Volume 95, Issue 2, 15 January 2004
Index of content:
- INTERDISCIPLINARY AND GENERAL PHYSICS (PACS 1-41, 43-47, 79, 81-84, 89-99)
Backscattering of low energy electrons from carbon films deposited on aluminum: A Monte Carlo simulation95(2004); http://dx.doi.org/10.1063/1.1633655View Description Hide Description
The low energy backscattering coefficient for the special case of film of carbondeposited on aluminum is investigated. The backscattering coefficient as a function of the primary energy shows an interesting property, i.e., the appearance—for carbonfilm thicknesses higher than on aluminum—of relative maxima of absorption (and relative minima of backscattering). It has been noted, for aluminum substrates, that the position of the relative minima of the backscattering coefficient is increasing as the carbonfilm thickness increases. If experimentally confirmed and quantitatively accurately defined, the results presented—here obtained through a Monte Carlo simulation—can be used as a way to measure the carbonfilm thickness by a set of measures of the backscattering coefficient.
Thermal conductivity of SiC fine particles reinforced Al alloy matrix composite with dispersed particle size95(2004); http://dx.doi.org/10.1063/1.1632022View Description Hide Description
The thermal conductivity of 10, 20, 30, and 40 vol % silicon-carbide-particulate-reinforced aluminum matrix composite was determined as a function of the volume fraction of SiC. The microstructures of the composites were examined with a scanning electron microscope. The size distributions of SiC particles were obtained by analyzing the micrographs. The interfacial thermal conductance was calculated with consideration of the particle size distribution. Both the thermal conductivity and interfacial thermal conductance decreased as the volume fraction of SiC increased.
95(2004); http://dx.doi.org/10.1063/1.1632552View Description Hide Description
Lightly doped-GaN samples were etched with reactive ion etching (RIE) in and plasmas. Replacing the argon by nitrogen in the plasma chemistry resulted in better etch rates, and in addition reduced etch damage for relatively low values of the plasma power. By treating the samples in a nitrogen plasma following etching, we dramatically reduced surface damage, as determined from Schottky IV characteristicsmeasurements. Specifically, the reverse breakdown voltages returned to 70% to that measured from control diode samples. Further, x-ray photoelectron spectroscopyanalysis showed that the post-etch nitrogen step decreased the Ga/N ratio. These results suggest that much of the damage induced by RIE plasma etching comes from a nitrogen loss mechanism.
95(2004); http://dx.doi.org/10.1063/1.1632015View Description Hide Description
The expected time evolution of the secondary electron emission (SEE) yield, δ, and charging of insulatorsirradiated with keV electron probes of various sizes is deduced from the use of basic laws of electrostatics. Simple models of trapped charge distributions permit, next, quantitative estimates. With respect to the linear increase of δ from 0 towards its nominal value, the initial phase is characterized by a deficit of δ for incident spots in the submicron range and incident charge of a few primary electrons (PEs). This deficit occurs even when charging is as a whole negative and it results from a partial mirroreffect for the less energetic secondary electrons (SEs) (directly excited by the PEs) combined to attraction of (excited by the backscattered electrons) towards the central spot while the more energetic SEs are successively focused and next defocused. The next phase starts for incident charges in the pC range and it concerns the evolution of the total yield, from its nominal value up to the unity. Besides the increase of the SEE yield, the external slowing down of the PEs plays the main role in the compression of the distribution of newly trapped electrons. The main dynamical aspects of the internal field are also established and its influence on the trapped charge distribution is easily deduced. The present analysis is supported by some published data and the consequences concern any type of insulating materialirradiated with defocused probes and “short” pulse excitation (for measurements) or stationary fine probes (for the investigation of the space charge effect by the mirror method) or scanning beams (in scanning electron microscopy).
95(2004); http://dx.doi.org/10.1063/1.1635969View Description Hide Description
The formation, the chemical and electronic properties, and the thermal stability of the Cu/ZnS(001) interface were investigated by x-ray photoelectron spectroscopy, x-ray fluorescence spectroscopy, and low energy electron diffraction(LEED). ZnS(001) films with 16 ML thickness (4.3 nm), grown on bulk GaP(001) were used as a substrate for Cudeposition. During the room-temperature deposition of the Cufilm, the initial submonolayer Cu atoms react with ZnS and the reaction is confined to the interface. Beyond 1 ML the Cu starts to display a metallic character. The Cudeposition induced a downward band bending of ZnS. In the emission spectrum, the Cudeposition results in a significant suppression of the -related doublet and creates a component at about 3.6 eV binding energy in the upper valence band. After annealing of room-temperature-deposited Cufilms at temperatures higher than 220 °C, as well as Cudeposition at 320 °C, the signals of photoelectrons reappear, as a result of Cu atoms diffusing into the substrate and reacting with GaP. From LEED observation and attenuation of intensity, we may conclude that the Cufilmgrows in an island mode at room temperature, whereas a partially ordered arrangement is adopted at the ZnS(001) surface following Cudeposition at 320 °C.