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Recent developments in the materials sciences have led toan enhanced interest in this rapidly growing field. In thisrespect, the discovery of high-temperature superconductingceramics coupled to an almost explosive progress insemiconductor and integrated circuit technology has shiftedan enormous amount of attention to these disciplines.Visible light microscopy is an invaluable tool for theinvestigation of samples in the materials sciences andengineering. An introduction to photomicrography at thehigh school level could provide interested students with auseful preview to research techniques in these areas.

INTRODUCTION

The biological and medical sciences have, for many years,relied heavily on microscopy to solve problems relating tothe gross morphological features of specimens as well as aquantitative tool for recording specific optical features anddata. In this respect, the transmitted light microscope hasproven useful in countless investigations into the mysteriesof life.

More recently, microscopy has been employed in thephysical and materials sciences as well as the semiconduc-tor industry to examine various aspects of new materials as,for example, birefringent liquid crystalline systems [1],high temperature superconductor thin-films [2], andintegrated circuit surfaces [3,4]. The nature of thesematerials requires, in some instances, examination byreflected (episcopic) illumination that departs from theclassical transmitted (diascopic) illumination techniquesthat have been so well developed in the biological sciences.

Transmitted light microscopy is a mature discipline inwhich a wide spectrum of illumination techniques areavailable for contrast enhancement. For instance, livingcells in tissue culture can be observed directly atamazingly high resolution using phase and differentialinterference contrast techniques. At high magnification,cellular internal features are clearly resolvable usingthese methods.

In contrast, reflected light microscopy is just emergingas an important tool for investigating surface features inthe materials sciences. A significant boost to reflectedlight microscopy has come from the semiconductorindustry which relies heavily on this technique tocapture microscopic details on integrated circuit wafersduring the manufacturing process. The need for contrastenhancement methods in reflected light microscopy hasled to the development of reflected light differentialinterference contrast objectives that rival, in quality,their counterparts on the transmitted light microscope.

Photomicrography has enjoyed a recent escalation inpopularity due, in part, to the introduction of newtransparency films with improved emulsions thatrespond correctly to the color spectrum generated bytungsten-halide light bulbs found in most microscopes.Improved glass alloys and optical coatings have enabledmanufacturers to provide microscope objectives thatwill produce crisp images of better quality than has beenpreviously possible. These developments coupled to thewide-spread availability of microprocessor-assistedinternal microscope exposure monitors have collectively

I N T R O D U C T I O N T O

P H O T O M I C R O G R A P H Y

Michael W. DavidsonInstitute of Molecular Biophysicsand Center for Materials Research and TechnologyThe Florida State University,Tallahassee, Florida 32306Telephone: 850-644-6114 / Telefax: 850-644-8281

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been directly responsible for the increased activity in thefield of visible light photomicrography.

Computer-assisted image analysis and confocal micros-copy [5,6] are surfacing as important techniques, howevertheir high cost will prohibit their entry into the highschool arena in the foreseeable future. Therefore, thisdiscussion will be limited to various aspects of photogra-phy using both transmitted and reflected light microscopy.

MICROSCOPE CONFIGURATION

The majority of microscopes found in public schools areof the transmitted light variety commonly used in biologi-cal laboratories. At relatively low cost, these microscopescan be converted for use in the materials and geologicalsciences as well.

Most microscope light sources emit visible light thatvibrates as a wave in all directions perpendicular to theoptical axis of the microscope. When used in this fashion,the microscope is said to be operating in the brightfieldmode. Placing a polarizing element into the light pathrestricts the passage of light, much as an optical slit, tothose waves that propagate in the vector plane of thepolarizing element. This action reduces the amount oftransmitted light to approximately 30% of the emittedvalue. A common microscopy technique involves the use

of crossed polarizers where two individual polarizingelements are inserted into the light path with their vectorpropagation planes crossed at a 90 angle with respect toeach other. When a sample is placed in the light pathbetween the crossed polarizers, the only light emitted willbe that which is refracted by the sample until it can passunimpeded through the second polarizer. In classicalnomenclature the first polarizer has been termed thepolarizer while the second polarizer is termed the ana-lyzer.

