An image sensor has a photocathode window assembly, an anode assembly, and a malleable metal seal. The photocathode window assembly has a photocathode layer. The anode assembly includes a silicon substrate that has an electron sensitive surface. The malleable metal seal bonds the photocathode window assembly and the silicon substrate to each other. A vacuum gap separates the photocathode layer from the electron sensitive surface. A first electrical connection and a second electrical connection are for a voltage bias of the photocathode layer relative to the electron sensitive surface.