The electron scattering at surfaces, interfaces, and grain boundaries is investigated using polycrystalline and single-crystal Cu thin films and nanowires. The experimental data is described by a Fuchs-Sondheimer (FS) and Mayadas-Shatzkes (MS) model that is extended to account for the large variation in the specific resistivity of different grain boundaries as well as in situ anneal and a subsequent etch to match the thickness of the SG samples. Nanowires are fabricated from the SG and LG thin films using a subtractive patterning process, yielding wire widths of 75-350 nm. Single-crystal and LG layers exhibit a 18-22% and 10-15% lower resistivity than SG layers, respectively. The resistivity decrease from SG to LG Cu nanowires is 7-9%. The thickness and grain size dependence of the resistivity of polycrystalline and singlecrystal Cu layers is well described by an exact version of the existing FS+MS model, but is distinct from the commonly used approximation which introduces an error that increases with decreasing layer thickness from 6.5% for d = 50 nm to 17% for d = 20 nm. The case of nanowires requires the FS+MS model to be extended to account for variation in the grain boundary reflection coefficient R, which effectively increases the overall resistivity by, for example, 16% for 50×45 nm 2 wires. The overall data from single and polycrystalline Cu layers and wires yields R = 0.25±0.05, and p = 0 at Cu-air and Cu-Ta interfaces.2

The dependence of electron-transfer rate constants on the driving force for interfacial charge transfer has been investigated using n-type ZnO electrodes in aqueous solutions. Differential capacitance versus potential and current density versus potential measurements were used to determine the energetics and kinetics, respectively, of the interfacial electron-transfer processes. A series of nonadsorbing, oneelectron, outer-sphere redox couples with formal reduction potentials that spanned approximately 900 mV allowed evaluation of both the normal and Marcus inverted regions of interfacial electron-transfer processes. All rate processes were observed to be kinetically first-order in the concentration of surface electrons and first-order in the concentration of dissolved redox acceptors. The band-edge positions of the ZnO were essentially independent of the Nernstian potential of the solution over the range 0.106-1.001 V vs SCE. The rate constant at optimal exoergicity was observed to be approximately 10 -16 cm 4 s -1 . The rate constant versus driving force dependence at n-type ZnO electrodes exhibited both normal and inverted regions, and the data were well-fit by a parabola generated using classical Marcus theory with a reorganization energy of 0.67 eV. NMR line broadening measurements of the self-exchange rate constants indicated that the redox couples had reorganization energies of 0.64-0.69 eV. The agreement between the reorganization energy of the ions in solution and the reorganization energy for the interfacial electron-transfer processes indicated that the reorganization energy was dominated by the redox species in the electrolyte, as expected from an application of Marcus theory to semiconductor electrodes.

The interfacial energetic and kinetics behavior of n-ZnO/H2O contacts have been determined for a series of compounds, cobalt trisbipyridine (Co(bpy)3 3+/2+), ruthenium pentaamine pyridine (Ru(NH3)5py3+/2+), cobalt bis-1,4,7-trithiacyclononane (Co(TTCN)2 3+/2+), and osmium bis-dimethyl bipyridine bis-imidazole (Os(Me2bpy)2(Im)2 3+/2+), which have similar formal reduction potentials yet which have reorganization energies that span approximately 1 eV. Differential capacitance vs potential and current density vs potential measurements were used to measure the interfacial electron-transfer rate constants for this series of one-electron outer-sphere redox couples. Each interface displayed a first-order dependence on the concentration of redox acceptor species and a first-order dependence on the concentration of electrons in the conduction band at the semiconductor surface, in accord with expectations for the ideal model of a semiconductor/liquid contact. Rate constants varied from 1 × 10-19 to 6 × 10-17 cm4 s-1. The interfacial electron-transfer rate constant decreased as the reorganization energy, λ, of the acceptor species increased, and a plot of the logarithm of the electron-transfer rate constant vs (λ + ΔG°‘)2/4λk B T (where ΔG°‘ is the driving force for interfacial charge transfer) was linear with a slope of ∼ −1. The rate constant at optimal exoergicity was found to be ∼5 × 10-17 cm4 s-1 for this system. These results show that interfacial electron-transfer rate constants at semiconductor electrodes are in good agreement with the predictions of a Marcus-type model of interfacial electron-transfer reactions.

Bundles of single wall carbon nanotubes have been proposed as an interconnect that could potentially replace copper in state-of-the-art ultralarge-scale-integrated circuits if theoretically predicted inductance, resistance, and capacitance scale with the number of carbon nanotubes within the bundle. The authors report direct measurement of the kinetic inductance of individual single wall carbon nanotubes and measurement of the high-frequency impedance of bundles showing that the bundle inductance scales with the number of individual carbon nanotubes.

Photoconductivity decay data have been obtained for NH4F(aq)-etched Si(111) and for air-oxidized Si(111) surfaces in contact with solutions of methanol, tetrahydrofuran (THF), or acetonitrile containing either ferrocene+/0 (Fc+/0), [bis(pentamethylcyclopentadienyl)iron]+/0 (Me10Fc+/0), iodine (I2), or cobaltocene+/0 (CoCp2 +/0). Carrier decay measurements were made under both low-level and high-level injection conditions using a contactless rf photoconductivity decay apparatus. When in contact with electrolyte solutions having either very positive (Fc+/0, I2/I-) or relatively negative (CoCp2 +/0) Nernstian redox potentials with respect to the conduction-band edge of Si, Si surfaces exhibited low effective surface recombination velocities. In contrast, surfaces that were exposed only to N2(g) ambients or to electrolyte solutions that contained a mild oxidant (such as Me10Fc+/0) showed differing rf photoconductivity decay behavior depending on their different surface chemistry. Specifically, surfaces that possessed Si−OCH3 bonds, produced by reaction of H-terminated Si with CH3OH−Fc+/0, showed lower surface recombination velocities in contact with N2(g) or in contact with CH3OH−Me10Fc+/0 solutions than did NH4F(aq)-etched, air-exposed H-terminated Si(111) surfaces in contact with the same ambients. Furthermore, the CH3OH−Fc+/0-treated surfaces showed lower surface recombination velocities than surfaces containing Si−I bonds, which were formed by the reaction of H-terminated Si surfaces with CH3OH−I2 or THF−I2 solutions. These results can all be consistently explained through reference to the electrochemistry of Si/liquid contacts. In conjunction with prior measurements of the near-surface channel conductance for p+−n−p+ Si structures in contact with CH3OH−Fc+/0 solutions, the data reveal that formation of an inversion layer (i.e., an accumulation of holes at the surface) on n-type Si, and not a reduced density of surface electrical trap sites, is primarily responsible for the long charge carrier lifetimes observed for Si surfaces in contact with CH3OH or THF electrolytes containing I2 or Fc+/0. Similarly, formation of an accumulation layer (i.e., an accumulation of electrons at the surface) consistently explains the low effective surface recombination velocity observed for the Si/CH3OH−CoCp2 and Si/CH3CN−CoCp2 contacts. Detailed digital simulations of the photoconductivity decay dynamics for semiconductors that are in conditions of inversion or depletion while in contact with redox-active electrolytes support these conclusions.