Nano Explorations

A student & Postdoc webinar series from MIT.nano

Nano Explorations started in 2020 as a way to keep our nano network connected during the COVID-19 pandemic. Its effective sharing of knowledge and positive community impact led to the continuation of this series into today. The talks are free and open to any interested viewers.

How to attend:
Each 45-minute seminar will consist of a 20-30 minute research talk followed by Q&A. Attendees can join and participate in the series via Zoom. Register to receive the link. All talks begin at 11AM EST unless otherwise noted.

How to present:
Are you a student or postdoc interested in presenting? Complete this webform. MIT.nano also welcomes recommendations for Nano Explorations speakers. Please contact Shereece Beckford [email] to nominate someone.

Upcoming Talks

Tuesday, May 14, 2024
Accelerated discovery with differentiable programming: From nanomaterials to chiplets design

Giuseppe Romano
Research Scientist, Institute for Soldier Nanotechnologies

Automatic Differentiation (AD) software initially developed for machine learning may benefit applications beyond neural networks. A prominent example is given by physics solvers, where language-wide differentiability enables large-scale inverse design. This talk will report on recent materials and systems optimization efforts, along with the implemented open-source software. 
Read more and register.


Past Talks

Tuesday, April 9, 2024
Superconducting nanowire electronics in magnesium diboride

Emma Batson
PhD candidate, MIT Department of Electrical Engineering & Computer Science

Emma Batson will present on research advancements in the fabrication of superconducting nanowire electronics on magnesium diboride. The introduction of uniform damage by helium ion irradiation of the films enables detection in micron-wide detectors operating at up to 20 K, setting the stage for broader adoption of this technology. SEM and STEM analysis shed light on potential mechanisms and limitations of the irradiation technique. Next steps include improving the reliability and scalability of the fabrication process through adoption of encapsulation techniques, reactive ion etching, and comparison of the performance of epitaxial versus sputtered magnesium diboride films.


Tuesday, March 5, 2024
Magnetic imaging with NV centers in diamond

Samuel Karlson, Second Lieutenant & Military Fellow
Quantum Information and Integrated Nanosystems Group, MIT Lincoln Laboratory
Graduate Student, Nuclear Science and Engineering, MIT

Nitrogen vacancy centers in diamond are a leading high-sensitivity quantum sensor for magnetic fields. Their applications range across various fields including biology, materials science, and circuit diagnostics. Our work with NV diamond ensembles demonstrates micron-scale resolution and millimeter-scale field-of-view magnetic imaging capabilities under ambient conditions.


Tuesday, February 6, 2024
Mapping three-dimensional atomic order in rare earth iron garnets

Allison Kaczmarek, PhD Candidate
Department of Materials Science & Engineering

Complex oxides offer rich magnetic and electronic behavior intimately tied to the composition and arrangement of cations within the structure. When a crystallographic site is populated by more than one type of ion, ordering of those ions can dramatically affect the material properties. Rare earth iron garnets are a class of ferrimagnetic complex oxides with extraordinary properties, making them essential materials for microwave and optical devices. Thin films of these materials exhibit a magnetic anisotropy along the growth direction which has long been believed, but not proven, to originate from the ordering of rare earth cations on dodecahedral sites.

In this presentation, Kaczmarek will discuss how researchers uncovered the three-dimensional ordering of rare earth ions in films of europium thulium iron garnet using both X-ray diffraction and atomically-resolved elemental mapping, specifically by aberration-corrected scanning transmission electron microscopy (STEM). Further, they quantified the resulting ordering-induced ‘magnetotaxial’ anisotropy as a function of Eu:Tm ratio. By solving this 50-year-old mystery, researchers have demonstrated that site ordering provides a powerful strategy to control matter on the atomic level and to augment the magnetic properties of complex oxides.


Tuesday, December 5, 2023
Engineering moiré ferromagnetism with helical trilayer graphene

Li-Qiao Xia, PhD Candidate
Department of Physics

Two-dimension van der Waals moiré materials recently emerged as highly-tunable platforms for studying various exotic electronic states. Among them, orbital magnetism and anomalous Hall effects (AHE) have been observed in several systems with broken C2z symmetry. Existing C2z-symmetry-broken moiré systems include at least one constituent layer that lacks this symmetry on its own.

This talk will introduce magic-angle helical-twisted trilayer graphene, which acts as the first example of breaking C2z symmetry locally on the moiré scale using C2z-symmetric constituent layers. The electrical transport measurements reveal correlated states and AHE with the highest reported Curie temperature among graphene-moiré systems, which shows the non-trivial band topology, and correlation-driven spontaneous time-reversal symmetry breaking. The hysteretic switching of magnetic states upon density sweeping points to first-order phase transitions across a spatial mosaic of Chern domains reflects the supermoiré-scale C2z symmetry.

This talk will look to the future of how engineering multiple moiré lattices could lead to emergent broken symmetries and flat topological bands, and stimulate the engineering of new moiré structures.


Tuesday, November 14, 2023
Radiation shielding of microelectronics via the additive manufacturing of nanocomposites

Avery Rosh, Assistant Staff
Advanced Materials and Microsystems Group
MIT Lincoln Laboratory

The miniaturization of satellite systems has compounded the need to protect microelectronic components from damaging radiation. Current approaches to mitigate this damage, such as indiscriminate mass shielding, built-in redundancies, and radiation hardened electronics, introduce high SWaP-C (Size, weight, and Power-Cost) penalties that reduce the overall performance of the satellite.

Additive manufacturing provides an appealing strategy to print radiation shielding only on susceptible components within an electronic assembly. Utilizing direct ink writing, we are able to conformally print customized nanocomposite inks at room temperatures directly and selectively onto commercial-off-the-shelf (COTS) electronics. The suite of inks uses a flexible styrene-isoprene-styrene block copolymer binder that can be filled with nanoparticles of varying atomic densities for varying radiation shielding capabilities.

Additionally, blended composites of both high and low Z fillers were created to investigate the performance in radiation attenuation depending on composition. We anticipate this low SWaP-C alternative to traditional shielding methods will enable the development of novel complex and compact satellite designs.


June 13, 2023
The critical materials revolution: Low-cost & sustainable sourcing for global electrification

Brendan Smith, MIT PhD '18
CEO, SiTration

Brendan Smith introduced the importance of critical materials to global electrification, and discuss SiTration's approach to providing a low-cost and sustainable process for extracting these materials from recycled lithium-ion batteries and waste streams in the mining sector. He also shared key learnings from SiTration's journey over the past three years since spinning out of MIT.


May 9, 2023
Laser-induced graphitization of carbonaceous precursors for electrochemical applications

Jatin Patil
PhD Candidate
Department of Materials Science and Engineering

Conductive, carbon-based membrane platforms are a promising technology for electrochemical applications such as water treatment and energy storage. However, current nanomaterial-based solutions such as carbon nanotubes often lack the performance and economic feasibility for these application requirements.

Laser-induced graphitization has been recently shown as a means to convert commercial polymers into highly-graphitic materials with a benchtop CO2 laser cutter. This talk will discuss cases in which this technique can be used for electrochemical applications to convert carbon-based feedstocks into highly-conductive membrane materials under ambient conditions, and discuss the resulting materials applications.


April 18, 2023
Additive manufacturing towards electronically-active surfaces

Mayuran Saravanapavanantham
PhD Candidate
Electrical Engineering and Computer Science

Ubiquitous and imperceptible integration of optoelectronics into the world around us would allow for novel modes of energy harvesting, communications, sensing, information display, and computing. To date, owing to the availability of foundries and scalable processing modalities, this has been achieved via fabrication of discrete elements that are then deterministically positioned throughout the world via pick-and-place assembly. Alternatively, availability of large-area, ultra-thin, and continuous elements would enable seamless integration of electronics onto surfaces around us much like a second skin.

Thin-film electronics, often fabricated with sub-micron device-functional layer thicknesses, present an avenue toward such mechanically imperceptible, large-area, and continuous integration of electronics onto any surface of choice – a paradigm that we refer to as "Active Surfaces". In this talk, Saravanapavanantham will discuss his work on developing transferable ultra-thin organic photovoltaics, decoupling their manufacturing from the final integration thereby allowing the electrification of any surface of interest. In particular, he will present on the scalable manufacturing methods to fabricate fully-printed, ultra-thin photovoltaic modules, their integration onto lightweight and high strength composite fabrics, discuss the development of equivalently ultra-thin encapsulation films, and highlight further advances necessary to translate this into a commercially viable technology.


March 7, 2023
Delocalized photonic deep learning on the Internet's edge

Alexander Sludds
PhD Candidate
Electrical Engineering & Computer Science

Advanced machine learning models are currently impossible to run on edge devices such as smart sensors and unmanned aerial vehicles owing to constraints on power, processing, and memory. Sludds will introduce an approach to machine learning inference based on delocalized analog processing across networks. In this approach, named Netcast, cloud-based “smart transceivers” stream weight data to edge devices, enabling ultraefficient photonic inference.

Sludds and his colleagues have demonstrated image recognition at ultralow optical energy of 40 attojoules per multiply (less than 1 photon per multiply) at 98.8% (93%) classification accuracy. They reproduced this performance in a Boston-area field trial over 86 kilometers of deployed optical fiber, wavelength multiplexed over 3 terahertz of optical bandwidth. Netcast allows milliwatt-class edge devices with minimal memory and processing to compute at teraFLOPS rates reserved for high-power (more than 100 watts) cloud computers.


February 14, 2023
Graphene-coated liquid metal droplet-based inertial sensor for motion monitoring and human machine interfaces

Wedyan Babatain
Postdoctoral Fellow
MIT Media Lab

Inertial sensing technologies, including accelerometers and gyroscopes, have been invaluable in numerous fields ranging from consumer electronics to healthcare and clinical practices. Inertial measurement units, specifically accelerometers, represent the most widely used microelectromechanical systems (MEMS) devices with excellent and reliable performance.

