Xianfan Xu - US grants

Xu DMI-9813758 The objective of this Small Grant for Exploratory Research (SGER) project is to develop and evaluate a curvature modification technique with precision on the order of sub-micro-radians. High precision curvature modification is useful in many manufacturing processes, particularly in microelectronics industry. For example, the required flatness of some components in a high capacity computer hard disk is on the order of ten nanometers; its curvature is less than one micro radian. Currently, no technique is available for modifying curvature with such high precision. A laser-based high-precision curvature modification technique is proposed. A controlled pulsed laser beam will be used to raise the temperature of the target material and induce plastic deformation, therefore, to change the curvature of target material. The project work will carry out exploratory research on the feasibility of using pulsed lasers for curvature modification. The repeatability of high precision curvature modification, and materials' structural and property changes due to laser irradiation will be investigated. Experimental studies will also be conducted to correlate laser processing parameters with the laser-induced curvature change. The outcome of the project will be instrumental to the evaluation and development of the precision laser bending technology. This project will provide research opportunities to graduate and undergraduate students. This research project could also become a topic in the course taught by the P.I, "Laser Processing", so that a large number of students will be introduced to novel laser processing techniques. Therefore, this project will contribute to the human resource development in the area of laser technology. 1

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This award will provide partial support for the acquisition of a versatile ultrafast optical laser system that is centered around two broadly-tunable high-pulse-energy femtosecond optical parametric amplifiers (OPA) with nonlinear harmonic generation, pumped by a fsec Ti:Sapphire laser and regenerative laser amplifier. This system will be a unique and open research and student training facility on the Purdue University Campus. The broadly interdisciplinary group of researchers from across the Purdue Campus will use the facility for advanced research on semiconductor, metal and biomaterials. The research facility will be closely integrated with Purdue University teaching goals at the undergraduate and graduate student level to give students broad exposure to advanced technology to prepare them for diverse careers in science and engineering.

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This equipment will significantly enhance the research and educational capability and infrastructure of the institution, its students, and its faculty.

The objective of this Grant Opportunity for Academic Liaison with Industry (GOALI) project is to develop a laser-based technique to adjust curvatures of computer hard drive components precisely, and to develop a fundamental understanding of the physical phenomena involved. This project will be conducted jointly by Purdue University and IBM. Manufacturing of components of high capacity computer hard drives requires curvature control with precision better than 10-4 degrees. Currently, there is no technique available to achieve such high precision. The laser-based technique to be developed will utilize a pulsed laser to heat and produce localized deformation on hard drive components. Because only a very small area is heated and deformed, the curvature is altered precisely by each laser pulse. Preliminary studies conducted have demonstrated the feasibility of this technique. Fundamental studies will be conducted to understand the laser curvature modification process and to quantitatively relate the processing parameters to the resulted curvature change. A laser curvature adjustment process will be developed and implemented in manufacturing.
Results of the fundamental studies will serve as guidelines for the manufacturing process. The success of the research will be instrumental to the development of high capacity computer hard drives, and will help the U. S. companies to maintain the leading position in hard drive manufacturing. This project will also provide research opportunities to several graduate and undergraduate students. In addition, a large number of students will be educated with this advanced laser technology through taking a new dual graduate/undergraduate level course on laser processing. Tberefore, this project will contribute to the human resource development in the area of laser-based manufacturing technology.

The proposal was submitted to the Chemical and Transport Systems Division in response to the FY2002 Information Technology Research solicitation, described in NSF Announcement. NSF 01-149, in the "Small" category. The proposal is for development of a comprehensive set of numerical models and techniques for the simulation of ultra-fast laser machining and to employ these techniques to obtain a detailed understanding of the fundamental physics of ultra-fast laser processing. In particular, the PIs propose to develop numerical multiscale finite volume and molecular dynamics models of these processes and to implement them on shared-memory parallel computers. Phenomenological issues to be addressed include melting and ejection of molten droplets due to recoil pressure and droplet redeposition. Large-scale simulation offers the possibility of resolving a number of fundamental questions concerning mechanisms of the ablation process in ultra-fast laser machining. The large-scale parallel computing aspects of the research will broaden the capabilities of thermal science researchers in this important information technology area. Other technologies that may be impacted by the development of these computational techniques include high speed microelectronics device simulation, microscale energy generation, and in a variety of emerging bio- and non-technologies. Educational impacts include expanded computational science expertise in graduate students involved with advanced manufacturing sciences and the expansion of content in upper level courses taught by the collaborating PIs. Funding is from funds reserved for ITR-Small grants in the CTS Division as well as from the Thermal Transport and Thermal Processing program.

This project was received in response to Nanoscale Science and Engineering initiative, NSF 01-157, category NER. The objective of this project is to develop a novel low cost nano-lithography technique. Conventional nano-manufacturing equipment, using electron beams or other radiation sources and operating in vacuum, costs well above $1,000,000. In contrary, this technique is based on a laser device and its accessories; its total cost will be less than $100,000. The key component in this nano-lithography system is a nanometric optical antenna capable of transmitting an incoming micrometer size laser beam into a nanometer size domain with high transmissivity (efficiency). This nano-lithography system can be further developed into a parallel manufacturing system, so that the time needed for the manufacturing process can be significantly reduced compared with other techniques.

