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Single crystal tin selenide (SnSe) is a semiconductor and an ideal thermoelectric material; it can directly convert waste heat to electrical energy or be used for cooling. When a group of researchers from Case Western Reserve University in Cleveland, Ohio, saw the graphene-like layered crystal structure of SnSe, they had one of those magical “aha!” moments.

Electric charges in a nanostructured tin selenide (SnSe) thin film flow from the hot end to the cold end of the material and generate a voltage. Credit: Xuan Gao

Electric charges in a nanostructured tin selenide (SnSe) thin film flow from the hot end to the cold end of the material and generate a voltage. Credit: Xuan Gao

The group reports in the Journal of Applied Physics, from AIP Publishing, that they immediately recognized this material’s potential to be fabricated in nanostructure forms. “Our lab has been working on two-dimensional semiconductors with layered structures similar to graphene,” said Xuan Gao, an associate professor at Case Western.

Nanomaterials with nanometer-scale dimensions — such as thickness and grain size — have favorable thermoelectric properties. This inspired the researchers to grow nanometer-thick nanoflakes and thin films of SnSe to further study its thermoelectric properties.

The group’s work centers on the thermoelectric effect. They study how the temperature difference in a material can cause charge carriers — electrons or holes — to redistribute and generate a voltage across the material, converting thermal energy into electricity.

“Applying a voltage on a thermoelectric material can also lead to a temperature gradient, which means you can use thermoelectric materials for cooling,” said Gao. “Generally, materials with a high figure of merit have high electrical conductivity, a high Seebeck coefficient — generated voltage per Kelvin of temperature difference within a material — and low thermal conductivity,” he said.

A thermoelectric figure of merit, ZT, indicates how efficiently a material converts thermal energy to electrical energy. The group’s work focuses on the power factor, which is proportional to ZT and indicates a material’s ability to convert energy, so they measured the power factor of the materials they made.

To grow SnSe nanostructures, they used a chemical vapor deposition (CVD) process. They thermally evaporated a tin selenide powder source inside an evacuated quartz tube. Tin and selenium atoms react on a silicon or mica growth wafer placed at the low-temperature zone of the quartz tube. This causes SnSe nanoflakes to form on the surface of the wafer. Adding a dopant element like silver to SnSe thin films during material synthesis can further optimize its thermoelectric properties.

At the start, “the nanostructure SnSe thin films we fabricated had a power factor of only ~5 percent of that of single crystal SnSe at room temperature,” said Shuhao Liu, an author on the paper. But, after trying a variety of dopants to improve the material’s power factor, they determined that “silver was the most effective — resulting in a 300 percent power factor improvement compared to undoped samples,” Liu said. “The silver-doped SnSe nanostructured thin film holds promise for a high figure of merit.”

In the future, the researcher hope that SnSe nanostructures and thin films may be useful for miniaturized, environmentally friendly, low-cost thermoelectric and cooling devices.

Thousands of miles of fiber-optic cables crisscross the globe and package everything from financial data to cat videos into light. But when the signal arrives at your local data center, it runs into a silicon bottleneck. Instead of light, computers run on electrons moving through silicon-based chips — which, despite huge advances, are still less efficient than photonics.

To break through this bottleneck, researchers are trying to integrate photonics into silicon devices. They’ve been developing lasers — a crucial component of photonic circuits — that work seamlessly on silicon. In a paper appearing this week in APL Photonics, from AIP Publishing, researchers from the University of California, Santa Barbara write that the future of silicon-based lasers may be in tiny, atomlike structures called quantum dots.

Such lasers could save a lot of energy. Replacing the electronic components that connect devices with photonic components could cut energy use by 20 to 75 percent, Justin Norman, a graduate student at UC Santa Barbara, said. “It’s a substantial cut to global energy consumption just by having a way to integrate lasers and photonic circuits with silicon.”

Silicon, however, does not have the right properties for lasers. Researchers have instead turned to a class of materials from Groups III and V of the periodic table because these materials can be integrated with silicon.

Initially, the researchers struggled to find a functional integration method, but ultimately ended up using quantum dots because they can be grown directly on silicon, Norman said. Quantum dots are semiconductor particles only a few nanometers wide — small enough that they behave like individual atoms. When driven with electrical current, electrons and positively charged holes become confined in the dots and recombine to emit light — a property that can be exploited to make lasers.

The researchers made their III-V quantum-dot lasers using a technique called molecular beam epitaxy. They deposit the III-V material onto the silicon substrate, and its atoms self-assemble into a crystalline structure. But the crystal structure of silicon differs from III-V materials, leading to defects that allow electrons and holes to escape, degrading performance. Fortunately, because quantum dots are packed together at high densities — more than 50 billion dots per square centimeter — they capture electrons and holes before the particles are lost.

These lasers have many other advantages, Norman said. For example, quantum dots are more stable in photonic circuits because they have localized atomlike energy states. They can also run on less power because they don’t need as much electric current. Moreover, they can operate at higher temperatures and be scaled down to smaller sizes.

In just the last year, researchers have made considerable progress thanks to advances in material growth, Norman said. Now, the lasers operate at 35 degrees Celsius without much degradation and the researchers report that the lifetime could be up to 10 million hours.

They are now testing lasers that can operate at 60 to 80 degrees Celsius, the more typical temperature range of a data center or supercomputer. They’re also working on designing epitaxial waveguides and other photonic components, Norman said. “Suddenly,” he said, “we’ve made so much progress that things are looking a little more near term.”

