Interference microscopes

Interference Microscope. There is an interference microscope based on the same general idea as DIG (13), ie, separation of a light beam into two beams that then traverse different paths through the object space. However, the separation of the two rays is much greater than with DIG, and some interference microscopes use other means than the WoUaston prism to separate the light beam into two parallel beams. Because the result then is not specifically increased contrast but increased physical characterization data, it will be discussed later. 

One of the more important uses of OM is the study of crystallization growth rates. K. Cermak constructed an interference microscope with which measurements can be taken to 50° (Ref 31). This app allows for study of the decompn of the solution concentrated in close proximity to the growing crystal of material such as Amm nitrate or K chlorate. In connection with this technique, Stein and Powers (Ref 30) derived equations for growth rate data which allow for correct prediction of the effects of surface nucleation, surface truncation in thin films, and truncation by neighboring spherulites... 

The application of interference techniques overcomes the limitations exerted by the large optical wavelengths. With commercial phase-measurement interference microscopes (PMIM), a surface resolution of the order of 0.6 nm can be achieved [33, 34]. In a microscope a laser beam is both reflected from the sample surface and from a semitransparent smooth reference surface (Fig. 3). The interference pattern is recorded on an area detector and modulated via the piezo-electric driven reference surface. The modulated interference pattern is fed into a computer to generate a two-dimensional phase map which is converted into a height level contour map of the sample surface. While the lateral resolution (typically of the... 

Fig. 3. Schematic beam path of a phase-measurement interference microscope (PMIM, Fizeau optics). The beam partially reflected at the reference plane and at the sample surface interfere with each other while the reference plane is moved by the piezoelectric transducer for automatic phase determination. A reflectivity of at least 1% is required for the sample surface...

Caspersson, T. Carlson, L Svensson, 6. A Scanning Interference Microscope Arrangement , Experimental Cell Research. 1954, 7, 601-602. 

The foam drainage, surface viscosity, and bubble size distributions have been reported for different systems consisting of detergents and proteins. Foam drainage was investigated by using an incident light interference microscope technique. 

Fig. 10.2 Schematic diagram of a reflected interference microscope 1 - tight source, 2 - heat reflecting filter, 3 - coUimator, 4 - diaphragm, 5 - light filter, 6 - photo film, 7 - projection ocular, 8 - semi-transparent silvered mirror, 9 - aperture diaphragm, 10- auxiliary lens, 11 - immersion lens, 12 - sample under investigation, 13 - substrate...

Section thickness is an important parameter. The absorbance is higher in thick sections than in thin ones and thus the contrast between light and shade in the UV microscopic image is greater in thick sections. However, the increase of section thickness introduces errors caused by light scattering, nonparallel illumination, and diffraction. After a detailed study of the various factors involved, Scott et al. (1969) recommended a section thickness of 0.5//m. The upper limit for section thickness for UV microscopy is about l-2//m (Boutelje and Jonsson 1980, Fujii 1987). For quantitative work it is necessary to know the section thickness accurately. This value may be estimated from the interference colors produced by the sections or from measurements with an interference microscope (Boutelje and Eriksson 1982, 1984). 

CdSe nanocrystal solutions in toluene were obtained from Evident Technologies (Troy, NY). Concentrations of 2.8 and 5.6-nm CdSe nanocrystals were 2.5mg/mL. Sensor films were spin-cast from 5% vol. solutions of nanocrystals in polymer/toluene. Polymers tested as matrices for the CdSe nanocrystals are fisted in Table 5.1. Film thickness measured using an interference microscope was found to be under 1 om. 

Others have used interference microscopic 36> and gravimetric methods 37> to compare the density of the residual polymer on the various steps. 

Two-beam interference microscopes operating according to the principle of the Michelson interferometer and accessory devices converting an ordinary microscope into a two-beam interferometer are commercially available. In such microscopes, collimated monochromatic light is half reflected onto the sample surface and half transmitted to an adjustable flat reference mirror by a beam splitter. The two reflected beams recombine in the microscope and the resulting variation in the optical path difference of the beams produces parallel interference lines of equal thickness which are also displaced at the position of the film step. The lines obtained are, however, relatively broad limiting the resolution and the accuracy of such measurements by the uncertainty in selecting the line centre. 

Ellipsometric Determination of Film Thickness. The principal use of the ellipsometer was to study the upper edge of the films on vertical plates where the thickness became less than 1000 A. and could not be observed with the interference microscope. The ellipsometric measurement of film thickness is described in the literature [4,6]. For the purposes to which the technique was applied here, the approximate equation given by Drude [6] relating the film thickness and refractive index with the optical parameters of the incident and reflected light was entirely adequate. In order to use the Drude approximations it was necessary to assume the refractive index of the liquid film to be the same as that of bulk liquid. These approximate equations are highly inaccurate for film thickness greater than 100 A. 

The extent and thickness of the primary film, which was invisible with the interference microscope but detectable by breath patterns. 

Fig. 33 Schematics of interference microscopy, a Two light beams, one passing through the crystal and the other through the simrounding atmosphere, b The interference microscope. c Interference patterns generated due to different optical properties of the media passed hy the two beams, d Concentration profiles calculated from the changes in interference patterns with time...

The compatibility of the polymers in solutions was determined by dynamic viscosity measurements using a rotational viscometer at 293 K and shear rate 1312 s. The morphology of the film cast from a solution was examined with a polarization-interference microscope by differential method, at magnification of 250x. Dynamic mechanical measurements were made using direct reading visco-elastometer, the Rheovibron. The temperature was scanned... 

The lateral texture can be studied by measuring the lateral birefringence in a thin fiber cross section [132, 134], or by registration of the retardation profile across the diameter of a whole filament with an optical interference microscope... 

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