ACS Photon. http://doi.org/cg2f (2017)

Nanomaterials that exhibit optical bistability provide routes for high-density integration of optical memory and switches. Now, Takushi Uda and co-workers from RIKEN and the University of Tokyo in Japan present an optical memory based on individual carbon nanotubes where excitonic resonance shifts induced by molecular adsorption and desorption give rise to optical bistability. The device in question is composed of individual carbon nanotubes suspended over trenches on silicon substrates. The nanotubes are excited by a laser and their photoluminescence spectra captured by a microscopy system. The team observed two different emission energy peaks during an up-sweep and down-sweep of laser excitation power, indicating the presence of optical bistability and the existence of a hot desorbed state and a cold adsorbed state. Reversible and reproducible optical memory operation using the two states was confirmed by time-resolved measurements. The findings aid the design of photonic memory devices that are a few orders of magnitude smaller than the optical diffraction limit.