Arto Nurmikko, Ph.D. - US grants

The proposed research is an investigation into the nonlinear optical properties of selected semiconductor superlattices. The work will specifically focus on optically induced changes near the excitonic resonances in II-VI compound semiconductors such as (Zn, Mn)Se and (Cd, Mn)Te. These materials are unique in that strongly coupled electronic and magnetic excitations are optically accessible. The proposed studies combine two aspects of new and advanced research, first, the use of sophisticated transient optical techniques on picosecond and femtosecond timescale, and second, the spectroscopy of novel ultrathin semiconductor layered superlattice structures. The basic portion of the work involves the characterization of the largely unknown exciton kinetics on such timescale while the more applied part focuses on the enhancement of the sought transient nonlinearities in a high density magnetically oriented exciton system. The longer term impact of this research includes possibilities for ultrafast optical switches and logic elements.

This equipment grant will support the construction of a high repetition rate amplifier system for femtosecond dye laser pulses. The PI plans to investigate the nonlinear optical properties of novel group II-VI semiconductor superlattices containing magnetic ions, when subjected to short pulses of nearly resonant high intensity laser radiation. The experimental work involves the use of high power picosecond and femtosecond laser techniques at visible wavelengths. Of specific physical interest are interactions in a dense exciton gas from the standpoint of insulator-metal transition, including the presence of an external magnetic field. Generally, such phenomena are associated with large optically induced changes in the material transparency, thereby providing a device connection to fast optical switches.

This project involves studies by ultrafast laser techniques of highly optically excited semiconductor microstructures, based on very recent advances in the fabrication of new II-VI compound superlattices and quantum wells. These microstructures have their optical resonances in the visible region of the spectrum, especially in the blue-green where semiconductor optoelectronics technology is presently very poorly developed. The work is expected to have direct impact in developing high speed optical switching and light emitting devices, based on miroscopic understanding of the physics of highly excited nonequilibrium electron-hole plasmas and excitonic complexes. A particular feature of the microstructures to be studied is the incorporation of magnetic elements in a highly spatially controllable fashion. This will be investigated from the standpoint of fast optically induced changes in magnetic ordering of the microstructures, with a view towards exploiting such phenomena in magneto-optical devices.

This Superconducting Quantum Interference Device Magnetometer enables state-of-the-art measurements of the magnetic properties of materials, under study in the Department of Physics, Department of Chemistry, and Division of Engineering at Brown University. The flux detection system and superconducting magnet are capable of measuring magnetization or susceptibility in a wide range of temperatures (1.8-400 Kelvins) and magnetic fields ranging from -5.5 to +5.5 Tesla, with high sensitivity, resolution, accuracy and stability. This instrument is particularly well suited to low magnetic fields and small samples. Its large dynamic range also accommodates strongly ferromagnetic samples in high magnetic fields.

This award will support collaborative research on the topic of semiconductor microstructures. The US investigators are Dr. Arto Nurmikko and Dr.Phillip Stiles, Brown University, and Dr. Bennet Goldberg, Boston University. The Austrian collaborator is Professor Gunther Bauer, Institut fur Physik, University of Linz, Austria. The goal of the project is to explore novel semiconductor microstructures, based on Narrow bandgap IV-VI compounds. A range of sophisticated experimental studies are proposed, with emphasis on lower dimensional electronic phenomena in quantizing magnetic fields. Specifically, compositional and doping superlattices, hetero- junctions and other microstructures of column four and column six elements will be grown, fabricated and studied by optical and transport experimental probes. The emphasis on PbTe- based systems is due to the inherent high carrier mobilities, ease of doping, and large dielectric constant unavailable in other materials. The study will concentrate on determining the unusual many body properties of systems when the Coulomb energy between carriers is of the same order of magnitude as the kinetic energy. They will also examine the reduced dimensional aspects of this interaction, by creating compositional and doping heterojunctions which confine the carriers in two dimensions. The experimental tools to be applied are magneto-transport, interband and intraband magneto-optics, and transient optical probes. Samples will be grown in Austria and patterned at Boston University and Brown University. The project will benefit from the complementary expertise of the US and Austrian investigators and their past history of successful collaboration.

The Microelectronics Facility at Brown University requires funds to upgrade clean-rooms. One thousand square feet of facility space will be upgraded to class-1000, or better, clean-room grade. In addition, some obsolete and broken equipment will be replaced. It is proposed that the funds be used to purchase rapid thermal processors and plasma-enhanced chemical vapor deposition equipment. Replacements or upgrades will be made to rf- sputtering systems, furnaces and vacuum equipment.

