35 research outputs found
Mechanically-Controlled Binary Conductance Switching of a Single-Molecule Junction
Molecular-scale components are expected to be central to nanoscale electronic
devices. While molecular-scale switching has been reported in atomic quantum
point contacts, single-molecule junctions provide the additional flexibility of
tuning the on/off conductance states through molecular design. Thus far,
switching in single-molecule junctions has been attributed to changes in the
conformation or charge state of the molecule. Here, we demonstrate reversible
binary switching in a single-molecule junction by mechanical control of the
metal-molecule contact geometry. We show that 4,4'-bipyridine-gold
single-molecule junctions can be reversibly switched between two conductance
states through repeated junction elongation and compression. Using
first-principles calculations, we attribute the different measured conductance
states to distinct contact geometries at the flexible but stable N-Au bond:
conductance is low when the N-Au bond is perpendicular to the conducting
pi-system, and high otherwise. This switching mechanism, inherent to the
pyridine-gold link, could form the basis of a new class of
mechanically-activated single-molecule switches
Characterizing the MetalâSAM Interface in Tunneling Junctions
his paper investigates the influence of the interface between a gold or silver metal electrode and an n-alkyl SAM (supported on that electrode) on the rate of charge transport across junctions with structure Met(Au or Ag)TS/A(CH2)nH//Ga2O3/EGaIn by comparing measurements of current density, J(V), for Met/AR = Au/thiolate (Au/SR), Ag/thiolate (Ag/SR), Ag/carboxylate (Ag/O2CR), and Au/acetylene (Au/CâĄCR), where R is an n-alkyl group. Values of J0 and ÎČ (from the Simmons equation) were indistinguishable for these four interfaces. Since the anchoring groups, A, have large differences in their physical and electronic properties, the observation that they are indistinguishable in their influence on the injection current, J0 (V = 0.5) indicates that these four Met/A interfaces do not contribute to the shape of the tunneling barrier in a way that influences J(V).Chemistry and Chemical Biolog