SCANNING ELECTRON MICROSCOPY The JSM-1 1 scanning electron microscope atCRNL has been used extensively for topographical studies of oxidized metals, fracture surfaces, entomological and biological specimens. A non-dispersive X-ray attach­ ment permits the microanalysis of thesurface features. Techniques for the production of electron channeling patterns have been developed.

Commercial scanning electron microscopes (SEM) more valuable information than that obtained by produce an image by causing a finely focussed beam replica electron microscopy. of electrons with energies of 5-50 keV to scan the Although perhaps the greatest advantage of the specimen surface in a raster, like that used to scan SEM is in topographical studies of macroscopic the image in a television camera. A signal obtained by specimens with rough surfaces, other techniques can collecting emitted secondary electrons, reflected pri­ be used to give a wide range of additional information; mary electrons, or the current absorbed by the for instance specimen (among other possible signals) is treated —The surface under examination may be analyzed electronically and scanned across a display tube in by means of non-dispersive or dispersive X-ray synchronism with the scanning of the specimen attachments which analyze the X-ray emission surface. Thus an image of the specimen is built up simulated by the primary beam. with a magnification determined by the ratio of the —Atomic number contrast may be obtained in the scan length on the display tube to the scan length on reflected electron image. the specimen. Typical useful magnifications for — Contrast due to surface potentials, conductivity commercial instruments range from X30 to X30,000. variations, or induced currents may be imaged and The SEM is competing therefore, in the range of mag­ can be used in studies of semiconducting devices. nifications commonly used in optical metallography and replica electron microscopy. — Crystallographic information can be obtained from The advantages over the optical microscope shown electron channeling patterns which may be produ­ by the SEM result from its much greater depth of ced from either large or small (down to 10/um di­ focus (300 to 1000 times greater than the optical ameter) areas of crystalline specimens. microscope depending upon conditions) and the — Specimen luminescence induced by the electron absence of contributions to the image from specular beam may be studied. reflection, which can cause considerable loss in image — Auger electrons emitted from the specimen surface quality in the optical microscone. may be analyzed with a suitably equipped micro­ Compared with replica electron microscopy the scope. principal advantages of the SEM result from the Examples of the various investigations which are natural “three dimensional” appearance of the secon­ possible with the SEM are provided in manufacturers’ dary electron image. This results from similarities brochures and more extensively in the Proceedings between the topographical variations in secondary of the Annual Conferences of Scanning Electron electron emission and the scattering of light by Microscopy(l). The use of the JSM-II microscope at objects which we are used to viewing. Thus, although CRNL has been predominantly for topographical the resolution of the commercial SEM is restricted to studies, although semiconducting devices have been 150-200 A the combination of a more realistic image studied and techniques for producing electron chan­ with the ease of specimen preparation (many speci­ neling patterns have been developed. The topo­ mens may be examined directly in the SEM with no graphical studies involve three main fields: preparation other than cutting to size) often yields (1) Studies of the surfaces of oxide films on

12 Scanning Electron Micrographs

Fracture surface of zirconium embrittled in liquid mercury at room Fracture of a thermally formed zirconium oxide film formed on temperature. (300 x) zirconium at 500°C. Note the columnar morphology (10,000 x)

Electron channelling pattern from a silicon monocrystal 3.28 degrees Head of Dahlbominus Fuscipennis (100 x). from q<210>pole. The indexing of several prominent lines is given on the figure.

13 zirconium alloys. Atomic Energy of Canada Ltd. Report, AECL- 3285 (February 1969). (2) Fractography of both mechanically and en­ vironmentally induced failures in zirconium (5) B. Cox, “The Zirconium-Zirconia Interface,” alloys. J. Aust. Inst. Metals, 1969, 14, 123. (3) Entomological and biological studies of muta­ (6) B. Cox, “Environmentally Induced Cracking of tions produced by the irradiation of insects and Zirconium Alloys, I. Topography of Stress of pathogenic spores. Corrosion Cracking in Methanolic Solutions,” Atomic Energy of Canada Ltd. Report, AECL- Work carried out at CRNL on the SEM is included in 3551 (January 1970). the bibliography. The accompanying figure shows some typical examples of micrographs produced during (7) I. Aitchison, “The Effect of Orientation of these studies. Hydride Precipitates on the Fracture Tough­ ness of Cold-Rolled Zircaloy-2 and 2.5 Nb Bibliography Zirconium,” Proceedings of the Conference on (1) Proceedings of the Annual Scanning Electron “Applications-Related Phenomenon in Zirco­ Microscope Symposium in Chicago, Illinois, nium and Its Alloys”, Philadelphia, (November IIIRI, 1968-1970. 1968), ASTM-STP 458 (December 1969) p. 160 (2) B. Cox, “Processes Occurring During the Break ­ (8) E.M. Schulson, “Electron Channeling Patterns down of Oxide Films on Zirconium Alloys,” in the Scanning Electron Microscope,” Atomic J. Nucl. Mat. 1969, 29, 50. Energy of Canada Ltd. Report, (to be published). (3) B. Cox and A.R. McIntosh, “The Oxide Topo­ (9) R.D. MacDonald, “UO2 Impregnated Graphite graphy on Crystalbar and Reactor Grade Sponge Fuel Elements Clad in Zircaloy Irradiated to Zirconium,” Atomic Energy of Canada Ltd. Burnups of 20% FIFA,” Atomic Energy of Report, AECL-3223 (November 1968). Canada Ltd. Report, AECV3380 (June 1969). (4) B. Cox, “The Morphology of Zirconia Films and and Its Relation to the Oxidation Kinetics,” B. Cox

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