Tag Archives: letter-materials-tech

Let there be light


June 17, 2016

University of Utah materials science and engineering associate professor Mike Scarpulla wants to shed light on semiconductors — literally.

Scarpulla and senior scientist Kirstin Alberi of the National Renewable Energy Laboratory in Golden, Colorado, have developed a theory that adding light during the manufacturing of semiconductors — the materials that make up the essential parts of computer chips, solar cells and light emitting diodes (LEDs) — can reduce defects and potentially make more efficient solar cells or brighter LEDs. The role of light in semiconductor manufacturing may help explain many puzzling differences between processing methods as well as unlock the potential of materials that could not be used previously.

Scarpulla and Alberi reported their findings in a paper titled “Suppression of Compensating Native Defect Formation During Semiconductor Processing Via Excess Carriers,” published June 16 in the journal, Scientific Reports. The research was funded by grants from the U.S. Department of Energy Office of Basic Energy Sciences.

Semiconductors are pure materials used to produce electronic components such as computer chips, solar cells, radios used in cellphones or LEDs. The theory developed by Scarpulla and Alberi applies to all semiconductors but is most exciting for compound semiconductors — such as gallium arsenide (GaAs), cadmium telluride (CdTe), or gallium nitride (GaN) — that are produced by combining two or more elements from the periodic table. GaAs is used in microwave radios in cellphones, CdTe in solar panels, and GaN in LED light bulbs.

The fact that compound semiconductors require more than one chemical element make them susceptible to defects in the material at an atomic scale, says Scarpulla, who also is a University of Utah electrical and computer engineering associate professor.

“Defects produce lots of effects like difficulty in controlling the conductivity of the material, difficulty in being able to turn sunlight into electricity efficiently in the case of solar cells or difficulty in emitting light efficiently in the case of LEDs,” he says.

For nearly a century, researchers have usually assumed that the numbers of these defects in semiconductors were uniquely defined by the temperature and pressure during processing. “We worked out a complete theory that couples light into that problem,” Scarpulla says.

The team discovered that if you add light while firing the material in a furnace at high temperatures, the light generates extra electrons that can change the composition of the material.

“We ran simulations of what happens,” Scarpulla says. “If you put a piece of a semiconductor in a furnace in the dark, you would get one set of properties from it. But when you shine light on it in the furnace, it turns out you suppress these more problematic defects. We think it may allow us to get around some tricky problems with certain materials that have prevented their use for decades. The exciting work is in the future though — actually testing these predictions to make better devices.”

The team is working to apply their theory to as many semiconductors as possible and testing the real world results. For example, the team believes this could improve the efficiency of solar panels that use thin films of cadmium telluride and even those made from silicon.

“It’s really cool to be working on this fundamental problem in semiconductors,” says Scarpulla. “Most of the ideas were worked out decades ago, so it is really exciting to be able to make a contribution to something fundamental. It feels like we have shined light onto a new path and we don’t know how far it will take us.”

Researchers at Case Western Reserve University have developed a way to swiftly and precisely control electron spins at room temperature.

The technology, described in Nature Communications, offers a possible alternative strategy for building quantum computers that are far faster and more powerful than today’s supercomputers.

“What makes electronic devices possible is controlling the movement of electrons from place to place using electric fields that are strong, fast and local,” said physics Professor Jesse Berezovsky, leader of the research. “That’s hard with magnetic fields, but they’re what you need to control spin.”

Other researchers have searched for materials where electric fields can mimic the effects of a magnetic field, but finding materials where this effect is strong enough and still works at room temperature has proven difficult.

“Our solution,” Berezovsky said, “is to use a magnetic vortex.”

Berezovsky worked with physics PhD students Michael S. Wolf and Robert Badea.

The researchers fabricated magnetic micro-disks that have no north and south poles like those on a bar magnet, but magnetize into a vortex. A magnetic field emanates from the vortex core. At the center point, the field is particularly strong and rises perpendicular to the disk.

