Ritesh Agarwal, Ph.D. - US grants

0609083
Agarwal
This project will develop a new type of nano-scale device called a nanowire spectrometer for chemical analysis. The work will involve four steps: (1) synthesis and characterization of CdS, CdSe and ZnS nanowires with energy band gaps in the UV-Visible region; (2) fluidic assembly of single nanowires and 2-D nanowire rafts onto insulator substrates; (3) fabrication and optical testing of self-aligned gaps within nanowires and nanowire rafts; and (4) fabrication of spectrometers (single and multiple wavelength) by integrating the nanowire light source and detector with microfluidics. The broader impacts of the project include closely coupled research and education plans. Successful completion of the project could lead the development of low-cost, portable, miniature optical spectrometers with potential applications in environmental monitoring, biomedicine and many other fields.

0644737

Intellectual Merit: The objective of this CAREER proposal is to synthesize and study the optical properties of self-assembled nanowire heterostructure materials ranging from molecular to microscopic length scales. Fundamental understanding and exploitation of quantum effects in optical devices holds great promise to revolutionize nanophotonic systems. The research will focus on the synthesis and characterization of nanowire heterostructures and devices in different geometries with accurate control over composition and dimension for investigating fundamental optical properties of systems in confined geometries. The following approach will be undertaken: 1) Develop the atomic-layer deposition technique to synthesize nanowire heterostructures. 2) Characterization of nanowire heterostructures using electron microscopy, optical, electrical, and optoelectronic measurements. 3) Fabrication of quantum-confined nanowire photonic devices such as diodes, lasers, and single-photon sources. The proposed research extends across several frontiers of science and engineering, with the main focus on studying optical properties of chemically grown nanowire heterostructures where finite size, surface and quantum effects become predominant. It will lead to the development of new sub-lithographic nanophotonic devices, which are difficult to assemble using conventional techniques including integration of photonic components with Si-based electronics.

Broader Impact: The proposed research will greatly impact the field of nanophotonics, which represents a major driver ushering the era of nanotechnology. Bottom up approach to self assemble nanostructures will create highly efficient nanosystems with functionalities not possible with any conventional technology. Integrated nanophotonics/electronics will allow development of new, cheaper and efficient devices that will impact areas such as telecommunications, computing, diagnostics, and sensors. The main focus of the educational plan of this proposal is to develop innovative teaching tools to enable students at all levels to acquire high-quality scientific education. The PI will integrate research activities and educational goals by: 1) Developing a new curriculum in nanosciences in the Materials Science department at Penn. 2) Involvement of undergraduates, underrepresented groups and minorities in the research program. 3) Develop Science Van project to take scientific equipment and experiments to under-equipped high schools in West Philadelphia.

Technical: This project addresses reversible crystalline to amorphous phase transition phenomena in self assembled Ge-Sb-Te nanowire (NW) materials at sub-lithographic length scales. The approach focuses on synthesis and characterization of complex, well defined Ge-Sb-Te NWs with control over composition and dimension for investigating fundamental phase switching properties, and assembly of prototype memory elements. Components of the approach include: 1) Development of pulsed laser deposition (PLD) growth technique to synthesize complex ternary Ge-Sb-Te NWs with precise control over NW chemical composition and diameters. 2) Characterization of structural and chemical composition of NWs with electron microscopy (SEM, TEM). 3) Investigation of electric field induced phase switching behavior and its dependence on chemical composition and size (diameter) of NWs. Study of the influence of size on thermodynamic parameters and its affect on phase transition mechanism in NWs. 4) Insitu TEM analysis of structural transformations in Ge-Sb-Te NWs as a function of applied current pulses. Size and chemical composition dependent study of amorphization and recrystallization mechanism in NWs. 5) Fabrication of novel NW memory devices based on insights obtained from the experiments described above.
Non-technical: The project addresses basic research issues in a topical area of electronic/photonic materials science with high technological relevance. Research and educational activities will be integrated by the involvement of undergraduates in the research program, incorporating new research results in a teaching module, and training high school and college teachers from the Philadelphia district with student population from minority and underrepresented sections.

