-adatom-stacking fault model structure appeared without reconstruction except the relaxation of dimer rows. When a higher biased tip (>2 V) was contacted, the top three layers were removed. Clear metastable structures such as c(2×4) and √3×√3 are observed in the holes, and the shape of these structures was easily changed with the expansion of the size of the hole. A staircase shape current drop was observed in the tip retraction process when the adatoms were removed. This is considerably related to the decrease of the number of Si atoms in the tip-substrate junction with atom-by-atom manner, which shows a clear contrast to the nanowire formation in the metal surface indentation. The last drop of the current to return to the tunneling region might correspond to a junction with a single atom between tip and substrate, which corresponds to 4×105 Ω. A part of the Si atoms in the junction remains on the tip which resulted in the removal of Si adatoms, which occurs with certain probability.
Core level photoemission study of As interaction with InP(110) and GaAs(110)
Authors: He Z. Q. , Khazmi Y. O. , Kanski J. , Ilver L. , Nilsson P. O. , Karlsson U. O.
Published: July 2002

We present a comparative core level photoemission study of the interaction between As and the (110) surfaces of GaAs and InP. In both cases it is found that As forms well ordered overlayers with the periodicity of the substrate surface. The interactions in the two cases are, nonetheless, very different. The bonding at GaAs is very weak, and the adsorbed species desorbs below 100 °C. In contrast, the interaction with InP (110) is significantly stronger, and at temperatures around 330 °C an As–P exchange reaction is indicated and is seen the core level spectra. The latter data are interpreted in terms of a recently proposed structure model involving an As-covered InAs layer.
Transport study in high mobility GaAs/AlGaAs lateral superlattices
Authors: Hannan M. , Giannetta R. W. , Grundbacher R. , Adesida I.
Published: July 2002

We report transport measurements in high mobility GaAs/AlGaAs heterostructures with lateral surface-induced periodic potentials. A modulation period of 1900 Å was produced with Schottky gates located above the two-dimensional electron gas. Both commensuration and Shubnikov–de Haas oscillations were observed. Nonlinear conductance (dI/dVds) measurements revealed a sharp feature near zero source-drain voltage. With zero magnetic field this feature is a conductance dip while finite B turns it into a conductance peak. We suggest that the conductance features result from Zener tunneling through a tilted miniband spectrum caused by the superlattice potential.
Low temperature selective growth of GaAs quantum wires by modulated flux chemical beam epitaxy
Authors: Ro Jeong-Rae , Kim Sung-Bock , Lee El-Hang , Lee Hai-Tai , Park Seong-Ju
Published: July 2002

We report that low-temperature selective growth of GaAs on GaAs(100) partially masked with SiNx and on nonplanar patterned GaAs(100) by employing a modulated flux method of chemical beam epitaxy (MFCBE), where triethylgallium, trimethylgallium, arsine, and monoethylarsine are used. To achieve MFCBE, group III and V source materials were alternately fed into the growth chamber with and without evacuation period between each source supply. The growth selectivity of the GaAs layer by MFCBE was significantly enhanced compared to that of the layers grown by the continuous beam method. Furthermore, the surface morphology of GaAs layers grown by MFCBE was greatly improved under the same growth conditions. The improvement of selectivity of samples grown by MFCBE is attributed to a decrease of catalytic decomposition of metalorganic compounds on the SiNx masks during evacuation and group III source supply periods. Our results also demonstrate that MFCBE can be a very powerful method for growth of ideal quantum wire structures.
Ion beam induced surface modification of chemical vapor deposition diamond for x-ray beam position monitor applications
Authors: Liu Chian , Shu D. , Kuzay T. M. , Wen L. , Melendres C. A.
Published: July 2002

