bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic force microscope images of collagen fibers
Authors: Chernoff Ellen A. G. , Chernoff Donald A.
Published: July 2002

Atomic force microscopy (AFM) was used to image fibrillar and monomeric type I collagen. Protocols were developed to produce samples of air dried fibrillar and monomeric collagen suitable for AFM analysis. Pepsin-extracted, type I bovine skin collagen was polymerized on mica substrates in pH 7.4 phosphate-buffered saline at 37 °C. Monomeric collagen was adsorbed onto mica substrates in 0.012 N HCl or pH 3 buffer at 21 °C. Control samples of buffer-treated mica were also prepared. AFM images of the fibrillar collagen showed well-defined D banding of the fibrils, with a period of 70 nm. Beneath the fibrils finer fibrillar material was seen, probably oligomeric collagen. Samples prepared at acidic pH showed a meshwork of monomeric collagen with an occasional structure of oligomeric size. Control samples of mica treated with buffer only had occasional tree structures formed of crystallized buffer salts. Collagen is an important component of animal tissues and forms extracellular matrix material in combination with other proteins and glycoproteins. The studies reported here form the basis for examination of more complex collagen-containing structures of biological importance.
Modification of chemical properties of materials by ion beam mixing and ion beam assisted deposition
Authors: Wolf G. K.
Published: July 2002

Ion beam mixing and ion beam assisted deposition are powerful techniques for influencing the surface properties of materials. In this contribution, the state of the art for the modification of chemical properties of materials, mainly corrosion and catalytic properties, is reviewed. Modern equipment and techniques are described, and selected examples for illustrating their potential are presented as follows: corrosion protection of aluminum and steel by thin Si, Al2O3, and Ta2O5 coatings; influence of tailored stress states on the corrosion protection of Cr and TiN overlayers; simultaneous reduction of corrosion and wear by multipurpose coatings; doping of powders with gold and platinum for catalytic purposes.
Ion sputter effects on HgTe, CdTe, and HgCdTe
Authors: Stahle C. M. , Helms C. R.
Published: July 2002

Preferential ion sputtering of HgTe and HgCdTe is the dominant ion sputter effect observed in these material systems. There is little preferential sputtering of CdTe. The ion sputter behavior of HgCdTe can be predicted from the ion sputter behavior of HgTe and CdTe. The weakness of the Hg–Te bond compared to the Cd–Te bond accounts for the greater ion sputter rate of HgTe to CdTe and causes Hg to have a large relative ion sputter yield compared to the other elements and, most likely, plays a dominant role in the preferential sputtering of Te in HgCdTe. Preferential ion sputtering is dependent on the chemistry of Hg1−xCdxTe; elemental ion sputter yields depend on the amount of HgTe in the sample.
Phase transitions of ethylene monolayers on graphite
Authors: Eden V. L. , Fain S. C.
Published: July 2002

Low-energy electron diffraction (LEED) measurements have detected seven solid phases for monolayer ethylene on graphite. Electron-beam induced effects (which presumably include decomposition and/or polymerization of the adsorbed ethylene) were minimized by exposing the adsorbed layer to the nanoamp beam for <100 s per crystal; data were obtained from four different crystals. We concentrate here on the phase transitions from the molecular-axisorientationally disordered low density (DLD) phase to the newly discovered commensurate molecular-axis-disordered low density (CDLD) phase and on the melting of the CDLD phase. The change in the principle q vector in the DLD-CDLD phase transition is presented for several different coverages. These data indicate an interesting incommensurate–commensurate (IC–C) transition which has not been suspected from previous studies. This transition preempts the melting transition: as a consequence we can rule out the possibility of a continuous melting transition as suggested by earlier heat capacity and neutron scattering experiments. In addition, LEED images of the fluid phase produced by melting of the CDLD phase are presented which show a modulated-ring-type structure.
Alkane activation by single-crystalline transition metal surfaces
Authors: Weinberg W. Henry
Published: July 2002

The measured rate coefficients (preexponential factors and activation energies) of the trapping-mediated, dissociative chemisorption of methane, ethane, and propane on Pt(110)-(1×2), and ethane on Ir(110)-(1×2) are reported and discussed. Moreover, the probabilities of primary and secondary C–H bond cleavage for propane activation on Pt(110)-(1×2) have been evaluated.
Self-diffusion on reconstructed and nonreconstructed Ir surfaces
Authors: Chen Chong-lin , Tsong Tien T.
Published: July 2002

Using the field ion microscope, we have studied random walk diffusion of single Ir atoms and small Ir atomic clusters on Ir surfaces. On the (1×1) Ir {001} surface, diffusion of Ir adatoms occurs by an atomic replacement mechanism along the 〈001〉 directions. On the (1×1) Ir {110} surface, self-diffusion occurs by atomic hopping along the 〈110〉 directions and by atomic replacement along the 〈001〉 directions. On the (1×2) reconstructed Ir {110} surface, self-diffusion occurs only by atomic hopping along the doubly spaced [1̄10] surface channels. Within the experimental accuracy, the pre-exponential factors are all in the 10−3 cm2/s range. Energies needed for these atomic replacements and the barrier heights for these atomic hoppings are also derived. Diffusion of diatomic clusters on the (1×1) Ir {110} surfaces has also been studied.
Interaction of hydrogen with Zr(0001) at room temperature
Authors: Zhang C. S. , Flinn B. J. , Griffiths K. , Norton P. R.
Published: July 2002

