Zhenan Bao - US grants

9909157
Pachavis

At the 1999 MRS Fall Meeting in Boston, MA (November 29 - December 3) a symposium will be held on "Electrical, Optical, and Magnetic Properties of Organic Solid-State Materials V" (Symposium BB). The goal of the symposium is to facilitate interdisciplinary interactions and information exchange within a broad spectrum of researchers with interests on electronic, optical and magnetic propeties of organic structures for photonics and electronics will be highlighted. The NSF funds will be used to support the attendance of young Americans scientists.

There are emerging opportunities related to the design, synthesis, physical properties, processing, and device applications of organic materials. Great potential for technological advances exist primarily in the area of communications that are based on solid state materials. This is a strategic area of emphasis at NSF.

This project aims to synthesize metal-organic semiconducting molecule-metal structures with nanoscale metallic contacts pre-assembled or templated by DNAs, or directly connected to the molecule as chemisorbed gold nanoparticles/nanowires. The metallic contacts will form ohmic contacts to molecular devices for circuits from DC to microwave frequencies. Precisely fabricated, ultrasmall gaps are not needed since the overall hybrid structure will be much longer than the organic molecule of interest. At optical frequencies, the metallic contacts will form an electromagnetic cavity around the molecular device, enhancing optical fields to be utilized in single-molecule spectroscopic measurements. Self-assembly of these new nanoscale objects will be investigated both theoretically and experimentally. Electrical devices will be fabricated to study charge transport through single molecules. New electrical, optical and physical phenomenon may arise from these unique nanoscale structures. The open planar geometry formed in this work is expected to allow electrostatic modification of electronic states using a nearby strongly-coupled gate electrode, and will reduce fluorescence quenching by nearby metallic electrodes. Single-molecule based transistors and light-emitting diodes may be generated from the proposed structures. The methods developed will lay the groundwork for developing molecular electronic and optical devices and integrating them into complex circuits.
Intellectual Merit. Fundamental advances across disciplines are essential to the advancement of nanoscale devices and to understanding their behavior. Molecular synthesis, self-assembly, and charge transport are essential components for realizing nanoscale devices with organic molecules. A coordinated team attack on such issues can advance the state of single-molecule devices. This project will be carried out by a team of two chemists, one solid-state physicist, one spectroscopist, and one theorist together with collaborators from industry, national labs, and foreign universities with expertise in polymer synthesis, surface chemistry, biochemistry, DNA self-assembly, DNA metallization, spectroscopy, charge transport, fluid dynamics simulation, and device fabrication.
Broader Impacts. This project may result in a new approach to make electrical contacts to single molecules, which will allow study of charge transport through single molecules with different chemical functionalities and length as well as measurement of unique optical properties arising from a single molecule confined in a nanogap. The proposed work will not only answer fundamental questions of intramolecular charge transport mechanisms in molecules with length scale of 5-100 nm, it will also provide answers to technological questions of whether organic molecules have sufficient performance for nanoelectronics and whether the mobility of molecular devices will be dramatically increased by alignment of organic semiconducting molecules between electrodes. This project also utilizes methods to self- assemble DNA-polymer-DNA and nanoparticle-molecule-nanoparticle structures using electrophoresis and dielectrophoresis to allow electrical connections to be made to single organic semiconducting molecules. The PIs will work closely with existing NSF centers and the Stanford Office of Science Outreach to reach a broad population ranging from K-12, community college, undergraduate, and graduate students as well as to prepare teachers of tomorrow for new areas of science and technology. Two internship positions every year for minority and/or women community college students are integral to the project. One research position per year will also be provided to a middle school or high school teacher during the summer; PIs will continue to work with them to develop their education plans after their summer research. PIs will also reach out to the general public through a public website and participation in various community events. The graduate students and postdoc involved in the project will actively interact with each other and have the opportunity to interact with researchers from industry, national labs, and international collaborators. They will be well equipped with a combination of technical engineering skills, basic scientific understanding, and communication skills, and poised to contribute to nanoscience and nanotechnology.

