Linda Wolin - Atomic Force Microscopes

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Atomic Force Microscopes

By Linda Wolin
President Writesaif, Inc.
www.writesaif.com
writesaif@sbcglobal.net

A major achievement that enabled the field of nanotechnology to emerge in the mid-1980s was instrument-advancement.(1) The Atomic Force Microscope (AFM) and the Scanning Tunneling Microscope (STM) were developed, so for the first time, researchers could view individual atoms and molecules.(1) Prior to this time, optical and electron microscopes were used to magnify images. With an optical microscope, images were magnified up to an approximate limit of 2,000x(2) and with electron microscopes up to 100,000x.(3) Further, magnified images were always seen in two dimensions. (The depth of an object's surface was not viewable.) AFMs enabled three-dimensional viewing(3) with images magnified up to 1,000,000x!(3) Seeing features at the nanometer scale became possible. (A nanometer is one-billionth of a meter or approximately 8 times the diameter of one-oxygen atom!(4)) An added bonus also was realized, viewed atoms and molecules could be manipulated!ญญญญญญญญญญญญ

Benefits of AFM Usage

Increased image-magnification is the most important advantage that AFM usage provides. However, significant other benefits also exist.

Atoms and molecules can be manipulated as well as viewed.(5)
Viewing can be done in varying environments, such as ambient or liquid.(1,6)
Samples are not destroyed when viewed, so they may be used repeatedly.(1)
No special treatment of samples is required.
Three-dimensional viewing of samples is obtained, so far more may be learned about samples' structures.
Insulating, as well as conducting materials, can be viewed.(6)

(The non-destruction of samples is particularly important in the health industry as painful and costly procedures sometimes are needed to obtain samples and multiple tests are required on the same sample.)

Uses of ATMs and Other Scanning Microscopes

As a result of the benefits of ATM usage (and other scanning microscopes that evolved from them), ATMs are increasingly being used worldwide in industry, research laboratories, and by governments. Some uses are for the:

Measurement of atoms' and molecules' locations.
Quantification of the movement of atoms and molecules across surfaces.
Measurement of surface features at the nanometer scale that cause roughness, smoothness, hardness, softness, and degrees of friction.(6)
Reengineering of motors and other structures that exist in living tissues.

Some applications of the data and knowledge obtained from the above are leading to:

Improvements in process development and control procedures that impact the semiconductor, photonics, and data-storage industries.(7)
Reengineering of molecular motors that exist in humans and other living organisms for improvements in medical diagnostic and therapeutic techniques and industrial processes and procedures.(8)
New materials that last longer and have enhanced properties.

More details on usage

In electronic industries such as semiconductors and data storage, contamination control of nano-sized particles is important for manufactured items to function efficiently. AFMs, with integrating software, are enabling the viewing and identification of contamination particles for process and quality improvements and control. Further, surface texture can change the optical properties of materials, the yield of silicon wafers, and the density of stored magnetic materials. AFM usage enables the viewing and changing of surface structures at the nanometer scale, so surface textures can more readily support properties that are needed.

Regarding health, AFMs facilitate the recognition of the adsorption of antibodies and the characteristics of antibodies.(9) Further, it is known that some processes that occur within living cells such as reproduction, growth of new tissue, and energy production are accomplished by molecular motors. Re-engineering these motors is creating the possibility for improved diagnostic and therapeutic tools that will be more effective in treating diseased conditions and less damaging to non-diseased tissue. Some of these motors may also be used for monitoring overall health for health maintenance and prevention of disease.

More Historical Facts about AFMs

Historically vertical dimensions were measured by stylus profilers. However, stylus profilers often collided with the surface features of samples causing distortions of images and destruction of samples. In 1971 Russell Young did work to correct these problems and the first Scanning Probe Microscopes, STMs ,were developed in the 1970s and in the early 1980s by Binnig and Rohrer at an IBM research laboratory.(10) STMs only worked with conducting materials, however. Insulators and organic materials like DNA could not be used with STMs, so Binnig, Quate, and Gerber developed an AFM in 1986(6,9) to work with insulators and biological materials like DNA.(10) Since the 1980s, numerous variations of Scanning Probe Microscopes have been manufactured to address varying needs of researchers, other scientists, business and government.(11)

How Do AFMs Work?

