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

• Gold nanoparticles catalyze growth of As–S crystallites on Si substrate. • A dendrite-like morphology was observed in As–S crystallite distribution. • The atomic composition of crystallites was found to be close to As 4 S 5 . • Raman and DFT studies indicate the formation of synthetic tetra-arsenic pentasulfide. • Structure of the synthesized As–S crystallites is analogue to that of uzonite mineral. 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 As 2 S 3 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 As 4 S 5 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.