Kitchen Gadget Inspires Scientist to Make More Effective Plastic Electronics

Fabricating single crystal organic field-effect transistors using ultra-thin polymer membrane for a gate insulator. In the upper row, the membrane is stretched over the transistor before vacuum is applied. In the lower row, the vacuum has been applied and the membrant is adhering to the organic crystal. Photos on the right are close-up views of the transistor, with the organic semiconductor crystal in red. (Credit: Credit: H. T. Yi, et. al.)

One day in 2010, Rutgers physicist Vitaly Podzorov watched a store employee showcase a kitchen gadget that vacuum-seals food in plastic. The demo stuck with him. The simple concept -- an airtight seal around pieces of food -- just might apply to his research: developing flexible electronics using lightweight organic semiconductors for products such as video displays or solar cells.

"Organic transistors, which switch or amplify electronic signals, hold promise for making video displays that bend like book pages or roll and unroll like posters," said Podzorov. But traditional methods of fabricating a part of the transistor known as the gate insulator often end up damaging the transistor's delicate semiconductor crystals.

Drawing inspiration from the food-storage gadget, Podzorov and his colleagues tried an experiment. They suspended a thin polymer membrane above the organic crystal and created a vacuum underneath, causing the membrane to collapse gently and evenly onto the crystal's surface. The result: a smooth, defect-free interface between the organic semiconductor and the gate insulator.

The researchers reported their success in the journal Advanced Materials. In the article,Podzorov and three colleagues describe how a single-crystal organic field effect transistor (OFET) made with this thin polymer gate insulator boosted electrical performance. The researchers further reported that they could remove and reapply membranes to the same crystal several times without degrading its surface.

Organic transistors electrically resemble silicon transistors in computer chips, but they are made of flexible carbon-based molecules that can be printed on sheets of plastic. Silicon transistors are made in rigid, brittle wafers of silicon.

The methods that scientists previously applied to organic transistor fabrication were based on silicon semiconductor processing, explained Podzorov, assistant professor in the Department of Physics and Astronomy, School of Arts and Sciences. These involved high temperatures, high-energy plasmas or chemical reactions, all of which could damage the delicate organic crystal surface and hinder the transistor's performance.

"People have tendencies to go with something they've known for a long time," he said. "In this case, it doesn't work right."

Podzorov's innovation builds upon a decade of Rutgers research in this field, including his invention of the first single crystal organic transistor in 2003. While his latest innovation is still a ways from commercial reality, he sees an immediate application in the classroom.

"Our technique takes 10 minutes," he said. "It should be exciting for students to actually build these devices and immediately see them work, all within one lab session."

Podzorov was actually trying to solve another problem when he first recalled the food packaging demo. He was thinking about how to protect organic crystals from airborne impurities when his lab shipped samples to collaborating scientists in California and overseas.

"We could place our samples between plastic sheets and pull a vacuum," he said. "Then I thought, 'why don't we try doing this for our gate insulator?'"

Funding for the research was provided by the U. S. Department of Energy and the Rutgers Institute for Advanced Materials and Devices for Nanotechnology. Collaborators in Podzorov's lab were postdoctoral researchers Hee Taek Yi and Yuanzhen Chen, and undergraduate student Krzysztof Czelen. The department's machine shop made a custom-designed vacuum chamber for the project

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Journal Reference:

1. H. T. Yi, Y. Chen, K. Czelen, V. Podzorov. Vacuum Lamination Approach to Fabrication of High-Performance Single-Crystal Organic Field-Effect Transistors. Advanced Materials, 2011; 23 (48): 5807 DOI:10.1002/adma.201103305

World's most efficient flexible organic light-emitting diodes created on plastic

ScienceDaily (Oct. 31, 2011) — Researchers in the University of Toronto's Department of Materials Science & Engineering have developed the world's most efficient organic light-emitting diodes (OLEDs) on plastic. This result enables a flexible form factor, not to mention a less costly, alternative to traditional OLED manufacturing, which currently relies on rigid glass.

The results are reported online in the latest issue of Nature Photonics.

OLEDs provide high-contrast and low-energy displays that are rapidly becoming the dominant technology for advanced electronic screens. They are already used in some cell phone and other smaller-scale applications.

Current state-of-the-art OLEDs are produced using heavy-metal doped glass in order to achieve high efficiency and brightness, which makes them expensive to manufacture, heavy, rigid and fragile.

"For years, the biggest excitement behind OLED technologies has been the potential to effectively produce them on flexible plastic," says Materials Science & Engineering Professor Zheng-Hong Lu, the Canada Research Chair (Tier I) in Organic Optoelectronics.

