Alexander A. Balandin - US grants

As the device size continues to shrink and integration density continues to increase, the size and spatial confinement effects on heat removal become increasingly important. A rapid emergence of nanotechnology as a nation's high-priority field and renewed interest to thermoelectrics add significance to the research on thermal management of nanoelectronic devices and circuits proposed in this NSF-CAREER project. Beside its fundamental science value, investigation of phonon transport at nanoscale is crucial for future progress in electronic and optoelectronic device technologies.

The goals of this project are (i) comprehensive investigation of heat conduction in nanoscale semiconductor structures, devices and circuits; (ii) derivation of new thermal management rules applicable to scaled-down devices; (iii) fundamental study of the effects of phonon confinement and boundary scattering on phonon propagation; and (iv) improvement of reliability of nanoelectronic devices and circuits.

The proposed education plan aims at jump-starting a new engineering specialization - Devices and Circuits with emphasis on nanotechnology and nanodevices. It will be accomplished by active course development, increase of the laboratory component of the curriculum, and student involvement in research. The cross-disciplinary nature of the project will allow students to gain a variety of skills required in a contemporary high-tech job market.

Investigation of thermal management of nanodevices will be carried out in a newly established Nanoelectronic Materials and Device Laboratory. The outcome of this research will add to the core knowledge of nanostructures, phonon transport, and quantum confinement. It will lay down the foundation of the novel enabling technology utilizing active phonon engineering.

This proposal was received in response to the National Science and Engineering Initiative, Program Solicitation NSF 01-157, in the NER category. The proposal focuses on a new approache to enhancement of the thermoelectric figure of merit ZT of semiconductor materials via tuning of electron-phonon interaction in multiple arrays of semiconductor quantum dots. Quantum dot arrays are potential candidates for the thermoelectric "electron transmitting - phonon blocking" material. At the same time, in order to achieve a significant ZT improvement and compete with conventional thermoelectrics one has to design and fabricate quantum dot superlattice where carrier transport is facilitated by the formation of carrier mini-bands. Indeed, hopping conductivity typical for lateral carrier transport in random quantum dot arrays has very low carrier mobility while mini-band transport may lead to very high mobility values, particularly if one manages to suppress at least partially the carrier scattering via smart mini-band engineering. The important task addressed in this proposal is theoretical proof-of-concept investigation of requirements for achieving mini-band transport regime and carrier scattering suppression in quantum dot superlattices.

Modification of acoustic phonon modes in quantum dot arrays due to spatial confinement and boundary scattering leads to a change in the phonon density of states, a decrease of the phonon group velocity, and corresponding drop of the in-plane lattice thermal conductivity. Acoustic phonon confinement, e.g. modification of phonon dispersion due to nanostructure boundaries, is much less researched phenomenon than carrier confinement effect. At the same time, it can serve as an additional tool to decrease the lattice thermal conductivity value and increase the effectiveness of the thermoelectric device. Thus, another task of this project is a study of the required structure parameters, e.g. dot size, shape, acoustic mismatch, etc., for achieving desirable acoustic phonon transport features such as low group velocity along direction of interest; resonant phonon scattering conditions; decoupling of phonon bath from electrons; etc. New efficient thermoelectric devices based on nanostructured materials may have a tremendous impact on a wide range of energy needs due to their inherent advantages such as high reliability, light weight, compactness, quit operation, and environmental safety.

The problem of heat removal becomes crucial for continuing CMOS downscaling, beyond CMOS nanoscale concepts, ULSI, and 3D architecture proposals. Conventional heat removal methods and post device-design / packaging level cooling solutions fail to work at nanoscale and in 3D architectures. This proposal introduces a drastic philosophy change in heat removal, e.g. thermal management features incorporated at the materials / device level, as well as two new radical concepts of heat removal via phonon engineering such as (i) thermal conductivity enhancement of the material along chosen directions via proper engineering of device heterostructures and (ii) smart arrangement of the nanoscale devices in ULSI circuits or in 3D architectures to achieve acoustic phonon interference and phonon annihilation, e.g. local cooling, in pre-determined locations.

The objective of this research is to demonstrate a possibility of the confined electron - confined phonon scattering rate suppression and corresponding enhancement of the electron mobility in the specially designed acoustically mismatched nanostructures. The novel nanophononic approach is based on the phonon depletion/accumulation effect in the semiconductor nanowires embedded within a barrier material characterized by a smaller acoustic impedance Z (which is a product of the material mass density and the sound velocity). The research is focused on the rigorous calculation of the electron mobility and electrical conductivity in the semiconductor channel embedded into the "acoustically softer" cladding layer; selection of the optimum nanowire and barrier material parameters for the maximum mobility enhancement; and experimental proof-of-the-concept demonstration using the prototype structures.

The research will have a strong impact on the electronic industry affecting both the conventional complementary metal-oxide-semiconductor (CMOS) technology and beyond-CMOS electronic device designs. The research will add to the core knowledge of the electron transport in nanostructures and nanodevices, and will help to develop the concept of phonon engineering. The envisioned phonon engineering (nanophononics) approach to the enhancement of the electronic device operation may have an impact comparable to that of the electron band-gap engineering, which brought a revolution to the electronic and optoelectronic industries. The methods developed under this project will be transferred to semiconductor industry. In addition, this interdisciplinary research will help in building a strong nanotechnology educational program in UC-Riverside, the minority serving institution, with the largest minority student population of all 10 University of California campuses.

EEC-0552562
Alexander a. Balandin

This REU award for a Site at the University of California Riverside supports 12 undergraduate students in year one and 16 students in years two and three for 9 weeks in the summer and up to 30 weeks of academic year activity.

The objective of this program is to provide meaningful research opportunities to undergraduates from institutions that do not have major research operations. The REU Site will take a multidisciplinary approach to nanoscience and technology based on the research agenda of the Center for Nanoscale Science and Engineering (CNSE) at the university. The program provides not only stimulating research opportunities, but it also offers guidance on preparation for graduate school and the graduate experience, and information for community college students on how to transfer to a bachelors program. Also, the program will include a module regarding real world ethics in research.

The program provides the opportunity for undergraduates to integrate research into their education as well as increase the participation of underrepresented groups in science and engineering. The involvement of these students in exciting research enhances the likelihood that community college students will consider transferring to a bachelors program and undergraduate students will consider post-graduate study. Many of the participants will be drawn from nearby accredited Minority Institutions and Hispanic Serving Institutions, thus contributing to a rich and diverse research environment..

Topological insulators constitute a new class of quantum materials with bulk insulating energy gaps and gapless Dirac-cone edge or surface states. The surface states are protected against time-reversal-invariant perturbations such as non-magnetic impurities, defects, and reconstruction. The charge is uniquely coupled to the spin, and charge current creates spin polarization. Since the surface states are topologically protected, and the momentum states are coupled to spin states, scattering is reduced and noise is suppressed. In thin topological insulators, a Rashba-type spin splitting occurs which can be controlled by a gate voltage. The thermoelectric figure of merit, ZT, increases as film thickness is reduced. In summary, topological insulators have shown exceptional properties for thermoelectric, charge, and spin transport. These materials and properties will be investigated from an engineering electronics point of view. Devices that exploit these properties will be built, modeled and characterized, and the performance metrics and fundamental limits of such devices will be determined.

Intellectual Merit:
This investigation will be simultaneously carried out both experimentally and theoretically. The project will (i) add to the fundamental knowledge of the material properties and physical processes in highly-scaled topological insulator materials; (ii) build, model, and characterize devices that exploit topological insulating properties for computation, signal processing, and sensing; (iii) determine the performance metrics and the fundamental limitations of such devices, (iv) explore the use of topological insulators for low-dissipation, low-noise interconnects; and (v) develop the electrochemical atomic layer deposition technique to grow few-atomic-layer films of topological insulators. All materials will be extensively characterized using a wide range of methods including atomic force, scanning electron, and transmission electron microscopy, low energy electron diffraction, X-ray spectroscopy, Auger spectroscopy, electron probe micro-analysis, micro-Raman spectroscopy, electrical, and thermal measurements. Experimental measurements will be compared to device models and ab initio, density functional theory calculations of the electronic structure and vibrational modes of the thin film and nanowire materials. Transformative concepts include the use of low-dissipation, low noise topologically protected states of topological insulators for electronic / spintronic devices and low-noise, low-power interconnects.

