Construction and test of phase zone plates for x-ray microscopy

We report the construction and test of an x-ray phase zone plate with 0.1-microm imaging resolution and >14% diffraction efficiency. The zone plate served as the focusing optic in a scanning microscope that operated in the water window, 2.5 nm < lambda < 4.5 nm, and therefore is optimally suited for imaging wet biological specimens. We enhanced the efficiency of the zone plate by using germanium for the absorbing zones, so that some of the incident radiation is transmitted with the correct phase shift to interfere constructively at the focal spot. The zone plate was supported on a relatively transparent membrane, giving the microscope a high absolute throughput.