#A new dimension for integrated circuits: 3-D nanomagnetic logic Electrical engineers at the Technical University Munich (TUM) have demonstrated a new kind of building block for digital integrated circuits.
Their experiments show that future computer chips could be based on three-dimensional arrangements of nanometer scale magnets instead of transistors.
As the main enabling technology of the semiconductor industry CMOS fabrication of silicon chips approaches fundamental limits, the TUM researchers and collaborators at the University of Notre dame are exploring"magnetic computing"as an alternative.
They report their latest results in the journal Nanotechnology. In a 3d stack of nanomagnets, the researchers have implemented a so-called majority logic gate
which could serve as a programmable switch in a digital circuit. They explain the underlying principle with a simple illustration:
Think of the way ordinary bar magnets behave when you bring them near each other, with opposite poles attracting
and like poles repelling each other. Now imagine bringing several bar magnets together and holding all but one in a fixed position.
Their magnetic fields can be thought of as being coupled into one, and the"north-south"polarity of the magnet that is free to flip will be determined by the orientation of the majority of fixed magnets.
Gates made from field-coupled nanomagnets work in an analogous way, with the reversal of polarity representing a switch between Boolean logic states,
the binary digits 1 and 0. In the 3d majority gate reported by the TUM-Notre dame team,
the state of the device is determined by three input magnets, one of which sits 60 nanometers below the other two,
and is read out by a single output magnet. This work builds on capabilities the collaborators have developed over several years,
ranging from sophisticated simulations of magnetic behavior to innovative fabrication and measuring techniques. It also represents not an end point but a milestone in a series of advances.
For example, they reported the world's first"domain wall gate"at last year's International Electron Devices Meeting.
The scientists use focused ion-beam irradation to change the magnetic properties of sharply defined spots on the device.
So-called domain walls generated there are able to flow through magnetic wires under the control of surrounding nanomagnets.
This 2d device, TUM doctoral candidate Stephan Breitkreutz explains, "enables signal routing, buffering, and synchronization in magnetic circuits, similar to latches in electrical integrated circuits."
"All players in the semiconductor business benefit from one industry-wide cooperative effort: developing long-range"roadmaps"that chart potential pathways to common technological goals.
In the most recent issue of the International Technology Roadmap for Semiconductors, nanomagnetic logic is given serious consideration among a diverse zoo of"emerging research devices."
"Magnetic circuits are nonvolatile, meaning they don't need power to remember what state they are in.
Extremely low energy consumption is one of their most promising characteristics. They also can operate at room temperature
and resist radiation. The potential to pack more gates onto a chip is especially important.
Nanomagnetic logic can allow very dense packing, for several reasons. The most basic building blocks, the individual nanomagnets, are comparable in size to individual transistors.
Furthermore, where transistors require contacts and wiring, nanomagnets operate purely with coupling fields. Also, in building CMOS and nanomagnetic devices that have the same function for example
a so-called full-adder it can take fewer magnets than transistors to get the job done.
Finally, the potential to break out of the 2d design space with stacks of 3d devices makes nanomagnetic logic competitive.
TUM doctoral candidate Irina Eichwald, lead author of the Nanotechnology paper, explains:""The 3d majority gate demonstrates that magnetic computing can be exploited in all three dimensions,
in order to realize monolithic, sequentially stacked magnetic circuits promising better scalability and improved packing density.""""It is a big challenge to compete with silicon CMOS circuits,
"adds Dr. Markus Becherer, leader of the TUM research group within the Institute for Technical Electronics."
"However, there might be applications where the nonvolatile, ultralow-power operation and high integration density offered by 3d nanomagnetic circuits give them an edge
#Blades of grass inspire advance in organic solar cells Using a biomimicking analog of one of nature's most efficient light-harvesting structures blades of grass an international research team led by Alejandro Briseno of the University of Massachusetts Amherst
has taken a major step in developing long-sought polymer architecture to boost power-conversion efficiency of light to electricity for use in electronic devices.
