Microscopy indirect examination

Because of this importance, different techniques have been developed to characterize the droplet size distribution in emulsions, each with its own pros and cons. Light microscopy, for example, is qualitative and only suited for particles larger than about 1 )im. When using electron microscopy, correct sample preparation is crucial to the examination and interpretation of the dispersions. The Coulter method is an indirect method which detects a... 

Hillbrick, G.C., McMahon, D.J., and McManus, W.R. (1999) Microstmcture of indirectly and directly heated ultra-high-temperature (UHT) processed milk examined using transmission electron microscopy and immunogold labelling. Lebensmiti. Wissen. Technol. 32, 486 94. 

In conclusion, it should be pointed out that none of the physicochemical techniques discussed above permits the direct measurement of the elements of the polymeric materials porous structure we measure the properties of the systems where the polymers interact with certain test substances (nitrogen, mercury, water, polystyrene standards, ions, etc.), and not the dimensions of the pores or other supramolecular elements of the material. Therefore, the evaluation of the surface area and diameters of pores available to the molecules of these substances must be considered as indirect methods of examining the porous structure. Because of this, all calculations are based on assuming certain models of the structure of the material and accepting certain assumptions as to the mechanism of interaction between the material and test molecules. Only transmittance, scanning, and, in particular, atomic force microscopy can be considered as direct methods of measuring dimensions and distances. However, up to now the last technique has not been appHed to microporous hypercrosslinked polymers. 

The electrochemical methods provide only indirect information about the structure of the UPD ad-atom layers in an atomic scale. In order to obtain more direct information about the structure of the UPD ad-atom layers, many investigators have adopted the use of in situ techniques, in which the electrode surface is examined with surface science methods. The methods mainly used are in situ X-ray diffraction [7,15-17], in situ scarming tunneling microscopy (STM) [18-23], and in situ atomic force microscopy (AFM) [24]. These methods have provided detailed information on the atomic structure, the thermodynamic stability, and the dependence of the structure on the potential for several UPD systems. Tfowever, little attempt has been made (and this mainly concerns the reduction of oxygen) to correlate directly the structure of the ad-atom... 

While it is not possible to remove the tip after preparation from the SECM cell and examine it by electron microscopy, information about the exposed area of the tip and the shapes of the tip and insulating sheaths can be obtained indirectly from SECM approach curves where ip is measured as a function of tip-substrate spacing, d, as the tip is moved toward the substrate. Tips with correct configuration show approach curves similar to those shown in Eigure 17.2.2. These curves were obtained with a solution containing 2 mM Cp2EeTMA and 1.0 M NaNOj, with the tip biased at 0.6 V vs. SCE (where CpjFeTMA oxidation is diffusion-controlled). In the experiment shown in curve 1, the n-TiOj substrate (a semiconductor) was biased at 0.7 V vs. SCE (a potential well negative of its flat-band... 

Model studies are generally conducted in university research laboratories where the thin, flat structure of a melt cast or drawn film provides an ideal specimen for study. Such thin films can be examined directly or indirectly by TEM as well as by optical microscopy, SEM, or SPM. Specimen preparation is minimal, and interpretation of the image is made easier for several reasons ... 

It is not our intention here to review all the varied techniques that have from time to time been applied to the study of the oxidation of metals. Attention will be directed to two techniques, one direct and the other indirect, both of which would normally be applied in association with replica and transmission electron microscopy, electron diffraction, and X-ray examination to characterize.the oxide layer. 

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