Data is only as good as humans’ ability to analyze and make use of it.

In materials research, the ability to analyze massive amounts of data–often generated at the nanoscale–in order to compare materials’ properties is key to discovery and to achieving industrial use. Jeffrey M. Rickman, a professor of materials science and physics at Lehigh University, likens this process to candy manufacturing:

“If you are looking to create a candy that has, say, the ideal level of sweetness, you have to be able to compare different potential ingredients and their impact on sweetness in order to make the ideal final candy,” says Rickman.

For several decades, nanomaterials–matter that is so small it is measured in nanometers (one nanometer = one-billionth of a meter) and can be manipulated at the atomic scale–have outperformed conventional materials in strength, conductivity and other key attributes. One obstacle to scaling up production is the fact that scientists lack the tools to fully make use of data–often in the terabytes, or trillions of bytes–to help them characterize the materials–a necessary step toward achieving “the ideal final candy.”

What if such data could be easily accessed and manipulated by scientists in order to find real-time answers to research questions?

The promise of materials like DNA-wrapped single-walled carbon nanotubes could be realized. Carbon nanotubes are a tube-shaped material which can measure as small as one-billionth of a meter, or about 10,000 times smaller than a human hair. This material could revolutionize drug delivery and medical sensing with its unique ability to penetrate living cells.

A new paper takes a step toward realizing the promise of such materials. Authored by Rickman, the article describes a new way to map material properties relationships that are highly multidimensional in nature. Rickman employs methods of data analytics in combination with a visualization strategy called parallel coordinates to better represent multidimensional materials data and to extract useful relationships among properties. The article, “Data analytics and parallel-coordinate materials property charts,” has been published in npj Computational Materials, a Nature Research journal.

“In the paper,” says Rickman, “we illustrate the utility of this approach by providing a quantitative way to compare metallic and ceramic properties–though the approach could be applied to any materials you want to compare.”

It is the first paper to come out of Lehigh’s Nano/Human Interface Presidential Engineering Research Initiative, a multidisciplinary research initiative that proposes to develop a human-machine interface to improve the ability of scientists to visualize and interpret the vast amounts of data that are generated by scientific research. It was kickstarted by a $3-million institutional investment announced last year.

The leader of the initiative is Martin P. Harmer, professor of materials science and engineering. In addition to Rickman, other senior faculty members include Anand Jagota, department chair of bioengineering; Daniel P. Lopresti, department chair of computer science and engineering and director of Lehigh’s Data X Initiative; and Catherine M. Arrington, associate professor of psychology.

“Several research universities are making major investments in big data,” says Rickman. “Our initiative brings in a relatively new aspect: the human element.”

According to Arrington, the Nano/Human Interface initiative emphasizes the human because the successful development of new tools for data visualization and manipulation must necessarily include a consideration of the cognitive strengths and limitations of the scientist.

“The behavioral and cognitive science aspects of the Nano/Human Interface initiative are twofold,” says Arrington. “First, a human-factors research model allows for analysis of the current work environment and clear recommendations to the team for the development of new tools for scientific inquiry. Second, a cognitive psychology approach is needed to conduct basic science research on the mental representations and operations that may be uniquely challenged in the investigation of nanomaterials.”

Rickman’s proposed method uses parallel coordinates, which is a method of visualizing data that makes it possible to spot outliers or patterns based on related metric factors. Parallel coordinates charts can help tease out those patterns.

The challenge, says Rickman, lies in interpreting what you see.

“If plotting points in two dimensions using X and Y axes, you might see clusters of points and that would tell you something or provide a clue that the materials might share some attributes,” he explains. “But, what if the clusters are in 100 dimensions?”

According to Rickman, there are tools that can help cut down on numbers of dimensions and eliminate non-relevant dimensions to help one better identify these patterns. In this work, he applies such tools to materials with success.

“The different dimensions or axes describe different aspects of the materials, such as compressibility and melting point,” he says.

The charts described in the paper simplify the description of high-dimensional geometry, enable dimensional reduction and the identification of significant property correlations and underline distinctions among different materials classes.

From the paper: “In this work, we illustrated the utility of combining the methods of data analytics with a parallel coordinates representation to construct and interpret multidimensional materials property charts. This construction, along with associated materials analytics, permits the identification of important property correlations, quantifies the role of property clustering, highlights the efficacy of dimensional reduction strategies, provides a framework for the visualization of materials class envelopes and facilitates materials selection by displaying multidimensional property constraints. Given these capabilities, this approach constitutes a powerful tool for exploring complex property interrelationships that can guide materials selection.”

Returning to the candy manufacturing metaphor, Rickman says: “We are looking for the best methods of putting the candies together to make what we want and this method may be one way of doing that.”

New frontier, new approaches

Creating a roadmap to finding the best methods is the aim of a 2½-day, international workshop called “Workshop on the Convergence of Materials Research and Multi-Sensory Data Science” that is being hosted by Lehigh University in partnership with The Ohio State University.

The workshop–which will take place at Bear Creek Mountain Resort in Macungie, PA from June 11-13, 2018–will bring together scientists from allied disciplines in the basic and social sciences and engineering to address many issues involved in multi-sensory data science as applied to problems in materials research.

“We hope that one outcome of the workshop will be the forging of ongoing partnerships to help develop a roadmap to establishing a common language and framework for continued dialogue to move this effort of promoting multi-sensory data science forward,” says Rickman, who is Principal Investigator on an National Science Foundation (NSF) grant, awarded by the Division of the Materials Research in support of the workshop.