Briseno with colleagues and graduate students at UMASS Amherst and others at Stanford university and Dresden University of Technology Germany report in the current issue of Nano Letters that by using single-crystalline organic nanopillars
or nanograss they found a way to get around dead ends or discontinuous pathways that pose a serious drawback when using blended systems known as bulk heterojunction donor-acceptor or positive-negative (p-n) junctions for harvesting energy in organic solar cells.
Briseno's research group is one of very few in the world to design and grow organic single-crystal p-n junctions.
He says This work is a major advancement in the field of organic solar cells because we have developed
and converting it to electricity. The breakthrough in morphology control should have widespread use in solar cells batteries
and vertical transistors he adds. Briseno explains: For decades scientists and engineers have placed great effort in trying to control the morphology of p-n junction interfaces in organic solar cells.
We report here that we have developed at last the ideal architecture composed of organic single-crystal vertical nanopillars.
Nanopillars are engineered nanoscale surfaces with billions of organic posts that resemble blades of grass and like grass blades they are particularly effective at converting light to energy.
The advance not only addresses the problem of dead ends or discontinuous pathways that make for inefficient energy transfer
but it also solves some instability problems where the materials in mixed blends of polymers tend to lose their phase-separated behavior over time degrading energy transfer the polymer chemist says.
Also materials in blended systems tend to be amorphous to semi-crystalline at best and this is a disadvantage
since charge transport is more efficient in highly crystalline systems. Specifically to control the molecular orientation
and packing at electrode surfaces the team combined knowledge about graphene and organic crystals. Though it was difficult Briseno says they managed to get the necessary compounds to stack like coins.
Stacked compounds are ideal for charge transport since this configuration has the largest charge transport anisotropy.
In this case the anisotropy is along the nanopillar perpendicular to the substrate. Briseno says The biggest challenge in producing this architecture was finding the appropriate substrate that would enable the molecules to stack vertically.
when an undergraduate chose the wrong substrate to grow crystals on. For over a week the student was growing vertical crystals
and we didn't even realize until we imaged the surface of the substrate with a scanning electron microscope.
We were shocked to see little crystals standing upright! We ultimately optimized the conditions and determined the mechanism of crystallization the polymer chemist adds.
Vertical nanopillars are ideal geometries for getting around these challenges Briseno says because charge separation/collection is most efficient perpendicular to the plastic device.
In this case our nanopillars highly resemble nanograss. Our systems share similar attributes of grass such as high density array system vertical orientations
and the ability to efficiently convert light into energy. The technique is simple inexpensive and applicable to a library of donor
and acceptor compounds that are commercially available he notes. We envision that our nanopillar solar cells will appeal to low-end energy applications such as gadgets toys sensors and short lifetime disposable devices s
#A heartbeat away? Hybrid'patch'could replace transplants Because heart cells cannot multiply and cardiac muscles contain few stem cells,
heart tissue is unable to repair itself after a heart attack. Now Tel aviv University researchers are literally setting a new gold standard in cardiac tissue engineering.
Dr. Tal Dvir and his graduate student Michal Shevach of TAU's Department of Biotechnology, Department of Materials science and engineering,
and Center for Nanoscience and Nanotechnology, have been developing sophisticated micro -and nanotechnological toolsanging in size from one millionth to one billionth of a metero develop functional substitutes for damaged heart tissues.
Searching for innovative methods to restore heart function especially cardiac"patches"that could be transplanted into the body to replace damaged heart tissue,
Dr. Dvir literally struck gold. He and his team discovered that gold particles are able to increase the conductivity of biomaterials.
In a study published by Nano Letters, Dr. Dvir's team presented their model for a superior hybrid cardiac patch,
which incorporates biomaterial harvested from patients and gold nanoparticles.""Our goal was said twofold Dr. Dvir.""To engineer tissue that would not trigger an immune response in the patient,
and to fabricate a functional patch not beset by signalling or conductivity problems.""A scaffold for heart cells Cardiac tissue is engineered by allowing cells, taken from the patient or other sources,
to grow on a three-dimensional scaffold, similar to the collagen grid that naturally supports the cells in the heart.