This project provides a fundamental understanding the parameters that affect the nucleation and growth of organic semiconductors from vapor phase for the fabrication of large arrays of organic transistor devices with single crystal channels. Due to the polycrystalline nature of thin films, thin film devices rarely reach the high mobilities of single crystal devices due to trapping at grain boundaries. In order to significantly improve device performance, single crystals and single crystalline films are being provided to produce large arrays of single crystal devices for practical applications. Although technologically challenging, the realization of large arrays of single crystal devices will lead to dramatic performance improvement of organic semiconductor based devices. Detailed studies will be carried out to investigate effects of surface topology,
chemical interactions between surface chemical functionalities and organic semiconductors, orientation of the chemical groups, ordering of the chemical groups, and distribution of chemical groups on the substrate surface.

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Organic semiconductors are promising candidates as the active elements in plastic circuits, particularly those using field-effect transistors (FETs) as switching or
logic elements. Providing the mechanisms for patterning and investigating the numerous parameters that affect the nucleation and growth of organic semiconductors from
vapor phase for the fabrication of large arrays of organic transistor devices with single crystal channels will advance an understanding of organic semiconductor nucleation and growth in general. This research will expose both under-represented graduate students and undergraduates to organic chemistry, surface chemistry, materials and thin film characterization, device fabrication, and device characterization. They will also learn the multidisciplinary approach to problem solving.

TITLE: EXP-SA: Ultra Sensitive Organic Transistor Based Explosives Detector

Stanford University
Zhenan Bao
0730710


Intellectual Merit: Organic monolayer transistors are attractive for ultra-sensitive detection of explosive chemical vapors. By using a mono-molecular layer as the active organic semiconductor layer, the effect of exposure to explosive chemicals is readily sensed and can lead to a much more dramatic change in the current flow than when a thicker organic semiconductor layer is used. Currently, such transistors are being fabricated using expensive electron beam lithography because only small ordered domain sizes are formed from self assembled monolayers. This research seeks to understand the materials requirements and design rules for organic semiconductors needed for explosive chemical sensing applications. The project pursues several methods to efficiently and reliably fabricate large arrays of monolayer transistors, including a new method for forming large ordered monolayers by simple spin-coating, Langmuir Blodgett film approach, and direct writing of electrodes onto vacuum evaporated organic semiconductor monolayers using Dip Pen Nanolithography. The project then investigates the sensing capability of such films. The project also designs and synthesizes new organic semiconductors or binding sites that can improve the sensitivity and selectivity of the monolayer transistor sensors for the detection of strongly oxidizing or reducing explosive chemicals.

Broader Impact: The research has the potential to significantly improve the understanding of organic semiconductor materials for explosive chemical detection. A new class of materials with high performance and robust properties is being designed, synthesized, and characterized using monolayer transistor sensor as a test bed. Graduate and undergraduate students involved in the project will be equipped with a combination of technical engineering skills, basic scientific understanding, and communication skills to prepare them to contribute to the forefront of sensor technology.

The objective of this research is to understand the fundamental mechanisms for the surface self-sorting of single-walled carbon nanotubes. The approach is to combine systematic experiments and ab-initio theoretical modeling to understand the nature of interactions between organic functional groups and single-walled carbon nanotubes.
The combination of superior electrical and mechanical properties in single-walled carbon nanotubes continues to advance applications including flexible electronics, bio/chemical sensors, and solar cell technology. Despite enormous progress achieved exhibiting potential applied uses of SWNT devices, such applications will not be realized unless fundamental issues concerning the controlled reproducible placement, alignment, and chirality/diameter separation can be solved. This work builds on the previous experimental findings of Bao that properly functionalized surfaces can selectively absorb either primarily semiconducting or primarily metallic single-walled carbon nanotubes. This work will lead to better understanding of the nature of interaction between SWNTs and surface functional groups.
The results from this work will have great impact in bringing single-walled carbon nanotubes closer to practical electronic devices. With the combination of both experimental and theoretical approaches, the students involved in the project will have exposure to an interdisciplinary approach for problem solving, applicable to a wide class of problems, beyond those tackled in this proposal. This research will expose both graduate students and undergraduates to organic chemistry, polymer chemistry, surface chemistry, quantum simulations, materials and thin film characterization, device fabrication, and device characterization. Both PIs are greatly committed and have been actively involved in outreach and education, which will be continued in this program.