Although MEMS-based accelerometers have many attractive attributes, such as their tiny footprint, high sensitivity, high reliability, and multiple functionalities, they are limited by their complex and expensive microfabrication processes and cumbersome, fragile structures that suffer from mechanical fatigue over time. Moreover, the rigid nature of beams and spring-like structures of conventional accelerometers limit their applications for wearable devices and soft-human machine interfaces where physical compliance that is compatible with human skin is a priority.

In this talk, Wedyan will discuss the development of practical resistive and capacitive-type inertial sensors using liquid metal as a functional proof mass material. Utilizing the unique electromechanical properties of liquid metal, the novel inertial sensor design confines a graphene-coated liquid metal droplet inside tubular and 3D architectures, enabling motion sensing in single and multiple directions. 

Combining the graphene-coated liquid metal droplet with printed sensing elements offers a robust fatigue-free alternative material for rigid, proof mass-based accelerometers. In this research, resistive and capacitive sensing mechanisms were both developed, characterized, and evaluated. Emerging rapid fabrication technologies such as direct laser writing and 3D printing were mainly adopted, offering a scalable fabrication strategy independent of advanced microfabrication facilities.

Wedyan will demonstrate the integrated sensor for real-time- monitoring of human health/ physical activity and for soft human-machine interfaces. She will discuss how the proposed inertial sensor architecture and materials offer a new paradigm for manufacturing these widely used sensors that have the potential to complement the performance of their silicon-based counterparts and extend their applications


January 10, 2023
Emergence of layered nanoscale mesh networks through bottom-up confinement self-assembly

Zehao Sun
PhD Candidate
Materials Science & Engineering

Classical block copolymer self-assembly enables access to a range of ordered nanostructure geometries—such as spheres, cylinders, gyroids, and lamellae—that are well-known and useful, but also limited. Nevertheless, there remains a large gap between the simple patterns commonly formed by block copolymers and the patterns required for many nanoscale applications. For example, single and multilayer mesh nanostructures are of particular interest in a range of technologies; their fabrication, however, has been a long-standing challenge. State-of-the-art techniques usually require successive alignment of layers of self-assembled line patterns on topographically patterned substrates. Thus far, a simple, straightforward fabrication process through “bottom-up” macromolecular design rather than “top-down” pre- or post-treatments has not been demonstrated.

The challenge arises from the spontaneous nature of block copolymer self-assembly. Without constraints in any direction in space, unconfined microphase separation tends to give cubic-symmetric networks, such as the most frequently observed gyroids. In this talk, Sun will introduce a bottom-up design of triblock bottlebrush copolymers that addresses this challenge.

Two Janus domains are present in these copolymers: one perpendicular and one parallel to the polymer backbone. The former enforces a lamellar superstructure that intrinsically confines the intra-layer self-assembly of the latter, giving rise to a low-symmetry, mesh-like monoclinic (54°) M15 network substructure with excellent long-range order, as well as a tetragonal (90°) T131 mesh. 3D reconstruction from scanning transmission electron microscope tomography was used to confirm the structures that have not been reported before among soft materials. Those layered mesh networks with a sub-10 nm half-pitch can be produced in large scale on flat silicon substrates through a simple solvent annealing step, without the need for specialized substrates or low-throughput templating techniques such as electron-beam lithography.

In addition, numerical simulations show that the spatial constraints exerted on the polymer backbone drive the emergence of M15, and yield T131 in the strong segregation regime. In summary, this work demonstrates that the intrinsic molecular confinement is a viable path to bottom-up assembly of new geometrical phases of soft matter, extending the capabilities of block copolymer nanofabrication.


December 13, 2022
Van der Waals integration beyond the limits of van der Waals forces

Peter Satterthwaite
PhD Candidate
Electrical Engineering & Computer Science

Realizing the full potential of electronic devices based on two-dimensional (2D) materials requires the fabrication of pristine interfaces between 2D and bulk materials. By creating interfaces held together by the universal van der Waals force, heterostructures of diverse materials can be realized, opening new functionalities and improved performance. Though universal, the van der Waals force is weak and cannot be tuned independently of the properties of the constituent materials, meaning the direct van der Waals integration of arbitrary materials is not possible. Conventional fabrication approaches address this through transfer with polymers/solvents, and device integration through damaging post-transfer processing, elements that can lead to device performance limited by processing artifacts rather than fundamental materials properties. 

This talk presents an alternative fabrication approach that allows for direct integration of 2D materials into van der Waals devices in a pristine, dry, and scalable manner. This single-step material-to-device integration is achieved by decoupling the forces inducing the 2D material transfer from the van der Waals forces at the interface of interest. Using this adhesive matrix transfer approach, Satterthwaite will present conventionally-forbidden van der Waals integration of diverse 2D (MoS2, WSe2, GaS, and graphene) and bulk (gold, SiO2, Al2O3) materials. He will further highlight the prospects of this approach for direct 2D material integration into pristine electronic devices through an example of MoS2 transistors demonstrated on both rigid and flexible substrates. 


November 8, 2022
Develop better quantum sensors and simulators with solid state spins

Guoqing Wang
PhD Candidate
Nuclear Science and Engineering

Quantum sensors, such as spin defects in diamond, have achieved excellent performance by combining high sensitivity with spatial resolution. Unfortunately, these sensors can only detect signal fields with frequency in a few accessible ranges (a narrow window around the sensors’ resonance frequency), and extracting vectorial information usually satisfies the sensor's nanoscale spatial resolution.

In this talk, Wang will introduce recent work on sensing arbitrary-frequency vector signals by using the sensor qubit as a quantum frequency mixer. The technique leverages nonlinear effects in periodically driven (Floquet) quantum systems to achieve quantum frequency mixing of the signal and an applied bias AC field. The frequency-mixed field can be detected using well-developed sensing techniques such as Rabi and CPMG.

In addition to enhancing the sensing performance by mediating spin transitions, the synthetic Floquet energy levels can improve the capabilities of quantum simulators, which is reported in another of Wang and his colleagues' work. By implementing modulated driving and performing projective measurements (generalized Rabi oscillation), they can engineer and characterize dynamical symmetries in time domain. In summary, Wang will discuss how their contributions are paving the way for building more powerful quantum sensors and simulating more interesting phases.


October 11, 2022
Towards High-Angular-Resolution Radar Imaging at Sub-THz

Xibi Chen
PhD Candidate
Electrical Engineering & Computer Science

Ultra-sharp beam forming in high-angular-resolution imaging poses overwhelming challenges to conventional radar hardware schemes. To achieve 1-degree response in both azimuth and elevation directions, the aperture size required at 77GHz is as large as hundreds of cm². Data conversion and processing also need to apply to over 100 signal channels in commonly adopted MIMO operations. The formed angular response also often has high sidelobe floors, making the radar susceptible to false detection.

In this talk, Chen discusses a technology path utilizing sub-THz carrier frequencies. Through tiled 22nm CMOS reflectarray chips at 265GHz, 98×98 electrically-controlled antennas are densely implemented within ~5×5cm² area. Through under-antenna memory, the hardware enables 2D steering of a 1-degree-wide beam with < -30dB sidelobe floor (or < -60dB if used for both TX and RX).

A high-angular-resolution imaging demo based on the reflectarray will be shared. Chen presents challenges and solutions for the sub-THz transceiver that drives the above reflectarray, especially regarding the TX-RX antenna co-location requirement to avoid TX and RX beam misalignment. To that end, a monostatic transceiver prototype that is free of the normal 6dB directional is discussed.


September 13, 2022
A solid-state ruby magnetometer

Reginald Wilcox
PhD Candidate, Electrical Engineering & Computer Science
Research Assistant, Lincoln Laboratory

Quantum sensors offer the potential for dramatic enhancements in sensitivity, accuracy, and size compared to their classical counterparts. In particular, solid-state spin-based quantum sensors have seen rapid development in recent years, with applications ranging from bio-medical imaging to magnetic mapping and navigation. Traditionally, these sensors have used optical methods to prepare and read out quantum states, which poses complications for reducing device size, power, and complexity, and limits sensing species to optically-polarizable defects.

In this talk, Wilcox demonstrates a fully non-optical solid-state quantum sensor architecture using chromium defects in sapphire. The novel state preparation technique harnesses thermal population imbalances induced by the defect's zero-field splitting. Readout is performed by extending the cavity-enhanced microwave technique recently demonstrated in NV diamond. The resulting magnetometer is broadband with a minimum sensitivity of 9.7 pT/sqrt(Hz) near 5 kHz and a compact sensing head. Future improvements could include enhanced sensitivity from cavity frequency-locking and expansion to full vector magnetometry.


Tuesday, April 19, 2022
Germanium-on-Silicon integrated photonics for the mid-wave infrared wavelength range

Rachel Morgan, PhD candidate
Aeronautics & Astronautics
MIT Lincoln Laboratory

Mid-wave infrared (MWIR, 2-5 um) integrated photonics is an active area of research with the potential to miniaturize optical devices for many applications such as environmental monitoring, chemical sensing, and astronomical observations. However, the traditional Silicon-on-Insulator (SOI) material platform becomes absorbent above 3.5 um, so alternate materials and fabrication approaches are needed to enable photonic integrated circuits at longer wavelengths. This talk will summarize the development of an integrated photonic Germanium-on-Silicon platform for the 2-5 um wavelength range including demonstrations of waveguides and ring resonators, and designs for active device integration.


Tuesday, March 8, 2022
Implantable soft robotic platform for enhanced drug delivery

Debkalpa Goswami, Postdoctoral Associate
Institute for Medical Engineering & Science (IMES)

Fibrous capsule formation, and its effect on molecular transport, can be detrimental to the long-term efficacy of implantable drug delivery devices, especially when precise spatial and temporal control is necessary for safe and effective therapy delivery. In this talk, Dr. Goswami describes an implantable platform that can overcome the diffusional barrier of the fibrous capsule to achieve enhanced transport of small and macromolecular therapy using multiple synergistic soft robotic strategies.

Using this platform, small amplitude dynamic actuation (preconditioning) applied to subcutaneous tissue in mice leads to a downstream functional effect: enhanced passive transport of insulin (a model macromolecule) and glycemic control. Furthermore, rapid actuation of the platform at the time of drug delivery can accelerate transport via convective fluid flow and overcome diffusional limitations caused by the fibrous capsule.