Using plastic can substantially reduce the cost of production, while providing designers with a more durable and flexible material to use in their products.

The research, which was supervised by Professor Lu and led by PhD Candidates Zhibin Wang and Michael G. Helander, demonstrated the first high-efficiency OLED on plastic. The performance of their device is comparable with the best glass-based OLEDs, while providing the benefits offered by using plastic.

"This discovery, unlocks the full potential of OLEDs, leading the way to energy-efficient, flexible and impact-resistant displays," says Professor Lu.

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Journal Reference:

Z. B. Wang, M. G. Helander, J. Qiu, D. P. Puzzo, M. T. Greiner, Z. M. Hudson, S. Wang, Z. W. Liu, Z. H. Lu. Unlocking the full potential of organic light-emitting diodes on flexible plastic. Nature Photonics, 2011; DOI: 10.1038/nphoton.2011.259

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Astronomers discover complex organic matter exists throughout the universe

ScienceDaily (Oct. 26, 2011) — Astronomers report in the journal Nature that organic compounds of unexpected complexity exist throughout the Universe. The results suggest that complex organic compounds are not the sole domain of life but can be made naturally by stars.

Prof. Sun Kwok and Dr. Yong Zhang of The University of Hong Kong show that an organic substance commonly found throughout the Universe contains a mixture of aromatic (ring-like) and aliphatic (chain-like) components. The compounds are so complex that their chemical structures resemble those of coal and petroleum. Since coal and oil are remnants of ancient life, this type of organic matter was thought to arise only from living organisms. The team's discovery suggests that complex organic compounds can be synthesized in space even when no life forms are present.

The researchers investigated an unsolved phenomenon: a set of infrared emissions detected in stars, interstellar space, and galaxies. These spectral signatures are known as "Unidentified Infrared Emission features." For over two decades, the most commonly accepted theory on the origin of these signatures has been that they come from simple organic molecules made of carbon and hydrogen atoms, called polycyclic aromatic hydrocarbon (PAH) molecules. From observations taken by the Infrared Space Observatory and the Spitzer Space Telescope, Kwok and Zhang showed that the astronomical spectra have features that cannot be explained by PAH molecules. Instead, the team proposes that the substances generating these infrared emissions have chemical structures that are much more complex. By analyzing spectra of star dust formed in exploding stars called novae, they show that stars are making these complex organic compounds on extremely short time scales of weeks.

Not only are stars producing this complex organic matter, they are also ejecting it into the general interstellar space, the region between stars. The work supports an earlier idea proposed by Kwok that old stars are molecular factories capable of manufacturing organic compounds. "Our work has shown that stars have no problem making complex organic compounds under near-vacuum conditions," says Kwok. "Theoretically, this is impossible, but observationally we can see it happening."

Most interestingly, this organic star dust is similar in structure to complex organic compounds found in meteorites. Since meteorites are remnants of the early Solar System, the findings raise the possibility that stars enriched the early Solar System with organic compounds. The early Earth was subjected to severe bombardments by comets and asteroids, which potentially could have carried organic star dust. Whether these delivered organic compounds played any role in the development of life on Earth remains an open question.

Prof. Sun Kwok is the Dean of Science and Chair Professor of Physics of the University of Hong Kong. He serves as Vice President of Division VI (interstellar matter) of the International Astronomical Union, and is the incoming Vice President of Commission 51 (bioastronomy) of the International Astronomical Union. He has published many books, including the recent book "Organic Matter in the Universe" (Wiley, 2011). Dr. Yong Zhang is a Research Assistant Professor at the University of Hong Kong. This work was supported by the Research Grants Council of Hong Kong.

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Journal Reference:

Sun Kwok, Yong Zhang. Mixed aromatic–aliphatic organic nanoparticles as carriers of unidentified infrared emission features. Nature, 2011; DOI: 10.1038/nature10542

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Meteorite holds clues to organic chemistry of early Earth

ScienceDaily (June 9, 2011) — Carbonaceous chondrites are a type of organic-rich meteorite that contain samples of the materials that took part in the creation of our planets nearly 4.6 billion years ago, including materials that were likely formed before our Solar System was created and may have been crucial to the formation of life on Earth. The complex suite of organic materials found in carbonaceous chondrites can vary substantially from meteorite to meteorite.

New research from Carnegie's Department of Terrestrial Magnetism and Geophysical Laboratory, published June 10 in Science, shows that most of these variations are the result of hydrothermal activity that took place within a few million years of the formation of the Solar System, when the meteorites were still part of larger parent bodies, likely asteroids.

