Cross-correlated experimental and theoretical characterisation of orpiment As2S3, a potential material for new advanced technological applications

In the ever-growing search for new materials in optical, electronic and photovoltaic applications, chalcogenides, such as amorphous diarsenic trisulfide (As2S3), are being deeply investigated. However, very few and incomplete data are available on crystalline As2S3 (space group P21/n), known as mineral orpiment. In the present work, several experimental techniques were employed to analyse the crystal structure, morphology, chemical composition and vibrational properties of the bulk and mechanically cleaved (010) orpiment surface. Also, cross-correlated atomic-scale ab initio simulations corroborated and explained the new experimental data. Orpiment showed a semiconducting behaviour, with an indirect band gap of 2.44 eV and an optical Γ-Γ gap of 2.63 eV, which agrees with previous optical-absorption edge measurements. Furthermore, the complete stiffness tensor and the phonon band structure were reported for the first time. All these quantities are of utmost importance for devising new possible applications of crystalline orpiment in the technological and materials science fields.