Category Archives: Process Materials

By Jamie Girard, Sr. Director, Public Policy, SEMI

Although many months past due, Congress on March 23 finalized the federal spending for the remainder of fiscal year (FY) 2018, only hours before a what would have been the third government shutdown of the year. Congressional spending has been allocated in fits and starts since the end of FY 2017 last September, with patchwork deals keeping things running amid pervasive uncertainty. While this clearly isn’t an ideal way to fund the federal government, the end result will make many in the business of research and development pleased with the addition of more resources for science and innovation.

There was grave concern over the future of federal spending with the release of the president’s FY 2018 budget, which would have cut the National Science Foundation (NSF) budget by 11 percent and National Institutes of Standards & Technology (NIST) spending by 30 percent. Relief came with early drafts from Congress that whittled those cuts down to between 2-9 percent. But the real boost was a February bipartisan Congressional agreement that lifted self-imposed spending caps and introduced a generous dose of non-defense discretionary spending, increasing NSF spending 3.9 percent over the previous year and the NIST budget an astounding 25.9 percent over FY 2017 levels.

SEMI applauds this much-needed support for basic research and development (R&D) at these agencies after their budgets were cut or flat-funded for multiple cycles. It is well understood that federal R&D funding is critical to U.S. competitiveness and future economic prosperity. With the stakes that high, full funding of R&D programs at the NSF and NIST should be a bipartisan national priority backed by a strong and united community of stakeholders and advocates in the business, professional, research, and education communities.

With the work for FY 2018 completed, Congress will now turn to FY 2019 spending – already behind schedule due to the belated completion of the previous year’s budget. With 2018 an election year, Congress will likely begin work on the FY 2019 budget in short order, but probably won’t complete its work prior to the November elections.  SEMI will continue to work with lawmakers to support the R&D budgets at the agencies and their important basic science research. If you’d like to know how you can be more involved with SEMI’s public policy work, please contact Jamie Girard, Sr. Director, Public Policy at [email protected].

Graphene is a two-dimensional nanocarbon material, having unique properties in electronic, optical and thermal properties, which can be applied for optoelectronic devices. Graphene-based blackbody emitters are also promising light emitters on silicon chip in NIR and mid-infrared region. However, although graphene-based blackbody emitters have been demonstrated under steady-state conditions or relatively slow modulation (100 kHz), the transient properties of these emitters under high-speed modulation have not been reported to date. Also, the optical communications with graphene-based emitters have never been demonstrated.

Square graphene sheet is connected to source and drain electrodes. Modulated blackbody emission is obtained from graphene by applying input signal. Credit: Keio University

Square graphene sheet is connected to source and drain electrodes. Modulated blackbody emission is obtained from graphene by applying input signal. Credit: Keio University

Here, a highly integrated, high-speed and on-chip blackbody emitter based on graphene in NIR region including telecommunication wavelength was demonstrated. A fast response time of ~ 100 ps, which is ~ 105 higher than the previous graphene emitters, has been experimentally demonstrated for single and few-layer graphene, the emission responses can be controlled by the graphene contact with the substrate depending on the number of graphene layers. The mechanisms of the high-speed emission are elucidated by performing theoretical calculations of the heat conduction equations considering the thermal model of emitters including graphene and a substrate. The simulated results indicate that the fast response properties can be understood not only by the classical thermal transport of in-plane heat conduction in graphene and heat dissipation to the substrate but also by the remote quantum thermal transport via the surface polar phonons (SPoPhs) of the substrates. In addition, first real-time optical communication with graphene-based light emitters was experimentally demonstrated, indicating that graphene emitters are novel light sources for optical communication. Furthermore, we fabricated integrated two-dimensional array emitters with large-scale graphene grown by chemical vapour deposition (CVD) method and capped emitters operable in air, and carried out the direct coupling of optical fibers to the emitters owing to their small footprint and planar device structure.

Graphene light emitters are greatly advantageous over conventional compound semiconductor emitters because they can be highly integrated on silicon chip due to simple fabrication processes of graphene emitters and direct coupling with silicon waveguide through an evanescent field. Because graphene can realize high-speed, small footprint and on-Si-chip light emitters, which are still challenges for compound semiconductors, the graphene-based light emitters can open new routes to highly integrated optoelectronics and silicon photonics.

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.

Veeco Instruments Inc. (NASDAQ: VECO) today announced it has completed installation of its 100th automated Molecular Beam Epitaxy (MBE) system. The installation of Veeco’s GEN10™ MBE System last month at Silanna Semiconductor PTY Ltd. in Australia marks this significant company milestone. The company also operates a Veeco Dual GEN200® MBE System for production of advanced nitride compound semiconductor devices including ultraviolet light emitting diodes (UV-LEDs).

