Tag Archives: letter-pulse-tech

Using advanced fabrication techniques, engineers at the University of California San Diego have built a nanosized device out of silver crystals that can generate light by efficiently “tunneling” electrons through a tiny barrier. The work brings plasmonics research a step closer to realizing ultra-compact light sources for high-speed, optical data processing and other on-chip applications.

The work is published July 23 in Nature Photonics.

The device emits light by a quantum mechanical phenomenon known as inelastic electron tunneling. In this process, electrons move through a solid barrier that they cannot classically cross. And while crossing, the electrons lose some of their energy, creating either photons or phonons in the process.

Left: schematics of the tunnel junction formed by two edge-to-edge silver single crystal cuboids with an insulating barrier of polyvinylpyrrolidone (PVP). The top inset shows that photons are generated through inelastic electron tunneling. The device performance can be engineered by tuning the size of the cuboids (a, b, c), the gap size (d), and the curvature of silver cuboid edges. Right: TEM image of the tunnel junction, where the gap is around 1.5 nm. Credit: Haoliang Qian/Nature Photonics

Plasmonics researchers have been interested in using inelastic electron tunneling to create extremely small light sources with large modulation bandwidth. However, because only a tiny fraction of electrons can tunnel inelastically, the efficiency of light emission is typically low–on the order of a few hundredths of a percent, at most.

UC San Diego engineers created a device that bumps that efficiency up to approximately two percent. While this is not yet high enough for practical use, it is the first step to a new type of light source, said Zhaowei Liu, a professor of electrical and computer engineering at the UC San Diego Jacobs School of Engineering.

“We’re exploring a new way to generate light,” said Liu.

Liu’s team designed the new light emitting device using computational methods and numerical simulations. Researchers in the lab of Andrea Tao, a professor of nanoengineering at the UC San Diego Jacobs School of Engineering, then constructed the device using advanced solution-based chemistry techniques.

The device is a tiny bow-tie-shaped plasmonic nanostructure consisting of two cuboid, single crystals of silver joined at one corner. Connecting the corners is a 1.5-nanometer-wide barrier of insulator made of a polymer called polyvinylpyrrolidone (PVP).

This tiny metal-insulator-metal (silver-PVP-silver) junction is where the action occurs. Electrodes connected to the nanocrystals allow voltage to be applied to the device. As electrons tunnel from a corner of a silver nanocrystal through the tiny PVP barrier, they transfer energy to surface plasmon polaritons–electromagnetic waves that travel along the metal-insulator interface–which then convert that energy to photons.

But what makes this particular junction more efficient at tunneling electrons inelastically is its geometry and extremely tiny size. By joining two silver single crystals together at their corners with a tiny barrier of insulator in between, researchers essentially created a high quality optical antenna with a high local density of optical states, resulting in more efficient conversion of electronic energy to light.

Metal-insulator-metal junctions have had such low light emission efficiency in the past because they were constructed by joining metal crystals along an entire face, rather than a corner, explained Liu. Giving electrons a high quality optical antenna with a much smaller gap to tunnel through allows efficient light emission, and this kind of structure has been difficult to fabricate with nanolithography methods used in the past, he said.

“Using chemistry, we can build these precise nanosized junctions that allow more efficient light emission,” said Tao. “The fabrication techniques we use give us atomic level control of our materials–we can dictate the size and shape of crystals in solution based on the reagents we use, and we can create structures that have atomically flat faces and extremely sharp corners.”

With additional work, the team aims to further boost efficiency another order of magnitude higher. They are exploring different geometries and materials for future studies.

Scientists at the University of Alberta in Edmonton, Canada have created the most dense, solid-state memory in history that could soon exceed the capabilities of current hard drives by 1,000 times.

Faced with the question of how to respond to the ever-increasing needs of our data-driven society, the answer for a team of scientists was simple: more memory, less space. Finding the way to do that, however, was anything but simple, involving years of painstaking incremental advances in atomic-scale nanotechnology.

