New detection system for HAADE and holography in STEM
A novel detection system has been designed and realized experimentally on the HB5 STEM instrument. Shadow images, diffraction patterns as well as high-angle annular dark field and bright field images are observed simultaneously with high efficiency using CCD and TV cameras. The microscope can be operated in a wide range of instrument modes which includes the implementation of new techniques for high resolution imaging.As shown in Fig. 1, the detection system has three triple choice stages. Diffracted beams can be collected by three P47 fast phosphor annular detectors inclined at 45 degree to the axis and having different inner and outer acceptance angles, which can be adjusted by the postspecimen lenses. The detector is observed through a window by a photomultiplier. The annular detectors have been used also for a new bright field STEM technique which utilizes the inner rim of the detectors to collect only the outermost annular part of the central beam and promises an improvement in resolution by a factor of about 1.6. Initial results show some promise (Fig. 2). The transmitted beam is then converted into a light signal in YAG and P47 detectors; optionally the central part of the beam can be detected in the EELS spectrometer. The generated light signal is reflected through a system of mirrors, exits the vacuum chamber and is collected with high efficiency by high aperture optical lenses.