Mark C. Hersam - US grants

This CAREER project addresses complementary scanned probe microscopy (SPM) techniques for covalently nanopatterning polymer and biological molecules on silicon surfaces with an integrated research and education plan. One approach explores feedback controlled lithography as a means for templating hydrogen passivated silicon surfaces for subsequent wet chemistry in ambient conditions, and a second approach, termed liquid phase nanolithography (LPN), attempts to pattern organic molecules onto silicon surfaces directly from solution using conductive AFM. In addition to nanolithography, this project explores innovative frequency dependent nanoelectronic and nanophotonic characterization schemes. Nanoscale impedance spectroscopy (NIS) will be developed to delineate the phase and amplitude response of current through a conductive AFM tip in response to a variable frequency applied bias. NIS would provide, in effect, a nanoscale spatial map of the frequency dependent electronic behavior of hybrid hard and soft materials. In the case of photoactive materials, photocurrent will be detected through the conductive AFM tip under sample illumination; whereas, photons emitted from electroluminescent materials will be measured with a photodiode and current preamplifier. The basic elements of these research ideas will be incorporated into a comprehensive interdisciplinary nanoscale education and outreach program. In an effort to induce interdisciplinary interactions among graduate and undergraduate students, the research includes domestic and international collaborations with faculty and industrial representatives from other academic departments.
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The project addresses fundamental research issues in a topical area of materials science having technological relevance. Outreach to undergraduates and underrepresented minorities will be addressed through a Research Experience for Undergraduates and Minority Internships in Nanotechnology program that the PI is co-organizing through the Northwestern University Nanoscale Science and Engineering Center. Additionally, the PI is involved in developing new web- based nanomaterials coursework. This undergraduate coursework will then be adapted for the development of a nanomaterials world module for K-12 students, non-science majors, and the general public both domestically and abroad. The scope of the project will expose students to new challenges and research approaches in materials synthesis, processing, and characterization. An important feature of the project is the strong emphasis on education, and the integration of research and education.
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The award from the Instrumentation for Materials Research Program in the Division of Materials Research will allow Northwestern University to acquire a new Fourier Transform Infrared Spectrometer (FTIR) Instrument for research and education in the Departments of Materials Science and Engineering, Chemical Engineering, and Chemistry. The proposed FTIR instrument will replace the current outdated equipment and will be housed in the Polymer Characterization Facility of the Materials Science department. The instrument will consist of two modules: a conventional turn-key FTIR spectrometer with an array of attachments for standard spectroscopic techniques, and a highly customizable module specifically designed for measurements of molecular structure in ultra-thin films of organic molecules. The former will make the instrument easily useful to a broad audience of Northwestern researchers, while the latter will allow measurements of molecular conformations in more difficult samples, especially in biomaterials and nanomaterials research. The instrument will facilitate the training of undergraduate and graduate students in all three departments, by being utilized in laboratory sections of polymer materials class offered to the engineering undergraduate students, and a spectroscopy class offered through the chemistry department. The more advanced capabilities of the spectrometer will greatly advance the ability of students involved in the interdisciplinary bio- and nanomaterials research at Northwestern to elucidate and understand the molecular-level details of structure in their samples.
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The award from the Instrumentation for Materials Research Program in the Division of Materials Research will allow Northwestern University to acquire a new Fourier Transform Infrared Spectrometer (FTIR) Instrument for research and education. The instrument will be housed in the Polymer Characterization Facility in the Materials Science and Engineering department, and will be used to characterize new polymeric, biological and nanomaterials prepared by researchers at Northwestern. In particular, it will enable measurements of the orientation, shape, and arrangement of molecules in extremely thin (just a few molecules thick) films deposited on the surfaces of solids and liquids. Such films are often critical in creating the new materials for biotechnology and nanoscience applications, governing, for example, the interactions of biomaterials with biological tissues, or the workings of nanoscale sensors capable of precisely measuring minute quantities of substances present in a gas or a liquid. The instrument will be used in instruction for several classes currently taught to science and engineering students at Northwestern. Moreover, students of the undergraduate and graduate levels will use the instrument for their research, improving the quality and scope of their training as future members of the science and engineering workforce.

