3D diamond detectors with millimeter-long graphite pillared electrodes

We introduce the electrical characterization of 2.5 mm-long graphite pillars buried in single crystal CVD diamond. A mode-locked Ti:Sapphire laser generating 5 ps pulses at the wavelength of 800 nm with a repetition rate of 1 kHz has been used to directly produce graphite columns with a diameter of about 10 m and an aspect ratio greater than 240. A pair of 12 pillars was realized within the diamond bulk starting from opposite lateral faces resulting in an interdigitated-like structure buried within the diamond volume. Tests with 2.28 MeV electrons emitted by 90Sr,Y collimated radioactive source demonstrate that the charge collected by the active volume saturates at 1.00±0.02 fC at an electric field strength evaluated as ±1.3 V/m with electrons impinging parallel to the rows. The collected charge, much lower than that expected by theoretical estimation, has been tentatively attributed to a loss of biasing due to the probable non-continuity of the graphite pillars within the sample.