Fig. 2: Effect of cryogelated overlayer on the durability of Sb₂Se₃ photocathodes.

a Time-lapse images of trapping, expansion, and escape of bubbles in the device with 800 μm-thick cryogel CG-800 μm. White dotted lines in the images represent the boundary of the device surface. The orange and green dotted lines indicate the boundary of the expanded bubbles before the initial bubble escape and the escaped bubbles. The time at the bubble escape was denoted as ‘T’. b Finite-element method (FEM) result of the stress on the overlayer by the inflation of the air bubble trapped inside the overlayer. c FEM result of the stress applied on the overlayer with varying thicknesses by the expanding bubble. The overlayer thickness normalized by the initial thickness of the air bubble in the overlayer was 0.3, 1, 3, and 6. The turquoise arrows in (b, c) represent the injection of the air into the trapped bubble. The color scale in (b, c) represents the normalized stress applied on the overlayer. d Maximum stress at the bubble-overlayer interface at various overlayer thicknesses normalized by the initial thickness of the trapped bubble when the relative area of the bubble to its initial value was 2 (black), 3 (magenta), and 4 (turquoise). e Schematic of the surface pore formed by the local fracture in the overlayer with varying thicknesses. The white solid line in the first image of (a) and black solid lines in (b, c) are the scale bars. The scale bar in (a) represents 0.5 mm and those in (b, c) represent 1 mm.