Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Pioneering Path to Electrical Conductivity in ‘Tinker Toy’ Materials to Appear in Science

11.12.2013
Sandia National Laboratories researchers have devised a novel way to realize electrical conductivity in metal-organic framework (MOF) materials, a development that could have profound implications for the future of electronics, sensors, energy conversion and energy storage.

A paper to appear in Science magazine, “Tunable Electrical Conductivity in Metal-Organic Framework Thin-Film Devices,” debuts in the Dec. 5 edition of Science Express.


Dino Vournas, Sandia National Labs

Sandia National Laboratories researchers Mark Allendorf, left, Alec Talin, center, and Francois Leonard measure the conductivity of a metal-organic framework (MOF) device. As described in a paper published in Science magazine, the team developed a technique that increases the electrical conductivity of one MOF by over six orders of magnitude.

The paper — co-authored by a group of Sandia researchers and collaborators at the National Institute of Standards and Technology (NIST) — describes a technique that experiments show successfully increases the electrical conductivity of one MOF by over six orders of magnitude.

“Fundamentally, this sheds enormous light on the conduction process in these materials,” said Alec Talin, a material scientist at Sandia and the paper’s lead author.

Applications for electrically conducting MOFs, said Sandia senior scientist Mark Allendorf, include chemical sensing, medical diagnostics, energy harvesting and storage and microelectronics.

MOFs: “tinker toys” for chemists

Materials researchers have considered MOF materials primarily for use in gas storage, drug delivery and other conventional applications for porous materials. Their crystalline structure, which resembles molecular scaffolding, consists of rigid organic molecules linked together by metal ions. This hybrid of inorganic and organic components produces an unusual combination of properties: nanoporosity, ultrahigh surface areas and remarkable thermal stability, which are attractive to chemists seeking novel materials that combine the superior performance of traditional inorganic semiconductors with the low cost and ease of fabrication typical of conducting organic polymers.

Allendorf, a chemist and MOF expert who called the research findings the most exciting development in his 28-year Sandia career, likens them to “tinker toys” for chemists.

“When you imagine the ‘tinker toys’ we played with as children, you recall they are essentially wooden balls with holes that you can link together with sticks,” Allendorf explained. “MOFs work the same way, only you substitute metal ions for the balls and organic molecules for the sticks.”

The resulting open space within the scaffolding can be filled with guest molecules, which gave Sandia’s Talin the idea to use the pore to make the MOFs electrically conducting.

“Importantly, MOFs possess a characteristic of molecules that allows us to adapt their properties to a specific application: we can perform chemistry on them, unlike traditional inorganic electronic materials, such as silicon and copper,” said Talin. Molecules, he said, represent the “ultimate, small-scale unit” at which electronic devices can be made. They are so difficult to manipulate and organize, however, that practical “molecular electronics” have not been realized. “How you connect to molecules, where you place them — those issues have consistently perplexed materials scientists,” said Talin.

The power of empty space

So he considered a different approach. “With MOFs, we can get around this problem by using the nanopores to organize molecules. The trick is to pick the right kind of molecule, so that it binds to and interacts with the entire framework.” Some MOFs, says Talin, have empty holes in the tinker-toy balls that can bind molecules that infiltrate the pores.

“This isn’t like silicon, which can’t change its electrical properties,” Talin said. “You can add tiny amounts of dopants to silicon or introduce other impurities, but with our approach, you suddenly have the potential to tailor the material to achieve exactly the properties you want. This is the beauty of molecular electronics.”

To test their hypothesis, Sandia and NIST’s researchers added a molecule known as tetracyanoquinodimethane, or TCNQ, to their framework. First, they took a substrate with platinum electrodes patterned on its surface and coated it with a thin film of the MOF. The substrate was then dipped in a solution containing the TCNQ molecule, which they knew would seep into the MOF’s tiny pores. The MOF film containing the TCNQ bridged the electrode connection points, which then could be connected to a current meter for measuring.

“Frankly, I thought it would never work,” said Allendorf. “But that’s the great thing about science: being wrong can be a good thing.”

The results are in, and they are good

The research team found that the MOF materials were conducting, though at relatively small quantities at first. “It was clear that something good was happening, so we were very excited,” said Allendorf.

The experiment was repeated several times with slight but important improvements in film quality achieved by optimizing the laboratory fabrication process.

“Conditions matter, and we had to be very deliberate in how we prepared the framework to accept the guest molecule,” said Allendorf. Removing the water and excess solvent from the film is no trivial matter, he said. The research team fine-tuned the process over the course of several months and, in doing so, began to see large leaps in electrical conductivity.

“The increase was massive,” said Talin. The conductivity in the material, he says, is now a million times higher than that of the starting material, and a thousand times higher than anything previously reported using a metal-organic framework.

The researchers plan on patenting their approach and also hope to land additional funding in order to experiment with other guest molecules.

Keeping up with Moore’s Law and other applications

“The overwhelming success of this project opens a whole new way to design electrically active materials,” said Talin. Organic materials, he pointed out, offer low costs and mechanical flexibility. “There are probably hundreds of potential applications for this work that come into play, such as breath analysis and microelectronics,” he said.

The ability to make smaller and faster electronic devices to keep up with Moore’s Law has always been a motivator in the field of molecular electronics, Allendorf said. MOFs have the potential to create molecular electronic devices on the scale of their pore dimensions, or approximately 1 nanometer.

Solar technology is another potential application, said Allendorf, and the Department of Energy’s Office of Energy Efficiency and Renewable Energy funded some of the initial research. “With electrically conducting MOFs, we might very well be able to combine the high efficiencies achievable with traditional inorganic thin film materials such as polycrystalline silicon with the low cost and flexibility aspects of organic photovoltaics,” he said.

“Our next step needs to be the exploration of other hosts and guest molecules,” said Talin. “We’d like to experiment with different MOF structures and different organic molecules to see if new behavior emerges. We want to see where this new learning takes us.”

Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corp., for the U.S. Department of Energy’s National Nuclear Security Administration. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies and economic competitiveness.

Sandia news media contact: Mike Janes, mejanes@sandia.gov, (925) 294-2447

Mike Janes | Newswise
Further information:
http://www.sandia.gov

More articles from Materials Sciences:

nachricht A new tool for discovering nanoporous materials
23.05.2017 | Ecole Polytechnique Fédérale de Lausanne

nachricht Did you know that packaging is becoming intelligent through flash systems?
23.05.2017 | Heraeus Noblelight GmbH

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Can the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

How herpesviruses win the footrace against the immune system

26.05.2017 | Life Sciences

Water forms 'spine of hydration' around DNA, group finds

26.05.2017 | Life Sciences

First Juno science results supported by University of Leicester's Jupiter 'forecast'

26.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>