The Advanced Photon Source at Argonne National Laboratory is a third-generation synchrotron facility that generates powerful x-ray beams on its undulator beamlines for a variety of scientific and industrial user research programs. It is very important to know the position and the angle of the x-ray beam during experiments. Due to very high heat flux levels, several patented x-ray beam position monitors (XBPMs) exploiting beneficial characteristics of chemical vapor deposition (CVD) diamond have been developed. These XBPMs have a thin layer of low-atomic-mass metallic coating so that photoemission from the x rays generates a minute but measurable current for position determination. Another concept has been the graphitization of the CVD diamond surface to create a very thin, intrinsic conducting layer that can stand much higher temperatures and have minimal x-ray transmission losses compared to coated metallic layers. In the present study, a laboratory sputter ion source was used to transform selected surfaces of a CVD diamond substrate into graphite. The effect of 1–5 keV argon ion bombardment on CVD diamond surfaces at various target temperatures from 200 to 500 °C was studied using Auger electron spectroscopy and in situ electrical resistivity measurements. Graphitization after the ion bombardment was confirmed, and optimum conditions for graphitization were studied. Raman spectroscopy was applied to identify the overall diamond structure in the bulk of CVD diamond substrate after the ion bombardments. It was found that the target temperature plays an important role in the stability and electrical conductivity of the irradiated CVD diamonds.
Investigation of the Cu/BCB and Cu/PPQ interfaces by photoelectron spectroscopy
Authors: Schühler N. , Oelhafen P.
Published: July 2002

Polyphenylquinoxaline (PPQ) and divinylsiloxane bis-benzocyclobutene (BCB) are of great technological interest concerning the fabrication of electronic multilayer devices. Both polymers own similar electrical properties but differ in their adhesion behavior towards copper. Photoelectron spectroscopy utilizing x-ray and ultraviolet radiation has been used to study the electronic structure of the Cu/PPQ and Cu/BCB interfaces. Thin layers of the polymers were produced by spin coating and their surface topologies were examined using atomic force microscopy. The metallization was done by evaporation and the gradual growth of the interface region was examined in situ after every metallization cycle. In both cases a reactive interface region with a low oxygen content is found. The difference in the adhesion between the two systems towards copper is discussed with respect to the differences of the interfaces formed during the metallization.
Morphological study of GaAs grown by periodic supply epitaxy on (111) B substrates
Authors: Allegretti F. E. , Roberts C. , Neave J. H.
Published: July 2002

Growth of GaAs on (111) B substrates masked by Si3N4 was studied with the periodic supply epitaxy (PSE) technique using a molecular beam epitaxy system. The conditions for selectivity to occur were investigated, together with the influence of the As4 overpressure on selectivity and on the morphology of the grown layer. It was found that an interruption time of 4 min was too short to allow for complete selective growth to take place, but it was sufficient to allow the formation of a depleted zone of 200–300 nm at the borders of the dielectric mask. Lateral overgrowth of the epitaxial layer was found possible in these partially selective conditions after 60 min of GaAs deposition in the PSE mode. The morphology of the ridges grown at different As4 overpressures was studied. At higher As4 pressures, the epitaxial layer grew without contact with the mask walls and developed independent {210} lateral sidewalls. The shrinkage rate of the top (111) B plane was remarkably fast at the highest As4 overpressure used. Selectivity was, however, more difficult to achieve in these conditions and a high As4 pressure was shown to be able to suppress reevaporation of the polycrystalline deposits on the mask.
Fabrication of cross-linked polymer shells for inertial confinement fusion experiments
Authors: Kubo Uichi , Nakano Hitoshi , Kim Hyo-gun
Published: July 2002

For inertial confinement fusion experiments, a copolymer of acrylonitrile and styrene (AS) shell overcoated with a cross-linked polyvinyl alcohol (PVA) has been fabricated in order to obtain good gas-barrier properties and resistance to beta decay of tritium. The fabrication method is based on the emulsion method using the interfacial poly-condensation reaction between water and oil phases. Cross-linked PVA with a thickness of 5 μm has been successfully overcoated on an AS shell. The surface roughness has been estimated using an atomic force microscope to be 0.5 nm (root mean square).
Precision gas flowmeter for vacuum calibration
Authors: Levine P. D. , Sweda J. R.
Published: July 2002

