Appl. Phys. Lett. 114, 011105 (2019)

A multilevel optical memory that encodes information as the strength of transmission of terahertz radiation through an indium oxide nanoparticle film has been fabricated by scientists in Beijing, China. Hongyu Ji and co-workers from Capital Normal University and the Institution of Semiconductors dissolved 10-nm-diameter indium oxide nanoparticles in ethanol and then spin-coated the mixture onto a quartz substrate and annealed it at 340 °C for 1 hour. Experiments indicate that the terahertz transmission of the sample could be strongly modified by exposure to short-wavelength (ultraviolet or blue) light. The drop in the transmission of the sample was shown to relate to the intensity of the light exposure. The team used four relative transmission levels of 1.0, 0.8, 0.6 and 0.4 to encode information into the sample. If the sample was stored in an oxygen-rich environment, such as air, the memory effect was shown to decay and disappear after the light exposure stopped, allowing information to be wiped. However, when stored in nitrogen, the memory became a stable, non-volatile device.