AVS 51st International Symposium
    Advanced Surface Engineering Monday Sessions
       Session SE-MoA

Paper SE-MoA5
Epitaxial Growth of B1-NaCl-Structure HfN@sub x@ Layers on MgO(001) by Ultrahigh Vacuum Magnetron Sputter Deposition

Monday, November 15, 2004, 3:20 pm, Room 303D

Session: Structure Control of Hard Coatings in Sputtering Processes
Presenter: H.-S. Seo, University of Illinois
Authors: H.-S. Seo, University of Illinois
T.-Y. Lee, University of Illinois
J.G. Wen, University of Illinois
D. Gall, Rensselaer Polytechnic Institute
I. Petrov, University of Illinois
J.E. Greene, University of Illinois
Correspondent: Click to Email
Group IVB metal nitrides are used in hard coating, wear-resistant, and diffusion barrier applications due to their excellent mechanical, electrical, and electrochemical properties. In the Hf-N system, unlike Ti-N where TiN is the terminal phase, several conflicting claims concerning the existence of N-rich phases have appeared in the literature. Here, we report the results of a systematic investigation of the properties of epitaxial HfN@sub x@ layers grown at 650°C on MgO(001) by ultrahigh vacuum reactive magnetron sputter deposition in mixed N@sub 2@/Ar discharges. X-ray diffraction and transmission electron microscopy analyses show that HfN@sub x@ with 0.8 @<=@ x @<=@ 1.38 grows epitaxially with a cube-on-cube orientational relationship to the substrate. HfN@sub x@ layers with x @<=@ 1.2 are single crystalline while films with x @>=@ 1.24 consist of a mixture of NaCl-structure HfN@sub x@(001) and a N-rich phase with large interplanar spacing (d = 2.7-3.0 Å). The relaxed bulk lattice parameter of HfN@sub x@(001) decreases only slightly with N/Hf ratio from 4.543 Å with x = 0.8 to 4.504 Å with x = 1.38. The room-temperature resistivity @rho@ of HfN@sub x@ varies from 14.2 µ@ohm@-cm for x = 1.0 to 2710 µ@ohm@-cm for x = 1.5, while the hardness H and elastic modulus E values of HfN@sub x@(001) with 0.8 @<=@ x @<=@ 1.5 are 28±4 GPa and 400±60 GPa, respectively. HfN@sub x@(001) layers with 0.8 @<=@ x @<=@ 1.32 are metallic with positive temperature coefficients of resistivity (TCR) between 10 and 300 K and temperature-independent carrier concentrations. They are also superconducting with the highest critical temperature, 9.18 K, obtained for layers with x = 1.0. At higher N/Hf ratios (x @>=@ 1.38), the layers exhibit significant changes in their electronic structure leading to a dramatic increase in @rho@ with a negative TCR, no superconducting transition above 2 K, and a decrease in H and E.