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Mean sticking times of helium on a glass surface are determined at very low pressures from nonstationary molecular flow through glass capillaries. The temperature range covered is 13.8 °K to 20.4 °K. Resulting sticking times are of the order of 10?7 to 10?5 sec. They show a characteristic dependence on temperature and pressure. These measurements can be interpreted by means of a simple model: He-atoms mostly are bound to the surface with an adsorption energyE of 229 cal/mol?0.01 eV (±20%). However with a probability of 10?4 the energy is 530 cal/mol?0.023 eV (±6%). In both cases sticking times τ follow the equation τ=τ0exp(E/RT) where τ0 is about 10?9 to 10?10 sec.  相似文献   

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Concluding the investigations of the positive surface ionization of alkali metals on incandescent clean polycristalline surfaces1–3 the absolutely determined ionization coefficientsΒ of cesium on platinum are 1.00 between 1120 and 1700 ?K. A maximum ionization of cesium on tungsten is observed between 1000 and 1340 ?K withΒ very near 1.00. At higher temperatures there is a slight decrease ofΒ in the case of tungsten in agreement with the Saha-Langmuir-equation.  相似文献   

4.
Continuing the systematic measurements of the positive surface ionization of alkali metals on incandescent clean polycrystalline surfaces the present absolute determination of the ionization coefficientβ of rubidium on platinum surfaces gives a value of 1.00 between 1200 and 1700 °K. A maximum ionization coefficient ofβ=0.95 was observed for the system Rb/W at a temperature of about 1150 °K. The ionization at higher temperatures and there the dependence on temperature are in agreement with the Saha-Langmuir-equation.  相似文献   

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Scattering of Electromagnetic Surface and Bulk Waves from Rough Surfaces. Part I. General Theory A classical theory of scattering of electromagnetic surface and bulk waves on rough surfaces (dielectrics or conductors) is given. The primary wave creates a surface polarization on the rough boundary presenting the source for the radiation of scattering. These roughness-caused polarization must be considered in the wave equations and in the boundary conditions of the fields, too. General expressions for the spectral power density of surface and bulk scattering waves will be given. The excitation of surface polarization can result from primary waves homogenously or inhomogenously.  相似文献   

6.
Differential and integral molar entropies of the adsorbed layer are calculated from the dependence of the coverage on pressure and temperature published in part I. The experimental entropies correspond up to coverages of 2 × 1014 molecules cm?2 with entropies of the localized adsorption and an additional vibration entropy of about 20 cal deg?1 mole?1 caused by vibrations of the adsorbed atoms in the order of magnitude of 1012 sec?1. At higher coverages the entropy increases and passes through a maximum. This is explained by the formation of a second adsorption state (γ state) probably consisting of molecular hydrogen.  相似文献   

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Using the electroreflectance method space charge layers on crystals of different conductivities have been identified. The space charge layers were formed by adsorption of oxygen or atomic hydrogen. The limit of sensitivity required the irradiation with 5×1013 photons/cm2×sec of band gap energy. After exposure to atomic hydrogen all samples showed accumulation layers. With a partial pressure of oxygen above 350 mm Hg crystals of high conductivity (σ=47 ohm?1 cm?1) exhibit depletion layers, which change into accumulation layers, if the partial pressure is reduced below the limit. Crystals of a lower conductivity (σ=10?3–10?1 ohm?1 cm?1) show accumulation layers up to the highest applied oxygen pressure of 760 mm Hg. The phenomena are attributed to a dynamical equilibrium between adsorption and photo-desorption of oxygen. This equilibrium depends on oxygen pressure and free carrier concentration. By comparing a calculated curve with the experimental results the value of 3.31 ev is obtained for the energy gap, light polarized perpendicular to thec-acis.  相似文献   

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The electromagnetic theory, which explains the scattering of light from a rough surface of a metal foil by means of normale surface currents, is extended to the case of arbitrary directions of this currents. This allows to calculate the scattered intensity ofp ands polarised light in all directions. It is shown that the excitation of surface plasmons (“radiative” and “non radiative”) can produce a characteristic maximum in the scattered light. Detailed calculations for silver foils deposited on a quartz hemisphere are presented and compared with experiments. Furthermore the theory is applied to calculate the decrease in the reflection at frequences near the surface plasma frequenceΩ s .  相似文献   

