Precursor Inlet for Metal-Organic Molecular Beam Epitaxy of WTe₂

Transition metal dichalcogenides display promising electronic properties such as tunable superconductivity and quantum spin Hall effects when synthesized as monolayer films. Molecular beam epitaxy (MBE) provides a means to synthesize high-purity films by thermally evaporating atomic species. However, some transition metals such as tungsten (W) have high melting points, requiring e-beam rather than thermal evaporation. The low flux stability of e-beam evaporation makes it hard to synthesize large stoichiometric films. To address this challenge, metal-organic precursors have been used in conjunction with MBE to synthesize WS₂ [1]. We adapt this process to synthesize WTe₂ by introducing the precursor W(CO)₆ into the MBE chamber. We developed a precursor inlet system consisting of a precision dosage valve, a nozzle to direct precursor into the substrate, and localized heating to steer precursor condensation and effusion on the way into the deposition chamber. Using mass spectrometry, we observe the precursor decomposing into its fundamental components.

[1] S. Tiefenbach et. al., Surf Sci. 318, L1161 (1994)