Archive : 27 March 2018 год
A bright-light emitting device that is millimetres wide and fully transparent when turned off has been built by a team of engineers at the University of California (UC), Berkeley. The light emitting material is a monolayer semiconductor, which is just three atoms thick.
According to the team, this discovery could pave the way in creating invisible displays – that would be bright when on, but see-through when off – on walls and windows or in applications such as light-emitting tattoos.
"The materials are so thin and flexible that the device can be made transparent and can conform to curved surfaces," said Der-Hsien Lien of UC Berkeley.
The device was developed in the laboratory of professor Ali Javey of UC Berkeley, whose work previously demonstrated that monolayer semiconductors are capable of emitting bright light, but stopped short of building a light-emitting device.
This new work is said to overcome the fundamental barriers in utilising LED technology on monolayer semiconductors, allowing for such devices to be scaled from sizes smaller than the width of a human hair, up to several millimetres. The researchers explained that this means the thickness can be kept small, while the lateral dimensions can be made large to offer higher light intensity.
Commercial LEDs consist of a semiconductor material that is electrically injected with positive and negative charges, which produce light when they meet. Typically, two contact points are used in a semiconductor-based light emitting device; one for injecting negatively charged particles and one injecting positively charged particles. Making contacts that can efficiently inject these charges is a challenge for LEDs, and it is particularly challenging for monolayer semiconductors since there is so little material to work with.
UC Berkeley claimed to have engineered a way to circumvent this challenge by designing device that only requires one contact on the semiconductor.
By laying the semiconductor monolayer on an insulator and placing electrodes on the monolayer and underneath the insulator, the researchers said they could apply an AC signal across the insulator. During the moment when the AC signal switches its polarity from positive to negative (and vice versa), the team explained, both positive and negative charges are present at the same time in the semiconductor, creating light.
The team claimed that this mechanism works in four different monolayer materials, all of which emit different colors of light.
This device is a proof-of-concept, and much research still remains – primarily to improve efficiency, according to the researchers.
Measuring this device's efficiency, however, is not straightforward, but the researchers think it's about 1% efficient. Commercial LEDs have efficiencies of around 25 to 30%.
"A lot of work remains to be done and a number of challenges need to be overcome to further advance the technology for practical applications," Javey said. "However, this is one step forward by presenting a device architecture for easy injection of both charges into monolayer semiconductors."
As the race for quantum computing continues, so does the development into quantum technologies targeted to neturalise the threat of hacking.
Classical cryptographic algorithms are complexity-based and can remain secure only for a certain period of time. Unlike its classical counterpart, quantum cryptography relies on the fundamental laws of physics and is thought to be capable of guaranteeing security of data transmission forever.
The operation principle is based on the fact an unknown quantum state can’t be copied without altering the original message, as a result the quantum communication line can’t be compromised without the sender and the receiver knowing.
Single photons are considered the best carrier for quantum bits. The principal behind this generation is: an excited quantum system can relax into the ground state by emitting exactly one photon.
From an engineering standpoint, a real-world physical system that reliably generates single photons under ambient conditions is required, but this isn’t easy to find.
Researchers from the Moscow Institute of Physics and Technology (MIPT) see a solution in silicon carbide. Through studying the physics of electroluminescence of colour centres in silicon carbide, the team came up with a theory of single-photon emission upon electrical injection that it says explains and accurately reproduces the experimental findings.
A colour centre is a point defect in the lattice structure of silicon carbide that can emit or absorb a photon at a wavelength to which the material is transparent in the absence of defects. This process is at the heart of the electrically driven single-photon source.
The researchers explain that their theory demonstrates how a single-photon emitting diode based on silicon carbide can be improved to emit up to several billion photons per second, which is required to implement quantum cryptography protocols at data transfer rates on the order of 1 Gbps.
New materials are likely to be found which rival silicon carbide in terms of brightness of single-photon emission, add MIPT. But unlike silicon carbide, they will require new technological processes to be used in mass production of devices.
By contrast, silicon carbide-based single-photon sources are compatible with the CMOS technology, which the team say makes it by far the most promising material for building practical ultrawide-bandwidth unconditionally secure data communication lines.
Using gold nanomaterials combined with a hybrid glass material, scientists from from RMIT University and the Wuhan Institute of Technology say they have demonstrated a new type of high-capacity optical disk that can hold data securely for more than 600 years.
This gold-generated next-generation optical disk is said to have up to 10TB capacity - a storage leap of 400% and a six-century lifespan.
According to the team, it has the potential to offer a more cost-efficient and sustainable solution to the global data storage problem, while enabling the critical pivot from Big Data to Long Data.
The technology could radically improve the energy efficiency of data centres, which consume about 3% of the world's electricity supply and rely on hard disk drives that have limited capacity and lifespans.
The team says it can use 1000 times less power than a hard disk centre through less cooling and ridding energy-intensive task of data migration every two years. Optical disks are also more secure than hard disks, it adds.
Lead investigator, Professor Min Gu of RMIT University, said the research paves the way for the development of optical data centres to address both the world's data storage challenge and support the coming Long Data revolution.
"All the data we're generating in the Big Data era - over 2.5 quintillion bytes a day - has to be stored somewhere, but our current storage technologies were developed in different times," Gu explained.
"While optical technology can expand capacity, the most advanced optical disks developed so far have only 50-year lifespans.
"Our technique can create an optical disk with the largest capacity of any optical technology developed to date and our tests have shown it will last over half a millennium.”
"Long Data offers an unprecedented opportunity for new discoveries in almost every field - from astrophysics to biology, social science to business - but we can't unlock that potential without addressing the storage challenge," adds Dr Qiming Zhang of RMIT.
How it works
The researchers have demonstrated optical long data memory in a nanoplasmonic hybrid glass matrix, different to the conventional materials used in optical discs.
The team explained that it combined glass with an organic material, halving its lifespan but radically increasing capacity.
To create the nanoplasmonic hybrid glass matrix, gold nanorods were incorporated into an organic modified ceramic.
The researchers chose gold because like glass, it is robust and durable. Gold nanoparticles are said to let information to be recorded in five dimensions - the three dimensions in space, plus colour and polarisation.
The technique relies on a sol-gel process, which uses chemical precursors to produce ceramics and glasses with better purity and homogeneity than conventional processes.