0923245
Carpick
U. of Pennsylvania

Technical Summary: High impact nanomaterials research requires the innovative combination of normally separate techniques into multifunctional instruments that gather multiple forms of com-plementary data. In particular, nanoscale spectromicroscopy - the combination of micro- and nano-scale microscopy with powerful spectroscopy - is a lynchpin approach. We propose the acquisition of an atomic force microscope (AFM), near-field scanning optical microscope (NSOM) and confo-cal Raman microscope combined in a single, multifunctional system. The light source will be not only a standard laser but also a powerful turnkey tunable laser that enables a broad range of spec-troscopy and femtosecond measurements of dynamic nanoscale phenomena. It will function in seamless combination with the microscope for spectromicroscopy and also serves as a stand-alone source for complementary spectroscopy work to maximize its use and value. It will aid a broad range of research in nanoscale phenomena, materials, and devices involving 18 identified users. The crucial combination of microscopy and spectroscopy allows observed phenomena to be asso-ciated with specific nanoscale features and entities, such as connecting optical and structural prop-erties of semiconducting nanowires, studying optical phenomena in nanocircuits, probing the nanostructure of the cell wall, characterizing nanomechanical behavior, and studying polymer nanocomposites. It will be installed and managed in the Probe Innovation Facility of Penn?s Nano Bio Interface Center for widespread access. Vigorous associated outreach efforts include graduate and undergraduate curricular development, and substantial high school teacher and student en-gagement through established outreach programs which emphasize connecting with students from underrepresented groups and economically disadvantaged backgrounds in greater Philadelphia.

Layman Summary: Nanotechnology is the study and development of new materials and devices that possess exciting and unprecedented properties thanks to having their structures controlled at the scale of a few atoms and molecules. It is extremely difficult to ?see?, ?feel? and ?listen? to at-oms, molecules, and nano-scale structures, yet we must do this to understand how they behave and make useful applications from them. Recently, researchers have developed ways to do this at the nanoscale with new techniques for microscopy (taking highly magnified images of the size and shape of objects) and spectroscopy (measuring the energy absorbed and emitted by objects). This funding will be used to purchase an instrument that combines both microscopy and spectroscopy in a multi-tasking system that includes a powerful, versatile laser. The laser illuminates the nanoscale objects being studied with light, where the color of the light can be selected from a wide palette. Simultaneously, the microscopy is used to determine where light is being absorbed, re-emitted, or scattered by the nanoscale objects being studied. As well, we can measure the size and shape of the objects, sense how stiff and strong they are, measure how sticky and frictional they are, and meas-ure how well they conduct electricity and heat. By making all of these measurements at once, or at least one right after the other in the same instrument, we will be able to quickly learn how the nanoscale objects behave. Researchers will use this equipment to study nanoscale materials and structures for applications including communicating information in new ways using light, develop-ing new ways to understand the cell and to treat and diagnose diseases, and creating new materials for strong, durable, lightweight structures and powerful, efficient electronic circuits. The system will be installed in Penn?s Nano Bio Interface Center, a leading national research center, for very open access. We will also use this instrument in several courses at Penn, and will engage high school teachers through programs in greater Philadelphia that connect with students from eco-nomically disadvantaged backgrounds and underrepresented groups in science and engineering.

Abstract:
Technical: The PI will study the electrical properties of phase-change nanowires (NW) self-assembled from Ge-Sb-Te alloys, which are important materials for their use in non-volatile random access memory devices. Chalcogenide materials (e.g., Ge-Sb-Te alloys) have been dominant in the field of nonvolatile optical and electrical storage applications because of their reversible crystalline-amorphous phase transition that is signified by large changes in the optical reflectivity and electrical resistivity. The realization of these advantages in memory device applications is, however, still limited with requirements for high scalability, low-power consumption and fundamental understanding of electrical transport, threshold switching and recrystallization mechanism from the amorphous phase. These challenges motivate the design and understanding of nanostructured materials with sub-lithographic features based on bottom-up approach. During the project they will develop NW-based experiments to systematically understand fundamental properties of size-dependent nanoscale electrical switching and phase transitions that are important in order to instruct the design of future memory devices. The evolution of the phase-change properties especially for amorphous phase nanostructured glass as a function of size has not been fully explored, mostly due to the lack of material systems that can be prepared in a controllable fashion with sufficient size control and without damaging the surfaces that occurs in top-down lithographic techniques. The study of NW phase-change materials will provide valuable information on the size-scaling of the phase-change mechanism down to sub-20 nm lengthscales that cannot be easily obtained from top-down patterned systems. The proposed research will be built upon the recent breakthroughs in the PI's laboratory in the area of phase change NWs, with demonstration of memory switching and remarkable size-dependent properties. The important questions that they will seek to obtain answers are: what is the conduction mechanism in the amorphous phase and its size and composition dependence; what is the mechanism of threshold switching and nucleation from amorphous to crystalline state; what role does stress or electronic relaxations play in temporal drift behavior of the amorphous phase. The PI will combine novel synthesis, structural characterization with detailed electrical measurements to answer these intriguing questions.
To accomplish the objectives, the following approach will be undertaken:
1) Synthesis of complex chalcogenide nanowires with precise control over their chemical composition and size. Capping of NWs with dielectric materials to prevent surface oxidation.
2) Study the conduction mechanisms in amorphous state of phase change nanowire devices.
3) Temporal drift behavior of phase change nanowires in the amorphous state
4) Nucleation and threshold switching and their statistics in amorphous phase nanowires.
Non-technical: Bottom up approach to self assembled nanostructures presents a unique way of creating highly efficient nanosystems that will have functionalities that are not possible with any conventional technology. The development of such a memory system will have tremendous impact on a variety of applications such as cheaper and highly efficient computer random access memory systems, and ubiquitous portable devices such as ipods and digital cameras. Research and educational activities will be integrated by the involvement of undergraduates in the research program, incorporating new research results in the teaching module, and training high school and college teachers from the Philadelphia district with student population from minority and underrepresented sections.

