The optical energy gap of Ge1−xSnx alloys has been determined from transmittance measurements, using a fast-Fourier-transform infrared interferometer. Our results show that the change from indirect to direct band gap occurs at a lower critical Sn concentration (xc) than the value predicted from the virtual crystal approximation, tight binding, and pseudopotential models. However, a close agreement between the experimental results and the predictions with deformation potential theory is observed. The concentration xc, which is theoretically expected to be 0.09, actually it is observed to lie between 0.10<xc<0.13.

Ge 1−x Sn x alloys were grown on Ge(001) substrates in a conventional rf sputtering system. We determined the in-plane and in-growth lattice parameters, as well as the alloy bulk lattice parameter of the alloys for different Sn concentrations by high resolution x-ray diffraction. The Sn concentration was determined assuming Vegard’s law for the alloy lattice parameter. At low concentrations, we observed that Ge1−xSnx layers have pseudomorphic characteristics for layer thickness from 320 to 680 nm. These characteristics of Ge1−xSnx layers agree with the People and Bean critical thickness model. This structural study opens the possibility of growing dislocation-free Ge1−xSnx alloys below the critical thickness.

The optical energy gap of Ge1−xSnx alloys (x⩽0.14) grown on Ge substrates has been determined by performing transmittance measurements at 4K using a fast fourier transform infrared interferometer. The direct energy gap transitions in Ge1−xSnx alloys behave following a nonlinear dependence on the Sn concentration, expressed by a quadratic equation, with a so called bowing parameter b0 that describes the deviation from a simple linear dependence. Our observations resulted in b0RT=2.30±0.10eV and b04K=2.84±0.15eV, at room temperature and 4K, respectively. The validity of our fit is limited for Sn concentrations lower than 15%.

Magnesium oxide nanoparticles (MgO NPs) were obtained by the calcination of precursor microparticles (PM) synthesized by a novel triethylamine-based precipitation method. Scanning electron microscopy (SEM) revealed a mean size of 120 nm for the MgO NPs. The results of the characterizations for MgO NPs support the suggestion that our material has the capacity to attack, and have an antibacterial effect against, Gram-negative and Gram-positive bacteria strains. The ability of the MgO NPs to produce reactive oxygen species (ROS), such as superoxide anion radicals (O2•-) or hydrogen peroxide (H2O2), was demonstrated by the corresponding quantitative assays. The MgO antibacterial activity was evaluated against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria, with minimum inhibitory concentrations (MICs) of 250 and 500 ppm on the microdilution assays, respectively. Structural changes in the bacteria, such as membrane collapse; surface changes, such as vesicular formation; and changes in the longitudinal and horizontal sizes, as well as the circumference, were observed using atomic force microscopy (AFM). The lipidic peroxidation of the bacterial membranes was quantified, and finally, a bactericidal mechanism for the MgO NPs was also proposed.