The interaction of hydrogen with a Zr(0001) surface at room temperature has been investigated by using 2H(3He,p)4He nuclear reaction analysis (NRA), dynamic secondary ion mass spectroscopy, static secondary ion mass spectroscopy, and Auger electron spectroscopy. The initial sticking coefficient (for D) obtained from the absolute deuterium coverage measured by NRA was found to be 0.38±0.16 which is higher than a previously published value by about four orders of magnitude. Secondary ion mass spectroscopy H+ integrated intensities were converted to hydrogen concentration by calibration using NRA. The sticking coefficient for H2 appears to be very similar to that for D2. It was found that the hydrogen atoms appear to stay at the surface until the surface concentration saturates at 0.77 monolayer (4 L exposure). Upon further exposure the hydrogen penetrates through the surface. The valence-band-related Auger transitions show a small but discernible change upon exposure to greater than 2 L hydrogen. This, as well as changes in the low-energy electron diffraction pattern, indicates the formation of hydride in the early stages of exposure. An uptake model was proposed, from which a good agreement for sticking coefficient with NRA results was obtained.
Molecular-beam epitaxy of strained silicon germanium/silicon structures
Authors: Kasper E. , Jorke H.
Published: July 2002

The growth of strained layer heterostructures is influenced by intentionally undesired phenomena as surface undulations, alloy clustering, defect generation, interface intermixing. The origin of these effects is explained and strategies to overcome them are discussed. Recently, in the silicon germanium (SiGe) system exciting progress toward layers controlled on a monolayer scale was obtained. The status will be demonstrated by doped and undoped heterostructures, multiple heterostructures, and superlattices. Special emphasis will be given to structures relevant for devices as heterobipolar transistors (HBT), modulation doped field effect transistors (MODFET), and novel optoelectronic devices. For all these structures the strain is explicitly utilized for band structure engineering. In several areas the progress in material preparation pushed an tremendous performance increase. Examples given are the low base sheet resistivity (1.6 kΩ/⧠) for high speed (42 GHz) SiGe–HBTs, the 4.2 K mobility increase in n-MODFET channels to 160 000 cm2/V s, and the luminescence from various strained SiGe structures.
TiN film coatings on alumina radio frequency windows
Authors: Michizono S. , Kinbara A. , Saito Y. , Yamaguchi S. , Anami S. , Matuda N.
Published: July 2002

Thin films of TiN having low secondary electron emission (SEE) yields are coated on alumina rf windows in order to suppress the occurrence of multipactor. It is necessary to form films with a proper thickness in order to obtain a sufficient reduction of SEE as well as to avoid any excessive ohmic loss in conductive TiN films. For an optimization of the film thickness on an alumina surface, measurements of the SEE coefficients, and ohmic losses in the rf (S-band) field were carried out. High-power examinations of the coated windows were also performed. The results show that TiN films with a thickness of 0.5 nm or greater on alumina ceramics have SEE coefficients of less than unity at an incident energy of 10 keV. High-power tests have revealed that the ‘‘going away’’ of TiN films is probably due to excessive ohmic losses taking place when the thickness is greater than 1.5 nm. It is concluded that optimized film thickness for window coatings is 0.5–1.5 nm.
Diamondlike carbon films sputter deposited with an electron cyclotron resonance reactor
Authors: Kidder J. N. , Varhue W. J.
Published: July 2002

Amorphous carbon thin films were sputter deposited using a microwave electron cyclotron resonance reactor with a graphite target. Films were deposited at a temperature range of −50–50 °C, at reactor pressures ranging between 0.1 and 0.4 Pa, and with the substrate rf biased, floating, and grounded. The films were shown to be hard, to have optical band gaps of 0.9–1.4 eV, refractive indices ranging between 2.0 and 3.0, and Raman spectra characteristic of diamondlike carbon material. The effect of process conditions on the physical properties of the deposited films is investigated. The refractive index showed a dependence on pressure, increasing slightly with decreasing pressure. Electrical resistivity decreased with rf substrate bias.
Material properties and tribological performance of hydrogenated sputter carbon overcoat on rigid disk
Authors: Lee H. J. , Zubeck R. , Hollars D. , Lee J. K. , Smallen M. , Chao A.
Published: July 2002

The structure and material properties of hydrogenated carbon films were studied and related to their tribological performance. Hydrogenated carbon films containing a range of 15–50 at. % of hydrogen were fabricated by magnetron sputtering using a mixture of argon and hydrocarbon gases. Raman spectroscopy was used for determining the structure of the H–C films. For physical property of H–C films, resistance of the film was measured. Nanohardness and elastic modulus of thin H–C films were also studied by measuring the load and displacement curve. The nanohardness and elastic modulus of H–C films were found to be very close to those of diamondlike carbon films fabricated by chemical vapor deposition. The stresses of H–C films were obtained by measuring the substrate curvature before and after deposition. Thermal expansion coefficients of the H–C films were obtained by measuring the change of stress of H–C film deposited on two known substrates as a function of temperature. The accelerated drag and contact start stop tests of H–C films were performed in various gas environments and it was found that the best tribological performance was obtained from the H–C overcoat with the highest hydrogen concentration.
Evolution of atomic-scale surface structures during ion bombardment: A fractal simulation
Authors: Shaheen M. A. , Ruzic D. N.
Published: July 2002

