Symposium X—MRS/The Kavli Foundation Frontiers of Materials

Taeghwan Hyeon, Seoul National University

Designing Inorganic Nanomaterials for Energy and Soft-Electronics Applications

Written by Elizabeth Wilson

Taeghwan Hyeon is a prolific materials scientist, with over 400 publications and 74,000 citations under his belt. At Thursday’s Symposium X, Hyeon, who is with Seoul University, took his audience on a tour of recent highlights in his over-30-year career, including advances in fuel cell materials, and soft electronics for heart failure, while always stressing the importance of collaboration with his many colleagues.

Proton-exchange membrane fuel cells are the future of energy for transportation, Hyeon said. But the  catalysts required to produce hydrogen rely on rare, expensive platinum. “It’s impossible to get a good quality fuel cell electrode out of non-platinum materials,” he said. They key, then, is to use less of it, and increase its activity. Many groups are working on this issue. Hyeon’s group’s angle was to develop nanoparticles made of platinum iron alloys. However, the synthesis requires heating the nanoparticles, which causes the nanoparticles to coalesce into larger particles. Their solution was to coat the nanoparticles with polydopamine before heat treatment, which protects the particles, and they remain small. The result is a fuel cell that loses only 3% activity after 100 hours operation, a record high 10 times higher activity than some other similar catalysts. 

Hyeon’s curiosity has also drawn him to materials with medical applications, in particular, heart failure. Heart disease is the leading cause of death in the U.S., and one third of those deaths are caused by heart failure. As a heart fails, it pumps less and less efficiently. Since the heart's activity is based on electrical impulses, soft-electronic materials that can be shaped around the organ hold promise to bolster the faltering activity of a failing heart. Hyeon’s groups took inspiration from recent work in which scientists transplanted a pig heart into a human. Although the patient survived only three months, it showed that pig hearts, which are similar to human hearts, can be used for experiments on soft-electronic materials.

Hyeon’s collaborative group first developed a stretchable, conductive cardiac mesh out of silver nanowires impregnated in rubber. They placed it on a rat heart, and showed the material could be used to pump blood over 50% more efficiently than the heart itself. Silver oxidizes easily, and the oxidized coating is not only toxic, it does not conduct. The group solved that problem by coating the wire with inert gold. They then wrapped the meshes around a pig heart. They were able to pinpoint areas where the heart was having problems, and apply electricity where it was needed.

Hyeon has many other irons in the fire, including the development of a photocatalytic enzyme that splits water to produce hydrogen. Current hydrogen production technologies are environmentally unfriendly, so his group is developing a catalyst that mimics the activity of a bacterial hydrogenase.

How does Hyeon manage such a wide variety of research projects? Collaboration, he said. “You cannot do it all.”

Other than his work, Hyeon's other passion is tennis. “I'm either in my office or on the tennis court,” he said.

Symposium X—MRS/The Kavli Foundation Frontiers of Materials features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.

 

Inorganic Nanomaterials for Energy and Soft-Electronics | MRS Symposium X

 

MRS TV talks with Spring 2023 Symposium X—MRS/The Kavli Foundation Frontiers of Materials featured speaker, Taeghwan Hyeon about his talk, "Designing Inorganic Nanomaterials for Energy and Soft-Electronics Applications."

Symposium X—MRS/The Kavli Foundation Frontiers of Materials

Kristin Persson, Lawrence Berkeley National Laboratory & University of California-Berkeley

The Era of Data-Driven Materials Innovation and Design

Written by Alison Hatt

At Wednesday’s Symposium X, Kristin Persson talked about the exciting era of data-driven materials innovation and design powered, in part, by the Materials Project, a research program that is revolutionizing materials research by leveraging the power of supercomputers and big data.

Creating a new material with specific properties has historically been slow, time consuming, resource intensive, and limited by human ingenuity. However, the past several decades have seen an explosion in computational materials capabilities, producing vast quantities of data and leading Persson to speculate, early in her career, about new ways of approaching materials design.

“Can we do accelerated learning on this simulated data?” asked Persson. “Can we correlate elastic tensors, dielectric tensors, and behaviors of materials, back to their crystal structure and their chemistry, and become smarter about where we go to look for new materials with specific properties?”

Those speculations drove Persson to create the Materials Project, a program that combines high-throughput calculations and databases of calculated and measured materials properties to enable rapid screening and identification of promising candidates for various applications. This data-driven approach has the potential to accelerate the discovery of new materials with tailored properties, saving time and resources compared to traditional synthetic methods.