Over time, the cells come together to form a tissue that generates its own electrical impulses
According to Dr. Dvir, recent efforts in the scientific world focus on the use of scaffolds from pig hearts to supply the collagen grid
However, due to residual remnants of antigens such as sugar or other molecules, the human patients'immune cells are likely to attack the animal matrix.
"At his Laboratory for Tissue Engineering and Regenerative medicine, Dr. Dvir explored the integration of gold nanoparticles into cardiac tissue to optimize electrical signaling between cells."
we deposited gold nanoparticles on the surface of our patient-harvested matrix, 'decorating'the biomaterial with conductors,
"The result was that the nonimmunogenic hybrid patch contracted nicely due to the nanoparticles, transferring electrical signals much faster and more efficiently than non-modified scaffolds."
"We now have to prove that these autologous hybrid cardiac patches improve heart function after heart attacks with minimal immune response,
#Nanotube cathode beats large pricey laser Scientists are a step closer to building an intense electron beam source without a laser.
Using the High-Brightness Electron Source Lab at DOE's Fermi National Accelerator Laboratory a team led by scientist Luigi Faillace of Radiabeam Technologies is testing a carbon nanotube cathode about the size of a nickel
Tests with the nanotube cathode have produced beam currents a thousand to a million times greater than the one generated with a large pricey laser system.
The technology has extensive applications in medical equipment and national security since an electron beam is a critical component in generating X-rays.
While carbon nanotube cathodes have been studied extensively in academia Fermilab is the first facility to test the technology within a full-scale setting.
People have talked about it for years said Philippe Piot staff scientist at Fermilab and professor at Northern Illinois University but what was missing was a partnership between people that have the know-how at a lab a university and a company.
Fermilab was sought out to test the experimental cathode because of its capability and expertise for handling intense electron beams one of relatively few labs that can support this project.
A U s. Department of energy Small Business Innovation Research grant funds the Radiabeam-Fermilab collaboration. The new cathode appears at first glance like a smooth black button
but at the nanoscale it resembles in Piot's words millions of lightning rods. When a strong electric field is applied it pulls streams of electrons off the surface of the cathode creating the electron beam.
The exceptional strength of carbon nanotubes prevents the cathode from being destroyed. Traditionally accelerator scientists use lasers to strike cathodes
in order to eject electrons through photoemission. The electric and magnetic fields of the particle accelerator then organize the electrons into a beam.
The tested nanotube cathode requires no laser: it only needs the electric field already generated by an accelerator to siphon the electrons off a process dubbed field emission n
#Nanoengineering enhances charge transport promises more efficient future solar cells Solar cells based on semiconducting composite plastics and carbon nanotubes is one of the most promising novel technology for producing inexpensive printed solar cells.
Physicists at Umeå University have discovered that one can reduce the number of carbon nanotubes in the device by more than 100 times
while maintaining exceptional ability to transport charges. This is achieved thanks to clever nanoengineering of the active layer inside the device.
Their results are published as front page news in the journal Nanoscale. Carbon nanotubes are more and more attractive for use in solar cells as a replacement for silicon.
They can be mixed in a semiconducting polymer and deposited from solution by simple and inexpensive methods to form thin and flexible solar cells.
The hybrid material is easy to spread out over a large surface and the nanotubes have outstanding electrical conductivity,
and they can effectively separate and transport electrical charges generated from solar energy. Earlier this year, Dr. David Barbero and his research team at Umeå University,
demonstrated for the first time that if carbon nanotubes are connected to each other in a controlled manner to form complex nanosized networks,
one can achieve significantly higher charge transport and electricity than had previously been possible using the same materials.
This means that the transport of electric charges occurs with a very little energy loss. Previous studies have reported that there is a percolation threshold for the amount of carbon nanotubes necessary to transport efficiently electric charges in a device.
