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

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Development of Particle Detectorson the Base of
Minsk Synthetic Monocrystalline Diamond

• K.Afanaciev, M.Batouritski, V.Gilewsky,
  G.Gusakov,
• I.Emeliantchik, A.Litomin, V.Shevtsov

National Center of Particle and High Energy
Physics Belorussian State University
International School-Seminar The Actual Problems
of Microworld Physics Belarus, Gomel July 23 -
August 3, 2007
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Particle physics needs extremely radiation hard
detectors
ILC ee- collider Initial phase 500 GeV,
upgradeable to 1 TeV
BeamCal is the innermost system in the forward
region and covers polar angle ranges of 5mrad
to about 28 mrad.
Expected annual dose 10 MGy / year
Diamond is the only material able to operate at
such doses
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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

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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

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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.
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Performance of the detector
10mV/div
Subpicoampere currents prove good quality of
metallization
Response to 90Sr ?-particles
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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 Thermobar
ic 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
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Results of thermobaric processing
C-defect
C-defect
A-defect
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.
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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 its close
to theoretical limit.
Avalanche multiplication caused by charge
gradient due to nitrogen content non-uniformity
can be an explanation.
Development of avalanche diamond detector could
be an interesting option, not researched so far.
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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