No abstract

A linear lattice model without adjustable parameters provides an accurate description of the magnitude and temperature dependence of the thermal conductivity of Kc of polyethylene crystals parallel (∥) and perpendicular (⟂) to the chain direction. The model shows that heat is transported principally by phonons polarized transverse (T) to the chain direction. Phonons polarized longitudinal (L) to the chain direction contribute about 20% to the heat transport along the chain direction, and negligibly to heat transport perpendicular to the chain direction. Thermal resistance is caused by LTT three‐phonon umklapp scattering in the parallel direction, and by TTT scattering in the perpendicular direction. The calculated values for large crystals are K italicc∥ = 465 W m−1 K−1, K italicc∥ = 0.16 W m−1 K−1 at 300 K, in agreement with experimental estimates and implying an anisotropy ratio of K italicc∥/K italicc⟂ ≈ 3000. The axial thermal conductivity of polyethylene crystals is extremely high and comparable to that of copper. Comparison with experimental data on semicrystalline samples at lower temperature yields a crude value of mean free path for boundary scattering of about 50 nm, agreeing in order of magnitude with the size of crystalline blocks.

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Metal silicides are promising candidates as electrical contacts to silicon nanowires. Metal vapor vacuum arc (MEVVA) ion source implantation is used by these authors to synthesize NiSi2/Si (see Figure) and CoSi2/Si on the surface of bare silicon nanowires. It is demonstrated that the structure of the metal silicide layer is sensitive to the annealing temperature and that, under appropriate conditions, the layer is well oriented with respect to the nanowire core.

A novel approach for the synthesis of cobalt-doped ZnO single-crystalline nanorods based on a wet chemical reaction has been developed. The as-doped ZnO nanorods have a length between 0.3 and 0.6 µm and a diameter between 30 and 60 nm. Structure and composition analyses indicate that the cobalt is incorporated into the ZnO lattice, forming a solid solution without any precipitation. Magnetic property measurements reveal that there is room-temperature ferromagnetism in the Zn1−xCoxO nanorods with Tc higher than 300 K.