Wenzhi Li, Ph.D. - US grants

Technical
This CAREER project aims to substantially enhance research and education in the area of nanometer-scale electronic materials. The research emphasis is on studying, identifying and understanding fundamental mechanisms of synthesis and electronic properties of new functional materials - Y-shaped carbon nanotube junctions (Y-junctions). It is anticipated that Y-junctions can be formed by fusing together three pieces of nanotubes with different structure and electronic properties through judicious introduction of topological defects, such as pentagons, heptagons and octagons, into the hexagonal carbon network. In this way metal-metal, metal-semiconductor and semiconductor-semiconductor junctions within individual nanotube molecules are sought. A goal is to elucidate the synthesis mechanism via answering a series of critical questions, including: Are the Yjunctions grown by splitting one nanotube to two or by merging two individual nanotubes to one? What is the growth thermodynamics? What is the relation between the type of topological defects and the chiralities (helicities) of the three branches? How does the nanostructure of Y-junctions affect the electronic/electrical properties? The approach includes: 1) Adapting a chemical vapor deposition technique to synthesize Y-junctions; 2) Detailed studies of nanostructure by a combination of scanning probe microscopy and transmission electron microscopy to reveal the growth mechanism; 3) Investigation of electronic/electrical properties by scanning probe microscopy and electrical transport measurement to relate the electronic/electrical properties to the nanostructures. The methodology established for synthesis, testing and analysis is expected to contribute to rational design of functional carbon nanotube heterostructures and the development of carbon nanotube based devices.
Non-Technical
Broader Impact: The project will provide training for students at FIU (Florida International University) in electronic material synthesis, characterization and design. Graduate and undergraduate students, especially women and minority students, will be recruited and involved in the proposed research projects. Students will be exposed to forefront research and will participate in scientific discovery in the rapidly developing nanoscience field. Advanced materials physics curricula with focus on nanoscience and nanotechnology will be developed for both undergraduate and graduate students to improve science achievement by enriching science teaching in both classroom and laboratories. It is anticipated that this research and education program will provide FIU students with fundamental knowledge and unique technological skills. It will also have substantial impact on the current Ph.D. program in Physics, and on the Ph.D. program in Materials Science and Engineering, currently in the final stages of approval. As an important part of the proposed outreach program, a "Summer Camp of Nanomaterials Science" for local high school students will be organized through collaboration with the on-going FIU "Physics Learning Center" (PLC) and "Upward Bound program" (UBP) programs serving high school students in South Florida. During the five-week "Summer Camp", students will be involved with research topics through presentations, interactive demonstrations, and hands-on-laboratory experiences. The PI will also participate in outreach to the local community through lectures with the aim of enhancing public understanding of nanoscience and nanotechnology.

This award provides funds to the Florida International University to acquire a Nanoimprinter for research and education. Nanoimprinting is not governed by the optical diffraction limit and has the capability of large area exposures with high throughput. It will enable researchers at FIU?s open-access lab to conduct several main cutting edge research projects, such as: the development of micro-batteries based on carbon nanoelectrodes; integrated nano-photonic devices based on polymers; the mechanics of nanostructured polymer materials; DNA array biomedical devices; Micro/Nano fluidic devices; and carbon-nanotube sensors. The proposed activities will advance knowledge in and across different fields. By acquiring this next level of capability, FIU researchers and collaborators will be able to perform research on nanotechnology devices and processes that have great potential for actual applications.
The successful development of the proposed projects, enabled by the Nanoimprinter acquisition, has broad implications in health care and homeland security. This instrumentation research will integrate undergraduate and graduate student?s training. Existing hands-on laboratory courses will be expanded to include experiments with this new nanoscale mass-production technology. Together with the exciting research topics, the enhanced infrastructure for research at FIU - one of the top Hispanic Serving Institutions in Florida - will attract more students from our underrepresented population into graduate school. A big impact on increasing the number of students in materials science, biomedical and electrical engineering from traditionally underrepresented groups is expected. Exposing graduate and undergraduate students to this new technology in an open-access laboratory will also help to boost interdisciplinary and multidisciplinary research collaboration across various research groups, blurring the boundary of departments and even institutions. The Nanoimprinter will be placed in the existing open-access Motorola Nanofabrication Research Facility, and will be easily accessible to campus users as well as other academic and industry users in south Florida.

This award provides funding to support a planning visit to the Wuhan National Laboratory for Optoelectronics in Wuhan, China. Participants in the trip will include Professor Wenzhi Li, one graduate student, and one undergraduate. The purpose of the trip is to develop a collaboration in research and education on synthesis and applications of carbon nanotubes and semiconducting nanowires in optoelectronic devices. The expertise of the Chinese collaborators in optoelectronics complements that of the PI in synthesis of novel nanomaterials.

In promoting research collaboration among the participants, this planning visit will develop new materials and more effective devices for important applications, such as advanced sensors and solar cells. The participation of the students in this international program will broaden their personal and professional perspectives. The PI plans to involve undergraduate students from underrepresented populations, and this experience should stimulate them to continue in a scientific career.