With the rapid progress in nano-technology, it is crucial to develop low cost manufacturing techniques with high throughput. Only with rapid and low cost manufacturing techniques could the nano-technology translate itself from research to industry, and to impact the society. The success of this work will provide a low cost nano-lithography technique for nano-manufacturing. This research will also provide training to undergraduate and graduate students, including underrepresented groups. The results of this research will be broadly disseminated.

This proposal was submitted and funded in response to solicitation NSF 03-537 High Speed Optical Communications and Networks.

Technological interest in dense wavelength division multiplexing (DWDM) systems is fast increasing since DWDM systems offer a very large transmission capacity and new novel network architectures. Major components in DWDM systems are the wavelength multiplexers and demultiplexers, such as arrayed waveguide grating (AWG). However, the capacity of current AWG devices is limited in terms of the number of channels that can be manufactured in a given volume because of their 2-D geometry using lithography techniques as well as algorithms used involving regular sampling and limited use of phase modulation.

The proposed work will design and manufacture a new generation, 3-D AWGs by combining novel design methodologies of AWGs and novel laser-based manufacturing techniques. A major bottleneck in phased-array types of devices used in DWDM is the free spectral range (FSR) allowed. We will develop a novel dense wavelength division multiplexing (DWDM) system in which there is only one effective order per wavelength so that the number of channels or images corresponding to different wavelengths is not restricted due to FSR. The method involves irregular sampling of zero-crossings of phase with linear and/or spherical reference waves. This method also allows the design of 3-D systems with a very large increase in the number of AWG channels. We will implement regularly and irregularly sampled AWGs in the design of 3-D DWDM systems using the femtosecond laser manufacturing technology. By focusing a femtosecond laser beam inside a dielectric media to increase the index of refraction at the laser focal point, and with the aid of 3-D computer aided design and manufacturing, truly 3-D waveguides, which are essential parts in the 3-D AWG devices can be fabricated. In order to optimize against various error sources and to incorporate multifunctional system behavior, we will also incorporate diffractive optical elements optimized with iterative minimum mean-squared error methods and a closed loop manufacturing technique.

The success of the proposed work will have very high potential for progress in multispectral communications, networking and computing. Topics such as ultra high capacity WDM will be more significant in the upcoming progress for communications of parts in complex micro/nano systems, and the demand for more and more number of wavelengths will increase. Progress in 3D will open up completely new possibilities and bring along tremendous increase in capacity, and totally new design techniques.

The project is being jointly sponsored by the Thermal Transport and Thermal Processing Program of the Chemical and Transport Systems Division and the Materials Processing and Manufacturing Program of the Design, Manufacturing and Industrial Innovation Division.

The objective of this research is to investigate novel femtosecond laser machining techniques for manufacturing a variety of microstructures and components. The approach is to optimize all laser operation parameters; in particular, the temporal shape of laser pulses by synthesizing femtosecond pulse bursts (1 femtosecond = 1/1,000,000,000,000,000 second), which are not available in commercial laser machining systems. In these femtosecond pulse bursts, the energy of each laser pulse will be individually controlled, and the pulse-to-pulse separation time will be adjusted from femtoseconds to nanoseconds. This will allow high quality microstructures to be machined in almost any materials. Fundamental physical phenomena during femtosecond laser-matter interaction will be investigated to assist the design of the pulse bursts.

This work, if successful, will greatly advance the laser machining technology. Despite many advantages of using femtosecond pulse lasers for micro-machining, clean and desirable structures are often not obtained due to melt ejection by laser irradiation and re-deposition of melt droplets. This work is aimed at solving common problems associated with laser micro-machining to achieve cleaner and higher precision machining results. The success of this work will impact many industries, including aerospace, automobile, microelectronics, and biotechnology where laser micro-machining is already widely used. The project will also contribute to education of the next generation high tech workforce. It will provide the students involved with cross-disciplinary trainings. The results of this research will be integrated into undergraduate and graduate curricula and disseminated to both academic and industrial laser processing communities.

This objective of this proposal is to develop an optical based, low cost, parallel nano-manufacturing technique. The key component in the proposed nano-manufacturing system is a nanoscale optical antenna capable of concentrating light into a nanometer domain with high efficiency, which was recently demonstrated in the PI's laboratory. In the proposed work, an array of such antennas, each to be individually controlled, will be used for parallel nano-manufacturing. Research will be conducted to optimize the antenna by computation and characterization, and to develop an algorism for parallel manufacturing. This project will also provide graduate and undergraduate students with trainings in nano-scale manufacturing, instrumentation design, and fundamentals of near field optics. Results obtained from this work will be used for teaching in a number of courses and instructional laboratories so that more students can benefit from this research.

The proposal work, if successful, will have a large impact on nano-manufacturing technology as well as nano-science and nano-technology in general. The advances in nano-science and nano-technology in the last decade are creating many new opportunities that may greatly change our society. In order to bring these newly developed nano-sciences and nano-technologies to the market, low cost, large scale nano-manufacturing technologies are needed. Conventional nano-fabrication involves sophisticated equipment with very high cost. In contrary, the proposed technique will use lasers and commercially available components, and its total cost is much lower. Additionally, being able to concentrate light into nanometer dimensions with high efficiency will significantly impact other areas of science and technology, from surface inspection to biological detection, to high density data storage.