This soft actuatable platform has potential clinical utility for mediating and overcoming the host fibrotic response, leading to enhanced delivery of drug therapy for a variety of indications, such as diabetes.


Tuesday, February 8, 2022
3D printing glass with metastable silicates

Devon Beck, Assistant Staff
Advanced Materials and Microsystems Group
MIT Lincoln Laboratory

Additive manufacturing of glass allows the fabrication of complex structures and geometries that traditional approaches cannot achieve. However, current strategies for 3D printing glass require thermal processes over 1000°C to produce functional parts.

In this talk, Beck described the development of low temperature process to 3D print glass and multimaterial composite glasses based on metastable silicate chemistry. The direct-write deposition process occurs at room temperature and the curing process only requires 250°C to achieve a stable glass structure. The properties of the printed glass can further be tailored in a plug-and-play fashion by introducing functional filler materials such as conductive particles. This straightforward strategy will enable the fabrication of a wide variety of microfluidic, electronic, and radio frequency devices with higher thermal stability without the need for extensive thermal processing.


Tuesday, January 11, 2022
Peptide beacon integrated planar waveguide-sensor for low-cost, rapid and highly sensitive detection of COVID19

Soumya Pratap Tripathy, PhD student
MIT Media Lab

The novel coronavirus SARS-CoV-2 continues to pose a significant global health threat. Along with vaccines and targeted therapeutics, there is a critical need for rapid diagnostic solutions. In this work, we employ a deep learning-based protein design to engineer molecular beacons that function as conformational switches for high sensitivity detection of the SARS-CoV-2 spike protein receptor-binding domain (S-RBD). The beacons contain two peptides, together forming a heterodimer, and a binding ligand between them to detect the presence of S-RBD.

In the absence of S-RBD (OFF), the peptide beacons adopt a closed conformation that opens when bound to the S-RBD and produces a fluorescence signal (ON), utilizing a fluorophore-quencher pair at the two ends of the heterodimer stems. We integrated these beacons on a planar waveguide-based fluorescence sensor to construct a point-of-care diagnostic platform for SARS-CoV-2. The device can detect the S-RBD with limits of detection (LoD) in the sub-femtomolar range. We envision that the platform will be a rapid at-home diagnostic device in the future. ​


Tuesday, June 22, 2021
Tuning nanoscale phase transitions to expand transformation-induced plasticity

Shaolou Wei, PhD Candidate
Materials Science & Engineering

Metals and alloys have been mankind’s most essential structural materials since the Bronze Age. To seek optimal strength-ductility balance in metallic alloys, athermic phase transformations during plastic deformation are regarded as one of the most effective approaches to promote strength while impeding plastic instability incipience. Decades of efforts in ferrous alloy design have documented the significant role of strain-induced martensitic transformation in mechanical performance improvement (namely, the transformation-induced plasticity effect, TRIP).

Although it has a mechanical benefit, the resulting transformation product of the TRIP-effect, martensite, can be detrimental. The extensive defect density within the martensitic phase and the hardenability discrepancy with its adjacency can lead to local embrittlement and eventual fracture. Wei’s talk reveals two potential solutions: a sequential martensitic transformation mechanism and a mechanical faulting response. Further insights into mechanistically-guided alloy design is also discussed.


Tuesday, June 8, 2021
Nanofabrication of diffractive optics for X-ray wavefront shaping and imaging

Kahraman Keskinbora, Research Scientist
Department of Physics

The use of coherent X-rays for materials characterization has a vast range of applications, from developing more efficient energy storage materials to imaging spin waves in modern magnetic materials. Diffractive optics are one of the best options to successfully focus and shape X-ray wavefronts to carry out a specific task, especially in the soft X-ray regime. Whether it is an imaging application or a more complex task, efficient shaping of X-rays requires a diffractive optic to have high aspect ratios and complex geometries. Owing to the specifics of X-ray matter interactions, the fabrication of diffractive optics for this energy range is still a serious nanofabrication challenge.

Keskinbora gave an overview of various ways to overcome this challenge. More specifically, this talk focused on the advantages of using ion beam lithography (IBL) to fabricate incredibly intricate diffractive optic patterns in a single fabrication step. Keskinbora talked about the benefits of the dedicated IBL instrument with a multi-species ion beam source that is part of the toolset at MIT.nano, and its applications to diffractive X-ray optics fabrication. Finally, Keskinbora briefly touched upon the soft X-ray beam-shaping applications of these fascinating X-ray optic devices.


Tuesday, May 25, 2021
Low-dimensional perovskites for light-emitting applications: What do we need and how to make it?

Jawaher Almutlaq, Postdoctoral Fellow
Research Laboratory of Electronics

To break free of the limitations imposed by three-dimensional (3D) perovskites, such as their lackluster stability, researchers have opened new frontiers into lower-dimensional perovskite derivatives. Thanks to advances in solvent-based synthesis methods, zero-dimensional (0D) inorganic perovskites, mainly Cs4PbBr6, have recently reemerged in various forms (from single crystals to nanocrystals) as materials with properties that bridge organic molecules and inorganic semiconductors.

The first part of this talk covered the controversy regarding the origin of emission in zero-dimensional perovskites (0D), Cs4PbBr6 and Cs4PbI6, through a comparative analysis between 0D and three-dimensional (3D) perovskites.

Then, Almutlaq addressed the shortcoming of lead-based perovskites in terms of toxicity and stability, motivated by the high demand for sustainable materials with analogous electrical and structural properties. Finally, Almutlaq shared the recent work on CsMnBr3 NCs, which reveals an intense red PL peak, a high PLQY with a remarkable excitation spectrum and surprisingly short lifetime. This work paves the way for finding sustainable materials for the next generation of light-emitting applications.


Tuesday, May 11, 2021
Waveguide quantum electrodynamics with artificial superconducting giant atoms

Bharath Kannan, PhD Candidate
Electrical Engineering & Computer Science
MIT Lincoln Laboratory

Models of light-matter interactions typically invoke the dipole approximation, within which atoms are treated as point-like objects when compared to the wavelength of the electromagnetic modes with which they interact. However, when the ratio between the size of the atom and the mode wavelength is increased, the dipole approximation no longer holds and the atom is referred to as a "giant atom."

Thus far, experimental studies with solid-state devices in the giant-atom regime have been limited to superconducting qubits that couple to short-wavelength surface acoustic waves, only probing the properties of the atom at a single frequency. Here, Kannan and others employ an alternative architecture that realizes a giant atom by coupling small atoms to a waveguide at multiple, but well separated, discrete locations.

Their realization of giant atoms enables tunable atom-waveguide couplings with large on-off ratios and a coupling spectrum that can be engineered by device design. They also demonstrate decoherence-free interactions between multiple giant atoms that are mediated by the quasi-continuous spectrum of modes in the waveguide—an effect that is not possible to achieve with small atoms. These features allow qubits in this architecture to switch between protected and emissive configurations in situ while retaining qubit-qubit interactions, opening new possibilities for high-fidelity quantum simulations and non-classical itinerant photon generation.


Tuesday, April 27, 2021
Cavity–enhanced microwave readout of a diamond sensor

Erik Eisenach, PhD Candidate
Electrical Engineering & Computer Science
MIT Lincoln Laboratory

Overcoming poor readout is an increasingly urgent challenge for devices based on solid-state spin defects, particularly given their rapid adoption in quantum sensing, quantum information, and tests of fundamental physics. In spite of experimental progress in very specific systems, solid-state spin sensors lack a universal, high-fidelity readout technique.

In this talk, Eisenach discusses how he and fellow researchers leverage strong coupling between an ensemble of solid-state spins and a dielectric microwave cavity for high-fidelity, room-temperature readout of nitrogen-vacancy centers. Using this strong collective interaction, they probe the spin ensemble’s microwave transition directly, overcoming the optical photon shot noise limitations of conventional fluorescence readout. Furthermore, they apply this technique to magnetometry, and show magnetic sensitivity approaching the Johnson–Nyquist noise limit of the system.


Tuesday, April 13, 2021
Small molecule assemblies with a bulletproof design: The aramid amphiphile

Ty Christoff-Tempesta, PhD Candidate
Materials Science & Engineering

Small molecule self-assembly offers a powerful bottom-up approach to producing nanostructures with high surface areas, tunable surfaces, and defined internal order. Historically, the dynamic nature of these systems has limited their use to specific cases, especially biomedical applications, in solvated environments.

In the talk, Christoff-Tempesta presents a self-assembling small molecule platform, the aramid amphiphile (AA), that overcomes these dynamic limitations. AAs incorporate a Kevlar-inspired domain within each molecule to produce strong interactions between molecules. Christoff-Tempesta and fellow researchers have observed AAs spontaneously form nanoribbons when added to water with aspect ratios exceeding 4000:1. Robust internal interactions suppress the ability of AAs to move between assemblies and result in nanoribbons with mechanical properties rivaling silk. 

The team harnesses this stability to – for the first time – extend small molecule assemblies to the solid-state, forming macroscopic threads that are easily handled and support 200 times their weight when dried. The AA platform offers a novel route to extend small molecule self-assembly to aligned macroscopic materials and beyond solvated environments.


Tuesday, March 30, 2021
Practical fiber batteries for wearables based on thermally drawn Zn-MnO2

Maximilian Ulbert
Ensign, U.S. Navy
Research Fellow, MIT Lincoln Laboratory

The concept of the Internet-of-Things has inspired growth in the field of wearable technology, from aesthetically pleasing color-changing fabrics to practical heart rate monitors, all interwoven into any variety of clothes (i.e.: shirts, pants, hats, blankets, bags, etc.). For a continuously operating wearable system, an energy storage vessel is needed: a battery.