Surfaces of interest in microelectronics have been shown to exhibit fractal topographies on the atomic scale. A model utilizing self-similar fractals to simulate surface roughness has been added to the ion bombardment code trim. The model has successfully predicted experimental sputtering yields of low energy (less then 1000 eV) Ar on Si and D on C using experimentally determined fractal dimensions. Under ion bombardment the fractal surface structures evolve as the atoms in the collision cascade are displaced or sputtered. These atoms have been tracked and the evolution of the surface in steps of one monolayer of flux has been determined. The Ar–Si system has been studied for incidence energies of 100 and 500 eV, and incidence angles of 0°, 30°, and 60°. As expected, normally incident ion bombardment tends to reduce the roughness of the surface, whereas large angle ion bombardment increases the degree of surface roughness. Of particular interest though, the surfaces are still locally self-similar fractals after ion bombardment and a steady state fractal dimension is reached, except at large angles of incidence.
X-ray energy dependent photochemistry of the adamantane (C10H16)/Si(111)-7×7 surface
Authors: Simons J. K. , Frigo S. P. , Taylor J. W. , Rosenberg R. A.
Published: July 2002

We have studied the synchrotron radiation (SR) induced photochemistry of the adamantane (C10H16) dosed Si(111)-7×7 surface using photoelectron spectroscopy. The adamantane/Si surfaces were characterized before and after they were exposed to broadband SR of varying energies and then annealed. When annealed to 525 K, the unexposed adamantane layers desorbed leaving only a layer of Si–H and hydrated Si–C species on the surface. When the adamantane adlayer was irradiated with broadband SR that contained energies greater than the C(1s) binding energy (284 eV), the surface reacted to form a layer similar to SiC. In contrast, when the surface was irradiated with broadband SR with energies below 284 eV, only the adamantane in direct contact with the Si surface dissociated. The remaining adamantane adlayer reacted with the surface in a manner which left the molecular structure of the reacted adamantane intact. The reacted adamantane layer was stable up to temperatures of at least 675 K.
Structure of coadsorbed bismuth and hydrocarbons on Pt(111)
Authors: Domagala Melanie E. , Campbell Charles T.
Published: July 2002

The structure of coadsorbed layers of bismuth with hydrocarbons on transition metal surfaces is of interest because of the utility that bismuth adatoms have for probing the surface chemistry of hydrocarbons on such surfaces. Herein we present the results of low-energy electron diffraction (LEED) studies of Bi coadsorbed with cyclohexane, cyclohexene, and benzene on Pt(111). When a low coverage (θBi=0.25) p(2×2) Bi adlayer is dosed with hydrocarbons, the Bi LEED pattern is destroyed, and no evidence is seen for higher coverage Bi domains. These results are consistent with a model whereby the Bi and hydrocarbon adatoms are randomly distributed across the Pt(111) surface when both are at low coverages. When Bi is predosed at high coverage (θBi=0.50), and then the hydrocarbon is dosed to the surface, the Bi c(4×2) pattern remains unchanged, suggesting that the hydrocarbon simply sits on top of the Bi adlayer. In the case of cyclohexane, this c(4×2)-Bi LEED pattern was also obtained using the reverse dosing sequence, which suggests that the postdosed Bi squeezes between the hydrocarbon and the Pt. This process seems to be kinetically prevented below 160 K in the case of cyclohexene and benzene, due to their stronger bonds to Pt.
Chemistry and physics of the ‘‘liquid’’/solid interface: A surface science perspective
Authors: Stuve E. M. , Kizhakevariam N.
Published: July 2002

Through experimental simulation of the electrochemical double layer under conditions of ultrahigh vacuum, surface science experiments can provide detailed and definitive information about the metal/electrolyte interface. The relevance of this somewhat nontraditional approach to the liquid/solid interface might appear questionable, but thermodynamic considerations, along with an ever expanding list of gas/solid to liquid/solid analogies, attests to its merit. In this article, thermodynamic arguments for the direct relationship between vacuum and electrochemical experiments are presented and supporting experimental results in the areas of solvent adsorption, surface solvation, hydrophilic and hydrophobic interactions, specific and nonspecific adsorption, adlayer solution theory of HF and H2O coadsorbed on Ag(110), and electrochemical charge transfer reactions in vacuum are reviewed. On the basis of these results a new, three-dimensional model of the metal/electrolyte interface is proposed.
Inexpensive spot-profile analysis reflection high energy electron diffraction
Authors: Idzerda Yves
Published: July 2002

A simple, photomultiplier based spot-profile analysis reflection high energy electron diffraction (SPARHEED) apparatus is described. A micrometer scanned, two pinhole aperture is coupled to an optical fiber and yields 38 μm spot-profile intensity resolution of RHEED patterns corresponding to an ultimate spatial resolution of ∼4000 Å along the RHEED pattern and 900 Å across the RHEED pattern. Long range scanning also allows for surface lattice net determination. Acquisition of selected RHEED intensity oscillations is straightforward. The device is easily mounted, rigid, and inexpensive.
Electronic excitation of metal carbonyls on Ag(111): The role of surface-mediated quenching
Authors: Ramsier R. D. , Yates J. T.
Published: July 2002

