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Small focus brings big rewards
by Patrick Young

Focusing on small things in innovative ways figured prominently in earning high honors for 10 researchers, the winners of six prized awards in physics.

Langmuir Prize
The American Physical Society (APS) awarded the Irving Langmuir Prize, which honors interdisciplinary research in chemistry and physics, to Phaedon Avouris of the IBM Thomas. J. Watson Research Center. He was recognized for his pioneering studies of nanostructures and atomic-scale phenomena at surfaces—work that has involved chemical physics, surface chemistry and physics, molecular electronics, and nanoscience. “Phaedon Avouris’s career has, in many ways, defined the progress in atomic- scale manipulation and nanotechnology, and the science behind it,” says Tony F. Heinz, professor of electrical engineering and physics at Columbia University.

Avouris’s accomplishments include the first demonstration of resonant electron scattering of molecules in the absorbed state. His explorations of semiconductor surface chemistry led to many important findings, including the correlation of surface reactivity with the presence of dangling bonds, and the discovery that, contrary to prevailing opinion, clean silicon surfaces are very reactive at cryogenic temperatures.

Figure 1. Atomic-force-microscope cross-sectional image of a carbon nanotube ring that is bridging two gold electrodes.
( Phaedon Avouris, IBM)
In the 1980s, Avouris introduced scanning tunneling microscopy (STM) to study surface chemistry atom-by-atom, and he developed chemically assisted field desorption, which allows the selective breaking of individual covalent bonds and the use of an STM tip to move individual strongly bonded atoms. Since the discovery of carbon nanotubes (CNTs), Avouris has focused largely on their electronic properties. His group fabricated the first field-effect transistor using a single CNT as the transistor’s channel and went on to make significant improvements in these transistors. “A great deal of fascinating science lies behind these accomplishments, from learning how to manipulate and contact nanotubes to in situ nanotube modification and doping,” Heinz says.

Keithley Award
Arthur Ashkin received the 2003 Joseph F. Keithley Award for Advances in Measurement Science. APS honored him for his pioneering work in laser cooling and the trapping of atoms and particles, as well as his invention of optical tweezers and their use to measure the physical forces generated by biological molecular motors. Ashkin’s theoretical and experimental contributions, made over more than three decades at Bell Laboratories, have had a profound impact on atomic, soft condensed- matter, and biological physics.

“Art was the first to demonstrate and understand how microscopic particles can be trapped, accelerated, and levitated with laser light,” says Steven Chu, professor of physics and applied physics at Stanford University. “He and his collaborators demonstrated that optical trapping could be done with a single focused laser beam, a technique now known as optical tweezers. He then went on to show how individual live cells, and even organelles within cells, can be moved and held in the optical trap without damage. In short, the introduction of force as another experimental measurable parameter in the study of microscopic and molecular systems was due to Art.”

Ashkin’s invention of the optical tweezers led to important experiments. These include studies of the rotary motor that propels the flagella of E. coli bacteria, the interaction of the muscle proteins actin and myosin, the enzymes that cleave the genetic molecules DNA and RNA, and the packing of DNA into the outer coatings of viruses. His early work also included studies of sharp Mie resonances in glass microspheres—work revived by other researchers 20 years later to study microlasers and cavity quantum electrodynamics.

Figure 2. Representation (upper image) of light emitted from a diode formed by crossing p-doped and n-doped nanowires, shown with their electrodes in the lower atomic-forcemicroscope image.
(X. Duan and Y. Huang Lieber Group, Harvard University)

Polymer Prize
APS’s Polymer Physics Prize went to Andrew J. Lovinger “for his contributions to fundamental understanding of structure, morphology, and properties in technologically important polymers”—work he started at Lucent Technologies’ Bell Laboratories and has continued on his own time since joining the National Science Foundation (NSF) in 1995. His quarter-century of contributions stems from five research areas: ferroelectric polymers, silicon-based polymers, high-temperature and high-strength engineering polymers, syndiotactic polypropylene, and organic- and polymerbased transistors. “Andy had been at the center of microstructural advances in a host of technologically significant semicrystalline polymers,” says Edwin L. Thomas of the Massachusetts Institute of Technology. “Even though now full-time at NSF, he continues his research with unabated dedication, and he has published 44 papers during this time.”

Since the early 1990s, Lovinger has focused on developing organic- and polymer- based transistors. During this time, he and his co-workers have carried out key structural and morphological studies that have provided a deeper understanding of these novel materials. They have shown that the critical issue for optimizing semiconducting properties is to orient the molecules so that their p–p orbital overlaps lie along the source-to-drain direction of the transistor. Lovinger has also demonstrated the crucial role of crystal morphology, order, and defects on the device’s semiconducting properties, and has shown that soluble regioregular polythiophene derivatives yield printable semiconducting polymeric field-effect transistors that have good flexibility and processing characteristics.

“His work combines deep insight into the fundamental factors for chain packing, with world-class experimental skills in transmission electron microscopy, electron and X-ray diffraction, and atomic force microscopy,” says Stephen Z. D. Cheng of the University of Akron. “He is a great experimentalist, clever and novel, and a great leader.”