DESCRIPTION (Provided by the applicant) Abstract: We propose to assemble nanowire devices with optoelectronic and electrical functionalities to probe intra- and inter-cellular dynamics with unprecedented spatial and temporal resolution. Arrays of electrically pumped nanowire waveguides, lasers, light emitting diodes, and photodetectors combined along with their ability to function as nanoelectrodes will be utilized to probe organelles and other subcellular targets with nanoscale resolution and measure in real-time chemical reaction kinetics, signal propagation, and reactions due to a locally delivered drug, amongst other complex phenomena occurring over any relevant length scales. The arrays of nanowire probes will be functionalized with fluorophores, quantum dots, plasmonic nanocrystals, either at their tips or on their surfaces to enable almost any type of biological imaging technique. Using a general nanowire probe platform will lead to the development of a very broad set of tools with novel functionalities, to enable imaging and electrical probing with label-free techniques with the unique capability of probing any desired spatial domain within living cells. These nanowire-probe substrates can be easily integrated with AFM cantilevers or the tips of conventional fibers, which can then be combined with standard 3-D nanopositioning systems, external electrical circuitry, and optical microscopes to probe specific domains of intracellular organelles/components. As an example, these nanowire devices will be used to create novel nanoscale interfaces with neurons and neuronal networks in the hippocampus to study neuronal signal integration and network functioning and then utilized to investigate the pathophysiology of diseases such as epilepsy. The integration of optoelectronic and electrical functionalities of nanowires on a common platform would lead to a new generation of nanosystems with unprecedented sensitivity and selectivity in probing subcompartments of living cells at the molecular level, which could revolutionize our knowledge of these biological systems and tremendously aid in future drug discoveries. Public Health Relevance: The ability to visualize in vitro intra- and inter- cellular processes in real time with multiplexed and nanoscale resolution detection with the proposed combined optoelectronic and electrical nanowire probes will elucidate new chemical and electrochemical processes and signaling pathways. Detailed knowledge of suband inter- cellular processes using nanowire probes will lead to a much better understanding of overall cellular processes and will aid the design of new drugs for a large number of diseases thereby impacting public health.

TECHNICAL SUMMARY
The objective of this Materials World Network project is to investigate comprehensively the material properties of phase change materials in mixed optical-electrical phase transitions. The underlying principle of memory storage in Ge-Sb-Te alloys is reversible crystalline to amorphous phase transitions that are associated with significant changes in optical reflectivity and electrical resistivity. Although the optical and electrical mechanisms have been independently investigated, there is no work done on the mixed-mode operation, i.e. switching the material optically while probing it electrically and vice-versa. This is however extremely important for a host of potentially game-changing applications ranging from optically gated ultra-fast transistors to non-von-Neumann arithmetic processing. This collaboration between PIs in US, UK and Germany will focus on investigating fundamental phase switching properties in mixed-mode, elucidating phase change mechanisms via dynamic optical probing of electrical phase transitions, and exploring the materials best suited for unconventional future arithmetic processors. The work will involve growth and characterization of new compositions of phase change nanowires, optical pulse induced switching which will be probed electrically, and detailed size- and composition-dependent studies of mixed mode operation in nanowires.

