Michael D. Dickey - US grants

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."

The objective of this research is to investigate microfluidic technology as a platform for highly flexible antennas and electronics. The approach is to fill flexible, elastomeric microchannels with a liquid metal that has unique rheological properties. These properties allow the liquid metal to maintain mechanical stability in the channels and to flow in response to deformation (stretching, flexing, wrapping) to ensure electrical continuity while providing significant tunability and conformability.

The proposed devices represent a significant improvement from conventional copper antennas, which cannot be stretched beyond ~2% strain without inducing irreversible damage. This collaborative project will have an impact on applications ranging from wireless devices to biomedical electronics. The research will provide a better understanding of the characteristics and limitations of the proposed systems, and will allow this technology to be incorporated into complex antenna architectures.

The proposed interdisciplinary research will benefit society by leading to advanced electronics that are (i) wearable, (ii) surface conformal, (iii) responsive to external stimuli, and (iv) durable / self-healing. Underrepresented students and undergraduates will be actively recruited for this project through established programs at NCSU. A prototype antenna will be developed as an outreach tool for presentations at the Engineering Open House and NCSU Undergraduate Research Symposium, which collectively attracts more than 1,500 high school and community college students and their parents to campus each year.

The research objective of this Faculty Early Career Development (CAREER) award is to identify the fundamental surface properties of a micromoldable liquid metal. The liquid metal is a low toxicity, gallium-based fluid with a low viscosity (like water) at room temperature. It forms a thin, solid 'skin' of oxide on its surface that allows the liquid to be micromolded into desirable shapes (e.g., wires, antennas) that may be useful for flexible electronics. The micromolded metal is stabilized mechanically by the skin, which dictates the electrical, mechanical, and chemical properties of the surface of the metal. The research will explore the fundamental properties of this surface and identify means of manipulating, modifying, and tuning it to form functional electronics with surface-dictated properties. For this project, new surface sensitive techniques will be developed and used to thoroughly characterize the unique properties of the skin of oxide on the liquid metal.

If successful, the research will enable the fabrication of soft, flexible, and stretchable electronic components with tunable properties. Example applications include soft electrodes for molecular electronics, deformable antennas, and electrical components for microfluidic devices. Devices made possible by the research will offer the advantages of durability and flexibility, and will be simple to fabricate. The research will be integrated into a new course at NC State and graduate and undergraduate engineering students will benefit directly from involvement in the research. An interactive module that discusses the research within the context of popular movies will be presented annually to an established program at NC State that aims to interest 11- to 14-year-old African-American and Hispanic boys in higher education and careers in science.

Objective: This proposal is for a new electron beam lithography and imaging system to augment the nanoscale fabrication capabilities at NC State University for a wide range of applications and users.

Intellectual Merit: This acquisition proposal is expected to lead to high-performance nano-devices for nanoelectronics, opto-electronics, nanofluidic bio-sensors, and nanogap sensors. The electron beam lithography system and imaging system will have the capability to reach the resolutions down to 10 nm on six inch wafers. The PI manages the Microelectronics center, where this new tool will be located. The new tool will be widely used, with over 40 faculty members actively involved in research that will be enabled by this tool; 20 specific research projects of high impact have been described in this proposal. This new instrument proposed here will catalyze and accelerate interdisciplinary research in nanoscience on a variety of technical fields.

Broader Impacts: The requested instrument will serve 4 colleges and 10 departments at NC State and hence is expected to serve a large population of faculty and their respective students. The research enabled by the requested system will have significant impact in both graduate and undergraduate research and training at NC State and the instrument will be integrated into several lab courses. Outreach activities include involvement with Shaw University, a local HBCU, and summer internships for minority students providing getting hands-on education and research training.

This award supports fundamental research on processing-structure-property relationships of conductive inks for 3D printing of metals at or near room temperature. The basis for this work is the recent discovery and demonstration that liquid metals can be printed into free-standing structures that are stabilized mechanically by a surface oxide. The research will focus on new conductive inks that can be dispensed at modest temperatures but solidify into solid, mechanically robust metallic structures after the structures are printed. The research team will study the formulation, dispensing, and solidification of these inks using a number of characterization techniques to elucidate the solidification process.

The research results will provide the knowledge and understanding necessary to meet a critical need to develop metallic components for additive manufacturing (3D printing). Additive manufacturing enables users to directly design, prototype, and print objects on demand. It is considered a transformative technology that is championed by President Obama to help keep America competitive in the manufacturing sector. Although metals are important materials for electronics, optics, and structural materials, current technologies to 3D print metals are expensive and rely on high temperatures. The research will enable for the first time 3D printing of metals at or near room temperature. In addition to supporting a graduate student, the project will involve undergraduate researchers recruited from a diverse group of engineering students at North Carolina State (NC State). The research team will partner with the NC State Hunt Library and the NC State Laboratory for Additive Manufacturing and Logistics to contribute to a number of integrated outreach activities designed to expose a broader audience to the science and technology of 3D printing.

