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M. A. Nitti, M. Colasuonno, E. Nappi, A. Valentini

Performance Analysis of Poly- and Nano-Crystalline Diamond based Photocathodes. M. A. Nitti, M. Colasuonno, E. Nappi, A. Valentini. INFN - Sezione di Bari - Via Amendola 173, 70126 Bari (Italy). 6 th International Workshop on Ring Imaging Cherenkov Counters (RICH 2007)

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M. A. Nitti, M. Colasuonno, E. Nappi, A. Valentini

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  1. Performance Analysis of Poly- and Nano-Crystalline Diamond based Photocathodes M. A. Nitti, M. Colasuonno, E. Nappi, A. Valentini INFN - Sezione di Bari - Via Amendola 173, 70126 Bari (Italy) 6th International Workshop on Ring Imaging Cherenkov Counters (RICH 2007) Stazione Marittima, Trieste, Italy 15 – 20 October 2007

  2. Diamond growth:F. Bénédic - Laboratoire d’Ingénierie des Matériaux et des Hautes Pressions, UPR1311 CNRS,Universite´ Paris 13, 99 av. J. B. Clément, 93430 Villetaneuse, France – Raman spectroscopy: G. Cicala - Istituto di Metodologie Inorganiche e dei Plasmi (IMIP-CNR) – Sezione di Bari - Via Amendola 122/D, 70126 Bari, Italy - Surface hydrogenation treatment: E. Milani, G. Prestopino -Dipartimento di Ingegneria Meccanica, Università di Roma “Tor Vergata”, Via del Politecnico 1, 00133 Roma, Italy - Surface morphology analysis: E. Fanizza - Dipartimento di Chimica, Università di Bari, Via Orabona 4, 70124 Bari, Italy - Other Contributors Maria Angela Nitti (INFN – Sezione di Bari)

  3. External Quantum Efficiency (QE) results, in the range 150-210 nm, of Poly- and Nano-Crystalline Diamond (PCD and NCD) PCs • Informations on the Surface Morphology, Bulk Structure and Crystallinity of PCD and NCD films • Photoemission Model • SurfaceHygrogenation Effects on the QE • Ageing due to air exposure • Concluding remarks Outline Maria Angela Nitti (INFN – Sezione di Bari)

  4. Why DIAMOND for UV Radiation detectors? • Wide Band Gap • Wide Radiation Transparency • High Carriers Mobility (> 2000 cm2V-1s-1 for e-) • High Thermal Conductivity (20 Wcm-1K-1@ 20°C) • High Radiation Hardness • Surface activation by hydrogen(NEA) Maria Angela Nitti (INFN – Sezione di Bari)

  5. Substrates =squaren-doped silicon (100)of approximately 1 cm2, ultrasonically abraded during 1h in a diamond powder suspension (~ 40 μm grain size). Diamond FilmsDEPOSITION PARAMETERS Poly and nanocrystalline diamond films were prepared by MWPECVD, at the LIMHP (Laboratoire d’Ingénierie des Materiaux et des Hautes Pressions) - CNRS-UPR- Paris. Maria Angela Nitti (INFN – Sezione di Bari)

  6. Best photoemission and th for the graphitic nanocrystalline diamond film Literature @  = 150 nm QE(%) < 0.5 A.S. Tremsin, O.H.W. Siegmund Proceedings SPIE, vol. 4139 San Diego, California (2000) • & • Diamond & Related Materials 14 (2005) 48-53 @  = 150 nm QE(%) = 7 External QE Comparison with Literature Maria Angela Nitti (INFN – Sezione di Bari)

  7. RAMAN SPECTRA of the diamond film photocathodes • The PCD film exhibits an intense and narrow diamond peak at 1332 cm-1,and a broad peak at 1550 cm-1sp3>sp2 • The NCD film exhibits typical peaks at: 1140 and 1470 cm-1 of transpolyacetylene, 1350 and 1580 cm-1 of graphite D and G bands 1332 cm-1 of broad diamond peak sp3 < sp2 • The GNCD film presents the typical bulk structure of a graphitic nanocrystalline sample, with peaks at 1350 and 1580 cm-1 of graphite D and G bands, and the low intensity diamond peak at 1332 cm-1 sp3 «sp2 (N. Wada, et al., J.Non Cryst. Solids 35/36 (1980) 543) Maria Angela Nitti (INFN – Sezione di Bari)

  8. 3D AFM surface image and distribution of heights of The distribution of heights is centred at a value of about 150 nmfor both samples hMAX = 150 nm hMAX = 120 nm The QE is comparable, and the GNCD PC presents a higher th with respect to the PCD one PCD GNCD Surface morphology & Quantum Efficiency of GNCD and PCD PCs Ra = 30.5 nm Ra = 30.3 nm Significant difference in their surface texture Maria Angela Nitti (INFN – Sezione di Bari)

  9. 3D AFM surface image and distribution of heights of 3D AFM surface image and distribution of heights of The distribution of heights of the NCDis centred at smaller value,about 90 nm, than that of the GNCD hMAX = 90 nm hMAX = 150 nm The QE of the NCD results to be lower Very similar morphology GNCD NCD Surface morphology & Quantum Efficiency of GNCD and NCD PCs Ra = 30.3 nm Ra = 26.4 nm Maria Angela Nitti (INFN – Sezione di Bari) Fig. 2.

