Growth of vanadium dioxide thin films on hexagonal boron nitride flakes as transferrable substrates.

Vanadium dioxide (VO) is an archetypal metal-insulator transition (MIT) material, which has been known for decades to show an orders-of-magnitude change in resistivity across the critical temperature of approximately 340 K. In recent years, VO has attracted increasing interest for electronic and photonic applications, along with advancement in thin film growth techniques. Previously, thin films of VO were commonly grown on rigid substrates such as crystalline oxides and bulk semiconductors, but the use of transferrable materials as the growth substrates can provide versatility in applications, including transparent and flexible devices. Here, we employ single-crystalline hexagonal boron nitride (hBN), which is an insulating layered material, as a substrate for VO thin film growth. VO thin films in the polycrystalline form are grown onto hBN thin flakes exfoliated onto silicon (Si) with a thermal oxide, with grains reaching up-to a micrometer in size. The VO grains on hBN are orientated preferentially with the (110) surface of the rutile structure, which is the most energetically favorable. The VO film on hBN shows a MIT at approximately 340 K, across which the resistivity changes by nearly three orders of magnitude, comparable to VO films grown on common substrates such as sapphire and titanium dioxide. The VO/hBN stack can be picked up from the supporting Si and transferred onto arbitrary substrates, onto which VO thin films cannot be grown directly. Our results pave the way for new possibilities for practical and versatile applications of VO thin films in electronics and photonics.