But their new discovery for atomic-scale rewritable memory–quickly removing or replacing single atoms–allows the creation of small, stable, dense memory at the atomic-scale.

To demonstrate the new discovery, Achal, Wolkow, and their fellow scientists not only fabricated the world’s smallest maple leaf, they also encoded the entire alphabet at a density of 138 terabytes, roughly equivalent to writing 350,000 letters across a grain of rice. For a playful twist, Achal also encoded music as an atom-sized song, the first 24 notes of which will make any video-game player of the 80s and 90s nostalgic for yesteryear but excited for the future of technology and society. Credit: Roshan Achal / courtesy Nature Communications

“Essentially, you can take all 45 million songs on iTunes and store them on the surface of one quarter,” said Roshan Achal, PhD student in Department of Physics at the University of Alberta and lead author on the new research. “Five years ago, this wasn’t even something we thought possible.”

Previous discoveries were stable only at cryogenic conditions, meaning this new finding puts society light years closer to meeting the need for more storage for the current and continued deluge of data. One of the most exciting features of this memory is that it’s road-ready for real-world temperatures, as it can withstand normal use and transportation beyond the lab.

“What is often overlooked in the nanofabrication business is actual transportation to an end user, that simply was not possible until now given temperature restrictions,” continued Achal. “Our memory is stable well above room temperature and precise down to the atom.”

Achal explained that immediate applications will be data archival. Next steps will be increasing readout and writing speeds, meaning even more flexible applications.

More memory, less space

Achal works with University of Alberta physics professor Robert Wolkow, a pioneer in the field of atomic-scale physics. Wolkow perfected the art of the science behind nanotip technology, which, thanks to Wolkow and his team’s continued work, has now reached a tipping point, meaning scaling up atomic-scale manufacturing for commercialization.

“With this last piece of the puzzle now in-hand, atom-scale fabrication will become a commercial reality in the very near future,” said Wolkow. Wolkow’s Spin-off company, Quantum Silicon Inc., is hard at work on commercializing atom-scale fabrication for use in all areas of the technology sector.

To demonstrate the new discovery, Achal, Wolkow, and their fellow scientists not only fabricated the world’s smallest maple leaf, they also encoded the entire alphabet at a density of 138 terabytes, roughly equivalent to writing 350,000 letters across a grain of rice. For a playful twist, Achal also encoded music as an atom-sized song, the first 24 notes of which will make any video-game player of the 80s and 90s nostalgic for yesteryear but excited for the future of technology and society.

A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.

The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses the speed and precision of roll-to-roll newspaper printing to remove a couple of fabrication barriers in making electronics faster than they are today.

Roll-to-roll laser-induced superplasticity, a new fabrication method, prints metals at the nanoscale needed for making electronic devices ultrafast. Credit: Purdue University image/Ramses Martinez

Cellphones, laptops, tablets, and many other electronics rely on their internal metallic circuits to process information at high speed. Current metal fabrication techniques tend to make these circuits by getting a thin rain of liquid metal drops to pass through a stencil mask in the shape of a circuit, kind of like spraying graffiti on walls.

“Unfortunately, this fabrication technique generates metallic circuits with rough surfaces, causing our electronic devices to heat up and drain their batteries faster,” said Ramses Martinez, assistant professor of industrial engineering and biomedical engineering.

Future ultrafast devices also will require much smaller metal components, which calls for a higher resolution to make them at these nanoscale sizes.

“Forming metals with increasingly smaller shapes requires molds with higher and higher definition, until you reach the nanoscale size,” Martinez said. “Adding the latest advances in nanotechnology requires us to pattern metals in sizes that are even smaller than the grains they are made of. It’s like making a sand castle smaller than a grain of sand.”

This so-called “formability limit” hampers the ability to manufacture materials with nanoscale resolution at high speed.

Purdue researchers have addressed both of these issues – roughness and low resolution – with a new large-scale fabrication method that enables the forming of smooth metallic circuits at the nanoscale using conventional carbon dioxide lasers, which are already common for industrial cutting and engraving.

