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We study the conductance through two types of graphene nanostructures: nanoribbon junctions in which the width changes from wide to narrow, and curved nanoribbons. In the wide-narrow structures, substantial reflection occurs from the wide-narrow interface, in contrast to the behavior of the much studied electron gas waveguides. In the curved nanoribbons, the conductance is very sensitive to details such as whether regions of a semiconducting armchair nanoribbon are included in the curved structure-such regions strongly suppress the conductance. Surprisingly, this suppression is not due to the band gap of the semiconducting nanoribbon, but is linked to the valley degree of freedom. Although we study these effects in the simplest contexts, they can be expected to occur for more complicated structures, and we show results for rings as well. We conclude that experience from electron gas waveguides does not carry over to graphene nanostructures. The interior interfaces causing extra scattering result from the extra effective degrees of freedom of the graphene structure, namely the valley and sublattice pseudospins.

The production of periodic ripple or wavelike structure by Si+, Ne+, Ar+ and Xe+ high-fluence ion bombardment at 20 and 30 keV of Si at 45° incidence angle and at target temperatures from 120 K to room temperature and observed by scanning electron and atomic force microscopy is described. Different species exhibit different behaviors at different temperatures with Xe+ producing transverse wave structures at room temperature and below, Ar+ producing more patchy ripple structures, and Ne+ and Si+ only producing wave structures at low temperatures. Possible reasons for the different behavior include implant ion incorporation which mediates flow and stress relief in the amorphized near-surface layer.

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The thermal radiation of small conducting particles was investigated in the region where the Stephan-Boltzmann law is not valid and strongly overestimates radiation losses. The new criterion for the particle size, at which black body radiation law fails, was formulated. The critical radius r c is expressed through a combination of temperature T and particle conductivity σ: thus r c = c(ћ/2πσkT) 1/2 . The approach is based on the magnetic particle polarization, which is valid until very small sizes (cluster size) where due to drop of particle conductivity the electric polarization prevails over the magnetic one. It was also shown that the radiation power of clusters, estimated on the basis of the experimental data, is lower than that given by theStephan-Boltzmann law.In the last years the amount of research in the field of nanotechnology, nanomaterials and nanosystems tremendously increased [1]. One of the most important trends in the nanotechnology is obtaining and using of nanopowders, which can be used in metallurgy, microelectronics, and medicine and food industry. Production and processing of nanopowders are frequently dealt with heating of nanoparticles to high temperatures when intensive thermal radiation can be expected.The problem is close related to dust plasma [2], and to the role of dust in fusion devices [3], where micro-and nano-particles are heated to high temperatures and radiation energy losses can play decisive role in the energy balance of the particles. The effect of metal clusters on emission spectra was discussed in [4].

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