Pure Organic TPB Single Crystal for Direct X-ray Detection

For a long time, single crystals of the organic compound TPB (1,3,5-triphenylbenzene) have been viewed as a scintillator material for indirect X-ray detection. We here attempt to explore their potential for direct detection. A TPB single crystal with a size of up to 20 x 6 x 4 mm3 and without obvious growth steps was obtained using a solvent volatilization method. It has an orthorhombic structure with a high-quality FWHM of as low as 0.059 and preferred grown orientations along (131) and (220). AFM images clarify the two-dimensional nucleation growth mechanism. The fitted bandgap of the as-grown crystal is about 3.65 eV. TPB detectors with vertical and coplanar electrodes with a resistivity of 2.56 x 1013 omega cm and 6.68 x 1013 omega cm, respectively, were prepared. The mobilities for electrons (mu e) and holes (mu h) for the coplanar device were calculated to be 1.12 cm2 V-1 s-1 and 1.02 cm2 V-1 s-1, respectively. Under a 50 kV X-ray beam, the detection limit is as low as 0.35 mu Gy s-1, and the sensitivity reaches 2.72 mu C Gy-1 cm-2. The TPB devices have the ability to detect 241Am@5.49 MeV alpha particles, showing the full-energy peak collected from the holes with an energy resolution of 39.13% at 700 V. The mobility lifetime product of the TPB devices for electrons (mu tau)e and holes (mu tau)h were calculated to be up to 2.24 x 10-5 cm2 V-1 and 4.04 x 10-5 cm2 V-1, respectively. The TPB detector could present a spectral response to 241Am@59.5 keV gamma-rays from the holes with an energy resolution of 44.25% at 1000 V, which shows the potential for both direct and indirect detection of high-energy radiation. High-quality TPB single crystals were obtained without obvious step-like growth morphology. The TPB devices could present alpha-particle and gamma-ray spectral responses with high energy resolution, showing potential for direct radiation detection.