We studied the variation in electrical conductivity of exfoliated RuO2 nanosheets and the modulation in the contact resistance of individual nanosheet devices using charge transfer doping effects based on surface metal nanoparticle decorations. The electrical conductivity in the monolayer and bilayer RuO2 nanosheets gradually increased due to the surface decoration of Cu, and subsequently Ag, nanoparticles. We obtained contact resistances between the nanosheet and electrodes using the four-point and two-point probe techniques. Moreover, the contact resistances decreased during the surface decoration processes. We established that the surface decoration of metal nanoparticles is a suitable method for external contact engineering and the modulation of the internal properties of nanomaterials.
Various chemical reaction processes have been adopted to synthesize Bi 2 Te 3 thermoelectric nanomaterials for achieving remarkably low thermal conductivities, but chemical contaminations were usually pointed out as flaws, severely deteriorating electrical conductivities. We devised a novel water-based chemical reaction process for a Bi 2 Te 2.7 Se 0.3 nanocompound in which the possibility for chemical contaminations was reduced. We successfully synthesized a small and highly distributed Bi 2 Te 2.7 Se 0.3 nanocompound with high purity and adequately packed it via a spark plasma sintering process to produce a nanobulk structure. The resulting nanobulk specimen exhibited a physical density as high as the theoretical one with highly distributed nanograins; thus, we were able to obtain remarkably high electrical conductivity while maintaining thermal conductivity as low as possible. The synergistic effect was greatly induced between the transport properties; thus, the highest reported figure of merit value was achieved for n-type Bi 2 Te 3 in the bulk phase.
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