1. Nitride Superlattice Thin Films for Superhard Coatings Ramou Akin-Cole MRSEC Program 2004 Advisor: Paul Salvador Graduate Student: Nitin Patel

2. Background  Hard materials (e.g. TiN, Al 2 O 3 ) used successfully as coatings to increase tool life by a factor of 4-20.  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 ?

3. 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

4. Experiments SrTiO 3 (Perovskite)MgO, TiN, AlN(Rocksalt) Deposition Parameters PRESSURE : 0.001 - 0.2 Torr TEMPERATURE:RT - 950 °C FLUENCE : 2-6 J/cm 2 FREQUENCY : 1-10 Hz COOLING: 10 -5 - 200 Torr

5. Ti 1-x Al x N films by alternating depositions Target Rate (Å/pulse) # of pulses Thickness (Å) TiN0.1291.08 AlN0.293/41.02 1.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

6. Monolithic Ti 1-x Al x N Films Intensity (a.u.) SrTiO 3 100 STO (200) Ti:Al =1:0 Intensity (a.u.)

7. Orientation Intensities and Lattice Parameter versus Composition Intensity (a.u.) Al:Ti ratio Lattice Parameter ( Å)

8. 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

9. Hardness versus Ti:Al ratio

10. 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