The vortices are coupled with diamond nanoparticles. In the diamond lattice inside each nanoparticle, several individual spins are trapped inside of defects called nitrogen vacancies.

The scientists use a pulse from a laser to initialize the spin. By applying microwaves and a weak magnetic field, Berezovsky’s team can move the vortex in nanoseconds, shifting the central point, which can cause an electron to change its spin.

In what’s called a quantum coherent state, the spin can act as a quantum bit, or qubit–the basic unit of information in a quantum computer,

In current computers, bits of information exist in one of two states: zero or one. But in a superposition state, the spin can be up and down at the same time, that is, zero and one simultaneously. That capability would allow for more complex and faster computing.

“The spins are close to each other; you want spins to interact with their neighbors in quantum computing,” Berezovsky said. “The power comes from entanglement.”

The magnetic field gradient produced by a vortex proved sufficient to manipulate spins just nanometers apart.

In addition to computing, electrons controlled in coherent quantum states might be useful for extremely high-resolution sensors, the researchers say. For example, in an MRI, they could be used to sense magnetic fields in far more detail than with today’s technology, perhaps distinguishing atoms.

Controlling the electron spins without destroying the coherent quantum states has proven difficult with other techniques, but a series of experiments by the group has shown the quantum states remain solid. In fact, “the vortex appears to enhance the microwave field we apply,” Berezovsky said.

The scientists are continuing to shorten the time it takes to change the spin, which is a key to high-speed computing. They are also investigating the interactions between the vortex, microwave magnetic field and electron spin, and how they evolve together.

In the 2015 movie “The Martian,” stranded astronaut Matt Damon turns to the chemistry of rocket fuel, hydrazine and hydrogen, to create lifesaving water and nearly blows himself up. But if you turn the process around and get the hydrazine to help, you create hydrogen from water by changing conductivity in a semiconductor, a transformation with wide potential applications in energy and electronics.

New research from Los Alamos National Laboratory researchers, "Efficient Hydrogen Evolution in Transition Metal Dichalcogenides via a Simple One-Step Hydrazine Reaction," not only presents one of the best hydrogen water splitting electrocatalysts to date, but also opens up a whole new direction for research in electrochemistry and semiconductor device physics. Credit: Los Alamos National Laboratory

New research from Los Alamos National Laboratory researchers, “Efficient Hydrogen Evolution in Transition Metal Dichalcogenides via a Simple One-Step Hydrazine Reaction,” not only presents one of the best hydrogen water splitting electrocatalysts to date, but also opens up a whole new direction for research in electrochemistry and semiconductor device physics. Credit: Los Alamos National Laboratory

“We demonstrate in our study that a simple chemical treatment, in this case a drop of dilute hydrazine (N2H4) in water, can dope electrons directly to a semiconductor, creating one of the best hydrogen-evolution electrocatalysts,” said Gautam Gupta, project leader at Los Alamos National Laboratory in the Light to Energy team of the Lab’s Materials Synthesis and Integrated Devices group. The research was published in Nature Communications.

Understanding how to use a simple, room-temperature treatment to drastically change the properties of materials could lead to a revolution in renewable fuels production and electronic applications. As part of the Los Alamos mission, the Laboratory conducts multidisciplinary research to strengthen the security of energy for the nation, work that includes exploring alternative energy sources.

In recent years, the materials science community has grown more interested in the electrical and catalytic properties of layered transition metal dichalcogenides (TMDs). TMDs are primarily metal sulfides and selenides (e.g., MoS2) with a layered structure, similar to graphite; this layered structure allows for unique opportunities, and challenges, in modifying electrical properties and functionality.

Gupta and Aditya Mohite, a physicist with a doctorate in electrical engineering, have been pioneering work at Los Alamos seeking to understand the electrical properties of TMDs and use that knowledge to optimize these semiconductors for renewable fuels production.

In this work, MoS2 shell — MoOx core nanowires, as well as pure MoS2 particles and 2D sheets — are tested for electrocatalysis of the hydrogen evolution reaction. The addition of dilute hydrazine to MoS2 significantly improves the electrocatalytic performance. Further characterization shows that the MoS2 changes from semiconducting behavior to having more metallic properties following the hydrazine exposure.

