While NaCl-structure transition-metal nitrides have been widely studied over the past two decades, little is known about the corresponding NaCl-structure rare-earth nitrides. Polycrystalline CeN, for example, has been reported by different groups to be both a wide band-gap semiconductor and a metal. To address this controversy, we have grown epitaxial CeN layers on MgO͑001͒ and measured their physical properties. The films were grown at 700°C by ultrahigh vacuum reactive magnetron sputter

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... tion in mixed Ar/N 2 discharges maintained at 4 mTorr ͑0.53 Pa͒. X-ray diffraction and transmission electron microscopy results establish the film/substrate epitaxial relationship as cube-on-cube, (001) CeN ʈ(001) MgO with ͓100͔ CeN ʈ͓100͔ MgO , while Rutherford backscattering spectroscopy shows that the layers are stoichiometric with N/Ceϭ0.99Ϯ0.02. CeN is metallic with a positive temperature coefficient of resistivity and a temperature-independent carrier concentration, as determined by Hall effect measurements, of 2.8Ϯ0.2ϫ10 22 cm Ϫ3 with a room temperature mobility of 0.31 cm 2 V Ϫ1 s Ϫ1 . At temperatures between 2 and 50 K, the resistivity is limited by defect scattering and remains constant at 29 ⍀ cm, while at higher temperatures it increases linearly, limited primarily by phonon scattering, to reach a room-temperature value of 68.5 ⍀ cm. The hardness and elastic modulus of CeN͑001͒ were determined from nanoindentation measurements to be 15.0Ϯ0.9 and 330Ϯ16 GPa.