Neuromodulation with a high spatial and directional specificity is highly desired but very challenging to achieve using electrode-based electrical stimulation. Microscopic magnetic stimulation, eliciting neural elements via induced eddy current, is a promising alternative as it is able to modulate neurons with unprecedented focality and directionality. Moreover, thanks to advanced microfabrication technology, it is possible to fabricate a micrometer-sized coil (i.e., micro-coil) array on a compliant substrate as an implant for long-term neuromodulation. Here we present our design and fabrication of an implantable planar micro-coil chip, consisting of an array of ten spiral-shaped micro-coils in a figure-8 configuration. The fabricated micro-coil array showed high consistency and reproducibility in impedance measurement, with a resistance range of about 10-20 Ω, and inductance of about 30 nH. We demonstrated the feasibility of micro-magnetic stimulation in rodent experiments, by using the fabricated chip on the sciatic nerve of an anesthetized rat, while measuring the elicited neuromuscular (EMG) responses which suggests the high focality of the micromagnetic stimulation system.

Twisted moiré photonic crystal is an optical analog of twisted graphene or twisted transition metal dichalcogenide bilayers. In this paper, we report the fabrication of twisted moiré photonic crystals and randomized moiré photonic crystals and their use in enhanced extraction of light in light-emitting diodes (LEDs). Fractional diffraction orders from randomized moiré photonic crystals are more uniform than those from moiré photonic crystals. Extraction efficiencies of 76.5%, 77.8% and 79.5% into glass substrate are predicted in simulations of LED patterned with twisted moiré photonic crystals, defect-containing photonic crystals and random moiré photonic crystals, respectively, at 584 nm. Extraction efficiencies of optically pumped LEDs with 2D perovskite (BA)2(MA)n-1PbnI3n+1ofn= 3 and (5-(2'-pyridyl)-tetrazolato)(3-CF3-5-(2'-pyridyl)pyrazolato) platinum(II) (PtD) have been measured.

Owing to its attractive optical and electronic properties, silicon carbide is an emerging platform for integrated photonics. However an integral component of the platform is missing—an electro-optic modulator, a device which encodes electrical signals onto light. As a non-centrosymmetric crystal, silicon carbide exhibits the Pockels effect, yet a modulator has not been realized since the discovery of this effect more than three decades ago. Here we design, fabricate, and demonstrate a Pockels modulator in silicon carbide. Specifically, we realize a waveguide-integrated, small form-factor, gigahertz-bandwidth modulator that operates using complementary metal-oxide-semiconductor (CMOS)-level voltages on a thin film of silicon carbide on insulator. Our device is fabricated using a CMOS foundry compatible fabrication process and features no signal degradation, no presence of photorefractive effects, and stable operation at high optical intensities (913 kW/mm 2 ), allowing for high optical signal-to-noise ratios for modern communications. Our work unites Pockels electro-optics with a CMOS foundry compatible platform in silicon carbide.