Co-Principal Investigator, Nancy Carlisle, assistant professor in Lehigh’s Department of Psychology, says the conference will bring together complementary areas of expertise to allow for new perspectives and ways forward.

“When humans are processing data, it’s important to recognize limitations in the humans as well as the data,” says Carlisle. “Gathering information from cognitive science can help refine the ways that we present data to humans and help them form better representations of the information contained in the data. Cognitive scientists are trained to understand the limits of human mental processing- it’s what we do! Taking into account these limitations when devising new ways to present data is critical to success.”

Adds Rickman: “We are at a new frontier in materials research, which calls for new approaches and partners to chart the way forward.”

UC Berkeley engineers have built a bright-light emitting device that is millimeters wide and fully transparent when turned off. The light emitting material in this device is a monolayer semiconductor, which is just three atoms thick.

The device opens the door to invisible displays on walls and windows – displays that would be bright when turned on but see-through when turned off — or in futuristic applications such as light-emitting tattoos, according to the researchers.

Gif of the device in action. Probes inject positive and negative charges in the light emitting device, which is transparent under the campanile outline, producing bright light. Credit: Javey lab.

Gif of the device in action. Probes inject positive and negative charges in the light emitting device, which is transparent under the campanile outline, producing bright light. Credit: Javey lab.

“The materials are so thin and flexible that the device can be made transparent and can conform to curved surfaces,” said Der-Hsien Lien, a postdoctoral fellow at UC Berkeley and a co-first author along with Matin Amani and Sujay Desai, both doctoral students in the Department of Electrical Engineering and Computer Sciences at Berkeley.

Their study was published March 26 in the journal Nature Communications. The work was funded by the National Science Foundation and the Department of Energy.

The device was developed in the laboratory of Ali Javey, professor of Electrical Engineering and Computer Sciences at Berkeley. In 2015, Javey’s lab published research in the journal Science showing that monolayer semiconductors are capable of emitting bright light, but stopped short of building a light-emitting device. The new work in Nature Communicationsovercame fundamental barriers in utilizing LED technology on monolayer semiconductors, allowing for such devices to be scaled from sizes smaller than the width of a human hair up to several millimeters. That means that researchers can keep the thickness small, but make the lateral dimensions (width and length) large, so that the light intensity can be high.

Commercial LEDs consist of a semiconductor material that is electrically injected with positive and negative charges, which produce light when they meet. Typically, two contact points are used in a semiconductor-based light emitting device; one for injecting negatively charged particles and one injecting positively charged particles. Making contacts that can efficiently inject these charges is a fundamental challenge for LEDs, and it is particularly challenging for monolayer semiconductors since there is so little material to work with.

The Berkeley research team engineered a way to circumvent this challenge by designing a new device that only requires one contact on the semiconductor. By laying the semiconductor monolayer on an insulator and placing electrodes on the monolayer and underneath the insulator, the researchers could apply an AC signal across the insulator. During the moment when the AC signal switches its polarity from positive to negative (and vice versa), both positive and negative charges are present at the same time in the semiconductor, creating light.

The researchers showed that this mechanism works in four different monolayer materials, all of which emit different colors of light.

This device is a proof-of-concept, and much research still remains, primarily to improve efficiency. Measuring this device’s efficiency is not straightforward, but the researchers think it’s about 1 percent efficient. Commercial LEDs have efficiencies of around 25 to 30 percent.

The concept may be applicable to other devices and other kinds of materials, the device could one day have applications in a number of fields where having invisible displays are warranted. That could be an atomically thin display that’s imprinted on a wall or even on human skin.

“A lot of work remains to be done and a number of challenges need to be overcome to further advance the technology for practical applications,” Javey said. “However, this is one step forward by presenting a device architecture for easy injection of both charges into monolayer semiconductors.”

On-site production an option for supply.

BY DR. PAUL STOCKMAN, Linde Electronics, Taipei, Taiwan

Hydrogen usage at leading-edge logic and foundry fabs has steadily increased over the past 20 years. What was supplied in individual cylinders is now frequently delivered by specialized bulk trucks carrying over one ton of hydrogen per vehicle; some fabs require multiple deliveries per day. With EUV (extreme ultraviolet) lithography nearing commercial, high-volume use, the demand for hydrogen will experience another inflection. In this article, we explain the current and future applications driving this demand, the geographical variation in supply, and on-site production solutions for high-volume customers.

Existing process applications

Hydrogen has been adopted as a material in processes throughout the fab. Its unique chemical properties continue to expand its usefulness. These applications typically use flows of 100s to 1,000s of sccm (standard cubic centimeter per minute):

• Epitaxy: Hydrogen is used as a reducing agent during the epitaxial growth of crystalline thin-films. This is often used to make a starting silicon surface for semiconductor manufacturing by reacting newly cut and polished silicon wafers with trichlorosilane (SiHCl3) in an epi-house or end-user fab. The hydrogen reduces the gas-phase chlorine atoms, and the HCl product is removed from the reactor as a gas. Leading- edge channel materials like strained silicon, silicon- germanium, and germanium are also grown using hydrogen-mediated epitaxy.

• Deposition: Hydrogen can also be incorporated directly into thin-films to disrupt crystal lattices to make them less crystalline, more amorphous. This is often used with silicon thin-films, which need to be made more electrically insulating.

