Nitride Superlattice Thin Films for Superhard Coatings Ramou Akin-Cole MRSEC Program 2004 Advisor: Paul Salvador Graduate Student: Nitin Patel
Background Hard materials (e.g. TiN, Al 2 O 3 ) used successfully as coatings to increase tool life by a factor of Diamond and cubic Boron Nitride are the hardest known materials. Diamond gets oxidized in air at high temperatures. Cubic Boron Nitride is difficult to produce as thin film. Cutting tool in operation How can we design materials that have hardness values approaching the hardest known materials ?
Project Objectives Study orientation effects and hardness with increasing Al content in monolithic Ti 1-x Al x N. Grow Thin Films using Physical Vapor Deposition(PVD) Technique called Pulsed Laser Deposition. Characterize films using X-Ray Diffraction and Nanoindenter Grow TiN/Ti 1-x Al x N superlattices in both (100) and (111) direction. Substrate TiN Ti 1-x Al x N TiN Ti 1-x Al x N TiN Ti 1-x Al x N TiN
Experiments SrTiO 3 (Perovskite)MgO, TiN, AlN(Rocksalt) Deposition Parameters PRESSURE : Torr TEMPERATURE:RT °C FLUENCE : 2-6 J/cm 2 FREQUENCY : 1-10 Hz COOLING: Torr
Ti 1-x Al x N films by alternating depositions Target Rate (Å/pulse) # of pulses Thickness (Å) TiN AlN0.293/ Deposit submonolayer of TiN (i.e., 1/4 unit cell thick) 2.Switch target 3.Deposit submonolayer of AlN (i.e., 1/4 unit cell thick) 4.Switch Target 5.Repeat to certain film thickness of Ti 1-x Al x N 200 nm Ti 0.5 Al 0.5 N : {9Ti / 3Al / 9Ti / 4Al} x 475
Monolithic Ti 1-x Al x N Films Intensity (a.u.) SrTiO STO (200) Ti:Al =1:0 Intensity (a.u.)
Orientation Intensities and Lattice Parameter versus Composition Intensity (a.u.) Al:Ti ratio Lattice Parameter ( Å)
TiN/Ti 0.25 Al 0.75 N multilayer MgO (111) SrTiO 3 STO (111) MgO Bragg (200) Peak Bragg (200) Peak Bragg (111) Peak MgO (200) Bragg (200) Peak MgO +1 SrTiO 3 Bragg (200) Peak STO (200) -2
Hardness versus Ti:Al ratio
Conclusion Al was difficult to grow in crystalline form TiN and Ti 1-x Al x N grow epitaxially in 100 direction and not in 111 direction. Superlattices grow well in 100 direction and not in 111 orientation The hardness values of superlattices show significant enhancement, over individual component Optimizing processing conditions can enable the growth of (111) oriented monolithic Ti 1-x Al x N films and superlattices