SCANNING PROBE MICROSCOPIES FOR MOLECULAR PHOTODIODES

Photo-electric conversion molecular devices, i.e. molecular photodiode s based upon the charge separation mechanism of the primary process of natural photosynthesis, have been studied in our laboratory. Amphiphi lic AS-D triad molecules can be oriented unidirectionally in monolayer s at the air-water interface, The resulting oriented monolayer assembl ies are fabricated into thin films on electrode surfaces by the Langmu ir-Blodgett (LB) technique. The A-S-D triads for charge separation tog ether with light harvesting antenna molecules can be assembled into su b-micron island domains by making use of phase separation of mixed mon olayers of hydrocarbon (HC) and fluorocarbon (FC) amphiphiles. The str ucture and properties of the domains of HC-FC mixed monolayers were st udied by various scanning probe microscopies (SPMs) such as atomic for ce microscopy, friction force microscopy, scanning surface potential m icroscopy (SSPM), and scanning near-field optical/atomic force microsc opy. Some SPMs can be used not only to characterize the LB films, but also to drive the molecular devices. The photo-induced charge separati on in unidirectionally oriented triad molecules embedded in alternate LB films was observed by SSPM.