Contacting self-ordered molecular wires by nanostencil lithography

Abstract

The authors grew self-ordered meso-(4-cyanophenyl)-substituted Zn(II) porphyrin molecular wires on thin epitaxial NaCl(001) layers on top of the GaAs substrates under ultrahigh vacuum (UHV) conditions. Molecules assembled to one- and two-dimensional wires with a length of several 10 nm, depending on the substrate conditions. In addition, using the nanostencil tool, a shadow-masking technique in UHV, they evaporated Au and Cr electrodes having lateral dimensions in the 100 nm regime. The resulting combined molecular and metal structures were investigated in situ by means of noncontact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM). While NC-AFM enabled control of the tip-sample distance on the very complex and partly insulating surface, KPFM was used to determine and compensate changes in the local contact potential difference.