Category Archives: Process Materials

Researchers first developed a three-dimensional dynamic model of an interaction between light and nanoparticles. They used a supercomputer with graphic accelerators for calculations. Results showed that silicon particles exposed to short intense laser pulses lose their symmetry temporarily. Their optical properties become strongly heterogeneous. Such a change in properties depends on particle size, therefore it can be used for light control in ultrafast information processing nanoscale devices. The study is published in Advanced Optical Materials.

Improvement of computing devices today requires further acceleration of information processing. Nanophotonics is one of the disciplines that can solve this problem by means of optical devices. Although optical signals can be transmitted and processed much faster than electronic ones, first, it is necessary to learn how to quickly control light on a small scale. For this purpose, one could use metal particles. They localize light efficiently, yet weaken the signal eventually causing significant losses. However, dielectric and semiconducting materials, such as silicon, can be used instead of metal.

Silicon nanoparticles are now actively studied by researchers all around the world, including ITMO University. The long-term goal of such studies is to create an ultrafast compact modulators for optical signal. They can serve as a basis for computers of the future. However, this technology will become feasible only once we understand how nanoparticles interact with light.

“When a laser pulse hits the particle, a lot of free electrons are formed inside,” explains Sergey Makarov, head of the Laboratory of Hybrid Nanophotonics and Optoelectronics of ITMO University. “As a result a region saturated with oppositely charged particles is created. It is usually called an electron-hole plasma. Plasma changes optical properties of particles and up to now everybody believed that it happens with the whole particle simultaneously, so that the symmetry is preserved. We showed that this is not entirely true and an even distribution of the plasma inside particles is not the only possible scenario.”

Scientists found that an electromagnetic disturbance caused by interaction between light and particles has a more complex structure. This leads to a light distortion, varying with time. Therefore, the symmetry of particles breaks and optical properties become different throughout one particle. “Using analytical and numerical methods we first looked inside the particle and saw that processes taking place there are far more complicated than we thought,” says Konstantin Ladutenko, a member of the International Research Center of Nanophotonics and Metamaterials of ITMO University. “Moreover, we found that by changing the particle size, we can affect its interaction with the light signal. So, we might be able to predict the signal path in a entire system of nanoparticles.”

In order to create a tool to study processes inside nanoparticles, scientists from ITMO University joined forces with colleagues from Jean Monnet University in France. “We proposed analytical methods to determine particle size and refractive index, which might provide a change in optical properties. Afterwards, with powerful computational methods we tracked processes inside particles. Our colleagues did calculations on a computer with graphics accelerators. Such computers are often used for cryptocurrency mining. However, we decided to enrich humanity with new knowledge, rather than enrich ourselves. What is more, bitcoin rate just started to fall then,” adds Konstantin.

Devices based on such nanoparticles may become basic elements of optical computers, just as transistors now are basic elements of electronics. They will make it possible to distribute and redirect or branch the signal. “Such asymmetric structures have a variety of applications yet we focus on ultra-fast signal processing,” continues Sergey. “Now we have a powerful theoretical tool which will help us to develop a quick and compact light management system.”

 

University of Groningen physicists have managed to alter the flow of spin waves through a magnet, using only an electrical current. This is a huge step towards the spin transistor that is needed to construct spintronic devices. These promise to be much more energy efficient than conventional electronics. The results were published on 2 March in Physical Review Letters.

Spin is a quantum mechanical property of electrons. Simply put, it makes electrons behave like small magnetic compass needles which can point up or down. This can be used to transfer or store information, creating spintronic devices that promise several advantages over normal microelectronics.

In a conventional computer, separate devices are needed for data storage (often using a magnetic process) and data processing (electronic transistors). Spintronics could integrate both in one device, so it would no longer be necessary to move information between storage and processing units. Furthermore, spins can be stored in a non-volatile way, which means that their storage requires no energy, in contrast to normal RAM memory. All this means that spintronics could potentially make faster and more energy-efficient computers.

Wave

To realize this, many steps have to be taken and a lot of fundamental knowledge has to be obtained. The Physics of Nano Devices group of physics professor Bart van Wees at the University of Groningen’s Zernike Institute of Advanced Materials is at the forefront of this field. In their latest paper, they present a spin transistor based on magnons. Magnons, or spin waves, are a type of wave that only occurs in magnetic materials. ‘You can view magnons as a wave, or a particle, like electrons’, explains Ludo Cornelissen, PhD student in the Van Wees group and first author of the paper.

