Ultrahigh-density data storage has received much attention in recent years because of its technological importance, and substantial progress has been made lately.[1±6] Haridas and coworkers have suggested three-dimensional high-density data storage based on two photos.[1] Chou et al. used nanoimprinting lithography for high-density data storage.[2,3] Scanning probe microscopy (SPM) has a potential application in high-density data storage due to its ability to make local electric fields from the tip on a nanometer scale.[7±14] Recording at the nanometer scale has been demonstrated by SPM on various materials. Among them, organic molecules have received much attention because of their controllable molecular structures and corresponding properties.[15±26,28] By changing molecular structure, it is possible to optimize recording on organic materials. Furthermore, the size of the recorded mark can possibly be at a molecular scale. In the past, we have reported molecular recording on a few organic materials up to a data density of about 1013 bits/cm2.[5±7,17] To decrease the size of the recorded marks, correspondingly increase their density, and furthermore understand the recording mechanism,we have designed and synthesized different molecules.In this communication, we report molecular recording on an organic p-nitrobenzonitrile (PNBN) thin film by STM under ambient conditions, which shows the smallest mark size among all the organic thin films previously studied. A possible
recording mechanism is discussed.