“Because we don’t have a hundred years to figure out some of our problems,” Persson said. “We have to be faster. We cannot do materials design as we have in the past.”

To illustrate the power of the Materials Project approach, Persson described a project to create a better photoanode for artificial photosynthesis, to meet precise criteria for the electronic structure and photochemical stability. Using the Materials Project tools, they identified a few thousand compounds that met some broader criteria, further filtered the list down to about 400 compounds, and then performed focused calculations to narrow those down to 34 compounds that met their more specific criteria. Working with John Gregoire at Caltech, the researchers rapidly synthesized the candidate compounds using inkjet printing, and identified 16 that met the stated criteria.

In a second example, Persson described efforts to find a lead-free piezoelectric material. Using a similar process, the team identified a potentially unstable phase of strontium hafnium oxide compound that met their criteria but presented substantial synthetic challenges. Collaborators at National Renewable Energy Laboratory eventually made the compound, but the entire process took two years, far slower than Persson envisions for the future of materials discovery.

The two examples highlighted the impact of experimental bottlenecks on the accelerated materials design process. Persson shared a vision for improving the process through automated synthesis capabilities, wherein the details of large numbers of experiments, both successful ones and failures, are recorded and made available to the broader community. She went on to reveal that last month, Gerd Cedar’s group at Lawrence Berkeley National Laboratory took their new tool for automated synthesis online and synthesized 39 completely new compounds from Materials Project predictions in just three weeks.

However, Persson also acknowledged the challenges and limitations of data-driven materials research. She emphasized the need for continuous efforts to improve the accuracy and reliability of computational methods, as well as the availability and quality of materials data. She also addressed the glittering promise of machine learning, which seems poised to revolutionize the field, and cautioned that we must use ML judiciously and not attempt to extrapolate beyond the available, real data.

Persson closed by lauding the power of the Materials Project to democratize materials data, as its powerful tools and vast databases can be used, for free, by researchers in any part of the world.  Faster, more powerful, and more equitable: it’s a compelling vision for the future of materials research.   

Symposium X—MRS/The Kavli Foundation Frontiers of Materials features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.

Data-Driven Materials Innovation and Design with Kristin Persson

MRS TV talks with Kristin Persson, the Daniel M. Teller Distinguished Professor at the University of California, Berkeley, and the Director of the Molecular Foundry, a user facility at Lawrence Berkeley National Lab. She is the Director and founder of the Materials Project, a world-leading resource for materials data and design, and shared her talk "The Era of Data-Driven Materials Innovation and Design" at Wednesday's Symposium X.

Symposium X—MRS/The Kavli Foundation Frontiers of Materials

50 Years of Materials Research

Written by Elizabeth Wilson

In the past 50 years, materials science advances, from cell phones to solar panels, have literally changed the world. At the Symposium X session, a group of past MRS presidents and journal editors chose their favorite past breakthroughs, including high temperature superconductors, conducting polymers, advances in microscopy, and solar technology.

But the group’s vision is united in what lies ahead: they predict artificial intelligence and deep learning will be crucial for solving ever more complex problems. And with climate change, sustainability and other world-wide issues, they foresee a sea change in how materials scientists approach problems. No longer can they afford to pursue developments without first considering their global implications. “There will be a huge transformation in the way materials scientists approach their work—to start to ask questions at the beginning,” said moderator Carolyn R. Duran, who is with Intel Corporation, and is immediate past MRS president.

The history of materials science has been undeniably rich. Some developments have progressed gradually, but high temperature superconductivity, “came out of the blue,” said Julia M. Phillips retired from Sandia National Laboratories. “This was one of the true revolutionary, as opposed to evolutionary advances,” she said.  First reported by IBM scientists in 1986, and which received the Nobel Prize in Physics in 1987, the discovery changed the way scientists think of materials. Their complex structures unleashed a flood of research on new materials, including magnetic oxides and perovskites. And advances in theory and simulation are now helping to guide experiments, rather than simply validate results, she said.

Conducting polymers are another materials science success story, said Rigoberto Advincula, at Oak Ridge National Laboratory and editor in chief of MRS Communications. Though research on conducting organic compounds began in the 1950s, it was the late 1970s and early 1980s that saw a breakthrough in the discovery of stable polymers that could compete with copper and other metals, Advincula said. The discovery won the 2000 Nobel Prize in Chemistry. Now, the field is flush with developments in organic light-emitting diodes and flexible electronics. “If you have a smart phone, or a TV with an LED screen, that is really the product of this period,” he said.