ABSTRACT

National Science Foundation

Proposal Number: CTS-0642696
Principal Investigator: Xu, Xianfan
Affiliation: Purdue University
Proposal Title: International Conference on Integration and Commercialization of Micro- and Nano-systems

This grant will provide partial funding to support the International Conference on Integration and Commercialization of Micro- and Nano-systems, to be held in Sanya, Hanan Province, China, January 9-12, 2007. The conference is sponsored by the U.S. ASME and the Chinese Mechanical Engineering Society. The importance of nano-science and engineering has been well recognized by research communities and governmental organizations worldwide. It is believed that breakthroughs in nano-science and technology will change all aspects of society, from energy utilization to homeland security. The uniqueness of this conference is that it places emphasis on the system level design, integration, and manufacturing, and commercialization of nano-technologies. It will deal with issues across the spatial scale, from fundamental phenomena at the atomic and molecular level to issues vital for system integration. It will bring very different technologies and expertise together to establish communication across disciplines. The broader impact of the conference is that it will bring together researchers in nano-science and engineering from diverse areas in materials, energy, transportation, environment, and health care. The conference will promote academic-industry collaboration and international collaboration, and promote technology transfer and commercialization. The NSF funding will in particular help to offset the expenses of young researchers, including junior faculty and graduate students, who are especially encouraged to attend the conference so as to provide them with opportunities of interaction and collaboration with their peers within and outside of the United States.

This research was received in response to the Active Nanostructures and Nanosystems initiative, NSF 06-595, category NIRT. The goal of this project is to develop a high-throughput hierarchical nano-manufacturing tool for producing components and devices with feature dimensions ranging from nanometers to centimeters. The technical approach to be used is based on a nanoscale optical antenna capable of concentrating light into a nanometer size with high efficiency, which was recently developed at Purdue. The concentrated radiation from the antenna will be used as the energy source for nano-manufacturing. For high-throughput manufacturing, an array of thousands of such antennas, each can be individually controlled but working in parallel, will be used for scaling up the manufacturing process. Since many products have features with both nanometer and larger dimensions, micrometer-size diffractive optical elements will be integrated with the proposed manufacturing tool for fabricating larger size features. The combined use of nanometer-scale antennas and micrometer-scale diffractive optical elements will further speed up manufacturing of devices with different feature dimensions. Parallel to the tool development, research will be conducted to investigate fundamentals relevant to the proposed manufacturing process, including nano-optics or near-field optics and diffractive optics. Theoretical and experimental studies of these optical devices will further improve their light concentration and light transmission efficiency, which in turn will improve the manufacturing throughput. The proposed project is also a collaboration with Seagate Technology, who is interested in using the nanoscale antenna for developing next generation data storage technologies.
Researches in the last decade have shown that devices with critical dimensions below 100 nm have superior functionalities. In order to bring these new devices from laboratories to the market, drastically new, low cost, large scale manufacturing techniques are necessary. The proposed low-cost, high-throughput, hierarchical manufacturing tool will produce devices with nanoscale features that can impact many industries. The proposed research will also contribute to many fields in science and engineering, including nano-optical science and nanoscale radiation enhancement, volume diffractive optics, nanoscale optical imaging, and mechanics and dynamics in complex systems. Furthermore, being able to concentrate light into a nanometer spot with high efficiency will have significant impact on many other areas of science and technology. Combined with established methods, parallel nanoscale light sources can be used, for example, for inspection of surface defects in microelectronics, for high speed biological detection and medical screening, and for high density data storage. This project will also contribute to human resource development. It will provide graduate and undergraduate students with trainings in interdisciplinary areas and industrial experience through internships. Special efforts will be made to recruit students from under-represented groups. Research outcomes will be introduced as new modules or special topics in a number of undergraduate and graduate level courses, including undergraduate and graduate laboratory courses. The project will also be outreached to high school students through existing Purdue outreach programs. Through these efforts, this project will make significant contributions to nano-science and engineering and to the education and human resource development.

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Lucht

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

Funds for the purchase of an advanced ultrafast laser system for nonlinear spectroscopy are requested. The system that specified is a Spectra-Physics Spitfire Pro 40F-5W ultrafast laser system. The pulse length of the fundamental output of the system is <40 femtoseconds (fs). The system can be operated at two different repetition rates, 1 kHz or 5 kHz. At the repetition rate of 5 kHz, the output pulse energy is >1 mJ; for the repetition rate of 1 kHz, the output pulse energy is > 5mJ. A state-of-the-art pulse shaper based on multiphoton intrapulse interference phase scan (MIIPS) is also requested. The MIIPS pulse shaper will be very useful for phase correction of Fourier-transform-limited pulses or for accurate phase-shaping using input phase functions. This ultrafast laser system user facility will be a resource for a wide range of interdisciplinary research. At present there is no comparable laser system at Purdue University. Consequently Purdue researchers are at a serious disadvantage in proposing research in emerging new fields such as diagnostic applications of femtosecond lasers, X-ray generation, and attosecond spectroscopy. Applications of the new laser system are proposed in biomedical spectroscopy, diagnostics in turbulent reacting flows, coherent phonon spectroscopy in the solid state, multiphoton spectroscopy for proton structure studies, soft X-ray generation, and attosecond spectroscopy.

