Gas Films Research Articles

5209 軸受剛性を最大化するスラスト気体軸受形状の最適化(S65-3 気体軸受,S65 トライボロジーの基礎と応用)

Hydrodynamic gas film bearings are widely used for very high speed, lightly loaded rotating machinery. In the design of hydrodynamic gas film bearings, it is of cardinal importance to enhance the stiffiaess of gas films for minimizing the vibration due to external excitations. Among various types of hydrodynamic gas film thrust bearings, grooved bearings have an advantage of high stiffness and load carrying capacity, but the stiffness of the bearings storongly depends on groove geometry. Therefore, when the groove geometry is designed suitably, it is expected to improve considerably the stability characteristics of the bearings. In this paper, the optimum design methodology is presented to maximize the stiffness of gas film for grooved thrust bearings, and the effectiveness of the methodology is verified experimentally.

Electron stimulated desorption of Cl? from adsorbed and condensed Cl2: Effects of environment and orientation

Electron stimulated desorption (ESD) of Cl(-) from condensed molecular chlorine in the energy range 0-15 eV is studied. Cl2 is deposited in either multilayer amounts directly on a cryogenically cooled gold crystal or in sub-monolayer quantities on rare gas films (Xe, Kr) or ammonia ice films. Cl(-) desorption from multilayer films shows an intense resonance peaking at 5.5 eV and a comparatively smaller feature at 3 eV in qualitative agreement with an earlier ESD experiment. The desorption signal is enhanced by about one order of magnitude when a 0.2 monolayer (ML) Cl2 is adsorbed on a multilayer rare gas film. In this case, the desorption signal shows two clearly separated resonances peaking at 2.5 and 5.5 eV closely resembling dissociative electron attachment (DEA) from gas phase Cl2. These resonances can be associated to the transitions Cl2(1Sigmag+) --> Cl2(-)(2Pig) and Cl2(1Sigmag+) --> Cl2(-)(2Piu), respectively, both final states representing core excited resonances. The shape of the resonance around 5.5 eV splits into different peaks when changing from grazing incidence of the electron beam to an impact angle of 45 degrees with respect to the surface normal. On the basis of the pronounced angular dependence of the Cl(-) intensity reported from gas phase DEA this observation is compatible with a situation in which the molecules are oriented along the surface normal. Compared to the noble gas films, ESD from sub-monolayer Cl2 on top of a multilayer NH3 film is suppressed while the overall shape of the yield function is approximately preserved. None of the present experiments show a Cl(-) desorption signal below 2 eV while the charging behaviour of the film indicates that electron attachment is still operative in this energy domain. This suggests that the transient anion in its electronic ground state (Cl2(-)#(2Sigmau+)) is still formed by low energy electron attachment but is subjected to effective energy dissipation creating either stabilized ions (Cl2(-)(2Sigmau+)) or fragment ions (Cl(-) (2P)) with insufficient kinetic energy to leave the surface.

Stability of Sputtered Hf-Silicate Films in Poly Si/Hf-Silicate Gate Stack Under the Chemical Vapor Deposition of Poly Si and by Annealing

We investigated the effects of SiH₄ gas on the surface of Hf-silicate films during the deposition of polycrystalline (poly) Si films and the thermal stability of sputtered Hf-silicate films in poly Si/Hf-silicate structure by using High Resolution Transmission Electron Microscopy (HR-TEM) and X-ray Photoelectron Spectroscopy (XPS). Hf-silicate films were deposited by using DC-magnetron sputtering with Hf target and Si target and poly Si films were deposited at 600℃ by using Low Pressure Chemical Vapor Deposition (LPCVD) with SiH₄ gas. After poly Si film deposition at 600℃, Hf-silicide layer was observed between poly Si and Hf-silicate films due to the reaction between active SiH₄ gas and Hf-silicate films. After annealing at 900℃, Hf silicide, formed during the deposition of poly Si, changed to Hf-silicate and the phase separation of the silicate was not observed. In addition, the Hf-silicate films remain amorphous phase.