Broader Impact:
The successful project has the potential to lead to new technologies that exploit the low-dissipation, low-noise states of topological insulators for computation, communications, and sensors. The broader impacts of this project affect all 5 example areas described within the grant proposal guide, and they are particularly strong in the areas of (i) broadening participation of underrepresented groups and (ii) promoting teaching and training through undergraduate research. The University of California Riverside is a Hispanic serving institution with the largest Hispanic student population among all of the University of California campuses. The principal investigator and co-principal investigator have a long history of successful supervision of underrepresented minorities, they served as principal investigator and co-principal investigator of the National Science Foundation Research Experience for Undergraduates Site for Nano Materials and Devices that focused on minority undergraduate student participation in research, and they plan to hire minority graduate and undergraduate students as research assistants for this project.

Intellectual Merit
This collaborative GOALI proposal between researchers of the University of California, Riverside (UCR), Florida International University (FIU), MagOasis LLC, and Western Digital Corporation (WDC) presents interdisciplinary research to study three-dimensional (3-D) magnetic recording, a promising and challenging near- and long-term solution to increasing the capacity of electronic and computer devices. Unlike 2-D alternatives, 3-D recording exploits advantages of using a 3rd spatial dimension to store information. The specific goals will include: (i) a study of different modes of 3-D recording, (ii) understanding the physics underlying write processes in 3-D systems, (iii) fabrication of 3-D media with three or more magnetic layers accessible for write/read processes, (iv) a basic study of 3-D media with a focus to understand thermal fluctuations in 3-D structures, (v) an investigation of new data coding channels to gain from the multilevel signal configuration in 3-D recording, and (vi) an industry-standard spinstand testing to demonstrate areal densities above 1 terabit/in2. One of the important research objectives will be to understand the physics of 3-D recording necessary for achieving effective areal densities substantially above 1 terabit/in2. The experimental study, involving (i) extensive fabrication via sputter deposition and combinatorial chemistry synthesis, ultra-high-density patterning via electron beam lithography (EBL), (ii) focused Kerr microscopy and ultra-high resolution magnetic force microscopy, (iii) measurements of heat propagation in 3-D, and (iv) a spinstand study to simulate recording systems, will be supported by numerical simulations to understand the micromagnetics in 3-D systems and a basic theoretical study to devise adequate multilevel data coding methods. Accordingly, the effort will follow a cross-disciplinary direction through involving experts in magnetic recording, materials science, micromagnetic modeling, and signal processing from both academia and industry. Particularly, the project will employ the complementing strengths of five co-investigators with a history of synergetic collaboration including (i) Sakhrat Khizroev at Florida International University (FIU) for Magnetic Recording and Nanofabrication, (ii) Alex Balandin at UCR for Heat Management at Nanoscale, (iii) Ilya Dumer at UCR for Data Coding, (iv) John Oti at MagOasis LLC for Micromagnetic Simulations, and (v) Rabee Ikkawi at Western Digital Corporation (WDC) for Disk Drive Integration and Spinstand Testing, respectively.