This IMR award provides Northwestern University with funds for the acquisition of a cluster of SMTP servers, having a 64-bit operating system, with a large memory subsystem and with Myrinet (medium speed) interconnects. This cluster will be used for computational chemistry and materials science research at Northwestern University, particularly applications in electronic structure, in computational electromagnetics, and in Monte Carlo and molecular dynamics calculations where large memory capabilities are essential. Distributed parallel applications will also be emphasized. The cluster will also be used in graduate and undergraduate courses in engineering and sciences, and in REU, REST, MRSEC and other initiatives which use software that require large memory capabilities.

This IMR award provides Northwestern University with funds for the acquisition of a cluster of computers that will be used for computational materials research in chemistry and engineering, and for related educational programs. The computers in this cluster will have specialized performance characteristics which make it possible to run programs that require an exceptionally large amount of computer memory, and which in addition allow for several computers to run in parallel on the same program. Research applications to be considered include the modeling of a wide range of properties of materials, including structures, energies, interaction with light, motions of atoms, making films and patterns, and thermal properties. The computer cluster will be used in a wide variety of educational programs, including computational modeling courses, laboratories and summer research programs.

PROPOSAL NUMBER.: 0304421
INSTITUTION: Northwestern University
NSF PROGRAM: NANOTECHNOLOGY UNDERGRAD EDUCATION
PRINCIPAL INVESTIGATOR: Hersam, Mark C.
PROPOSAL TITLE: NUE: Development of a Nanotechnology Undergraduate Education Global Network

ABSTRACT:

This award is part of the Nanoscale Science and Engineering Initiative, NSF 02-148, within the Nanotechnology Undergraduate Education (NUE) Category and is administered by the Design Automation for Micro and Nano Systems Program. Led by Professor Mark Hersam of the Materials Science and Engineering Department at Northwestern University, this program entitled "NUE: Development of a Nanotechnology Undergraduate Education Global Network" is developing an internet infrastructure for the worldwide exchange and dissemination of nanotechnology undergraduate educational ideas and materials. Initially, a pre-existing course in nanomaterials at Northwestern University will be used as a prototype for developing modules on the NUE Global Network in collaboration with the International Virtual Institute led by Professor Robert Chang. The nanomaterials course employs novel pedagogical techniques, including interdisciplinary problem-based learning and peer assessment, that are well-suited for undergraduate teaching and learning in the emerging field of nanotechnology. Once the web-based interface has been formalized for this course, the NUE Global Network will be expanded to other courses at Northwestern University and other institutions of higher learning. Ultimately, the NUE Global Network is designed to evolve into a nanotechnology educational forum that will allow educators, students, government, and industry to interact in a truly global sense.

With support from the Major Research Instrumentation (MRI) Program, Richard Van Duyne and colleagues from the Chemistry Department at Northwestern University will develop a new optical nanoprobe scanning tunneling microscope for nanoscale science and engineering research and education. They will design, develop, apply and bring to the marketplace a new class of ultrahigh vacuum scanning tunneling microscope (UHV-STM) that combines the extraordinary spatial resolution of the STM with the unparalleled sensitivity and broad system applicability of advanced optical spectroscopic techniques. They will integrate high sensitivity, chemical information-rich optical spectroscopic methods with STM in such a way that sub-nanometer spatial resolution is preserved. In particular, they will use the ultra-sensitive methods of electron beam-excited, localized surface plasmon resonance (LSPR) spectroscopy, dark-field photon-excited LSPR spectroscopy, and various surface-enhanced spectroscopies.

The development of the optical nanoprobe STM will enhance the education experiences at Northwestern University as it is incorporated into a number of courses. In addition, through the development of network control hardware/software, other educational institutions will have access. The principal investigators will collaborate with an industrial partner to ensure the transition of this instrument to the commercial sector.

