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We comprehensively explored the impact of RF magnetron sputtering conditions on the physical properties of CdS thin films for the first time. Structural, morphological, and compositional properties were altered to a great extent by the sputtering conditions. Very high average transmittances of 94%, 92.5%, 91% and 89% were achieved in CdS thin films with thicknesses of 40, 60, 80, and 100 nm, respectively. A 100-nm thick CdS thin film showed an excessively high mobility of 92 cm2/V·s with an optimum carrier concentration of 1017 cm−3 and resistivity of 103 Ω·cm. An ultra-thin CdTe film (480 nm) with a smooth and crack-free surface was achieved with RF magnetron sputtering. As proof of concept, ultra-thin CdTe solar cells were fabricated by incorporating CdS thin films with thicknesses varying from 40 to 100 nm, and the power conversion efficiency was enhanced from 1.18% to 4.13%, respectively. This work highlights the importance of investigating sputtering conditions to achieve CdS with superior physical properties and enhance ultra-thin CdTe solar cell performance.

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.

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).

Zinc oxide (ZnO) thin films were deposited on soda lime glass substrates by the ultrasonic spray pyrolysis technique (USP), starting from zinc acetylacetonate. A novelty process was implemented to the Zn precursor, previous to the solution preparation, namely, the Zn precursor was milled in a planetary ball milling equipment at different speed and time conditions, in order to generate new chemical species. The starting solutions were prepared by dissolving the milled precursor in a mix of methanol, acetic acid, and water. ZnO thin films were deposited at different substrate temperatures, 375, 400 and 450 °C and constant deposition time, 6 min. Sprayed ZnO films were characterized by X-ray diffraction, XRD, UV–Vis spectrophotometry and scanning electron microscopy, SEM. All films presented a wurtzite hexagonal phase confirmed from XRD, and corroborated by SEM analysis. Films exhibited a maximum optical transmittance oscillating between 80 and 85%. A band gap varying between 3.3 and 3.4 eV was estimated from the transmittance spectra. The photocatalytic response of ZnO thin films was tested by monitoring the bleaching of methylene blue (MB) dye at different time periods, under UV light irradiation. It was observed an increase in the degradation performance of the dye in all the films deposited from milled precursor, as compared with those deposited from unmilled precursor, since the MB degradation increased from 40 to 99% in 3 h. Novel mechanochemical process implemented to conventional chemical techniques enhanced the photocatalytic response of ZnO films.

In this work, we have studied the effect of aluminium dopant precursor type and doping concentration on the structural, morphological, optical and electrical properties of Al and In co-doped zinc oxide (AIZO) thin films deposited by ultrasonic spray pyrolysis. Zinc acetate dihydrate and indium acetate were used as zinc and indium precursors, respectively. Aluminium chloride and aluminium sulphate were used as aluminium precursors. The doping concentrations of Al (1 to 3 at%) and In (1 to 3 at%), were varied equally and the physical properties were analyzed. X-ray diffraction examinations confirmed that AIZO films were poly crystalline and grown as a hexagonal wurtzite structure. Scanning electron microscopy observations revealed that thin films were grown with different types of hexagonal nanostructures. From the optical and electrical measurements, the figure of merit was estimated. The values were 4.09 × 10− 3/Ω and 0.75 × 10− 3/Ω for the AIZO thin films deposited using aluminium chloride and aluminium sulphate respectively.

Indium and gallium co-doped zinc oxide (IGZO) thin films were deposited on glass substrates by ultrasonic spray pyrolysis . Physical properties such as structural, morphological, optical and electrical properties were examined on IGZO thin films with respect to the changes in the substrate temperature (425, 450 and 475 °C). Structural results showed that IGZO films were crystalline and presented hexagonal wurtzite structure. Morphological studies proved that the substrate temperature changed the sizes of hexagonal nanostructures of IGZO. Optical transmittance in the UV–vis region and electrical measurements confirmed that IGZO films were transparent (>70%) with a minimum electrical resistivity ~10.5×10 −3 Ω cm.

