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AN INTEGRATED SYSTEM FOR COLLECTION AND PROCESSING OF ANALYTICAL AND IMAGE
DATA FROM THE SEM/STEM
J. Mccarthy, J. Benson
To cite this version:
J. Mccarthy, J. Benson. AN INTEGRATED SYSTEM FOR COLLECTION AND PROCESSING
OF ANALYTICAL AND IMAGE DATA FROM THE SEM/STEM. Journal de Physique Colloques,
1984, 45 (C2), pp.C2-215-C2-218. �10.1051/jphyscol:1984247�. �jpa-00223960�
30URNAL DE PHYSIQUE
Colloque C2, supplément au n°2, Tome h5, février 1984 page C2-215
AN INTEGRATED SYSTEM FOR COLLECTION AND PROCESSING OF ANALYTICAL AND IMAGE DATA FROM THE SEM/STEM
J . J . McCarthy and J . P . Benson
Traoor Northern, Inc., 2551 West Beltline Highway, Middleton, Wisconsin 53562, U.S.A.
Résumé - Ce papier décrit un système géré par ordinateur qui donne la possi- bilité de traiter simultanément la microanalyse, le contrôle de l'instrument et l'analyse d'images en mode SEM ou STEM.
A b s t r a c t - This paper describes a c o m p u t e r - b a s e d system t h a t provides t h e capability t o i n t e g r a t e microanalysis, instrument control, and image processing for SEM and STEM.
T h r e e i m p o r t a n t applications of on-line digital c o m p u t e r s t o e l e c t r o n microscopy have e m e r g e d in t h e last d e c a d e ; 1) microanalysis by s p e c t r a l d a t a acquisition and processing;
2) control of instrument p a r a m e t e r s ; and 3) image processing and analysis. The first two applications have b e c o m e quite routine due t o t h e development of t h e minicomputer-based multichannel analyzer (MCA) and t h e associated interfacing techniques. Since image processing requires manipulation of large amounts of image d a t a , this application t r a d i - tionally has been pursued only by r e s e a r c h e r s with a c c e s s t o off-line c o m p u t e r s y s t e m s . Minicomputer and m i c r o c o m p u t e r s y s t e m s have b e c o m e available which provide (at a reasonable cost) sufficient memory, peripheral s t o r a g e , display devices, and c o m p u t a t i o n a l speed t o p e r m i t on-line acquisition, s t o r a g e , and processing of i m a g e d a t a from t h e e l e c t r o n microscope. These developments offer t h e exciting opportunity to c h a r a c t e r i z e specimens by integrating analytical microanalysis, image processing and image analysis in a single, on-line i n t e r a c t i v e d a t a processing s y s t e m . This paper describes such a s y s t e m . SYSTEM DESCRIPTION
The system is based upon t h e TN-5500 c o m p u t e r i z e d multichannel a n a l y z e r . The TN-5500 incorporates a DEC LSI-11/23 a s t h e main CPU, and a number of microprocessor-based sub-units. A simplified block diagram is presented in Figure 1.
The CPU monitors and controls t h e o t h e r system c o m p o n e n t s and processes analytical and image d a t a . Up to 4 m e g a b y t e s of RAM memory may be used for computations, or programs, for s t o r a g e of s p e c t r a l or image d a t a . P e r m a n e n t s t o r a g e is available via t h e floppy disks, Winchester hard disk, or removable p l a t t e r hard disks.
The color video monitor contains a 512 by 256 by 8-bit image memory, and several programmable hardware lookup tables for color selection. Any pixel may be assigned one of 256 colors, s e l e c t e d from a p a l e t t e containing in excess of a quarter-million color hues.
This ability provides g r e a t flexibility in t h e g e n e r a t i o n of pseudo-color e l e m e n t a l and video images, but also permits micrograph quality continuous-tone (64 gray levels) images t o be viewed on t h e display s e p a r a t e l y or in combination with color graphics and pseudo-color images. The display f o r m a t is also q u i t e flexible. Two 256 by 256 by 8-bit images can be seen side-by-side or in a split screen mode with different color scales. A dual magnification image display with pan and zoom about t h e cursor position is another useful display f o r m a t .
The digital scan g e n e r a t o r positions t h e e l e c t r o n beam with 12-bit a c c u r a c y in e i t h e r fast r a s t e r or programmed position modes. Video signals a r e conditioned and then digitized by a fast 8-bit analog-to-digital c o n v e r t e r (ADC). Image d a t a may be averaged on a pixel-by-pixel basis, and an e n t i r e line can be c o l l e c t e d before t r a n s f e r t o t h e CPU for s t o r a g e or processing.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984247
JOURNAL DE PHYSIQUE
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Fig. 1
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Block diagram o f t h e TN-5500 system. Each of t h e modules on t h e TN-5500 bus contains one o r more microprocessor(s). Functions of principal modules a r e discussed in t h e text.The EDS and EELS interfaces provide both spectral and image pixel d a t a t o t h e CPU.
