Characterization of self-assembled dendrimers on Au(111) substrate by scanning probe microscopy

To investigate the characteristics of the single dendrimer molecule, we attempt to measure morphology and electrical property of the self-assembled G3-16[tpy-Pt-py] dendrimers on Au(111) substrate by tapping-mode AFM and scanning tunneling spectroscopy (STS). The same self-assembly procedure was used for two different concentrations, 10 and 100 μmol/ml. In the case of lower concentration, we were able to measure the diameter and the height of the single molecule from the tapping-mode AFM image. The imaged single molecules were dome-shaped and the average diameter and height were 15.6 and 1.2 nm, respectively. From these sizes, we could calculate the volume of the single molecule. The volume of the single molecule was estimated to be about 116 nm3. However, with that of higher concentration, it was difficult to obtain a clear image of the single molecule. In addition, we measured I–V curve using STS, which shows the ohmic contact between −0.22 and 0.22 V and, beyond that range, the current was increased exponentially.