Electron Beam Excitation and Damage of Biological Molecules; Its Implications for Specimen Damage in Electron Microscopy

Isaacson, M.; Johnson, Dale E.; Crewe, A. V.

doi:10.2307/3573678

Cited by 122 publications

(52 citation statements)

References 22 publications

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“…The signal output from this detector is nearly proportional to the elastic scattering intensity and will be referred to as the elastic signal. Since elastic scattering increases approximately as Z3/2, where Z is the atomic number of the material (13) (16).…”

mentioning

confidence: 99%

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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mentioning

confidence: 99%

Scanning Transmission Electron Microscopy at High Resolution

Wall

Langmore

Isaacson

et al. 1974

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

Self Cite

124

View full text Add to dashboard Cite

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“…Such a polymer, for example, poly(ethylene terephthalate) has a critical dose of typically 2Â10 2 e À =Å 2 at 100 keV, measured by the vanishing of the EELS signal [82,89,114,115]. This value is close to the limit of 80 e À =Å 2 in TEM cryotomography at 300 keV of vitrified samples at liquid nitrogen temperature [36][37][38][39].…”

Section: Radiation Dosementioning

confidence: 55%

“…This equation can be compared with an earlier relation to estimate the resolution d as function of the dose [114], x= p (qC 2 f), with C 2 f defining the contrast and the efficiency of the detection. For d ¼ 0.08 nm and T ¼ 90 nm Equation 11.15 gives z ¼ 1.7 nm.…”

Section: Dose-limited Resolutionmentioning

confidence: 99%

“…Typically, the signal should be atleast a factor of x ¼ 3 larger than the signal-to-noise ratio SNR [82,114,121]. Note that smaller values can be allowed when objects, for example lines, can be clearly recognized in the image [14].…”

Section: Confidence Level Of Detectionmentioning

confidence: 99%

“…The amount of signal that can be obtained from a sample is limited by the maximal radiation dose that the sample accumulates [89,113,114]. Dose limits of organic materials depend on the chemical composition and on the electron beam energy.…”

Section: Radiation Dosementioning

confidence: 99%

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