Figure 1: Description/characterization of the RF molecular rectifier.
(a) Schematic representation of the molecular junction composed of a gold nanocrystal, Ferrocenyl undecanethiol (FcC11) molecules enabling rectification properties, and a Pt tip. Nanocrystals form an ohmic contact to a highly doped silicon substrate. The Pt tip is biased (through a bias-T) to both d.c. and HF (1–18 GHz) excitation simultaneously. (b) Picture of a 1 cm × 1 cm array of gold nanocrystals used for X-ray photoemission spectroscopy (XPS) or Cyclic Voltammetry measurements. The picture is taken just after dipping the sample into HF (for removal of the SiO2 covering dots), the gold nanoarray area being identified through an hydrophilic/hydrophobic contrast. (c) Gold nanodot array imaged by Scanning Electron Microscope (SEM). Scale bar, 200 nm. (d) XPS measurements for SAMs of FcC11 grafted on gold nanocrystals (∼1 billion dots fabricated by high-speed lithography) showing the presence of a Fe doublet related with ferrocene at 707.8 eV and 720.7 eV (Fe 2p3/2 and Fe 2p1/2, respectively), anda Fe doublet related to ferricenium at at 710.6 eV at 723.9 eV (2p3/2 and 2p1/2, respectively). The XPS signal for the bare Au nanoarray is also shown as a reference. Inset: schematic representation of the SAM with Ferricenium molecules located at dots borders due to the presence of a negatively charged silica. (e) Cyclic voltammetry measurements supports the presence of ferrocenyl molecules on the nanodots with a double peak at E=0.34 V and 0.37 V versus Ag/AgCl as a reference electrode in agreement with previous studies15. (f) 2D histogram (normalized to 1) showing the I–V (and J–V) curve from one hundred junctions on 20 nm gold nanoparticles. The voltage step is 0.1 V, and the 2D histogram is obtained by the contour plot function (Originlab). The applied load was 18 nN (see Supplementary Note 4 for a detailed discussion on the tip load).
