摘要:

A compact confocal single‐mode optical fibre scanning microscope for imaging magnetic domain structures, based on the polar magneto‐optic Kerr effect, has been developed. The images obtained correspond to those obtained using single mirror scanning but this design offers a more compact structure and can be made more immune from system depolarization which makes two‐axis mirror scanning difficult to implement when very small changes in polarization need to be det

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.1310691.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The major factor limiting resolution of metal‐shadowed surfaces for electron and scanning tunnelling microscopy is the granularity of the metal film. This granularity had been believed to result from a recrystallization of the evaporated film, and hence could be limited by use of higher melting point materials for replication, or inhibited by adding carbon or other impurities to the film. However, evaporated and sputtered films of amorphous metal alloys that do not crystallize also show a granularity that decreases with increasing alloy melting point. A simple thermodynamic analysis shows that the granularity results from a dewetting of the typically low surface energy sample by the high surface energy metal film, similar to the beading up of drops of spilled mercury. The metal granularity and the resulting resolution of the metal‐coated surface is proportional to the mobility of the metal on the surface after evaporation, which is related to the difference in temperature between the melting point of the metal and the sample surface temperat

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.1210678.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The properties of microalloyed steels and HSLA steels depend predominantly on the size and composition of nanometre‐sized MX precipitates consisting of Nb, Ti, V, C and N. In this work we present a rapid and powerful method for visualizing these small precipitates directly in the steel matrix.This can be achieved by energy‐filtering TEM in a 200‐kV microscope. We have recorded elemental maps (three‐window method) and jump‐ratio images (two‐window method) using the inner‐shell ionization edges; e.g. Fe‐M23, Fe‐L23, V‐M23, V‐L23, Nb‐N23, Nb‐M45, C‐K and N‐K edges. We have found that precipitates in a steel matrix can be best visualized by recording the jump‐ratio image of the matrix element. If the specimens are thinner than 30 nm and high resolution in the images and low detection limits are essential, low energy‐loss edges should be used preferentially; in the case of steels the Fe‐M23edge should be used instead of the Fe‐L23edge. If the jump‐ratio images are recorded with the Fe‐M23edge, precipitates about 2 nm in diameter may be detected. With thicker samples and if high resolution is not as essential, higher energy‐loss edges are preferable, because diffraction effects are less possible.The chemical composition of the larger precipitates (10 nm) could be determined by recording EDX spectra using an STEM probe. We found Nb and V with an atomic ratio of about 3, but we could not detect carbon or nitrogen in the spectra. The Nb and V distribution could be best visualized with a jump‐ratio image including both the Nb‐N23and the V‐M23edges. However, it was not possible to image the carbon or nitrogen content of the precipitates unequivocally due to overlap

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.1240682.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Element microanalysis with energy‐filtering transmission electron microscopy can be performed in different ways. Electron energy‐loss spectroscopy (EELS) records the intensity as a function of the energy loss from selected regions. Elemental mapping with electron spectroscopic imaging (ESI) uses energy‐filtered images at an element‐specific energy loss from which a background image has to be subtracted. A combination of these two approaches is Image‐EELS, which records a series of energy‐filtered images, each at a different energy loss and measures the intensity of selected regions as a function of the energy loss. As an additional procedure ESI contrast analysis is introduced; with this we can investigate the image contrast as a function of the energy loss. The contrast can be measured for the total image or for selected regions as the standard deviation of the grey levels divided by the mean grey level. This procedure is added as a new feature to the existing Image‐EELS program, so that EELS intensity spectra and the contrast can be directly compared. Alternatively, the contrast can be calculated step by step from individually recorded electron spectroscopic images, so that only simple equipment for image analysis is sufficient to realize this new method.Inner shell ionizations produce characteristic, but often weak element edges in energy‐loss spectra which can be detected more sensitively and reliably as a rapid increase in contrast. Regional analysis of the contrast as a function of the energy loss, combination of data from different regions and the possibility to increase the intensity during recording of the images expand the application range of this new analytical method which bridges the gap between ESI and EELS analysis. With ESI contrast analysis it is possible to discriminate between faint element signals and artefacts in elemental mapping.This new approach for element detection is especially advantageous for biological objects which usually contain very small amounts of the interesting elements in heterogeneous and complex objects. As an example, nervous tissue of a fish was analysed after cytochemical precipitation of end

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.1290688.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The chemical reactions that take place at surfaces as well as internally in nanoscale particles are of great scientific interest. Such reactions control the catalytic properties of small metal particles and thus are technologically very important. In order to allow enhancement of the performance of such catalytic systems, an understanding of the processes taking place at the atomic scale is necessary. Z‐contrast imaging and electron energy‐loss spectroscopy (EELS) in the dedicated scanning transmission electron microscope can give atomic‐scale information and thus provide a unique opportunity to study such nanoscale systems. Here, iron particles from known positions in a ferrocene‐seeded flame and their effects on soot formation are studied. Using EELS, spatial variations in oxidation state of the metal atoms are detected across individual nanometre‐sized particles collected from the post‐flame region. The surfaces of these particles are found to be less oxidized than their centres. Additionally, the particles are imaged with atomic resolution allowing their structure to be identified. Using these results and those for particles collected from in‐flame regions, direct evidence is provided for the catalytic role of Fe‐containing particles in the removal of carbonaceous soot produced during combustion of hydrocar

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.1020659.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

A multivariate statistical analysis method has been used to examine the information content of a series of EDX spectra acquired using a FEG‐STEM recorded across a segregated grain boundary in a ferritic steel. The spectra have been factored into a set of orthogonal information components (eigenspectra), each of which corresponds to an independent source of information. Two meaningful eigenspectra are identified: one is related to the segregation of P and Cr and the other to a combination of self‐absorption and coherent bremsstrahlung. Spectra are reconstructed from the meaningful eigenspectra to reduce noise and improve the sensitivity for detection of trace element segregat

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.1400698.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Estimation of the rose of directions is a simple way to analyse the anisotropy of structures made of lines, objects or interconnected phases. However, when used on an automatic image analyser with a square frame, the rose of directions obtained from circles is not uniform. This problem is analysed here. It originates in the interpretation of the discrete rose of directions, which is not a histogram, but an averaging with non‐constant angular mask and weight function. New coefficients are proposed to get a pseudo‐rose of directions which is uniform for isotropic structures such as assemblies of circ

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.1190672.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The size distribution of liposomes is often determined using freeze fracture, cryoelectron microscopy or dynamic light scattering. However, the resulting size distributions do not directly coincide owing to the different weighting of the techniques. We present several methods which correct for these effects and allow a comparison of liposome size distributions as obtained by freeze fracture, cryoelectron microscopy or dynamic light scattering. These methods are based on theoretical models for the weighting of the size distribution of liposomes, which result from the preparation procedure for freeze fracture electron microscopy and from the measurement by dynamic light scattering. The proposed transformation methods are then experimentally tested with a sample of lecithin liposomes, whose size distribution was determined by dynamic light scattering, freeze fracture and cryoelectron microscopy. Furthermore, the weaknesses of the experimental techniques and hence of the resulting size distributions are discussed.

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.1280687.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY