Formation of transition metal chalcogenide thin films by electrochemical atomic layer deposition (E-ALD)
Tsang, Chu Fan
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This dissertation describes the deposition of transition metal dichalcogenide (TMDC) thin films by electrochemical atomic layer deposition (E-ALD). E-ALD was proposed to grow chalcogenide (S, Se and Te) films involving valve metals (Ta, Nb and Ti). Tantalum is a refractory metal that readily forms a stable and protective surface oxide layer when exposed to ambient conditions. In a Ta chalcogenide deposition process, the surface oxide of Ta must be removed prior to depositing a chalcogen onto it. The nature of the Ta oxide was studied, and attempts to electrochemically reduce the oxide were made. Te, S, and Cu were deposited onto reduced Ta surfaces. These processes were examined by in-situ electrochemical scanning tunneling microscopy (EC-STM), cyclic voltammetry (CV), and X-ray photoelectron spectroscopy (XPS). Molybdenum is another valve metal that is electrochemically similar to tantalum. The electrochemistry of Mo was also investigated with the intent to form Mo chalcogenides using E-ALD. Preliminary MoSe2 films were grown by this method. The electrodeposition processes were explored using CV, coulometry. and XPS. The MoSe2 films were characterized by electron probe micro-analyzer (EPMA), X-ray diffraction (XRD), photoelectrochemistry (PEC), scanning electron microscopy (SEM), scanning tunneling microscopy (STM), micro-Raman spectroscopy, and XPS.