| AVS 57th International Symposium & Exhibition | |
| Thin Film | Monday Sessions |
| Session TF+EM-MoM |
| Session: | Nanostructuring Thin Films |
| Presenter: | B. Howe, University of Illinois at Urbana-Champaign |
| Authors: | B. Howe, University of Illinois at Urbana-Champaign E. Sammann, University of Illinois at Urbana-Champaign J.-G. Wen, University of Illinois at Urbana-Champaign M. Sardela, University of Illinois at Urbana-Champaign T. Spila, University of Illinois at Urbana-Champaign J. Greene, University of Illinois at Urbana-Champaign L. Hultman, Linköping University, Sweden I. Petrov, University of Illinois at Urbana-Champaign |
| Correspondent: | Click to Email |
Transition metal nitrides (TMN) are well known to have a remarkable range of unique physical properties. One method used to further enhance the physical properties of many transition metal nitrides is to alloy them with a second, thermodynamically immiscible nitride. The most famous example is Ti1-xAlxN; many have reported drastically enhanced physical properties including super hardness, increased oxidation resistance, age-hardening behavior, and the formation nanoscale compositional modulations during film growth and post annealing experiments. However, very little has been reported on the ability to control this nanostructure, nor has the effect of these nanostructures on the physical properties of the films. We have chosen Hf1-xAlxN as a model system to study the nanostructures of interest. We begin by reporting on the effects of nanostructure on the opto-electronic, thermal transport and elastic constant properties of Hf1-xAlxN single crystal layers grown on MgO(001) using ellipsometry, temperature dependent hall effect, and picosecond probe acoustic transport measurements, respectively. We continue by summarizing a systematic study into the effects of growth parameters (ion energy, Ei, ion-to-metal flux ratio, Jion/Jme, and substrate temperature, Ts) on single crystal reactively sputtered Hf0.7Al0.3N/MgO(001) layers in order to controllably manipulate the nanostructure and study its effects on the physical properties. Films are deposited from a Hf/Al 70/30 (at. %) target in 5% N2/Ar mixtures while Jion/Jme is varied from 0.7 to 12.6, Ts from 400 to 700 ° C, and Ei from 10 to 80 eV. Jion/Jme has a strong effect on the formation of 3D nanoscale (2-3nm) compositional modulations as indicated by HR-XRD and HR-TEM. Nanoindentation experiments reveal an increase in film hardness from 31.7 ± 0.6 GPa to 38.9±0.6 GPa. Ei has a strong effect on the AlN incorporation probability, which can be adjusted between ~ 0 and 100% by varying the ion energy (Ei) incident at the growing film over a narrow range, 10-40 eV. Epitaxial film compositions vary from x = 0.30 with Ei = 10 eV, to 0.27 with Ei = 20 eV, 0.17 with Ei = 30 eV, and ≤ 0.002 with Ei ≥ 40 eV. This extraordinary range in real-time manipulation of film chemistry during deposition is due to the efficient resputtering of Al atoms (27 amu) by Ar+ ions (40 amu) backscattered from Hf atoms (178.5 amu). We demonstrate that this effect can be used to grow superlattices with abrupt interfaces at high deposition rates from a single target by switching Ei. We grew superlattices with bilayer thicknesess from 1-6nm and films exhibited an increase in hardness from 32.5±0.9 GPa to 37.8±1.2 GPa.