 |
|
Magnetism flicks switch on 'dark excitons'
January 11, 2006Tests at leading magnetic labs shed light on nanotube mystery
In new experimental research appearing in this week's issue of Physical Review Letters, a Rice University-led team of nanoscientists and electrical engineers has flipped the switch on 'dark excitons' in carbon nanotubes by placing them inside a strong magnetic field.
The research offers new insight into the fundamental optical properties of semiconducting nanotubes, hollow straw-like molecules of pure carbon. Leading computing companies would like to use nanotubes as optical components in next-generation microchips that are faster, more powerful and more energy efficient.
"Single-walled carbon nanotubes offer engineers the intriguing possibility of building chips where electrical inputs can be converted into light and moved about the chip as optical signals rather than electrical signals," said lead researcher Junichiro Kono, associate professor of electrical and computer engineering at Rice. "Thus far, the poor optical performance of nanotubes - in some cases as few as one in 100,000 incoming photons causes a fluorescent emission - has prevented engineers from developing the technology for applications."
Kono said the new research may help scientists formulate new tests to answer some of the most perplexing questions about the optical properties of nanotubes. For example, scientists are currently debating whether low fluorescence efficiencies in nanotubes arise from the intrinsic physical structure of nanotubes or from external factors like structural defects and impurities. Some of the leading theories have the missing light disappearing into "dark" excitons - odd quantum pairings of electrons and electron "holes" that are forbidden by quantum rules from fluorescing. The new magnetic method of overcoming this dark exciton effect could be used to probe the intrinsic properties of nanotubes and help settle the debate.
The team tested materials in some of the world's most powerful magnetic fields. Experiments were conducted at both the Laboratoire National des Champs Magnétiques Pulsés in Toulouse, France, and at the National High Magnetic Field Laboratory at New Mexico's Los Alamos National Laboratory.
"We hope that our experimental methods will help better inform theorists and ultimately aid in the development of new devices with far superior functions than those based on existing technology," said Sasa Zaric, whose doctoral dissertation will be based on the work.
Nanotubes are a fraction of the size of transistors used in today's best microchips. As electronic components, nanotubes could reduce power demands and heating in next-generation chips. But as optical components they offer far more. The replacement of copper cables with fiberoptics revolutionized the volume and speed of data transmission in the telecom industry 20 years ago, and the parallels in microchips are tantalizing.
Rice University
Kono said the new research may help scientists formulate new tests to answer some of the most perplexing questions about the optical properties of nanotubes. For example, scientists are currently debating whether low fluorescence efficiencies in nanotubes arise from the intrinsic physical structure of nanotubes or from external factors like structural defects and impurities. Some of the leading theories have the missing light disappearing into "dark" excitons - odd quantum pairings of electrons and electron "holes" that are forbidden by quantum rules from fluorescing. The new magnetic method of overcoming this dark exciton effect could be used to probe the intrinsic properties of nanotubes and help settle the debate.
The team tested materials in some of the world's most powerful magnetic fields. Experiments were conducted at both the Laboratoire National des Champs Magnétiques Pulsés in Toulouse, France, and at the National High Magnetic Field Laboratory at New Mexico's Los Alamos National Laboratory.
"We hope that our experimental methods will help better inform theorists and ultimately aid in the development of new devices with far superior functions than those based on existing technology," said Sasa Zaric, whose doctoral dissertation will be based on the work.
Nanotubes are a fraction of the size of transistors used in today's best microchips. As electronic components, nanotubes could reduce power demands and heating in next-generation chips. But as optical components they offer far more. The replacement of copper cables with fiberoptics revolutionized the volume and speed of data transmission in the telecom industry 20 years ago, and the parallels in microchips are tantalizing.
Rice University
Excitons Current Events and Excitons News RSSJQI researchers create entangled photons from quantum dots
To exploit the quantum world to the fullest, a key commodity is entanglement-the spooky, distance-defying link that can form between objects such as atoms even when they are completely shielded from one another.
Discovery Brings New Type of Fast Computers Closer to Reality
Physicists at UC San Diego have successfully created speedy integrated circuits with particles called "excitons" that operate at commercially cold temperatures, bringing the possibility of a new type of extremely fast computer based on excitons closer to reality.
Light sensor breakthrough could enhance digital cameras
New research by a team of University of Toronto scientists could lead to substantial advancements in the performance of a variety of electronic devices including digital cameras.
Oregon physicists don't flip spin but find possible electron switch
University of Oregon researchers trying to flip the spin of electrons with laser bursts lasting picoseconds (a trillionth of a second) instead found a way to manipulate and control the spin -- knowledge that may prove useful in a variety of new materials and technologies.
On the Energy Trail: Berkeley Researchers Find New Details Following the Path of Solar Energy During Photosynthesis
Imagine a technology that would not only provide a green and renewable source of electrical energy, but could also help scrub the atmosphere of excessive carbon dioxide resulting from the burning of fossil fuels.
Nanotube flickering reveals single-molecule rendezvous
In the quantum world, photons and electrons dance, bump and carry out transactions that govern everything we see in the world around us.