1510772 - Dickey

This award supports fundamental research on a new class of surfactants that can be controlled electrically to manipulate the shape and flow of liquid metals. These liquid metals are based on alloys of gallium and provide a low-toxicity alternative to mercury, which is a common liquid metal that has been limited historically by its toxicity. These metals are liquids like water, yet have electrical properties similar to metals. This combination of properties could enable electronic devices that are soft, stretchable, or shape-reconfigurable. The proposed work focuses on a new method to control the shape of liquid metals by utilizing electrical signals to control the surface properties of the metal and thereby manipulate the liquid metal at small length scales. The ability to control the shape or flow of metals using low voltages may enable new types of switches, antennas, wires, and electronics.

The scientific goals focus on understanding this new method to control the interfacial tension of liquid metal via electrochemical deposition (or removal) of an ultra-thin oxide layer on its surface. Unlike conventional surfactants (e.g., soaps or detergents), this approach can tune the interfacial tension of liquid metal significantly (from ~500 mN/m to near zero), rapidly, and reversibly using only modest voltages (~1 V). The proposed work seeks to understand this complex interfacial system by characterizing the role of the surface oxide on interfacial tension through three tasks. These studies will provide new fundamental understanding of soft material interfaces and in turn, help extend this phenomenon to other materials that form surface oxides as well as enable entirely new micro-scale phenomena involving shape reconfigurable metals using low voltages. The work will also establish the importance of surface oxides as a new class of fluid surfactants, which bring about some of the largest changes in surface tension ever reported.
The project will produce new techniques to control the shape of liquid metals and thereby enable new types of reconfigurable optics, microfluidics, and electronics. It will also lay the foundation for new, innovative opportunities for the use of liquid metals that go beyond toxic mercury.

The research will be integrated with an outreach module called "The Science of the Terminator" that describes liquid metals within the context of the popular motion picture. A partnership with the Engineering Place at NC State will ensure that the presentations are appropriately targeted and widely disseminated. The project will integrate undergraduate, high school, and exchange students on research projects and will continue to do so with this project by using the visually appealing nature of this project to attract students.

NONTECHNICAL SUMMARY
This EAGER award supports research and education involving a new collaboration kindled at the MATDAT18 Datathon event focused on using the methods of data science to make progress on challenging problems in materials science, in the mechanisms of case liquid metal embrittlement. When certain liquid metals come into contact with specific solid metals, the solid metals can undergo a catastrophic reduction in strength and/or ductility; this is termed "liquid metal embrittlement." While liquid metal embrittlement has been studied for over a century, a full understanding of the phenomenon is lacking. There is currently no means to predict the occurrence or severity of liquid metal embrittlement under given conditions. The PIs aim to use a method where computers can "learn" from the data obtained from many studies to create a model that can predict the severity of liquid metal embrittlement as a function of the experimental conditions, including liquid composition, solid composition, temperature, deformation rate, and microscopic structure of the solid metal which is largely visible through powerful optical microscopes. The machine learning model created as part of this research may enable the use of liquid metals in engineering applications, such as in stretchable circuits, and allow for future study of the fundamental physical mechanisms responsible for liquid metal embrittlement. The project strongly emphasizes the education and professional development of students of all ages. Graduate and undergraduate researchers with a materials science background will be trained in both conventional laboratory skills and in data science methods for engineers. Additionally, outreach modules targeted to middle and high school students will be developed as part of this project and distributed to the broader community through programs including the Minorities in Engineering Program and The Engineering Place at North Carolina State University.