Below this threshold, the device become completely inefficient and no current can be generated. In this new study, Dr. Barbero and his team at Umeå University show that this threshold can be reduced by more than 100 times in a semiconducting polymer
and still generate high currents and charge transport at very low nanotube loadings, thereby strongly reducing materials costs o
#Scientists improve microscopic batteries with homebuilt imaging analysis (Phys. org) In a rare case of having their cake
and eating it too scientists from the National Institute of Standards and Technology (NIST) and other institutions have developed a toolset that allows them to explore the complex interior of tiny multilayered batteries they devised.
It provides insight into the batteries'performance without destroying them resulting in both a useful probe for scientists and a potential power source for micromachines.
The microscopic lithium-ion batteries are created by taking a silicon wire a few micrometers long and covering it in successive layers of different materials.
Instead of a cake however each finished battery looks more like a tiny tree. The analogy becomes obvious
when you see the batteries attached by their roots to silicon wafers and clustered together by the million into nanoforests as the team dubs them.
But it's the cake-like layers that enable the batteries to store and discharge electricity
and even be recharged. These talents could make them valuable for powering autonomous MEMS#microelectromechanical machines
#which have potentially revolutionary applications in many fields. With so many layers that can vary in thickness morphology
and other parameters it's crucial to know the best way to build each layer to enhance the battery's performance as the team found in previous research.**
**But conventional transmission electron microscopy (TEM) couldn't provide all the details needed so the team created a new technique that involved multimode scanning TEM (STEM) imaging.
With STEM electrons illuminate the battery which scatters them at a wide range of angles.
To see as much detail as possible the team decided to use a set of electron detectors to collect electrons in a wide range of scattering angles an arrangement that gave them plenty of structural information to assemble a clear picture of the battery's interior down to the nanoscale level.
The promising toolset of electron microscopy techniques helped the researchers to home in on better ways to build the tiny batteries.
We had a lot of choices in what materials to deposit and in what thicknesses and a lot of theories about
what to do team member Vladimir Oleshko says. But now as a result of our analyses we have direct evidence of the best approach.
MEMS manufacturers could make use of the batteries themselves a million of which can be fabricated on a square centimeter of a silicon wafer.
But the same manufacturers also could benefit from the team's analytical toolset. Oleshko points out that the young rapidly emerging field of additive manufacturing which creates devices by building up component materials layer by layer often needs to analyze its creations in a noninvasive way.
For that job the team's approach might take the cake. Explore further: Toward making lithium-sulfur batteries a commercial reality for a bigger energy punch More information:
V p. Oleshko T. Lam D. Ruzmetov P. Haney H. J. Lezec A v. Davydov S. Krylyuk J. Cumings and A a. Talin.
Miniature all-solid-state heterostructure nanowire Li-ion batteries as a tool for engineering and structural diagnostics of nanoscale electrochemical processes.
Nanoscale DOI: 0. 1039/c4nr01666a Aug 15 2014
#Research mimics brain cells to boost memory power RMIT University researchers have brought ultra-fast, nanoscale data storage within striking reach,
using technology that mimics the human brain. The researchers have built a novel nanostructure that offers a new platform for the development of highly stable and reliable nanoscale memory devices.
The pioneering work will feature on a forthcoming cover of materials science journal Advanced Functional Materials (11 november.
Project leader Dr Sharath Sriram, co-leader of the RMIT Functional Materials and Microsystems Research Group, said the nanometer-thin stacked structure was created using thin film, a functional oxide
material more than 10,000 times thinner than a human hair.""The thin film is designed specifically to have defects in its chemistry to demonstrate a'memristive'effect where the memory element's behaviour is dependent on its past experiences,
"Dr Sriram said.""With flash memory rapidly approaching fundamental scaling limits, we need novel materials
and architectures for creating the next generation of nonvolatile memory.""The structure we developed could be used for a range of electronic applications from ultrafast memory devices that can be shrunk down to a few nanometers,
to computer logic architectures that replicate the versatility and response time of a biological neural network.""While more investigation needs to be done,
our work advances the search for next generation memory technology can replicate the complex functions of human neural system bringing us one step closer to the bionic brain."
