Phase interference microscopy

In the second half of the 20th century, a number of advanced variants of optical microscopy were invented. They include phase-contrast microscopy (invented in France) and multiple-beam interference microscopy (invented in England), methods... 

While electron or ion beam techniques can only be applied under ultra-high vacuum, optical techniques have no specific requirements concerning sample environment and are generally easier to use. The surface information which can be obtained is, however, quite different and mostly does not contain direct chemical information. While with infra-red attenuated total reflection spectroscopy (IR-ATR) a deep surface area with a typical depth of some micrometers is investigated, other techniques like phase-measurement interference microscopy (PMIM) have, due to interference effects, a much better surface sensitivity. PMIM is a very quick technique for surface roughness and homogeneity inspection with subnanometer resolution. 

The direct visnalization of microstructure may be accomplished by various forms of microscopy. Recent refinements in microscopy techniques are epitomized by video-enhanced interference phase-contrast microscopy, which is emerging as a workhorse probe for colloidal suspensions and other microstructnred liqnids. 

Later, differential interference microscopy was developed, enabling the detection of difference in levels as sensitively as phase contrast microscopy, and, because this technique was easier to use, it came to be used in preference to the former techniques [6]. Differential interference microscopy is superior to phase contrast microscopy in the observation of vicinal or curved surfaces, which are impossible to observe under a phase contrast microscope because the contrast is too high. 

Powerful methods that have been developed more recently, and are currently used to observe surface micro topographs of crystal faces, include scanning tunnel microscopy (STM), atomic force microscopy (AFM), and phase shifting microscopy (PSM). Both STM and AFM use microscopes that (i) are able to detect and measure the differences in levels of nanometer order (ii) can increase two-dimensional magnification, and (iii) will increase the detection of the horizontal limit beyond that achievable with phase contrast or differential interference contrast microscopy. The presence of two-dimensional nuclei on terraced surfaces between steps, which were not observable under optical microscopes, has been successfully detected by these methods [8], [9]. In situ observation of the movement of steps of nanometer order in height is also made possible by these techniques. However, it is possible to observe step movement in situ, and to measure the surface driving force using optical microscopy. The latter measurement is not possible by STM and AFM. 

Jhe theoretical lower limit of resolution of the light microscope is about 0.2 micron—i.e., 2000 A. This figure can be reduced in favorable circumstances by using phase-contrast or interference microscopy. Ultraviolet microscopy of coal was attempted at the Division of Coal Research, but without success owing to the opacity of coal to ultraviolet radiation. Vigorous attempts are being made to develop x-ray microscopy, and its limit of resolution is already an order better than that of the light microscope. 

Nomarski differential interference contrast microscopy is an alternative to phase contrast microscopy which gives an almost three... 

Lebedeff AA (1930) Interferometre a polarisation et ses applications Rev Opt 9 385-413 Musha Y, Goring DAI (1975) Distribution of syrmgyl and guaiacyl moieties in hardwoods as indicated by ultraviolet microscopy Wood Sci Technol 9 45-58 Ross KFA (1967) Phase contrast and interference microscopy for cell biologists Edward Arnold, London, 238 pp... 

Two rather specialized methods are available to measure contact angles less than approximately 60". The method of interference microscopy makes use of fringe patterns reflected from the drop surface to calculate the contact angle [13]. Fisher [14] obtained contact angles less than 30 by simultaneously measuring the mass of the drop and the radius of the three-phase line. The contact angle was then derived from a semiempirical relationship involving these two quantities. 

A EXPERIMENTAL FIGURE 5-44 Live cells can be visualized by microscopy techniques that generate contrast by interference. These micrographs show live, cultured macrophage cells viewed by bright-field microscopy (/eft), phase-contrast microscopy middle), and differential interference contrast (DIC) microscopy righti. In a phase-contrast image, cells... 

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