This Engineering Research Equipment Grant will be used by the Division of Engineering and the Center for Advanced Materials Research at Brown University to purchase components, instrumentation, and software in order to convert an existing field- emission scanning electron microscope for use as a direct-write electron-beam lithography tool. The e-beam lithographic capability will support several investigators pursuing individual research projects that represent a broad spectrum of materials, devices, physics, and technology, including fundamental electronic, magnetic, and optoelectronic properties of lower dimensional systems, II-VI and III-V semiconductor heterostructures and devices, ultra-fine magnetic particles, mesoscopic normal-metal superconductor structures, and Moire microscopy of layered microelectronic structures. The conversion project entails installation of beam-blanking hardware in the electron optical column of the microscope, enhancement of the microscope sample stage, construction of a Faraday cup sensor, and configuring the computer and controls for pattern generation and writing. Direct writing of feature sizes at and below 1000 A will be realized. By making use of existing electron optics, this project will provide a significant research capability to a multidisciplinary group in a timely and cost-effective fashion. Specific technological advances that are expected to accrue from the application of this resource include the development of coherent electron transistors, high-density magnetic recording media, optimized blue- green diode lasers, and a versatile materials testing and failure analysis system for microelectronics. These new technologies will emerge from ongoing substantive and comprehensive investigations of the various underlying physical phenomena of quantum confinement and transport, exciton-phonon interaction, and microstructural mechanics.

The Tenth International Conference on the Electronic Properties of Two-Dimensional Systems (EP2DS-10) will be held in Newport, Rhode Island from May 31-June 4, 1993. This conference is the tenth in a series and has the tradition of providing a forum for lively interaction and discussion with strong international participation. The emphasis of EP2Ds-10 will be on the fundamental physics of the electronic states and phenomena associated with reduced dimensionality (less than 3). The conference proceedings will be published in a special edition of Surface Science. The subject matter of the conference covers the following topical areas: *Nanostructures; quantum wires and dots; and mesoscopic effects *Many-body interactions, collective effects, and Coulomb blockade; optical spectroscopy of correlated states *Semiconductor heterostructures, quantum wells, and superlattices; III-V, IV, and II-VI materials *Integral and fractional Quantum Hall Effect and low dimensional electron solids *Electrical transport in strained-layer heterostructures *Novel fabrication techniques *Electrons on helium and cryogenic solid surfaces *Low dimensional organic polymers %%%

9417502 Nurmikko This poject concentrates on research in which high speed optical and optoelectronic techniques are applied to the study of lower dimensional electronic excitations in small heterostructures in compound semiconductors. In particular, new terahertz transient spectroscopic methods will be applied to the study of few and many electron systems in quantum wires and dots in quantizing magnetic fields, with emphasis on the ballistic and coherent response. Enhanced spatial resolution in high amplitude THz fields will be provided by near field imaging methods. % % % This project aims at the study of electrom motion in small semiconductor structures, on a scale much smaller than a micrometer. The electrons may be confined along a very thin wire or in a box, this will make them behave more as waves rather than particles. Ultrashort laser pulse techniques are applied to provide an initial impact of excitation of the electrons and to follow their subsequent motion on a timescale of about one trillionth of a second. In particular, a novel spectroscopic arrangement that uses so-called terahertz techniques will be employed. ***

Computer workstations perform calculations and display graphics fast enough to make real qualitative improvements in teaching engineering. This project is using 18 SUN SPARC 20 Model 61 Workstations to bring computer-aided design and scientific simulation into our core courses. Freshmen and sophomores in all six engineering programs take a common core, lasting through part of the third year, that gives a broad background in physics and engineering science. The new machines make possible three things: first, students will have four years' exposure to a uniform set of UNIX tools, allowing expertise to develop; second, computer-aided design will begin in the earliest courses as a better basis for later study; finally, engineers will develop improved insight into the engineering sciences by simulation of fundamental exemplary problems. Traditionally, simple examples that can be solved by hand are the main tool for teaching introductory science. Many suitable problems that could extend one's physical intuition are neglected because they are hard to compute or draw, a difficulty that workstations can overcome. For example, one such problem in electricity and magnetism is the electrostatic focusing of a beam of electrons in a CRT. The actual lens is just three concentric tubes set end to end at different potentials. Its analysis shows potential theory, electric field visualization, and particle dynamics in an economically important context. This project is developing software with simple interfaces for a suite of such examples as a new teaching tool.