The electronic excitation of adsorbed Fe(CO)5 on clean Ag(111) has been studied using both ultraviolet light (4.8 eV) and electron impact (3–132 eV). Comparisons to photoreaction measurements for Fe(CO)5 adsorbed on an inert spacer layer show that substrate-adsorbate quenching effects of electronically excited Fe(CO)5 on Ag(111) are essentially nonexistent. These results suggest that the CO ligands of Fe(CO)5 themselves act as a spacer layer for electronically excited Fe(CO)5 (ads) species. Both photodissociation and electron impact dissociation of Fe(CO)5 on Ag(111), causing loss of one or more CO ligands, produce new metal carbonyl species which are more strongly bound to Ag(111) than the parent Fe(CO)5 molecule. These new species exhibit a lower cross section for further photodissociation compared to the parent Fe(CO)5 molecule. This is postulated to be due to an increased Ag–Fe interaction for the coordinately unsaturated species produced by photolysis, causing enhancement of adsorbate-substrate quenching. Comparisons are also made between electron impact studies of Fe(CO)5, Ni(CO)4, and C6D6Cr(CO)3 adsorbed on Ag(111). All three carbonyls exhibit similar behavior upon the loss of CO or benzene ligands.
Electrical and chemical stability of Al/SiNx/InP–metal–insulator– semiconductor diodes with gas phase polysulfide exposure on InP
Authors: Kwok R. W. M. , Lau W. M. , Landheer D. , Ingrey S.
Published: July 2002

Releasing the Fermi-level pinning of InP by gas phase polysulfide exposure has recently been demonstrated by surface charge spectroscopy [Lau et al., Surf. Sci. 271, 579 (1992)]. The present article reports a study of capacitance–voltage (C–V) measurements on metal–insulator–semiconductor (MIS) diodes fabricated using a process which includes this polysulfide passivation. The effectiveness of this passivation technique in reducing interface trap densities (Dit) was confirmed. The optimized MIS fabrication procedure involved (a) surface cleaning and polysulfide exposure; (b) immediate deposition of silicon nitride by remote plasma chemical vapor deposition (RPCVD); and (c) deposition of aluminum and annealing at 500 °C for 15 min in forming gas. The C–V results gave a Dit of 5×1010 cm−2 eV−1 via the Terman analysis and 5×1011 cm2 eV−1 via the high–low frequency method. The MIS properties were unchanged after a two months air exposure and a one week 110 °C heating in air. It was also found that the replacement of aluminum with Ti/Pt/Au, and of RPCVD with plasma enhanced chemical vapor deposition all led to higher Dit values.
X-ray photoelectron and Auger electron spectroscopy study of ultraviolet/ozone oxidized, P2S5/(NH4)2S treated GaAs(100) surfaces
Authors: Chester M. J. , Jach Terrence , Dagata J. A.
Published: July 2002

In this report we discuss the results of a study undertaken to investigate the composition and thermal stability of ultraviolet/ozone oxidized, P2S5/(NH4)2S treated GaAs(100) surfaces. In particular, we have used x-ray photoelectron spectroscopy and Auger electron spectroscopy to probe the oxide and interface at room temperature and as a function of annealing temperature. The room temperature data indicate that S is buried between the oxide overlayer and the GaAs substrate. This oxide contains a variety of As and Ga bonding configurations which, after moderate annealing, are transformed into thermally more stable phases, such as As2O3 and Ga2O3 . Complete desorption of the oxide occurs after annealing at 600 °C. Annealing the as-oxidized surface to high temperatures also has a profound effect on the S. Heating the sample to 495 °C causes some S to diffuse towards the oxide surface, while annealing at higher temperatures leads to S diffusion into the GaAs substrate. Even after complete desorption of the O, a small amount of S remains embedded in the GaAs lattice.
Deposition of crystalline binary nitride films of tin, copper, and nickel by reactive sputtering
Authors: Maya Leon
Published: July 2002

Crystalline binary nitride films of tin, copper, and nickel were prepared by reactive sputtering in a nitrogen plasma generated in a dc glow discharge. The chemical composition and thermal behavior of the films were established. The films were characterized by additional physicochemical techniques. Tin nitride, Sn3N4 has an electrical resistivity of 0.02 Ω cm and decomposes into the elements at a maximum rate at 615 °C. The thermal decomposition of Cu3N takes place at 465 °C, while Ni3N decomposes at 405 °C in a stepwise fashion through an intermediate stage at 305 °C. Tin, copper, and nickel nitride decompose into the elements. Nickel nitride crystallized in a new cubic phase with a lattice parameter of 0.446 nm.
Characterization of silver films deposited by radio frequency magnetron sputtering
Authors: Maréchal N. , Quesnel E. , Pauleau Y.
Published: July 2002

Silver thin films have been deposited on various substrates at floating potentials by radio frequency magnetron sputtering of a silver target in pure argon plasma using load-locked sputtering equipment. Under the experimental conditions investigated, the deposition rate of silver films was about 70 nm/min so that metal films as thin as 200 nm could be deposited within easily controllable deposition durations. Film surfaces and cross sections were examined by scanning electron microscopy. The morphology was fully dense. The crystallographic structure was investigated by x-ray diffraction. The grains were preferentially oriented with the (111) lattice planes parallel to the film surface and without preferred azimuthal orientation. The films analyzed by Rutherford backscattering spectroscopy were free of detectable impurities. The residual stresses were determined to be tensile from the measurements of the curvature radius of silicon substrates. The calculated value of the thermal stress showed that the intrinsic stress in the films was compressive. The effective Knoop hardness of 2-μm-thick silver films deposited on glass substrates was in the range 1600–1800 MPa, i.e., three times higher than the hardness of the bulk metal. Pure silver films exhibited an electrical resistivity of 1.5–2 μΩ cm, nearly equal to the bulk resistivity.
Growth and characterization of cubic boron nitride thin films
Authors: Kester D. J. , Ailey K. S. , Lichtenwalner D. J. , Davis R. F.
Published: July 2002

