Photoexcited carrier effect on scanning tunneling microscopy of zinc-phthalocyanine and coronene molecules on Si(100)2x1 surfaces

Photocurrent images of zinc-phthalocyanine (ZnPc) and coronene molecules adsorbed on Si(100)2 x 1 surfaces have been obtained by scanning tunneling microscopy. The photocurrent images of molecules mainly reflect the contribution of the surface photovoltage in proportion to the local density of stales (LDOS). In the photocurrent observations rile ZnPe molecules are seen as bright images. indicating the large LDOS at the bias voltage. On the other hand, the images of coronene molecules show a wide variety of contrasts which depend strongly on the adsorption site against the Si dimer rows. This dissimilarity may be attributed to the difference in the tunneling probability of the photoexcited carriers, a difference which reflects the variation of the surface electronic stale formed by a molecule and Si dimers. (C) 1997 Elsevier Science B.V.