Technical: This project addresses a critical obstacle to the widespread use of carbon nanotubes, that of controlled sorting. The project approach involves surfactant mixtures and density gradient ultracentrifugation (DGU) to sort single wall nanotubes (SWNTs) by diameter, chirality and electronic structure. Preliminary results for DGU on surfactant encapsulated SWNTs have demonstrated potential for the approach. The following tasks will be pursued: understanding and tuning the structure-density relationship for surfactant encapsulated SWNTs as a function of surfactant type, co-surfactant ratio, density gradient, and pH; optimizing iterative separations where the DGU conditions are sequentially varied to achieve concurrent diameter and metal/semiconductor separation; improved characterization of the structure and properties of chirality-resolved SWNTs using a complementary suite of characterization techniques including optical absorption spectroscopy, photoluminescence spectroscopy, pump-probe spectroscopy, Raman spectroscopy, scanning probe microscopy, and charge transport measurements; exploring the utility of chirality-resolved SWNTs in a wide range of device and materials applications such as complementary logic, transparent conductors, ultra-fast optical spectroscopy, templated assembly, nanocomposites, multi-analyte biosensors, and cell growth substrates.
Non-technical: The project addresses basic research issues in a topical area of electronic/photonic materials science with high technological relevance. An important component of the proposed activity is an education and outreach plan that complements and is well integrated with the research objectives. Education and outreach activities will include: undergraduate curriculum development in the form of nanoscience modules that can be directly inserted into the Materials Science and Engineering undergraduate curriculum; undergraduate research opportunities both in the PI's laboratory and across campus as enabled by the his role as Director of the Nanoscale Science and Engineering Center Research Experience for Undergraduates Program; outreach to pre-college students by collaborating with the Boy Scouts, Girl Scouts, and Explorer Scouts on nanoscience events and a Nanotechnology Merit Badge; dissemination to the general public via the PI's membership on the Chicago Museum of Science and Industry (MSI) Physical Sciences Exhibit Advisory Panel.

This REU Site in Nanoscale Science and Engineering will involve ten undergraduates in hands-on nanoscale science and engineering focused research for a 9-week summer period. The program will provide undergraduates with opportunities to develop the fundamental skills necessary to succeed in careers in science and engineering including pragmatic training in public speaking, technical writing, the peer-review process, and research and laboratory skills.

The students' research experience will be enhanced by their participation in social and educational activities including technical writing and professional speaking workshops, weekly meetings/seminars, a field trip to Argonne National Laboratory, and a summer picnic. During the final week of the program, participants will work closely with their advisors to prepare both oral and written reports. Students will present their project results at a formal Closing Symposium. Also a final project report in the format of a scientific paper will be required at the end of the program. It is anticipated that some of the papers and presentations prepared by participants will be suitable for academic journals and conferences. Additional opportunities for technological transfer are possible through Nanoscape: the Journal of Undergraduate Research in Nanotechnology published by the Northwestern University Nanoscale Science and Engineering Center (NSEC).

Recruitment efforts will be targeted to undergraduate students majoring in engineering or the physical sciences. Attention will be given to attracting a diverse group of students including racial and ethnic minorities, women, persons with disabilities, as well as students from smaller schools were research opportunities are limited or nonexistent.

Technical: Carbon-based nanomaterials, including single-walled carbon nanotubes (SWNTs), double-walled carbon nanotubes (DWNTs), multi-walled carbon nanotubes (MWNTs), and graphene, have attracted significant interest in the scientific research community due to their superlative electronic, thermal, mechanical, and chemical properties. While impressive performance has been achieved on selected samples, large-scale technological development has been hindered by the structural inhomogeneity of as-synthesized carbon-based nanomaterials. In an effort to overcome this polydispersity problem, a technique called density gradient ultracentrifugation is employed to sort carbon-based nanomaterials by their physical and electronic structure. This project seeks to resolve the outstanding issues surrounding the preparation, characterization, and application of monodisperse carbon-based nanomaterials. Specific research objectives include: (1) Tuning co-surfactant ratio and loading to achieve monodisperse small diameter (< 1 nm) SWNTs due to their spectral advantages for near-infrared optoelectronic applications. (2) Demonstrating diameter and electronic type sorting of DWNTs in an effort to elucidate exciton energy transfer between concentric carbon nanotube shells. (3) Quantifying structure-density relationship for surfactant dispersed graphene as a function of surfactant type, co-surfactant ratio, density gradient, and pH. (4) Employing monodisperse carbon-based nanomaterials in electronic device and materials applications such as transistors, optoelectronics, transparent conductors, and sensors.
Non-technical: The project addresses basic research issues in a topical area of materials science with high technological relevance. It is anticipated that this research will lead to substantial intellectual property and commercialization opportunities. Furthermore, an important component of the project is an education and outreach plan that is well integrated with the aforementioned research objectives including: (1) Undergraduate curriculum development through a revision and updating of an interdisciplinary course entitled Nanomaterials. (2) Hands-on, inquiry and design-based curriculum development for pre-college students in collaboration with the Materials World Modules program. (3) Engaging students and the general public about science and science policy via the Northwestern University Science Policy Action Network.