McGroddy Prize
Charles Lieber of Harvard University earned the APS James C. McGroddy Prize for his outstanding contributions in nanostructured and functional nanostructured materials. “He has been spectacularly successful in developing methods of incorporating his materials into prototype devices that yield solid, physics-based measurements, and in taking the first steps toward building prototype integrated circuits using self-assembly,” says Harvard colleague George M. Whitesides.

Lieber began in the mid-1980s with the study of carbon nanotubes, and over the years he systematically examined their electronic properties and how small differences in their molecular structure affect these properties, including whether they are insulators or semiconductors. He also addressed the difficulty of growing nanotubes and assembling them into primitive devices. Lieber developed a way to reproducibly grow nanorods of single crystalline silicon and compound semiconductors using liquid–vapor–catalytic growth, and to demonstrate an impressive range of new devices and phenomena. Last year, for example, he and his team laid down a simple crossbar arrangement of silicon and gallium nitride nanowires that allowed communication among the wires and demonstrated that logic functions for complex circuits can be constructed using this bottom-up assembly method.

“Both the materials that he is synthesizing and the strategies that he is demonstrating will have enormous impact on the future of materials science,” predicts Whitesides. “His work may change device physics and perhaps, ultimately, electronics in a most profound way.”

Pake Prize
Physicist C. Paul Robinson received the APS’s 2003 George E. Pake Prize in recognition of his leadership as director of Sandia National Laboratories, his arms-control negotiating skills, and “his pioneering contributions to the development of highexplosives lasers, e-beam-initiated chemical lasers, and molecular laser-isotope separation methods.”

Figure 3. C. Paul Robinson, director of Sandia National Laboratories, was awarded the George E. Pake Prize for his international leadership roles and laser research.
(Randy Montoya, Sandia National Laboratories)
Robinson spent much of his early career at Los Alamos National Laboratory, where his research included nuclear weapons, fusion, nuclear-materials safeguards, and arms-control verification. From 1988 through most of 1990, he held the rank of ambassador and led the U.S. delegation to the Nuclear Testing Talks with the Soviet Union in Geneva, Switzerland. The negotiations produced two major agreements, the protocols to the Threshold Test Ban Treaty and the Peaceful Nuclear Explosions Treaty. “Both were ratified unanimously by the U.S. Senate and remain in force today, testifying to his exceptional ability to achieve broad acceptance of government operations and policies both nationally and internationally,” says Alton D. Romig, Sandia’s chief technology officer and vice president for science and technology and partnerships.

In 1995, Robinson became Sandia’s director and has led efforts to increase its ties to industry and its transfer of technology to small businesses. “Sandia has created more than 350 advanced research projects and 1,200 partnerships with small business, as well as providing short-term technical assistance to many companies,” Romig said. “Dr. Robinson’s leadership has greatly advanced science.”

Europhysics Prize
The 2002 Agilent Europhysics Prize went to Dante Gatteschi and Roberta Sessoli of the University of Florence in Italy, Bernard Barbara and Wolfgang Wernsdorfer of the Louis Néel Laboratory in Grenoble, France, and Jonathan Friedman of Amherst College. The European Physics Society (EPS) cited the five for their exploration of the quantum effects in the mag netic dynamics of molecular nanomagnets. “This observation of quantum behavior at an intermediate scale between microscopic and macroscopic is an important breakthrough that has revived the field of mesoscopic magnetism,” the EPS said.

Molecular nanomagnets contain a small number of magnetic atoms and carry a global collective magnetic moment. They have been studied since the early 1980s, and Gatteschi and Sessoli have played a key role in the precise characterization of their magnetic structures. One example is their work with the spin-cluster molecule [Mn12O12(CH3COO)16(H2O)], informally called Mn12. Below 3 K, the molecule’s mesoscopic magnetic moment is blocked along one of the directions of its anisotropy axis; applying a magnetic field reverses the moment at about 9.6 T.

In 1996, Barbara, Gatteschi, and Sessoli, collaborating on studies of single crystals of Mn12—and Friedman, then a Ph.D. candidate at City College of New York working independently with Mn12 powders—discovered that the magnetic-moment reversal can occur at a smaller field in a series of period steps. These steps can be explained by quantum tunneling of magnetization (QTM). The discovery of QTM in Mn12 triggered experiments on many magnetic molecules, which showed remarkable quantum properties in a molecule called Fe8. The most spectacular property was the existence of topological interference effects, discovered by Wernsdorfer and Sessoli in 1999, which confirmed the coherent character of the tunneling.

Although the scientists’ work is primarily of interest “in the field of quantum mesoscopic magnetism, their breakthrough may also be important for future applications,” the EPS noted.

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The Forum department is initiated by the American Physical Society’s Forum on Industrial and Applied Physics (FIAP). For more information about the Forum, please visit the FIAP Web site or contact the chair, Gordon A. Thomas .

 

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