“Printing tiny metal components like newspapers makes them much smoother. This allows an electric current to travel better with less risk of overheating,” Martinez said.

The fabrication method, called roll-to-roll laser-induced superplasticity, uses a rolling stamp like the ones used to print newspapers at high speed. The technique can induce, for a brief period of time, “superelastic” behavior to different metals by applying high-energy laser shots, which enables the metal to flow into the nanoscale features of the rolling stamp – circumventing the formability limit.

“In the future, the roll-to-roll fabrication of devices using our technique could enable the creation of touch screens covered with nanostructures capable of interacting with light and generating 3D images, as well as the cost-effective fabrication of more sensitive biosensors,” Martinez said.

Researchers have shown that it is possible to train artificial neural networks directly on an optical chip. The significant breakthrough demonstrates that an optical circuit can perform a critical function of an electronics-based artificial neural network and could lead to less expensive, faster and more energy efficient ways to perform complex tasks such as speech or image recognition.

Researchers have shown a neural network can be trained using an optical circuit (blue rectangle in the illustration). In the full network there would be several of these linked together. The laser inputs (green) encode information that is carried through the chip by optical waveguides (black). The chip performs operations crucial to the artificial neural network using tunable beam splitters, which are represented by the curved sections in the waveguides. These sections couple two adjacent waveguides together and are tuned by adjusting the settings of optical phase shifters (red and blue glowing objects), which act like ‘knobs’ that can be adjusted during training to perform a given task. Credit: Tyler W. Hughes, Stanford University

“Using an optical chip to perform neural network computations more efficiently than is possible with digital computers could allow more complex problems to be solved,” said research team leader Shanhui Fan of Stanford University. “This would enhance the capability of artificial neural networks to perform tasks required for self-driving cars or to formulate an appropriate response to a spoken question, for example. It could also improve our lives in ways we can’t imagine now.”

An artificial neural network is a type of artificial intelligence that uses connected units to process information in a manner similar to the way the brain processes information. Using these networks to perform a complex task, for instance voice recognition, requires the critical step of training the algorithms to categorize inputs, such as different words.

Although optical artificial neural networks were recently demonstrated experimentally, the training step was performed using a model on a traditional digital computer and the final settings were then imported into the optical circuit. In Optica, The Optical Society’s journal for high impact research, Stanford University researchers report a method for training these networks directly in the device by implementing an optical analogue of the ‘backpropagation’ algorithm, which is the standard way to train conventional neural networks.

“Using a physical device rather than a computer model for training makes the process more accurate,” said Tyler W. Hughes, first author of the paper. “Also, because the training step is a very computationally expensive part of the implementation of the neural network, performing this step optically is key to improving the computational efficiency, speed and power consumption of artificial networks.”

A light-based network

Although neural network processing is typically performed using a traditional computer, there are significant efforts to design hardware optimized specifically for neural network computing. Optics-based devices are of great interest because they can perform computations in parallel while using less energy than electronic devices.

In the new work, the researchers overcame a significant challenge to implementing an all-optical neural network by designing an optical chip that replicates the way that conventional computers train neural networks.

An artificial neural network can be thought of as a black box with a number of knobs. During the training step, these knobs are each turned a little and then the system is tested to see if the performance of the algorithms improved.

“Our method not only helps predict which direction to turn the knobs but also how much you should turn each knob to get you closer to the desired performance,” said Hughes. “Our approach speeds up training significantly, especially for large networks, because we get information about each knob in parallel.”

On-chip training

The new training protocol operates on optical circuits with tunable beam splitters that are adjusted by changing the settings of optical phase shifters. Laser beams encoding information to be processed are fired into the optical circuit and carried by optical waveguides through the beam splitters, which are adjusted like knobs to train the neural network algorithms.

