Simple, Low-Temperature Route To Synthesize ZnO Nanoparticles and Their Optical Neuromorphic Characteristics

Wurtzite ZnO nanoparticles were synthesized using a simple one-step process at temperatures of 30–100 °C. X-ray diffraction (XRD) analyses show a conversion of crystalline phase of Zn(OH)2 to wurtzite ZnO at a synthesis temperature of 60 °C. High-resolution transmission electron microscope (HRTEM) images show that the resulting ZnO nanoparticles are highly crystalline. Photoluminescence spectra of the samples show that the oxygen vacancies that generally cause the green emission in ZnO is spectacularly low in these samples, which were further illustrated using X-ray photoelectron spectroscopy (XPS) analyses. The band gap was estimated using optical absorption spectroscopy. Further, the samples were analyzed using micro-Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. Photodetectors constructed using ZnO nanoparticles show a clear photoresponse to ultraviolet (UV) light. Further, we measured the photosynaptic response of the devices to ultraviolet light pulses. The excitatory postsynaptic current (EPSC) with a constant paired pulse facilitation (PPF) shows that these nanoparticle devices are promising candidates for linear optical synaptic devices.