9503708 Zaslavsky The addition of this processing extension equipment will enable new research in nansostructure fabrication by regrowth and in the transport, optical properties, and device physics of novel nanostructures. This processing extension will permit regrowth of modulation-doping, contacting and isolating layers on patterned heterostructures prepared with in-situ etched and clearned regrowth surfaces. The processing extension will have the following capabilities: low-damage electron-cyclotron resonance (ECR) plasma reactive ion etching of III-V semiconductors; ECR hydrogen plasma cleaning of etched substrates; surface cleanliness monitoring by Auger spectroscopy; and invacuum transfer of patterned substrates into the MBE growth chamber. The properties of strained and unstained uniform quantum wires fabricated by etching through quantum wells and regrowth with modulation-doping layers on the sidewalls will be studied. A heavily-doped gate electrode layer in the regrowth sequence will permit carrier density modulation in these wires independent of the confining potentials determined by the original heterostructure. Analogously, by pregrowing the appropriate barrier potentials, gated 2-dimensional tunneling structures and superlattices in III-V heterostructures will be fabricated and their transport and optical properties will be investigated down to the quantum dot limit. % This equipment will be used by a group of investigators having complimentary expertise ranging from semiconductor epitaxial growth to nanofabrication and fro transport and optical characterization to device physics and engineering. It represents fundamental materials research important for understanding processing of semiconductor materials, and is ultimately relevant for manufacturing.

9508401 Nurmikko The goal of this research is to initiate the development of a new generation of blue-green semiconductor lasers, based on vertical cavity and microresonator devices. The lasers are based on wide bandgap II-VI semiconductors which have recently seen a brisk pace of development in the conventional edge emitter geometry. The principal investigator's group has been a part of these advances and has achieved considerable experience in the physics and engineering of these quantum well heterostructure devices, expertise that will be of direct benefit in the proposed research. For example, spectroscopic characterization of gain, application of bandgap engineering techniques for electrical contacts, nanostructure fabrication techniques, and low temperature device processing methods have been accomplished. From applications point of view, the emergence of compact blue-green lasers has significant potential impact on optical storage, display, and printing technologies. ***

9701579 Xiao In this GOALI supported research program magnetic tunnel junctions (MTJ) will be prepared and studied with ultra-fast laser spectroscopy, near-field optics, and magneto- tunneling. The purpose is to study the fundamental and technological issues essential to the performance and competitiveness of the MTJ. The proposed work is closely linked to activities at IBM Research, Yorktown Heights. IBM will, where appropriate, pay for the support of students for work done at IBM Research. This activity is jointly supported by DMR and the OMA office of the MPS Directorate. %%% Magnetic tunnel junctions are devices which are actively pursued by industry as the new memory and sensor elements such as data storage reading heads and non-volatile magnetic random-access-memory (MRSM) cells. The scientific issues include gaining a more complete understanding of the magnetic behavior of these systems, especially while illuminated by light and the effect of reducing the device size. The GOALI supported work links expertise at the academic institution with activities at IBM Research, Yorktown Heights. IBM will, where appropriate, pay for the support of students for work done at IBM Research. This activity is jointly supported by DMR and the OMA office of the MPS Directorate. ***