The theme of the Northwestern University CEMRI* is Multifunctional Nanoscale Materials Structures. The main emphasis of the Center is to train visionary and globally competitive U.S. materials researchers to significantly impact the U.S. economy and solve global challenges, to innovate in an atmosphere of cooperation and healthy competition among national and international partners in both public and private sectors, and to integrate efforts in research, education, knowledge/technology transfer and networking. The Center manages and maintains shared experimental facilities accessed by both Northwestern and external researchers, fosters interactions with National Labs (especially with nearby Argonne National Lab), other universities, industry (including both MRSEC-initiated start-up companies and large corporations) as well as other institutions (including The Art Institute of Chicago), and develops innovative educational programs including the science-themed performances hosted by the MRSEC-sponsored Educational Transdisciplinary Outreach Program in the Arts (ETOPiA).

The research goals of the center consist of understanding the fundamental principles and behaviors of complex nanomaterials systems, transferring results into the development of new functional devices and systems leading to new technologies and industries, and initiating close cooperation among national and international partners to improve research capabilities and infrastructure. Researchers are organized into Interdisciplinary Research Groups (IRGs) investigating: "Controlling Fluxes of Charge and Energy at Hybrid Interfaces", "Fundamentals of Amorphous Oxide Semiconductors" and "Plasmonically-Encoded Materials for Amplified Sensing and Information Manipulation", as well as seed programs. The research strategy is to investigate novel phenomena through the interactions of charges, photons, plasmons and excitons in nanostructured materials, including discrete and collective effects in model materials using theory, simulation, modeling and detailed measurements. An understanding of the underlying science will provide a basis for the design of new and extended classes of functional nanostructures for potential applications in sensing and communication, energy and environmental uses.

The educational goals of the Center are to develop and disseminate instructional materials for pre-college Science, Technology, Engineering, Mathematics (STEM) classrooms based on Center research, to offer opportunities for graduate and undergraduate students to develop skills in innovation and entrepreneurship, to work with international partners and programs to equip U.S. students with global leadership capabilities and a global research perspective, and to provide national leadership in vertically-integrated STEM learning and teaching from middle-school to graduate school in order to improve quality and reduce the cost of education. The Center has a long history of developing Materials World Modules for implementation into STEM classrooms and providing summer research training for teachers and undergraduates in Research Experience for Teachers (RET) and Research Experience for Undergraduates (REU) programs. Partnerships with the International Materials Institute at Northwestern and with industrial partners are providing new opportunities to develop international programs and opportunities for undergraduate and graduate students to participate in innovation and entrepreneurship-based research activities.

*a NSF Materials Research Science and Engineering Center (MRSEC)

Communications systems such as WiFi, GPS, wireless sensor networks, and radio frequency electronics are critical to the nation?s infrastructure and have had a transformative impact on daily life. However, existing applications of wireless technologies are often limited by the power consumption and speed of the underlying electronic switches, or transistors, that send and receive signals. Furthermore, current classes of transistors must be integrated into complex circuits to perform simple functions. This award supports the fundamental research necessary to make new classes of transistors that can improve the performance of existing communications technologies and open up new applications by enabling simplified circuit designs on flexible substrates. The development of inexpensive and scalable approaches to new transistor materials will facilitate the incorporation of these devices into new technologies. Computer models of novel transistors and communications circuits will be shared with industry partners to facilitate the transfer of knowledge and capabilities to industry, growing the high-tech economy. Outreach programs including cooperation with the Chicago Museum of Science and Industry will recruit a broad group of young people to careers in science and technology crucial to the nation?s economy and defense.