Broader Impacts
This project might have a significant impact on the data storage industry especially today when the progress in the multi-billion-dollar industry is facing a fundamental limit to scaling due to thermal instabilities in the recording media. The main targeted deliverable of the project is a cross-disciplinary basic study to demonstrate a record high information density over 1 terabit/in2 using the disruptive technology of 3-D magnetic recording. As one of the pioneering concepts in the broad area of 3-D devices, 3-D recording may pave a way to the new era of 3-D magneto-electronics and 3-D electronics applications in general3. The proposed educational component includes a new university-wide initiative to establish a channel for industry internships for both undergraduate and graduate level students. The connection to the industry will be secured through involvement of John Oti, President of MagOasis LLC, and Rabee Ikkawi, a Principal Engineer of Western Digital Corporation, as the industry Co-PI and Senior Personnel, respectively. UCR is one of America?s most ethnically diverse research institutions with a dominant Asian American body and 35% Hispanic enrollment. FIU is the largest Hispanic serving institution in the mainland U.S.A. The investigators commit to make every effort to assure diversity among the students who work on this project. In particular, they intend to do this in part by recruiting from the student chapters of the Society of Women Engineers, the National Society of Black Engineers, and the Society of Hispanic Professional Engineers, among others. In addition, the PIs have established a tradition of hosting local high-school students to give them tours of state-of-the-art research labs with the goal to attract students to become future engineers. Finally, the PIs intend to organize the next anticipated IEEE Nanoscale Device and System Integration (NDSI)-2012 conference to help broaden the research preparation of current students in the minority serving institutions and further attract talent with an emphasis on underrepresented students.

Intellectual Merit: This project is awarded under the Nanoelectronics for 2020 and Beyond competition, with support by multiple Directorates and Divisions at the National Science Foundation as well as by the Nanoelectronics Research Initiative of the Semiconductor Research Corporation. Continuing evolution of electronics beyond the limits of the conventional silicon technology requires innovative approaches for solving the heat dissipation, speed and scaling issues. Alternative state variables other than dissipative charge transfer hold promise for drastic improvements in computational power. Collective states of magnetization, spin waves, and exciton condensates are being considered, but, to date, the performance results are modest. This project proposes a revolutionary new approach for the collective states that carry electrical signals, do not require magnetic fields, and can be realized at room temperature. The alternative state variables will be implemented with charge-density waves. The charge-density wave effects have been known for decades but never considered for information processing. The intellectual merit of this project includes better understanding of the material properties and physical processes of charge-density wave materials in highly-scaled, low-dimension regimes that have not yet been explored. The results of the project will lead to optimized device designs for exploiting charge-density waves and accurate understanding of the fundamental limits of the performance metrics. The intellectual merit also includes performance evaluation of the low-noise topological insulator interconnects proposed as part of new architectures. The project will result in new knowledge of the properties of the charge-density wave materials obtained with the help of optical microscopy, atomic-force microscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and other techniques.

Broader Impact: The proposed project will lead to a revolutionary new technology for replacing or complementing conventional silicon complementary metal-oxide-semiconductor technology. The phase, frequency and amplitude of the collective current of the interfering charge waves will encode information and allow for massive parallelism in information processing. The possibility of using the phase for logic operations allows one to minimize the required number of elements per circuit, reduce the power consumption, and ease the scaling requirement. The charge-density wave devices will be implemented with an alternative growth technique ? electrochemical atomic layer deposition ? with demonstrated potential for synthesis of crystalline atomically-thin layers of pertinent materials. The technique will allow the research team to experiment with new chemistries and heterogeneous integration of a variety of charge-density wave materials. The low-dissipation, massively parallel information processing with the collective state variables can satisfy the computational, communication, and sensor technology requirements for decades to come. The successful project will (i) improve the economic competitiveness of the United States; (ii) contribute to national security; and (iii) increase participation of underrepresented minorities in science and engineering. The project will result in improved student education and training at the University of California ? Riverside, a minority serving institution with a large Hispanic student population. The broader impact includes contributions to the development of a synergetic interdisciplinary Materials Science and Education program, as well as contributions to graduate and undergraduate training focused on materials synthesis, at the University of Georgia.

Graphene transistors are widely considered exciting candidates for analog, mixed-signal, and radio frequency systems in high-frequency applications. This collaborative research project is aimed at the design, development, and demonstration of monolithically integrated graphene circuits for radio frequency and analog mixed-signal systems. It will add to the core knowledge of the principles of circuit design based on ambipolar graphene field-effect transistors, with an emphasis on amplifiers, phase detectors, and comparators - three promising candidate solutions for practical radio frequency applications. Through closely coordinated theoretical, computational, and experimental efforts, it will be demonstrated that such graphene circuits can not only reduce the complexity of the electronic circuits, but also realize larger bandwidth, higher frequency, and lower power consumption than state-of-the-art circuits implemented with conventional semiconductor materials.