• Plasma etch: Hydrogen and hydrogen-containing plasmas are used to directly react with the surface of the wafer in order to clean or remove unwanted thin films, especially for removing unwanted fluorocarbon deposits on silicon oxides.

• Anneal: Silicon wafers are heated to temperatures over 1,000 C, often at elevated pressure, in order to repair their crystal structures. Hydrogen assists by transferring heat uniformly over the surface of the wafer, and also by penetrating into the crystal lattice to react with atomic impurities.

• Passivation: Hydrogen is used to react and remove native oxides on silicon surfaces and to mediate the reconstruction of silicon-silicon bonds in the final layers of the crystal.

• Ion implantation: With more precision than bulk annealing and passivation, protons produced from hydrogen gas can be implanted to specific depths and concentrations in a thin film using ion implanters. Not only can hydrogen atoms be inserted to modify a thin film, but in higher doses and implantation energies, it can be used to cleave slivers of silicon and sapphire wafers.

• Carrier gas: Hydrogen is used as a carrier gas to entrain (entrap) and transport less volatile chemicals— ordinarily liquids at atmospheric pressure and room temperature—into the reaction chamber. The hydrogen is heated and bubbled through the liquid chemicals. Because the mass of hydrogen is very light compared to entrained chemical vapor, specialized mass flow controllers can then be used to sense, measure, and precisely control the amount of chemical vapor dispensed.

• Material stabilization: The addition of hydrogen extends the shelf life of important electronic materials like diborane (B2H6) and digermane (Ge2H6), which otherwise slowly decompose.

• Polysilicon manufacturing: Although not part of the process flow in semiconductor fabs, hydrogen is used in large quantities in the upstream process of manufacturing polysilicon: thousands of Nm3 per hour hydrogen are used, and typically an on-site hydrogen plant is required. Polysilicon is the starting material for making crystallized silicon, from which silicon wafers are sliced.

Application for EUV

Extreme ultraviolet (EUV) lithography is the much- anticipated new application expected to simplify the process patterning complexity for critical dimensions in leading-edge devices. While it has taken a long time for this technology to come close to commercialization, top-tier manufacturers are coalescing their predictions for volume manufacturing adoption in the 2018-2020 window. Whereas other hydrogen-consuming applica- tions have a usage rate of 100s of sccm, EUV will require much larger flows of 100s of slm (standard liters per minute), or roughly 100 to 1,000x more per individual tool.

Deep ultraviolet (DUV) lithography, the current workhorse of the patterning tools, uses an electrical discharge in neon or krypton mixed with halogen gases like fluorine to produce UV light at 193 nm and 248 nm; EUV light production is much more complicated. Tin metal is heated above its melting point of 232 C, and small droplets of tin (~25 μm diameter) are rapidly (50,000 droplets per second) produced. These droplets are first vaporized and then excited with high-power CO2 lasers. The excited tin atoms emit EUV light at 13.5 nm, which is more than 14 times shorter than the DUV tools.

The light is emitted in all directions and is collected and collimated (aligned) by an array of mirrors. The light is then passed to the primary lithography tool for focusing and image transfer before illuminating the photoresist on the wafer. All materials heavily absorb EUV light. Absorption losses are minimized by using multi-layer reflective optics instead of the transmissive lenses used in DUV lithography, and the entire light source and patterning systems are housed in vacuum chambers. These highly complex tools are expected to cost end users around $100 million USD each, and when fully adopted, a leading-edge fab could require 20 or more of these tools.

Scattered tin debris from the vaporization of droplets is a major potential source of contamination of both the collector and focusing optics. Unmitigated, the lifetimes of these expensive components would be unacceptable. Hydrogen gas is used to shroud the tin excitation region, and tin vapor and aberrant droplets are reacted to form stannane (SnH4), which is then removed from that section of the housing by means of the vacuum line. Higher flows of hydrogen can be used in periodic plasma-based cleaning to remove tin that deposits on the collector optics.

Demand and supply

Even before the adoption of EUV technology, leading- edge logic and foundry processes have begun consuming several normal cubic meters (1,000 liters) of hydrogen per wafer processed. This usage trend is expected to continue increasing in the 10 nm and 7 nm nodes commercialized before wide-spread EUV use. Conse- quently, major fabs now use hundreds of Nm3 per hour. EUV, when fully extended to all of the critical layers, will roughly double the amount of hydrogen used in these fabs. In a related application, the largest LED fabs also use hundreds of Nm3 of hydrogen per hour, primarily as a carrier gas and diluent for the gallium, arsine, and phosphorus precursors used to make the light-emitting devices.

Supply of hydrogen to electronics customers has been historically driven by regional source types, engineering and transportation codes, and by end user preferences and process qualification. However, steep demand curves are causing users to consider new supply schemes for access to larger volumes, greater supply chain security, and lessening of local fab logistics.

Over 60 million metric tons of hydrogen are produced globally, almost exclusively from hydrocarbon feedstocks: natural gas, oil, and coal. Most of this is used as a chemical intermediate to make ammonia, methanol, and trans- portation fuels. Electronics uses much less than 1% of hydrogen, yet relies on industrial technologies and sources as supply origins.

Screen Shot 2018-03-23 at 1.17.54 PM

Hydrogen is supplied in the following modes (FIGURES 1 and 2):

• Cylinders: In smaller volumes, hydrogen is supplied in standard-sized gas cylinders, which hold about 7 m3 of gas pressurized at approximately 175 bar (250 cu ft at 2,500 psi). The largest fabs now consume this amount in less than one minute. Individual cylinders can be manifolded together to create larger packs of cylinders, which are typically mounted into metal pallets for easier handling. These packs can even be arrayed into full truck trailers of connected cylinders. Despite the increased volume, there is a limitation on the level of mass flow that can be safely achieved from this configuration.

