Improved Buffered Substrates for YBCO Coated Conductors

65706 Negative-electron-affinity (NEA) photocathodes, which produce polarized electrons, are a vital component of electron accelerators. For the next Linear Collider (NLC), the polarized electron beam intensity must be at least 20 times greater than that produced by strained GaAs, used in the current generation of photocathodes. Additionally, the degree of electron polarization needs to be increased beyond the 75% currently attainable, and intrinsic materials properties must be tailored to improving the surface charge limit. This project will develop a new generation of photocathodes capable of yielding intense, highly polarized electron beams for use in advanced electron colliders. A strained-superlattice, formed from altering layers of GaAs and GaAsP approximately ten monolayers thick, will be utilized. In Phase I, the development of a new superlattice structure using GaAs and GaAsP was begun. Record breaking 86% polarization with 1% quantum efficiency was achieved and theoretical considerations indicated that >90% polarization should be achievable. Phase II will further explore the superlattice parameter space, optimize the molecular beam epitaxy (MBE) growth condition, and develop the superlattice characterization techniques to predict charge and polarization performance. The goal of Phase II is to achieve 90% or greater polarization photocathodes and develop a manufacturing process. Commercial Applications and Other Benefits as described by the awardee: A highly efficient polarized electron source should find use in experimental research at SLAC and other electron collider facilities. As much as 25.6% increase in beam line efficiency may be achieved due to high polarization and beam current, leading to a significant increase in physics opportunities. Other areas of application include magnetic imaging research, surface analysis, quantum computing and cryptography