The Primary Standards Laboratory at Lockheed Martin Missiles and Space has developed an orifice flow vacuum calibration station for in-house calibration of spinning rotor and ion gages. A flowmeter supplies gas to a vacuum chamber partitioned by an orifice of calculable conductance. The pressure generated within the chamber is defined by the flowrate and the orifice conductance for molecular flow conditions. Orifice conductance is calculated from dimensional measurements, the flowrate is determined by measuring pressure drop at constant volume within the flowmeter. The design, development, and operation of the flowmeter is fully explained and illustrated. Chamber pressures as predicted from flowrate measurements are compared to those measured using a spinning rotor gage calibrated at the National Institute of Standards and Technology. Data for the extension of the calibration range beyond that of spinning rotor gages will be presented. An analysis of uncertainties inherent to the flowmeter is also presented.
Vector magnetometry in ultrathin magnetic structures with atomic layer resolution by polarized neutron reflection
Authors: Bland J. A. C.
Published: July 2002

Polarized neutron reflection (PNR) can be used for directly determining the layer dependent magnetic moment distribution in magnetic thin film structures with atomic layer resolution. The interface roughness amplitude and layer thickness can be accurately determined and diffuse scattering measurements can be used to probe spin and structural disorder at interfaces. These capabilities are illustrated in this review of recent experimental results obtained by PNR. Measurements of the interface magnetization in X/Fe/Ag(001) structures prepared by molecular beam epitaxy (MBE) with X=Pd, Ag, Au, and Cu are compared with the predictions based on theoretical calculations which take into account the measured interface roughness. For the case of strained fct Ni/Cu(001) structures prepared by MBE, the thickness dependence of the magnetic moments reveals a strong variation in Ni moment which is reflected in the variation of the ratio of orbital and spin moments with thickness determined from x-ray circular dichroism (XMCD) measurements. It is shown that the magnetic moments determined from applying sum rules to the XMCD results agree with the absolute moments determined by PNR using the same test sample. PNR can be used in these structures to determine the degree of uniformity of the magnetization profile across the depth of the Ni layers, so allowing a test of models which assume that the reduced magnetization to be of interfacial origin. The thickness obtained from an analysis of the wavevector dependence of the reflectivity is shown to agree with that obtained from x-ray reflectivity measurements. Measurements of the layer dependent moments in FeNi/Cu/Co spin valve structures are presented and it is shown that by comparing the PNR measurements with superconducting quantum interference device magnetometry measurements of the total sample moment it is possible to determine the interface moments on an atomic scale. Vector magnetometry measurements of the layer dependent magnetic moment orientations are shown to provide a powerful approach to studying spin orientations in ferromagnetic (FM)/nonmagnetic (NM)/FM trilayer structures. For epitaxial FeNi/Cu/Co(001) spin valve structures with negligible coupling, it is shown that the layer dependent moment orientation and amplitude can be determined with percent precision as a function of applied field.
Generalized description of magnetic x-ray circular dichroism in Fe 3p photoelectron emission
Authors: Tobin J. G. , Goodman K. W. , Schumann F. O. , Willis R. F. , Kortright J. B. , Denlinger J. D. , Rotenberg E. , Warwick A. , Smith N. V.
Published: July 2002

Extending a single electron picture previously developed by Venus, it will be shown that a generalized prediction of the magnetic x-ray circular dichroism in the angle-resolved photoelectron spectroscopy of the Fe 3p can be obtained. This determination can be performed without resorting to time-consuming and difficult spectral simulations.
Metal overlayers on organic functional groups of self-organized molecular assemblies: VII. Ion scattering spectroscopy and x-ray photoelectron spectroscopy of Cu/CH3 and Cu/COOCH3
Authors: Herdt G. C. , Czanderna A. W.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) were used to characterize octadecanethiol [ODT, HS(CH2)17CH3] and methylmercaptohexadecanoate [MMHD, HS(CH2)15COOCH3] self-assembled monolayers (SAMs) before and after depositing up to 1.0 nm Cu at ca. 10−7 Torr. Results from XPS O 1s, Cu 2p, and C 1s spectra do not indicate that a complex is formed (no chemical shifts) between Cu and the COOCH3 of MMHD or ODT organic functional groups (OFG) at 295 K. Although no direct evidence for Cu/COOCH3 interactions is evident, the initial value for ISS Cu peak intensities for 1.0 nm of Cu on COOCH3 of MMHD requires 7 h before it disappears compared with less than 150 min for Cu on CH3 of ODT. These times are also bracketed from XPS results, which are less sensitive than ISS to loss of copper from the M/SAM surface. The longer penetration time through MMHD versus ODT might be explained by weak interactions between Cu and COOCH3 of MMHD by different defect densities in the SAMs. The actual Cu deposition versus a layer-by-layer growth model and narrowing of the XPS Cu 2p peaks both provide support for formation of Cu clusters on the OFGs prior to penetration to the SAM/Au interface.
Reactions of acetone on the surfaces of the oxides of uranium
Authors: Madhavaram H. , Buchanan P. , Idriss H.
Published: July 2002