9726938 Nurmikko The PI proposes a research program whose objective is to focus on specific areas of basic and applied semiconductor science to aid in the the continued development of the group III-nitride based semiconductor blue lasers and extension of such devices to the near ultraviolet. Further progress in this field of vast technological potential requires systematic scientific efforts. The PI identifies and addresses two critical areas in the proposed program: (a) the study of optical gain and related radiative processes in the nitride quantum wells for optimizing the active region of the laser and implementing a low threshold device design, and (b) development of understanding at a microscopic level of the p-type ohmic contact problem. In addition to the overall idiosyncracies of a widegap semiconductor, both of these problem areas are impacted by the complex and rich microstructure of the nitride heterostructures. In the planned work we thus also look for key links between the crystal microstructure and optoelectronic properties which are presently poorly understood. Apart from our early results on nitride-based diode light emitters, the PI takes advantage of our experience with bluegreen II-VI semiconductor lasers where the issues of gain, device design, and contacts were successfully pursued by the PIs for advancing these quantum well diode devices. Significant differences and distinct challenges do, of course, exist in the nitrides; however, given the common features that are shared by wide bandgap semiconductors at a fundamental level provides a very useful base of comparison for quantitatively and scientifically meaningful comparisons, The proposed research takes advantage of special capabilities and techniques adapted to the study of both nitride-based heterostructures and diode laser devices. For example, advanced laser-based spectroscopic techniques, including ultrafast real-time spectroscopy will be applied to study the optical gain and dynamics of a high density lo w dimensional electron-hole pair in a disordered system such as the InGaN QW where electronic localization effects are important. The techniques include high spatial resolution probes such as near-field optical microscopy. For the p-type contact studies, in-situ deposition of metallization and InN heterostructures in UHV environment is proposed as a means to study the microscopic properties of the metal-nitride interface in order to optimize a low resistance contact for diode laser application. ***

9871213
Nurmikko
An exceptionally versatile Ultrafast Optical Spectroscopic Laser/Optoelectronic laboratory instrumentation system, based on new developments in the state of the art technology, will be acquired and implemented during this project that is funded by the Major Research Instrumentation program. The research instrumentation utilizes compact all-solid state new laser technology based on titanium, which are integrated into a high performance tabletop ultrafast time-domain ellipsometric/photometric laboratory tool. Incorporating multichannel spectral analysis with significant real-time computational power, the instrumentation is configured for high precision measurements of time varying optical constants that are induced within a broad spectrum of photoexcitation experiments, with time resolution below 30 femtoseconds. The instrumentation features an integrated data processing capability, which will enable a rapid real-time analysis of the complex numerical problems in transient ellipsometry/photometry, such as occurring in heterogeneous optical media. The optical system also integrates a near-field optical microscope that will combine the ultrafast time resolution with submicron spatial resolution for femtosecond microscopy on small material structures. The two principal investigators on this project will be joined in close collaborative research by six other faculty co-investigators at Brown and by several industrial partners/collaborators.
%%%
The new instrumentation, which will be acquired from funding from the National Science Foundation's Major Research Instrumentation program, will provide an opportunity for postgraduate and postdoctoral training in state-of-the-art modern optical instrumentation and laser spectroscopy. In addition to the basic scientific content within the proposed project areas, this training reaches into areas of applied technology that are bridged by elements within the proposed research that look for active opportunities in the development of optoelectronic instrumentation development for advanced metrology and spectroscopy.
***

This Focused Research Group project involves two faculty members and several industrial collaborators who will study ultrafast, spin dependent processes that reflect nonequilibrium magnetization dynamics in ferromagnetic thin films and heterostructures on a picosecond time scale and below. A core question relates to the ultimate "speed limits" of magnetization reversal, which will be approached experimentally by employing all-optical, ultrashort pulse laser techniques. Unlike conventional approaches, which use pulsed magnetic fields to study magnetization switching in storage media, the physics in this research focuses on selective optical excitations of spins within the ordered magnetic medium, so as to modulate the exchange interaction and related electronic correlations by light in an nonthermal manner. In addition to studying optically activated magnetoelectronic processes in laterally uniform magnetic multilayers and exchange biased bi- and multilayers, the project includes the study the dynamics of collective micromagnetic effects in high density planar arrays where the individual submicron magnetic particles are coupled via dipolar (or possibly exchange bias) forces. Thin films of conventional transition metals (Co, NiFe) form the starting materials base for the project work, but a significant component of the research emphasizes selected transition metal oxides, most notably the half metallic ferromagnet CrO2. The research involves students and postdocs in cutting-edge fundamental research that has immediate relevance to current technology. The training prepares student for a variety of careers in academe, industry or government.
%%%
The slowest part of a typical computer is the magnetic hard drive. While there are several steps involved in storing and retrieving data from the thin film disk medium, the process of encoding information into magnetically aligned atoms is reaching its practical limits of speed. In this project work we aim to use ultrashort laser pulses to influence the disk material's magnetic properties and to achieve the reversing the magnetic alignment of groups of atoms in as little as a few trillionth of a second-approximately a hundred times faster than the speed of the process in today's disk drives. The all-optical technique allows the team to investigate the fundamental interactions involved in such fast magnetic switching, and it may lead to extremely fast data storage devices in the future. One specific approach focuses on aiming the laser pulses at a sandwich of two magnetically coupled thin film magnetic films, whose collective interaction determines the overall magnetic properties of the bilayer which is efficient in resisting an externally applied magnetic field. By selectively absorbing the laser radiation at the interface, only a few atomic layers thick, the magnetic coupling between the two materials is abruptly interrupted, freeing one of the layers (the 'free' ferromagnet) to be rapidly reversed by an oppositely-directed static magnetic field, applied from the outside. While the concept could some day be used in fast data storage, the team will be using it mostly to study the basic processes of "flipping ultrasmall compass needles" at unprecedented speeds. Many physicists have studied the reversal of a single atom's magnetic moment, but the collective process of flipping the moments of many thousands of atoms at once is not well understood at a fundamental level. The research involves students and postdocs in cutting-edge fundamental research that has immediate relevance to current technology. The training prepares student for a variety of careers in academe, industry or government

