Electrical transport in ultrathin Metal-insulator-semiconductor (MIS) tunnel junctions is analyzed using the temperature dependence of current density and admittance characteristics, as illustrated by Hg//C 12 H 25 -n Si junctions incorporating n-alkyl molecular layers (1.45 nm thick) covalently bonded to Si(111). The voltage partition is obtained from J(V, T) characteristics, over eight decades in current. In the low forward bias regime (0.2-0.4 V) governed by thermionic emission, the observed linear T-dependence of the effective barrier height, qU EFF ðTÞ¼qU B þðkTÞb 0 d T , provides the tunnel barrier attenuation, expðÀb 0 d T Þ, with b 0 ¼ 0.93 Å À1 and the thermionic emission barrier height, U B ¼ 0:53 eV. In the high-forward-bias regime (0.5-2.0 V), the bias dependence of the tunnel barrier transparency, approximated by a modified Simmons model for a rectangular tunnel barrier, provides the tunnel barrier height, U T ¼ 0:5 eV; the fitted prefactor value, G 0 ¼ 10 À10 X À1 , is four decades smaller than the theoretical Simmons prefactor for MIM structures. The density distribution of defects localized at the C 12 H 25 -n Si interface is deduced from admittance data (low-high frequency method) and from a simulation of the response time s R ðVÞ using Gomila's model for a non equilibrium tunnel junction. The low density of electrically active defects near mid-gap (D S < 2  10 11 eV À1 .cm À2 ) indicates a good passivation of dangling bonds at the dodecyl -n Si (111) interface.

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The cleaved surfaces of untwinned, single-crystal YBa2Cu3069 have been probed with synchrotronradiation photoemission, utilizing both high energy and angular resolution. Acute spectral structure was observed, both at the Fermi energy and at higher binding energies, particularly near the high-symmetry points of the two-dimensional Brillouin zone, I, X, Y, and S. Many band crossings of the Fermi energy were seen, with obvious and important differences between the bands near X and those near Y. A large superconducting gap was not observed: The data are consistent with a gap of less than 10 meV. The assignment of bands and Fermi-level crossings to chain and plane states will be discussed, including comparisons to the predictions of theory, particularly local-density-approximation calculations.

The covalent attachment of ester-, pyridine-, and ferrocene-functionalized organic layers to amorphous carbon surfaces, grown by graphite sputtering in Ar−H2 mixtures, is reported. The surface modification is based on a low temperature (160 °C) liquid-phase process. Thermally assisted grafting of linear alkenes is investigated by means of X-ray photoelectron spectroscopy (XPS), atomic force microscopy, and contact angle measurements. The beneficial role of surface oxygen removal by argon ion sputtering or thermal treatment prior to the ester grafting step is also discussed. Careful XPS data analysis provides a quantitative estimate of the density (0.2−4.3 × 1014 cm-2) of attached molecules as a function of surface preparation. The large packing density has been confirmed by the voltammetric response of a ferrocene-functionalized carbon surface.