Any brightfield microscope can easily beconverted for use with polarizing elements. Twopolarizers will be needed to convert the microscope foruse with polarized light. The polarizer responsible forpolarizing the light emitted from the microscope lightsource is placed either directly on the field lens or can betaped (with masking tape) to the substage condenser (referto Figure 1 for a detailed microscope description). Onmicroscopes with an internally directed lamp, it issufficient to place a polarizer onto the field lens as isillustrated in Figure 1. This polarizer should be largeenough to cover the lens completely. Low cost polarizersdesigned for camera lenses are sufficient for this purpose.But, if an external light source is reflected into thesubstage condenser through a mirror (Figure 1), it be-comes necessary to tape a polarizer onto the bottom of thecondenser. Many science supply houses and distributorsoffer an excellent selection of polarizing materials atsomewhat low cost. When purchasing polarizing ele-ments, remember to select materials that are as close to aneutral grey as possible. Avoid materials that are amber orgreen in color. These off color materials will cause colorshifts that must be corrected for in color photomicrogra-phy.

The second polarizer (which is termed the analyzer, asdescribed above) is inserted inside the body of themicroscope between the main body tube and the eyepiecetube. There is usually a lens mount covering the top mainbody tube and the analyzer can be taped or simply resteddirectly on this mount. Because of the restricted spacewithin the main body tube, the analyzer is limited inphysical size to 1-3 cm in diameter. An analyzer of thissize can be obtained by cutting a small section from asheet of polarizing material or by purchasing a smallpolarizer from a dealer. The analyzer and upper mainbody lens should be thoroughly cleaned to eliminate dustand fingerprints before reassembly of the microscope.After both polarizers are in place, activate the microscopelight source, place a specimen on the stage, and viewdirectly into the oculars (eyepieces). Next, bring theimage into focus and rotate the polarizer on the micro-scope base until the viewfield becomes very dark (maxi-mum extinction). At this point, the polarization directionis perpendicular between the polarizer and analyzer andyou then have crossed polarizers as described above.

Figure 1. Schematic illustration of a transmitted lightmicroscope.

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Some microscope manufacturers offer a low budgetpolarization kit ($150.00 to $300.00) that is easily userinstalled. It is advisable to contact your microscope’sdistributor or manufacturer concerning the availability ofthese items if your budget is healthy.

Among the useful methods of enhancing sample contrastare the interference methods in which contrast augmenta-tion is similar to that observed in phase contrast micros-copy with the elimination of edge “halo” effects. Differ-ential interference contrast microscopy requires expensiveobjectives equipped with a special set of prisms termedWollaston prisms that are optically matched to eachobjective [7]. A relatively low-cost substitute for theinterference contrast effect generated by the Wollastonprisms involves adapting a polarized light microscopewith Savart plates serving in place of the polarizers.Savart plates are flat plates of a suitable quartz crystal cutand polished to produce the necessary divided interfer-ence beams of light in order to generate the three-dimensional effect of interference contrast. Savart platesare commonly available from optical supply houses.

The renovations described above apply only to transmittedlight microscopy where polarized visible light passesdirectly through the sample. In reflected light micros-copy, the light beam is reflected from the surface of thesample directly into the microscope objective. It is not a

straightforward process to convert a biological transmittedlight microscope for use with either polarized or interfer-ence contrast reflected illumination methods. To avoidinvesting in expensive reflected light attachments, obliqueillumination from an external light source can be substi-tuted to produce the reflected light effect. A high-intensity light source such as a fiber optics lamp (availablefor under $200.00) provides an excellent substitute. Toachieve a semi-polarized light effect, the analyzer can beleft in place and polarizers attached (by tape) to theexternal light source. Before final attachment, thepolarizers should be rotated as described above to producemaximum extinction. Unpolarized room light, that willunavoidably be reflected into the objective, will slightlydiminish the total amount of light extinction. This methodof microscopy is particular well suited for examination ofintegrated circuits and other specimens that possessintricate surface detail.

Common biological stereo-binocular (dissecting) micro-scopes are also useful for reflected light examination ofmaterials science samples. These microscopes areparticular useful for photomicrography of the largerintegrated circuits such as microprocessors. To adapt astereo microscope for polarized light, tape a large polar-izer (such as a model designed to mount onto a (cameralens) onto the lower portion of the main body tube. Insurethat the polarizer completely covers the lens mounted in

Figure 2. Transmitted polarized light micrograph of a high density liquid crystalline DNA phase.

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Figure 4. Reflected differential interference contrast photomicrographs of the 8080 microprocessor. This 8-bitdata engine, powered by 6000 transistors, was introduced by Intel in 1974 as the first stand alone microprocessorfor personal computers. Data busses and registers, which are clearly delineated in the micrographs, can load andexecute byte-sized commands in the processors’ 16 kilobit internal memory. The photomicrograph was taken witha Nikon prototype 2.5x DIC objective and with Fujichrome 64T transparency film.

