D C I CIDS: Center of Interface Dynamics for Sustainability D C I Dynamics of molecular interactions at surfaces Experiments and Eley-Rideal reactions with hyperthermal N atoms Aart W. Kleyn 1 Materials innovation institute (M2i), The Netherlands 2 FOM Institute DIFFER, The Netherlands 3 Center of Interface Dynamics for Sustainability, Chengdu Development Center for Science and Technology, China Academy of Engineering Physics, Chengdu, China 4 HIMS, Faculty of Science, University of Amsterdam, The Netherlands 5 Leiden Institute of Chemistry, Leiden University, The Netherlands

D C I Dalian 2/ 56 Outline 1.Mechanisms and experiments on dynamics at surfaces 2.Physisorption interaction: Ar + Ag(111) or Ru(0001) 3.Chemisorption: N-atom scattering at Ag(111) 4.Role of electronically excited N-atoms 5.Interactions at adsorbates: and with fast N 2 6.Eley – Rideal or direct reactions: 7.Conclusions

D C I Dalian 3/ 56 Dynamics of Gas-Surface Interactions: Direct scattering Trapping desorption Chemisorption Often used in molecular flow simulation codes such as DSMC

D C I Dalian 4/ 56 Dynamics of Gas-Surface Reactions: A + BC → AB + C Langmuir Hinschelwood: Trapping Dissociation / Diffusion Recombination Eley-Rideal: Direct concerted reaction without accomodation of kinetic and potential energy

D C I Dalian 5/ 56 Hyperthermal Gas surface dynamics is relevant for (esoteric) applications: fusion, space, semiconductor manufacturing

D C I Dalian 6/ 56 Shuttle glow: a surface reaction courtesy Edmond Murad

D C I Dalian 7/ 56 Background: EUV lithography 7  Goal: study the interaction of reactive nitrogen environments (N-atoms) with Ru surfaces Multilayer mirror with capping layer

D C I Dalian 8/ 56 Dynamics of gas-surface reactions: N+O ads →NO 8 Langmuir Hinschelwood: (LH): Trapping, (Dissociation), Diffusion, Reaction, Desorption Eley-Rideal:Direct pick-up reaction NO acc LH dominant by far

D C I Dalian 9/ 56 Distribution of HCl formed in H+Cl ads 9 HCl formed between specular and normal directions Parallel momentum H conserved Light atom ER, heavy atom??? Fast HCl peak (ER) and thermal HCl (LH) Rettner, JCP 101 (1994) 1529

D C I Dalian 10/ 56 ER abstraction O + + O ads → O 2 -, E i > 20 eV O removed from Si(100)-O Abstraction with ions at excess translational energy Sputtering excluded (isotopic labeling) Quinteros, Tzvetkov, Jacobs, J.Chem.Phys. 113 (2000) O 2 - yield

D C I Dalian 11/ 56 HARPOEN scattering experiments 11

D C I Dalian 12/ 56 Energy determination by TOF technique: ‘effusive’ 4-5 eV fast beam ( kJ/Mol) Energy of N and N 2 plasma produced neutral beam N: E i FWHM / ~1.16 N 2 : E i FWHM / ~1.14 Operation of cascaded arc source: total tip current ~60 A, ~88(150) V for Ar(N 2 ) stagnation pressure ~230(325) mbar for Ar(N 2 ) plasma cascaded arc plates (  =2.5 mm) nozzle (  =3 mm), skimmer (  =0.5 mm) collimator (  =1 mm) Created at Technische Universiteit Eindhoven cathode tips Gas

D C I Dalian 13/ 56 HARPOEN set-up

D C I Dalian 14/ 56

D C I Dalian 15/ 56 Outline 1.Mechanisms and experiments on dynamics at surfaces 2.Physisorption interaction: Ar + Ag(111) or Ru(0001) 3.Chemisorption: N-atom scattering at Ag(111) 4.Role of electronically excited N-atoms 5.Interactions at adsorbates: and with fast N 2 6.Eley – Rideal or direct reactions: 7.Conclusions

