AVS 50th International Symposium
    Advanced Surface Engineering Tuesday Sessions
       Session SE-TuM

Paper SE-TuM2
Growth and Physical Properties of Epitaxial CeN and Nanocrystalline Ti@sub 1-x@Ce@sub x@N Layers

Tuesday, November 4, 2003, 8:40 am, Room 323

Session: Nanostructured, Nanocomposite, and Functionally Gradient Coatings
Presenter: T.-Y. Lee, University of Illinois at Urbana-Champaign, United States
Authors: T.-Y. Lee, University of Illinois at Urbana-Champaign, United States
D. Gall, Rensselaer Polytechnic Institute
C.-S. Shin, Hynix Corporation
N. Hellgren, Intel Corporation
J.G. Wen, University of Illinois at Urbana-Champaign
R.D. Twesten, University of Illinois at Urbana-Champaign
I. Petrov, University of Illinois at Urbana-Champaign
J.E. Greene, University of Illinois at Urbana-Champaign
Correspondent: Click to Email
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 bandgap semiconductor and a metal. To address this controversy, we have grown epitaxial CeN layers on MgO(001) and measured their physical properties. CeN is metallic with a positive temperature coefficient of resistivity and a temperature-independent carrier concentration of 2.8±0.2x10@super22@cm@super-3@ with a room temperature mobility of 0.31 cm@super2@ V@super-1@-s@super-1@. At temperatures between 2 and 50 K, the resistivity remains constant at 29 µ@ohm@-cm, while at higher temperatures it increases linearly to reach a room-temperature value of 68.5 µ@ohm@-cm. The hardness and elastic modulus of CeN(001) were determined from nanoindentation measurements to be 15.0±0.9 and 330±16 GPa. We further explore the possibility to alter the microstructure evolution in metastable Ti@sub1-x@Ce@subx@N quasi-binary alloys by controlling, using low-energy ion irradiation, the kinetics of phase separation driven by the large lattice mismatch of the two components (a@subCeN@ = 0.504 nm, a@subTiN@ = 0.424 nm). We observed nanophase films with x > 0.1. During reactive sputter-deposition of alloys, we observe nanophase films with x>0.1. Under conditions of low ion-irradiation, the nanostructure consists of equiaxed nanometer-size grains which form due to continuous renucleation induced by CeN segregation, which is analogous to the one observed in the nanocomposites of TiN/Si@sub3@N@sub4@. In contradistinction, a nanocolumnar structure forms when the alloys are grown under intense ion-irradiation with J@subi@/J@subMe@ ~ 15 and E@subi@ = 45 eV. The intense ion mixing in the near surface area allows sufficient adatom mobility to form local TiN- and CeN-rich areas that propagate along the growth direction.