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this lower portion of the tube. Next, adapt a polarizer to theexternal light source. If fiber optics illumination device isused, simply tape the polarizer over the end of the fiberoutlet tube. Fiber optics sources can be obtained that havea beam-splitter to divide the output light into two tubes.These sources are ideal for illumination of samples withreflected light because a sample can be illuminated fromseveral directions to eliminate a shadow effect. In thiscase, be sure to cover both fiber outlet tubes with a polar-izer. Place a mirror on the stage to reflect light directly intothe objective and rotate the polarizers on the fiber outlettubes until maximum extinction is reached. It is usuallyeasier to block the light from one tube and adjust the otherfor maximum extinction, repeating the process again for theblocked tube.

Attaching a camera to the microscope is the last step.Microscope viewing heads come in three varieties: mo-nocular (one eyepiece), binocular (two eyepieces), andtrinocular (two eyepieces and a photography tube). Acamera can be adapted to each of these viewing heads.Commercially available aftermarket camera adaptersusually are attached to one of the viewing tubes with athumbscrew and adjusted to be parfocal with the eyepiecesby sliding the adapter up or down on the viewing tube. Asimple camera back will be sufficient for photomicrographybecause the camera is required only to store, expose, andadvance the film. The microscope itself acts as a cameralens. After a camera back has been adapted to a micro-scope, one should not rely on exposure values computed byin camera exposure monitors. It is best to bracket expo-sures to get a handle on exposure times as is discussed inthe section on photomicrography. For optimal photomicro-graphy, it is very important to insure that your microscopeis aligned to produce an even illumination across theviewfield. Information on microscope alignment isavailable in owners manuals or in textbooks dealing withmicroscopy and photomicrography [8].

PREPARATION OF SAMPLES FOR PHOTOMICROGRAPHY

The laboratory chemicals found in high school chemistrystockrooms provide an excellent source for samples. Mostcrystals are anisotropic and birefringent which means thatthey will refract plane polarized light emitted from thepolarizer and will “bend” it until it is visible through theanalyzer under cross-polarized illumination.

To prepare crystals for examination in the microscope,deposit a few milligrams of the appropriate chemical on aglass microscope slide and carefully place a coverslip overthe powder. Next, heat the bottom side of the microscopeslide carefully with a bunsen burner or hot plate until thepowder has completely melted. Some chemicals decom-pose upon heating and will provide poor subjects formicroscope examination. Salts are notorious as bad

candidates for the melt-recrystallization process. Themelting point of most salts is usually very high and anyorganic portion of the molecule undergoes degradationbefore melting. When melted, the molten chemical willflow underneath the coverslip and fill the entire volumebetween the coverslip and microscope slide. Either allowthe slide to cool slowly before examination or place themelted chemical sandwich onto the microscope stage andexamine the crystallization process occurring [9]. Certainchemicals recrystallize very rapidly (within a few min-utes) while others may recrystallize slowly over a periodof days, weeks, or even months. Urea, sulfur, and benzoicacid are excellent examples of common laboratorychemicals that will recrystallize rapidly enough to beexamined directly after melting. Some chemicals formmore interesting crystals when cooled slowly over aperiod of hours or days. This can be accomplished byplacing the microscope slide with it’s melted chemicalsandwich on a hot plate at 50-70 ºC and reduce thetemperature by 5-10 ºC/hr over a period of several hours.By comparing the slowly recrystallized sample to one thatwas rapidly recrystallized, any differences in recrystalliza-tion can be noted. Figure 2 illustrates a color photomicro-graph of crystallites derived from melt-recrystallization ofthe common vitamin, ascorbic acid (vitamin C). Theinstructor and students should experiment with availablechemicals to identify those that are optimal for micro-scopic analysis.

Another very effective method of preparing crystals is todissolve the chemical in a suitable solvent such as water,ethanol, acetone, or mineral spirits. A drop of the solutionis then sandwiched between the microscope slide andcoverslip and the solvent allowed to evaporate resulting information of crystalline patterns. This method is espe-cially useful for chemicals in the salt family that usuallydecompose upon heating leaving a tar-like mess. In someinstances, increasing the time for solvent evaporation willresult in a dramatic increase in crystallite size. Theevaporation time can be controlled by partially sealing thecoverslip with a bead of polymethylmethacrylate mount-ing medium leaving only a small edge of the coverslipexposed to the atmosphere. This will retard solventevaporation to allow a slower recrystallization process tooccur usually resulting in larger, more well-formedcrystallites.