Electronic displays that fit on clothing could power revolution in lighting
A thin film of plastic which conducts electricity and produces solar power could be the basis for a revolution in the way we light our homes and design clothes.
Quantum Secrets of Photosynthesis Revealed
Through photosynthesis, green plants and cyanobacteria are able to transfer sunlight energy to molecular reaction centers for conversion into chemical energy with nearly 100-percent efficiency.
Bose-Einstein condensation in the solid state
New experimental research shows that half-matter, half-light quasi-particles called polaritons show compelling evidence of Bose-Einstein condensation at the relatively high temperature of 19 degrees Kelvin.
New materials for high efficiency organic solid state lighting
A new organic molecule developed by Pacific Northwest National Laboratory scientists may significantly improve the efficiency of organic solid state lighting. Direct conversion of electricity to light in "solid state" thin films of organic molecules occurs in organic light emitting devices which can be far more efficient than conventional "incandescent" light bulbs.
More Excitons Current Events and Excitons News Articles
|
Theory of Excitons by Robert S. Knox (Author) | |
 |
Excitons in Low-Dimensional Semiconductors: Theory, Numerical Methods, Applications (Springer Series in Solid-State Sciences) by Stephan Glutsch (Author) Low-dimensional semiconductors have become a vital part of today's semiconductor physics, and excitons in these systems are ideal objects that bring textbook quantum mechanics to life. Furthermore, their theoretical understanding is important for experiments and optoelectronic devices. The author develops the effective-mass theory of excitons in low-dimensional semiconductors and describes numerical methods for calculating the optical absorption including Coulomb interaction, geometry, and external fields. The theory is applied to Fano resonances in low-dimensional semiconductors and the Zener breakdown in superlattices. Comparing theoretical results with experiments, the book is essentially self-contained; it is a hands-on approach with detailed derivations, worked examples,... |
 |
Photosynthetic Excitons by Herbert Van Amerongen (Author), Leonas Valkunas (Author), Rienk Van Grondelle (Author) Contents include structural organization, spectral properties and excitation energy transfer in photosynthesis, the exciton concept, spectral shapes, spectroscopy of excitons in molecular crystals and aggregates, exciton dynamics, nonlinear annihilation of excitons, and more. |
|
Primary Photoexcitations in Conjugated Polymers: Molecular Exciton Versus Semiconductor Band Model by Niyazi Serdar Sariciftci (Editor) Collects and presents all the arguments on the controversial debate on the nature of primary photoexcitations in conjugated polymers displayed against each other. | |
|
Excitons: Their Properties and Uses by Donald C. Reynolds (Author) | |
 |
Bose-Einstein Condensation of Excitons and Biexcitons: And Coherent Nonlinear Optics with Excitons by S. A. Moskalenko (Author), D. W. Snoke (Author) Bose-Einstein condensation of excitons is a unique effect in which the electronic states of a solid can self-organize to acquire quantum phase coherence. The phenomenon is closely linked to Bose-Einstein condensation in other systems such as liquid helium and laser-cooled atomic gases. Covering theoretical aspects as well as recent experimental work, the book provides a comprehensive survey of the field. After introducing the relevant basic physics of excitons, the authors discuss exciton-phonon interactions as well as the behavior of biexcitons. They also cover exciton phase-transitions and give particular attention to nonlinear optical effects including the optical Stark effect and chaos in excitonic systems. The thermodynamics of equilibrium, quasiequilibrium, and nonequilibrium... |
 |
Self-Trapped Excitons (Springer Series in Solid-State Sciences) by K. S. Song (Author), R. T. Williams (Author) Self-Trapped Excitons discusses the structure and evolution of the self-trapped exciton (STE) in a wide range of materials. It includes a comprehensive review of experiments and extensive tables of data. Emphasis is given throughout to the unity of the basic physics underlying various manifestations of self-trapping, with the theory being developed from a localized, atomistic perspective. The topics treated in detail in relation to STE relaxation include spontaneous symmetry breaking, lattice defect formation, radiation damage, and electronic sputtering. |
|
Excitons in molecular crystals;: Theory and applications (Frontiers in chemistry) by David Parker Craig (Author) | |
|
Excitons at high density (Springer tracts in modern physics) by H Haken (Author) | |
 |
Exciton: Webster's Timeline History, 1957 - 2007 by Icon Group International (Author) Webster's bibliographic and event-based timelines are comprehensive in scope, covering virtually all topics, geographic locations and people. They do so from a linguistic point of view, and in the case of this book, the focus is on "Exciton," including when used in literature (e.g. all authors that might have Exciton in their name). As such, this book represents the largest compilation of timeline events associated with Exciton when it is used in proper noun form. Webster's timelines cover bibliographic citations, patented inventions, as well as non-conventional and alternative meanings which capture ambiguities in usage. These furthermore cover all parts of speech (possessive, institutional usage, geographic usage) and contexts, including pop culture, the arts, social sciences... |
| © 2009 BrightSurf.com |