TECHNICAL

This Gordon Research Conference on "Electronic Processes in Organic Materials" is supported by the Solid State and Materials Chemistry (SSMC) and Electronic and Photonics (EPM) programs and provides an ideal setting to discuss in depth transformative developments with leading scientists from academia, government, and industry. The field of organic electronics and photonics has enjoyed tremendous progress since the discoveries in the late seventies of conducting polymers and in the late eighties of efficient electroluminescent devices based on small organic molecules or polymers. The market for organic electronics-based products is now projected to reach over $30 billion by 2015. Various sessions will be devoted to the chemistry, physics, biology, materials science, optical science, nanoscience, engineering, and device fabrication of electrically-active and optically-active organic materials. This conference has consistently hosted presentations at the cusp of important new directions for the field. Meetings have driven progress at critical stages of developments in areas including organic opto-electronics, polymer light-emitting diodes, single-molecule studies, organic electronics, and organic solar cells.

NON TECHNICAL

Key researchers will be present to address the critical questions through a combination of presentations and informal discussions. Invited speakers and session chairs represent the highly interdisciplinary nature of the Organic Materials field with experts from chemistry, physics, material science and engineering, chemical engineering, and electrical engineering with both experimental and theoretical approaches. Speakers and sessions chairs are from a diverse background, including 7 from outside US and 4 female. A primary goal of this funding request is to assist researchers in the early stages of their careers (students, postdoctoral researchers, and/or new faculty) to participate in the conference and join the "Electronic Processes in Organic Materials" community. The conference will enhance their research programs and proposals by inspiring goals and ideas at the leading edge of the field. At the same time, the intimate atmosphere of the conference will allow them to have more exposure of their work within the community and make important connections.

Technical: This project aims for measurement and understanding of charge transport in single molecules. The approach to achieve ohmic contact is to synthesize conductor-organic semiconducting molecule-conductor with nanoscale metallic or molecularly doped contacts self-assembled or templated by DNAs. The conducting contacts are self-aligned and make contacts with each end of the organic semiconductor molecule (OSM) with length scale ranges from 5-100 nm. Precisely fabricated, ultrasmall gaps are not needed since the overall hybrid structure will be much longer than the organic molecule of interest. Experiments on electrostatic modification of molecular electronic states via a nearby strongly coupled gate electrode are included. The methods developed are expected to lay the groundwork for developing useful molecular electronic devices and eventually integrating them into complex circuits.
Non-technical: The project addresses basic research issues in a topical area of materials science and macromolecular chemistry with technological relevance, and is expected to provide unique opportunities for graduate and undergraduate training in an interdisciplinary field. The proposed work will allow direct measurement of charge transport through single molecules with different chemical functionalities and length, providing critical information on whether organic molecules have sufficient performance for nanoelectronics. The PI will continue with her activities to reach out to a broad population ranging from K-12, community college, undergraduate, and graduate students as well as efforts to engage and prepare the teachers of tomorrow for new areas of science and technology. This project will expose both graduate students and undergraduates to organic chemistry, polymer chemistry, surface chemistry, materials and thin film characterization, device fabrication, and device characterization. Students will experience an interdisciplinary approach to problem solving and become equipped with a combination of technical engineering skills, basic scientific understanding, and communication skills. This project is co-supported by the DMR Electronic and Photonic Materials and CHE MSN (Macromolecular, Supramolecular and Nanochemistry) programs.

This award focuses on creating a comprehensive processing and design infrastructure to enable and accelerate research on robust VLSI technology using Carbon Nanotube Field-Effect Transistors (CNFETs) for next generation energy-efficient computing systems. CNFETs represent a significant departure from traditional silicon technologies, and can potentially enable computing systems with more than an order of magnitude better energy efficiency compared to silicon-CMOS. Moreover, a unique aspect of CNFET technology enables massive monolithic three-dimensional integration. However, several fundamental challenges must be overcome before such benefits can be achieved. This requires significant inventions in inter-disciplinary fields of devices, processing, VLSI design and CAD, and integrated computing system design. Hence, a significant amount of infrastructure is required, where robust and repeatable processing and design flows are established (unlike stand-alone prototypes). Such a comprehensive infrastructure for CNFET VLSI, created in this project, will enable easy adaptability and integration of new inventions. This will help build a research community around a common CNFET VLSI processing and design platform.
It will also provide unique opportunities for exploring new research frontiers, and solid training of the next generation of researchers and practitioners.