“The most interesting thing about this result is that it is different than conventional doping, where actual chemicals are added to a semiconductor to change its charge carrier concentration. In the case of hydrazine treatment, we are ‘doping’ electrons directly to the material, without modifying the original chemistry,” said Dustin Cummins, first author on this project, currently a postdoctoral researcher in the Laboratory’s Sigma Division working on the DOE/NNSA CONVERT Program, exploring fuel fabrication for next-generation reactors.

Cummins first found the hydrogen-production result working with Gupta at Los Alamos as a graduate student research affiliate from the University of Louisville (advisor: Dr. Mahendra Sunkara) and he continued to conduct experiments and refine discussion while working as a postdoc.

“Hydrazine acting as an electron dopant in inorganic semiconductors has been observed since the 1970s, but there is limited understanding of the process,” Cummins noted. “Our biggest hurdle was to prove to that hydrazine was actually changing the conductivity of the MoS2 system, and that is what results in increased catalytic activity,” which was demonstrated on single-flake devices, he said.

Multiple areas of Los Alamos staff expertise in layered semiconductors, chemistry, spectroscopy, electrical device fabrication and more all came together to provide some of the best understanding and mechanism to date for hydrazine acting as an electron dopant.

This paper, “Efficient Hydrogen Evolution in Transition Metal Dichalcogenides via a Simple One-Step Hydrazine Reaction,” not only presents one of the best hydrogen water splitting electrocatalysts to date, but also “it opens up a whole new direction for research in electrochemistry and semiconductor device physics in general,” said Gupta.

An ultrathin film that is both transparent and highly conductive to electric current has been produced by a cheap and simple method devised by an international team of nanomaterials researchers from the University of Illinois at Chicago and Korea University.

Highly conductive ultrathin film on skin between clips. Credit: Sam Yoon, Korea University

Highly conductive ultrathin film on skin between clips.
Credit: Sam Yoon, Korea University

The film — actually a mat of tangled nanofiber, electroplated to form a “self-junctioned copper nano-chicken wire” — is also bendable and stretchable, offering potential applications in roll-up touchscreen displays, wearable electronics, flexible solar cells and electronic skin.

The finding is reported in the June 13 issue of Advanced Materials.

“It’s important, but difficult, to make materials that are both transparent and conductive,” says Alexander Yarin, UIC Distinguished Professor of Mechanical Engineering, one of two corresponding authors on the publication.

The new film establishes a “world-record combination of high transparency and low electrical resistance,” the latter at least 10-fold greater than the previous existing record, said Sam Yoon, who is also a corresponding author and a professor of mechanical engineering at Korea University.

The film also retains its properties after repeated cycles of severe stretching or bending, Yarin said — an important property for touchscreens or wearables.

Manufacture begins by electrospinning a nanofiber mat of polyacrylonitrile, or PAN, whose fibers are about one-hundredth the diameter of a human hair. The fiber shoots out like a rapidly coiling noodle, which when deposited onto a surface intersects itself a million times, Yarin said.

“The nanofiber spins out in a spiral cone, but forms fractal loops in flight,” Yarin said. “The loops have loops, so it gets very long and very thin.”

The naked PAN polymer doesn’t conduct, so it must first be spatter-coated with a metal to attract metal ions. The fiber is then electroplated with copper — or silver, nickel or gold.

The electrospinning and electroplating are both relatively high-throughput, commercially viable processes that take only a few seconds each, according to the researchers.

“We can then take the metal-plated fibers and transfer to any surface — the skin of the hand, a leaf, or glass,” Yarin said. An additional application may be as a nano-textured surface that dramatically increases cooling efficiency.

Yoon said the “self-fusion” by electroplating at the fiber junctions “dramatically reduced the contact resistance.” Yarin noted that the metal-plated junctions facilitated percolation of the electric current — and also account for the nanomaterial’s physical resiliency.

