Real-time electron-spin-resonance measurement of plasma induced surface interactions

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1 Realtime electronspinresonance measurement of plasma induced surface interactions 1 Naoya Sumi, 1 Kenji Ishikawa, 2 Hideo Horibe, 2 Akihiko Kono, 1 Keigo Takeda, 1 Hiroki Kondo, 1,3 Makoto Sekine and 1,3 Masaru Hori 1 Nagoya Univ., 2 Kanazawa Inst. of Technol., 3 JSTCREST ISPlasma2011 1

2 Outline of this talk Background Comprehensive understanding of surface reaction Chemical bond breaking process under plasma process Experimental setup Real time in situ electronspinresonance (ESR) Results and discussion Hydrogen plasma on PTE (C 2 C 2 ) Not only individual effect but also synergistic interactions of ions, radicals, and photons Summary ISPlasma2011 2

3 Background of this study Plasmasurface interactions are complex! Electrons, Ions, reactive neutrals, and photons Gaseous radical Light illumination Plasma Individual role and synergistic effects > PAPE Electrons Ion irradiation Surface reactions Materials (Semiconductor, softflexible, biocompatible) ISPlasma2011 3

4 Background PAPE (Pallet for Plasma process Evaluation) Transparent windows and shadowing plates With or without gap between the surface Si Mg 2 Mg 2 psioch (a) Radical psioch (b) Light after Uchida, et al. J. Appl. Phys. 103, (2008). psioch (c) Radical and Light ISPlasma2011 4

5 Background In line measurements Rupture of chemicalbonds, then danglingbonds creation. Only in line methods was previously succeeded. in line method (w/o air exposure) Plasma reactor In situ analyzer after K. Ishikawa, et al Appl.Phys. Lett., 81, 1773 (2002). After processes, samples may be changed. Thus realtime in situ analysis is required. ISPlasma2011 5

6 Objective of this research Establishment of realtime ESR measurement for analyzing plasmainduced surface reactions Realtime measurement of poly(tetrafluoroethylene) (PTE) surface irradiated by H 2 plasma Strong bondenergy for C (5.05 ev) Candidates for biocompatibles H H Can H atoms break C? Analyzed by using ESR and PAPE C C C ISPlasma2011 6

7 ElectronSpinResonance (ESR) Energy Magnetic field Unpaired electron Zeeman splitting Absorption Microwave energy H d I d H Typical ESR spectrum gvalue Intensity ΔH pp H Resonance condition h g H B 0 h B : Planck s constant : Bohr magnetron H 0 g : requency of microwave : Magnetic field : g value Detect microscopic nature surrounding dangling bonds ISPlasma2011 7

8 Realtime ESR Measurement Setup Plasma source Gas Microwave (2.45 GHz) Radical d distance, d Plasma emission ESR cavity <Cross section> PTE Microwave Glass tube Φ10 mm Exhaust ESR Magnet <ESR condition> Microwave frequency Microwave power Modulation amplitude : 9.53 GHz : 20 mw : 2.0 G ESR Cavity Quartz tube PTE ESR Magnet Magnetic field ISPlasma2011 8

9 PAPE (Plasma process Evaluation) Radical Lights Shadowing plate Light (Plasma emissions) Radical Transparent window (Mg 2 or Quartz) Individual effects of species can be analyzed. ISPlasma2011 9

10 Intensity [arb.unit] C dangling bond creation by H 2 plasma <Experimental condition> H 2 : 50 sccm Microwave : 50 W d : 15 cm Pressure : 10 Pa Irradiation time : 15 min g Simulated spectrum of C 2 C*C 2 H 2 plasma irradiation initial g value C The ESR signal was identified as fluoroalkyl radicals. ISPlasma C C Hyperfine interaction from atom having nuclear spins [1] M. Kuzuya et al., Appl. Surf. Sci. 60/61 (1992).

11 Influence of air exposure Intensity [arb.unit] After O 2 exposure C 2 COO*C 2 Before O 2 exposure C 2 C*C 2 5 <Experimental condition> Step1. H 2 plasma irradiation Step2. O 2 exposure: O 2 : 5 sccm Pressure : 10 Pa Exposure time : 15 min : C 2 C*C 2 reacted with O g value C 2 COO*C 2 was formed [2] [2] A. Oshima et al. Radiat. Phys. Chem. 55 (1999). no fluoroalkyl radical was observed by exsitu. ISPlasma

12 Results of Realtime Measurement Surface radical density [ cm 2 ] <Experimental condition> H 2 : : 50 sccm Microwave power: 50 : W50 W Pressure : 10 Pa d : : cm Irradiation time : 21 : min 21 min aster rate Time [min] Radical formation speed [ cm 2 min 1 ] Time [min] The realtime ESR enable us to measure dynamics of formation. ISPlasma

13 Effects of atomic H and Optical emissions <H atom> <Plasma emissions> Intensity [arb.unit] After irradiation initial g value No radical formation Intensity [arb.unit] After irradiation initial g value luoroalkyl radicals were formed. ISPlasma

14 Radical formation speed cm 2 min 1 ] Wavelength dependence of emissions light (Mg 2 t=1 mm) light (Mg 2 t= 5mm) light (quartz) Time [min] Quartz: No surface dangling bond formation Windows:Mg 2 (1, 5 mm thick), Quartz H 2 : 50 sccm Power : 50 W Pressure : 10 Pa distance : 20 cm Processing period : 21 min Shorter wavelength than 250 nm Mg 2 : ormation of surface dangling bonds Saturated rates with light intensity ISPlasma

15 Synergistic effects of atomic H and vacuum UV Radical formation speed [ cm 2 min 1 ] H atom vacuum UV only vacuum UV Time [min] Why plasma process enhances to reactions. ISPlasma

16 Synergistic effects of atomic H and vacuum UV < VUV > Rupture of C bonds recombine the bonds before was desorbed > slow rate H atom H H < H atom > Not enough energy to break C bonds > no reaction Light C C C Photocatalytic process enables to modify! ISPlasma

17 Concluding remarks We established the realtime ESR measurement setup. The synergistic enhancement of H atom and vacuum UV in modifying PTE was found. insitu measurement luoroalkyl radicals were formed when PTE film was irradiated with H 2 plasma because of peroxy radical was formed by air exposure. realtime measurement We found that a synergistic effect of yielding radicals by H atom and vacuum UV emissions. ISPlasma

18 Thank you for your attention. This was in part supported by Tokai region of the Knowledge cluster Initiative (The second stage). Author: Kenji Ishikawa Plasma Nanotechnology Research Center (PLANT) ISPlasma