0070887
Nurmikko

In this project, Nurmikko, his graduate students, and collaborators aim to study, design, and develop optoelectronic device and optical physics concepts that will lead to the realization of blue and ultraviolet vertical cavity light emitters, based on wide band gap nitride semiconductor heterostructures. In particular, the specific goals of the three year program are the demonstration and fabrication of (a) a resonant cavity light emitting diode (RCLED), and (b) a vertical cavity surface emitting laser (VCSEL). Although closely interconnected, the technical challenges facing the development of these new, compact short wavelength devices can be logistically grouped into into two broad areas: (i) the approach and implementation of the optical microresonator structure and (ii) the design and realization of a pn-junction based injector structure. To achieve high Q-factor vertical cavities for InGaN and AlGaN heterostructures, Nurmikko and co-workers aim is to create processing techniques that will create optical structures reaching Q-factors in the 1000-2000 range for reducing the laser threshold requirements. The approach is based on monolithic integration of two dielectric DBRs and also focus on "hybrid" structures with one dielectric and one as-grown DBR. Study of the optical gain spectra of the VCSEL structures forms another key project area, to detail the gain spectra of the InGaN and AlGaN active media for optimizing these for low threshold VCSELS. Nurmikko and co-workers will study fundamental microcavity physics to enhance light emission from InGaN and AlGaN VCSELs and RCLEDS. Excitonic enhancement to oscillator strength can concentrate optical gain so as to significantly reduce a nitride VCSEL threshold. Similarly, spontaneous emission properties for an RCLED are expected to be dramatically enhanced.

For achieving a diode vertical cavity emitter, Nurmikko and co-workers will study lateral p-injection in two types of experiments: (i) the use of near field imaging techniques to study lateral diffusion, and (ii) the design of LED microstructures where current spreading can be obtained from electroluminescence spatial imaging. For the blue and NUV VCSEL work they will also concentrate on the incorporation of p-GaN/AlGaN modulation doped heterostructures for enhancing the p-side conductivity. One of the specific features that they will address concerns the tailoring of the electronic structure so that interface scattering can be reduced (hence the hole mobility enhanced). They propose to use the very large built-in piezoelectric and spontaneous dielectric polarization effects to electrostatically design the heterojunction confinement profile. They will also study the use of epitaxial lateral overgrowth (ELOG) to facilitate both the incorporation of "buried" DBR mirrors as well as to define current apertures for channeling hole transport to the active device region (as defined by the vertical resonator).

A specific characteristic of the ongoing research is a close collaboration with Hewlett-Packard (both HP Labs and the Optoelectronic Division, now renamed Agilent Technologies), as well as Sandia National Laboratories. This industry/government laboratory connection will be an integral part of the project work.
***

0423566
Nurmikko
The proposed research will adapt and advance compact wide bandgap semiconductor light emitter devices (LEDs) at short wavelengths for their application to imaging of biological materials/systems. In particular, they will design, fabricate, and tailor blue and violet LEDs into versatile multi-element arrays that will enable the real-time imaging of the dynamics of neural cell networks via fluorescence-based excitation, on-chip. Further, ultraviolet LEDs will be employed to impart photochemical excitation of such cellular networks in a spatio-temporally selective manner for the goal of implementing an interactive interface between neural circuits and man-made optoelectronic circuits.