This is the final report for the project “All-Digital Plug and Play Passive RFID Sensors for Energy Efficient Building Control”, funded by DOE, and performed by Clemson University, Phase IV Engineering and Harvard University from October 1, 2016 to December 31, 2020. The main objective of this project is to develop, demonstrate and pre-commercialize a novel, plug & play, battery-free, wireless sensor technology to enable low-cost (<$10 per node) indoor and outdoor temperature and humidity measurement for energy efficient building controls and operations. The proposed technology is based on the novel concept of all-digital sensing and its seamless integration with the passive RFID technology. This project focuses on the design, fabrication, material optimization, interrogation electronics, validation, and demonstration of the novel sensor nodes for building applications. The specific objectives of this research program include: (1) Design, fabricate and optimize a compact, robust, and high-resolution digitizer, which could convert rotation angle into digital numbers. (2) Develop the multi-physics-based modeling and simulation of the temperature/humidity transducer to derive a rational design of the architecture, dimension, structure, materials (i.e., mechanical, electrical, thermal and hygroscopic) properties and functions of the sensor node. (3) Design, fabricate and optimize the bi-material based humidity sensitive coil which could linearly transduce the environmental relative humidity variations to rotation angles. (4) Design, fabricate and optimize an UHF RFID platform which could support long-range passive wireless communications of 8-bit digital numbers. (5) Design, fabricate and optimize the miniaturized all-digital sensor using MEMS technology. (6) Validate the integrated all-digital sensing system in a real building environment to test the system’s performance. To achieve the above challenging goals, we have formed a multidisciplinary research team consisting of four members from two universities, and a small business company with complementary skills and strong facilities. The team worked collaboratively on fundamental and applied research on the following five major technical areas: (1) Modeling and simulation of the bi-material structure for temperature and humidity sensing The spiral-shaped bi-material coil transduces humidity/temperature variation to rotation angles. The dimension and geometry parameters of the coil, such as thickness and the ratio between material, number of coils, radius, and height, directly relates to its humidity/temperature response. Analytical and numerical modeling and simulation methods was conducted to derive the design criteria for humidity/temperature coils. Based on the analogy between CTE and CME, three case studies were performed with the simultaneous consideration of the temperature variation and humidity variation. Finally, based on the theoretical and numerical study and the availability of sensor materials, two recommended designs of the coil sensor are proposed. (2) Development and fabrication of the humidity sensitive coil The team developed a humidity sensitive coil which could transduce the environmental humidity changes as rotation angles. The sensing material is required to have high sensitivity, linear response, large measurement range (20%-80%RH), and long service time. The candidate humidity sensitive polymers (Hydroxyl-containing polymers) were synthesized and tested. The material’s moisture absorption and desorption behaviors were studied. This humidity sensitive material was then integrated with both metal spring and 3D printed polymer coils. Optimizations related to humidity sensitivity and responses at high humidity level (>80%) were conducted. (3) Design, fabrication and optimization of all-digital sensor We developed an all-digital sensor which is composed of a digitizer and a humidity/temperature transducer. The digitizer transfers physical movements (i.e., rotation angle or linear displacement) into coded digital numbers. Such device mainly comprised of an encoding pad and an interrogation head. When the head is sliding through the pad, the absolute angle or displacement is encoded as binary digital numbers. Two different coding methods, nature code and gray code, were examined. The design, fabrication and assembly of the pad and head were developed. Emphases were placed on the analysis and the elimination of erroneous readings. All-digital temperature or humidity sensors were then developed by assembling the digitizer with temperature or humidity sensitive coils, respectively. We also conducted the validation experiments for each type of sensor. In addition, we also worked on other types of digitizer with different features, such as the side-wall encoder and the non-contact capacitive reading design. The all-digital sensing can be seen as a mechanical analog-to-digital converter, which use a rotary or linear encoder to digitize the physical quantities, such as temperature and humidity. Such mechanical structure has the potential to utilize MEMS technology to shrink the size or increase the resolution. To this end, the team proposed several designs and implemented the fabrication process to confirm its feasibility and find problems. We discussed the design and fabrication of capacitive and conductive reading digitizer based on MEMS technology, respectively. (4) Development of the UHF RFID platform Various commercially available RFID readers and RFID chips were investigated to determine the most suitable ones for building sensors. The RFID tag circuit mainly includes antenna, RFID chip, sensor interface, and energy harvester. Design, debugging and optimization of each part were conducted. An RF switch was used to transform the two-antenna mode (the receiving and transmitting antennas are separated) to single-antenna mode. We also proposed several different designs for digital sensor interface using MCU or MUX. A working distance of over 10 m was achieved by using the energy harvesting technique. (5) Field test with integrated BACnet interface to building management system The proposed RFID sensor reading platform was integrated with BACnet communication protocol to establish the interface to the building management system. We also optimized the software to increase the system’s robustness, increase the sensor reading rate, and make the sensor more user friendly. The sensing system was successfully demonstrated in both lab and in real building management systems. In summary, under the close collaborations among the three research groups, we have completed all the tasks and fulfilled the proposed research objectives. All the technical milestones have been achieved and the project has been completed successfully. The technical breakthroughs obtained under this project lead to the successful demonstration of a novel concept of “all-digital sensing”, which powers the sensor to operate without on-node signal processing and battery. By seamlessly integrating the sensor nodes with the latest passive radio frequency identification (RFID) technology, each sensor node is assigned with a unique digital ID and many nodes can be wirelessly interrogated using a single RFID reader without ambiguity. Integrating with BACnet communication protocols, these sensors were remotely registered to the BMS in a “plug & play” fashion. Both temperature and humidity were accurately monitored and transferred to the BMS for improvement of the energy efficiency and indoor environmental quality. The developed technology can be widely adopted for residential and commercial building temperature and humidity monitoring and control. Based on the BTO market calculator, the total market size in 2030 would be 10.8 Quads. The proposed wireless sensor network energy management system can save an average of 3% and up to 8% in overall building energy consumption. The primary energy saving is potentially at least 0.3 Quads. From the cost effectiveness point of view, the proposed sensor will cost less than $10 per node without the requirement of battery. The lifetime duration will be more than 5 years. Compared with current wireless censoring technology ($100 per node with 10-year lifetime), the simple payback period will be reduced by 80% (several months to 2 years). With such high primary energy savings, great technical potentials, and low simple payback period. The funded R&D work has validated the designs, proven the feasibility, optimized the materials and fabrication procedures, and characterized the performance of the sensor devices and systems, paving the ways for full commercialization.

