Transparent all-oxide hybrid NiON/TiO2 heterostructure for optoelectronic applications

Nickel oxide (NiO) is a p-type oxide and nitrogen is one of the dopants used for modifying its properties. Until now, nitrogen-doped NiO has shown inferior optical and electrical properties than those of pure NiO. In this work, we present nitrogen-doped NiO (NiO:N) thin films with enhanced properties compared to those of the undoped NiO thin film. The NiO:N films were grown at room temperature by sputtering using a plasma containing 50% Ar and 50% (O2 + N2) gases. The undoped NiO film was oxygen-rich, single-phase cubic NiO, having a transmittance of less than 20%. Upon doping with nitrogen, the films became more transparent (around 65%), had a wide direct band gap (up to 3.67 eV) and showed clear evidence of indirect band gap, 2.50–2.72 eV, depending on %(O2-N2) in plasma. The changes in the properties of the films such as structural disorder, energy band gap, Urbach states and resistivity were correlated with the incorporation of nitrogen in their structure. The optimum NiO:N film was used to form a diode with spin-coated, mesoporous on top of a compact, TiO2 film. The hybrid NiO:N/TiO2 heterojunction was transparent showing good output characteristics, as deduced using both I-V and Cheung’s methods, which were further improved upon thermal treatment. Transparent NiO:N films can be realized for all-oxide flexible optoelectronic devices

An assessment of sputtered nitrogen-doped nickel oxide for all-oxide transparent optoelectronic applications: The case of hybrid NiO:N/TiO2 heterostructure

ransition metal oxides present a unique category of materials due to their versatile optical, electrical and mechanical properties. Nickel oxide (NiO) is an intrinsic p-type oxide semiconductor. P-NiO with controllable and reproducible physico-chemical properties, if combined with transparency and low temperature (low-T) fabrication processes, can be fully exploited in many transparent and/or flexible devices for applications, like energy management (production, manipulation, storage), sensing, wearable and health care electronics, etc. Reproducibility, transparency and low-T fabrication processes of p-type NiO are the motivation of this work. Nitrogen is one of the dopants used for modifying the properties of NiO. Until now, nitrogen-doped NiO, has shown inferior properties than those of pure NiO. In this work, we present nitrogen-doped NiO (NiO:N) thin films with enhanced properties compared to those of the undoped NiO. The NiO:N films were grown by sputtering on room-temperature substrates in plasma containing 50% Ar and 50% (O2+N2) gases. The undoped NiO film was oxygen-rich, single-phase cubic NiO, having transmittance less than 20%. Upon doping with nitrogen, the films became more transparent (around 65%), had a wide direct band gap (up to 3.67 eV) and showed clear evidence of indirect band gap, 2.50-2.72 eV, depending on %(O2-N2) in plasma. The changes in the properties of the films such as structural disorder, energy band gap, Urbach states and resistivity were correlated with the incorporation of nitrogen in their structure. The optimum NiO:N film was used to form a diode with spin-coated, mesoporous on top of a compact, TiO2 film. The hybrid NiO:N/TiO2 heterojunction was transparent showing good output characteristics, as deduced using both I-V and Cheung’s methods. The diode’s transparency and characteristics were further enhanced upon thermal treatment and this was attributed to improved NiO:N properties with annealing. Transparent NiO:N films can be realized for all-oxide flexible optoelectronic devices

Study on the Ozone Gas Sensing Properties of rf-Sputtered Al-Doped NiO Films

Al-doped NiO (NiO:Al) has attracted the interest of researchers due to its excellent optical and electrical properties. In this work, NiO:Al films were deposited on glass substrates by the radio frequencies (rf) sputtering technique at room temperature and they were tested against ozone gas. The Oxygen content in (Ar-O2) plasma was varied from 2% to 4% in order to examine its effect on the gas sensing performance of the films. The thickness of the films was between 160.3 nm and 167.5 nm, while the Al content was found to be between 5.3 at% and 6.7 at%, depending on the oxygen content in plasma. It was found that NiO:Al films grown with 4% O2 in plasma were able to detect 60 ppb of ozone with a sensitivity of 3.18% at room temperature, while the detection limit was further decreased to 10 ppb, with a sensitivity of 2.54%, at 80 °C, which was the optimum operating temperature for these films. In addition, the films prepared in 4% O2 in plasma had lower response and recovery time compared to those grown with lower O2 content in plasma. Finally, the role of the operating temperature on the gas sensing properties of the NiO:Al films was investigated

Thermochromic Behavior of VO2/Polymer Nanocomposites for Energy Saving Coatings

Vanadium dioxide (VO2) is a well-known thermochromic material that can potentially be used as a smart coating on glazing systems in order to regulate the internal temperature of buildings. Most growth techniques for VO2 demand high temperatures (>250 °C), making it impossible to comply with flexible (polymeric) substrates. To overcome this problem, hydrothermally synthesized VO2 particles may be dispersed in an appropriate matrix, leading to a thermochromic coating that can be applied on a substrate at a low temperature (<100 °C). In this work, we reported on the thermochromic properties of a VO2/Poly-Vinyl-Pyrrolidone (PVP) nanocomposite. More specifically, a fixed amount of VO2 particles was dispersed in different PVP quantities forming hybrids of various VO2/PVP molar ratios which were deposited as films on fused silica glass substrates by utilizing the drop-casting method. The crystallite size was calculated and found to be 35 nm, almost independent of the PVP concentration. As far as the thermochromic characteristics are concerned, the molar ratio of the VO2/PVP nanocomposite producing VO2 films with the optimum thermochromic properties was 0.8. These films exhibited integral solar transmittance modulation (overall wavelengths) ΔTrsol = 0.35%–1.7%, infrared (IR) switching at 2000 nm ΔTrIR = 10%, visible transmittance at 550 nm TrVis = 38%, critical transition temperature TC = 66.8 °C, and width of transmittance hysteresis loop ΔTC = 6.8 °C. Moreover, the critical transition temperature was observed to slightly shift depending on the VO2/PVP molar ratio

Investigation of the Effects of Rapid Thermal Annealing on the Electron Transport Mechanism in Nitrogen-Doped ZnO Thin Films Grown by RF Magnetron Sputtering

Nitrogen-doped ZnO (ZnO:N) thin films, deposited on Si(100) substrates by RF magnetron sputtering in a gas mixture of argon, oxygen, and nitrogen at different ratios followed by Rapid Thermal Annealing (RTA) at 400 °C and 550 °C, were studied in the present work. Raman and photoluminescence spectroscopic analyses showed that introduction of N into the ZnO matrix generated defects related to oxygen and zinc vacancies and interstitials. These defects were deep levels which contributed to the electron transport properties of the ZnO:N films, studied by analyzing the current–voltage characteristics of metal–insulator–semiconductor structures with ZnO:N films, measured at 298 and 77 K. At the appliedtechnological conditions of deposition and subsequent RTA at 400 °C n-type ZnO:N films were formed, while RTA at 550 °C transformed the n-ZnO:N films to p-ZnO:N ones. The charge transport in both types of ZnO:N films was carried out via deep levels in the ZnO energy gap. The density of the deep levels was in the order of 1019 cm−3. In the temperature range of 77–298 K, the electron transport mechanism in the ZnO:N films was predominantly intertrap tunneling, but thermally activated hopping also took place