Jonathan Fan is an Assistant Professor in the Department of Electrical Engineering at Stanford University, where he is researching new design methodologies and materials approaches to nanophotonic systems. He received his bachelor’s degree with highest honors from Princeton University and his doctorate from Harvard University. He is the recipient of the Air Force Young Investigator Award, Sloan Foundation Fellowship in Physics, Packard Foundation Fellowship, and the Presidential Early Career Award for Scientists and Engineers.
Director, Fast Turnaround Facility in the Stanford Nanofabrication Facility (2014 - Present)
Honors & Awards
SPIE Rising Researcher, SPIE (2020)
Okawa Foundation Research Award, Okawa Foundation (2019)
3M Untenured Faculty Award, 3M (2018)
Packard Foundation Fellowship, Packard Foundation (2016)
Sloan Foundation Award in Physics, Sloan Foundation (2016)
AFOSR Young Investigator Award, Department of Defense (2015)
Invitee to the National Academy of Engineering Frontiers Symposium, National Academy of Engineering (2014)
Presidential Early Career Award for Scientists and Engineers, Department of Defense (2014)
Beckman Postdoctoral Fellowship, University of Illinois, Urbana-Champaign (2011)
Jeffrey O. Kephard ’80 Engineering Physics Award, Princeton University (2004)
National Science Foundation Graduate Fellowship, National Science Foundation (2004)
Peter Marks Prize for Solid State Physics, Princeton University (2004)
Boards, Advisory Committees, Professional Organizations
Technical Committee Member of the Electronic Materials Symposium, Electronic Materials Symposium (2017 - Present)
Technical Committee Member of the OSA Novel Materials and Applications Conference, OSA (2019 - Present)
Technical Committee Member of the SPIE Metamaterials conference, SPIE (2019 - Present)
Technical Group Member of the OSA Optical Materials Group, OSA (2018 - Present)
Member of MRS, MRS (2020 - Present)
Member of IEEE, IEEE (2020 - Present)
Member of OSA, OSA (2014 - Present)
Member of SPIE, SPIE (2014 - Present)
Stanford SystemX Alliance
PhD, Harvard University, Applied Physics (2010)
MS, Harvard University, Applied Physics (2006)
BSE, Princeton University, Electrical Engineering (2004)
John A. Rogers, Sheng Xu, Jonathan A. Fan, Younggang Huang, Yihui Zhang. "United States Patent 10497633 Stretchable electronic systems with containment chambers", The Board Of Trustees Of The University Of Illinois, Northwestern University, Dec 3, 2019
James D. Plummer, Kai Zhang, Xue Bai Pitner, Jonathan A. Fan. "United States Patent 10435814 Single metal crystals", The Board of Trustees of the Leland Stanford Junior University, Oct 8, 2019
John A. Rogers, Jonathan Fan, Woon-Hong Yeo, Yewang Su, Yonggang Huang, Yihui Zhang. "United States Patent 10192830 Self-similar and fractal design for stretchable electronics", The Board of Trustees of the University of Illinois, Northwestern University, Jan 29, 2019
Federico Capasso, Nanfang Yu, Jonathan Fan. "United States Patent US8328396 Methods and apparatus for improving collimation of radiation beams", President And Fellows Of Harvard College, Dec 11, 2012
Current Research and Scholarly Interests
Optical engineering plays a major role in imaging, communications, energy harvesting, and quantum technologies. We are exploring the next frontier of optical engineering on three fronts. The first is new materials development in the growth of crystalline plasmonic materials and assembly of nanomaterials. The second is novel methods for nanofabrication. The third is new inverse design concepts based on optimization and machine learning.
