Mie Theory

German physicist Gustav Mie played a role in nanotechnology with his theory of light scattering by particles. His theory shows that light scatters from particles more efficiently at short wavelengths than at long wavelengths.

For example, we see the sky as being blue because the molecules in the air (which are extremely small particles) scatter light from the sun more efficiently for blue light than for yellow or red, as blue light has the shorter wavelength. When the sun sets, the sunlight travels through the atmosphere over a longer distance than when it's overhead. The most important scattering in this case arises from dust particles. These particles still scatter light more effectively for blue colors, so the light that is not scattered is a mixture of red and yellow. This produces the characteristic red color of the setting sun.

Mie theory helped scientists to realize that the size of particles determines the colors that we see. Mie went on to develop a way to calculate the size of particles by determining the light scatter. For nanoparticles and larger particles, this theory requires a huge number of calculations, so it was rarely used until about 20 years ago when supercomputers became available. Now, Mie theory (as well as others developed more recently) helps researchers predict and determine the size of nanoparticles.

First Electron Microscope

Although light microscopes have been around since the Renaissance, they were unable to recognize objects that were smaller than the wavelength of visible light (0.4-0.7 micrometers) until the early 20th century.

To see particles smaller than this, scientists had to bypass light altogether and use a different sort of "illumination," one with a shorter wavelength. In 1931, German scientists Max Knott and Ernst Ruska developed an entirely new type of microscope that would eventually reveal a new "small" world.

With the electron microscope, electrons are accelerated in a vacuum until their wavelength is extremely short, only one hundred-thousandth that of white light. Beams of these fast-moving electrons are focused at a sample. Some parts of the sample soak up the electrons, while other parts scatter them. An electron-sensitive photographic plate "records" this action and creates an image.

In 1933, the electron microscope was able to exceed the detail and clarity of the traditional light microscope. This was an important first step in the development of techniques and instrumentation that would eventually enable research at the nanoscale.

(Knoll, M. and Ruska, E.; Ann. Physik 12, 607-640 and 641-661, 1932, submitted 10 September 1931)


The Transistor

Until the mid-1940s, vacuum tubes were the state-of-the-art in electronics.

Capable of converting alternating current to direct current (AC to DC) and amplifying an electronic signal, vacuum tubes were used in everything from switching telephone calls to building the first high-speed computer, ENIAC. But the limitations were clear. The tubes were bulky, and to make more powerful computers, more tubes were needed (17,000 tubes were used in ENIAC). The tubes were also fragile and overheated easily.

In 1945, Bell Labs established a research group to look into finding a solution. The group was led by William Shockley and included Walter Brattain and John Bardeen. After two years, Bardeen and Brattain created an amplifying circuit that seemed to work, using the element germanium. They called it the point-contact transistor. The discovery did not gain attention until 1951, when Shockley improved upon the original idea with a junction transistor. The transistor was a solid (giving rise to the term "solid-state technology"), but had the electrical properties of a vacuum tube. Furthermore, it was inexpensive, sturdy, used little power, worked instantly, and, best of all, was tiny. The three men shared the 1956 Nobel Prize in physics for "their researches on semiconductors and their discovery of the transistor effect."

The invention of the transistor and the integrated circuit marked the beginning of microelectronics, a field that relies on tools for miniaturization. The semiconductor industry is one of the largest technology drivers in the field of nanotechnology. Researchers today are looking to enable the creation of chips holding billions or even trillions of nanoscale transistors.

(US Patent 2,569,347, Sept. 25, 1951, applied for June 26, 1948).


Erwin Mueller's Field-Ion Electron Microscope

The development of nanotechnology was, and is, dependent upon advances in scientific instrumentation.

Erwin Mueller, a professor at Penn State University's department of physics, made an important contribution when he invented the field-ion electron microscope in 1951. For the first time in history, individual atoms and their arrangement on a surface could be seen. For this accomplishment, Professor Mueller is known as the first person to "see" atoms. The device was a landmark advance in scientific instrumentation that allowed a magnification of more than 2 million times.

Born in Berlin in 1911, Erwin was the only child of a family of modest means. His father was a construction worker who specialized in plastering ceilings in houses. He obtained his doctorate in engineering from the Technische Hochschule Berlin-Charlottenburg in 1936. Erwin was recruited by Penn State. He and his family moved there in 1952 and he became a US citizen in 1962. His achievements were recognized by numerous awards, including election to the prestigious National Academy of Sciences.

