Influence of the Growth Parameters on RF-Sputtered CNTs and Their Temperature-Selective Application in Gas Sensors

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.