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In this work, we address the charge trapping properties of Ge dangling bond (DB) defects - GePb1 centers as typified by electron spin resonance spectroscopy (ESR) - found at the interfaces between condensation-grown Si1− xGe x (0.28 < x < 0.8) alloys and insulating SiO2. The ESR observation of singly-occupied paramagnetic GePb1 centers, carried out at 4.3 K, is complemented by temperature-dependent positron annihilation spectroscopy (PAS) in the Doppler broadening mode, which enables observation of the neutral-to-negative defect transitions as the temperature increases from 50 to 300 K. Through correlation of this re-charging behavior with the temperature-induced shift of the Fermi energy, the energy of the Ge DB −/0 transition in the Si0.27Ge0.73 alloy is inferred to be energetically distributed in a ∼0.1 eV interval above the top of the semiconductor valence band. This result refines previous estimates from capacitance-voltage measurements, thus providing independent affirmation that the energy levels of Ge DBs lie inside the band gap of the Si1− xGe x alloys. [ABSTRACT FROM AUTHOR]

Abstract: 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine (OMPC, edelfosine) and 1-hexadecylphosphocholine (HePC, miltefosine) represent two groups of synthetic ether lipid analogues with anti-tumor activity. Because of their hydrophobic nature, they may become incorporated into plasma membranes of cells, and it has been argued that they may act via association with lipid rafts. With the quenching of steady-state fluorescence of probes preferentially partitioning into sterol-rich ordered domains (cholestatrienol and trans-parinaric acid), we showed that OMPC and HePC by themselves did not form sterol-rich domains in fluid model membranes, in contrast to the two chain ether lipid 1,2-O-dihexadecyl-sn-glycero-3-phosphocholine. Nevertheless, all three ether lipids significantly stabilized palmitoyl–sphingomyelin/cholesterol-rich domains against temperature induced melting. In conclusion, this study shows that anti-tumor ether lipids are likely to affect the properties of cholesterol–sphingomyelin domains (i.e., lipid rafts) when incorporated into cell membranes. [Copyright &y& Elsevier]

Sphingomyelin and phosphatidylcholine are important components in the external leaflet of cellular plasma membranes. In this review we compare the structure of these lipid molecules, with emphasis on the differences in hydrogen bonding capacity and membrane properties that arise from the small but significant differences in molecular structure. The membrane properties of sphingomyelins and the implications that these have, or might have, in biological membranes and for raft function are further discussed. [Copyright &y& Elsevier]

Examines the effect of double-bond position in the sterol tetracyclic ring structure on the sterol-induced upregulation of phosphatidylcholine synthesis in cultured fibroblasts. Importance of cholesterol and phospholipids in cell membranes; Increase of cell sterol content; Effect of sterol enrichment on the formation of sterol.

Analyzes the natural and synthetic sphingomyelins using high-performance thin-layer chromatography (TLC). Hydrolysis of sphingomyelin to yield sphingosylphosphorylcholine to synthesize specific sphingomyelins; Use of TLC to separate and identify lipids; Effects of acyl chain in chromatographic behavior.