Boron nitride (BN) thin films have been grown on [100] oriented single crystal Si, diamond, Cu and Ni substrates by ion beam assisted deposition using electron beam evaporation of boron together with simultaneous bombardment by nitrogen and argon ions. Characterization by Fourier-transform infrared spectroscopy and high-resolution transmission electron microscopy showed that the films on Si and diamond consisted of initial noncubic (amorphous and hexagonal BN) layers, followed by the growth of cubic BN (c-BN). This growth sequence was attributed primarily to increasing compressive intrinsic stress with increased film thickness. Increasing the substrate temperature above 400 °C led to the onset of c-BN at a greater film thickness while increased ion flux resulted in earlier growth of this phase. These results may be explained by the relaxation of the intrinsic stress in the films at higher temperatures due to increased adatom mobility and to increased intrinsic stress in the films resulting from increased ion bombardment. Lower temperatures led to mixed phase growth. A minimum substrate temperature (200–300 °C) is required for nucleation and growth of single phase c-BN by this technique. It is believed that the interstitial Ar observed in Rutherford backscattering spectrometry studies is primarily responsible for the stress generation in the films. A combination of h-BN and c-BN was deposited on Ni; only h-BN was obtained on Cu substrates.
Fundamental research and device applications of molecular beam epitaxy grown heterostructures
Authors: Weisbuch C.
Published: July 2002

Molecular beam epitaxy (MBE) has been and remains the premier growth technique to explore new concepts in heterostructure physics and applications. We review the various effects which have been put to use in new physical phenomena or novel electronic and optoelectronic devices. The progress in the last few years both in basic research (electronic properties of the two-dimensional electron or hole gas, coherent light-matter coupling in microcavities,...), in materials choices (wide or small band gap III–V’s and II–VI’s, strained materials pairs,...), in structured growth (either lithography-aided or self-organized), in device concepts (electron ‘‘mirrors,’’ structures with controlled spontaneous emission,...) evidences that the rate of appearance of novel MBE applications is undiminished, to the contrary.
Direct current sputter deposition of titanium nitride controlled in situ by soft x-ray emission spectroscopy
Authors: Legrand P. B. , Dauchot J. P. , Hecq M. , Charbonnier M. , Romand M.
Published: July 2002

Thin films of TiNx are synthesized by reactive dc sputtering of a titanium cathode in an Ar/N2 gas mixture. The substrates (glass, stainless steel, and silicon) are negatively biased at −200 or −300 V. The composition is monitored in situ by the measurement of the Ti Lα,β, Ti Ll,n, N Kα, and O Kα x-ray line or band intensities. The x-ray emission is induced in the film during the deposition by the high energy secondary electrons (about 4 keV) emitted by the cathode. After deposition, x-ray measurements are also carried out while using a cold cathode electron gun. The oxygen content of the films measured during deposition is low (<1 wt. %). The titanium nitride films appear to become rapidly overstoichiometric (up to TiN1.4) when the nitrogen partial flow rate increases. These overstoichiometric films show an x-ray diffraction pattern corresponding mostly to fcc TiN with the plane (111) oriented parallel to the substrate surface. These results are correlated to the changes of the Ti Lα,β emission band profile which depends drastically on the titanium chemical environment.
Preparation and properties of Ti(Y)N coatings
Authors: Yu Zhiming , Jin Zhujin , Liu Changqing , Yu Li , Dai Shaoxia
Published: July 2002

Ti(Y)N and TiN coatings were deposited by the reactive ion plating method. Phase identification and examination of the texture of Ti(Y)N and TiN coatings were performed using x-ray diffraction analysis. The addition of yttrium causes a strong modification of the growth orientation of TiN crystallites in the coating. The distribution of yttrium across the interface of the Ti(Y)N coating and the substrate was analyzed by means of electron probe microanalysis. The rare-earth element Y was concentrated in the transition zone between the TiN coating and the substrate. The interfacial structure of the Ti(Y)N coating to the substrate was studied by transmission electron microscopy. The influence of the interface structure on the adhesion of the coating to the substrate is also discussed. The corrosion resistance and the wear resistance of the Ti(Y)N coatings were also studied. The results show that the Ti(Y)N coating exhibits an excellent corrosion resistance and high wear resistance that are improved compared to TiN by the presence of yttrium.
Effect of residual gas on Cu film deposition by partially ionized beam
Authors: Koh Seok-Keun , Jin Zhegao , Lee Jiyun , Jung Hyung-Jin , Kim Ki-hwan , Choi Doo-jin
Published: July 2002

Cu films were deposited on Si(100) substrate by partially ionized beam in a pressure of 10−6 Torr. Ion beam current densities were measured with and without Cu evaporation, respectively, in order to evaluate an effect of residual gas on the Cu deposition process. The ion beam current density measured without Cu evaporation, which is mainly due to ionized residual gas, was linearly increased with acceleration voltage, and the dependence of the ion beam current density on vacuum pressure was significantly decreased with 10−5–10−7 Torr. Total ion beam current density measured during Cu deposition, effects of ionized Cu particles and residual gas, was increased with acceleration voltage, and the magnitude of the total ion beam current density is nearly the same as the ion beam current density due to ionized residual gas. Growth rate and preferred orientation were increased with acceleration voltage, and grain size of the deposited films was in a range of 1000 Å, which was not dependent on acceleration voltage. Root-mean-square roughness of deposited films was reduced from 138 to 18 Å with a change in acceleration voltage from 0 to 3 kV. These changes of the film’s features could be attributed to the bombardment effect of ionized residual gas.
Properties of transparent zinc-stannate conducting films prepared by radio frequency magnetron sputtering
Authors: Minami T. , Takata S. , Sato H. , Sonohara H.
Published: July 2002

