Mg 2 Si is a semiconductor with a band gap previously reported to be in the range 0.6-0.8 eV. In spite of potential optoelectronic applications in an important infrared range, the growth of Mg 2 Si thin films on silicon substrates has received scant attention. This may be due to the difficulty of preparing Mg 2 Si in thin-film form. We find that intended reactive deposition of magnesium onto a silicon substrate, at temperatures from 200 to 500°C, results in no accumulation of magnesium. However, codeposition of magnesium with silicon at 200°C , using a magnesium-rich flux ratio, gives a stoichiometric Mg 2 Si film. The amount of magnesium which accumulates is determined by the total amount of silicon which was codeposited; the excess magnesium in the flux does not condense. Measurements of the optical transmittance of thin films thus obtained reveal an absorption edge. Extraction of the absorption coefficient from the data, and analysis of its energy dependence, suggest an indirect band gap of ϳ0.74 eV, plus direct transitions at ϳ0.83 and ϳ0.99 eV.

The development and properties of doped nanomaterials including doped titanium dioxide, doped silicon, and doped cadmium telluride are reviewed, as well as their ultrafast dynamics. Doping nanomaterials provides a flexible way to tune to the properties of the materials while maintaining their high surface areas. The electronic, optical, photochemical, photoelectrochemical, photocatalytic and photoexcited relaxation properties can be tuned towards the desired direction by doping different elements. The materials can be engineered towards specific applications through careful selection of the dopants.

No abstract

No abstract

No abstract