Characterization of the squeeze film damping effect on the quality factor of a microbeam resonator

The squeeze film damping effect on a beam resonator is analyzed on the basis of the coupled elastic beam theory and the Reynolds equation for isothermal incompressible gas films. Under the condition of small amplitude oscillation, linearization of the governing equations leads to the solution that characterizes the squeeze film damping effect on the beam resonator by two dimensionless parameters. These two parameters, in analogy with the damping and mass parameters of the simple mass-spring-damping system, are completely determined by the physical properties of the beam and gas. It is shown that the calculation of these two parameters can be considerably simplified according to the value of the squeeze number.

Homogenization of the Generalized Reynolds Equation for Ultra-Thin Gas Films and Its Resolution by FEM

We address the numerical modeling of roughness or texture effects in ultra-thin gas films. Rarefaction (high Knudsen number) effects are dealt with using the Generalized Reynolds Equation, and a homogenization procedure is proposed to rigorously account for arbitrary roughness/texture shapes. The presentation is focused on head-disk magnetic storage devices, but the techniques proposed are general. Some details of the implementation, along with numerical tests, are included. By removing the small space and time scales from the problem, the methodology allows for efficient modeling of slider bearings with small-scale features.

Etch characteristics of CoZrNb and CoTb magnetic thin films in a high density plasma

The dry etching of CoZrNb and CoTb magnetic thin films was carried out using Cl2 and C2F6 etch gases in an high density plasma. These new magnetic materials exhibited the etching characteristic of monotonous decrease in etch rate with increasing gas concentration. The etch rates of CoZrNb and CoTb films were faster in Cl2 gas than in C2F6 gas. The etch rates of CoZrNb and CoTb films were in the range of 30 ∼ 60 nm/min for Cl2 gas while in the case of C2F6 gas, CoZrNb and CoTb films showed the etch rate of less than 20 nm/min. The etch profiles of CoZrNb and CoTb films exhibited clean without any etch residues but the etch slopes were shallow. As the concentration of Cl2 gas increases, the etch slope became slanted. At the etch conditions used in this study, it is thought that the concentration of 20 ∼ 40% Cl2/Ar gas is optimum to give fast etching and clean profiles. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The hydrophobic force: nanobubbles or polymeric contaminant?

The implication of surface-adsorbed nanoscopic gas films, or nanobubbles, on the origin of the hydrophobic force and theoretical models of this force are investigated. Rather than question the validity of the model we examine the strength of the experimental observation which has led to this model.

Low-temperature chemical vapor deposition and scaling limit of ultrathin Ru films

Thermal chemical vapor deposition at temperatures as low as 423 K, using Ru3(CO)12 with no accompanying reactive gas, forms pure, uniform, and smooth Ru films on Ta and low-resistivity films on SiO2. A 2.5-nm-thick Ru film fully covers the underlying Ta and the Ru film is thermally stable up to 573 K. Unlike Ta, Ru films exhibit excellent wetting by Cu even when the Ru surface is contaminated with small amounts of oxygen.

単結晶金属表面上の物理吸着層を観察するための２パラメータ自動消光偏光解析装置の開発

A two-parameter auto-null ellipsometer system was constructed and applied for precise observation of the growth of rare gas films physisorbed on a metal surface in quasi equilibrium condition. We obtained the adsorption isobar of Xe/Ag (111) at P = 2.5×10-6Pa, which shows the layer by layer growth of the Xe film up to the third layer. The relative of polarizability of a Xe atom in the second and the third layer to that of the first layer are 0.94 and 0.91, respectively.

