Research on CuxTi1-xO2 Thin Films Acting as Buffer Layers for VO₂-Based Smart Window Applications (Raw data)

This folder contains the raw experimental data of Cu-doped TiO₂ thin films, which will be used for the writing and publication of my scientific paper. It also includes some optical data of VO₂ films grown on CuTiO₂ buffer layers. About experiment: The CuxTi1-xO2 layers were deposited by radio-freqency (RF) sputtering on quartz substrates (Suprasil). We used a 4-inch target of ceramics TiO2 at a distance of 4 inches from the substrate. In order to alloy the TiO2 thin films with Cu, several pure Cu lines were mounted onto the target manually. This combination allowed us to achieve CuTiO2 alloy with various Ti:Cu ratios and, thus, to deposit CuxTi1-xO2 thin films. All thin films were sputtered to obtain a thickness from 100 to 200 nm at 200°C to 400°C heater temperature. A mixture of Ar and O2 with a pressure of 3.4×10−3 mbar were used to generate the plasma. The O2 gas flux was varied between 0–3 sccm at a fixed Ar flux of 31 sccm. Anatase and rutile thin films were prepared by ion beam sputtering at room temperature and 560°C, respectively. VO2 thin films were prepared via RF sputtering using a 4-inch metallic vanadium target. The deposition temperature of the VO2 films was controlled within the range of 300°C to 400°C. The RF plasma was generated using a mixture of Ar and O2 gases at a pressure of 3.4×10−3 mbar. The gas flux ratio was set at 1.1 sccm for O2 and 31 sccm for Ar. All VO2 thin films had a thickness of 50 nm. The layer thicknesses and densities were analyzed with X-ray Reflection (XRR). The film structure was analyzed with Grazing-Incidence X-Ray Diffraction (GIXRD). In this mode of XRD, the X-rays are incident on the sample at a grazing angle, meaning they skim along the surface rather than striking it directly perpendicularly. Thus, this shallow angle enables an enhanced sensitivity to surface structures. Both, XRR and XRD, were performed using a Rigaku SmartLab diffractometer that operates a 9 kW rotating Cu anode. X-ray Photoelectron Spectroscopy (XPS) was employed for the comprehensive analysis of both the elemental composition within the film and the valence states inherent to each individual element. We used a PHI VersaProbe II spectrometer with a monochromated Al Kα (1486.6 eV) X-ray anode directed at 45° towards the surface normal. Charge compensation was achieved using a combination of an electron gun and an Ar+ ion gun. The samples were exposed to a focused Ar+ beam at an acceleration voltage of 1 kV to remove adsorbed impurities. Raman spectroscopy with 515 nm laser excitation and a spectral resolution of 1.5 cm−1 (Renishaw inVia Raman microscope system) was used for phase identification of the CuxTi1-xO2 and VO2 thin films, providing complementary confirmation to the findings obtained by XRD. A Zeiss-Merlin scanning electron microscope (SEM) equipped with an InLens detector was used for investigating the film morphology. Optical transmittance measurements were conducted using a PerkinElmer Lambda 900 UV–Vis–NIR spectrometer. For temperature-dependent measurements, a resistively heated sample holder, controlled by a Eurotherm heating controller and integrated with a Peltier cooling device, was used to achieve precise heating and cooling rates. A PT100 sensor was employed to monitor the sample's actual temperature. Optical simulations were conducted using the Essential MacLeod software, based on optical constants obtained from spectroscopic ellipsometry for all constituent layers, TiO2, VO2 and CuxTi1-xO2, respectively.

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Research on CuxTi1-xO2 Thin Films Acting as Buffer Layers for VO₂-Based Smart Window Applications (Raw data)

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