Tag Archives: letter-pulse-tech

A new device being developed by Washington State University physicist Yi Gu could one day turn the heat generated by a wide array of electronics into a usable fuel source.

The device is a multicomponent, multilayered composite material called a van der Waals Schottky diode. It converts heat into electricity up to three times more efficiently than silicon — a semiconductor material widely used in the electronics industry. While still in an early stage of development, the new diode could eventually provide an extra source of power for everything from smartphones to automobiles.

“The ability of our diode to convert heat into electricity is very large compared to other bulk materials currently used in electronics,” said Gu, an associate professor in WSU’s Department of Physics and Astronomy. “In the future, one layer could be attached to something hot like a car exhaust or a computer motor and another to a surface at room temperature. The diode would then use the heat differential between the two surfaces to create an electric current that could be stored in a battery and used when needed.”

Gu recently published a paper on the Schottky diode in The Journal of Physical Chemistry Letters.

A new kind of diode

In the world of electronics, Schottky diodes are used to guide electricity in a specific direction, similar to how a valve in a water main directs the flow of liquid going through it. They are made by attaching a conductor metal like aluminum to a semiconductor material like silicon.

Instead of combining a common metal like aluminum or copper with a conventional semiconductor material like silicon, Gu’s diode is made from a multilayer of microscopic, crystalline Indium Selenide. He and a team of graduate students used a simple heating process to modify one layer of the Indium Selenide to act as a metal and another layer to act as a semiconductor. The researchers then used a new kind of confocal microscope developed by Klar Scientific, a start-up company founded in part by WSU physicist Matthew McCluskey, to study their materials’ electronic properties.

Unlike its conventional counterparts, Gu’s diode has no impurities or defects at the interface where the metal and semiconductor materials are joined together. The smooth connection between the metal and semiconductor enables electricity to travel through the multilayered device with almost 100 percent efficiency.

“When you attach a metal to a semiconductor material like silicon to form a Schottky diode, there are always some defects that form at the interface,” said McCluskey, a co-author of the study. “These imperfections trap electrons, impeding the flow of electricity. Gu’s diode is unique in that its surface does not appear to have any of these defects. This lowers resistance to the flow of electricity, making the device much more energy efficient.”

Next steps

Gu and his collaborators are currently investigating new methods to increase the efficiency of their Indium Selenide crystals. They are also exploring ways to synthesize larger quantities of the material so that it can be developed into useful devices.

“While still in the preliminary stages, our work represents a big leap forward in the field of thermoelectrics,” Gu said. “It could play an important role in realizing a more energy-efficient society in the future.”

Leti, a technology research institute of CEA Tech, and Mentor, a Siemens business, today announced Leti will provide access to the Mentor Veloce emulator to SMEs and startups and will introduce emulation technology to global companies beginning Q3 2017. The Veloce emulator is Mentor’s high-capacity, high-speed, multi-application tool for emulation of system-on chip (SoC) designs that was installed at Leti in 2013.

Emulation is a vital process for more efficient development of complex digital circuits that includes debugging the design at early stages and validating the upstream, onboard software operation.

The Veloce emulator accelerates block and full SoC register-transfer level (RTL) simulations during all phases of the design process, ending the long delay between starting simulations and getting results. It enables pre-silicon testing and debug, can use real-world data, while both hardware and software designs are still fluid.

“Veloce dramatically speeds up the design cycle, because it is 1,000 times faster than traditional RTL simulation tools,” said Thierry Colette, head of Leti’s Architecture, IC Design and Embedded Software division. “It is now possible to verify multi-processor circuits that have several billion transistors – a real competitive advantage that improves return on investment and speeds time to market. But because this powerful tool represents a major investment for microelectronics manufacturers or design houses, Leti is launching this special emulation service to provide our partners direct access to this technology and the benefits it offers.”

“Mentor’s cooperation with CEA-Leti spans a variety of research topics over multiple years,” says Eric Selosse, vice president and general manager of the Mentor Emulation Division. “The intent to proliferate state-of-the-art hardware emulation-based verification methodology to the high technology market is a very attractive goal and we’re proud to contribute to it with our Veloce solutions.”

