1. RD05 Conference Florence, October 6 th, 2005 SINGLE CRYSTAL CVD DIAMOND DETECTORS Cristina Tuvè Department of Physics and Astronomy, University of Catania and INFN Cristina.Tuve@ct.infn.it M. Angelone 1, V. Bellini 4, A. Balducci 2, M.G. Donato 3, G. Faggio 3, M. Marinelli 2, G. Messina 3, E. Milani 2, M.E. Morgada 2, M. Pillon 1, R. Potenza 4, G. Pucella 2, G. Russo 4, S. Santangelo 3, M. Scoccia 2, C. Sutera 4, A. Tucciarone 2, G. Verona ‑ Rinati 2 1 Associazione EURATOM-ENEA sulla Fusione, Frascati (Roma), Italy 2 Dip. di Ing. Meccanica, University of Roma “Tor Vergata”, Italy 3 Dip. Meccanica dei Materiali, University of Reggio Calabria, Italy 4 Department of Physics, University of Catania ad INFN, Italy

2. RD05 Conference Florence, October 6 th, 2005 OUTLINE  Diamond films were grown in the Laboratories of Roma “Tor Vergata” University by CVD  Polycristalline CDV diamond -  -particle detection -  -particle detection - 12 C particle detection at National Southern Laboratories (LNS) in - 12 C particle detection at National Southern Laboratories (LNS) in Catania (Italy) Catania (Italy) - Neutron monitoring at Joint European Torus (JET) in Culham (U.K.) - Neutron monitoring at Joint European Torus (JET) in Culham (U.K.)  Single crystal CVD diamond growth  Characterization  Radiation detectors -  -particle detection -  -particle detection - Neutron detection - Neutron detection  Conclusions

3. RD05 Conference Florence, October 6 th, 2005 Structural characterization M.G. Donato, G. Faggio, G. Messina, S. Santangelo Dip. Meccanica e Materiali Università di Reggio Calabria - Italy Micro-Raman and Micro-PL FWHM = 2.4 cm -1, comparable with that of natural mono-crystals (FWHM=2 cm -1 ) FWHM = 2.4 cm -1, comparable with that of natural mono-crystals (FWHM=2 cm -1 ) PL band practically absent (A PL /A p <1/60) PL band practically absent (A PL /A p <1/60) Growth Parameters: Plasma Composition CH 4 / H 2 1% gas mixture Temperature 750 ºC Temperature 750 ºC Growth rate 0.7  m/h Growth rate 0.7  m/h Diamonds are grown in the Laboratories of Roma “Tor Vergata” University by MicroWave Plasma Enhanced Chemical Vapor Deposition (MWPECVD)

4. RD05 Conference Florence, October 6 th, 2005 Diamond Detectors Samples showing a very narrow Raman peak and extremely low photoluminescence background can present very different behaviour when used as particle detectors Particle detection can be used as a very sensitive probe for carrier trapping characterization   Efficiency  = Q C /Q 0   Q C : collected charge   Q 0 : total charge   Charge Collection Distance (CCD) :  = e + h = (  e  e +  h  h ) E : mean drift distance  : mobility  :  lifetime E : applied electric field Au contact 7 mm 2 wide 100 nm thick Ag contact paint Q c : charge induced for each e-h pair L : detector thickness e : charge of the carriers x : total distance the e and h move apart Charge Sensitive Amplifier Bias Ionizing particle Out CVD Diamond p - Si e h Au electrode Ag electrode x The response of the detector is related to the presence of traps

5. RD05 Conference Florence, October 6 th, 2005 PolyCVD Diamond detector 241 Am  -particle spectra as measured by a policrystalline CVD diamond sample M. Marinelli et al. Applied Physics Letters 75 (1999) 3216 Low energy resolution Low energy resolution The dispersion around mean efficiency depends of the The dispersion around mean efficiency depends of the fluctuations of the defect density. fluctuations of the defect density. Effect of pumping Effect of pumping Pumping is the procedure to saturate types of defects by means of  -particles from 90 Sr. Increased efficiency  and charge colection distance after ioniziong radiation exposure

6. RD05 Conference Florence, October 6 th, 2005  Spectra: PolyCVD diamond Positive bias – Pumped Negative bias – Pumped D G l h e + _ Negative Polarization l h e + _ Positive Polarization h >> e Because  + >  -

