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Paracetamol-assisted zinc oxide (ZnO) highly porous micro-flakes were synthesized by a rapid two-step synthesis: precipitation (with sodium hydroxide) and calcination (at 250°C for 1 h). Addition of paracetamol during the synthesis not only inhibited the growth of ZnO grains but also originated self-assembly of the micro-flakes resulting in highly porous flower like structures. Increase in paracetamol concentration also increased porosity on ZnO microstructures due to the self-assembly of thinner flakes without any structural changes. X-ray diffraction (XRD) shows the preferential orientation of powders in the (101) direction of hexagonal structure. Raman spectra is dominated by E2 (high) optical mode due to vibration of oxygen atoms. Samples were tested for gas detection at 50, 100, 200, 400, 800 and 1000 (parts per million) PPM concentration of carbon dioxide (CO2). ZnO porous microstructures were obtained with a high concentration of paracetamol, enhancing the carbon dioxide sensing response from 20% to 90% with a response time of 60 s. These simple, low-cost and highly porous self-assembled ZnO structures with enhanced CO2 detection will be of interest for several researchers in the chemical sensor fabrication field.

Pure titanium dioxide (TiO2) thin films were deposited and investigated as gas sensors for carbon monoxide (CO) detection. TiO2 thin films were deposited by ultrasonic spray pyrolysis technique, starting from titanium(IV) oxyacetilacetonate, onto soda-lime glass substrates. Structural, morphological, and compositional properties of the TiO2 films were obtained utilizing X-ray diffractometry, energy dispersive X-ray, scanning electron microscopy, and secondary ion mass spectroscopy techniques, respectively. Films deposited above 400 °C were polycrystalline, and its X-ray pattern fit well to the TiO2 anatase structure, and no other phases were detected, whereas films deposited at lower temperatures presented an amorphous structure. The sensitivity of the TiO2 films is analyzed by varying both thickness and deposition temperature. In addition, the sensor response was measured for CO concentrations from 1 to 300 ppm at different operation temperatures, 100, 200, and 300 °C. The highest sensitivity (~ 300) was obtained for TiO2 thin films deposited with the lowest film thickness, at a substrate temperature of 350 °C. The results obtained in this work show that the TiO2 films processed by ultrasonic spray pyrolysis exhibit very promising results for detection of CO.

An enhancing awareness about the hazardous gaseous environment in the domestic and industrial sectors is on the rise across the globe. Thus, the necessity to efficiently detect and monitor the potentially hazardous gases, mainly that are toxic and flammable, is widely being researched. Propane, a liquefied petroleum gas (LPG), is highly inflammable and explosive when it comes in contact with an ignition source. Therefore, it is highly important to develop an upgraded propane gas sensor that could be used in various places such as household appliances, liquid natural gas (LNG) and petrochemical industry, automobile and aerospace industry, and relevant sectors where the propane is used. In the present work, ultrathin intrinsic zinc oxide (i-ZnO) films were deposited by the radio frequency (RF) sputtering technique at various working pressures (2–8 mTorr) at constant 100 W for gas sensing applications. Thus, deposited films were characterized by various techniques such as X-ray diffractometry (XRD), field-emission scanning electron microscopy (FESEM), ultra-violet spectrophotometry (UV–Vis), and finally by a gas sensing technique for their structural, morphological, optical, and sensing characteristics. XRD pattern confirms the formation of hexagonal phase of ZnO with a preferred orientation along the (002) plane. The bandgap of the deposited films was determined to be between 3.19 and 3.21 eV as measured from UV–Vis spectra. The scanning electron micrographs revealed the formation of vertically aligned and cross-linked nanowall structures at lower working pressures. Finally, the gas sensing properties of the films were exclusively studied, at various operating temperatures (100, 200, and 300 °C), for different propane gas concentrations. The film deposited at 2 mTorr exhibited a gas sensitivity of 0.998 and almost equal to 30 s of response time and 35 s of recovery time at an operating temperature of 300 °C for the propane gas concentration of 500 ppm, which implies the potentiality of using this film as a propane gas sensor.

Aluminium and indium co-doped zinc oxide (AIZO) thin films were deposited using ultrasonic spray pyrolysis. Depositions were performed by varying the acetic acid and water content in the spraying solution which resulted in the formation of different nanostructures like hexagons, flowers, chisels, curved nanostructures, hexagonal pyramids, super grown hexagons, and inter-connected nanostructures. Further, the physical properties such as structural, optical, electrical, and surface texture parameters were examined. The structural studies showed that films were of crystalline nature, with different crystallite sizes and grown with a preferential orientation along (002) plane. The optical transmittance assessments proved that films were highly transparent (> 80%) in the visible region. The electrical sheet resistance was found to be in the range 29–1K Ω/□. Surface parameters like average roughness, root mean square roughness, and peak-valley height values helped to understand the homogeneity of the thin films. Finally, the suitability of AIZO films for transparent conductive oxide applications were tested by estimating the figure of merit (FOM). Among the different solution conditions, films fabricated using a starting solution containing 25 ml of acetic acid and 25 ml of water exhibited the lowest resistivity (2.47 ± 0.03 × 10−3 Ω-cm) along with the highest FOM (5.83 ± 0.42 × 10−3/Ω).