Antimonide thin films : topological and thermoelectric properties

Antimony and antimony-based thin films attract great attention as topological and thermoelectric materials. In this study, Sb, BiSb and ZnSb thin films were deposited by di_erent physical vapour deposition techniques on various substrates in high and ultrahigh vacuums. The structure, composition and topography of the films were investigated using various microscopy and diffraction techniques. The optical and electrical properties of the films were measured using several complementary methods. The effects of increasing the surface area of thin films of the topological insulator BiSb were studied. To achieve this, BiSb thin films were deposited on both normal flat InP single crystal substrates and nano-patterned ones prepared by ion bombardment. The crystalline texture of the BiSb films was different on _at versus nano-patterned substrates. The electrical conductivity was smaller on nano-patterned substrates, but the contribution of the surface conduction was larger. Both undoped and In-doped ZnSb thin films were studied for potential application in flexible thermoelectric devices. Films were deposited on rigid glass substrates and flexible polyimide (Kapton) films. The electrical and optical properties of both types were similar. In addition, flexible films showed stability in both electrical and optical measurements before and after 10,000 cycles of bending. Thermoelectric measurements of BiSb and ZnSb were performed by collaborators and showed promising power factors. Finally, pure Sb films were grown on both InAs and glass substrates. The films on InAs were single crystal and epitaxial, while on glass a strong (003) texture was evident. On InAs, Sb films were affected by In segregation upon annealing (affecting the work function), while films on glass were stable. The direct band gap of the semimetallic films on glass was determined optically to be 228 meV. This value agrees with published tight-binding band structure calculations

Calibrated in-vacuum quantum efficiency system for metallic and III-V thin-film photocathodes

The construction and calibration of a high vacuum system for thin film growth and in situ quantum efficiency (QE) measurement are described. Surface cleaning by in situ argon ion sputtering and annealing is supported. The QE measurement is based on an external 265 nm LED and in situ positively biased collector grid. The system is applied to two metallic and two semiconducting photocathodes: polycrystalline silver and copper, and single crystal InP and InSb. Surface cleaning protocols are shown to have a dramatic effect on the QE for all of these materials. The maximum QE values achieved for clean InSb and InP are around 8 × 10−5, for Cu 9 × 10−5 and for Ag 2 × 10−4

Calibrated in-vacuum quantum efficiency system for metallic and III-V thin-film photocathodes

The construction and calibration of a high vacuum system for thin film growth and in situ quantum efficiency (QE) measurement are described. Surface cleaning by in situ argon ion sputtering and annealing is supported. The QE measurement is based on an external 265 nm LED and in situ positively biased collector grid. The system is applied to two metallic and two semiconducting photocathodes: polycrystalline silver and copper, and single crystal InP and InSb. Surface cleaning protocols are shown to have a dramatic effect on the QE for all of these materials. The maximum QE values achieved for clean InSb and InP are around 8 × 10−5, for Cu 9 × 10−5 and for Ag 2 × 10−4