"Photonically Strongly Coupled Organic/Inorganic Nanocomposites for Light
Emitter and Photovoltaic Applications" (ECCS-0725740)


In this research, fundamental photonic phenomena are combined with new types of organic/inorganic intercalated media on the nanoscale, with the aim to derive exceptionally strong light-matter interaction for applications ranging from compact light emitters to novel photovoltaics. The intellectual merit of the work lies in creating organic-inorganic hybrid photonic materials whose electronic excitations couple beyond the perturbative regime for enhanced light- matter interaction, which exceeds that in present optical devices. This is accomplished by special combination of resonantly interacting materials, exploiting two classes of material which each possess significant optical oscillator strengths, but in a highly contrasting electronic environment. The organic subcomponent of the hybrid nanoscale media is formed from J-aggregate polymers which exhibit exceptional absorption and emission concentrated in narrow spectral ranges across the visible and near infrared. Spectrally matching the organic components are inorganic colloidal II-VI semiconductor quantum dots, which provide pathways via excitation and charge transfer to the organic and external electrical interfaces, respectively. The key physical feature of the intercalated hybrid medium is resonant electromagnetic excitation transfer, which can have near 100% efficiency as an electronic energy transfer channel within the two subsystems, at room temperature.

The broader impact of the proposed work is the potential to insert exceptionally high performance entirely new active photonic material into functional optoelectronic devices, such as light emitters and photovoltaics, spread hyperspectrally across the visible into the near IR portions of the spectrum. The device goals aim to search for novel application spaces presently not accessible or enabled by conventional approaches to these technologies by inorganic and organic semiconductors, respectively, including visual arts. Scientifically, bridging the two rather separate branches of active optical technologies, based on inorganic and organic materials/devices, offers a new prism to view opportunities for synergy and vision to emerging photonics technologies, as well as training of interdisciplinary new generation of technologists. The subject matter of innovative, and structurally flexible and spatially extendable photonic materials offers also an excellent vehicle for outreach and connection to science, including lab experience for undergraduates and teaching aids for GK-12, the latter exploiting Brown University's excellent outreach infrastructure.

ABSTRACT

Integration of Dynamic Sensing and Actuating of Neural Microcircuits
PI: Arto V. Nurmikko

The proposed EFRI program aims to develop transformative paradigms in our understanding of the complex nonlinear dynamics of brain microcircuits and their function, by developing and fusing a new generation biosensing (recording) and actuation (neurostimulation) techniques to a potent toolbox. The proposed research engages brain circuits with external photonic and microelectronic interfaces in animal models, in particular for the study of the so-called "working memory" - the brain's "random access memory". At the neuroengineering level, the proposed research integrates new set of neural sensing and actuation tools on the microscale that are applied to engage with specific sensing and planning action by the brain - in particular the dynamics of information processing in the prefrontal cortex. A key experimental driver is the development of a new micro-optical/photonic device technology that will enable precise spatio-temporal targeting through sensory pathways of cortical microcircuitry and the imaging of this circuitry in real time in specific animal models. The unique device technology elements in the sensor/actuator engineering integrate ultracompact multi-element arrays of light emitters and microelectronic chip-scale sensors for excitation and mapping of the brain microcircuitry in real-time, which has been rendered both stimulus responsive and recordable by cellular-level genetic and nanomaterial sensitizing. The goal of the development of sensing/actuation microtools with associated brain science paradigms is to pave way for microdevice interfaces for bidirectional access across a population of neurons in the brain. Bidirectionality requires that both neural recording and neural stimulation can be achieved simultaneously at cellular level for multiple neurons, and ultimately multiple brain sites, spatially and temporally. Development of a class of specific brain-interfaces probes which synergize approaches from contemporary photonics/optoelectronics for "reading" and "writing" neural information from/to brain's microcircuits is the contributing aim of this planned EFRI proposal.

In a broader context, the research aims to facilitate the implementation of a closed-loop feedback compact device technology that offers the promise of entirely new classes of neural interfaces for (i) advancing the understanding of the brain from sensing to actuation- with cellular level resolution of microcircuit dynamics, (ii) aim the application of the technology to potentially therapeutic and prosthetic applications. For example, the study of the working memory function in the brain is closely associated with neurological diseases such as schizophrenia, attention deficit disorder and has been linked to epilepsy. The team aims to leverage the research outcomes from this program in mammalian animal models (in vitro and in vivo) so that key brain science paradigms such as the fundamentally important "working memory" will find translation to human neuroscience and rehabilitative goals. By including within the team a clinical neurology interface, our proposed research is envisioned to contribute to our unraveling of neurological disease, pave way for elucidating and exploring the applicability the nature of the brain-like systems to other technologies, as well as improve U.S. competitiveness in the global economy through advanced technology development in a frontier area at the intersection of physical and life sciences. The research on these topics is also expected to create a generation of "neuroengineering" graduate students with true interdisciplinary education, as well as innovative businesses and entrepreneurs.