The Leti offer, which targets European chipmakers, includes Leti’s expert support, such as taking control of device design, optimized implementation within the emulator, debug and analysis of results. Leti also will provide access and support to additional specific tools available in its Grenoble facility, as needed.

To ensure data security, this emulator offer will include:

  • a new chassis and cards representing an emulation capacity of 50 Mgates at this stage
    (could be upgrade on demand)
  • a dedicated and secure network for customers
  • servers dedicated to this offer, connected to a secure network to manage emulation with internal tools.

The network architecture is designed so that Leti partners in this program can remotely view emulation progress or retrieve results.

A group of international physicists, jointly with NUST MISIS researchers, have conducted a series of experiments on graphene bombardment by swift heavy ions. The experimental results show that such a bombardment allows for the creation of nanopores in graphene. The diameter of these nanopores can be adjusted in a range of 1 to 4 nanometers.

The experimental results on graphen bombardment by swift heavy ions, conducted by NUST MISIS scientists together with colleagues from the University of Helsinki and Aalto University (Finland), the University of Nottingham (the United Kingdom), the University of Duisburg-Essen (Germany), the University of Vienna (Austria), the Center of Research on Ions, Materials and Photonics CIMAP (France), Ruder Boskovic Institute (Croatia), and the Institute of Ion Beam Physics & Materials Research (Germany) have been published in Carbon journal.

The experimental results on grapheme bombardment with a large amount of ions of different masses of C, O, Si, I, Au, Ta, Xe with high-energy  (up to 91 MeV) have shown that it is possible to create nanopores with a diameter from 1 to 4 nm when changing the energy of ions. Information on the dependence of nanopores on the energy of ions brings scientists closer to a controlled obtainment of such structures.

“We have experimentally and theoretically studied the process of nanopores occurrence (pores) in graphene after interaction between graphene with ions, as well as studying the dependence of pores` sizes on the type and ions` energy, and the nature of the appearance of these defects in grapheme have been explained,” said Arkady Krasheninikov, visiting Professor at NUST MISIS, Candidate of Physical and Mathematical Sciences, research author, and head of the ‘Minimization of degradation of two-dimensional inorganic materials with the use of atomistic calculations’ project.

According to Krasheninikov, “The current development of grapheme research is connected with studies of the possibility of controlled changes of its properties, for example by introduction of defects in its structure. The creation of defects in graphene can significantly change its electronic and conductive properties, and even lead to the induction of magnetism. One of the possible ways of introducing defects into a graphene structure is a bombardment of ions of different elements.”

Krasheninikov also added that scientists have been interested in nanoporous graphene for quite a while. He believes that the obtained nanostructures can be widely used in various fields of science and technology, in particular in the capacity of materials for the purification of liquids, DNA sequencing, etc.

“One expects that with a regular arrangement of pores in graphene, its spectrum would be readjusted into a semiconductive state and that would allow us to use it in electronics,” added Krasheninikov.

 

Imagine repeatedly lifting 165 times your weight without breaking a sweat — a feat normally reserved for heroes like Spider-Man.

Rutgers University-New Brunswick engineers have discovered a simple, economical way to make a nano-sized device that can match the friendly neighborhood Avenger, on a much smaller scale. Their creation weighs 1.6 milligrams (about as much as five poppy seeds) and can lift 265 milligrams (the weight of about 825 poppy seeds) hundreds of times in a row.

Its strength comes from a process of inserting and removing ions between very thin sheets of molybdenum disulfide (MoS2), an inorganic crystalline mineral compound. It’s a new type of actuator – devices that work like muscles and convert electrical energy to mechanical energy.

The Rutgers discovery — elegantly called an “inverted-series-connected (ISC) biomorph actuation device” — is described in a study published online today in the journal Nature.

“We found that by applying a small amount of voltage, the device can lift something that’s far heavier than itself,” said Manish Chhowalla, professor and associate chair of the Department of Materials Science and Engineering in the School of Engineering. “This is an important finding in the field of electrochemical actuators. The simple restacking of atomically thin sheets of metallic MoS2 leads to actuators that can withstand stresses and strains comparable to or greater than other actuator materials.”

Actuators are used in a wide variety of electromechanical systems and in robotics. They have applications such as steerable catheters, aircraft wings that adapt to changing conditions and wind turbines that reduce drag, the study notes.

