A5022100994- Metamaterials and Metasurfaces Applications
- Quantum Dots Synthesis And Properties
- Transition Metal Oxide Nanomaterials
- Organic Electronics and Photovoltaics
- Photonic Crystals and Applications
- Thermal Radiation and Cooling Technologies
- Near-Field Optical Microscopy
- Conducting polymers and applications
- Molecular Junctions and Nanostructures
- 2D Materials and Applications
- Spectroscopy and Quantum Chemical Studies
- Photoacoustic and Ultrasonic Imaging
- Perovskite Materials and Applications
- Ga2O3 and related materials
- Terahertz technology and applications
- Machine Learning in Materials Science
- Chalcogenide Semiconductor Thin Films
- Advanced Antenna and Metasurface Technologies
- Acoustic Wave Resonator Technologies
- Plasmonic and Surface Plasmon Research
- Neural Networks and Applications
- Laser and Thermal Forming Techniques
- Photonic and Optical Devices
- Radio Wave Propagation Studies
- Advanced Memory and Neural Computing
Duke University
2020-2024
University of Colorado Boulder
2015-2023
Joint Institute for Laboratory Astrophysics
2019-2023
Lawrence Berkeley National Laboratory
2016-2020
National Institute of Standards and Technology
2016
University of Technology Sydney
2016
University of California, San Diego
2010-2014
University of California, Irvine
2006
Many classes of two-dimensional (2D) materials have emerged as potential platforms for novel electronic and optical devices. However, their physical properties are strongly influenced by nanoscale heterogeneities in the form edges, twin boundaries, nucleation sites. Using combined tip-enhanced Raman scattering photoluminescence (PL) nanospectroscopy nanoimaging, we study associated effects on excitonic monolayer WSe2 grown vapor deposition. With ∼15 nm spatial resolution, resolve...
Abstract Deep neural networks (DNNs) are empirically derived systems that have transformed traditional research methods, and driving scientific discovery. Artificial electromagnetic materials (AEMs)—including metamaterials, photonic crystals, plasmonics—are fields where DNN results valorize the data driven approach; especially in cases conventional methods failed. In view of great potential deep learning for future artificial research, status field with a focus on recent advances, key...
Many phase transitions in correlated matter exhibit spatial inhomogeneities with expected yet unexplored effects on the associated ultrafast dynamics. Here we demonstrate combination of nondegenerate pump-probe spectroscopy far from equilibrium excitation, and scattering scanning near-field optical microscopy (s-SNOM) for nanoimaging. In a femtosecond near-IR (NIR) pump mid-IR (MIR) probe study, investigate photoinduced insulator-to-metal (IMT) transition nominally homogeneous VO2...
Scattering scanning near-field optical microscopy (s-SNOM) has emerged as a powerful imaging and spectroscopic tool for investigating nanoscale heterogeneities in biology, quantum matter, electronic photonic devices. However, many materials are defined by wide range of fundamental molecular states at far-infrared (FIR) resonant frequencies currently not accessible s-SNOM. Here we show ultrabroadband FIR s-SNOM nanoimaging spectroscopy combining synchrotron infrared radiation with novel fast...
Scattering scanning near-field optical microscopy (s-SNOM) has emerged as a powerful nanoscale spectroscopic tool capable of characterizing individual biomacromolecules and molecular materials. However, applications scattering-based techniques in the infrared (IR) to native biosystems still await solution how implement required aqueous environment. In this work, we demonstrate an IR-compatible liquid cell architecture that enables imaging nanospectroscopy by taking advantage unique...
We demonstrate tuning of a metamaterial device that incorporates form spatial gradient control. Electrical the is achieved through vanadium dioxide layer which interacts with an array split ring resonators. in magnitude permittivity, writeable using single transient electrical pulse. This induced our observed on sc ales order one wavelength at 1 THz. Thus, we show viability elements for use future devices potential applications beamforming and communications
Abstract Deep neural networks (DNNs) have shown marked achievements across numerous research and commercial settings. Part of their success is due to ability “learn” internal representations the input ( x ) that are ideal attain an accurate approximation () some unknown function f is, y = ). Despite universal capability, a drawback DNNs they black boxes, it how or why work. Thus, physics discovered by DNN remains hidden. Here, condition causality enforced through Lorentz layer incorporated...
In this work we investigate the use of deep inverse models (DIMs) for designing artificial electromagnetic materials (AEMs) - such as metamaterials, photonic crystals, and plasmonics to achieve some desired scattering properties (e.g., transmission or reflection spectrum). DIMs are neural networks (i.e., learning models) that specially-designed solve ill-posed problems. There has recently been tremendous growth in solving AEM design problems however there little comparison these approaches...
Abstract Ultrafast infrared nano-imaging has demonstrated access to ultrafast carrier dynamics on the nanoscale in semiconductor, correlated-electron, or polaritonic materials. However, mostly limited short-lived transient states, contrast obtained remained insufficient probe important long-lived excitations, which arise from many-body interactions induced by strong perturbation among carriers, lattice phonons, molecular vibrations. Here, we demonstrate based excitation modulation and...
