Ion mixing of markers in SiO2 and Si

The amount of atomic mixing in amorphous SiO2 and Si is studied by measuring the redistribution of thin metal markers due to irradiation with 300-keV Xe+ ions. In SiO2, the mixing efficiency appears to be independent of the chemical nature of marker atoms and can be explained in terms of a linear cascade model. In Si, the mixing is found to correlate with thermally activated diffusivities of the marker species

X-ray rocking curve study of Si-implanted GaAs, Si, and Ge

Crystalline properties of Si-implanted GaAs, Si, and Ge have been studied by Bragg case double-crystal x-ray diffraction. Sharp qualitative and quantitative differences were found between the damage in GaAs on one hand and Si and Ge on the other. In Si and Ge the number of defects and the strain increase linearly with dose up to the amorphous threshold. In GaAs the increase in these quantities is neither linear nor monotonic with dose. At a moderate damage level the GaAs crystal undergoes a transition from elastic to plastic behavior. This transition is accompanied by the creation of extended defects, which are not detected in Si or Ge

Epitaxial regrowth of thin amorphous GaAs layers

Channeling and transmission electron microscopy have been used to investigate the parameters that govern the crystal quality following capless funace annealing at low temperature (~ 400 °C) in ion-implanted GaAs. From the results obtained, we concluded that the crystal quality after annealing depends strongly on the thickness of the amorphous layer generated by ion implantation and the number of residual defects increases linearly with the thickness of the implanted layer. Single-crystal regrowth free of defects detectable by megaelectron volt He + channeling was achieved for a very thin amorphous layer (<~ 400 Å)

Development of the health and economic consequences of smoking interactive model

Objective-To describe the health and economic consequences of smoking model, a user friendly, web based tool, designed to estimate the health and economic outcomes associated with smoking and the benefits of smoking cessation. Results-An overview of the development of the model equations and user interface is given, and data from the UK are presented as an example of the model outputs. These results show that a typical smoking cessation strategy costs approximately pound 1200 per life year saved and pound 22 000 per death averted. Conclusions-The model successfully captures the complexity required to model smoking behaviour and associated mortality, morbidity, and health care costs. Furthermore, the interface provides the results in a simple and flexible way so as to be useful to a variety of audiences and to simulate a variety of smoking cessation methods

Principles of Feedlot Runoff Control.

4 p

Ab initio many-body calculations on infinite carbon and boron-nitrogen chains

In this paper we report first-principles calculations on the ground-state electronic structure of two infinite one-dimensional systems: (a) a chain of carbon atoms and (b) a chain of alternating boron and nitrogen atoms. Meanfield results were obtained using the restricted Hartree-Fock approach, while the many-body effects were taken into account by second-order M{\o}ller-Plesset perturbation theory and the coupled-cluster approach. The calculations were performed using 6-31$G^{**}$ basis sets, including the d-type polarization functions. Both at the Hartree-Fock (HF) and the correlated levels we find that the infinite carbon chain exhibits bond alternation with alternating single and triple bonds, while the boron-nitrogen chain exhibits equidistant bonds. In addition, we also performed density-functional-theory-based local density approximation (LDA) calculations on the infinite carbon chain using the same basis set. Our LDA results, in contradiction to our HF and correlated results, predict a very small bond alternation. Based upon our LDA results for the carbon chain, which are in agreement with an earlier LDA calculation calculation [ E.J. Bylaska, J.H. Weare, and R. Kawai, Phys. Rev. B 58, R7488 (1998).], we conclude that the LDA significantly underestimates Peierls distortion. This emphasizes that the inclusion of many-particle effects is very important for the correct description of Peierls distortion in one-dimensional systems.Comment: 3 figures (included). To appear in Phys. Rev.

Strong mass effect on ion beam mixing in metal bilayers

Molecular dynamics simulations have been used to study the mechanism of ion beam mixing in metal bilayers. We are able to explain the ion induced low-temperature phase stability and melting behavior of bilayers using only a simple ballistic picture up to 10 keV ion energies. The atomic mass ratio of the overlayer and the substrate constituents seems to be a key quantity in understanding atomic mixing. The critical bilayer mass ratio of $\delta < 0.33$ is required for the occurrence of a thermal spike (local melting) with a lifetime of $\tau > 0.3$ ps at low-energy ion irradiation (1 keV) due to a ballistic mechanism. The existing experimental data follow the same trend as the simulated values.Comment: 4 pages, 4 figures, preprin