(a) RHEED pattern of the Cs3Sb film. Distances between reflection peaks were used to calculate the corresponding d-spacing. (b) The X-ray diffraction peaks as a function of azimuth angle. Both RHEED and XRD show peaks corresponding to Miller indices (400), (422) and (620). (c) Schematics of probable orientations that could result in epitaxy between the film and substrate with matching lattice-plane periodicity between Cs3Sb (blue) graphene (purple) and with corresponding unit cells (black lines).

Ordered alkali antimonide photocathodes are emerging as a promising platform for producing high-brightness electron beams. Building on previous demonstrations of single crystal Cs₃Sb growth on 3C-SiC (001) using molecular beam epitaxy (MBE), we further explore this study by growing highly ordered Cs₃Sb films on graphene-coated 4H-SiC (0001) and 3C-SiC (001) substrates at the National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory using an innovative pulsed laser deposition (PLD) method. Operando diagnostics, including X-ray diffraction (XRD) and reflection high-energy electron diffraction (RHEED), reveal that films grown on graphene exhibit highly ordered domains consisting of crystallites, with Laue oscillations around Bragg peaks further highlighting their ordered structure (see Figure). Additionally, tensile strain release in thicker films grown on graphene suggests a potential epitaxial relationship between the film and substrate at lower thicknesses. The films exhibit high quantum efficiency (QE) given their relatively low thicknesses, with QE values at approximately one percent when illuminated by 532 nm light. This work demonstrates a valuable step toward high brightness alkali antimonides through ordering of the material structure, in addition to the in-vacuum structural analyses of thin films that become possible by utilizing both RHEED and XRD.

Reference:
C. Pennington, M. Gaowei, E. M. Echeverria, K. Evans-Lutterodt, A. Galdi, T. Juffmann, S. Karkare, J. Maxson, S. J. van der Molen, P. Saha, J. Smedley, W. G. Stam, and R. M. Tromp, “A structural analysis of ordered Cs3Sb films grown on single crystal graphene and silicon carbide substrates.” arXiv, Jul. 16, 2024. doi: 10.48550/arXiv.2407.12224. Available: http://arxiv.org/abs/2407.12224