• Compressed gaseous hydrogen (CGH) trailers: To improve on both mass distribution and packaging/handling costs, specialized trailers with much larger, pressurizable vessels are used. These CGH (compressed gaseous hydrogen) trailers can hold 10,000 Nm3 at pressures similar to smaller packages, yet are the distribution equiv- alent to over 1,400 individual cylinders. Just as importantly, fewer, larger vessels are faster to fill, and easier to maintain quality to the very high standards required by the semiconductor industry. Fewer components and human interactions also reduce safety risks.

• Liquefied hydrogen transport: In North America and much of Europe, liquefied hydrogen transport is allowed. This further increases the amount of hydrogen per truck to 40,000 Nm3 gas, or the equivalent of around 6,000 cylinders. In addition to increasing the volume, liquefication of hydrogen is also an added purification step. By cooling the material down to the boiling point of 21 K (-252 C), most impurities are solidified and can be reduced in concentration by absorption.

Screen Shot 2018-03-23 at 1.18.04 PM

These benefits come with a trade-off, however. Liquefying hydrogen to the very low required temperatures consumes a lot of energy, and mandates additional safety protocols. Moreover, there are fewer liquid hydrogen production sources versus gaseous facilities, and transportation distances and supply logistics can be substantially increased. It is important to note that liquid hydrogen transport is not allowed in the primary semiconductor producing countries of Asia (China[1], Japan, Singapore, South Korea, and Taiwan), and therefore not a consideration for users in that region.

On-site hydrogen production

A solution that is becoming appropriate for some fabs is on-site hydrogen production (FIGURES 3 and 4). All major fabs already have either direct on-site production of gaseous nitrogen, or are supplied via pipeline by local plants. On-site hydrogen production has similar consid- erations of planning, footprint, redundancy, and back-up.

Screen Shot 2018-03-23 at 1.18.11 PM

• Planning and footprint: On-site gas production should be planned at the outset of the entire fab concept. Like on-site nitrogen production, construction of the hydrogen facility usually begins at the same time as groundbreaking for the fab. The footprint of the plant and auxiliary equipment needs to be accounted for, either on the user’s property, or on an adjacent parcel reserved for the gas supplier. Pipeline delivery needs to be routed. And importantly for hydrogen, permits must be applied for which differ according to location.

• Redundancy and back-up: Continuous supply is essential for all semiconductor material supply chains. On-site production must ensure continuous supply for planned and unplanned equipment downtime, or in the case that fab demand grows past the on-site generating capacity. This can be accomplished by choosing from among three alternatives. If liquefication of on-site generated hydrogen is part of the production and purification scheme, excess hydrogen can be liquefied and stored in cryogenic tanks. Hydrogen generators appropriate to produce semiconductor-grade material are often modular, meaning that several will be used in parallel to make the full requirement of a fab. By installing an additional or redundant module, excess capacity is available in the event of planned maintenance or other event. Finally, off-site hydrogen is usually qualified as a supplement or temporary replacement. Often, this is the original source for the process of record for the manufacturer.

Screen Shot 2018-03-23 at 1.18.19 PM

On-site hydrogen technologies suitable for semiconductor processes are either electrolysis of water, or so-called “reforming” and “shifting” of hydrocarbon feedstocks.

• Electrolysis: Electrolysis uses direct current electricity to split a water molecule into elemental hydrogen and oxygen. Actually, the reaction takes place in two physically distinct electrical poles of the equipment – the anode and the cathode – as two separate half-reactions. The net reaction is

2H2O(l) → 2H2 (g) +O2 (g)

Electrolysis is relatively expensive at volume because of the energy needed to break water molecule bonds even though achieving purity in the feedstock water is relatively simple.

• Steam Reforming and Shifting: More economical are the industrial steam reforming and shifting processes, using hydrocarbon feedstocks like natural gas, LPG (liquefied petroleum gas – mostly propane and butane), and methanol. In fact, this is the process which produces most of the bulk hydrogen already used by existing semiconductor fabs, and is responsible for 95% of global hydrogen production. Natural gas (CH4) and steam are heated over a catalyst to form syngas (a mixture of hydrogen and carbon monoxide).

CH4 +H2O→CO+3H2

The syngas is then separated to give hydrogen. The carbon monoxide can then be further reacted (shifted) with the steam to yield additional hydrogen.

CO+H2O→CO2 +H2

Taken together, these process plants are known as steam methane reformers, or SMR plants. Choices for the exact plant technology depend upon the local feedstocks available and the customer quality profile requirements.

Regardless of whether the hydrogen is supplied in gaseous or liquefied containers or made on-site, semiconductor hydrogen supply schemes incorporate on-site, and often additional point-of-use, purification using various technologies: adsorption, gettering, and application of the unique property of hydrogen to diffuse through palladium metal membranes, which are impervious to most other molecules. In addition, hydrogen purity is monitored at several points in the distribution by multiple types of detectors.

