Battery Metals

Gold prices nudged higher on October 19 as Asian shares fell on renewed political and economic concerns including China’s weak growth. The metal saw a third straight weekly gain.

China’s economy grew 6.5 percent in the third quarter from a year earlier, its weakest pace since the global financial crisis, and missed expectations as a years-long campaign to tackle debt risks and the trade war with the United States began to bite.

With Chinese equity markets continuing to drift lower, and lingering geopolitical risks such as Fed interest rate hikes, Italian budget concerns, and the US-China trade war, stock markets are still shaky. This enhances the safe haven status of gold further in the near-term.

The recent sell-off in global stock markets has boosted the appeal for gold, which is seen as a safe store of value during political and economic uncertainty.

Another indicator of safe haven buying returning to gold is the reversal in sentiment towards the metal increased holding in SPDR Gold Trust, the largest gold-backed ETF. It rose 1.3 percent to 73 tonnes last week. It was the first time since the ETF witnessed inflows since July.

It is also the largest inflow since March 2018. As long as gold was trading in a range, we were witnessing huge outflows, as investors were showing a preference for equity and were focusing on safe-haven currencies like the dollar.

The yellow metal has declined about 10 percent from its April peak after investors preferred the dollar as the US-China trade war unfolded against a background of higher US interest rates.

Gold Technical Analysis:

From the above Comex Gold chart, we can see prices were in a sustained downtrend from April 2018 ($1,360) till August 2018 ($1,170). After that, we have seen some kind of stability and consolidation in the prices.

In this phase of consolidation between August and October 2018 prices have formed an Ascending Triangle pattern depicted by trend line (T1) and (T2) in the above chart and recently prices have given a breakout on the higher side and the measured move of the triangle comes at $1,270.

The prices are comfortably trading above the 20 day SMA (Pink Line) at $1,207 and 50day SMA (Orange Line) at $1,201 which is a positive indication in the short-term and these levels could provide supports again if prices give a dip.

The relative strength index or the RSI is also trading above 50 marks indicating strength in prices for near term. Thus our favoured view is that one can buy gold around $1,200-1,210 zones and look for targets around $1,206-1275 zones in short to medium term.

In MCX we have seen a sharp rise in gold prices that are to rupee weakening towards 74 against the US dollar, so if one is taking positions in MCX Gold needs to hedge it against rupee also and trade accordingly.

Since the isolation of graphene in 2004, the high mobility and unique transport properties of 2-dimensional semiconductors have tantalized physicists and materials scientists. Their in-plane carrier transport and lack of dangling bonds potentially can minimize line/edge scattering and other effects of extreme scaling.

While 2-D materials cannot compete with silicon at current device dimensions, their performance may degrade less quickly as feature sizes shrink. According to Iuliana Radu, distingished member of the technical staff at Imec, 2-D semiconductors may be the only alternative for sub-15 nm devices.

But 2-D semiconductors also offer a vivid demonstration of the large gap between simulations and laboratory experiments, and from there to devices that can be manufactured by the billions using existing fab infrastructure. There is no clear path to consistent fabrication of 2-D single crystals at this time, Radu noted. Nor are there clear integration paths to achieve stable, repeatable device performance, or processes of record for such fundamental operations as doping and contact formation.

Van der Waals forces build nano sheet stacks

The obstacles to 2-D device development begin with the fabrication of the materials. Graphene was first isolated through mechanical exfoliation, a fancy name for a fairly crude procedure in which single layers are pulled from a bulk sample using adhesive tape. The difficulties inherent in scaling that method to hundreds, much less billions of devices, should be obvious.

One alternative, electrochemical intercalation, infiltrates an inert molecule into a chemical vapor deposition film, chemically isolating the top layer while continuing to use the substrate for mechanical support. Another depends on atomic layer deposition of individual layers, followed by a passivation layer. Layer-by-layer deposition methods can be used to construct van der Waals heterostructures, in which a stack is held together by van der Waals forces while each layer retains its 2-D character.

The properties of van der Waals heterostructures depend on the number of layers, their composition, and the twist angle between them, giving designers wide latitude to achieve the behavior they want. The twist angle in particular can be used to impose long-range periodicity in the absence of three-dimensional crystalline structures.

Moreover, as demonstrated with stacked MoS2 monolayers, the number of layers can define the bandgap of the structure. The coefficients of thermal expansion of the substrate and of individual layers can be tuned to control strain, further adjusting the electrical properties.

When building such structures, though, it’s important to remember that 2-D semiconductors are not a single material, but an entire class of compounds. Conventional III-V and II-VI semiconductors share many structural and electrical characteristics with silicon, germanium, and each other. So materials scientists can vary semiconductor composition as needed to tune the band gap, lattice parameters, and other properties without dramatic changes to the overall integration scheme.

Two-dimensional semiconductors, in contrast, come from different parts of the periodic table. They have different electrical properties, different lattice structures, and different chemical characteristics.

Toward 2-D devices

For example, black phosphorus offers high mobility, but it is unstable in both air and water. Researchers have attempted to turn its need for layer transfer-based fabrication techniques into a virtue, pointing out that low-temperature processes reduce the impact of thermal expansion and lattice mismatch between the semiconductor and the substrate.

Nicolò Oliva, a graduate student at École Polytechnique Fédérale de Lausanne, and his colleagues transferred exfoliated black phosphorus to a prepared substrate with embedded silver or gold electrodes, then passivated the structure with boron nitride followed by an Al2O3 dielectric. In these devices, the contact work function determined the gate polarity, with gold contacts favoring holes and silver favoring electrons.

The gate and drain voltage can be used to modulate the Fermi level and band alignments. Performance was promising, with a 70 mV/decade sub-threshold swing. But making such a device in large quantities is sure to be challenging.

Boron nitride, used as a passivating layer for black phosphorus and as a dopant for graphene, has also attracted attention as a 2-D semiconductor in its own right. One group deposited hexagonal boron nitride directly onto cobalt and iron electrodes. In such magnetic tunnel junctions, among the building blocks of spintronics, hBN serves as the tunneling barrier between cobalt and iron. Switching the polarities of magnetic domains changes the height of the tunneling barrier, causing the device to behave as a magnetometer.

The last group of 2-D semiconductors, the dichalcogenides, are reasonably stable and can be fabricated by such relatively mature processes as chemical vapor deposition. Unfortunately, Tarun Agarwal, a postdoctoral researcher at ETH Zurich, along with researchers at Imec, reported at last year’s IEDM that simulation results for these materials are relatively poor, with low mobility and low drive currents. Competitive devices probably will need to be based on stacks of nanosheets rather than single layers.

As in other stacked nano sheet devices, the number of layers, the components of the stack, and the internal structure of the stack all contribute to device characteristics. As is the case in silicon, double-gate devices offer better electrostatics and better currents than single-gate devices.

Conclusion

Even this brief survey raises as many questions as it answers about the commercial prospects for 2-D semiconductor devices. Yet Imec’s Radu explained that the industry does not appear to have a choice. “Probably, the alternative to 2D semiconductors is changing the computing paradigm,” she said.

The lower effective mass of III-V semiconductors means that direct source-drain tunneling becomes a problem at longer gate lengths than in silicon. Quantum dots provide very little current, limiting their viability for general-purpose logic. Though 2-D materials pose challenges, as well, Radu noted, “there are lots of things we haven’t figured out how to do, but we don’t see any fundamental roadblock.”

She expects any commercial applications of the materials are probably at least 10 years away. For 5nm devices, the decision point is probably five or six years away. She expects it will take that much time for the industry to understand the scaling limitations of 2-D materials and find a realistic path to commercialization.

Future high-efficiency solar cells molded to the surface of a car, ultrasmall photonics chips, and low-power, long-lasting wearable devices will all require something no one’s yet been able to achieve, namely chips made from high-efficiency materials that are flexible, thin, and inexpensive to manufacture.

