The National Science Foundation has awarded $1.2 million to three research groups at Indiana University to advance research on self-assembling molecules and computer-aided design software required to create the next generation of solar cells, circuits, sensors and other technology.

This interdisciplinary team in the IU Bloomington College of Arts and Sciences’ Department of Chemistry is led by Amar Flood, Steven Tait and Peter Ortoleva in collaboration with Mu-Hyun Baik of the Korea Advanced Institute of Science and Technology, who previously served at IU.

Designing new materials at the molecular level is a key goal of the U.S. government’s Materials Genome Initiative, a project launched in 2011 to reduce the cost, and speed the creation, of these materials. As recipients of funds from the NSF’s Designing Materials to Revolutionize and Engineer our Future program, the IU scientists will contribute to this national initiative.

“There are more than 100 million known molecules, but in the vast majority of cases we cannot predict what sort of structure they will form when those molecules start packing together,” said Amar Flood, James F. Jackson Professor of Chemistry and Luther Dana Waterman Professor in the IU Bloomington Department of Chemistry, who is the principal investigator on the grant. “We want to be able to predict, as well as design, those structures.”

The results would represent a “transformative approach to the discovery of organic materials,” he said, combining computer-aided design, chemical synthesis and molecular characterization methods.

And recently, Flood and colleagues have shown such an ambitious goal is achievable.

In a paper published Nov. 23 in Chemistry–A European Journal, the IU scientists describe an innovative “one-pot” method to synthesize a new macromolecule called a tricarbazolo triazolophane, or “tricarb.”

A multifunctional, ring-shaped structure, tricarb molecules bear alignment markers so that they line up perfectly with each other upon contact to form highly organized, multilayered patterns. Tricarb molecules also have a central pocket to capture the negatively charged particles known as anions.

“Amar has developed a very elegant synthesis,” said Steven Tait, an associate professor of chemistry who is a co-author on the paper and also a co-investigator on the NSF grant. “The result is molecules that recognize each other in a very specific way to order and stack in beautiful, flower-shaped crystalline patterns with potentially transformative properties.”

The NSF-funded project will support creating molecular structures, like the tricarb molecule, that are specifically pre-programmed to self-assemble into three-dimensional structures that go beyond the comparatively simple, two-dimensional molecular arrangements.

“Creating building blocks that self-assemble into functional materials will be a major breakthrough in materials science and is a key component of the Materials Genome Initiative,” said Stephen C. Jacobson, chair of the IU Bloomington Department of Chemistry. “I am pleased that the NSF has recognized our faculty’s combined expertise in synthesis, characterization and theory in selecting them to contribute to this important initiative.”

Specifically, Flood said, the ability to alternate different molecules in highly ordered patterns is a key step in creating organic electronics, a new class of material whose applications include highly efficient solar panels and advanced computer circuitry.

“The best solar cells right now are made of extremely pure silicon, which requires a very precise — and expensive — production process,” Tait said. “But if we can create extremely pure, self-assembling organic materials, controlling the order of their interfaces and components at the molecular level, the performance of these organic materials will improve significantly, and their costs will go down.”

Most important for the creation of new molecular structures, the IU team will use the grant to develop computer-aided design software enabling virtual experimentation with the potential to examine the millions of molecular compounds of interest to material scientists.

Currently, Flood explained, scientists must engage in an arduous and time-consuming process of trial-and-error to design new structures with highly specialized properties since no blueprint exists for how molecules will react upon coming into contact with each other. But with virtual experimentation, molecular engineers could screen 100 potential molecular combinations over 100 days, only then devoting time and resources to synthesize the top five candidates, which can itself require about 100 days per compound, creating enormous time-savings.

“CAD software is prevalent in electrical, mechanical and civil engineering, and we need that same technology at our fingertips for molecular and materials engineering,” Flood said. “The innovations coming from our computational collaborators are key.”

These collaborations are with Ortoleva, a Distinguished Professor in the IU Bloomington Department of Chemistry who will help develop the CAD software using recent advances in multi-scale simulation that employ Baik’s work on atomic-level force fields.

“Ultimately, we plan to show experimentally how molecules can be programmed so that they assemble themselves into 2-D and 3-D arrangements, as well as produce a working, operational and accurate simulation software,” Flood added. “Our goal will be to achieve high fidelity between theory, design and experimentation.”

In the production of power, nearly two-thirds of energy input from fossil fuels is lost as waste heat. Industry is hungry for materials that can convert this heat to useful electricity, but a good thermoelectric material is hard to find.

Increasing the efficiency of thermoelectric materials is essential if they are to be used commercially. Northwestern University researchers now report that doping tin selenide with sodium boosts its performance as a thermoelectric material, pushing it toward usefulness. The doped material produces a significantly greater amount of electricity than the undoped material, given the same amount of heat input.

Details of the sodium-doped tin selenide — the most efficient thermoelectric material to date at producing electricity from waste heat — will be published Nov. 26 by the journal Science.

The Northwestern development could lead to new thermoelectric devices with potential applications in the automobile industry, glass- and brick-making factories, refineries, coal- and gas-fired power plants, and places where large combustion engines operate continuously (such as in large ships and tankers).

