Highly sensitive large-scale tin oxide (SnO2) nanostructures were grown on a glass substrate by thermal evaporation of a mixture of anhydrous tin (II) chloride (SnCl2) and zinc chloride (ZnCl2) powders at 550°C in air. We demonstrate a single cell vapor deposition system to precisely control nanostructural morphology of SnO2 by changing the weight ratio of SnCl2 and ZnCl2 and growth temperature. The morphology and structural property of as-grown nanostructures were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The SEM images revealed that the SnO2 nanostructures with different densities, sizes, and shapes can be achieved by adjusting the weight ratio of SnCl2 and ZnCl2. A thin film gas sensor based on SnO2 nanostructures with diameter ∼20 nm and length ∼100 nm showed ∼85% sensitivity and 53 seconds of response time, whereas the nanorods with diameter ∼100 nm and length ∼ 1μm showed ∼50% sensitivity with 198 seconds response time. The nanostructured material with small size and shape showed better sensitivity on sensing at room temperature compared to previously reported SnO2 based sensors.

One of the ways to mitigate the world energy crisis is to harvest clean and green energy from waste-heat, which is abundant, ubiquitous, and free. Energy harvesting of this waste-heat is one of the most encouraging methods to capture freely accessible electrical energy. Ferroelectric materials can be used to harvest energy for low power electronic devices, as they exhibit switchable polarization, excellent piezoelectric and pyroelectric properties. The most important characteristic of ferroelectric materials, in the context of energy harvesting, is their ability to generate electric power from a time-dependent temperature change. In this work, we grew highly c-axis oriented heterostructures of BaZr0.2Ti0.8O3 (barium zirconium titanate, BZT)/Ba0.7Ca0.3TiO3 (barium calcium titanate, BCT) on SrRuO3 (strontium ruthenate, SRO) and deposited on SrTiO3 (strontium titanate, STO) single crystalline substrate using pulsed laser deposition (PLD) technique. We investigated the structural, electrical, dielectric, and pyroelectric properties of the above-mentioned fabricated heterostructures. The wide range of θ–2θ X-ray diffraction (XRD) patterns only shows (00l) reflection peaks of heterostructures and the substrate which confirmed that the films are highly c-axis oriented. We are also capable to convert the low-grade waste-heat into electrical energy by measuring various temperature-dependent ferroelectric hysteresis loops of our nanostructure films via pyroelectric Ericsson cycles and the structures show an energy conversion density ~ 10,970 kJ/m3 per cycle. These devices exhibit a large pyroelectric current density of ~ 25 mA/m2 with 11.8 °C of temperature fluctuation and the corresponding pyroelectric coefficient of 3425 μC/m2K. Our research findings suggest that these lead-free relaxor-ferroelectric heterostructures might be the potential candidates to harvest electrical energy from waste low-grade thermal energy.

The metal-to-insulator transition (MIT) closest to room temperature of 68-70 °C as shown by vanadium oxide (Vo 2), compared with other transition metal oxides, makes it a potential candidate for smart window coating. We have successfully fabricated a potential smart window device after the optimum design of a multilayered thin film structure made out of transparent conducting oxide (aluminum doped zinc oxide) and pure Vo 2 using pulsed laser deposition technique. This comprehensive study is based on two different configurations for multi-layered structure approach, with the intention to reduce the transition temperature, as well as to maintain the Mit properties that would strengthen the potential of the structure to be used for a smart window device. By creating a multi-layered structure, we were able to create a low powered device that can operate less than 15 V that leads to significant decline in the infrared transmission by a magnitude of over 40% and provided sufficient heat to trigger the MIT at a temperature around 60 °C, which is almost 10 °C lower than its bulk counterpart. This finding would positively impact the research on Vo 2 thin films, not only as smart windows but also for numerous other applications like bolometers, infrared detectors, Mott transistors and many more.

The addition of suitable metallic dopants into the indium or zinc oxide matrix is essential to obtain transparent conducting oxide (TCO) thin films for high-performance optoelectronics devices. However, scarcity of indium is one of the major challenges for the common use of indium doped tin oxide (ITO) as a TCO material for future state-of-the-art devices. To overcome the challenge, doped zinc oxide is used an alternative material for traditional ITO and retains both high transparency and electrical conductivity. One such potential material is gallium-doped zinc oxide (GZO). GZO thin films were deposited onto glass as well as Kapton substrates using the pulsed laser deposition technique. Structural, optical, and electro-thermal properties of these films were studied to assess the performance of the films as thin-film transparent heaters. The samples show a good transmittance value greater than 85% in the visible range of the electromagnetic spectrum. At room temperature, the electrical resistivity of GZO films showed a value of 110.46 × 10−4 Ω cm on glass and 2.90 × 10−4 Ω cm on the Kapton substrate, followed by a Joule heating effect, with temperatures reaching more than 120 °C at an applied voltage of ∼12 V. This high transparency, cost-effectiveness, low sheet resistance, and small surface roughness make GZO a unique and potential candidate for various practical applications not only as a transparent electrode but also as an indium free thin-film transparent heater and an affordable transparent conducting oxide in displays.

Vanadium oxide (VO2) thin films have drawn significant research and development interest in recent years because of their intriguing physical origin and wide range of functionalities useful for many potential applications, including infrared imaging, smart windows, and energy and information technologies. However, the growth of highly epitaxial films of VO2, with a sharp and distinct controllable transition, has remained a challenge. Here, we report the structural and electronic properties of high quality and reproducible epitaxial thin films of VO2, grown on c-axis oriented sapphire substrates using pulsed laser deposition at different deposition pressures and temperatures, followed by various annealing schedules. Our results demonstrate that the annealing of epitaxial VO2 films significantly enhances the Semiconductor to Metal Transition (SMT) to that of bulk VO2 transition. The effect of oxygen partial pressure during the growth of VO2 films creates a significant modulation of the SMT from around room temperature to as high as the theoretical value of 68 °C. We obtained a bulk order transition ≥104 while reducing the transition temperature close to 60 °C, which is comparatively less than the theoretical value of 68 °C, demonstrating a clear and drastic improvement in the SMT switching characteristics. The results reported here will open the door to fundamental studies of VO2, along with tuning of the transition temperatures for potential applications for multifunctional devices.