Nano-scale carbon onions produced by laser photolysis of toluene for detection of optical, humidity, acetone, methanol and ethanol stimuli

Laser liquid medium pyrolysis (LLMP) process has been used to deposit an onion like carbon (OLC) hierarchical structure using toluene as carbon source at various laser power density settings of 2.54, 6.62 and 9.17 W/cm2 on Si (1 0 0). The coin tower structure of carbon deposits was observed for 2.54 W/cm2 and the wheat flower structure consists of OLC for 6.62 and 9.17 W/cm2 of laser power. The formation of OLC hierarchical structure deposition has been confirmed using Scanning Electron Microscopy, X-ray Diffraction, Transmission Electron Microscopy, Electron Energy Loss Spectroscopy and Raman Spectroscopic studies. The mechanism of OLC hierarchical structure formation has been discussed. The gas sensing station incorporated with flat heater has been established to sense the Volatile Organic Compounds (VOC) e.g. methanol, ethanol and acetone at room temperature (25 °C) and 32% of relative humidity (RH). A good linear relationship between sensitivity and VOCs concentration has been observed in the range of 34-148 ppm. The selectivity of OLC device to alcohol (20.5) is found to be double as compared to acetone (10). The p- to n-type semiconductor transition of the OLC has been observed with the increasing Relative Humidity (RH). The OLCs response to the light reveals photoelectric effect and the conduction is found to be incident photon wavelength dependence.