FAYETTEVILLE, Ark. — Using the world’s strongest microscope to peer at atoms, University of Arkansas researchers have made discoveries about the surface of a two-dimensional crystal that will allow researchers to better understand and manipulate gallium arsenide (GaAs), a material commonly used in lasers for CD players, high-speed fiber-optic telecommunication equipment and transistors for cellular phones.
Paul Thibado, Vincent P. LaBella, D.W. Bullock, M. Anser, Z. Ding, C. Emery and Laurent Bellaiche, all of the physics department, found that the two-dimensional surface of the crystal forms a system predicted by the Ising model, a cornerstone in the field of many-body physics. They report their findings in today’s issue of Physical Review Letters.
"We have defined what governs atomic movement at the surface," Thibado said. "It’s a whole new way of looking at these systems."
Scientists make high-tech communications devices by depositing layers of atoms on top of this single crystal surface. To produce better devices, researchers need a fundamental understanding of the physics that governs the motion of atoms on that surface.
Thibado and LaBella’s group have for the first time looked at images of individual atoms on the surface of a crystal and charted their presence or absence as they form islands at high temperatures.
They found that the spontaneous formation of atomic islands follows the Ising model, which describes a large collection of objects interacting with their neighbors. Earnst Ising originally developed the model in 1926 to explain the spontaneous magnetization of magnetic materials as they are cooled from high temperatures. As a graduate student, Ising solved the model in one dimension.
About 20 years later Lars Onsager solved the Ising model in two dimensions, a solution considered to be one of the greatest theoretical achievements of the 20th century. The two-dimensional model is expressed in the GaAs system, according to the researchers.
LaBella illustrates the Ising model using a social phenomenon like the Pokemon craze: It came about by word-of-mouth, spreading from neighbor to neighbor. Last summer, Pokemon caught on like wildfire, and now everyone seems to know about it. The atoms on the crystal surface behave in the same way, going from a few atoms present on the surface to many in a flash, at a certain critical temperature.
By applying the Ising model to this surface, scientists can model the growth of a device and potentially become more efficient in creating useful materials.
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