The objective of this program is to create a stable and robust electronic sensor platform capable of sensitive and selective detection of analytes in complex liquid media. This project will investigate the fabrication and functionalization strategies for sensors. This project will utilize numerous pathways of attaching receptors for small molecule and biological analytes on and around the nanotube surfaces. The approaches and methods proposed here are expected to lay the groundwork for future highly sensitive sensor technologies.
The intellectual merit is to develop a technology that utilizes electrical engineering and materials science in the development of device architectures capable of functioning in complex media. The sensor platform is based on our unique solution-based method of "surface sorting" to create primarily semiconducting carbon nanotubes (scSWNTs) and our specially synthesized organic semiconductors. The project will enable a new approach to detection technology using organic electronics. The proposed studies will allow probing of biological processes as well as monitoring analyte concentrations in real time and within the required complex media. The proposed work is expected to provide a major step towards the incorporation of organic electronics within practical sensors.
The broader impacts are the participation of community college students, graduate students and undergraduates, and the development of interdisciplinary research in the United States and to promote public understanding of the impact of organic electronics on industrial and economic development. The development of a highly sensitive, selective and robust sensing platform will have applications ranging from biomedical, environmental, defense to food security.

TECHNICAL SUMMARY
Charge transfer doping is crucial in enabling highly efficient organic light emitting diodes and organic solar cells, and is needed for controlling the electrical characteristics of organic field effect transistors. Whereas the development of p-type dopants is well advanced, there is still a lack of effective air-stable solution processabile n-type dopants, due to limited knowledge on the detailed doping mechanisms. To address this gap, this Materials World Network project, supported by the Solid State and Materials Chemistry program and the Office of Special Programs, Division of Materials Research, aims at a) understanding the design rules for air-stable n-dopants based on a promising class of dopants with (1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl (DMBI) as the model system and b) understanding the detailed doping mechanisms of n-type doping. The three groups involved in the project have a unique combination of complementary expertise. The Bao group will synthesize DMBI dopants with systematically varied energy levels and substituents for better miscibility with the matrix to aid the understanding of doping mechanisms. The chemical process of doping will be investigated with UV-vis-NIR and electron paramagnetic resonance. The morphology of doped layers will be studied by atomic force microscopy, various X-ray techniques and nanoSIMS. The Leo group in Germany will study the physical mechanisms of doping by impedance spectroscopy, ultraviolet photoelectron spectroscopy, the Seebeck measurement, and modeling of the charge transport characteristic by a master equation model. The air-stability will be tested and the dopants will be used in state-of-the art organic devices such as light emitting diodes, solar cells, or transistors. Finally, the Cuniberti group in Germany will study the doping effect on a single molecular level by high resolution scanning tunneling microscopy and will model the doping process by ab initio calculations based on density functional theory.

NON-TECHNICAL SUMMARY:
Charge transfer doping is crucial in enabling highly efficient displays, solid-state lighting, organic solar cells, and is needed for controlling the electrical characteristics of organic field effect transistors. Whereas the development of p-type dopants is well advanced, there is still a lack of effective air-stable solution processabile n-type dopants, due to limited knowledge on the detailed doping mechanisms. This Materials World Network project will advance the understanding of the chemistry and physics of doping through an international co-operation across the disciplines of chemistry/ chemical engineering, fundamental physics and theory. These findings will lead to better understanding of design rules for stable and efficient n-dopants and more efficient devices. This project will train students and postdocs with a solid fundamental understanding as well as a global experience. This project will help to foster economic growth by furthering the field of organic electronics and the associated industry. This project will train students with exposure to interdisciplinary research and diverse cultures. Bao will work closely with Stanford NSF centers and Office of Science Outreach to reach out to a broad population ranging from K-12, community college, undergraduate, and graduate students, as well as prepare the teachers of tomorrow for new areas of science and technology.

