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S.Wyczawska 1 , M.Buck 3 , P. Cyganik 2 , P. Lievens 1 ,

LAP 2006, 10-15 Sep 2006. STRUCTURE DEPENDENT IRRADIATON-INDUCED DESORPTION OF BIPHENYL ALKANETHIOL SELF-ASSEMBLED MONOLAYERS. S.Wyczawska 1 , M.Buck 3 , P. Cyganik 2 , P. Lievens 1 , R. E. Silverans 1 , E. Vandeweert 1 , F. Vervaecke 1 , and Z. Postawa 2.

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S.Wyczawska 1 , M.Buck 3 , P. Cyganik 2 , P. Lievens 1 ,

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  1. LAP 2006, 10-15 Sep 2006 STRUCTURE DEPENDENT IRRADIATON-INDUCED DESORPTION OF BIPHENYL ALKANETHIOL SELF-ASSEMBLED MONOLAYERS S.Wyczawska1, M.Buck3, P. Cyganik2, P. Lievens1, R. E. Silverans1, E. Vandeweert1, F. Vervaecke1, and Z. Postawa2 1 Laboratory of Solid State Physics and Magnetism, K.U.Leuven, Celestijnenlaan 200D, B 3001 Leuven, Belgium 2 Institute of Physics, Jagiellonian University, ul. Reymonta 4, PL 30-059 Krakow, Poland 3School of Chemistry, St Andrews University, North Haugh, St Andrews, KY16 9ST, United Kingdom

  2. Outline • Introduction • Experimental setup • Polymorphism in biphenyl-based SAMs 4. Odd/even effect in BPn/Au 5. Conclusions

  3. Tail Spacer Head Typical mM concentrations in solvent (ethanol) Substrate Introduction Self-Assembled Monolayer: (SAM) Highly ordered and oriented assemblies that are formed spontaneously by the adsorption of a surfactant with a specific affinity of the headgroup to a substrate. Tail : surface properties Spacer : intermolecular interactions ordening and orientation molecules Head : bound to substrate atom

  4. Introduction Interaction of energetic projectiles with self-assembled monolayers: Aim: to investigate the fundamental influence ofthe detailed geometric and electronic structure of SAMs on projectile-induced desorption • Characterization: • damage induced during standard characterization techniques such as SIMS and AES • Controlled modification: SAMs are promising to be used as ultrathin resist in lithographic patterning

  5. BP2 Introduction 2 stable hybridization: We investigated biphenyl-based SAMs: BPn, n=1, 2, 3, 4, 5, 6 R sp CH3 C =180° S (CH2)n Phenyl chromophore Au sp3 R S C S =104° 4,4’-biphenyl-substituted alkanethiol Au

  6. charged particles Experimental setup SAM substrate

  7. + charged particles + + + + + laser pulse Experimental setup TOF and ion detector SAM substrate

  8. + M m n 9 5 2 m 0 n M 9 5 2 Experimental setup Ionization of neutral molecules • Detection of neutral molecules • Photo-ionization but also photofragmentation

  9. + M m M* n 9 5 2 m 0 n M 9 5 2 Experimental setup Resonance-enhanced multiphoton ionization • Detection ofneutralmolecules • Photo-ionization but also photofragmentation • Introduction of a suitable chromophore M*  resonance enhanced • increase of the ionization efficiency • reduction of laser intensity •  reduction of the photofragmentation Aromatic rings act as chromophores 1. Vandeweert et al., Nucl. Instrum. and Meth. in Phys. Res. B 164-165 (2000)

  10. Experimental setup Spectra Physics 15 keV Ar+ Fion = 1011ions/cm² • = 259nm Fphoton = 1017ph/cm2 (m/Dm)lin = 200 (m/Dm)ref = 800 1 keV Ar+ Fion = 1015electrons/cm² P = 10-10 Torr

  11. Ar+ irradiation BP2/Au m/z = 168 Ion signal (arb.u.) Flight time (µs) Experimental observables 1. Flight-time distributions:  probing ion signal in function of flight time ( = difference between ion and laser pulse) kinetic energy of desorbing particles 2 ejection mechanisms: [2] 1.Ballisticejection: direct momentum transfer (~ 1 eV) 2.Thermal-likeejection: bond cleavage by reactive species (~ 0.02 eV) T B 2. Riederer et al., J. Am. Chem. Soc. 119 (1997)