In the new training protocol, the laser is first fed through the optical circuit. Upon exiting the device, the difference from the expected outcome is calculated. This information is then used to generate a new light signal, which is sent back through the optical network in the opposite direction. By measuring the optical intensity around each beam splitter during this process, the researchers showed how to detect, in parallel, how the neural network performance will change with respect to each beam splitter’s setting. The phase shifter settings can be changed based on this information, and the process may be repeated until the neural network produces the desired outcome.

The researchers tested their training technique with optical simulations by teaching an algorithm to perform complicated functions, such as picking out complex features within a set of points. They found that the optical implementation performed similarly to a conventional computer.

“Our work demonstrates that you can use the laws of physics to implement computer science algorithms,” said Fan. “By training these networks in the optical domain, it shows that optical neural network systems could be built to carry out certain functionalities using optics alone.”

The researchers plan to further optimize the system and want to use it to implement a practical application of a neural network task. The general approach they designed could be used with various neural network architectures and for other applications such as reconfigurable optics.

Taking a multiband approach explains ‘electron-hole reverse drag’ and exciton formation

Mystifying experimental results obtained independently by two research groups in the USA seemed to show coupled holes and electrons moving in the opposite direction to theory.

Now, a new theoretical study has explained the previously mysterious result, by showing that this apparently contradictory phenomenon is associated with the bandgap in dual-layer graphene structures, a bandgap which is very much smaller than in conventional semiconductors.

The study authors, which included FLEET collaborator David Neilson at the University of Camerino and FLEET CI Alex Hamilton at the University of New South Wales, found that the new multiband theory fully explained the previously inexplicable experimental results.

Excitons travel across an ultra-low energy transistor without wasted dissipation of energy. Credit: FLEET: ARC Centre of Excellence in Future Low Energy Electronics Technologies

Exciton transport

Exciton transport offers great promise to researchers, including the potential for ultra-low dissipation future electronics.

An exciton is a composite particle: an electron and a ‘hole’ (a positively charged ‘quasiparticle’ caused by the absence of an electron) bound together by their opposite electrical charges.

In an indirect exciton, free electrons in one 2D sheet can be electrostatically bound to holes that are free to travel in the neighbouring 2D sheet.

Because the electrons and holes are each confined to their own 2D sheets, they cannot recombine, but they can electrically bind together if the two 2D sheets are very close (a few nanometres).

If electrons in the top (‘drive’) sheet are accelerated by an applied voltage, then each partnering hole in the lower (‘drag’) sheet can be ‘dragged’ by its electron.

This ‘drag’ on the hole can be measured as an induced voltage across the drag sheet, and is referred to as Coulomb drag.

A goal in such a mechanism is for the exciton to remain bound, and to travel as a superfluid, a quantum state with zero viscosity, and thus without wasted dissipation of energy.

To achieve this superfluid state, precisely engineered 2D materials must be kept only a few nanometres apart, such that the bound electron and hole are much closer to each other than they are to their neighbours in the same sheet.

In the device studied, a sheet of hexagonal-boron-nitride (hBN) separates two sheets of atomically-thin (2D) bilayer graphene, with the insulating hBN preventing recombination of electrons and holes.

Passing a current through one sheet and measuring the drag signal in the other sheet allows experimenters to measure the interactions between electrons in one sheet and holes in the other, and to ultimately detect a clear signature of superfluid formation.

Only recently, new, 2D heterostructures with sufficiently thin insulating barriers have been developed that allow us to observe features brought by strong electron-hole interactions.

Explaining the inexplicable: negative drag

However, experiments published in 2016 showed extremely puzzling results. Under certain experimental conditions, the Coulomb drag was found to be negative – i.e. moving an electron in one direction caused the hole in the other sheet to move in the opposite direction!

These results could not be explained by existing theories.

In this new study, these puzzling results are explained using crucial multi-band processes that had not previously been considered in theoretical models.

Previous experimental studies of Coulomb drag had been performed in conventional semiconductor systems, which have much larger bandgaps.

However bilayer graphene has a very small bandgap, and it can be changed by the perpendicular electric fields from the metal gates positioned above and below the sample.