- Electromagnetic Waves
EE 242 (Aut)
- Engineering Electromagnetics
EE 142 (Win)
- Optics and Electronics Seminar
APPPHYS 483 (Aut)
Independent Studies (7)
- Master's Thesis and Thesis Research
EE 300 (Win, Sum)
- Special Studies and Reports in Electrical Engineering
EE 191 (Win, Spr, Sum)
- Special Studies and Reports in Electrical Engineering
EE 191A (Aut)
- Special Studies and Reports in Electrical Engineering
EE 391 (Aut, Win, Spr, Sum)
- Special Studies and Reports in Electrical Engineering (WIM)
EE 191W (Aut, Win, Spr, Sum)
- Special Studies or Projects in Electrical Engineering
EE 190 (Aut, Sum)
- Special Studies or Projects in Electrical Engineering
EE 390 (Aut, Win, Spr, Sum)
- Master's Thesis and Thesis Research
Prior Year Courses
- Advanced Micro and Nano Fabrication Laboratory
ENGR 241 (Spr)
- Electromagnetic Waves
EE 242 (Aut)
- Engineering Electromagnetics
EE 142 (Spr)
- Introductory Research Seminar in Electrical Engineering
EE 301 (Sum)
- Advanced Micro and Nano Fabrication Laboratory
Doctoral Dissertation Reader (AC)
Pranav Ramesh, Jinhie Skarda, Nathan Zhao
Postdoctoral Faculty Sponsor
Qinglan Huang, Yan Liu, Shangjie Yu
Doctoral Dissertation Advisor (AC)
Mingkun Chen, Lucia Gan, Jiaqi Jiang, Thaibao Phan, John Roberts, Evan Wang
Master's Program Advisor
Nancy Ammar, Chien-yi Chang, Mingkun Chen, Shi Dong, Ella Thomson, Xiangjin Wu
- Codoping Mg-Mn Based Oxygen Carrier with Lithium and Tungsten for Enhanced C-2 Yield in a Chemical Looping Oxidative Coupling of Methane System ACS SUSTAINABLE CHEMISTRY & ENGINEERING 2021; 9 (7): 2651–60
- Highly Selective Production of Syngas from Chemical Looping Reforming of Methane with CO2 Utilization on MgO-supported Calcium Ferrite Redox Materials APPLIED ENERGY 2021; 282
- Multiobjective and categorical global optimization of photonic structures based on ResNet generative neural networks NANOPHOTONICS 2021; 10 (1): 361–69
- Deep neural networks for the evaluation and design of photonic devices NATURE REVIEWS MATERIALS 2020
- Mechanistic Insight into Hydrogen-Assisted Carbon Dioxide Reduction with Ilmenite ENERGY & FUELS 2020; 34 (12): 15370–78
- Cyclic redox scheme towards shale gas reforming: a review and perspectives REACTION CHEMISTRY & ENGINEERING 2020; 5 (12): 2204–20
- Design Space Reparameterization Enforces Hard Geometric Constraints in Inverse-Designed Nanophotonic Devices ACS PHOTONICS 2020; 7 (11): 3141–51
- Driving Towards Highly Selective and Coking-Resistant Natural Gas Reforming Through a Hybrid Oxygen Carrier Design CHEMCATCHEM 2020
- SBA-16-Mediated Nanoparticles Enabling Accelerated Kinetics in Cyclic Methane Conversion to Syngas at Low Temperatures ACS APPLIED ENERGY MATERIALS 2020; 3 (10): 9833–40
- Multiple Tunable Hyperbolic Resonances in Broadband Infrared Carbon-Nanotube Metamaterials PHYSICAL REVIEW APPLIED 2020; 14 (4)
Thermoelectric response from grain boundaries and lattice distortions in crystalline gold devices.
Proceedings of the National Academy of Sciences of the United States of America
The electronic Seebeck response in a conductor involves the energy-dependent mean free path of the charge carriers and is affected by crystal structure, scattering from boundaries and defects, and strain. Previous photothermoelectric (PTE) studies have suggested that the thermoelectric properties of polycrystalline metal nanowires are related to grain structure, although direct evidence linking crystal microstructure to the PTE response is difficult to elucidate. Here, we show that room temperature scanning PTE measurements are sensitive probes that can detect subtle changes in the local Seebeck coefficient of gold tied to the underlying defects and strain that mediate crystal deformation. This connection is revealed through a combination of scanning PTE and electron microscopy measurements of single-crystal and bicrystal gold microscale devices. Unexpectedly, the photovoltage maps strongly correlate with gradually varying crystallographic misorientations detected by electron backscatter diffraction. The effects of individual grain boundaries and differing grain orientations on the PTE signal are minimal. This scanning PTE technique shows promise for identifying minor structural distortions in nanoscale materials and devices.
