Scanning tunneling microscopy is used to characterize the electronic structure of 1 ML films of c(2 x 2)N/Cu(100) (i.e., Cu2N). By varying nitrogen coverage, a variety of morphologies are prepared, including (1) isolated similar to 25 nm(2) 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 4 eV. 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). (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3010720]