Spectral d a t a is routed directly t o a 4 K channel, 24-bit d a t a memory, while pixel d a t a is transferred t o t h e CPU on a pixel-by-pixel or i m a g e line basis. The EDS i n t e r f a c e microprocessor provides continuous z e r o energy stabilization, system resolution checks, and program control of t h e pulse processor. The EELS i n t e r f a c e contains 8 scaler inputs and a variety of input and output control signals. Two high performance (>50 MHz) scalers a r e available f o r EELS d a t a collection. T h e controls signals will i n t e r f a c e t o most common spectrometers. When not used for EELS, t h e microprocessor in this i n t e r f a c e c a n function a s a n X-ray dot mapping enhancer, r a t e m e t e r , or general purpose multichannel scaling (MCS) input.
Control of instrumental p a r a m e t e r s and automation of various motor driven devices (WDS, s t a g e axes) is accomplished by t h e programmable automation chassis. This unit contains i t s own microprocessor for control and display functions, and additional modules for digital and analog input and output, stepper motor control and scaler/timers f o r WDS systems.
SELECTED APPLICATIONS FOR SEMISTEM Automated Microanalysis
The tedium of manual point-to-point microanalysis c a n b e eliminated by use of t h e digital scan generator or a u t o m a t e d stage. For example, a quantitative composition profile c a n b e readily obtained. A t e a c h point, t h e beam or s t a g e is stepped a discrete amount, and a n X-ray spectrum collected, while t h e previous spectrum is processed. Net intensity of k-ratio results a r e stored a f t e r e a c h point. A t t h e end of d a t a collection, t h e stored d a t a c a n b e recalled for f u r t h e r processing including matrix corrections, averaging and statistical analysis, o r plotting on t h e video display.
Image Processing
Enhancement of selected f e a t u r e s of a n image can b e readily accomplished by a variety of transformations (both linear and non-linear) of t h e gray levels in t h e image, o r by processing t h e image with selected filter operators. In addition t o t h e standard logarithmic and g a m m a gray s c a l e transforms, t h e system permits a variety of non-linear transforms t o b e constructed by manipulation of t h e gray-scale histogram. The e f f e c t of e a c h transform c a n b e viewed in real-time on t h e display. Several operators, including low pass (nearest-neighbor smoothing), gradient, Laplace and Sobel filters, c a n b e applied t o a n image. A typical filtration of a 256 by 256 pixel image takes 30 t o 60 seconds. More traditional operations such a s image segmentation t o produce binary images, erosion and dilation a r e also available. Examples of t h e s e techniques have been discussed in a previous publication / I / .
On-line F e a t u r e Analysis
The basic principles of on-line f e a t u r e analysis a s incorporated in this instrument have been published previously 121. The combination of f e a t u r e s i z e and shape analysis (based upon a video signal) with elemental typing from t h e X-ray spectrum provides more information about t h e sample than c a n normally b e obtained from standard video-only techniques. In t h e TN-5500 system, t h e particle measurements procedures have been refined t o accurately measure complex pa'rticulates, including fibers. In addition, f e a t u r e analysis may b e performed a t high resolution directly from t h e microscope or a t lower resolution from stored images when appropriate.
Digital S t e r e o Microscopy
The right and left-hand images of a s t e r e o pair c a n b e collected and stored a s s e p a r a t e images and displayed side-by-side f o r viewing. A much m o r e useful f o r m a t can b e obtained by combining both images digitally and displaying this image with a red and blue color transform. When viewed through glasses with corresponding red and blue filters, a 3-dimensional representation of t h e image c a n 'be seen on t h e video display. F e a t u r e
C2-218 JOURNAL DE PHYSIQUE
height measurements c a n b e obtained by t h e use of a dual red-blue cursor system. Height measurements a r e calculated using t h e t i l t angle, magnification, and t h e parallax obtained from t h e position of t h e t w o cursors.
Scanned TEM Imaging
Several TEM/STEM systems have o r c a n b e f i t t e d with post-specimen s c a n coils. By placing a n a p e r t u r e before t h e transmitted electron detector, and driving t h e s e coils with t h e digital scan generator, it is possible t o digitize various types of TEM images, including diffraction patterns. These images may b e enhanced a s described earlier. Software is being developed t o analyze collected diffraction patterns.
The authors wish t o acknowledge t h e assistance and collaboration of Dr. R. J. L e e and Dr.
J. Walker of U. S. Steel Research Laboratories.
REFERENCES
1. McCARTHY, J. J. and FERRARA, P. R., "On-Line Processing Digital SEM Images,"
Microbeam Analysis (1982) 1 18-120.
2. McCARTHY, J. J., FISHER, R. M., and LEE, R. J., "Applications of Computers in Electron Microscopy," Ultramicroscopy
