Optical probes of molecules as nano-mechanical switches

Abstract

Molecular electronics promises a new generation of ultralow-energy information technologies, based around functional molecular junctions. Here, we report optical probing that exploits a gold nanoparticle in a plasmonic nanocavity geometry used as one terminal of a well-defined molecular junction, deposited as a self-assembled molecular monolayer on flat gold. A conductive transparent cantilever electrically contacts individual nanoparticles while maintaining optical access to the molecular junction. Optical readout of molecular structure in the junction reveals ultralow-energy switching of ∼50 zJ, from a nano-electromechanical torsion spring at the single molecule level. Real-time Raman measurements show these electronic device characteristics are directly affected by this molecular torsion, which can be explained using a simple circuit model based on junction capacitances, confirmed by density functional theory calculations. This nanomechanical degree of freedom is normally invisible and ignored in electrical transport measurements but is vital to the design and exploitation of molecules as quantum-coherent electronic nanodevices.

Intermolecular and Electrode-Molecule Bonding in a Single Dimer Junction of Naphthalenethiol as Revealed by Surface-Enhanced Raman Scattering Combined with Transport Measurements

“…The histogram of the energy of the vibrational modes observed in the SERS spectra shows prominent peaks at 1067 and 1380 cm –1 originating from the ring breathing mode and CH bending mode of NT, respectively, together with the other vibrational modes also assigned to NT molecule (Figure b, Supporting Information S5). The enhanced SERS signal observed in the typical conductance range of the molecules supports the formation of the molecular junction (Supporting Information S6), representing the presence of the NT molecule at the nanogap. − ,,− In addition, the nonlinear behaviors in the I – V curves simultaneously measured with the SERS spectra demonstrate that the NT molecule is involved in the electron transport. , The synchronized SERS signal with the I – V response represents the formation of the molecular junction. The conductance histogram from the I – V responses showed two conductance states: high conductance state (H state) around 10 –1.8 G 0 and the low conductance state (L state) around 10 –2.8 G 0 accompanied by the satellite peak (Figure c).…”

Full Control of Plasmonic Nanocavities Using Gold Decahedra‐on‐Mirror Constructs with Monodisperse Facets

“…To localize growth solely on the NDoM top, a protective PMMA layer is spin‐coated onto the sample and etched back to reveal the top NDoM facets (see Note S3, Supporting Information). [ 44 ] Pulsed deposition is then used to grow additional Au of different volume (Figure S22, Supporting Information) by tuning the deposition time, after which the PMMA is dissolved. DF images show the deposition is highly uniform at a large scale.…”

Molecular Electronics: Creating and Bridging Molecular Junctions and Promoting Its Commercialization

“…In this configuration, the molecular junction can be constructed by both a single-molecule [340,341] and a molecular ensemble. [342] For singlemolecule junctions, [343][344][345] as shown in Figure 17B, a metallic tip gently approaches the surface of a metallic substrate (as the bottom electrode) under constant DC bias until a fused metal-metal contact is formed with a conductance greater than a few G 0 (G 0 = conductance quantum, 2e 2 /h). [346] The tip is then withdrawn at constant speed to stretch the metallic contact, which causes stepwise drops in the quantized conductance as a function of displacement and eventually shows a plateau at 1 G 0 when the contact is thinned down to a single-atom-wide constriction.…”