0933559
Ruan

Summary

The objective of the proposed research is to understand and reduce thermalization loss in solar cell materials by using the phonon bottleneck effect in nanocrystals, and therefore to increase the energy conversion efficiency. Due to the broadband of solar spectrum, photons with energy higher than the bandgap can generate hot electrons at a temperature much higher than the lattice. Normally these hot electrons rapidly pass their excess potential energy to the lattice through electron-phonon scattering processes, losing their excess energy to heat and causing lower solar energy conversion efficiency. In nanocrystals the continuous bands become discrete energy levels and the spacing can be engineered to be larger than the energy of a single phonon, making the electron relaxation through phonons a slow process. This "phonon bottleneck effect" can lead to significantly reduced electron-phonon relaxation rates and enhanced solar cell efficiency. However, the current understanding of this phenomenon is very limited - the experimental data are often inconsistent, and the theoretical models are only qualitative, preventing the predictive design of optimum nanocrystals that maximize the phonon bottleneck effect.

Intellectual Merits: In this study, the PIs will integrate theory, simulation, synthesis, and characterizations to minimize the hot electron relaxation in nanocrystal solar materials. A non-adiabatic molecular dynamics method will be developed to simulate the phonon-assisted hot electron relaxation rates, and will be used to determine the optimum size, shape, and surface terminations that give the slowest hot electron relaxation. Based on the numerical results the PIs anticipate to gain a profound understanding of how atomic structures of nanomaterials affect their electron-phonon coupling. The computed nanostructures with optimum electron-phonon coupling will be synthesized with precise size and shape control. These materials will then be characterized using femtosecond lasers for the slowed relaxation rates. Solar cells based on these optimized quantum dots will be fabricated and tested and their efficiencies will be compared with their bulk counterpart. The combined computation, synthesis, and characterization will allow optimization of the nanocrystals to achieve the phonon bottleneck effect and higher solar cell efficiency.

Broader impact: The research addresses one of the grand energy challenges for the nation. The project is part of the PIs' efforts to include fundamental physics into an integrated research-education effort in energy transport and conversion. The new knowledge acquired from this project will significantly enrich the courses taught by the PIs. The PIs have been actively recruiting underrepresented groups in their research programs. The team will extensively engage in energy education and outreach activities for K-12 and local community through workshops, seminars, and demonstration projects. The PIs will also engage in the outreach activities with the heat transfer and nanotechnology research communities via nanoHUB and thermalHUB

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Xu

This project seeks to develop both fundamental understanding and new technology to accelerate the efficient and cost-effective harvesting of waste heat in automotive exhaust systems.

Intellectual Merit: Scientific issues to be addressed include thermoelectric materials development, advanced systems-level thermal management and design, heat sink design, development of novel thermal interface materials, and advanced metrology for material and system assessment. Thermoelectric materials to be investigated include filled-skutterudites that are currently being investigated by the corporate partner, General Motors, as well as nanowire-based materials, nanocrystalline ceramic compounds, and metal/conductor superlattices to be developed at Purdue. Systems-level thermal modeling will be conducted to maximize the temperature difference across the thermoelectric material, thereby increasing the efficiency with which waste heat can be converted to electric power. Novel durable nanoscale thermal interface materials will be developed to minimize thermal resistances in order to promote high energy conversion efficiency.. Properties will be measured using a photoacoustic method and a laser thermal reflectance method at Purdue in conjunction with use of facilities at the Oak Ridge National Laboratory.

Broader Impact: The collaboration between researchers at Purdue and General Motors will accelerate the development of new technology that will promote the efficient and cost-effective thermoelectric conversion of waste heat to electric power in vehicle applications. Successful development and ultimate implementation will improve fuel economy and reduce emissions. The research results will be disseminated by traditional means, as well as through Purdue?s nanoHUB and thermalHUB web portals. The research will provide graduate students with interdisciplinary research experiences, as well as industrial experience through internships in industry. The research will be integrated with undergraduate and graduate courses and serve as the basis for undergraduate design projects. Outreach activities to high school students, including students from underrepresented groups, have been planned.

This Scalable NanoManufacturing (SNM) grant provides funding for the development of a high throughput, scalable nanomanufacturing machine for parallel nanolithography and parallel manufacturing of nanomaterials and devices. Research in the past two decades has demonstrated superior properties and performances of nanomaterials and devices. However, technologies for producing nanomaterial-based devices suffer from low throughput. To bring the advances in nano-science and technology to society, nanomanufacturing methods scalable to economically and industrially relevant production levels are needed. This machine will greatly expand the capability of commercial machines in terms of high throughput, high resolution, and high precision manufacturing, and will be the first commercial scale manufacturing machine capable of both parallel nanolithography and parallel nanomaterials synthesis. The development of the machine will be based on advances in using nanoscale optical antennas for nanomanufacturing. The nanoscale antenna produces high intensity, localized light spot; and an array of antennas is used for parallel nanomanufacturing. To synthesize nanomaterials, the localized energy from antenna will create localized chemical reaction environment for producing nanomaterials at precise locations, ready for device fabrication using standard semiconductor manufacturing tools.