The reactions of acetone were investigated on α U3O8 (stoichiometric and H2 reduced) by temperature programmed desorption. The surface and bulk characteristics of U oxides were investigated by x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD). The comparison between the XPS U 4f7/2 binding energy of β UO3, α U3O8, and UO2 indicated that the U cations in U3O8 are composed of +5/+6 (2/1) or +4/+6 (1/2) oxidation states. XPS of H2 reduced α U3O8 (at 800 K) indicated a shift of the U 4f7/2 binding energy from 381.6 (unreduced) to 380.5 eV (reduced) as well as the appearance of two satellites at 387.0 and 397.4 eV. These new XPS lines’ positions are characteristic of U+4 cations of UO2. Similar results were observed upon Ar-ion sputtering of α U3O8. Ar-ion sputtering of β UO3 also results in the reduction of U+6 cations to U+4 cations. XRD of H2 reduced α U3O8 indicated that all of the α U3O8 phase was transformed to the UO2 phase. A considerable difference between the reactivity of the surfaces of U3O8 and UO2 towards acetone was observed. A carbon–carbon bond formation reaction giving isobutene was observed only on the α U3O8 surface indicating its structure-sensitive nature and/or its sensitivity towards changing the oxidation state of U cations. This reaction has not been observed on the surfaces of actinide oxides before. On the other hand, acetone reacted on UO2 to give mainly propene. This latter reaction (which is a C–O bond dissociation) is most likely due to the capacity of UO2 to accommodate large numbers of atomic oxygen in interstitial positions while maintaining its structure intact.
TiO
2
electrochromic thin films by reactive direct current magnetron sputtering
Authors: Yoshimura K. , Miki T. , Tanemura S.
Published: July 2002

TiO 2 electrochromic thin films have been prepared by reactive dc magnetron sputtering under various conditions and their electrochromic properties have been investigated by using 1 M LiClO4 in propylene carbonate as an electrolyte. Total pressure was found to be the most important parameter to control the electrochromic properties of sputtered TiO2 films. The sample deposited under high pressure conditions (8–10 Pa) showed good electrochromic properties; its visible transmittance changed from 14% (colored state) to 81% (bleached state) and the coloration efficiency was 29 cm2/C.
Temperature-programmed desorption study of the etching of Ni(110) with 2,4-pentanedione
Authors: Nigg H. L. , Masel R. I.
Published: July 2002

Ni contamination is an increasing problem in the fabrication of thin microelectronic films on Si. In previous work, we discussed nickel removal from nickel surfaces using oxygen and 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (Hhfac). In that study, Ni was etched cleanly by the precursors under net oxidizing conditions between 280 and 480 K with a maximum around 390 K. Decomposition pathways were prevalent, however, under reducing conditions. In this article we use temperature-programmed desorption to examine the use of a nonhalogenated β-diketone, 2,4-pentanedione (Hacac) and oxygen in the same process. Nonhalogenation of ligands decreases the acidity of the precursor and it is our intent to see how this affects reaction pathways, notably etching and decomposition. Ni was etched cleanly on the oxidized surface by the desorption of Ni-bis(acac) between 290 and 390 K with a maximum at 330 K. Interestingly, Ni-bis(acac) and 2,4-pentanedione desorb at lower temperatures than Ni-bis(hfac) and hexafluoropentanedione, a reversal of expectations based on volatility. Etching ceased as decomposition products formed. This was most notable above 450 K as several species including propanone, acetaldehyde, propanol and H3CCOCH2CHO (at high temperature) desorbed. The structures of decomposition products on both surfaces indicate that nickel promotes β-bond scission of the C-CH3 and C-CH/C-CH2 bonds in 2,4-pentanedione.
Generation of atomic nitrogen flux monitoring by an atomic absorption detection system at 120 nm
Authors: Wang Weizhi , Hammond R. H. , Arnason S. B. , Beasley M. R.
Published: July 2002

