Synthesis of zinc oxide nanoparticles via laser ablation on porous silicon for gas sensors application

Zinc Oxide nanoparticles (ZnO NPs) were prepared using a pulsed laser ablation process, using Q-switched Nd: YAG laser pulses of 1064 nm wavelength, 1 Hz pulse repetition rate, pulse duration of 9 ns, with different laser pulse energy (350 mJ, 500 mJ, 650 mJ), and the porous silicon prepared by electrochemical etching with fixed parameters (25% HF, current density of 15 mA/cm2 for 10 min). The X-ray diffraction test shows a broadening diffraction peak of the PS as a decrease in the crystallite size. The sharp peaks of the ZnO NPs refer to the high orientation of ZnO NPs along the c-axis vertical to the PS layer. FE-SEM shows a highly porous surface with a uniform distribution of holes on the silicon surface. Increasing the value of laser energy leads to larger particle sizes and more spherical, homogeneous, and broad size distribution. The examination of optical characteristics revealed that the ZnO NPs have a direct energy gap ranging from 3.47 to 3.79 eV, dependent on laser energy. These results lead to the smaller size of nanoparticles with narrow size distributions, which increases the quantum confinement effects. The sensor gas results for ZnO NPs/PS for NO2 and NH3 gases show that the sensitivity of the gas detector is higher with a smaller nanoparticle size, (S% 70.5 for NO2 at 150 degrees C) and (S % 55 for NH3 at 250 degrees C). This comes with quantum efficiency for the nanoparticles and increased surface area to volume ratio.