Organic material in carbonaceous chondrites shares many characteristics with organic matter found in other primitive samples, including interplanetary dust particles, comet 81P/Wild-2, and Antarctic micrometeorites. It has been argued by some that this similarity indicates that organic material throughout the Solar System largely originated from a common source, possibly the interstellar medium.

A test of this common-source hypothesis stems from its requirement that the organic diversity within and among meteorites be due primarily to chemical and thermal processing that took place while the meteorites were parts of their parent bodies. In other words, there should be a relationship between the extent of hydrothermal alteration that a meteorite experienced and the chemistry of the organic material it contains.

If--as many have speculated--the organic material in meteorites had a role to play in the origin of life on Earth, the attraction of the common-source hypothesis is that the same organic material would have been delivered to all bodies in the Solar System. If the common source was the interstellar medium, then similar material would also be delivered to any forming planetary system.

The research team -- led by Christopher Herd of the University of Alberta, Canada, and including Carnegie's Conel Alexander, Larry Nittler, Frank Gyngard, George Cody, Marilyn Fogel, and Yoko Kebukawa -- studied four meteorite specimens from the shower of stones, produced by the breakup of a meteoroid as it entered the atmosphere, that fell on Tagish Lake in northern Canada in January 2000. The samples are considered very pristine, because they fell on a frozen lake, were collected without hand contact within a few days of landing and have remained frozen ever since.

The samples were processed and analyzed on the microscopic level using a variety of sophisticated techniques. Examination of their inorganic components indicated that the specimens had experienced large differences in the extent of hydrothermal alteration, prompting an in-depth examination of their organic material. The team demonstrated that the insoluble organic matter found in the samples has properties that span nearly the entire range found in all carbonaceous chondrites and that those properties correlate with other measures of the extent of parent body alteration. Their finding confirms that the diversity of this material is due to processing of a common precursor material in the asteroidal parent bodies.

The team found large concentrations of monocarboxylic acids, or MCAs, which are essential to biochemistry, in their Tagish Lake samples. They attributed the high level of these acids to the pristine nature of the samples, which have been preserved below zero degrees Celsius since they were recovered. There was variety in the types of MCAs, which they determined could also be due to alterations that took place on the parent bodies.

The samples also contained amino acids -- the essential-for-life organic building blocks used to create proteins. The types and abundances of amino acids contained in the samples are consistent with an extraterrestrial origin, and were clearly also influenced, albeit in a complex way, by the alteration histories of their host meteorites.

"Taken together these results indicate that the chemical and thermal processing common to the Tagish Lake meteorites likely occurred when the samples were part of a larger parent body that was created from the same raw materials that formed our Solar System," said Larry Nittler of Carnegie's DTM. "These samples can also provide important clues to the source of organic material, and life, on Earth."

Funding was provided by Natural Sciences and Engineering Research Council of Canada, Alberta Innovates, NASA (Astrobiology, including NASA Astrobiology Institute teams at the Carnegie Institution and the Goddard Center for Astrobiology; Origins of Solar Systems; Cosmochemistry and Postdoctoral Programs), the U.S. Office of Naval Research, Carnegie Institution for Science, Grant MacEwan University, and the Carnegie Institution of Canada. Some data was acquired at Advanced Light Source, which is supported by the Director of the Office of Science, Department of Energy, and by a W.M. Keck Foundation grant to the Carnegie Institution for Science.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Carnegie Institution, via EurekAlert!, a service of AAAS.

Journal Reference:

Christopher D. K. Herd, Alexandra Blinova, Danielle N. Simkus, Yongsong Huang, Rafael Tarozo, Conel M. O’D. Alexander, Frank Gyngard, Larry R. Nittler, George D. Cody, Marilyn L. Fogel, Yoko Kebukawa, A. L. David Kilcoyne, Robert W. Hilts, Greg F. Slater, Daniel P. Glavin, Jason P. Dworkin, Michael P. Callahan, Jamie E. Elsila, Bradley T. De Gregorio, Rhonda M. Stroud. Origin and Evolution of Prebiotic Organic Matter As Inferred from the Tagish Lake Meteorite. Science, 2011; 332 (6035): 1304-1307 DOI: 10.1126/science.1203290

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Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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Meteorite holds clues to organic chemistry of early Earth

ScienceDaily (June 9, 2011) — Carbonaceous chondrites are a type of organic-rich meteorite that contain samples of the materials that took part in the creation of our planets nearly 4.6 billion years ago, including materials that were likely formed before our Solar System was created and may have been crucial to the formation of life on Earth. The complex suite of organic materials found in carbonaceous chondrites can vary substantially from meteorite to meteorite.

