Matthew Grayson - US grants

****NON-TECHNICAL ABSTRACT****
A Bose-Einstein condensate is like a cold gas, but instead of liquefying into a high-density droplet at low temperatures, the gas particles remain dilute. However, they behave collectively like a large single quantum particle. To make electrons form a Bose-Einstein condensate, one must find a way to cause them to bind together in pairs before they can collapse into this curious low temperature phase. It is the goal of this Faculty Early Career Development project at Northwestern University to study a new way of pairing electrons inside of thin layers of the semiconductor aluminum arsenide, in order to realize a Bose-Einstein condensate. Discovering and studying new realizations of quantum condensates will deepen our understanding of this exotic phenomenon, and the technology developed along the way may illuminate new concepts for making quantum computers. The educational component of this project will train both graduate and undergraduate students in the techniques of solid-state research. The outreach element will bring science into the public eye by coordinating the efforts of students and faculty in the theater, engineering, and science departments to present scientifically themed plays. The plays will be performed in the lecture halls of the science and engineering building for an audience of university students, local high school students, and community members.

****TECHNICAL ABSTRACT****
A Bose-Einstein condensate is a rare example of a quantum coherent state of matter. Particles must first pair to form bosons, and then at low enough temperatures, these bosons condense into a single coherent wave-like ground state characterized collectively by a single order parameter. In aluminum arsenide, electrons have an extra label called the valley index, and it is the goal of this Faculty Early Career Development project at Northwestern University to apply high magnetic fields and low temperatures to a single quantum well of aluminum arsenide to induce the electrons from different valleys to pair and Bose-condense. Discovering and studying new realizations of quantum condensates will deepen our understanding of quantum coherence, and the technology developed along the way may illuminate new concepts for quantum information storage and manipulation. The educational component of this project will train both graduate and undergraduate students in the techniques of solid-state research. The outreach element will bring science into the public eye by coordinating the efforts of students and faculty in the theater, engineering, and science departments to present scientifically themed plays. The plays will be performed in the lecture halls of the science and engineering building for an audience of university students, local high school students, and community members.

0960120
Chandrasekhar
Northwestern U.

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

This project is for the development of a facility to enable low-temperature, time-, frequency- and spatially-resolved radiofrequency and microwave measurements for a wide variety of experiments in condensed matter and materials physics at Northwestern University. Four sets of experiments will be attempted during the project period: investigation of cross-correlation noise in mesoscopic devices; magnetization dynamics of nanoscale ferromagnets; time-of-flight measurements in Luttinger liquids in semiconductor devices; and persistent currents in normal metals. However, the usefulness of this new facility will extend far beyond these initial experiments, involving other groups at Northwestern, and enabling research groups at Northwestern to actively incorporate high-frequency techniques in their future experimental research plans. It will also allow undergraduate and graduate students and post-docs at Northwestern to gain familiarity with radio and microwave frequency techniques, a skill that is becoming increasing important in both academia and industry.


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

The increasing miniaturization of electronic circuitry that allows the development of fast computers and slim cell phones is also accompanied by a desire to make these devices work even smaller and faster. Reducing the size of device elements to the scale of nanometers--one billionth the size of a meter--presents new experimental challenges in trying to study their behavior at time scales of a nanosecond or shorter, time scales that are increasingly important for cutting-edge electronic devices. This project is devoted to developing instrumentation to study the behavior of nanoscale materials at frequencies starting at a few gigahertz, the frequencies at which the current fastest desktop computers operate, to a few tens of gigahertz. In addition to providing insight into better ways to make the next generation of nanoscale, high-frequency devices, the instrumentation that will be developed will enable experiments exploring fundamental quantum phenomena at high frequency, and in the process train the next generation of scientists and engineers in these essential techniques.

Power consumed by integrated circuits (ICs) converts to heat and dissipates through the material of the IC and the surrounding packaging. Heat dissipation from the interior of an IC to the ambient becomes highly constrained when power hungry high performance chips are stacked vertically to create 3D ICs. Pockets of accumulated heat with poor heat conduction paths to the ambient is then trapped in between stacked IC layers. As a result, overheating within ICs threaten the safety and performance of future computing systems that rely on this important new IC design methodology. This project will develop a new thermal sensor design that is especially well suited to be integrated into 3D ICs during semiconductor processing steps. It is smaller by design, i.e., an arbitrarily large number of sensors can monitor an unprecedented part of the IC, and they do not consume additional power. This will impact the sustainability and computational power of future computing systems by enabling them to operate at maximal frequencies without the need for costly active cooling solutions. They also affect the pricing of the chip products and therefore have a direct impact on the industry and economy. The PIs will continue to train graduate and undergraduate students in the basic research that underlies creative technological developments and actively promote science and technology in outreach events to the community. One of the PIs will also leverage her membership in the Diversity Committee at her institution to attract underrepresented minority graduate student applicants.