The discovery at Rutgers University-New Brunswick was made by Muharrem Acerce, study lead author and a doctoral student in Chhowalla’s group, with help from E. Koray Akdo?an, teaching assistant professor in Department of Materials Science and Engineering, said Chhowalla, senior author of the study.

Molybdenum disulfide — a naturally occurring mineral — is commonly used as a solid-state lubricant in engines, according to Chhowalla, who also directs the Rutgers Institute for Advanced Materials, Devices and Nanotechnology. It’s a layered material like graphite, with strong chemical bonding within thin layers but weak bonding between the layers. Thus, individual layers of MoS2 can be easily separated into individual thin sheets via chemistry.

The extremely thin sheets, also called nanosheets, remain suspended in solvents such as water. The nanosheets can be assembled into stacks by putting the solution onto a flexible material and allowing the solvent to evaporate. The restacked sheets can then be used as electrodes — similar to those in batteries – with high electrical conductivity to insert and remove ions. Inserting and removing ions leads to the expansion and contraction of nanosheets, resulting in force on the surface. This force triggers the movement — or actuation — of the flexible material.

Chhowalla and his group members found that their MoS2-based electrochemical device has mechanical properties such as stress, strain and work capacity that are extraordinary considering the electrodes are made by simply stacking weakly interacting nanosheets.

“The next step is to scale up and try to make actuators that can move bigger things,” Chhowalla said.

SEMI, with its Strategic Association partner MEMS & Sensors Industry Group (MSIG), today announced its shortlist of competitors for the Technology Showcase, which will take place on September 21 at the SEMI European MEMS & Sensors Summit 2017 in Grenoble. Selected by a committee of industry experts, five finalist companies will demonstrate advancements in MEMS and sensors for markets that span Internet of Things (IoT), consumer electronics, robotics and biomedical. The audience will vote for a winner, which will be announced at the Summit’s conclusion.

“We congratulate the finalists of the Technology Showcase, an event where attendees experience some of the newest and most fascinating MEMS and sensors technology in an interactive setting,” said Laith Altimime, president, SEMI Europe. “While this is SEMI’s first Technology Showcase at our European MEMS & Sensors Summit, this excellent group of contenders should make it an audience favorite.”

Technology Showcase finalists include:

Bosch Sensortec GmbH: BML050 — a high-precision MEMS scanner for interactive laser projection applications, which offers a virtual user interface solution for IoT applications such as home appliances, tablets and social robots.

Fraunhofer Institute for Photonic Microsystems: Integrated Capacitive Micromachined Ultrasonic Transducers (CMUTs) — provides miniaturized, highly sensitive, low-power, and customer-specific sensors and sensor nodes for applications in liquid and gases. Applications include human-machine interaction, robotics, biomedical, and smart consumer systems.

Hap2U: Ultrasonic Piezoelectric Actuators for Smart Touchscreen Applications — gives users the sensation of feeling sliders, knobs and buttons while touching their display. Hap2U’s new approach to haptic feedback drastically reduces applied power and power consumption.

Philips Innovation Services: CMUTs for Ultrasound and Non-Ultrasound Devices — complements conventional technology with advantages such as large bandwidth, easy fabrication of large arrays, and monolithic integration of ASIC functionality. Through Philips MEMS Foundry, CMUTs are available for medium- and high-volume manufacturing.

Si-Ware Systems: NeoSpectra MEMS Spectral Sensors —features an FT-IR spectrometer on MEMS die. NeoSpectra MEMS Spectral Sensors enable tiny low-cost spectral sensors that are highly integrated, scalable and reliable, making them ideal for in-field and inline applications in various industries, including consumer electronics.

The Technology Showcase at SEMI European MEMS & Sensors Summit (September 20-22, 2017) will take place from 11:00 am-12:00 pm on September 21 at the MINATEC innovation campus at 3 parvis Louis Néel, Grenoble, France.

Unlike the slow ferroelastic domain switching expected for ceramics, high-speed sub-microsecond ferroelastic domain switching and simultaneous lattice deformation are directly observed for the Pb(Zr0.4Ti0.6)O3 thin films. This exciting finding paves the way for high-frequency ultrafast electromechanical switches and sensors.

