Crystalline thin films of stoichiometric Cu3N and intercalated Cu3NMx (M = metals): Growth and physical properties

The growth of stoichiometric samples of thermally unstable noble-metal nitrides remains a challenge. Thin films of nearly stoichiometric Cu3N have been successfully grown on Si (100) wafers by reactive magnetron sputtering of Cu target with mixed nitrogen and argon. The controversies regarding bandgap, lattice constant, decomposition temperature, room-temperature electrical resistivity, etc., can be resolved. Nitrogen re-emission leads to the formation of Cu3N nanocrystallites, generally 40-60 nm in size, enclosed by Cu-terminated {111} facets. Samples with a slight Cu excess may turn into a metallic conductor with excellent electrical conductivity via a percolation mechanism. Unfavorable growth conditions may give rise to blistering or even mesocaled fivefold symmetrical relief structures in the deposit. These structures result from the rearrangement of nanocrystals via gliding along the {111} facets. Ternary Cu3NMx (M = Pd, Cu, In, Zn, etc.) compounds, with the excessive metal atoms occupying the cell centers of the Cu3N lattice, can be obtained by cosputtering under similar conditions. Such ternary compounds can easily be made metallic. In Cu3NPd0.238 a constant electrical resistivity was measured in a temperature range similar to 200 K. Incorporation of In or O atoms may raise the decomposition temperature but not to more than 400 degrees C if the decomposition products are required to be as good a conductor as Cu. The present results might be relevant for growing films of thermally unstable materials. The peculiar electrical conduction behavior in the Cu3NMx structures is expected to inspire the search for nearly zero-band materials similar to Cu3NPd0.238 as well as to promote an indepth exploration of potential applications of these materials.