摘要:

Some laboratory experiments have been performed to study the electrification of dust clouds created by blowing different types of dusts into a dust chamber. The polarity and magnitude of the space charge in such dust clouds have been found to be sensitive to the mineral constituents of the dust. Even a single dust cloud, if allowed to settle under gravity in a field‐free space with no charge added to it, can have opposite polarities of space charge at different times of its sedimentation. The space charge produced increases with an increase in the length of the surface over which the dust is blown. It also increases with an increase in the temperature and velocity and a decrease in the relative humidity of the blowing air. External electric fields of up to a few hundred V/cm, applied to the surface from which the dust is blown, have little effect on the generated space charge. Size distributions of positively and negatively charged particles show a greater abundance of smaller (∼ 3 &mgr;) particles compared to those of small neutral particles.

ISSN:0021-8979    

DOI:10.1063/1.1661846

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Some secondary electron (SE) emission characteristics, i.e., total SE's, elastically and inelastically backscattered primaries, true SE's, and plasma loss spectra, of single‐crystal Si(111) were observed as a function of primary energyEp. A small fraction of total SE's was introduced to a retarding field energy analyzer placed at 45° to the normally incident primary beam. As a result, a fraction of total SE's and of elastically backscattered (including diffracted) primaries showed quite similar fine structure even in detail, when observed as a function ofEp. By filtering a fraction of total SE's into individual energy ranges, the fine structures in true SE's were found at the sameEp's as in elastically backscattered primaries, but were in the opposite direction to the corresponding structures in the elastically backscattered primaries. On the other hand, the fine structures of inelastically backscattered primaries, i.e., energy‐loss primaries, showed quite a complex correlation to those of elastically backscattered primaries. It is concluded that the fine structures in &sgr; (total SE yield) vsEpand &eegr; (backscattering coefficient) vsEpcurves should be caused by the elastically backscattered primaries. The considerable number of electrons subjected to the surface and the first bulk plasma losses were found to be emitted from within a few atomic layers from the surface. Some problems on the Auger electron excitation are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.1661847

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The quantitative reliability of theoretical expressions for Hall and thermoelectric effects has been tested under thermal equilibrium conditions in high‐conductivity, nondegenerate, and degenerate CdS single crystals, and under nonequilibrium steady‐state and transient conditions in low‐conductivity photosensitive CdS crystals. The thermal equilibrium measurements were made as a function of temperature, hence of scattering and degeneracy, and the nonequilibrium measurements were made as a function of excitation intensity and temperature. Good agreement is found in every case between the values of the electron density and mobility calculated from the Hall effect and the values of these quantities calculated from the thermoelectric effect. The results confirm both the reliability of the present state of the theory for materials like CdS, and the extension of this theory far from equilibrium conditions provided that the equilibrium Fermi level is replaced by the steady‐state or quasi‐Fermi level.

ISSN:0021-8979    

DOI:10.1063/1.1661848

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

An electron gun with an effective concentric‐spheres electrode geometry has been used to investigate the energy distribution of electrons emitted by a space‐charge‐limited dispenser cathode at four different temperatures. A spherical monochromator is used to select different portions of the initial energy spectrum. Electrons so selected are scattered through 90° by an atomic beam of helium. The initial electron energy is inferred from the accelerating potential needed to attain the 19.3‐eV helium resonance energy. Energy spectra so obtained are compared with computed spectra based on an initially half‐Maxwellian distribution filtered by the space charge in front of the cathode. The form of this space charge is known from an exact solution of Poisson's equation in the spherical geometry of the gun. The only adjustable parameter in the computation is Richardson's constant which is given a value ofA= 7 × 104A/m2(°K)2. The close agreement between the observed and computed energy spectra is in disagreement with observations of many other investigators. Reasons for this disagreement are suggested.

ISSN:0021-8979    

DOI:10.1063/1.1661850

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A simple model of the photoelectric yield is proposed and predictions of the yield and yield spectrum based upon this model are compared with published experimental data for aluminum. Furthermore, simple expressions for the electron emission current for arbitrary incident photon fluxes are derived for the higher‐energy components of the photoelectric yield. Since the electrons are assumed to propagate isotropically, no distinction is made between forward and backward scatter.

ISSN:0021-8979    

DOI:10.1063/1.1661851

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A technique has been developed to take short‐time‐exposure photographic spectra of ac arcs between separating electric contacts. In these experiments the arc was formed in both argon and air between copper electrodes which separated a total of 0.96 cm. Side‐on spectra were taken for five axial positions at ±500 &mgr;sec around the current maximum (1100 A). In order to obtain a symmetrical arc with less than 0.01% copper vapor impurity, freshly polished electrodes had to be used each time the arc was formed. The spectra were used to calculate the arc temperature and the arc radius. The argon arc had a maximum temperature of 16 000 K and a diameter of 1.6 cm. The air arc had a temperature of 21 000 K and a diameter of 0.7 cm. The assumption of LTE (local thermodynamic equilibrium) which was used in the analysis of these arcs, was shown to be a reasonable assumption for the argon arc. The random introduction of a small percentage of zinc vapor into the argon arc was analyzed and found not to affect the assumptions made in this investigation.

ISSN:0021-8979    

DOI:10.1063/1.1661852

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A floating voltage swept double probe is described and the components of the plasma sheath admittance (Y= 1/R + j&ohgr;C) are measured as a function of time in argon and hydrogen. The measurements are carried out in the double inverse pinch device (DIPD Mark I), a pulsed device, which generates a quadrupole magnetic field. The probe is swept at 500 kHz with a sinusoidal voltage. Sheath capacitance and resistance are measured at one point in space and at a variety of times following preionization. The plasma sheath parameters are discussed in terms of equivalent circuits which are found to simulate the plasma sheath response. The sheath capacitance is larger than predicted by present theories. Estimates of plasma temperature and density are made from the sheath measurements and are found to be low owing to the theoretical uncertainty in capacitance. With improvement in sheath theory, the technique should give accurate temperature and density measurements in transient plasmas.

ISSN:0021-8979    

DOI:10.1063/1.1661853

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The scattering of a spherical electromagnetic wave from a radially moving spherical discontinuity in index of refraction is analyzed. The Doppler shifts are found to depend on the radius as well as the velocity of the discontinuity. As an example the scattering from a tenuous evaporating dielectric sphere is found. The plane‐wave scattering problem is formulated and it is shown that the scattered frequencies have a satisfying physical interpretation in the geometrical optics limit.

ISSN:0021-8979    

DOI:10.1063/1.1661854

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Photoemission measurements on copper phthalocyanine films were made for photon energies of 7–23 eV. The spectral quantum yield was determined. The energy distribution of the photoemitted electrons for photon energies above 16 eV shows structure characteristic of the density of states. In addition, the attenuation length of electrons photoinjected into copper phthalocyanine was measured. For electrons of approximately 1.5 eV above the vacuum level, the electron‐electron mean free path is estimated to be 11 Å.

ISSN:0021-8979    

DOI:10.1063/1.1661855

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Electrical resistivity and Seebeck coefficients were determined for NiSb and CoSb as a function of composition. The results indicate that clustering of defects occurs for large deviations from the stoichiometric composition in CoSb, and that these compounds cannot be classified as electron compounds.

ISSN:0021-8979    

DOI:10.1063/1.1661856

出版商:AIP    

年代:1973

数据来源: AIP