Category Archives: Packaging Materials

Japanese researchers have developed a new method to build large areas of semiconductive material that is just two molecules thick and a total of 4.4 nanometers tall. The films function as thin film transistors, and have potential future applications in flexible electronics or chemical detectors. These thin film transistors are the first example of semiconductive single molecular bilayers created with liquid solution processing, a standard manufacturing process that minimizes costs.

Top surface view of 3-D computer model (left) and Atomic Force Microscopy image (right) of the new film made by University of Tokyo scientists. The well-organized structure of the molecules is visible in both the 3-D computer model and microscope image as a herringbone or cross-hair pattern. The color differences in the microscopy image are a result of the different lengths of the molecules' tails; the length differences cause the geometric frustration that prevents layers from stacking. pm = picometers, nm = nanometers. Credit: Shunto Arai and Tatsuo Hasegawa

Top surface view of 3-D computer model (left) and Atomic Force Microscopy image (right) of the new film made by University of Tokyo scientists. The well-organized structure of the molecules is visible in both the 3-D computer model and microscope image as a herringbone or cross-hair pattern. The color differences in the microscopy image are a result of the different lengths of the molecules’ tails; the length differences cause the geometric frustration that prevents layers from stacking. pm = picometers, nm = nanometers. Credit: Shunto Arai and Tatsuo Hasegawa

“We want to give electronic devices the features of real cell membranes: flexible, strong, sensitive, and super thin. We found a novel way to design semiconductive single molecular bilayers that allows us to manufacture large surface areas, up to 100 square centimeters (39 square inches). They can function as high performance thin film transistors and could have many applications in the future,” said Assistant Professor Shunto Arai, the first author on the recent research publication.

Professor Tatsuo Hasegawa of the University of Tokyo Department of Applied Physics led the team that built the new film. The breakthrough responsible for their success is a concept called geometric frustration, which uses a molecular shape that makes it difficult for molecules to settle in multiple layers on top of each other.

The film is transparent, but the forces of attraction and repulsion between the molecules create an organized, repeated herringbone pattern when the film is viewed from above through a microscope. The overall molecular structure of the bilayer is highly stable. Researchers believe it should be possible to build the same structure out of different molecules with different functionalities.

The individual molecules used in the current film are divided into two regions: a head and a tail. The head of one molecule stacks on top of another, with their tails pointing in opposite directions so the molecules form a vertical line. These two molecules are surrounded by identical head-to-head pairs of molecules, which all together form a sandwich called a molecular bilayer.

Researchers discovered they could prevent additional bilayers from stacking on top by building the bilayer out of molecules with different length tails, so the surfaces of the bilayer are rough and naturally discourage stacking. This effect of different lengths is referred to as geometric frustration.

Standard methods of creating semiconductive molecular bilayers cannot control the thickness without causing cracks or an irregular surface. The geometric frustration of different length tails has allowed researchers to avoid these pitfalls and build a 10cm by 10cm (3.9 inches by 3.9 inches) square of their film using the common industrial method of solution processing.

The semiconductive properties of the bilayer may give the films applications in flexible electronics or chemical detection.

Semiconductors are able to switch between states that allow electricity to flow (conductors) and states that prevent electricity from flowing (insulators). This on-off switching is what allows transistors to quickly change displayed images, such as a picture on an LCD screen. The single molecular bilayer created by the UTokyo team is much faster than amorphous silicon thin film transistors, a common type of semiconductor currently used in electronics.

The team will continue to investigate the properties of geometrically frustrated single molecular bilayers and potential applications for chemical detection. Collaborators based at the National Institute of Advanced Industrial Science and Technology, the Nippon Kayaku Company Limited, Condensed Matter Research Center, and High Energy Accelerator Research Organization also contributed to the research.

Cheap, flexible and sustainable plastic semiconductors will soon be a reality thanks to a breakthrough by chemists at the University of Waterloo.

Professor Derek Schipper and his team at Waterloo have developed a way to make conjugated polymers, plastics that conduct electricity like metals, using a simple dehydration reaction the only byproduct of which is water.

“Nature has been using this reaction for billions of years and industry more than a hundred,” said Schipper, a professor of Chemistry and a Canada Research Chair in Organic Material Synthesis. “It’s one of the cheapest and most environmentally friendly reactions for producing plastics.”