“But most of it is holes,” he said, which makes it 92 percent transparent. “You don’t see it.”

VTT Technical Research Centre of Finland developed an extremely efficient small-size energy storage, a micro-supercapacitor, which can be integrated directly inside a silicon microcircuit chip. The high energy and power density of the miniaturized energy storage relies on the new hybrid nanomaterial developed recently at VTT. This technology opens new possibilities for integrated mobile devices and paves the way for zero-power autonomous devices required for the future Internet of Things (IoT).

Supercapacitors resemble electrochemical batteries. However, in contrast to for example mobile phone lithium ion batteries, which utilize chemical reactions to store energy, supercapacitors store mainly electrostatic energy that is bound at the interface between liquid and solid electrodes. Similarly to batteries supercapacitors are typically discrete devices with large variety of use cases from small electronic gadgets to the large energy storages of electrical vehicles.

The energy and power density of a supercapacitor depends on the surface area and conductivity of the solid electrodes. VTT’s research group has developed a hybrid nanomaterial electrode, which consists of porous silicon coated with a few nanometre thick titanium nitride layer by atomic layer deposition (ALD). This approach leads to a record large conductive surface in a small volume. Inclusion of ionic liquid in a micro channel formed in between two hybrid electrodes results in extremely small and efficient energy storage.

The new supercapacitor has excellent performance. For the first time, silicon based micro-supercapacitor competes with the leading carbon and graphene based devices in power, energy and durability.

Micro-supercapacitors can be integrated directly with active microelectronic devices to store electrical energy generated by different thermal, light and vibration energy harvesters and to supply the electrical energy when needed. This is important for autonomous sensor networks, wearable electronics and mobile electronics of the IoT.

VTT’s research group takes the integration to the extreme by integrating the new nanomaterial micro-supercapacitor energy storage directly inside a silicon chip. The demonstrated in-chip supercapacitor technology enables storing energy of as much as 0.2 joule and impressive power generation of 2 watts on a one square centimetre silicon chip. At the same time it leaves the surface of the chip available for active integrated microcircuits and sensors.

VTT is currently seeking a party interested in commercializing the technique.

Nanomaterials have the potential to improve many next-generation technologies. They promise to speed up computer chips, increase the resolution of medical imaging devices and make electronics more energy efficient. But imbuing nanomaterials with the right properties can be time consuming and costly. A new, quick and inexpensive method for constructing diamond-based hybrid nanomaterials could soon launch the field forward.

University of Maryland researchers developed a method to build diamond-based hybrid nanoparticles in large quantities from the ground up, thereby circumventing many of the problems with current methods. The technique is described in the June 8, 2016 issue of the journal Nature Communications.

The process begins with tiny, nanoscale diamonds that contain a specific type of impurity: a single nitrogen atom where a carbon atom should be, with an empty space right next to it, resulting from a second missing carbon atom. This “nitrogen vacancy” impurity gives each diamond special optical and electromagnetic properties.

By attaching other materials to the diamond grains, such as metal particles or semiconducting materials known as “quantum dots,” the researchers can create a variety of customizable hybrid nanoparticles, including nanoscale semiconductors and magnets with precisely tailored properties.

“If you pair one of these diamonds with silver or gold nanoparticles, the metal can enhance the nanodiamond’s optical properties. If you couple the nanodiamond to a semiconducting quantum dot, the hybrid particle can transfer energy more efficiently,” said Min Ouyang, an associate professor of physics at UMD and senior author on the study.

Evidence also suggests that a single nitrogen vacancy exhibits quantum physical properties and could behave as a quantum bit, or qubit, at room temperature, according to Ouyang. Qubits are the functional units of as-yet-elusive quantum computing technology, which may one day revolutionize the way humans store and process information. Nearly all qubits studied to date require ultra-cold temperatures to function properly.

A qubit that works at room temperature would represent a significant step forward, facilitating the integration of quantum circuits into industrial, commercial and consumer-level electronics. The new diamond-hybrid nanomaterials described in Nature Communications hold significant promise for enhancing the performance of nitrogen vacancies when used as qubits, Ouyang noted.