(Mueller, E.W., Zeitschrift fuer Physik, 131, 136, 1951).


Discovery of DNA

One of the landmark achievements in the 20th century was the discovery of DNA. By the 1950s, scientists already knew that DNA - deoxyribonucliec acid - carried genetic information, but they didn't know what it looked like or how it worked.

In 1953, Dr. James Watson and Professor Francis Crick published an article in Nature describing the double helix structure of DNA. They showed that when cells divide, the two strands that make up the DNA helix separate and a new "other half" is built on each strand, a copy of the one before. This means that DNA can reproduce itself without changing its structure, except for occasional errors or "mutations." James Watson, Francis Crick, Maurice Wilkins, and Rosalind Franklin all played critical roles in this discovery of the DNA structure.

In 1962, Wilkins shared the Nobel Prize with Watson and Crick. Tragically, Rosalind Franklin had died a few years earlier at the age of 37, and since Nobel Prizes are not awarded posthumously, she was not included in the honor.

Decades later, DNA's ability to self-assemble into tiny structures would inspire researchers to use the same principles to develop nanoscale structures with specific dimensions and chemical properties.


Tunneling Phenomenon

In 1958, Leo Esaki, a Japanese physicist working at Sony Corporation, discovered that electrons could sometimes "tunnel" through a potential barrier formed at the junctions of certain semiconductors even though classical theory predicted that this was not possible.

What Dr. Esaki observed was an example of how materials at the nanoscale are controlled by different laws of behavior, i.e. they are controlled by quantum mechanics as opposed to classical physics. The discovery lead to the creation of the tunneling diode (sometimes called the Esaki diode), an important component of solid-state physics, and the first time that tunneling (an important nano-electronics phenomenon) was used in a real device. Dr. Esaki was awarded the 1973 Nobel Prize in physics for this discovery along with physicists Ivar Giaver of Norway and Brian D. Josephson of Great Britain.

(L. Esaki, Phys. Rev., 109, 603, 1958)


Richard Feynman

Richard P. Feynman is often credited with predicting the possibilities and potentials of  nano-sized materials.

Feynman, who would go on to win the Nobel Prize in physics, gave a talk on Dec. 29, 1959 entitled, "There's Plenty of Room at the Bottom." In his speech, he stated:

"What I want to talk about is the problem of manipulating and controlling things on a small scale. As soon as I mention this, people tell me about miniaturization, and how far it has progressed today. They tell me about electric motors that are the size of the nail on your small finger. And there is a device on the market, they tell me, by which you can write the Lord's Prayer on the head of a pin. But that's nothing; that's the most primitive, halting step in the direction I intend to discuss. It is a staggeringly small world that is below. In the year 2000, when they look back at this age, they will wonder why it was not until the year 1960 that anybody began to seriously move in this direction."

(Feynman, R.P. American Physical Society Meeting, Pasadena, CA, Dec. 29, 1959)



In the 1960s, NASA researchers were trying to find ways to control liquids in space.

They discovered that nano-sized magnetic particles of iron that were given a chemical coating, or surfactant, that prevented them from clumping together could be dispersed in oil or water. They could then control the location of the fluid (called a ferrofluid) with a magnet.

On Earth, ferrofluids are used inside loudspeakers, where they help keep the inner parts cool. They are also used on computer hard drives and in semiconductor manufacturing, as seals to keep out the dust and other contaminants.

Nanotechnologists want to harness ferrofluids for other important uses such as developing tiny sensors, or inside the body as biomedical devices to deliver drugs, absorb toxins, or treat hypothermia. It is even possible that ferrofluids could be used to help clean up hazardous waste spills.


Zeolite Catalysts

A zeolite is an inorganic porous material which works as a kind of molecular sieve - allowing some molecules to pass through while excluding or breaking down others. Zeolites can be natural or synthetic, and new zeolites are still being discovered and invented.

In 1960, Charles Plank and Edward Rosinski developed a process to use zeolites to speed up chemical reactions. Plank and Rosinski's process focused on using zeolites to break down petroleum into gasoline more quickly and efficiently.