The objective of the proposed work is to create, characterize, understand, and exploit new classes of electronic and optoelectronic devices by integrating promising two-dimensional monolayer transition metal dichalcogenides with other low dimensional semiconductors including p-type organic semiconductors, sorted semiconducting single walled carbon nanotubes, and other two-dimensional materials. The project will fabricate novel ultrathin p-n heterojunctions of mixed dimensionality that exhibit unique and quantitatively advantageous properties arising from gate transparency and flexibility, and characterize the devices with advanced scanned probe techniques in addition to conventional current and capacitance versus voltage measurements. Custom chemical precursors will be designed and synthesized with the goal of achieving scalable growth and fabrication of ultrathin dichalcogenides by atomic layer deposition over large areas at reduced temperatures. To understand how the device physics leads to new properties and circuit performance, phenomenological models will be integrated into industry accepted nanodevice simulators, and a compact model will be developed. The fundamental knowledge and predictive models of ultrathin heterojunctions will expand engineering frontiers through quantitative understanding of charge transport, the demonstration of novel device characteristics, such as the recently discovered anti-ambipolar behavior, and the exploitation of these behaviors to create novel electronic circuits on flexible substrates with simpler designs and fewer elements than conventional unipolar field effect transistor-based circuits.

DESCRIPTION (provided by applicant): There is a fundamental gap in understanding how the physicochemical properties of carbon nanotubes (CNTs) contribute to hazard generation in the lung. Without this knowledge, it is difficult to evaluate CNT safety in a predictive and affordable manner. The long-term goal of our multidisciplinary approach is to develop a predictive toxicological approach for CNT safety assessment in which the physicochemical properties leading to hazardous interactions at the nano/bio interface can be used to understand the materials' pro-inflammatory and pro-fibrogenic effects in the lung. The overall objective of this application is to develop a series of single- wall (SW) and multi-wall carbon nanotube (MWCNT) libraries that can be screened by robust cellular assays to establish quantitative structure activity relationships (SARs) and hazard ranking of the tubes' potential to induce pulmonary damage. Our central hypothesis is that tube dimensions (including length, diameter and aspect ratio), state of dispersion, catalytic surface chemistry, electronic properties and purity play key roles in initiating cooperative cellular interactions in macrophages and cellular elements from the epithelial- mesenchymal trophic unit, which are key to the development of development of pulmonary inflammation and fibrosis. The rationale for the proposed research is that once the quantitative contributions of specific physicochemical properties to hazard generation is known, it will be possible to use a predictive toxicology approach for expedited safety assessment of CNTs as well as their safer design. Guided by strong preliminary data, this hypothesis will be tested by pursuing three specific aims: Aim 1: To develop hazard ranking that relates the properties of well-prepared and characterized MWCNT and SWCNT libraries to mechanistic toxicological responses in epithelial cells and macrophages, with a view to develop quantitative structure- activity relationships (SARs) that predict in vivo injury potential. Aim 2: To develop and validate a predictive toxicological paradigm for pulmonary hazard potential of well-characterized commercial and purified CNTs, using in vitro SAR-based hazard ranking and grouping of materials that can also be used towards a tiered risk assessment approach. Aim 3: To use covalent and non-covalent surface modification to demonstrate the feasibility of safe-by-design approaches for CNTs, using a predictive toxicological approach. Our approach is innovative, because it represents a substantive departure from the status quo, namely the use of purified and well- prepared CNTs that are investigated according to robust toxicological mechanisms that predict the in vivo toxicological outcome. The proposed research is significant because: (i) it addresses the concern of how to perform CNT safety assessment using a robust, quantitative scientific platform; (ii) the establishment of a robust safety platform based on grouping of CNT properties that can be used for control banding and read- across risk assessment; (iii) the research will develop an affordable and rational scientific platform for regulatory decision-making and product approval towards the marketplace.