Specifically, interwoven or fabric-based systems demand that the battery be integrated in the fabric or fibers themselves. The primary challenge for such an integrated battery is rendering the active components of a battery (cathode, anode, and electrolyte) into a fiber. Existing challenges for fiber batteries include high materials costs, low power output, and complicated assembly approaches. Further, for the practical implementation of a fiber battery into wearable systems that make direct skin contact and are exposed to the ambient environment, battery safety is of key importance.

This work seeks to address both assembly and safety issues by developing an easily manufacturable fiber battery by means of a thermal draw tower using a safer Zn-ion chemistry (Zn/MnO2) with a gel polymer electrolyte (GPE). The GPE offers a high ionic conductivity, mechanical properties compatible with thermal draw towers, and provides a physical separator between cathode and anode. The performance of lab scale prototypes and a drawn-fiber prototype is discussed.


Tuesday, March 16, 2021
Integrated photonics and electronics for chip-scale quantum control of trapped ions

Jules Stuart, Graduate Student
Quantum Information and Integrated Nanosystems, MIT Lincoln Laboratory
Physics PhD candidate, 2021

Trapped atomic ions are promising candidates for quantum information processing and quantum sensing. Current state-of-the-art trapped-ion systems require many lasers and electronics to achieve precise timing and control over quantum states.  Usually, electronic signals are sent into vacuum chambers via wire feedthroughs, and laser light is focused down to a trapped ion’s location with external lenses mounted outside of viewports on the chamber. These requirements lead to dense and complex setups that may be prone to drift and limit the amount of control that can be achieved.

In this presentation, Stuart reported on recent progress toward integrating control technology into the substrate of the ion trap itself. By using a planar trap design, which is compatible with lithographic fabrication, other well-developed processes may be implemented in order to enhance the function of the ion trap. In one experiment, researchers demonstrate an ion trap with integrated, CMOS-based high-voltage sources, which can be used to control the motional frequency and position of a trapped ion. In another demonstration, they use photonic waveguides and diffractive grating couplers to route light around a chip and focus it onto ions trapped above the surface.

Integrating controls into ion traps has the potential to increase the density of independently controllable ions on a chip in next-generation systems, but there are also many immediate practical benefits. Reducing the number of required feedthroughs allows chambers to be made more compact, which may be useful for ion-based clocks or sensors. The researchers also show that integrated-photonic platforms help to reduce vibration-induced noise seen when using external optics, which may enable portable systems based on trapped-ion quantum information processing.


Tuesday, March 2, 2021
Challenges and opportunities for the next generation of power electronic devices

Ahmad Zubair, Postdoctoral Associate
Microsystems Technology Laboratories (MTL)

By 2030, about 80% of all United States electricity is expected to flow through power electronics and the market size is expected to exceed 1000 TW-unit per year from the current market size of 2 TW unit. This exponential growth will require power electronics devices and circuits with much higher efficiency and smaller form-factor than today’s silicon-based systems. III-Nitride semiconductors and other ultra-wide bandgap materials are ideal material systems for energy-efficient new generation of power electronics, thanks to the combination of excellent transport properties and the high critical electric field enabled by their wide bandgap.

Vertical FinFETs are promising high voltage switches for the next generation of high-frequency power electronics applications. Thanks to a nanostructured vertical fin channel, the device offers excellent electrostatic control, eliminating the need for epitaxial regrowth or p-type doping unlike other vertical power transistors. Vertical GaN FinFETs with 1200 V breakdown voltage (BV) and 5A current rating have been demonstrated recently on free-standing GaN substrate. The high current density of these devices, in combination with minimum parasitics, allow these devices to achieve beyond-state-of-the-art switching performance.

This talk discusses the recent progress of GaN vertical power FinFETs on native GaN substrate highlighting the device and materials level opportunities as well as challenges to push performance limits of these devices.  Despite this promising performance, the commercialization of these devices has been limited by the high cost ($50-$100/cm2) and small diameter (2-4 inch) of free-standing GaN substrates. The use of Si could potentially reduce the substrate cost by 1000x and enable heterogeneous integration. This talk also discusses the recent efforts on the heterogeneous integration of GaN vertical power FinFETs on Si platform.


Tuesday, February 16, 2021
Silicate-based composite as heterogeneous integration packaging material for extreme environments

James McRae, Graduate Student
Mechanical Engineering (MechE)
MIT Lincoln Laboratory, Advanced Materials & Microsystems

Electronic microsystems are foundational to today’s computational, sensing, communication, and information processing capabilities, therefore impacting industries such as microelectronics, aerospace, healthcare, and many more. Cell phones are an example of what is possible when a variety of systems can be tightly integrated into a highly portable and capable system. However, as we aim to improve our ability to interact and operate (e.g., sense, communicate, record, compute, move, etc.) in extreme environments (such as outer space or the human body), new methods and materials must be developed to manufacture such integrated systems that will endure post-processing, environmental, and operational challenges.

Typical organic-based packaging materials (e.g., polymer adhesives, coatings, and molding materials) often suffer from outgassing and leaching that can lead to system contamination, as well as coefficient of thermal expansion (CTE) mismatches that can lead to warpage and breakage with fluctuations in system temperature during operation. This work demonstrates an alternative, by using a silicate-based inorganic glass composite as an electronics packaging material for stability in extreme environments. Combining liquid alkali sodium silicate (water glass) and nanoparticle fillers, composites can be synthesized and cured at low temperatures into chemically, mechanically, and thermally (up to 400 oC) stable structures using high throughput processing methods such as spin and spray coating. Further, this material can be processed into thick layers (10s to 100s of microns), fill high aspect ratio gaps (13:1), withstand common microfabrication processes, and have its CTE tailored to match various substrates.


Tuesday, February 2, 2021
Large-scale integration of artificial atoms with photonic circuits

Noel Wan, PhD candidate
Electrical Engineering & Computer Science (EECS)

The construction of large, controllable quantum systems is a formidable task in quantum science and technology. In the context of quantum networks, single emitters in diamond have emerged as leading quantum bits that combine long coherence times with efficient optical interfaces. Despite their potential manufacturability, such solid-state qubits have been limited to small-scale quantum network demonstrations due to their low system efficiencies, deteriorated properties in devices, and low yields.

To address these challenges, Wan and fellow researchers report the development of a nanophotonic platform in diamond for the efficient control and routing of photons. In particular, Wan described the fabrication and coupling of qubits to single-mode waveguides and photonic crystal resonators. He then demonstrated the large-scale heterogeneous integration of diamond waveguide-coupled qubits with photonic circuits in another material system.

This hybrid quantum chip architecture enables the combination of coherent qubits in diamond with low-loss active photonics in aluminum nitride or silicon nitride. This modularity also circumvents the low device yields associated with monolithic chips, enabling here a 128-channel, qubit-integrated photonic chip with frequency tunability and high optical coherence. As an outlook, Wan discussed ongoing efforts that combine the advances towards the construction of a quantum repeater microchip.


Tuesday, December 22, 2020
Decoding complexities in relaxor ferroelectrics using electron microscopy

Abinash Kumar, PhD candidate
Materials Science & Engineering (DMSE)

Relaxor ferroelectrics show slim hysteresis loops, low remanent polarization, high saturation polarization, and exceptional electromechanical coupling, finding applications in ultrasound imaging and energy storage devices. Developing a structure-property relationship in relaxors has been a seemingly intractable problem due to the presence of nanoscale chemical and structural heterogeneities.

In this presentation, Kumar discusses how researchers employed aberration-corrected scanning transmission electron microscopy (STEM) to quantify the various contributions of nanoscale heterogeneity to relaxor ferroelectric properties in PMN-PT system. Specifically, they found three main contributions—chemical ordering, oxygen octahedral tilting, and oxygen octahedral distortion—that are difficult to otherwise differentiate. Through STEM, the elusive connection between chemical and structural heterogeneity and local polarization variation is revealed. Further, the effects of strain and thickness on PMN-PT thin films are discussed. Through these measurements, design principles for next generation relaxor material are elucidated.


Tuesday, December 8, 2020
Fluorescent Janus droplet and its application in biosensing of Listeria Monocytogenes

Jie Li, Postdoctoral associate

Dynamic complex droplets afford versatile platforms for biosensing. The biosensing methods based on droplets enable a combination of advantages including speed, cost-effectiveness, and portability. In this talk, Li discusses a sensing method based on the agglutination of Janus emulsions for Listeria Monocytogenes, a gram-positive bacterium responsible for a potentially lethal foodborne bacterial illness.

The bio-recognition interface created between the Janus emulsions comprises an equal volume of hydrocarbon and fluorocarbon oils in Janus morphology. This is done by attaching antibodies to a functional surfactant polymer with a tetrazine/trans-cyclooctene (TCO) click reaction. The Listeria antibodies will be on the surface of the hydrocarbon hemisphere, since the surfactant will stay at the interface of hydrocarbon and water phase. Agglutinations of Janus droplets are formed when Listeria is added because of the strong binding between Listeria and the Listeria antibody located at the hydrocarbon surface of the emulsions.

By incorporating one emissive dye in the fluorocarbon phase and a blocking dye in the hydrocarbon phase of Janus droplets, Li can conduct a two-dye assay, which enables the rapid detection of trace Listeria in less than two hours via an emissive signal produced in response to Listeria binding. Specifically, the Janus structure is tilted from its equilibrium position as a result of the formation of agglutinations, and produces emission that would ordinarily be obscured by a blocking dye. Overall, this method not only provides rapid and inexpensive Listeria detection with high sensitivity, but also can be paired with antibodies or related recognition elements to create a new class of biosensors.


Tuesday, November 24, 2020
Highly tunable junctions in magic angle twisted bilayer graphene tunneling devices

Daniel Rodan-Legrain, PhD candidate

The recent observation of superconductivity and correlated insulating states in ‘magic-angle’ twisted bilayer graphene (MATBG) featuring nearly-flat bands at twist angles close to 1.1 degrees presents a highly tunable two-dimensional material platform capable of behaving as a metal, an insulator, or a superconductor. Local electrostatic control over these phases may enable the creation of versatile quantum devices that were previously not achievable in other single material platforms.

