Tuning of 2D Nanographene Adlayers on Au(111) by Electrodeposition of Metal Halide Complexes

The electrodeposition of AuBr₄^- and PtBr₄^2- onto an adlayer of circobiphenyl-a structurally defined nanographene with low symmetry-on a Au(111) electrode was investigated via electrochemical scanning tunneling microscopy (EC-STM) to control and understand the formation of characteristic nanoclusters. By immersing a circobiphenyl-coated Au(111) substrate in a 0.1 mM aqueous AuBr₄^- solution, AuBr₄^- was spontaneously reduced, and a characteristic mixed adlayer consisting of circobiphenyl molecules and Br^- ions with monatomic Au islands was produced on the Au(111) surface. A similar electrodeposition process was performed in an aqueous solution of PtBr₄^2-, and an identical mixed adlayer was obtained with Pt nanoclusters. The electrodeposition of Au and Pt complexes was facilitated by the "negatively charged" reconstructed Au(111) surface, which is stabilized by the formation of a highly ordered circobiphenyl adlayer. EC-STM revealed the formation of characteristic dimers of Pt clusters ranging 2-4 nm in diameter on the circobiphenyl adlayer. Thus, Br^- metal complexes were found to play an important role in controlling the structure and size of a mixed adlayer containing Br^- and the shape of Pt clusters.