Most semiconducting materials, such as silicon, have only one conduction band to work with for doping, but tin selenide is unusual and has multiple bands; the researchers took advantage of these bands. They showed they could use sodium to access these channels and send electrons quickly through the material, driving up the heat conversion efficiency.

“The secret to our material is that multiband doping produces enhanced electrical properties,” said Mercouri G. Kanatzidis, an inorganic chemist who led the multidisciplinary team. “By doping multiple bands, we are able to multiply the positive effect. To increase the efficiency, we need the electrons to be as mobile as possible. Tin selenide provides us with a superhighway — it has at least four fast-moving lanes for hole carriers instead of one congested lane.”

Kanatzidis, a Charles E. and Emma H. Morrison Professor of Chemistry in the Weinberg College of Arts and Sciences, is a world leader in thermoelectric materials research. He is a corresponding author of the paper.

To produce a voltage, a good thermoelectric material needs to maintain a hot side — where the waste heat is, for example — while the other side remains cool. (A voltage can be harvested as power.) Less than two years ago, Kanatzidis and his team, with postdoctoral fellow Lidong Zhao as protagonist, identified tin selenide as a surprisingly good thermoelectric material; it is a poor conductor of heat (much like wood) — a desirable property for a thermoelectric — while maintaining good electrical conductivity.

Kanatzidis’ colleague Christopher M. Wolverton, a computational theorist, calculated the electronic structure of tin selenide. He found the electrical properties could be improved by adding a doping material.

“Tin selenide is very unusual, not only because of its exceedingly low thermal conductivity, but also because it has many conduction lanes,” said Wolverton, a senior author of the paper and professor of materials science and engineering in the McCormick School of Engineering and Applied Science. “Our calculations said if the material could be doped, its thermal power and electrical conductivity would increase. But we didn’t know what to use as a dopant.”

Sodium was the first dopant the researchers tried, and it produced the results they were looking for. “Chris’ computations opened our eyes to doping,” Kanatzidis said. He and Zhao successfully grew crystals of the new doped material.

The researchers also were pleased to see that adding sodium did not affect the already very low thermal conductivity of the material. It stayed low, so the heat stays on one side of the thermoelectric material. Electrons like to be in a low-energy state, so they move from the hot (high-energy) side to the cool side. The hot side becomes positive, and the cool side becomes negative, creating a voltage.

“Previously, there was no obvious path for finding improved thermoelectrics,” Wolverton said. “Now we have discovered a few useful knobs to turn as we develop new materials.”

The efficiency of waste heat conversion in thermoelectrics is reflected by its “figure of merit,” called ZT. In April 2014, the researchers reported that tin selenide exhibits a ZT of 2.6 at around 650 degrees Celsius. That was the highest ZT to date — a world record. But the undoped material produced that record-high ZT only at that temperature. (There is a ZT for every temperature.)

The new doped material produces high ZTs across a broad temperature range, from room temperature to 500 degrees Celsius. Thus, the average ZT of the doped material is much higher, resulting in higher conversion efficiency.

“Now we have record-high ZTs across a broad range of temperatures,” Kanatzidis said. “The larger the temperature difference in a thermoelectric device, the greater the efficiency.”

Just one century ago, entanglement was at the center of intense theoretical debate, leaving scientists like Albert Einstein baffled. Today, however, entanglement is accepted as a fact of nature and is actively being explored as a resource for future technologies including quantum computers, quantum communication networks, and high-precision quantum sensors.

Entanglement is also one of nature’s most elusive phenomena. Producing entanglement between particles requires that they start out in a highly ordered state, which is disfavored by thermodynamics, the process that governs the interactions between heat and other forms of energy. This poses a particularly formidable challenge when trying to realize entanglement at the macroscopic scale, among huge numbers of particles.

“The macroscopic world that we are used to seems very tidy, but it is completely disordered at the atomic scale. The laws of thermodynamics generally prevent us from observing quantum phenomena in macroscopic objects,” said Paul Klimov, a graduate student in the University of Chicago’s Institute for Molecular Engineering and lead author of new research on quantum entanglement. The institute is a partnership between UChicago and Argonne National Laboratory.

Previously, scientists have overcome the thermodynamic barrier and achieved macroscopic entanglement in solids and liquids by going to ultra-low temperatures (-270 degrees Celsius) and applying huge magnetic fields (1,000 times larger than that of a typical refrigerator magnet) or using chemical reactions. In the Nov. 20 issue of Science Advances, Klimov and other researchers in David Awschalom’s group at the Institute for Molecular Engineering have demonstrated that macroscopic entanglement can be generated at room temperature and in a small magnetic field.

The researchers used infrared laser light to order (preferentially align) the magnetic states of thousands of electrons and nuclei and then electromagnetic pulses, similar to those used for conventional magnetic resonance imaging (MRI), to entangle them. This procedure caused pairs of electrons and nuclei in a macroscopic 40 micrometer-cubed volume (the volume of a red blood cell) of the semiconductor SiC to become entangled.

