Direct electronic visualization of high‐voltage TEM images by sequential pixel acquisition

Abstract

A hybrid imaging mode is described that allows direct electronic detection and manipulation of TEM images. Such imaging mode should be of particular interest and usefulness in highvoltage instruments, in which image visibility is notably poor, but it can also be adapted to conventional electron microscopes. Pixels are detected sequentially by electron-optically sweeping the whole transmitted beam in a two-dimensional raster past a defining aperture located below the camera. Pixel data are obtained directly in digital form and can thus be conveniently manipulated on-line or stored for subsequent processing. Preliminary results obtained in one dimension confirm satisfactorily the anticipated characteristics of two-dimensional images. Possible consequences, applications and extensions of this electronic image acquisition mode are discussed. 0 1982 The Royal Microscopical Society cost. 18 265

Electronic image formation in high‐voltage TEM by sequential pixel acquisition

“…In an attempt to reduce some of these limitations of high-voltage electron microscopy (HVEM), a hybrid imaging mode has been recently described (Fotino, 1979(Fotino, , 1980(Fotino, , 1982 that benefits from the flexibility of electronic pixel detection and manipulation without the massive and difficult development of a high-voltage STEM. Its central operating feature consists of sweeping the entire transmitted beam in a raster in front of a defining aperture, located below the camera, that accepts electrons into a well-shielded single electronic detection channel.…”

“…Without analysing the image characteristics or the pixel statistics required in the present hybrid imaging mode for such features as contrast and resolution, which have been discussed earlier in detail (Fotino, 1982, hereafter quoted as I), it could be argued that this mode is inefficient because only one pixel is collected at any given moment and consequently that high radiation damage is caused to the specimen. It should be stressed that, far from being envisaged as a general substitute for visualization by fluorescent screens or photographic film, image formation by sequential pixel acquisition appears nevertheless of interest: (i) when used in many applications involving amorphous or crystalline objects and in a majority of routine biological specimens not much affected by high beam exposure, (ii) when restricted to small areas of radiation-sensitive biological specimens and thus not entailing a large accumulation of beam-induced effects, (iii) when accompanied by special experimental procedures (such as cryoprotectants, low-temperature imaging or radiationresistant negative staining embedment) aimed at reducing or alleviating the radiation damage, or (iv) when accompanied by worthwhile compensations deriving from the electronic versatility.…”