Hard Coatings & Coatings Competence Center (Ingenia S3p TM )

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1 Willkommen Welcome Bienvenue Hard Coatings & Coatings Competence Center (Ingenia S3p TM ) Prof. Dr. Hans Hug, Empa Nanoscale Materials Science Lab

2 Outline Nanocomposite Hard Coatings by reactive sputtering Ti on PEEK by HiPIMS Diamond-like thin films Diamond-like Carbon by PaCVD tetrahedral amorphous Carbon by HiPIMS Ingenia Sp3 TM

3 Nanocristalline TiN/a-Si 3 N 4 50 nc-tin/a-si 3 N Hardness (GPa) M. Diserens, et al., Surf. Coat. Tech (1998), 241. S. Vepřek, et al., Surf. Coat. Tech. 109 (1998), 138. Nanohadrness [GPa] TiN Si 3 N F. Vaz, et al., Surf. Coat. Tech (2000), Amorphous phase (at%) Si 3 N 4 content [at%] J. Patscheider, et al., Surf. Coat. Tech (2001), nanometer-sized grains suppress dislocation formation high hardness ultrathin amorphous binder phase fabricated by reactive sputtering of materials that phase-separate hardness higher than that of constituent materials typ. 30 GPa

4 Reactive Magnetron Sputtering Sample introduction Heating sample substrate holder Plasma MHz Substrate Turbo Pressure: p 0 ~ 10-6 Pa, p dep ~ 0.3 Pa Sputter gas: Ar & reactive gas N 2 / O 2 Substrates: Si, glass, SiO 2, WC-Co Subs. Temp: C Deposition rate: ~250 to 650 nm/h Thickness: ~1-2 µm Si target Al Si Magnetrons Al target N 2 Ar Magnetrons (closed field) reactive sputtering can be challenging because of target poisoning

5 AlN Nanocomposite a hard & optically transparent coating AlN is transparent because of its wide band gap AlN is hard (used for bullet-proof windows in single-crystalline form) reactive sputtering of Al & Si in Ar/N 2 to form AlN (?) and a-si 3 N 4 -grain boundary phase Al in Ar/N 2 /O 2 to form AlN (?) and a-al 2 O 3 -grain boundary phase Hardness [GPa] Si [at.%] Hardness [GPa] Hardness [GPa] Glass 10 % Si uncoated O content in film (at%) O [at.%] coated both materials systems are hard and transparent

6 but incomplete phase separation XRD analysis: c spacing [Å] 4,98 4,97 4,96 4,95 4, O content in film (at%) lattice shrinkage with increasing Si/O content soluability limit formation of grain boundary phase how can Si and O be incorportated into the AlN to form Al-Si-N or Al-O-N?

7 Valence Charge Compensation element / ion # e - donated (+) accepted (-) radii [pm] covalent ionic Al / Al Si / Si N / N O / O AlSiN: smaller Si +4 for Al +3 "cation" / e - -donor replacement AlON: smaller O -2 for N -3 "anion" / e - -acceptor replacement Si (3s2p2): 1 e- more than Al (3s2p1) O (2s2p4): 1 e- more than N (2s2p3) extra valence charge must be compensated 1 Al vacancy per 3 substituent atoms ab-initio calculations confirm lattice shrinking annealing 1400 C show that defective state is metastable entropy plays a role for the formation of the amorphous grain boundary phase

8 Metallization of Polymers using HiPIMS Clinical Problem PEEK: Bone-like elastic modulus; radiolucent & artifact-free Titanium: good osseointegration Approach/ Aim Coat PEEK implants with Titanium to improve integration Warrant adhesion: 22 MPa + 6σ (static tensile test, ISO) Retain primary stability, coat complete surface K. Thorwarth et al. T-PAL PEEK spinal spacer (DePuy Synthes) T-PAL PEEK spinal spacer (Ti, HiPIMS coated at Empa)

9 Metallization of Polymers using HiPIMS Example Research at University of Oxford to refine the design and use of chronic implants in long term neuroscience experiments with macaques. Collaboration between University of Basel, University of Zurich, University of California, Newcastle University and Oxford University Advantages Ti coated PEEK allows for radiolucency Adhesion: <30 MPa; Ahesion 35 MPa; HiPIMS Good 3-d coverage No change on primary stability features

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12 How to obtain even harder coatings? dense coatings & good adhesion hardness: 48 GPa E-module: 280 MPa & super smooth surface AFM reveals ±8nm ARC Evaporation high ionization sp3 C dense coatings & good adhesion hardness: 58 GPa E-module: 748 MPa brittle but: Particles! wear polishing needed OC Oerlikon Ingenia S3p TM scalable pulsed power plasma HiPIMS high ionization? CTI: Oerlikon (OSS) - Empa

13 How to obtain t-ac Biaxial stress is critical to produced high sp 3 films - David.R. McKenzie A fraction α enters the film at depth R, while a fraction (1- α) fails to penetrate and increases film thickness. Schematic diagram of the thermal spike. The hemispherical spike has an initial radius r 0 and a temperature of 5000 K, while the substrate is initially at 300 K J. Robertson. Diamond and Related Materials, 2 (1993) 984 N. Marks. Phys. Rev. B, 56 (1997) 2441

