Structural analysis of hydrogenated nano-crystalline silicon suboxide (nc-SiOx:H, x < 1) thin films with SAXS for a potential application as phase change material

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Bam B., Rüzgar K., Bacıoğlu A., İde S.

SURFACE & COATINGS TECHNOLOGY, vol.374, pp.164-170, 2019 (SCI-Expanded) identifier identifier


Hydrogenated nano-crystalline silicon suboxide (nc-SiOx:H; x < 1) is a two-phase material in which nanometersized silicon (nc-Si) region enclosed by hydrogenated amorphous silicon suboxide (a-SiOx:H) matrix. nc-SiOx:H thin films are produced by using highly hydrogen-diluted (d(H) >= 90%) plasma of silane and carbon-dioxide mixture, in a Plasma Enhanced Chemical Vapor Deposition (PECVD) system. The high concentration of the H-atoms in the plasma assist the silicon atoms on the growing film surface to crystallize. Small Angle X-Ray Scattering (SAXS) method was used to determine the nano-scale structures of nc-SiOx:H thin films, for varying hydrogen dilution ratios. The size, shape and the distribution of the nano-formations are found to depend strongly on the preparation conditions. From FTIR absorption and Raman scattering experiments, atomic oxygen and hydrogen contents and also the crystal ratio of the samples are evaluated. As results of nano-structural analyses, the morphologies, sizes and distributions of the nano-aggregations are found to be closely related to the crystallization of the films. From the SAXS results of the samples prepared at the hydrogen dilution ratio of 90%, the nano-aggregations are found to form in uniformly distributed core-shells. However, as the hydrogen dilution is increased to higher ratios to 95% and further to 99%, the nano-scaled fractals are deduced to form. The oxygen and hydrogen contents in nc-SiOx:H are strictly related to the crystal ratio of the samples. The crystal ratio is determined by the hydrogen dilution ratio during the deposition. The two-phase structure of nc-SiOx:H samples and the dependence on the hydrogen dilution ratio may suggest these materials are candidates for phase change materials. Depending on the deposition parameters, smaller nc-Si structures may be prepared which may have different (lower) electron densities required to melt the amorphous region and make the phase change possible due to explosive crystallization.