Assistant Professor Longji Cui has received a prestigious  for research he hopes will improve the next generation of nanoelectronics and renewable energy technology.

As nanotechnology continues to miniaturize to near atomic scale, while simultaneously becoming more powerful, the need to understand heat transfer at the fundamental single molecule level becomes crucial. And yet the behavior of heat at the microscopic scale, and the ways in which it can be leveraged to make devices more efficient and less wasteful, is little understood.

With the help of this funding, Cui is looking to fill that knowledge gap. NSF CAREER Awards provide over $500,000 over a period of five years for early career faculty who are dedicated to research and education.

“One of the major challenges for the next generation of nanoelectronic devices is heat transport and dissipation,” Cui said. “When you’re at that smallest physical scale possible, heat is dissipating over a much smaller area, which makes the density of it even higher.”

Cui has remained focused on this problem throughout his academic career. In 2019, he published a groundbreaking paper in  called “,” which carried out the first study that measured thermal conductance through a single molecule.

Not only was Cui the first to make these measurements, but the tools and techniques with which he made them were of his own creation, too.

Cui developed a heat-detecting microscope that operates with sub-nanometer spatial resolution and picowatt (one trillionth of a watt) energy resolution. Called ultra-high resolution scanning thermal probe microscopy, or SThM, the microscope allowed Cui to carry out the measurements.

With the funding from the NSF CAREER Award, Cui will continue to push his research to the bleeding edge. In his experiments, Cui has begun to pioneer a new field called molecular phononics, which studies how certain quantum phononic effects could influence thermal transfer.

“Phonons are major carriers for thermal transport at the quantum level,” said Cui, “like electrons for electrical transport.”

Cui thinks a better understanding of different quantum electronic and phononic thermal effects could be crucial to improving heat dissipation and thermoelectric energy conversion at the microscopic level. 

This bottom-up approach to energy conversion could not only have outsized effects on the next generation of nanotechnology but on the field of renewable energy, too. Cui’s research will investigate how the conversion of heat to electricity at the molecular level could lead to a more efficient waste heat harvesting technology in the future.

“puts you in direct contact with some of the leading new fields in thermodynamics and quantum mechanics,” PhD student said. “He’s very ambitious.”

Cui wants the next generation of nanoengineers and thermal scientists to be at the vanguard of this research. He also wants to make sure that women and other groups underrepresented in engineering are a major part of this new generation.

“The cutting-edge fields of nano and quantum thermal engineering are something a mechanical engineer are perfectly suited for,” Cui said. “But first we need to update the curriculum.”

Cui is already teaching a class on quantum engineering for graduate students, but he wants to offer the class at the undergraduate level as well. Cui also plans on developing project-based, hands-on teaching modules for K-12 students that incorporate his expertise in ultra-high resolution scanning thermal probe microscopy.

 “Students know about the worlds of nano and quantum technology,” said Cui, “but we need to get it at their fingertips.”

Cui is a faculty member in the Paul M. Rady Department of Mechanical Engineering and the Materials Science and Engineering Program. Six faculty members from the College of Engineering and Applied Science received CAREER Awards in 2023.

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Engineers at ŷ���ڱ���Ƶ Boulder have designed a new, rubber-like film that can leap high into the air like a grasshopper—all on its own and without needing outside intervention. Just heat it up and watch it jump! 

The researchers Jan. 18 in the journal Science Advances. They say that similar materials could one day help embody “soft robots” (those that don’t need gears or other hard components to move) to leap or lift.

The material system responds a bit like how grasshoppers jump by storing and releasing energy in their legs, said study co-author Timothy White.  

“In nature, a lot of adaptations like a grasshopper’s leg utilize stored energy, such as an elastic instability,” said White, Gallogly Professor of chemical and biological engineering at ŷ���ڱ���Ƶ Boulder. “We’re trying to create synthetic materials that emulate those natural properties.”

The new research takes advantage of the unusual behavior of a class of materials called liquid crystal elastomers. These materials are solid and stretchy polymer versions of the liquid crystals found in laptops or TV displays. 