Piezo micro electro mechanical systems (piezoMEMS) are miniaturized devices exhibiting piezoelectricity, i.e., the appearance of an electric charge under applied mechanical stress. These devices have many diverse applications in energy harvesters, micropumps, sensors, inkjet printer heads, switches, and so on. In permanently polarized (ferroelectric) materials, ferroelastic domain switching affects the piezoelectric properties significantly, and this behavior can be exploited for piezoMEMS applications.

Pb(Zr1-xTix)O3 (PZT) thin films have excellent piezoelectric and ferroelectric properties; therefore, they are potential candidates for MEMS applications. Under an applied electric field, both lattice elongation and 90° ferroelastic domain switching are observed in tetragonal PZT thin films. In particular, non-180° ferroelastic domain switching has important implications for the future realization of high-performance piezoMEMS devices.

However, before the recent investigation, the speed of this 90° domain switching was unknown. In addition, the relationship between the speeds of the lattice deformation and ferroelastic domain switching had not been determined. To investigate these speeds, the research team led by Hiroshi Funakubo examined the switching behavior of Pb(Zr0.4Ti0.6)O3 thin films under applied rectangular electric field pulses.

To observe the changes in the lattice and the domain structure, time-resolved in situ synchrotron X-ray diffraction was carried out in synchronization with a high-speed pulse generator. These observations were performed at the BL13XU beamline at the SPring-8 synchrotron radiation facility. The electric field pulses were applied to the PZT thin films through Pt top electrodes, which were fabricated on top of the films.

Investigation of the diffraction peaks in the PZT thin films revealed elongation of the surface normal c-axis lattice parameter of the c-domain with a simultaneous decrease in the surface normal a-axis lattice parameter of the a-domain under the applied electric field. The intensities of the diffraction peaks also changed under the electric field. These observations provided direct evidence of 90° domain switching.

To determine the switching speed, the lattice elongation and domain switching behaviors were plotted as functions of time (Figure 1). These plots revealed that these processes were completed within 40 ns and occurred simultaneously in response to the applied electric field. The switching behavior was also shown to be perfectly repeatable.

The (a-f) capacitance, strain, tilting angle, intensity, difference capacitance, and volume fraction of the c domain were measured as functions of time, respectively. The elastic deformation and ferroelastic domain switching were completed within 40 ns. Credit: Scientific Reports

The (a-f) capacitance, strain, tilting angle, intensity, difference capacitance, and volume fraction of the c domain were measured as functions of time, respectively. The elastic deformation and ferroelastic domain switching were completed within 40 ns. Credit: Scientific Reports

The high-speed switching observed in these experiments was limited by the present electrical equipment, but is faster than that reported in previous studies. Further, this high-speed 90° switching is reversible and can be used to enhance the piezoelectric response in piezoMEMS devices by several tens of nanoseconds. Therefore, this finding is of considerable importance for the ongoing development of ultrafast electromechanical switches and sensors.

Over the last two years, Waterloo based Siborg Systems Inc. teamed up with Sensor Creations Inc. from Camarillo, California in development of a practical tool for simulation of the process flow and optical sensor performance.

The companies collaborated in both the semiconductor process and device simulation for optical sensor structures. They have large sizes and require many fabrication steps such as epitaxial growth, implantation, deposition, etching, annealing and oxidation. Due to the large size, use of conventional simulation tools lead to high CPU time. In contrast, MicroTec was able to run a typical process simulation within a few minutes on a regular PC.

Doping profile for 3-junction optical sensor simulated with MicroTec. For 100,000 required CPU time was about 2 minutes on regular PC. (PRNewsfoto/Siborg Systems Inc.)

Doping profile for 3-junction optical sensor simulated with MicroTec. For 100,000 required CPU time was about 2 minutes on regular PC. (PRNewsfoto/Siborg Systems Inc.)

MicroTec provides steady-state two-dimensional semiconductor device simulation that is not sufficient for capacitance extraction. A new method was developed allowing to calculate capacitance of a semiconductor structure by solving equation for the total current conservation. The method is equally applicable to 1D, 2D and 3D structures but limited to low frequencies and low-leakage conditions. The most straightforward method is solving the equation of the total current conservation, mutual capacitances may be calculated simply by the formula C=Idt/dV.