Ferroic materials are well known to exhibit heterogeneity in the form of domain walls. Understanding properties these boundaries is crucial for controlling functionality with external stimuli and realizing their potential ultra-low power memory logic devices as novel computing architectures. In this work, we employ synchrotron-based near-field infrared nano-spectroscopy reveal vibrational ferroelastic (90[Formula: see text] ferroelectric) walls hybrid improper ferroelectric Ca[Formula:...
Infrared transmission and electrical resistivity measurements reveal that single crystals of LaMnPO${}_{1\ensuremath{-}x}$F${}_{x}$ ($x\ensuremath{\leqslant}0.28$) are insulating. The optical gap obtained from is nearly unaffected by doping, decreasing only slightly 1.3 eV in undoped LaMnPO to 1.1 for $x=0.04$. activation gaps smaller at least an order magnitude, signaling the presence states within gap. At low temperatures, described well variable range hopping conduction between these...
Abstract Topological insulators (TIs) are quantum materials with topologically protected surface states surrounding an insulating bulk. However, defect‐induced bulk conduction often dominates transport properties in most TI materials, obscuring the Dirac states. In order to realize intrinsic topological properties, it is thus of great significance identify spatial distribution defects, understand their formation mechanism, and finally control or eliminate influence. Here, electronic...
We report on infrared (IR) absorption and dc electrical measurements of thin films poly(3-hexylthiophene) (P3HT) that have been modified by a fluoroalkyl trichlorosilane (FTS). Spectra for FTS-treated were compared to data electrostatically-doped P3HT in an organic field-effect transistor (OFET). The appearance prominent polaron band mid-IR supports the assertion hole doping via charge-transfer process between FTS molecules P3HT. In highly-doped with significantly enhanced band, we find...
Much of the electronic transport, photophysical, or biological functions molecular materials emerge from intermolecular interactions and associated nanoscale structure morphology. However, competing phases, defects, disorder give rise to confinement many-body localization wavefunction, disturbing performance material. Here, we employ vibrational excitons as a sensitive local probe coupling in hyperspectral infrared scattering scanning near-field optical microscopy (IR s-SNOM) with...
The temperature-dependent noise of individual, single-walled carbon nanotubes is measured here in a variety different gases and liquids. ambient environment found to have only weak relationship with device noise, even cases where adsorption significantly changes the dc resistance. Correspondingly, 450 K degassing procedure typically reduces by 1 order magnitude. An important exception this finding pronounced, 100-fold increase observed near gas−liquid phase transitions ambient. Wide-range...
A resurgence in the use of donor-acceptor approach synthesizing conjugated polymers has resulted a family high-mobility ambipolar systems with exceptionally narrow energy bandgaps below 1 eV. The ability to transport both electrons and holes is critical for device applications such as organic light-emitting diodes transistors. Infrared spectroscopy offers direct access low-energy excitations associated injected charge carriers. Here we diffraction-limited IR microscope probe spectroscopic...
Creation and control of spatial gradients in electromagnetic properties is a central theme underlying optical device design. In this work, we demonstrate that through modification the temporal distribution current, can obtain increased over shape these gradients. We are able to write spatially sharp with ∼50% change index refraction length scales only few wavelengths as observed diffraction limited terahertz spectroscopy. Furthermore, assess potentials for such beam-steering applications.
Abstract This paper describes laser exposure to tune the infrared (IR) emissivity of a film eutectic gallium indium (EGaIn) particles. EGaIn – liquid metal at room temperature forms native oxide that keeps particles from spontaneously percolating. Photothermal energy CO 2 percolates into conductive network. Here, it also causes decrease in IR 0.4 0.24 over range 7.5–13 µm wavelength (measured by an camera) with increase fluence 1.4 1.9 J cm −2 . The percolate most prominently bottom film,...
Infrared (IR) vibrational scattering scanning near-field optical microscopy (s-SNOM) has advanced to become a powerful nanoimaging and spectroscopy technique with applications ranging from biological quantum materials. However, full spatiospectral s-SNOM continues be challenged by long measurement times drift during the acquisition of large associated datasets. Here, we demonstrate novel approach computational transforming basis stationary frame into rotating IR carrier frequency. We an...
Abstract Multimodal multiscale characterization provide opportunities to study organic semiconducting thin films with multiple length scales, across platforms, elucidate crystallization mechanisms of the various microstructures that impact functionality. With polarized scanning transmission X‐ray and 4D‐scanning electron microscopy, hybrid crystalline structures in rubrene which large domains surround a common nucleus transition spherulite morphology at larger radii is observed. These...
Deep neural networks have demonstrated capability to solve challenging forward and inverse problems in electromagnetic metamaterials. However, they often require large quantities of data achieve a given level accuracy, which poses bottleneck issue an initial delay progress. Here we demonstrate two informed deep learning approaches address the metamaterial design. We show that through direct inclusion physics required network size as well dataset can be reduced compared vanilla feed network....
Donor-acceptor (D-A) copolymers have recently emerged as versatile materials for use in a large variety of device applications. Specifically, these systems possess extremely narrow band gaps, enabling ambipolar charge transport when integrated solution-processed organic field-effect transistors (OFETs). However, the fundamentals electronic this class remain unexplored. We present systematic investigation injection narrow-gap D-A conjugated polymers polybenzobisthiadiazole-dithienopyrrole...