Much of the exploration of new materials is possible thanks to advances in the ability to look at them, even at the atomic level, said Susan Trolier-McKinstry, at The Pennsylvania State University; these include electron microscopy, aberration correction in microscopy, new ways of controlling electron beams, massive advances in the ability to resolve space and time.

Peter F. Green, at the National Renewable Energy Laboratory, highlighted progress in perovskite solar cell technology. First developed in 2009-2012, they are the highest efficiency solar cell ever made on plastic. Their efficiencies have increased from 3.8% in 2009 to almost 30% today. Their light weight, long lifetimes, and high defect tolerances make them attractive for many solar applications, including space missions. Scientists are hoping production can be scaled up cheaply and widely commercialized.

Looking toward the next 50 years in materials science, all research will be accelerated by advances in artificial intelligence, machine learning, and deep learning, the group agreed.

With this power comes responsibility. Scientists are now thinking about how their research affects society and the impact on the world, Phillips said, “not just this really cool materials research problem.” Doing this, she added, requires bringing in disciplines beyond sciences and engineering, including the social sciences and the people who will be impacted and the planet itself.

Crucial to this philosophical shift, the group agreed, will be to engage students in STEM early in their education, even elementary school. “Materials science is a great entry point for young kids,” said Phillips.

Symposium X—MRS/The Kavli Foundation Frontiers of Materials

Elisabeth Bik, Harbers Bik LLC

The Dark Side of Science: Misconduct in Biomedical Research

Written by Alison Hatt

In her Symposium X presentation, Elisabeth Bik talked about her efforts to identify and address misconduct in the scientific literature. “Science should be self-correcting,” she said, “and I try to be part of that process, because that’s going to make science better.” 

Science misconduct can take the form of plagiarism, falsification, or fabrication of data. Much of Bik’s work has focused on inappropriate image duplication, in which authors use the same image or data set multiple times to represent different experiments or results, often altering or repositioning elements using image-editing software. While most of her work is focused on the biomedical field, Bik showed several concerning examples from materials science publications where, for example, the same x-ray diffraction pattern appeared to be used to represent different materials compositions or a micrograph was clearly a composite image of the same few nanoparticles repeated over and over again.

Bik shared results of a study where she scanned more than 20,000 biomedical papers by eye and identified duplicated images in 4% of them, about half of which appeared to be cases of misconduct. Disappointingly, reporting these papers to the journals in which they appear does little to solve the problem. Of hundreds of papers Bik has reported, only about a third get retracted or corrected, and in most cases the journal takes no action. And even when journals do act, they tend to do so slowly, often allowing fraudulent papers to remain in the scientific literature for five or more years in the meantime.

Disillusioned by this response, Bik now posts her concerns to the website PubPeer.com rather than reporting to the individual journals. She encouraged the audience to install the freely available PubPeer extension that identifies papers that have received comments from the community, so researchers can avoid building their own work on problematic data.

The individual researchers who commit misconduct are typically driven by desperate situations, Bik noted, saying that behind every misconduct case is a sad story. Researchers may be subject to unrealistic requirements or expectations of their employers, or they could be junior researchers working under a bullying professor who demands results. Bik is more critical of the journals that allow papers to pass through peer review without apparent scrutiny and institutions that impose strict mandates on the number of publications needed for career advancement.

Bik is also critical of papermills that sell fake articles written by ghostwriters using fabricated data. She showed an example of an identical data set appearing in several very different papers. Another approach used by papermills is synonymized plagiarism, in which an article is copied verbatim but every word or phrase is replaced by a synonym, resulting in bizarre but comprehensible prose.

The rise of advanced computing and artificial intelligence complicates matters. Computer programs can more rigorously scour publications to identify duplicated images and problematic data, but their results are prone to false positives and need to be validated by humans. Meanwhile, AI is getting increasingly good at creating fake pictures and will almost certainly be capable of generating images for research articles that won’t be easily detected by journals or reviewers.

Bik presented several measures to help prevent misconduct in scientific literature. We should continue the trend toward open science, where researchers share full data sets and not just the snippets that appear in articles. Culturally, we should reduce our emphasis on publications as measures of research productivity and focus on mentoring students and junior researchers in good research methods. Reports of misconduct should be resolved quickly by journals and not allowed to remain in the literature, and strong consequences should be imposed on those who commit misconduct. Journals should also take greater responsibility for checking the papers they publish. Finally, the people who report misconduct need to be protected from retaliation, as the work is a necessary part of the self-correcting scientific process. 

