For Use with Chapter 2
Data Analysis

Atomic Force Microscopy
Posted November 1st, 2001

For many scientists, the thrill of chemistry is in the discovery and explanation of things unknown. But there is just as much excitement, research, and development involving the tools of the trade. Recently, atomic force microscopy (AFM) has made it possible for scientists to see and understand some of the most spectacular surfaces of chemistry.


The Quest for Detail and Accuracy

Many microscopes can view a sample and produce two-dimensional images. But in many circumstances it is critically important to be able to see and understand the microscopic surface characteristics of a material. Atomic force microscopy is a technique that lets scientists get "up close and personal" to visualize and map intricate surfaces in three dimensions. Although this capability holds promise for nearly all areas of chemistry, AFM is becoming especially valuable to life scientists who are challenged to learn the fundamentals of biological systems. With AFM, important details of form can be seen so the details of function can be deciphered.

Atomic force microscopy is a relatively new and still developing technology that relies on the interaction of the sample surface and a probe. In a simple description, the atomic force microscope consists of a sensitive arm with a probe attached, a laser beam that is focused on the arm/probe assembly, and a sensor that records the interaction of the laser and the probe. A translator apparatus is required to convert the laser/probe activity to digital data. Rounding out the package is a computer and monitor to process the data.

AFM images are the result of the arm/probe assembly gently skimming the surface of the sample. Probes can be fashioned from various materials, depending on the particular surface to be examined. As the probe touches the surface, the light from the laser that is trained on the arm is affected, and the light-detecting sensor records the changes. The translator apparatus converts this activity to data that is then transformed by specialized software into detailed, three-dimensional images.

The technique just described is commonly used to map the hard surfaces of inert materials. But modifications exist that allow AFM to be used safely with soft biological samples that cannot withstand the constant contact of the probe. In the "tapping" mode, the arm vibrates and actually hops across the surface, which reduces the actual contact on the surface. Data is obtained during the period in which the probe is in contact. A "noncontact" mode is available for the most delicate surfaces. In noncontact mode, the probe hovers and sweeps just above the surface. The map is determined from the attractive forces that exist between the probe and the sample.


The Art of Science

The spectacular images that are possible with AFM are as artistic as they are scientific. Many AFM software packages incorporate vivid colors and show such detail that the information can be appreciated as an art form. Trained scientists, of course, continue to harness the data provided by AFM to uncover the mysteries of chemistry and develop the techniques and capabilities of AFM, but even the most analytical scientists often catch their breath at the beautiful images they’ve created.


Activity

Make a slide show presentation or compile an album of AFM images. You can find many such images on the Internet or in scientific journals. Try to find images that use color and texture to emphasize the surface details. Then, if possible, find some images taken from a microscope that produces two-dimensional images. Compare and contrast the results of the technologies.

References

Wright-Smith, C.; Smith, C. M. The Scientist; 2001, 15(2); 23–24.

picture of AFM equipment
see The Scientist web page, archive article in Jan 22, 2001 issue online

2–3 colorful, interesting afm images