TECHNICAL SUMMARY
This EAGER award supports research and education involving a new collaboration kindled at the MATDAT18 Datathon event focused on using the methods of data science to make progress on challenging problems in materials science, in the mechanisms of case liquid metal embrittlement. To date, no predictive phenomenological or mechanistic models of liquid metal embrittlement have been successfully developed. The phenomenon of liquid metal embrittlement is incredibly complex, with embrittlement behavior shown to depend on nearly every experimental variable ever tested including temperature, strain rate, solid metal grain size, solid composition, liquid composition, and more. Due to this complex phenomenology and the experimental challenge of independently varying the large number of involved, purely empirical studies of liquid metal embrittlement are intractable. This project takes an alternative approach to establish a predictive liquid metal embrittlement model: the Citrination platform will be used to conduct sequential learning. In this approach, an initial model is trained using preliminary data and used to suggest the next round of experiments which will have the greatest likelihood of improving the predictive capability of the model. The PI recently developed an initial model trained on data extracted from the literature. The model was used to suggest preliminary experiments, which were conducted and used to refine the model. However, further iterations are required for the model to achieve predictive capability. The PIs aim to iteratively refine the model. Once the model has sufficient predictive capability, a second objective of this work is to test the hypothesis that liquid metal embrittlement is not a monolithic phenomenon but is composed of several distinct mechanisms. The last main objective of this work is to identify "archetypal" systems for each identified potential mechanism and ideal candidates for future mechanistic study. If the hypothesis of multiple mechanisms is supported, this could reconcile seemingly contradictory reports of liquid metal embrittlement behavior present in the literature.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Liquid metals such as gallium and its alloys have a variety of prospective applications such as in electronic devices, catalysis, energy harvesting and biomedical use but face challenges with manufacturing, tunability and cost that limit them from widespread use. This research project seeks to investigate how incorporating small-scale solid and/or fluid fillers into the liquid metal, i.e. liquid-metal pastes, have the potential to extend the range of physical and chemical properties and increase their economic appeal for additive manufacturing and other technologies. To overcome the challenges associated with the high cohesive energy density of liquid metals, the team proposes to use naturally formed nanometer-thin gallium-oxide shells as a wetting agent (or surfactant) for encapsulating foreign materials of different phases. The resultant liquid-metal pastes represent a novel class of materials with unexplored properties that can advance wearable electronics, soft robotics, and thermal management of electronics. The visual and hands-on nature of the proposed research will enable multiplatform community outreach including engaging K-12 tour groups with a hands-on activity using a video-game controller to operate a three-dimensional printer in making liquid-metal parts.

This research aims to realize a generalized way to encase gases, liquids, and solids inside liquid metals and to understand the role of the encasing native oxide in doing so, which creates a unique ?surfactant? that forms in situ. These multiphase materials will be formed by mixing (or bubbling fluids) under controlled conditions and subsequently characterized thoroughly to establish process-structure-property relationships. The investigation will elucidate the mechanism by which this oxide ?surfactant? works to create foams and pastes with trapped air pockets and liquids or solid objects, respectively. The oxide ?enveloping? ability will enable a new class of conductive multiphase pastes with highly tunable density, rheology, as well as electrical and thermal conductivities. With the new fundamental insight, this project will also aim to create liquid-metal based materials that can be effectively three-dimensionally printed onto substrates with almost any composition and shape for two specific studies. The first one is to achieve a foam that is up to 10 times more cost-effective and lighter than pure liquid metals and yet fits for stretchable electronic devices. The second study is to create a paste that secretes small amounts of secondary liquid when applied and thereby improves thermo-mechanical contacts of next-generation thermal interface materials.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

This Major Research Instrumentation award supports the acquisition of a class 1, pico-second laser and a complementary reverse-pulse electroplating system for North Carolina State University (NC State). These tools will greatly enhance the fabrication capabilities of the university which also serves researchers from nearby universities, colleges, high schools, and industry. The equipment will find immediate use in a wide range of research activities led by the PI, 3 co-PIs, and 16 senior personnel in the areas of electronics, materials engineering, and biology. Moreover, the instruments will be located in the Nanofabrication Facility (NNF), a shared facility and part of the Research Triangle Nanotechnology Network (RTNN), which will ensure easy access to a rich variety of users from NC State, local universities and industry. This will create technological impact by enabling new strategies for processing materials, synthesizing unconventional nano/micro materials, and fabricating devices while stimulating new inter and intra-university research and strengthen NC State’s relationships with industry. The proposed instruments are uniquely suited for training next generation researchers with a low learning curve since the tool accepts standard computer aided design files and includes an intuitive user interface. This creates the opportunity to involve and educate undergraduates, graduates, and high school students, as well as teachers from nearby high schools and community colleges through existing outreach programs. The tools will therefore be useful for various advanced research and training purposes. <br/><br/>The pico-second laser will allow cutting/patterning of features as small as 20 microns and can process a wide range of materials (soft, hard, organic, inorganic, metallic) for applications ranging from energy to inorganics, electronics, biomedical systems, and soft materials. The tool is especially useful in processing materials that are either incompatible and/or result in poor resolution when patterned using conventional tools such as standard lithography, printing, or carbon dioxide lasers. The laser is particularly useful in heterogenous fabrication crucial for realizing next-generation devices that are not easily achievable through conventional techniques. The PI/co-PIs and senior personnel intend to process numerous materials such as polymers, carbon nanomaterials, metals, inorganics, glass, silicon, paper, and textiles for 1) tissue-integrated sensors; 2) organic, semiconducting, and self-folding electronics; 3) robotics and actuators; 4) opto-electronic materials; and 5) microfluidics.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.