14 Our own Theory Work Density Building an Amorphous Bulk sp2/sp3 content Deposition on Amorphous Bulk Hardness

15 Building an Amorphous Bulk Amorphous Cell (atoms randomly) [SlabOS code] density 2.01 g/cm 3 graphite: 2.26 g/cm 3 density 3.02 g/cm 3 Range: g/cm 3 Cell size 50 Å x 50 Å x 50 Å diamond: 3.53 g/cm 3

16 Deposition on Amorphous Bulk Deposited atom 50 ev Final energy onto the substrate 200 ev = bias + initial kinetic energy 50.0 Å... Deposition onto 1.52 g/cm 3 substrate 0 atoms 100 atoms 1000 atoms Deposition onto 3.51 g/cm 3 substrate 0 atoms 100 atoms 1000 atoms 150eV energy leads to high sp3 content of growing layer on any substrate

17 Classical Magnetron Sputtering versus HiPIMS - what matters? Kinetic energy of condensing ions determines: Cristallinity, Texture & Density Film Stress Interface mixing Sub-plantation depth energy of deposited atom is the key parameter for film texture A. Anders, Appl. Phys. Lett. 80 (2002) 1100 A. Anders, Thin Solid Films 518 (2010) 4087 S. Van Steenberge, Appl. Phys. Lett. 105 (2014)

18 Classical Magnetron Sputtering versus HiPIMS - what matters? HiPIMS: higher ion energies higher ion/neutral ratio HiPIMS: higher Ti/Ar ion ratio self-sputtering Technology Gas Ar 1+ Ar 2+ Ti 1+ Ti 2+ DC Ar HIPIMS Ar increase impact energy with substrate bias, but ions NOT neutrals are needed! increased self sputtering less Ar implantation A. P. Ehiasarian et al., Plasma Process. Polym. 4 (2007) 309

19 HiPIMS for ta-c Multiple attempts to make ta-c Highest sp 3 fraction is a challenge Likely explanation is the low ionization efficiency of carbon Electron density n e (10 17 m 3 ) higher electron density in plasma higher ionization fraction of C high density plasma needed achieve this by extreme HiPIMS conditions

20 Rapid Discharge is needed Former work by R. Ganesan: Discharge is delayed for more than 50 to 90 µs depending upon the pulse. Present work with Ingenia S3p TM by R. Empa: quick discharge within 10µs multiple pulses per cycle Current (A) µs x 4 1.6µbar Current (A) Time (µs) Time (µs) Tucker & Ganesan et al. J. Appl Phys. 119 (2016)

21 Rapid Discharge is needed Voltage (arb. units) Target 2 Target 3 Trigger pulse Auxillary pulse Target 1 Present work with Ingenia S3p TM by R. Empa: quick discharge within 10µs multiple pulses per cycle Current (A) µs x 4 1.6µbar Current (A) Time (µs) Time (µs) Ingenia S3p TM higher ionization density Time (µs) achieved by modification of power supply and sample temperature management

22 Results Density (g/cm 3 ) Hydrogen fraction (%) Bias of -120 V is ideal µs; recent result 50 µs; 15 kw P Peak Pressure (µbar) 9.5% of H in Kapton (ref) 0.27% of H Channels -120 V Bias -140 V Bias -160 V Bias puls with 15kW P Peak low H content high T application (normally H-free is less than 5% H) Density (g/cm 3 ) Argon (at %) µbar; -120 V Bias ; 15 kw P Peak ; 3.75 kw P Avg µbar, -120V bias puls 15kW P Peak 3 µbar; -120 V Bias ; puls with 15kW P 15 kw P Peak ; 3.75 kw Peak P Avg sp 3 in % tuning non-disclosed parameter higher density 3µbar, -120V bias tuning non-disclosed parameter reasonable Ar content

23 High Hardness & good Elasticity high hardness Hardness (GPa) recent result 30 µs puls with 15kW P Peak 2.5 µbar 3 µbar 3.5 µbar 4 µbar 50 µs; 15 kw P Peak ; 3.75 k W P Avg Negative Substrate Bias (-V B ) good adhesion 100 µm with With Cr interlayer & gradient coating II: Diamond-likecarbon I: Cr metal Base layer: Stainless steel thermal 300 C V Bias V B = -120V 300 C as deposited Wavenumber (cm -1 ) 100 µm without Without Cr interlayer delamination The young's modulus (E) of the hardest sample did not exceed 280 GPa, shows the capability of the coating to overcome the usual failure aspects that occurs to FCVA deposited film

24 Short Pulses Flat Surfaces µbar; -120 V Bias ; 15 kw P Peak ; 3.75 kw P Avg. Arcing rate (s -1 ) tuning non-disclosed parameter arc suppression smooth films arc depositon HiPIMS (SEM) HiPIMS (AFM) topography: ± 8nm p-p 20µm 20µm 1µm high S3p TM -HiPIMS, hard & elastic ta-c coating with no particles

25 Collaborators Experiments Dr. Kerstin Thorwarth (Group Leader) Dr. Rajesh Ganesan Maria Fischer (Ph.D. Student) Mathis Trant (Ph.D. Student) Dr. Sebastien Guimond (Oerlikon Surface Solutions) Theory: Dr. Daniele Passerone (Group Leader) Dr. Carlo Pignedoli Dr. Daniele Scopece Thank you for your Attention