"The research relies on memristors, touted as a transformational replacement for current hard drive technologies such as Flash, SSD and DRAM.
Memristors have potential to be fashioned into nonvolatile solid-state memory and offer building blocks for computing that could be trained to mimic synaptic interfaces in the human brain n
#How to make a perfect solar absorber The key to creating a material that would be ideal for converting solar energy to heat is tuning the material's spectrum of absorption just right:
It should absorb virtually all wavelengths of light that reach Earth's surface from the sun but not much of the rest of the spectrum since that would increase the energy that is reradiated by the material
and thus lost to the conversion process. Now researchers at MIT say they have accomplished the development of a material that comes very close to the ideal for solar absorption.
The material is a two-dimensional metallic dielectric photonic crystal and has the additional benefits of absorbing sunlight from a wide range of angles
and withstanding extremely high temperatures. Perhaps most importantly the material can also be made cheaply at large scales. The creation of this material is described in a paper published in the journal Advanced Materials co-authored by MIT postdoc Jeffrey Chou professors Marin Soljacic Nicholas Fang Evelyn Wang and Sang-Gook
Kim and five others. The material works as part of a solar-thermophotovoltaic (STPV) device: The sunlight's energy is converted first to heat
which then causes the material to glow emitting light that can in turn be converted to an electric current.
Some members of the team worked on an earlier STPV device that took the form of hollow cavities explains Chou of MIT's Department of Mechanical engineering who is the paper's lead author.
They were empty there was air inside he says. No one had tried putting a dielectric material inside so we tried that
and saw some interesting properties. When harnessing solar energy you want to trap it and keep it there Chou says;
It's a very specific window that you want to absorb in he says. We built this structure
Earlier lab demonstrations of similar systems could only produce devices a few centimeters on a side with expensive metal substrates so were not suitable for scaling up to commercial production he says.
which would add greatly to the complexity and expense of a solar power system. This is the first device that is able to do all these things at the same time Chou says.
While the team has demonstrated working devices using a formulation that includes a relatively expensive metal ruthenium we're very flexible about materials Chou says.
In theory you could use any metal that can survive these high temperatures. This work shows the potential of both photonic engineering
and materials science to advance solar energy harvesting says Paul Braun a professor of materials science and engineering at the University of Illinois at Urbana-Champaign who was involved not in this research.
In this paper the authors demonstrated in a system designed to withstand high temperatures the engineering of the optical properties of a potential solar thermophotovoltaic absorber to match the sun's spectrum.
Of course much work remains to realize a practical solar cell however the work here is one of the most important steps in that process.
The group is now working to optimize the system with alternative metals. Chou expects the system could be developed into a commercially viable product within five years.
He is working with Kim on applications from this project t
#New research points to graphene as a flexible low-cost touchscreen solution New research published today in the journal Advanced Functional Materials suggests that graphene-treated nanowires could soon replace current touchscreen technology
significantly reducing production costs and allowing for more affordable flexible displays. The majority of today's touchscreen devices such as tablets and smartphones are made using indium tin oxide (ITO)
which is both expensive and inflexible. Researchers from the University of Surrey and AMBER the materials science centre based at Trinity college Dublin have demonstrated now how graphene-treated nanowires can be used to produce flexible touchscreens at a fraction of the current cost.
Using a simple scalable and inexpensive method the researchers produced hybrid electrodes the building blocks of touchscreen technology from silver nanowires and graphene.
Dr Alan Dalton from the University of Surrey said The growing market in devices such as wearable technology
and bendable smart displays poses a challenge to manufacturers. They want to offer consumers flexible touchscreen technology but at an affordable and realistic price.
At the moment this market is limited severely in the materials to hand which are both very expensive to make
and designed for rigid flat devices. Lead author Dr Izabela Jurewicz from the University of Surrey commented Our work has cut the amount of expensive nanowires required to build such touchscreens by more than fifty times as well as simplifying the production process.
