Optical microscopy, computer

Until the advent of modem physical methods for surface studies and computer control of experiments, our knowledge of electrode processes was derived mostly from electrochemical measurements (Chapter 12). By clever use of these measurements, together with electrocapillary studies, it was possible to derive considerable information on processes in the inner Helmholtz plane. Other important tools were the use of radioactive isotopes to study adsorption processes and the derivation of mechanisms for hydrogen evolution from isotope separation factors. Early on, extensive use was made of optical microscopy and X-ray diffraction (XRD) in the study of electrocrystallization of metals. In the past 30 years enormous progress has been made in the development and application of new physical methods for study of electrode processes at the molecular and atomic level. 

The computer age has brought about considerable innovation in the operation of laboratory instrumentation. One consequence of this is the wider acceptance and utilization of the optical microscope as a quantitative analytical instrument. A brief literature survey illustrates the diversity of disciplines and optical methods associated with the development of computer interfaced optical microscopy. This is followed by a description of how our methods of fluorescence, interferometry and stereology, nsed for characterizing polymeric foams, have incorporated computers. 

For samples thicker than the depth of field, the images are blurred by out-of-focus fluorescence. Corrections using a computer are possible, but other techniques are generally preferred such as confocal microscopy and two-photon excitation microscopy. It is possible to overcome the optical diffraction limit in near-field scanning optical microscopy (NSOM). 

FIGURE 2.24 Example of a stack of micromolded PU structures viewed by (a) optical microscopy or (b) micro-computer tomography. Scale bar = 1 mm [160]. Reprinted with permission from Springer Science and Business Media. 

Obviously, classical microscopy is the first option. Conventional optical microscopy has a resolution down to about 500 nm, depending on the wavelength of the light used. This is usually not enough to establish sizes and shapes of. for instance, colloidal particles. When coherent light waves are used and the Interference analyzed by computer, normal resolution down to 1 nm, as compared with a horizontal resolution of about 10 pm, is attainable. However, over the past decades a host of other physical techniques have been developed. 

Although FCS has now been invoked in about 3,000 scientific publications, now at 400 per year, its use before about 1990 was limited by severe technological barriers involving instability of laser light sources, poor sensitivity of photon detectors, noisy electronics, and insufficient computer capacities for the correlation computations. These problems inhibited application of FCS, until suddenly about 1990 the electro-optical and computational technologies advanced so that it became feasible. These advances occurred in synchrony with our creation of Multiphoton Laser Scanning Microscopy, which has enabled effective research on the molecular dynamics of life in living tissues and animals [14]. 

As a result of extreme depth discrimination (optical sectioning), the resolution is considerably improved (by up to 40% compared to optical microscopy). The CLSM technique acquires images by laser scanning or uses computer software to subtract out-of-focus details from the in-focus image. The images are stored as the sample is advanced through the focal plane in increments as small as 50 nm. Three-dimensional images can be constructed to show the shape of the particles. 

Fig. 8.7. Onset of pitting corrosion obser >ed with optical microscopy. (A) Snapshots of a computer processed video sequence obtained with optical microscopy green stars mark the iiucleatioii of new pits. (B) Space-time plot along the line ab in A. (C) Total number of pits on a logarithmic scale, (D) Total current as a function of time. The reaction conditions were T = 20.3 C with the potential held at 615 mV nh E Reproduced from [23],...

The AFM has been employed in manufacturing and quality control of microelectronics, including semiconductor silicon wafers, MEMS devices, CDs/ DVDs, and computer hard disks. The AFM is capable of identifying defects that are too small to be seen using optical microscopy. 

The macroscopic structure of matter can be assessed, for example, by optical microscopy and can then be linked to its microscopic origin through X-ray, neutron, or electron diffraction experiments and the various forms of electron and atomic-force microscopy. A factor of 10 -10 separates the atomic, nanometer scale from the macroscopic, micrometer scale. Macroscopic dynamic techniques ultimately linked to molecular motion are, for example, dynamic mechanical and dielectric analyses and calorimetry. In order to have direct access to the details of the underlying microscopic motion, one must, however, use computational methods. A realistic microscopic description of motion has recently become possible through accurate molecular dynamics simulations and will be described in this review. It will be shown that the basic large-ampHtude molecular motion exists on a picosecond time scale (1 ps = 10 s), a ffictor at... 

Electronics electrical engineering physics oj> tical physics atomic physics mathematics statistics imj e analysis materials science photomicrogp aphy interferometry electromagnetics quantum electrodynamics computer science nanotechnology metallography electron microscopy optical microscopy scanning probe microscopy cell biology chemistry. 

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