In their experiments, Cornelissen and Van Wees generate magnons in materials that are magnetic, but also electrically insulating. Electrons can’t travel through the magnet, but the spin waves can – just like a wave in a stadium moves while the spectators all stay in place. Cornelissen used a strip of platinum to inject magnons into a magnet made of yttrium iron garnet (YIG). ‘When an electron current travels through the strip, electrons are scattered by the interaction with the heavy atoms, a process that is called the spin Hall effect. The scattering depends on the spin of these electrons, so electrons with spin up and spin down are separated.’

Spin flip

At the interface of platinum and YIG, the electrons bounce back as they can’t enter the magnet. ‘When this happens, their spin flips from up to down, or vice versa. However, this causes a parallel spin flip inside the YIG, which creates a magnon.’ The magnons travel through the material and can be detected with a second platinum strip.

‘We described this spin transport through a magnet some time ago. Now, we’ve taken the next step: we wanted to influence the transport.’ This was done using a third platinum strip between injector and detector. By applying a positive or negative current, it is possible to either inject additional magnons in the conduction channel or drain magnons from it. ‘That makes our set up analogous to a field effect transistor. In such a transistor, an electric field of a gate electrode reduces or increases the number of free electrons in the channel, thus shutting down or boosting the current.’

Cornelissen and his colleagues show that adding magnons increases the spin current, while draining them causes a significant reduction. ‘Although we were not yet able to switch off the magnon current completely, this device does act as a transistor’, says Cornelissen. Theoretical modelling shows that reducing the thickness of the device can increase the depletion of magnons enough to stop the magnon current completely.

Superconductivity

But there is another interesting option, explains Cornelissen’s supervisor Bart van Wees: ‘In a thinner device, it could be possible to increase the amount of magnons in the channel to a level where they would form a Bose-Einstein condensate.’ This is the phenomenon that is responsible for superconductivity. And it occurs at room temperature, contrary to normal superconductivity, which only occurs at very low temperatures.

The study shows that a YIG spin transistor can be made, and that in the long run this material could even produce a spin superconductor. The beauty of the system is that spin injection and control of spin currents is achieved with a simple DC current, making these spintronic devices compatible with normal electronics. ‘Our next step is to see if we can realize this promise’, concludes Van Wees.

A new progress in the scaling of semiconductor quantum dot based qubit has been achieved at Key Laboratory of Quantum Information and Synergetic Innovation Center of Quantum Information & Quantum Physics of USTC. Professor GUO Guoping with his co-workers, XIAO Ming, LI Haiou and CAO Gang, designed and fabricated a quantum processor with six quantum dots, and experimentally demonstrated quantum control of the Toffoli gate. This is the first time for the realization of the Toffoli gate in the semiconductor quantum dot system, which motivates further research on larger scale semiconductor quantum processor. The result was published as ‘Controlled Quantum Operations of a Semiconductor Three-Qubit System ‘ (Physical Review Applied 9, 024015 (2018)).

This is the Toffoli Gate in a three-qubit system. Credit: University of Science and Technology of China

This is the Toffoli Gate in a three-qubit system. Credit: University of Science and Technology of China

Developing the scalable semiconductor quantum chip that is compatible with modern semiconductor-techniques is an important research area. In this area, the fabrication, manipulation and scaling of semiconductor quantum dot based qubits are the most important core technologies. Professor GUO Guoping’s group aims to master these technologies and has been devoted to this area for a long time. Before the demonstration of the three-qubit gate, they have realized ultrafast universal control of the charge qubit based on semiconductor quantum dots in 2013(Nature Communications. 4:1401 (2013)), and achieved the controlled rotation of two charge qubits in 2015(Nature Communications. 6:7681 (2015)).

The Toffoli gate is a three-qubit operation that changed the state of a target qubit conditioned on the state of two control qubits. It can be used for universal reversible classical computation and also forms a universal set of qubit gates in quantum computation together with a Hadamard gate. Furthermore, it is a key element in quantum error correction schemes. Implementation of the Toffoli gate with only single- and two-qubit operations requires six controlled-NOT gates and ten single-qubit operations.