This formula could be improved by using a relation involving resistances as well as capacitances. In order to do that, one more data point is required. Although this expression is more accurate than the first one, it is still not equivalent to the actual compact model of the semiconductor structure because, strictly speaking, it is a set of interconnected transmission lines and therefore any simplification of the equivalent circuit results in a loss of accuracy. The current based method is not very accurate and requires simulation with a properly selected ramp speed. If it is too fast, voltage drop due to Ohm’s law distorts the capacitance, and if it is too slow, displacement current becomes too small and is swamped by the numerical noise. Practically this method has a limited application due to high sensitivity to the ramp time.

In contrast to the current method, the charge method provides charges affiliated with the contacts rather than the currents, thus eliminating the problem of result interpretation using equivalent R-C circuit. To calculate the charges we solve the same equation but instead of calculating currents, we use the response to the excitation applied to a contact as a weight function when integrating the charge in the structure. The charges are easily calculated by a convolution of the “affiliation” function with the carrier density. This method appeared very stable and accurate and was successfully used for capacitance calculation in optical sensors.

The picture below shows the capacitance calculated by the charge based method at various ramp speeds. Note that all 4 curves virtually coincide. The method applicability is questionable when significant minority charge is injected as in the case of forward biased junctions. The proposed method has a wider range of applicability but the extent of its accuracy still needs to be studied.

“We used Two-dimensional Semiconductor Process and Device Simulation Software MicroTec from Siborg intensively for the last couple of years. We found it very useful in our practical optical sensor prototype development. It significantly outperforms other available commercial tools by the speed, ease-of-use and robustness. Last, but not least, the license cost is significantly lower as well,” says Stefan Lauxtermann from Sensor Creations.

MicroTec is a TCAD tool that has been used by major semiconductor manufacturers such as Hitachi, Texas Instruments, Matasushita, etc. As an educational tool, MicroTec and three-dimensional SibLin are simple and easy to learn.

Many next-generation electronic and electro-mechanical device technologies hinge on the development of ferroelectric materials. The unusual crystal structures of these materials have regions in their lattice, or domains, that behave like molecular switches. The alignment of a domain can be toggled by an electric field, which changes the position of atoms in the crystal and switches the polarization direction. These crystals are typically grown on supporting substrates that help to define and organize the behavior of domains. Control over the switching of domains when making crystals of ferroelectric materials is essential for any future applications.

Now an international team by Nagoya University has developed a new way of controlling the domain structure of ferroelectric materials, which could accelerate development of future electronic and electro-mechanical devices.

“We grew lead zirconate titanate films on different substrate types to induce different kinds of physical strain, and then selectively etched parts of the films to create nanorods,” says lead author Tomoaki Yamada. “The domain structure of the nanorods was almost completely flipped compared with [that of] the thin film.”

Lead zirconate titanate is a common type of ferroelectric material, which switches based on the movement of trapped lead atoms between two stable positions in the crystal lattice. Parts of the film were deliberately removed to leave freestanding rods on the substrates. The team then used synchrotron X-ray radiation to probe the domain structure of individual rods.

The contact area of the rods with the substrate was greatly reduced and the domain properties were influenced more by the surrounding environment, which mixed up the domain structure. The team found that coating the rods with a metal could screen the effects of the air and they tended to recover the original domain structure, as determined by the substrate.

“There are few effective ways of manipulating the domain structure of ferroelectric materials, and this becomes more difficult when the material is nanostructured and the contact area with the substrate is small.” says collaborator Nava Setter. “We have learned that it’s possible to nanostructure these materials with control over their domains, which is an essential step towards the new functional nanoscale devices promised by these materials.”

The article, “Charge screening strategy for domain pattern control in nanoscale ferroelectric systems,” was published in Scientific Reports at DOI:10.1038/s41598-017-05475-x

 

Two-dimensional materials are a sort of a rookie phenom in the scientific community. They are atomically thin and can exhibit radically different electronic and light-based properties than their thicker, more conventional forms, so researchers are flocking to this fledgling field to find ways to tap these exotic traits.

Applications for 2-D materials range from microchip components to superthin and flexible solar panels and display screens, among a growing list of possible uses. But because their fundamental structure is inherently tiny, they can be tricky to manufacture and measure, and to match with other materials. So while 2-D materials R&D is on the rise, there are still many unknowns about how to isolate, enhance, and manipulate their most desirable qualities.