7. RD05 Conference Florence, October 6 th, 2005 LNS - Experimental set-up Beam Gold target Faraday cup Diamond detectors Vacuum pumps L.N.S. Tandemaccelerator Si detector Target: Au 300  g/cm 2 Beams: 12 C, 6 Li Beam Energy: 12 C: 16÷91 MeV We mounted the samples on a rotating holder. In order that, the penetration depth of the incident particles could vary over a factor of 6. The incidence angle  varied in the 0 o ÷ 80 o range. Combining both the angle and energy scans, the penetration depth can be varied from 2  m to 85  m. Incident particles Rotating sample holder Gold contact Diamond sample ˆ n 

8. RD05 Conference Florence, October 6 th, 2005 Nuclear particle penetration as probe of defect distribution: results 12 C hit the detector on the growing side in all cases G  L h e + _ Negative Polarization  h e + _ Positive Polarization E= 1 V/  m L= 55  m pumped Defects are concentrated near the substrate side e = 1/a e = 0.8  m; h = 1/a h = 33  m

9. RD05 Conference Florence, October 6 th, 2005 Grain Boundaries effect model x In-grain defects In grain defects: uniformly distributed inside the sample; not dependent on position Grain boundaries defects Grain boundaries defects: concentrated at the substrate side; same contribution for both carrier types R.Potenza and C.Tuvè, Carbon: the future for advanced technology applications Springer series Topics in Applied Physics Electron and hole contributions to the conduction mechanism were successfully separated and evaluated.

10. RD05 Conference Florence, October 6 th, 2005 Neutron detection (JET) Comparison between the temporal response of CVD diamond, Silicon detector and Fission chamber for a JET pulse Very similar trend for the three detectors Very similar trend for the three detectors Lower statistic for diamond Lower statistic for diamond  Smaller sensitive volume  Quite far from the plasma (about 7 m) Good stability over 5 week of uninterrupted operation Good stability over 5 week of uninterrupted operation CVD Diamond detector count rates Vs Silicon detector ones for all the TTE campaign at JET (5 weeks) Diamond detector installed at Joint European Torus (JET) in a tokamak (Toroidal Kamera Magnitnaya) Monitoring of the 14 MeV neutrons produced by the D-T plasma during the Trace Tritium Experiment (TTE) lasted 5 weeks M. Angelone et al., Rev.of Sc. Instr 76(2005)013506

11. RD05 Conference Florence, October 6 th, 2005 Why would we like to grow CVD diamond on natural diamond ? To proceed towards better energy resolution, we observed that defects concentrate near the substrate on which the growth begins; this can be explained with the fact that Si substrate and diamond crystals have different reticular constants, so that the first shells in the initial growth are not free of defects and produce a columnar growth of the whole diamond deposit. (Heteroepitaxial growth) Diamond: reticular constant: 3.561 Amg Silicon: reticular constant: 5.43086 Amg So: we attempted homoepitaxial growth using reactor parameters that optimize heteroepitaxial grown crystals. low stability – low reproducibility Low Energy Resolution It is possible use pCVDs as counters Dosimeters Beam monitors Neutron flux monitors Poly CVD diamond detectors

12. RD05 Conference Florence, October 6 th, 2005 Microwave Chemical Vapor Deposition MW-CVD Typical growth parameters Plasma composition H 2 -CH 4, CO 2 -CH 4 etc. Temperature650 - 950 °C Microwave power 600 - 1000 W Pressure50 - 130 mbar Gas flow rate40 - 200 sccm COOLING Substrates (100) HPHT (Element 6, Sumitomo, others) (100) HPHT (Element 6, Sumitomo, others) Natural diamond Natural diamond Type Ib, IIa, B-doped Type Ib, IIa, B-doped

13. RD05 Conference Florence, October 6 th, 2005 Particle detector Oscilloscope Multichannel analyzer Shaping Amplifier Charge amplifier Bias Ionizing particle CVD diamond HPHT substrate e h CVD Layer 110  m thick CVD Layer 110  m thick Substrate: Substrate: B-doped HPHT diamond, 315  m thick Circular Al contacts: Circular Al contacts: 3mm diameter, 100nm thick