In this work, we report the effect of deposition time on the physical properties such as structural, morphological, optical and electrical properties of aluminium and indium co-doped ZnO (AIZO) thin films. AIZO films were deposited by ultrasonic spray pyrolysis technique on glass substrates at different deposition times (10, 12 and 15 min) using ball milled zinc precursor. A change in crystalline nature was observed from structural analysis with respect to growth time. AIZO thin films with hexagonal nanostructures and optical transmittance higher than 70% were confirmed from the morphological and optical studies. AIZO films showed an electrical resistivity varying in the range of 2.35–4.59×10−3 Ω cm. Finally, when we compared these results with AIZO films deposited using unmilled zinc precursor; we found that ball milling the precursor has a beneficial effect in enhancing the physical properties.

In this work, we reported a chemical approach to prepare aluminium and indium co-doped ZnO thin films (AIZO) by ultrasonic spray pyrolysis. Film depositions were carried out on soda lime glass substrates at 425 °C by using a spray solution containing zinc acetate as zinc precursor, aluminium acetylacetonate as Al dopant source and indium (III) acetate as In dopant source. Physical properties such as structural, morphological, optical and electrical properties were studied with respect to the equal variations in co-dopants concentration (0.5–3 at%). X-ray diffraction patterns proved that films are poly crystalline with (002) preferential orientation. Scanning electron microscopy analysis showed that AIZO films grown like hexagonal nanopyramids, elongated grains and irregular trigonals. Optical transmittance ~85% and a minimum resistivity of 1.3×10−3 Ω cm, are achieved for films when co-doped with 1.5 at% of Al and 1.5 at% of In, confirm that AIZO films are suitable for transparent conductive oxide (TCO) applications.

Undoped zinc oxide (ZnO) thin films were reactively deposited on soda-lime glass substrates by radio frequency (rf) sputtering at room temperature. We have studied the importance of substrate rotation speed on the structural, optical and morphological properties. The rotation speeds used were 0, 20, 40, 60, and 80 rpm. The XRD measurements confirmed that films were grown with (002) plane preferential orientation. The average transmittance was above 90% in the UV–vis region. The SEM images revealed that films deposited with substrate rotation are more homogeneous than the films deposited without rotation.

In this letter, we have reported a cost-effective thin film of zinc oxide (ZnO) sensor for propane gas detection. ZnO thin films were deposited on soda lime glass by ultrasonic spray pyrolysis using zinc acetylacetonate as a precursor in the starting solution. Thin film deposition was carried out at 450 °C, by varying the water content in the spraying (starting) solution. Structural, morphological, and gas sensing properties were studied in detail. Variations in the water content resulted change in crystallinity, geometries, and gas sensitivity. ZnO thin film exhibited maximum sensitivity ~7, when measured at 100 °C.

Aluminum doped zinc oxide (ZnO:Al) thin films were deposited on soda-lime glass substrates by the chemical spray technique. The atomization of the solution was carried out by ultrasonic excitation. Six different starting solutions from both unmilled and milled Zn and Al precursors, dissolved in a mix of methanol and acetic acid, were prepared. The milling process was carried out using a planetary ball mill at a speed of 300 rpm, and different milling times, namely, 15, 25, 35, 45, and 60 min. Molar concentration, [Al]/[Zn] atomic ratio, deposition temperature and time, were kept at constant values; 0.2 M, 3 at.%, 475 °C, and 10 min, respectively. Results show that, under the same deposition conditions, electrical resistivities of ZnO:Al thin films deposited from milled precursors are lower than those obtained for films deposited from unmilled precursors. X-ray diffraction analysis revealed that all films display a polycrystalline structure, fitting well with the hexagonal wurtzite structure. Changes in surface morphology were observed by scanning electron microscopy (SEM) as well, since films deposited from unmilled precursors show triangular shaped grains, in contrast to films deposited from 15 and 35 min milled precursors that display thin slices with hexagonal shapes. The use of milled precursors to prepare starting solutions for depositing ZnO:Al thin films by ultrasonic pyrolysis influences their physical properties.