“Veeco has earned a reputation for consistently developing innovative and reliable MBE technology from research scale to production,” said Petar Atanackovic, Ph.D., chief scientist of Silanna Semiconductor PTY Ltd. “The flexibility and deposition capability of the GEN10 system will enable us to develop new materials at the atomic level allowing us to exploit new quantum properties. Veeco’s technology portfolio and leadership in MBE systems provides us with a clear path to easily scale to volume production in the future.”

Silanna is using the GEN10 system for advanced oxide research and development (R&D) for optoelectronic devices. The GEN10 is built upon almost 20 years of cumulative automation knowledge and derived from the company’s proven production MBE systems. Adopted by numerous leading corporations, institutions and universities for all major MBE applications, many customers choose the GEN10 because of its flexibility, which allows them to configure the system based on their application. This gives customers optimal performance with any material set, including those related to III-V group elements, oxides and nitrides.

“Silanna has achieved remarkable results on its previous MBE systems and Veeco is honored to celebrate this momentous accomplishment in our company history in partnership with Dr. Atanackovic and the Silanna team,” said Gerry Blumenstock, vice president and general manager, Veeco MBE Products. “As our customers explore novel materials and new applications, they can rely on Veeco to deliver innovative MBE systems, sources and components for use in complex R&D, as well as high-volume production environments.”

MBE is a highly precise thin-film deposition method for creating crystals by building up orderly layers of molecules on top of a substrate. MBE is used in industrial production processes as well as nanotechnology research in high-growth advanced computing, optics and photonics applications, to name a few. With over 600 systems shipped worldwide, Veeco provides the industry’s broadest portfolio of proven, reliable MBE systems, sources and components to serve a wide variety of markets and applications.

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.”

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.

Some novel materials that sound too good to be true turn out to be true and good. An emergent class of semiconductors, which could affordably light up our future with nuanced colors emanating from lasers, lamps, and even window glass, could be the latest example.

These materials are very radiant, easy to process from solution, and energy-efficient. The nagging question of whether hybrid organic-inorganic perovskites (HOIPs) could really work just received a very affirmative answer in a new international study led by physical chemists at the Georgia Institute of Technology.

Laser light in the visible range is processed for use in the testing of quantum properties in materials in Carlos Silva's lab at Georgia Tech. Credit: Georgia Tech/Allison Carter

Laser light in the visible range is processed for use in the testing of quantum properties in materials in Carlos Silva’s lab at Georgia Tech. Credit: Georgia Tech/Allison Carter

The researchers observed in an HOIP a “richness” of semiconducting physics created by what could be described as electrons dancing on chemical underpinnings that wobble like a funhouse floor in an earthquake. That bucks conventional wisdom because established semiconductors rely upon rigidly stable chemical foundations, that is to say, quieter molecular frameworks, to produce the desired quantum properties.

“We don’t know yet how it works to have these stable quantum properties in this intense molecular motion,” said first author Felix Thouin, a graduate research assistant at Georgia Tech. “It defies physics models we have to try to explain it. It’s like we need some new physics.”

Quantum properties surprise

Their gyrating jumbles have made HOIPs challenging to examine, but the team of researchers from a total of five research institutes in four countries succeeded in measuring a prototypical HOIP and found its quantum properties on par with those of established, molecularly rigid semiconductors, many of which are graphene-based.

“The properties were at least as good as in those materials and may be even better,” said Carlos Silva, a professor in Georgia Tech’s School of Chemistry and Biochemistry. Not all semiconductors also absorb and emit light well, but HOIPs do, making them optoelectronic and thus potentially useful in lasers, LEDs, other lighting applications, and also in photovoltaics.

The lack of molecular-level rigidity in HOIPs also plays into them being more flexibly produced and applied.

Silva co-led the study with physicist Ajay Ram Srimath Kandada. Their team published the results of their study on two-dimensional HOIPs on March 8, 2018, in the journal Physical Review Materials. Their research was funded by EU Horizon 2020, the Natural Sciences and Engineering Research Council of Canada, the Fond Québécois pour la Recherche, the Research Council of Canada, and the National Research Foundation of Singapore.

The ‘solution solution’

Commonly, semiconducting properties arise from static crystalline lattices of neatly interconnected atoms. In silicon, for example, which is used in most commercial solar cells, they are interconnected silicon atoms. The same principle applies to graphene-like semiconductors.

“These lattices are structurally not very complex,” Silva said. “They’re only one atom thin, and they have strict two-dimensional properties, so they’re much more rigid.”

“You forcefully limit these systems to two dimensions,” said Srimath Kandada, who is a Marie Curie International Fellow at Georgia Tech and the Italian Institute of Technology. “The atoms are arranged in infinitely expansive, flat sheets, and then these very interesting and desirable optoelectronic properties emerge.”

These proven materials impress. So, why pursue HOIPs, except to explore their baffling physics? Because they may be more practical in important ways.