Schipper and his team have successfully applied this reaction to create poly(hetero)arenes, one of the most studied classes of conjugated polymers which have been used to make lightweight, low- cost electronics such as solar cells, LED displays, and chemical and biochemical sensors.

Dehydration is a common method to make polymers, a chain of repeating molecules or monomers that link up like a train. Nature uses the dehydration reaction to make complex sugars from glucose, as well as proteins and other biological building blocks such as cellulose. Plastics manufacturers use it to make everything from nylon to polyester, cheaply and in mind-boggling bulk.

“Synthesis has been a long-standing problem in this field,” said Schipper. “A dehydration method such as ours will streamline the entire process from discovery of new derivatives to commercial product development. Better still, the reaction proceeds relatively fast and at room temperature.”

Conjugated polymers were first discovered by Alan Heeger, Alan McDonald, and Hideki Shirakawa in the late 1970s, eventually earning them the Nobel Prize in Chemistry in 2000.

Researchers and engineers quickly discovered several new polymer classes with plenty of commercial applications, including a semiconducting version of the material; but progress has stalled in reaching markets in large part because conjugated polymers are so hard to make. The multi-step reactions often involve expensive catalysts and produce environmentally harmful waste products.

Schipper and his team are continuing to perfect the technique while also working on developing dehydration synthesis methods for other classes of conjugated polymers. The results of their research so far appeared recently in the journal Chemistry – A European Journal.

 

SEMI, the global industry association representing the electronics manufacturing supply chain, today announced that in 2017 the global semiconductor materials market grew 9.6 percent while worldwide semiconductor revenues increased 21.6 percent from the prior year.

According to the SEMI Materials Market Data Subscription, total wafer fabrication materials and packaging materials totaled $27.8 billion and $19.1* billion, respectively, in 2017. In 2016, the wafer fabrication materials and packaging materials markets logged revenues of $24.7 billion and $18.2 billion, respectively, for 12.7 percent and 5.4 percent year-over-year increases.

For the eighth consecutive year, Taiwan, at $10.3 billion, was the largest consumer of semiconductor materials due to its large foundry and advanced packaging base. China solidified its hold on the second spot, followed by South Korea and Japan. The Taiwan, China, Europe and South Korea markets saw the strongest revenue growth, while the North America, Rest of World (ROW) and Japan materials markets experienced moderate single-digit growth. (The ROW region is defined as Singapore, Malaysia, Philippines, other areas of Southeast Asia and smaller global markets.)

2016 and 2017 Regional Semiconductor Materials Markets (US$ Billions)

Region
2016**
2017
% Change
Taiwan
9.20
10.29
12%
China
6.80
7.62
12%
South Korea
6.77
7.51
11%
Japan
6.76
7.05
4%
Rest of World
5.39
5.81
8%
North America
4.87
5.29
9%
Europe
3.03
3.36
11%
Total
42.82
46.93
10%

Source: SEMI, April 2018

Note: Summed subtotals may not equal the total due to rounding.

* Includes ceramic packages and flexible substrates

** 2016 data have been updated based on SEMI’s data collection programs

The Materials Market Data Subscription (MMDS) from SEMI provides current revenue data along with seven years of historical data and a two-year forecast. The annual subscription includes four quarterly updates for the materials segment reports revenue for seven market regions (North America, Europe, ROW, Japan, Taiwan, South Korea, and China).

In a recent study published in Science, researchers at ICFO – The Institute of Photonic Sciences in Barcelona, Spain, along with other members of the Graphene Flagship, reached the ultimate level of light confinement. They have been able to confine light down to a space one atom, the smallest possible. This will pave the way to ultra-small optical switches, detectors and sensors.

Light can function as an ultra-fast communication channel, for example between different sections of a computer chip, but it can also be used for ultra-sensitive sensors or on-chip nanoscale lasers. There is currently much research into how to further shrink devices that control and guide light.

New techniques searching for ways to confine light into extremely tiny spaces, much smaller than current ones, have been on the rise. Researchers had previously found that metals can compress light below the wavelength-scale (diffraction limit), but more confinement would always come at the cost of more energy loss. This fundamental issue has now been overcome.

