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We present molecular and lattice dynamics calculations of the thermal conductivity of nanoporous silicon, and we show that it may attain values 10-20 times smaller than in bulk Si for porosities and surface-to-volume ratios similar to those obtained in recently fabricated nanomeshes. Further reduction of almost an order of magnitude is obtained in thin films with thickness of 20 nm, in agreement with experiment. We show that the presence of pores has two main effects on heat carriers: appearance of non-propagating, diffusive modes and reduction of the group velocity of propagating modes. The former effect is enhanced by the presence of disorder at the pore surfaces, while the latter is enhanced by decreasing film thickness.

A 2.25 at.% V decorated Mg nanoblade array has been fabricated by a dynamic shadowing growth technique. It can absorb and desorb hydrogen rapidly at temperatures T>500 K after activation by one hydrogenation cycling, with low hydrogen absorption activation energy of 35.0 +/- 1.2 kJ/mol H2 and desorption activation energy of 65.0 +/- 0.3 kJ/mol H2. The saturated hydrogen content in Mg nanoblades decreases gradually with the number of cyclings, which is mainly caused by the formation and growth of Mg2Si hillock defects at the nanoblade/substrate interface even though a diffusion barrier layer consisting of a 500 nm Ti nanorod array and 500 nm Ti film was deposited between the Mg nanoblades and the Si substrate. The improved hydrogen sorption kinetics is attributed to both the catalytic effect of the V coating and the unique nanoblade morphology with large surface area and small hydrogen diffusion length.

A two-turn, eight-armed, rectangular Si/Ni heterogeneous nanospring structure on Si(100) has been fabricated using a multilayer glancing-angle deposition technique. The multilayered nanosprings with a height of approximately 1.98 mum were composed of alternating layers of amorphous Si nanorods approximately 580 nm in length and face-centered cubic Ni nanorods approximately 420 nm in length, both with a diameter of approximately 35 nm. The magnetic anisotropy of the nanosprings showed that the in-plane easy and hard axes were parallel and perpendicular to the Ni nanorod plane, respectively. The out-of-plane magnetic hysteresis loop was very sensitive to the applied magnetic field direction when rotating the nanosprings about their in-plane hard axis, and the magnetization measurement revealed that the nanosprings tilted at approximately 7.5 degrees toward the plane of the Si nanorods. The magnetic anisotropy of the nanosprings is determined by their structure, and the experimental results can be interpreted by the shape anisotropy energy.

Abstract: We investigate the anode performance of Si-based nanorods by tuning its composition using an oblique (co)deposition technique. Our results show that pure Si nanorods have a higher initial anodic capacity of 1500mAhg−1, but the capacity diminishes after 50 cycles due to the morphological change and pulverization. By introducing approximately 70at.% Cu into Si nanorods, the Si–Cu composite nanorods demonstrate 500mAhg−1 of capacity sustainable in 100 cycles, which is attributed to the flexibility and improved toughness of Si–Cu composite nanorods. [Copyright &y& Elsevier]

During the oblique angle co-deposition of Si and Cu, the nanoculumn tilting angle β changes systematically with the relative composition of Si and Cu when the vapor incident angle θ is fixed. This result demonstrates that the β-θ relationship does depend closely on the material property and composition, which is very different from the predictions of the well-known 'universal' models, such as tangent or cosine rules. A statistic model based on the size, spacing, and stacking of Si and Cu atoms has been proposed and the predicted result agrees well with the experimental data. [ABSTRACT FROM AUTHOR]

The deformation behavior and mechanical properties of a tilted Si nanorod array structure on Cu/Ti bilayer film coated Si substrate were studied for the first time by coupled atomic force microscopy and nanoindentation techniques. The individual Si nanorods fabricated by an oblique angle deposition technique are composed of many fine Si nanofibers with the diameter ranging from 10 to 50 nm. They are not brittle, but ductile. The ductile metallic Cu/Ti bilayer film roots contribute remarkably to the mechanical robustness of the Si nanorods. The toughening mechanism of such Si-based nanoanodes has been elucidated by experimental mechanics studies. [ABSTRACT FROM AUTHOR]

The hydrogenation of Mg film and Mg nanoblade array fabricated on Ti coated Si substrates has been studied and compared. The nanoblades start to absorb hydrogen at a temperature between 250 and 300 °C, which is much lower than 350 °C for Mg film. However, the saturated total hydrogen uptake in nanoblades is less than half of that in the film, resulting from MgO formation by air exposure. The nanoblade morphology with large surface area and small hydrogen diffusion length, and the catalytic effect of Ti layer, are two main reasons for the nanoblade hydrogenation behavior. [ABSTRACT FROM AUTHOR]