All posts by bgamm

Dissertation published!

Finally, several months after finishing my work on electrostatic phaseplates at the Karlsruhe Institute of Technology, I finished my thesis late in 2012, and had my Disputation in January 2013.

My dissertation on “Phasecontrast with electrostatic phaseplates in transmission electron microscopy” has been published in german language. You can find the work, free of charge (Open Access policy) here:

http://digbib.ubka.uni-karlsruhe.de/volltexte/1000033741

 

Improved Fabrication and Application of electrostatic Phase-Plates

A work showing improved applications with Zach phase-plates has recently been published. The work shows how charging of the phase-plates can be overcome. This allows much better infocus images while changing phase contrast by the phase-plate potential.

Titel: “Improving Fabrication and Application of Zach Phase Plates for Phase-Contrast Transmission Electron Microscopy

Abstract

Zach phase plates (PPs) are promising devices to enhance phase contrast in transmission electron microscopy. The Zach PP shifts the phase of the zero-order beam by a strongly localized inhomogeneous electrostatic potential in the back focal plane of the objective lens. We present substantial improvements of the Zach PP, which overcome previous limitations. The implementation of a microstructured heating device significantly reduces contamination and charging of the PP structure and extends its lifetime. An improved production process allows fabricating PPs with reduced dimensions resulting in lower cut-on frequencies as revealed by simulations of the electrostatic potential. Phase contrast with inversion of PbSe nanoparticles is demonstrated in a standard transmission electron microscope with LaB6 cathode by applying different voltages.

 

You can find the paper here:  Microscopy and Microanalysis

Quantitative Single Atom Imaging Paper published

Recently my work on quantitative imaging of single atoms in high resolution transmissions electron microscopy was published in Microscopy and Microanalysis.

Titel: “Quantitative High-Resolution Transmission Electron Microscopy of Single Atoms”

Abstract

Single atoms can be considered as the most basic objects for electron microscopy to test the microscope performance and basic concepts for modeling image contrast. In this work high-resolution transmission electron microscopy was applied to image single platinum, molybdenum, and titanium atoms in an aberration-corrected transmission electron microscope. The atoms are deposited on a self-assembled monolayer substrate that induces only negligible contrast. Single-atom contrast simulations were performed on the basis of Weickenmeier-Kohl and Doyle-Turner form factors. Experimental and simulated image intensities are in quantitative agreement on an absolute intensity scale, which is provided by the vacuum image intensity. This demonstrates that direct testing of basic properties such as form factors becomes feasible.

 

You can find the paper here:  Microscopy and Microanalysis

or at Arxiv.org: http://arxiv.org/abs/1009.2393

Phase-Plate Holography

In 2010 my work on holography involving physical electrostatic phase plates in transmission electron mircoscopy was published in Ultramicroscopy.

Titel: “Object wave reconstruction by phase-plate transmission electron microscopy”

Abstract

A method is described for the reconstruction of the amplitude and phase of the object exit wave function by phase-plate transmission electron microscopy. The proposed method can be considered as in-line holography and requires three images, taken with different phase shifts between undiffracted and diffracted electrons induced by a suitable phase-shifting device. The proposed method is applicable for arbitrary object exit wave functions and non-linear image formation. Verification of the method is performed for examples of a simulated crystalline object wave function and a wave function acquired with off-axis holography. The impact of noise on the reconstruction of the wave function is investigated.

You can find the paper here: ScienceDirect

or at Arxiv.org: http://arxiv.org/abs/1009.4615

Phase plates and Cs-Correction

In 2008 I published my first work, with the title:

“Effect of a physical phase plate on contrast transfer in an aberration-corrected transmission electron microscope “

Abstract

In this theoretical study we analyze contrast transfer of weak-phase objects in a transmission electron microscope, which is equipped with an aberration corrector (Cs-corrector) in the imaging lens system and a physical phase plate in the back focal plane of the objective lens. For a phase shift of π/2 between scattered and unscattered electrons induced by a physical phase plate, the sine-type phase contrast transfer function is converted into a cosine-type function. Optimal imaging conditions could theoretically be achieved if the phase shifts caused by the objective lens defocus and lens aberrations would be equal to zero. In reality this situation is difficult to realize because of residual aberrations and varying, non-zero local defocus values, which in general result from an uneven sample surface topography. We explore the conditions—i.e. range of Cs-values and defocus—for most favourable contrast transfer as a function of the information limit, which is only limited by the effect of partial coherence of the electron wave in Cs-corrected transmission electron microscopes. Under high-resolution operation conditions we find that a physical phase plate improves strongly low- and medium-resolution object contrast, while improving tolerance to defocus and Cs-variations, compared to a microscope without a phase plate.

You can find the paper at ScienceDirect: http://www.sciencedirect.com/science/article/pii/S0304399108000375

Or at Arxiv.org: http://arxiv.org/abs/1009.4038