  10. 3D AFM surface image and distribution of heights of SCD @  = 150 nm SCDQE(%) = 2.5 lower than that of GNCD, PCD and NCD PCs hMAX = 150 nm hMAX = 5 nm Very differentmorphology GNCD Surface morphology & Quantum Efficiency of GNCD and SCD PCs Ra = 30.4 nm Ra = 1.8 nm Maria Angela Nitti (INFN – Sezione di Bari)

  11. hv UV Photons hv hv Photoemission model of CsI PCs grown with two different deposition techniques two completelydifferent morphologies hv hv  Electron photoexcitement regions FILM SUBSTRATO SUBSTRATE SUBSTRATE (a) Film deposited by thermal evaporation (b) Film deposited by IBS FILM RICH 2004 M. A. Nitti et al. NIM A 553 (2005) 157-164 Maria Angela Nitti (INFN – Sezione di Bari)

  12. Distribution of heights Diamond films which present: (a) a low distribution of heights UV Photons a larger portion of the electron photo-excitement regions is far from the film surface; therefore, many photoelectrons have to travel a too long path before escaping Electron photoexcitement regions Lower QE (b) a highdistribution of heights most of the electron photo-excitement region is located near to the surface, and so many more photoelectrons can escape from the film Film Film Higher QE Substrate Substrate (a) (b) PHOTOEMISSION MODELfor Diamond Photocathodes Maria Angela Nitti (INFN – Sezione di Bari)

  13. GNCD GNCD th= 203 nm PCD th = 195 nm NCD th = 189 nm SCD th = 189 nm hMAX = 150 nm hMAX = 90 nm hMAX = 120 nm hMAX = 5 nm PCD Dependence of the QE on the distribution of heigths NCD SCD Maria Angela Nitti (INFN – Sezione di Bari)

  14. (400) (400) (442) (220) (111) (111) (111) High LOCAL crystalline quality Crystalline structure (XRD) Maria Angela Nitti (INFN – Sezione di Bari)

  15. QE (%) @ 150 nm = 13 QEenhancement @ each  • SURFACE effect reduction in the photoemission threshold ENERGY Eth NEA properties Hydrogenation effect on the QE Maria Angela Nitti (INFN – Sezione di Bari)

  16. Comparisonbetween the of: • a CsI PC • the hydrogenatedGNCD PC After 24h air exposure: RQECsI< RQE hydrogenatedGNCD the hydrogenatedGNCD PCis more stable than theCsI one Sample stability against ageing due to air exposure Maria Angela Nitti (INFN – Sezione di Bari)

  17. QE (%) @ 150 nm = 18 QE (%) @ 150 nm = 3 I HYDROGEN-treatment: - photoemissionenhancement @ each  - reduction in the photoemissionthreshold energy Eth (SURFACE effect) IIHYDROGEN-treatment,after 24h AIR exposure: - completerecovery of theQE (%) and Ethat the same values of the IHYDROGENATION Repeated H2 plasma treatments: effects on the QE Maria Angela Nitti (INFN – Sezione di Bari)

  18. Concluding remarks • NCD PCs, that generally show a lower QE with respect to PCD ones, enhance their photoemission if a graphiticcomponent is present in the film • Not closed dependence of QE and grain size • A possible explanation for the observed higherQE has been described in the light of a photoemissionmodel correlated to the distribution of heights • QE of Diamond based PCs  QE of CsI PCs • The hydrogenated diamond PC evidences: - the enhancement of the photoemission with respect to the untreated sample, and the lowering of the photoemissionenergythreshold - a stability in air better than the CsIone - the recovery of the initial QE value after air exposure, if the H2 plasma treatment is repeated multiple times Maria Angela Nitti (INFN – Sezione di Bari)

  19. Work is in progress in order to: better understand the role of the graphite and crystallinedefects contribution to the photoemission studydopeddiamond film PCs implement an innovative diamond deposition technique, and a new surface treatment Outlook Maria Angela Nitti (INFN – Sezione di Bari)

  20. Thank You for Your Kind Attention !!! Maria Angela Nitti - mariangela.nitti@ba.infn.it - Maria Angela Nitti (INFN – Sezione di Bari)

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