HREM applications to industrial products: Observation of thick-film resistors with very large electron transparent area

HRTEM is a very powerful tool for structural characterization of materials. However, its role in industry is still very limited and electron microscopy is generally considered as a secondary support technique, although it can uniquely provide microstructural information leading to understanding and improvement of product quality, especially for those materials in the form of films. An example in the semiconductor industry is recendy described by Anderson. He points out that the main concerns of imaging using a conventional cross-section sample preparation method are too small imaged areas, not representative of the product, and artifacts that may be introduced during the ion-milling process. Here we apply HREM to thick film resistors and attempt to overcome these obstacles.

Misfit dislocations in heteroepitaxial systems with low dislocation density

The growth of heteroepitaxial layers causes stress across the interface which in a certain range of layer thickness may he relaxed by the formation of misfit dislocations at the interface. Systematic investigations of such misfit structures by transmission electron microscopy (TEM) have previously heen conducted only on systems with a relatively large misfit parameter f, i.e. with a high dislocation density. However, this case presents difficulties in the analysis because of the complexity of the dense structures.Interfaces containing a low density of misfit dislocations, e.g. heteroepitaxial systems with low misfit, should consequently be investigated. High voltage electron microscopy (HVEM) enables us to study specimens of several μm in thickness and offers decisive advantages over 100 kV TEM: i) generally, specimens can he prepared by thinning the substrate only, ii) thick foils are mechanically stable, which allows the preparation of specimens with an electron transparent area of several mm2.We report here new results on the initial formation of misfit dislocation structures in the heteroepitaxial system Ge on GaAs (f = 0.074%).

Characteristic cytoplasmic structures in microorganisms utilizing n-butane and 1-butanol

Intracellular structures were observed in two Arthrobacter spp. and in Candida utilis in media containing n-butane or 1-butanol as the sole source of carbon; these structures were absent in the same organisms grown in the presence of glucose. These substrate-specific structures consisted of electron-dense bodies nearly surrounded by a round electron-transparent area, and connected to the main cytoplasm by a bridge. These structures may represent sites of hydrocarbon or alcohol oxidation, and the name "oxisome" is proposed for them. The microorganisms contained about 8 times as much iron when growing on n-butane as when growing on glucose, and about 3 to 4.5 times as much when growing on 1-butanol. When one of the Arthrobacter sp. was grown on n-butane in the absence of iron, more diffuse and less structured concentrations of electron-dense particles appeared. Extraction of n-butane-grown cells suggests that the electron transport system is different from other known electron carriers.

The Fine Structure of Chloroplasts and Pyrenoids in Some Marine Dinoflagellates

The chloroplasts of some members of the Dinophyceae are bounded by an envelope consisting of three membranes and having a mean thickness of 230 A°. Within the chloroplast are arranged, in a more or less parallel manner, many lamellae normally composed of three apposed thylakoids, although the number of thylakoids often varies and may reach 30 in a single stack. By study of disintegrated chloroplasts it was found that the thylakoids are circular in shape with a diameter of 0.15-3.6 µ and a mean thickness of 240 A°;. Ribosomes, lipid droplets and DNA areas are present in the chloroplast stroma. No connexions were seen between the chloroplasts and any other organelles, nor did the chloroplasts contain girdle lamellae. Stalked pyrenoids, which are found in some dinoflagellates, are shown to arise from the inner face of the chloroplasts, to contain a finely granular material and to be frequently surrounded by an electron-transparent area. These findings are discussed in relation to the fine structure of the chloroplasts and pyrenoids of other algal classes.