If successful, the project will result in a unique and first of its kind machine for nanolithography and for manufacturing of nanomaterials that can be readily used for developing many types of nano/multi-scale devices. The development of such a commercial high throughput nanomanufacturing machine will enable manufacturing of nanoscale devices at economically and industrially relevant production levels, which will impact every sector in industry. The project will address fundamental and engineering challenges critical for the development of the machine, including nano-optics, on-line metrology, manufacturing engineering, and system integration. The project will also advance the relevant science and engineering. The ability to concentrate light into a nanometer spot with high efficiency has significant impact not only on nanomanufacturing but also on other areas in science and technology, from biological/chemical sensing to next-generation data storage. The project will also provide graduate and undergraduate students, including students from under-represented groups with trainings in interdisciplinary areas and industrial experience through internships in industry. Undergraduate students will be recruited to the project through Purdue undergraduate research fellowship programs. Research results will be introduced as new modules or special topics in a number of courses and undergraduate senior design projects, and will be outreached to high school students through Purdue outreach programs. Therefore, this project will have broader impacts on human resource development.

This PFI: AIR Technology Translation project focuses on translating science and technology in nanoscale optical antenna to fill the gap for Heat-Assisted Magnetic Recording (HAMR). The translated science and technology in nanoscale optical antenna has the following unique features: the nanoscale optical antenna focuses light into nanoscale size with high efficiency, and moreover, can be manufactured using industrial standard technology for mass production. HAMR has been identified as the next generation data storage technology. The key component in HAMR is a near field transducer (NFT) for producing a light spot of tens of nanometers in size for localized heating. The proposed nanoscale optical antenna is an ideal candidate for being used as the NFT to provide high efficiency and a small light spot when compared to the other NFT designs.

The project accomplishes this goal by proof-of concept design and analysis, prototype development, and demonstration of a fully functional NFT. Our partnership engages Advanced Storage Technology Consortium (ASTC), the consortium of the data storage companies, to provide guidance in the prototype development and commercialization as they pertain to the potential to translate the technology along a path that may result in a competitive commercial reality. The potential economic impact is expected to affect the next generation hard disk drives which currently have a market of 600 million units per year, which will contribute to the U.S. competitiveness in the data storage industry.

The societal impact, long term, will be on science and engineering and human resource development. The outcome of this project will have direct impact on the development of the next generation data storage technology. The project will also advance the relevant science and engineering. The ability to concentrate light into a nanoscale spot with high efficiency has significant impact not only on the HAMR technology development but also many other areas, from biological/chemical sensing to nano-photonics devices. Results of fundamental research will be broadly disseminated by journal publications, conference presentations, and websites, including Purdue's nanoHUB web portal. The proposed research will also contribute to human resource development, including providing graduate and undergraduate students with trainings in interdisciplinary areas and experience in technology transfer, integrating research outcomes with curriculum, outreaching to high school students, and recruiting and educating students from under-represented groups.

Optical lithography is the critical enabling process of transferring fixed geometric patterns on a mask to wafers to make semiconductor chips and other nanotechnology products. Current tools cost more than 50 million US dollars each, and the costs for masks far outweigh those for tools. Yet, to increase chip capabilities to match Moore's law, tools will soon become too costly for both industry and scientists. Also, the current process cannot meet the long-term demand to produce faster chips with more functions. This award supports fundamental research to provide needed knowledge for the development of a new lithography technology. Results from this research will strengthen the U.S. manufacturing foundation for future information-technology growth and profoundly impact applications in high-performance computing, data storage, communications, healthcare and energy. This award will help broaden participation of underrepresented groups in engineering research and create an education pipeline in a multidisciplinary and collaborative environment.

Scanning electron beam writers can direct pattern semiconductor chips at very high resolution without the need of expensive photomasks but only in low throughput. Practical throughput is possible only by using millions of parallel electron beams. Researchers have been unable to find a robust method to generate a massive number of beams with satisfactory brightness and uniformity. This research is to address this challenge and enable massively-parallel electron-beam lithography by transforming the team's recent breakthroughs in nanoscale optics into a low-cost nanomanufacturing scheme. This technology uses a novel device to focus optical energy at nanoscale and locally excite electrons to form massively-parallel electron beams, which can be used to perform maskless lithography in mass quantities. The research team will investigate the fundamentals of localized electron excitation, build a proof-of-concept device and study device response, and implement the device into their scalable nanomanufacturing platforms to demonstrate lithography over a large area.