The colorful crystalline pattern illustrated in Figure 3derives from a highly concentrated liquid crystalline DNAsample in which the aqueous solvent was allowed toevaporate slowly as described above. Under thesecircumstances a dilute solution of DNA will undergo aseries of liquid crystalline phase transitions until aconcentration is reached that is depicted in Figure 3.DNA exists in nature at very high concentrations, and it ispossible that liquid crystalline DNA phases have aninvaluable function in biological systems [10-13]. Many

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chemicals can display a wide spectrum of polymorphiccrystalline patterns depending on whether they are melt-recrystallized or recrystallized by solution evaporation.

Samples for reflected light microscopy usually requirevery little preparation. Reflected light microscopy can belikened to topographical surface examination with a high-power magnifying glass, and almost anything can beexamined in microscopic detail with this technique. Forexample, the fine details of surface structure can berevealed on leaves, coins, printed paper, insects, and avariety of other specimens.

Perhaps the most interesting subjects for reflected lightexamination are integrated circuits. These doped silicon“chips” are generally packaged by either molding into anepoxy resin case or cemented into a ceramic case. It isvirtually impossible to recover an integrated circuit froman epoxy resin case. During the manufacturing process,the resin flows onto the surface of the chip and penetratesinto the etched microstructure. When the epoxy cases arebroken or cracked open, the silicon fractures through thecenter of the integrated circuit and all surface detail islost. The cement in a ceramic case can, however, bescored with a hacksaw and split with a fine chisel to revealthe internal chip. Most programmable read-only memory(PROM), microprocessors, math coprocessors, and somerandom access memory (RAM) integrated circuits areprotected with ceramic cases. It should be possible tobuild a substantial collection of integrated circuits using

discarded computer parts. Examination of integratedcircuits with reflected light can serve many purposes. Forinstance, details of a particular circuit structure such asregister areas, data busses, memory storage, and logicunits are readily apparent (see Figure 4). Also, byobserving differences in the architecture of variousintegrated circuits, students can begin to get a handle onthe complex electronics involved in modern devices suchas radio, television, and computers. Figure 4 illustrates aNippon Electric Company (NEC) copy of the famous Intel8080 microprocessor introduced in 1974 as the first stand-alone microprocessor. The introduction of this revolution-ary microprocessor was a key factor in the early growth ofa fledgling personal computer industry. Figure 4 illus-trates the integrated circuit photographed with colortransparency film. Notice the advantage of color photomi-crography with respect to differentiation of various areason the integrated circuit. The presence of different huesand shades of color allows the eye to register more detailsof the integrated circuit even though both photomicro-graphs are of comparable resolution. This consequencecan be equated to the use of color graphics monitors onmodern computers where color-coordinated screens havea more pleasing and restful effect on viewers than domonochrome screens with varying grey scales.

As described above, the biological stereo microscope canbe very useful in the examination of surface detail onintegrated circuits. This is especially true of the largermicroprocessors that may exceed 1 cm2 in area. By

Figure 4. Reflected differential interference contrast photomicrograph of a high-temperature superconducting crystal ofthe ceramic, Bi

2Sr

2CaCu

2O

x.

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adding color filtration to the light sources for reflectedlight microscopy of integrated circuits, one may acquirecolored highlighting effects that enhance the appearanceof integrated circuits in photomicrographs. It is interest-ing to experiment with several light sources each with adifferent color filter. Quite a number of special highlight-ing effects can be obtained in this manner. Reflected lightmicroscopy has become an indispensable tool for thesemiconductor industry due to its usefulness in character-izing manufacturing defects and monitoring the succes-sive stages of integrated circuit fabrication.

The phenomena of superconductivity has dominatedphysics and the materials sciences since the recentdiscovery of new ceramics that superconduct at liquidnitrogen temperatures [14]. Several of the newer ceramicsuperconductors are commercially available [15]. Thesesamples can serve a dual purpose in the classroom as ademonstration of the superconductivity effect and ascandidates for reflected light photomicrography. Experi-ments of this type will give students an exciting previewof this important field.