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Scattering of Electromagnetic Surface and Bulk Waves from Rough Surfaces. Part II. The Indicatrix of Scattering; the Coupling of Surface and Bulk Waves In this paper, we present the calculation of the spectral power density of light scattered from homogenously isotropic and rough surfaces which are influenced by bulk or surface waves. A classification of all possible scattering cases in dependence on the wave types which arise in the regions z > O and z < O is given. The dependence of scattered light on scattering angles for the different possibilities of polarisation variantes (∥ and ?) will be presented. The relationship between the correlation function of roughness and the efficiency of coupling between bulk and surface modes will be discussed and compared with the results of other authors.  相似文献   

13.
The decay characteristics of ZnS/(10?4) Cu have been investigated by ion pulse excitation. The excitation density could be varied by using ions of different masses. The decay is exponential. The decay times depend on the ion pulse duration and on the penetration depth of the used ions. The green emission shows two different decay times. The intensity of the slower component of the green emission could be altered by excitation with UV-light before decay measurement. In the case of the slower component of the green emission we suppose an interaction between the excited states of the luminescence centres and energetically deep electron traps.  相似文献   

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Chemisorption of hydrogen on a platinum-foil has been studied by the flash-filament technique and by the capillary-flow method. Isobars were determined at temperatures between 140 and 600° K and at pressures between 10−4 and 10−6 torr. The dependence of the isosteric heat of adsorption E on the coverage σ is given by E = 16.3 −1.4 × 10−14σ (kcal/mole) with σ<2.5 × 1014 molecules/cm2. At higher coverages E reaches values smaller than 5 kcal/mole. Adsorption and desorption at low coverages are second order processes. The initial sticking probability is 4.5 × 10−3. The results are discussed in terms of an atomic and a molecular state of the adsorbed hydrogen.  相似文献   

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Zeitschrift für Physik A Hadrons and nuclei - The specific heats of Zr-Rh alloys have been measured between 0.9 and 12 °K, and at atomic percent Rh concentrations between 0 and 8. The...  相似文献   

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In den vergagenen Jahren konnte gezeigt werden, daβ sich mit Zeolithen gefüllte Säulen zur Trrennung der Wasserstoffisotope eignen. Um zu püfen, on sich auch die Isotope des Stickstoffs und des Sauerstoffs an Zeolithen trennen lassen, wurden die elementaren Trennfaktoren für die Isotope dieser Elemente an verschieden beladenen Zeolithen im Temperaturbereich von 77…100 °K bestimmt.  相似文献   

18.
A New Method of Determining the Autocorrelation Function of Polished Optical Surfaces Starting with a general theory of light scattering a measuring procedure for determining the autocorrelation function of surface roughness of well polished substrates is deduced. In this method light intensity scattered into a fixed direction has to be measured in dependence on the dimensions of the scattering area. The results are tested for a glass surface polished by different methods.  相似文献   

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The synthesis of ozone on the surface S cooled with liquid nitrogen O + O2·S→O3·S[1] was used to measure the concentration of atoms in a flow tube downstream of a d.c. discharge. The flow tube was constructed in the form of a U-tube. The ozone was deposited as a blue liquid film in the neighbourhood of the surface of the liquid nitrogen on the walls of the part of the U-tube, which was connected with the discharge tube. The oxygen atom decay in the U-tube was observed by measuring the production of ozone as the distance between the discharge tube (diameter: 5,2 cm) and the surface of the liquid nitrogen was varied. The decay is first order in atom concentration for the pressures p > 1 torr. But for the pressures below p = 1 torr near by the discharge tube we observed deviations from the law of decay In [O]0/[O] = k·t for the currents of about i = 100 mA. This effect was attributed to the process From the extrapolation of an ozone production curve atom concentrations in the discharge have been obtained. The transition from the ?H”? form to the ?T”? form (striated, low average electric field) of the discharge [2] caused the dissociation to decrease rapidly. The highest dissociation (10%) was obtained in the ?H”? form at high currents (i = 120 mA) and low pressures (p = 0,60 torr). The yield of atomic oxygen per kilowatt hour of energy was measured as functions of pressure and gas flow rate for i = 100 mA and i = 50 mA.  相似文献   

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