Identifying and Correcting Scan Noise and Drift in the Scanning Transmission Electron Microscope

AbstractThe aberration-corrected scanning transmission electron microscope has great sensitivity to environmental or instrumental disturbances such as acoustic, mechanical, or electromagnetic interference. This interference can introduce distortions to the images recorded and degrade both signal noise and resolution performance. In addition, sample or stage drift can cause the images to appear warped and leads to unreliable lattice parameters being exhibited. Here a detailed study of the sources, natures, and effects of imaging distortions is presented, and from this analysis a piece of image reconstruction code has been developed that can restore the majority of the effects of these detrimental image distortions for atomic-resolution data. Example data are presented, and the performance of the restored images is compared quantitatively against the as-recorded data. An improvement in apparent resolution of 16% and an improvement in signal-to-noise ratio of 30% were achieved, as well as correction of the drift up to the precision to which it can be measured.

Download Full-text

Resolution in the Scanning Transmission Electron Microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100095522 ◽

1972 ◽

Vol 30 ◽

pp. 454-455

Author(s):

M. G. R. Thomson

Keyword(s):

Electron Microscope ◽

Transmission Electron Microscope ◽

Spherical Aberration ◽

Signal To Noise Ratio ◽

Scanning Transmission Electron Microscope ◽

Dark Field ◽

Objective Lens ◽

Scanning Transmission Electron ◽

Transmission Electron ◽

Scanning Transmission

The variation of contrast and signal to noise ratio with change in detector solid angle in the high resolution scanning transmission electron microscope was discussed in an earlier paper. In that paper the conclusions were that the most favourable conditions for the imaging of isolated single heavy atoms were, using the notation in figure 1, either bright field phase contrast with β0⋍0.5 α0, or dark field with an annular detector subtending an angle between ao and effectively π/2.The microscope is represented simply by the model illustrated in figure 1, and the objective lens is characterised by its coefficient of spherical aberration Cs. All the results for the Scanning Transmission Electron Microscope (STEM) may with care be applied to the Conventional Electron Microscope (CEM). The object atom is represented as detailed in reference 2, except that ϕ(θ) is taken to be the constant ϕ(0) to simplify the integration. This is reasonable for θ ≤ 0.1 θ0, where 60 is the screening angle.

Download Full-text

A General Method for Spectrometer Design in the Scoff Approximation

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100092657 ◽

1976 ◽

Vol 34 ◽

pp. 538-539

Author(s):

J. R. Fields

Keyword(s):

Electron Microscope ◽

Transmission Electron Microscope ◽

Energy Analysis ◽

Incident Beam ◽

Scanning Transmission Electron Microscope ◽

Chemical Identification ◽

Scanning Transmission Electron ◽

Transmission Electron ◽

Scanning Transmission ◽

General Method

The energy analysis of electrons scattered by a specimen in a scanning transmission electron microscope can improve contrast as well as aid in chemical identification. In so far as energy analysis is useful, one would like to be able to design a spectrometer which is tailored to his particular needs. In our own case, we require a spectrometer which will accept a parallel incident beam and which will focus the electrons in both the median and perpendicular planes. In addition, since we intend to follow the spectrometer by a detector array rather than a single energy selecting slit, we need as great a dispersion as possible. Therefore, we would like to follow our spectrometer by a magnifying lens. Consequently, the line along which electrons of varying energy are dispersed must be normal to the direction of the central ray at the spectrometer exit.

Download Full-text