While such applications hold promise for the future, Ouyang and colleagues’ main breakthrough is their method for constructing the hybrid nanoparticles. Although other researchers have paired nanodiamonds with complementary nanoparticles, such efforts relied on relatively imprecise methods, such as manually installing the diamonds and particles next to each other onto a larger surface one by one. These methods are costly, time consuming and introduce a host of complications, the researchers say.

“Our key innovation is that we can now reliably and efficiently produce these freestanding hybrid particles in large numbers,” explained Ouyang, who also has appointments in the UMD Center for Nanophysics and Advanced Materials and the Maryland NanoCenter, with an affiliate professorship in the UMD Department of Materials Science and Engineering.

The method developed by Ouyang and his colleagues, UMD physics research associate Jianxiao Gong and physics graduate student Nathaniel Steinsultz, also enables precise control of the particles’ properties, such as the composition and total number of non-diamond particles. The hybrid nanoparticles could speed the design of room-temperature qubits for quantum computers, brighter dyes for biomedical imaging, and highly sensitive magnetic and temperature sensors, to name a few examples.

“Hybrid materials often have unique properties that arise from interactions between the different components of the hybrid. This is particularly true in nanostructured materials where strong quantum mechanical interactions can occur,” said Matthew Doty, an associate professor of materials science and engineering at the University of Delaware who was not involved with the study. “The UMD team’s new method creates a unique opportunity for bulk production of tailored hybrid materials. I expect that this advance will enable a number of new approaches for sensing and diagnostic technologies.”

The special properties of the nanodiamonds are determined by their nitrogen-vacancies, which cause defects in the diamond’s crystal structure. Pure diamonds consist of an orderly lattice of carbon atoms and are completely transparent. However, pure diamonds are quite rare in natural diamond deposits; most have defects resulting from non-carbon impurities such as nitrogen, boron and phosphorus. Such defects create the subtle and desirable color variations seen in gemstone diamonds.

The nanoscale diamonds used in the study were created artificially, and have at least one nitrogen vacancy. This impurity results in an altered bond structure in the otherwise orderly carbon lattice. The altered bond is the source of the optical, electromagnetic and quantum physical properties that make the diamonds useful when paired with other nanomaterials.

Although the current study describes diamonds with nitrogen substitutions, Ouyang points out that the technique can be extended to other diamond impurities as well, each of which could open up new possibilities.

“A major strength of our technique is that it is broadly useful and can be applied to a variety of diamond types and paired with a variety of other nanomaterials,” Ouyang explained. “It can also be scaled up fairly easily. We are interested in studying the basic physics further, but also moving toward specific applications. The potential for room-temperature quantum entanglement is particularly exciting and important.”

Marianna Kharlamova (the Lomonosov Moscow State University Department of Materials Science) examined different types of carbon nanotubes’ “stuffing” and classified them according to the influence on the properties of the nanotubes. The researcher’s work was published in the high-impact journal Progress in Materials Science (impact factor — 26.417).

An 87 pages long overview summarized the achievements of scientists in the field of the investigation of the electronic properties of single-walled carbon nanotubes (SWNTs). ‘A detailed systematic study of 430 works was conducted, including 20 author’s works, most of which had been published during the last 5 years, as the area under study is actively developing,’ says Marianna Kharlamova. Apart from analytical systematization of the existing data, the author considers the theoretical basis of such studies — the band theory of solids, which describes the interaction of the electrons in a solid.

The Many Faces of carbon: diamonds, balls, tubes

Carbon has several forms of existence (allotropic modifications) and can be found in different structures. It forms coal and carbon black, diamond, graphite, from which slate pencils are made, graphene, fullerenes and others. The whole organic chemistry is based on carbon which forms the molecular backbone. In diamonds the carbon atoms are kept on a strictly specified positions of the crystal lattice (which leads to its hardness). In graphite, the carbon atoms are arranged in hexagonal layers resembling honeycombs. Each layer is rather weakly interacting with the one above and the one below, so the material is easily separated into flakes which look to us like a pencil mark on the paper. If you take one such layer of hexagons and roll it into a tube, you get what is called a carbon nanotube.