Enhanced Optical Pressure from Nanostructured Metal Films
Kevin Webb and Xianfan Xu, Purdue University

A combined theoretical and experimental study of optical forces in nanostructured material is proposed to establish a method to control the nanometer-scale force on a small particle and to provide enhancement in the total pressure on a structured surface. Consequently, large forces on small particles and an increase in the total force on a membrane are expected. While optical tweezers are now commercially available, they are effective for moving large beads to which, for example, biological molecules are attached. Positioning nanoparticles like quantum dots requires large and local forces that can be achieved with control over the geometry of a metal surface. This would circumvent the need for the large beads in optical tweezers and provide an approach for synthesizing new materials by nano-scale optical assembly. Furthermore, the substantial increase in the relatively weak pressure provided by light will allow weaker optical signals to be used in mechanical control. The resulting optomechanical system can be simpler and more versatile than optoelectronic systems, opening communication and sensing opportunities. Specifically, while it has been recognized that all-optical networks can increase both speed and efficiency, there remain challenges as to how to provide network reconfiguration that this approach could address. At the fundamental level, this work will provide experimental force data on the nanometer scale that will be used in establishing a model that can be used for device design.

The goal of this project is to design and fabricate gold films with resonant nanometer-scale slots that are expected to produce a dramatic enhancement in the overall pressure.
The verification of this method for increasing the force will allow the approach to be used to mechanically control a surface using laser light in various free space and waveguide arrangements. The project will lay the design foundations for nanophotonic structures that impart substantial and controllable optical forces to actuate tuning elements in photonic networks. This will simplify switching technology and the approach has the potential to reduce energy consumption and cost. This project will facilitate sensing, allowing a molecule to be moved to a region with large field and hence large Raman dipole moment for identification. Such nanoscale traps could be used in material synthesis, allowing trapping of quantum dots in nanocavities for achieving optical sources and detectors, for instance. While optical tweezers are becoming more common, determination of the absolute force relies on macroscopic calibration procedures that do not provide access to the force on the nanometer scale. By evaluating the relationship between materials and geometry and the force, it should be possible to design tweezers with larger forces to move smaller objects or larger objects locally. There should also be new opportunities through control of the optical material properties, both electric and magnetic. At the fundamental level, the proposed work may provide an answer to a century-long debate about the description of the optical force.

Semiconductor nanowires have unique properties that make them prominent candidates for the next generation high-performance electronic devices, chemical and biological sensors, solar cells, and photonics devices that can potentially impact every industrial sector. However, current technologies for producing nanowires are not suitable for commercial scale manufacturing. Because nanowires are often produced as an entangled mesh, complicated fabrication procedures are required to select, position, and align nanowires in placement required for making devices. This award supports research to investigate a novel semiconductor nanowire manufacturing technology that overcomes the above-mentioned obstacles. The research team will develop a unique and first of its kind technology for manufacturing nanowires with controlled dimension, composition, orientation, placement, property, and functionality necessary for large scale manufacturing of nanowire devices. The project will involve multiple disciplines including nanomanufacturing, computational modeling of materials synthesis, high precision control, and manufacturing system integration. As nanowire devices will find a broad range of applications in energy, healthcare, consumer electronics, and defense, results from this research will benefit the U.S. economy and society. In addition, the project will also help broaden participation of underrepresented groups in research, increase impact on education, and increase public awareness of nanoscience and nanotechnology.

The enabling technology of the project is a laser-induced chemical vapor deposition (CVD) method recently developed at Purdue University. In this process, a laser beam is incident on a substrate, above which precursor gases such as silane and germane are heated and dissociated. Moving the substrate under computer control allows laser-guided growth of semiconductor nanowires with ultrahigh precision. The key to producing nanowires with dimensions of a few tens of nanometers is to utilize the interference effect between the incident laser beam and the surface scattered laser radiation. The research team will focus on computationally-guided manufacturing. It will generate computational models of the nanowire manufacturing process, and integrate them with advanced metrology tools, and feedback control in to a single manufacturing platform. As a result, this research will realize real-time control of the nanowire dimensions, properties, placements, and properties that is necessary for manufacturing nanowire devices at large scale.

As semiconductor chips are widely used in computers, phones, automobiles, appliances, etc., more capable yet more efficient semiconductor chips can have profound societal impact such as in reducing electric power consumption and in prolonging the battery life of portable electronics. Today, each semiconductor chip may contain billions of transistors that are made of silicon ‒ the most popular semiconductor. However, as transistors are made smaller and thinner so that more of them can be crammed on the same chip to perform more functions at a faster speed, silicon-based transistors will sooner or later run into physical limitations dictated by quantum mechanics. The physical limitations of silicon will cause transistors to fail to turn on and off efficiently and chips to consume more power and run hotter. To address the physical limitations of silicon, scientists have explored new materials such as graphene, made of a single layer of carbon atoms, as an alternative to silicon in making very small and very thin transistors. However, although graphene allows electrons to be highly mobile in a transistor, graphene lacks an energy gap that could be used to turn the transistor on and off efficiently. This shortcoming of graphene has motivated scientists to explore other atomic-layered materials such as transition-metal dichalcogenids which have an energy gap, but they turned out to have a different shortcoming in allowing electrons to have only low mobility. To solve this dilemma of atomic-layered materials, phosphorene, made of a single layer of phosphorus atoms, was recently discovered to have both a high electron mobility and a sizable energy gap. Thus, phosphorene is a promising replacement for silicon in future-generation semiconductor chips.