The calculation of transport in both conduction and valence bands in each of the graphene bilayers was the ‘missing link’ that marries theory to experimental results. The strange negative drag happens when the thermal energy approaches the bandgap energy.

The strong multiband effects also affect the formation of exciton superfluids in bilayer graphene, so this work opens up new possibilities for exploration in exciton superfluids.

The study Multiband Mechanism for the Sign Reversal of Coulomb Drag Observed in Double Bilayer Graphene Heterostructures by M. Zarenia, A.R. Hamilton, F.M. Peeters and D. Neilson was published in Physical Review Letters in July 2018.

Acknowledgement: The study was led by David Neilson, and by Mohammad Zarenia while at the University of Antwerp, Belgium. The authors of the theoretical study worked with data provided by experimentalists from the two US groups: Cory Dean (Columbia University) and Emanuel Tutuc (University of Texas at Austin) who discovered the original puzzling results. The research was supported by the Flemish government (Belgium), the University of New South Wales, the University of Camerino and by the Australian Research Council via FLEET.

Superfluids and FLEET

Exciton superfluids are studied within FLEET’s Research theme 2 for their potential to carry zero-dissipation electronic current, and thus allow the design of ultra-low energy exciton transistors.

The use of twin atomically-thin (2D) sheets to carry the excitons will allow for room-temperature superfluid flow, which is key if the new technology is to become a viable ‘beyond CMOS’ technology. A bilayer-exciton transistor would be a dissipationless switch for information processing.

In a superfluid, scattering is prohibited by quantum statistics, which means that electrons and holes can flow without resistance.

In this single, pure quantum state, all particles flow with the same momentum, so that no energy can be lost through dissipation.

FLEET (the Australian Research Council Centre of Excellence in Future Low-Energy Electronics Technologies) brings together over a hundred Australian and international experts, with the shared mission to develop a new generation of ultra-low energy electronics.

The impetus behind such work is the increasing challenge of energy used in computation, which uses 5-8% of global electricity and is doubling every decade.

A key challenge of such ultra-miniature devices is overheating – their ultra-small surfaces seriously limit the ways for the heat from electrical currents to escape.

Working to address “hotspots” in computer chips that degrade their performance, UCLA engineers have developed a new semiconductor material, defect-free boron arsenide, that is more effective at drawing and dissipating waste heat than any other known semiconductor or metal materials.

This could potentially revolutionize thermal management designs for computer processors and other electronics, or for light-based devices like LEDs.

Illustration showing a schematic of a computer chip with a hotspot (bottom); an electron microscope image of defect-free boron arsenide (middle); and an image showing electron diffraction patterns in boron arsenide. Credit: Hu Research Lab / UCLA Samueli

The study was recently published in Science and was led by Yongjie Hu, UCLA assistant professor of mechanical and aerospace engineering.

Computer processors have continued to shrink down to nanometer sizes where today there can be billions of transistors on a single chip. This phenomenon is described under Moore’s Law, which predicts that the number of transistors on a chip will double about every two years. Each smaller generation of chips helps make computers faster, more powerful and able to do more work. But doing more work also means they’re generating more heat.

Managing heat in electronics has increasingly become one of the biggest challenges in optimizing performance. High heat is an issue for two reasons. First, as transistors shrink in size, more heat is generated within the same footprint. This high heat slows down processor speeds, in particular at “hotspots” on chips where heat concentrates and temperatures soar. Second, a lot of energy is used to keep those processors cool. If CPUs did not get as hot in the first place, then they could work faster and much less energy would be needed to keep them cool.

The UCLA study was the culmination of several years of research by Hu and his students that included designing and making the materials, predictive modeling, and precision measurements of temperatures.

The defect-free boron arsenide, which was made for the first time by the UCLA team, has a record-high thermal conductivity, more than three-times faster at conducting heat than currently used materials, such as silicon carbide and copper, so that heat that would otherwise concentrate in hotspots is quickly flushed away.

