Purely Organic 4HCB Single Crystal Exhibiting High Hole Mobility for Direct Detection of Ultralow-Dose X-Radiation
Precise detection of low-dose X-radiation by the purely organic direct detectors is vital for tissue-equivalent dosimeter and safety control in medical radiation treatment, but it still remains a challenge. Here, we report on a promising organic radiation detector based on 4-hydroxycyanobenzene (4HCB, C7H5NO) single crystal. Plate-like 4HCB single crystals up to 18×15×1.2 mm3 in size are obtained by the optimized solvent evaporation method, thanks to the clarification of the two-dimensional nucleation growth mechanism. After the post surface treatment, the leakage current of 4HCB detector is no larger than 0.1 pA under an electric field of 600 V cm-1. The fabricated detectors show a capability of detecting 241Am 5.49 MeV α particles with a well resolved full energy peak. The calculated hole mobility (µh) and hole mobility lifetime product (µτ)h are 3.40 cm2 V-1 s-1 and 8.50×10-5 cm2 V-1, respectively. Simultaneously, under a 50 kVp X-ray beam, a detection limit as low as 0.29 μGyair s-1 with a high sensitivity of 10 μC Gyair-1 cm-2 is achieved at the bias range of 40-100 V, which contributes to a superior X-ray imaging capability with a spatial resolution of 0.9 lp mm-1 at a low-dose rate (below 150 μGyair s-1) exposure.