View details for DOI 10.1073/pnas.2002284117
View details for PubMedID 32900922
- Robust Freeform Metasurface Design Based on Progressively Growing Generative Networks ACS PHOTONICS 2020; 7 (8): 2098–2104
- Numerical Optimization Methods for Metasurfaces LASER & PHOTONICS REVIEWS 2020
- Cobalt doping modi fication for enhanced methane conversion at low temperature in chemical looping reforming systems CATALYSIS TODAY 2020; 350: 156–64
MetaNet: a new paradigm for data sharing in photonics research
2020; 28 (9): 13670–81
Optimization methods are playing an increasingly important role in all facets of photonics engineering, from integrated photonics to free space diffractive optics. However, efforts in the photonics community to develop optimization algorithms remain uncoordinated, which has hindered proper benchmarking of design approaches and access to device designs based on optimization. We introduce MetaNet, an online database of photonic devices and design codes intended to promote coordination and collaboration within the photonics community. Using metagratings as a model system, we have uploaded over one hundred thousand device layouts to the database, as well as source code for implementations of local and global topology optimization methods. Further analyses of these large datasets allow the distribution of optimized devices to be visualized for a given optimization method. We expect that the coordinated research efforts enabled by MetaNet will expedite algorithm development for photonics design.
View details for DOI 10.1364/OE.388378
View details for Web of Science ID 000530854700092
View details for PubMedID 32403837
- 3D Electromagnetic Reconfiguration Enabled by Soft Continuum Robots IEEE ROBOTICS AND AUTOMATION LETTERS 2020; 5 (2): 1704–11
- Freeform metasurface design based on topology optimization MRS BULLETIN 2020; 45 (3): 196–201
Mid-IR and UV-Vis-NIR Mueller matrix ellipsometry characterization of tunable hyperbolic metamaterials based on self-assembled carbon nanotubes
Journal of Vacuum Science & Technology B
View details for DOI 10.1116/1.5130888
Broadband Mid-Infrared Resonances in Aligned Carbon Nanotube Films
View details for Web of Science ID 000612090001385
Reparameterization to Enforce Constraints in the Inverse Design of Metasurfaces
View details for Web of Science ID 000612090000187
Highly confined plasmons in individual single-walled carbon nanotube nanoantennas
View details for Web of Science ID 000612090002178
Free-Form Diffractive Metagrating Design Based on Generative Adversarial Networks.
A key challenge in metasurface design is the development of algorithms that can effectively and efficiently produce high-performance devices. Design methods based on iterative optimization can push the performance limits of metasurfaces, but they require extensive computational resources that limit their implementation to small numbers of microscale devices. We show that generative neural networks can train from images of periodic, topology-optimized metagratings to produce high-efficiency, topologically complex devices operating over a broad range of deflection angles and wavelengths. Further iterative optimization of these designs yields devices with enhanced robustness and efficiencies, and these devices can be utilized as additional training data for network refinement. In this manner, generative networks can be trained, with a one-time computation cost, and used as a design tool to facilitate the production of near-optimal, topologically complex device designs. We envision that such data-driven design methodologies can apply to other physical sciences domains that require the design of functional elements operating across a wide parameter space.
View details for DOI 10.1021/acsnano.9b02371
View details for PubMedID 31314492
Global Optimization of Dielectric Metasurfaces Using a Physics-Driven Neural Network.
We present a global optimizer, based on a conditional generative neural network, which can output ensembles of highly efficient topology-optimized metasurfaces operating across a range of parameters. A key feature of the network is that it initially generates a distribution of devices that broadly samples the design space and then shifts and refines this distribution toward favorable design space regions over the course of optimization. Training is performed by calculating the forward and adjoint electromagnetic simulations of outputted devices and using the subsequent efficiency gradients for backpropagation. With metagratings operating across a range of wavelengths and angles as a model system, we show that devices produced from the trained generative network have efficiencies comparable to or better than the best devices produced by adjoint-based topology optimization, while requiring less computational cost. Our reframing of adjoint-based optimization to the training of a generative neural network applies generally to physical systems that can utilize gradients to improve performance.