“One of the compelling advantages is that they’re all made using low-temperature processing from solutions,” Silva said. “It takes much less energy to make them.”

By contrast, graphene-based materials are produced at high temperatures in small amounts that can be tedious to work with. “With this stuff (HOIPs), you can make big batches in solution and coat a whole window with it if you want to,” Silva said.

Funhouse in an earthquake

For all an HOIP’s wobbling, it’s also a very ordered lattice with its own kind of rigidity, though less limiting than in the customary two-dimensional materials.

“It’s not just a single layer,” Srimath Kandada said. “There is a very specific perovskite-like geometry.” Perovskite refers to the shape of an HOIPs crystal lattice, which is a layered scaffolding.

“The lattice self-assembles,” Srimath Kandada said, “and it does so in a three-dimensional stack made of layers of two-dimensional sheets. But HOIPs still preserve those desirable 2D quantum properties.”

Those sheets are held together by interspersed layers of another molecular structure that is a bit like a sheet of rubber bands. That makes the scaffolding wiggle like a funhouse floor.

“At room temperature, the molecules wiggle all over the place. That disrupts the lattice, which is where the electrons live. It’s really intense,” Silva said. “But surprisingly, the quantum properties are still really stable.”

Having quantum properties work at room temperature without requiring ultra-cooling is important for practical use as a semiconductor.

Going back to what HOIP stands for — hybrid organic-inorganic perovskites – this is how the experimental material fit into the HOIP chemical class: It was a hybrid of inorganic layers of a lead iodide (the rigid part) separated by organic layers (the rubber band-like parts) of phenylethylammonium (chemical formula (PEA)2PbI4).

The lead in this prototypical material could be swapped out for a metal safer for humans to handle before the development of an applicable material.

Electron choreography

HOIPs are great semiconductors because their electrons do an acrobatic square dance.

Usually, electrons live in an orbit around the nucleus of an atom or are shared by atoms in a chemical bond. But HOIP chemical lattices, like all semiconductors, are configured to share electrons more broadly.

Energy levels in a system can free the electrons to run around and participate in things like the flow of electricity and heat. The orbits, which are then empty, are called electron holes, and they want the electrons back.

“The hole is thought of as a positive charge, and of course, the electron has a negative charge,” Silva said. “So, hole and electron attract each other.”

The electrons and holes race around each other like dance partners pairing up to what physicists call an “exciton.” Excitons act and look a lot like particles themselves, though they’re not really particles.

Hopping biexciton light

In semiconductors, millions of excitons are correlated, or choreographed, with each other, which makes for desirable properties, when an energy source like electricity or laser light is applied. Additionally, excitons can pair up to form biexcitons, boosting the semiconductor’s energetic properties.

“In this material, we found that the biexciton binding energies were high,” Silva said. “That’s why we want to put this into lasers because the energy you input ends up to 80 or 90 percent as biexcitons.”

Biexcitons bump up energetically to absorb input energy. Then they contract energetically and pump out light. That would work not only in lasers but also in LEDs or other surfaces using the optoelectronic material.

“You can adjust the chemistry (of HOIPs) to control the width between biexciton states, and that controls the wavelength of the light given off,” Silva said. “And the adjustment can be very fine to give you any wavelength of light.”

That translates into any color of light the heart desires.

The ConFab — an executive invitation-only conference now in its 14th year — brings together influential decision-makers from all parts of the semiconductor supply chain for three days of thought-provoking talks and panel discussions, networking events and select, pre-arranged breakout business meetings.

In the 2018 program, we will take a close look at the new applications driving the semiconductor industry, the technology that will be required at the device and process level to meet new demands, and the kind of strategic collaboration that will be required. It is this combination of business, technology and social interactions that make the conference so unique and so valuable. Browse this slideshow for a look at this year’s speakers, keynotes, panel discussions, and special guests.

Visit The ConFab’s website for a look at the full, three-day agenda for this year’s event.

KEYNOTE: How AI is Driving the New Semiconductor Era

Rama Divakaruni_June_2014presented by Rama Divakaruni, Advanced Process Technology Research Lead, IBM

The exciting results of AI have been fueled by the exponential growth in data, the widespread availability of increased compute power, and advances in algorithms. Continued progress in AI – now in its infancy – will require major innovation across the computing stack, dramatically affecting logic, memory, storage, and communication. Already the influence of AI is apparent at the system-level by trends such as heterogeneous processing with GPUs and accelerators, and memories with very high bandwidth connectivity to the processor. The next stages will involve elements which exploit characteristics that benefit AI workloads, such as reduced precision and in-memory computation. Further in time, analog devices that can combine memory and computation, and thus minimize the latency and energy expenditure of data movement, offer the promise of orders of magnitude power-performance improvements for AI workloads. Thus, the future of AI will depend instrumentally on advances in devices and packaging, which in turn will rely fundamentally on materials innovations.

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