Microstructures, thermoelectric and nanomechanical properties of Bi2Se2Te thin films grown on SiO2/Si(100) substrates: Effects of helium pressure during pulsed laser deposition

Structural, electrical–thermoelectric, and nanomechanical properties of a series of Bi 2 Se 2 Te thin films grown on SiO 2 (300 nm)/Si(100) substrates by using pulsed laser deposition (PLD) at 150°C under helium pressures ( P He ) ranging from 0.027 to 86.7 Pa were systematically investigated. Morphological analyses indicate that the Bi 2 Se 2 Te films are essentially composed of nano-sized crystallites with (015)- and (00 l)-preferred orientations. Increasing the in-situ background helium pressure during PLD appeared to have refined the grain size from 21.5 to 6.9 nm and promoted a transition of film growth mode from densely packed and almost featureless surface structure to columnar-granular morphology. Energy dispersive spectroscopy (EDS) analysis revealed that all films are having compositional characteristic of Bi-rich and slightly Te-deficient, while the Se-deficiency evidently can be eliminated by increasing P He and approaches stoichiometry at P He ≈ 86.7 Pa. Hall measurements revealed that the carrier mobility and concentration both decreased with increasing P He , from 12.0 to 2.1 cm 2 /V·s and 9.4 × 10 20 –4.0 × 10 20 cm −3 for P He increasing from 0.027 to 86.7 Pa, which could be attributed to the enhanced grain-boundary scattering and reduced Se vacancies. Correspondently, the electrical conductivity decreased from 1801.3 to 136.8 S·cm −1 , whereas the Seebeck coefficient increased from 48.8 to 69.3 µV·K −1 , respectively. The maximum power factor of 4.29 µW·cm −1 ·K −2 was achieved for the sample obtained at P He ≈ 0.027 Pa. Nanoindentation results showed pressure-driven strengthening, with hardness and the Young’s modulus increasing from 2.1 GPa and 72.8 GPa ( P He @ 0.027 Pa) to 3.6 GPa and 104.2 GPa ( P He @ 86.7 Pa), respectively. Similarly, the critical shear stress and fracture toughness of the Bi 2 Se 2 Te films improved from 0.7 GPa and 1.2 MPa·m 1/2 to 1.2 GPa and 1.7 MPa·m 1/2 , respectively. These findings demonstrate that the in-situ background helium pressure deployed in the deposition chamber can serve as an effective parameter for tailoring the nanostructure, charge transport, thermoelectric performance, and mechanical resilience of PLD-derived Bi 2 Se 2 Te thin films and advancing them for flexible thermoelectric applications. • Nanocrystalline Bi2Se2Te thermoelectric films were grown by PLD with controlled helium pressure. • Films deposited at 0.027 Pa showed high conductivity (1801 Scm⁻¹), Seebeck coefficient of 48.8 µV K⁻¹, and PF of 4.29 µW cm⁻¹ K⁻². • Higher helium pressure reduced grain size, improved stoichiometry, and changed morphology to a columnar–granular structure. • Hardness (2.1–3.6 GPa) and Young’s modulus (72.8–104.2 GPa) increased with helium pressure. • Critical shear stress and fracture toughness were significantly enhanced at higher helium pressures.