Researchers are currently working to design zeolite catalysts at the nanoscale. By adjusting the size of the zeolite pores on the nanoscale, they can control the size and shape of molecules that can enter. In the case of gasoline production, this technique could mean that we would get more and cleaner gasoline from every barrel of oil. It is hoped that nanotechnology will help reduce the cost and pollution associated with producing gasoline and other petroleum products.

(US Patent #3,140,249)


Moore's Law

Writing for Electronics magazine in 1965, Gordon E. Moore, the founder of Intel Corporation, noted that the number of transistors per integrated circuit had doubled every two years.

He predicted that this trend would continue for another ten years, and his prediction was quickly dubbed "Moore's Law" by the press. Moore's prediction turned out to be prophetic. In fact, the complexity of a chip continued to double yearly, long after 1975. The rate of doubling has only recently slowed to about every 18 months. Many researchers believe that devices which use electronic nanotechnology and molecular electronics will keep Moore's Law accurate into the future.

(Electronics Magazine, 38, 114-117, 1965)


Sir John Pople's Software

Mathematics is a foundation for science; it provides mathematical descriptions of complex real-world phenomena, or "models."

Modeling develops hand-in-hand with the science it describes. Developing new mathematical formulas is an essential part of science, and as science becomes more complicated, new, faster formulas are needed. Although computers had become dramatically more powerful by 1970, new software had to be developed in order for that power to be useful. Up until this time, it was very difficult to solve the complex mathematical equations needed to determine the properties of molecules.

In 1970, John Pople and his research group developed Gaussian, a software program that would perform these calculations. This pioneer in the use of computers to predict the behavior of atoms and molecules also developed many of the algorithms that made computer-based modeling at the nanoscale possible. For his work, Dr. Pople, a Northwestern University Board of Trustees professor and British citizen, shared the 1998 Nobel Prize for chemistry and was knighted by Queen Elizabeth in 2003.

(Quantum Chemistry Program Exchange, Program No. 237, 1970)

The Term "Nanotechnology" First Used

The term "nanotechnology" was first used by Norio Taniguchi of the Tokyo Science University.

He used the word to refer to "production technology to get the extra high accuracy and ultrafine dimensions, i.e. the preciseness and fineness on the order of 1 nanometer."

("On the Basic Concept of Nanotechnology," Proceedings of the International Conference of Production Engineering, 1974)



Molecular Electronics

In 1974, Northwestern University Charles and Emma Morrison Professor of Chemistry, Mark A. Ratner, and A. Aviram of IBM proposed that individual molecules might exhibit the behavior of basic electronic devices, thus allowing computers to be built from the bottom up by turning individual molecules into circuit components.

This hypothetical application of nanotechnology, formulated long before the means existed to test it, was so radical that it wasn't pursued or even widely understood for another 15 years. For this groundbreaking work, Ratner is widely credited as the "father of molecular-scale electronics," and his contributions were recognized in 2001 with the Feynman Prize in Nanotechnology.

(Chem. Phys. Lett. 29, 277, 1974).


Surface Enhanced Raman Spectroscopy (SERS)

Some of the tools needed in the field of nanotechnology were many years in the making. For example, spectroscopy is a set of techniques that use the interaction of light with matter to obtain information about its identity and structure of molecules.

Sir Chandrasekhara Venkata Raman (Calcutta University) won the 1930 Nobel Prize in Physics for his 1928 discovery that the scattering of light by molecules could be used to provide information about a sample's chemical composition and molecular structure. Although a ground-breaking technique, Raman Spectroscopy was not capable of detecting at the nanoscale. The technique was greatly improved in the 1960s by the invention of the laser, but it wasn't until 1977, when Richard P. Van Duyne (Northwestern University) discovered Surfaced Enhanced Raman Spectroscopy, that nanoscale studies became possible.

Van Duyne deduced that when molecules were attached to a surface which had hills and valleys that were approximately 50-100 nanometers in size, the Raman intensity was amplified 1,000,000 times. The discovery of SERS completely transformed Raman Spectroscopy from one of the least sensitive to one of the most sensitive techniques in all of molecular spectroscopy. Today, SERS is used to study the chemical reactions of molecules in electrochemistry, catalysis, materials synthesis, and biochemistry. The sensitivity of SERS is now so high that even single molecules can be studied.

