Theory-Based High-QE Photocathode Development

While substantial advancements have been made in realizing tube based large area detectors such as the Large Area Picosecond Photo-Detector (LAPPD), there is widespread agreement in the cathode community that a higher QE bialkali cathode is possible, and that the present understanding is largely-recipe driven without the adequate control or understanding to achieve the previously observed high yield of narrowly clustered QE & apos;s. Thus, the goal of this SBIR is to develop high quantum efficiency photocathodes, based on a robust understanding of the underlying physics and chemistry. The challenges associated with the deposition of multi-alkali-antimony photocathode will be addressed using two main strategies, 1) pre-synthesis of multi-alkali-antimony compounds using specialized technique, and 2) deposition of the synthesized compound to form a high QE photocathode. In-situ monitoring of photocathode growth using such techniques as dynamic X-Ray Diffraction (XRD) will permit process optimization to realize as yet unattainable QE response with significant gains in process yields. The process thus developed will be amenable for large scale production of large area photocathodes in a cost effective manner. The key accomplishment of the Phase I research is the invention of a novel synthesis route for ultrapure photocathode compound from its constituents, whose chemical composition and lattice parameters perfectly match the calculated theoretical model slated to perform with significantly higher QEs than is currently demonstrated. Deposition of this material to form a photocathode film was performed and its characteristic properties demonstrated. A joint patent application from the participating institutions has been filed. The Phase II research will extend the Phase I study to further enhance the photocathode QE through a robust understanding of the correspondence between theory, the materials growth, and thin film fabrication. Technology commercialization efforts will be undertaken in parallel with the research. Commercial Applications and Other Benefits: The ability to consistently make photocathodes with high QE at high yields will substantially lower the cost per detected photon in large water Cherenkov counters for short- and long-baseline neutrino experiments, Positron-Emission Tomography, and other applications limited by photon counting. The improved QE also ameliorates the difference in QE between vacuum-based and silicon technologies, while retaining the big advantage in noise, gain, and bandwidth. In addition, a robust theoretical understanding of the relationship between cathode growth procedures and electronic band- structure, scattering, and morphology will allow improvements in cathodes for other regions of the spectrum, including in the UV (liquid-Argon, liquid-Xe) and the IR (defense and astronomy).