Highly transparent and conductive amorphous zinc-stannate thin films were prepared by rf magnetron sputtering using a target with a Zn/(Zn+Sn) content of 33 at. %. The resistivity distribution of the zinc-stannate films having a composition near ZnSnO3 and deposited on the surface of substrates placed parallel to the target surface was successfully controlled by optimizing both the sputter gas pressure and oxygen partial pressure. A uniform distribution with a resistivity of 4–5×10−3 Ω cm and an average transmittance above 80% in the visible range was obtained for undoped zinc-stannate films deposited on substrates from room temperature to 300 °C. The zinc-stannate films were found to be thermally and chemically more stable than undoped SnO2 and ZnO films.
Effect of N+2 ion bombardment on the compositional change and residual stress of AlN film synthesized by ion beam assisted deposition
Authors: Kim Ig-Hyeon , Kim Seon-Hyo
Published: July 2002

The compositional change and residual stress of aluminum nitride film synthesized by ion-assisted evaporation and sputtering are discussed in terms of ion bombardment. In the growth of AlN film, N+2 ion bombardment could increase the N incorporation probability and reduce oxygen impurities. The stoichiometric nitride was obtained at an arrival ratio of N/Al higher than 1.5. With increasing ion flux and energy the residual stress shows a tendency to shift from tensile to compressive stress. Except for the low region of ion flux and energy, the compressive stress shows a linear proportionality to the momentum parameter of incident ions defined as the product of ion flux and (ion energy)1/2 in the ion beam assisted deposition process. The temperature dependence of residual stress is also discussed.
Delineation of pn junctions by scanning tunneling microscopy/ spectroscopy in air and ultrahigh vacuum
Authors: Silver R. M. , Dagata J. A. , Tseng W.
Published: July 2002

Lateral dopant profiling of cleaved, passivated abrupt GaAs pn junctions using scanning tunneling microscopy/spectroscopy is demonstrated both in ultrahigh vacuum and air. A combination of forward- and reverse-bias imaging and position-dependent tunneling spectroscopy makes it possible to delineate the metallurgical junction location of abrupt asymmetric n+p and symmetric n+p+ junctions. The experimental results are shown to be consistent with simulations based on the metal–insulator–semiconductor band-bending model when surface states and bulk transport through the pn junction are properly taken into account in the calculations.
Characterization of silicon surfaces and interfaces by optical vibrational spectroscopy
Authors: Chabal Yves J. , Hines Melissa A. , Feijóo Diego
Published: July 2002

Chemical reactions at semiconductor surfaces and interfaces can be indirectly studied by characterizing the surface species with vibrational spectroscopy. We review here the various optical techniques available to study surface and interfacial adsorbates including both linear techniques, such as infrared absorption and Raman scattering, and nonlinear techniques, such as sum–frequency generation. We also review the different optical geometries appropriate to each technique. These methods differ dramatically in both their overall sensitivity to surface adsorbates as well as their sensitivity to adsorbate geometries as obtained from calculations of the local surface electric field and oscillator response. Illustrative examples from recent studies of the interfacial chemistry of bonded wafers as well as structural studies of HF-etched silicon surfaces are presented.
Directed growth of Uromyces hyphae on integrated circuit substrates
Authors: Kozicki Michael N. , Roberson Robert W. , Whidden Thomas K. , Kersey Susan E.
Published: July 2002

We report on the initial findings of a program involving the directed growth of fungal hyphae on custom-designed integrated test circuits for the purpose of creating a biohybrid integrated system. The biological element in this work is Uromyces appendiculatus, an organism which has been shown to exhibit precise and unique topographical signal recognition. The integrated circuit is fabricated using standard semiconductor processing techniques, with guiding elements etched into the final layer of metallization. The spores germinate on contact pads in the circuit and this results in the formation of germ tubes which are guided by the vectoring elements toward other contacts. We show that the vectoring structures are capable of steering the hyphae to intended connection/termination points through a wide range of angles. In addition, we demonstrate that self-assembled monolayers of n-octadecyltrichlorosilane on the circuit materials result in superior germination characteristics compared to untreated surfaces. We also speculate on the potential applications of such cell–circuit hybrids.
In situ analysis of the tribochemical films formed by SiC sliding against Mo in partial pressures of SO2, O2, and H2S gases
Authors: Singer I. L. , Le Mogne T. , Donnet C. , Martin J. M.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were used to identify gas reaction layers and tribochemical films formed during reciprocating sliding tests in an ultrahigh vacuum (UHV) tribometer. Tests were performed on UHV cleaned SiC pins and Mo flats during or after exposure to SO2, O2, or H2S gas at pressures around 40 Pa. XPS identified the gas reaction layers on Mo to be chemisorbed MoS2 and/or MoO2 phases less than 1 nm thick. AES of Mo wear tracks showed tribochemical films similar in composition to, but thicker than, the reaction layers. AES of SiC wear scars in all three gases indicated tribochemical films containing Si oxide and/or Si sulfide and possibly graphite. In addition, transfer films of Mo oxysulfide and Mo oxide were found in SO2 and O2 tests, respectively, but no transfer films were detected in H2S tests. Thermochemical calculations of stable reaction products of the gas–solid reactions were in good agreement with the phases inferred from XPS and AES. An explanation for the agreement between thermochemical predictions and tribochemical results is given.
Thermo-oxidative erosion of amorphous hydrogenated carbon films
Authors: Haasz A. A. , Chiu S. , Pierre J. E. , Gudimenko Y. I.
Published: July 2002

