- Email: [email protected]
Mass spectrometric investigation of ion desorption induced by slow electrons
Abstracts of papers
of the gas falls. Depending upon the extent of the saturation of the film by the gas, the pressure rises towards the initial value. During the investigation the dependence of pressure variations of the gas under study above the film on time is recorded. Calculations are carried out according to the method proposed by Becker for the "flash" technique. (J Phys Chem, 57, 157, 1953). Values are determined for the boundary surface solubility of hydrogen, nitrogen and carbon monoxide in condensed titanium films at temperatures of 77 ° and 293°K. Field emission-adsorption spectrometry by noise-glow curves-- a new, microscopic desorption method
Ch. Kleint, Physikal Institut d KMU, Leipzig, E Germany Desorption spectrometry is a now widely and successfully used method for investigating adsorption under UHV conditions, but it suffers from some difficulties in relation to the pumping constant and the influence of measuring equipment on the partial pressure ratio during desorption. Moreover, it is seldom possible to measure the properties of single crystal faces and the desorption properties at low temperatures. Therefore a new method is proposed using the current noise of a Mueller-type field-emission microscope, which may represent a useful counterpart to macroscopic desorption methods. After adsorption the temperature of the tip is regulated by means of a transistorized heating current-controller in a linear hyperbolic temperature-time function similar to that used desorption spectrometry. Following high amplification and filtering either the noise power or mean square deviation of the emission current is recorded and simultaneously the emitteranode voltage that is needed to maintain a constant value of the mean emission current. The noise- and voltage-glow curves obtained are analysed in terms of adsorption processes at the emitter surface, because there is a strong connection between surface diffusion and desorption processes and the current noise, which has been established in recent theoretical and experimental work. Some noise-glow curves of xenon and nitrogen desorption are presented and discussed, for example, desorption energy of xenon is deduced. The concluding remarks refer to the extension of the method to measure surface diffusion processes and to further improvement with respect to single-face investigations. Interaction of heavy particles with metal surfaces
J Kistemaker, D Onderdelinden, F W Saris, W F van der Weg, FOM Institute for Atomic and Molecular Physics, Kruislaan 407 Amsterdam, Netherlands The collisions of heavy particles with metal surfaces govern many physical and chemical phenomena. Three fundamental aspects of these interactions will be discussed: (l) Sputtering, ie the removal of metal particles due to kinetic energy transfer. The contributions of focusing, channeling and surface effects to the sputtering mechanism. (2) Reflection of primary and scattering of secondary heavy particles. These are the high energy (mostly charged) particles which originate from two body collisions on the metal surface. (3) Inelastic energy transfer leads to emission of photons and secondary electrons from reflected particles and from inside the solid as well. Here Auger, resonance and radiative transitions are involved.
Since several excellent reviews on these subjects have been published, we confine ourselves primarily to recent investigations. Electron induced desorption of cases from aluminium
E L Garwin, E W Hoyt, J Jurow, and M Rabinowitz, Stanford Linear Accelerator Center, Stanford, California, 94305, USA In designing an ultrahigh vacuum system for an electronpositron storage ring 1, it is of crucial importance to predict (and minimize) the gas produced when synchrotron radiation from circulating beams strikes the chamber wall. It is suggested that photo-electron induced desorption plays the primary role in accounting for the observed pressure increases measured in existing storage rings 1. This paper will briefly outline the ultrahigh vacuum problems unique to high-current, high-energy storage rings. One such problem arises from the high energy density of the synchrotron radiation striking the chamber wall. In the case of the proposed 3 BeV e-e + SLAC ring, the energy at the wall can be as high as 2.5 kilowatt per square centimeter. A good thermal conducter must be used to intercept the synchrotron radiation, while the reflected synchrotron radiation from the absorber (fluorescent photons) must be minimized in order to reduce electron desorption of gas from the internal electrode structures. Thus, interest is drawn to aluminium and its alloys. The electron-induced gas desorption from aluminum has been extensively studied in an ultrahigh vacuum system equipped with a quadrupole residual analyzer having a detection limit of about 10 -1~ torr. By using isotopically enriched (90 per cent CO xS) sorbed gas, surface and bulk effects of the electron desorption may be separated. The discussion of our experiments will focus on the following aspects of electron desorption from aluminum: (1) The amount and kinds of gas species desorbed, and their secondary exchange-reaction products. (2) The number of sorbed states and their respective crosssections for desorption. (3) Dependence on electron-energy, and probable bulk effects from deeply penetrating electrons. (4) Functional dependence of the net desorption yield on the angle of incidence of photons and electrons. (5) Temperature dependence. (6) Readsorption dependence on partial pressures and possible synergistic effects due to co-adsorption of different gases. Reference i Particle Storage Rings, G K O'Neil, Scientific American,November,1966.
