Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Building nanotubes of gallium nitride rather than carbon yields optically active nanotubes

11.04.2003


Transparent gallium nitride nanotubes made by depositing the semiconducting material on nanowires and then evaporating the nanowires. The tubes are hollow with capped ends. (Credit: Peidong Yang/UC Berkeley)


Nanowires and carbon nanotubes, each with their pluses and minuses, are advertised as the next-generation building blocks for electronic circuits a thousand times smaller than today’s semiconductor circuits.

Peidong Yang, a University of California, Berkeley, chemist, has now fabricated a new type of nanotube, made of gallium nitride, that, he says, "captures some of the great properties from nanowires and carbon nanotubes, and eliminates the not-so-good characteristics of both.

"Each of these - semiconductor nanowires, carbon nanotubes and semiconductor nanotubes - will play a big role in nanocircuits of the future."



Yang, an assistant professor of chemistry at UC Berkeley and a faculty scientist at Lawrence Berkeley National Laboratory (LBNL), chemistry graduate student Joshua Goldberger and their colleagues will publish details of their synthesis in the April 10 issue of Nature.

Unlike many other inorganic nanotubes created to date, these nanotubes are perfect single crystals with interesting optical properties carbon nanotubes don’t have. And because it is easy to attach organic molecules to gallium nitride surfaces, the hollow tubes hold promise as chemical sensors.

Gallium nitride also is a material well known in the semiconductor industry, and is used in many optical, high-temperature and high-voltage electronic circuits. Industry’s ability to manipulate gallium nitride means that Yang’s development paves the way for relatively inexpensive, large-scale production of high-quality, uniform nanotubes.

The molecular structure of a carbon nanotube is often depicted as rolled chicken wire, though, in fact, the tube is pure carbon, with dimensions on the order of 1 to 10 nanometers wide and perhaps 100 to 1,000 times that in length. By comparison, a hair is about 100,000 nanometers across. Depending on details of their synthesis, carbon nanotubes can act like conducting metals or semiconductors, and have found use in elementary transistors and chemical sensors.

The tubes have problems, however. It is difficult to make them with predictable properties, and, because they’re hydrophobic, that is, they repel water, it is hard to attach organic molecules like proteins without destroying their electronic properties.

Similarly, nanowires of zinc oxide (ZnO) can be made 100 to 1,000 times longer than their width, and, as Yang proved in 2001, they can be made to emit blue through ultraviolet laser light.

Using his expertise in fabricating zinc oxide nanowires, Yang tried making nanotubes by casting gallium nitride (GaN) around nanowires and then dissolving the nanowires, in a method similar to the lost wax process employed by sculptors in bronze.

Because the crystal or lattice structures of ZnO and GaN are similar, he was able to grow pure crystalline GaN around the nanowires via chemical vapor deposition, then heat everything up to evaporate the ZnO. The precision of his technique led him to call it epitaxial casting, after epitaxy, a precise method of applying thin chemical films to semiconductors and other materials.

Yang’s standard technique for making nanowires creates millions of them at a time in arrays that look, under an electron microscope, like the hairs of a brush. As a result, his first attempts at casting nanotubes employing nanowire templates produced a forest of hollow GaN nanotubes. Tubes can be created with inner diameters ranging from 30 to 200 nanometers and wall thicknesses ranging from 5 to 50 nanometers. Yang sees no barrier to creating GaN nanotubes as long as 20 or more microns, several hundred times their width.

Since his initial experiments, he has succeeded in growing single nanotubes, and he predicts they will have great usefulness in microfluidics to move molecules from one microscopic chamber to another. A process called nanocapillary electrophoresis could separate molecules in the same way as do today’s microscale labs-on-a-chip.

"This opens up the possibility of using these very new nanotubes for nanofluidic applications," said Yang. "For example, you could use them to mimic ion channels like those in cells of the body."

Current techniques for creating nanochannels are low yield and very expensive, he said.

Because GaN nanotubes are essentially transparent, molecules also could be trapped inside and probed with various wavelengths of light.

Yang is particularly intrigued by the potential to attach molecules to the inside and/or outside of these nanotubes and use them as sensors - like little noses that, when they smell something, alter the electrical properties of the nanotube and trigger an electrical signal.

Yang also notes that his epitaxial casting technique could be used to create thin-walled nanotubes of other types of semiconducting materials.

Coauthors with Yang and Goldberger are Rongrui He and Haoquan Yan of UC Berkeley and Yanfeng Zhang, Sangkwon Lee and Heon-Jin Choi of LBNL.

The research was supported by the Camille and Henry Dreyfus Foundation, the Research Corporation, the Hellman Family Faculty Foundation. the Beckman Foundation, the National Science Foundation and the U.S. Department of Energy.

Robert Sanders | UCB
Further information:
http://www.berkeley.edu/news/media/releases/2003/04/09_tubes.shtml

More articles from Life Sciences:

nachricht New catalyst controls activation of a carbon-hydrogen bond
21.11.2017 | Emory Health Sciences

nachricht The main switch
21.11.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Nanoparticles help with malaria diagnosis – new rapid test in development

The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.

Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

Previous evidence of water on mars now identified as grainflows

21.11.2017 | Physics and Astronomy

NASA's James Webb Space Telescope completes final cryogenic testing

21.11.2017 | Physics and Astronomy

New catalyst controls activation of a carbon-hydrogen bond

21.11.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>