Safety

As with all chemical supplies, safety is paramount. With hydrogen, the main safety risk is associated with its wide range of flammability and explosivity. Throughout production and packaging, multiple types of redundant protocols are used to ensure that no oxidizers are contacted or incorporated into the hydrogen and plant designs minimize the risk for leaks. Specialized clothing resistant to fire and static is worn in some hydrogen producing and using environments. Materials of construction and component qualification are also important to guard against a phenomenon known as hydrogen embrit- tlement, where at elevated temperatures and/or pressures, hydrogen can permeate and weaken certain metals and alloys. Finally, liquefied hydrogen introduces the additional risk associated with cryogenic materials and the need to use insulating vessels and personal protection.

Conclusion

Semiconductor manufacturing has long used hydrogen in an essential and expanding portfolio of applications. Already, hydrogen supply is considered a bulk material scheme, with source, transport, and logistic considerations. The adoption of EUV at leading-edge fabs in the next few years will accelerate the pace of hydrogen consumption, and drive the consideration of new supply schemes. End users should evaluate hydrogen supply options for future fabs as part of their advanced planning to ensure that their quality, supply and process integrity requirements will be met.

References

1. China is in the process of approving liquefied hydrogen transport at the time of this publication. The details are not yet defined.

Scientists from Australia and China have drawn on the durable power of gold to demonstrate a new type of high-capacity optical disk that can hold data securely for more than 600 years.

The technology could offer a more cost-efficient and sustainable solution to the global data storage problem while enabling the critical pivot from Big Data to Long Data, opening up new realms of scientific discovery.

The recent explosion of Big Data and cloud storage has led to a parallel explosion in power-hungry data centres. These centres not only use up colossal amounts of energy – consuming about 3 per cent of the world’s electricity supply – but largely rely on hard disk drives that have limited capacity (up to 2TB per disk) and lifespans (up to two years).

Now scientists from RMIT University in Melbourne, Australia, and Wuhan Institute of Technology, China, have used gold nanomaterials to demonstrate a next-generation optical disk with up to 10TB capacity – a storage leap of 400 per cent – and a six-century lifespan.

The technology could radically improve the energy efficiency of data centres – using 1000 times less power than a hard disk centre – by requiring far less cooling and doing away with the energy-intensive task of data migration every two years. Optical disks are also inherently far more secure than hard disks.

Lead investigator, RMIT University’s Distinguished Professor Min Gu, said the research paves the way for the development of optical data centres to address both the world’s data storage challenge and support the coming Long Data revolution.

“All the data we’re generating in the Big Data era – over 2.5 quintillion bytes a day – has to be stored somewhere, but our current storage technologies were developed in different times,” Gu said.

“While optical technology can expand capacity, the most advanced optical disks developed so far have only 50-year lifespans.

“Our technique can create an optical disk with the largest capacity of any optical technology developed to date and our tests have shown it will last over half a millennium.

“While there is further work needed to optimise the technology – and we’re keen to partner with industrial collaborators to drive the research forward – we know this technique is suitable for mass production of optical disks so the potential is staggering.”

The world is shifting from Big Data towards Long Data, which enables new insights to be discovered through the mining of massive datasets that capture changes in the real world over decades and centuries.

Lead author, Senior Research Fellow Dr Qiming Zhang from RMIT’s School of Science, said the new technology could expand horizons for research by helping to advance the rise of Long Data.

“Long Data offers an unprecedented opportunity for new discoveries in almost every field – from astrophysics to biology, social science to business – but we can’t unlock that potential without addressing the storage challenge,” Zhang said.

“For example, to study the mutation of just one human family tree, 8 terabytes of data is required to analyse the genomes across 10 generations. In astronomy, the Square Kilometre Array (SKA) radio telescope produces 576 petabytes of raw data per hour.

“Meanwhile the Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative to ‘map’ the human brain is handling data measured in yottabytes, or one trillion terabytes.

“These enormous amounts of data have to last over generations to be meaningful. Developing storage devices with both high capacity and long lifespan is essential, so we can realise the impact that research using Long Data can make in the world.”

The novel technique behind the technology – developed over five years – combines gold nanomaterials with a hybrid glass material that has outstanding mechanical strength.

The research progresses earlier groundbreaking work by Gu and his team that smashed through the seemingly unbreakable optical limit of blu-ray and enabled data to be stored across the full spectrum of visible light rays.

How it works

The researchers have demonstrated optical long data memory in a novel nanoplasmonic hybrid glass matrix, different to the conventional materials used in optical discs.

Glass is a highly durable material that can last up to 1000 years and can be used to hold data, but has limited storage capacity because of its inflexibility.

The team combined glass with an organic material, halving its lifespan but radically increasing capacity.

To create the nanoplasmonic hybrid glass matrix, gold nanorods were incorporated into a hybrid glass composite, known as organic modified ceramic.

The researchers chose gold because like glass, it is robust and highly durable. Gold nanoparticles allow information to be recorded in five dimensions – the three dimensions in space plus colour and polarisation.

The technique relies on a sol-gel process, which uses chemical precursors to produce ceramics and glasses with better purity and homogeneity than conventional processes.

 

Working up a sweat from carrying a heavy load? That is when the textile works at its best. Researchers at Chalmers University of Technology have developed a fabric that converts kinetic energy into electric power, in cooperation with the Swedish School of Textiles in Borås and the research institute Swerea IVF. The greater the load applied to the textile and the wetter it becomes the more electricity it generates. The results are now published in the Nature Partner journal Flexible Electronics.

Chalmers researchers Anja Lund and Christian Müller have developed a woven fabric that generates electricity when it is stretched or exposed to pressure. The fabric can currently generate enough power to light an LED, send wireless signals or drive small electric units such as a pocket calculator or a digital watch.