NON-TECHNICAL SUMMARY
The von Neumann model of computing, which is currently used in computer architecture, utilizes designs with separate divisions for processing, logic and memory. Although this design has been highly successful for today's computers, there is clearly a need to go beyond von Neumann's model to keep up with the ever-increasing demand for faster computers with unprecedented capabilities. Combining arithmetic processing capabilities via optical excitation with electronic memory on a common platform is one possible solution to go beyond the conventional computer architecture and phase change materials are very promising in this regard. This Materials World Network project plans to study for the first time the optical-electrical mixed mode behaviour of phase change materials. Although the remarkable properties of these materials have made them commercially successful in memory devices, the fundamental material properties that govern their phase transitions between crystalline and amorphous states are still quite unknown. The project will provide fundamental and novel insights into how the electrical behaviour of these materials is influenced by optical excitation and vice versa. The research seeks to transfer best practises between PIs in three participating countries. The results of this work will greatly impact the development of non-von Neumann computing using arithmetic processing techniques that can revolutionize computing as we know it. Research and educational activities will be integrated by the involvement of undergraduates in the research program; incorporating new research results in the teaching module, and training high school teachers from the local school districts in three countries. In addition, international collaborative opportunities will give students opportunities to spend time in another laboratory and will provide a unique opportunity to pursue cutting edge research across national boundaries.

This project is supported by the Electronic and Photonic Materials program and Office of Special Programs, Division of Materials Research.

EFMA - 1542879
PI: Johnson, Alan T.

This project will develop new chemical sensors composed of biological molecules coupled to two-dimensional atomic crystals. The biological molecules will act as sensors by binding chemical targets in liquid and air samples. The atomic crystal layers will act as readouts by changing their optical or electronic properties when chemical targets are bound by the coupled biological molecules. The team will explore several biological molecules capable of binding specific targets coupled to various atomic crystals composed of compounds called transition metal dichalcogenides. The project will involve fabrication of the crystal layers, measurements of their electronic and optical properties, attachment of the biological molecules, and analysis of the resulting sensor capabilities. Experiments will be conducted in tandem with computational modeling to understand the response of the atomic crystals and predict sensor performance. Results of the project will lead to improved chemical sensors with unprecedented sensitivity and specificity for a variety of applications, including diagnosis of disease, environmental monitoring and law enforcement. The team will use the project to increase awareness of local communities about research at the frontier of nano-biotechnology and to involve student researchers, especially members of groups traditionally underrepresented in science and engineering.

The goal of the project is to develop the basic scientific and engineering knowledge needed to advance nano-biosensor research towards implementation of transition metal dichalcogenides-based biosensors with optical and/or electronic readout. The team will develop scalable chemical vapor deposition approaches to large-area synthesis of MoS2, WS2, SnS2, and other materials identified through materials exploration. The material properties of these systems will be rigorously benchmarked using a combination of advanced structural, chemical, optical, electronic, and scanned probe measurements. A comprehensive set of chemical functionalization techniques will be developed suitable for fabrication of protein-functionalized biosensors with plasmonic, nanophotonic, and/or electronic readout. The impact of chemical functionalization on the electrical and optical properties will be systematically investigated. The measurements will be correlated with multi-scale computational models appropriate for simulating the response of the biosensors, with the goal of developing simulation methodologies suitable for predicting biosensor performance and guiding sensor design.

Nontechnical Description:

Almost all electronic products utilize memory devices to store and access information. The requirements for these memory devices include high-density information storage capacity, fast read/write speed and low power consumption. There is a need to continuously discover new materials for memory devices with superior properties to meet the increasing demand of the information technology. Amongst many types of materials, phase change materials are a very promising system as they can switch very rapidly and reversibly between high and low resistance states when electrical current pulses are applied. However, many challenges remain to be overcome in order to make the technology commercially viable. A major one is that a large electrical current is required to change the resistance states. The large current reduces power efficiency and leads to material's degradation. This research project tackles this materials science challenge and studies the degradation mechanisms via advanced microscopy techniques. The research findings can be used to design better materials for future electronic memory devices. In this project, research, training and educational activities are tightly integrated. The latters include (1) the involvement of undergraduates in the research laboratory, (2) incorporation of the latest research results in the teaching module, and (3) training of high-school and college teachers in the Philadelphia district with a high minority student population.


