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C Colliex

Publications and source records attributed to C Colliex.

11 recordsLinked to original sources
PubMed1992

New STEM multisignal imaging modes, made accessible through the evaluation of detection efficiencies.

With its specific design for recording simultaneous signals, the scanning transmission electron microscope (STEM) offers unique imaging capabilities. In order to use them fruitfully, we have implemented, on a VG STEM equipped with a magnetic spectrometer, home-made detectors for recording multisignal images. This paper first describes a method developed for the quantitative evaluation of detection efficiency of all data-acquisition channels involved in these multisignal images. At this stage, new imaging modes become accessible, which can be classified following their specificity and sensitivity; scattering power image, elastic and inelastic images mean free path ratio images. Original applications encountered in the biological as well as in the materials science fields illustrate the possibilities of these various approaches, which can be of great interest in quantitative microscopy, analytical imaging or low-dose observation.

Animals↗
PubMed1991

Elemental analysis and fine structure of mitochondrial granules in growth plate chondrocytes studied by electron energy loss spectroscopy and energy dispersive X-ray microanalysis.

Electron energy loss spectrometry--EELS, and energy dispersive X-ray microanalysis--XRMA, were used to study the elemental composition of mitochondrial dense granules-mdg. The study was performed on dry cut thin sections (80-200 nm) of freeze-dried and low temperature embedded cartilage. Results obtained by means of XRMA clearly showed high phosphorus and calcium content in the mdg. Using EELS at 100 kV primary voltage we found that small concentrations of elements (i.e. below typically 1% atomic weight) are difficult to analyze and map, this especially in sections thicker than 50-60 nm. Surprisingly, analysis of calcium can be successfully performed on thicker sections though the edge lies above the carbon K edge while this is not possible for the phosphorus edge which is located at lower energies. This is likely due to the edge shapes (sharp for calcium and delayed for phosphorus), and to the more intense contribution of multiple low loss scattering in the background for phosphorus between 100 and 130 eV. By means of EELS elemental mapping a centrally located core was found in numerous mdg. In the calcium map the signal was strongest in the middle of mdg which corresponds to the area of reduced carbon signal. We found that carbon maps might be used for high resolution structural studies of chemically unfixed and anhydrously processed biological tissues. As carbon is the main constituent of Lowicryl resin its distribution is reversed to the distribution of biological tissue in which the proportion of carbon is lower, but is proportional to water content in the specimen in vivo. Use of EELS in combination with electron microscope with accelerating voltages in range of 140-200 kV together with anhydrous techniques of the tissue preparation will provide a new type of information which might lead to better understanding of the etiology and function of small structures in the cell.

Animals↗
PubMed1989

Energy filtered STEM imaging of thick biological sections.

Energy filtered imaging of thick biological specimens was analysed using a dedicated STEM fitted with an energy loss spectrometer and interfaced with a sophisticated data collection setup. All images were digital, thus permitting a quantitative analysis of the data. We also present a mathematical explanation of the data, which is useful in predicting the quality of thick specimen images formed with energy filtered electrons. It is known that increasing specimen thickness leads to a decrease of the zero energy loss intensity and an increase in higher (multiply scattered) energy loss electrons. We show that contrast decreases gradually with increased energy loss but, most important, the signal to noise ratio is maximal at an energy loss position slightly below the intensity maximum. This is the optimal position for imaging thick specimens. Moreover our studies confirm that the following parameters have similar effects on the energy loss spectra: (1) increased thickness (t); (2) higher average Z number elements (or lower mean free path); and (3) lower primary voltage (V0).

Animals↗
PubMed1988

Evaluation and optimization of the performance of elastic and inelastic scanning transmission electron microscope imaging by correlation analysis.

Scanning Transmission Electron Microscopes (STEM) offer specific characters, such as multidetector configuration, energy loss spectroscopy, external control of the probe raster, which make them quite suited to digital image acquisition and innovative data processing. Considering pixel intensities as random variables, one can apply cross-correlation techniques to pairs of duplicated images. Such methods are used to investigate imaging properties of the instrument, such as the point resolution and the signal to noise ratio, in its different working modes. Concerning the annular dark field, one shows that there exist optimum values for defocus and angle of illumination which minimize the probe size at a value of about 0.5 nm. The same techniques are also used to evaluate the characteristics of energy filtered images recorded in a specific energy window loss around an ionization edge: the degradation in edge resolution with respect to the accompanying ADF images is only of the order of 0.2 to 0.3 nm, which sets the delocalization parameter for an energy loss of 100 eV (i.e. for U-O4-5) well below 1 nm in agreement with theoretical predictions.

