Science 1663

Dialogue

"Nano" World—Where less is more: Toni Taylor and Alexander Balasky on the Center for Integrated Nanotechnologies.

Sasha Balatsky (left) and Toni Taylor.

1663: How would you define nanotechnology?

Taylor: Nanotechnology is about using bits of matter—nanoblocks about 10 to 1000 atoms on a side—to build devices with specific properties that are designed for, say, transferring energy efficiently or detecting pathogens or making stronger structures.

1663: Will nanoscience become a defining factor in practical technologies?

Balatsky: Very likely. By looking at how matter behaves in very small regions, we are discovering totally unexpected properties and truly novel ways to make things work.

One driver for nanotechnology is the high-tech industry’s desire to continue miniaturizing computer chips. Have you wondered why cell phones have more and more functions? It’s because the number of transistors per computer chip is doubling every 18 months. But that trend, which has continued since 1965, will run into a steep wall in about 2015 when the transistor reaches the atomic scale.

Taylor: Even now we’re running into size limitations. Some computing elements are already at the nanometer scale, containing only a thousand atoms and only a hundred or so free electrons to carry the electric current. (By comparison, a cube of matter a centimeter on a side contains about a trillion trillion atoms.) The number of free electrons always varies, but with the total number so small, the variation can affect how well the element performs.

1663: Does nanotechnology provide a way around the size limitation?

Taylor: Yes, but not by making smaller and smaller transistors. In nanotechnology we try to find the smallest structure—a nanoblock—that can produce the specific function we need. It could be a single molecule, and it could be organic, inorganic, or biological.

Balatsky: Here’s an example that Toni is working on at CINT.

Imagine you want to design a hand-held sensor to detect airborne molecules. And let’s say the sensor consists of a solid-state laser shining light on a tiny surface and a detector that looks at the light that’s scattered, or deflected, from molecules that land on the surface.

If you pattern the tiny surface with a set of shaped, nanometer-size objects, they will interact with the molecules to create an electric field that amplifies by a millionfold the scattered light intensity from the molecules. Now you have an ultrasensitive molecular sensor.

This enormous amplification of the signal came as a surprise, but surprises are common when you look at small groups of atoms. The nanoscale is a new sandbox for scientists, and we don’t really have any theories to guide us.

Taylor: Another big surprise came when Victor Klimov (the CINT nanophotonics thrust leader) and his team tried to convert sunlight into electric current with quantum dots, bits of material made from a few hundred atoms. They discovered that one photon (or quantum unit) of sunlight can loosen and potentially free up to seven electrons in a quantum dot. If they can make those electrons carry electric current, quantum dots would be seven times more efficient at converting sunlight to electric current than standard solar cells.

1663: That would revolutionize the solar energy industry.

Balatsky: Another novel aspect of nanomaterials is their phenomenal strength.

A cutting tool made from nanometer-thick layers becomes ultrastrong because it has many natural boundaries where it can relax under stress instead of cracking. A single crystal made of exactly the same stuff has fewer ways to relieve stress and cracks much more easily.

1663: Are these ultrastrong materials being made at CINT?

Taylor: Yes. We are also engineering metamaterials, materials that respond to incoming light in new ways because we’ve patterned their surfaces with tiny structures (see the Spotlight “T-Ray Vision” on page 25).

Balatsky: By applying either laser light or a voltage, you can, in a trillionth of a second, switch this metamaterial from transmitting most of the incoming light to reflecting most of it. So it can be a very fast switch.

Taylor Ultimately, I think these kinds of metamaterials will be used as interconnects on chips, allowing light to carry information from one part of the chip to another. When electrons carry the information, they generate heat, which is why your computer needs a fan. Optical interconnects like these reduce the overall heat load.

1663: Is nanotechnology only about building tiny objects?

Nanoscale domains of a high-temperature superconductor as seen by an atmoic microscope.

Taylor: Extremely short times are also very important—processes that occur in trillionths of a second or even a thousand times faster (femtoseconds). We have a big effort at CINT to look at ultrafast phenomena on the nanoscale, phenomena like the response of quantum dots to sunlight.

Balatsky: And of course to develop the properties of objects at the nanoscale, you have to have tools to measure what is happening at very short time and length scales. One of CINT’s strengths is our world-class suite of experimental tools. Users from universities and industry can come here and find everything in one place. There are important new principles to be discovered, but only if you have the tools to look at materials in new ways.

Taylor: We use tools like atomic microscopes that see individual atoms, but we also need to marry those microscopes to other devices that measure changes in properties from one atom to the next and from one moment to the next because those changes really do occur.

Sasha, working with Seamus Davis at the Cornell University, has shown that exotic materials like high-temperature superconductors and colossal magneto-resistive materials are not at all homogeneous. Instead they’re like a patchwork quilt of nanoscale regions (see picture at left) with distinctly different characters, basically different material phases living side by side in one material.

Balatsky: Yes, and the coexistence of different phases may explain the exotic properties of these novel materials. Without the computerized instrumentation to measure and record the properties of thousands and thousands of atoms in a reasonable amount of time, we would never have discovered those tiny, separate domains.

Taylor: CINT’s combination of instruments and scientists makes the facility unique. We have complete laboratories where it becomes possible to combine concepts like metamaterials, nanolayered structures, quantum dots, and so on.

Entrance to the CINT gateway at Los Alamos. The CINT core facility is at Sandia National Laboratories in Albuquerque.

Bringing these exotic materials together in an integrated form is where we are heading. That’s what the “I” in CINT is about—integrating different kinds of nanotechnologies to come up with functional devices and systems.

The nanotech revolution is still in the formative stage, but in 10 or 20 years, we can expect it to have a major impact on every area of technology, from pharmaceutical delivery systems that affect only the targeted organ to advanced methods for cleaning up the environment. Also, the environmental impact of nanotechnology is just beginning to be looked at. That is potentially another area in which CINT can become a leader.