Search

The Mars Global Surveyor (MGS) z-axis accelerometer has obtained over 200 vertical structures of thermospheric density, temperature, and pressure, ranging from 110 to 170 kilometers, compared to only three previous such vertical structures. In November 1997, a regional dust storm in the Southern Hemisphere triggered an unexpectedly large thermospheric response at mid-northern latitudes, increasing the altitude of thermospheric pressure surfaces there by as much as 8 kilometers and indicating a strong global thermospheric response to a regional dust storm. Throughout the MGS mission, thermospheric density bulges have been detected on opposite sides of the planet near WE and 90 ° W in the vicinity of maximum terrain heights. This wave 2 pattern may be caused by topographically-forced planetary waves propagating up from the lower atmosphere., The Mars thermosphere is that portion of the upper atmosphere where the global mean temperatures increase with height above a minimum (~120 K) at altitudes of 100 to 120 kin [...]

The growth of thin films of the ferromagnetic semiconductor EuS on (100) oriented GaAs substrates by electron-beam evaporation is demonstrated. Structural characterization by X-ray diffraction reveals (100) oriented growth. In general, the magnetic and transport properties can strongly be influenced by the deposition parameters. We systematically investigate the influence of the growth temperature [T.sub.s] in the range [T.sub.s] = 235 K-675 K on the above properties. The Curie temperature increases with decreasing growth temperature, while the magnetic transition becomes broader. The resistivity decreases over four orders of magnitude with decreasing substrate temperature. The behavior of the magnetic properties and the resistivity can be explained by a change in stoichiometry, leading to higher carrier concentrations for lower substrate temperatures. Hall-effect measurements, magnetoresistance, and temperature dependence of the resistivity show a qualitative behavior known from bulk EuS samples. The demonstrated tunability of the magnetic and transport properties opens a wide range of possible applications for EuS in spin-electronics. Index Terms--Eu-chalcogenides, ferromagnetic semiconductors, spin-electronics.

The film morphology and magnetization of TiO2:Co as a function of the TiO2 growth phase and substrate material is presented and the magnetic and electrical transport properties are investigated. The difference in cobalt distribution is reflected by the large change in magnetic moment found in rutile structures and hence cobalt rutile films appear promising for spintronics applications.

A report of the variation for both anatase and rutile in conjunction with the reported sensitivity of the magnetism to growth parameters is given. The results from the films grown on SrTiO(sub 3) substrates show the presence of a thin surface rutile (111) layer, into which the cobalt appears to migrate.

CO and H2 structure and reactivity on single-crystal transition metal surfaces (platinum, rhodium, and palladium) were examined by surface-sensitive techniques including scanning tunneling microscopy (STM) and sum frequency generation (SFG) in high-pressure surface science studies. The studies indicated that ordered CO structures not observed in ultrahigh vacuum (UHV) can form at high pressure (10-6–103 torr). In addition, CO and H2 induce metal atom mobility and restructure the surface. On platinum, CO dissociates at high temperature (≥ 500 K), and a platinum carbonyl precursor is implicated. Concerning catalytic reactions, structure sensitive CO dissociation plays an important role in the ignition of CO oxidation, whereas CO poisons olefin hydrogenation, which becomes CO desorption limited. Lastly, solid-state hydrogen atoms are more active for hydrogenation than surface hydrogen atoms. These results suggest that spatially and temporally resolved techniques would permit molecular studies of reaction intermediates of CO and H2 in the future. [ABSTRACT FROM AUTHOR]

CO and H2 structure and reactivity on single-crystal transition metal surfaces (platinum, rhodium, and palladium) were examined by surface-sensitive techniques including scanning tunneling microscopy (STM) and sum frequency generation (SFG) in high-pressure surface science studies. The studies indicated that ordered CO structures not observed in ultrahigh vacuum (UHV) can form at high pressure (10-6–103 torr). In addition, CO and H2 induce metal atom mobility and restructure the surface. On platinum, CO dissociates at high temperature (≥ 500 K), and a platinum carbonyl precursor is implicated. Concerning catalytic reactions, structure sensitive CO dissociation plays an important role in the ignition of CO oxidation, whereas CO poisons olefin hydrogenation, which becomes CO desorption limited. Lastly, solid-state hydrogen atoms are more active for hydrogenation than surface hydrogen atoms. These results suggest that spatially and temporally resolved techniques would permit molecular studies of reaction intermediates of CO and H2 in the future. [ABSTRACT FROM AUTHOR]