Structure and optical properties of Ge/Si superlattice grown at Si substrate by MBE at different temperatures

Abstract Multilayer structures in silicon containing submonolayers of Ge in the matrix were grown by MBE on Si substrates at different temperatures. An additional peak at 1.068 eV was observed in photoluminescence spectra (PL) from the samples grown at T=600, 650 and 700°C, whereas it was absent in specimens grown at 750°C. Electron microscopy structure investigations showed a high density of spherical, coherent Ge inclusions in samples grown at 650°C, whereas they were not generated at higher growth temperature, such as at 750°C. This fact indicates that the observed PL peak is unambiguously related to the Ge inclusions. High temperature growth at 750°C results in formation of modulated structure where the composition sinusoidally changes with periodicities between 1.2 and 0.44 nm along 113 and 112 directions, respectively. This results in a distortion of the cubic symmetry and in a relaxation of the misfit stress causing changes in the electronic properties

Founding BRCA1 mutations in hereditary breast and ovarian cancer in southern Sweden.

Nine different germ-line mutations in the BRCA1 breast and ovarian cancer susceptibility gene were identified in 15 of 47 kindreds from southern Sweden, by use of SSCP and heteroduplex analysis of all exons and flanking intron region and by a protein-truncation test for exon 11, followed by direct sequencing. All but one of the mutations are predicted to give rise to premature translation termination and include seven frameshift insertions or deletions, a nonsense mutation, and a splice acceptor site mutation. The remaining mutation is a missense mutation (Cys61Gly) in the zinc-binding motif. Four novel Swedish founding mutations were identified: the nucleotide 2595 deletion A was found in five families, the C 1806 T nonsense mutation in three families, the 3166 insertion TGAGA in three families, and the nucleotide 1201 deletion 11 in two families. Analysis of the intragenic polymorphism D17S855 supports common origins of the mutations. Eleven of the 15 kindreds manifesting BRCA1 mutations were breast-ovarian cancer families, several of them with a predominant ovarian cancer phenotype. The set of 32 families in which no BRCA1 alterations were detected included 1 breast-ovarian cancer kindred manifesting clear linkage to the BRCA1 region and loss of the wild-type chromosome in associated tumors. Other tumor types found in BRCA1 mutation/haplotype carriers included prostatic, pancreas, skin, and lung cancer, a malignant melanoma, an oligodendroglioma, and a carcinosarcoma. In all, 12 of 16 kindreds manifesting BRCA1 mutation or linkage contained ovarian cancer, as compared with only 6 of the remaining 31 families (P<.001). The present study confirms the involvement of BRCA1 in disease predisposition for a subset of hereditary breast cancer families often characterized by ovarian cancers