  We report here metal to insulator transition, colossal Seebeck coefficient
and ultralow thermal conductivity (0.0057th of its bulk value, significantly
smaller than many well-known thermoelectric materials and silicon, showing
potential applications in thermoelectrics, electronics and photonics for heat
dissipation) in monodispersed well characterized Ni nanoparticles. As a
consequence, thermoelectric power factor and figure of merit are significantly
enhanced compared to their bulk counterpart. Interestingly, a systematic
crossover from metallic to semiconducting to finally electrically insulating
behavior, large negative temperature coefficient of resistance and n-type
conduction to p-type conduction with decrease in particle size have been
observed. These results are mainly attributed to formation of metal/organic
interfaces, enhancement in local electronic density of sates and multiscale
electron and phonon scattering by various defects. Thus, this study will open a
new avenue to make better thermoelectrics through incorporation of such
nanoparticles in semiconducting hosts.