As a result, a single-step Toffoli gate can reduce the number of quantum operations dramatically, which can break the limit of coherence time and improve the efficiency of quantum computing. Researchers from Guo’s group found the T-shaped six quantum dot architecture with openings between control qubits and the target qubit can strengthen the coupling between qubits with different function and minimize it between qubits with the same function, which satisfies the requirements of the Toffoli gate well. Using this architecture with optimized high frequency pulses, researchers demonstrated the Toffoli gate in semiconductor quantum dot system in the world for the first time, which paves the way and lays a solid foundation for the scalable semiconductor quantum processor.

The reviewer spoke highly of this work, and thought this is an important progress in the field of semiconductor quantum dot based quantum computing.”The work is detailed and clearly demonstrates a high level of experimental technique and would be of high interest to people working in the field of electrostatically defined quantum dots for quantum computation”.

 

Novel photonics materials are becoming pivotal for energy conversion, communications, and sensing, largely because there is a global desire to enhance energy efficiency, and reduce electricity consumption. As Dr. Can Bayram, assistant professor in the Department of Electrical and Computer Engineering at the University of Illinois at Urbana-Champaign, notes, “Who doesn’t want to consume less electricity for the same quality of lighting?”

When the 2014 Nobel Prize in Physics was awarded to a trio of researchers for inventing a new (In)GaN-based energy-efficient, more environmentally friendly light source, this idea was brought to the forefront and gained more widespread recognition.

In related work, the Innovative COmpound semiconductoR Laboratory (ICOR) team led by Prof. Bayram has published a well-received paper titled “High internal quantum efficiency ultraviolet emission from phase-transition cubic GaN integrated on nanopatterned Si(100)”. Richard Liu, a Ph.D. candidate advised by Prof. Bayram, and whose primary research areas are optoelectronics and nanophotonics, is the lead author for this paper.

The team’s paper and its promise for a novel emitter have recently been featured in Compound Semiconductor and Semiconductor Today.

GaN materials (also known as III-Nitrides) are one of the most exotic photonic materials, and in the U of I team’s work, they investigate a new phase of Gallium Nitride materials: cubic. Using aspect ratio nanopatterning technology, they report a hexagonal-to-cubic phase transition process in GaN, enabled through aspect ratio patterning of silicon substrate. The emission efficiency of optimized cubic GaN, thanks to the polarization-free nature of cubic GaN, is measured to be approximately 29%, in sharp contrast to the general percentages of 12%, 8%, and 2%, respectively, of conventional hexagonal GaN on sapphire, hexagonal free-standing GaN, and hexagonal GaN on Si.

Bayram comments that “New photonic materials are critical in next-generation energy conversion devices. GaN-on-Si, enabled through phase-transition technology, provides an efficient, scalable, and environmental solution for integrated visible photonics.”

The discovery of graphene, with its high strength-to-weight ratio, flexibility, electrical conductivity, and ability to form an impenetrable barrier, led to an explosion of interest in 2D solids. Weak, long-range interactions give 2D solids some of their most interesting behaviors; therefore, understanding these interactions is crucial for further developing these materials. However, experimental support for theoretical modelling of the van der Waals interactions that hold these materials’ layers together has been wanting.

Now, an international research group led by the University of Tsukuba and Aarhus University has performed synchrotron X-ray diffraction experiments on titanium disulfide (TiS2) — a transition metal dichalogenide (TMD) material with a layered 2D structure–and compared the results with theoretical calculations. Their benchmark work was recently published in Nature Materials.

“The interaction between layers in van der Waals materials such as TiS2 has a significant bearing on their modification, processing, and assembly,” study co-author Eiji Nishibori says. “By modelling experimental synchrotron data and comparing it with density functional theory calculations, we revealed surprising information about the nature of the electron sharing between layers in these materials.”

