Dopant Spatial Distributions: Sample Independent Response Function And Maximum Entropy Reconstruction

We demonstrate the use of maximum entropy based deconvolution to reconstruct boron spatial distribution from the secondary ion mass spectrometry (SIMS) depth profiles on a system of variously spaced boron $\delta$-layers grown in silicon. Sample independent response functions are obtained using a new method which reduces the danger of incorporating real sample behaviour in the response. Although the original profiles of different primary ion energies appear quite differently, the reconstructed distributions agree well with each other. The depth resolution in the reconstructed data is increased significantly and segregation of boron at the near surface side of the $\delta$-layers is clearly shown.Comment: 5 two-columne pages, 3 postscript figures, to appear in Phys. Rev. B1

Elemental boron doping behavior in silicon molecular beam epitaxy

Boron-doped Si epilayers were grown by molecular beam epitaxy (MBE) using an elemental boron source, at levels up to 2×1020 cm−3, to elucidate profile control and electrical activation over the growth temperature range 450–900 °C. Precipitation and surface segregation effects were observed at doping levels of 2×1020 cm−3 for growth temperatures above 600 °C. At growth temperatures below 600 °C, excellent profile control was achieved with complete electrical activation at concentrations of 2×1020 cm−3, corresponding to the optimal MBE growth conditions for a range of Si/SixGe1−x heterostructures

The Depth Resolution of Secondary Ion Mass Spectrometers: A Critical Evaluation

The ability of five Secondary Ion Mass Spectrometry (SIMS) instruments to resolve thin layer and modulated dopant structures by depth profiling has been assessed. Three magnetic sector instruments (two Cameca IMS 3f\u27s and one 4f), which use optical gating and a high extraction field, were used, together with two different quadrupole based instruments (EVA 2000 and Atomika) , which use electronic gating and a low extraction field. The test structure, a thirty-one peak boron-in-silicon modulating dopant structure, was grown by Molecular Beam Epitaxy (MBE). In all the depth profiles the near surface peaks appeared narrow and asymmetric, being broadened only by fundamental processes (e.g., atomic mixing and recoil implantation). As the profiles proceeded, however, further broadening was observed. This phenomena varied markedly both from one instrument to another and from one experiment to another on the same instrument. In some cases the loss of depth resolution with depth was manifested by broadening mainly in the leading edge, in others the trailing edge, of successive boron peaks. The \u27order of merit\u27 of the instruments thus depended on the parameter used to define depth resolution. The loss of peak (depth) resolution with depth was due to variations in primary ion beam density across the gated area of the crater, which led to uneven etching. The changes in peak shape with depth can be explained by a numerical model of the etching process. These observations dictate that the depth resolution of a SIMS instrument should not be measured in terms of a single interface width, such as the leading or trailing edge

ER and HER2 expression are positively correlated in HER2 non-overexpressing breast cancer

PMCID: PMC3446380This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

A pilot trial to evaluate the acute toxicity and feasibility of tamoxifen for prevention of breast cancer.

Epidemiological and experimental evidence indicates that oestrogens are involved in the carcinogenic promotion of human breast cancer. We have undertaken a pilot trial of tamoxifen, an anti-oestrogen, compared to placebo given to 200 women at a high risk of developing breast cancer. The results of this trial show that acute toxicity is low and that accrual and compliance are satisfactory. Furthermore, biochemical monitoring of lipids and clotting factors indicate that tamoxifen may reduce the risk of cardiovascular deaths. At this stage no untoward long-term risks have been identified, and it is therefore proposed that a large multicentre trial should be started