Interfacial Characterization of Al2O3-Coated p-Type Bi–Sb–Te Powders by Thermal and UV-assisted Atomic Layer Deposition

Interface engineering is an effective strategy for enhancing thermoelectric performance by modulating carrier and phonon transport at interfaces. Atomic layer deposition (ALD), which enables uniform, conformal, and thickness-controlled coatings, is particularly well-suited for this purpose. In this study, p-type Bi0.35Sb1.6Te3 (BST) powders were coated with Al2O3 using thermal ALD and UV-assisted ALD (UV-ALD) at 85 °C.Scanning electron microscopy showed that neither process substantially altered the morphology of the BST powders. However, particle size analysis revealed that the UV-ALD sample exhibited a greater tendency toward partial agglomeration, which may be associated with the more pronounced OH-related band observed in the Fourier-transform infrared spectroscopy results.Cs-corrected scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy mapping revealed continuous Al₂O₃-based coating layers approximately 2–3 nm thick on the BST particle surfaces, forming a core–shell structure. Fast Fourier transform analysis suggested that the coating layers were amorphous, and X-ray photoelectron spectroscopy indicated Al–O bond formation while the main chemical states of BST were preserved.These results demonstrate that both thermal ALD and UV-ALD can effectively deposit continuous amorphous Al₂O₃-based interfacial layers on BST powders, providing a structural basis for future studies of interface-engineered thermoelectric materials.