ATOMIC IMAGES OF SATURATED AND UNSATURATED FATTY-ACIDS AT LIQUID GRAPHITE INTERFACE AND DIFFERENCE OF TUNNELING CURRENTS BETWEEN THEM OBSERVED BY SCANNING-TUNNELING-MICROSCOPY/

Structures of arachidic acid and elaidic acid molecules adsorbed onto a graphite substrate were investigated using a scanning tunneling micr oscope. The ordered arrangements of the molecules were observed with a tomic resolution. The image of an arachidic acid molecule is composed of nineteen bright spots at the individual hydrocarbon groups in the a lkyl chain and a dark region at the carboxyl group. The image of an el aidic acid molec;le with an unsaturated hydrocarbon chain is similar t o that of an arachidic acid molecule except for a much brighter spot a t, the double bond in the hydrocarbon chain. As a result, functional g roups such as hydrocarbon chains, carboxyl groups and double bonds cou ld be distinguished by the tunnel currents.