Monday, 22 February 2016

Researchers at RMIT University and the University of Adelaide have joined forces to create a stretchable nano-scale device to manipulate light.

The device manipulates light to such an extent that it can filter specific colours while still being transparent and could be used in the future to make smart contact lenses.
 nanoscale glass structures that filter or manipulate light
credit: RMIT/
The University of Adelaide
Using the technology, high-tech lenses could one day filter harmful optical radiation without interfering with vision – or in a more advanced version, transmit data and gather live vital information or even show information like a head-up display.

The light manipulation relies on creating tiny artificial crystals termed  “dielectric resonators”, which are a fraction of the wavelength of light – 100-200 nanometers, or over 500 times thinner than a human hair.

The research combined the University of Adelaide researchers’ expertise in interaction of light with artificial materials with the materials science and nanofabrication expertise at RMIT University.

Dr Withawat Withayachumnankul, from the University of Adelaide’s School of Electrical and Electronic Engineering, said: “Manipulation of light using these artificial crystals uses precise engineering.

“With advanced techniques to control the properties of surfaces, we can dynamically control their filter properties, which allow us to potentially create devices for high data-rate optical communication or smart contact lenses.

“The current challenge is that dielectric resonators only work for specific colours, but with our flexible surface we can adjust the operation range simply by stretching it.”

Associate Professor Madhu Bhaskaran, Co-Leader of the Functional Materials and Microsystems Research Group at RMIT, said the devices were made on a rubber-like material used for contact lenses.

“We embed precisely-controlled crystals of titanium oxide, a material that is usually found in sunscreen, in these soft and pliable materials,” she said.

“Both materials are proven to be bio-compatible, forming an ideal platform for wearable optical devices.

“By engineering the shape of these common materials, we can create a device that changes properties when stretched. This modifies the way the light interacts with and travels through the device, which holds promise of making smart contact lenses and stretchable colour changing surfaces.”

Lead author and RMIT researcher Dr. Philipp Gutruf said the major scientific hurdle overcome by the team was combining high temperature processed titanium dioxide with the rubber-like material, and achieving nanoscale features.

“With this technology, we now have the ability to develop light weight wearable optical components which also allow for the creation of futuristic devices such as smart contact lenses or flexible ultrathin smartphone cameras,” Gutruf said.

source ; RMIT news release link : click here

This post is copied from the materials in the RMIT website(news)

Saturday, 13 February 2016

UW scientists create ultrathin semiconductor heterostructures for new technological applications...............

Heterostructures formed by different three-dimensional semiconductors form the foundation for modern electronic and photonic devices. Now, University of Washington scientists have successfully combined two different ultrathin semiconductors — each just one layer of atoms thick and roughly 100,000 times thinner than a human hair — to make a new two-dimensional heterostructure with potential uses in clean energy and optically-active electronics. The team, led by Boeing Distinguished Associate Professor Xiaodong Xu, announced its findings in a paper published Feb. 12 in the journal Science.
An illustration of the strong valley exciton interactions and transport in a 2-D semiconductor heterostructure.Pasqual Rivera, Kyle Seyler
              Senior author Xu and lead authors Kyle Seyler and Pasqual Rivera, both doctoral students in the UW physics department, synthesized and investigated the optical properties of this new type of semiconductor sandwich.
“What we’re seeing here is distinct from heterostructures made of 3-D semiconductors,” said Xu, who has joint appointments in the Department of Physics and the Department of Materials Science and Engineering. “We’ve created a system to study the special properties of these atomically thin layers and their potential to answer basic questions about physics and develop new electronic and photonic technologies.”
When semiconductors absorb light, pairs of positive and negative charges can form and bind together to create so-called excitons. Scientists have long studied how these excitons behave, but when they are squeezed down to the 2-D limit in these atomically thin materials, surprising interactions can occur.
While traditional semiconductors manipulate the flow of electron charge, this device allows excitons to be preserved in “valleys,” a concept from quantum mechanics similar to the spin of electrons. This is a critical step in the development of new nanoscale technologies that integrate light with electronics.
“It was already known that these ultrathin 2-D semiconductor have these unique properties that you cannot find in other 2-D or 3-D arrangements,” said Xu. “But as we show here, when we put these two layers together — one on top of the other — the interface between these sheets becomes the site of even more new physical properties, which you don’t see in each layer on its own or in the 3-D version.”
Xu and his team wanted to create and explore the properties of a 2-D semiconductor heterostructure made up of two different layers of material, a natural expansion of their previous studies on atomically thin junctions, as well as nanoscale lasers based on atomically thin layers of semiconductors. By studying how laser light interacts with this heterostructure, they gathered information about the physical properties at the atomically sharp interface.
“Many groups have studied the optical properties of single 2-D sheets,” said Seyler. “What we do here is carefully stack one material on top of another, and then study the new properties that arise at the interface.”
The team obtained two types of semiconducting crystals, tungsten diselenide (WSe2) and molybdenum diselenide (MoSe2), from collaborators at Oak Ridge National Laboratory. They used facilities developed in-house to precisely arrange two layers, one derived from each crystal, a process that took a few years to fully develop.
“But now that we know how to do it properly, we can make new ones in one or two weeks,” said Xu.
Getting these devices to emit light posed a unique challenge, due to the properties of electrons in each layer.
“Once you have these two sheets of material, an essential question is how to position the two layers together,” said Seyler. The electrons in each layer have unique spin and valley properties, and “how you position them — their twist angle — affects how they interact with light.”
By aligning the crystal lattices, the authors could excite the heterostructure with a laser and create optically active excitons between the two layers.
“These excitons at the interface can store valley information for orders of magnitude longer than either of the layers on their own,” said Rivera. “This long lifetime allows for fascinating effects which may lead to further optical and electronic applications with valley functionality.”
Now that they can efficiently make a semiconductor heterostructure out of 2-D materials, Xu and his team would like to explore a number of fascinating physical properties, including how exciton behavior varies as they change angles between the layers, the quantum properties excitons between layers and electrically driven light emission.
“There’s a whole industry that wants to use these 2-D semiconductors to make new electronic and photonic devices,” said Xu. “So we’re trying to study the fundamental properties of these new heterostructures for things like efficient laser technology, light-emitting diodes and light-harvesting devices. These will hopefully be useful for clean energy and information technology applications. It is quite exciting but there’s a lot work to do.”
Other co-authors are Hongyi Yu and Wang Yao at the University of Hong Kong; Jiaqiang Yan and David Mandrus at Oak Ridge National Laboratory and the University of Tennessee; and UW physics postdoctoral researcher John Schaibley. The UW authors were primarily funded by the U.S. Department of Energy, with additional support from the UW’s Clean Energy Institute and the National Science Foundation.