View details for DOI 10.1021/acs.nanolett.9b01857
View details for PubMedID 31294997
- Tunable Hyperbolic Metamaterials Based on Self-Assembled Carbon Nanotubes NANO LETTERS 2019; 19 (5): 3131–37
- Coupling between subwavelength nano-slit lattice modes and metal-insulator-graphene cavity modes: a semi-analytical model OSA CONTINUUM 2019; 2 (4): 1296–1309
- Review of numerical optimization techniques for meta-device design [Invited] OPTICAL MATERIALS EXPRESS 2019; 9 (4): 1842–63
Syngas production by CO2 reforming of methane over iron-titanium composite oxygen carrier in a cyclic redox mode
AMER CHEMICAL SOC. 2019
View details for Web of Science ID 000478860506233
- Ternary content-addressable memory with MoS2 transistors for massively parallel data search NATURE ELECTRONICS 2019; 2 (3): 108–14
- Large-area MRI-compatible epidermal electronic interfaces for prosthetic control and cognitive monitoring NATURE BIOMEDICAL ENGINEERING 2019; 3 (3): 194-+
- Robust design of topology-optimized metasurfaces OPTICAL MATERIALS EXPRESS 2019; 9 (2): 469–82
Near 100% CO selectivity in nanoscaled iron-based oxygen carriers for chemical looping methane partial oxidation.
2019; 10 (1): 5503
Chemical looping methane partial oxidation provides an energy and cost effective route for methane utilization. However, there is considerable CO2 co-production in current chemical looping systems, rendering a decreased productivity in value-added fuels or chemicals. In this work, we demonstrate that the co-production of CO2 can be dramatically suppressed in methane partial oxidation reactions using iron oxide nanoparticles embedded in mesoporous silica matrix. We experimentally obtain near 100% CO selectivity in a cyclic redox system at 750-935 °C, which is a significantly lower temperature range than in conventional oxygen carrier systems. Density functional theory calculations elucidate the origins for such selectivity and show that low-coordinated lattice oxygen atoms on the surface of nanoparticles significantly promote Fe-O bond cleavage and CO formation. We envision that embedded nanostructured oxygen carriers have the potential to serve as a general materials platform for redox reactions with nanomaterials at high temperatures.
View details for DOI 10.1038/s41467-019-13560-0
View details for PubMedID 31796744
Tunable Hyperbolic Plasmons in Self-Assembled Carbon Nanotube Metamaterials
View details for Web of Science ID 000482226300251
Generating high performance, topologically-complex metasurfaces with neural networks
View details for Web of Science ID 000482226300137
Simulator-based training of generative neural networks for the inverse design of metasurfaces
View details for DOI 10.1515/nanoph-2019-0330
High-Throughput Growth of Microscale Gold Bicrystals for Single-Grain-Boundary Studies.
Advanced materials (Deerfield Beach, Fla.)
The study of grain boundaries is the foundation to understanding many of the intrinsic physical properties of bulk metals. Here, the preparation of microscale thin-film gold bicrystals, using rapid melt growth, is presented as a model system for studies of single grain boundaries. This material platform utilizes standard fabrication tools and supports the high-yield growth of thousands of bicrystals per wafer, each containing a grain boundary with a unique <111> tilt character. The crystal growth dynamics of the gold grains in each bicrystal are mediated by platinum gradients, which originate from the gold-platinum seeds responsible for gold crystal nucleation. This crystallization mechanism leads to a decoupling between crystal nucleation and crystal growth, and it ensures that the grain boundaries form at the middle of the gold microstructures and possess a uniform distribution of misorientation angles. It is envisioned that these bicrystals will enable the systematic study of the electrical, optical, chemical, thermal, and mechanical properties of individual grain boundary types.
View details for DOI 10.1002/adma.201902189
View details for PubMedID 31197897
High-efficiency, large-area, topology-optimized metasurfaces.