We have demonstrated a lamp-based atomic absorption detection system at 120 nm for monitoring atomic nitrogen generation in microwave discharge. Atomic nitrogen flux and dissociation ratio were evaluated by the atomic absorption. Delivery of atomic nitrogen with a quartz tube was investigated. By suppressing the recombination of the atomic nitrogen with the Teflon insert, the delivered atomic nitrogen flux was enhanced by a factor of 3–10. At a microwave power of 300 W, an atomic flux of 5×1016 cm−2 s−1, sufficient for growth of nitride thin films, was achieved. A model of recombination was used for explaining the experimental results, a maximum dissociation ratio of ∼2% at the plasma region was estimated based on the measured atomic nitrogen densities.
X-ray emission study of ion beam mixed Cu/Al films on polyimide
Authors: Kurmaev E. Z. , Zatsepin D. A. , Winarski R. P. , Stadler S. , Ederer D. L. , Moewes A. , Fedorenko V. V. , Shamin S. N. , Galakhov V. R. , Chang G. S. , Whang C. N.
Published: July 2002

Cu (40 nm)/Al/polyimide/Si was mixed with 80 keV Ar+ and N2+ from 5.0×1015 to 15×1015 ions/cm2. Ultrasoft x-ray emission valence spectra (XES) of Cu, C, N and O excited by electron and photon radiation were used for study of chemical reactions in Cu/Al/PI/Si and PI/Si systems induced by ion beam mixing in dependence of type of ions and dose. It is found that ion beam mixing changes the chemical state of Cu atoms with respect to that of pure metal. These changes depend on the dose of ion beam bombardment and type of ions and are attributed to a formation of CuAl2O4 interfacial layer, which can be responsible for enhanced interfacial adhesion strength. On the other hand, it is shown that the shape of C Kα, N Kα and O Kα XES of ion beam mixed polyimide layer (PI/Si) is modified with ion bombardment. This means that the ion-beam mixing process is able to break the bonding of constituent atoms of irradiated PI layers and can induce the formation of chemically bonded complexes linking atoms in the Cu, Al and PI layers.
Degree of Cl2 dissociation and etching characteristics in high-density plasmas
Authors: Samukawa Seiji
Published: July 2002

At the same input power (1000 W), inductive coupled plasma (ICP) and ultrahigh-frequency (UHF) plasma sources produced electron densities of 1×1011 cm−3 at 3.5 mTorr, yet the UHF plasma was much less dissociated (30%) than the ICP (70%). This can be attributed to differences in the electron energy distribution functions between the ICP and the UHF plasma, especially at low pressure. Under these conditions, Al etching profiles and doped poly-Si-etching rates were investigated to determine how the degree of dissociation influences etching reactions. UHF plasmas produced completely anisotropic Al and poly-Si etching independent of the dopant used when Cl2 was feed gas, whereas under the same conditions, the ICP produced isotropic Al etching profiles and the poly-Si-etching rate was strongly dependent on the dopant used under the same conditions. This implies that the degree of dissociation strongly influences the surface reaction in a high-density Cl2 plasma.
Improvement of morphological stability of Ag thin film on a TiN layer with a thin interposing metal layer
Authors: Hong C. Y. , Peng Y. C. , Chen L. J. , Hsieh W. Y. , Hsieh Y. F.
Published: July 2002