TiS2 is an archetypal van der Waals material, with layers comprising sheets of titanium and sulfur interacting through strong chemical bonds, where electrons are shared between atoms, resulting in a relatively fixed structure. Between these sheets, long-range S…S van der Waals interactions attract the layers to one another allowing them to build up, forming solid materials. These interactions are known to be much weaker than those within the 2D sheets, however, using high-energy synchrotron X-ray radiation to precisely measure a single TiS2 crystal, the researchers were able to show that the interlayer interactions are in fact stronger than theory indicates, and involve significant electron sharing.

“This work provides a fundamental understanding of an exciting class of materials with numerous potential applications in technologies such as ion batteries, catalysis, and superconductors,” lead author Hidetaka Kasai says. “Our experiments are the first to reveal the true nature of the interactions that make 2D materials so interesting, and we hope they will underpin many future developments in this area.”

The outstanding agreement of the synchrotron diffraction data with theoretical calculations in describing the intralayer Ti-S interactions, supports the validity of these new-found differences for the long-range interactions across the interlayer gaps. The findings are expected to substantially contribute to the fundamental understanding of weak chemical bonding in 2D layered materials in general, and to the development of TMD materials.

 

A new smart and responsive material can stiffen up like a worked-out muscle, say the Iowa State University engineers who developed it.

Stress a muscle and it gets stronger. Mechanically stress the rubbery material – say with a twist or a bend – and the material automatically stiffens by up to 300 percent, the engineers said. In lab tests, mechanical stresses transformed a flexible strip of the material into a hard composite that can support 50 times its own weight.

Examples of the new smart material, left to right: A flexible strip; a flexible strip that stiffened when twisted; a flexible strip transformed into a hard composite that can hold up a weight. Credit: Christopher Gannon/Iowa State University

Examples of the new smart material, left to right: A flexible strip; a flexible strip that stiffened when twisted; a flexible strip transformed into a hard composite that can hold up a weight. Credit: Christopher Gannon/Iowa State University

This new composite material doesn’t need outside energy sources such as heat, light or electricity to change its properties. And it could be used in a variety of ways, including applications in medicine and industry.

The material is described in a paper recently published online by the scientific journal Materials Horizons. The lead authors are Martin Thuo and Michael Bartlett, Iowa State assistant professors of materials science and engineering. First authors are Boyce Chang and Ravi Tutika, Iowa State doctoral students in materials science and engineering. Chang is also a student associate of the U.S. Department of Energy’s Ames Laboratory.

Iowa State startup funds for Thuo and Bartlett supported development of the new material. Thuo’s Black & Veatch faculty fellowship also helped support the project.

Development of the material combined Thuo’s expertise in micro-sized, liquid-metal particles with Bartlett’s expertise in soft materials such as rubbers, plastics and gels.

It’s a powerful combination.

The researchers found a simple, low-cost way to produce particles of undercooled metal – that’s metal that remains liquid even below its melting temperature. The tiny particles (they’re just 1 to 20 millionths of a meter across) are created by exposing droplets of melted metal to oxygen, creating an oxidation layer that coats the droplets and stops the liquid metal from turning solid. They also found ways to mix the liquid-metal particles with a rubbery elastomer material without breaking the particles.

When this hybrid material is subject to mechanical stresses – pushing, twisting, bending, squeezing – the liquid-metal particles break open. The liquid metal flows out of the oxide shell, fuses together and solidifies.

“You can squeeze these particles just like a balloon,” Thuo said. “When they pop, that’s what makes the metal flow and solidify.”

The result, Bartlett said, is a “metal mesh that forms inside the material.”

Thuo and Bartlett said the popping point can be tuned to make the liquid metal flow after varying amounts of mechanical stress. Tuning could involve changing the metal used, changing the particle sizes or changing the soft material.

In this case, the liquid-metal particles contain Field’s metal, an alloy of bismuth, indium and tin. But Thuo said other metals will work, too.

“The idea is that no matter what metal you can get to undercool, you’ll get the same behavior,” he said.

The engineers say the new material could be used in medicine to support delicate tissues or in industry to protect valuable sensors. There could also be uses in soft and bio-inspired robotics or reconfigurable and wearable electronics. The Iowa State University Research Foundation is working to patent the material and it is available for licensing.

“A device with this material can flex up to a certain amount of load,” Bartlett said. “But if you continue stressing it, the elastomer will stiffen and stop or slow down these forces.”

And that, the engineers say, is how they’re putting some muscle in their new smart material.

