We report on a comprehensive combined experimental and theoretical study of Curie temperature trends in ͑Ga,Mn͒As ferromagnetic semiconductors. Broad agreement between theoretical expectations and measured data allows us to conclude that T c in high-quality metallic samples increases linearly with the number of uncompensated local moments on Mn Ga acceptors, with no sign of saturation. Room temperature ferromagnetism is expected for a 10% concentration of these local moments. Our magnetotransport and magnetization data are consistent with the picture in which Mn impurities incorporated during growth at interstitial Mn I positions act as double-donors and compensate neighboring Mn Ga local moments because of strong nearneighbor Mn Ga u Mn I antiferromagnetic coupling. These defects can be efficiently removed by post-growth annealing. Our analysis suggests that there is no fundamental obstacle to substitutional Mn Ga doping in high-quality materials beyond our current maximum level of 6.8%, although this achievement will require further advances in growth condition control. Modest charge compensation does not limit the maximum Curie temperature possible in ferromagnetic semiconductors based on ͑Ga,Mn͒As.

First-principles calculations are carried out to investigate the hydrogen separation characteristics of two-dimensional carbon allotropes consisting of sp-and sp 2 -hybridized carbon atoms, i.e., graphyne, graphdiyne, and rhombic-graphyne. The selectivities for H 2 over several gas molecules, including CO, N 2 , and CH 4 , are found to be sensitive to the pore sizes and shapes. The penetration barriers generally decrease exponentially with the pore sizes. Our results reveal that graphyne with small pores is unsuitable for the purpose of hydrogen separation. Graphdiyne, with larger pores, exhibits a high selectivity (10 9 ) for hydrogen over large gas molecules such as CH 4 , but a relatively low selectivity (10 3 ) over small molecules such as CO and N 2 . The large differences in diffusion barriers for molecules penetration through a rhombic-graphyne monolayer, which possesses pore size in between that of graphyne and graphdiyne, lead to a high selectivity (>10 16 ) for hydrogen separation from the others. The results suggest that the abundant pores of different sizes in these carbon allotropes make them ideal molecular sieves for gas separation applications directed toward different separation needs and objectives.

In this article, we report the fabrication of highly ordered TiO2 nanowire arrays by anodic oxidative hydrolysis of TiCl3 within a hexagonal close-packed nanochannel alumina (NCA). The single-crystalline anatase TiO2 nanowires with diameters about 15 nm and lengths about 6 μm are obtained after annealing at 500 °C. Finally, the fabrication and characterization of highly ordered Au and Ni nanowire arrays with selectable diameters are also reported.

We demonstrate that GaMnAs films grown with As 2 have excellent structural, electrical and magnetic properties comparable or better than similar films grown with As 4 . Using As 2 , a Curie temperature of 112K has been achieved, which is slightly higher than the best reported to date. However, more significantly films showing metallic conduction have been obtained over a much wider range of Mn concentrations from 1.5 to 8% than has previously been reported for films grown with As 4 . The improved properties of the films grown with As 2 are related to the lower concentration of anti-site defects at the low growth temperatures employed.