The objective of this award is to develop and test a novel nanofluidic-nanoelectronic device with high specificity and sensitivity for biological sensing applications. To exploit the recently discovered nanofluidic advantages of carbon nanotube (CNT) nanochannel, nanofluidic devices based on high quality horizontally aligned single-walled CNT (SWCNT) arrays will first be fabricated. Then, the electrokinetic motion of analytes passing through the interior of CNT arrays will be characterized and controlled. Subsequently, practical approaches will be developed in these CNT nanofluidic devices to utilize several CNT based electrical sensing methods, including field effect transistor (FET), electrochemical sensing and capacitive charge sensing methods. Fundamental understandings of these sensing methods when they are incorporated into nanofluidic devices will be developed and different sensing methods will be combined together to achieve multimode sensing. Finally, the biosensor performance will be evaluated through the detection of secreted small molecules from individual living cells in real time.

If successful, this highly interdisciplinary research will develop new ways to integrate nanofluidics and nanoelectronics into one device. The knowledge and methods obtained from this project can be applied to other metallic or semiconducting nanotubes and nanopores. This project will lead to a new type of all-electrical biosensor, which will be ultrasensitive, highly selective, portable, cheap, requiring a low sample and power consumption. A new class of biosensor for single living cell sensing will be developed. The developed biosensor is also potentially applicable to a wide variety of areas: clinic diagnostics, environment protection and preservation, health improvement, national defense and bioterrorism prevention.

NON-TECHNICAL DESCRIPTION: In this project, tin oxide-coated carbon nanotubes are being used as a model material to investigate the mechanism for lithium storage. Tin oxide is considered one of the most promising metal-oxide anode materials for lithium ion batteries due to its high lithium ion storage capacity. However, the practical application of tin oxide as anode material is restricted by its large volume change (up to 300%) during charge-discharge cycles, which can cause its disintegration and electrical disconnection from the current collector. To circumvent this problem, a three-dimensional carbon nanotube-tin oxide core-shell nanowire array is being developed by growing tin oxide shells on vertically-aligned carbon nanotubes. The carbon nanotubes serve as the backbone of the tin oxide shell to buffer the large volume change, while the cylindrical tin oxide shell alleviates its degradation during the lithiation process. This project's outcomes will be beneficial to conventional lithium ion battery research and development, as well as on-chip micropower development. A better understanding of the electrochemical properties is making a significant contribution to the development and rational design of three-dimensional hierarchical electrode nanomaterials for lithium ion batteries. Each year, these researchers provide two public lectures to convey new knowledge of material science and technology. A diverse set of students are engaged in the research at Florida International University, a Hispanic-Serving Institution. Each year, graduate and undergraduate students participate in the research, and they have the opportunity to work at Sandia National Laboratories. Annually, 60 high school students and 10 high school teachers are invited for on-campus lab tours and research demonstrations.

TECHNICAL DETAILS: Carbon nanotube-metal oxide core-shell composite materials are promising candidates for application as anode materials in lithium ion batteries. However, the electrochemical lithiation-delithiation behavior and mechanism of this type of materials remain unclear. A comprehensive understanding of the lithiation mechanism at the nanoscale benefits the design and development of high-performance lithium ion battery materials. This project develops a synergistic approach for the synthesis and characterization of vertically aligned carbon nanotube-tin oxide core-shell nanowire arrays to manipulate their electrochemical property at the time of synthesis. The vertically-aligned carbon nanotube arrays are synthesized directly on a current collector using plasma enhanced chemical vapor deposition, and the tin oxide shell on the carbon nanotubes is synthesized via chemical-solution and vapor deposition routes. The microstructure and the electrochemical properties of the carbon nanotube-tin oxide core-shell nanowires are being investigated by a combination of electron microscopy, electron energy loss spectroscopy, energy dissipation spectroscopy, X-ray diffraction (both in situ and ex situ), charge-discharge measurement, cyclic voltammetry, electrochemical impedance spectroscopy, and in situ transmission electron microscopy observation of the lithiation process. The study provides a better understanding of the lithiation mechanism of the core-shell nanowire array and the influence of their microstructure on their electrochemical properties. The research results provide new insight into the electrochemical process of carbon nanotube-metal oxide composite materials in lithium ion batteries. Graduate and undergraduate students receive research training in advanced electrochemical material synthesis, characterization and design.

The broader impact/commercial potential of this I-Corps project will be in the improvement of lithium-ion batteries (LIBs). Current LIBs are often limited in energy density and charging speed due to their graphite anode. These limits result in larger sizes and weights of LIBs for advanced applications such as long-range electric vehicles (EVs). The proposed technology involves a novel nanomaterial, nickel sulfide-filled carbon nanotubes, that can replace the conventional graphite anode and enhance the performance of LIBs. This innovation can alleviate the aforementioned problems in current anode technologies and can enable development of the next generation of high performance LIBs for EVs, grid energy storage, and electric aviation. By enabling wider adoption of LIB technologies, this project can help reduce emissions linked to climate change.

This I-Corps project will advance the knowledge in the fundamental electrochemical properties of metal sulfide-filled carbon nanotubes. Specifically, the team will help to understand how the solid core-shell structure affects the transport of electrons and lithium ions and how the volume expansion of the lithiated nanowire filler is accommodated by the carbon shells. The expected results will provide new insight into the electrochemical properties of carbon nanotubes filled with metal sulfide nanowires in lithium-ion battery (LIB) applications. In this project, nanomaterials of nickel sulfide filled carbon nanotubes are developed together with techniques to synthesize these materials on flexible carbon cloth. These nanomaterials have been shown to exhibit energy storage capacity which is several times that of the current commercial graphite anode materials. Further, the nanomaterials have shown exceptional charging-discharging stability.

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.