Application of optical techniques for in situ surface analysis of carbon based materials T. Tanabe, Kyushu University Necessity of development of (1) in-situ tritium detection technique To determined where and how much tritium is retained at particular locations in tokamak (2) in-situ removing technique Different techniques will be required depending on tritium retaining materials and its concentration 9th ITPA meeting on SOL/divertor physics, Garching, May 7-10, 2007

Optical techniques can be in-situ surface analysis systems with assistance of optical fibers, mirrors and lens UV to Visible Optical absorption/emission spectroscopy Infrared to far-infrared IR, FT-IR, Raman Laser light Optical emission/absorption Energy loss (Laser Raman) Neutral particle emission (Thermal Desorption Spectrosocpy) Ion emission (TOF-MASS) Electron energy loss or electron emission spectroscopy can be used but require sophisticated energy analyzing systems in vacuum

UV to Visible Optical absorption/emission spectroscopy Infrared to far-infrared IR, FT-IR, Raman In this work, Application of for carbon materials retaining hydrogen. Lots of works have been done for thin films (a:C-H film) but not much for bulk carbon materials, because graphite is a conductor and opaque. Need to analyze reflecting light, which gives limited information of near surface region.

In-situ high resolution observation & diffraction B  c 5 nm Initial 300s 1300s 1900s B  c HOPG Fiber

Intensity [a.u.] Raman Shift (cm -1 ) HOPG B  c Laser Raman Spectra of Hydrogen ion irradiated HOPG Electron diffraction h hs s

D + ion irradiation Original Graphite layers 2D modification Defect production in the layers 3D modification Defect formation between the layers Amorphous Homogenous in 3D K. Niwase et al., J. Nucl. Mater (1992)

He + irradiationD + ion irradiation Amorphous

Re-deposited layer inboard Eroded area JT-60: Open divertor tiles

Line analysis

Crystalline size [ nm ] ○ Redeposited area ○ Eroded area TEXTOR ALT- ｌｌ tile

Irradiation with very high flux and high temperature at NAGDIS-II Cooperation with Drs. Ohno and Takamura 10mm 1200K Irradiation 7.7×10 26 /m K Irradiation 3.4×10 26 /m -2 Mostly eroded Eroded Deposited

Amorphous FWHM 1580 cm -1 I 1355 /I Crystalline size [ nm ] 700 K 700 K(100eV) 600 ～ 700K (25keV) Ion implantation 25keV Unirradiated 1200K Deposited area Eroded area 1200K

B. Disher, et al. Appl. Phys.Lett. 42(1983)636 G. Compagnini, Phys. Rev. B51(1995)11168 Wider band gap Higher sp 3 C Optical absorption and band gap of a:C-H film Absorption coeff. of three a:C-H film with different refractive index. Absorption edge of diamond is shown for comparison IR region CH stretch band

FT-IR spectra in the CH stretch band region of the VGCF after successive irradiations of 6.0, 3.0 and 1.0 keV H+ ions to saturation. (a) 373 K, (b) 623 K, (c) 823 K, (d) 923 K. The separated- band assignment, band frequency are indicated at the resolved bands. Estimated relative CHx density in the hydrogen-ion implanted VGCF with or without the post-irradiation heat-treatment, as a function of the heat-treatment temperature Ion irradiated carbon fiber (VGCF) FT-IR spectra in the CH stretch band region

FT-IR Spectra of hydrogen implanted HOPG in reflection geometry ion/cm ion/cm ion/cm 2 ※ Reference: HOPG Gap widening C-H Stretching Polarized light Reflected light Standing wave Sample

Conclusions Following techniques are probed to be useful for in situ surface analysis of carbon materials Laser induced optical emission Need to understand ablation physics Laser Raman Spectroscopy determines micro-structure but hard to get H/C. Optical absorption Spectroscopy Band gap width could be related to H/C. FT-IR could give H/C but sill need to increase S/N.

Laser induced visible light emission SAR 266 Emission from C 2, C, C + & C 2 + WAR 266 Emission from C 2 Y. Sakawa et al. J. Nucl. Mater. in press

Laser induced Time Of Flight Mass Spectrometry (TOFMS) SAR 266 Emission of C +, C 2+ ions WAR 266 Carbon clusters (C n + ) Y. Sakawa et al. J. Nucl. Mater in press