D C I Dalian 16/ 56 6 eV Ar scattering at Ru(0001): T S dependence (  i =60 o ) Angular E f /E i distribution 60 ° T S =xx K Ueta, Gleeson, Kleyn, J. Chem. Phys, 138 (2011) Beam normalized Angular flux distribution

Dalian 17/ 56 D C I Probing physisorption: Ar scattering – M Ru =101, M Ag =108 – Ru: hcp, Ag: fcc potential energy surface (PES) z V(z) Ar-Ag(111) potential: Lahaye et al, Surf. Sci.338 (1995) 169

Dalian 18/ 56 D C I Comparison Ru and Ag (D-)Ru(0001)Ag(111) 40 ° Energy transfer Scattered intensity

Dalian 19/ 56 D C I (D-)Ru(0001) (T S =0 K) MD simulations: Ar/Ag(111)* Ag(111) * Lahaye, Kleyn, Stolte and Holloway, Surf. Sci., 338, 169 (1995). Comparison Ru and Ag

Dalian 20/ 56 D C I (T S =0 K) (D-)Ru(0001)Ag(111) MD simulations: Ar/Ag(111)* * Lahaye, Kleyn, Stolte and Holloway, Surf. Sci. 338 (1995) 169 Comparison Ru and Ag

Dalian 21/ 56 D C I (T S =0 K) MD simulations: Ar/Ag(111)* Ru is stiffer and exhibits structure scattering (D-)Ru(0001) * Lahaye, Kleyn, Stolte and Holloway, Surf. Sci., 338, 169 (1995). rainbow scattering** Increasing E i Less surface atom vibration

Dalian 22/ 56 D C I Physisorption:Ar => Ru(0001) & Ag(111) low T S & adding D – rainbow scattering (presence of structure scattering) high T S – remaining structure scattering  Ru has much higher stiffness than Ag  D makes Ru even stiffer Ueta, Gleeson, Kleyn, J. Chem. Phys, 138 (2011)

D C I Dalian 23/ 56 Outline 1.Mechanisms and experiments on dynamics at surfaces 2.Physisorption interaction: Ar + Ag(111) or Ru(0001) 3.Chemisorption: N-atom scattering at Ag(111) 4.Role of electronically excited N-atoms 5.Interactions at adsorbates: and with fast N 2 6.Eley – Rideal or direct reactions: 7.Conclusions

Dalian 24/ 56 D C I Probing chemisorption N atom probes chemisorption well Ar atom probes repulsive wall z V(z) N & Ar atoms scattering from Ag(111)

Dalian 25/ 56 D C I Experimental 4-6 eV N, N 2, Ar at Ag(111) Incident angle of 40°and 60° Surface temperature 600 K (zero N coverage limit), 300 K full N-coverage 600 K 40 ° 60 ° thermal desorption

Dalian 26/ 56 D C I Experimental conditions N and N 2 mixed beam Incident angle of 40°and 60° TOF technique: ‘effusive’ 4-5 eV fast beam ( kJ/Mol) 600 K 40 ° 60 ° N: E i FWHM / ~1.16 N 2 : E i FWHM / ~1.14

D C I Dalian 27/ 56 DFT Potentials for N-Ag(111) Note the corrugation at hollow sites Note the distance of closest approach, due to well From: N-Ag(111) potential: Ludovic Martin-Gondre et al., Comp. Theor. Chem. 990 (2012) 126.

D C I Dalian 28/ 56 Potentials for Ar-Ag(111) and N-Ag(111) Note the big difference in corrugation Trajectory calculations give broad angular distributions N-Ag(111) potential: Ludovic Martin-Gondre et al., Comp. Theor. Chem. 990 (2012) 126. Ar-Ag(111) potential: Lahaye et al, Surf. Sci.338 (1995) 169

D C I Dalian 29/ 56 N & Ar scattering angular distribution (Θ i =60 o ) 60 ° T S =600 K ExperimentTheory N flux distribution: Sharp distribution (Ar like) + Broad distribution (non-Ar) DFT + CTC Theory misses the specular contribution, for all lattice dynamics models Specular contribution is attributed to excited N-atoms in the beam. Ueta, Gleeson, Kleyn, J. Chem. Phys, 138 (2011) ; Martin-Gondre, Bocan, Blanco-Rey, Alducin, Juaristi, Diez Muino, J. Phys. Chem. C 117 (2013) 9779.