Nontechnical Description: With the increasing importance of portable and wearable electronic technologies, new materials are needed that combine superlative electronic properties with other requirements such as mechanical flexibility, low power consumption, and scalable manufacturing. Emerging two-dimensional nanoelectronic materials that are atomically thin meet many of these requirements, but no single material can achieve all of them concurrently. Consequently, this project develops heterostructures that synergistically integrate the desirable properties of multiple two-dimensional nanoelectronic materials, thus overcoming the design tradeoffs imposed by single materials utilized in isolation. Solution-processing methods are further employed to achieve highly homogenous nanoelectronic heterostructures in a manner that is compatible with large-scale, low-cost additive manufacturing. The results of this project are disseminated through a comprehensive set of education and outreach activities that include graduate curriculum development, undergraduate laboratories, and a materials science exhibit at the Chicago Museum of Science and Industry.

Technical Description: To realize reproducibly high performance in electronic and optoelectronic devices, nanoelectronic materials must be produced via scalable methods that possess high structural monodispersity. Furthermore, the resulting nanoelectronic material components need to be assembled into morphologies that preserve their superior properties and are amenable to subsequent fabrication methods. Towards these goals, dispersion chemistries, solvents, and density gradient media are identified that enable density gradient ultracentrifugation sorting of transition metal dichalcogenides, boron nitride, and black phosphorus with exceptional structural and electronic purities. These high purity samples facilitate fundamental studies of two-dimensional nanoelectronic materials as a function of structural parameters such as thickness and lateral size. In addition, homogeneous two-dimensional nanomaterial dispersions are assembled via vacuum filtration and layer-by-layer assembly to form multi-component bulk heterojunction nanocomposite films and thin-film heterostructures that are suitable for the fabrication and testing of large-area nanoelectronic devices and circuits. In this manner, the role of surface and interfacial chemistry on electronic properties are elucidated at the two-dimensional limit.

Nontechnical Description:

The Northwestern University Materials Research Science and Engineering Center (NU-MRSEC) advances world-class materials research, education, and outreach via active interdisciplinary collaborations within the Center and with external partners in academia, industry, national laboratories, and museums, both domestically and abroad. The intellectual merit of the NU-MRSEC resides primarily within its interdisciplinary research groups (IRGs) and seed-funded projects that promote dynamic evolution of Center research foci. IRG-1, entitled "Reconfigurable Responses in Mixed-Dimensional Heterojunctions", explores nanoelectronic materials systems that simultaneously process and store information to provide functionality comparable to that exhibited by complex biological systems such as neural networks. IRG-2, entitled "Functional Heteroanionic Materials via the Science of Synthesis", brings together experts in materials synthesis, computational design of materials, and advanced characterization, to expand a relatively unexplored class of materials with unconventional combinations of electrical and thermal properties. The NU-MRSEC achieves broad impact through several programs including professional development of graduate students and postdocs, research experiences for undergraduates and teachers, as well as outreach to K-12 students and the general public. These activities are enhanced by partnerships with Argonne National Laboratory, Art Institute of Chicago, Chicago Children's Museum, Chicago Museum of Science and Industry, Chicago O'Hare International Airport, Chicago Public Schools, and Chicago City Colleges.

Technical Description:

The Northwestern University Materials Research Science and Engineering Center (NU-MRSEC) integrates materials research, education, and outreach through two interdisciplinary research groups (IRGs) and with external partners in academia, industry, national laboratories, and museums, both domestically and abroad. IRG-1, entitled "Reconfigurable Responses in Mixed-Dimensional Heterojunctions", explores how heterojunctions consisting of nanoelectronic materials of differing dimensionality are influenced by dielectric screening, electronic band/level offsets, and interfacial regions. By utilizing low-dimensional materials synthesis, surface chemical functionalization, spatially and spectrally resolved characterization, and advanced computation, IRG-1 develops quantitative descriptions of the nonlinear responses in mixed-dimensional heterojunctions. Elucidation of the mechanisms governing structural changes, and the corresponding changes in optoelectronic properties, allows controllable reconfiguration in response to a multitude of physical and chemical stimuli, with implications for neuromorphic computing. IRG-2, entitled "Functional Heteroanionic Materials via the Science of Synthesis", develops new heteroanionic materials with tunable electronic, ionic, thermal, and optical properties, which are otherwise inaccessible from simpler homoanionic structures and chemistries. Discovery of heteroanionic materials is facilitated by synthetic and characterization methods that provide a panoramic view of crystallization and diffusion processes, in which emerging phases of interest are revealed and growth mechanisms are delineated. By emphasizing synthesis as the central science, the tools, protocols, and databases formulated in IRG-2 enable synthesis-on-demand of complex materials suggested by computational discovery. The research of the NU-MRSEC informs a diverse range of education and outreach activities that target all levels including postdocs, graduate students, undergraduates, K-12 students and teachers, as well as the general public. Examples include Transdisciplinary Engineering and Theater Workshops that create original science-themed plays, and Jugando con la Ciencia (Playing with Science) that translates outreach curricula and texts into Spanish.