Symposium X—MRS/The Kavli Foundation Frontiers of Materials features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.

Symposium X—MRS/The Kavli Foundation Frontiers of Materials

Xinliang Feng, Technische Universität Dresden

Advances in Organic 2D Crystals—From On-Water Surface Chemistry to Functional Applications.

Written by Vineeth Venugopal

In his Symposium X presentation,  Xinliang Feng of the Technische Universität Dresden spoke about inorganic two-dimensional (2D) crystals such as dichalcogenides, boron nitride, black phosphorus, metal oxides, and nitrides beyond graphene. He noted that there has been much less development in organic 2D crystalline materials, including the bottom-up organic/polymer synthesis of graphene nanoribbons, 2D metalorganic frameworks, and 2D polymers/supramolecular polymers, as well as the supramolecular approach to 2D organic nanostructures. 

Organic two-dimensional soft matter are 2D nanostructures that can be easily deformed by thermal stresses or thermal fluctuations at about room temperature. They include graphene oxide, 2D supramolecular organic nanoarchitectures, from surface synthesis, amphiphile, colloids, biomembrane, and liquid crystal. Organic 2D materials can include synthetic graphene, 2D polymers/supramolecular polymers, single/ few layer 2D COFs/MOFs, and crystalline polymer nanosheets, for example. These have applications, for example, in energy storage, photo/electro catalysis, sensors, superconductivity, topological insulators, and spintronics. 

Recently, Feng’s research group observed fractional edge excitations in nanographene spin chains. This has led to work on G-nanostructures and organic 2D materials such as 2D polymers and conjugated polymers. 

One of the central chemical challenges is to realize a controlled polymerization in two distinct dimensions under thermodynamic/kinetic control in solution and at the surface/interface. In this talk, Feng presented his group’s recent efforts in bottom-up synthetic approaches toward novel organic 2D crystals with structural control at the atomic/molecular level. On-water surface synthesis provides a powerful synthetic platform by exploiting surface confinement and enhanced chemical reactivity and selectivity. 

Feng presented a surfactant-monolayer-assisted interfacial synthesis (SMAIS) method that is highly efficient to promote programmable assembly of precursor monomers on the water surface and subsequent 2D polymerization in a controlled manner. Two-dimensional conjugated polymers and coordination polymers belong to such materials classes. The unique 2D crystal structures with possible tailoring of conjugated building blocks and conjugation lengths, tunable pore sizes and thicknesses, as well as impressive electronic structures, make them highly promising for a range of applications in electronics, optoelectronics, and spintronics. Other physicochemical phenomena and application potential of organic 2D crystals, such as in membranes, were also discussed.

Symposium X—MRS/The Kavli Foundation Frontiers of Materials features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.

Symposium X—MRS/The Kavli Foundation Frontiers of Materials

Suman Datta, Georgia Institute of Technology

Plenty of Room at the Top and Bottom

Written by Alison Hatt

In Thursday’s Symposium X symposium, Suman Datta took the audience through two decades of his work on transistor technologies and highlighted some formidable challenges currently on the horizon. His talk was titled, “Plenty of room at the top and bottom,” and he stressed that early-career scientists entering the field today will still find ample research opportunities for decades to come. “No matter what you hear in the press about things coming to an end,” he said, “the semiconductor industry is actually pretty healthy.”

When Datta’s career was starting in the early 2000s, the semiconductor industry was in the era of “geometric scaling,” continually reducing the dimensions and operating voltages of transistors in order to improve performance and fit ever more transistors on a chip. In his early work at Intel, Datta and colleagues brought transistor dimensions down almost to single-digit nanometer scales, developing a 10 nm silicon transistor using spacer lithography. The device pushed the boundary of what was possible at the time but had major technological problems, including direct tunneling of current through the very thin gate oxide, which meant the transistor effectively couldn’t be shut off.

The team (and the broader field) realized they needed to find other ways to scale the technology and started pursuing new approaches to improving transistor performance, resulting in three key innovations. First they developed innovative ways to introduce strain into the transistors to change the effective mobility and velocity of carriers in the channel. Next they replaced the silicon dioxide with high-k transition metal oxides to overcome reductions in mobility caused by phonon scattering. Finally they changed the planar transistor geometry to a non-planar configuration, referred to as tri-gate or FinFET.

