Atomic hydrogen cleaning is used to clean InP͑100͒ negative electron affinity photocathodes. Reflection high-energy electron diffraction patterns of reconstructed, phosphorus-stabilized, InP͑100͒ surfaces are obtained after cleaning at ϳ400°C. These surfaces produce high quantum efficiency photocathodes ͑ϳ8.5%͒, in response to 632.8 nm light. Without atomic hydrogen cleaning, activation of InP to negative electron affinity requires heating to ϳ530°C. At this high temperature, phosphorus evaporates preferentially and a rough surface is obtained. These surfaces produce low quantum efficiency photocathodes ͑ϳ0.1%͒. The use of reflection high-energy electron diffraction to measure the thickness of the deposited cesium layer during activation by correlating diffraction intensity with photoemission is demonstrated.
An algorithm was proposed for very fast and low-complexity computation of three-dimensional Zernike moments. The 3D Zernike moments were expressed in terms of exact 3D geometric moments where the later are computed exactly through the mathematical integration of the monomial terms over the digital image/object voxels. A new symmetry-based method was proposed to compute 3D Zernike moments with 87% reduction in the computational complexity. A fast 1D cascade algorithm was also employed to add more complexity reduction. The comparison with existing methods was performed, where the numerical experiments and the complexity analysis ensured the efficiency of the proposed method especially with image and objects of large sizes.
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