 

Graphene on toast, anyone?


February 13, 2018

Rice University scientists who introduced laser-induced graphene (LIG) have enhanced their technique to produce what may become a new class of edible electronics.

Rice University graduate student Yieu Chyan, left, and Professor James Tour. Credit: Jeff Fitlow/Rice University

Rice University graduate student Yieu Chyan, left, and Professor James Tour. Credit: Jeff Fitlow/Rice University

The Rice lab of chemist James Tour, which once turned Girl Scout cookies into graphene, is investigating ways to write graphene patterns onto food and other materials to quickly embed conductive identification tags and sensors into the products themselves.

“This is not ink,” Tour said. “This is taking the material itself and converting it into graphene.”

The process is an extension of the Tour lab’s contention that anything with the proper carbon content can be turned into graphene. In recent years, the lab has developed and expanded upon its method to make graphene foam by using a commercial laser to transform the top layer of an inexpensive polymer film.

The foam consists of microscopic, cross-linked flakes of graphene, the two-dimensional form of carbon. LIG can be written into target materials in patterns and used as a supercapacitor, an electrocatalyst for fuel cells, radio-frequency identification (RFID) antennas and biological sensors, among other potential applications.

The new work reported in the American Chemical Society journal ACS Nano demonstrated that laser-induced graphene can be burned into paper, cardboard, cloth, coal and certain foods, even toast.

“Very often, we don’t see the advantage of something until we make it available,” Tour said. “Perhaps all food will have a tiny RFID tag that gives you information about where it’s been, how long it’s been stored, its country and city of origin and the path it took to get to your table.”

He said LIG tags could also be sensors that detect E. coli or other microorganisms on food. “They could light up and give you a signal that you don’t want to eat this,” Tour said. “All that could be placed not on a separate tag on the food, but on the food itself.”

Multiple laser passes with a defocused beam allowed the researchers to write LIG patterns into cloth, paper, potatoes, coconut shells and cork, as well as toast. (The bread is toasted first to “carbonize” the surface.) The process happens in air at ambient temperatures.

“In some cases, multiple lasing creates a two-step reaction,” Tour said. “First, the laser photothermally converts the target surface into amorphous carbon. Then on subsequent passes of the laser, the selective absorption of infrared light turns the amorphous carbon into LIG. We discovered that the wavelength clearly matters.”

The researchers turned to multiple lasing and defocusing when they discovered that simply turning up the laser’s power didn’t make better graphene on a coconut or other organic materials. But adjusting the process allowed them to make a micro supercapacitor in the shape of a Rice “R” on their twice-lased coconut skin.

Defocusing the laser sped the process for many materials as the wider beam allowed each spot on a target to be lased many times in a single raster scan. That also allowed for fine control over the product, Tour said. Defocusing allowed them to turn previously unsuitable polyetherimide into LIG.

“We also found we could take bread or paper or cloth and add fire retardant to them to promote the formation of amorphous carbon,” said Rice graduate student Yieu Chyan, co-lead author of the paper. “Now we’re able to take all these materials and convert them directly in air without requiring a controlled atmosphere box or more complicated methods.”

The common element of all the targeted materials appears to be lignin, Tour said. An earlier study relied on lignin, a complex organic polymer that forms rigid cell walls, as a carbon precursor to burn LIG in oven-dried wood. Cork, coconut shells and potato skins have even higher lignin content, which made it easier to convert them to graphene.

Tour said flexible, wearable electronics may be an early market for the technique. “This has applications to put conductive traces on clothing, whether you want to heat the clothing or add a sensor or conductive pattern,” he said.

At DESY’s X-ray source PETRA III, scientists have followed the growth of tiny wires of gallium arsenide live. Their observations reveal exact details of the growth process responsible for the evolving shape and crystal structure of the crystalline nanowires. The findings also provide new approaches to tailoring nanowires with desired properties for specific applications. The scientists, headed by Philipp Schroth of the University of Siegen and the Karlsruhe Institute of Technology (KIT), present their findings in the journal Nano Letters. The semiconductor gallium arsenide (GaAs) is widely used, for instance in infrared remote controls, the high-frequency components of mobile phones and for converting electrical signals into light for fibre optical transmission, as well as in solar panels for deployment in spacecraft.