New research from Carnegie's Department of Terrestrial Magnetism and Geophysical Laboratory, published June 10 in Science, shows that most of these variations are the result of hydrothermal activity that took place within a few million years of the formation of the Solar System, when the meteorites were still part of larger parent bodies, likely asteroids.

Organic material in carbonaceous chondrites shares many characteristics with organic matter found in other primitive samples, including interplanetary dust particles, comet 81P/Wild-2, and Antarctic micrometeorites. It has been argued by some that this similarity indicates that organic material throughout the Solar System largely originated from a common source, possibly the interstellar medium.

A test of this common-source hypothesis stems from its requirement that the organic diversity within and among meteorites be due primarily to chemical and thermal processing that took place while the meteorites were parts of their parent bodies. In other words, there should be a relationship between the extent of hydrothermal alteration that a meteorite experienced and the chemistry of the organic material it contains.

If--as many have speculated--the organic material in meteorites had a role to play in the origin of life on Earth, the attraction of the common-source hypothesis is that the same organic material would have been delivered to all bodies in the Solar System. If the common source was the interstellar medium, then similar material would also be delivered to any forming planetary system.

The research team -- led by Christopher Herd of the University of Alberta, Canada, and including Carnegie's Conel Alexander, Larry Nittler, Frank Gyngard, George Cody, Marilyn Fogel, and Yoko Kebukawa -- studied four meteorite specimens from the shower of stones, produced by the breakup of a meteoroid as it entered the atmosphere, that fell on Tagish Lake in northern Canada in January 2000. The samples are considered very pristine, because they fell on a frozen lake, were collected without hand contact within a few days of landing and have remained frozen ever since.

The samples were processed and analyzed on the microscopic level using a variety of sophisticated techniques. Examination of their inorganic components indicated that the specimens had experienced large differences in the extent of hydrothermal alteration, prompting an in-depth examination of their organic material. The team demonstrated that the insoluble organic matter found in the samples has properties that span nearly the entire range found in all carbonaceous chondrites and that those properties correlate with other measures of the extent of parent body alteration. Their finding confirms that the diversity of this material is due to processing of a common precursor material in the asteroidal parent bodies.

The team found large concentrations of monocarboxylic acids, or MCAs, which are essential to biochemistry, in their Tagish Lake samples. They attributed the high level of these acids to the pristine nature of the samples, which have been preserved below zero degrees Celsius since they were recovered. There was variety in the types of MCAs, which they determined could also be due to alterations that took place on the parent bodies.

The samples also contained amino acids -- the essential-for-life organic building blocks used to create proteins. The types and abundances of amino acids contained in the samples are consistent with an extraterrestrial origin, and were clearly also influenced, albeit in a complex way, by the alteration histories of their host meteorites.

"Taken together these results indicate that the chemical and thermal processing common to the Tagish Lake meteorites likely occurred when the samples were part of a larger parent body that was created from the same raw materials that formed our Solar System," said Larry Nittler of Carnegie's DTM. "These samples can also provide important clues to the source of organic material, and life, on Earth."

Funding was provided by Natural Sciences and Engineering Research Council of Canada, Alberta Innovates, NASA (Astrobiology, including NASA Astrobiology Institute teams at the Carnegie Institution and the Goddard Center for Astrobiology; Origins of Solar Systems; Cosmochemistry and Postdoctoral Programs), the U.S. Office of Naval Research, Carnegie Institution for Science, Grant MacEwan University, and the Carnegie Institution of Canada. Some data was acquired at Advanced Light Source, which is supported by the Director of the Office of Science, Department of Energy, and by a W.M. Keck Foundation grant to the Carnegie Institution for Science.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Carnegie Institution, via EurekAlert!, a service of AAAS.

Journal Reference:

Christopher D. K. Herd, Alexandra Blinova, Danielle N. Simkus, Yongsong Huang, Rafael Tarozo, Conel M. O’D. Alexander, Frank Gyngard, Larry R. Nittler, George D. Cody, Marilyn L. Fogel, Yoko Kebukawa, A. L. David Kilcoyne, Robert W. Hilts, Greg F. Slater, Daniel P. Glavin, Jason P. Dworkin, Michael P. Callahan, Jamie E. Elsila, Bradley T. De Gregorio, Rhonda M. Stroud. Origin and Evolution of Prebiotic Organic Matter As Inferred from the Tagish Lake Meteorite. Science, 2011; 332 (6035): 1304-1307 DOI: 10.1126/science.1203290

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Pentagonal tiles pave the way towards organic electronics

ScienceDaily (May 8, 2011) — New research paves way for the nanoscale self-assembly of organic building blocks, a promising new route towards the next generation of ultra-small electronic devices.