In this talk, Rodan-Legrain will introduce MATBG as a new arena to investigate strongly correlated physics. He will then show how they can exploit the electrical tunability of MATBG to engineer Josephson junctions and tunneling transistors all within one material, defined solely by electrostatic gates. The research group's multi-gated device geometry offers complete control over the Josephson junction, with the ability to independently tune the weak link, barriers, and tunneling electrodes. Utilizing the intrinsic bandgaps of MATBG, they also demonstrate monolithic edge tunneling spectroscopy within the same MATBG devices and measure the energy spectrum of MATBG in the superconducting phase.

Furthermore, by inducing a double barrier geometry, the devices can be operated as a single-electron transistor, exhibiting Coulomb blockade. These MATBG tunneling devices, with versatile functionality encompassed within a single material, may find applications in graphene-based tunable superconducting qubits, on-chip superconducting circuits, and electromagnetic sensing in next-generation quantum nanoelectronics.


Tuesday, November 10, 2020
Nanoscale mechanical switches with squeezable molecular springs—Squitches

Jinchi Han, PhD candidate
Electrical Engineering & Computer Science (EECS)

Nanoelectromechanical (NEM) switches are a candidate technology for beyond-CMOS energy-efficient computing. They can exhibit near-zero static leakage, large on-off current ratio, steep subthreshold slope, and high robustness in harsh environments. NEMs are, however, challenged by significant van der Waals interaction at the nanoscale between their contacting electrodes, which can result in compromised performance in terms of turn-on voltage and switching speed, critical characteristics for good device reliability.

A way to address the NEM electrode stiction challenge will be presented in this talk, which will explore an approach of fabricating an electrostatically-controlled nanogap using self-assembled molecular spacer layer sandwiched between atomically-smooth conductive nanostructures. The molecular layer acts like a spring between the two sandwiching electrodes, compressing as needed under the electrostatically-applied “squeeze” to modify the tunneling current. Hence, we referred to this NEM structure as the squeezable-switch or the “squitch”. The operating squitch structures show a sharp electrical switching behavior with several-orders-of-magnitude on-off current ratio, as the tunneling gap is modified by only ~1 nm in distance. This unique working principle allows squitches to simultaneously achieve low turn-on voltages and low time delays, while surmounting the challenge of NEM device electrode stiction.


Tuesday, October 27, 2020
Strategies for high-performance solid-state photon upconversion based on triplet exciton annihilation

Ting-An Lin, PhD candidate
Electrical Engineering & Computer Science (EECS)

Photon upconversion, a non-linear optical process to convert low-energy photons into higher energies, has various applications such as photovoltaics, infrared sensing, and bio-imaging. Particularly, upconversion based on triplet exciton annihilation is one of the most promising approaches to achieve high efficiency at low excitation intensity for practical applications. However, the reported performance in solid-state is limited due to energy back transfer, material aggregation, and weak optical absorption, which complicates the integration with solid-state applications.

In this talk, Lin discussed the research group's proposed strategies to improve the performance in solid-state. In a green-to-blue upconverter consisting of a bilayer of an absorbing and an upconverting material, they reduced energy back transfer by inserting a blocking layer in between and mitigate aggregation by doping the absorber into a host material. The upconversion efficiency had a 7-fold enhancement with the excitation intensity reduced by 9 times. To improve optical absorption, they investigated an infrared-to-visible upconverter and integrate the up-converting layers into a Fabry-Pérot microcavity. At the resonant wavelength, absorption increases 74-fold and the threshold excitation intensity is reduced by two orders of magnitude to a sub-solar flux. Their work demonstrates the importance of device structure engineering to improve the performance of solid-state photon upconversion, and offers a path toward practical applications.


Thursday, July 30, 2020
Integrating object form and electronic function in rapid prototyping and personal fabrication

Junyi Zhu, PhD candidate
Electrical Engineering & Computer Science (EECS)

Rapid prototyping is a key technique that enables users to quickly realize their digital designs, therefore it has been widely used in early-stage prototyping and small-scale customized fabrication. A long-term vision in Human-Computer Interaction is to create interactive objects for which all functions are directly integrated with the form and fabricated in one-go. So far, rapid prototyping has mainly focused on fabricating passive objects for which the form of an object can be freely designed, but recently we have also moved towards digital specification and fabrication of object functions for interactive design. These advances offer the promise that eventually in rapid function prototyping, the interactive object form and function would be under the same design consideration, therefore the object form could follow its designated function, and function adapt upon its physical form, and vice versa.

In this talk, Zhu presents two projects in this domain: MorphSensor and CurveBoards. MorphSensor is a 3D electronics design tool for designing electronic function in the context of a prototype’s three-dimensional shape. MorphSensor unifies electronic and physical object design in one 3D workspace as one complete workflow, which leads to better form and function integration. CurveBoards are 3D breadboards directly integrated into the surface of physical prototypes. CurveBoards better preserve the object’s look and feel while maintaining high circuit fluidity, which enables designers to prototype and iterate function in the context of form.


Tuesday, July 28, 2020
Solid-state platform for Boston quantum network

Michael Walsh, PhD
Electrical Engineering & Computer Science (EECS)

Quantum emitters, such as color centers (e.g., nitrogen-vacancy color centers in diamond), have a wide range of applications in quantum information processing, bio-imaging, and quantum-sensing. Such quantum emitters are typically addressed optically and store their quantum state as an electron spin that can subsequently be read out optically. For this process to work effectively, an efficient light-matter interaction must be achieved, which is difficult given the small interaction cross-section of an atomic memory with the optical field.

In this talk, Walsh addresses two problems that relate to the engineering of a device that demonstrates a quantum advantage. The first problem centers on the fact that most quantum emitters are randomly positioned throughout their host lattice making it difficult to lithographically pattern structures intended to increase the light-matter interaction. While there is a non-zero chance that a small number of randomly aligned structures will coincide with randomly positioned emitters, when efforts to scale such a system are made the yield drops exponentially. The second problem has to do with scaling. As systems scale up to larger sets of interacting qubits, it becomes increasingly necessary to produce quantum emitters with narrow optical transitions and long spin coherence times.


Thursday, July 23, 2020
Fast and energy-efficient monocular depth estimation on embedded systems

Diana Wofk, MEng '20
Electrical Engineering & Computer Science (EECS)

Depth sensing is a critical function for many robotic tasks such as localization, mapping and obstacle detection. There has been a significant and growing interest in performing depth estimation from monocular RGB camera images, due to the relatively low cost, size, weight and power of cameras. However, state-of-the-art depth estimation algorithms are based on fairly large deep neural networks, which have high computational complexity and energy consumption. This poses a significant challenge when performing real-time depth estimation on an embedded system, for instance, a mobile phone or a platform mounted on a Micro Aerial Vehicle (MAV).

Our work addresses this problem of fast and energy-efficient depth estimation on embedded platforms. Our proposed network, FastDepth, runs at 178 fps on the Jetson TX2 embedded GPU, with active power consumption of 8.8 W. We seek to further improve energy efficiency by deploying onto a low-power embedded FPGA. Using an algorithm-hardware co-design approach, we develop a dataflow design and an accelerator architecture that minimizes off-chip memory accesses and offers dedicated support for depthwise separable convolutional layers. This talk will give an overview of our approach and the strategies we take in accelerating learning-based depth estimation on embedded systems.


Tuesday, July 21, 2020
2D-Material enabled colloidal electronics

Albert Liu, PhD candidate
Chemical Engineering

Graphene and other 2D materials possess desirable mechanical and functional properties for incorporation into or onto novel colloidal particles, potentially granting them unique electronic and optical functions. However, this application has not yet been realized because conventional top-down lithography scales poorly for the production of colloidal solutions.

Liu describes an “autoperforation” technique providing a means of spontaneous assembly for colloidal microparticles comprised of 2D molecular surfaces at scale. Such particles demonstrate remarkable chemical, mechanical and thermal stability. They can function as aerosolizable memristor arrays capable of storing digital information, as well as dispersible and recoverable probes for large-scale collection of chemical information in water and soil.


Thursday, July 16, 2020
Building neuromorphic computing units with battery materials

Juan Carlos Gonzalez Rosillo, Postdoctoral Associate
Materials Science and Engineering (DMSE)

Specialized hardware for neural networks requires materials with tunable symmetry, retention and speed at low power consumption. Advances over the last years on understanding and implementing memristor technology had positioned them as a major candidate to overcome bottlenecks in current electronic-based transistors in terms of downscaling capabilities and energy consumption. The vast majority of memristive devices are based on two types of ions: either oxygen vacancy migration, in the so-called Valence Change Memories (VCM), or a metal cation, usually Ag+ and Cu2+, in the so-called Electrochemical Metallization Cells (ECM). Despite their excellent performance, their widespread implementation in today’s integrated circuits is delayed due to the need to address cycle-to-cycle and device-to-device variabilities while circumventing electroforming and asymmetry, which are inherent issues associated to the filamentary nature of the switching mechanism.

Recently, Li-ion is emerging as an alternative, given the higher diffusivity of Li+ when compared to oxygen, and the ability of Li-oxides solid state conductors to accumulate and deplete lithium at the interfaces and bulk. We have proposed lithium titanates, originally developed as Li-ion battery anode materials, as promising candidates for memristive-based neuromorphic computing hardware.

In this seminar, Gonzalez Rosillo discusses the non-volatile, non-filamentary bipolar resistive switching characteristics of lithium titanates compounds, Li4+3xTi5O12, as a function of the lithiation degree. We have employed a recently proposed strategy to overcome lithium loss during thin film deposition and finely control the final lithiation degree of the films to create stoichiometrically lithiated Li4Ti5O12 spinel phase and a highly lithiated Li7Ti5O12 rock- salt phase memristive devices. By using ex- and in-operando spectroscopy to monitor the Lithium filling and emptying of structural positions during electrochemical measurements, we investigate the controlled formation of a metallic phase (Li7Ti5O12) percolating through an insulating medium (Li4Ti5O12) with no volume changes under voltage bias, thereby controlling the spatially averaged conductivity of the film device.

