Large Co cluster deposition on naturally and artificially patterned substrates

Monodispersed Co clusters with mean cluster diameter d=13 nm have been deposited on a stepped graphite surface and a lithography-patterned Si wafer using a plasma-gas-condensation cluster beam deposition apparatus. High-resolution scanning electron microscope observation indicates that 1) cluster aggregation is much more limited at the steps than on the flat terrace regions of the graphite surface, and 2) cluster density is much higher in the grooves than on the flat top of the lithography-patterned Si wafers. These results suggest the possibility of the regular arrangement of monodispersed Co clusters if the pattern size (the width of grooves and tops) is comparable with the cluster size

Porous silicon nanocracking

We report on the collapse of porous silicon on the nanometer scale observed during a study of freeze dried low doped p-type samples. During the drying process highly porous layers, about 4 mu m in depth, changed their colour from an initial bright brown to a well defined green at the end of the procedure. However, the mirror aspect of the sample was kept. This phenomenon which results from a change of the optical path (nd) cannot uniquely be attributed to a refractive index variation. Simulation of reflectivity spectra shows that compared to the expected values, the thickness is lower and the density of material higher. An analysis of the profile shows that the volume can be reduced by as much as a factor of six. X-ray and TEM observations have confirmed these data and have shown that these samples have lost their crystallinity and are completely amorphous. In situ observations shows that this compression occurs during the sublimation or evaporation phase. During this phase, if the sample is wetted again the initial colour of the sample can be recovered as an effect of the elasticity of the PS structure. We attributed the origin of this compaction to nanoscopic cracking due to capillary effects, as in the case of the well known macroscopic cracking. (C) 2000 Elsevier Science S.A. All rights reserved

X-ray diffraction and reflectometry studies of porous silicon

International audienceX-ray diffraction and reflectometry allows the measurements of various parameters (thickness, porosity, roughness and strain) of thin layers of porous silicon. Measurements on n-type porous silicon layers of different doping give very different results: for lightly doped samples, the layer properties vary smoothly as a function of formation time, while for heavily doped samples several regimes are observed for short formation times. X-ray satellites have been observed in the X-ray reflexion or diffraction from holographic gratings

Quasi-common-path heterodyne grating interferometernal Performance--Empirical Evidence in Taiwan

[[abstract]]A quasicommon-path heterodyne grating interferometer for displacement measurement is proposed. This measurement system includes a heterodyne light source, a moving grating, a few optical elements and a lock-in amplifier for phase measurement. The phase shift of the diffracted beams from grating is measured by the heterodyne technique. The grating displacement is determined by the relationship of the optical phase variation and grating pitch. The experimental results demonstrated the measurement resolution of 1 nm and the high system stability. Benefiting from the heterodyne interferometric phase measurement, this method has advantages of high measurement resolution, relatively straightforward operation.[[notice]]補正完畢[[conferencetype]]國際[[conferencedate]]20101207~20101210[[iscallforpapers]]Y[[conferencelocation]]Maca

NO2 monitoring at room temperature by a porous silicon gas sensor

A study on reactivity of p(+) porous silicon layers (PSL) to different gas atmosphere has been carried out. Substrate doping was 5-15 m Omega cm and 0.5 Omega cm, porosity ranged from 30 to 75% and the thickness of the porous layers was 20-30 mu m. Three different processes to insure good electrical contact are proposed and discussed. PSL were kept at constant bias and current variations due to interaction with different concentrations of NO(2) were monitored at constant relative humidity (R.H.). Measurements were performed at room temperature (R.T.) and at atmospheric pressure. Concentrations as low as 1 ppm were tested, but the high sensitivity of the sensor makes possible to test lower values. The recovery time of the sensor is of the order of one minute. Response to interfering gases (methanol, humidity, CO, CH(4), NO, NO(2)) has been examined also. In-situ FTIR spectroscopy in NO(2) atmosphere shows a fully reversible free-carrier detrapping in the IR region. confirming the validity of the models proposed in the recent past for electrical conduction in mesoporous silicon. (C) 2000 Elsevier Science S.A. All rights reserved