PEEM and MEEM of chloroaluminum phthalocyanine ultrathin film on MoS2

Surface images of a chloroaluminum phthalocyanine (ClAlPc) film, which cons ists of monolayer and doublelayer regions, were observed by two surface sen sitive microscopy, photoelectron emission microscopy (PEEM) using photons o f the ionization threshold energy of the film and metastable electron emiss ion microscopy (MEEM) using metastable He. In PEEM, an image contrast, whic h directly reflects slight difference of ionization threshold energies betw een monolayer and doublelayer regions, was obtained, while in MEEM Little c ontrast was detected because of the use of all emitted electrons for the im aging. The PEEM result indicates that the ionization threshold energy of th e film depends on the film thickness. Using PEEM, we can map the slight dif ference of electronic states due to the thickness difference of an organic thin film. (C) 2001 Elsevier Science B.V. All rights reserved.