“This material could help greatly improve performance and reduce energy demand in all kinds of electronics, from small devices to the most advanced computer data center equipment,” Hu said. “It has excellent potential to be integrated into current manufacturing processes because of its semiconductor properties and the demonstrated capability to scale-up this technology. It could replace current state-of-the-art semiconductor materials for computers and revolutionize the electronics industry.”

The study’s other authors are UCLA graduate students in Hu’s research group: Joonsang Kang, Man Li, Huan Wu, and Huuduy Nguyen.

In addition to the impact for electronic and photonics devices, the study also revealed new fundamental insights into the physics of how heat flows through a material.

“This success exemplifies the power of combining experiments and theory in new materials discovery, and I believe this approach will continue to push the scientific frontiers in many areas, including energy, electronics, and photonics applications,” Hu said.

Amkor Technology, Inc. (Nasdaq: AMKR), a provider of outsourced semiconductor packaging and test (OSAT) services, today announced it has partnered with Mentor to release Amkor’s SmartPackage™ Package Assembly Design Kit (PADK), the first in the industry to support Mentor’s High-Density Advanced Packaging (HDAP) design process and tools. Amkor’s award-winning High-Density Fan Out (HDFO) process can now be used in conjunction with Mentor’s software to deliver early, rapid and accurate verification results of advanced packages required for Internet-of-Things, automotive, high-speed communications, computing and artificial intelligence applications.

“Amkor leads the way in HDFO technology for OSAT companies, and with the rise of complex ICs with multi-die packages, we prioritized the creation of Mentor-based PADKs to significantly reduce cycle time,” said Ron Huemoeller, corporate vice president, Research & Development, Amkor Technology. “Since the Mentor flow includes Calibre, the golden sign-off tool for the fabless ecosystem, our customers can easily close any physical verification issued for their entire solution.”

The complex and compact design of devices for today’s smart applications is driving the need for sophisticated packaging techniques such as heterogeneous integration and Advanced System-in-Package. These solutions combine one or more ICs of different functionality with increased I/O and circuit density in 2.5D (side-by-side) and 3D constructions. With Amkor’s SmartPackage PADK and Mentor’s proven HDAP tool flow, mutual customers of Amkor and Mentor have the ability to create and review multiple assemblies and LVS (layout vs. schematic), connectivity, geometry and component spacing scenarios using Amkor’s HDFO process. The graphic environment features robust data and is straightforward to use before and during the implementation of physical design, resulting in faster sign-off and fewer verification cycles.

“Amkor was the first OSAT company to join the Mentor OSAT Alliance program, and now the first to build and make available a PADK for its customers,” said AJ Incorvaia, vice president and general manager of Mentor’s BSD division. “By providing a fully validated PADK for Amkor’s HDFO process for Mentor’s proven HDAP tool flow, customers can more easily transition from classic chip design to 2.5 and 3D solutions.”

The OSAT Alliance program helps promote the adoption, implementation and growth of HDAP throughout the semiconductor ecosystem and design chain, enabling system and fabless semiconductor companies to have a friction-free path for emerging packaging technologies.

The international team of scientist of Peter the Great St. Petersburg Polytechnic University (SPbPU), Leibniz University Hannover (Leibniz Universität Hannover) and the Ioffe Institute found a way to improve nanocomposite material which opens a new opportunities to use it in hydrogen economy and other industries. The obtained results are explained in the academic article “The mechanism of charge carrier generation at the TiO2–n-Si heterojunction activated by gold nanoparticles” published in journal Semiconductor Science and Technology.

The study is dedicated to the composite material, a semiconductor based on titanium dioxide. Its applications are widely studied by the researchers all over the world. But the processes which take place in this material are very complex. Therefore, to use the semiconductor more effectively, it is necessary to ensure that the energy enclosed between its layers can be released and transmitted.

In framework of the experiments the researchers of SPbPU, Leibniz University Hannover and Ioffe Institute propose a qualitative model to explain the complex processes.