The broader impact of this project includes technical advances required to harness the early science of graphene transistors into practical solutions for radio frequency applications. The graphene circuits to be designed and demonstrated in this project can be used in consumer electronics and communication gadgets such as smart-phones as well as in radars and wireless sensors. The unique material properties of graphene combined with the innovative circuit designs that exploit these properties are expected to lead to major increase in the performance of the radio frequency devices as well as a reduction in their weight and power consumption. Another core outcome of this project with broad technological impact will be an integrated test-bed and web-based resources to facilitate research in graphene electronics. Through collaborations with a broad range of academic, industry, and government investigators, this collaborative effort will strengthen ties between the device, circuit, and radio frequency communities, and accelerate convergence to key design parameters essential for the large scale integration and application of graphene electronics. The project plan will help in educating undergraduate and graduate students in technical disciplines in both participating universities. The project will produce a positive impact on educating students underrepresented in science and engineering via their early involvement in the practically relevant computational and experimental research.

The objective of this program is to investigate the effect of rotation angle on the thermal conductivity of twisted bilayer graphene. The experimental and theoretical evidence is clear that the electronic states of the individual layers in twisted bilayer graphene are decoupled. The effect of the twist angle on the phonon dispersion is still an open question, and the effect of twist angle on the in-plane thermal transport has yet to be studied. These questions are intimately related since the heat is carried by the phonons. If the phonon coupling in twisted graphene layers were suppressed, then the multi-layer twisted graphene films would have enhanced thermal conductivity of single 2D layers acting in parallel, thus allowing for transfer of extraordinary large heat fluxes.
The intellectual merit of this program is in creating fundamental knowledge determining the relation of twist angle to the thermal conductivity of bilayer graphene. The possibility of maintaining 2D properties of graphene in bulk materials through the use of misoriented stacking is a transformational concept giving us the best of both worlds ? the enhanced performance of 2D combined with the capacity of 3D.
The broader impact the project includes new applications of graphene for thermal management. It has the potential to increase the US technological competitiveness. It will increase the participation of women and underrepresented minorities and contribute to undergraduate and graduate STEM education at UC Riverside, which is the minority serving institution with the largest Hispanic student population among all UC campuses.
This project is jointly funded by the Electronics, Photonics, and Magnetic Devices Program (EPMD) in the Division of Electrical, Communications and Cyber Systems (ECCS) and by the Electronic and Photonic Materials Program (EPM) in the Division of Materials Research (DMR).

The goal of this collaborative research is to build a computational framework with experimental validation to systematically engineer designer materials that provide targeted properties. Defects in materials significantly influence their properties, for instance in energy transfer. The current state-of-the-art techniques allow one to induce defects in materials controllably and subsequently predict and correlate relevant properties to the defect concentration. In this research, computational and experimental approaches will be integrated to construct designer defect-engineered materials that will provide desired properties. In this approach, first a targeted property will be ascertained, and then the defect concentration and distribution will be predicted to synthesize novel material structures that provide the predetermined property. The hybrid computational framework will motivate the general scientific community to leverage advanced computing infrastructures. The efforts will establish new research and learning communities for computational-experimental data-enabled science and engineering through promotion of diversity and undergraduate research experience, outreach to community college students and work-force development, outreach to the general public (through education about the power of simulation-based engineering with an online gaming tool and hands-on activities at science centers) and integration of research with education.

This project is a comprehensive effort to rigorously integrate developments in high throughput synthesis and characterization with improving access and availability to high performance computing resources towards solving an inverse design of materials problem. A computational framework that sweeps through millions of possible structural permutations and combinations for property prediction will be developed and validated against experiments. The framework will (1) employ massively parallel molecular dynamics simulations to predict transport properties of nanomaterials, (2) synthesize defect engineered nanostructures and measure the corresponding transport properties, (3) integrate the above nanoscale computations and experiments through a genetic algorithm based hybrid optimization scheme to predict the optimal material structure for specified transport properties and formulate a hierarchy of increasingly complex duals of cost-functionals and design parameters, and finally (4) close the loop by validating the inverse design results experimentally.