“Graphene keeps surprising us: nobody thought that confining light to the one-atom limit would be possible. It will open a completely new set of applications, such as optical communications and sensing at a scale below one nanometer,” said ICREA Professor Frank Koppens at ICFO – The Institute of Photonic Sciences in Barcelona, Spain, who led the research.

This team of researchers including those from ICFO (Spain), University of Minho (Portugal) and MIT (USA) used stacks of two-dimensional materials, called heterostructures, to build up a new nano-optical device. They took a graphene monolayer (which acts as a semi-metal), and stacked onto it a hexagonal boron nitride (hBN) monolayer (an insulator), and on top of this deposited an array of metallic rods. They used graphene because it can guide light in the form of plasmons, which are oscillations of the electrons, interacting strongly with light.

“At first we were looking for a new way to excite graphene plasmons. On the way, we found that the confinement was stronger than before and the additional losses minimal. So we decided to go to the one atom limit with surprising results,” said David Alcaraz Iranzo, the lead author from ICFO.

By sending infra-red light through their devices, the researchers observed how the plasmons propagated in between the metal and the graphene. To reach the smallest space conceivable, they decided to reduce the gap between the metal and graphene as much as possible to see if the confinement of light remained efficient, i.e. without additional energy losses. Strikingly, they saw that even when a monolayer of hBN was used as a spacer, the plasmons were still excited, and could propagate freely while being confined to a channel of just one atom thick. They managed to switch this plasmon propagation on and off, simply by applying an electrical voltage, demonstrating the control of light guided in channels smaller than one nanometer.

This enables new opto-electronic devices that are just one nanometer thick, such as ultra-small optical switches, detectors and sensors. Due to the paradigm shift in optical field confinement, extreme light-matter interactions can now be explored that were not accessible before. The atom-scale toolbox of two-dimensional materials has now also proven applicable for many types of new devices where both light and electrons can be controlled even down to the scale of a nanometer.

Professor Andrea C. Ferrari, Science and Technology Officer of the Graphene Flagship, and Chair of its Management Panel, added “While the flagship is driving the development of novel applications, in particular in the field of photonics and optoelectronics, we do not lose sight of fundamental research. The impressive results reported in this paper are a testimony to the relevance for cutting edge science of the Flagship work. Having reached the ultimate limit of light confinement could lead to new devices with unprecedented small dimensions.”

Versum Materials, Inc. (NYSE: VSM), a materials supplier to the semiconductor industry, announced today the grand opening of its new research and development (R&D) facility at its semiconductor materials manufacturing site in Hometown, Pennsylvania. The ribbon-cutting ceremony took place April 10, 2018. Versum employees, members of the community, local government, customers and strategic partners attended the event.

The R&D laboratory is dedicated to new materials used in the manufacture of semiconductors. Scientists in the facility will synthesize and purify new molecules down to parts per billion impurity levels and below using the latest technologies available in the industry. The researchers can assess the applications for these new molecules and scale up the molecules to larger quantities for customer evaluation. These new organometallic compounds will be deposited on semiconductor wafers through cutting-edge technologies to test their performance for semiconductor applications. Additionally, the facility is capable of small-volume manufacturing and advanced analytical and quality assessment.

State Senator Dave Argall commended Versum for being the region’s third largest employer and for the company’s investments in the local community. Approximately 30 employees, half of which hold advanced degrees in chemistry or chemical engineering, are based in the new facility. The company’s Hometown campus now totals 250 highly-skilled employees.

The latest expansion is part of a $60MM multi-year investment in the Hometown campus. Last year the company announced it had increased production capacity and modified equipment configuration to reduce manufacturing bottlenecking. Versum’s Hometown manufacturing facility produces a variety of high purity specialty gases and chemicals for semiconductor manufacturers around the world, including Tungsten Hexafluoride, WF6 and Nitrogen Trifluoride, NF3. WF6 is used as a metallization source for the formation of tungsten interconnects between multiple layers in semiconductor devices. It is an important material in the production of both logic and memory (DRAM and NAND) devices. NF3 is primarily used for chamber cleaning of chemical vapor deposition reactors.