To fabricate the wires, the scientists employed a procedure known as the self-catalysed Vapour-Liquid-Solid (VLS) method, in which tiny droplets of liquid gallium are first deposited on a silicon crystal at a temperature of around 600 degrees Celsius. Beams of gallium atoms and arsenic molecules are then directed at the wafer, where they are adsorpted and dissolve in the gallium droplets. After some time, the crystalline nanowires begin to form below the droplets, whereby the droplets are gradually pushed upwards. In this process, the gallium droplets act as catalysts for the longitudinal growth of the wires. “Although this process is already quite well established, it has not been possible until now to specifically control the crystal structure of the nanowires produced by it. To achieve this, we first need to understand the details of how the wires grow,” emphasises co-author Ludwig Feigl from KIT.

To observe the growth as it takes place, Schroth’s group installed a mobile experimental chamber, specially developed by KIT for X-ray experiments and partially funded by the Federal Ministry of Education and Research (BMBF), in the brilliant X-ray beam of DESY’s synchrotron radiation source PETRA III at experimental station P09. At one-minute intervals the scientists took X-ray pictures, which allowed both the internal structure and the diameter of the growing nanowires to be simultaneously determined. In addition, they measured the fully-grown nanowires using the scanning electron microscope at the DESY NanoLab. “To ensure the success of such complex measurements, an extensive period of growth characterisation and optimisation at the UHV Analysis Lab at KIT was a prerequisite,” explains co-author Seyed Mohammad Mostafavi Kashani from University of Siegen.

Over a period of about four hours, the wires grew to a length of some 4000 nanometres. One nanometre (nm) is one millionth of a millimetre. However, not only did the wires become longer during this time, but also thicker: their diameter increased from an initial 20 nm to up to 140 nm at the top of the wire, still making them around 500 times thinner than a human hair.

“One rather exciting feature is that the images taken under the electron microscope show the nanowires to have a slightly different shape,” says co-author Thomas Keller from DESY NanoLab. Although the wires were thicker at the top than at the bottom, just as indicated by the X-ray data, the diameter measured under the electron microscope was larger in the lower region of the wire than what was observed using X-rays.

“We found out that the growth of the nanowires is not only due to the VLS mechanism but that a second component also contributes, which we were able to observe and quantify for the first time in this experiment. This additional sidewall growth lets the wires gain width,” explains Schroth. Independently of VLS growth, the vapour deposited material also attaches itself directly to the side walls, particularly in the lower region of the nanowire. This additional contribution can be determined by comparing the X-ray measurements taken early on during the growth of the wire, with the electron microscope measurement after growth has ended.

Furthermore, the gallium droplets are constantly becoming larger as further gallium is added in the course of the growth process. Using growth models, the scientists were able to deduce the shape of the droplets, which had also been affected by the increasing droplet size. The effect of this is far-reaching: “As the droplet changes in size, the angle of contact between the droplet and the surface of the wires also changes. Under certain circumstances, the wire then suddenly continues growing with a different crystal structure,” says Feigl. Whereas the fine nanowires initially crystallise in a hexagonal, so-called wurtzite structure, this behaviour changes after some time and the wires adopt a cubic zinc blende structure as they continue to grow. This change is important when it comes to applications, since the structure and shape of the nanowires have important consequences for the properties of the resulting material.

Such detailed findings not only lead to a better understanding of the growth process; they also provide approaches for customising future nanowires to have special properties for specific applications – for example to improve the efficiency of a solar cell or a laser.

This research is also part of the strategic collaboration between the two Helmholtz Centres KIT and DESY within the framework of the Helmholtz programme “From Matter to Materials and Life” (MML).

DESY is one of the world’s leading particle accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – ranging from the interaction of tiny elementary particles to the behaviour of innovative nanomaterials and the vital processes that take place between biomolecules to the great mysteries of the universe. The accelerators and detectors that DESY develops and builds at its locations in Hamburg and Zeuthen are unique research tools. DESY is a member of the Helmholtz Association, and receives its funding from the German Federal Ministry of Education and Research (BMBF) (90 per cent) and the German federal states of Hamburg and Brandenburg (10 per cent).