D C I Dalian 30/ 56 Outline 1.Mechanisms and experiments on dynamics at surfaces 2.Physisorption interaction: Ar + Ag(111) or Ru(0001) 3.Chemisorption: N-atom scattering at Ag(111) 4.Role of electronically excited N-atoms 5.Interactions at adsorbates: and with fast N 2 6.Eley – Rideal or direct reactions: 7.Conclusions

D C I Dalian 31/ 56 Presence of excited state of N atoms in beam Beam contains not only ground state N( 4 S) but also electronically excited states atoms N( 2 P) + N( 2 D) Ratio not determined Appearance potential measurements N( 4 S) : N( 2 D) : N( 2 P)=100 : 30 : 10, Alagia et al., Isr. J. Chem., 37, 329 (1997). N( 4 S) : N( 2 D) : N( 2 P)=100 : 4 : 1.3, Lin and Kaufman, J. Chem. Phys., 55, 3760 (1971). N( 4 S) : N( 2 D) : N( 2 P)=100 : 17 : 6, Foner and Hudson, J. Chem. Phys., 37, 1662 (1962).

D C I Dalian 32/ 56 Interpretation: 2 D specular scattering cluster calculations* * Kokh, Buenker and Whitten, Surf. Sci., 600, 5104 (2006). ** Wang, Jiang, Pang, Nakamura, J. Phys. Chem. B, 109, (2005) & Martin-Gondre et al. Two-component angular distribution Broad (non-Ar) >> Sharp dist. (Ar like) Presence of two states of N atoms in incident beam Potential crossing in MRD-CI * E b (N-Ag)  eV (DFT) ** Z eq  1.1 – 1.5 Å (fcc hollow) ** N( 2 D) appears inert: large coupling

D C I Dalian 33/ 56 Harpooning van Salm ( ))

Dalian 34/ 56 D C I Polanyi’s flame experiments 1932 Oversized cross sections Los and Kleyn, in Alkali halide vapors,1979, Academic Press: New York. p Alkali age: Harpooning and large cross sections K + Br 2  KBr + Br

D C I Dalian 35/ 56 Ion-pair formation, Landau-Zener transitions in Na + I → Na + + I - Simple physics thanks to discrete states Surface science situation more difficult (Wodtke, AuerbachTully et al.) Experimental sophistication needed: state selection

D C I Dalian 36/ 56 Outline 1.Mechanisms and experiments on dynamics at surfaces 2.Physisorption interaction: Ar + Ag(111) or Ru(0001) 3.Chemisorption: N-atom scattering at Ag(111) 4.Role of electronically excited N-atoms 5.Interactions at adsorbates: and with fast N 2 6.Eley – Rideal or direct reactions: 7.Conclusions

D C I Dalian 37/ 56 N atoms scattering from N-covered Ag(111) Ueta, Gleeson, Kleyn, J. Chem. Phys. 135 (2011) For N atoms: Ag(111) = N-Ag(111 Corrugation remains Reactivity remains? => potential unchanged?? Do Eley-Rideal reactions occur? 60 ° T S =300 K

D C I Dalian 38/ 56 Good agreement on absolute scale! Specular peak absent (Excited states?) Similarity between bare and N-covered surface coincidental? Calculations indicate presence of ER reactions Blanco-Rey, Martin-Gondre, Díez Muiño, Alducin, Juaristi, J. Phys. Chem. C 116 (2012) N interaction at N-Ag(111): angular distributions 60 ° T S =300 K

D C I Dalian 39/ 56 N 2 and Ar scattering at Ru (900K) 39 Specular scattering for 5 eV N 2. No dissociation visible. No corrugation, no intensity at 20 o, Ru is flat for N 2 and Ar T. Zaharia, Kleyn, Gleeson, Zeitschrift Phys. Chem 227 (2013) 1511