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

Objective: The objective of this research is to enable development of nanopatterned conformal oxides for device applications. The approach is to acquire a processing module comprised of complementary inductively-coupled plasma (ICP) etch and atomic-layer deposition (ALD) tools for the Brown Microelectronics Central User Facility.

Intellectual Merit: This equipment cluster will enable the fabrication of nanopatterned conformal oxides for cutting-edge applications in electronic, fluidic, photonic, and implantable devices. Specifically, the proposed equipment will help researchers: (1) deposit high-?Û dielectrics for nanoelectronic devices; (2) control the dimensions and surface chemistry of nanofluidic channels; (3) pattern and protect optically active materials, including luminescent rare-earth oxides, for light emitters and detectors; and (4) encapsulate implants with bio-compatible coatings that prevent infection and promote tissue growth.




Broader impacts: Located in a central user facility with ongoing technical and administrative support, this equipment will constitute a linchpin of the Brown University infrastructure for research training in nanoscale science and engineering for years to come. Housed in a publicly accessible cleanroom, this equipment will be made available to researchers from many university departments, including Engineering, Physics, Chemistry, Biology and Medicine, as well as outside users from local industry and academic institutions via the Materials Research Facilities Network. Furthermore, this program will be enriched by established connections with outreach through the NSF sponsored GK-12 ¡§Physical Processes in the Environment¡¨ program in the Providence Public School system and the collaborative REU program offered by the Brown Materials Research Science and Engineering Center (MRSEC) and the Leadership Alliance.

Objective: To penetrate the full visible spectrum using a single nanocrystalline material system, based on colloidal semiconductor quantum dots, to develop coherent microemitters and their arrays. The proposed approach is guided by two key research objectives: (a) methods to create ultrahigh density closely-packed quantum dot thin film red- green-blue optical gain media which can be tightly adhered on selected substrates and microscale patterned surfaces, and (b) integration of optical microresonators with the quantum dot media which incorporate the high gain medium to enable operation for a color-tunable microlaser at room temperature under practical and realistic excitation conditions.

Intellectual merit: At the basic level, research aims to maximize the optical gain in densely packed colloidal quantum dot-based microresonators by investigating fundamental competition and interaction within interacting quantum dot excitonic states between radiative (stimulated emission) and nonradiative processes. At the applied level, this knowledge is employed to design low-cost thin film gain media which can be patterned and/or conformally deposited and integrated within optical microcavities for microscale lasers.

Broader impacts: The single material based full spectrum coherent microemitters may offer a transformative means to develop new types pixelated laser projection devices, a technologically important outcome for portable displays. The PI aims to recruit women and other minority students under the REU program and will participate in outreach events with students and teachers through the already established program at Brown with Providence Public Schools system. Graduate students will have opportunity to work with a start-up company to gain experience transitioning research to technologies.

1264816
Nurmikko, Arto

The proposed research aims to contribute to the emerging field of neurotechnology by providing a new class of brain "write-in"/ "read-out" devices with unique attributes for bidirectional communication with neural circuits. The project aims to have an impact on both basic neuroscience while providing an important technology piece to future prospects for treating severely neurologically impaired individuals via electronic communications with brain circuits. This is a development project that lies at the very intersection of biomedical engineering and health sciences. More specifically, its aim is to create a new generation of devices that enables the combination of spatially and temporally specific stimulation of and recording from brain circuits in vivo mobile animal models, to advance the understanding of brain function at a fundamental level on one hand, while extrapolating squarely at possible applications e.g. to cases of neurological injury on the other.

