Low temperature scanning tunneling microscopy of phthalocyanine multilayers on Au(1 1 1) surfaces

We have studied epitaxial trilayer films of cobalt–phthalocyanine (CoPc) on Au(1 1 1) 22×3 surfaces using a scanning tunneling microscope at 78 K. Molecules in each layer were found to form square lattices and stacked along the [1 1̄ 0] axis of the Au(1 1 1) surface. While CoPc molecules in the first layer were observed at bias voltages of −2.5 to +2.5 V, there were certain ranges of bias voltage in which molecules in the upper layers were invisible. The electronic structures of molecules in upper layers are more localized than those of the first layer, which is affected by the substrate surface.