Nontechnical Summary:
Researchers have recently learned how to produce atomically thin materials that are referred to as two-dimensional (2D) materials since they are extended in two dimensions (i.e., length and width) but are confined in the third dimension (i.e., depth) at the atomic scale. Due to a range of superlative properties and new physics in the atomically thin limit, 2D materials have attracted significant interest for fundamental studies and prototype device development. Thus far, chemically inert 2D materials have been the most widely studied since they can be processed in ambient conditions with minimal further precautions. However, the family of 2D materials has hundreds of additional members, which have been underexplored due to their high chemical reactivities that introduce challenges in preparing and handling samples for electronic testing. To address this knowledge gap, this project develops encapsulation and related sample preparation protocols to enable characterization of the fundamental properties of chemically reactive 2D materials. Of particular interest are the 2D metal halides since they are theoretically predicted to possess unique combinations of electronic and magnetic properties that are relevant to next-generation computing and quantum technologies. These research results are widely disseminated to diverse audiences through a series of education and outreach activities including Illuminate, which assists and enables low-income, first-generation, and/or underrepresented minority students to attend and complete college, and Science with Seniors, which organizes visits to retirement homes for interactive science presentations and demonstrations.

Technical Summary:
Among the most chemically reactive two-dimensional (2D) materials are the layered van der Waals transition metal halides. Due to their high chemical reactivity, experimental studies of bulk metal halides are rare and have traditionally required an inert environment and/or vacuum equipment. However, theoretical models have predicted many layered metal halides to be mechanically exfoliatable due to low cleavage energies and large in-plane bond strength, suggesting that they could be explored in the 2D limit if suitable passivation and processing conditions were identified. This project develops atomic layer deposition encapsulation layers that allow 2D metal halides to be handled, processed, and tested in ambient conditions. Preceding atomic layer deposition, the 2D metal halides are passivated with organic buffer layers that minimize charge trapping and scattering, thus allowing intrinsic properties to be probed. The interplay among the electronic, magnetic, and optical properties of 2D metal halides is characterized as a function of temperature using lateral field-effect transistors, vertical heterostructures, and Hall bar electrode arrays. By elucidating fundamental charge transport phenomena such as the quantized anomalous Hall effect, this work provides guidance to emerging efforts to incorporate 2D metal halides into advanced magneto-electronic applications including spintronic devices, quantum technologies, and non-volatile memory.

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.

The ongoing COVID-19 pandemic has led to a shortage of critical medical equipment, including N95 masks. In order to conserve resources and maintain some level of protection against COVID-19, medical workers have begun reusing masks. While ultraviolet germicidal irradiation (UVGI), a widely used sterilization technique in medical settings, has been shown to be effective at disinfecting mask filters, it is not recommended by mask manufacturers due to deterioration of elastomeric components such as the nose foam and head straps that prevents an effective fit following sterilization. UVGI utilizes radiation in the deep-UV portion of the electromagnetic spectrum due to its strong absorption by microbial nucleic acids, which leads to their degradation. However, currently used elastomeric materials are similarly compromised at these deep-UV wavelengths. Therefore, it is of high urgency to develop elastomeric materials that are resistant to UVGI irradiation to enable decontamination and reuse of N95 masks. It would be of even greater interest if the same UV-resistant elastomeric materials also possessed intrinsic antimicrobial properties to further minimize the spread of COVID-19. Hydrated graphene oxide is known to possess both of these desirable attributes concurrently ? namely, strong optical absorption at deep-UV wavelengths and proven antimicrobial properties. This project thus aims to rapidly develop elastomeric composites based on hydrated graphene oxide in order to enable the sterilization and reuse of N95 masks. Importantly, the outcomes of this research not only address the current COVID-19 crisis, but are applicable for general medical use including future pandemics.