Amorphous C:D (or C:H) films were deposited on the inner surface of a spherical ultrahigh vacuum chamber by means of a direct current glow discharge in a ∼75% D2 (or H2) and ∼25% CD4 (CH4) gas mixture. Laser Raman spectroscopy analysis of the film exhibited the absence of a diamond peak at 1334.3 cm−1. The general appearance of the spectra was indicative of a polymerlike film. Upon exposure of the C:D film to 18O2, almost all of the released deuterium was seen to be in the D218O chemical form, with less than 1% released as D2. C18O2 was observed to be the main C-containing reaction product of the 18O2 exposure. No methane release was detected. x-ray photoelectron spectroscopy and secondary ion mass spectroscopy analyses of the films indicated the appearance of carbonyl groups (≳C=O) and an increase in the concentration of hydroxyl groups (—COD) due to surface oxidation. The generally accepted scheme for simple thermal oxidation of hydrocarbon polymers was used to provide a plausible reaction mechanism leading to emissions of the reaction products D2O, CO2, and CO.
Analysis of pulse-time modulated high-density discharges
Authors: Meyyappan M.
Published: July 2002

Time modulation of the input power has been used recently to improve processing rates and etch selectivity in high-density discharges. Plasma characteristics of a pulse-time modulated high-density discharge is investigated here with the aid of a spatially averaged model. The model consists of mass and energy conservation equations for neutral and ionic species. Results are presented for chlorine and CF4 discharges for a range of pulse periods and duty ratios.
Si/XeF2 etching: Temperature dependence
Authors: Vugts M. J. M. , Verschueren G. L. J. , Eurlings M. F. A. , Hermans L. J. F. , Beijerinck H. C. W.
Published: July 2002

The temperature dependence of the Si(100)/XeF2 etch reaction is studied quantitatively in a molecular beam setup. At a sample temperature of 150 K the reaction probability reaches unity initially, after which the XeF2 condenses on the surface and blocks the etching process. For increasing temperatures the XeF2 reaction probability initially decreases from 100% at 150 K down to 20% around 400 K, but for temperatures above 600 K it increases again up to 45% at 900 K. In a simple reaction scheme the high etch rate at low temperatures is explained by a XeF2-precursor, with an activation energy for desorption of 32±4 meV. Furthermore the increased etch rate at high temperatures is explained by the desorption of SiF2 with an activation energy of 260±30 meV. The steady-state fluorine content of the SiFx reaction layer, measured using thermal desorption spectroscopy, reaches a maximum of 5.5 monolayers at 300 K. For increasing temperatures it decreases to a submonolayer coverage above 700 K. The temperature dependence of the formation of the reaction layer is described well by including the XeF2-precursor in a previously developed adsorption model.
Si/XeF2 etching: Reaction layer dynamics and surface roughening
Authors: Vugts M. J. M. , Eurlings M. F. A. , Hermans L. J. F. , Beijerinck H. C. W.
Published: July 2002

The etching of Si(100) is studied quantitatively in a molecular beam setup. After exposing the silicon surface to XeF2 doses between 102 and 104 monolayers (MLs) of XeF2, thermal desorption spectroscopy is used to study the SiFx content of the reaction layer. Large values of the fluorine content (up to 30 ML) are observed. These are explained by surface roughening due to the etching process, which increases the effective surface by up to a factor of 6 after 105 ML of XeF2, corresponding to 104 ML of etched Si. This implies a porous or canyon-like structure. The dose dependence of the fluorine content is not single exponential; it increases rapidly for the first 102 ML and much more slowly thereafter, saturating after approximately 104 ML. This behaviour is described by the rapid formation of a monolayer of SiFx species in the initial regime, followed by the slow formation of a steady state multilayer of SiF–SiF2–SiF3 and SiF2–SiF3 chains. The etch rate shows a similar dose dependence, increasing from 12% of the incident flux in the monolayer regime to 20% in the multilayer regime. Finally, it is shown that fluorine diffusion into the silicon bulk is not an important process in the reaction layer formation.
Influence of surface oxygen on chemoresistance of tin oxide film
Authors: Kac̆iulis S. , Mattogno G. , Galdikas A. , Mironas A. , S̆etkus A.
Published: July 2002

The oxygen controlled chemoresistance of tin oxide based gas sensors was investigated in the temperature range from 20 to 320 °C. Polycrystalline thin film gas sensors were fabricated by the reactive dc-magnetron sputtering. The parameters of the sensors were also modified by additional Pt or Sb doping. The effect of surface oxygen species on the chemoresistance was studied by x-ray photoelectron spectroscopic (XPS) analysis of the surface chemical composition before and after different sample treatments. The oxygen peak at a binding energy 531.8 eV in the XPS core level spectrum was found to be related to the chemisorbed molecular oxygen O−2. The variation of an amount of the O−2 species is found to be the main cause of gas sensitivity of tin oxide films at temperatures from 20 to 230 °C.
Pumping characteristics of the St707 nonevaporable getter (Zr 70 V 24.6-Fe 5.4 wt %)
Authors: Benvenuti C. , Chiggiato P.
Published: July 2002