Ring-like molecules with unusual five-fold symmetry bind strongly to a copper surface, due to a substantial transfer of charge, but experience remarkably little difficulty in sideways diffusion, and exhibit surprisingly little interaction between neighbouring molecules. This unprecedented combination of features is ideal for the spontaneous creation of high-density stable thin films, comprising a pavement of these organic pentagonal tiles, with potential applications in computing, solar power and novel display technologies.

Currently, commercial electronics use a top-down approach, with the milling or etching away of inorganic material, such as silicon, to make a device smaller. For many years the computing power of a given size of computer chip has been doubling every eighteen months (a phenomenon known as Moore's law) but a limit in this growth is soon expected. At the same time, the efficiency of coupling electronic components to incoming or outgoing light (either in the generation of electricity from sunlight, or in the generation of light from electricity in flat-screen displays and lighting) is also fundamentally limited by the development of fabrication techniques at the nanometre scale (a nanometre being one billionth of a metre).

Researchers are therefore looking for ingenious solutions in the creation of ever smaller electronics. The field of nanotechnology is taking a bottom-up approach of creating electronics using naturally self-assembling organic components, such as polymers, which will be capable of spontaneously forming devices with the desired electronic or optical characteristics.

The latest findings are from scientists at the University of Cambridge and Rutgers University who are working on the development of new classes of organic thin films on surfaces. By studying the fundamental forces at play in self-assembling thin films, they are developing the knowledge that will allow them to tailor these films into molecular-scale organic-electronic devices, creating smaller components than would ever be possible with conventional fabrication techniques.

Dr Holly Hedgeland, of the Department of Physics at the University of Cambridge, one of the co-authors of the paper reporting the research, said: "With the semiconductor industry currently worth an estimated $249 billion per year there is a clear motivation towards a molecular scale understanding of innovative technologies that could come to replace those we use today."

It is not simply the electronic properties of a molecule on a surface that will control its potential to form part of a device, but also whether it will move by itself into the required structural configuration and remain stable in that position even if the device becomes heated in use.

Molecules that are strongly bound to the substrate with a high degree of transfer of charge offer a range of new possibilities, though little is currently known of their behaviour. A number of organic molecules, usually featuring carbon rings across which electronic charge can conduct, potentially demonstrate the right electronic properties, but the long-range forces which will govern their self-assembly during the first phases of growth often remain a mystery.

Now the interdisciplinary team based in the Departments of Physics and Chemistry at the University of Cambridge, and the Department of Chemistry and Chemical Biology at Rutgers University, have reported the first dynamical measurements for a new class of organic thin film where cyclopentadienyl molecules (C5H5) receive significant electronic charge from the surface, yet diffuse easily across the surface and show interactions with each other that are much weaker than would typically be expected for the amount of charge transferred.

Hedgeland explained: "By coupling the experimental helium spin echo technique with advanced first-principles calculations, we were able to study the dynamic behaviour of a cyclopentendienyl layer on a copper surface, and to deduce that the charge transfer between the metal and the organic molecule was occurring in a counter-intuitive sense."

Dr Marco Sacchi, of the Department of Chemistry at the University of Cambridge, who carried out the calculations that helped explain the startling new experimental results, said that "the key to the unique behavior of cyclopentadienyl lies in its pentagonal (five-fold) symmetry, which prevents it latching onto any one site within the triangular (three-fold) symmetry of the copper surface through directional covalent bonds, leaving it free to move easily from site to site; at the same time, its internal electronic structure is just one electron short of an extremely stable `aromatic' configuration, encouraging a high degree of charge transfer from the surface and creating a strong non-directional ionic bond."

The researchers' findings, reported in Physical Review Letters on May 6, highlight the potential of a new category of molecular adsorbate, which could fulfill all the criteria required for useful application.

Hedgeland concluded: "The unusual character of the charge transfer in this case prevents the large repulsive interactions between adjacent molecules that would otherwise have been expected, and hence should enable the formation of unusually high-density films. At the same time, the molecules remain highly mobile and yet strongly bound to the surface, with a large degree of thermal stability. In all, this is a combination of physical properties that offers huge potential benefit to the development of new classes of self-assembled organic films relevant for technological applications."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Cambridge.

Journal Reference:

H. Hedgeland, B. Lechner, F. Tuddenham, A. Jardine, W. Allison, J. Ellis, M. Sacchi, S. Jenkins, B. Hinch. Weak Intermolecular Interactions in an Ionically Bound Molecular Adsorbate: Cyclopentadienyl/Cu(111). Physical Review Letters, 2011; 106 (18) DOI: 10.1103/PhysRevLett.106.186101

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