The morphological stability of Ag thin film on a TiN layer with a thin interposing metal layer has been investigated. Due to the formation of Ag spikes at the Ag/Si interface, a diffusion barrier is needed to buffer the interdiffusion of Ag with Si. TiN films deposited by physical vapor deposition (PVD) or metalorganic chemical vapor deposition (MOCVD) were used. A Au or Ti (∼3 nm) layer was used as the glue layer between Ag and TiN. In a Ag/Au/TiN system, a mixed Ag–Au layer is stable on PVD-TiN at temperatures as high as 450 °C. In Ag/Ti/TiN systems, the thermal stability of Ag on CVD-TiN is superior to that on PVD-TiN. Ag layers were found to be discontinuous after annealing at 300 and 350 °C on PVD-TiN and CVD-TiN systems, respectively.
Simple catalytic cell for restoring He leak detector sensitivity on vacuum systems with high D2 backgrounds
Authors: Busath J. , Chiu H. K.
Published: July 2002

The DIII–D National Fusion Facility at General Atomics (GA) focuses on plasma physics and fusion energy science. The DIII–D tokamak is a 35 m3 toroidal vacuum vessel with over 200 ports for diagnostic instrumentation, cryogenics, microwave heating, and four large neutral beam injectors. Maintaining vacuum in the 10−8 Torr range is crucial for producing high performance plasma discharges. He leak checking the DIII–D tokamak and the neutral beamlines has historically been difficult. D2 is used as the fuel gas in most plasma discharges and neutral beams. After plasma operations, D2 outgassing from the torus walls and internal beamline components can exceed 10−4 std cm3/s. The mass of the D2 molecule (4.028 u) is indistinguishable from that of the He atom (4.003 u) to a standard mass spectrometer leak detector. High levels of D2 reduce leak detector sensitivity and effectively mask the He trace gas signal rendering normal leak checking techniques ineffective. A simple apparatus was developed at GA to address these problems. It consists of a palladium based catalyst cell and associated valves and piping placed in series with the leak detector. This reduces the D2 throughput by a factor greater than 10 000, restoring leak detector sensitivity. This article will briefly discuss the development of the cell, the physical processes involved, the tests performed to quantify and optimize the processes, and the operational results at DIII–D.
Pumping mechanism of helical grooved molecular drag pumps
Authors: Sawada T. , Sugiyama W.
Published: July 2002

The flow on a rotor of a molecular drag pump varies from viscous to slip to free molecule flow according to the decrease in pressure. As the first step, flow through a groove that is facing a wall which is moving along the groove is analyzed. The Navier–Stokes equations are simplified in the viscous and slip flow regimes and can be solved numerically with relative ease. In the free molecule flow regime, drag is caused by the momentum carried to a wall piece by gas molecules colliding with the wall piece, and the drag must be equated to the force exerted by the pressure on the two cross sections sandwiching the wall piece. A weighted linear combination of the two equations for slip and free molecule flows can illustrate the flow through the three flow regimes. The flow in ridges which leads to a leak is treated in a similar way to the flow in grooves. Then, the flows in grooves and ridges are hitherto treated separately and connected by the continuity condition of the mass flow rate normal for the groove-ridge interface. The pressure gradient which is discontinuous at the groove-ridge interface is smoothed by Boon and Tal’s “narrow groove theory” [E. F. Boon and S. E. Tal, Chemie-Ingenieur Technik 31, 202 (1959)]. The theory proposed here satisfactorily predicts the measured pumping performance throughout the three flow regimes including the transition regime from free molecule to slip flows.
Direct simulation Monte Carlo method for molecular and transitional flow regimes in vacuum components with static and moving surfaces
Authors: Boulon O. , Mathes R. , Thibault J-P.
Published: July 2002