(Chemical and Biochemical Applications of Lasers, ed. CB Moore, 4:101-185, Academic Press, New York, 1979).


Self-Assembled Monolayers (SAMS)

In 1980, Jacob Sagiv at the Weitzman Institute in Israel discovered that molecules containing a chemical called octadecyl trichlorosilane, or OTS, would spontaneously react with a glass surface to assemble by themselves into individual layers.

In 1983, a Bell Labs research team lead by David Allara discovered that molecules with thiol groups (groups containing sulfur) on a gold surface would also self-assemble into individual or mono-layers. These self-assembled monolayers are typically a few nanometers thick (determined by the choice of molecule) and allow researchers to tailor the properties of a surface. For the first time, scientists could envision building three-dimensional nanoscale structures layer-by-layer, like laying rows of bricks to build a wall. These structures are being used to build molecule-based electronic devices, biosensors, and new types of optical materials.

(Sagiv, J. J. Am. Chem. Soc., 102, 92-98, 1980)
(J. Am. Chem. Soc., 105, 4481, 1983)


Scanning Tunneling Microscope

In 1981, the scanning tunneling microscope was invented by Gerd Binning and Heinrich Rohrer at IBM's Research Laboratory in Zurich Switzerland. This invention allowed scientists to not only observe nanoscale particles, atoms, and small molecules, but to control them.

 The STM scans the tip of a needle, or "probe," just a few atoms above the surface of the sample. A voltage is applied between the tip of the probe and the surface. As the electric current begins to flow, the STM can determine minute variations in the distance electrons travel. In this way, the STM maps the surface of the sample. The information is saved in a data file, and a "picture" of the surface is created by the computer. In this way, the STM can "see" atomic-scale objects. The STM helps researchers determine the size and form of molecules, observe defects and abnormalities, and discover how chemicals interact with the sample.

The STM quickly became standard equipment in laboratories throughout the world. Binning and Rohrer were awarded the Nobel Prize in physics in 1986 along with German scientist Ernst Ruska, who designed the first electron microscope.

(US Patent #4,343,993)

The "Buckyball"

Another nanotechnology breakthrough occurred in 1985, when Richard Smalley, Robert Curl, and graduate student James Heath at Rice University and Sir Harry Kroto at the University of Sussex discovered C60, a carbon nanoparticle shaped like a soccer ball.

The unique molecule was named Buckminsterfullerene after the visionary American architect and engineer Buckminster Fuller, who designed the geodesic dome. More commonly called a "buckyball," the molecule is extremely rugged, capable of surviving collisions with metals and other materials at speeds higher than 20,000 miles per hour.

Because of this ruggedness, buckyballs show promise in the development of fuel cells that might power the automobiles of the future. Researchers are also investigating the possibility of using buckyballs as tiny drug delivery systems. Smalley, Curl, and Kroto won the 1996 Nobel Prize in Chemistry "for their discovery of fullerene."

(J. Phys. Chem., 90, 525-528, 1986)


Atomic Force Microscope

Invented by Gerd Binnig and his colleague Christoph Gerber at IBM and Calvin Quate at Stanford University, the atomic force microscope (AFM) uses a cantilever to "read" a surface directly, the way a record player's needle reads a record.

Atomic force microscopy works by passing the cantilever - so sharp that its tip is composed of a single atom - within a few nanometers of a surface. The atomic forces exerting a pull on the cantilever are measured to create an atom-by-atom topographical map. The AFM makes 3D images of an object's surface topography with extremely high magnifications (up to 1,000,000 times).

(Phys. Rev. Lett., 56, no. 9; 3; p.930 3, 1986)


Single Electron Tunneling Transistor

In 1987, Dmitri Averin and Konstantin Likharev, then at the University of Moscow, proposed the idea of a new device called a single-electron tunneling (SET) transistor.

Two years later, Theodore Fulton and Gerald Dolan at Bell Labs in the US built such a device. In this structure, the controlled movement of individual electrons through a nanoscale device was first achieved.

Single-electron devices are based on what is called the tunnel effect. When two metallic electrodes are separated by an insulating barrier about one nanometer thick (approximately 3 atoms in a row), the electrons are able to "tunnel" through the insulator, even though classical theory suggests that this is impossible.