TECHNICAL SUMMARY:
Solution processing is highly desirable for large area production of organic electronic devices. Film deposition from solution is usually performed at the kinetic crystallization regime in high throughput industrial fabrication processes. Attaining single crystals directly through solution printing remains challenging due to kinetic solvent evaporation, stochastic nucleation, and fluid flow instabilities during the printing process. Most solution processing techniques for fabricating single crystals operate at slow quasi-equilibrium conditions, rendering these methods undesirable for industrial applications. These challenges call for a better fundamental understanding of solution crystallization processes of organic semiconductors (OSCs) to allow the development of better solution processing methods for high-throughput fabrication of high performance electronic devices. In this project, supported by the Solid State and Materials Chemistry program, ways to control crystal nucleation and molecular packing will be obtained using a solution shearing (SS) platform as a model system. The parameters for controlled crystal growth from single nucleation sites and methods to obtain patterned single-crystalline domains will be investigated. Finally, a comprehensive understanding and approach will be developed for achieving patterned single-crystalline domains with desired molecular packing. Charge transport properties of the resulting films will be measured to characterize effects of morphology and molecular packing on charge transport. This work will develop fundamental understanding on tuning molecular packing and morphology in OSCs. This is essential for unprecedented performance and future large-scale production of organic electronics.

NON-TECHNICAL SUMMARY:
Solution processing is highly desirable for large-area manufacturing of organic electronic devices. The proposed work will result in a systematic understanding of nucleation and growth in solution processing of organic semiconductors (OSCs). This is crucial for advancing the field of organic electronics, as well as, providing insights for future manufacturing of these devices (e.g. organic light emitting diodes, organic solar cells, transistors and sensors). The PI and student involved will work closely with the Stanford Office of Science Outreach Office to reach out to a broad population ranging from K-12, community college, undergraduate, and graduate students as well as prepare the teachers of tomorrow for new areas of science and technology. This research will expose both graduate students and undergraduates to a broad range of disciplines as well as a wide range of organic electronics technologies. Students will receive training on effective communication, a multidisciplinary approach to problem solving, thus, obtaining an impressive combination of technical engineering, basic scientific understanding, and communication skills. This research is also expected to support the development of interdisciplinary research in the United States and to promote public understanding of the impact of organic electronics on industrial and economic development.

DMREF: A High-Throughput Computational Morphology Prediction for Organic Photovoltaics
Zhenan Bao (Stanford), Vijay Pande (Stanford), Michael Toney (SSRL)

Non-Technical Description: Organic photovoltaic cells (OPVs) are alternatives to conventional solar cells as they promise low-cost mass production combined with lightweight and flexible applications. In particular, they offer a prospect to provide basic electricity to the millions of people in rural areas of undeveloped countries who lack access to the power grid. Many OPV materials have been reported in the literature, but few have shown efficiencies greater than 8%. The key challenge is to design materials that fulfill all the requirements. A typical OPV consists of a donor and an acceptor blended together. Predicting the nanoscale morphology remains one of the biggest challenge in predicting OPV performance. Therefore, many material combinations and large processing parameter space (e.g. donor/acceptor ratio, solvents, annealing conditions, film thickness) presently need to be screened.

Technical Description: This project aims at an integrated research plan for the high throughput morphology prediction of OPV materials. A continuous feedback loop between theory, synthesis and characterization will facilitate the exchange of results and streamline the overall development process. A central theme of this project is to develop high-throughput techniques for computational morphology calculation and experimental characterization. The computational development takes advantage of the massive computing power provided by distributed volunteer computing networks. Pande will retool his massive Folding@home simulation engine (which was originally developed for molecular mechanics/dynamics research on biomolecules) to predict the bulk-heterojunction blend morphology for OPVs. Folding@home has allowed Pande and coworkers to perform calculations that could not be performed before, by allowing them to reach timescales that are thousands to millions of times longer than would be possible by traditional means. Bao will design synthesis routes to prepare model compounds for thin film preparation and comparison with theoretically predicted morphology. Bao and Toney will together perform optoelectronic, structural, and morphological measurements on the compounds. The characterization will establish and employ new high-throughput instrumentation. The experimental data, regardless of positive or negative outcome, will be made available to the theory group where it will be added to a collection of empirical data. The latter is utilized in calibration schemes and provides the parameterization for many of the employed models. Extending this data set will improve the related modeling efforts and their predictive capacity. This in turn will lead to an adjustment of the development processes. An extensive results and reference database will serve as the hub for the information exchange between the three participating groups. The vast amount of data accumulated in the course of this project will provide the foundation for a better understanding of the molecular structure/morphology correlations, and it will be an openly available resource for the OPV community.