“We know that the spin states of atomic nuclei associated with semiconductor defects have excellent quantum properties at room temperature,” said Awschalom, Liew Family Professor in Molecular Engineering and a senior scientist at Argonne National Laboratory. “They are coherent, long-lived and controllable with photonics and electronics. Given these quantum ‘pieces,’ creating entangled quantum states seemed like an attainable goal.”

In addition to being of fundamental physical interest, “the ability to produce robust entangled states in an electronic-grade semiconductor at ambient conditions has important implications on future quantum devices,” Awschalom said.

In the short-term, the techniques used here in combination with sophisticated devices enabled by advanced SiC device-fabrication protocols could enable quantum sensors that use entanglement as a resource for beating the sensitivity limit of traditional (non-quantum) sensors. Given that the entanglement works at ambient conditions and the fact that SiC is bio-friendly, one particularly exciting application is biological sensing inside a living organism.

“We are excited about entanglement-enhanced magnetic resonance imaging probes, which could have important biomedical applications,” said Abram Falk of IBM’s Thomas J. Watson Research Center and a co-author of the research findings.

In the long term, it might even be possible to go from entangled states on the same SiC chip to entangled states across distant SiC chips. Such efforts could be facilitated by physical phenomena that allow macroscopic quantum states, as opposed to single quantum states (in single atoms), to interact very strongly with one another, which is important for producing entanglement with a high success rate. Such long-distance entangled states have been proposed for synchronizing global positioning satellites and for communicating information in a manner that is fundamentally secured from eavesdroppers by the laws of physics.

In certain nanomaterials, electrons are able to race through custom-built roadways just one atom wide. To achieve excellent efficiency, these one-dimensional paths must be paved with absolute perfection–a single errant atom can stop racing electrons in their tracks or even launch it backwards. Unfortunately, such imperfections are inevitable.

Now, a pair of scientists from the U.S. Department of Energy’s Brookhaven National Laboratory and Ludwig Maximilian University in Munich have proposed the first solution to such subatomic stoppage: a novel way to create a more robust electron wave by binding together the electron’s direction of movement and its spin. The trick, as described in a paper published November 16 in Physical Review Letters and featured as an Editor’s Selection, is to exploit magnetic ions lacing the electron racetrack. The theory could drive advances in nanoscale engineering for data- and energy-storage technologies.

“One-dimensional materials can only be very good conductors if they are defect-free, but nothing in this world is perfect,” said Brookhaven physicist Alexei Tsvelik, one of two authors on the paper. “Our theory, the first of its kind, lays out a way to protect electron waves and optimize these materials.”

The work relies on a model system called a Kondo chain, where flowing electrons interact with local magnetic moments within a material. Properly harnessed, this powerful interaction could allow materials to behave like perfect conductors and offer high efficiency.

Protecting the transport

Atom-wide channels only allow motion in one of two opposing directions: right or left. Electrons traveling through such a narrow path–racing along in what are called charge-density waves–can be easily reversed by virtually any obstacle.

“The wave rises like an electronic tsunami that is expected to carry electrons smoothly in one direction,” Tsvelik said. “But it turns out that this tsunami can be very easily pinned by disorder, by impurities in the material.”

This “tsunami” shifts direction through a conductivity-smothering phenomenon called backscattering–like a wave breaking against sheer cliffs. But while direction is easily reversed, another feature of the electron is much more resilient: spin. The spin of an electron–like a perpetually spinning quantum top–can only be described as either up or down, and it is impervious to simple imperfections in the material. The trick, then, is to teach the directional wave to lean on spin for support.

“As the electrons flow, they interact with magnetic moments embedded in the material–these pockets of intrinsic magnetism are the key to producing the bound state,” said Ludwig Maximilian University physicist Oleg Yevtushenko, the other collaborator on the paper. “The magnetic moments bind spin and direction tightly together, so any disturbance would need to flip the electron’s spin in order to change its direction.”

These rolling electron waves could then be described as right-moving with spin up, left-moving with spin down, and so on. In each instance, the direction is bolstered by spin.

Building an electron bicycle

Imagine walking along a narrow path barely wide enough for both feet. In such a simple system, turning around is easy–one can pivot around at the slightest provocation.

“But what if we give our pedestrian a bicycle?” Tsvelik said. “It suddenly becomes very difficult to break that angular momentum and change directions–especially on such a narrow path. This bound spin-direction state is like our electron’s bicycle, keeping it rolling along powerfully enough to overcome bumps in the one-dimensional road.”

To verify the efficacy of this theoretical electron bicycle, scientists will need to apply this theory to stringent tests.

“The magnetic ions in materials such as cesium, iron, and manganese all make excellent candidates for generating and exploring this promising bound state,” Yevtushenko said.

The process of synthesizing functional one-dimensional materials–as thin metallic wires or paths conjured by chemistry–continues to evolve and push both theory and industry forward. Scientists in Brookhaven Lab’s Condensed Matter Physics and Materials Science Department and Center for Functional Nanomaterials specialize in similar one-of-a-kind atomic architectures.

“We hope our colleagues will leap at this challenge, especially as it’s the only method proposed to enhance flow at this 1D scale,” Tsvelik said. “Who knows where these fundamental concepts might lead? The wonder of science is that it brings surprise.”