This work deals with the peculiarities of the growth of carbon nanotubes (CNTs) by radiofrequency (RF) magnetron sputtering and with the effect of deposition parameters on the RF sputtering. In the deposition process, a type of plasma gas, power of the RF generator, deposition time of catalysts, and a type of catalyst metals were modified to reveal the impact of these changes on the CNT's growth. The obtained nanostructures were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) as well as energy-dispersive X-ray (EDX) and Raman spectroscopies. The best results were obtained when the deposition conditions were as follows: argon-assisted plasma, generator power 120 W, catalyst sputtering duration 20 s, and nickel serving as a catalyst. A flexible propylene glycol vapor (PGV) and hydrogen peroxide vapor (HPV) sensors based on RF-sputtered CNTs combined with the Fe2O3:ZnO material were fabricated, and its DC and AC gas-sensing properties were studied. Impedance spectroscopy was used to evaluate an equivalent electrical circuit of the sensor. Temperature modulation led to the effective use of the same nanostructured film for PGV and HPV detection at 150 and 50 °C, respectively. At 50 °C temperature, the sensor response ranged from 3 to 27 values in the HPV concentrations of 0.5-25 ppm, respectively, demonstrating short response/recovery times, high response repeatability, and temporal stability.

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This work presents a novel nanostructured material SnO2/multiwalled carbon nanotubes (MWCNTs) as a sensing film for the detection of acetone and ethanol vapors. The fabrication of SnO2/MWCNT chemoresistive sensors demonstrates a cost-effective hydrothermal method using a centrifugation technique. The material investigation of the synthesized SnO2/MWCNTs nanocomposite represents various techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) elementary analysis, EDX mapping, and X-ray diffraction (XRD) analysis. The SnO2/MWCNTs sensor exhibits rapid response/recovery behavior toward acetone (53/5 s) and ethanol (86/3 s) while showing satisfactory values of responsiveness (S act = 90.5 and S etn = 21, n = 100 ppm). The low detection limit of these vapors is assigned a concentration of 1 ppm, where discernible responses are elicited. Thus, the SnO2/MWCNTs sensor production efforts have yielded a high-end volatile organic compound (VOC) detector, highly suitable for human technological and engineering activity.

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The aim of this work is to synthesize and characterize a nanostructured material with improved parameters suitable as a chemiresistive gas sensor sensitive to propylene glycol vapor (PGV). Thus, we demonstrate a simple and cost-effective technology to grow vertically aligned carbon nanotubes (CNTs) and fabricate a PGV sensor based on Fe2O3:ZnO/CNT material using the radio frequency magnetron sputtering method. The presence of vertically aligned carbon nanotubes on the Si(100) substrate was confirmed by scanning electron microscopy and Fourier transform infrared (FTIR), Raman, and energy-dispersive X-ray spectroscopies. The uniform distribution of elements in both CNTs and Fe2O3:ZnO materials was revealed by e-mapped images. The hexagonal shape of the ZnO material in the Fe2O3:ZnO structure and the interplanar spacing in the crystals were clearly visible by transmission electron microscopy images. The gas-sensing behavior of the Fe2O3:ZnO/CNT sensor toward PGV was investigated in the temperature range of 25-300 °C with and without ultraviolet (UV) irradiation. The sensor showed clear and repeatable response/recovery characteristics in the PGV range of 1.5-140 ppm, sufficient linearity of response/concentration dependence, and high selectivity both at 200 and 250 °C without UV radiation. This is a basis for concluding that the synthesized Fe2O3:ZnO/CNT structure is the best candidate for use in PGV sensors, which will allow its further successful application in real-life sensor systems.

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