Indium doped zinc oxide [ZnO:In] thin films have been deposited at 430°C on soda-lime glass substrates by the chemical spray technique, starting from zinc acetate and indium acetate. Pulverization of the solution was done by ultrasonic excitation. The variations in the electrical, structural, optical, and morphological characteristics of ZnO:In thin films, as a function of both the water content in the starting solution and the substrate temperature, were studied. The electrical resistivity of ZnO:In thin films is not significantly affected with the increase in the water content, up to 200 mL/L; further increase in water content causes an increase in the resistivity of the films. All films show a polycrystalline character, fitting well with the hexagonal ZnO wurtzite-type structure. No preferential growth in samples deposited with the lowest water content was observed, whereas an increase in water content gave rise to a (002) growth. The surface morphology of the films shows a consistency with structure results, as non-geometrical shaped round grains were observed in the case of films deposited with the lowest water content, whereas hexagonal slices, with a wide size distribution were observed in the other cases. In addition, films deposited with the highest water content show a narrow size distribution.

Fluorine doped tin oxide, SnO2:F, thin films were deposited by ultrasonic chemical spray starting from tin chloride and hydrofluoric acid. The physical characteristics of the films as a function of both water content in the starting solution and substrate temperature were studied. The film structure was polycrystalline in all cases, showing that the intensity of (200) peak increased with the water content in the starting solution. The electrical resistivity decreased with the water content, reaching a minimum value, in the order of 8 × 10-4 Ωcm, for films deposited at 450℃ from a starting solution with a water content of 10 ml per 100 ml of solution; further increase in water content increased the corresponding resistivity. Optical transmittances of SnO2:F films were high, in the order of 75%, and the band gap values oscillated around 3.9 eV. SEM analysis showed uniform surface morphologies with different geometries depending on the deposition conditions. Composition analysis showed a stoichiometric compound with a [Sn/O] ratio around 1:2 in all samples. The presence of F into the SnO2 lattice was detected, within 2 at % respect to Sn.

The physical properties and the effect of effective surface area (ESA) on the sensing properties of tin dioxide [SnO2] thin films in air and propane [C3H8] atmosphere as a function of operating temperature and gas concentration have been studied in this paper. SnO2 thin films with different estimated thicknesses (50, 100 and 200 nm) were deposited on glass substrates by the chemical spray technique. Besides, they were prepared at two different deposition temperatures (400 and 475 °C). Tin chloride [SnCl4 · 5H2O] with 0.2 M concentration value and ethanol [C2H6O] were used as tin precursor and solvent, respectively. The morphological, and structural properties of the as-prepared films were analyzed by AFM and XRD, respectively. Gas sensing characteristics of SnO2 thin solid films were measured at operating temperatures of 22, 100, 200, and 300 °C, and at propane concentration levels (0, 5, 50, 100, 200, 300, 400, and 500 ppm). ESA values were calculated for each sample. It was found that the ESA increased with the increasing thickness of the films. The results demonstrated the importance of the achieving of a large effective surface area for improving gas sensing performance. SnO2 thin films deposited by spray chemical were chosen to study the ESA effect on gas sensing properties because their very rough surfaces were appropriate for this application.

A study on the propane gas-sensing properties of Cu-doped ZnO thin films is presented in this work. The films were deposited on glass substrates by sol-gel and dip coating methods, using zinc acetate as a zinc precursor, copper acetate and copper chloride as precursors for doping. For higher sensitivity values, two film thickness values are controlled by the six and eight dippings, whereas for doping, three dippings were used, irrespective of the Cu precursor. The film structure was analyzed by X-ray diffractometry, and the analysis of the surface morphology and film composition was made through scanning electron microscopy (SEM) and secondary ion mass spectroscopy (SIMS), respectively. The sensing properties of Cu-doped ZnO thin films were then characterized in a propane atmosphere, C₃H₈, at different concentration levels and different operation temperatures of 100, 200 and 300 °C. Cu-doped ZnO films doped with copper chloride presented the highest sensitivity of approximately 6 × 10⁴, confirming a strong dependence on the dopant precursor type. The results obtained in this work show that the use of Cu as a dopant in ZnO films processed by sol-gel produces excellent catalysts for sensing C₃H₈ gas.