A probe [with a sharp tip that is often a nanotube (a tube with a diameter in nanometers (12))] is attached to a cantilever that moves and scans the surface below it. (The probe or the sample may be moved during a scan.) The probe on a cantilever's tip responds to a force between the tip and the sample.(10,11,13) Usually, AFMs employ an optical technique, so when the cantilever flexes, light from a laser is reflected onto a split photo-diode, and the difference in signals to the diodes is measured.(14) Piezoelectric ceramics are a common choice for materials(14) that make up the scanners as these materials expand and contract under the influence of voltage gradients and create gradients when they expand or contract.(6,15) This enables feedback loops that provide excellent information on the sample. Further, scanners made of piezoelectric ceramics are one piece and very stable.(6)

Future of AFMs

Instrumentation and interrelated software keeps evolving to meet the advances in many fields that are requiring more rigorous viewing and analyzing abilities of smaller and smaller samples.

For example, today instruments exist that can measure 4 dimensions, 3 of space and one of time. The 4DXRD developed by the European Synchroton Radiation Facility in Grenoble is enabling researchers to view three spatial dimensions of crystals and one of time (the time needed for crystals to grow).(16) Other instruments are offering information on the evolving structures for metals, ceramics and polymers.(16)

Software integrated with the use of AFMs is enabling more accuracy in measurements and the analysis of more complex data. Viewing needs for microscopy and spectroscopy are combining, producing new equipment and enabling more use of scanning equipment. Today fields as varied as forensics, semiconductors, pharmaceuticals, explosives, corrosion analysis and polymer chemistry(17) all use AFMs or derivatives of them to examine, analyze and sometimes improve samples of increasing miniturization.(17)

References

1. Oscar H. Willemsen, Margot M. E. Snel, Alessandra Cambi, Jan Greve, Bart G. De Grooth, and Carl G. Figdo. Biophys Journal, December 2000; Vol. 79, No. 6: 3267-3281. Available at: link. Accessed: October 9, 2004.
2. Willett, E. Microscopes. 2002. Available at: link. Accessed: October 10, 2004
3. "Microscope," Microsoftฎ Encartaฎ Online Encyclopedia 2004 link ฉ 1997-2004 Microsoft Corporation. All Rights Reserved.
4. Freitas Jr., RA. Nanomedicine, Volume 1: Basic Capabilities. Austin, Texas: Landes Bioscience; 1999:383.
5. TheFreeDictionary.com. Atomic force microscopes. Available at: link. Accessed: October 8, 2004.
6. Baselt, D. "Atomic force microscopy." 1993. Available at: link. Accessed: 8/10/2004.
7. Crandal, BC. Nanotechnology Molecular Speculations on Global Abundance. Cambridge, Massachusetts; London, England: The MIT Press;2000:36.
8. Crandal, BC. Nanotechnology Molecular Speculations on Global Abundance. Cambridge, Massachusetts; London, England: The MIT Press;2000:35.
9. Biotechnology; atomic force microscopy useful for analysis of adsorbed antibodies. Medical Devices & Surgical Technology Week. Atlanta: Aug. 8, 2004; 24. Available at: link. Accessed: 8/9/2004.
10. Freitas Jr., RA. Nanomedicine, Volume 1: Basic Capabilities. Austin, Texas: Landes Bioscience; 1999:56.
11. Freitas Jr., RA. Nanomedicine, Volume 1: Basic Capabilities. Austin, Texas: Landes Bioscience; 1999:57.
12. Freitas Jr., RA. Nanomedicine, Volume 1: Basic Capabilities. Austin, Texas: Landes Bioscience; 1999:418.
13. Wikipedia, The Free Encyclopedia. Atomic force microscopes. Aug. 10, 2004. Available at: link. Accessed: October 10, 2004.
14. Round, A. (editor). University of Bristol, H.H. Wills Physics Laboratory. Atomic Force Microscopy. Available at: link. Accessed: 8/10/2004
15. Freitas Jr., RA. Nanomedicine, Volume 1: Basic Capabilities. Austin, Texas: Landes Bioscience; 1999:154.
16. Offerman, SE. Microsstructures in 4D. Science. July 2004;305 9:190.
17. Sidawi, D. Microscopes embrace hyphenation and nanotechnology. R & D Highlands Ranch. Feb 2004;46 2:40-44 Available at: link Accessed August 8, 2004.

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Atomic Force Microscopes