Recently, white-matter fiber tract pathways carrying neural signals through the brain were shown to follow curved, orthogonal grids. This study focuses on how these white-matter fibers may be selectively excited using micromagnetic stimulation (μMS), a new type of neuronal stimulation, which generates microscopic eddy currents capable of directionally activating neurons. One of the most remarkable properties of this novel type of stimulation is that the μMS fields provide unique directional activation of neuronal elements not seen with traditional electrical stimulation. An initial prototype built with SU-8 based photolithography technology shows that the structure can be fabricated. The coil design was optimized through electrical resistance calculations and electric field simulations to elicit the brain's maximal focal and directional neural responses.

The electro-optic modulator encodes electrical signals onto an optical carrier, and is essential for the operation of global communication systems and data centers that society demands. An ideal modulator results from scalable semiconductor fabrication and is integrable with electronics. Accordingly, it is compatible with complementary metal-oxide-semiconductor (CMOS) fabrication processes. Moreover, modulators using the Pockels effect enables low loss, ultrafast, and wide-bandwidth data transmission. Although strained silicon-based modulators could satisfy these criteria, fundamental limitations such as two-photon absorption, poor thermal stability and a narrow transparency window hinder their performance. On the other hand, as a wide bandgap semiconductor material, silicon carbide is CMOS compatible and does not suffer from these limitations. Due to its combination of color centers, high breakdown voltage, and strong thermal conductivity, silicon carbide is a promising material for CMOS electronics and photonics with applications ranging from sensors to quantum and nonlinear photonics. Importantly, silicon carbide exhibits the Pockels effect, but a modulator has not been realized since the discovery of this effect more than three decades ago. Here we design, fabricate, and demonstrate the first Pockels modulator in silicon carbide. Specifically, we realize a waveguide-integrated, small form-factor, gigahertz-bandwidth modulator that can operate using CMOS-level drive voltages on a thin film of silicon carbide on insulator. Furthermore, the device features no signal degradation and stable operation at high optical intensities (913 kW/mm 2 ), allowing for high optical signal-to-noise ratios for long distance communications. Our work unites Pockels electro-optics with a CMOS platform to pave the way for foundry-compatible integrated photonics.

We fabricate suspended single-mode optical waveguides and ring resonators in 3C-SiC that operate at telecommunication wavelength, leverage post-fabrication thermal annealing to minimize optical propagation losses and demonstrate Q of over 41,000.

This work further advances the micromagnetic stimulation (μMS) technology, which has shown the capability of stimulating the nervous system using magnetic induction in a focal region of tissue by discharging a time-varying current through a sub-millimeter size coil. However, μMS was originally based on commercial off the shelf (COTS) inductors, which are designed to maximize efficiency and minimize its losses albeit shielding off the magnetic field from reaching the neural tissue. In this work, we study and fabricate microscale coil structures for next-generation μMS devices. The coil was designed to optimize the flux injected into the tissue by using a planar square spiral coil geometry, which was previously shown to be optimal for neuronal stimulation. The results of the electromagnetic Finite Elements Method (FEM) simulations of the proposed μMS device show that even though the spiral has a fully symmetric design, it nonetheless exhibits an asymmetry in the induced electric field in the tissue that can potentially be used for activating neurons with a specific axonal orientation. Such devices could become the brain and heart stimulators of the future with their contactless ability to deliver the neuronal stimulation needed for therapeutic efficacy in patients in need of implantable cardioverter-defibrillators or pace-makers, or patients with Parkinson's disease, epilepsy.

