Evidence for an adsorbate-dependent mechanism for surface resistivity: formic acid, oxygen and CO on Cu(100)

Effects of ordered islands on surface resistivity: Ni on Au(111)

The change in surface resistivity due to the formation of nickel islands on gold(111) was studied by measuring the resistance of a thin film of Au as a function of Ni coverage, θ. Previous studies showed that the Au(111) herringbone reconstruction provides a template for the periodic growth of ordered islands. Ni islands grow radially until θ ≈ 0.3 ML, after which subsequent Ni atoms contribute primarily to a second layer. Since Ni atoms on Au(111) grow in ordered nanoclusters, a nonlinear dependence of resistance on θ might be anticipated. Our results, however, show a linear dependence for Ni atoms in the first layer, as if they were independent point scatterers. Above θ ≈ 0.3 ML, there is little change in resistivity, which we attribute to Ni atoms in the second layer making no significant contribution to the resistivity. Although we did not directly image the islands, our results are consistent with the growth model and structures previously observed with scanning tunneling microscopy. Our results serve as an indirect probe of the growth kinetics of this system, as well as determining the contributions of Ni islands to the surface resistivity of the Au film.

A chemically-responsive nanojunction within a silver nanowire

The formation of a nanometer-scale chemically responsive junction (CRJ) within a silver nanowire is described. A silver nanowire was first prepared on glass using the lithographically patterned nanowire electrodeposition method. A 1-5 nm gap was formed in this wire by electromigration. Finally, this gap was reconnected by applying a voltage ramp to the nanowire resulting in the formation of a resistive, ohmic CRJ. Exposure of this CRJ-containing nanowire to ammonia (NH(3)) induced a rapid (<30 s) and reversible resistance change that was as large as ΔR/R(0) = (+)138% in 7% NH(3) and observable down to 500 ppm NH(3). Exposure to water vapor produced a weaker resistance increase of ΔR/R(0,H(2)O) = (+)10-15% (for 2.3% water) while nitrogen dioxide (NO(2)) exposure induced a stronger concentration-normalized resistance decrease of ΔR/R(0,NO(2)) = (-)10-15% (for 500 ppm NO(2)). The proposed mechanism of the resistance response for a CRJ, supported by temperature-dependent measurements of the conductivity for CRJs and density functional theory calculations, is that semiconducting p-type Ag(x)O is formed within the CRJ and the binding of molecules to this Ag(x)O modulates its electrical resistance.

Bonding-site dependence of surface resistivity: CO on epitaxial Cu(100) films

The authors have measured the contribution of CO adsorbed on different bonding sites to the resistivity of epitaxial Cu(100) films. Through an analysis of the correlation between surface resistivity and temperature-programed desorption measurements, CO on terraces is found to affect the resistance much more strongly than CO on defect sites. Two possible explanations are considered: a reduced scattering cross section of defect CO owing to the different local electronic structure at defect sites or strong scattering by the bare defect that is not significantly affected by the adsorption of CO.