Nano-carbon pixels array for ionizing particles monitoring

The paper deals on the response of a polycrystalline diamond sensor, 500 pm thick, to particles from a Sr-90 beta-source. 21 x 21 nano-carbon pads, with 0.18 mm x 0.18 mm area each, were realized by ArF excimer laser irradiation on one diamond face, whereas a 7 x 7 mm(2) backside contact was fabricated and used for sensor biasing during characterization of sensor under beta-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 mean value gives < Q > (coll) = 1.67 +/- 0.02 fC (10,430 +/- 120 electrons). The charge collection distance was measured taking into account the effect induced by high-energy electrons and found to be 285 +/- 3 mu m, demonstrating the absence of bulk defects induced by the laser graphitization processing. Cross-talk effects between nearest neighbor pixels have 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. (C) 2016 Elsevier B.V. All rights reserved.