Collection deficiencies of scanning electron microscopy signal contrasts measured and corrected by differential hysteresis image processing

Abstract

Summary:Limitations of scanning electron microscopy (SEM) image resolution and quality were measured in digital image data and their effect on image contrasts was analyzed and corrected by differential hysteresis (DH) processing. DH processing is a mathematical procedure that utilizes hysteresis properties of intensity variations in the image for a segmentation of differential contrast patterns. These patterns display contrast properties of the data as coherent full-frame images. The contrast segmentation is revertible so that the original image can be restored from the sum of the sequentially extracted DH contrast patterns. DH imaging enhances weak contrast components so that they are more easily recognizable and displays SEM image data free of signal collection efficiency contrasts. Example image data include environmental SEM (ESEM) and SEM images of low and mediumhigh magnifications where collection deficiencies included charging of the specimen surface, obstructions from specimen topography, and uneven signal collection properties of the detector. ESEM low-vacuum image data, which appear to be of high quality, contained local areas of reduced contrasts due to residual surface charging. In such areas, signal contrasts were reduced up to 80%, which suppressed most of the weak short-range contrasts. In low-magdication SEM images, up to 93% of the local high precision contrast was lost from the various adverse effects which diminished the pixel-related contrast resolution of the microscope and resulted in images with low detail. Also, at medium magmfication, surface charging effects dramatically reduced the image quality because contrasts resulting from local electron beardspecimen interactions were reduced by as much as 71%. DH imaging restored the local contrast losses by elimination of the collected distorted fraction of signal contrasts and reconstitution of the collected maintained fraction. Restored DH images are Support Erom a Connecticut Department of Economic Development Grant 92H18 is thankfully acknowledged. Address for reprints:Klaus-Ruediger Peters, Ph.D. Biomolecular Shucture Analysis Center university of Connecticut Health Center 263 Farmington Avenue Farmington, C T 06030-201 7, USA of superior quality and enhance the imaging capability of the conventional SEM. DH contrast segmentation provides an improved basis for the measurement of various signal contrast components and detector performances. The DH analysis will ultimately facilitate a precise deduction of specimen properties from extracted contrast patterns.

Differential contrast imaging of secondary electron signals in cryo‐field‐emission scanning electron microscopy

“…Scanning electron microscopy signal contrasts are compromised by inherently limited signal collection efficiencies (Peters 1995b(Peters , 1996a which arise from detector-dependent collection properties, a specimen-dependent charging, and specimen topography. The collection deficiencies may reduce the electron-beam generated contrasts in the high-vacuum as well as the environmental SEM by as much as 75-97% and thus corrupt the visibility of small high-resolution surface contrasts.…”

“…This signal processing technology (Peters 1995a(Peters , 1996a) is very different from conventional image processing (Russ 1992) including conventional bandwidth filters ["differential contrast enhancement (DCE) filter," SIS brochure SIM/9604dce_e, 1996]. Image hysteresis characterizes the significance of intensity variations with a simple hysteresis (intensity) value that describes the minimum significant contrast range (Peters 1996a). The maximum contrast range is given by the intensity range (IR) of the image data and all image data contrasts can be measured in proportion of the IR.…”

“…2). These four tasks are the essential functions in DHP contrast imaging (Peters 1996a) and none can be achieved by conventional image processing procedures irrespective of how complex and cumbersome, that is, the SIS DCE filter.…”

“…We found a further factor that limits the high-resolution imaging capabilities of the cryo-FESEM in the reduced collection efficiency of surface contrasts caused by detector deficiencies and by specimen charging. This paper describes how a recently introduced signal processing technology, known as differential hysteresis processing (DHP) (Peters 1996a) can be used in low-temperature FESEM to avoid the adverse effects of collection deficiencies on the display of the electron beam-generated high-resolution surface information. DHP can segment all collected high-resolution surface contrasts from the signal and display these contrasts as an image with reduced collection deficiencies and charging effects.…”

The trajectories of secondary electrons in the scanning electron microscope

“…The different appearance of micrographs of the same specimen acquired in different SEM devices can follow from the unequal WDs. The real situation is further complicated by the ability of the detector to collect not only the true, primary electron-excited SEs (Oatley 1983, Peters 1996, Reimer 1998 and by the presence of local fields on the specimen, connected with charging, contamination, etc.…”