The gas flow through a vacuum component can be continuous, transitional, or molecular depending on the pressure range and geometries involved. Dilute gas flows in molecular and transitional regimes were simulated using the direct simulation Monte Carlo method. The computational model takes as data combination of pressure, temperature of gas, type of gas, and geometry of the vacuum components. The results of the computations are gasflow, local velocities, and molecular density distribution. The model was first tested and validated for several simple geometries, such as circular and rectangular finite length tubes with static and moving walls, for different flow conditions. The Couette flow problem is treated in all the transition regime, from the molecular regime to the beginning of the viscous regime. The model was found to agree well with other published results, and allowed us to better understand flow phenomena for the different regimes from the molecular case to the viscous case. This first study was conducted to develop, in the future, a model that we can adapt to more complicated geometries of vacuum components, such as stages of turbomolecular or molecular pumps, to predict the flow rate from molecular to transition flow regimes.
Thermochemical stability of silicon–oxygen–carbon alloy thin films: A model system for chemical and structural relaxation at SiC–SiO2 interfaces
Authors: Wolfe D. M. , Hinds B. J. , Wang F. , Lucovsky G. , Ward B. L. , Xu M. , Nemanich R. J. , Maher D. M.
Published: July 2002

Alloy thin films of hydrogenated silicon–oxygen–carbon (Si,C)Ox x<2, were deposited and analyzed in terms of changes in structure and bonding as a function of rapid thermal annealing between 600 and 1100 °C using a combination of Fourier transform infrared spectroscopy, Raman scattering and high-resolution transmission electron microscopy. Results showed that three structural/chemical transformations took place upon annealing. The initial reaction (600–800 °C) involved the loss of hydrogen bonded to both silicon and carbon. At intermediate temperatures (900–1000 °C) a Si–O–C type bond was observed to form, and subsequently disappear after annealing to 1050 °C. The formation of ordered amorphous-SiC regions, nanocrystalline-Si regions, and stoichiometric, thermally relaxed SiO2 accompanied the disappearance of the Si–O–C bond at the 1050 °C annealing temperature. Using this alloy as a model system, important information is obtained for optimized processing of SiC–SiO2 interfaces for device applications.
Surface derivatization of nanoscale tungsten probes for interfacial force microscopy
Authors: Graham J. F. , Griffiths K. , Kovar M. , Norton P. R. , Ogini F. , Warren O. L.
Published: July 2002

Interfacial force microscopy is a novel technique for imaging and quantitative determination of the mechanical properties of a material such as elastic modulus, hardness, etc., with nm spatial resolution and nN force resolution. Due to the extreme pressures generated during probe-surface contact (many GPa), passivation of the chemical interactions, specifically adhesion, between the parabaloidal tungsten probe tips (radii 35<r<200 nm) and the substrate under investigation is often required. Convenient and effective protective monolayers are not generally available for many substrates, and it is necessary to develop a general procedure for passivation of the tip. We have derivatized tungsten(100) surfaces with the silane coupling agent (octadecyltrichlorosilane, OTS) and applied the same techniques to nm-scale tungsten tips. Force versus displacement (f–d) curves were recorded for the following tip–substrate interactions: underivatized tungsten tip against underivatized Au(111) surface, underivatized tungsten tip against derivatized Au(111) surface (C-18 thiol SAM), and derivatized tungsten tip (OTS) against underivatized Au(111). The data clearly show that the OTS derivatized tips were passivated against adhesive contact even at pressures of many GPa, thereby demonstrating the stability necessary for use in nanoindentation experiments.
Nitrogen incorporation and trace element analysis of nanocrystalline diamond thin films by secondary ion mass spectrometry
Authors: Zhou D. , Stevie F. A. , Chow L. , McKinley J. , Gnaser H. , Desai V. H.
Published: July 2002

Nitrogen has been successfully incorporated into nanocrystalline diamond films produced by a CH4/N2 microwave plasma-enhanced chemical vapor deposition method. High mass resolution secondary ion mass spectrometry (SIMS) characterization shows that the density of the incorporated nitrogen, monitored via CN−, can be as high as 1021 atoms/cm3, depending on the ratio of CH4 to N2 in the reactant gas and on the substrate temperature used for the film preparation. SIMS depth profiles demonstrate that the incorporated nitrogen is uniform within the diamond films (about 1.5 μm thick) except at the surfaces and at the interface between film and substrate. Furthermore, the SIMS analyses reveal that alkali elements such as Na, K, and Li appear to be contaminants at the surface of nanocrystalline diamond films produced using a CH4/Ar or CH4/H2 discharge, but are bulk impurities only for the films prepared using a CH4/N2 plasma. These alkali impurities can play an important role in electronic properties such as electron field emissions of nanocrystalline diamond thin films.
Dynamics of the striped nanostructure of the oxidized Cu(110) surface: A momentum-resolved electron stimulated desorption ion angular distribution study
Authors: Mocuta D. , Ahner J. , Lee J.-G. , Denev S. , Yates J. T.
Published: July 2002