A single-walled nanotube is a single rolled layer, and a multi-walled looks like the Russian ‘matryoshka’ doll, consisting of several concentric tubes. The diameter of each tube is a few nanometers, and the length is up to several centimeters. The ends of the tube are closed by hemispheric “caps” — halves of fullerene molecules (fullerenes are another form of elemental carbon resembling a soccer ball stitched together from hexagons and pentagons). To make and fill the carbon nanotube is much more challenging than to stuff a wafer curl : to tailor these structures scientists use laser ablation techniques, thermal dispersion in an arc discharge or vapor deposition of hydrocarbons from the gas phase.

SWNT is no cookie

What is so special about them then? The properties of the graphite (electrical conductivity, ductility, metallic shine) remind metals, yet carbon nanotubes have quite different properties, which can be used in electronics (as components of prospective nanoelectronic devices — gates, memory and data transmission devices etc.) and biomedicine (as containers for targeted drug delivery). The conductivity of carbon nanotubes can be changed depending on the orientation of the carbon hexagons relative to the tube axis, on what is included in its wall besides carbon, on which atoms and molecules are attached to the outer surface of the tube, and what it is filled with. Besides, single-walled carbon nanotubes (or SWNTs) are surprisingly tear-proof and refract light in a particular way.

Marianna Kharlamova was the first to classify types of nanotubes’ “stuffing” according to their impact on the electronic properties of SWNTs. The author of the review considers the method of filling SWNTs as the most promising for tailoring their electronic properties.

‘This is due to four main reasons,’ Marianna Kharlamova says. ‘Firstly, the range of substances that can be encapsulated in the SWNT channels is wide. Second, to introduce the substances of different chemical nature into the SWNT channels several methods have been developed: from the liquid phase (solution, melt), the gas phase, using plasma, or by chemical reactions. Third, as a result of the encapsulation process, high degree of the filling of SWNT channels can be achieved, which leads to the significant change in the electronic structure of nanotubes. Finally, the chemical transformation of the encapsulated substances allows controlling the process of tailoring the electronic properties of the SWNTs by selecting an appropriate starting material and conditions of the nanochemical reaction.’

The author herself conducted experimental studies of the filling of nanotubes with 20 simple substances and chemical compounds, revealed the influence of “stuffing” on the electronic properties of nanotubes, found the correlation between the temperature of the formation of inner tubes and the diameter of the outer tubes, and explained which factors influence the degree of the nanotubes’ filling.

A research group at Tohoku University’s WPI-AIMR has succeeded in finding the origin and the mechanism of ferromagnetism in Mn-doped GaAs. The discovery is significant as it will accelerate the development of the spintronic element.

GaAs, like silicon, is a well-known semiconductor commonly used in high-speed electronic devices and laser diodes.

When manganese (Mn) atoms are doped into a GaAs crystal ((Ga,Mn)As), the crystal exhibits characteristics and properties of both the semiconductor and magnet (Fig. 1). Since it is possible to use an electric field to control the magnetism in (Ga,Mn)As, Mn-doped GaAs has been a key material in spintronic devices and a significant contributor to the development of spintronics technology.

Fig.1: Crystal structure of (Ga,Mn)As. Mn ions substituted for Ga have a magnetic moment, and the magnetic moment of each Mn ion aligns along the same direction when (Ga,Mn)As becomes a ferromagnet. Credit: Seigo Souma

Fig.1: Crystal structure of (Ga,Mn)As. Mn ions substituted for Ga have a magnetic moment, and the magnetic moment of each Mn ion aligns along the same direction when (Ga,Mn)As becomes a ferromagnet. Credit: Seigo Souma

However, although it has been 20 years since that discovery, the mechanism of ferromagnetism in (Ga,Mn)As is still not widely understood or well explained. There remains fierce debate and confusion, leading to obstacles preventing the progress and further development of spintronics technology.