The scientific group used a composite material consisting of a silicon wafer (standard silicon wafer used in electronic devices), gold nanoparticles and a thin layer of titanium dioxide. In the framework of the experiment to transfer the energy inside the material, the researchers intended to isolate nanoparticles from silicon. If nanoparticles are not isolated from the silicon wafer, then the energy can’t be transmitted neither to the silicon nor to the titanium dioxide. It leads to the energy loss.

“The obtained material was a silicon wafer with pillar-like structures grown on its surface. It was used as a substrate for the sample. Gold nanoparticles were situated on top of these pillars and the whole structure was coated with titanium oxide. Thus, nanoparticles contacted only titanium dioxide, and simultaneously were isolated from silicon. The number of boundaries between the layers decreased, we tried to describe the processes in the material. In addition, we assumed that this structure would increase the efficiency of using the energy of light illuminating the surface of our material”, says Dr. Maxim Mishin, professor of Physics, Chemistry, and Technology of Microsystems Equipment Department of SPbPU.

In St. Petersburg, an international scientific group established a model of a new structure, then the main part of the structure was created in Hannover: a silicon wafer with pillars and gold nanoparticles situated on top of it.

The experiment was performed as follows. At first, the wafer was oxidized, i.e. it was covered with a layer of the substrate, and gold nanoparticles were put on top of it.

“After that, we faced the next task: to create pillars and to perform the etching of the substrate so that it is remained under the particles and not and in between them. Considering that we are dealing with nanosizes, the diameter of gold nanoparticles is about 10 nanometers, and the height of the pillar is 80 nanometers, this is not a trivial task. The development of modern nanoelectronics makes it possible to use the so-called “dry” etching methods such as reactive ion etching”, adds Dr. Marc Christopher Wurz from the Institute of Micro Production Technology at Leibniz University Hannover.

According to scientists, the process of technology development had not been rapid: at the first stages of the experiment, while using the ion etching, all gold nanoparticles were simply demolished from the oxidized wafer. In the course of one week, the researchers were selecting the parameters for etching plasma system, so that the gold nanoparticles remained on the surface. The whole experiment was conducted within 10 days.

This scientific project is ongoing. The researchers mention that this nanocomposite material can be used in optical devices operating in the visible light spectrum. In addition, it can be used as a catalyst to produce hydrogen from water, or, for example, to purify water by stimulating the decomposition of complex molecules. In addition, this material may be useful as an element of a sensor which detects a gas leak or increased concentration of harmful substances in the air.

Billions of objects ranging from smartphones and watches to buildings, machine parts and medical devices have become wireless sensors of their environments, expanding a network called the “internet of things.”

As society moves toward connecting all objects to the internet – even furniture and office supplies – the technology that enables these objects to communicate and sense each other will need to scale up.

Researchers at Purdue University and the University of Virginia have developed a new fabrication method that makes tiny, thin-film electronic circuits peelable from a surface. The technique not only eliminates several manufacturing steps and the associated costs, but also allows any object to sense its environment or be controlled through the application of a high-tech sticker.

Eventually, these stickers could also facilitate wireless communication. The researchers demonstrate capabilities on various objects in a paper recently published in the Proceedings of the National Academy of Sciences. A YouTube video is available at https://youtu.be/8tNrPVi4OGg.

“We could customize a sensor, stick it onto a drone, and send the drone to dangerous areas to detect gas leaks, for example,” said Chi Hwan Lee, Purdue assistant professor of biomedical engineering and mechanical engineering.

Most of today’s electronic circuits are individually built on their own silicon “wafer,” a flat and rigid substrate. The silicon wafer can then withstand the high temperatures and chemical etching that are used to remove the circuits from the wafer.

But high temperatures and etching damage the silicon wafer, forcing the manufacturing process to accommodate an entirely new wafer each time.

Lee’s new fabrication technique, called “transfer printing,” cuts down manufacturing costs by using a single wafer to build a nearly infinite number of thin films holding electronic circuits. Instead of high temperatures and chemicals, the film can peel off at room temperature with the energy-saving help of simply water.