As he described each of these innovations, Datta noted a recurring theme whereby the solution to one challenge would often bring other unexpected benefits through a kind of technological serendipity.

Today the industry is in a mode Datta described as “hyper scaling,” where dimensions of transistors are on the order of Angstroms. He described efforts needed to fabricate the increasingly complex geometries involved and the challenges of thermal management when delivering power to billions of transistors in a single chip.

While advances in transistor performance continue to grow our logic capabilities, Datta noted that we’re now coming up against a memory bottleneck. Conventional computers make data locally available to logic cores by moving it from off-chip DRAM into a local cache (SRAM) that can be accessed with very high internal bandwidth. However, applications like training neural networks require enormous amounts of data that can’t fit in a local cache, creating a bottleneck in how fast the data can be accessed on off-chip memory. Datta discussed his work developing embedded on-chip DRAM, stacking up cache memory directly on the chip instead, which comes with a plethora of technological challenges. He also discussed efforts to reduce data-shuttling needs by performing some logic in the memory itself, again highlighting areas rich with research challenges for young researchers.

Datta identified a list of needs to maintain compute performance gains in the coming decades: accelerated development of materials with tailored properties; monolithic three-dimensional technologies for logic, memory, power delivery, and thermal management; design automation to help assemble mix-and-match technologies; and co-optimization of devices, circuits, systems, and applications for maximal use of hardware resources.

Symposium X—MRS/The Kavli Foundation Frontiers of Materials features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.

Symposium X—MRS/The Kavli Foundation Frontiers of Materials

Jennifer A. Hollingsworth, Los Alamos National Laboratory

From Flask to Devices—The Making of Exceptionally Functional Colloidal Quantum Dot Emitters

Written by Don Monroe

In her Symposium X talk, Jennifer Hollingsworth discussed designing and making nanocrystal quantum dots that could potentially address the demanding requirements of quantum information technology.

The optical transitions in semiconducting quantum dots are shifted to higher energies by quantum confinement of their electrons and holes. Their optical properties can therefore be tuned by changing their size, typically a few nanometers in diameter. Colloidal synthesis techniques, such as successive ionic layer adsorption and reaction (SILAR) provide “angstrom-level control over size,” notably for CdSe. Quantum dots have many applications involving photon conversion, emission, and photocarrier generation.

For quantum computing, defect states like the “NV” center in diamond feature coupled spin and visible-light degrees of freedom that could be useful for quantum information processing. Hollingsworth asked whether an “artificial NV center” might be made through chemistry, with the spin degree of freedom of a metal-containing molecule coupled to the polarized emission of a separately optimized quantum dot. The strict requirements for the quantum dot are challenging however, including on-demand, tunable emission of near-infrared “telecom” wavelengths with high purity, brightness, and directionality. The devices will also need to be integrated with devices, and indistinguishability of the photons is “probably the most challenging factor that we face,” Hollingsworth said.

CdSe nanoparticles coated with a thin CdS shell historically had problems with “blinking” (going dark and recovering) and “bleaching” (getting progressively dimmer). Hollingsworth attributed these issues to two mechanisms: non-radiative Auger recombination that imparts the energy to a nearby electron instead of a photon and trapping of photoexcited carriers in surface states. More than a decade ago, she and others dramatically reduced these effects using thick CdS shells, 15-20 nm in thickness, to make “giant quantum dots.”

A second important design tool is the band offsets between the core and shell. “Type I” offsets confine both the electrons and holes to the core, while “Type II” only confines one carrier. A related approach uses a graded transition between core and shell rather than an abrupt one. With these new design parameters, Hollingsworth and her colleagues have explored an entire family of giant quantum dots. The improved stability opened a range of applications, such as long-term single-molecule tracking.

She also studied the differences between the “very tedious” monolayer-by-monolayer SILAR method and an alternate “continuous injection” method. Although both methods avoid blinking and bleaching, there are other important differences, where she traced different numbers of stacking fault, chemical terminations, and alloying. An even better hybrid method starts with SILAR but ends with continuous injection and a long anneal. “We have achieved on-demand single-photon sources,” Hollingsworth said.

CdSe quantum dots are limited to the visible, but giant quantum dots with a PbS core emit at room temperature in the near-infrared telecom bands around 1.3 micron and 1.5 micron, which is desirable for optically transmitting quantum information.

Hollingsworth also described advances in the brightness toward the roughly 10⁹ photons per second needed for quantum information. One approach exploits the localized surface plasmon resonance of a nearby conductive particle to enhance the spontaneous emission rates. However, the popular noble-metal particles do not support these resonances in the infrared, so researchers are looking at other materials, including tunably doped semiconductors and the spinel magnetite_.