A research group at MIT has announced a couple of developments in recent weeks that bring such a confluence of innovations closer to the achievable. Jeehwan Kim’s research group announced separately this month in Nature Materials and Science that they can inexpensively mass-produce ultrathin gallium arsenide and gallium nitride chips as well as harvest the monolayer materials necessary for manufacturing other 2D electronics, like tiny photonics devices.

“We [found] the way to go to expensive semiconducting materials so you can keep producing high-quality, high-performance semiconductors with a cheaper price,” says Kim, associate professor of mechanical engineering and materials science at MIT. “The bonus is, you can have flexible semiconducting devices, and because they’re really thin, you can stack them up.”

As IEEE Spectrum reported last year, Kim’s group essentially uses graphene sheets as nanosize silk screens through which expensively manufactured exotic-material-based semiconductors can be laid down.

The recipe: Take a costly, manufactured, ultrathin film of pure semiconducting material like gallium arsenide and lay a single-layered sheet of graphene on top of it. Then flow atoms of gallium and arsenide over the graphene, and the intermediary sheet acts as a surface on which an identical copy of the underlying ultrathin film is copied on top of the graphene— although how and why the process worked as well as it did had previously been unclear.

In the current work, Kim’s group has expanded and generalized their previous finding—discovering, on one hand, single-atom crystals like silicon cannot be replicated by the “silk screen” technique (what the group calls remote epitaxy) but on the other hand that practically any 2D sheet or film whose molecules carry any net electric polarity to them can be mass-produced via remote epitaxy.

The reason, the group discovered, is that electrically the graphene behaves as if it’s not even there, transmitting the ionic electric fields from the 2D material up to the slurry of raw materials resting on top of the graphene. The fields then guide the slurry into forming a perfect duplicate of the expensively manufactured thin film below.

Kim uses the shorthand term “copy-paste” to describe the simple and seemingly inexpensive procedure as it’s now being developed. (He admits, however, he cannot give price quotes at the moment, because they haven’t yet done an economic analysis of the process.)

“We were able to copy-paste…through graphene for many types of compound materials in the periodic table,” says Kim. “That is a big discovery. Based on that understanding, we were able to make single-crystalline, freestanding, very, very thin membrane compound materials.”

Kim says his research group is working with “six major companies” in Korea, Japan, and the United States to scale up the ultrathin chip manufacturing processes they’re developing. He expects some of these technologies might only need “a couple years” before they’re potentially ready for commercial application.

The industries and product lines Kim says could find use for the remote epitaxy process include solar energy (cheap but ultra-efficient GaAs solar panels have long been a dream), photonics (layering multiple ultrathin films on top of each other, say, so that each are efficient at transmitting red LED light and blue LED light), wearables (making electronics ultraflexible but also low power is a holy grail in the field), and IoT (ditto).

The group has a portfolio of published results that includes the graphene remote epitaxy process. Also in the running is another 2D material manufacturing technique, the one published in Science.

“We developed a way to handle wafer-scale two-dimensional materials with atomic precision,” Kim says. The idea is that other materials that could be useful as conductors, insulators, and semiconductors may not necessarily work with the graphene method. In which case, Kim’s group has a second method for peeling off individual atom-thick monolayers.

As they spell out in the Science paper, they discovered that other ultrathin films that may for various reasons not work as well with remote epitaxy could still be copied in another way. Compounds like hexagonal boron nitride (attractive as a lubricant, electrical insulator, or light emitter) and tungsten disulfide (another possible post-silicon solar panel material) can be flaked off into single-atom-thick sheets with a process Kim’s lab calls “controlled crack propagation.”

The process involves growing a thick material on a wafer and then attaching the top of that material to a nickel plate. (2D films adhere more strongly to nickel.) The nickel plate can then be pulled up, in the process exfoliating a single-atom-thick layer of the target material. The exfoliated 2D film can then be laid down onto a host wafer as part of that wafer’s manufacturing process.

Arbitrarily, many single-atom-thick layers can be laid down this way, Kim says, leading to new kinds of electronic devices that demand complex semiconducting substrates.

“There has been no way of handling this one-atom-thick layer controllably,” Kim says. “That’s why industry has not been discussing using 2D materials in next-generation electronics. [But] we can just grow thick 2D material on the wafer. Then we just peel off one monolayer, then one monolayer. We can harvest a lot of 2D materials from…the wafer.”