Extracting information about functional connectivity and performance of neural circuits by electrical recording by arrays of sensing microelectrodes is a well-established and powerful technique. For example, by acquiring resolution at a single neuron level from cortical circuits by implanted multielectrode arrays with real-time decoding the intention of a brain to execute motor action has recently enabled a human tetraplegic patient, with neural signal pathways from the brain to spinal cord inoperative, to control a robotic arm and hand by "thought". Supported further by several powerful demonstrations in non-human primates of brain control, a grand challenge to future neural prostheses is to "close-the-loop" for cortical control of assistive devices, for instance by providing a proxy by brain stimulation for lost sensory capability such as touch. Stimulation by electrical means has been traditionally used to excite the brain across multiple spatial scales for both research and has today specific therapeutic use. Importantly, however, the ability to specifically access well-targeted neural circuits for both excitation and inhibition has been now opened by techniques of "optogenetics", a pioneering new approach in basic and applied brain science and neurotechnology. The optical method offers a much more direct and less ambiguous stimulation of brain circuits to inform brain circuits. To reach this goal, a multielement biomedical implant device is proposed where up to 100 microscale elements are integrally arrayed for dual use - in simultaneously delivering light to and electrically reading out neural circuit dynamics ("100 points of light"). Meeting both fundamental physical and practical physiological challenges, a specific class of so-called wide bandgap crystalline semiconductors is exploited - which have the unusual combinatorial attributes of optical transparency and high electrical conductivity. The proposed device-driven research program leverages directly from expertise in the PIs laboratory where work on development of new neural recording methods (such as by wireless implants) intersects with other research strands where wide-bandgap semiconductors are studied and microfabricated to different types of light-emitting devices. In culmination of the research, the new optical stimulation/electrical read-out capability will be tested and employed in vivo in mobile animal models for fundamental brain science and neurotechnology development purposes.

Proposal CBET - 1402803
"Bidirectional Wireless Optoelectronic Device for Interfacing Brain Circuits"

The proposed research aims to contribute to the field of neurotechnology by providing a new class of brain "write-in"/ "read-out" devices with unique attributes for bidirectional communication with neural circuits. By developing the new technology for the broader scientific community, the project aims to have an impact on basic neuroscience, especially for primates, while providing an important piece of technology to development of future prospects for treating severely neurologically impaired individuals via direct electronic communications with brain circuits. The proposed technology is based by innovative use of special types of optoelectronic materials combined with advanced microdevice design and fabrication from microcircuits to mobile microsystems. The PI seeks to develop a compact, combinatorial stimulating/recording device system platform for accessing the brain circuits at spatial and temporal specificity not possible before. Further, the entirely wireless, high speed bidirectional electronic communication link to brain circuits will enable testing the new capability in in-vivo mobile animal models for fundamental brain science and neurotechnology development purposes.

Technical Description:
The goal of this neuroengineering project is to enable access to a crucial piece in our understanding of the brain, namely mapping of targeted brain circuits to advance fundamental understanding of how units composed of hundreds or thousands of individual neural cells act as a dynamical system while computing e.g. a primate's planning of such motor action as reaching and grasping coupled to perception and other sensory modalities. While sub-centimeter imaging of the functioning brain can be visualized by functional magnetic resonance equipment, we currently lack the full ability to track network dynamics at the spatial and temporal level which defines the most meaningful, yet simplest truly functional computational circuit. The term "mesoscale" has been recently introduced to designate such basic modular constructs which might contain hundreds to thousands of interacting neural cells. The PI proposes to engineer a powerful wireless neurotechnology platform to create a real-time link between targeted brain microcircuits for animal models including non-human primates. The engineering core of the system is a compact, lightweight photonic-microelectronic device, implanted and head-mounted on a subject, with high-speed radio-frequency link to external information processing systems. In summary the aim is to implement a broadband bidirectional wireless neural interface for targeted brain areas of interest. Bidirectionality implies simultaneous neural recording and neural stimulation. The proposed high-speed wireless device technology accomplishes this task for simultaneous recording and stimulation with spatial and temporal resolution to single neuron-level resolution. Having means for precisely controlled spatio-temporally patterned neurostimulation capability of neural circuits enables the tracking and identification of the dynamical trajectories of the associated perturbed brain states by precisely controlled stimulus (excitation and/or inhibition). The recorded neural signals capture all of their relevant temporal information across the multiple probe points, namely as action potentials (spikes), high-frequency oscillations field potentials (LFP), and the underlying low-frequency brain rhythms. The project is a fusion of sophisticated microelectronics and computational neuroscience. Embedded in the research are multiple disciplinary components: photonics, microbiology (of optogenetics), material science and nanofabrication processing, ultralow-power integrated circuits design, high speed microwave telemetry, and computer engineering hardware/software for neural signal processing.



.