14. RD05 Conference Florence, October 6 th, 2005 EM transverse view of a CVD diamond grown on Si substrate (columnar growth of the whole diamond deposit) EM transverse view of a CVD diamond grown on natural diamond substrate Comparison between hetero - homoepitaxially grown diamonds: transverse view

15. RD05 Conference Florence, October 6 th, 2005 EM surface view of a CVD diamond grown on Si substrate Comparison between hetero-homoepitaxially grown diamonds: surface view Comparison between hetero-homoepitaxially grown diamonds: surface view CENTERBOUNDARY EM surface view of a CVD diamond grown on natural diamond substrate

16. RD05 Conference Florence, October 6 th, 2005 X-ray diffraction and Raman spectra : d=3.567 Å Lattice parameter: d=3.567 Å M.G. Donato, G. Faggio, G. Messina, S. Santangelo Dip. Meccanica e Materiali Università di Reggio Calabria - Italy Micro Raman 514 nm Ar laser 514 nm Ar laser Peak @ 1332.9 cm –1 Peak @ 1332.9 cm –1 FWHM = 1.8 cm –1 FWHM = 1.8 cm –1 (including instrum. broadening) (including instrum. broadening) Extremely low photoluminescence background Extremely low photoluminescence background Homogeneous results all over the sample surface Homogeneous results all over the sample surface

17. RD05 Conference Florence, October 6 th, 2005 Polycrystal – Single Crystal detectors Poly crystal Very poor resolution Very poor resolution Strongly sensitive to “Priming” effect Strongly sensitive to “Priming” effect Single Crystal Diamond High resolution High resolution No priming (pumping) effects No priming (pumping) effects

18. RD05 Conference Florence, October 6 th, 2005 Energy resolution and peak energy vs. Voltage   The best resolution is obtained with electric fields E ≈ 1V/  m   Peak energy saturates at sufficiently high applied voltages

19. RD05 Conference Florence, October 6 th, 2005  -particles detection High detection efficiency High resolution ( 1.1% ) Low noise No pumping effects Good stability Triple  source ( 239 Pu, 241 Am, 244 Cm) emitting 5.16 MeV, 5.48 MeV and 5.80 MeV  ‑ particles respectively The detector is in the “as grown state” this means that no “priming” procedure was adopted. The same results are observed after 5 krad 90 Sr  particle irradiation (i.e. our usual procedure to drive our sample in a fully pumped state).

20. RD05 Conference Florence, October 6 th, 2005 Frascati Neutron Generator (FNG) 241 Am α-particle source Collimator Diamond detector Ti – T target θ = 0° θ = 90° 260 keV Deuterium beam θ   D-T fusion reactions neutrons   Neutron energy and energy-spread depends on the emission angle with respect to the D beam The D-T fusion reactions is simulated inside the neutron transport MCNP code 0°  E = 14.8 MeV, FWHM = 0.5 MeV 90°  E = 14.1 MeV, FWHM = 0.3 MeV Neutrons and  particles simultaneously irradiated

21. RD05 Conference Florence, October 6 th, 2005 Neutron detection (FNG) Simultaneous neutrons and 241 Am  -particle irradiation. Correct position of both Correct position of both Calibration obtained by scaling the horizontal axe with respect to the 241 Am  peak 12 C(n,  ) 9 Be peak E = 9.1 MeV FWHM = 0.5 MeV 12 C(n,  ) 9 Be peak E = 8.4 MeV FWHM = 0.3 MeV 0° Position measurement 90° Position measurement Correct position Same of the incident neutrons

22. RD05 Conference Florence, October 6 th, 2005CONCLUSIONS The reliable use of polycrystalline diamond for neutron detection in fusion experiments has been demonstrated. High quality single crystal diamond films were homoepitaxially grown by CVD onto HPHT diamond substrates. Single crystal diamond particle detectors were produced and tested with  -particle, and neutrons. A resolution of 1.1% (including electronic noise) have been measured when irradiating with  -particles. No “ priming ” or “ pumping ” effect was observed. 14 MeV Neutron spectra showed a clear 12 C(n,  ) 9 Be peak with a energy resolution lower than 3.6% (energy spread of the incident neutrons).