EFRI-1433395
Balandin (Univ. of California-Riverside)


Non-tecnmical description: This research addresses a new class of ultra-thin film materials, termed van der Waals materials, and heterostructures implemented with such materials; specifically this project investigates novel electrical, optical, and thermal phenomena in such materials and heterostructures. The work will result in new material synthesis techniques and enable practical applications of ultra-thin film materials in electronic switches, optical detectors, low-power information processing and direct energy conversion. The novel devices implemented with the ultra-thin films of van der Waals materials have potential for high speed and low energy dissipation. The creation of all-metallic switches and electrical-optical transducers will have a strong impact on the Nation's defense needs owing to the inherent radiation hardness of all-metallic devices. The software tools developed in this project will be made freely available to a broad R&D community. This research will increase US economic competitiveness, develop a globally competitive STEM workforce, and contribute to undergraduate and graduate STEM education. The project team developed a detailed Broadening Participation Plan that will impact K-12, undergraduate and graduate education of minorities underrepresented in STEM fields.


Technical description: This interdisciplinary project investigates the broad class of two-dimensional materials and heterostructures of transition-metal dichalcogenides, which reveal a range of novel switching phenomena related to confinement-induced modification of electron and phonon band structure, proximity effects, exciton condensation and strongly correlated phenomena. The project goals are to synthesize high-quality, atomically-thin transition-metal dichalcogenide films with controlled crystalline phase (e.g., 1T vs. 2H); fabricate suspended two-dimensional transition-metal dichalcogenide films and field-effect-transistor type devices; explore electrical, optical and thermal phenomena in these structures and devices; and utilize novel switching phenomena observed in these structures for the creation of low-power logic gates, all-metallic radiation-hard switches and optical-electrical transducers. To achieve these goals, the interdisciplinary project team includes recognized researchers with complementary expertise, prior experience of cooperation and an extensive publication record in two-dimensional materials. The results of this transformative research will add to the growing core knowledge about the electrical, optical and thermal properties of two-dimensional materials and heterostructures implemented with transition-metal dichalcogenides and related layered structures. The project will lead to a better understanding of correlated phenomena, excitonic effects, and the hetero-interface electronic and phonon properties of two-dimensional materials. The information about the electron and phonon transport properties of heterostructures will allow the team to exploit novel electrical and optical switching phenomena for developing innovative devices. The team will produce a detailed Materials Property Database with electron and phonon materials data for transition-metal dichalcogenide films, heterostructures, and twisted few-layer materials. The research project addresses all three EFRI thrust areas.

A large amount of energy is lost as waste heat in many engineering systems such as automobiles and turbomachinery. Significant energy gains may be obtained by efficiently scavenging such waste heat through appropriate energy conversion mechanisms. One particularly promising opportunity lies in the conversion of temperature gradients in time into electricity, referred to as the pyroelectric effect. This project will utilize experiments and theoretical modeling to explore the pyroelectric effect in nanowires, and will build prototype pyroelectric-based energy harvesting microdevices. Research will help understand the nature of pyroelectric effect in nanowires, including the amount of energy that may be realistically harvested from nanowire based devices, performance limits, etc. which will help guide further development of potential energy conversion devices. All three institutions involved in this collaborative research are minority serving institutions located in highly populated Hispanic areas. PIs will leverage this opportunity to excite and recruit minority and women students to the emerging nano/microscale energy harvesting area. The PIs will carry out outreach to local high schools to excite K-12 students about energy harvesting, and encourage them to consider further STEM education and careers.

