Physically and chemically smooth cesium-antimonide photocathodes on single crystal strontium titanate substrates

The performance of x-ray free electron lasers and ultrafast diffraction experiments is largely dependent on the brightness sources from photoinjectors. maximum photoinjectors at a particular accelerating gradient limited by mean transverse energy (MTE) electrons emitted photocathodes. For high quantum efficiency (QE) cathodes like alkali-antimonide thin films, which are essential to mitigate effects non-linear photoemission MTE, smallest possible MTE and, hence, highest nanoscale surface roughness chemical inhomogeneity. In this work, we show that QE Cs3Sb films grown lattice-matched strontium titanate (STO) substrates have factor 4 smoother, chemically uniform surfaces compared those traditionally disordered Si surfaces. We perform simulations calculate induced based measured topographical surface-potential variations STO these small enough no consequential impact brightness.