To this end, a team of scientists from Purdue University, Lehigh University and Michigan State University propose to explore phosphorene which can potentially overcome the challenges of silicon as well as other two-dimensional atomic-layered materials for ultra-scaled thin-body transistor applications thereby transforming the electronics industry. A collaborative and highly integrated interdisciplinary approach will be used to address three thrust areas: 1) exploration of phosphorene by exfoliation with focus on electrical and optical properties and device applications, 2) synthesis by chemical vapor deposition and nanomanufacturing in collaboration with government and industry labs, and 3) first-principles modeling to guide experiments and to interpret the results. Being the only other elemental material that can be exfoliated like graphene, phosphorene represents a unique opportunity as the basic material for future-generation devices. The initial exploration through exfoliation will guide the development for high-quality, defect-free materials and processes that enable safe and easy integration into device architectures. Additionally, the highly puckered structure of phosphorene dictates that each single layer comprises two tightly bonded atomic layers ? a property that can be exploited to develop a large-scale chemical vapor deposition manufacturing process. The puckered structure also makes phosphorene highly anisotropic ? a property that can be exploited for thermoelectric applications. To reduce the environmental sensitivity of phosphorene and to explore other novel architectures and properties, heterojunctions between phosphorene and graphene, hexagonal boron nitride, molybdenum disulfide, or other chalcogenides and oxides will be explored. For example, unlike most other atomic-layered materials, phosphorene is naturally p-type, and p-type phosphorene transistors can be combined with n-type molybdenum-disulfide transistors to form energy-efficient complementary circuits and tunneling transistors. Moreover, black phosphorus in bulk form has a direct band gap of 0.3 eV, which makes it a useful elemental infrared detector. When black phosphorus is thinned to a single phosphorene layer, the band gap increases monotonically to above 2 eV ? a property that can be exploited for efficient solar cells and tunable photodetectors.
This award is co-funded by the Air Force Office of Scientific Research (AFOSR)

This project investigates novel ways to transport, guide and direct thermal energy (heat) based on the new paradigm of topological thermal transport. Through this paradigm, heat can be guided to flow only along the boundary of a material while avoiding its interior, as well as in a highly directional ways that are also robust to material disorder and other defects. To achieve this, the team will harness and engineer special topological properties of materials and devices involving various heat carriers including electrons, phonons (crystal lattice vibrations) or light. Discoveries and innovations from this project could impact many technological areas involving the control and transport of thermal energy, such as on-chip heat management and cooling in modern electronic and photonic systems, as well as energy generation, conversion and harvesting through thermoelectrics and photothermovoltaics. The project could also lead to new schemes for thermal management such as thermal insulation, ?cloaking? and directed thermal flow. The research team will contribute to an online forum called ?Thermal Hub? within NSF-funded NanoHub that counts millions of subscribers and users. The forum is expected to facilitate sharing and exchange of information in the emerging field of ?topological thermal transport?, and benefit research and development in nanoscale thermal engineering in general. Both graduate and undergraduate students will be actively involved in the research and learning activities of the program. Particular attention will be placed on broadening the participation of women & minority students via various diversity and outreach activities by the team. The project will leverage several existing programs at their institutions and partnerships with several undergraduate and minority colleges.

Topological states of electrons such as quantum Hall effect (QHE) and topological insulators (TI) are some of the most important developments in contemporary condensed matter physics. Such topological electronic states feature topologically-protected electronic transport along the boundary of an insulating bulk sample that is immune to scattering by various impurities. This project will pursue topological concepts in the so-far-unexplored realm of thermal transport. The proposed approach will harness or engineer topological properties of three different types of heat carriers ? electrons, phonons and phonon-polaritons, to realize topologically guided and protected thermal transport that can be further controlled by external forces and fields. The first theme of the program will explore high-quality electronic topological insulators with insulating bulk and conducting topological surface states of spin-helical Dirac electrons to demonstrate optically and magnetically controlled, and non-reciprocal electronic thermal conduction, and other novel thermal transport carried by such topological surface electrons. The second and third themes of the project will focus on the extension and analogs of several key physical mechanisms underlying the electronic topological states --- such as spin-momentum coupling/locking, chirality/valley states, and spin/valley Hall effects --- to phonons and hybrid phonon-photon polaritons, toward realizing various topological phononic states and phonon/thermal transport.

Additive manufacturing is a powerful technique for myriad applications ranging from product visualization to making three-dimensional (3D) engineered parts and devices. 3D nanostructures and devices are useful in many applications including energy, clean water, and health care. However, most additive manufacturing or 3D printing methods are extremely slow because they rely on layer-by-layer fabrication processes. A recent breakthrough has dramatically improved the speed of additive manufacturing. This novel technique demonstrates the fabrication of polymeric 3D parts continuously out of the resin at rates of hundreds of millimeters per hour with resolutions below 100 microns. The entire fabrication takes minutes as opposed to hours. This Scalable NanoManufacturing (SNM) award will develop methods for rapid 3D printing of nanostructures, with feature resolution of ~100 nm and printing speed orders of magnitude faster than any current nanoprinting technique. The project will also address many fundamental and engineering challenges for developing this 3D nanoprinter. It is expected to generate a wealth of scientific and engineering knowledge that will advance the rapid 3D nanoprinting method of making structures and devices with nano-scale precision. In addition, the project will broaden participation of underrepresented groups through programs such as Purdue's Luis Stokes Alliance for Minority Participation, increase impact on education, and increase public awareness of nanoscience and nanotechnology.

