Study on the Surface Morphology of Thermochromic Rf-Sputtered VO\({}_{2}\) Films Using Temperature-Dependent Atomic Force Microscopy  
[PERSON]  
1 Institute of Electronic Structure & Laser (IESL), Foundation for Research and Technology (FORTH) Hellas, P.O. Box 1385, 70013 Heraklion, Crete, Greece  
[PERSON]  
2 International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japan  
[PERSON]  
2 International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japan  
[PERSON]  
1 Institute of Electronic Structure & Laser (IESL), Foundation for Research and Technology (FORTH) Hellas, P.O. Box 1385, 70013 Heraklion, Crete, Greece  
[PERSON]  
1 Institute of Electronic Structure & Laser (IESL), Foundation for Research and Technology (FORTH) Hellas, P.O. Box 1385, 70013 Heraklion, Crete, Greece  
[PERSON]  
1 Institute of Electronic Structure & Laser (IESL), Foundation for Research and Technology (FORTH) Hellas, P.O. Box 1385, 70013 Heraklion, Crete, Greece  
[PERSON]  
1 Institute of Electronic Structure & Laser (IESL), Foundation for Research and Technology (FORTH) Hellas, P.O. Box 1385, 70013 Heraklion, Crete, Greece  
[PERSON]  
1 Institute of Electronic Structure & Laser (IESL), Foundation for Research and Technology (FORTH) Hellas, P.  
Furthermore, it is well known that the thermochromic parameters of VO\({}_{2}\) films, such as the critical transition temperature, the width of the transmittance hysteresis loop as well as the IR variation upon heating, are strongly affected by mechanical stress or strain effects that can be caused in the film structure as a result of doping [18; 19; 20], oxygen vacancies [21; 22] or the lattice mismatch between the film and the substrate due to different structures [23; 24]. In specific, by doping the VO\({}_{2}\) films with tungsten (W) atoms, a great decrease in the critical transition temperature is succeeded; however, their thermochricity is decreased [25; 26]. In contrast, structural defects caused by oxygen deficiency, according to the V-O system [27], low deposition temperature (<400 \({}^{\circ}\)C) [28] or the buffer layer [29; 30; 31; 32], leading to a reduced critical transition temperature, without affecting the IR variations (IR-switching). Thus, the growth parameters, as well as the substrate, play critical roles in the thermochromic behavior of VO\({}_{2}\) films. Various growth techniques such as rf or dc sputtering [33; 34], Pulsed Laser Deposition (PLD) [22], Atmospheric Pressure Chemical Vapor Deposition (APCVD) [35], sol-gel [36] and hydrothermal synthesis [37] have been used to synthesize thermochromic VO\({}_{2}\) films with low critical transition temperature as well as hysteresis width and with enhanced IR-switching. In addition, ZnO [38], SnO\({}_{2}\)[39], TiO\({}_{2}\)[40], Si\({}_{3}\)N\({}_{4}\)[28] and BN [41] are some of the materials that have been used as buffer layers in order to boost the thermochromic performance of VO\({}_{2}\) films that were deposited on them.  
In the present work, the effect of surface changes upon heating on the thermochromic performance of rf-sputtered VO\({}_{2}\) films was investigated using Temperature-dependent Atomic Force Microscopy (T-AFM). It should be noticed here that only a few works have been referred to in the literature concerning the application of the latter technique on VO\({}_{2}\) thermochromic films [42]. As a result, it was found a slight decrease in the RMS roughness of the films' surface upon heating, regardless of the substrate used, which can be ascribed to the phase transition between the monoclinic (for T \(<\) T\({}_{\text{C}}\)) phase and the rutile (for T \(>\) T\({}_{\text{C}}\)) one. Furthermore, all films appeared to have a reduced critical transition temperature compared to the pristine one, and IR-switching that was varied with the substrate and mean luminous transmittance was less than 40%.