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sics Polymer coating method develo N , Y EN ne 2 th y-m 00 m dia ese RI Beam Factory [1]. In this situation we thus had to The process of deposition of PPX-C (molecular structure is shown in Fig. 1) consists of three steps as shown in 2005; a photograph of the system is shown in Fig. 3. Three or four glass substrates of 12.6 cm in diameter coated with carbon layer were mounted inside the deposition chamber ARTICLE IN PRESS and an appropriate amount of dimer was placed in the vapourizer to obtain 20–30-mg/cm2-thick layer of PPX-C on the carbon foil. We chose this thickness range because 0168-9002/$ - see front matter r 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2008.02.059 �Corresponding author. Tel.: +8148467 9472; fax: +81 48 462 4643. E-mail address: hasebe@riken.jp (H. Hasebe). develop a method of producing large area (10 cm diameter) carbon foils, which could withstand necessary manipula- tions. It was found that the poly-monochloro-para-xylylene (PPX-C) with its advantage of relatively easy evaporation when irradiated by beams could be used as a strengthening polymer. 2. Deposition process of PPX-C 3. Production of PPX-C-coated C-foils 3.1. Coating of PPX-C The process of the carbon foil reinforcement by Parylene-C (PPX-C) was performed using the vapour deposition system LABCOTER (PDS 2010 by Specialty Coating Systems) [2] installed in our laboratory in August 1. Introduction Thin carbon foils (C-foils) have a well-known problem of handling; they easily break during floating processes or when mounted to a holder. This becomes especially challenging when large area foils are considered. C-foils strengthened by coating with polymer are commercially available with the thicknesses of 3–20 mg/cm2, but they are not thick enough to be used as a stripper foil at the RIKEN Fig. 2. The first step is to vapourize a solid dimer at approximately 448K (175 1C). The second step is to cleave the methylene–methylene bonds of dimer (pyrolysis) at approximately 963K (690 1C) in order to yield stable monomeric diradical, monochloro-para-xylylene. In the final step the vapour of monomer adhere to the substrate and polymerize. This step is performed in a room temperature deposition chamber where vapour of mono- meric diradical is transported from pyrolysis container. Keywords: Carbon foil; Stripper; Stripper lifetime; Polymer coating Hiroo Hasebe�, Hiromichi Ryuto, Masayuki Kase Nishina Center for Accelerator-Based Science, RIK Available onli Abstract The problem of handling the fragile carbon foils (mounting on self-supporting has been solved by coating carbon foils with pol method could also be used to produce carbon foils thicker than 1 para-xylylene layers. Carbon foil of 500 mg/cm2 thick and 10 cm in Results of lifetime measurement for singly coated foils are also pr r 2008 Elsevier B.V. All rights reserved. PACS: 29.20.Hm; 29.25.Pj; 81.15.Ef; 81.15.Gh; 85.40.Sz Nuclear Instruments and Methods in Phy e frame, placing in the stripper changer) that easily break when onochloro-para-xylylene. It was found that the polymer-coating g/cm2 by alternated deposition of carbon and poly-monochloro- meter was produced by this method and mounted to a foil holder. nted. Research A 590 (2008) 13–17 ped for carbon stripper foils obuhisa Fukunishi, Akira Goto, asushige Yano , 2-1 Hirosawa, Wako, Saitama 351-0198, Japan March 2008 www.elsevier.com/locate/nima thinner PPX-C caused easy breakage of the foils while mounting on the frame or placing in the stripper changer, and thicker PPX-C caused shorter lifetime of the foil during the irradiation. The thickness of PPX-C was determined by measuring the difference of weight of the test sample, placed near the substrate, before and after the deposition. It took approximately an hour for one cycle of coating process. 3.2. Single-layer C-foil coated with PPX-C The single layer foils were prepared using the carbon foil supplied by Arizona Carbon Foil Co. They were coated with PPX-C using the procedure described above. The photos of ACF-40 carbon foil (Arizona Carbon Foil with thickness of 40 mg/cm2) [3] with and without deposition of 20–30 mg/cm2 PPX-C (Fig. 4) show the surface smoothing effect of coating layer. Photographs were obtained using Atomic Force Microscope (AFM). ARTICLE IN PRESS Poly-monochloro-para-xylylene CH2 CH2 Cl n (PPX-C) Fig. 1. Molecular structure of poly-monochloro-para-xylylene (PPX-C). Fig. 3. Photograph of LABCOTER (PDS 2010). H. Hasebe et al. / Nuclear Instruments and Methods in Physics Research A 590 (2008) 13–1714 Fig. 2. Deposition process of PPX-C. ARTICLE IN PRESS ethods H. Hasebe et al. / Nuclear Instruments and M 3.3. Multi-layer of carbon and PPX-C When reinforcing ACF carbon foils with PPX-C layer we noticed that the carbon deposited on the PPX-C layer adhere to it very strongly. This observation resulted with the idea that the thick carbon foil can be prepared by alternating deposition of both materials. The first layer of carbon can be prepared either by arc discharge or by the magnetron sputtering technique but the second and following layers of carbon had to be deposited using magnetron sputtering for evaporation. The arc discharge evaporation technique although suitable for Fig. 4. AFM photographs of ACF-40: (a) without deposition and (b) with deposition of 20�30 mg/cm2 of PPX-C. Fig. 5. Multi-layer of carbon and PPX-C on a substrate. pre of car thi the ph 45- a 1 wa thi gla age foi 3.4 lar � Fig