J. S. Kraus

Electron and photon stimulated desorption of positive ions from alkali halide surfaces

Note: Univ wisconsin,dept phys,madison,wi 53706. Pian, tr, bell tel labs inc,murray hill,nj 07974.ISI Document Delivery No.: QV061 Reference LSE-ARTICLE-1983-013 Record created on 2006-10-03, modified on 2017-05-12

Energy dependence of electron stimulated desorption of excited neutral alkalis from alkali halides

We have measured the incident electron energy dependence of excited alkali neutral desorption arising from electron bombardment of alkali halide surfaces. Substrate core hole formation is shown to play an important role in the initial energy transfer process. In each case only the lowest resonance lines are observed. The yields for excited alkali (10−5/electron) are measured to be at least two orders of magnitude greater than those obtained for ion ejection due to electron stimulated desorption. Our measurements provide added insight into the mechanisms of electronic excitation, ejection, and subsequent particle-surface interaction responsible for the desorption of excited alkali neutrals.

Elliptic Polarization from Grazing-Incidence Collisions of Hydrogen Ions on Polycristalline and Single-Crystal Surfaces

Abstract Strong elliptic polarization has been observed in Balmer radiation (H α , 656.3 nm) following low-energy grazing-incidence collisions of H − , H + , H 2+ 2 , and H + 3 on a clean lead polycrystalline surface and on a clean nickel single crystal (110) in all cases maintained under ultrahigh vacuum. In explanation of the basic phenomenon a two-step surface-interaction model is presented based on anisotropic near-resonant electron pickup followed by quantum mechanical phase evolution. The influence of a single crystal target surface on the intensity and polarization of the radiation is discussed.

Electron stimulated desorption of excited alkali atoms from alkali halide surfaces

We have measured the alkali resonance photon intensity due to electron stimulated desorption of excited particles from NaCl and KCl targets as a function of incident electron energy (20 to 1000 eV) and sample temperature (room temperature to 300 °C). The energy dependence data suggest a correlation between excited Na and K desorption thresholds and substrate core levels. These are the first experimental correlations of the desorption of neutral atoms, specifically excited neutral atoms, with the creation of core holes. The intensity of emitted radiation is observed to rise sharply and then saturate with increasing temperature.

Earth potential over 4000 km between Hawaii and California

Measurements of the value of the large-scale (4050 km) mean earth potential between California and Hawaii are reported as determined over a one year interval in 1990–91. The mean electric field measured during quiet geomagnetic intervals, 0.183 ± 0.056 mV/km, is about six times larger than that reported for a shorter interval over a slightly longer distance in the Atlantic [Lanzerotti et al., 1985], but of the same sign. The present results are also about three standard deviations from a null value, in contrast to the previous results, which were consistent with a null mean. If the mean potential is entirely attributable to leakage of a poloidal electric field from the core-mantle boundary, then under some models of the mantle conductivity one can conclude that the deduced toroidal magnetic field intensity in the core would be of the same order as the poloidal magnetic field at the core-mantle boundary. The measured potential gradient is smaller than that which might be expected from thermoelectric emfs at the core-mantle boundary. The potential could also correspond to a south to north quasi-steady water flow of ∼0.6 cm/sec.

Desorption Induced by Electronic-Transitions

Abstract Recent work on electronically induced desorption of surface atoms and molecules resulting from the impact of electrons and UV photons with surfaces is reported. Since the overwhelming majority of emitted particles are neutral, emphasis is given to studies of excited and ground state desorbed neutral atoms and molecules. In particular, first measurements of velocity distributions of desorbed particles obtained using laser induced fluorescence are discussed.

Possible measurements of small‐amplitude tid's using parallel, unpowered telecommunications cables

The authors report the observation of {approximately}40 min quasiperiodic variations during local daytime conditions in the differences between the voltages measured on two parallel (separation distance {approximately}100 km) unpowered telecommunications cables between California and Hawaii (length of each {approximately}4,000 km). The events are inferred to be produced by small changes in magnitude and/or position of the Sq ionosphere current system, the focus of which passes on average daily over the cables. The changes in the current system are probably produced by medium-scale traveling ionospheric disturbances (TIDs). This dual cable system appears to provide a very sensitive technique for measuring small amplitude, medium-scale mid-latitude changes in ionospheric currents, especially those produced by TIDs.

The Electronic Desorption of Excited Alkali Atoms from Alkali Halide Surfaces

Alkali halides have long been known to erode under electron and photon bombardment. The detailed nature of the electronic mechanisms responsible for the erosion remains, however, a matter of vigorous discussion. In order to elucidate some of these mechanisms we present recent measurements of the incident beam energy dependence of excited alkali neutral desorption arising from electron and photon bombardment of alkali halide surfaces. In all cases, the yields for excited alkali neutrals are measured to be much greater than those obtained for positive ion ejection due to electron or photon stimulated desorption. Substrate core hole formation is seen to play an important role in the initial energy transfer process. In each case only the lowest resonance excited states are observed. The energy dependent yield of excited neutrals arising from electron bombardment is found to differ markedly from the corresponding photon bombardment data. Present theories dealing with (a) the production and migration of defects, and (b) the ejection of ions, are not adequate to explain the desorption of neutral alkalis in excited states. In both the incident electron and photon cases, our observations suggest microscopic models which take into account the mechanisms of initial electronic excitation of the surface, subsequent ejection of a surface particle and possible electron exchange as the particle leaves the surface.

Outer-shell electronic processes in Ne+ collisions with a Ni(110) surface

Abstract By performing simultaneous detection of forward-scattered Ne + ions and photons emitted by Ne and Ni excited atoms when a Ni(110) surface was bombarded by 4 keV Ne + ions at near-grazing incidence, we studied the ion and photon yields as a function of the azimuthal angle. The variations observed in the yield anisotropies show the different degrees of influence of the surface structure on outer-shell electronic processes during ion-surface collisions.

The creation of excited hydrogenic states near surfaces

Abstract In order to clarify the mechanisms responsible for formation of hydrogenic excited states near solid surfaces, we have carried out measurements of elliptic polarization produced by both grazing incidence and tilted foil collision interactions. The data suggest that hydrogenic oriented and aligned states are formed at the surface with no memory of bulk interactions, and that the observed populated states form a coherent superposition of angular momentum states.