The prism-like color spectrum pictured in Figure 5 arisesfrom crystalline thickness gradients on the surface of asynthetic high-temperature superconducting crystal(Bi

2Sr

2CaCu

2O

x) platelet. This reflected light photomicro-

graph yields information about the surface topography ofthe superconductor and helps to provide investigators withan insight into the marvels of superconductivity. Figure 6is a transmitted light photomicrograph of a lanthanumaluminate (LaAlO

3) wafer. The wafer was cut and

polished, from a slowly grown 5 cm diameter singlecrystal, to serve as a substrate for the deposition ofsuperconductor thin-films. These are only severalexamples of the numerous types of samples that can beimaged and photographed with reflected light microscopy.

PHOTOMICROGRAPHY

A necessary responsibility of microscopy is to capture theimages seen in the microscope onto photographic film toobtain “hard copy” for research records. In a high schoolenvironment, classical photography assignments can becoupled with science microscopy studies to provide amultidisciplinary program in photomicrography.

Photomicrography encompasses the techniques of bothblack and white and color photography. Black and whitefilm processing is substantially lower in cost that colorfilm, if processing is done in-house. Unfortunately, manycommercial film processors no longer offer black andwhite processing services or charge exorbitant amountsfor this service. If budget restrictions force the exclusive

Figure 5. Transmitted polarized light micrograph of a lanthanum aluminate (LaAlO3) wafer.

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use of black and white photomicrography, it is advisableto invest in darkroom equipment so students can developand print their own photomicrographs.

A green gelatin or interference filter should be insertedinto the microscope lightpath between the light source andthe first polarizer (see Figure 1) for black and whitephotomicrography. With built-in illumination, the filtercan be placed on the field lens prior to the placing of thepolarizer. On microscopes that use an external lightsource, the filter can be taped below the polarizer on thesubstage condenser.

I recommend the use of Kodak Technical pan film (or it’sequivalent) with HC-110 developer for crisp images withexcellent contrast and resolution. This film providesintricate detail imaging and reduces the continuous tonaltendencies of the popular black and white films. Printingcan be done on Kodak Polycontrast (or again, it’s equiva-lent) paper with Dektol developer. After processing a rollof film, carefully cut the negatives into sections of 5frames each and store in specially made polyethylenestorage sheets. Contact prints can be made by placing asheet of negatives directly onto an 8" x 10" piece ofPolycontrast paper and exposing for a few seconds withthe enlarger lens aperture opened to the widest f-stop.Contact sheets are an ideal way of cataloging data andthey provide a compact method for storing or sortingthrough many images. When an enlargement is needed,simply remove the appropriate negative strip from theprotective sheet and print with an enlarger.

Color photomicrography is considerably more compli-cated than black and white photomicrography becausecolor film emulsions are color balanced for a particularspectrum of light 16. The term color temperature refers tothe wavelength spectrum emitted by a particular lightsource. For instance, films intended to be used outside inordinary daylight or under fluorescent lighting arebalanced during manufacture for a color temperature of5500 K while films made for indoor tungsten lightbulb useare balanced for a color temperature of 3200 K.

The majority of microscopes use a tungsten-halide bulb asa light source. These types of bulbs emit a wavelengthspectrum centered in the 3200 K color temperature region.Therefore, films color balanced for this type of illumina-tion will produce the best results. Using daylight bal-anced films under tungsten illumination will shift all colortones towards a decidedly yellow cast. Likewise, usingtungsten balanced films under daylight illumination willshift color tones towards a bluer cast.

All major film manufacturers have one or several 3200 Kfilms available in 35 mm transparency format. Transpar-ency film is preferable to color negative film for severalreasons. Most importantly, all color negative films are

color balanced for 5500 K and must be manipulatedduring printing to avoid the yellow cast mentioned above.Most photo processors cannot or will not produce satisfac-tory results with photomicrographs on color negative film.Also, the contrast and color saturation in transparency filmcannot be equaled by color negative film. Finally, colortransparencies are easier to label, store, and catalog andthey can be projected at seminars.

With a 20 to 100 watt tungsten-halide bulb in yourmicroscope, exposure times are usually very short andallow the use of slow films such as Ektachrome 50 orFujichrome 64T. Using slow films reduces the grain sizein photomicrographs and leads to higher quality enlarge-ments. If tungsten balanced films are not available, aKodak 80A or equivalent filter can be inserted into thelightpath between the light source and the first polarizer toallow the use of daylight balanced films with minimalcolor shift. If this filter is used, exposure times must beincreased 1-3 f-steps to allow for a reduction in lightintensity. Recently, Polaroid introduced a slow speed (ISO40) color transparency film, designated Polachrome HC,with high contrast that is ideal for photomicrography. Thisfilm produces superb contrast and color saturation and canbe user-processed in only 2 minutes with a low costPolaroid processor.

