Maximilian Haider

Electron microscopy image enhanced

One of the biggest obstacles in improving the resolution of the electron microscope has always been the blurring of the image caused by lens aberrations. Here we report a solution to this problem for a medium-voltage electron microscope which gives a stunning enhancement of image quality.

Residual wave aberrations in the first spherical aberration corrected transmission electron microscope

Here we demonstrate the optical properties of a spherical aberration corrected transmission electron microscope by means of beam tilt series. The high-resolution capabilities are characterized by the measured residual wave aberrations up to the fifth order. Limits for the wave aberration coefficients are determined. We compare the phase-contrast transfer function of the corrected versus the uncorrected objective lens with the help of diffractograms. The information limit and the improvement of the point resolution is discussed.

Transmission electron microscopy at 20 kV for imaging and spectroscopy

The electron optical performance of a transmission electron microscope (TEM) is characterized for direct spatial imaging and spectroscopy using electrons with energies as low as 20 keV. The highly stable instrument is equipped with an electrostatic monochromator and a C(S)-corrector. At 20 kV it shows high image contrast even for single-layer graphene with a lattice transfer of 213 pm (tilted illumination). For 4 nm thick Si, the 200 reflections (271.5 pm) were directly transferred (axial illumination). We show at 20 kV that radiation-sensitive fullerenes (C(60)) within a carbon nanotube container withstand an about two orders of magnitude higher electron dose than at 80 kV. In spectroscopy mode, the monochromated low-energy electron beam enables the acquisition of EELS spectra up to very high energy losses with exceptionally low background noise. Using Si and Ge, we show that 20 kV TEM allows the determination of dielectric properties and narrow band gaps, which were not accessible by TEM so far. These very first results demonstrate that low kV TEM is an exciting new tool for determination of structural and electronic properties of different types of nano-materials.

Upper limits for the residual aberrations of a high-resolution aberration-corrected STEM

The development of correctors for electron optical systems has already brought the improvement of resolution for a low-voltage scanning electron microscope and a commercially available transmission electron microscope and is anticipated in the near future for a dedicated scanning transmission electron microscope (STEM). The resolution attainable especially of a probe-forming system at 200 kV cannot only be estimated from calculations ignoring all non-rotationally symmetric axial aberrations in an electron optical system. For a certain resolution, one would like to attain, the influence of the deviations from the ideal, aberration-free system has to be investigated. Therefore, in the following we have carried out the evaluation of the required accuracy for the compensation of the various residual aberrations in order to achieve a resolution in the sub-Angstrom regime with a probe-forming system.

Advancing the hexapole Cs-corrector for the scanning transmission electron microscope.

Aberration correctors using hexapole fields have proven useful to correct for the spherical aberration in electron microscopy. We investigate the limits of the present design for the hexapole corrector with respect to minimum probe size for the scanning transmission electron microscope and discuss several ways in which the design could be improved by rather small and incremental design changes for the next generation of advanced probe-forming systems equipped with a gun monochromator.

First application of Cc-corrected imaging for high-resolution and energy-filtered TEM

Contrast-transfer calculations indicate that C(c) correction should be highly beneficial for high-resolution and energy-filtered transmission electron microscopy. A prototype of an electron optical system capable of correcting spherical and chromatic aberration has been used to verify these calculations. A strong improvement in resolution at an acceleration voltage of 80 kV has been measured. Our first C(c)-corrected energy-filtered experiments examining a (LaAlO(3))(0.3)(Sr(2)AlTaO(6))(0.7)/LaCoO(3) interface demonstrated a significant gain for the spatial resolution in elemental maps of La.

Information Transfer in a TEM Corrected for Spherical and Chromatic Aberration

For the transmission electron aberration-corrected microscope (TEAM) initiative of five U.S. Department of Energy laboratories in the United States, a correction system for the simultaneous compensation of the primary axial aberrations, the spherical aberration Cs, and the chromatic aberration Cc has been developed and successfully installed. The performance of the resulting Cc /Cs-corrected TEAM instrument has been investigated thoroughly. A significant improvement of the linear contrast transfer can be demonstrated. The information about the instrument one obtains using Youngs fringe method is compared for uncorrected, Cs-corrected, and Cc /Cs-corrected instruments. The experimental results agree well with simulations. The conclusions might be useful to others in understanding the process of image formation in a Cc /Cs-corrected transmission electron microscope.

Aberration corrected 1.2-MV cold field-emission transmission electron microscope with a sub-50-pm resolution

Atomic-resolution electromagnetic field observation is critical to the development of advanced materials and to the unveiling of their fundamental physics. For this purpose, a spherical-aberration corrected 1.2-MV cold field-emission transmission electron microscope has been developed. The microscope has the following superior properties: stabilized accelerating voltage, minimized electrical and mechanical fluctuation, and coherent electron emission. These properties have enabled to obtain 43-pm information transfer. On the bases of these performances, a 43-pm resolution has been obtained by correcting lens aberrations up to the third order. Observations of GaN [411] thin crystal showed a projected atomic locations with a separation of 44 pm.

CHAPTER 2 – Present and Future Hexapole Aberration Correctors for High-Resolution Electron Microscopy

A deeper understanding of the non-ideal hexapole corrector with manufacturing tolerances and alignment elements attained by computer algebraic perturbation methods was helpful to trim the tree of possibilities. Of equal importance was the increasing availability of hardware for numerical image processing to characterize the state of alignment in an efficient and reliable manner and to generate the required feedback for the corrector control. Therefore, the required rotation of the inner two hexapole elements might not matter too much because it can be fixed by design. However, this version of an aplanat has two more transfer lenses and therefore is longer than the other solutions. It seems very likely that an aplanatic system will be the next step in the future development of the hexapole corrector for applications that demand a large isoplanatic field of view.

Electron nanodiffraction using sharply focused parallel probes

The authors describe an electron-optical configuration for producing a nanometer-scale sharply focused parallel electron probe in the transmission electron microscope. The configuration utilizes one of the round lenses in an objective prefield aberration corrector and generates a sharply focused parallel probe of 10 nm in diameter, with better than 0.2 nm edge acuity. Such a probe makes it possible to obtain electron diffraction patterns from nanometer-scale volumes of the specimen with unprecedented precision. A method for measuring the transverse coherence of the probe is also described.