Multitasking nanotechnology

Confocal microscope image of a self-assembled monolayer of a polychlorotriphenyl methyl radical patterned on a quartz surface. This multifunctional molecule behaves as an electroactive switch with optical and magnetic response.

Tiny electronically active chemicals can be made to form ordered layers on a surface, thanks to research supported by the European Science Foundation (ESF) through the EUROCORES programne SONS 2 (Self-Organised NanoStructures).

These nanostructured layers may one day be used to build the components of electronics devices, such as transistors and switches, for a future generation of powerful computers based on molecules rather than silicon chips.

Speaking at the European Materials Research Society (EMRS) meeting in Strasbourg, SONS II scientist Marta Mas-Torrent explained the potential of nanotechnology: "Currently, there is a great interest in employing functional molecules as building blocks for preparing devices since this will facilitate the move towards device miniaturization."

On this scale, manipulating nanoscopic components requires skill and determination but by exploiting molecular self assembly, the researchers hope to build ordered layers just a single molecule thick using microcontact printing techniques borrowed from the electronics industry.

They are now creating different arrangements of monolayers on gold, silica, and other materials.

Mas-Torrent works with Nuria Crivillers and Concepcio Rovira in Jaume Veciana's group at CSIC, in Barcelona, Spain, and is a member of the Fun-SMARTs project of ESF's SONS initiative. In her talk, which won the symposium's most original research work, sponsored by Advanced Materials, she explained the importance of multifunctional organic radicals, molecules with a spare electron, such as polychorotriphenylmethyl (PTM) radicals, which can undergo self-assembly into these organised layers.

Organic free radicals are usually highly reactive because of their spare electron. The moment they come into contact with another molecule the electron triggers an often-explosive chemical reaction. PTM radicals are different because their spare electron is shrouded by bulky chlorine atoms that hinder any explosive behaviour.

PTM radicals are often highly coloured and exhibit fluorescence in the red region of the visible spectrum, colour and fluorescence always have the potential to be exploited in optical electronics devices. Just as importantly, PTM radicals are also electroactive. This means they can be easily and reversibly reduced (or oxidized) to their positively or negatively charged (cationic or anionic) species. The different oxidised and reduced forms of PTM are different colours but neither oxidized nor reduced form is magnetic or fluorescent.

Mas-Torrent explained the relevance of this clutch of changeable properties for her self-assembled monolayers (SAMs). "The preparation of SAMs functionalised with PTM radicals on substrates results in multifunctional surfaces which are electrochemically, optically and magnetically active," she said, "We have demonstrated that these SAMs can be used as chemical and electrochemical redox switches with optical and magnetic responses."

Mas-Torrent and her colleagues did not stop with standalone SAMs. They have now added long hydrocarbon side-chains to their PTMs and found that these can also self-assemble on a graphite surface. They then studied behaviour at the interface between the graphite surface and a liquid and found that the self-assembly process is hierarchical and can give rise to complex three-dimensional ordered nanostructures that form double rows composed by a magnetic core of radicals surrounded by the side-chains.

By modifying a surface with molecules that can switch between two states - bistable compounds - the team hopes to open up the possibility of using these systems in memory devices. Surfaces functionalised with PTM radicals will allow them to fabricate multifunctional surfaces which can be interconverted between two states that exhibit different optical and magnetic properties that can be used as read-out mechanisms.

"The ultimate goal is to employ these radical building blocks to construct nanometre-scale devices addressed to specific applications,"

explains Mas-Torrent. By immobilizing them on specially prepared surfaces they could control and observe electrical and magnetic behaviour and in the future perhaps hook them up to input and output devices.

Key to the team's success is the collaborative possibilities opened up by the program. "Veciana's group started working on the functionalisation of surfaces after the collaboration initiated with the group of Reinhoudt from the MESA+ Research Institute in Twente within the SONS Programme," explains Mas-Torrent. "The combination of the expertise of surface functionalisation from Twente with the expertise of functional molecules of Barcelona emerged in our recent results focused on the functionalisation of different surfaces with multifunctional molecules (paramagnetic, electroactive and fluorescent) which can act as molecular switches," Mas-Torrent adds.

Mas-Torrent concedes that "much more fundamental research works need to be carried out" before applications become available. "We hope that in the future, molecular devices will play an important technological role in our society," she adds.

Source: ESF

Related stories:

Investigating the failure mechanisms of fuel cells will improve their durability
Fuel cells can be expensive and they typically don’t last as long as their internal combustion counterparts.
Researchers 'hammer' proteins
A team of chemists, led by an ASU professor, has come up with an elegant method for cutting proteins into more manageable pieces for analysis. The method, which uses industrial fillers commonly found in paint and light, could significantly aid the development of bioanalysis tools that identify human remains – and might aid ushering in the age of personalized medicine.
Titanium dioxide -- It slices, it dices ...
Chemists from the National Institute of Standards and Technology and Arizona State University have proposed an elegantly simple technique for cleaving proteins into convenient pieces for analysis. The prototype sample preparation method, detailed recently in Analytical Chemistry, uses ultraviolet light and titanium dioxide and could be ideal for new microfluidic “lab-on-a-chip” devices designed to rapidly analyze minute amount of biological samples.
Laser probe of a brain pigment's anatomy may offer insight into Parkinson's disease
In a finding that may offer clues about Parkinson's disease, a team led by Duke University researchers used a sophisticated laser system to gain evidence that a dark brown pigment that accumulates in people's brains consists of layers of two other pigments commonly found in hair.
High-performance computing aids calculations of combustion kinetics
Even though combustion provides 85 percent of the energy humans use, little is known about many of its most basic chemical reactions. Researchers in Argonne's Chemistry Division have brought together advances in theoretical chemical kinetics and high-performance computing to speed research in the chemistry of fuel combustion.
Researchers couple chemistry, large-scale computing for combustion calculations in a flash
Chemists at the U.S. Department of Energy's Argonne National Laboratory have brought together advances in theoretical chemical kinetics and high-performance computing to speed research in the chemistry of fuel combustion that may lead to cleaner more efficient combustion devices. The scientists developed a new approach to predict the rates of chemical reactions that greatly increases efficiency while maintaining accuracy, cutting costs and allowing research on larger molecules.
Scientists discover new method for creating high-yield single-walled carbon nanotubes
Cousins of the 1996 Nobel Prize-winning buckyball, carbon nanotubes have taken the nanotechnology industry by storm. Exhibiting extraordinary strength, flexibility and unique electrical, mechanical and optical properties, these hollow microscopic fibers are being integrated into numerous electronic and biological products—high-performance computer chips, combat jackets, bomb detectors and drug delivery devices for the treatment of diseases.
Newly detected air pollutant mimics damaging effects of cigarette smoke
A previously unrecognized group of air pollutants could have effects remarkably similar to harmful substances found in tobacco smoke, Louisiana scientists are reporting in a study scheduled for presentation today at the 236th National Meeting of the American Chemical Society. Inhaling those pollutants exposes the average person up to 300 times more free radicals daily than from smoking one cigarette, they added.

News discussion:

Nanotechnology news