The project involves a new paradigm for design of thermal sensors using Thin Film Bimetallic Thermocouples (TFBTs), which senses temperature according to an intrinsic material property that is independent of process variation and thermal conditions of the environment. Since TFBTs are passive, they do not consume power or dissipate heat during sensing. Significant challenges remain in better understanding and modeling of the materials as well as the integration of the TFBTs into 3D ICs. The project will study the basic science of these thermocouple metals as a function of layer thickness, since thin film Seebeck coefficients are known to differ significantly from bulk. Particularly, experiments will be undertaken to investigate the dependence of the Seebeck coefficient on film thickness and on the choice of various candidate metals for thermocouples. Samples using integrated resistive heater elements on semiconductor substrates will simulate hot spots underneath arrays of bimetallic thermocouples, generating thermal maps with high spatial resolution. Design optimizations for effective integration into 3D ICs will be developed. Novel thermal management schemes that can make use of the resulting fine-grain, robust, and low cost sensor array will be developed
and evaluated.

Part 1
The NSF-IRES program Nanomaterials undergraduate Research in Germany (NanoRING) will provide 10-week nanoresearch opportunities at the Technical University of Munich (TUM), Germany for five US undergraduates from the combined student pool of Northwestern University (NU) and the Univerity of Texas in San Antonio (UTSA), a minority serving institution and partner of NU. The specific research focus is on nanomaterials covering the subtopics of nanoelectronics, nanophotonics, and nano-biomaterials. This thematic base leverages TUM?s International Graduate School of Science and Engineering (IGSSE).
The research opportunity will be for undergraduates only, in order to motivate and inspire young US researchers to invest in a future research career. Particularly at UTSA, specific efforts will be made to reach out to underrepresented groups in STEM disciplines so that the cohort?s constituency will meet or exceed NSF?s goals for representation. Individual German collaborators from within IGSSE have provided letters of collaboration to host visiting student researchers.

Part 2
Unique materials science expertise outside of the U.S. is particularly strong in Germany. Electron transport experiments, crystal growth, heterostructure design, graphene characterization, quantum dot spectroscopy, biosensor nanotechnology, and photonic emitters / detectors all represent topics of research expertise and mentorship that will benefit U.S. students. By training U.S. graduate and undergraduate students at these facilities, students can learn unique skills to advance their education and training. Furthermore, since they are researching
abroad, students will develop an identity within the international scientific community, building up a professional network and getting a first-hand perspective of larger scope of a research career. The administrative structure of NanoRING will leverage existing infrastructures at German universities through TUM?s graduate school for international students IGSSE where the administrators have exhaustive experience hosting international student research visitors.

One of the greatest intended payoffs of a student research-abroad experience is career retention. By developing engineering and science skills in a supportive and engaging multicultural environment, undergraduates will recognize their place within an international peer community and will be motivated to continue their positive experience in a career in STEM research. This is particularly important for underrepresented groups within STEM disciplines. To enhance participation of underrepresented groups, outreach to target student groups will meet or exceed NSF goals for representation by coordinating with minority student groups at both NU and UTSA. After the visit abroad, students will make a scientific presentation to their home institution, and to their underrepresented group, where applicable. The will also have the opportunity to apply for an additional Publication Award to publish or present their scientific work at a conference, promoting broad dissemination of results. A post-program assessment will assess program structure & content, track career choices, and a questionnaire will discern the impact that these research-abroad experience had on the students, their peers, and the broader scientific community.

Non-technical Description: By understanding a material's structure, it is possible to predict and design its properties. Whereas crystals are well-understood by their regular pattern of atoms, the structure of amorphous materials with their randomly bonded atoms is extremely challenging to determine. Yet this disorganized structure is exactly what makes these materials advantageous for many technological applications. For example, large-areas can be coated with amorphous materials in smooth layers for application in the next-generation flexible flat panel displays. An important objective of this project is to gather, decipher, integrate, and organize large experimental and computer generated data to accurately describe the structure and properties of a large class of complex amorphous materials. This materials data along with open-source statistical software developed within the project will be made accessible as part of the Global Materials Network to accelerate the discovery of new materials with unique features and performance and to help produce new products at a much faster pace and reduced cost.