The room temperature pumping speeds of the St707 nonevaporable getter (NEG) have been measured both for individual gases and for gas mixtures as a function of the quantities of gas pumped. The interesting feature of this NEG consists in its moderately low activation temperature. Therefore particular attention has been devoted to defining the optimum temperature and duration of the activation process to obtain the highest possible pumping speed in a given practical situation. It has been found that heating at 400 °C for about 1 h, or at 350 °C for one day, results in pumping speeds of about 1000 ℓ s−1 m−1 for H2, 2000 ℓ s−1 m−1 for CO, and 450 ℓ s−1 m−1 for N2, values very close to those obtained after activation at the higher temperature of 740 °C. The St707 NEG is therefore particularly suitable for passive activation during bakeout of stainless steel vacuum systems, avoiding the need for electrical insulation and feedthroughs which are mandatory when activation is carried out by resistive heating.
Scattering of H2 (v=1, J=1) from Cu(110): Survival probability versus incident energy
Authors: Gostein Michael , Sitz Greg O.
Published: July 2002

We have measured the relative survival probability of H2 in the single rovibrational state (v=1, J=1) scattered from room temperature Cu(110) versus incident translational energy. The relative survival probability is found to decrease smoothly from its maximum at 0.08 eV incident translational energy to 0.5 times the maximum at 0.23 eV. We discuss possible loss channels and compare the results to dynamical calculations.
Kinetics and dynamics of the trapping-mediated dissociative chemisorption of oxygen on Ru(001)
Authors: Wheeler M. C. , Seets D. C. , Mullins C. B.
Published: July 2002

Supersonic molecular beam techniques were used to determine the initial dissociative chemisorption probability, S0, of O2 on the Ru(001) surface as a function of incident kinetic energy, Ei, angle of incidence, θi, and surface temperature, Ts. For Ts between 77 and 900 K, two kinetic energy regimes are observed as Ei increases from 30 to 700 meV. In this article we discuss the mechanism for chemisorption in the low kinetic energy regime. S0 decreases with Ei for incident energies less than ∼70 meV, and there is little dependence of S0 on θi in this low energy range. Additionally, S0 decreases rapidly as Ts is increased in this regime, and we believe that a simple trapping-mediated mechanism dominates adsorption. The low Ei data are fit to a simple one-dimensional potential energy surface model that includes the molecule initially trapping into a physical adsorption well and then surmounting a barrier into the dissociatively chemisorbed state. Analysis of an Arrhenius construction yields a difference in activation energies for desorption and dissociation from the physically adsorbed state that is approximately 28 meV below the vacuum zero, for both Ei =30 and 53 meV.
Numerical study of apparent activation energies of diamond growth rates in hot filament chemical vapor deposition systems
Authors: Behrendt Frank , Deutschmann Olaf , Ruf Bernhard , Warnatz Jürgen
Published: July 2002

Diamond growth in a hot-filament chemical vapor deposition system is investigated numerically and results are compared with experiments. The mathematical model for the description of the gas phase assumes a stagnation-point flow and the corresponding governing equations for mass, momentum, chemical species mass fractions, and energy are solved in their one-dimensional form. A detailed surface reaction mechanism for diamond growth is used which accounts for the incorporation of the CH3 radical in the diamond lattice on the reconstructed C(100) surface. This reaction scheme describes the surface-temperature dependence of the diamond growth rate correctly. In agreement with the experiment, this temperature dependence can be characterized by an apparent activation energy of about 84 kJ/mol for temperatures below 1200 K. A sensitivity analysis of the surface reaction scheme is performed to gain insight into the sources of this apparent activation energy. It is shown that a single surface reaction is responsible for the temperature dependence of the diamond growth rate.
Elemental steps in the growth of AlN thin films on NiAl upon thermal decomposition of ammonia
Authors: Gassmann P. , Schmitz G. , Boysen J. , Bartolucci F. , Franchy R.
Published: July 2002

Ammonia adsorption at T=80 K on NiAl(111) and NiAl(001) and subsequent thermal decomposition at elevated temperatures leads to the formation of aluminum nitride (AlN). After annealing to T=600 K, NH3 is dissociated completely and atomic nitrogen is adsorbed on the surface. At temperatures between 800 and 1200 K, an intermediate AlN state is found. The formation process of AlN has finished after annealing to 1200 K. Well-ordered AlN thin films on NiAl(001) and NiAl(111) can be prepared by several cycles of ammonia adsorption at T=80 K and annealing to 1250 K. The films render a distinct low-energy electron diffraction pattern with hexagonal (AlN/NiAl(111)) or pseudo-twelvefold (AlN/NiAl(001)) symmetry. High resolution electron energy loss spectra of ordered AlN films show a Fuchs–Kliewer phonon mode at 865 cm−1 in good agreement with theoretical spectra on the base of the dielectric theory. The electronic gap of the thin AlN films is determined to be Eg≂6.1 eV. Gap states at 1.1 and 5.1 eV were found for AlN/NiAl(111) as well as for AlN/NiAl(001).
Study of ultrathin polyamide-6,6 films on clean copper and platinum
Authors: Charlier J. , Detalle V. , Valin F. , Bureau C. , Lécayon G.
Published: July 2002

The aim of this work is to present an interaction reactor which allows us to build very thin organic coatings on metallic substrates. This reactor is coupled to an analytic device which further enables an investigation of the interfacial region by very-surface-sensitive analytical means. The use of such an integrated installation makes it possible to follow the growth of the interfacial region step by step and to focus on the nature of the chemical structure that is identified in the interfacial region between a well-defined polymer phase and an atomically clean metallic substrate. As an illustration we compare the behavior of PA-6,6 on copper and platinum.