“It’s like the red paint on San Francisco’s Golden Gate Bridge – paint peels because the environment is very wet,” Lee said. “So in our case, submerging the wafer and completed circuit in water significantly reduces the mechanical peeling stress and is environmentally-friendly.”

A ductile metal layer, such as nickel, inserted between the electronic film and the silicon wafer, makes the peeling possible in water. These thin-film electronics can then be trimmed and pasted onto any surface, granting that object electronic features.

Putting one of the stickers on a flower pot, for example, made that flower pot capable of sensing temperature changes that could affect the plant’s growth.

Lee’s lab also demonstrated that the components of electronic integrated circuits work just as well before and after they were made into a thin film peeled from a silicon wafer. The researchers used one film to turn on and off an LED light display.

“We’ve optimized this process so that we can delaminate electronic films from wafers in a defect-free manner,” Lee said.

This technology holds a non-provisional U.S. patent. The work was supported by the Purdue Research Foundation, the Air Force Research Laboratory (AFRL-S-114-054-002), the National Science Foundation (NSF-CMMI-1728149) and the University of Virginia.

With companies like Google, Microsoft, and IBM all racing to create the world’s first practical quantum computer, scientists worldwide are exploring the potential materials that could be used to build them.

Now, Associate Professor Yang Hyunsoo and his team from the Department of Electrical and Computer Engineering at the National University of Singapore (NUS) Faculty of Engineering have demonstrated a new method which could be used to bring quantum computing closer to reality.

“The NUS team, together with our collaborators from Rutgers, The State University of New Jersey in the United States and RMIT University in Australia, showed a practical way to observe and examine the quantum effects of electrons in topological insulators and heavy metals which could later pave the way for the development of advanced quantum computing components and devices,” explained Assoc Prof Yang.

The findings of the study were published in the scientific journal Nature Communications in June 2018.

The advantage of quantum computers

Quantum computers are still in the early stages of development but are already displaying computing speeds millions of times faster than traditional technologies. As such, it is predicted that when quantum computing becomes more readily available, it will be able to answer some of the world’s toughest questions in everything from finance to physics. This remarkable processing power is made possible by the radical way that quantum computers operate – using light rather than electricity.

Classical computers push electrons through devices which code information into binary states of ones and zeros. In contrast, quantum computers use laser light to interact with electrons in materials to measure the phenomenon of electron “spin”. These spinning electron states replace the ones and zeros used as the basis for traditional computers, and because they can exist in many spin states simultaneously, this allows for much more complex computing to be performed.

However, harnessing information based on the interactions of light and electrons is easier said than done. These interactions are incredibly complex and like anything in the quantum world there is a degree of uncertainty when trying to predict behaviour. As such, a reliable and practical way to observe these quantum effects has been sought-after in recent research to help in the discovery of more advanced quantum computing devices.

Visualising quantum spin effects

The real breakthrough from the scientists at NUS was the ability to “see” for the first time particular spin phenomena in topological insulators and metals using a scanning photovoltage microscope.

Topological insulators are electronic materials that are insulating in their interior but support conducting states on their surface, thus enabling electrons to flow along the surface of the material.

Assoc Prof Yang and his team examined platinum metal as well as topological insulators Bi2Se3 and BiSbTeSe2. An applied electrical current influenced the electron spin at the quantum level for all of these materials and the scientists were able to directly visualise this change using polarised light from the microscope.

Additionally, unlike other observational techniques, the innovative experimental setup meant that the results could be gathered at room temperature, making this a practical method of visualisation which is applicable to many other materials.

Mr Liu Yang, who is a PhD student with the Department and first author of the study, said, “Our method can be used as a powerful and universal tool to detect the spin accumulations in various materials systems. This means that developing better devices for quantum computers will become easier now that these phenomena can be directly observed in this way.”

Next steps

Moving forward, Assoc Prof Yang and his team are planning to test their new method on more novel materials with novel spin properties. The team hopes to work with industry partners to further explore the various applications of this unique technique, with a focus on developing the devices used in future quantum computers.