In typical 3D additive nanoprinting, a laser beam is used to polymerize a photo-curable resin in a point-by-point and layer-by-layer manner. The key objective of this award is to accelerate the polymerization process by developing a photoinhibition method to create a dead zone right below the polymerization zone. In this dead zone, photoexcited states needed for polymerization are depleted or terminated, hence the resin remains in liquid phase for continuous, rather than layer-by-layer printing. In addition, the method can be made scalable, i.e., hundreds of parts can be printed in parallel, by simultaneously utilizing an array of optical elements. The research will focus on investigations in novel manufacturing methods, advanced optical systems, high precision metrology tools, design and synthesis of functional photo-polymers, and 3D manufacturing system integration. Finally, the project will strive to develop low-cost 3D nanoprinting systems using commercially available low-cost light sources and low-cost optical and mechanical components. As a result, this project will realize an affordable, high throughput-high resolution 3D nanoprinting technology.

Radiation is an important energy transfer process that has wide applications in energy harvesting, production, and utilization. Radiation energy transfer can be accomplished by far-field radiation, where radiative surfaces are separated by a distance longer than the radiation wavelength (typically several to tens of micrometers) and near-field radiation, in which the surfaces are separated by a distance shorter than the radiation wavelength. In this project, engineered surfaces with specifically designed very small (microscale) patterns, called meta-surfaces, are studied to achieve specific far-field radiation properties and to enhance near-field radiation for applications such as thermal-photovoltaics in solar energy harvesting. The project aims to generate a wealth of scientific and engineering knowledge to advance the fundamentals and engineering of radiation energy transfer. It can also be applied to other fields of science and engineering, including high resolution imaging, sensing, and infrared radiation sources. In addition, the project provides education and training to the next generation scientists and engineers, broadens participation of underrepresented groups, and increases public awareness of radiation science and technology.

This project designs novel meta-surfaces that are advantages for the desired radiation properties and transfer processes. Specifically, meta-surfaces capable of enhancing the magnetic radiation field in addition to the electrical radiation field are studied. This approach provides the design space for manipulating both electric and magnetic properties to achieve desired far- and near-field performances, while using relatively simple two-dimensional meta-surface structures. Advanced experimental techniques are used in this project, including near-field radiation measurements with surface separation distances of tens of nanometers, FTIR (Fourier Transform Infrared spectroscopy) coupled with near-field scanning optical microscopy, FTIR near-field emission microscopy, and far-field FTIR spectroscopy. These studies provide a complete micro-to-macro spectroscopic picture of the designed meta-surfaces to validate the design theories, therefore, to advance far- and near-field radiation research and facilitate their applications.

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

This grant supports research that contributes new knowledge related to a nanomanufacturing process, promoting both the progress of science and advancing national prosperity and security. Three-dimensional printing or 3D printing is the process of creating three-dimensional (3D) objects from a digital computer model. It has been widely used for applications ranging from product visualization to making engineered parts. Nanoscale 3D printing is useful for making miniaturized structures and devices and can enable new product functions for many applications. However, the common 3D nanoprinting methods are slow and costly because they typically rely on serial point-by-point scanning of an expensive laser beam. This award supports fundamental research to provide the needed knowledge for the development of a fast nanoscale 3D printing method, which uses a low-cost compact light source, similar to that used in laser pointers, and digital light projection for high-throughput fabrication of 3D nanostructures. The single photon 3D nanoprinter’s potential use spans applications in information technology, communications, energy, healthcare, and biomedical industries, which benefits the U.S. economy and society. This multi-disciplinary research involves several disciplines including manufacturing, photochemistry, optics, and materials science. The project helps broaden the participation of women and underrepresented groups in research and training and impacts engineering education and development of the future workforce.<br/><br/>3D nanostructures have properties and functions exceeding those of bulk structures or even properties traditionally not possible. Printing of 3D nanostructures requires a nonlinear process to locally define high-resolution features. The state-of-the-art is femtosecond laser two-photon polymerization (2PP) process. However, the 2PP process is slow, costly and generates structures with micron-scale resolutions. This research is to fill the knowledge gap in the development of a high resolution, high throughput, low-cost 3D nanoprinter. The research team aims to develop a system that uses a low-cost diode laser and single-photon dosage nonlinearity to achieve 1000 times higher throughput, at least 10 times less cost and 50 nm or less resolutions than those possible with conventional 2PP. The team plans to investigate and understand the nanoscale nonlinear single-photon polymerization process, control the diffusion of inhibiting radicals to prevent unwanted polymerization to improve feature resolution, develop a parallel projection method to print entire nanolayers at a time to speed up the printing throughput, and create a machine learning (ML)-guided digital-twin database that connects the desired functionality of the manufactured parts with the build parameters for its future broad adoption as a cyber 3D nanomanufacturing platform. <br/><br/>This project is supported with co-funding from Civil, Mechanical and Manufacturing Innovation (CMMI) Division in the Engineering (ENG) Directorate, and the Chemistry (CHE) Division in the Directorate for Mathematical and Physical Sciences (MPS).<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.