Carbon Nanotubes Self-Assemble Into Tiny Transistors

Carbon nanotubes can be used to make very small electronic devices, but they are difficult to handle. University of Groningen (Netherlands) scientists, together with colleagues from the University of Wuppertal and IBM Zurich, have developed a method to select semiconducting nanotubes from a solution and make them self-assemble on a circuit of gold electrodes. The results look deceptively simple: a self-assembled transistor with nearly 100 percent purity and very high electron mobility. But it took ten years to get there. University of Groningen Professor of Photophysics and Optoelectronics Maria Antonietta Loi designed polymers which wrap themselves around specific carbon nanotubes in a solution of mixed tubes. Thiol side chains on the polymer bind the tubes to the gold electrodes, creating the resultant transistor.

polymer wrapped nanotube

In our previous work, we learned a lot about how polymers attach to specific carbon nanotubes, Loi explains. These nanotubes can be depicted as a rolled sheet of graphene, the two-dimensional form of carbon. ‘Depending on the way the sheets are rolled up, they have properties ranging from semiconductor to semi-metallic to metallic.’ Only the semiconductor tubes can be used to fabricate transistors, but the production process always results in a mixture.

We had the idea of using polymers with thiol side chains some time ago‘, says Loi. The idea was that as sulphur binds to metals, it will direct polymer-wrapped nanotubes towards gold electrodes. While Loi was working on the problem, IBM even patented the concept. ‘But there was a big problem in the IBM work: the polymers with thiols also attached to metallic nanotubes and included them in the transistors, which ruined them.’

Loi’s solution was to reduce the thiol content of the polymers, with the assistance of polymer chemists from the University of Wuppertal. ‘What we have now shown is that this concept of bottom-up assembly works: by using polymers with a low concentration of thiols, we can selectively bring semiconducting nanotubes from a solution onto a circuit.’ The sulphur-gold bond is strong, so the nanotubes are firmly fixed: enough even to stay there after sonication of the transistor in organic solvents.

Over the last years, we have created a library of polymers that select semiconducting nanotubes and developed a better understanding of how the structure and composition of the polymers influences which carbon nanotubes they select’, says Loi. The result is a cheap and scalable production method for nanotube electronics. So what is the future for this technology? Loi: ‘It is difficult to predict whether the industry will develop this idea, but we are working on improvements, and this will eventually bring the idea closer to the market.’

The results were published in the journal Advanced Materials on 5 April.

Artificial Molecules Revolutionize 3D Printing

Scientists at ETH Zurich and IBM Research Zurich have developed a new technique that enables for the first time the manufacture of complexly structured tiny objects joining together microspheres. The objects have a size of just a few micrometres and are produced in a modular fashion, making it possible to program their design in such a way that each component exhibits different physical properties. After fabrication, it is also very simple to bring the micro-objects into solution. This makes the new technique substantially different from micro 3D printing technology. With most of today’s micro 3D printing technologies, objects can only be manufactured if they consist of a single material, have a uniform structure and are attached to a surface during production.

3D printing process ETHArtificial molecules. The individual components are marked with different fluorescent dyes (molecule size: 2-7 micrometres; compilation of microscopic images)

To prepare the micro-objects, the ETH and IBM researchers use tiny spheres made from a polymer or silica as their building blocks, each with a diameter of approximately one micrometre and different physical properties. The scientists are able to control the particles and arrange them in the geometry and sequence they like.

The structures that are formed occupy an interesting niche in the size scale: they are much larger than your typical chemical or biochemical molecules, but much smaller than typical objects in the macroscopic world. “Depending on the perspective, it’s possible to speak of giant molecules or micro-objects,” says Lucio Isa, Professor for Interfaces, Soft matter and Assembly at ETH Zurich. He headed the research project together with Heiko Wolf, a scientist at IBM Research. “So far, no scientist has succeeded in fully controlling the sequence of individual components when producing artificial molecules on the micro scale,” says Isa.


Spray-on Solar Power

Pretty soon, powering your tablet could be as simple as wrapping it in cling wrap. Illan Kramer and colleagues from the University of Toronto (U of T) have just invented a new way to spray solar cells onto flexible surfaces using miniscule light-sensitive materials known as colloidal quantum dots (CQDs)—a major step toward making spray-on solar cells easy and cheap to manufacture. Solar-sensitive CQDs printed onto a flexible film could be used to coat all kinds of weirdly shaped surfaces, from patio furniture to an airplane’s wing. A surface the size of your car’s roof wrapped with CQD-coated film would produce enough energy to power three 100-Watt light bulbs — or 24 compact fluorescents. He calls his system sprayLD, a play on the manufacturing process called ALD, short for atomic layer deposition, in which materials are laid down on a surface one atom-thickness at a time.
In two recent papers in the journals Advanced Materials and Applied Physics Letters, Kramer showed that the sprayLD method can be used on flexible materials without any major loss in solar-cell efficiency. Kramer built his sprayLD device using parts that are readily available and rather affordable—he sourced a spray nozzle used in steel mills to cool steel with a fine mist of water, and a few regular air brushes from an art store.
spray-on solar cells
My dream is that one day you’ll have two technicians with Ghostbusters backpacks come to your house and spray your roof,” said Kramer, a post-doctoral fellow with The Edward S. Rogers Sr. Department of Electrical & Computer Engineering at the University of Toronto and IBM Canada’s Research and Development Centre.
This is something you can build in a Junkyard Wars fashion, which is basically how we did it,” said Kramer.

“As quantum dot solar technology advances rapidly in performance, it’s important to determine how to scale them and make this new class of solar technologies manufacturable,” said Professor Ted Sargent (ECE), vice dean, research in the Faculty of Applied Science & Engineering at University of Toronto and Kramer’s supervisor. “We were thrilled when this attractively manufacturable spray-coating process also led to superior performance devices showing improved control and purity.”


