Commensurate ordering of iron phthalocyanine on Ag(1Â 1Â 1) surface

Epitaxial growth of iron phthalocyanine on a silver (1 1 1) surface has been studied with scanning tunneling microscopy in ultrahigh vacuum. While several structures were observed, this report concentrates on what appeared to be the most stable phase. This phase has commensurate two-dimensional ordering with oblique unit vectors (b1, b2) where b1 = 5a1 + 2a2 and b2 = 5a2, where a1 and a2 are unit vectors of Ag(1 1 1) surface. The rotation angle of iron phthalocyanine relative to the silver [1 0 1¯] direction was determined to be 16.63° from the high-resolution image analysis. The oblique structure is more commensurate than that of iron phthalocyanine on graphite and of copper phthalocyanine on the Ag(1 1 1) surface. The observed FePc on Ag(1 1 1) structure is similar to that of FePc on Au(1 1 1), but has significantly higher surface density. Bias dependence of the images was observed and is consistent with the expected small HOMO-LUMO gap.