Unfortunately, this plasmonic technique enhances the nonradiative rates as well as the radiative rates, Hollingsworth said. To enhance only the radiative rate, she collaborated with Maiken Mikkelsen’s group at Duke University to couple quantum dots to nanopatch antennas, reducing the radiative lifetime from microseconds to nanoseconds—yielding nearly a thousandfold brightness increase—or even shorter.

She also collaborated with Ronen Rapaport of the Hebrew University of Jerusalem, using dip-pen lithography to place quantum dots in the center of a bullseye antenna. These techniques enhance the brightness and produce directed emission that enhances collection efficiencies.

Hollingsworth sees paths forward in achieving better photon purity and device integration. To achieve the longer-term challenge of indistinguishable photons, she said, “we need to combine strategies of synthesis and integration.”

Symposium X—MRS/The Kavli Foundation Frontiers of Materials features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.

Symposium X—MRS/The Kavli Foundation Frontiers of Materials

Jian Cao, Northwestern University

Physics-based AI-assisted Property Control in Metal Additive Manufacturing

Written by Sophia Chen

During Tuesday’s Symposium X, mechanical engineer Jian Cao of Northwestern University described research efforts to incorporate machine learning and simulation to improve the technology’s consistency in a talk titled “Physics-based AI-assisted Property Control in Metal Additive Manufacturing.”

In metal additive manufacturing, machines build a metal component layer by layer out of metallic powder or wire and fuse the layers using heat from lasers, electron beams, or other sources. The technology, popularly known as metal 3D printing, dates back to the 1990s, when engineers first used the 3D printed components for rapid prototyping and testing.

Today, engineers use the technology to create components for aerospace, biomedical, and automobile applications. In the last decade or so, metal 3D printing has begun to play a role in final production. However, scalability poses an issue, as the printed components lack consistency. One prototype may have vastly different mechanical properties than another ostensibly identical component.

Cao’s group studies how machine learning and physics simulations could help the metal additive manufacturing process be more consistent. Her talk centered on “how mechanics and AI work together for manufacturing process, design, modeling, and control,” she said. The physics and AI-based modeling predicts how the powder or wire melts and cools, which in turn determines the component’s mechanical properties. Based on those predictions, the researchers can adjust the manufacturing process to achieve the mechanical properties they want.

For example, Cao’s group recently devised a process that used both machine learning and physics to reduce the number of holes that form between metal layer. The holes constitute an undesirable property known as porosity that weakens the material. One way to control the material’s porosity is to make the melt pool—the area of the component that the laser melts—as consistently as possible.

The physics-based strategy involved numerically simulating the melt pool. Porosity is related to the geometry of the melt pool, Cao explained. To accurately simulate melt pools, the researchers first conducted high-speed x-ray imaging of the 3D printing process at the Advanced Photon Source at Argonne National Laboratory in Illinois. Specifically, they studied a metal 3D printing process known as directed energy deposition. In their setup, focused heat from a laser melts metal powder.

Cao’s team studied how the laser scanning speed, the rate of deposition, among other variables, affected the printed component’s porosity. To study these variables more efficiently, they developed a high-throughput setup that could easily adjust the parameters of the 3D printing process. Using these x-ray images, they characterized the geometry of the melt pool and the pores that formed. In addition, they simulated the depth of the melt pool. The researchers found that by controlling the laser’s intensity, they could produce a melt pool with more consistent depth, and thus control the porosity.

They then took samples out of the materials produced in this process and correlated the material’s mechanical properties with how it cooled, also known as its thermal history. This was the AI part of the process, as they used a purely data-driven algorithm known as a random forest without incorporating any physics knowledge. Using this information, the researchers created a type of AI model called a neural network which they combined with a physics model that could control the material’s thermal history.

In the future, the field needs to work on bridging designers with manufacturers, said Cao.  In particular, she highlighted the need for databases between the two groups. “Materials science has been doing pretty well to generate common databases,” she said. “On the manufacturing side, not really. This is something that we need to catch up.”

In addition, the field needs to continue developing new techniques to measure and characterize the process, an area Cao refers to as functional metrology. They need new ways of determining what kinds of flaws are permissible, beyond studying the melt pool geometry and the texture of the surface.

Symposium X—MRS/The Kavli Foundation Frontiers of Materials features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.