This project is synthesizing elastomeric composites based on hydrated graphene oxide (hGO) to enable N95 mask sterilization and reuse during COVID-19 and future pandemics. Not only does hGO provide resistance to ultraviolet germicidal irradiation (UVGI) irradiation, it also imparts antimicrobial properties. UVGI resistance results from the fact that polymeric additives that absorb UV light provide UV resistance to the composite. In this case, like all graphene materials, hGO is highly absorbing at deep-UV wavelengths due to the conjugated portions of the hGO structure. In addition, the high radical content of hGO is known to induce lipid peroxidation, destroying the integrity of lipid membranes and hence imparting nearly ubiquitous antimicrobial properties. Since enveloped viruses like COVID-19 also possesses lipid membranes, hGO is expected to be effective as an antiviral agent in this context. To assess the effect of UVGI on elastomeric mechanical properties, the hGO composites are subjected to tensile and cyclic fatigue testing following deep-UV exposure for stress/strain measurements and lifetime durability. Electron paramagnetic resonance spectroscopy on control and deep-UV irradiated samples further quantify the radical content imparted by hGO, thus providing insight into how deep-UV exposure affects radical production and antimicrobial efficiency. By varying the amount of hGO and/or related chemically functionalized graphene materials, a durable elastomeric composite is being realized in which the UV resistance, mechanical properties, and antimicrobial activity are optimized for N95 mask sterilization and reuse.

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.

The increasing complexity of deep-learning systems has pushed conventional computing technologies to their limits. While the memristor is one of the prevailing technologies for deep-learning acceleration, it is only suited for classical learning layers where two operands, namely weights and inputs, are processed at a time. Meanwhile, to improve the computational efficiency of deep learning for emerging applications, a variety of non-traditional layers, requiring concurrent higher-order processing of many operands, are becoming popular. For example, hypernetworks improve their predictive robustness by simultaneously processing weights and inputs against the application context. Two-electrode memristor grids cannot natively support such operations of emerging layers. Addressing the unmet need, this research will develop Neuroplane -- a novel deep-learning accelerator of gated memtransistor crossbars. Exploiting crossbars' gate controllability, multiple operands can be processed within the same crossbar unit in Neuroplane. Many advanced inference architectures that can generalize beyond a typical passive crossbar will thus be possible. Overall, the ultra-low-power, higher-order processing of Neuroplane will harness high robustness and efficiency of emerging deep-learning layers within area/power-constrained devices such as mobile, sensor, and embedded systems.

The investigators will develop fabrication methods for nanometer node gate-tunable dual-gated crossbars of MoS2 memtransistors. A self-aligned fabrication method with defect passivation and process variability compensation will be created. Exploiting the gate-tunability of MoS2 memtransistors, a new generation of crossbar platforms with many runtime control knobs will be developed, rendering the design a high elasticity and agile computing space. For example, computing methods will be created for the gated crossbars to utilize crossbar elements for product-sum digitization, thereby preventing the critical overheads in current crossbar technologies. Similarly, control-flow methods will be developed for gated crossbars to adapt their inference paths depending on the input characteristics by dynamically deactivating input/output neurons to conserve processing energy. A coherent collection of software and hardware-based correction techniques is proposed to minimize the impact of process variability. Unlike the current schemes, by following the train-once-deploy-anywhere tenet, the proposed crossbar correction methods can scale to millions of deployments without considerable overhead. An annual workshop will be conducted at local high schools with substantial ethnic and gender diversity to mentor underrepresented students. Undergraduate research projects will be sponsored using paid summer internships and university-level programs such as summer undergraduate fellowship. An inter-university senior-design mentoring program will be created for students among participating institutions.

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.