DNA↗
PubMed1988

Developments in processing image sequences for elemental mapping.

Elemental mapping consists in searching the distribution of a given chemical species over an extended specimen area, with relation to topographical or structural features. It can be done with EELS core signals from a combination of several energy filtered images. One major problem encountered in the processing of such sequences of images lies in the extrapolation errors due to a difficult estimate of the background below the characteristic signal. The chosen method must be sufficiently reliable to avoid the risk of both "false positive" and "false negative" values: the first category may stem from spurious signals or from a non-satisfactory fit of the background. The second category is mainly due to a limited sensitivity. The EELS signal is often much weaker than the background intensity; an extrapolation error can therefore transform a negative value into a positive one, or vice versa. The purpose of the present contribution is to check the validity of the processing at different levels: i) different mathematical models of background; ii) different types of fitting procedures (one-parameter and two-parameters fits); iii) different fitting methods and several associated manipulations, such as a quasi local estimation of the involved fitting parameters. The statistical validity of those techniques is discussed through several tests on real images obtained from different specimens (Co/CeO2 catalysts, ferritin molecules, U and Tb staining clusters). Progress is made on the way of quantitative elemental mapping at a given confidence level, and towards the identification of single atoms.

Electron Probe Microanalysis↗
PubMed1985

Subunit arrangement of Escherichia coli F1-ATPase studied by scanning transmission electron microscopy.

The shape and the arrangement of subunits in Escherichia coli F1-ATPase (ECF1) lacking the delta subunit have been explored with a high performance scanning transmission electron microscope. In tilting experiments, the ECF1 molecule appeared as a flat cylinder whose width (approx. 120 A) was about twice its height. The symmetry of front view projections of ECF1 has been investigated by computer analysis. In a population taken at random from the data bank, one third of the particles showed five-fold radial symmetry components, one third six-fold radial symmetry components and the last third no typical symmetry. The six-fold radial symmetry was consistent with a hexagonal arrangement of six large peripheric masses, which probably correspond to the three alpha and the three beta subunits of ECF1. The five-fold radial symmetry was tentatively explained by a fusion of two juxtaposed peripheric subunits. Lateral projections showed a zig-zag organization of the large masses, suggesting that the large alpha and beta subunits are located on two levels, with some degree of intercalation between the subunits of the two levels.

Cell Membrane↗
PubMed1978

About the use of electron energy-loss spectroscopy for chemical mapping of thin foils with high spatial resolution.

Core-loss energy-filtered images have been suggested as a substantial contribution to the development of an analytical electron microscope with high spatial resolution. However, for many problems in complex materials, the characteristic signals can only be detected as slope variations of the continuously decreasing background. Therefore further data processing techniques are needed to extract satisfactorily the true chemical information. A discussion of the present limits and of the existing solutions clearly shows that the method can only be developed at the expense of more elaborate systems such as simultaneous detection channels (quite well suited to the STEM instruments). Typical numbers for realistic situations illustrate the field of application of the technique.

Electrons↗
PubMed1977

Fresnel fringes in STEM.

Experiments carried out with a field emmission STEM show several Fresnel fringes along specimen edges, similar to CTEM observation. Analysis of the data shows agreement with computer profiles for idealized edges and the influence of defocusing distance and collector aperture size is discussed. In very coherent detection conditions the number of visible fringes is limited maily by signal-to-noise ratio considerations. In order to observe the maximum number of fringes, a collector aperture must be chosen so that there is a compromise between the limits imposed by the coherence of the detection and the signal-to-noise ratio.

Electrons↗
PubMedDate not supplied

Contribution of electron energy loss spectroscopy to the development of analytical electron microscopy.

The combined use of an electron energy loss spectrometer and an electron microscope provides some chemical information at the nanometer scale. The physics of the interaction processes between the incident electron beam and the thin sample foil is reviewed in terms of energy and momentum transfer. This analysis of the content of an electron energy loss spectrum allows us to establish rules for a satisfactory use of the information and to discuss the detection limits of this newly developed microanalytical technique.

Electron Probe Microanalysis↗