We present a theoretical model to explain the observed hysteretic switching behavior based on electrochemical nonequilibrium thermodynamics, in which the metal-insulator transition results from electrically driven phase separation of Li4Ti5O12 and Li7Ti5O12. Permittivity enhancement drives lithium ions to regions of high electric field intensity, which become metallic filaments above a critical applied bias, and the ions relax back to their low-conductivity initial state at lower voltages. One of the most striking outcomes is that the metal-insulator transition of llithium titanate can be uniquely modulated for neuromorphic computing purposes, such as control of the neural pulse train symmetry in conductance and the resistance on-to-off ratio, simply by adjusting the lithium stoichiometry and phase pattern of the films. We report ability of highly lithiated phase of Li7Ti5O12 for Deep Neural Network applications, given the large retentions and symmetry, and opportunity for the low lithiated phase of Li4Ti5O12 towards Spiking Neural Network applications, due to the shorter retention and large resistance changes. Our findings pave the way for lithium oxides to enable thin-film memristive devices with adjustable symmetry and retention.


Tuesday, July 14, 2020
New frontiers in THz quantum cascade lasers

Ali Khalatpour, PhD
Electrical Engineering & Computer Science

Terahertz (THz) frequencies remain among the least utilized in the electromagnetic spectrum, largely due to the lack of powerful and compact sources. The invention of THz quantum cascade lasers (QCLs) was a major breakthrough to bridge the so-called “THz gap” between semiconductor electronic and photonic sources. However, their demanding cooling requirement has confined the technology in a laboratory environment. A portable and high-power THz laser system will have a qualitative impact on applications in medical imaging, communications, quality control, security, and biochemistry.

Here, by adopting a novel design strategy to achieve a clean 3-level system, we have developed THz QCLs (at ~4 THz) with a maximum operating temperature of 250 K, far exceeding the existing records. The new record is the major breakthrough in the THz QCL field since its invention in 2001. The high operating temperature enables portable THz systems to perform real-time imaging with a room-temperature THz camera, as well as fast spectral measurements with a room-temperature detector.


Thursday, July 9, 2020
Liquid-crystal-based integrated optical phased arrays for augmented reality

Milica Notaros, PhD candidate
Electrical Engineering & Computer Science

Augmented reality (AR) head-mounted displays that project information directly in the user’s field of view have many wide-reaching applications in defense, medicine, engineering, gaming, etc. However, current commercial head-mounted displays are bulky, heavy, and indiscreet. Moreover, these current displays are not capable of producing holographic images with full depth cues; this lack of depth information results in users experiencing eyestrain and headaches that limit long-term and widespread use of these displays (an effect known as the vergence-accommodation conflict).

In this talk, recent advances in the development of Visible Integrated Photonics Enhanced Reality (VIPER), a novel integrated-photonics-based holographic display, are reviewed. The VIPER display consists of a single transparent chip with integrated liquid crystal that sits directly in front of the user’s eye and projects visible-light 3D holograms that only the user can see. It presents a highly-discreet and fully-holographic solution for the next generation of AR displays.


Tuesday, July 7, 2020
Solid-state spin-integrated circuits for quantum sensing and control

Christopher Foy, PhD
Electrical Engineering & Computer Science

Spin systems are an increasingly important quantum-sensing platform. In particular, atomic defect centers in diamond called nitrogen-vacancy (NV) centers offer impressive room temperature imaging capabilities for both magnetic fields and temperature. NV-based sensing platforms have found utility in solid-state physics, biological systems, and vector magnetometry. These applications highlight the immense promise of NV quantum sensors. Despite this promise, the use of NV centers within commercial devices remains limited to date, with many impediments to transitioning this platform from the laboratory.

This talk describes the development of solid-state spin-integrated circuits (S3IC) for quantum sensing and control with the overarching goal of creating scalable NV platforms. We present two major experiments that develop S3IC. These expand the application space of NV centers and improve device functionality. The first application was to develop an NV spin microscope capable of wide-field temperature and magnetic field imaging to elucidate functional device behavior at the microscopic scale. The second experiment was integrating the essential components of an NV spin microscope, spin control and detection, with integrated electronics. In this manner, S3IC combines the exceptional sensitivity of NV centers with the robustness and scalability of modern electronic chip-scale platforms.

This co-integration of spin systems into integrated electronics shows a potential path for migrating previous proof-of-principal sensing demonstrations into affordable packages that demonstrate both much greater system integration and custom electronic architectures. In short, this work demonstrates advances in NV-ensemble quantum sensing platforms and establishes a foundation for future integration efforts, perhaps inspiring innovations in both application space and the development of new quantum devices.


Thursday, July 2, 2020
Dynamically programmable surfaces for high-speed optical modulation

Cheng Peng, PhD
Electrical Engineering & Computer Science

Dynamically programmable surfaces for spatiotemporal control of light are crucial to many optoelectronic technologies including high-speed optical communication, display and projection, autonomous driving, optical information processing, imaging, and optical control in quantum computation. Currently available electro-optic spatial light modulators (SLMs) are often bulky, inefficient, and have limited operation speeds.

This talk describes the development of a compact, high-speed, electro-optic SLM architecture based on a two-dimensional array of tunable microcavities. Optimized microcavity designs can enable high-speed, high diffraction efficiency SLMs with standard-CMOS-compatible driving voltages. High-speed electro-optic material options are also discussed.


Tuesday, June 30, 2020
Programming a quantum computer with quantum instructions

Morten Kjaergaard, Postdoctoral Associate
Electrical Engineering & Computer Science

The use of quantum bits to construct quantum computers opens the door to dramatic computational speedups for certain problems. The maturity of modern quantum computers has moved the field from being predominantly a quantum device-focused research area to also include practical quantum-computing application focused research.

In this talk, Kjaergaard discusses a new experimental result on a foundational aspect of how to program quantum computers. A central principle of classical computer programming is the equivalence between data and instructions about what to do with that data. In quantum computers this equivalence is broken: Classical hardware is used to generate the sequence of operations to be executed on the quantum data stored in the quantum computer. Our experiment shows for the first time how the instruction-data symmetry can be restored to quantum computers. We use superconducting qubits as a platform to implement high-fidelity quantum operations enabling the so-called Density Matrix Exponentiation algorithm, to generate these quantum instructions. This algorithm provides large quantum speedups for a family of other quantum algorithms, which Kjaergaard briefly discusses.


Thursday, June 25, 2020
Miniaturizing power electronics through piezoelectric energy storage

Jessica Boles, PhD candidate
Electrical Engineering & Computer Science

Power electronics play a vital role in the technological advancement of transportation, energy systems, manufacturing, healthcare, information technology, and many other major industries. Demand for power electronics with smaller volume, lighter weight, and lower cost often motivates designs that better utilize a converter's energy storage components (ie. magnetics). However, further progress in converter miniaturization will eventually require new energy storage technologies with fundamentally higher energy density and efficiency capabilities. This prompts investigation into piezoelectric energy storage for power conversion; piezoelectrics have comparatively superior volume scaling properties. 

This talk explores the realm of practical, low-loss dc-dc converter implementations that leverage piezoelectric resonators (PRs) as their only energy storage components for high power density. We find auspicious converter implementations through (1) identifying topologies and switching sequences that best utilize the PR and (2) constraining their operation for high-efficiency behaviors. Effective use of the PR's resonant cycle enables these implementations to achieve strong experimental performance, suggesting that these PR-based converters are promising alternatives to those based on traditional energy storage. With further development, PR-based converters may pave the way for high-performance miniaturization of power electronics.


Tuesday, June 23, 2020
Bandwidth-scalable integrated-fluxgate magnetometers for contactless current sensing

Preet Garcha, PhD
Electrical Engineering & Computer Science

Contactless current sensing has many applications, including power management, motor health monitoring, and electric vehicle battery management. Prof. Lang's group recently demonstrated the use of an array of integrated fluxgate (IFG) magnetometers to replace traditional Hall sensors with field concentrators, for a low-cost, low-area, and easy-to-install current sensing solution. However, IFG sensors burn current in a feedback loop to balance out high magnetic fields in the core for linearity, making them power hungry. Moreover, previous implementations can not be duty cycled efficiently to save power, because of the inherent non-linearity of IFG and the long convergence time needed to settle to a new value. Prior works in IFG also have limited bandwidth, which is insufficient for fault detection.

In this talk, Garcha presented a bandwidth-scalable IFG magnetic-to-digital converter for energy-efficient contactless current sensing. The system uses a mixed signal front-end design to enable efficient duty cycling by waking up from the last converged point, along with employing quick convergence techniques, leading to significant reduction in power consumption at low bandwidths of 1 kHz for power monitoring. It also employs fast read-out circuits to achieve a high sampling rate and a bandwidth > 100 kHz for motor health diagnosis. The digital integrator enables > 2 mT measured range of magnetic fields, for indirect current measurement of over +/50 A at 0.5 cm distance from the wire.


Thursday, June 18, 2020
Electronic cells: Autonomous micromachines from 2D materials

Volodymyr Koman, Postdoctoral Associate
Chemical Engineering

Electronic cells are micromachines encompassing autonomous on-board functions, such as sensing, computation, communication, locomotion, and power management. Akin to their biological counterparts, electronic cells bring specialized capabilities to previously inaccessible locations. Here, we present the design and fabrication of the first in its kind electronic cell composed of the nanoelectronic circuit on top of a SU-8 particle. Powered by a 2D material-based photodiode, the on-board circuit connects a chemiresistor element and a memristor element, enabling on-board detection and storage capabilities.

Koman demonstrates how the research group's cells sense and record information about the presence of ammonia and dispersed soot when aerosolized in the enclosed tubes, dispersed in a hydrodynamic flow of pipelines, or sprayed over large surfaces. Electronic cells may find widespread application as probes in confined environments, such as the human digestive tract, oil and gas conduits, chemical and biosynthetic reactors, and autonomous environmental sensors. Ref: Nature Nano 13, 819–827 (2018).