Versum’s Senior Vice President of Materials, Ed Shober addressed the attendees stating, “We enable the largest tech companies around the world to stretch the boundaries of science and technology, whether it be supporting computing power, mobility, connectivity, artificial intelligence, virtual/augmented reality, the Internet of Things, Big Data and machine learning. Versum Materials is at the core of enabling all these technologies. Our Versum Materials team delivers valued products and solutions that bring this cutting-edge innovation to the market safer, faster, easier and more reliably than ever before.”

Physicists at the University of Warwick have today, Thursday 19th April 2018, published new research in the fournal Science today 19th April 2018 (via the Journal’s First Release pages) that could literally squeeze more power out of solar cells by physically deforming each of the crystals in the semiconductors used by photovoltaic cells.

This is an artists impression of squeezing more power out of solar cells by physically deforming each of the crystals in the semiconductors used by photovoltaic cells. Credit: University of Warwick/Mark Garlick

This is an artists impression of squeezing more power out of solar cells by physically deforming each of the crystals in the semiconductors used by photovoltaic cells. Credit: University of Warwick/Mark Garlick

The paper entitled the “Flexo-Photovoltaic Effect” was written by Professor Marin Alexe, Ming-Min Yang, and Dong Jik Kim who are all based in the University of Warwick’s Department of Physics.

The Warwick researchers looked at the physical constraints on the current design of most commercial solar cells which place an absolute limit on their efficiency. Most commercial solar cells are formed of two layers creating at their boundary a junction between two kinds of semiconductors, p-type with positive charge carriers (holes which can be filled by electrons) and n-type with negative charge carriers (electrons).

When light is absorbed, the junction of the two semiconductors sustains an internal field splitting the photo-excited carriers in opposite directions, generating a current and voltage across the junction. Without such junctions the energy cannot be harvested and the photo-exited carriers will simply quickly recombine eliminating any electrical charge.

That junction between the two semiconductors is fundamental to getting power out of such a solar cell but it comes with an efficiency limit. This Shockley-Queisser Limit means that of all the power contained in sunlight falling on an ideal solar cell in ideal conditions only a maximum of 33.7% can ever be turned into electricity.

There is however another way that some materials can collect charges produced by the photons of the sun or from elsewhere. The bulk photovoltaic effect occurs in certain semiconductors and insulators where their lack of perfect symmetry around their central point (their non-centrosymmetric structure) allows generation of voltage that can be actually larger than the band gap of that material (the band gap being the gap between the valence band highest range of electron energies in which electrons are normally present at absolute zero temperature and the conduction band where electricity can flow).

Unfortunately the materials that are known to exhibit the anomalous photovoltaic effect have very low power generation efficiencies, and are never used in practical power-generation systems.

The Warwick team wondered if it was possible to take the semiconductors that are effective in commercial solar cells and manipulate or push them in some way so that they too could be forced into a non-centrosymmetric structure and possibly therefore also benefit from the bulk photovoltaic effect.

For this paper they decided to try literally pushing such semiconductors into shape using conductive tips from atomic force microscopy devices to a “nano-indenter” which they then used to squeeze and deform individual crystals of Strontium Titanate (SrTiO3), Titanium Dioxide (TiO2), and Silicon (Si).

They found that all three could be deformed in this way to also give them a non-centrosymmetric structure and that they were indeed then able to give the bulk photovoltaic effect.

Professor Marin Alexe from the University of Warwick said:

“Extending the range of materials that can benefit from the bulk photovoltaic effect has several advantages: it is not necessary to form any kind of junction; any semiconductor with better light absorption can be selected for solar cells, and finally, the ultimate thermodynamic limit of the power conversion efficiency, so-called Shockley-Queisser Limit, can be overcome. There are engineering challenges but it should be possible to create solar cells where a field of simple glass based tips (a hundred million per cm2) could be held in tension to sufficiently de-form each semiconductor crystal. If such future engineering could add even a single percentage point of efficiency it would be of immense commercial value to solar cell manufacturers and power suppliers.”

Collaborative research team of Prof. Jun Takeda and Associate Prof. Ikufumi Katayama in the laboratory of Yokohama National University (YNU) and Nippon Telegraph and Telephone (NTT) successfully observed petahertz (PHz: 1015of a hertz) electron oscillation. The periodic electron oscillations of 667-383 attoseconds (as: 10-18 of a second) is the fastest that has ever been measured in the direct time-dependent spectroscopy in solid-state material.

