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Template-Free Vapor-Phase Growth of Patrónite by Atomic Layer Deposition

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posted on 09.03.2017, 00:00 by Matthew S. Weimer, Robert F. McCarthy, Jonathan D. Emery, Michael J. Bedzyk, Fatih G. Sen, Alper Kinaci, Maria K. Y. Chan, Adam S. Hock, Alex B. F. Martinson
Despite challenges to control stoichiometry in the vanadium–sulfur system, template-free growth of patrónite, VS4, thin films is demonstrated for the first time. A novel atomic layer deposition (ALD) process enables the growth of phase pure films and the study of electrical and vibrational properties of the quasi-one-dimensional (1D) transition metal sulfide. Self-limiting surface chemistry during ALD of VS4 is established via in situ quartz crystal microbalance and quadrupole mass spectrometry between 150 and 200 °C. The V precursor, unconventionally, sheds all organic components in the first half-cycle, while the H2S half-cycle generates the disulfide dimer moiety, S2–2, and oxidizes V3+ to V4+. X-ray analysis establishes VS4 crystallinity and phase purity, as well as a self-limiting growth rate of 0.33 Å/cy, modest roughness of 2.4 nm, and expected density of 2.7 g/cm3. Phase pure films enable a new assignment of vibrational modes and corresponding Raman activity of VS4 that is corroborated by density functional theory (DFT) calculations. Finally, at elevated growth temperatures, a change in the surface mechanism provides a synthetic route to a second vanadium–sulfur phase, V2S3.