Computer simulation of atomic mixing during ion bombardment

Correlated optical and isotopic nanoscopy

The isotopic composition of different materials can be imaged by secondary ion mass spectrometry. In biology, this method is mainly used to study cellular metabolism and turnover, by pulsing the cells with marker molecules such as amino acids labelled with stable isotopes (¹⁵N, ¹³C). The incorporation of the markers is then imaged with a lateral resolution that can surpass 100 nm. However, secondary ion mass spectrometry cannot identify specific subcellular structures like organelles, and needs to be correlated with a second technique, such as fluorescence imaging. Here, we present a method based on stimulated emission depletion microscopy that provides correlated optical and isotopic nanoscopy (COIN) images. We use this approach to study the protein turnover in different organelles from cultured hippocampal neurons. Correlated optical and isotopic nanoscopy can be applied to a variety of biological samples, and should therefore enable the investigation of the isotopic composition of many organelles and subcellular structures.

Secondary ion mass spectrometry is effective for imaging cellular turnover, but it cannot identify subcellular structures such as organelles. Here the authors show a method for correlating this technique with high-resolution fluorescence microscopy, enabling the measurement of turnover in cellular compartments.

Neutron microscopy. The low-damage imaging of specialized organic materials

It is shown that, insofar as radiation damage is concerned, transmission neutron microscopy using neutrons in the energy range approximately 0.0001-1.0 eV is extremely attractive for the imaging of specialized organic materials. By "specialized organic materials" is meant organic specimens composed entirely of specific isotopes that have been selected on the basis of their favorable properties with regard to radiation damage. In connection with such specimens, it is demonstrated that at a resolution of, for example, 100 A, neutrons will have an advantage over soft X-rays in terms of radiation damage, provided that the inherent (neutron) bright field image contrast turns out to be greater than 10(-5). Suggestions relating to (a) the comprehensive calculation of the radiation damage sustained by specialized organic specimens under slow neutron irradiation, (b) the construction of a theory of image formation in the neutron microscope, (c) the development of neutron lenses/focusing devices, and (d) the development of a brighter neutron source (essential for neutron microscopy) are outlined in some detail. The paper concludes with two appendices, which provide important background material.

Nonoptical characterization of optical coatings

Besides the theoretical design of optical interference coatings, the knowledge of their nonoptical properties like chemical composition, structural features, mechanical peculiarities, and environmental stability is often a basic condition for their industrial production. After some remarks on specifications and standards relevant for optical coatings this paper gives a review on various possibilities for nonoptical characterization of optical coatings. Those methods of surface analysis, depth profiling, and electron microscopy available to and widely used by a major coating manufacturer-like Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS), scanning electron microscopy (SEM), energy dispersive (ED) and wavelength dispersive (WD) electron probe microanalysis (EPMA)-are pointed out in more detail and illustrated with examples from daily practice. Other characterization methods, which are less common but very interesting, are also briefly reviewed.