Microscopy light

The main role of the light microscope is to image structures, either natural or man made, which are not observable to the naked eye, but have features greater than 0.1 pm. It is extensively used during the preparation of samples for observation by other analytical techniques, such as SEM or AFM, and should always be the first step in a materials analysis. 

For examination in reflected light, the sample is mounted in a plastic resin and is cut and polished using only non-aqueous lubricants. The most generally useful etchant is probably HF vapour, which has the merit of not removing alkali sulphates the slide is inverted over a vessel containing 40% aqueous HF for 10-20 seconds. Treatment with water followed by 0.25% HNO3 in ethanol and finally ethanol is also widely used, and many other etchants have been employed for specific purposes. The etchants produce thin films of decomposition products, which yield interference colours when viewed in reflected light. 

There should be little free lime. What there is should occur as rounded grains, typically 10-20 pm in size, and associated with alite and interstitial material. Lime appears cream in sections etched with HF vapour. Its presence may be confirmed by a microchemical test using White s reagent (5 g of phenol in 5 ml of nitrobenzene + 2 drops of water) long, birefringent needles of calcium phenate are formed. The test also responds to CH. Alkali sulphates occur in the clinker pore structure they are etched black with HF vapour, and inhibit the etching of silicate phases with which they are in contact. 

This technique allows the observation of a polymeric sample in order to obtain important information about its structure, processing or manufacturing, and failure or damage causes. Therefore, it is a very common technique for quality control, troubleshooting, and failure analysis. 

For sample preparation, a microtome with a range from 0 to 340 microns with 0.5 micron resolution and a polishing machine are required. 

Colorimetry involves the treatment of a sample to impart color to selected materials in the sample. For instance, in multi-layer film it can be difficult to distinguish the different layers when natural polymers are used (no colorants added). Certain chemicals color certain polymers but do not color others. For example, iodine will color nylon-6 red, EVOH brown, and typical tie layers gray, but will not change the color of PE or PET. 

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Two nucleation processes important to many people (including some surface scientists ) occur in the formation of gallstones in human bile and kidney stones in urine. Cholesterol crystallization in bile causes the formation of gallstones. Cryotransmission microscopy (Chapter VIII) studies of human bile reveal vesicles, micelles, and potential early crystallites indicating that the cholesterol crystallization in bile is not cooperative and the true nucleation time may be much shorter than that found by standard clinical analysis by light microscopy [75]. Kidney stones often form from crystals of calcium oxalates in urine. Inhibitors can prevent nucleation and influence the solid phase and intercrystallite interactions [76, 77]. Citrate, for example, is an important physiological inhibitor to the formation of calcium renal stones. Electrokinetic studies (see Section V-6) have shown the effect of various inhibitors on the surface potential and colloidal stability of micrometer-sized dispersions of calcium oxalate crystals formed in synthetic urine [78, 79]. 

It is interesting to note the analogy of developments in light microscopy during the last few decades. The confocal microscope as a scaiming beam microscope exceeds by far the nomial fluorescence light microscope in resolution and detection level. Very recent advances in evanescent wave and interference microscopy seem to promise to provide even higher resolution (B1.18). 

Light microscopy is of great importance for basic research, analysis in materials science and for the practical control of fabrication steps. Wlien used conventionally it serves to reveal structures of objects which are otherwise mvisible to the eye or magnifying glass, such as micrometre-sized structures of microelectronic devices on silicon wafers. The lateral resolution of the teclmique is detennined by the wavelength of tire light... 

Light microscopy allows, in comparison to other microscopic methods, quick, contact-free and non-destmctive access to the stmctures of materials, their surfaces and to dimensions and details of objects in the lateral size range down to about 0.2 pm. A variety of microscopes with different imaging and illumination systems has been constmcted and is conunercially available in order to satisfy special requirements. These include stereo, darkfield, polarization, phase contrast and fluorescence microscopes. 

Pluta M 1988 Advanced Light Microscopy, voi 1 Principies and Basic Properties (Amsterdam Elsevier)... 

Brabury S and Everett B 1996 Contrast Techniques In Light Microscopy, Microscopy Handbooks 34 (Oxford BIOS Scientific Publishers)... 

Light Green SF Yellowish Light microscopy Light naphtha... 

Microscopy (qv) plays a key role in examining trace evidence owing to the small size of the evidence and a desire to use nondestmctive testing (qv) techniques whenever possible. Polarizing light microscopy (43,44) is a method of choice for crystalline materials. Microscopy and microchemical analysis techniques (45,46) work well on small samples, are relatively nondestmctive, and are fast. Evidence such as sod, minerals, synthetic fibers, explosive debris, foodstuff, cosmetics (qv), and the like, lend themselves to this technique as do comparison microscopy, refractive index, and density comparisons with known specimens. Other microscopic procedures involving infrared, visible, and ultraviolet spectroscopy (qv) also are used to examine many types of trace evidence. 

W. C. McCrone, L. C. McCrone, and J. G. DeUy, Polarised Light Microscopy, Ann Arbor Science PubHshers, Inc., Ann Arbor, Mich., 1979. 

Nc.ar-Fi ld Scanning Optical Microscope.. The near-field scanning optical microscope (NSOM) should, strictiy speaking, be NSLM for near-field scanning light microscopy because "optical" includes electron optical as well as light optical and NSOM is a light microscope. 

R. D. McLaughlin, Special Methods in Light Microscopy, Microscope Pubhcations, Chicago, lU., 1977. 

Plant-fiber identification is described in TAPPI T8 and TIO. In order to identify synthetic fibers, it usually is necessary to conduct solubihty and physical properties tests in addition to light microscopy observations. Systematic sampling is required to obtain quantitative information on sample composition. Because different types of pulps contain varying numbers of fibers per unit weight, it is necessary to multiply the total number of each kind of fiber by a relative weight factor, thereby the weight percentage that each fiber type contributes to the sample can be deterrnined. 

Optical properties of fibers are measured by light microscopy methods. ASTM D276 describes the procedure for fiber identification using refractive indexes and birefringence. Other methods for determining fiber optical properties have been discussed (3,38—44). However, different methods of determining optical properties may give different results (42). 

If elemental or compound data are required, the material needs to be mounted for the appropriate analytical instrument. For example, if light microscopy shows a... 

M. Pluta. Advanced Light Microscopy. Elsevier, Amsterdam, 1988. 

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