Light, science & applications
2019; 8: 48
Metasurfaces are ultrathin optical elements that are highly promising for constructing lightweight and compact optical systems. For their practical implementation, it is imperative to maximize the metasurface efficiency. Topology optimization provides a pathway for pushing the limits of metasurface efficiency; however, topology optimization methods have been limited to the design of microscale devices due to the extensive computational resources that are required. We introduce a new strategy for optimizing large-area metasurfaces in a computationally efficient manner. By stitching together individually optimized sections of the metasurface, we can reduce the computational complexity of the optimization from high-polynomial to linear. As a proof of concept, we design and experimentally demonstrate large-area, high-numerical-aperture silicon metasurface lenses with focusing efficiencies exceeding 90%. These concepts can be generalized to the design of multifunctional, broadband diffractive optical devices and will enable the implementation of large-area, high-performance metasurfaces in practical optical systems.
View details for DOI 10.1038/s41377-019-0159-5
View details for PubMedID 31149333
View details for PubMedCentralID PMC6538635
- Enhanced methane conversion in chemical looping partial oxidation systems using a copper doping modification APPLIED CATALYSIS B-ENVIRONMENTAL 2018; 235: 143–49
- Metal oxide redox chemistry for chemical looping processes NATURE REVIEWS CHEMISTRY 2018; 2 (11): 349–64
- Understanding Interlayer Coupling in TMD-hBN Heterostructure by Raman Spectroscopy IEEE TRANSACTIONS ON ELECTRON DEVICES 2018; 65 (10): 4059–67
- C-2 Selectivity Enhancement in Chemical Looping Oxidative Coupling of Methane over a Mg-Mn Composite Oxygen Carrier by Li-Doping-Induced Oxygen Vacancies ACS ENERGY LETTERS 2018; 3 (7): 1730–36
- New Insight into the Development of Oxygen Carrier Materials for Chemical Looping Systems ENGINEERING 2018; 4 (3): 343–51
- Ultra-High-Efficiency Anomalous Refraction with Dielectric Metasurfaces ACS PHOTONICS 2018; 5 (6): 2402–7
- A Tip-Extending Soft Robot Enables Reconfigurable and Deployable Antennas IEEE ROBOTICS AND AUTOMATION LETTERS 2018; 3 (2): 949–56
Single-crystal metal growth on amorphous insulating substrates
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2018; 115 (4): 685–89
Metal structures on insulators are essential components in advanced electronic and nanooptical systems. Their electronic and optical properties are closely tied to their crystal quality, due to the strong dependence of carrier transport and band structure on defects and grain boundaries. Here we report a method for creating patterned single-crystal metal microstructures on amorphous insulating substrates, using liquid phase epitaxy. In this process, the patterned metal microstructures are encapsulated in an insulating crucible, together with a small seed of a differing material. The system is heated to temperatures above the metal melting point, followed by cooling and metal crystallization. During the heating process, the metal and seed form a high-melting-point solid solution, which directs liquid epitaxial metal growth. High yield of single-crystal metal with different sizes is confirmed with electron backscatter diffraction images, after removing the insulating crucible. Unexpectedly, the metal microstructures crystallize with the [Formula: see text] direction normal to the plane of the film. This platform technology will enable the large-scale integration of high-performance plasmonic and electronic nanosystems.
View details for PubMedID 29311332
- High-performance axicon lenses based on high-contrast, multilayer gratings APL PHOTONICS 2018; 3 (1)
Evaluating the Microwave Performance of Epidermal Electronics with Equivalent Transmission Line Modeling
IEEE. 2018: 40–42
View details for Web of Science ID 000502126700092
- Freeform Metagratings Based on Complex Light Scattering Dynamics for Extreme, High Efficiency Beam Steering ANNALEN DER PHYSIK 2018; 530 (1)
- A General Strategy for Stretchable Microwave Antenna Systems using Serpentine Mesh Layouts ADVANCED FUNCTIONAL MATERIALS 2017; 27 (46)
- Periodic Dielectric Metasurfaces with High-Efficiency, Multiwavelength Functionalities ADVANCED OPTICAL MATERIALS 2017; 5 (23)
- Strain-Limiting Substrates Based on Nonbuckling, Prestrain-Free Mechanics for Robust Stretchable Electronics JOURNAL OF APPLIED MECHANICS-TRANSACTIONS OF THE ASME 2017; 84 (12)
- Improved cyclic redox reactivity of lanthanum modified iron-based oxygen carriers in carbon monoxide chemical looping combustion JOURNAL OF MATERIALS CHEMISTRY A 2017; 5 (38): 20153–60
Analysis of material selection on dielectric metasurface performance
2017; 25 (20): 23899–909
Dielectric metasurfaces are ultra-thin devices that can shape optical wavefronts with extreme control. While an assortment of materials possessing a wide range of dielectric constants have been proposed and implemented, the minimum dielectric contrast required for metasurfaces to achieve high-efficiency performance, for a given device function and feature size constraint, is unclear. In this Article, we examine the impact of dielectric material selection on metasurface efficiency at optical frequencies. As a model system, we design transmissive, single-layer periodic metasurfaces (i.e., metagratings) using topology optimization, and we sweep device thickness and light deflection angle for differing material types. We find that for modest deflection angles below 40 degrees, materials with relatively low dielectric constants near 4 can be used to produce metagratings with efficiencies over 80%. However, ultra-high-efficiency devices designed for large deflection angles and multiple functions require materials with high dielectric constants comparable to silicon. We also identify, for all materials, a minimum device thickness required for optimal metagrating performance that scales inversely with dielectric constant. Our work presents materials selection guidelines for high-performance metasurfaces operating at visible and infrared wavelengths.
