摘要:

Bombardment of solids by low-energy electrons (<500 eV) can cause various changes in the surface region, particularly if the surface contains an adsorbed layer. Electron bombardment can promote the desorption of energetic neutral and ionic fragments from the surface, can alter the bonding of surface species, and in some cases can cause decomposition of the surface region. These processes are termed electron-stimulated desorption (ESD) phenomena, and this review is primarily concerned with the use of ESD in studies of species adsorbed on surfaces. Topics covered include experimental methods, a theoretical discussion of physical mechanisms, and a detailed discussion of certain specific and well-studied adsorbate–substrate systems.

ISSN:0022-5355    

DOI:10.1116/1.1315200

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

An analytical model, describing the flux of reactive-gaseous species surviving transit through a cylindrical reactor with apertures at either end, is developed. The magnitude of the surviving flux is evaluated as a function of the reaction probability of the wall, which may be discontinuous from point-to-point within the reactor, and of the relative dimensions of the vessel. Numerical solutions were obtained for vessels with values of the ratio length–radius in the range 2–6. The model is compared with a simplified approximation that is particularly applicable for reactor geometries with small values of length–radius.

ISSN:0022-5355    

DOI:10.1116/1.1315201

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

Submicron particles of chromium, produced by evaporation and condensation at reduced pressure in a helium atmosphere, were entrained in a stream of helium where they were coated withZrO2. Factors affecting the chromium-particle growth rate were evaporation temperature and inert-gas overpressure. A model of particle growth was formulated which predicted particle sizes which were in reasonable agreement with those produced experimentally. The difference noted by other investigators in particle size resulting from substitution of one inert gas for another is also explained by the model.

ISSN:0022-5355    

DOI:10.1116/1.1315202

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

This paper describes a high-vacuum induction furnace for sintering cemented carbides. The special features of this installation which are described in detail are (a) a dewaxing unit which prevents any wax condensation inside the furnace, (b) a temperature measuring device, which gives reproducible values, withstands the attack of CO and has a lifetime of more than 1000 h, (c) a cooling tower which shortens the cooling-down time by 60–80%, and (d) a newly developed automatic-control unit which permits any temperature and pressure program for sintering cemented carbides in a fully automatic manner. Hydrogen flushing is also automatic so that the furnace has only to be charged and discharged manually.

ISSN:0022-5355    

DOI:10.1116/1.1315203

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

Epitaxial growth of semiconductors in real crystal substrates begins by two- and three-dimensional nucleation. It is necessary to take into account the nucleus–substrate boundary energy and substrate surface defects, as well as the misfit angle of nucleus and substrate lattices. For the homoepitaxial growth the calculation of two- and three-dimensional nucleation rate on the surface (111), (110), (111) for different supersaturations for quasispherical nuclei is made. It is shown that for GaAs in gas transport processes the formation of films on singular facets is realized by the three-dimensional nucleation. Deviation of substrate orientation from that for the singular planes increases the contribution of the mechanisms of two-dimensional nucleation and of growth by step propagation.

ISSN:0022-5355    

DOI:10.1116/1.1315204

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

A systematic experimental investigation of the cryosorption ofH2by cold cryodeposited-CO2frost is reported. It is shown that the sorption capacity of the frost depends upon the conditions at which the frost was formed and its temperature history. Frosts formed in a manner to make them porous or disordered are shown to possess greater sorption capacities. It appears that surface diffusion of absorbed molecules into a disordered frost structure is the basic pumping mechanism. Isotherms forH2sorbed byCO2frosts formed over a wide range of conditions are presented. Also, the reuse sorption capacity of the frost is well documented. As a result of the present tests, it is now possible to put the process of frost-cryosorption pumping into better perspective.

ISSN:0022-5355    

DOI:10.1116/1.1315205

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

Collector and grid end-cap currents were measured as a function of pressure, electron current, grid, and end-cap potentials in a Bayard–Alpert gauge-like geometry. After an analysis of the electrical fields produced in the grid volume by electrode potentials and electron and ion space charges, the main experimental results are discussed. An explanation is proposed for the discrepancy between the experimental and theoretical values of the collection factor, for the mechanism leading to an increased collection when positive grid end-caps are used, and for other experimental results. The information obtained is useful for a better understanding of the processes taking place in Bayard–Alpert gauges; some light is thrown upon the difficulties which might occur when using the Bayard–Alpert geometry as a spectrometer for subthermal velocities.

ISSN:0022-5355    

DOI:10.1116/1.1315206

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

Process advantages of vacuum are compared with conventional inert-gas atmospheres with respect to purity, repeatability, and operating cost. Recognition of vapor pressures of workloads, containers, and furnace hot-zone parts is essential to predicting system performance parameters, maintenance schedules, and pumping equipment selection. Cooling requirements of batch equipment are evaluated with respect to quench characteristics, equipment turn-around time, and workpiece surface quality. Design features of system details are evaluated for such factors as heat removal (jacketing vs traced cooling), safety (one-piece electrode design), integrity at full vacuum, and partial pressure operation. Typical systems are examined for conformity to design criteria established.

ISSN:0022-5355    

DOI:10.1116/1.1315207

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

The thermal desorption of carbon dioxide from an oxygen-covered silver powder was studied from 25 ° to 150 °C by applying a nominal heating rate of 2 °C/min and measuring the mass lost with a vacuum microbalance. A maximum rate of desorption was reached at 49 °C and the desorption was completed at about 100 °C. The temperature at which the maximum rate of desorption occurred was independent of the initial coverage of carbon dioxide to within 2 °C. However, the data could not be simply explained by a fit to the first order Wigner–Polanyi desorption equation, in which it is assumed that the frequency factor (ν) and the desorption energy (E) are independent of coverage and temperature. Beyond the maximum, a slow decrease in the experimental rate of desorption, which was found in contrast to the usual sharp cutoff for a first order process, was attributed to desorbing oxygen, readsorption of carbon dioxide, or a variation ofEat low coverages. Parallel studies with a residual gas analyzer showed that small quantities of oxygen were desorbed in addition to the carbon dioxide. The experimental desorption curve could be fit to the Wigner–Polanyi equation by assuming that the desorption consisted of all the adsorbed carbon dioxide and a small amount of oxygen. The desorption parameters for carbon dioxide which were obtained ranged fromE = 20to 24 kcal/mol andν = 1011to1013 sec−1.

ISSN:0022-5355    

DOI:10.1116/1.1315208

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

A surface elemental-analysis technique, ionization spectroscopy, is described and the characteristics of ionization spectra for contaminated vanadium, nickel, palladium, and molybdenum surfaces are examined. The minimum energies required to ionize the core shells of surface atoms, determined from ionization spectroscopy, are demonstrated to identify those elements. Ionization spectra are shown to be somewhat sensitive to the chemical state of the elements. It is concluded that combined Auger and ionization spectroscopy, using the same instrument, can yield improved analysis of surfaces.

ISSN:0022-5355    

DOI:10.1116/1.1315209

出版商:American Vacuum Society    

年代:1971

数据来源: AIP