Instrumentation, optical microscopy

The techniques, instrumentation and underlying theory of optical microscopy for materials scientists have been well surveyed by Telle and Petzow (1992). One of the last published surveys including metallographic techniques of all kinds, optical and electronic microscopy and also techniques such as microhardness testing, was a fine book by Phillips (1971). 

The impact of electron-optical instruments in materials science has been so extreme in recent years that optical microscopy is seen by many young research workers as faintly fuddy-duddy and is used less and less in advanced research this has the unfortunate consequence, adumbrated above, that the beneficial habit of using a wide range of magnifications in examining a material is less and less followed. 

There are various reasons to study the composition of ancients cements. The actual composition of a cement, for example, provides information on its nature, the technology used for making it, and the provenance of its components (Middendorf et al. 2005). It may also elicit differences between the nature of an original cement used for building and that used for later repairs (Streicher 1991 Jedrzejewska 1990). Most analytical work concerning ancient cement in the recent past has been based mainly on the use of optical microscopy and classical analysis techniques. Sometimes, such studies are complemented with information derived by instrumental techniques (Blauer-Bohm and Jagers 1997). 

Optical microscopy is often coupled with infra-red spectroscopy. We use the optical portion of the instrument to identify regions of interest, onto which we direct a highly focused infra-red beam. We obtain an infra-red spectrum from the radiation that penetrates the sample. The region of interest may be as small as 250 pm (250 x iff"6 m) In diameter. We can compare the spectrum with a library of reference samples in order to identify the chemical structure of the area of interest. Polymer scientists make extensive use of this technique when examining multi-layer samples or when performing contaminant analyses. 

Figure 8.5 Monitoring the in vivo time course of P. yoleii malaria infection in mice inoculated with live parasites at day 0.15 (Upper trace) Parasite count obtained by microscopy of blood smear, folded with anemia model from the literature (para-sites/vol) = (parasites/RBC) x (RBC/vol). (Lower trace) Integrated LDMS heme signal from 300 shots across three consecutive sample wells each sample (30 pil) is processed following protocol C, and examined on a commercial LD TOF instrument. Infection is more easily and more rapidly discerned both at earlier and later times by LDMS, compared to the traditional optical microscopy examination.

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. 

Because of the particle sizes involved, classically the optical microscope has been the instrument of choice especially for lyophobic colloids. Excellent books and manuals are available (Bradbury 1991 Cherry 1991 Schaeffer 1953) on the numerous variations of optical microscopy, and we do not go into all the details. Our purpose here is merely to point out some very elementary principles that make this method ideally suited for direct examination of colloids. We also use this introduction as a first step in pointing out modern techniques that fall under the class of microscopy but use principles (e.g., electron tunneling see Vignette 1.8) and radiation (e.g., electron or x-ray) other than those used in optical microscopy. 

Refs. [i] Minsky M (1988) Scanning 10 128 [ii] Wilson T, Sheppard CJR (1984) Scanning optical microscopy Academic Press, London [Hi] Corle TG, Kino GS (1996) Confocal scanning optical microscopy and related techniques. Academic Press, New York [iv] Delhaye M, Barbil-lat J, Aubard J, Bridoux M, Da Silva E (1996) Instrumentation. In Rur-rell G, Corset J (eds) Raman microscopy developments and applications. Academic Press, San Diego [v] Ren B, Lin XF, Jiang YX, Cao PG, Xie Y, Huang QJ, Tian ZQ (2003) Appl Spectrosc 57 419... 

Optical Microscopy The resist pattern was examined under an optical microscope normally at the stage shortly after the development. The Nikon Optiphot microscope was supplied by Nikon Instrument Division of Garden City, New York. 

The mechanical sieving of bottom ashes from different periods during combustion shows that when die sand addition decreases, the size of the particles in the bottom ash increases. This is most evident in the fractions around 0.71 nun. When these particles were crushed with a mortar and studied by optical microscopy, it was seen that they consisted of a kernel with a suirounding shell. The kernel was actually mini agglomerates of transparent small particles whilst the shell was more concrete like. The crushed samples were mechanically separated into shells and kernels. A comparative analysis of these was made with an ICP-OES instrument. 

Liquid crystal textures were observed by optical microscopy between crossed polars. The instrument used was an Olympus BH-2 polarizing microscope equipped with a Linkam TH-600RH hot stage. 

The optical microscope is a sophisticated instrument capable of providing images with a resolution of the order of 1 p,m, molecular information via birefringence, and chemical information via colour changes or through the use of specific dyes. When these factors are combined with relative ease of sample preparation (c.f. electron microscopy) and purchase cost, optical microscopy is a powerful technique for the study of many materials, particularly those that transmit in the visible region of the spectrum. 

The WITec alpha300 R confocal Raman microscope can be upgraded to perform atomic force microscopy (AFM), tip-enhanced Raman spectrometry and near-field scanning optical microscopy, and is arguably the most versatile instrument for Raman microspectroscopy available today. 

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