Transforming a laser beam into a mass flow has been a challenge both scientifically and technologically. We report the discovery of a new optofluidic principle and demonstrate the generation of a steady-state water flow by a pulsed laser beam through a glass window. To generate a flow or stream in the same path as the refracted laser beam in pure water from an arbitrary spot on the window, we first fill a glass cuvette with an aqueous solution of Au nano-particles. A flow will emerge from the focused laser spot on the window after the laser is turned on for a few to tens of minutes; the flow remains after the colloidal solution is completely replaced by pure water. Microscopically, this transformation is made possible by an underlying plasmonic nanoparticle-decorated cavity, which is self-fabricated on the glass by nanoparticle-assisted laser etching and exhibits size and shape uniquely tailored to the incident beam profile. Hydrophone signals indicate that the flow is driven via acoustic streaming by a long-lasting ultrasound wave that is resonantly generated by the laser and the cavity through the photoacoustic effect. The principle of this light-driven flow via ultrasound, that is, photoacoustic streaming by coupling photoacoustics to acoustic streaming, is general and can be applied to any liquid, opening up new research and applications in optofluidics as well as traditional photoacoustics and acoustic streaming.

This paper describes the use of a nanoindenter, equipped with a diamond tip, to form patterns of indentations on planar substrates (epoxy, silicon, and SiO(2)). The process is called "Indentation Lithography" (IndL). The indentations have the form of pits and furrows, whose cross-sectional profiles are determined by the shapes of the diamond indenters, and whose dimensions are determined by the applied load and hardness of the substrate. IndL makes it possible to indent hard materials, to produce patterns with multiple levels of relief by changing the loading force, and to control the profiles of the indentations by using indenters with different shapes. This paper also demonstrates the transfer of indented patterns to elastomeric PDMS stamps for soft lithography, and to thin films of evaporated gold or silver. Stripping an evaporated film from an indented template produces patterns of gold or silver pyramids, whose tips concentrate electric fields. Patterns produced by IndL can thus be used as substrates for surface-enhanced Raman scattering (SERS) and for other plasmonic applications.

Detailed studies on fiber optic pressure and temperature sensors for oil down-hole applications are described in this paper. The sensor head is an interferometric based fiber optic senor in which the air-gap will change with the pressure or temperature. For high-speed applications, a novel self-calibrating interferometric/intensity-based (SCAB) scheme, which realizes compensations for both the light source drift and the fiber loss variation, was used to demodulate the pressure (or temperature) signals. An improved white light system was developed for sensor fabrication. This system is also used as the signal demodulation system providing very high resolution. Experiment results show that the SCIIB system achieves 0.1% accuracy with a 0-8000psi working range for the pressure sensor and a 0-600degreesC working range for the temperature sensor. The resolution of the white light system is about +/-0.5 nm with adynamic range up to 10 micrometers. The long-term testing results in the oil site are also presented in this paper.

Small size fiber optic devices integrated with chemically sensitive photonic materials are emerging as a new class of high-performance optical chemical sensor that have the potential to meet many analytical challenges in future clean energy systems and environmental management. Here, we report the integration of a proton conducting perovskite oxide thin film with a long-period fiber grating (LPFG) device for high-temperature in situ measurement of bulk hydrogen in fossil- and biomass-derived syngas. The perovskite-type Sr(Ce(0.8)Zr(0.1))Y(0.1)O(2.95) (SCZY) nanocrystalline thin film is coated on the 125 microm diameter LPFG by a facile polymeric precursor route. This fiber optic sensor (FOS) operates by monitoring the LPFG resonant wavelength (lambda(R)), which is a function of the refractive index of the perovskite oxide overcoat. At high temperature, the types and population of the ionic and electronic defects in the SCZY structure depend on the surrounding hydrogen partial pressure. Thus, varying the H(2) concentration changes the SCZY film refractive index and light absorbing characteristics that in turn shifts the lambda(R) of the LPFG. The SCZY-coated LPFG sensor has been demonstrated for bulk hydrogen measurement at 500 degrees C for its sensitivity, stability/reversibility, and H(2)-selectivity over other relevant small gases including CO, CH(4), CO(2), H(2)O, and H(2)S, etc.

