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Development of Particle Detectors on the Base of Minsk Synthetic Monocrystalline Diamond

Development of Particle Detectors on the Base of Minsk Synthetic Monocrystalline Diamond. National Center of Particle and High Energy Physics Belorussian State University. K.Afanaciev, M.Batouritski, V.Gilewsky, G.Gusakov, I.Emeliantchik, A.Litomin, V.Shevtsov. International School-Seminar

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Development of Particle Detectors on the Base of Minsk Synthetic Monocrystalline Diamond

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  1. Development of Particle Detectorson the Base of Minsk Synthetic Monocrystalline Diamond National Center of Particle and High Energy Physics Belorussian State University K.Afanaciev, M.Batouritski, V.Gilewsky, G.Gusakov, I.Emeliantchik, A.Litomin, V.Shevtsov International School-Seminar The Actual Problems of Microworld Physics Belarus, Gomel July 23 - August 3, 2007

  2. Particle physics needs extremely radiation hard detectors ILC: e+e- collider Initial phase 500 GeV, upgradeable to 1 TeV BeamCal isthe innermost system in the forward region and covers polarangle ranges of 5mrad to about 28 mrad. Expected annual dose: 10 MGy / year Diamond is the only material able to operate at such doses

  3. Poly- or monocrystalline diamond? • Types of synthetic • detector-grade diamond: • polycrystalline CVD • monocrystalline HPHT • Problems of polycrystalline CVD detectors: • high density and non-uniformity of structural defects due to polycrystalline nature • development of high excess currents with dose accumulation • strong dependence of response amplitude on radiation environment • Monocrystalline synthetic diamond is a much more promising material due to • absense of highly defective intercrystallite boundaries

  4. Difficulties on the way towards a good diamond detector Ideally diamond detector is just a solid state ionization chamber • In reality next problems exit: • impurities limit the life time • of free charge carriers • defective surface layer creates • undesirable space charge • diamond-metal junction constitutes • Shottki diod causing nonlinear • field distribution Following techniques can help to provide good detector quality: • thermobaric processing converts nitrogen defects into less active aggregated state; • thermochemical surface procesiing removes defective layer and microcracks; • two-layer metallization with carbidized precoat provides ohmic contact

  5. Monocrystalline particle detectorson the base of Minsk synthetic diamond Parallel-sided plates cut out of crystals with mass 0.5  1.5 carat were used as initial samples. Temperature gradient method in Fe-Co-C environment was implemented with help of “split sphere” apparatus. Metallization was performed by thermal sputtering of titanium and gold with subsequent annealing for carbidization. Clamping contact device was used for electric measurements.

  6. Performance of the detector 10mV/div Subpicoampere currents prove good quality of metallization Response to 90Sr -particles

  7. Detectors on the base of thermobarically processed diamond Nitrogen is the main impurity in diamond C-defects (nitrogen in replacing position) prevail in synthetic diamonds Thermobaric processing allows to convert C-defects into (less harmful) A-defects P = 6.7GPa T = 1800C t = 4 hours Conditions of thermobaric processing: Types of defects are seen in IR absorbtion spectra: C-defect: 1135cm-1 A-defect: 1282cm-1

  8. C-defect C-defect A-defect Results of thermobaric processing A-defect IR spectrum of the diamond detector before thermobaric processing IR spectrum of the diamond detector after thermobaric processing 10mV/div 20mV/div Response to -particles of diamond detector (sample 219) before thermobaric processing. Response to -particles of diamond detector (sample 219) after thermobaric processing.

  9. Avalanche-like behavior of one of the samples 200mV/div Response to 90Sr -particles Response amplitude is much greater than expected, even greater than that of our reference diamond of De Beers production, where it’s close to theoretical limit. Avalanche multiplication caused by charge gradient due to nitrogen content non-uniformitycan be an explanation. Development of avalanche diamond detector could be an interesting option, not researched so far.

  10. Conclusions • Extremely radiation hard detectors are much needed currently, • and synthetic diamond is able to satisfy this need; • Synthetic monocrystalline diamond have advantages over commonly accepted • CVD plates due to absense of highly defective intercrystallite boundaries; • Tested samples proved that monocrystalline diamonds, • produced with split sphere method, are able to work as particle detectors • Low cost of crystals produced with this method together with high radiation • hardness can provide wide range of applications for these detectors

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