Tuesday, June 16, 2020
Low-frequency energy harvesting at the MEMS scale

Haluk Akay, PhD candidate
Mechanical Engineering

Vibrational energy harvesting devices seek to deliver useable electric power in remote or mobile applications by drawing energy from ambient sources of vibration. Due to the spectrum of such ambient vibrations occurring at a very low frequency (below 100Hz), major design challenges must be overcome when developing a piezoelectric energy harvesting device to function in these conditions, namely generating strain at the micro-scale and operating over a wide bandwidth of low input frequencies.

The culmination of three generations of this MEMS design effort by our research group is a bi-stable buckled beam energy harvester that relies on non-linear oscillations to translate input vibrations to axial strain of piezoelectric elements to produce electric energy and achieve state-of-the art energy harvesting operation among MEMS harvesters of 50% bandwidth below 70Hz at 0.5g. This talk will focus on the device’s design and fabrication, as well as characterization of dynamic performance to identify opportunities of continued device design optimization.


Thursday, June 4, 2020
Nanoscale membranes for electromechanical systems

Apoorva Murarka, Postdoctoral Associate
Electrical Engineering & Computer Science

Micro- and nano-electromechanical systems (MEMS/NEMS) are a technology field that branched out of semiconductor integrated circuit (IC) manufacturing about four decades ago, and one that forms the backbone of the Internet of Things era. However, as MEMS devices have become ubiquitous, they have also been limited by the narrow platform of IC material sets and design parameters, which significantly constrain prevalent MEMS functions and applications. In order to expand the application space of MEMS/NEMS, it is imperative that novel material platforms and manufacturing methods are considered.

This talk will explore an approach that simplifies fabrication of mechanically-active nanostructured elements over relatively large areas, and yields electromechanical systems with low operating voltages and high energy efficiency. Specifically, a suspended membrane of nanoscale thickness (or "nanomembrane") is first separately fabricated, and then additively donated via contact-transfer printing to complete a nanostructured variable-capacitance device. These purely metallic, suspended nanomembranes exhibit ideal spring-like behavior at human auditory frequencies, and the resulting variable-capacitance NEMS are utilized as electrostatic speakers. The NEMS speakers demonstrate superior acoustic performance in terms of acoustic pressure frequency response uniformity in both free-field and pressure-field radiation, below 10 Volts actuation.


Tuesday, June 2, 2020
Nanophotonic designs for wide field-of-view chip-scale LiDAR

Josuè Jacob Lopez, PhD candidate
Electrical Engineering & Computer Science

Optical beam steering has numerous applications including light detection and ranging (LiDAR) for autonomous navigation and free-space optical communication. Ideal solutions need to be low in size, weight, power consumption, and cost (SWaP-C) while maintaining long distance ranging, high resolution, and a large field-of-view (FOV). Although there has been significant progress and investment, there is still no long-term solution for long range LiDAR applications. 

Recently, the Soljačić Group has proposed a planar lens-based solution that overcomes challenges for on-chip optical beam steering. We discuss the recent developments of this approach including the second-generation Luneburg lens inspired design that leverages both nanophotonic design and wafer-scale fabrication. The nanophotonic lens has a proposed in-plane FOV of 160° with near diffraction-limited resolution and no off-axis aberrations. This approach opens a path towards chip-scale optical beam steering with low SWaP-C.


Thursday, May 28, 2020
Perovskite quantum dots as potentially scalable quantum light emitters

Hendrik Utzat, Postdoctoral Associate

Chemically prepared colloidal semiconductor quantum dots have long been proposed as scalable and color-tunable single emitters in quantum optics, but they have typically suffered from prohibitively incoherent emission. Using advanced photon-correlation spectroscopy, Utzat will demonstrate that individual colloidal lead halide perovskite quantum dots (PQDs)—unlike any other colloidal quantum dot material—display highly efficient single-photon emission with optical coherence times as long as 80 ps, an appreciable fraction of their 210ps radiative lifetimes.

These measurements suggest that PQDs should be explored as building blocks in sources of indistinguishable single photons and entangled photon pairs for optical communication applications. Utzat will demonstrate chemical tunability of the single-emitter photo-physics of PQDs as an avenue to rationally design perovskite-based quantum emitters that will benefit from the straightforward hybrid-integration with nano-photonic components that has been demonstrated for colloidal materials.


Tuesday, May 26, 2020
Engineering myelination in vitro

Daniela Espinosa-Hoyos, PhD candidate
Chemical Engineering

Oligodendrocyte progenitor cells (OPCs) are a class of multipotent cells that, when differentiated properly, engage and enclose neuronal axons with a myelin sheath. Poor remyelination, due to hindered OPC migration, axon engagement, or differentiation, is associated with poor nervous system function in diseases such as multiple sclerosis. Understanding causes and potential treatments of disorders characterized by incomplete myelin production or myelin degeneration are particularly challenging due to a lack of preclinical, in vitro tools that replicate key aspects of the OPC- and oligodendrocyte-neuron interactions, including the physical and mechanical properties of this biological niche.

Espinosa-Hoyos discusses the development hybrid polymers that can be microfabricated using light-based additive manufacturing with enhanced biocompatibility and mechanical tunability. The research group used these polymers to fabricate three-dimensional arrays of polymeric microfibers representing key geometric, mechanical, and surface chemistry components of biological axons, which enable the study of OPC engagement and subsequent myelination in vitro. Using these artificial axons, they mimicked features of demyelinating lesions and demonstrated that murine oligodendrocyte production and wrapping of myelin-like membranes depend on physical and biochemical properties of these fibers. Furthermore, they demonstrated cell-material interactions with human oligodendrocytes that can now facilitate assays for the discovery and development of new therapeutics.


Thursday, May 21, 2020
Pushing the efficiency limit of lead halide perovskite solar cells

Jason Yoo, PhD candidate

Lead halide perovskite solar cells are an emerging technology that can be solution processed to yield low-cost, light weight, and flexible photovoltaics. Much of the early work has been focused on developing device structures and processing techniques to improve light absorption and eliminate detrimental traps within the bulk of the perovskite active layer. As a result, the device efficiency of perovskite solar cells has improved from ~3% up to ~20% in less than a decade. However, the device efficiency of perovskite solar cells still needs to be improved to compete with traditional photovoltaic technologies, such as Silicon and GaAs, and to ultimately realize the theoretically determined Shockley-Queisser efficiency limit. 

In this talk, Yoo presents work on further improving the device efficiency by developing a novel interface passivation strategy called selective precursor dissolution (SPD) strategy. The post treatment of the bulk perovskite thin film with 2D perovskites via SPD strategy prevented formation of a detrimental non-perovskite phase at the interface and resulted in much improved thin film quality with reduced detrimental interface recombination. As a result, a certified power conversion efficiency of 22.6% is achieved from a quasi steady-state measurement along with an electroluminescence efficiency up to ~9%. In addition, Yoo discusses the challenges that need to be tackled in order for perovskite solar cells to become a successful photovoltaic technology at a commercial level.


Tuesday, May 19, 2020
External field effects on defects in functional oxides: Experiments and simulations

Yen-Ting Chi, PhD candidate
Materials Science & Engineering

Functional oxides have been widely used in important applications such as solid oxide fuel cells, batteries, and memristive devices. In most cases, functional oxides operate under harsh environments including high temperature, strain, or electric field. In this talk, Chi will illustrate the effect of elastic strain on electronic defect type switching, and ultra-high electric field effect assisted defect formation using SrTiO3 as perovskite model material.

Sub-nano scale defects play important roles in determining functional oxides properties. With device dimension scaling down to tens or few nano meters, high strain can be induced or applied to alter defect properties. We assessed the effects of biaxial strain on the stability of electronic defects computationally, consistent with prior experimental observations with epitaxial thin films. We also demonstrated an experimental technique capable of applying dynamic strain and measuring the transport properties of the same functional oxide thin film at any operation conditions (temperatures, oxygen partial pressure) in-situ.

Thin film devices such as memristor operate under very high electric field. We developed a computational model that accurately reflects both macroscopic and microscopic material properties under electric field simultaneously. We identified a direct relationship between point defect polarizability and lattice constant, which can be generalized to other materials with similar crystal structure. Together, this model and identification of driving factors in defect displacement under electric field contribute generalizable approaches to study and optimization of materials that exhibit memristive switching.


Thursday, May 14, 2020
Nanoscale phenomena during evaporation of saline drops: Salt patterns & crystal ejection 

Samantha McBride, MechE PhD '19
Lecturer, Materials Science & Engineering

Evaporation of a single drop on a surface is a surprisingly complex phenomena with applications ranging across fields of self-assembly and nanotechnology. Particles or solutes within an evaporating drop will arrange into different patterns due to competing processes of evaporative flow, recirculation, and microscale energetic interactions.

In this talk, McBride presents on two novel phenomena that arise during evaporation of a saline drop as a result of nanoscale interactions. First, she shows how crystallizing salt from an evaporating film on a highly hydrophilic material leaves a patterned record of thin film instabilities that arise from microscopic forces. The crystallized material creates a number of extraordinarily ordered nano- and micro-structures including hexagonal lattices, lines, branches, and triangular sawtooth structures. This simple method can be used for inexpensive preparation of nano/micro-scale patterns and textures.

Next, McBride discusses a curious phenomenon in which salt globes grown from evaporating drops on heated superhydrophobic surfaces proceed to self-eject via growth of crystalline legs. The unusual ejecting effect is caused by the specific texture of the nano-structured superhydrophobic surface, which prevents crystal intrusion/spreading and confines evaporation to limited points at the surface. The striking effect could find application in fouling-resistant materials exposed to saline waters.


Tuesday, May 12, 2020
Hybridized magnons in van der Waals antiferromagnets and circuit quantum electrodynamics

Justin Tony Hou, PhD candidate
Electrical Engineering & Computer Science

Magnons are collective excitations of spin waves in magnetic materials. In hybridized magnon systems, magnons can be coherently converted to other excitations, such as photons and qubits, with potential applications to hybrid quantum systems and quantum information processing. 

