In an effort to explore the boundary between thermodynamics and quantum mechanics — two fundamental yet seemingly incompatible theories of physics — a team from the UCLA Department of Physics and Astronomy has created the world's smallest incandescent lamp.
The team, which is led by Chris Regan, assistant professor of physics and astronomy and a member of the California NanoSystems Institute at UCLA, and includes Yuwei Fan, Scott Singer and Ray Bergstrom, has published the results of their research May 5 in the online edition of the journal Physical Review Letters.
Thermodynamics, the crown jewel of 19th-century physics, concerns systems with many particles. Quantum mechanics, developed in the 20th century, works best when applied to just a few. The UCLA team is using their tiny lamp to study physicist Max Planck's black-body radiation law, which was derived in 1900 using principles now understood to be native to both theories.
Planck's law describes radiation from large, hot objects, such as a toaster, the Sun or a light bulb. Some such radiation is of fundamental and current scientific interest; the thermal radiation left over from the Big Bang, for instance, which is called the cosmic microwave background, is described by Planck's law.
The incandescent lamp utilizes a filament made from a single carbon nanotube that is only 100 atoms wide. To the unaided eye, the filament is completely invisible when the lamp is off, but it appears as tiny point of light when the lamp is turned on. Even with the best optical microscope, it is only just possible to resolve the nanotube's non-zero length. To image the filament's true structure, the team uses an electron microscope capable of atomic resolution at the Electron Imaging Center for Nanomachines (EICN) core lab at CNSI.
With less than 20 million atoms, the nanotube filament is both large enough to apply the statistical assumptions of thermodynamics and small enough to be considered as a molecular — that is, quantum mechanical — system.
"Our goal is to understand how Planck's law gets modified at small length scales," Regan said. "Because both the topic (black-body radiation) and the size scale (nano) are on the boundary between the two theories, we think this is a very promising system to explore."
The carbon nanotube makes an ideal filament for this experiment, since it has both the requisite smallness and the extraordinary temperature stability of carbon. While the intensive study of carbon nanotubes only began in 1991, using carbon in a light bulb is not a new idea. Thomas Edison's original light bulbs used carbon filaments.
The UCLA research team's light bulb is very similar to Edison's, except that their filament is 100,000 times narrower and 10,000 times shorter, for a total volume only one one-hundred-trillionth that of Edison's.
This research is supported by an National Science Foundation Career award #0748880.
The California NanoSystems Institute (CNSI) is an integrated research center operating jointly at UCLA and UC Santa Barbara whose mission is to foster interdisciplinary collaborations for discoveries in nanosystems and nanotechnology; train the next generation of scientists, educators and technology leaders; and facilitate partnerships with industry, fueling economic development and the social well-being of California, the United States and the world. The CNSI was established in 2000 with $100 million from the state of California and an additional $250 million in federal research grants and industry funding. At the institute, scientists in the areas of biology, chemistry, biochemistry, physics, mathematics, computational science and engineering are measuring, modifying and manipulating the building blocks of our world — atoms and molecules. These scientists benefit from an integrated laboratory culture enabling them to conduct dynamic research at the nanoscale, leading to significant breakthroughs in the areas of health, energy, the environment and information technology.
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