**Wen-Jen Lee \* and Yong-Han Chang**

Department of Applied Physics, National Pingtung University, Pingtung 90003, Taiwan; crocodile710280@gmail.com

**\*** Correspondence: wenjenlee@mail.nptu.edu.tw; Tel.: +886-8-7663800

Received: 18 October 2018; Accepted: 26 November 2018; Published: 27 November 2018 -

**Abstract:** Vanadium dioxide (VO2) is a multifunctional material with semiconductor-to-metal transition (SMT) property. Organic vanadium compounds are usually employed as ALD precursors to grow VO2 films. However, the as-deposited films are reported to have amorphous structure with no significant SMT property, therefore a postannealing process is necessary for converting the amorphous VO2 to crystalline VO2. In this study, an inorganic vanadium tetrachloride (VCl4) is used as an ALD precursor for the first time to grow VO2 films. The VO2 film is directly crystallized and grown on the substrate without any postannealing process. The VO2 film displays significant SMT behavior, which is verified by temperature-dependent Raman spectrometer and four-point-probing system. The results demonstrate that the VCl4 is suitably employed as a new ALD precursor to grow crystallized VO2 films. It can be reasonably imagined that the VCl4 can also be used to grow various directly crystallized vanadium oxides by controlling the ALD-process parameters.

**Keywords:** vanadium dioxide; atomic layer deposition; vanadium oxide; vanadium tetrachloride; semiconductor-to-metal transition