Low-Cost, Ultra Fast DNA Reader

A team of scientists from Arizona State University’s Biodesign Institute and IBM’s T.J. Watson Research Center have developed a prototype DNA reader that could make whole genome profiling an everyday practice in medicine.
DNA readerOur goal is to put cheap, simple and powerful DNA and protein diagnostic devices into every single doctor’s office,” said Stuart Lindsay, an ASU physics professor and director of Biodesign’s Center for Single Molecule Biophysics. Such technology could help usher in the age of personalized medicine, where information from an individual’s complete DNA and protein profiles could be used to design treatments specific to their individual makeup.

The device is sensitive enough to distinguish the individual chemical bases of DNA (known by their abbreviated letters of A, C, T or G) when they are pumped past the reading head.

Proof-of-concept was demonstrated, by using solutions of the individual DNA bases, which gave clear signals sensitive enough to detect tiny amounts of DNA (nanomolar concentrations), even better than today’s state-of-the-art, so called next-generation DNA sequencing technology. Making the solid-state device is just like making a sandwich, just with ultra high-tech semiconductor tools used to slice and stack the atomic-sized layers of meats and cheeses like the butcher shop’s block. The secret is to make slice and stack the layers just so, to turn the chemical information of the DNA into a change in the electrical signal.


How To Transmit Massive Amounts Of Data With Very Low Power Consumption

A team of IBM researchers working on a U.S. Defense Advanced Research Projects Agency (DARPA)-funded program have found a way to transmit massive amounts of data with unprecedentedly low power consumption. Scientists predict that the supercomputers of the future—so-called “exascale computers“—will enable them to model the global climate, run molecular-level simulations of entire cells, design nanostructures, and more.

datasWe envision machines reaching the exascale mark around 2020, but a great deal of research must be done to make this possible,” says Jonathan E. Proesel, a research staff member at the IBM T. J. Watson Research Center in Yorktown Heights, N.Y. To reach that mark, researchers must develop a way to quickly move massive amounts of data within the supercomputer while keeping power consumption in check.


Stretchable Electronics Are The Future Of Mobile Phones

According to the University of Delaware‘s Professor Bingqing Wei, stretchable electronics are the future of mobile electronics, leading giants such as IBM, Sony and Nokia to incorporate the technology into their products.
Beyond traditional electronics, potential stretchable applications include biomedical, wearable, portable and sensory devices, such as cyber skin for robotic devices and implantable electronics. All established classes of high-performance electronics exploit single-crystal inorganic materials, such as silicon or gallium arsenide, in forms (i.e., semiconductor wafers) that are fundamentally rigid and planar. The human body is, by contrast, soft and curvilinear. This mismatch in properties hinders the development of devices capable of intimate, conformal integration with biological tissues, for applications ranging from basic measurement of electrophysiological signals, to delivery of advanced therapies, to establishment of human-machine interfaces. One envisioned solution involves the use of organic electronic materials, whose flexible properties have generated interest in them for potential use in paper-like displays, solar cell, and other types of consumer electronic devices.

Advances in soft and stretchable substrates and elastomeric materials have given rise to an entirely new field,” says Wei, a mechanical engineering professor at UD.
But even if scientists can engineer stretchable electronics — what about their energy source?
Rechargeable and stretchable energy storage devices, also known as supercapacitors, are urgently needed to complement advances currently being made in flexible electronics,” explains Wei.

Terrorism Against Science

A loose coalition of eco-anarchist groups is increasingly launching violent attacks on scientists. A group calling itself the Olga Cell of the Informal Anarchist Federation International Revolutionary Front has claimed responsibility for the non-fatal shooting of a nuclear-engineering executive on 7 May in Genoa, Italy. The same group attempted to bomb IBM’s nanotechnology laboratory in Switzerland in 2010; and has ties with a group responsible for at least four bomb attacks on nanotechnology facilities in Mexico

Science in centuries past promised us a golden age, but it is pushing us towards self-destruction and total slavery,” explains the Olga Cell  in a letter and continues: “With this action of ours, we return to you a tiny part of the suffering that you, man of science, are pouring into this world.” The group also threatened to carry out further attacks. In August 2011, a group called Individuals Tending Towards Savagery sent a parcel bomb that wounded two nanotechnology researchers at the Monterrey Institute of Technology. One received burns to his legs and a perforated eardrum and the other had his lung pierced by shrapnel (G. Herrera Corral Nature 476,373; 2011). The package contained enough explosive to collapse part of the building, according to police, but failed to detonate properly.Earlier that year, the same group sent two bombs to the nanotechnology facility at the Polytechnic University of the Valley of Mexico


A 5 millions times smaller hard drive

Scientists from IBM and the German Center for Free-Electron Laser Science (CFEL) have built the world's smallest magnetic data storage unit. It uses just twelve atoms per bit, the basic unit of information, and squeezes a whole byte (8 bit) into as few as 96 atoms. A modern hard drive, for comparison, still needs more than half a billion atoms per byte. The team present their work in the weekly journal Science (13 January 2012). CFEL is a joint venture of the research centre Deutsches Elektronen-Synchrotron DESY in Hamburg, the Max-Planck-Society (MPG) and the University of Hamburg "With CFEL the partners have established an innovative institution on the DESY campus, delivering top-level research across a broad spectrum of disciplines," says DESY research director Edgar Weckert.



 An illustration of I.B.M.'s technique for storing data on a single atom. An iron atom on a copper surface could store a single bit of binary data, with "0" or "1" indicated by the orientation of the atom's magnetic field.