As youngsters we have all probably tried to see how small we could write our name or a message to a school-mate. Maybe the quest was pushed to the limit by using the finest pen-nib we could find. But how small can we reproduce text using the techniques scientists have developed over the last century?
This article illustrates the following techniques:
- 19th century microphotography to display an image of the Lord's Prayer on this sized dot '.'
- the modern use of microfiche to print the entire Holy Bible on an area little more than the size of a postage stamp
- using electron beams to 'write' on surfaces, and capable of putting a 29 volume Encyclopaedia on a pin-head
- and the ultimate in microwriting, write your name with individual atoms!
The 19th century microscopists in Victorian England didn't 'miss a trick' when the new technique of photography was announced. Soon after the silver halide based photographic emulsion had been developed, these microscopists had started to use their microscopes to produce microphotographs ie tiny photographs on a microscope slide.
It's a neat idea .... if you can use a microscope to magnify tiny objects so that the eye could observe them, why not use the optics of the microscope in reverse to project an image of say a painting through the microscope to create a tiny image on a microscope slide. If the slide had been pre-treated with photographic emulsion and developed like a photograph, 'hey presto' you have a permanent microphotograph of the painting which can only be viewed under a microscope. What better novelty to impress your friends with at the next meeting of amateur microscopists ... and this is exactly what many of the early microphotographic slides were used for, as microscopy was a popular past-time with Victorian 'society'.
The Victorian microscopist's used this technique to prepare a wide variety of photomicrographs including works of art, portraits of famous people and landscapes. To ensure the final image on the slide was a 'positive' the usual technique was to take a normal photograph of the subject and shine light through the developed negative, a glass plate in those days, down the microscope to create a 'positive' image on the slide, which was typically 1mm square.
The image of the Lord's prayer below is an example of microphotography to miniaturise text. The block of text is 0.38 x 0.28 mm in size on the original microscope slide and therefore the entire text could comfortably fit on the full stop at the end of this sentence. A microscope at about 40x magnification is required to read the microphotograph.
The text on the slide is 13 - 25 microns in height, so if the original text was 2 mm high, the linear reduction of the text achieved in the microphotograph is approximately 150:1. At the highest magnifications the individual silver grains which make up the image can be seen, and they are typically 0.8 um across. The finer the silver grains the early microscopists were able to achieve the higher the quality of the final image.
In the twentieth century the technique of microphotography was developed for the storage of photo-reduced text and images on microfilm and microfiche. The reproduction of printed text in a greatly reduced form on film is called microform. When the copying medium used is sheet rather than roll film it is termed microfiche and each sheet usually has a readable legend on the sheet for cataloguing.
An example of the capabilities of modern microfiche is shown on the right. It was produced by The NCR Corporation using their 'PCMI® Microform' technique. The block of text on the sheet of film is 33x33 mm in size and contains the entire 1,245 pages of the 'Holy Bible'! The match head shown on the left of the microfiche gives a sense of scale. The text can be read comfortably under a microscope at about 100x. Each page of double column text is about 0.5 mm wide and 1 mm high (shown in the first blow-up). Each text character is 8 um high (ie 8/1000ths of a millimetre). NCR note on the paper wallet which the microform comes in, that this is a linear reduction of about 250:1 or an area reduction of 62,500:1. (This would correspond to the original text being ca. 2 mm high).
To put this into perspective, NCR also note in the accompanying leaflet with the microfiche, that if this reduction was used on the millions of books on the 270+ miles of shelving in the Library of Congress, then the library could be stored in six standard filing cabinets. (Note: I have been asked if these bibles are still available - I'm afraid I don't know.)
Microform is still widely used. In the author's local library for example, many of the catalogues are folders of loose microfiches, and the past issues of local newspapers are accessible as microfilm cartridges which can be magnified, read on a screen and selections printed out if desired. However, the increasingly widespread use of digital information storage with its inherent benefits may eventually supersede the use of microform.
The use of photographic reduction techniques is also widely used in photolithography during the production of integrated circuits on computer 'chips'. The etching and coating stages used to build up the complex three dimensional structure of an integrated circuit is accomplished by shining light through photomasks which act as miniature stencils. Where the mask allows light to shine through, chemicals can etch the exposed area or semiconductor material can be deposited.
Scientists have found that they have almost pushed the capabilities of photoreduction to the limit for computer chip manufacture, because the ultimate linear reduction achievable, which is about 1 micron, is restricted by the wavelength of light used. Recently electron beams are being used instead of ultra-violet light to project the images through the photomask to produce the integrated circuit. This will allow much greater circuit densities to be achieved on the microchip.
Scientists are also experimenting with the use of an intense electron beam to write patterns directly onto inorganic surfaces. This process called SCRIBE (Sub-nanometre Cutting and Ruling with an Intense Beam of Electrons) can make lines of only 1 nanometre wide (ie one millionth of a millimetre). Using this technique it would be possible to write the entire contents of the 29 volume Encyclopaedia Britannica on a pin-head! A small section of the original text from the Encyclopaedia reproduced onto a film of aluminium fluoride is shown on the right. Each text character is approximately 0.03 micron high, compared with microfiche characters above which are 8 micron high.
But the ultimate in minute text must be the manipulation of individual atoms to create text with characters tens of atoms across. A famous example of 'atomic writing' created by IBM scientists can be seen on the IBM Almaden Research Centre's Web site. The letters 'IBM' were created by positioning xenon atoms on a nickel surface using a special scanning tunnelling microscope. The letters are each about 6 nanometres across, which is close to the ultimate in microwriting.
IBM researchers have also created a magnificent image of Japanese characters by the manipulation of atoms, which is also displayed at the Almaden Web site.
Manipulation of individual atoms may seem just a scientific curiousity but the development of such techniques may allow significant advances in the fabrication of very high density computer chips. Also the manipulation of atoms and molecules to build micro-machines is the basis of the rapidly developing field of nanotechnology. Experts predict that in the next century nanotechnology will be the basis for how we manufacture complex miniature devices, treat disease and even explore the universe ..... the microscopic world around us and the technology we are developing to control this scale of nature gets more exciting every day!
Picture credits and Web sites to visit
The microphotograph image of the Lord's Prayer was sourced from a microscope slide distributed by the Postal Microscopical Society, UK.
Visit the IBM Almaden Research Center Web site to view awesome images created with individual atoms.
The electron beam lithograph image is credited to the
Department of Materials Science and Engineering, University of Liverpool,
Visit the Department of Materials Science and Engineering, University of Liverpool, UK Web site to learn about their current research activities.
A wide selection of Web sites providing details of electron beam lithography and scanning tunnelling microscopy (STM) and the related atomic force microscopy (AFM) can be found by an appropriate keywords search at www.altavista.digital.com.
Read a Micscape Web article by Roy Winsby on John Dancer, a pioneer of the production of microphotographs.
Read a recent Micscape article by Roy Winsby which describes the microphotograph slides of Dancer and Suter in more detail.
1) Micrography - The Making of Microscopic Size Photographs by N G Groom. Microscopy, 1986, 35 (6), pp.445-450. A modern practical guide to making microphotographs on microscope slides.
2) Diamond Writing, 1853-1946 by B Bracegirdle and S E Warren. Quekett J. Microscopy, 1996, 37, (part 8), pp. 621 - 632. A fascinating historical summary of the men and machines producing microscopic writing.
Microscopy, now the Quekett Journal of Microscopy, is the Journal of the Quekett Microscopical Club, a club for amateurs and professionals worldwide.
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Walker welcomed. (The author is an amateur microscopist with a
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