Between remote epitaxy and controlled crack propagation, Kim says many more flexible and efficient electronic, photonic, and other thin-film-based technologies can now be more reliably mass-produced.

Fuels, plastics, and other products are made using catalysts, materials that drive chemical reactions. To design a better catalyst, scientists must get the right atoms in the right spot. Positioning the atoms can be difficult, but new research makes it easier.

Researchers determined the exact location of single oxygen atoms, which act like anchors for catalysts. In the case of a layer of carbon atoms atop a metal support, single oxygen atoms appear in predictable spots.

Knowing where the atomic anchors are, the team can create patterns of catalytic atoms, designing what’s needed to get the job done.

Creating catalysts that make reactions faster and less wasteful means designing the catalysts from the bottom up.

Rather than search among countless possibilities, scientists want to design the right structures at a molecular level.

New fundamental research shows scientists how to take advantage of precise spots — where the oxygen atoms bind on graphene — to build model catalysts.

This research redefines what is known about oxygen binding, which is vital to creating hard-working catalysts.

The team began with a flat piece of ruthenium metal. On top of the metal, they grew graphene, which is a one-atom-thick layer of carbon.

In this structure, some carbon atoms bind to the metal, while others don’t.

By combining experimental and computational resources, the team examined these carbon atoms. They showed that single oxygen atoms, which act as ideal spots to attach catalytic sites, bind preferentially to carbon atoms that are close to the underlying metal but not bound to it.

Less preferred sites for oxygen binding are between two carbon atoms; carbon atoms that are, in turn, bound to ruthenium; and untethered carbon atoms far from the ruthenium.

This research redefines what scientists know about oxygen binding to carbon atoms on metal-supported graphene. The work is vital to designing efficient, selective catalysts.

Batteries present a major difficulty from an R&D perspective. Because they’re mostly “black boxes,” it’s very difficult to observe what’s going on inside of them while they’re functioning, and a destructive autopsy is far different and less insightful than live exploration. However, a team based at Columbia University has contributed a major solution to this shortcoming by using Raman-scattering microscopy, an advanced spectroscopic electro-optical technique widely used in biomedical testing, chemical-process investigation, and materials science.

Their paper “Operando and three-dimensional visualization of anion depletion and lithium growth by Stimulated Raman microscopy,” published in Nature Communications, describes in great detail how they used this approach to investigate a long-standing issue: How does the concentration of lithium ions in a battery cell relate to uneven lithium deposition? Visualization of the ion transport is of great interest because it can provide deep insight into the dynamics of the electrolyte movement and transformations. Furthermore, they were able to develop new understanding and even arrive at likely conclusions based on their arrangement.

Batteries present a major difficulty from an R&D perspective. Because they’re mostly “black boxes,” it’s very difficult to observe what’s going on inside of them while they’re functioning, and a destructive autopsy is far different and less insightful than live exploration. However, a team based at Columbia University has contributed a major solution to this shortcoming by using Raman-scattering microscopy, an advanced spectroscopic electro-optical technique widely used in biomedical testing, chemical-process investigation, and materials science.

Their paper “Operando and three-dimensional visualization of anion depletion and lithium growth by Stimulated Raman microscopy,” published in Nature Communications, describes in great detail how they used this approach to investigate a long-standing issue: How does the concentration of lithium ions in a battery cell relate to uneven lithium deposition? Visualization of the ion transport is of great interest because it can provide deep insight into the dynamics of the electrolyte movement and transformations. Furthermore, they were able to develop new understanding and even arrive at likely conclusions based on their arrangement.

In theory, using pure lithium for a battery electrode will improve its efficiency, but the nonuniform flux of ions near that electrode is detrimental, encouraging nucleation and growth of detrimental dendrite-like crystals that reduce efficiency (and may even cause dangerous short circuits). The research challenge is to measure the growth of these crystals by imaging the movement of the ions themselves, but this is a very difficult goal due to their low concentration and fast reaction times.

