Transport Properties of Nanostructures within Porous Materials
Nanostructures can be obtained by confining a solid or liquid within the nanometer-sized pores of different porous materials. The advantages of such objects are connected with the possibility to produce nanostructures with different geometries (2D, 1D, 0D), with very large range of characteristic sizes (ª1nm- ª100nm), with very large total amount of nanomaterial ( up to some cubic cm) and from different substances ( metals, semiconductors, insulators). Quantum wires of a wide class of materials were prepared in regular set of closely packed parallel dielectric nanotubes of natural chrysotile asbestos mineral ( Mg3Si2O5(OH)4 ) with external diameters of ª30nm ( this value determines the distance between the centers of neighbour nanochannels), and with internal diameters of 2-10 nm depending of the origin of the mineral. A filling of the nanochannels with molten materials ( Hg, Sn, In, Bi, Pb, InSb, Se, Te ) under high pressure conditions ( up to 15 kbars) gives the possibility of obtaining a regular systems of parallel identical nanowires. The superconducting transitions of a complete series of such samples by the contact method were studied, and a temperature spread that is due to fluctuations which are significant for such thin elements was observed. Critical temperatures vs diameter were measured for mercury, tin and indium nanowires from 2nm to 15 nm. The resistance of metallic nanowires in a normal state increases as the temperature is lowered as DR/R~T-3/2 (1< T < 60K). Such temperature dependence is interpreted as demonstration of weak localization in one-dimension. Electrical resistance and thermopower of nanowires ( diameters 5±1 nm) from semiconductors ( InSb, Te) demonstrated behavior different from bulk materials that cannot be accounted for in terms of ordinary single-electron theories and exhibits features expected for impure Luttinger liquid.