Technical Description:

This research project studies the effect of electric field on the structural and chemical changes in phase change nanowires made of germanium-antimony-tellurium (Ge-Sb-Te) alloys. The research team utilizes a unique lateral configuration of nanowire devices to directly investigate the changes in Ge-Sb-Te nanowire structure, morphology and chemical composition via in-situ electron microscopy measurements while operating the device under an electrical bias. The goal is to understand the fundamental mechanisms operative behind the functioning of phase change materials, especially the effect of electric field and current on atomic migration and recrystallization. The research provides insights into the atomic processes that are responsible for the functioning of phase change memory devices and their failure mechanisms. The insights obtained will impact the development of novel materials for non-volatile, ultra-dense, ultrafast and energy efficient memory devices .

Electronic materials form the core of critical technologies that drive continuing advances in computing, information technology, diagnostics and other applications. It is becoming increasing clear that conventional computers which use silicon crystals to perform most of the computing tasks will not be able to keep up with the demands for massive computing and information processing systems. It is believed that quantum computers, which work on the principles of quantum mechanics, can provide new technologies for large scale computation. Synthesizing new quantum materials is an important challenge for the development of quantum computers. Professors Ritesh Agarwal and Andrew Rappe of the University of Pennsylvania utilize the unique chemistries and reactivities of nanoscale materials to synthesize new quantum nanomaterials. They then test these materials for unique quantum electronic properties and evaluate their performance. The researchers augment the teaching curricula at the University of Pennsylvania at both the undergraduate and graduate levels. Research and educational activities are integrated by the involvement of undergraduates in research, by incorporating the latest research results into the curricula, and by training high school and college teachers from Philadelphia where there is a large percentage of underrepresented minority students.

With support from the NSF Macromolecular, Supramolecular, and Nanochemistry Program, Professors Agarwal and Rappe develop a tightly integrated experimental and theoretical program to synthesize new topological quantum materials by chemically transforming semiconductor nanostructures, while preserving structural attributes of the parent compound (e.g. crystal lattice, nanoscale morphology). Topological materials represent the next generation of quantum materials, yet the classes of topological materials realized via experiments is very small. Theoretical predictions have suffered from the lack of appropriate materials for testing. The ion exchange synthesis method, in conjunction with recent advances in connecting quantum chemistry and topology, offers a route towards successfully addressing these synthetic challenges. Attaining a high level of independent control over chemical composition and crystal structure is highly desirable and motivates this research. This research advances the development of materials for applications in quantum computing, cryptography and sensing that may lead to increased security and economic competitiveness for the US.

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 description:
Quantum information science, which utilizes the inherent principles of quantum mechanics, is leading the next revolution of electronic and photonic technologies with application in computing, communication, and sensing. Integrated quantum communication systems that go beyond the individual devices and components, are crucial to continue pushing the frontier of quantum information science. Novel approaches towards effective device integration into quantum technologies become necessary. In this project, the investigators will leverage the state-of-the-art integrated photonics technology to develop a disruptive integrated quantum photonic platform. The developed higher-dimensional control of photons will deliver high-density information capacity and a higher level of security against quantum hacking, as needed for quantum communication. This research is closely integrated with the existing educational activities, providing both undergraduate and graduate students with the opportunity to participate in cutting-edge science and technology in an innovative way. The investigators also provide educational outreach activities to promote the interests and participations of K-12 students and broaden the participations from underrepresented groups.

Technical description:
With funding from the Electrical, Communications and Cyber Systems Division, the investigators from the University of Pennsylvania and Stevens Institute of Technology are developing a disruptive integrated higher-dimensional quantum photonic platform based upon twisted single photons, ranging from deterministic twisted single-photon emission, to transmission and high-fidelity detection. The elusive symmetry and topology of twisted single photons will be explored, together with their interplay with quantum materials and device geometry, to produce efficient signal generation and high-fidelity detection of quantum qudits. To engineer the media-links between qudits' emitter and receiver enabling the fully integrated quantum system, novel optical fiber configurations will be investigated to support simultaneous transmission of multiple twisted photons. The investigators have highly complementary expertise on deterministic quantum emitters, integrated lasing and photo-detection, which will be actively synergized to perform high-density quantum key distribution with twisted single-photons, featuring the increased information capacity and enhanced robustness against eavesdropping and quantum cloning.

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.