The technical goal of this combined experimental and theoretical-simulation research is to measure and characterize the pyroelectric effect in nanowires (GaN, ZnO, etc.) for developing micro- and nano-scale devices for thermal energy harvesting and sensors applications. Despite its potential to convert waste heat into usable electricity, the pyroelectric effect has been largely unexplored, in particular at the micro/nanoscale. This is partially due to lack of methodologies for characterization of this effect at small scales. Recent theoretical findings suggest a dramatically higher pyroelectric coefficient in nanowires, similar to enhancements observed in thermoelectric and piezoelectric performance of nanowires, albeit this prediction has not been confirmed experimentally. In this effort, a methodology based on microfabricated devices will be developed to quantitatively measure and characterize the pyroelectric properties of individual suspended nanowires. In addition, theoretical models and computational tools will be developed for (i) interpretation and analysis of the experimental pyroelectric data; (ii) prediction of the pyroelectric response of various nanostructured materials (individual nanowires; nanowires arrays); and (iii) optimization of the nanostructure parameters (material composition, size, shape, interface) for enhancing the pyroelectric voltage. The proposed models will include strong non-uniformity of the polarization distribution in nanostructures and possible phonon and electron confinement effects. Based on the learning from experiment and theory, prototype pyroelectric-based energy harvesting microdevices will be built using a single and an array of nanowires. Experimental data on pyroelectric coefficient of nanowires and dependence on nanowire size, temperature, etc. will contribute to the fundamental understanding of this effect. A fundamental understanding of pyroelectric transport in single nanowires may lead to a new paradigm of high efficiency energy conversion devices that take advantage of nanoscale engineering of materials to optimize pyroelectric performance.

Nontechnical Description:
This major research instrumentation (MRI) development project aims to build an integrated micro-Raman-Brillouin-Mandelstam spectrometer system with a capability for samples held at cryogenic temperatures. Raman scattering and Brillouin-Mandelstam scattering are inelastic light scattering processes, which are used to measure energies of various types of elemental excitations, such as phonons and magnons, in solid materials. Phonons are quanta of crystal lattice vibrations, which are associated with sound velocities of solids and also reveal themselves in electrical, thermal and optical phenomena in materials. Magnons are quanta of electron spin waves, which determine characteristics of magnetic materials. The capability of conducting measurements at low temperatures is particularly important for studying magnetic materials. The spectral range and design of the spectrometer allow for its use for samples of small dimensions and thicknesses. The project provides an impetus to development of the Brillouin spectroscopy instrumentation, and its elevation to the level currently enjoyed by Raman spectroscopy. Information obtained with the spectroscopy system facilitates synthesis and characterization of new materials, and helps in better understanding of their properties. The instrument increases research competitiveness and enhances science and engineering education at the University of California - Riverside, which is an accredited Hispanic Serving Institution.

Technical Description:
The characteristics of the micro-Raman-Brillouin-Mandelstam spectrometer system make it a multi-user facility, and enable science and engineering researchers from universities and industry to conduct studies in a wide range of topics: from the cutting-edge fundamental solid-state physics of magnons, phonons and non-trivial topological states to engineering measurements of the elastic constants of composites. The advanced features of the system include (i) a specially designed rotating microscopy stage and imaging system for measuring the energy dispersion of phonons, magnons, and other elemental excitations in the temperature range from 4 K to 700 K; (ii) a high spatial resolution for the samples with the atomic thickness, lateral dimensions approximately 250 nanometers for magnons and about 1 micrometer for phonons; (iii) a modulus for recording phonon and magnon energies substantially below the current 1-GHz limit of conventional spectrometers; and (iv) a stage for simultaneous excitation and observation of coherent phonons and magnons with high spatial and temporal resolution. The possibility of investigating atomically-thin films with lateral dimensions in the micrometer range allows researchers to measure acoustic phonon energy dispersion. The capabilities of the system provide fundamental knowledge of phonons and magnons in two-dimensional and one-dimensional materials; the strength of the magnon-phonon and spin-lattice interactions in magnetic materials; elastic constants, phonon velocities and Gruneisen parameters in low-dimensional materials; charge density waves in quantum materials; as well as characteristics of other quasiparticles in novel materials, heterostructures and biological systems.

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.