The researchers at Tohoku University, led by Profs. H. Ohno and T. Takahashi, have succeeded in directly observing the electronic states which participate in creating the ferromagnetism by photoemission spectroscopy. They found that doped Mn atoms extract electrons from As atoms, leaving “holes” (empty states of electrons) in the As orbital. This then causes the ferromagnetism in (Ga,Mn)As.

“This finding resolves the long-standing problem in the mechanism of ferromagnetism in (Ga,Mn)As,” says researcher Seigo Souma. “It also accelerates the materials engineering of magnetic semiconductors, as well as the tunable controlling of spin states in spintronic devices. This is very significant result and we’re excited about the potential it represents.”

Electron movements form the basis of electronics as they enable storage, processing and transfer of information. State-of-the-art electronic circuits have reached maximum clock rates of several billion switching cycles per second, limited by the heat accumulated in the process of switching power on and off.

The electric field of light changes its direction a trillion times per second and is able to move electrons in solids at this speed. Thus light waves could form the basis for future electronic switching once the induced electron motion and its influence on heat accumulation is precisely understood.

Physicists from the Laboratory for Attosecond Physics have already found out that it is possible to manipulate the electronic properties of matter at optical frequencies. In a follow-up experiment the researchers, in a manner similar to their previous approach, shot extremely strong, femtosecond-laser pulses (one femtosecond is a millionth of a billionth of a second) onto silicon dioxide glass.

A single oscillation

The light pulse comprises only a single strong oscillation cycle of the field, hence the electrons are moved left and right only once. The full temporal characterization of the light field after transmission through the thin glass plate now, for the first time, provides direct insight into the attosecond electron dynamics, induced by the light pulse in the solid.

This measurement technique reveals that electrons react with a delay of only some ten attoseconds (one attosecond is a billionth of a billionth of a second) to the incoming light. This time delay in the reaction determines the energy transferred between light and matter.

Since it is now possible to measure this energy exchange within one light cycle, the parameters of the light-matter interaction can be understood and optimized to reach out for the ultimate speed in signal processing. The more reversible the exchange and the smaller the residual energy left in the medium after the light pulse has passed, the more suitable the interaction for future light field-driven electronics.

Cool relationship

To understand the observed phenomena and identify the best set of experimental parameters to that end, the experiments were backed up by a novel simulation method based on first principles developed at the Center for Computational Sciences at University of Tsukuba. The theorists there used the K computer, currently the fourth fastest supercomputer in the world, to compute electron movement inside solids with unprecedented accuracy.

Finally, the researchers succeeded in optimizing the energy consumption by adapting the amplitude of the light field. At certain field strengths energy is transferred from the field to the solid during the first half of the pulse cycle and is almost completely emitted back in the second half of the light.

These findings verify that a potential switching medium for future light-driven electronics need not overheat. Thus the ‘cool relationship’ between glass and light might provide an opportunity for dramatically accelerating electronic signal and data processing, up to the ultimate limit.

By Dr. Khasha Ghaffarzadeh, Research Director, IDTechEx

The first generation of wearable devices are constructed using mature, rigid technologies put inside a new box that can be worn. These are often bulky devices that are not truly wearable in the sense that our clothes are. This is, however, beginning to change, albeit slowly. New conformal, clothing-based components are emerging. Further announcements last week from Google’s Project Jacquard, in collaboration with Levis, shows that the technology and fashion industries are starting to make real progress through collaboration.

This project is but one example of work being done and the IDTechEx Research report, E-Textiles 2016-2026: Technologies, Markets, and Players, finds that electronic textiles (e-textiles) are on the cusp of rapid growth, forecasting the market to increase from under $150m in 2016 to over $3.2bn by 2026.  Many still argue that e-textiles are solutions looking for a problem, but IDTechEx Research finds that there is tremendous interest and progress right across the value chain. This includes material suppliers, traditional textile companies, contract manufacturers, brand owners, etc.