SCATTERING OF ELASTIC WAVES BY THE ISOLATED LINEAR CHAIN OF PHYSISORBED ATOMS ON THE SURFACE IN A TWO-DIMENSIONAL WAVEGUIDE

The scattering and transmission properties of vibrational waves in a perturbed two-dimensional wave-guide in the harmonic approximation are presented. The perturbation is characterized by an isolated adatom defect boundary separating two planar waveguide crystalline lattices, illustrated by a linear chain of defect masses. The theoretical approach using the matching procedure for calculating phonon scattering at their domain boundaries is also presented. The reflection and transmission probabilities in the scattering region are calculated and illustrated for heavy and light defect masses. The conductance properties, in full accordance with the Landauer–Büttiker description of electron transport, are also calculated in these two cases. It is shown that the influence of defect masses can be explained by the strong decreases of conductance values caused by the asymmetric Fano resonance type. The realistic example presented here is instructive and may constitute a precursor model for analyzing the scattering of vibrational waves by an isolated defect in the two-dimensional crystalline lattice formed by atoms adsorbed on the surface of crystal substrates such as physisorbed noble gas films on close-packed atomic planes of the metal surface. A detailed discussion on the vibrational waves in the scattering region is given.

Time‐of‐flight studies of secondary ions produced by 400 eV He+ ion impact on Ar, Kr, and Xe thin films at 8 K

AbstractSecondary ions produced by 400 eV He+ ion impact on Ar, Kr, and Xe thin films deposited on a silicon substrate at 8 K were measured as a function of film thickness using a time‐of‐flight secondary‐ion mass spectrometer. For Ar, the cluster ions Arn+ up to n = 4 as well as the monomer ion (n = 1) were observed and they showed characteristic film‐thickness dependence with increase of the film thickness up to ∼200 monolayers. This is due to the momentum transfer in the elastic collision between the incident He+ ion and the matrix Ar atoms and also to the relaxation of electronic excitations (e.g., holes and excitons) to phonons resulting in the film erosion. In contrast, neither dimer nor cluster ions were detected for solid Kr and Xe films. This is due to the less efficient momentum transfer in the elastic collision between He+ and Rg's (Rg = Kr and Xe) and also to the efficient electronic energy migration in solid Kr and Xe. The ions originating from the silicon substrate such as Si+, SiCH3+, SiOH+, and C+ were found to be sensitized by the deposition of Xe film in the range of 0–40 monolayers. The penetration depths of the primary ion He+ through the rare gas films increase in the order Ar < Kr < Xe. Copyright © 2002 John Wiley & Sons, Ltd.

Phase separation in argon/neon mixtures

The desorption behaviour of quench-condensed rare gas films has been investigated using high-frequency surface acoustic waves. Measurements on the binary mixture Argon 1− x /Neon x have been carried out. For small and very large concentrations x Ne a behaviour is found, which indicates the existence of a substitutionally disordered solid. In contrast, for concentrations 0.25< x Ne<0.92 two discrete temperatures for Ne desorption exist. This indicates that for a wide range of concentration, quite surprisingly, two separate phases, one of pure Ne and the other of crystallites with either AB 2 or AB 3 structure, are formed.

Novel array-type gas sensors using conducting polymers, and their performance for gas identification

Novel gas sensor devices have been developed using polythiophene (pTh) film and poly(3-n-dodecylthiophene) (pDpTh) film coated over pTh film. These polymer films were electrochemically deposited and doped by cyclic voltammetry on thin-film electrodes where the isolation gap was formed by a micromachining process. We examined the response characteristics of the conducting polymer films against various sample gases over a range of temperatures of the sensitive layer. The resistance changes of both sensitive layers of pTh and pDpTh were highly dependent on the kind of layer. In particular, pTh film responded to ammonia gas and pDpTh films clearly responded to hydrophobic gases, such as chloroform, methane and ethanol. The response of these films to several gases was analyzed with a pattern recognition (PARC) algorithm. It was found that our simple gas sensor device could discriminate between the gases that were used here.

