Two-dimensional molecular array of porphyrin derivatives with bright and dark spots as a model of two-digit molecular-dot memory

Scanning tunneling microscopic (STM) observation of an array of 5,10,15,20-tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)porphyrin molecules deposited on a Au(1 1 1) surface revealed dark and bright spots within the regular two-dimensional pattern, which are due to conformational diversity of the adsorbed molecules caused by distortion of the porphyrin core. With this structure, two-digit information can be input with ca. 2-nm interval, which would correspond to an information density of 25 terabit/cm2 if exploited in a memory device.