In-situ STM observation of the phase transition of two-dimensional 2,5-distyrylpyrazine nanostructure adsorbed on Au(111) in an electrochemical environment

Abstract

The phase transition of 2,5-distyrylpyrazine (DSP) adsorbed on Au(111) substrate was studied as a function of the substrate potential in 0.1 M HClO₄, using an in situ scanning tunneling microscope (STM). Depending on the applied electric field, DSP formed three distinctly different, two-dimensionally^(2D) ordered, supramolecular nanostructures on the Au(111) surface. In the potential range of 0.55 V < E < 0.75 V, the DSP molecules formed a close-packed stripe pattern with the adlayer structure $\left( {\begin{array}{*{20}c} { - 1} \\ 8 \\ \end{array} \begin{array}{*{20}c} 3 \\ 6 \\ \end{array} } \right)$. When the potential was reduced to 0.45 V < E < 0.55 V, a ridge-like pattern built from dimer subunits was observed, with the adlayer structure $\left( {\begin{array}{*{20}c} 4 \\ { - 12} \\ \end{array} \begin{array}{*{20}c} 5 \\ 4 \\ \end{array} } \right)$. Further decreasing in the electrode potential to 0.2 V < E < 0.45 V caused the appearance of a herringbone-like pattern consisting of dimer subunits, with the adlayer structure $\left( {\begin{array}{*{20}c} 9 \\ 3 \\ \end{array} \begin{array}{*{20}c} 0 \\ 9 \\ \end{array} } \right)$. The potential-induced phase transitions revealed the structure-determining role of substrate-adsorbate coordination and intermolecular interaction in forming the distinct 2D adlayer motifs.