Microstructure and the Boson-peak in thermally-treated In_(x)O films

We report on the correlation between the boson-peak and structural changes associated with thermally-treating amorphous indium-oxide films. In this process, the resistance of a given sample may decrease by a considerable margin while its amorphous structure is preserved. In the present study, we focus on the changes that result from the heat-treatment by employing electron-microscopy, X-ray, and Raman spectroscopy. These techniques were used on films with different stoichiometry and thus different carrier-concentration. The main effect of heat-treatment is material densification, which presumably results from elimination of micro-voids. The densified system presents better wavefunction-overlap and more efficient connectivity for the current flow. X-ray, and electron-beam diffraction experiments indicate that the heat-treated samples show significantly less spatial heterogeneity with only a moderate change of the radial-distribution function metrics. These results are consistent with the changes that occur in the boson-peak characteristics due to annealing as observed in their Raman spectra.