Interplay between boron doping and epitaxial relationships in VO2 films grown by laser ablation

We investigated the effect of boron doping on the functional and structural properties of VO2 thin films. Temperature-dependent measurements were performed on pure and boron-doped (0.5 and 1.3 at.%) VO2 films grown on Al2O3(0001) by Reactive Pulsed Laser Deposition. The transition temperature is initially reduced by the insertion of boron; decreasing from ca. 346 K in the case of the pure sample to 335 K for a 0.5 at.% boron amount. Further increase of the boron concentration leads to a slight decrease of the transition temperature (−2 K), a significantly broader hysteresis loop and a reduced resistivity contrast (less than 3 orders of magnitude). Raman spectroscopy and high-resolution X-ray diffraction were performed to elucidate the nature of the involved phases and their structure. A correlation was found between increasing the boron concentration and the formation of two peculiar in-plane epitaxial relationships, the VO2 films evolving from one to the other. We also evidenced the presence of the transient M2 phase in the highest doped sample.