Entegris, Inc. (NasdaqGS: ENTG), a developer of specialty chemicals and advanced materials solutions for the microelectronics industry, today reported its financial results for the Company’s fourth quarter and fiscal year ended December 31, 2017.

The Company reported sales of $1.3 billion for fiscal 2017, an increase of 14 percent from the prior year. Net income for the year was $85.1 million, or $0.59 per diluted share, which included amortization of intangible assets of $44.0 million, asset impairment charges of $13.2 million, $2.7 million of severance expenses, $20.7 million related to the refinancing of senior notes, and $66.7 million related to the effects of the Tax Cuts and Jobs Act. In the prior year, net income was $97.1 million, or $0.68 per diluted share, which included amortization of intangible assets of $44.3 million, asset impairment charges of $5.8 million, and $2.4 million of severance expenses. Non-GAAP net income for fiscal 2017 was $206.3 million, or $1.44 per diluted share, which increased from $132.8 million, or $0.94 per diluted share, in the prior year.

Fourth-quarter sales were $350.6 million, an increase of 14 percent from the same quarter last year and 1 percent higher sequentially. Fourth-quarter net loss was $28.3 million, or $0.20 per diluted share, which included amortization of intangible assets of $11.0 million, $20.7 million related to the refinancing of senior notes, and $66.7 million related to the effects of the Tax Cuts and Jobs Act. Non-GAAP net income was $59.7 million, or $0.42 per diluted share, which compared to $34.3 million, or $0.24 per diluted share, in the same quarter a year ago. In the fourth quarter of 2017, the Company generated cash from operations less capital expenditures, or free cash flow, of $60.1 million.

Bertrand Loy, president and chief executive officer, said: “The fourth quarter marked our fifth consecutive record quarter, capping the most successful year in Entegris’ 51-year history. We grew fiscal 2017 sales 14 percent to $1.3 billion, achieving growth across all three divisions, driven by demand for our solutions in advanced memory, logic, and mainstream semiconductor production. We were very pleased with the quality of execution by the Entegris teams around the world. We delivered on our commitment to grow our bottom line at twice the rate of our top line, increasing our adjusted EBITDA by 35 percent to a record high of $357 million, or 26.6 percent of sales for the year. This strong cash flow is allowing us to create significant value through a balanced capital allocation strategy consisting of internal growth investments, strategic acquisitions, and returning available cash to shareholders through dividends and share repurchases.

Mr. Loy added: “As we look ahead, we have great conviction that the semiconductor industry is in the midst of a multi-year period of growth driven by broadening demand related to artificial intelligence, automotive, industrial, and other new applications. Our value proposition, which is built on a broad array of solutions, is enabling us to expand our served markets and will allow us to continue to outpace our markets.”

The end of the silicon age has begun. As computer chips approach the physical limits of miniaturization and power-hungry processors drive up energy costs, scientists are looking to a new crop of exotic materials that could foster a new generation of computing devices that promise to push performance to new heights while skimping on energy consumption.

Unlike current silicon-based electronics, which shed most of the energy they consume as waste heat, the future is all about low-power computing. Known as spintronics, this technology relies on a quantum physical property of electrons — up or down spin — to process and store information, rather than moving them around with electricity as conventional computing does.

On the quest to making spintronic devices a reality, scientists at the University of Arizona are studying an exotic crop of materials known as transition metal dichalcogenides, or TMDs. TMDs have exciting properties lending themselves to new ways of processing and storing information and could provide the basis of future transistors and photovoltaics — and potentially even offer an avenue toward quantum computing.

For example, current silicon-based solar cells convert realistically only about 25 percent of sunlight into electricity, so efficiency is an issue, says Calley Eads, a fifth-year doctoral student in the UA’s Department of Chemistry and Biochemistry who studies some of the properties of these new materials. “There could be a huge improvement there to harvest energy, and these materials could potentially do this,” she says.

There is a catch, however: Most TMDs show their magic only in the form of sheets that are very large, but only one to three atoms thin. Such atomic layers are challenging enough to manufacture on a laboratory scale, let alone in industrial mass production.