source: UW TODAY  link: click here

Monday, 28 December 2015

Technical University of Denmark (DTU) researchers from DTU Nanotech and DTU Fotonik have reproduced a colour image of Mona Lisa which is less than one pixel on an iPhone Retina display.

A nanotechnology breakthrough from DTU revolutionizes laser printing technology, allowing you to print high-resolution data and colour images of unprecedented quality and microscopic dimensions.

Researchers from DTU Nanotech and DTU Fotonik have succeeded in printing a microscopic Mona Lisa. She is 50 micrometres long or about 10,000 times smaller than the real Mona Lisa in the Louvre in Paris.
credit: DTU

                                                                                                                                                                    Using this new technology, DTU researchers from DTU Nanotech and DTU Fotonik have reproduced a colour image of Mona Lisa which is less than one pixel on an iPhone Retina display. The laser technology allows printing in a mind-blowing resolution of 127,000 DPI. In comparison, weekly or monthly magazines are normally printed in a resolution equivalent to 300 DPI.

Printing the microscopic images requires a special nanoscale-structured surface. The structure consists of rows with small columns with a diameter of merely 100 nanometres each. This structured surface is then covered by 20 nanometres of aluminium. When a laser pulse is transmitted from nanocolumn to nanocolumn, the nanocolumn is heated locally, after which it melts and is deformed. The temperature can reach up to 1,500°C, but only for a few nanoseconds, preventing the extreme heat from spreading.

The intensity of the laser beam determines which colours are printed on the surface, since the extent of column deformation decides which colour is reflected. Low-intensity laser pulses lead to a minor deformation of the nanocolumn, resulting in blue and purple colour tone reflections. Strong laser pulses create a drastic deformation, which gives the reflection from the nanocolumn an orange and yellow colour tone.

The DTU researchers believe that there is considerable scope for application of the new laser printing technology. Professor Anders Kristensen from DTU Nanotech elaborates: "It will be possible to save data invisible to the naked eye. This includes serial numbers or bar codes of products and other information. The technology can also be used to combat fraud and forgery, as the products will be labelled in way that makes them very difficult to reproduce. It will be easier to determine whether the product is an original or a copy."

The new laser printing technology can also be used on a larger scale to personify products such as mobile phones with unique decorations, names, etc. Foreign companies producing parts for cars, such as instrument panels and buttons, are already taking a keen interest in the technology as it can simplify the production. Today, the large number of different instrument panels must be adapted to the various accessories that the car has, including airconditioning, USB, cigarette lighters, etc.
The technology has been patented, and the researchers will now focus on developing the technology, so that it can replace the conventional laser printers that we have at our offices and in our homes.

SOURCE: Technical University of Denmark (DTU) link : click here