In this talk, Justin Hou introduces two novel hybridized magnon systems: layered van der Waals antiferromagnets CrCl3 for strong magnon-magnon coupling, and on-chip superconducting resonator systems for scalable magnon-photon coupling. The results on CrCl3 established it as a convenient platform for studying antiferromagnetic dynamics in GHz and demonstrated magnon-magnon coupling within a single material. The results on superconducting resonator systems demonstrated a circuit quantum electrodynamics architecture for magnon-photon coupling, which opens up opportunities to study spintronic effects in quantum limit and applications of spintronic effects to quantum information processing.


Thursday, May 7, 2020
2D-material-enabled multifunctional mid-IR optoelectronics

Skylar Deckoff-Jones, PhD candidate
Materials Science & Engineering

Layered van der Waals (2D) materials have demonstrated huge potential for photonic devices with their varied and tunable optical properties. They can be easily integrated into planar photonic structures on virtually any substrate due to their van der Waals bonding, thereby enhancing light matter interaction. Recently, our group has developed the integration of 2D materials with chalcogenide glasses to realize high performance photonic devices with unique architectures. This platform offers a versatile method to prototype devices that can fully utilize the properties of 2D materials. In this presentation, Deckoff-Jones shows how 2D materials such as graphene, black phosphorus, and tellurene can be employed to realize high performance optoelectronics devices in the mid-infrared.


Tuesday, May 5, 2020
Development of an artificial spiking neuron using superconducting nanowires

Emily Toomey, PhD '20
Electrical Engineering & Computer Science

In light of the growing need for faster, more energy-efficient computation, researchers are rapidly developing architectures inspired by the parallelism and performance of the human brain. Spiking neural networks are perhaps the most bio-realistic approach, mimicking the unique spiking dynamics of neurons to attain superior energy efficiency with the additional benefit of temporal information.

In this talk, Toomey presents a power-efficient artificial neuron made from superconducting nanowires, which naturally generates spiking based on the nonlinear transition between the superconducting and resistive states. Simulations are used to evaluate designs of different neuron components, including a synapse that uses nanowires as a tunable inductor to allow for fan-out with adjustable connectivity. Experimental results of a soma fabricated in 25-nm-thick niobium nitride will also be presented.


Tuesday, April 28, 2020
Commercializing a new nanofiltration technology: Pressure, concentration, and rejection

Brendan Smith, Postdoctoral Associate
Materials Science & Engineering

Approximately 10% of total global energy consumption is spent on industrial separations, processes which trade energy for entropy to transform complex mixtures into their individual components. Despite filling an essential and often central role across today’s mega-industries, the majority of separations are still carried out via antiquated and inefficient methods such as thermal distillation. Membrane filtration is an attractive alternative with the potential to achieve identical outcomes while using as little as one-tenth of the energy and reducing capital and operational costs; however, its implementation has been limited by the lack of ultra-durable and sufficiently selective membrane technologies.

This talk explores the development of a new type of silicon-based filtration membrane that aims to fill this void, and shares experiences from the parallel market research journey, which has inspired the inventors to apply the technology in the industrial world through a startup venture.


Thursday, April 23, 2020
Seeing superlattices: Imaging hidden moiré periods at the nanoisland-2D material interface using 4D scanning transmission electron microscopy

Kate Reidy, PhD candidate
Materials Science & Engineering

Opportunities are emerging to combine van der Waals (2D) materials with (3D) metals/semiconductors to explore fundamental charge-transport phenomena at their interfaces, and exploit them for devices. Recent advances in scanning transmission electron microscopy (STEM) allow detailed analysis of atomic structure, properties, and ordering at these interfaces.

In this talk, Reidy describes the use of 4D STEM to directly image hidden moiré periodicities arising from epitaxial growth of nanoislands on 2D materials in ultra-high vacuum (UHV). Reidy will highlight the role of emerging microscopy techniques in unveiling the alignment and ordering of moiré superlattices, and discuss the implications of moiré periodicities on the properties of 2D/3D junctions.


Tuesday, April 21, 2020
Sensing presence in virtual reality

Yuwei Li, PhD candidate
Device realization laboratory, Mechanical Engineering

Marwa AlAlawi, Undergraduate
Mechanical Engineering

What is presence? How can we measure and enhance presence in VR? In this talk, Yuwei and Marwa introduce their research on presence-inducing VR experiences and the corresponding physiological and behavioral responses from the VR users.

This talk was originally scheduled as part of Talk SENSE, a monthly series powered by SENSE.nano that focuses on topics related to sensors, sensing systems, and sensing techniques.


Thursday, April 16, 2020
Nanoscale insights into the mechanisms of cellular growth and proliferation

Kacper Rogala, Postdoctoral Associate
Whitehead Institute for Biomedical Research

Growth and proliferation of human cells is controlled by a large molecular machine called mTORC1 that acts as a molecular equivalent of an AND logic gate. mTORC1 integrates multiple environmental signals, such as nutrients and growth factors, and orders the cell to either grow and divide in times of plenty, or stand-by and recycle when nutrients are scarce. Using electron cryomicroscopy we were able to reveal how mTORC1 recognizes nutrient signals, which provided a nanoscale-precision blueprint for the design of therapies aimed at deregulated mTORC1 in diseases of cellular growth, such as cancer.


Tuesday, April 14, 2020
Reconfigurable meta-optics with chalcogenide alloys

Mikhail Shalaginov, Postdoctoral Associate
Materials Science & Engineering

Recent progress in nanophotonics has enabled planar-interface systems, termed as metasurfaces, which hold a potential to extend the functionalities of light manipulation and provide size, weight, power, and cost (SWaP-C) benefits. Significant efforts nowadays are geared toward building active metasurfaces, whose properties can be varied post-fabrication. Numerous switchable meta-devices have been demonstrated; however, almost all of them either have a miniscule tuning range or suffer from excessive optical losses.

In this seminar, Mikhail Shalaginov shares his team’s approach to implement high-performance reconfigurable metasurfaces made of low-loss optical phase-change materials. More specifically, the team has developed a new non-volatile chalcogenide alloy GeSbSeTe exhibiting high index contrast and broadband transparency in both amorphous and crystalline states. Based on this material platform, they demonstrated a mid-infrared varifocal metalens that features diffraction-limited performance, focusing efficiencies above 20% in both states, and a record-high switching contrast ratio of 30dB. Their work demonstrates that non-mechanical active metasurfaces can achieve optical quality on par with conventional precision bulk optics involving mechanical moving parts, thereby pointing to a cohort of exciting applications fully unleashing the SWaP-C benefits of active metasurface optics in imaging, sensing, display, and optical ranging.


Thursday, April 9, 2020
Dance-inspired investigation of human movement

Praneeth Namburi, Postdoctoral Associate
Research Laboratory of Electronics (RLE), Electrical Engineering & Computer Science 

In this talk, Namburi focuses on his group's efforts to formalize a dancer’s approach to movement. Their overarching hypothesis is that dancers stabilize their joints through stretches – which is observed during common activities such as walking and running. However, most untrained individuals are only able to apply this form of stabilization during activities such as walking, that seemingly ‘just happen’, much like how we ‘see’. In contrast, the best dancers and athletes are able to generalize this stretch-based joint stabilization beyond walking to their art form.

To understand how dancers organize movement through stretches, we use motion tracking and electromyography. This talk focuses on our hypotheses, preliminary findings, and how our work can potentially benefit several fields, including soft robotics, neuroscience, and AI.

This talk was originally scheduled as part of Talk SENSE, a monthly series powered by SENSE.nano that focuses on topics related to sensors, sensing systems, and sensing techniques.


Tuesday, April 7, 2020
Magnetism in the ultrathin limit

Dahlia Klein, PhD candidate

A primary question in the emerging field of two-dimensional van der Waals magnetic materials is how exfoliating crystals to the few-layer limit influences their magnetism. Studies on CrI3 have shown a different magnetic ground state for ultrathin exfoliated films, but the origin is not yet understood. We use electron tunneling through few-layer crystals of the layered antiferromagnetic insulator CrCl3 to probe its magnetic order, finding a ten-fold enhancement in the antiferromagnetic interlayer exchange compared to bulk crystals. Moreover, polarization-dependent Raman spectroscopy reveals that exfoliated thin films of CrCl3 possess a different low temperature stacking order than bulk crystals. 

Temperature-dependent Raman spectra further attribute this difference in stacking to the absence of a stacking phase transition in these thin films, even though it is well established in bulk CrCl3. We hypothesize that this difference in stacking is the origin of the unexpected magnetic ground states in the ultrathin chromium trihalides. Our work provides new insight into the connection between stacking order and interlayer interactions in novel two-dimensional magnets, which may be relevant for correlating stacking faults and mechanical deformations with the magnetic ground states of other more exotic layered magnets.


Thursday, April 2, 2020
On-chip BioPhotonic particle and gas sensors: Ensuring a safe environment indoors and outdoors

Robin Singh, PhD candidate
Mechanical Engineering

There are a number of unintended situations for potential exposure to bioaerosols such as viruses, bacteria, and fungi. For instance, the current pandemic scenario of COVID-19 occurring across the world. It is crucial to develop ultra-sensitive, low cost, and scalable methods to sense and detect such micro/nanoparticles and gas molecules in the air.

In this talk, Singh discusses current research work on developing an on-chip photonic particle and gas sensor operating in near-IR and mid-IR ranges to perform IR spectroscopy. These sensors enable the in-situ physio-chemical characterization of aerosol particles without compromising their functionality and sensitivity.


Tuesday, March 31, 2020
Manufacturing large-area perovskite thin films: The good, the bad, and the ugly

Richard Swartwout, PhD candidate
Electrical Engineering & Computer Science

Lead halide perovskites have gained considerable interest due to desirable optoelectronic properties that make them useful for next generation photovoltaics. However, despite impressive gains in solar power conversion efficiency ( > 25%) with small scale devices there are still challenges with scaling perovskites to a competitive commercial scale.

Although easy to form, these materials are also easy to break down, requiring highly toxic solvent systems for processing. Lead salts, which give perovskites their unique defect tolerance is also highly regulated and toxic. In this talk, Swartwout will discuss the current manufacturing challenges for perovskite thin films and how we have approached solutions.