Steep plasma gradients studied with spatially resolved Thomson scattering measurements

Plasmas created by the microwave torch Torche à Injection Axiale (TIA), which are around 2 mm in diameter and 15 mm long, are investigated. In these plasmas large gradients are present so that the edge is supposed to play an important role. Using global Thomson scattering measurements, in which global refers to the fact that the size of the laser beam is approximately equal to the diameter of the plasma, the electron densities and temperatures were determined. However, these results lead to discrepancies in the particle balance: the production of free electrons is much larger than the classical losses due to recombination, convection and diffusion. Radially resolved Thomson scattering measurements show the plasma has a hollow structure. Although this enhances the losses due to diffusion, still a large discrepancy remains between production and destruction of free electrons in the argon plasmas. Probably some molecular processes are significant as well. A good candidate is the charge transfer between argon ions and nitrogen molecules, since mixing with the surrounding air has a large impact on the plasma

Characterisation of plasmas produced by the "torche à injection axiale"

Two different kinds of plasmas created by the microwave driven Torche a' Injection Axiale (TIA) are investigated: one with helium and the other with argon as the main gas. By using abs. line intensity measurements, the densities of the excited states are detd. Applying the ideal gas law gives the ground state d. It is found that both plasmas are ionizing and that the excitation temps. range from 3000 to 11,000 K. The electron temp. and the electron d. are detd. using Thomson scattering. In the plasma with helium as the main gas, av. densities between 0.64 and 5.1 x 1020 m-3 and temps. around 25,000 K are found. In an argon plasma, the electron temp. is lower and the electron d. is higher: 17,000 K and around 1021 m-3 resp. Radial profiles of the electron d., obtained by focusing the laser beam, appear to have a donut-like shape. [on SciFinder (R)

Ion channeling for strain analysis in buried nanofilms (

The title should have been: \"Ion channeling for strain anal. in buried nanofilms

Evidence for strain in and around InAs quantum dots in GaAs from ion-channeling experiments

Strain in and around pyramidal InAs/GaAs quantum dots (QD’s) fabricated by molecular-beam-epitaxy influences the density of states of the confined charge carriers. The presence of strain in QD’s is required to explain their optical properties. In this paper MeV ion-channeling experiments are presented which provide evidence for the presence of strain in and around InAs QD’s in GaAs. The small dimensions of the QD’s (typical height 4 nm) and the presence of a wetting layer complicate the interpretation of channeling measurements, but our experiments show that extended strain fields around the QD’s induce ion steering which accounts for the observed channeling behavior

Planar MeV ion channeling on strained buried nanofilms

Planar MeV ion channeling experiments have been used to characterize a buried Si1-xGex film with a thickness of 2.2 nm in a silicon host crystal. The tetragonal deformation in the film shows up as a translation of the {0 1 1} planes across the film, which was measured as a step in the yield of the planar channeled Rutherford backscattering spectra. The flux distribution between the planes acts as a probe for the position of the planes. The angular dependence of the step height has been measured for different incident ion energies and interpreted with Monte Carlo calculations. Simulations only resemble the measured spectra when the Hartree–Fock potential is used for the ion–atom interaction. The translation of the planes can be measured with an accuracy of approximately 10%, which is comparable to results obtained with axial channeling experiment

Transmitted ion energy loss distributions to detect cluster formation in silicon

The energy loss distribution of He+ ions transmitted through a 5.7 +- 0.2 mm thick Si crystal was measured and simulated with the Monte Carlo channeling simulation code FLUX. A general resemblance between the measured and simulated energy loss distributions was obtained after incorporation of an energy dependent energy loss in the simulation program. The energy loss calcns. were used to investigate the feasibility to detect the presence of clusters of light element dopants in a host crystal from the shape of the energy loss distribution, with transmission ion channeling. A curved crystal structure was used as a model for a region in the host crystal with clusters. The presence of the curvature does have a large influence on the transmitted energy distribution, which offers the possibility to det. the presence of dopant clusters in a host crystal with transmission ion channelin