The current state of high resolution scanning electron microscopy

Crewe, A. V.

doi:10.1017/s0033583500004431

Cited by 132 publications

(19 citation statements)

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“…Using a field emission electron source of high brightness, our laboratory has developed a practical scanning transmission electron microscope (STEM) (9,10) which is limited by the electron lenses to the same ultimate resolution as the CTEM and which can form high contrast images with good signal to noise ratios. The fact that the CTEM and STEM have nearly the same ultimate resolution can be seen from the reciprocity theorem (11) which states that the path of rays through any optical system remains unchanged if the direction of rays is reversed.…”

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confidence: 99%

“…Unscattered electrons pass through the hole while 60-80% of the elastically scattered electrons strike this annular detector (13). About 90% of the inelastically scattered electrons also pass through this hole where they are separated from the unscattered electrons by a spherical electrostatic analyzer and detected by another silicon surface barrier detector (9,10). A second set of magnetic double deflection coils is located below the specimen to "unscan" the unscattered beam, placing it on the optic axis at the annular detector plane.…”

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“…The pressure before evaporation was always maintained between 10-7 and 10-9 Torr. Evaporation times between 10 and 100 see were used.…”

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Scanning Transmission Electron Microscopy at High Resolution

Wall

Langmore

Isaacson

et al. 1974

Proc. Natl. Acad. Sci. U.S.A.

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124

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We have shown that a scanning transmission electron microscope with a high brightness field emission source is capable of obtaining better than 3 A resolution using 30 to 40 keV electrons. Elastic dark field images of single atoms of uranium and mercury are shown which demonstrate this fact as determined by a modified Rayleigh criterion. Point-to-point micrograph resolution between 2.5 and 3.0 A is found in dark field images of micro-crystallites of uranium and thorium compounds. Furthermore, adequate contrast is available to observe single atoms as light as silver.The ability to obtain high resolution images of very small objects is of considerable importance in the biological and material sciences. The only instrument heretofore available for this purpose has been the conventional transmission electron microscope (CTEM).Invented in the 1930's, the basic design of this instrument is an electron analog of the light microscope. The performance of the CTEM has steadily improved during the last few decades, and it is now limited primarily by diffraction effects and the large aberrations inherent in electromagnetic lenses.For the moment, we will ignore the effects of chromatic aberration. This is justifiable if the electron energy is high enough. Then one can minimize the combined effect of diffraction and spherical aberration to calculate the objective aperture which gives the best instrumental resolution. In this case, a hypothetical point source of scattered electrons in the specimen plane would be imaged as a modified Airy disc whose radius to the first intensity minimum is given by a = 0.43 Cs1/4X" [1] where C, is the coefficient of spherical aberration (generally of the order of 1 mm in high quality objective lenses) and X is the wavelength of the incident electron (0.037 A for 100-keV electrons) (1). The image of two incoherent point objects separated by this distance 6 will have an intensity minimum between them of 0.75 of the peak intensity and will be resolved according to the modified Rayleigh criterion of Scherzer (1). In order to obtain this resolution, the objective aperture should subtend a half-angle at the specimen given by (2) a(pt = (4X/Cs) 1/4.

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Scanning Transmission Electron Microscopy at High Resolution

Wall

Langmore

Isaacson

et al. 1974

Proc. Natl. Acad. Sci. U.S.A.

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124

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“…The total inelastic scattering cross-section can be related to the total elastic scattering cross section by the approximate relationship (Crewe, 1970a) Z 19 U,/Ui = -.…”

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“…Most of the developmental effort on this type of machine has taken place in our own laboratory, and the majority of this work has been on the technological aspects of the instrument (Crewe, 1970a). Applications have been few so far, and we can assume that the full potentials and capabilities of the STEM will not be known until it comes into more general use.…”

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Scanning transmission electron microscopy*

Crewe¹

1974

Journal of Microscopy

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SUMMARY The scanning transmission electron microscope is of quite recent origin, and it is only in the last few years that it has been shown that this instrument is capable of giving the same high resolution as the conventional electron microscope. In this article we examine the conditions necessary for the achievement of high resolution and also the various modes of contrast which can be obtained from this instrument. Finally, we suggest other ways in which the microscope can be used in future investigations.

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Section II: Electron energy loss spectroscopy

Leapman

1986

J. Elec. Microsc. Tech.

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The current state of high resolution scanning electron microscopy

Abstract: It has been known for many years that there are two distinct ways of designing an electron microscope.

Cited by 132 publications

References 22 publications

Scanning Transmission Electron Microscopy at High Resolution

Scanning Transmission Electron Microscopy at High Resolution

Scanning transmission electron microscopy*

Section II: Electron energy loss spectroscopy

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