MANIPULATION OF RECTANGULAR ARRANGEMENT OF SE-RING-TYPE MOLECULES ON GRAPHITE (HIGHLY ORIENTED PYROLYTIC-GRAPHITE) SURFACES

A rectangular lattice arrangement of Se(n) (n=5-8) ring clusters has been fabricated for the first time on the c plane of graphite (highly oriented pyrolytic graphite) crystal and has been examined by a scanning tunnel microscope (STM) image which was found to consist of a 0.72 nmX0.85 nm lattice spacing with individual molecules of 0.53+/-0.05 nm in diameter. Each lattice point consist of Se-ring-type molecules, most probably six-membered. The STM images were taken with the bias voltage V(T) between probe and sample as a parameter. For -0.7 V<V(T)<+0.7 V the patterns of the rectangular lattice remained similar, whereas at V(T) almost-equal-to -0.7 V the regular arrangement suddenly collapsed to a random distribution of larger clusters, their diameter consisting of a range up to 5 nm anywhere. The process of the phase change in the lattice system is not reversible with respect to the bias voltage.