Investigating Metal–Insulator Transition and Structural Phase Transformation in the (010)-VO2/(001)-YSZ Epitaxial Thin Films

Abstract

The VO2 thin films with sharp metal–insulator transition (MIT) were epitaxially grown on (001)-oriented Yttria-stabilized zirconia substrates (YSZ) using radio-frequency (RF) magnetron sputtering techniques. The MIT and structural phase transition (SPT) were comprehensively investigated under in situ temperature conditions. The amplitude of MIT is in the order of magnitude of 104, and critical temperature is 342 K during the heating cycle. It is interesting that both electron concentration and mobility are changed by two orders of magnitude across the MIT. This research is distinctively different from previous studies, which found that the electron concentration solely contributes to the amplitude of the MIT, although the electron mobility does not. Analysis of the SPT showed that the (010)-VO2/(001)-YSZ epitaxial thin film presents a special multi-domain structure, which is probably due to the symmetry matching and lattice mismatch between the VO2 and YSZ substrate. The VO2 film experiences the SPT from the M1 phase at low temperature to a rutile phase at a high temperature. Moreover, the SPT occurs at the same critical temperature as that of the MIT. This work may shed light on a new MIT behavior and may potentially pave the way for preparing high-quality VO2 thin films on cost-effective YSZ substrates for photoelectronic applications.

The Effect of Substrate Biasing during DC Magnetron Sputtering on the Quality of VO2 Thin Films and Their Insulator–Metal Transition Behavior

“…The phase inhomogeneity inVO 2 bulk or thin films limits their potential applications by rendering the MIT phase transition broad and diffusive [3,7]. The effects of strain, grain size, stoichiometry, substrate temperature, and substrate material have been extensively studied and optimized to achieve good crystallinity with a higher optical transmittance and a higher near-IR switching contrast [8,9,10,11,12,13,14,15]. In addition to optical transmittance and switching contrast enhancement, extensive efforts have been devoted to modifying the transition temperature ( T t ) of VO 2 .…”

Design and reactive magnetron sputtering of thermochromic coatings

“…There are several important achievements (how to achieve them is discussed below) to note: (i) There is a development trend characterized by a simultaneous enhancement of both T lum and ΔT sol , from, e.g., T lum ≈ 30% and ΔT sol ≈ 3%-4% (year 2003) 15 to, e.g., T lum ≈ 50% and ΔT sol ≈ 10% (year 2020). 40 It is also fair to mention the development in terms of ρ: the state-of-the-art Δlog ρ of sputtered VO 2 is ≈3.3 (only the transition in itself ) 17,19,22,27 or ≈4.0 (over the usual T m range, also including the conventional temperature dependence of the ρ of semiconductors). (ii) The state-of-the-art coatings exhibit a trade-off between T lum and ΔT sol (depending, e.g., on the VO 2 thickness); see the results of various laboratories along the line from T lum ≈ 35% and ΔT sol ≈ 14% through T lum ≈ 50% and ΔT sol ≈ 10% to T lum ≈ 60% and ΔT sol ≈ 6%.…”

“…Indeed, ZrO 2 layers are being increasingly applied in architectural glass as a protective overcoat for advanced low-emissivity stacks. 100 Furthermore, cubic yttria-stabilized ZrO 2 (YSZ) reportedly 27 constitutes an even better template than the usual monoclinic ZrO 2 , allowing the epitaxial growth of (010) VO 2 on (001) YSZ. The (001) orientation, despite its high surface energy, can be achieved by optimized ion bombardment.…”

“…[50][51][52] Reactive magnetron sputter deposition with its versatility and the potential of scaling up to large substrate sizes is probably the most important preparation technique of VO 2 -based thermochromic coatings. 7,8,53,54 The previous efforts utilized all main versions of this technique, ranging from frequently used dc sputtering, [2][3][4][5][6][7][8][9][10] rf sputtering, [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] and high-power impulse sputtering (HiPIMS) [30][31][32][33][34][35][36][37][38][39][40][41] to rf-superimposed dc sputtering, 42 inductively coupled plasma assisted sputtering,…”

Special Issue “Advances in Epitaxial Materials”-Editorial Preface

“…Photovoltaic applications are represented by polymorphism-based MOF (metalorganic frameworks) [ 8 ]. Many electronic devices, as memories, thermochromic smart windows, or Mott field effect transistors, are based on vanadium oxide, as described by Yuanjun Yang [ 9 ].…”