High Sensitivity Hard X-ray Detector for Characterization of Biological Systems

Advanced photon sources capable of providing intense X-ray beams over a wide energy range have proven to be outstanding resources for studying bio-energy processing-induced protein molecular structure changes in plant systems via static and time-resolved X-ray diffraction. The hard X-ray regime of the available flux also promises to significantly enhance the applicability of these sources to yield further advances in bio-energy sciences. Current detector platforms rely on the use of a Silicon, or a CdTe semiconductor bump bonded to a readout platform. While CdTe extends the detector energy range, a further increase in energy performance is required. Also, the bump bonding process is difficult which causes defects and makes the detector expensive. To address these issues, RMD proposes to develop an x-ray imaging platform based on a TlBr semiconductor sensor that can be directly deposited on a readout sensor using an economical vapor deposition process. With its extraordinary stopping power arising from its high effective atomic number (ZTlBr=~72) and high density (7.6 gm/cm3), high resistivity, and excellent charge transport properties, TlBr is extremely attractive for highresolution X-ray imaging even for energies well above 100 KeV. The low melting point and cubic nature of TlBr (480 °C) permit vapor deposition directly onto the readout chip, thereby eliminating the need for bump bonding. The Phase I effort developed the design concept and the film deposition process and characterized candidate TlBr films to demonstrate stability at operating bias with suitable electrode materials. The electrical characterization of the films involved measurements of the resistivity and the current-voltage curves, and the radiological characterization involved the measurement of x-rays. The imaging of 60-keV X-ray photons demonstrated the efficacy of the proposed hard X-ray detector. The Phase-II effort will further optimize the TlBr deposition process, deposit the film on the Timepix3 and Timepix4 chips, characterize the imaging performance, and develop a readout platform suitable for structural biology applications at synchrotron facilities. Experimental validation of the detector for relevant applications will be performed at BNL. The access to Timepix chips and readout electronics will be through our other collaborator at UC Berkeley, who is a Medipix collaboration member. Thus, the outcome of the proposed Phase I/Phase II program will be an advanced hard X-ray detector with high sensitivity for energies ranging from 8 keV to 100 keV and above that can operate at high global count rates with wide dynamic range, single photon sensitivity, and high spatial and energy resolution. The commercial potential of such a detector is high and RMD will pursue that path, which will encompass the arrangements for licensing the technology for X-ray detector manufacturers.