Diamond detectors with laser induced surface graphite electrodes

We report on the response of metal-less CVD polycrystalline-diamond pixel sensors under -particles irradiation. A 21×21 array of 0.18×0.18 mm2 pixels was realized on one side of a 10.0×10.0×0.5 mm3 polycrystalline diamond substrate by means of laser induced surface graphitization. With the same technique, a large graphite contact, used for detector biasing, was fabricated on the opposite side. A coincidence detecting method was used with two other reference polycrystalline diamond detectors for triggering, instead of commonly used scintillators, positioned in the front and on the back of the sensor-array with respect to the impinging particles trajectory. The collected charge distribution at each pixel was analyzed as a function of the applied bias. No change in the pulse height distribution was recorded by inverting the bias voltage polarity, denoting contacts ohmicity and symmetry. A fairly good pixel response uniformity was obtained: the collected charge most probable value saturates for all the pixels at an electric field strength of about ±0.6 V/μm. Under saturation condition, the average collected charge was equal to = 1.64 ± 0.02 fC, implying a charge collection distance of about 285 m. A similar result, within 2%, was also obtained for 400 MeV electrons at beam test facility at INFN Frascati National Laboratory. Experimental results highlighted that more than 84% of impinging particles involved only one pixel, with no significant observed cross-talk effects

Polycrystalline CVD diamond pixel array detector for nuclear particles monitoring

We report the 90Sr beta response of a polycrystalline diamond pixel detector fabricated using metal-less graphitic ohmic contacts. Laser induced graphitization was used to realize multiple squared conductive contacts with 1mm × 1mm area, 0.2 mm apart, on one detector side while on the other side, for biasing, a 9mm × 9mm large graphite contact was realized. A proximity board was used to wire bonding nine pixels at a time and evaluate the charge collection homogeneity among the 36 detector pixels. Different configurations of biasing were experimented to test the charge collection and noise performance: connecting the pixel at the ground potential of the charge amplifier led to best results and minimum noise pedestal. The expected exponential trend typical of beta particles has been observed. Reversing the bias polarity the pulse height distribution (PHD) does not changes and signal saturation of any pixel was observed around ±200V (0.4 V/μm). Reasonable pixels response uniformity has been evidenced even if smaller pitch 50÷100 μm structures need to be teste

Diamond-graphite pixel array for particles detection

The response of graphite-diamond pixel detectors to 90Sr b-particles is reported. Laser induced graphitization was used to realize 200 mm 200 mm square conductive graphite pads on one detector side whereas a large area graphite contact was realized on the other face for biasing. A board with nine hybrid charge sensitive pre-amplifier channels was used to test homogeneity of response of nine pixels at a time. In the dark the current is Ohmic up to 100V where the current increases with a power law. While the bulk pixel resistance is 2:51012W, the resistance between adjacent pixels depends on voltage following a power law. Under irradiation a resolved b-spectrum well separated from the noise contribution was observed on each pixel. The most probable value of the collected charge distribution is voltage dependent and saturates around 300V (0.6 V/mm) with a value of 0.700.05 fC (4300300 equivalent electrons charge)