The parameters of reactive pulsed laser deposition were successfully optimized for fabrication of vanadium dioxide thin films. It is observed that the O2 concentration in Ar gas and the total deposition pressure are critical in stabilizing the single VO2 phase. Thermochromic VO2 and V1−xWxO2 (x=0.014) thin films were synthesized on various substrates (silicon, quartz, and sapphire) at 5% of O2/Ar ratio gas and total pressure of 90 mTorr. The structural properties of the deposited films were analyzed by x-ray diffraction, while their semiconductor-to-metal phase transitions were studied by electrical resistivity using the four-point technique and infrared transmittance from room temperature up to 100 °C. The observed transition temperature was about 36 °C for W-doped VO2 compared to 68 °C for VO2 films. This transition temperature was then lowered by about 22.85 °C per 1 at. % of W added. The temperature coefficient of resistance was about 1.78%/°C for VO2 and about 1.90%/°C for W-doped VO2. Using the pump-probe experiment, the application of these thermochromic films as optical switches was demonstrated at the wavelength of 1.55 μm. The transmission switching was about 25 dB for VO2 and 28 dB for W-doped VO2. In addition, application of VO2 on optical fiber components was demonstrated by direct VO2 coating on the end faces of cleaved single mode optical fibers and optical fiber connectors.

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Thermochromic La1−xSrxMnO3 (x=0.1, 0.175, and 0.3) (LSMO) smart coatings were synthesized on (100) silicon and (0001) sapphire substrates by means of reactive pulsed laser deposition process at relatively low substrate temperature (500°C) and without postannealing. X-ray diffraction patterns indicated that all deposited LSMO films have polycrystalline structures. The energy dispersive x-ray spectroscopy analysis indicated approximately the same La∕Sr ratio in the formed LSMO coatings as in their corresponding targets. While, the x-ray photoelectron spectroscopy analysis of the LSMO/sapphire revealed that the strontium segregate at the film surface. The thermochromism of LSMO coatings was investigated by measuring their infrared reflectance as a function of temperature (up to 160°C). It was observed that the reflectance decreased as the temperature increased. Reflectance switching of about 25% was achieved in La0.7Sr0.3MnO3∕Si at a wavelength of 5μm. The sheet electrical resistivity as a function of temperature (up to 130°C) of LSMO/sapphire was investigated by means of the standard four-point probe technique. The resistivity decreased with increasing the temperature and no metallic-to-insulator transition was observed. However, it is found that the resistivity is very sensitive to the concentration level of Sr dopant: the resistivity decreased as the concentration of Sr increased. In addition, at room temperature, a higher temperature coefficient of resistance of −2.30%∕°C was achieved in La0.9Sr0.1MnO3 thin films. Finally, these LSMO smart coatings are promising materials for optical switching and IR uncooled bolometer devices.

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