Many efforts are underway to design atomically thin materials for quantum communication, low-power electronics and solar cells, according to Oliver Monti, a professor in the department and Eads’ adviser. Studying a TMD consisting of alternating layers of tin and sulfur, his research team recently discovered a possible shortcut, published in the journal Nature Communications.

“We show that for some of these properties, you don’t need to go to the atomically thin sheets,” he says. “You can go to the much more readily accessible crystalline form that’s available off the shelf. Some of the properties are saved and survive.”

Understanding electron movement

This, of course, could dramatically simplify device design.

“These materials are so unusual that we keep discovering more and more about them, and they are revealing some incredible features that we think we can use, but how do we know for sure?” Monti says. “One way to know is by understanding how electrons move around in these materials so we can develop new ways of manipulating them — for example, with light instead of electrical current as conventional computers do.”

To do this research, the team had to overcome a hurdle that never had been cleared before: figure out a way to “watch” individual electrons as they flow through the crystals.

“We built what is essentially a clock that can time moving electrons like a stopwatch,” Monti says. “This allowed us to make the first direct observations of electrons move in crystals in real time. Until now, that had only been done indirectly, using theoretical models.”

The work is an important step toward harnessing the unusual features that make TMDs intriguing candidates for future processing technology, because that requires a better understanding of how electrons behave and move around in them.

Monti’s “stopwatch” makes it possible to track moving electrons at a resolution of a mere attosecond — a billionth of a billionth of a second. Tracking electrons inside the crystals, the team made another discovery: The charge flow depends on direction, an observation that seems to fly in the face of physics.

Collaborating with Mahesh Neupane, a computational physicist at Army Research Laboratories, and Dennis Nordlund, an X-ray spectroscopy expert at Stanford University’s SLAC National Accelerator Laboratory, Monti’s team used a tunable, high-intensity X-ray source to excite individual electrons in their test samples and elevate them to very high energy levels.

“When an electron is excited in that way, it’s the equivalent of a car that is being pushed from going 10 miles per hour to thousands of miles per hour,” Monti explains. “It wants to get rid of that enormous energy and fall back down to its original energy level. That process is extremely short, and when that happens, it gives off a specific signature that we can pick up with our instruments.”

The researchers were able to do this in a way that allowed them to distinguish whether the excited electrons stayed within the same layer of the material, or spread into adjacent layers across the crystal.

“We saw that electrons excited in this way scattered within the same layer and did so extremely fast, on the order of a few hundred attoseconds,” Monti says.

In contrast, electrons that did cross into adjacent layers took more than 10 times longer to return to their ground energy state. The difference allowed the researchers to distinguish between the two populations.

“I was very excited to find that directional mechanism of charge distribution occurring within a layer, as opposed to across layers,” says Eads, the paper’s lead author. “That had never been observed before.”

Closer to mass manufacturing

The X-ray “clock” used to track electrons is not part of the envisioned applications but a means to study the behavior of electrons inside them, Monti explains, a necessary first step in getting closer toward technology with the desired properties that could be mass-manufactured.

“One example of the unusual behavior we see in these materials is that an electron going to the right is not the same as an electron going to the left,” he says. “That shouldn’t happen — according to physics of standard materials, going to the left or the right is the exact same thing. However, for these materials that is not true.”

This directionality is an example of what makes TMDs intriguing to scientists, because it could be used to encode information.

“Moving to the right could be encoded as ‘one’ and going to the left as ‘zero,'” Monti says. “So if I can generate electrons that neatly go to the right, I’ve written a bunch of ones, and if I can generate electrons that neatly go to the left, I have generated a bunch of zeroes.”

Instead of applying electrical current, engineers could manipulate electrons in this way using light such as a laser, to optically write, read and process information. And perhaps someday it may even become possible to optically entangle information, clearing the way to quantum computing.

“Every year, more and more discoveries are occurring in these materials,” Eads says. “They are exploding in terms of what kinds of electronic properties you can observe in them. There is a whole spectrum of ways in which they can function, from superconducting, semiconducting to insulating, and possibly more.”

The research described here is just one way of probing the unexpected, exciting properties of layered TMD crystals, according to Monti.

“If you did this experiment in silicon, you wouldn’t see any of this,” he says. “Silicon will always behave like a three-dimensional crystal, no matter what you do. It’s all about the layering.”