Ultrahigh-density data storage on a 3-phenyl-1-ureidonitrile (PUN) thin fil
m was performed using a scanning tunneling microscope. The recorded marks o
f 0.8 nm in diameter were obtained when voltage pulses of 4 V for 10ms were
applied between the STM tip and highly ordered pyrolytic graphite substrat
e. The current-voltage relations at the local regions of the films indicate
that the recorded region is conductive and the unrecorded region is in a h
igh impedance state. A possible mechanism of this data storage was suggeste
d and discussed.