In the study, the team fabricated small wafers of liquid crystal elastomers about the size of a contact lens, then set them on a hot plate. As those films heated up, they began to warp, forming a cone that rose up until, suddenly and explosively, it flipped inside out—shooting the material up to a height of nearly 200 times its own thickness in just 6 milliseconds. 

“This presents opportunities for using polymer materials in new ways for applications like soft robotics where we often need access to these high-speed, high-force actuation mechanisms,” said study lead author Tayler Hebner who earned her doctorate degree in chemical and biological engineering at ŷ���ڱ���Ƶ Boulder in 2022.

Serendipitous discovery

Hebner, now a postdoctoral researcher at the University of Oregon, and her colleagues discovered this leaping behavior almost by accident. 

She was experimenting with designing different kinds of liquid crystal elastomers to see how they changed their shape under shifting temperatures. Joselle McCracken, a senior research associate in White’s lab, joined her to observe.

Graphic showing how a cone slowly builds up in an "elastomer" film, then inverts to launch the film high into the air over the span of less than a second. (Credit: Hebner et al., 2023, Science Advances; this work is licensed under )

“We were just watching the liquid crystal elastomer sit on the hot plate wondering why it wasn’t making the shape we expected. It suddenly jumped right off the testing stage onto the countertop,” Hebner said. “We both just looked at each other kind of confused but also excited.”

With careful experimentation and help from collaborators at the California Institute of Technology, the team discovered what was making their material do the high jump. 

White explained that each of these films are made up of three layers of elastomer. These layers shrink when they get hot, he said, but the top two layers shrink faster than the bottom one. That incongruity, combined with the orientation of the liquid crystal molecules within the layers, causes the film to contract and form a cone shape. It’s a bit like how painted vinyl sidings can warp in the sun’s rays. 

As the cone forms, strain builds up in the film until, all at once—snap! The cone inverts, slapping the surface and knocking the material up. The same film can also hop several times without wearing out. 

“When that inversion happens, the material snaps through, and just like a kid’s popper toy, it leaps off the surface,” White said. 

Leaps ahead

Unlike those poppers, however, the team’s liquid crystal elastomers are versatile. The researchers can tweak their films so that they hop when they get cold, for example, not hot. They can also give the films legs to make them jump in a particular direction.

Most robots probably wouldn’t be able to use this kind of popping effect to make their parts move. But White said that the project shows what similar kinds of materials could be capable of—storing an impressive amount of elastic energy, then releasing it a single go. And, Hebner said, the project brought a bit of fun to the lab.

“It’s a powerful example of how the fundamental concepts we study can transform into designs that perform in complex and amazing ways,” she said.

Grasshoppers, meet your new competition.

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Assistant Professor Mija Hubler is a recipient of a three year, $548,000 National Science Foundation (NSF) Faculty Early Career Development (CAREER) award for her proposal “.”&�Բ�����;&�Բ�����;

Major advances are being made in the study of living building materials that can be grown in the laboratory and could replace concrete, a significant driver of CO2 emissions in the construction industry 

“This research is about creating a mechanical model for living building material,” Hubler said. “The model will enable the design of structures and the engineering of living building material to achieve the desired performance needed for structural applications.” 

NSF CAREER awards support early career faculty who are dedicated to research and education. Hubler is using this project to integrate her education and research goals through the study of mechanics in civil infrastructure materials, as well as to improve the recruitment and retention of female and non-traditional students in research and innovation career tracks. 

“These activities can help meet a growing workforce demand and support cross-disciplinary innovation for infrastructure materials,” Hubler said. “I hope to grow interest in research careers from a broad audience in this area in part by working with ŷ���ڱ���Ƶ Mesa University to engage students there in working with living building materials.” 

Hubler said that using living building materials for structural applications will help replace concrete as the main building material used in construction today. 

“Living building material does not require cement, which is the binding ingredient of concrete that drives its large carbon footprint,” Hubler said. “It is much more crack resistant than concrete and enables material recycling.” 

