Optical microscopy artifacts

The compensation birefringence measurement is very easily coupled to optical microscopy in the transmission and reflection modes, thus allowing characterizing orientation with a spatial resolution of a few hundreds of nanometers [14]. Polarizing microscopes are widely available and are often used for birefringence studies even if spatial resolution is not required. Objectives specifically designed for cross-polarized microscopy are necessary to avoid artifacts. 

Hecht, B., Bielefeldt, H., Inouye, Y, Pohl, D. W., and Novotny, L. 1997. Facts and artifacts in near-field optical microscopy. J. Appl. Phys. 81 2492-98. 

Hecht B, Bielefeldt H, Inouye Y, Pohl DW, Novotny L (1997) Facts and artifacts in nearfield optical microscopy. J Appl Phys 81 2492... 

The practical lower limit of emulsion sizing with optical microscopy is on the order of 0.5 (xm. This limit is much lower with electron microscopy, on the order of 0.1 (xm or less with direct observation of frozen samples in a scanning electron microscope, and 0.01 xm or less with replicas and transmission electron microscopy. Sizes smaller than these lower limits can be recognized with each of these techniques, but quantification of the size distribution becomes difficult. Furthermore, at levels of about 0.01 xm, it is extremely difficult to avoid artifacts and subsequent misinterpretations. As mentioned earlier, sample preparation is an extremely important consideration in both optical and electron microscopic techniques. With optical... 

For optical microscopy of fracture surfaces usually little or no surface preparation is necessary. However, because plastics have poor electrical conductivity, for SEM examinations the sample surface generally needs to be coated with a conductive layer that prevents charging and heating. The energy carried into the sample can melt the polymer or vaporize low molecular contents locally and change the fracture surface irreversibly, making its interpretation impossible. On the other hand, to ensure artifact-free imaging, the applied layer itself must not have any visible structure and must be so thin that the structures on the surface are not hidden. 

A similar limit may exist for the lower end of the size distribution if sizing is done by optical microscopy. Because of the optical limitations explained in Section 20.2, particles less than about 0.3 m in diameter are not included in the size distribution. This 0.3- m limit, sometimes called the optical cutoff, curves the lower end of the size distribution line so that it never goes below 0.3 pm. An example of data having both cutoffs is shown in Fig. 4.13. These cutoffs are artifacts of the sampling and measurement system. If the cutoffs affect only a small fraction of the distribution, it is acceptable to ignore them when fitting a straight line to the data on a log-probability plot. 

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