Employing Ion-Beam Sputter Deposited TiO₂ Buffer Layers for VO₂-Related Devices

Vanadium dioxide (VO 2 ) is considered to be the most promising material for thermochromic smart windows due to its insulator-to-metal transition causing an abrupt change of transmittance near ambient temperature. TiO 2 buffer layers are expected to have a beneficial impact on the growth and performance of the functional VO 2 thin film, as they may induce crystallinity at lower growth temperatures and act as a barrier layer for ion diffusion from glass substrates. However, a systematic evaluation of TiO 2 buffer layers of different phases and thicknesses to assess potentially competing impacts is still lacking. Here, we grow TiO 2 buffer layers by ion-beam sputter deposition (IBSD) at different substrate temperatures to obtain amorphous TiO 2 as well as crystalline TiO 2 in the anatase and rutile phase, respectively. We investigate the buffer layers themselves and shed light on how these buffer layers influence the performance of the functional VO 2 layer grown on top by combining experimental and theoretical means. We find that the VO 2 ||TiO 2 interface is the most crucial part of the multilayer structure with an urgent need for minimum roughness. The two types of crystalline TiO 2 buffers yield similar results in terms of optical performance; however, we find that only rutile buffer layers significantly relieve the growth conditions needed.