Stimulated Raman Scattering

That’s where stimulated Raman scattering (SRS) offers a new approach. In non-stimulated, spontaneous technique, the energy of spontaneous photon scattering of the target molecule is measured, thus revealing its natural vibration frequency (see figure). (Note: to avoid confusion, spontaneous Raman scattering is not called SRS.) In the stimulated scattering variation, a synchronized pump-laser beam and a swept-wavelength Stokes laser beam are combined, and that interacts with the sample, which causes it to generate a coherent optical response.

By measuring the vibrational resonances as the impinging beam is swept, the detailed “fingerprints” of the target molecules are revealed. The stimulated Raman scattering setup that was used accelerated the fairly slow speed of standard spontaneous Raman scattering by eight orders of magnitude. It combined high sensitivity of better than 0.5 millimoles (mM) with fast imaging speed of about 2 µs/pixel and resolution of 300-500 nm.

Research Results

In the experiment, the research team measured the intensity of anion response, which functions as an “analog” for the lithium-ion concentration, as they have similar concentration to the lithium cations (a difference of less than 0.1 mM) and bond with them. The results revealed a multi-stage positive-feedback mechanism resulting in uneven growth of ion concentration. Those regions that had a higher concentration underwent a higher growth rate, which in turn led to further increase in concentration and accelerated growth rate of the undesirable dendrite crystals.

This insight also led them to develop a possible approach to mitigate the problem. The researchers developed a coating of lithium phosphate (Li3PO4) acting as an artificial solid electrolyte interphase, which was tough enough to suppress the undesired protrusions on the electrodes. It did this by functioning as a chemical buffer, which made the local Li-ion concentration more homogenous and blocked the positive-feedback loop, thus decreasing the crystal growth rate without affecting the voltage charge/discharge profile.

Beyond the analysis results and insight, the researchers demonstrated that this stimulated Raman technique provides a valuable and viable imaging tool. It can be used to investigate ion transport and processes in battery research, and even be extended to observing material separation, the dynamics of ion movement in confined channels, and associated catalytic processes.

The Stena Jutlandica has now completed its first month of operation as a battery hybrid vessel. Experiences from these first weeks have exceeded expectations.

“It’s really exciting to be running with electrical power on the Stena Jutlandica. This project is an important part of our focused efforts to find ways of reducing our impact on the environment. As both the size and cost of batteries decrease, battery operation is becoming a very attractive alternative to traditional fuel for shipping since emissions should be possible to completely eliminate in the future,” says Erik Lewenhaupt, Head of Sustainability at Stena Line.

The project to convert Stena Jutlandica on the Gothenburg-Frederikshavn route to a battery hybrid vessel is being carried out in steps.

Step one, which is presently underway, is about switching to electrical operation to reduce the use of diesel generators, as well as for maneuvering and powering the bow thrusters when the ship is in port.

In the second step, battery power will be connected to two of the four primary machines, which means that the Stena Jutlandica will be able to run on electrical power for about 10 nautical miles inside the Gothenburg archipelago out to Vinga Lighthouse.

In step three, all four primary machines will be connected to the batteries and the ship will be able to cover the 50 nautical miles between Sweden and Denmark solely on electrical power.

Positive effects have already been noted after just one month.

“As an example, we’ve been able to strongly reduce our use of the diesel generators and now only need to use one instead of three. Another positive effect concerns safety; by having constant access to electricity, we minimize the risk for power outages”, says Johan Stranne, Senior Chief Engineer on the Stena Jutlandica.

Only in step one, the environmental savings from using battery power for reduced generator usage and maneuvering in port amounts to about 500 tons of fuel, 1,500 tons of CO2. This in turn corresponds to the annual emissions from approximately 600 cars.

The reason for execution in multiple steps is to enable testing and assessment while the project is underway. If the project is successful, battery power can be considered for other vessels within the Stena Line fleet. Work with step two has begun and the goal is for implementation within about three years.

The technical solutions in the first step have been developed by Stena Teknik in collaboration with the Callenberg Technology Group, with half of the funding for the project coming from the Swedish Transport Administration and the EU.