  12. BP2/Au: 168 Ar+ irradiation 195 167 181 Ion Signal (arb.u.) 228 194 165 181 227 Mass (a.m.u.) Experimental observables 2. Desorption fragmentation pattern:  probing which particles are desorbed • parent molecule desorbed • desulphurized fragment desorbed • m/z = 181 photofragment • m/z = 168 desorbed • m/z = 165 photofragment

  13. a BP4/Au: b BP4/Au: BP3/Au: • grown at 295 K • 27.01 Ų/molecule • C-S-Au bond angle f> 130° Only one phase –no changes when prepared at elevated temperature • post-annealed at 423 K • 32.4 Ų/molecule • C-S-Au bond angle f< 130° Polymorphism in BPn/Au Detailed geometric and electronic structure depends on growth parameters [3] 3. Cyganik et al., J. Am. Chem. Soc. 126 (2004)

  14. Au Au Polymorphism in BPn/Au n = even α-BPn β- & -BPn • prepared at 295 K • angle C-S-Au > 130° • prepared at 423 K • angle C-S-Au < 130°

  15. 181 difference in desorption behavior of BP4 and BP4-S a BP4/Au BP4 168 BP4-S Ion signal (arb.u.) 181 b BP4/Au BP4-S 168 BP4 Mass (a.m.u.) Polymorphism in BPn/Au Ion-induced desorption: Probing desorption mass spectra during 15-keV Ar+ irradiation of aand b/d even BPn/Au

  16. BPn BPn-S a phase b/d phase Normalized ion signal (arb.u.) n n Polymorphism in BPn/Au Ion-induced desorption: Desorption probability of the parent molecule is larger for athan for b/deven BPn/Au Desorption probability of the BPn-S molecule is larger for b/dthan for aeven BPn/Au bond scission efficiency of the S-Au bond is larger for a than for b/d even BPn/Au bond scission efficiency of the C-S bond is larger for b/d than for a even BPn/Au

  17. BPn BPn-S a phase b/d phase Normalized ion signal (arb.u.) n n Polymorphism in BPn/Au Ion-induced desorption: RT BP5/Au and HT BP5/Au: no change in desorption probability • changes in bond scission efficiency between aandb/d even BPn/Au are related to structural change and not to annealing

  18. intermolecular interactions suppressed due to energy addition Au f f f f f f f f f Au Au Au Polymorphism in BPn/Au Discussion: optimization bond geometry optimization 2 dimensional packing f ~ 104 ° a even BPn/Au: b even BPn/Au: f < 130 ° f > 130 °

  19. f f f f f f Au Au S-Au weakest bond C-S weakest bond Polymorphism in BPn/Au Discussion: b/deven BPn/Au: a even BPn/Au: f > 130 ° f < 130 °

  20. [2] a BP4/Au: BP3/Au: • grown at 295 K • 27.01 Ų/molecule • C-S-Au bond angle f> 130° • grown at 295 K • 21.6 Ų/molecule • C-S-Au bond angle f ~ 109° 4. Azzam et al., Langmuir, 19 (2003) Odd/even effect in BPn/Au Detailed geometric and electronic structure depends on growth parameters and alkane chain: [3,4] 3. Cyganik et al., J. Am. Chem. Soc. 126 (2004)

  21. Au Au Odd/even effect in BPn/Au n = odd n = even α-BPn • prepared at 295 K • angle C-S-Au ~ 109° • prepared at 295 K • angle C-S-Au > 130°

  22. 181 BP3-S difference in desorption behavior of BPn and BPn-S BP3/Au 168 Ion signal (arb.u.) BP3 168 BP4/Au 181 BP4-S BP4 Mass (a.m.u.) Odd/even effect in BPn/Au Ion-induced desorption: Probing desorption mass spectra during 15-keV Ar+ irradiation of odd and even BPn/Au

  23. BPn BPn-S Normalized ion signal (arb.u.) n n Odd/even effect in BPn/Au Ion-induced desorption: Desorption probability of the parent molecule is larger for even than for odd BPn/Au Desorption probability of BPn-S molecule is larger for odd than for even BPn/Au bond scission efficiency of the C-S bond is larger for odd than for even BPn/Au bond scission efficiency of the S-Au bond is larger for eventhan for odd BPn/Au

  24. f f f f f f Au Au C-S weakest bond S-Au weakest bond Odd/even effect in BPn/Au Discussion: Odd BPn/Au: Even BPn/Au f~ 109° f > 130° both interactions result in same structure conflict between interactions

  25. difference in geometric and electronic structure changes in bond scission efficiency induced by projectile irradiation difference in desorption probability of different molecular fragments Conclusions competition between molecule-substrate bond and intermolecular interactions

  26. THANK YOU

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