Sunday, October 2, 2011

New hybrid carbon material discovered

A new hybrid carbon material, which combines graphene and nanotubes in the form of graphene nanoribbons encapsulated into single-walled carbon nanotubes (GNR@SWNTs) -- has been discovered by researchers from Aalto University in Finland and Umea University in Sweden.

Carbon nanotubes and graphene materials have attracted enormous interest from a broad range of specialists.

"We came up with the idea to create a novel hybrid material, which combines two most fascinating carbon nanomaterials -- single-walled carbon nanotubes and grapheme," says Dr. Albert Nasibulin from Aalto University.

SWNTs have a hollow space inside, which was used in this study as an 'one-dimensional' chemical reactor. An intriguing property of this space is that chemical reactions occur differently compared to the bulk 3-D conditions. Large polyaromatic hydrocarbon molecules (coronene and perylene), which can be imagined as small pieces of graphene, were used as building blocks to produce long and narrow graphene nanoribbons inside the nanotubes.

It was found that the shape of encapsulated graphene nanoribbons can be modified by using different kinds of polyaromatic hydrocarbon molecules. Nanoribbons can be either metallic or semiconductor depending on their width and type. Interestingly, SWNTs can also be metallic, semiconducting (depending on their chirality) or insulating when chemically modified.

This creates enormous potential for a wide range of applications: now it is possible to prepare GNR@SWNT in all possible combinations. For example, metallic nanoribbon inside insulating nanotube can be considered as the thinnest insulated nanowire. Nanoribbons can be used directly inside of SWNTs to generate light (e.g., as light emitting diodes), which will easily go through nanotubes and GNRs and by using of existing energy barrier will became a nano-lamp. Semiconducting nanoribbons can be used for transistor or solar cell applications. Metallic-metallic combination is in fact a new kind of coaxial nanocables (widely used as transmitters of radio signals) in nanosize since the nanoribbons are not connected with nanotubes due to hydrogen atoms, which occupy all the edges of nanoribbons.

"Precise control of the width and angle of the graphene nanoribbons will help assembly materials based on graphene with strict control of the band gap. Such control is not possible for a macroscopic graphene, obtained by traditional technology," says Dr. Ilya Anoshkin.

The method of GNR@SWNT synthesis is very simple, easily scalable and allows to obtain almost 100% filling of tubes with nanoribbons. As it follows from theoretical results included in the paper, graphene nanoribbons should keep their unique properties inside of nanotubes while protected from environment by encapsulation and aligned within bundles of SWNTs.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Aalto University, via AlphaGalileo.

Journal Reference:

Alexandr V. Talyzin, Ilya V. Anoshkin, Arkady V. Krasheninnikov, Risto M. Nieminen, Albert G. Nasibulin, Hua Jiang, Esko I. Kauppinen. Synthesis of Graphene Nanoribbons Encapsulated in Single-Walled Carbon Nanotubes. Nano Letters, 2011; 110902093500003 DOI: 10.1021/nl2024678

Blood vessels from your printer?

 Researchers have been working at growing tissue and organs in the laboratory for a long time. Today, tissue engineering enables us to build up artificial tissue, although science still hasn't been successful with larger organs. Now, researchers at Fraunhofer are applying new techniques and materials to come up with artificial blood vessels in their BioRap project that will be able to supply necessary nutrients to artificial tissue and maybe even complex organs in the future.

They are exhibiting their findings at the Biotechnica Fair that will be taking place in Hannover, Germany on October 11-13.

There were more than 11,000 people on the waiting list for organ transplantation in Germany alone at the beginning of this year, although on the average hardly half as many transplantations are performed. The aim of tissue engineering is to create organs in the laboratory for opening up new opportunities in this field. Unfortunately, researchers have still not been able to supply artificial tissue with nutrients because they do not have the necessary vascular system.