200 nm diameter Au contacts were fabricated by e-beam lithography on sputtered thin film vanadium oxide grown on conducting substrates and current perpendicular to plane electron transport measurements were performed with a conducting tip atomic force microscope. Sharp jumps in electric current were observed in the I-V characteristics of the nano-VO2 junctions and were attributed to the manifestation of the metal-insulator transition. The critical field and dielectric constant were estimated from quantitative analysis of the current-voltage relationship and compared with reported values on micrometer and larger size scale devices. These results are of potential relevance to novel oxide electronics utilizing metal-insulator transitions.

A crystalline titanosilicate material, Engelhard titanosilicate-4 (ETS-4), contains monatomic (i.e., one-atom-thick) semiconductor ⋯Ti–O–Ti–O–Ti⋯ (titania) chains in its framework, which are hypothesized to be “intrinsic” quantum wires. Monolithic ETS-4 crystals were individually embedded between gold electrodes using a photolithography based fabrication methodology, forming a device architecture in microcircuit configuration. Electrical transport measurements were performed, and current-voltage characteristics of the monatomic titania chains in ETS-4 were investigated. A non-Ohmic behavior with higher conductivities at higher bias voltages was observed.

The authors have developed a nanomanufacturing platform based on wafer-level nanoreplication with mold and nanopattern transfer by nanolithography. The nanoreplication process, which is based on imprinting a single-layer spin-coated ultraviolet (UV)-curable resist, achieved good nanopatterning fidelity and on-wafer uniformity with high throughput. Some manufacturing issues of the nanoreplication process, such as the impact of wafer and mold surface particles on nanoreplication yield, are also discussed. Nano-optic devices, such as, quarter-wave plates and polarizers, were manufactured with the nanomanufacturing platform. An average wafer-level optical performance yield of 86% was achieved. The developed technology is applied for high-throughput and low-cost manufacturing nanostructure-based optical devices and integrated optical devices.

We developed various optical devices and integrated optical devices based on innovative nano-optical structures and design. The nano-optical devices and integrated devices were fabricated through a nano-manufacturing platform based on wafer level nano-replication with mold and nano-pattern transfer by nano-lithography. The nano-replication process, which based on imprinting a single-layer spin-coated UV curable resist, achieved excellent nano-patterning fidelity and on-wafer uniformity with high-throughput. Excellent wafer level performance and yield were achieved. Nano-optic devices, such as, quarter wave plates and polarizers, and integrated nano-optical devices, such as monolithically integrated semi-isolators, were manufactured with the nano-manufacturing platform. The developed technology is suitable for high-throughput and low cost manufacturing needs for commercializing nano-structure based optical devices and integrated optical devices.

Commercial quality high-performance true zero-order quarter waveplates based on artificial dielectric nanostructures were made by high throughput and low cost wafer-based nanofabrication processes. Both precise phase retardation (90°±2° across a 100mm-in-diameter glass wafer) and a high transmittance (>98.8%) were achieved. The quarter waveplates with different center wavelengths, such as, 780nm and 660nm, have been fabricated for optical pick-up (CD/DVD) applications. The nanostructure based true zero-order quarter waveplates are operational at a large wavelength and temperature range under a wide incident angle. The developed high quality true zero-order quarter waveplates have the potential for many cost-sensitive optical applications. Furthermore, it opens the potential for integrated optical applications thanks to the nanofabrication processes.

We developed a new type of wire-grid polarizer, the so-called nanowire-grid polarizer, which has achieved commercial quality optical performance and reliability, The nanowire-grid polarizer has cores composed of silicon dioxide nanowalls with metal coating on one side. These cores are surrounded by multilayer thin films for antireflection. The core nanowire grid utilizes nano-sized high-aspect ratio dielectric walls as a support for forming a high aspect ratio metal nanowire grid, which significantly reduces energy loss due to metal absorption for the transmitted beam While achieving high extinction ratio for the blocked beam. For all design simulations, we utilized a rigorous coupled-wave analysis and modal method. The nanowire-grid structure was fabricated by a wafer-based nanoreplication lithography and pattern-transfer techniques, which are capable of producing a large-area high aspect ratio nanostructure with high throughput and low cost. The optical performance of the nanowire-grid polarizer was characterized thoroughly. Furthermore,. the nanowire-grid polarizer has been integrated monolithically with a Faraday magnetooptic garnet, which results in an integrated semi-isolator. Full free-space isolators based on the integrated semi-isolators have been also developed, which achieved excellent performance, good enough for commercial applications.