Gold nanoparticle assisted synthesis and characterization of As–S crystallites: Scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray and Raman spectroscopy combined with DFT calculations

Abstract

Gold nanoparticle assisted thermally initiated chemical vapor deposition was used to synthesize nanostructured As-S films. The nanostructures were grown on heated Si substrates covered by spherical gold nanoparticles of different (5, 20, 40 and 60 nm) sizes. In contrast to polycrystalline As-S films prepared by ordinary thermal evaporation and chemical vapor deposition of As2S3 glass without the use of gold nanoparticles, the gold nanoparticle assisted synthesis leads to growth of particular type of crystal-like As-S nanostructures. The As-S micro-crystallites with well-defined size and shape were obtained with 43.9 and 56.1 at% As and S atomic content, respectively. The local structure of the As-S microcrystallites was investigated by Raman and/or surface-enhanced Raman spectroscopy. To assist the interpretation of the experimental Raman spectra and to identify the structure of the crystallites, the vibrational spectra of different cage-like nanocluster models were also calculated by using the density functional theory. Results show that at specific deposition conditions a stimulated formation of As4S5 molecules occurs which activates the growth of micro-crystallites on the gold nanoparticle coated Si surface with well distinguished shape. The structure and properties of nanostructured As-S films synthesized with and without the use of gold nanoparticles were investigated and the gold nanoparticle assisted selective growth of a new type of As–S microcrystallite is discussed.