Spatial sampling of the thermospheric vertical wind field at auroral latitudes

Results are presented from two nights of bistatic Doppler measurements of neutral thermospheric winds using Fabry!Perot spectrometers at Mawson and Davis stations in Antarctica. A scanning Doppler imager (SDI) at Mawson and a narrow-field Fabry-Perot spectrometer (FPS) at Davis have been used to estimate the vertical wind at three locations along the great circle joining the two stations, in addition to the vertical wind routinely observed above each station. These data were obtained from observations of the 630.0 nm airglow line of atomic oxygen, at a nominal altitude of 240 km. Low!resolution all-sky images produced by the Mawson SDI have been used to relate disturbances in the measured vertical wind field to auroral activity and divergence in the horizontal wind field. Correlated vertical wind responses were observed on a range of horizontal scales from ~150 to 480 km. In general, the behavior of the vertical wind was in agreement with earlier studies, with strong upward winds observed poleward of the optical aurora and sustained, though weak, downward winds observed early in the night. The relation between vertical wind and horizontal divergence was seen to follow the general trend predicted by Burnside et al. (1981), whereby upward vertical winds were associated with positive divergence and vice versa; however, a scale height approximately 3–4 times greater than that modeled by NRLMSISE-00 was required to best fit the data using this relation

Electronic and structural properties of doped amorphous and nanocrystalline silicon deposited at low substrate temperatures by radio-frequency plasma-enhanced chemical vapor deposition

The gas phase doping of hydrogenated amorphous silicon and hydrogenated nanocrystalline silicon thin films deposited on glass and on plastic (polyethylene terephthalate) substrates is reported. Two substrate temperatures were used during deposition: 25 degreesC and 100 degreesC. Films were deposited by radio-frequency plasma-enhanced chemical vapor deposition using phosphine or diborane for n- or p-type doping, respectively. Similar electronic and structural properties are obtained for the doped films deposited on either substrate. Hydrogen dilution of silane is used to improve the electronic and structural properties of the amorphous films and to obtain nanocrystalline films. The most conductive amorphous films have n-type dark conductivity at room temperature similar to10(-3) Omega(-1) cm(-1) and similar to10(-5) Omega(-1) cm(-1) when deposited at 100degreesC and 25degreesC, respectively, or p-type room-temperature dark conductivity similar to10(-7) Omega(-1) cm(-1) at both substrate temperatures. The most conductive nanocrystalline films deposited at 100 degreesC have n- and p-type dark conductivity at room temperature above 10(-2) Omega(-1) cm(-1) while nanocrystalline films deposited at 25 degreesC only have p-type conductivity higher than 10(-2) Omega(-1) cm(-1) at room temperature. Isochronal annealing at temperatures up to 300 degreesC showed that the dopants are fully activated at the deposition temperature in doped nanocrystalline samples and that they are only partially activated in amorphous films deposited at low substrate temperatures.Fundação para a Ciência e Tecnologia (FCT) Universidade do Minho (UM

Thermospheric winds and temperatures above Mawson, Antarctica, observed with an all-sky imaging, Fabry-Perot spectrometer

A new all-sky imaging Fabry-Perot spectrometer has been installed at Mawson station (67°36' S, 62°52' E), Antarctica. This instrument is capable of recording independent spectra from many tens of locations across the sky simultaneously. Useful operation began in March 2007, with spectra recorded on a total of 186 nights. Initial analysis has focused on the large-scale daily and average behavior of winds and temperatures derived from observations of the 630.0 nm airglow line of atomic oxygen, originating from a broad layer centered around 240 km altitude, in the ionospheric F-region. <br><br> The 1993 Horizontal Wind Model (HWM93), NRLMSISE-00 atmospheric model, and the Coupled Thermosphere/Ionosphere Plasmasphere (CTIP) model were used for comparison. During the geomagnetically quiet period studied, observed winds and temperatures were generally well modelled, although temperatures were consistently higher than NRLMSISE-00 predicted, by up to 100 K. CTIP temperatures better matched our data, particularly later in the night, but predicted zonal winds which were offset from those observed by 70–180 ms<sup>−1</sup> westward. During periods of increased activity both winds and temperatures showed much greater variability over time-scales of less than an hour. For the active night presented here, a period of 45 min saw wind speeds decrease by around 180 ms<sup>−1</sup>, and temperatures increase by approximately 100 K. Active-period winds were poorly modelled by HWM93 and CTIP, although observed median temperatures were in better agreement with NRLMSISE-00 during such periods. <br><br> Average behavior was found to be generally consistent with previous studies of thermospheric winds above Mawson. The collected data set was representative of quiet geomagnetic and solar conditions. Geographic eastward winds in the afternoon/evening generally continued until around local midnight, when winds turned equatorward. Geographic meridional and zonal winds in the afternoon were approximately 50 ms<sup>−1</sup> weaker than expected from HWM93, as was the transition to equatorward flow around midnight. There was also a negligible geographic zonal component to the post-midnight wind where HWM93 predicted strong westward flow. Average temperatures between 19:00 and 04:00 local solar time were around 60 K higher than predicted by NRLMSISE-00

CVD of CrO2 Thin Films: Influence of the Deposition Parameters on their Structural and Magnetic Properties

This work reports on the synthesis of CrO2 thin films by atmospheric pressure CVD using chromium trioxide (CrO3) and oxygen. Highly oriented (100) CrO2 films containing highly oriented (0001) Cr2O3 were grown onto Al2O3(0001) substrates. Films display a sharp magnetic transition at 375 K and a saturation magnetization of 1.92 Bohr magnetons per f.u., close to the bulk value of 2 Bohr magnetons per f.u. for the CrO2. Keywords: Chromium dioxide (CrO2), Atmospheric pressure CVD, Spintronics.Comment: 5 pages, 6 figure

Electronic transport in low-temperature silicon nitride

Perpendicular current transport through thin silicon nitride films deposited at 100 degreesC by radio frequency chemical vapor deposition (RF) is measured between patterned square contacts with side lengths between 5 and 200 mum. Hydrogen dilution, silane-to-ammonia ratio, and total gas flow were varied to achieve control of film properties. The dependence of the current on the applied field and measurement temperature are correlated to structural parameters such as the index of refraction, etching rate in buffered hydrofluoric acid and infrared vibrational band strengths. Using the appropriate deposition parameters, it is possible to prepare, at 100 degreesC, silicon nitride dielectric films with electronic properties compatible with use as gate dielectrics of thin-film transistors.Fundação para a Ciência e Tecnologia (FCT) Universidade do Minho (UM

Eclipsing Binaries Showing Light Time Effect

Four eclipsing binaries, which show apparent changes of period, have been studied with respect to a possible presence of the light time effect. With a least squares method we calculated new light elements of these systems, the mass function of the predicted third body, and its minimum mass. We discuss the probability of the presence of such bodies in terms of mass function, changes in radial velocity and third light in solution of light curves.Comment: 4 pages, 4 figures, 1 table, conference proceeding

CVD of CrO2: towards a lower temperature deposition process

We report on the synthesis of highly oriented a-axis CrO2 films onto (0001) sapphire by atmospheric pressure CVD from CrO3 precursor, at growth temperatures down to 330 degree Celsius, i.e. close to 70 degrees lower than in published data for the same chemical system. The films keep the high quality magnetic behaviour as those deposited at higher temperature, which can be looked as a promising result in view of their use with thermally sensitive materials, e.g. narrow band gap semiconductors.Comment: 13 pages, 4 figure