View details for DOI 10.1364/OE.25.023899
View details for Web of Science ID 000412048500045
View details for PubMedID 29041339
Topology-optimized metasurfaces: impact of initial geometric layout
2017; 42 (16): 3161–64
Topology optimization is a powerful iterative inverse design technique in metasurface engineering and can transform an initial layout into a high-performance device. With this method, devices are optimized within a local design phase space, making the identification of suitable initial geometries essential. In this Letter, we examine the impact of initial geometric layout on the performance of large-angle (75 deg) topology-optimized metagrating deflectors. We find that when conventional metasurface designs based on dielectric nanoposts are used as initial layouts for topology optimization, the final devices have efficiencies around 65%. In contrast, when random initial layouts are used, the final devices have ultra-high efficiencies that can reach 94%. Our numerical experiments suggest that device topologies based on conventional metasurface designs may not be suitable to produce ultra-high-efficiency, large-angle metasurfaces. Rather, initial geometric layouts with non-trivial topologies and shapes are required.
View details for DOI 10.1364/OL.42.003161
View details for Web of Science ID 000407640000027
View details for PubMedID 28809897
Large-Angle, Multifunctional Metagratings Based on Freeform Multimode Geometries.
We show that silicon-based metagratings capable of large-angle, multifunctional performance can be realized using inverse freeform design. These devices consist of nonintuitive nanoscale patterns and support a large number of spatially overlapping optical modes per unit area. The quantity of modes, in combination with their optimized responses, provides the degrees of freedom required to produce high-efficiency devices. To demonstrate the power and versatility of our approach, we fabricate metagratings that can efficiently deflect light to 75° angles and multifunctional devices that can steer beams to different diffraction orders based on wavelength. A theoretical analysis of the Bloch modes supported by these devices elucidates the spatial mode profiles and coupling dynamics that make high-performance beam deflection possible. This approach represents a new paradigm in nano-optical mode engineering and utilizes different physics from the current state-of-the-art, which is based on the stitching of noninteracting waveguide structures. We envision that inverse design will enable new classes of high-performance photonic systems and new strategies toward the nanoscale control of light fields.
View details for DOI 10.1021/acs.nanolett.7b01082
View details for PubMedID 28459583
- Morphology evolution and nanostructure of chemical looping transition metal oxide materials upon redox processes ACTA MATERIALIA 2017; 124: 568-578
In-Plane Deformation Mechanics for Highly Stretchable Electronics.
2017; 29 (8)
Scissoring in thick bars suppresses buckling behavior in serpentine traces that have thicknesses greater than their widths, as detailed in a systematic set of analytical and experimental studies. Scissoring in thick copper traces enables elastic stretchability as large as ≈350%, corresponding to a sixfold improvement over previously reported values for thin geometries (≈60%).