Five Fraunhofer-institutes joined forces in 2009 to come up with biocompatible artificial blood vessels. It seemed practically impossible to build structures such as capillary vessels that are so small and complex, especially the branches and spaces in between. But production engineering came to the rescue because rapid prototyping makes it possible to build workpieces specifically according to any complex 3-D model. Now, scientists at Fraunhofer are working on transferring this technology to the generation of tiny biomaterial structures by combining two different techniques: the 3-D printing technology established in rapid prototyping and multiphoton polymerization developed in polymer science.

Successful Combination

A 3-D inkjet printer can generate 3-dimensional solids from a wide variety of materials very quickly. It applies the material in layers of defined shape and these layers are chemically bonded by UV radiation. This already creates microstructures, but 3-D printing technology is still too imprecise for the fine structures of capillary vessels. This is why these researchers combine this technology with two-photon polymerization. Brief but intensive laser impulses impact the material and stimulate the molecules in a very small focus point so that crosslinking of the molecules occurs. The material becomes an elastic solid, due to the properties of the precursor molecules that have been adjusted by the chemists in the project team. In this way highly precise, elastic structures are built according to a 3-dimensional building plan. Dr. Günter Tovar is the project manager at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB based in Stuttgart.

When ink becomes an artificial vessel system

You have to have the right material to manufacture 3-dimensional elastic solids. This is the reason why the researchers came up with special inks because printing technology itself calls for very specific properties. The later blood vessels have to be flexible and elastic and interact with the natural tissue. Therefore, the synthetic tubes are biofunctionalized so that living body cells can dock onto them. The scientists integrate modified biomolecules -- such as heparin and anchor peptides -- into the inside walls. They also develop inks made of hybrid materials that contain a mixture of synthetic polymers and biomolecules right from the beginning. The second step is where endothelial cells that form the innermost wall layer of each vessel in the body can attach themselves in the tube systems. Günter Tovar points out that "the lining is important to make sure that the components of the blood do not stick, but are transported onwards." The vessel can only work in the same fashion as its natural model to direct nutrients to their destination if we can establish an entire layer of living cells.

Opportunities for Medicine

The virtual simulation of the finished workpieces is just as significant for project success as the new materials and production techniques. Researchers have to precisely calculate the design of these structures and the course of the vascular systems to ensure optimum flow speeds while preventing back-ups. The scientists at Fraunhofer are still at the dawn of this entirely new technology for designing elastic 3-dimensionally shaped biomaterials, although this technology offers a whole series of opportunities for further development. Günter Tovar acknowledges "we are establishing a basis for applying rapid prototyping to elastic and organic biomaterials. The vascular systems illustrate very dramatically what opportunities this technology has to offer, but that's definitely not the only thing possible." One example would be building up completely artificial organs based on a circulation system with blood vessels created in this fashion to supply them with nutrients. They are still not suited for transplantations, but the complex of organs can be used as a test system to replace animal experiments. It would also be conceivable to treat bypass patients with artificial vessels. In any event, it will take a long time until we will actually be able to implant organs from the laboratory with their own blood vessels.

This is a project that the Fraunhofer Institute for Applied Polymer Research IAP in Potsdam, Germany, the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart, Germany, the Fraunhofer Institute for Laser Technology ILT in Aachen, Germany, the Fraunhofer Institute for Manufacturing Engineering and Automation IPA in Stuttgart, Germany and the Fraunhofer Institute for Material Mechanics IWM in Freiburg, Germany are all participating in. They are exhibiting a large model of an artificial blood vessel printed with conventional with rapid prototyping technologies and samples of their current developments in Hall 9, Stand D10 at the Biotechnica Fair.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Fraunhofer-Gesellschaft.

Fast switching and printable transistor invented

 A fully functional, fast switching and printable transistor in cheap plastic is invented by researcher Lars Herlogsson, Linkoping University in Sweden.

All six articles in his doctoral thesis were recently published in journal Advanced Materials.

The thesis claims that with the help of polymers, plastics, which are already manufactured on a large scale, it is possible to manufacture transistors that are fast and can run on small printed batteries, where the drive voltage is around 1 volt.

They are particularly suitable for printed electronics.

The transistor is made up of two polymers, one of which acts as a semiconductor and the other as an electrolyte; a substance containing mobile charged ions that controls the current flowing through the transistor.