Now, a science team at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has precisely measured some previously obscured properties of moly sulfide, a 2-D semiconducting material also known as molybdenum disulfide or MoS2. The team also revealed a powerful tuning mechanism and an interrelationship between its electronic and optical, or light-related, properties.

To best incorporate such monolayer materials into electronic devices, engineers want to know the “band gap,” which is the minimum energy level it takes to jolt electrons away from the atoms they are coupled to, so that they flow freely through the material as electric current flows through a copper wire. Supplying sufficient energy to the electrons by absorbing light, for example, converts the material into an electrically conducting state.

As reported in the Aug. 25 issue of Physical Review Letters, researchers measured the band gap for a monolayer of moly sulfide, which has proved difficult to accurately predict theoretically, and found it to be about 30 percent higher than expected based on previous experiments. They also quantified how the band gap changes with electron density – a phenomenon known as “band gap renormalization.”

“The most critical significance of this work was in finding the band gap,” said Kaiyuan Yao, a graduate student researcher at Berkeley Lab and the University of California, Berkeley, who served as the lead author of the research paper.

“That provides very important guidance to all of the optoelectronic device engineers. They need to know what the band gap is” in orderly to properly connect the 2-D material with other materials and components in a device, Yao said.

Obtaining the direct band gap measurement is challenged by the so-called “exciton effect” in 2-D materials that is produced by a strong pairing between electrons and electron “holes” ¬- vacant positions around an atom where an electron can exist. The strength of this effect can mask measurements of the band gap.

Nicholas Borys, a project scientist at Berkeley Lab’s Molecular Foundry who also participated in the study, said the study also resolves how to tune optical and electronic properties in a 2-D material.

“The real power of our technique, and an important milestone for the physics community, is to discern between these optical and electronic properties,” Borys said.

The team used several tools at the Molecular Foundry, a facility that is open to the scientific community and specializes in the creation and exploration of nanoscale materials.

The Molecular Foundry technique that researchers adapted for use in studying monolayer moly sulfide, known as photoluminescence excitation (PLE) spectroscopy, promises to bring new applications for the material within reach, such as ultrasensitive biosensors and tinier transistors, and also shows promise for similarly pinpointing and manipulating properties in other 2-D materials, researchers said.

The research team measured both the exciton and band gap signals, and then detangled these separate signals. Scientists observed how light was absorbed by electrons in the moly sulfide sample as they adjusted the density of electrons crammed into the sample by changing the electrical voltage on a layer of charged silicon that sat below the moly sulfide monolayer.

Researchers noticed a slight “bump” in their measurements that they realized was a direct measurement of the band gap, and through a slew of other experiments used their discovery to study how the band gap was readily tunable by simply adjusting the density of electrons in the material.

“The large degree of tunability really opens people’s eyes,” said P. James Schuck, who was director of the Imaging and Manipulation of Nanostructures facility at the Molecular Foundry during this study.

“And because we could see both the band gap’s edge and the excitons simultaneously, we could understand each independently and also understand the relationship between them,” said Schuck, now at Columbia University. “It turns out all of these properties are dependent on one another.”

Moly sulfide, Schuck also noted, is “extremely sensitive to its local environment,” which makes it a prime candidate for use in a range of sensors. Because it is highly sensitive to both optical and electronic effects, it could translate incoming light into electronic signals and vice versa.

Schuck said the team hopes to use a suite of techniques at the Molecular Foundry to create other types of monolayer materials and samples of stacked 2-D layers, and to obtain definitive band gap measurements for these, too. “It turns out no one yet knows the band gaps for some of these other materials,” he said.

The team also has expertise in the use of a nanoscale probe to map the electronic behavior across a given sample.

Borys added, “We certainly hope this work seeds further studies on other 2-D semiconductor systems.”

The Molecular Foundry is a DOE Office of Science User Facility that provides free access to state-of-the-art equipment and multidisciplinary expertise in nanoscale science to visiting scientists.

Researchers from the Kavli Energy NanoSciences Institute at UC Berkeley and Berkeley Lab, and from Arizona State University also participated in this study, which was supported by the National Science Foundation.