Conductors will inevitably play an indispensable role in any e-textile system. Naturally, therefore, conductive inks suppliers are all very interested. In parallel, conductive ink suppliers face challenging conditions in their traditional well-established market sectors.

For example, IDTechEx Research report, Conductive Ink Markets 2016-2026: Forecasts, Technologies, and Players, forecasts that the combined market for the previously well-established photovoltaic and touch screen edge electrodes will achieve a measly CAGR of 1-2% between 2016 and 2026.  The latter segment is forecast to decline whilst growth in the former will be hugely constrained thanks to the decreasing average silver consumption per cell.

In fact, these traditional markets are increasingly characterised by low demand growth, intense competition, high customer price sensitivity, and low customer loyalty.  This is yet another reason why conductive inks suppliers are hugely interested in new high-growth applications areas such as e-textiles.

Source: IDTechEx Research

Source: IDTechEx Research

Conductive inks win on their universality?

Conductive ink suppliers are touching and feeling their way into the e-textile market. Many have launched specially-designed inks on the market. Some examples are shown below. Most are also having to proactively help form and develop the nascent value chain. This is currently still more of a push than a pull market.

conductive inks

This is a complex space since conductive inks are one of many approaches being concurrently developed for e-textiles. To name a few, these approaches include metal cabling, textile cabling, conducting knits, conductive wovens, conductive inks, etc. There is a paucity of verified technical information and well-defined figures-of-merit on the market. We have therefore developed our semi-qualitative benchmarking based on many end users and supplier discussions, which can be found within the IDTechEx report: E-Textiles 2016-2026: Technologies, Markets, and Players.

There is no clear-cut winner. This is because some approaches win, say, on ease of integration with existing processes or maturity,whereas others win on increased clothing-like appearance and feel. Project Jacquard’s smart jacket, built specifically for urban bikers, is an excellent example of a compromise in these areas, with the look and feel being key in the selection of conductive yarns as the primary material. Still, there is no one-size-fits-all solution and the winner will be specific to an end use and/or a production process.

This makes sense as the traditional textile world itself includes many fabric types, production processes, and end uses. Despite the appearance of familiarly, this is an incredibly diverse and complex industry.  The technology composition will therefore be a mixed bag in the medium-term as e-textile manufacturers will likely select their conductor of choice based on the specific requirements of each application and their own existing production processes.

In the long-term, e-textile conductive inks will have a larger addressable market than all the other solutions. This is because they offer the highest degree of universal applicability: their integration is a post-production process that can be used by almost any textile manufacturer unless the fabrics cannot withstand high laminating temperatures or are very loose.

In the short to medium term, the risk however is that some end applications are more equal than others. For example, IDTechEx Research finds that smart sports clothing alone will make up 65% of the market by 2020. The challenge is therefore in identifying, targeting and winning in specific high-growth application sectors. IDTechEx Research can help you find and penetrate these sectors.

For more information please refer IDTechEx Research report, Conductive Ink Markets 2016-2026: Forecasts, Technologies, and Players.

Not the finished article yet

The ink technology however is not yet finished article. Achieving washability, direct-on-fabric printability, and high stretchability are challenging technical requirements. The industry is only beginning to accumulate expertise here. Therefore, this is the beginning of the beginning and we expect better e-textile conductive inks in the future.

The process currently is too complicated because the inks need to be printed and cured on a substrate such as TPU before being encapsulated using a similar substrate. The film then needs to be hot laminated over the fabric. This approach improves washability and durability, and does away with the technical headache of having to develop a different ink optimised for each fabric substrate, but screams out to be simplified.

TPU itself is the first choice of encapsulate but not likely to be the last. This is because it is not the most stretchable thus restricting the clothing-like feeling of e-textiles particularly if large areas are covered. Already companies are experimenting with othermaterial systems such as TPU/silicone combinations.

Silver costs can also be a limiting factor. This opens the way for carbon or graphene based inks in applications where high conductivity is not required. In the long term copper inks may also be an option but they have a long way to go to prove their reliability and technology maturity.