Polymers consist of linked chains of molecules. Thanks to the fact that one type of charged particle in the electrolyte, be it positive or negative ions, binds to the polymer chain in the semiconducting polymer. The active layer, in which the electric field is concentrated in the electrolyte, becomes very thin (1 nanometre) irrespective of the thickness of the electrolyte layer.

Whether it is a negative or positive ion that binds depends on whether it is a transistor that is hole-conducting (p-channel) or if it is electron-conducting (n-channel).

The thin active layer permits the use of very low driving voltages. By combining p- and n-channel transistors, Lars Herlogsson has constructed complementary circuits, CMOS circuits, which reduces the power consumption.

"This is robust CMOS technology which allows for very low drive voltages, and besides that, it is well suited to printed electronics," he says.

To achieve these low drive voltages using conventional technology would require nanometre thin layers. Printing such thin layers is impossible because the printing surface on paper or plastic film is typically rough. However, printing a 100-nanometre thick layer, as in this case, is possible using conventional printing techniques.

The idea of creating a thin active layer also impressed electronics Professor Christer Svensson, now emeritus of the examining committee.

"A scientifically very neat job, an intelligent idea that he clearly showed works in reality. There may be applications for this type of electronics such as in large TV screens where silicon is unable to compete," Svensson says.

The focus of Lars Herlogssons thesis has been to produce a material system for polymer-based organic transistors that can be printed at a reasonable price. The result is a transistor that within traditional electronics is called a field-effect transistor. Four of the thesis articles are related to just that, but the other two articles are related to the following:

one addresses woven electronics where the organic electrolyte transistors are embedded in the intersections between textile microfibers.The other shows how to produce an organic field-effect transistor with a drop of water as the electrolyte.

All of the six articles in the dissertation have been published in the scientific journal Advanced Materials.

Now, after spending years on research, Lars Herlogsson has taken a step closer to production. September 1, he began working at the company Thin Film Electronics in Linkoping to develop inexpensive printed memories.

"As scientists, our task is to push the boundaries and show what is practical and possible. Industry can produce the organic electronics better than we can and there are many talented plastic electronics companies, says Magnus Berggren, Professor of organic electronics at Linkoping University.

Thesis: Electrolyte-Gated Organic Thin-Film Transistors, Lars Herlogsson, Department of Science and Technology, Linköping University, Campus Norrköping, 2011

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Linkoeping Universitet, via AlphaGalileo.

Journal Reference:

Loig Kergoat, Lars Herlogsson, Daniele Braga, Benoit Piro, Minh-Chau Pham, Xavier Crispin, Magnus Berggren, Gilles Horowitz. A Water-Gate Organic Field-Effect Transistor. Advanced Materials, 2010; 22 (23): 2565 DOI: 10.1002/adma.200904163

'Synthetic biology' could replace oil for chemical industry

 Vats of blue-green algae could one day replace oil wells in producing raw materials for the chemical industry, a UC Davis chemist predicts.

Shota Atsumi, an assistant professor of chemistry, is using "synthetic biology" to create cyanobacteria, or blue-green algae, that convert carbon dioxide in the air into complex hydrocarbons, all powered by sunlight.

Cyanobacteria are single-celled organisms that, like green plants, can use sunlight to turn carbon dioxide and water into sugars and other carbohydrates.

The U.S. Department of Energy has set a goal of obtaining a quarter of industrial chemicals from biological processes by 2025. Today, 99 percent of the raw materials used to make paint, plastics, fertilizers, pharmaceuticals and other chemical products come from petroleum or natural gas, according to Atsumi.

While some chemicals, such as biofuels, can be obtained from converted plant material, plants are relatively slow to grow, and using farms to grow fuel takes arable land out of food production.

Instead, Atsumi is engineering cyanobacteria to make chemicals they do not make in nature. By carefully analyzing genes in these and other organisms, his team will assemble artificial synthetic pathways and put them into living cells.

"We can use genes as building blocks to create these new functions," Atsumi said.

The work is supported by a contract from Asahi Kasei, a major Japanese chemical manufacturer.

Story Source:

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