While lithium-ion batteries, widely used in mobile devices from cell phones to laptops, have one of the longest lifespans of commercial batteries today, they also have been behind a number of recent meltdowns and fires due to short-circuiting in mobile devices. In hopes of preventing more of these hazardous malfunctions researchers at Drexel University have developed a recipe that can turn electrolyte solution — a key component of most batteries — into a safeguard against the chemical process that leads to battery-related disasters.

Yury Gogotsi, PhD, Distinguished University and Bach professor in the College of Engineering, and his research team from the Department of Materials Science and Engineering, recently published their work — entitled “Nanodiamonds Suppress Growth of Lithium Dendrites” — in the journal Nature Communications. In it, they describe a process by which nanodiamonds — tiny diamond particles 10,000 times smaller than the diameter of a hair — curtail the electrochemical deposition, called plating, that can lead to hazardous short-circuiting of lithium ion batteries.

As batteries are used and charged, the electrochemical reaction results in the movement of ions between the two electrodes of a battery, which is the essence of an electrical current. Over time, this repositioning of ions can create tendril-like buildups — almost like stalactites forming inside a cave. These battery buildups, called dendrites, are one of the main causes of lithium battery malfunction. As dendrites form inside the battery over time, they can reach the point where they push through the separator, a porous polymer film that prevents the positively charged part of a battery from touching the negatively charged part. When the separator is breached, a short-circuit can occur, which can also lead to a fire since the electrolyte solution in most lithium-ion batteries is highly flammable.

To avoid dendrite formation and minimize the probability of fire, current battery designs include one electrode made of graphite filled with lithium instead of pure lithium. The use of graphite as the host for lithium prevents the formation of dendrites. But lithium intercalated graphite also stores about 10 times less energy than pure lithium. The breakthrough made by Gogotsi’s team means that a great increase in energy storage is possible because dendrite formation can be eliminated in pure lithium electrodes.

“Battery safety is a key issue for this research,” Gogotsi said. “Small primary batteries in watches use lithium anodes, but they are only discharged once. When you start charging them again and again, dendrites start growing. There may be several safe cycles, but sooner or later a short-circuit will happen. We want to eliminate or, at least, minimize that possibility.”

Gogotsi and his collaborators from Tsinghua University in Beijing, and Hauzhong University of Science and Technology in Wuhan, China, focused their work on making lithium anodes more stable and lithium plating more uniform so that dendrites won’t grow.

They’re doing this by adding nanodiamonds to the electrolyte solution in a battery. Nanodiamonds have been used in the electroplating industry for some time as a way of making metal coatings more uniform. While they are much, much smaller — and cheaper — than the diamonds you’d find in a jeweler’s case, nanodiamonds still retain the regular structure and shape of their pricey progenitors. When they are deposited, they naturally slide together to form a smooth surface.

The researchers found this property to be exceedingly useful for eliminating dendrite formation. In the paper, they explain that lithium ions can easily attach to nanodiamonds, so when they are plating the electrode they do so in the same orderly manner as the nanodiamond particles to which they’re linked. They report in the paper that mixing nanodiamonds into the electrolyte solution of a lithium ion battery slows dendrite formation to nil through 100 charge-discharge cycles.

If you think about it like a game of Tetris, that pile of mismatched blocks inching perilously close to “game over” is the equivalent of a dendrite. Adding nanodiamonds to the mix is kind of like using a cheat code that slides each new block into the proper place to complete a line and prevent a menacing tower from forming.

Gogotsi notes that his group’s discovery is just the beginning of a process that could eventually see electrolyte additives, like nanodiamonds, widely used to produce safe lithium batteries with a high energy density. Initial results already show stable charge-discharge cycling for as long as 200 hours, which is long enough for use in some industrial or military applications, but not nearly adequate for batteries used in laptops or cell phones. Researchers also need to test a large number of battery cells over a long enough period of time under various physical conditions and temperatures to ensure that dendrites will never grow.

“It’s potentially game-changing, but it is difficult to be 100 percent certain that dendrites will never grow,” Gogotsi said. “We anticipate the first use of our proposed technology will be in less critical applications — not in cell phones or car batteries. To ensure safety, additives to electrolytes, such as nanodiamonds, need to be combined with other precautions, such as using non-flammable electrolytes, safer electrode materials and stronger separators.”