This work presents the design and test results of a charged-particle solid-state detector with ultrafast signal response based on polycrystalline chemical-vapor-deposition (pCVD) diamond as active detector material and a high-bandwidth RF amplifier. We tested the detector at the Indiana University Cyclotron Facility Bloomington, IN, in a proton beam with a kinetic energy ranging from 55 to 200 MeV. The detector signals showed an average pulsewidth of 1.38 ns, which enables single-particle counting at instantaneous rates approaching the gigahertz range. The detector operated with a signal-to-noise ratio of 7 : 1 for 200-MeV protons and a single-particle detection efficiency up to 99%.

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A fast low-noise charged-particle CVD diamond detector

Ion implantation of diamond and diamond films

We have undertaken a study of the common green or orange-brown spots at the surface of rough diamond specimens, which are caused by alpha particles emanating from radioactive sources outside the diamond. Richly coloured haloes represent elevated levels of structural damage, indicated by strong broadening of the main Raman band of diamond, intense strain birefringence, and up-doming of spots due to their extensive volume expansion. Green radio-colouration was analogously generated through the irradiation of diamond with 8.8 MeV helium ions. The generation of readily visible radio-colouration was observed after irradiating diamond with ≥1015 He ions per cm2. The accumulation of such a high number of alpha particles requires irradiation of the diamond from a radioactive source over long periods of time, presumably hundreds of millions of years in many cases. In the samples irradiated with He ions, amorphisation was observed in volume areas where the defect density exceeded 5 × 10−3 A−3 (or 0.03 dpa; displacements per target atom). In contrast, graphitisation as a direct result of the ion irradiation was not observed. The green colouration transformed to brown at moderate annealing temperatures (here 450 °C). The colour transformation is associated with only partial recovery of the radiation damage. The colour change is mainly due to the destruction of the GR1 centre, explained by trapping of vacancies at A defects to form the H3 centre. An activation energy of ~2.4 ± 0.2 eV was determined for the GR1 reduction. The H3 centre, in turn, causes intense yellowish-green photoluminescence under ultraviolet illumination. Radio-colouration and associated H3 photoluminescence are due to point defects created by the ions irradiated, whereas lattice ionisation is of minor importance. This is concluded from the depth distribution of the colouration and the photoluminescence intensity (which corresponds to the defect density but not the ionisation distribution pattern). The effect of the implanted He ions themselves on the colour and photoluminescence seems to be negligible, as radio-colouration and H3 emission were analogously produced through irradiation of diamond with C ions. The photoluminescence emission becomes observable at extremely low defect densities on the order of 10−6 A−3 (or 0.000006 dpa) and is suppressed at moderate defect densities of ~5 × 10−4 A−3 (or ~0.003 dpa). Intensely brown-coloured diamond hence does not show the H3 emission anymore. Anneals up to 1,600 °C has reduced considerably irradiation damage and radio-colouration, but the structural reconstitution of the diamond (and its de-colouration) was still incomplete.

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Radio-colouration of diamond: a spectroscopic study

http://www-adamas.gsi.de/ADAMAS02/talks/schirru_ADAMAS02_alpha.pdf

Thin single crystal diamond detectors for alpha particle detection

Ion irradiation effects in diamond and diamond like carbon thin films

By employing Raman and photoluminescence spectroscopies, and transient photoconductivity, we have studied the damage caused by 5 MeV alpha-particle bombardment on both CVD and type IIa natural diamonds over the fluence range of 1.6×1012 cm−2 to 8×1015 cm−2. The H3 PL peak at 2.46 eV is seen and it dominates the Raman/PL spectra for fluences greater than 1×1014 cm−2. By introducing additional trapping/recombination centers into the diamond films via atomic displacements, dramatic changes in electrical properties are observed. The effects of polycrystallinity on radiation damage in CVD diamond relative to single-crystal, natural diamond are discussed.

Radiation damage study of polycrystalline CVD and natural type IIA diamonds using Raman and photoluminescence spectroscopies

Confocal fluorescence microscopy has been used to measure the three‐dimensional distribution of the H3 color center produced in type IIa natural diamonds by 5 MeV He+ irradiation at a total fluence of 8×1015 cm−2. The peak of the H3 emission occurs 16 μm below the surface of the irradiated side of the diamond, which is in fair agreement with the peak of the vacancy distribution predicted by a Monte Carlo calculation (transport of ions in matter or trim). The H3 distribution is broader in the direction normal to the surface (10 μm full width at half maximum) than the trim calculation. This is attributed to diffusion of vacancies caused by self‐annealing during irradiation.

Spatially resolved measurement of lattice damage in alpha‐particle‐irradiated type IIa natural diamond by confocal photoluminescence microscopy

Temporally resolved response of a natural type IIA diamond detector to single-particle excitation

Raman and photoluminescence spectroscopy was used to investigate radiation damage by 5 MeV He+ ions at room temperature in prototype CVD-diamond detector material. Amorphization of the diamond is not observed at fluences up to 8×1015 cm−2. A threshold behavior is seen in the formation of the H3 vacancy-dinitrogen color center. The defect is not observed for fluences in the range 1.6×1012 to 1.6×1013 cm−2; a linear behavior increase in H3 intensity is observed over the range 1.6×1014 to 1.6×1015 cm−2. The formation mechanism of the H3 color center under He+ irradiation involves a self-annealing effect that allows vacancies to diffuse to, and complex with, nitrogen complexes.

Ron S. Wagner

Papers

Radiation damage study of polycrystalline CVD and natural type IIA diamonds using Raman and photoluminescence spectroscopies

Spatially resolved measurement of lattice damage in alpha‐particle‐irradiated type IIa natural diamond by confocal photoluminescence microscopy

Temporally resolved response of a natural type IIA diamond detector to single-particle excitation

Characterization of Cvd Diamond Films by Optical Spectroscopies