We achieved this using graphene a material that can conduct electricity and interpret touch commands
whilst still being transparent. Co-author Professor Jonathan Coleman AMBER added This is a real alternative to ITO displays
and could replace existing touchscreen technologies in electronic devices. Even though this material is cheaper and easier to produce it does not compromise on performance.
We are currently working with industrial partners to implement this research into future devices and it is clear that the benefits will soon be felt by manufacturers and consumers alike.
Explore further: Conductive nanofiber networks for flexible unbreakable and transparent electrode e
#Harnessing an unusual'valley'quantum property of electrons Yoshihiro Iwasa and colleagues from the RIKEN Center for Emergent Matter Science the University of Tokyo and Hiroshima University have discovered that ultrathin films of a semiconducting material have properties that form the basis for a new kind of low-power electronics
termed'valleytronics'.'Electronic components store transmit and process information using the electrical charge of an electron.
The use of charge however requires physically moving electrons from one point to another which can consume a great deal of energy particularly in computing applications.
Researchers are therefore searching for ways to harness other properties of electrons such as the'spin'of an electron as data carriers in the hope that this will lead to devices that consume less power.
Valleytronics is based on the quantum behavior of electrons in terms of a material's electronic band structure.
Semiconductors and insulators derive their electrical properties from a gap between the highest band occupied by electrons known as the valence band
and the lowest unoccupied band or'conduction band'in the band structure explains Iwasa. If there are two
or more dips in the conduction band or peaks in the valence band we say that the band structure contains valleys.
Molybdenum disulfide is a member of a family of materials known as transition metal dichalcogenides which are currently the focus of intense research because of the unusual electronic properties they display
#Solar cell compound probed under pressure Gallium arsenide Gaas a semiconductor composed of gallium and arsenic is well known to have physical properties that promise practical applications.
In the form of nanowires and nanoparticles it has particular potential for use in the manufacture of solar cells
and optoelectronics in many of the same applications that silicon is used commonly. But the natural semiconducting ability of Gaas requires some tuning
New work from a team led by Carnegie's Alexander Goncharov explores a novel approach to such tuning.
Their work is published in Scientific Reports. The research team includes Wei Zhou Xiao-Jia Chen Xin-Hua Li and Yu-Qi Wang of the Chinese Academy of Sciences and Jian-Bo Zhang of South China
University of Technology. Metallic substances conduct electrical current easily whereas insulating (nonmetallic) materials conduct no current at all.
Semiconducting materials exhibit mid-range electrical conductivity. When semiconducting materials are subjected to an input of a specific energy bound electrons can be moved to higher energy conducting states.
The specific energy required to make this jump to the conducting state is defined as the band gap.
Fine-tuning of this band gap has the potential to improve gallium arsenide's commercial potential. There are different methods available to engineer slight tweaks to the band gap.
Goncharov's team focused on the novel application of very high pressure which can cause a compound to undergo electronic changes that can alter the electron-carrier properties of materials.
It had already been demonstrated on nanowires made from one crystalline form of gallium arsenide the cubic so-called zincblende structure that the band gap widens under pressure.
The present research focused instead on nanowires of a less-common crystalline form the hexagonal so-called wurtzite structure.
The team subjected wurtzite gallium arsenide to up to about 227000 times normal atmospheric pressure (23 gigapascals) in diamond anvil cells.
They discovered the band gap that the electrons need to leap across to also widened although not as much as in the case of the zincblende crystal nanowires.
Significantly they discovered that around 207000 times normal atmospheric pressure (21 gigapascals) the wurtzite gallium arsenide nanowires underwent a structural change that induced a new phase the so-called orthorhombic one
which may possibly have metallic electronic properties. The similarity in behavior when subjected to high pressure
but resulting in significant differences in the size of the'band gap'between the two crystalline structures of gallium arsenide suggests that both types of Gaas structures could theoretically be incorporated into a single device
or even a single nanowire and realize much more complex and useful electronic functions through interactions across the phases Goncharov said.
We believe these findings will stimulate further research into gallium arsenide for both basic scientific and practical purposes s
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