Nanostructured surfaces 

Characterization by scanning electron microscopy and energy-dispersive X-ray and Raman spectroscopy of As-S crystallites synthesized by nano-gold c catalysis
R. Holomb1,2*, O. Kondrat1, V. Mitsa1, A. Mitsa1, D. Gevczy1, D. Olashyn1, M. Veres2, L. Himics2, I. Rigó2, T. Váczi2, A. Czitrovszky2, A. Csík3 ,V. Takats3
1 Uzhhorod National University, Pidhirna Str., 46, 88000 Uzhhorod, Ukraine.
E-mail: oleksandr.kondrat@uzhnu.edu.ua
2 Wigner Research Centre for Physics, 1121 Budapest, Hungary.
3 Institute for Nuclear Research, H-4001 Debrecen, Hungary.

Due to the advantageous combination of infrared transparency, optical activity, structural photosensitivity and high level of third-order optical non-linearity amorphous and crystalline chalcogenides attract significant attention in modern optoelectronics and photonics [1]. Arsenic sulphide, especially in nanocrystalline form, has an anticancer effect, especially on hematological cancer, which can also be related to the realgar to pararealgar transformation under light illumination.
As-S nanostructures were grown by thermal evaporation on heated Si substrates covered by spherical gold nanoparticles of different size (5, 40 and 60 nm). As-S micro-crystallites with well-defined size and shape were obtained with 43.9 and 56.1 % As and S atomic content, respectively. The presence of gold nanoparticles allowed to study the local structure of the As-S microcrystallites by using 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 cage-like nanocluster models were also calculated by using the density functional theory approach. Results show that at specific conditions stimulated formation of As4S5 molecules occurs that activates the micro-crystallites growth on the film surface. The structure and properties of this nanostructured As-S film were investigated, and the catalyzed growth and the structure of a new type of As-S microcrystallite are discussed in detail.

1.	R. Holomb, O. Kondrat, V. Mitsa, M. Veres, A. Czitrovszky, A. Feher, N. Tsud, M. Vondráček, K. Veltruská, V. Matolín, K.C. Prince. Super-bandgap light stimulated reversible transformation and laser-driven mass transport at the surface of As2S3 chalcogenide nanolayers studied in-situ. // J. Chem. Phys. 149, 214702 (2018).