The broad vision for this project is to develop new tools for future biomanufacturing through cross-cutting collaborations of scientists?chemists, biologists, physicians, and engineers?united by the immense opportunity of building functional materials with, and within, biological life. The proposed methodologies establish the biomanufacturing toolbox for genetically-targeted chemical synthesis of a variety of functional materials within living cells, tissues and animals. Diverse cell-specific chemical syntheses enable a broad array of functional characteristics and assembled structures. In the long term, such techniques enable building electronics directly within biological systems by harnessing the complex assembly structures within cells. The application of these techniques to develop the capability to create new conductive pathways within the brain may lead to rewiring of neural circuits. Moreover, genetically-targeting the peripheral nerve may allow cell-specific nerve stimulation and recording for neuroprosthesis. Further investigation of the deposited material on neural activity may lead to treatments for diseases such as Alzheimer?s disease (AD) and amyotrophic lateral sclerosis (ALS), or selectively repair demyelinated areas for treatment of multiple sclerosis (MS). Even though current work only focuses on basic tool development and initial understanding of the impact of the modifications on neural activities, the tools can be potentially expanded to diverse cell types for therapeutics and creation of new materials and assemblies. This project offers direct training opportunities for the students and postdocs involved in terms of research as well as important skills for interdisciplinary collaboration. These trainees subsequently further the development of biomanufacturing and their method of collaboration by running their own independent research groups in academia or by incorporating their knowledge into future industrial developments. A Training Core program in this project provides hands-on training on basic biomanufacturing techniques for hundreds of students, instructors and researchers.

Despite existing ability to engineer materials with diverse form and functionality, a high-level of structural and functional complexity found in multicellular living systems are still challenging to realize. The capability of genetically targeting enzymes and other proteins to specific cell types has yet to be harnessed to direct complex assembly of functional structures instructed by biological systems. This project integrates the fields of molecular genetics, tissue biology, chemistry, and materials science in unprecedented ways to transform the biomanufacturing of complex structures. The project focuses on building novel structures in vivo, creating natural and unnatural polymers within targeted cell-types of living organisms. This approach is extended to the development of a universal shared methodology for targeted chemistry within living beings. The work proposed focuses on developing and applying novel toolboxes for diverse genetically-targeted synthetic processes while engineering for biocompatibility, characterizing the synthesized molecules/materials, and understanding the mechanisms and implications of forming synthetic materials for eliciting natural and novel biological functions.

This award is co-funded by the Division of Molecular and Cellular Biosciences, the Division of Chemical, Bioengineering, Environmental and Transport Systems and the Division of Chemistry, and also by the Division of Industrial Innovation and Partnerships, the Division of Engineering Education and Centers, and the Division of Materials Research.

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.

A shared objective of precision health and psychiatry is to precisely measure relevant symptoms and sustain mental health with high precision. Best mental health practices propose the need to identify the early signs of risk factors such as stress. However, mental health research focuses primarily on late-stage symptom assessment via self-report data such as surveys. As a result, clinical practice for mental health mostly consists of reactive treatments. This grant seeks to advance precision mental health by developing an Artificial Intelligence (AI) -enabled platform for continuous and precise measurements of stress. This platform leverages data from a skin-like wearable device that measures cortisol, a stress hormone from sweat, and from sensing techniques based on estimating muscle stiffness changes derived from ?fight or flight? stress response, by ?repurposing? signals available in billions of existing mobile and computing devices. These data streams will be combined using Machine Learning (ML) algorithms for optimizing data collection, power consumption, and accuracy. Since stress and its effect on mental health deterioration are pervasive, the broader impact of this work could be enormous as well as the basis for new research on precision health in psychiatry.