Technical Description: Unlike Si-based semiconductors, amorphous oxide semiconductors exhibit optical, electrical, thermal, and mechanical properties that are comparable or even superior to those possessed by their crystalline counterparts. Most notably, carrier mobility of amorphous oxide semiconductors is an order of magnitude larger than that of amorphous hydrogenated silicon commonly used in solar cells and flat-panel displays. Within unified theoretical and experimental framework, this project aims to establish genomic deposition-structure-property relationships in complex amorphous oxide and chalcogenide semiconductors in order to systematically record and organize the data into a searchable database. The research will integrate controlled synthesis, advanced characterization, multi-scale modeling, time-dependent studies, and accurate first-principles calculations to provide microscopic understanding of the complex interplay between the nanostructure, morphology, and electron transport regimes across the entire crystalline-to-amorphous transition. Development of realistic approaches for non-stoichiometric-melt cooling and time-dependent statistical analysis, will enable studies of defect formation and dynamics, ion diffusion, structural evolution and stretched-exponential relaxation, phase transformation, and crystallization processes, bringing the computer-aided design of amorphous materials to a new level. The PIs plan to release the Amorphous Structure Analysis (AStA) as open source and build a user community around the language by ensuring that interested researchers are able to contribute to AStA codebase. This will allow a wider growth of the project. This aspect is of special interest to the software cluster in the Office of Advanced Cyberinfrastructure, which has provided co-funding for this award.

Touchpads and touchscreens in today's computers and cell phones have two disadvantages - first, they are rigid, and second, they require a complex manufacturing process with many individual sensors. A flexible and easy-to-manufacture pressure sensor could function as an artificial skin for people and objects and could lead to cheap and convenient solutions for wearable computer interfaces, touch enabled spaces, and biomedical movement diagnostics. Such a device with a wireless interface will allow for ease-of-use in sensor interfaces. With the help of an unconventional sensor mapping method called resistive tomography, it is possible to create such a platform using only a single piece of easy-to-manufacture pressure-sensitive material to map pressures. Device fabrication for such a flexible sensor is trivial in comparison to standard sensor arrays, with the complexity shifted to the signal processing needed to interpret the pressure pattern. Multiple measurements using various combinations of contacts can create the full pressure map. It is expected that the technology that is developed from this effort will lead to new kinds of flexible sensors for wearable touch-pad like interfaces and biomedical movement diagnostics.

Most of today's two dimensional (2D) touch sensors and strain sensors require an indexed array of individual sensors in order to gather spatial information, requiring significant complexity in the fabrication stage, while impairing durability and broader applicability. This work proposes a new means of gathering 2D spatial data combining touch sensing and strain mapping that uses a trivial fabricated composite membrane to serve as the spatial pressure sensor, with the complexity shifted from fabrication to the computational domain through a tomographic mapping algorithm. This research will develop new tomographic algorithms based on a Zernike moment analysis to convert resistive four-point measurements at the periphery of a strain-sensitive membrane into a 2D map of the local pressures applied throughout the area of the membrane. The membrane will be made of a nanotube-silicone conducting composite rubber developed for this purpose. An energy-efficient measurement architecture and wireless interface to the membrane will allow this strain-sensor map to be easily employed in-the-field for various mechanical, medical, engineering, and personal-user applications. The low cost of fabrication will lend itself to ubiquitous touch sensors and novel modes of interaction for wearable and Internet-of-Everything applications. The trivial fabrication method of the sensor component and the conformability of the sensor around any shape make for a mass-producible, easily implemented, and highly versatile strain sensor and flexible touchpad. The exact algorithms to be investigated here can be applied on a much broader class of systems, expanding the utility of tomographic methods in sensing. The conducting elastomer sensor material will be developed to optimize the tomography application envisioned here. The ideas generated in the course of this proposal are expected to generate new intellectual property in the area of sensors, such as flexible, wearable touchpads for computer interfaces, likely to spawn new industry products. The conformal ability to shape such a sensor will lead to broader applications in the health industry for rehabilitation, such as a tomographic sock to sense bending and mechanical strain at the elbow, knee, or torso for health monitoring. Durable, long-lasting, zero-maintenance haptic skin for prosthetic limbs and robotics can be produced at extremely low cost with the technology proposed here. This effort will train graduate students in essential skills for critical thinking and design methodologies, as well as developing skills in applied math, physics, and materials design with newly developed courses including subject matter developed under this 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.