Three types of microscopes cover a variety of applications.

The scanning electron microscope has a high resolution of 3 nanometers and is used in a variety of applications. Source: JOEL USA

The optical microscope has evolved dramatically since its origins in the seventeenth century. Despite numerous refinements, however, the capabilities of the optical microscope have been limited by manufacturability constraints and, ultimately, by the physics of light itself.

Electron, scanning probe and focused ion beam microscopy have attempted to address these limitations, and constantly evolving requirements and imaging technologies continue to push the envelope of future technology development. Yet optical microscopes still command a primary position in microscope sales worldwide.

The selection of microscope type is largely determined by end-use. Applications in the classroom vary considerably from those in medical laboratories and research facilities. Resolution, magnification, depth of field, field of view, illumination method, degree of automation and type of produced image all come into play when determining the appropriate equipment for each application.

Categories

There are essentially three categories of microscopes: electron, confocal

and compound.

While the specimen is suspended in a vacuum chamber, electron microscopes direct a stream of electrons at the subject, while attached computers analyze the scatter patterns produced.

Transmission electron microscopes give scientists a view of 2-D slices of the object at varying depths. Degree of magnification and resolution or sharpness of the image is very high with such powerful instruments. Researchers at IBM have devised a way to observe liquid chemical reactions as they occur with a transmission electron microscope. The technique has already been used to capture images showing how copper atoms bond to each other and to electrodes. Such information could eventually lead to smaller circuits or more efficient chip manufacturing because chip designers will have exact information on what happens when molecules meet.

This spectral confocal microscope is ideal for research laboratories and pharma-biotechnology applications. Source: Leica Microsystems Inc.

Scanning electron microscopes vary slightly in that they scan a gold-plated specimen to give a 3-D view of the surface of an object. This view is in black and white, yet its excellent resolution provides a clear picture.

A confocal microscope, a step down from the previous types, uses a laser beam to illuminate a specimen, whose image is then digitally enhanced for viewing on a computer monitor. Often the specimen is dyed a bright color to provide a more contrasting image for the laser. The specimen is mounted on a glass slide and the microscope is controlled automatically, with motorized auto-focus.

The confocal microscope attains very high resolution because it focuses a point-source signal on a specimen and images the reflected light as a point using a pin-hole aperture. The aperture eliminates all out-of-focus signals. Of course, this arrangement limits the microscope's field of view. Thus, the examination of a typical object requires that either the object or the focal point be scanned. The data gathered during a scan can be used to generate a 3-D image.

Confocal microscopes are employed in biological, medical, semiconductor and industrial applications. They are used in systems for optical inspection of silicon wafers and lithographic masks, and for the inspection of disks used in data storage.

Finally, there is the simplest type, the compound microscopes. Microscopes are classified as being compound when the magnification takes place in two stages. The compound microscope is the most popular microscope used today.

Compound microscopes are used in industry for materials image analysis, image acquisition, part inspection for defects and measuring. While they provide a 2-D slice of an object, they can attain adequate magnification. However, resolution may be poor and the image a little blurry.

This stereo dynascopic microscope is an eyepieceless microscope, which helps reduce eyestrain and operator fatigue. Source: Vision Engineering

Stereoscopic microscopes, as the name implies, provide a 3-D image that is ideal for operations that call for handheld manipulation and inspection. Stereomicroscopes also provide the advantage of having a long working distance, which is the free space between the lens and the part being inspected. These microscopes are used in many industrial applications, including general manufacturing, medical devices, electronics, precision engineering, plastics and rubber.

With the introduction of new products, such as the confocal laser scanning microscope, the scanning tunneling microscope, the atomic force microscope and the video microscope, microscopy has been able to consistently reach beyond its earlier confines.

Growth

While nobody has a marketing crystal ball, the conservative prediction is that while there may be few technological developments in the next 5 to 10 years, there should be an increase in application development as techniques find their true place in the industry.

Unforeseen innovations are always possible, but in the traditional areas of optical microscopy it would appear that resolution and the development in basic techniques have peaked. Innovative manufacturers, seeking to forge ahead of the competition, will undoubtedly focus on design, ergonomics, field of view, image analysis and data handling. This technology will impact the microscope market and it is likely that image analysis products may be sold by microscope suppliers as standard accessories.

According to a report from Business Communications Co., the global market for microscopes and accessories is estimated to reach $2.77 billion by 2009 at an average annual growth rate of 11%. The fastest-growing segment of the market is for scanning probe microscopes, at an average annual growth rate of 20%. The scanning probe microscopy market covers several related technologies for imaging and measuring surfaces on a fine scale, down to the level of molecules and groups of atoms. Charged particle microscopes represent the largest segment, growing annually at 13% to $1.3 billion in 2009. Life science is the dominant end-user market, while nanotechnology and semiconductor manufacturing are the fastest growing, with an average annual growth rate of 20% and 14%, respectively.

Lisa Hickey is marketing manager at Vision Engineering (New Milford, CT). For more information, e-mail [email protected] or visit www.visioneng.com.