Development of LiInP2Se6 for Ultra-High Resolution Neutron Imaging

Direct neutron detection presents a tremendous challenge as neutrons interact weakly with most matter. In practice, only 3He, 10B, and 6Li combine high neutron-capture cross sections with detectable decay products, and these isotopes have been incorporated into various detector architectures. Solid state detectors are highly desirable and 6LiF-based scintillators, lithium loaded plastic scintillators,1 6LiF-filled micro-structured semiconductor detectors,2 are the most successful. Neutron-sensitive semiconductors could offer direct detection with high efficiency but are lacking. 6Li- or 10B-containing semiconductors are emerging technologies that promise highly efficient detectors since the concentration of neutron-absorbing isotopes is much greater in solids. Direct conversion semiconductors utilize a single material for both neutron capture and charge collection allowing for simpler detector geometry with intrinsic thermal neutron detection efficiencies approaching 100%. The semiconductors, however, must be extremely pure with low carrier trapping because neutron fluxes can be very low, creating very small numbers of excited charges. The materials based on direct conversion that has received most of the prior attention is LiInSe214–16 but it suffer from severe drawbacks that limit performance. Recently, we demonstrated the outstanding neutron detection capabilities of the new layered semiconductor LiInP2Se6. The compound offers the requisite properties needed to achieve direct thermal neutron detection. Bulk LiInP2Se6 was synthesized phase pure via a slightly off-stoichiometric solid-state reaction at 750 ºC. LiInP2Se6 crystallizes in the trigonal space group P-31c with lattice parameters a = b = 6.3975(9) Å, c = 13.351(3) Å, γ = 120°. LiInP2Se6 comprises polyhedral layers separated by Van der Waals gaps, Figure 1a,b. The LiInP2Se6 is easy to synthesize and melts at 717 °C which is about 400 °C lower than LiInSe2.