Nano-carbon pixels array for ionizing particles monitoring

The paper deals on the response of a polycrystalline diamond sensor, 500 μm thick, to particles from a 90Sr β-source. 21×21 nano-carbon pads, with 0.18 mm×0.18 mm area each, were realized by ArF excimer laser irradiation on one diamond face, whereas a 7×7 mm2 backside contact was fabricated and used for sensor biasing during characterization of sensor under β-source irradiation. The carbon pads embrace a number of grains, which show different degrees of surface graphitization dependent on the grain orientations. Each carbon pad exhibits a linear I(V) response up to 200 V. The average number of charge carriers collected by a single pixel, as well as the distribution of pixels involved by the impinging particle tracking, is analyzed as a function of the applied voltage recording the signals acquired by 16 pixels at a time. The pulse height distribution is not affected by reversing the bias polarity. For a single pixel, the most probable collected charge value is 1.40±0.02 fC whereas the main value gives <Q>coll=1.67±0.02 fC (10430 ±120 electrons). The charge collection distance was measured tacking into account the effect induced by high- energy electrons and found to be 285±3 μm, demonstrating the absence of bulk defects induced by the laser graphitization processing. Cross-talk effects between nearest-neighbor pixels has been excluded analyzing the results obtained in a batch of more than 1000 events even if the same cannot be excluded under higher energy particles.