The technology is based on the piezoelectric effect, which results in the generation of electricity from deformation of a piezoelectric material, such as when it is stretched. In the study the researchers created a textile by weaving a piezoelectric yarn together with an electrically conducting yarn, which is required to transport the generated electric current.

“The textile is flexible and soft and becomes even more efficient when moist or wet,” Lund says. “To demonstrate the results from our research we use a piece of the textile in the shoulder strap of a bag. The heavier the weight packed in the bag and the more of the bag that consists of our fabric, the more electric power we obtain. When our bag is loaded with 3 kilos of books, we produce a continuous output of 4 microwatts. That’s enough to intermittently light an LED. By making an entire bag from our textile, we could get enough energy to transmit wireless signals.”

The piezoelectric yarn is made up of twenty-four fibres, each as thin as a strand of hair. When the fibres are sufficiently moist they become enclosed in liquid and the yarn becomes more efficient, since this improves the electrical contact between the fibres. The technology is based on previous studies by the researchers in which they developed the piezoelectric fibres, to which they have now added a further dimension.

“The piezoelectric fibres consist of a piezoelectric shell around an electrically conducting core,” Lund says. “The piezoelectric yarn in combination with a commercial conducting yarn constitute an electric circuit connected in series.”

Previous work by the researchers on piezoelectric textiles has so far mainly focused on sensors and their ability to generate electric signals through pressure sensitivity. Using the energy to continuously drive electronic components is unique.

“Woven textiles from piezoelectric yarns makes the technology easily accessible and it could be useful in everyday life. It’s also possible to add more materials to the weave or to use it as a layer in a multi-layer product. It requires some modification, but it’s possible,” Lund says.

The researchers consider that the technology is, in principle, ready for larger scale production. It is now mainly up to industrial product developers to find out how to make use of the technology. Despite the advanced technology underlying the material, the cost is relatively low and is comparable with the price of Gore-Tex. Through their collaboration with the Swedish School of Textiles in Borås the researchers have been able to demonstrate that the yarn can be woven in industrial looms and is sufficiently wear-resistant to cope with the harsh conditions of mass production.

Magnolia Optical Technology, Inc. announced that it is working with the Defense Advanced Research Projects Agency (DARPA) under the Phase II SBIR Program for Development of High-Performance Thin-Film Solar Cells for Portable Power Applications (Contract No D15PC00222).

Photovoltaic devices can provide a portable source of electrical power for a wide variety of defense and commercial applications, including mobile power for dismounted soldiers, unmanned aerial vehicles, and remote sensors.

“The goal of the current program is to develop high-efficiency GaAs-based solar cells that maintain their performance over changing environmental conditions, and that are thinner and thus more cost-effective to produce,” said Dr. Roger Welser, Magnolia’s Chief Technical Officer. “By combining thin III-V absorbers with advanced light-trapping structures, single-junction GaAs-based devices provide a means to deliver high efficiency performance over a wide range of operating conditions at a fraction of the cost of the multi-junction structures typically employed for space power. In addition, the incorporation of nano-enhanced III-V absorbers provides a pathway to extend infrared absorption and increase the photovoltaic power conversion efficiency of cost-effective thin-film solar cells.”

Dr. Ashok Sood, President of Magnolia stated “changes in the solar spectrum can dramatically degrade the performance of traditional multi-junction devices – changes that occur naturally throughout the day, from season to season, and from location to location as sunlight passes through the earth’s atmosphere. Moreover, multi-junction III-V cells require thick, complex epitaxial layers and are therefore inherently expensive to manufacture. The technology under development as part of this DARPA-funded program addresses these key weaknesses in the established high-performance photovoltaic technology. The photovoltaic market is a rapidly growing segment of the energy industry with a wide range of commercial and defense applications.”

Magnolia specializes in developing optical technologies for defense and commercial applications. Based in Woburn, MA, Magnolia develops both thin film and nanostructure-based technologies that cover the ultraviolet, visible, and infrared part of the spectrum. These technologies are developed for use in advanced military sensors and other commercial applications including solar cells.

If scientists are ever going to deliver on the promise of implantable artificial organs or clothing that dries itself, they’ll first need to solve the problem of inflexible batteries that run out of juice too quickly. They’re getting closer, and today researchers report that they’ve developed a new material by weaving two polymers together in a way that vastly increases charge storage capacity.

The researchers will present their work today at the 255th National Meeting & Exposition of the American Chemical Society (ACS). ACS, the world’s largest scientific society, is holding the meeting here through Thursday. It features more than 13,000 presentations on a wide range of science topics.

Supercapacitors woven like the red and white of a candy cane could have increased charge storage capacity compared to current technology. Credit: Tiesheng Wang

Supercapacitors woven like the red and white of a candy cane could have increased charge storage capacity compared to current technology. Credit: Tiesheng Wang

“We had been developing polymer networks for a different application involving actuation and tactile sensing,” Tiesheng Wang says. “After the project, we realized that the stretchable, bendable material we’d made could potentially be used for energy storage.”

Batteries, specifically lithium-ion batteries, dominate the energy storage landscape. However, the chemical reactions underlying the charging and discharging process in batteries are slow, limiting how much power they can deliver. Plus, batteries tend to degrade over time, requiring replacement. An alternate energy storage device, the supercapacitor, charges rapidly and generates serious power, which could potentially allow electric cars to accelerate more quickly, among other applications. Plus, supercapacitors store energy electrostatically, not chemically, which makes them more stable and long-lasting than many batteries. But today’s commercially available supercapacitors require binders and have low energy density, limiting their application in emerging go-anywhere electronics.

