Scanning tunneling microscopy is used to characterize the electronic structure of 1 ML films of CuN on Cu(100). We find that CuN acts as an insulator with a band gap that exceeds 4eV. Measurements of the tunneling barrier height and image potential states indicate that the CuN work function is ∼0.9eV larger than bare Cu. This suggests a significant surface dipole, consistent with charge transfer predicted by theory. Our results indicate that CuN films are useful for controlling the electronic coupling between adsorbates and surface electron density on the nanometer scale.
Scanning tunneling microscopy is used to characterize the electronic structure of 1 ML films of c(2×2)N∕Cu(100) (i.e., Cu2N). By varying nitrogen coverage, a variety of morphologies are prepared, including (1) isolated ∼25nm2 islands, (2) close-packed arrays of islands, and (3) quasicontinuous monolayer films. In all three regimes, the authors find that Cu2N acts as an insulator, with a band gap that exceeds 4eV. The insulating Cu2N films are used to control the coupling of adsorbed Co atoms to the Cu(100) surface electron density. Tunneling spectroscopy of Co on Cu2N reveals an unoccupied atomic resonance, Kondo effect, and spin-flip excitation. These features depend on binding site within the Cu2N film, and are distinctly different than corresponding spectra for Co on Cu(100).
We use a scanning tunneling microscope operating in a low-temperature ultrahigh vacuum environment to study the atomic structure of single layer films of Cu 2 N grown on Cu͑100͒. The c͑2 ϫ 2͒ lattice of Cu 2 N is incommensurate, with a lattice constant of 0.372Ϯ 0.001 nm that is 3% larger than the bare Cu͑100͒ surface. This finding suggests that the strain due to lattice mismatch contributes to self-assembly in this system. We find that the image contrast on Cu 2 N islands depends on bias voltage, which reconciles several interpretations in the literature. We assign features in these STM images to the Cu, N, and hollow sites in the Cu 2 N lattice with the aid of coadsorbed CO molecules. This atomic registry allows us to characterize four different defects on Cu 2 N, which influence the sticking coefficient and electronic coupling of adsorbates.
We report experimentally measured cross sections for pressure broadening of ammonia inversion transitions by J=0, ortho-D2 at temperatures of 18-40 K. These measurements were made in a quasiequilibrium cell using the collisional cooling technique. Cross sections for broadening of the metastable (J,K)=(1, 1), (2, 2) and (3, 3) inversion transitions ranged from 67.5 A2 for (1, 1) at 20.0 K to 100.1 A2 for (3, 3) at 25.0 K. The J=0, ortho-D2 cross sections were found to be consistently larger than previously measured cross sections for low temperature broadening of NH3 by both He and H2.
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