High-resolution three-dimensional tomographic diffractive microscopy of transparent inorganic and biological samples

We have developed a tomographic diffractive microscope, equipped with a fluorescence confocal scanner. We measure experimentally the lateral resolution using an edge method and by comparing tomographic images of the same samples with wide-field and laser scanning confocal microscopy images; a scanning electron microscope image serves as a reference. The experimental resolution is shown to be to about 130 nm, or lambda/(3.5 NA). This instrument also permits one to measure 3D, complex index of refraction distributions, a quantity that is not accessible to conventional microscopes, and we show how this feature may be used to observe KCl crystals, absorption of which is very weak.

Conducting, semiconducting and insulating objects observed by low-energy electron holography

To demonstrate the potential of low energy in line projection holography, we study the reconstruction of the experimental holograms of three electrically different objects: a conducting, a semiconducting and an insulating object. The reconstructions of these holograms provide meaningful results for a large range of magnification of the object. The comparison between the reconstructed images and the scanning electron microscopy (SEM) micrographs of the same objects shows that the shapes and the dimensions of the reconstructed objects are identical to those obtained by conventional SEM. So, the simple assumptions needed to the reconstruction are justified. The reconstructions show a 2 nm resolution and appear superior than the best obtained SEM micrographs, when available. We also show some limitations of the reconstruction process. We point out that both numerical artifacts and experimental conditions are responsible for these limitations.

Improved low energy electron projection in-line holograms reconstruction: application to the holograms of a tungsten tip

A modification of the classical calculation algorithm is presented which allows to minimize the effect of the long range oscillations created by the twin object in the reconstruction process of in-line holograms obtained by low energy electron projection microscopy. The reconstructed shapes of a tungsten tip, observed with different magnifications are shown.

Imaging charged objects using low-energy-electron coherent beams

The microscopic shapes, unobservable by conventional electron optics, of objects surrounded by electrostatic fields are observed. The method directly uses electron-coherent-beam imaging concepts and is successfully applied to recently developed low-energy-electron projection holography. Experimental demonstrations on objects charged in a controlled way like a biased metallic tip as well as on a self-charging insulator object are shown.