Effects of stoichiometry on structural, morphological and nanomechanical properties of bi₂ se₃ thin films deposited on inp(111) substrates by pulsed laser deposition

In the present study, the structural, morphological, compositional, nanomechanical, and surface wetting properties of Bi₂ Se₃ thin films prepared using a stoichiometric Bi₂ Se₃ target and a Se-rich Bi₂ Se₅ target are investigated. The Bi₂ Se₃ films were grown on InP(111) substrates by using pulsed laser deposition. X-ray diffraction results revealed that all the as-grown thin films exhibited were highly c-axis-oriented Bi₂ Se₃ phase with slight shift in diffraction angles, presumably due to slight stoichiometry changes. The energy dispersive X-ray spectroscopy analyses indicated that the Se-rich target gives rise to a nearly stoichiometric Bi₂ Se₃ films, while the stoichiometric target only resulted in Se-deficient and Bi-rich films. Atomic force microscopy images showed that the films’ surfaces mainly consist of triangular pyramids with step-and-terrace structures with average roughness, R_a, being ~2.41 nm and ~1.65 nm for films grown with Bi₂ Se₃ and Bi₂ Se₅ targets, respectively. The hardness (Young’s modulus) of the Bi₂ Se₃ thin films grown from the Bi₂ Se₃ and Bi₂ Se₅ targets were 5.4 GPa (110.2 GPa) and 10.3 GPa (186.5 GPa), respectively. The contact angle measurements of water droplets gave the results that the contact angle (surface energy) of the Bi₂ Se₃ films obtained from the Bi₂ Se₃ and Bi₂ Se₅ targets were 80^◦ (21.4 mJ/m² ) and 110^◦ (11.9 mJ/m² ), respectively.