Alternatives to concrete are of interest to civil engineers and the construction industry to address both building durability concerns and CO2 impact. Although past new construction materials have been rejected due to lacking the mechanical properties and behavior of traditional materials, Hubler said living building materials show major promise. 

“I have been inspired to better understand what features of the material control the mechanics to engineer new materials to better meet expectations, and also to develop mechanical models of new construction materials to enable them to be adopted into design practices,” Hubler said. 

Hubler believes that the model her group will develop will also be applicable to other novel materials, including reinforced metal foams and stabilized soils. She anticipates developing a practical model for living building materials within the next two years, with a five-year goal of using the model to design a full-scale beam composed of living material. 

Hubler is a faculty member at the Department of Civil, Environmental and Architectural Engineering and the Materials Science and Engineering Program and serves as the Co-Director of the Center for Infrastructure, Energy and Space Testing. Six faculty members within the College of Engineering and Applied Science received CAREER Awards from the National Science Foundation in 2022.

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McGehee, Toney and Yin

Three Materials Science and Engineering faculty members were recognized by Clarivate as this year. Clarivate recognizes "the production of multiple highly-cited papers that rank in the top 1% by citations for field and year" via their .

The three faculty recognized were Professor Michael McGehee, Professor Michael Toney and Assistant Professor Xiaobo Yin.

Professor Michael McGehee of the Department of Chemical and Biological Engineering, Renewable and Sustainable Energy Institute and the National Renewable Energy Laboratory specializes in perovskite solar cells and dynamic windows with adustable tinting for sustainable energy production and efficiency.

Professor Michael Toney of the Department of Chemical and Biological Engineering focuses on studying the underlying physics and chemistry of materials for sustainable energy, as well as the social justice implications of clean energy.

Assistant Professor Xiaobo Yin of the Paul M. Rady Mechanical Engineering Department specializes in nanomaterials and metamaterials, synthetic materials with novel properties and mechanic and electronic properties not found in nature.

These researchers were among 17 faculty from ŷ���ڱ���Ƶ Boulder recognized this year.

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Associate Professor Wil Srubar recently participated in the "Pride in Stem: A Conversation about Research, Mentorship and Advocacy" panel, a National Science Foundation Distinguished Lecture. The panel included NSF staff from the Office of Diversity and Inclusion, the LGBTQ+ and Allied Employee Resource Group and fellow NSF CAREER awardees who have demonstrated committment to the LGBTQ+ community through their work.

[video:https://www.youtube.com/watch?v=csGPpb0pUs8]

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Professor Stephanie J. Bryant was recently elected by her fellow Materials Science and Engineering faculty to lead the program as its new director, starting on July 1.

“I am deeply honored that the MSE faculty has entrusted me to lead the program,” Bryant said. “The MSE faculty members span multiple departments across the College of Engineering and Applied Science and the College of Arts and Sciences, which makes the nomination an even greater honor. The faculty is committed to this program and its success, and I’m truly excited to work with them to build an even stronger MSE community.”

Bryant aims to grow the PhD and professional MS programs while increasing the diversity of the program’s student population. She plans on enhancing their training and education experiences while fostering a greater sense of community.

“The MSE program has some of the world’s leading experts in areas such as energy, soft matter and biomaterials,” Bryant said. “My vision is to help the MSE faculty build Centers of Excellence over the next few years, which will elevate ŷ���ڱ���Ƶ Boulder’s national and international reputation in the field.”

The outgoing director, Professor Robert McLeod, is confident he is leaving the program in good hands.

“Dr. Bryant has been with the program from its inception, and led many of the efforts that are now pillars of the program,” McLeod said. “She is an extremely accomplished materials scientist as well as passionate about student success. I have no doubt that the program will continue to flourish under her leadership.”

In a collegewide announcement, interim Dean Keith Molenaar emphasized Bryant’s dedication to the program as a founder and associate director, as well as her qualifications as a researcher and leader.

“Professor Bryant is a leading expert in biomaterials and functional tissue engineering, with collaborative professional ties across campus and the nation,” Molenaar said. “I am confident that her vision and leadership will inspire the MSE faculty to a new level of excellence.”

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