The overall goal of this project is to develop a multimodal sensing platform leveraging AI/ML algorithms to optimize stress prediction and hardware performance. The first step involves validating the skin-inspired wearable for lab stress measurements, followed by redesigning, and validating as a continuous in-the-wild device. It features a set of physiological sensors for collecting heart rate variability (HRV) and electrodermal activity (EDA) data, signals directly correlated with the autonomous nervous system (ANS) response. Two types of sensors for continuous measurement of cortisol level will be tested for high accuracy and selectivity. However, processing and transmitting sensor data continuously in-the-wild requires significant battery capacity. To address this issue, the second step combines the wearable with passive biomechanical sensors and AI/ML algorithms to optimize for continuous stress detection in-the-wild. Additionally, passive sensors transform computer peripheral data (e.g., mice, trackpads, smartphone screens) into parameters correlated to muscle stiffness linked to the ?fight or flight? stress response. For example, the system uses inverse filtering techniques to approximate mass-spring-damper (MSD) models derived from mouse displacements or force models derived from the area under the finger on a trackpad. The system employs several AI/ML algorithms including a) compressive sensing to optimize energy efficiency, b) autoencoder models to correct for artifacts, missing data or sensor failures, c) active learning to discover optimal collection times of stress events and labels, and d) cloud computing powered data collection and processing to make predictions based on the best available data. The intellectual merits of this work include 1) a multimodal stress monitoring wearable that measures cortisol from sweat and other physiological signals, 2) biomechanical sensing algorithms that repurpose movement and touch data into muscle stiffness, and 3) AI/ML algorithms that integrate this data to optimize wearable and smartphone power usage, learn ideal sensing scenarios with high precision, improve privacy, optimize data labeling, and optimize the early prediction of stress.

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.

NON-TECHNICAL:

Polymer semiconductors are promising for flexible electronics. However, their charge carrier mobilities are limited by the highly disordered thin film morphology and trap-dominated charge transport. Thus, it remains a grand challenge to reduce the disorder and realize the full potential of conjugated polymers for charge transport. The goal of this project is to explore a method for epitaxial growth of polymer semiconductor single crystals with two-dimensional metal halide perovskite (MHP) single crystals as interacting substrates. If successful, it will allow direct measurement of intrinsic intra- and interchain charge transport in polymer semiconductors. With less defects as traps, it may be possible to observe unprecedented charge transport. This work will provide fundamental insights on conjugated polymer heteroepitaxial crystal growth. The techniques investigated here may be further developed in the future for larger-scale assembly and for systematic investigation of the structure-property relationship for charge transport in polymer semiconductors. Breaking the disorder-dominated charge transport limit of conjugated polymers may potentially bring the field to a new level and opens new applications previously not possible for various optoelectronic and sensing applications. The materials investigated here can be readily integrated into teaching, education, and outreach.


TECHNICAL:

Polymer semiconductors are promising for flexible electronics. However, their charge carrier mobilities are limited by the highly disordered thin film morphology and trap-dominated charge transport. Thus, it remains a grand challenge to reduce the disorder and realize the full potential of conjugated polymers for charge transport. The goal of this project is to explore a method for epitaxial growth of polymer semiconductor single crystals with two-dimensional metal halide perovskite (MHP) single crystals as interacting substrates. If successful, it will allow direct measurement of intrinsic intra- and interchain charge transport in polymer semiconductors. With less defects as traps, it may be possible to observe unprecedented charge transport. Polymer semiconductors will be prepared to systematically investigate structure property relationships for single crystalline structure formation and charge transport. Various types of two-dimensional perovskite single crystals will be used as templates to guide the assembly of organic semiconducting oligomers and polymers. This work will provide fundamental insights on conjugated polymer heteroepitaxial crystal growth. The techniques investigated here may be further developed in the future for larger-scale assembly and for systematic investigation of the structure-property relationship for charge transport in polymer semiconductors. Breaking the disorder-dominated charge transport limit of conjugated polymers may potentially bring the field to a new level and opens new applications previously not possible for various optoelectronic and sensing applications. The materials investigated here can be readily integrated into teaching, education, and outreach.
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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.