Wang, a graduate student in the lab of Stoyan Smoukov, Ph.D., at the University of Cambridge (U.K.) suspected that a flexible conducting polymer-based material from another project they were working on could be a better alternative. Conducting polymers, such as poly(3,4-ethylenedioxythiophene) (PEDOT), are candidate supercapacitors that have advantages over traditional carbon-based supercapacitors as charge storage materials. They are pseudocapacitive, meaning they allow reversible electrochemical reactions, and they also are chemically stable and inexpensive. However, ions can only penetrate the polymers a couple of nanometers deep, leaving much of the material as dead weight. Scientists working to improve ion mobility had previously developed nanostructures that deposit thin layers of conducting polymers on top of support materials, which improves supercapacitor performance by making more of the polymer accessible to the ions. The drawback, according to Wang, is that these nanostructures can be fragile, difficult to make reproducibly when scaled-up and poor in electrochemical stability, limiting their applicability.

So, Smoukov and Wang developed a more robust material by weaving together a conducting polymer with an ion-storage polymer. The two polymers were stitched together to form a candy cane-like geometry, with one polymer playing the role of the white stripe and the other, red. While PEDOT conducts electricity, the other polymer, poly(ethylene oxide) (PEO), can store ions. The interwoven geometry is instrumental to the energy storage benefits, Wang says, because it allows the ions to access more of the material overall, approaching the “theoretical limit.”

When tested, the candy cane supercapacitor demonstrated improvements over PEDOT alone with regard to flexibility and cycling stability. It also had nearly double the specific capacitance compared to conventional PEDOT-based supercapacitors.

Still, there’s room for improvement, Smoukov says. “In future experiments, we will be substituting polyaniline for PEDOT to increase the capacitance,” he says. “Polyaniline, because it can store more charge per unit of mass, could potentially store three times as much electricity as PEDOT for a given weight.” That means lighter batteries with the same energy storage can be charged faster, which is an important consideration in the development of novel wearables, robots and other devices.

Researchers at RIT have found a more efficient fabricating process to produce semiconductors used in today’s electronic devices. They also confirmed that materials other than silicon can be used successfully in the development process that could increase performance of electronic devices. This fabrication process–the I-MacEtch, or inverse metal-assisted chemical etching method–can help meet the growing demand for more powerful and reliable nano-technologies needed for solar cells, smartphones, telecommunications grids and new applications in photonics and quantum computing.

“What is novel about our work is that for the first time we are looking at applying I-MacEtch processing to indium-gallium-phosphide materials. I-MacEtch is an alternative to two conventional approaches and is a technique that has been used in the field–but the materials that have been explored are fairly limited,” said Parsian Mohseni, assistant professor of microsystems engineering in RIT’s Kate Gleason College of Engineering. He is also director of the EINS Laboratory at the university.

Demands for improved computer processing power have led researchers to explore both new processes and other materials beyond silicon to produce electronic components, Mohseni explained. The I-MacEtch process combines the benefits of two traditional methods–wet etching and reactive ion etching, or REI. Indium-gallium-phosphide is one of several materials being tested to complement silicon as a means to improve current capacity of semiconductor processing.

“This is a very well-known material and has applications in the electronics and solar cell industries,” he said. “We are not re-inventing the wheel; we are establishing new protocols for treating the existing material that is more cost effective, and a more sustainable process.”

Semiconductor devices are created on wafers through a multi-step process to coat, remove or pattern conductive materials. Traditional processes are wet etch, where a sample with blocked aspects is immersed in an acid bath to remove substances, and reactive ion etching, where ions bombard exposed surfaces on the wafer to change its chemical properties and remove materials in those exposed regions. Both have been used to develop the intricate electronic patterns on circuits and use silicon as a foundation for this type of patterning. Improving patterning methods by I-MacEtch could mean reducing fabrication complexity of various photonic and electronic devices.

Researchers and semiconductor fabrication scientists have been using MacEtch extensively for processing silicon. At the same time, assessments of other materials in the III-V range of individual elements that may be conducive to this same type of fabrication with similar advantages are underway. In his research, Mohseni is also looking at different alloys of those III-V materials, namely the ternary alloys such as indium-gallium-phosphide (InGaP).

The research detailed in the upcoming issue of the American Chemical Society’s Applied Materials and Interfaces journal highlights how the nanofabrication methodology was applied to InGaP and how it can impact the processing of device applications and generation of high aspect ratio and nano-scale semiconductor features, said Thomas Wilhelm, a microsystems engineering doctoral student and first-author of the paper. The novel processing method can be significant in the development of ordered arrays of high aspect ratio structures such as nanowires.

For solar cells, the goal is to minimize the cost-to-power-produced ratio, and if it is possible to lower the cost of making the cell, and increasing the efficiency of it, this improves the device overall. Exploring new methods of fabricating the existing, relevant materials in a way that allows for faster, less expensive and more controlled processing by combining the benefits of wet etching and RIE has been the focus of Mohseni’s work. The improved process means avoiding expensive, bulky, hazardous processing methods.

“We are using a simple benchtop set up and we end up with very similar structures; in fact, one can argue that they are higher in quality than the structures that we can generate with RIE for a fraction of the cost and with less time, less steps throughout, without the higher temperature conditions or expensive instrumentation,” he said.