Researchers have long considered whether SET transistors could be used for digital electronics, but the random variations in voltage from device to device caused serious problems. Working at the nanoscale, today's researchers are considering how to overcome this problem by combining all of the components of the SET transistor into a single molecule. It is possible that conventional circuits will one day be replaced by electronics based on individual molecules and form the basis for a new class of nanoelectronics.

(Theory - DV Averin and KK Likharev, J. Low Temp. Physics. 62, 345, 1986).
(Demonstrated - TFulton and GJ Dolan, Phys. Rev. lett. 59, 109, 1987).

Discovery of Quantum Dots

In the early 1980s, Dr. Louis Brus and his team of researchers at Bell Laboratories made a significant contribution to the field of nanotechnology when they discovered that nano-sized crystal semiconductor materials made from the same substance exhibited strikingly different colors.

These nanocrystal semiconductors were called quantum dots, and this work eventually contributed to the understanding of the Quantum Confinement Effect, which explains the relationship between size and color for these nanocrystals.

Due to their extraordinarily small size, the electrons inside the quantum dots exhibit unique behavior. Specifically, the electrons are confined to far fewer energy levels than allowed in bulk semiconductor materials. As a result, the quantum dots emit very intense light of a specific color when the electrons make transitions between these discrete energy levels. Small differences in the size of the quantum dot change the allowed electron energies and therefore alter the color of light which they emit. Scientists have learned how to control the size of the quantum dots, making it possible to obtain a broad range of color (see Medieval Period and stained glass).

Quantum dots have the potential to revolutionize the way solar energy is collected, improve medical diagnostics by providing efficient biological markers, and advance the development of optical devices such as light-emitting diodes (LEDs).

(J. Am. Chem. Soc. 110, 30466, 1988)


Manipulation of Atoms

Using a Scanning Tunneling Microscope (STM), IBM researchers Donald Eigler and Erhard Schweizer were able to arrange individual Xe atoms on a surface.

Although the process was painstakingly slow, the remarkable image allowed researchers to place individual xenon atoms with nanoscale precision and to visualize the results. This now famous image of the atomic world "hangs" in IBM's STM Image Gallery, and demonstrates early attempts to create structures one atom at a time.

(Nature, 344, 524, 1990).

Carbon Nanotubes

In 1991, Sumio Iijima at NEC in Japan discovered a new form of carbon called nanotubes, which consisted of several tubes nested inside each other.

Two years later, Iijima, Donald Bethune at IBM in the US, and others observed single-walled nanotubes just 1-2 nanometers in diameter. Nanotubes behave like metals or semiconductors but can conduct electricity better than copper, transmit heat better than diamond, and are among the strongest materials known. Nanotubes could play a pivotal role in the practical applications of nanotechnology if their remarkable electrical and mechanical properties can be exploited.

(S Iijima, Nature, 354, 56, 1991)


Using DNA & Gold Colloids to Assemble Inorganic Materials

Since Faraday's discovery of the unique electronic and optical properties of gold colloids in 1857, researchers have sought to harness these capabilities.

In 1996, Northwestern Unversity researchers Chad Mirkin and Robert Letsinger discovered a way to do this. They attached strands of synthetic DNA onto gold nanoparticles. Since complementary strands of DNA can recognize and bind to each other, the DNA served as a blueprint, a construction worker, and a sorter to create new inorganic materials. By manipulating the DNA, they were able to make materials with the same unusual properties as the nanoscale building blocks that they are made from.  This advance generated an explosion of interest in making designer bio-inorganic architectures at the nanoscale.

(Nature, 382, 607-609, 1996)


Development of Dip-Pen Nanolithography

A pivotal development in the constellation of nanotechnology tools was Dip-Pen Nanolithography (DPN).

Invented in 1999 by Chad Mirkin (Rathmann Professor of Chemistry and Director of the Institute of Nanotechnology at Northwestern University), the concept is based upon a classic quill pen - a 4,000-year-old technology. Using an atomic microscope tip, DPN allows researchers to precisely lay down or "write" chemicals, metals, biological macromolecules, and other molecular "inks" with nanometer dimensions and precision on a surface.

DPN has progressed to include 1,000,000 tip serial and parallel processing - opening the door to credible nano-manufacturing techniques for smaller, lighter weight, faster, and more reliably produced electronic circuits and devices, high-density storage materials, and biological and chemical sensors.

(Science, 283, 661, 1999)