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Washington State University
CAS Connect February 2014

Our shrinking world

The first known example of nanotechnology is a Roman drinking cup from the 4th century. When lit from the front, the Lycurgus Cup is a beautiful opaque green.

But when lit from the back, particles of gold and silver in the glass—nano-sized particles, it turns out—transform the cup into a fiery red scene.

The Lycurgus Cup. Photos from The British Museum
The Lycurgus Cup. Photos from The British Museum

The cup surfaced in the European art world in the mid-1850s, about the same time an English researcher named Michael Faraday discovered gold colloids—tiny particles of gold that remained suspended in a solution and displayed very different optical and electrical properties from their original state. Gold, we now know, reflects green light when the particles are roughly 50 nanometers in size. Silver ranges from red to beige to dark blue as particles get smaller and smaller.

Size-dependent properties are the primary reason nanotechnology has such astonishing potential. The threshold is different for different materials, but as an object becomes smaller, its melting point, conductivity, flammability, optical, magnetic, and many other properties can change dramatically.

Just how small is small?

red blood cells, a virus, and DNAFor most of us, it’s a challenge to put “nano” into perspective. For example, a sheet of paper for your printer checks in at approximately 100 micrometers thick. That’s 100,000 nanometers.

A very fine human hair, just about the limit of what is visible with the naked eye, measures around 20 micrometers, or 20,000 nanometers, in diameter.

The red blood cells coursing through your veins are roughly 800 nanometers across.

But it’s not until the measurement shrinks to at least 100 nanometers is something considered to be “nano scale.”

A single virus cell averages 100 nanometers in diameter; a strand of DNA is roughly 2 nanometers wide and a single hydrogen atom is just one nanometer.

Capturing electrons

Nanotechnology is the science of building functional systems on a molecular scale. A successful research project often requires input from experts in chemistry, physics, bioengineering, mechanical engineering, and other disciplines.

At WSU, the Materials Science and Engineering Program (MSEP) is the leader in nano research and has been bringing together faculty and students from different disciplines for nearly 50 years. What began as a doctoral program in chemical physics has evolved into a vibrant state-of-the-art collaborative program between the College of Arts and Sciences and the College of Engineering and Architecture.

Yi Gu
Yi Gu

Yi Gu, associate professor of physics, is working with several different materials to create nanowire semiconductors for laser and light-emitting devices as well as solar cell applications. His work is just one of many advanced materials endeavors under development within the MSEP.

“The advantage of nanowire solar cells is they have a higher efficiency than conventional solar cells. Plus, nanowires require a smaller amount of material to generate the same amount of electricity,” said Gu.

Like current silicon solar cells, nanowires absorb the incoming photons, but they can trap more of the available photons (light energy) and are better at transporting the free electrons to the collector to generate more electricity.

Even though nanowire solar cells are very small, they could be assembled by the millions into large-scale panels for use on rooftops and other outdoor collection sites. So far, copper indium selenide (CuInSe2) nanowires are the solar cell front-runners in Gu’s laboratory.

Creating the team

The growing field of nanotechnology will allow scientists to tailor materials from the atomic level upwards and will likely lead to the creation of yet-unimagined devices and components. Physics and chemistry are two of the key disciplines in this research: chemistry helps to characterize material properties and physics examines and explains atomic-scale phenomena.

The MSEP at WSU is a voluntary research collaborative: faculty self-assemble around common interests and work together to investigate and potentially influence energy, information, environment, infrastructure, health and security. Currently more that 30 WSU faculty and 60 graduate students are affiliated with the MSEP.

“They are here because they are excited about working with each other, using the shared facilities, using the shared resources,” said Indranath Dutta, MSEP director and a professor in the WSU School of Mechanical and Materials Engineering.

Advancements in materials have proven so important that periods of human history have been named after them: the Stone Age, Bronze Age, Iron Age, etc. And just as new materials enabled new technology during the Industrial Revolution, it’s a good bet that nano and other advanced materials will play a central role in 21st-century innovation.