3207 気液 2 層潤滑の基本特性解析 : 走行する無限幅線圧力による表面変形特性

3207 気液 2 層潤滑の基本特性解析 : 走行する無限幅線圧力による表面変形特性

８ＫにおけるＡｒ，Ｋｒ，およびＸｅ薄膜の４００ｅＶ Ｈｅ｀＋´イオン衝撃による二次イオンのＴＯＦ解析

Secondary ions produced by 400 eV He+ ion impact on Ar, Kr, and Xe thin films deposited on a silicon substrate at 8 K were measured as a function of film thickness using a time-of-flight secondary-ion mass spectrometer. For Ar, the cluster ions Arn+ up to n=4 as well as the monomer ion (n=1) were observed and they showed characteristic film-thickness dependence with increase of the film thickness up to ~200 monolayers. This is due to the momentum transfer in the elastic collision between the incident He+ ion and the matrix Ar atoms and also to the relaxation of electronic excitations (e.g., holes and excitons) to phonons resulting in the film erosion. In contrast, neither dimer nor cluster ions were detected for solid Kr and Xe films. This is due to the less efficient momentum transfer in the elastic collision between He+ and Rg's (Rg=Kr and Xe) and also to the efficient electronic energy migration in solid Kr and Xe. The C+ ions originating from the carbonic contaminants on the silicon substrate were found to be sensitized by the deposition of rare gas films. The penetration depths of the primary ion He+ through the rare gas films increase in the order of Ar<Kr<Xe.

Desorption behavior of quench-condensed argon-neon mixtures.

The desorption behavior of quench-condensed rare gas films has been investigated using high frequency surface acoustic waves. Measurements of pure films of argon and neon and of the binary mixture Ar(1-c)/Ne(c) have been carried out. For small and very large neon concentration c(Ne) a behavior is found which indicates the existence of a substitutionally disordered solid. In contrast, in the wide range of concentration 0.25< c(Ne)< 0.92 two discrete temperatures for neon desorption exist. The data clearly indicate the occurrence of two separate phases, one of pure neon, the other of crystallites with either Ar(2)Ne or Ar(3)Ne structure.

Electric Field Induced Heating and Energy Relaxation in GaN

AbstractWe report results of an investigation of electric field induced heating at low temperature in GaN 3-dimensional electron gas films grown on sapphire substrates. The excess noise of the electron gas in a patterned GaN film, while the substrate is held at low temperature, is used to determine the electron temperature. We calculate the rate of power dissipation and compare our results with a calculation of acoustic deformation potential scattering processes in GaN. We discuss the existence of a thermal boundary resistance between the GaN film and the sapphire substrate.

Hydrodynamics and mass transfer phenomena in counter-current packed column at elevated pressures

The aim of this study is to determine mass transfer parameters such as interfacial area a and volumetric liquid side mass transfer coefficient k L a during gas–liquid absorption in a packed column according to pressure within the range 0.1–1.3 MPa. A preliminary hydrodynamic study was carried out in order to characterize gas and liquid flows according to the operating pressure. The residence time distribution method shows that fluids flows can be modeled as plug flow with axial dispersion. In contrast to the liquid flow, an effect of pressure on the gas flow has been observed. The axial dispersion coefficient of the gas increases with pressure. These results allow modeling of the gas–liquid absorption in a packed column with or without chemical reaction and at elevated pressures. The basic equations defining the hydrodynamic profile of the gas and liquid films are completed by the terms describing mass transfer coupled with an irreversible chemical reaction in the liquid phase. The numerical resolution of the system of equations obtained has allowed the study of the influence of pressure on the interfacial area a. This parameter increases with pressure. The same result has been observed with the volumetric liquid side mass transfer coefficient k L a. The coefficient k L is independent of pressure.

Passivation of GaAs surface by GaS

The thermal evaporation of a GaS single crystal has been used to passivate the GaAs surface. The passivation effect of GaAs surface by GaS has been studied by low-energy electron-loss spectroscopy (LEELS) and photoluminescence (PL). The LEELS spectra shows that the surface related peaks of GaAs disappeared immediately after starting the deposition, suggesting the effective passivation of dangling bonds of GaAs surface by S atoms included in the evaporated species. PL measurements suggest that the GaAs surface is effectively passivated by GaS films.

Annealing of quench-condensed noble gas films

We have measured the internal friction of quench-condensed thin neon films (0.16– 1.5 μm ) above 50 mK , and have found it to be of the same order as that of amorphous films, indicating considerable disorder, even after extended annealing. The rapid rise of the internal friction above 4 K is interpreted as the onset of plastic deformation. In addition, we are able to measure vapor pressures on the order of 10 −12 Torr .