NIR femtosecond pulse (pump pulse) induces the electron oscillation, which is monitored by the extreme ultraviolet IAP (probe pulse) based on the transient absorption spectroscopy. Credit: Nippon Telegraph and Telephone (NTT)

NIR femtosecond pulse (pump pulse) induces the electron oscillation, which is monitored by the extreme ultraviolet IAP (probe pulse) based on the transient absorption spectroscopy. Credit: Nippon Telegraph and Telephone (NTT)

As high-speed shutter cameras capture motions of fast-moving objects, researchers generally use laser (pulse) like instantaneous strobe light in order to observe the ultrafast motion of an electron underlying a physical phenomenon. The shorter the pulse duration, the faster the electron oscillation can be observed. The frequency of the lightwave-field in the visible and ultraviolet region can reach the petahertz (PHz: 1015 of a hertz), which means that the oscillation periodicity can achieve attosecond (as: 10-18 of a second) duration.

In previous studies, NTT researchers of the team generated an isolated attosecond pulse (IAP) [H. Mashiko et al., Nature commun. 5, 5599 (2014)] and monitored the electron oscillation with 1.2-PHz frequency using gallium-nitride (GaN) semiconductor [H. Mashiko et al., Nature Phys. 5, 741 (2016)]. The next challenges are the observation of faster electron oscillation in the chromium doped sapphire (Cr:Al2O3) insulator and the characterization of the ultrafast electron dephasing.

The paper, published in the journal Nature communications reports a successful observation of the near-infrared (NIR) pulse-induced multiple electronic dipole oscillations (periodicities of 667-383 as) in the Cr:Al2O3 solid-state material. The measurement is realized by the extreme short IAP (192-as duration) and the use of stable pump (NIR pulse) and probe (IAP) system (timing jitter of ~23 as). The characterized electron oscillations are the fastest that has ever been measured in the direct time-dependent spectroscopy. In addition, the individual dephasing times in the Cr donor-like intermediate level and the Al2O3 CB state are revealed.

Dr. Hiroki Mashiko, a NTT scientist of the team, said, “We contrived the robust pump-probe system with an extremely short isolated attosecond pulse, which led to the observation of the fastest electron oscillation in solid-state material in recorded history. The benefits of this study are directly related to the control of various optical phenomena through the dielectric polarization, and the results will help the development of future electronic and photonic devices.”

Over the past decades, computers have become faster and faster and hard disks and storage chips have reached enormous capacities. But this trend cannot continue forever: we are already running up against physical limits that will prevent silicon-based computer technology from attaining any impressive speed gains from this point on. Researchers are particularly optimistic that the next era of technological advancements will start with the development of novel information-processing materials and technologies that combine electrical circuits with optical ones. Using short laser pulses, a research team led by Misha Ivanov of the Max Born Institute in Berlin together with scientists from the Russian Quantum Center in Moscow have now shed light on the extremely rapid processes taking place within these novel materials. Their results have appeared in the prestigious journal Nature Photonics.

Of particular interest for modern material research in solid state physics are “strongly correlated systems”, so called for the strong interactions between the electrons in these materials. Magnets are a good example of this: the electrons in magnets align themselves in a preferred direction of spin inside the material, and it is this that produces the magnetic field. But there are other, entirely different structural orders that deserve attention. In so-called Mott insulators for example, a class of materials now being intensively researched, the electrons ought to flow freely and the materials should therefore be able to conduct electricity as well as metals. But the mutual interaction between electrons in these strongly correlated materials impedes their flow and so the materials behave as insulators instead.

By disrupting this order with a strong laser pulse, the physical properties can be made to change dramatically. This can be likened to a phase transition from solid to liquid: as ice melts, for example, rigid ice crystals transform into free-flowing water molecules. Very similarly, the electrons in a strongly correlated material become free to flow when an external laser pulse forces a phase transition in their structural order. Such phase transitions should allow us to develop entirely new switching elements for next-generation electronics that are faster and potentially more energy efficient than present-day transistors. In theory, computers could be made around a thousand times faster by “turbo-charging” their electrical components with light pulses.

The problem with studying these phase transitions is that they are extremely fast and it is therefore very difficult to “catch them in the act”. So far, scientists have had to content themselves with characterising the state of a material before and after a phase transition of this kind. Researchers Rui E. F. Silva, Olga Smirnova, and Misha Ivanov of the Berlin Max Born Institute, however, have now devised a method that will, in the truest sense, shed light on the process. Their theory involves firing extremely short, tailored laser pulses at a material – pulses that can only recently be produced in the appropriate quality given the latest developments in lasers. One then observes the material’s reaction to these pulses to see how the electrons in the material are excited into motion and, like a bell, emit resonant vibrations at specific frequencies, as harmonics of the incident light.

“By analysing this high harmonic spectrum, we can observe the change in the structural order in these strongly correlated materials ‘live’ for the first time,” says first author of the paper Rui Silva of the Max Born Institute. Laser sources capable of targetedly triggering these transitions have only been available since very recently. The laser pulses namely have to be amply strong and extremely short – on the order of femtoseconds in duration (millionths of a billionth of a second).

In some cases, it takes only a single oscillation of light to disrupt the electronic order of a material and turn an insulator into a metal-like conductor. The scientists at the Berlin Max Born Institute are among the world’s leading experts in the field of ultrashort laser pulses.

“If we want to use light to control the properties of electrons in a material, then we need to know exactly how the electrons will react to light pulses,” Ivanov explains. With the latest-generation laser sources, which allow full control over the electromagnetic field even down to a single oscillation, the newly published method will allow deep insights into the materials of the future.

Researchers from Tomsk Polytechnic University together with their international colleagues have discovered a method to modify and use the one-atom thin conductor of current and heat, graphene without destroying it. Thanks to the novel method, the researchers were able to synthesize on single-layer graphene a well-structured polymer with a strong covalent bond, which they called ‘polymer carpets’. The entire structure is highly stable; it is less prone to degradation over time that makes the study promising for the development of flexible organic electronics. Also, if a layer of molybdenum disulfide is added over the ‘nanocarpet’, the resulting structure generates current under exposure to light. The study results were published in Journal of Materials Chemistry C.

This is the scheme for obtaining a hybrid structure of 'graphene-polymer'. Credit: Tomsk Polytechnic University

This is the scheme for obtaining a hybrid structure of ‘graphene-polymer’. Credit: Tomsk Polytechnic University

Graphene is simultaneously the most durable, light and an electrically conductive carbon material. It can be used for manufacturing solar batteries, smartphone screens, thin and flexible electronics, and even in water filters since graphene films pass water molecules and stop all other compounds. Graphene should be integrated into complex structures to be used successfully. However, it is a challenge to do that. According to scientists, graphene itself is stable enough and reacts poorly with other compounds. In order to make it react with other elements, i.e. to modify it, graphene is usually at least partially destroyed. This modification degrades the properties of the materials obtained.

Professor Raul D. Rodriguez from the Research School for Chemistry & Applied Biomedical Sciences says: ‘When functionalizing graphene, you should be very careful. If you overdo it, the unique properties of graphene are lost. Therefore, we decided to follow a different path.

In graphene, there are inevitable nanodefects, for example, at the edges of graphene and wrinkles in the plane. Hydrogen atoms are often attached to such defects. It is this hydrogen that can interact with other chemicals.’

To modify graphene, the authors use a thin metal substrate on which a graphene single-layer is placed. Then graphene is covered with a solution of bromine-polystyrene molecules. The molecules interact with hydrogen and are attached to the existing defects, resulting in polyhexylthiophene (P3HT). Further exposed to light during the photocatalysis, a polymer begins to ‘grow’.

‘In the result, we obtained the samples which structure resembles ‘polymer carpets’ as we call them in the paper. Above such a ‘polymer carpet’ we place molybdenum disulfide. Due to a unique combination of materials, we obtain a ‘sandwich’ structure’ that functions like a solar battery. That is, it generates current when exposed to light. In our experiments a strong covalent bond is established between the molecules of the polymer and graphene, that is critical for the stability of the material obtained,’ notes Rodriguez.

According to the researcher, the method for graphene modification, on the one hand, enables obtaining a very sturdy compound; on the other hand, it is rather simple and cheap as affordable materials are used. The method is versatile because it makes growing very different polymers directly on graphene possible.

‘The strength of the obtained hybrid material is achieved additionally because we do not destroy graphene itself but use pre-existing defects, and a strong covalent bond to polymer molecules. This allows us to consider the study as promising for the development of thin and flexible electronics when solar batteries can be attached to clothes, and when deformed they will not break,’ the professor explains.

NUST MISIS scientists have finally found out why a material that could potentially become the basis for ultra-fast memory in new computers is formed. Professor Petr Karpov and Serguei Brazovskii, both researchers at NUST MISIS, have managed to develop a theory which explains the mechanism of the latent state formation in layered tantalum disulfide, one of the most promising materials for modern microelectronics. The latent state of matter (which will be discussed further) was discovered by Serguei Brazovskii with a group of experimenters from Slovenia in 2014. The experiment that led to the beginning of the “boom” for the studies of layered materials lied in the fact that the tantalum disulfide sample, which was less than 100 nanometers big, was affected by an ultrashort laser (an electric pulse). The state of the material changed because of pulses in the irradiated area, and the sample became either a conductor of dielectrics or vice versa, depending on the experimenters’ wish. The switching even occurred in just one picosecond –a far quicker rate than in the “fastest” materials used as storage mediums in modern computers. That condition didn’t fade after exposure, but instead persisted. Accordingly, the material has become a potential candidate for the basis of the next generation of information data mediums.

Serguei Brazovskii is currently serving as the leading scientist of the “Theory of locally adjustable electronic states in layered materials” project at NUST MISIS, as well as working as a leading scientist at the University of Paris-Sud (Orsay, France) Laboratory of Theoretical Physics and Statistical Models.

Professor Petr Karpov, engineer at the NUST MISIS Department for Theoretical Physics and Quantum Technologies, explained the root of the matter, “The ‘boom’ in the study of layered tantalum disulfide happened, as well as a number of articles on this topic in different journals being published, after our colleagues from Slovenia discovered the latent state of the matter, unattainable in conventional (thermodynamic) phase transitions. However, most of these works were experimental, and the theory lagged behind. That is, the state could have been received but why did it turn out [that way]? What were the mechanisms of its formation? What its nature is in general, remained unclear. Why doesn’t the system return to its original state, continuing to remain in modified form indefinitely? In this article we tried to find the theoretical justification of the occurring processes”.

Tantalum disulfide belongs to a special group of conductor materials in which so-called charge-density waves are formed. This means that in addition to the natural peaks of electron density caused by the presence of an atom, there is also another periodicity that is several times greater than the distance between the adjacent atoms of the crystal lattice. In this case, the degree of that periodicity is the “root of thirteen”, so there is quite a large difference.

Picture A shows a layer of tantalum atoms. The period between the “superpeaks” is marked with a red arrow. The state of the different sites in the tantalum disulfide layer differ from each other in the fact that the maximum electron density is centered on tantalum atoms. The red ones show one state, while the “blue” and “white” ones show other states.

The work of NUST MISIS scientists consisted of constructing and studying a universal theoretical model that could describe the most important and intriguing property of the newly discovered state: the formation and transformation of nano-structural mosaics (pic. b). Some of the metal atoms fly out of the lattice after the processing of electrical impulses in the sample of layered tantalum disulfide, and that causes defects — charged vacancies in the electronic crystal.

However, instead of keeping a maximum distance from each other, the charges are “smeared” along the linear chains of tantalum atoms, forming boundaries of zones with different states of tantalum atoms. These “domains” then essentially chain up, connected to a global network. Manipulating these nanosets is the reason for the switching and memory effects observed in the material.

“We tried to find out why similar charges in such a structure do not repel, but, in fact, are attracted to each other. It turned out that this process is energetically more profitable than the maximum removal of positive charges from each other because the formation of fractional charged domain walls minimizes the charge of the constituent wall of atoms, which is why the domain system becomes more stable. This is completely confirmed by the experiment, and the whole crystal can be taken to such a state with a domain mosaic and globules dividing the walls”, — added Petr Karpov.

According to the scientists, thanks to the development of this theory, it is possible to confirm that the domain state of tantalum disulfide can be used for long-term storage and super-fast operation of information.