Preparation of nanostructured materials and electrical conductance in complex physical systems

Production of materials with controlled physical characteristics presents a fundamentally new method for materials science. A new facility has been designed and built using evaporation onto a moving liquid surface. Using this technique metallic particles with diameters less than 200 A with well-characterized surfaces can be prepared. The applications of these nanostructured particles to fundamental investigations is discussed. Particular attention has been given to the investigations of electrical transport in three complex physical systems.; Aqueous colloidal dispersions of {dollar}alpha - Fesb2Osb3{dollar} particles (average diameter 65 nm) have been prepared at different volume concentrations. The electrical conduction of these composites has been investigated as a function of particle concentration, temperature (from 77 K to 300 K), frequency (including the d.c. case) of the applied electric field, and the strength (up to 7 kOe) of the applied magnetic field. The conductivity increases with particle concentration and with temperature. The frequency dependence of conductivity obeys a power law with an index slightly less than unity and decreasing somewhat with increasing temperature. These observations are interpreted with a model of conduction by electron hopping between localized states. The composites also show an increase in conductivity with the application of a magnetic field. This conductivity enhancement is believed to result from field-induced agglomeration and particle chaining.; The ferromagnetic Curie temperature ({dollar}Tsb{lcub}c{rcub}{dollar}) has been determined for Fe-Ge alloys as a function of Ge concentration (up to {dollar}sim{dollar}10 at.%) using electrical resistivity studies. The investigation shows that addition of Ge to Fe causes a small, gradual increase in {dollar}Tsb{lcub}c{rcub}{dollar}, reaching the maximum value of {dollar}sim{dollar}1050 K at {dollar}sim{dollar}1.5 at.%Ge, followed by a gradual decrease with higher Ge concentrations. This behavior is in sharp contrast with the usual theories which predict decrease of {dollar}Tsb{lcub}c{rcub}{dollar} with increasing the concentration of non-magnetic particles. At present time, there are no theories capable of explaining this phenomenon.; The electrical conductivity of polypyrrole as a function of temperature has been investigated. The observed temperature dependence can be described by ln{dollar}sigma propto Tsp{lcub}-{lcub}1over 4{rcub}{rcub}{dollar}. The experimental results are quantitatively analyzed in the framework of Mott's variable range hopping model. Although this model gives a reasonable description of the conductivity, it does not afford a complete description of the transport properties of polypyrrole.