The striped structure of the partially oxidized Cu(110) surface has been studied using a novel technique, momentum-resolved electron stimulated desorption ion angular distribution (ESDIAD) Long …O–Cu–O… strings oriented in the 〈001〉 direction and exhibiting attractive interactions with each other form periodically arranged stripes with widths in the nanometer range [D. J. Coulman et al., Phys. Rev. Lett. 64, 1761 (1990); K. Kern et al., ibid. 67, 855 (1991)]. Two different oxygen sites were detected, leading to a twofold symmetrical four-beam O+ ESDIAD pattern with 22° tilting of the beams in the 〈11̄0〉 azimuth (A) direction and 8° in the 〈001〉 azimuth (B) direction. The relative intensities of the four beams have been compared for a wide range of oxygen coverages leading to a model in which the A beams correspond to O+ ions desorbing from the edges of the stripes and the B beams from the internal regions of the stripes. This model is confirmed by studying the effect of the coadsorption of Ar at 32 K on the oxidized structure where the Ar is preferentially adsorbed on the edges of the stripes. The dynamical motion of the one-dimensional …O–Cu–O… oscillator chains situated at the edges of the stripes has been studied by momentum-resolved ESDIAD measurements over a broad range of temperatures (80–650 K).
Quantitative high-resolution imaging with sputter-initiated resonance ionization spectroscopy
Authors: Willey K. F. , Arlinghaus H. F. , Whitaker T. J.
Published: July 2002

The demand for submicron lateral analysis, as a result of decreasing material size, has been met by the development of liquid metal ion gun (LMIG) sources capable of achieving spot sizes less than 50 nm. The trade-off, however, is the reduction in ion beam current at the sample. Therefore, highly sensitive detection techniques are required. Our technique, sputter-initiated resonance ionization spectroscopy (SIRIS), incorporates resonant ionization of sputtered neutral particles with time-of-flight mass detection. The two major advantages this approach has over conventional secondary ion mass spectrometry are that analysis of neutrals generally increases the detection efficiency by at least two orders of magnitude, and that resonance ionization nearly eliminates mass interferences. Additionally, analysis of neutrals substantially removes matrix effects, which is crucial for quantitative surface analysis. Sputtering is achieved with a gallium LMIG, a mass-filtered microbeam ion gun, and a mass-filtered low-energy sputtering ion gun. Submicron lateral resolution and few nanometer depth resolution have been obtained by eroding the sample with the low-energy ion gun while analyzing with the LMIG. In our presentation, we will describe the SIRIS technique and its dynamic range for quantitative analysis and imaging capabilities as they pertain to semiconductor research. In particular, Ge and B depth profiles on near 1 μm spot size and Cu trace element images obtained from Cd precipitates in CdZnTe films will be presented.
Optimization of hardness by the control of microwave power in TiN thin film deposited by electron cyclotron resonance assisted sputtering in a nitrogen plasma
Authors: Carney Carl , Durham Delcie
Published: July 2002

Research has been conducted to investigate ways to make thinner, yet more cohesive TiN films. Plasma vapor deposition techniques were used in conjunction with electron cyclotron resonance to deposit TiN films on substrates of Inconel 718 (nickel-based superalloy). Previous parts of this investigation have focused on the relationship between process (i.e., film deposition) parameters, film microstructure, and film mechanical properties. The final part of this study extends the research focus to discuss what effect a change in the power setting of the microwave plasma has on the resulting Meyer hardness of the TiN-coated sample. The crystal orientation and texture of these films are also discussed. Optimum hardness of greater than 46 GPa was found at low microwave power of 200 W and a substrate bias of −100 V. Lowering microwave power to 200 W more than doubled the number of (111)-oriented grains. Substrate bias of −100 V or greater resulted in a greater than twofold decrease in (200)-oriented grains.