Ultrathin Films of VO₂ on r-Cut Sapphire Achieved by Postdeposition Etching

Abstract

The metal-insulator transition (MIT) properties of correlated oxides thin films, such as VO2, are dramatically affected by strain induced at the interface with the substrate, which usually changes with deposition thickness. For VO2 grown on r-cut sapphire, there is a minimum deposition thickness required for a significant MIT to appear, around 60 nm. We show that in these thicker films an interface layer develops, which accompanies the relaxation of film strain and enhanced electronic transition. If these interface dislocations are stable at room temperature, we conjectured, a new route opens to control thickness of VO2 films by postdeposition thinning of relaxed films, overcoming the need for thickness-dependent strain-engineered substrates. This is possible only if thinning does not alter the films' electronic properties. We find that wet etching in a dilute NaOH solution can effectively thin the VO2 films, which continue to show a significant MIT, even when etched to 10 nm, for which directly deposited films show nearly no transition. The structural and chemical composition were not modified by the etching, but the grain size and film roughness were, which modified the hysteresis width and magnitude of the MIT resistance change.

An Invariable Temperature during the Phase Transition of W Doped VO2 Film

“…According to the reports, this kind of shift originated from the lattice mismatch between the M‐VO 2 (020) and sapphire (0001) planes. For example, the size (25.61 Å 2 ) of the repeat unit in sapphire (0001) is smaller than that (25.97 Å 2 ) of M‐VO 2 (020) …”

Heterogeneous integration of single-crystalline rutile nanomembranes with steep phase transition on silicon substrates

“…By contrast, the freestanding NM was chemically released from the substrate by selective etching of sacrificial layers 18 , 19 , 21 ; these chemical lift-off methods are less destructive than physical methods. However, the harsh wet condition with a strong acid or base etchant typically leaves roughening and residue on the host substrates or released membrane after the chemical etch 23 , 24 . Recently, atomically thin perovskite oxide NM was gently released by dissolving water-soluble Sr 3 Al 2 O 6 sacrificial layers 11 , but the moisture-sensitive nature of these layers prevents long-time exposure of the sacrificial layers, which restricts practical application for heterogeneous integration of oxide NM.…”

High-performance thermal sensitive VO2(B) thin films prepared by sputtering with TiO2(A) buffer layer and first-principles calculations study

“…Vanadium dioxide (VO 2 ) is an abundant and polymorphous compound with fascinating thermal, electrical and optical properties. [1][2][3] It has been reported that there are at least six polymorphs for VO 2 , among which the rutile VO 2 (R) 4 and monoclinic VO 2 (M) 5 phases are stable structures, while the tetragonal VO 2 (A), 6 monoclinic VO 2 (B), 7 monoclinic VO 2 (D) 8 and paramontroseite VO 2 (P) 9 are metastable phases. As we all know, VO 2 must change its resistance with temperature, and the temperature coefficient of resistance (TCR) (b ¼ (1/R)vR/vT) charactering such a change should be sufficiently high; here b is the TCR, R is the resistance and T is the temperature of VO 2 lm.…”