AbstractFor the development of high quantum efficiency photocathodes, the bi-alkali (K-Cs-Sb) photocathode growth process was studied through in-situ X-ray scattering measurements, including X-ray diffractometry (XRD) and X-ray reflectometry (XRR). Characterization during real-time growth revealed correlations between growth parameters and microscopic structural change of the photocathode. This paper presents preliminary results of an ongoing experiment to understand the growth mechanism. X-ray diffractometry enabled the observation of selective growth of specific crystalline orientation during the deposition and evaporation of an Sb layer. A phase transition of the Sb layer was also measured. X-ray reflectometry revealed surface roughness changes during the growth process and permitted layer thickness measurements while the K layer was evaporated on an ex-situ grown Sb layer, in addition to in-situ Sb layer growth.