thin in Physics Research A 590 (2008) 13–17 15 paration of the first layer cannot be applied for deposition further layers as it generates pinholes in the existing bon–polymer layers. It was found that the most suitable ckness of each carbon layer was approximately 50mg/cm2; thicker carbon also caused pinholes. Fig. 5 shows a otograph of the film consisting of 11 layers of approximately mg/cm2-thick carbon, and 10 layers of PPX-C deposited on 2.6-cm-diameter glass substrate. Another layer of PPX-C s deposited on the surface of the multi-layer foil. To prepare s foil vapours of carbon and PPX-C were deposited on the ss covered with NiCl2, LaCl3, or NaCl used as releasing nt. The colour of 20–30-mg/cm2-thick PPX-C on a carbon l is blue due to interference of light. . Mounting of a large-sized foil to a foil holder We applied the following procedures for mounting a ge-sized foil to a foil holder: Foil, still on the substrate, was annealed at approxi- mately 423K (150 1C) for 4–5 h in order to avoid the foil curling at later step of releasing from substrate. . 6. Foil being mounted to the holder using a ring-frame with several threads interlaced to support the foil. � The edge of substrate was scrapped off the foil with a cutter knife, and then the foil–substrate contact line was gently wetted (by dripping the water using pipette) with water at 303–313K (30–40 1C) to release the edge of the foil. � Foil was floated on the water by slow immersing of the substrate with foil into a bawl with distilled water. � Released foil was fished on intermediate ring-frame consisting of several fine threads interlaced to sustain the foil. � Foil was then dried on a hot plate at approximately 423K (150 1C). � When dry, the edge of the foil was loosened from the ring-frame by blowing nitrogen gas along the foil–frame contact line. � Finally, the foil was transferred from ring-frame to stripper foil holder. The carbon foil stuck to the holder with the help of small amount of vacuum grease spread along the holder edge. The grease viscosity enables foils to adhere to the holder (see Figs. 6 and 7). results of the measurement are shown in Fig. 9 where ARTICLE IN PRESS Fig. 7. Foil mounted to the holder. Fig. 8. Holder installed on the ‘‘rotating cylinder stripper’’. 0 ACF-20 ACF-20+PPX-C ACF-40 ACF-40+PPX-C ACF-80 ACF-80+PPX-C L H. Hasebe et al. / Nuclear Instruments and Methods in Physics Research A 590 (2008) 13–1716 0 50 100 15 ACF-10 ACF-10+PPX-C Fig. 9. Measured lifetimes of the C-foils with and without PPX-C coa ife ti ting 200 250 300 350 400 me (sec) lifetimes of C-foils with and without PPX-C coating are compared for all four studied thicknesses. It was found that the coating caused no significant decrease of the lifetime of stripper foil. We also measured the lifetime of a long-lived The holder with this large-sized foil will be mounted on ‘‘rotating cylinder stripper’’ which rotates at a speed of 1000 rpm [4] (see Fig. 8). 4. Results of lifetime measurement In order to investigate the influence of the PPX-C coating on the foil lifetime we measured the lifetime of singly coated C-foils. The C-foils: ACF-10, 20, 40 and 80 with thicknesses of 10, 20, 40 and 80 mg/cm2, respectively, were used for this study. The measurements were carried out by irradiating the C-foils with a 32 keV/u 136Xe9+ beam at an intensity of 420 pnA delivered by a 500 kV Cockcroft–Walton terminal. The diameter of the beam spot focused on the C-foil was 5mm. The lifetime was determined by monitoring both the beam intensity of stripped ions and the C-foil image on a TV display. The . No significant decrease of the lifetime due to coating is seen. C-foil prepared by the method developed by us [5], and as well observed no decrease of the lifetime due to coating. 5. Conclusion We have solved the problem of handling the fragile thin carbon foils by strengthening the C-foil with layer of PPX-C. The method described in this paper remarkably improved the yield rate of successful mounting of the carbon stripper foils to the stripper holders. It was found in the irradiation by heavy ion beams tests that the coating caused no significant decrease of the lifetimes of carbon foils. We succeeded as well to produce the thick multi-layer self-supported carbon foil of total thickness of approxi- mately 500 mg/cm2, and mount on the frame with aperture of 10 cm in diameter. References [1] H. Ryuto, N. Fukunishi, H. Hasebe, N. Inabe, S. Yokouchi, O. Kamigaito, A. Goto, M. Kase, Y. Yano, in: Proceedings of 2005 Particle Accelerator Conference, 2005, Knoxoille, Tennessee, USA, p. 3751. [2] Specialty Coating Systems (SCS), URL: /http://www.scscoatings. com/S. [3] ACF-Metals Arizona Carbon Foil Co. Inc., URL: /http://www. techexpo.com/firms/acf-metl.htmlS. [4] H. Ryuto, H. Hasebe, N. Fukunishi, S. Yokouchi, A. Goto, M. Kase, Y. Yano, Nucl. Instr. and Meth. A 569 (2006) 697. [5] H. Hasebe, M. Kase, H. Ryuto, Y. Yano, in: Proceedings of 17th International Conference on Cyclotrons and their Applications (Cyclotrons 2004), Tokyo, Japan, October 2004, p. 313. ARTICLE IN PRESS H. Hasebe et al. / Nuclear Instruments and Methods in Physics Research A 590 (2008) 13–17 17 Polymer coating method developed for carbon stripper foils Introduction Deposition process of PPX-C Production of PPX-C-coated C-foils Coating of PPX-C Single-layer C-foil coated with PPX-C Multi-layer of carbon and PPX-C Mounting of a large-sized foil to a foil holder Results of lifetime measurement Conclusion References