Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scientists Discover How to Flip a Molecular Switch

21.11.2005


A means for controlling single-molecule switches by engineering their design and surrounding environment has been developed by a research team led by scientists at Penn State, Rice University, and the University of Oregon. The research demonstrates that single-molecule switches can be tailored to respond in predictable and stable ways, depending on the direction of the electric field applied to them--while some switches were engineered to turn on, others were engineered to turn off in response to the same applied electric field. The discovery, which is an essential step in the emerging field of molecular electronics, could further the development of nano-components--as small as molecules or atoms--for use in future generations of computers and other electronic devices.


Credit: Lewis et al.
Sequential STM images of FAPPB/R1ATC9 obtained at alternating sample biases of +1.0 and -1.0 V. The majority of the FAPPB molecules (apparent protrusions, displayed as bright spots) switch conductance states between OFF at +1.0 V and ON at -1.0 V sample bias. The red and green boxes follow one FAPPB molecule that exhibits this bias dependence. Imaging conditions: 4000 ‰ × 4000 ‰, I = 2 pA.



A paper describing the research results, titled "Molecular Engineering of the Polarity and Interactions of Molecular Electronic Switches," will be published in the Journal of the American Chemical Society on 21 December 2005. "This research confirms our hypothesis of how single-molecule switches work," says Penn State Professor of Chemistry and Physics Paul S. Weiss, whose lab tested the molecules. "Molecular switches eventually may become integrated into real electronics, but not until after someone discovers a way to wire them." In addition to Weiss, the research team includes Penelopie Lewis of Penn State, who now is at Columbia University; James Tour and Francisco Maya at Rice University; and James Hutchison and Christina Inman at the University of Oregon.

The research is the latest achievement in the team’s ongoing studies of a family of stiff, stringy molecules known as as OPEs--oligo phenylene-ethynylenes--which the scientists have tailored in a number of ways to have a variety of physical, chemical, and electronic characteristics. The potential for using these OPE molecules as switches had been limited by their troublesome tendency to turn on and off at random, but Weiss and his colleagues recently discovered a way to reduce this random switching. In their current research, the scientists demonstrated, with a number of definitive experiments, how and why it is possible to control these molecular switches.


To study the properties of individual OPE molecules, the scientists first inserted them into a hairbrush-like matrix of similarly shaped molecules, which Weiss describes as a "self-assembled amide-containing alkanethiol monolayer." One end of each molecular "bristle" is attached to the thin gold base of the microscopic hairbrush. With the individual OPE molecules surrounded by the matrix of alkanethiol molecules, all anchored in gold, Weiss and his team were able to study the properties of the OPE molecules with a powerful scanning tunneling microscope (STM). The molecules were synthesized in Tour’s lab at Rice University and the matrix was synthesized in Hutchinson’s lab at the University of Oregon.

The team synthesized a variety of OPE molecules, some with a large dipole--the difference in strength and polarity of the electric charge between one end of the molecule and the other--and others with a weaker dipole. Some of the OPE molecules were designed to have a positive charge on the end facing away from the gold base while others were designed to have a negative charge at that end. Weiss’s lab found that the tip of the microscope pulled an OPE molecule up higher than the surrounding matrix--or "on"--if the OPE molecule had a sufficiently strong dipole and if the charge of its exposed end was opposite that of the STM tip, making the two electrically attractive. "The OPEs that we engineered to have the strongest dipoles are the most reliable," Weiss says.

The researchers also found that if the charge of the STM tip was the same as that on the end of an OPE, and therefore electrically repulsive, the molecule was pushed down--or "off"--causing it to lean sideways into the matrix. They discovered that this position alters the molecule’s interaction with the system’s gold base, changing the system’s electrical conductance. "When the molecule is tilted over, electrons have a harder time going through this bond, so the switch is more resistive," Weiss explains.

The scientists also demonstrated that it is important to engineer the chemical environment, as well as the electronic environment, that surrounds the OPE molecule. "We repositioned a nitro group attached on the side of one of the varieties of OPE switches so it had a strong-enough dipole and could interact with the amide groups on the surrounding matrix molecules through hydrogen bonding," Weiss says. The team also redesigned the matrix so it would be able to interact better with the new functionality of this repositioned group. The team’s studies show that interactions of the molecular switches with the surrounding matrix molecules have a big effect on how long switches stayed in the on or off state, which is critical for information storage. These states remain stable and can be read back for hours in the systems that Weiss and his colleagues designed, assembled, and measured. "These chemical interactions stabilize the "on" and "off" states, reducing random switching," Weiss reports.

"With these studies, we have been able to confirm that we now have the predictive power to design molecular switches that can be turned on or off at will, which was a critical test of our understanding of their function."

This research was funded, in part, by the Army Research Office (ARO), Defense Advanced Research Projects Agency (DARPA), Department of Energy (DOE), National Science Foundation (NSF), National Institutes of Standards and Technology (NIST), and Office of Naval Research (ONR).

Barbara K. Kennedy | EurekAlert!
Further information:
http://www.science.psu.edu/alert/Weiss11-2005.htm
http://www.psu.edu

More articles from Life Sciences:

nachricht Could this protein protect people against coronary artery disease?
17.11.2017 | University of North Carolina Health Care

nachricht Microbial resident enables beetles to feed on a leafy diet
17.11.2017 | Max-Planck-Institut für chemische Ökologie

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

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,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

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

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>