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

2. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 2 Other Contributors 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 -

3. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 3 Outline  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  Surface Hygrogenation Effects on the QE  Ageing due to air exposure  Concluding remarks

4. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 4  Wide Band Gap  Wide Radiation Transparency  High Carriers Mobility (> 2000 cm 2 V -1 s -1 for e - )  High Thermal Conductivity (20 Wcm -1 K -1 @ 20°C)  High Radiation Hardness  Surface activation by hydrogen (NEA) Why DIAMOND for UV Radiation detectors?

5. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 5 Diamond Films DEPOSITION PARAMETERS Diamond film Film Thickness (  m) Input Microwave Power (W) Total Gas Pressure (mbar) Surface Deposition Temperature (° C) Gas Ratio Ar/H 2 /CH 4 (%) GNCD2.2160020099096/3/1 PCD2.091000509000/98/2 NCD4.1860020089096/3/1 PolynanocrystallineMWPECVD Poly and nanocrystalline diamond films were prepared by MWPECVD, at the LIMHP (Laboratoire d’Ingénierie des Materiaux et des Hautes Pressions) - CNRS-UPR- Paris. Substrates = square n-doped silicon (100) of approximately 1 cm 2, ultrasonically abraded during 1h in a diamond powder suspension (~ 40 μm grain size).

6. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 6 External QE Comparison with Literature Comparison with Literature @ = 150 nm QE(%) < 0.5 Literature Proceedings SPIE, vol. 4139 San Diego, California (2000) A.S. Tremsin, O.H.W. Siegmund & Diamond & Related Materials 14 (2005) 48-53 @ = 150 nm QE(%) = 7 Best photoemission and th for the graphitic nanocrystalline diamond film

7. RICH 2007 - Trieste - 17 th OctoberMaria 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  sp 3 > sp 2  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  sp 3 < sp 2  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  sp 3 « sp 2 (N. Wada, et al., J.Non Cryst. Solids 35/36 (1980) 543)

8. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 8 GNCD h MAX = 150 nm PCD h MAX = 120 nm Significant difference in their surface texture Surface morphology & Quantum Efficiency of GNCD and PCD PCs The distribution of heights is centred at a value of about 150 nm for both samples The QE is comparable, and the GNCD PC presents a higher th with respect to the PCD one 3D AFM surface image and distribution of heights of R a = 30.3 nm R a = 30.5 nm

9. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 9 NCD h MAX = 90 nm Fig. 2. Surface morphology & Quantum Efficiency of GNCD and NCD PCs Very similar morphology GNCD 3D AFM surface image and distribution of heights of R a = 26.4 nm The distribution of heights of the NCD is centred at smaller value, about 90 nm, than that of the GNCD The QE of the NCD results to be lower R a = 30.3 nm 3D AFM surface image and distribution of heights of h MAX = 150 nm

10. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 10 GNCD h MAX = 150 nm SCD @ = 150 nm SCD QE(%) = 2.5 lower than that of GNCD, PCD and NCD PCs R a = 1.8 nm Surface morphology & Quantum Efficiency of GNCD and SCD PCs Very different morphology 3D AFM surface image and distribution of heights of h MAX = 5 nm R a = 30.4 nm

11. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 11 RICH 2004 (a) Film deposited by thermal evaporation (b) Film deposited byIBS Electron photoexcitement regions FILM SUBSTRATO hv FILM hv UV Photons SUBSTRATE  hv Photoemission model of CsI PCs grown with two different deposition techniques two completely different morphologies M. A. Nitti et al. NIM A 553 (2005) 157-164

12. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 12 UV Photons Electron photoexcitement regions Film Substrate Distribution of heights (a)(b) PHOTOEMISSION MODEL for Diamond Photocathodes Diamond films which present: (a) a low distribution of heights (b) a high distribution 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 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 Lower QE Higher QE

13. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 13 Dependence of the QE on the distribution of heigths GNCD th = 203 nm PCD th = 195 nm NCD th = 189 nm SCD th = 189 nm GNCD h MAX = 150 nm PCD h MAX = 120 nm NCD h MAX = 90 nm h MAX = 5 nm SCD

14. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 14 Crystalline structure (XRD) (111) (220) (111) (400) High LOCAL crystalline quality (400) (442)

15. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 15 Hydrogenation effect on the QE  SURFACE effect  reduction in the photoemission threshold ENERGY E th NEA properties QE enhancement @ each QE (%) @ 150 nm = 13

16. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 16 Sample stability against ageing due to air exposure Comparison between the of:  a CsI PC  the hydrogenated GNCD PC After 24h air exposure: RQE CsI < RQE hydrogenated GNCD stable the hydrogenated GNCD PC is more stable than the CsI one

17. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 17 I HYDROGEN-treatment: - photoemission enhancement @ each - reduction in the photoemission threshold energy E th (SURFACE effect) II HYDROGEN-treatment, after 24h AIR exposure: - complete recovery of the QE (%) and E th at the same values of the I HYDROGENATION Repeated H 2 plasma treatments: effects on the QE QE (%) @ 150 nm = 18 QE (%) @ 150 nm = 3

18. RICH 2007 - Trieste - 17 th OctoberMaria 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 graphitic component is present in the film  Not closed dependence of QE and grain size  A possible explanation for the observed higher QE has been described in the light of a photoemission model 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 photoemission energy threshold - a stability in air better than the CsI one - the recovery of the initial QE value after air exposure, if the H 2 plasma treatment is repeated multiple times

19. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 19 Outlook Work is in progress in order to:  better understand the role of the graphite and crystalline defects contribution to the photoemission  study doped diamond film PCs  implement an innovative diamond deposition technique, and a new surface treatment

20. RICH 2007 - Trieste - 17 th OctoberMaria Angela Nitti (INFN – Sezione di Bari) 20 Thank You for Your Kind Attention !!! Maria Angela Nitti - mariangela.nitti@ba.infn.it -