When photographing new samples or after makingchanges to the microscope (such as installation ofpolarizers), the new exposure characteristics should bedetermined on a test roll of film. Bracket several expo-sures of the same viewfield at least one and preferably twof-steps over and under previous exposure times. This willassure at least one or several good exposures and willyield exposure time information useful for photomicrogra-phy of future samples.

The best film, in my opinion, is Fujichrome 64T, a highlycolor-saturated E-6 transparency film with excellentcontrast. Recently, a new emulsion of this film wasintroduced that is designed to allow push processing withvery little reduction in image quality. Push processing is amethod developed to increase contrast (inherently low inphotomicrographs) and color saturation. This is done byunderexposing the film 1 to 2 f-steps and increasing theprocess time in the first developer during the E-6 process.

C O N C L U S I O N S

By introducing polarized light microscopy and photomi-crography to high school students, you give them experi-ence with a technique that is becoming a main staple ofcurrent scientific and industrial research apparatus.Students will find that their creativity in photomicrogra-phy is limited only by the boundaries of their imagina-tions.

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A C K N O W L E D G E M E N T S

The author would like to thank the Nikon InstrumentGroup for providing photomicrography equipment and theFSU Center for Materials Research and Technology forcontinued support.

R E F E R E N C E S

1. Saeva, F. D., “Liquid Crystals: The Fourth State of Matter”,2nd Edition (Marcel Dekker, 1979)491 pages.

2. Feldman, L. C., “Fundamentals of Surface and Thin FilmAnalysis”, 2nd Edition, (North-Holland,1986), 352 pages.

3. Davidson, M. W., “Photomicrography of Integrated Circuits”,Microscope Technology and News,1990, in press.

4. Silverman, D. A., “Microscapes: The Hidden Art of HighTechnology”, Functional Photography,1987, 22, 24-29.

5. Inoue, S., “Video Microscopy”, 1st Edition (Plenum Press,1986), 584 pages.

6. Pawley, J. B., “Handbook of Biological Confocal Micros-copy”, (Plenum Press, 1989), 232 pages.

7. Howard, T., “The Nomarski Method”, Microscope Technol-ogy and News, 1990, 2, 4-6.

8. Delly, J. G., “Photography Through the Microscope” 9thEdition (Eastman Kodak Company, 1988) Chapter 3.

9. Davidson, M. W. “Fascinating Photography With A SimpleLight Microscope”, PHOTOgraphic Magazine, 1990, in press.

10. Strezlecka, T. E., Davidson, M. W., and Rill, R. L., “MultipleLiquid Crystalline Phases of DNA at High Concentrations”,Nature, 1988, 331, 457-460.

11. Livolant, F., Levelut, A. M., Doucet, J., and Benoit, J. P.,“The Concentrated DNA Liquid Crystalline Phase is ColumnarHexatic”, Nature, 1989, 339, 724-728.

12. Rill, R. L., Livolant, F., Aldrich, H. C., and Davidson, M. W.,“Electron Microscopy of Liquid Crystalline DNA: DirectEvidence for Cholesteric-like Organization of DNA in Di-noflagellate Chromosomes”, Chromosoma, 1989, 98, 280-286.

13. Van Winkle, D. H., Davidson, M. W., Chen, W-X., and Rill,R. L., “Cholesteric Helical Pitch of Near Persistence LengthDNA”, Macromolecules, 1990, 23, 4140-4148.

14. Schecter, B., “The Path of no Resistance: The Story of theRevolution in Superconductivity”,1st Edition, (Simon andSchuster, 1989), 200 pages.

15. Mims, F. M., “Superconductors”, Science Probe!, 1990, 1,68-74.16. Davidson, M. W. and Rill, R. L., “Photomicrography:Common Ground For Art and Science”, Microscopy andAnalysis, 1989, May, 7-12.

A U T H O R I N F O R M AT I O N

Michael W. Davidson is a research associate holding jointappointments at the Institute of Molecular Biophysics andthe Center for Materials Research and Technology. Hisresearch interests include macromolecular liquid crystal-line systems, DNA packaging in virus heads, and theinteraction of small molecules with DNA. He is currentlydeveloping a multi-user light microscopy and scanningtunnelling microscopy facility at the Florida StateUniversity.