D C I Dalian 40/ 56 Outline 1.Mechanisms and experiments on dynamics at surfaces 2.Physisorption interaction: Ar + Ag(111) or Ru(0001) 3.Chemisorption: N-atom scattering at Ag(111) 4.Role of electronically excited N-atoms 5.Interactions at adsorbates: and with fast N 2 6.Eley – Rideal or direct reactions: 7.Conclusions

D C I Dalian 41/ 56 Ar, N or N 2 scattering at N-Ru (400K) 41 Direct pick-up reactions? N + N  N 2 N and Ar scattering similarly broadened Large broadening for scattered N 2. Extra scattering pathway?? T. Zaharia, Kleyn, Gleeson, Zeitschrift Phys. Chem 227 (2013) 1511

D C I Dalian 42/ 56 Very deep wells for N-atoms throughout the unit cell! Blanco-Rey, Martin-Gondre, Díez Muiño, Alducin, Juaristi, J. Phys. Chem. C 116 (2012) N interaction at N-Ag(111): potentials T S =300 K

D C I Dalian 43/ 56 N+N 2 scattering & formation at N-Ag(111) theory & experiment 43 Broadening for scattered N 2. Extra scattering pathway?? ER reaction!! Maria Blanco-Rey et al. J.Phys.Chem.Lett 4 (2013) 3704 Hirokazu Ueta et al. J.Chem.Phys. 135 (2011)

D C I Dalian 44/ 56 Cross section for reaction N + N ads → N 2 σ ER < 5 Å 2 << σ unit cell Maria Blanco-Rey et al. J.Phys.Chem.Lett 4 (2013) 3704

D C I Dalian 45/ 56 Formation in N scattering at O-Ru 45 NO formed in sub-specular direction with strongly above thermal energy (5 eV); thermal desorption impossible/invisible here. Strong evidence for direct pick-up reaction

D C I Dalian 46/ 56 NO formation from N + O ads 46 NO formed between specular and normal directions Parallel momentum N conserved Heavy atom ER Zaharia, Kleyn, Gleeson, PRL in press.

D C I Dalian 47/ 56 NO energy and kinetics of decay Not all N can react (cutoff on NO energy), in fact about 0.4 I NO =ke -60 → σ NO ≈ 34Å 2 assuming O-removal only. Cross section larger than unit cell size: contradiction Zaharia, Kleyn, Gleeson, PRL in press. τ≈50 s

D C I Dalian 48/ 56 Ru(0001)-O(2×1) surface 48 Ru O 2.8 Å σ unit cell ≈ 13 Å 2

D C I Dalian 49/ 56 Decay and rise times for NO and N 2 production using full beam exposure Other processes to decrease NO decay: competition with N deposition and removal; not all NO removed in ‘fast’ process, also LH active N 2 increase factor 11 higher than NO decrease (vibrational effect?) σ O-removal ≈ 5 Å 2 Zaharia, Kleyn, Gleeson, PRL in press. Eley-Rideal Langmuir- Hinschelwood

D C I Dalian 50/ O Ru N NO Eley-Rideal – fast NO

D C I Dalian 51/ O Ru N NO Hot Atom – fast NO

D C I Dalian 52/ O Ru N NO Langmuir-Hinschelwood – thermal NO

D C I Dalian 53/ Ru N N2N2 ER – fast N 2

D C I Dalian 54/ 56 Simultaneous ER reactions forming NO and N 2 ER reactions cause rapid removal of strongly bound surface species Hyperthermal N-atom beams deposit and remove at the same time Zaharia, Kleyn, Gleeson, PRL in press.

D C I Dalian 55/ 56 Summary and conclusions  Eley Rideal reactions conclusively observed for incident N atoms; first time for non hydrogenic reactants  fast N atoms can pick up N or O from Ru surfaces – potential cleaning application  cross section of N+O  NO ER reaction is ~30 Å 2 Mainly due to efficient N 2 formation with deposited N-atoms  State resolved experiments needed! 55

D C I Dalian 56/ 56 Future plans: