Category Archives: Materials

Mentor, a Siemens business, today announced LightSuite™ Photonic Compiler – the industry’s first integrated photonic automated layout system. This new tool enables companies designing integrated photonic layouts to describe designs in the Python language, from which the tool then automatically generates designs ready for fabrication. The resulting design is “Correct by Calibre” – with the implementation precisely guided by Mentor’s Calibre® RealTime Custom verification tool. LightSuite Photonic Compiler enables designers to generate as well as update large photonic layouts in minutes versus weeks.

With this breakthrough technology, companies can dramatically speed the development of integrated photonic designs that will bring speed-of-light communications directly into high-speed networking and high-performance computing (HPC) systems. It also speeds the development of more cost-effective LiDAR technology, which is seen as essential to enabling the mass deployment of autonomous vehicles.

“Mentor’s LightSuite Photonic Compiler represents a quantum leap in automating what has up to now been a highly manual, full-custom process that required deep knowledge of photonics as well as electronics,” said Joe Sawicki, vice president and general manager of the Design-to-Silicon Division at Mentor, a Siemens business. “With the new LightSuite Photonic Compiler, Mentor is enabling more companies to push the envelope in creating integrated photonic designs.”

“LightSuite Photonic Compiler fixes the biggest roadblocks preventing industry-wide adoption of electro-optical design and simulation of photonic chips,” said M. Ashkan Seyedi, Ph.D., senior research scientist, Hewlett Packard Enterprise. “Photonic chips promise amazing performance, but designing circuits today is just too difficult and requires specialized knowledge. LightSuite Photonic Compiler circumvents those challenges and enables scalability. I’m thrilled to have worked with Mentor to develop this tool to make it possible for anyone to design and build photonic circuits as easily as designing electronic circuits.”

Until now, photonic designers have been forced to use analog, full-custom IC tools to create photonic designs. In this flow, designers manually place components from a process design kit (PDK) and then interconnect those components manually. Photonic components must be interconnected with curved waveguides. After they have manually placed and interconnected the components, they typically perform a full Calibre physical verification run to check for design rule violations, as Calibre DRC can find violations even in photonic designs.

Mentor designed the new LightSuite Photonic Compiler specifically for photonic layout so that engineers have complete control of their layouts and can use the tool to automatically perform the placement and interconnecting of both photonic and electrical components. The designers create a Python script that is used to drive the LightSuite Photonic Compiler. Initial placement can also be defined in Python, or come from a pre-placed OpenAccess design. Next, the tool interconnects photonics components with curved wave guides. As some of the components might contain built-in electrical elements, the tool will route these electrical connections simultaneously along with the curved waveguides.

LightSuite Photonic Compiler uses Calibre RealTime Custom during the inner placement and routing loop, resulting in a layout that is design-rule correct. The tool enables designers to perform “what-if” design exploration for photonics designs, which was prohibitively time consuming with manual layout. With this new level of automation, designers can generate a new layout in minutes versus weeks for large designs.

Mentor will demonstrate LightSuite Photonic Compiler at ECOC in Rome, September 24 – 26 at Stand 436. LightSuite Photonic Compiler will be available on October 1.

SUNY Polytechnic Institute (SUNY Poly) announced today that Professor of Nanobioscience Dr. Nate Cady has been awarded $500,000 in funding from the National Science Foundation to develop advanced computing systems based on a novel approach to the creation of non-volatile memory architecture. This research, which will also support student opportunities, aims to advance today’s typical computing model, in which processing and memory are separate, by bringing them together to make the entire process faster and more energy efficient.

“I am proud to congratulate Professor Cady on this National Science Foundation (NSF) award which is focused on enabling advanced computing capabilities, and notably, has important implications for advances in artificial intelligence,” said SUNY Poly Interim President Dr. Grace Wang. “The NSF’s selection of Dr. Cady’s research for this funding exemplifies the quality and impact of SUNY Poly’s research where our faculty and students leverage our world-class high-tech resources, explore new frontiers, and develop critical technologies for our society.”

The research will enable the design of a scalable computing infrastructure that uses nanoscale non-volatile memory (NVM) devices for both storage and computation. One of the current limits to computing speed is the result of current personal computing architecture, which separates the processor and memory and leads to a cap on data throughput, known as the “von Neumann bottleneck.” By combining storage and computation on the same device, the project circumvents this barrier and creates scalable solutions for extreme-scale computing—computing that is up to one thousand times more capable than current comparable computing—based on wires that cross each other to form memory cells at every intersection. This more powerful capability is made possible because each memory cell, acting like a synapse of the human brain, can be switched on or off, similar to the 1’s and 0’s of current computing, but it can also store many other values between the on or off states, increasing the amount of information that a given memory cell can store exponentially.

“This grant showcases the incredible potential of our faculty to tackle real-world problems with high-tech solutions that stem from the SUNY Poly’s advanced labs, cleanrooms, and capabilities. This news is especially exciting for a number of our graduate students who will be able to focus on this promising research area where they will be at the cutting-edge,” said SUNY Poly Interim Provost Dr. Steven Schneider.

“Dr. Cady’s research is a powerful example of the kind of expertise that SUNY Poly’s faculty possess as our innovation-centered ecosystem provides us with unique opportunities to move the technologies of the future forward,” said SUNY Poly Interim Dean of the College of Nanoscale Sciences; Empire Innovation Professor of Nanoscale Science; and Executive Director, Center for Nanoscale Metrology Dr. Alain Diebold.

“I look forward to advancing this non-volatile memory research at SUNY Poly, using the institution’s cutting-edge fabrication facilities in order to address current computing bottlenecks that slow computing capability and waste energy,” said Dr. Cady. “This grant will drive the development of computing and memory infrastructure that will be evaluated using high-performance simulations and experimental benchmarking within our state-of-the-art laboratory at SUNY Poly where we are eager to develop the architecture that can help revolutionize processing and memory capabilities for next-gen computers.”

Dr. Cady’s research will support SUNY Poly graduate students who will be able to obtain hands-on experience developing the computing/memory structures. The materials for this project will be developed, demonstrated, and then integrated with traditional complementary metal-oxide-semiconductor (CMOS) computer chips as part of a larger production, which will utilize SUNY Poly’s 200mm and 300mm state-of-the-art fabrication facilities. The University of Central Florida is receiving its own funds for collaborative research related to this effort.

Computing using multiple parallel flows of current through data stored in nanoscale “crossbars” is often fast and more energy-efficient, but the design of such crossbars is highly unintuitive for human designers. More specifically, this project explores formal methods for more efficiently conducting Boolean searches and using artificial intelligence techniques such as best-first search, in addition to automatically synthesizing non-volatile memory crossbar designs from specifications written in a high-level programming language.

A new technique makes it possible to obtain an individual fingerprint of the current-carrying edge states occurring in novel materials such as topological insulators or 2D materials. Physicists of the University of Basel present the new method together with American scientists in Nature Communications.

Measured tunneling current and its dependence on the two applied magnetic fields: The fans of red/yellow curves each correspond to a fingerprint of the conducting edge states. Each individual curve separately shows one of the edge states. Credit: University of Basel, Department of Physics

While insulators do not conduct electrical currents, some special materials exhibit peculiar electrical properties: though not conducting through their bulk, their surfaces and edges may support electrical currents due to quantum mechanical effects, and do so even without causing losses.

Such so-called topological insulators have attracted great interest in recent years due to their remarkable properties. In particular, their robust edge states are very promising since they could lead to great technological advances.

Currents flowing only along the edges

Similar effects as the edge states of such topological insulators also appear when a two-dimensional metal is exposed to a strong magnetic field at low temperatures. When the so-called quantum Hall effect is realized, current is thought to flow only at the edges, where several conducting channels are formed.

Probing individual edge states

Until now, it was not possible to address the numerous current carrying states individually or to determine their positions separately. The new technique now makes it possible to obtain an exact fingerprint of the current carrying edge states with nanometer resolution.

This is reported by researchers of the Department of Physics and the Swiss Nanoscience Institute of the University of Basel in collaboration with colleagues of the University of California, Los Angeles, as well as of Harvard and Princeton University, USA.

In order to measure the fingerprint of the conducting edge states, the physicists lead by Prof. Dominik Zumbühl have further developed a technique based on tunneling spectroscopy.

They have used a gallium arsenide nanowire located at the sample edge which runs in parallel to the edge states under investigation. In this configuration, electrons may jump (tunnel) back and forth between a specific edge state and the nanowire as long as the energies in both systems coincide. Using an additional magnetic field, the scientists control the momentum of tunneling electrons and can address individual edge states. From the measured tunneling currents, the position and evolution of each edge state may be obtained with nanometer precision.

Tracking the evolution

This new technique is very versatile and can also be used to study dynamically evolving systems. Upon increasing the magnetic field, the number of edge states is reduced, and their distribution is modified. For the first time, the scientists were able to watch the full edge state evolution starting from their formation at very low magnetic fields.

With increasing magnetic field, the edge states are first compressed towards the sample boundary until eventually, they move towards the inside of the sample and then disappear completely. Analytical and numerical models developed by the research team agree very well with the experimental data.

“This new technique is not only very useful to study the quantum Hall edge states,” Dominik Zumbühl comments the results of the international collaboration. “It might also be employed to investigate new exotic materials such as topological insulators, graphene or other 2D materials.”

Sandwiching two-dimensional materials used in nanoelectronic devices between their three-dimensional silicon bases and an ultrathin layer of aluminum oxide can significantly reduce the risk of component failure due to overheating, according to a new study published in the journal of Advanced Materials led by researchers at the University of Illinois at Chicago College of Engineering.

An experimental transistor using silicon oxide for the base, carbide for the 2D material and aluminum oxide for the encapsulating material. Credit: (Image: Zahra Hemmat).

Many of today’s silicon-based electronic components contain 2D materials such as graphene. Incorporating 2D materials like graphene — which is composed of a single-atom-thick layer of carbon atoms — into these components allows them to be several orders of magnitude smaller than if they were made with conventional, 3D materials. In addition, 2D materials also enable other unique functionalities. But nanoelectronic components with 2D materials have an Achilles’ heel — they are prone to overheating. This is because of poor heat conductance from 2D materials to the silicon base.

“In the field of nanoelectronics, the poor heat dissipation of 2D materials has been a bottleneck to fully realizing their potential in enabling the manufacture of ever-smaller electronics while maintaining functionality,” said Amin Salehi-Khojin, associate professor of mechanical and industrial engineering in UIC’s College of Engineering.

One of the reasons 2D materials can’t efficiently transfer heat to silicon is that the interactions between the 2D materials and silicon in components like transistors are rather weak.

“Bonds between the 2D materials and the silicon substrate are not very strong, so when heat builds up in the 2D material, it creates hot spots causing overheat and device failure,” explained Zahra Hemmat, a graduate student in the UIC College of Engineering and co-first author of the paper.

In order to enhance the connection between the 2D material and the silicon base to improve heat conductance away from the 2D material into the silicon, engineers have experimented with adding an additional ultra-thin layer of material on top of the 2D layer — in effect creating a “nano-sandwich” with the silicon base and ultrathin material as the “bread.”

“By adding another ‘encapsulating’ layer on top of the 2D material, we have been able to double the energy transfer between the 2D material and the silicon base,” Salehi-Khojin said.

Salehi-Khojin and his colleagues created an experimental transistor using silicon oxide for the base, carbide for the 2D material and aluminum oxide for the encapsulating material. At room temperature, the researchers saw that the conductance of heat from the carbide to the silicon base was twice as high with the addition of the aluminum oxide layer versus without it.

“While our transistor is an experimental model, it proves that by adding an additional, encapsulating layer to these 2D nanoelectronics, we can significantly increase heat transfer to the silicon base, which will go a long way towards preserving functionality of these components by reducing the likelihood that they burn out,” said Salehi-Khojin. “Our next steps will include testing out different encapsulating layers to see if we can further improve heat transfer.”

Scientists have developed a photoelectrode that can harvest 85 percent of visible light in a 30 nanometers-thin semiconductor layer between gold layers, converting light energy 11 times more efficiently than previous methods.

In the pursuit of realizing a sustainable society, there is an ever-increasing demand to develop revolutionary solar cells or artificial photosynthesis systems that utilize visible light energy from the sun while using as few materials as possible.

The research team, led by Professor Hiroaki Misawa of the Research Institute for Electronic Science at Hokkaido University, has been aiming to develop a photoelectrode that can harvest visible light across a wide spectral range by using gold nanoparticles loaded on a semiconductor. But merely applying a layer of gold nanoparticles did not lead to a sufficient amount of light absorption, because they took in light with only a narrow spectral range.

Left: The newly developed photoelectrode, a sandwich of semiconductor layer (TiO2) between gold film (Au film) and gold nanoparticles (Au NPs). The gold nanoparticles were partially inlaid onto the surface of the titanium dioxide thin-film to enhance light absorption. Right: The photoelectrode (Au-NP/TiO2/Au-film) with 7nm of inlaid depth traps light making it nontransparent (top). An Au-NP/TiO2 structure without the Au film are shown for comparison (bottom). Credit: Misawa H. et al., Nature Nanotechnology, July 30, 2018

In the study published in Nature Nanotechnology, the research team sandwiched a semiconductor, a 30-nanometer titanium dioxide thin-film, between a 100-nanometer gold film and gold nanoparticles to enhance light absorption. When the system is irradiated by light from the gold nanoparticle side, the gold film worked as a mirror, trapping the light in a cavity between two gold layers and helping the nanoparticles absorb more light.

To their surprise, more than 85 percent of all visible light was harvested by the photoelectrode, which was far more efficient than previous methods. Gold nanoparticles are known to exhibit a phenomenon called localized plasmon resonance which absorbs a certain wavelength of light. “Our photoelectrode successfully created a new condition in which plasmon and visible light trapped in the titanium oxide layer strongly interact, allowing light with a broad range of wavelengths to be absorbed by gold nanoparticles,” says Hiroaki Misawa.

When gold nanoparticles absorb light, the additional energy triggers electron excitation in the gold, which transfers electrons to the semiconductor. “The light energy conversion efficiency is 11 times higher than those without light-trapping functions,” Misawa explained. The boosted efficiency also led to an enhanced water splitting: the electrons reduced hydrogen ions to hydrogen, while the remaining electron holes oxidized water to produce oxygen — a promising process to yield clean energy.

“Using very small amounts of material, this photoelectrode enables an efficient conversion of sunlight into renewable energy, further contributing to the realization of a sustainable society,” the researchers concluded.

Air Products (NYSE : APD ) today announced it has been awarded by Samsung Electronics additional gaseous nitrogen and hydrogen supply to its semiconductor fab in Giheung, South Korea.

Air Products, who has been supplying industrial gases to Samsung Electronics’ Giheung site since 1998, will invest in building a new air separation unit, multiple hydrogen plants, and pipelines, which are scheduled to be operational in 2020 to supply the customer’s increased demand.

“We are proud to expand our longstanding relationship with Samsung Electronics and have their continued confidence in our ability to support their technological development and growth plans,” said Kyo-Yung Kim, president of Air Products Korea. “Our latest investment once again reinforces Air Products’ commitment to serving our strategic customer, as well as the broader semiconductor and electronics industries, with our safety, reliability, efficiency and excellent service.”

Air Products supplies many of Samsung’s operations worldwide, including its semiconductor cluster in the north region of South Korea spanning Giheung, Hwaseong and Pyeongtaek. In Pyeongtaek, the company has been undertaking a multi-phase expansion project to support Samsung Electronics’ multibillion dollar fab.

A leading integrated gases supplier, Air Products has been serving the global electronics industry for more than 40 years, supplying industrial gases safely and reliably to most of the world’s largest technology companies. Air Products is working with these industry leaders to develop the next generation of semiconductors and displays for tablets, computers and mobile devices.

Schottky diode is composed of a metal in contact with a semiconductor. Despite its simple construction, Schottky diode is a tremendously useful component and is omnipresent in modern electronics. Schottky diode fabricated using two-dimensional (2D) materials have attracted major research spotlight in recent years due to their great promises in practical applications such as transistors, rectifiers, radio frequency generators, logic gates, solar cells, chemical sensors, photodetectors, flexible electronics and so on.

The understanding of 2D material-based Schottky diode is, however, plagued by multiple mysteries. Several theoretical models have co-existed in the literatures and a model is often selected a priori without rigorous justifications. It is not uncommon to see a model, whose underlying physics fundamentally contradicts with the physical properties of 2D materials, being deployed to analyse a 2D material Schottky diode.

Reporting in Physical Review Letters, researchers from the Singapore University of Technology and Design (SUTD) have made a major step forward in resolving the mysteries surrounding 2D material Schottky diode. By employing a rigorous theoretical analysis, they developed a new theory to describe different variants of 2D-material-based Schottky diodes under a unifying framework. The new theory lays down a foundation that helps to unite prior contrasting models, thus resolving a major confusion in 2D material electronics.

Schematic drawing of a 2D-material-based lateral (left) and vertical (right) Schottky diode. For broad classes of 2D materials, the current-temperature relation can be universally described by a scaling exponent of 3/2 and 1, respectively, for lateral and vertical Schottky diodes. Credit: Singapore University of Technology and Design

“A particularly remarkable finding is that the electrical current flowing across a 2D material Schottky diode follows a one-size-fits-all universal scaling law for many types of 2D materials,” said first-author Dr. Yee Sin Ang from SUTD.

Universal scaling law is highly valuable in physics since it provides a practical “Swiss knife” for uncovering the inner workings of a physical system. Universal scaling law has appeared in many branches of physics, such as semiconductor, superconductor, fluid dynamics, mechanical fractures, and even in complex systems such as animal life span, election results, transportation and city growth.

The universal scaling law discovered by SUTD researchers dictates how electrical current varies with temperature and is widely applicable to broad classes of 2D systems including semiconductor quantum well, graphene, silicene, germanene, stanene, transition metal dichalcogenides and the thin-films of topological solids.

“The simple mathematical form of the scaling law is particularly useful for applied scientists and engineers in developing novel 2D material electronics,” said co-author Prof. Hui Ying Yang from SUTD.

The scaling laws discovered by SUTD researchers provide a simple tool for the extraction of Schottky barrier height – a physical quantity critically important for performance optimisation of 2D material electronics.

“The new theory has far reaching impact in solid state physics,” said co-author and principal investigator of this research, Prof. Lay Kee Ang from SUTD, “It signals the breakdown of classic diode equation widely used for traditional materials over the past 60 years, and shall improve our understanding on how to design better 2D material electronics.”

Nova (NASDAQ : NVMI ) announced today that a major foundry recently placed an order for its VeraFlex advanced X-Ray metrology solution for 5nm technology node.

Nova’s solution utilizes X-ray Photoelectron Spectroscopy (XPS) to simultaneously measure composition and thickness of complex film stacks through the fabrication process. The integration of these film stacks is significantly more complicated than previous nodes both in terms of the materials used and their multi-layer composition, requiring sophisticated process control to minimize device variation. The VeraFlex product portfolio provides the requisite sensitivity and precision needed for these challenging measurements.

As a result of this selection, Nova expects more than $12 million in aggregate business from this customer across 2018 and 2019.

“We are excited about this selection which confirms the applicability of our technology for 5nm and emphasizes the growing need for advanced materials metrology solutions in advanced nodes,” said Adrian Wilson, General Manager of Nova’s Materials Metrology Division. “In order to achieve better performance in smaller devices, our Logic customers are required to modify their materials strategy beyond the traditional architectural changes. These innovative developments increase the need for Materials control and our available market accordingly. We look forward to additional orders as 5nm moves into volume production and further applications are qualified.”

Nova is a innovator and key provider of metrology solutions for advanced process control used in semiconductor manufacturing.

An international research group improved perovskite solar cells efficiency by using materials with better light absorption properties. For the first time, researchers used silicon nanoparticles. Such nanoparticles can trap light of a broad range of wavelengths near the cell active layer. The particles themselves don’t absorb light and don’t interact with other elements of the battery, thus maintaining its stability. The research was published in Advanced Optical Materials.

Perovskite solar cells have become very popular over the last few years. This hybrid material allows scientists to create inexpensive, efficient, and easy to use solar cells. The only problem is that the thickness of a perovskite layer should not exceed several hundred nanometers, but at the same time a thin perovskite absorbs less amount of incident photons from the Sun.

For this reason, scientists had to find a way to enhance light harvesting properties of the absorbing perovskite layer without increasing its thickness. To do this, scientists use metal nanoparticles. Such particles allow for better light absorption due to surface plasmon excitation but have significant drawbacks. For example, they absorb some energy themselves, thus heating up and damaging the battery. Scientists from ITMO University, in collaboration with colleagues from St. Petersburg State University, Italy and the USA, proposed using silicon nanoparticles to solve these problems.

“Dielectric particles don’t absorb light, so they don’t heat up. They are chemically inert and don’t affect the stability of the battery. Besides, being highly resonant, such particles can absorb more light of a wide range of wavelengths. Due to special layout characteristics, they don’t damage the structure of the cells. These advantages allowed us to enhance cells efficiency up to almost 19%. So far, this is the best known result for this particular perovskite material with incorporated nanoparticles,” shares Aleksandra Furasova, a postgraduate student at ITMO’s Faculty of Physics and Engineering.

According to the scientists, this is the first research on using silicon nanoparticles for enhancing light harvesting properties of the absorbing upper layer. Silicon nanoparticles have already surpassed plasmonic ones. The scientists hope that a deeper study of the interaction between nanoparticles and light, as well as their application in perovskite solar cells will lead to even better results.

“In our research, we used MAPbI3 perovskite, which allowed us to study in detail how resonant silicon nanoparticles affect perovskites solar cells. Now we can further try to use such particles for other types of perovskites with increased efficiency and stability. Apart from that, the nanoparticles themselves can be modified in order to enhance their optical and transport properties. It is important to note that silicon nanoparticles are very inexpensive and easy to produce. Therefore, this method can be easily incorporated in the process of solar cells production,” commented Sergey Makarov, head of ITMO’s Laboratory of Hybrid Nanophotonics and Optoelectronics.

Scientists at the Department of Energy’s Oak Ridge National Laboratory induced a two-dimensional material to cannibalize itself for atomic “building blocks” from which stable structures formed.

The findings, reported in Nature Communications, provide insights that may improve design of 2D materials for fast-charging energy-storage and electronic devices.

“Under our experimental conditions, titanium and carbon atoms can spontaneously form an atomically thin layer of 2D transition-metal carbide, which was never observed before,” said Xiahan Sang of ORNL.

He and ORNL’s Raymond Unocic led a team that performed in situ experiments using state-of-the-art scanning transmission electron microscopy (STEM), combined with theory-based simulations, to reveal the mechanism’s atomistic details.

“This study is about determining the atomic-level mechanisms and kinetics that are responsible for forming new structures of a 2D transition-metal carbide such that new synthesis methods can be realized for this class of materials,” Unocic added.

The starting material was a 2D ceramic called a MXene (pronounced “max een”). Unlike most ceramics, MXenes are good electrical conductors because they are made from alternating atomic layers of carbon or nitrogen sandwiched within transition metals like titanium.

The research was a project of the Fluid Interface Reactions, Structures and Transport (FIRST) Center, a DOE Energy Frontier Research Center that explores fluid-solid interface reactions that have consequences for energy transport in everyday applications. Scientists conducted experiments to synthesize and characterize advanced materials and performed theory and simulation work to explain observed structural and functional properties of the materials. New knowledge from FIRST projects provides guideposts for future studies.

The high-quality material used in these experiments was synthesized by Drexel University scientists, in the form of five-ply single-crystal monolayer flakes of MXene. The flakes were taken from a parent crystal called “MAX,” which contains a transition metal denoted by “M”; an element such as aluminum or silicon, denoted by “A”; and either a carbon or nitrogen atom, denoted by “X.” The researchers used an acidic solution to etch out the monoatomic aluminum layers, exfoliate the material and delaminate it into individual monolayers of a titanium carbide MXene (Ti3C2).

The ORNL scientists suspended a large MXene flake on a heating chip with holes drilled in it so no support material, or substrate, interfered with the flake. Under vacuum, the suspended flake was exposed to heat and irradiated with an electron beam to clean the MXene surface and fully expose the layer of titanium atoms.

MXenes are typically inert because their surfaces are covered with protective functional groups–oxygen, hydrogen and fluorine atoms that remain after acid exfoliation. After protective groups are removed, the remaining material activates. Atomic-scale defects–“vacancies” created when titanium atoms are removed during etching–are exposed on the outer ply of the monolayer. “These atomic vacancies are good initiation sites,” Sang said. “It’s favorable for titanium and carbon atoms to move from defective sites to the surface.” In an area with a defect, a pore may form when atoms migrate.

“Once those functional groups are gone, now you’re left with a bare titanium layer (and underneath, alternating carbon, titanium, carbon, titanium) that’s free to reconstruct and form new structures on top of existing structures,” Sang said.

High-resolution STEM imaging proved that atoms moved from one part of the material to another to build structures. Because the material feeds on itself, the growth mechanism is cannibalistic.

“The growth mechanism is completely supported by density functional theory and reactive molecular dynamics simulations, thus opening up future possibilities to use these theory tools to determine the experimental parameters required for synthesizing specific defect structures,” said Adri van Duin of Penn State.

Most of the time, only one additional layer [of carbon and titanium] grew on a surface. The material changed as atoms built new layers. Ti3C2 turned into Ti4C3, for example.

“These materials are efficient at ionic transport, which lends itself well to battery and supercapacitor applications,” Unocic said. “How does ionic transport change when we add more layers to nanometer-thin MXene sheets?” This question may spur future studies.

“Because MXenes containing molybdenum, niobium, vanadium, tantalum, hafnium, chromium and other metals are available, there are opportunities to make a variety of new structures containing more than three or four metal atoms in cross-section (the current limit for MXenes produced from MAX phases),” Yury Gogotsi of Drexel University added. “Those materials may show different useful properties and create an array of 2D building blocks for advancing technology.”

At ORNL’s Center for Nanophase Materials Sciences (CNMS), Yu Xie, Weiwei Sun and Paul Kent performed first-principles theory calculations to explain why these materials grew layer by layer instead of forming alternate structures, such as squares. Xufan Li and Kai Xiao helped understand the growth mechanism, which minimizes surface energy to stabilize atomic configurations. Penn State scientists conducted large-scale dynamical reactive force field simulations showing how atoms rearranged on surfaces, confirming defect structures and their evolution as observed in experiments.

The researchers hope the new knowledge will help others grow advanced materials and generate useful nanoscale structures.