Small is Different

Years ago, when Uzi Landman and his colleagues set out to uncover some of the rules that govern why a non-reactive metal like gold acts as a catalyst when it is in nanoclusters only a few atoms in size, they didn’t sit down in a lab with the precious metal. Instead, they ran computer simulations and discovered that gold is a very effective catalyst when it is in clusters of eight to two dozen atoms. They also found that electrical charging of gold is crucial to its catalytic capabilities. Six years later, the team has verified their earlier predictions experimentally, and they stand ready to further explore environmental effects on catalysis.

This practice of partnering computer simulations with real-world experiments is becoming more vital as scientists delve deeper into realms where the actors are measured on the nanoscale, Landman told a group of scientists Thursday, February 17 at the annual meeting of the American Association for the Advancement of Science (AAAS).

"Small is different,” said Landman, director of the Center for Computational Materials Science and professor of physics at the Georgia Institute of Technology. “We cannot use the way physical systems behave on the large scale to predict what will happen when we go to levels only a few atoms in size. In this size regime, electrons transport electricity in a different way, crystallites have different mechanical properties and gold nanowires have strength twenty times larger than a big bar of gold, and inert metals may exhibit remarkable catalytic activity. But we know the rules of physics, and we can use them to create model environments in which we can discover new phenomena through high-level computer-based simulations.”

Computers are constantly becoming more powerful and capable of conducting more detailed explorations at the same time scientists across the globe are increasing their interest in the science of the small. The intersection of these two trends, said Landman, is allowing scientists to investigate realms that are too small for today’s technology to explore experimentally.

It’s not just a matter of making faster calculations, he said. “Experimentally, we can’t always go down to the resolution we need to see, explain and predict things, but with computer simulations we can go to any resolution we need,” said Landman. “Therefore, you can ask questions, deeper questions, on how materials behave on the small scale, even if you can’t get to that fine resolution experimentally.”

This doesn’t mean that experiments aren’t necessary, said Landman. “It’s a supplementary and complimentary approach. The pillars of scientific methodology are composed now of experimentation, analytical theory and computer simulation.”

In addition to their work on nanocatalysis, Landman and colleagues have used simulations to explore other phenomena, such as the possibility of producing and maintaining a stable flow of liquid on the nanoscale. Their models predicted that it is possible to produce liquid jets only six nanometers wide. To date, in collaboration with Landman’s theory group, there are teams of engineers building nozzles that can produce jets in the 100 nanometer range. Within one year, said Landman, they expect to produce “nanojets” in the 10 nanometer range.

"The opportunity to make new discoveries in ways that weren’t possible before is an incredible gift and it has come about only because we can now simulate environments on the computer that are either not yet possible, too expensive or too dangerous to do in the lab,” said Landman. “We are now at a point in history where the science of the small holds the promise of producing a windfall of scientific discoveries. Computers serve tools for discovery in this exciting adventure.”

Source: Georgia Institute of Technology

Related stories:

Physicists discover gold can be magnetic on the nanoscale
Physicists at the Georgia Institute of Technology have made important findings regarding gold on the nanoscale. They found that applying an electrical field on a surface-supported gold nanocluster changes its structure from a three-dimensional one to a planar flat structure. In another paper, they relate their discovery that gold in this size regime can be made magnetic through oxygenation of gold nanowires.
Tightly packed molecules lend unexpected strength to nanothin sheet of material
Scientists at the University of Chicago and Argonne National Laboratory have discovered the surprising strength of a sheet of nanoparticles that measures just 50 atoms in thickness.
Research Shows How Water May Enhance Nanocatalysis
Researchers at the Georgia Institute of Technology have uncovered important evidence that explains how water, usually an inhibitor of catalytic reactions, can sometimes promote them. The findings could lead to fewer constraints on reaction conditions potentially leading to the development of lower cost techniques for certain industrially important catalytic reactions. The results appear in the September 6, 2005 issue of Physical Review Letters.
Scientists find evidence of electrical charging of nanocatalysts
Researchers at the Georgia Institute of Technology and Technical University Munch have discovered evidence of a phenomenon that may lead to drastically lowering the cost of manufacturing of materials from plastics to fertilizers. Studying nano-sized clusters of gold on a magnesium oxide surface, scientists found direct evidence for electrical charging of a nano-sized catalyst. This is an important factor in increasing the rate of chemical reactions. The research will appear in the 21 January, 2005, issue of the journal Science, published by the AAAS, the science society, the world's largest general scientific organization.
Study reveals principles behind stability and electronic properties of gold nanoclusters
A report published in the July 8 issue of the journal Proceedings of the National Academy of Sciences (PNAS) is the first to describe the principles behind the stability and electronic properties of tiny nanoclusters of metallic gold. The study, which confirms the "divide and protect" bonding structure, resulted from the work of researchers at four universities on two continents.
Water flows like molasses on the nanoscale
A Georgia Tech research team has discovered that water exhibits very different properties when it is confined to channels less than two nanometers wide – behaving much like a viscous fluid with a viscosity approaching that of molasses. Determining the properties of water on the nanoscale may prove important for biological and pharmaceutical research as well as nanotechnology. The research appears in the March 15 issue of the journal Physical Review B.
Fluid dynamics theory works on nanoscale outside vacuum
In 2000, Georgia Tech researchers showed that fluid dynamics theory could be modified to work on the nanoscale, albeit in a vacuum. Now, seven years later they've shown that it can be modified to work in the real world, too – that is, outside of a vacuum. The results appear in the February 9 issue of Physical Review Letters.
Physicists discover structures of gold nanoclusters
Using different experimental techniques, two separate and independent research groups in collaboration with a team from the Center for Computational Materials Science (CCMS) at the Georgia Institute of Technology, have unveiled the size-dependent evolution of structural and electronic structural motifs of gold nanoclusters ranging in size from 11 to 24 atoms. The experiments, in conjunction with the theoretical analysis performed by the Georgia Tech team, show near perfect agreement pertaining to the cluster structures occurring in the experiments.

News discussion:

Technology news