Mass spectrometric investigation of ion desorption induced by slow electrons
W K ttuber and C Rettinghaus, Balzers Aktiengesellschaft fiir Hochvakuumtechnik und Diinne Schichten, Balzers, Fiirstentum Liechtenstein Pressure measurements by means of ionisation gauges and mass spectrometric partial pressure analysers are generally based on ionisation by electron impact. In many devices, particularly in Bayard-Alpert-gauges and in high sensitive ion sources, the ionisation of free gas molecules inside the volume is more or less 125
of the gas falls. Depending upon the extent of the saturation of the film by the gas, the pressure rises towards the initial value. During the investigation the dependence of pressure variations of the gas under study above the film on time is recorded. Calculations are carried out according to the method proposed by Becker for the "flash" technique. (J Phys Chem, 57, 157, 1953). Values are determined for the boundary surface solubility of hydrogen, nitrogen and carbon monoxide in condensed titanium films at temperatures of 77 ° and 293°K. Field emission-adsorption spectrometry by noise-glow curves-- a new, microscopic desorption method
Ch. Kleint, Physikal Institut d KMU, Leipzig, E Germany Desorption spectrometry is a now widely and successfully used method for investigating adsorption under UHV conditions, but it suffers from some difficulties in relation to the pumping constant and the influence of measuring equipment on the partial pressure ratio during desorption. Moreover, it is seldom possible to measure the properties of single crystal faces and the desorption properties at low temperatures. Therefore a new method is proposed using the current noise of a Mueller-type field-emission microscope, which may represent a useful counterpart to macroscopic desorption methods. After adsorption the temperature of the tip is regulated by means of a transistorized heating current-controller in a linear hyperbolic temperature-time function similar to that used desorption spectrometry. Following high amplification and filtering either the noise power or mean square deviation of the emission current is recorded and simultaneously the emitteranode voltage that is needed to maintain a constant value of the mean emission current. The noise- and voltage-glow curves obtained are analysed in terms of adsorption processes at the emitter surface, because there is a strong connection between surface diffusion and desorption processes and the current noise, which has been established in recent theoretical and experimental work. Some noise-glow curves of xenon and nitrogen desorption are presented and discussed, for example, desorption energy of xenon is deduced. The concluding remarks refer to the extension of the method to measure surface diffusion processes and to further improvement with respect to single-face investigations. Interaction of heavy particles with metal surfaces
J Kistemaker, D Onderdelinden, F W Saris, W F van der Weg, FOM Institute for Atomic and Molecular Physics, Kruislaan 407 Amsterdam, Netherlands The collisions of heavy particles with metal surfaces govern many physical and chemical phenomena. Three fundamental aspects of these interactions will be discussed: (l) Sputtering, ie the removal of metal particles due to kinetic energy transfer. The contributions of focusing, channeling and surface effects to the sputtering mechanism. (2) Reflection of primary and scattering of secondary heavy particles. These are the high energy (mostly charged) particles which originate from two body collisions on the metal surface. (3) Inelastic energy transfer leads to emission of photons and secondary electrons from reflected particles and from inside the solid as well. Here Auger, resonance and radiative transitions are involved.
Since several excellent reviews on these subjects have been published, we confine ourselves primarily to recent investigations. Electron induced desorption of cases from aluminium
E L Garwin, E W Hoyt, J Jurow, and M Rabinowitz, Stanford Linear Accelerator Center, Stanford, California, 94305, USA In designing an ultrahigh vacuum system for an electronpositron storage ring 1, it is of crucial importance to predict (and minimize) the gas produced when synchrotron radiation from circulating beams strikes the chamber wall. It is suggested that photo-electron induced desorption plays the primary role in accounting for the observed pressure increases measured in existing storage rings 1. This paper will briefly outline the ultrahigh vacuum problems unique to high-current, high-energy storage rings. One such problem arises from the high energy density of the synchrotron radiation striking the chamber wall. In the case of the proposed 3 BeV e-e + SLAC ring, the energy at the wall can be as high as 2.5 kilowatt per square centimeter. A good thermal conducter must be used to intercept the synchrotron radiation, while the reflected synchrotron radiation from the absorber (fluorescent photons) must be minimized in order to reduce electron desorption of gas from the internal electrode structures. Thus, interest is drawn to aluminium and its alloys. The electron-induced gas desorption from aluminum has been extensively studied in an ultrahigh vacuum system equipped with a quadrupole residual analyzer having a detection limit of about 10 -1~ torr. By using isotopically enriched (90 per cent CO xS) sorbed gas, surface and bulk effects of the electron desorption may be separated. The discussion of our experiments will focus on the following aspects of electron desorption from aluminum: (1) The amount and kinds of gas species desorbed, and their secondary exchange-reaction products. (2) The number of sorbed states and their respective crosssections for desorption. (3) Dependence on electron-energy, and probable bulk effects from deeply penetrating electrons. (4) Functional dependence of the net desorption yield on the angle of incidence of photons and electrons. (5) Temperature dependence. (6) Readsorption dependence on partial pressures and possible synergistic effects due to co-adsorption of different gases. Reference i Particle Storage Rings, G K O'Neil, Scientific American,November,1966.
Mass spectrometric investigation of ion desorption induced by slow electrons
W K ttuber and C Rettinghaus, Balzers Aktiengesellschaft fiir Hochvakuumtechnik und Diinne Schichten, Balzers, Fiirstentum Liechtenstein Pressure measurements by means of ionisation gauges and mass spectrometric partial pressure analysers are generally based on ionisation by electron impact. In many devices, particularly in Bayard-Alpert-gauges and in high sensitive ion sources, the ionisation of free gas molecules inside the volume is more or less 125