View details for DOI 10.1002/adma.201604989
View details for PubMedID 28004863
- Impact of 1% Lanthanum Dopant on Carbonaceous Fuel Redox Reactions with an Iron-Based Oxygen Carrier in Chemical Looping Processes ACS ENERGY LETTERS 2017; 2 (1): 70-74
2D Molybdenum Disulfide (MoS2) Transistors Driving RRAMs with 1T1R Configuration
View details for Web of Science ID 000424868900117
Characterization of Stretchable Serpentine Microwave Devices for Wearable Electronics
IEEE. 2017: 207–10
View details for Web of Science ID 000425241500055
- Visible Light Metasurfaces Based on Single-Crystal Silicon ACS PHOTONICS 2016; 3 (10): 1919-1925
Electrochemically Programmable Plasmonic Antennas.
2016; 10 (7): 6716-6724
Plasmonic antennas are building blocks in advanced nano-optical systems due to their ability to tailor optical response based on their geometry. We propose an electrochemical approach to program the optical properties of dipole antennas in a scalable, fast, and energy-efficient manner. These antennas comprise two arms, one serving as an anode and the other a cathode, separated by a solid electrolyte. As a voltage is applied between the antenna arms, a conductive filament either grows or dissolves within the electrolyte, modifying the antenna load. We probe the dynamics of stochastic filament formation and their effects on plasmonic mode programming using a combination of three-dimensional optical and electronic simulations. In particular, we identify device operation regimes in which the charge-transfer plasmon mode can be programmed to be "on" or "off." We also identify, unexpectedly, a strong correlation between DC filament resistance and charge-transfer plasmon mode frequency that is insensitive to the detailed filament morphology. We envision that the scalability of our electrochemical platform can generalize to large-area reconfigurable metamaterials and metasurfaces for on-chip and free-space applications.
View details for DOI 10.1021/acsnano.6b02031
View details for PubMedID 27328022
Methane adsorption and dissociation on iron oxide oxygen carriers: the role of oxygen vacancies
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
2016; 18 (24): 16423-16435
We performed ab initio DFT+U calculations to explore the interaction between methane and iron oxide oxygen carriers for chemical looping reaction systems. The adsorption of CH4 and CHx (x = 0-3) radicals on α-Fe2O3(001), and the influence of oxygen vacancies at the top surface and on the subsurface on the adsorption properties of the radicals was investigated. The adsorption strength for CH4 and C radicals at the top of the α-Fe2O3(001) surface in the presence of oxygen vacancies is lower than that on the stoichiometric surface. However, for methyl (CH3), methylene (CH2) and methine (CH) radicals, it is correspondingly higher. In contrast, the oxygen vacancy formation on the subsurface not only increases the adsorption strength of CH3, CH2 and CH radicals, but also facilitates C radical adsorption. We found that oxygen vacancies significantly affect the adsorption configuration of CHx radicals, and determine the probability of finding an adsorbed species in the stoichiometric region and the defective region at the surface. With the obtained adsorption geometries and energetics of these species adsorbed on the surface, we extend the analysis to CH4 dissociation under chemical looping reforming conditions. The distribution of adsorbed CH4 and CHx (x = 0-3) radicals is calculated and analyzed which reveals the relationship between adsorbed CHx radical configuration and oxygen vacancies in iron oxide. Also, the oxygen vacancies can significantly facilitate CH4 activation by lowering the dissociation barriers of CH3, CH2 and CH radicals. However, when the oxygen vacancy concentration reaches 2.67%, increasing the oxygen vacancy concentration cannot continue to lower the CH dissociation barrier. The study provides fundamental insights into the mechanism of CH4 dissociation on iron based oxygen carriers and also provide guidance to design more efficient oxygen carriers.
View details for DOI 10.1039/c6cp01287f
View details for Web of Science ID 000381056500043
View details for PubMedID 27265327
Oxygen vacancy promoted methane partial oxidation over iron oxide oxygen carriers in the chemical looping process
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
2016; 18 (47): 32418-32428
We perform ab initio DFT+U calculations and experimental studies of the partial oxidation of methane to syngas on iron oxide oxygen carriers to elucidate the role of oxygen vacancies in oxygen carrier reactivity. In particular, we explore the effect of oxygen vacancy concentration on sequential processes of methane dehydrogenation, and oxidation with lattice oxygen. We find that when CH4 adsorbs onto Fe atop sites without neighboring oxygen vacancies, it dehydrogenates with CHx radicals remaining on the same site and evolves into CO2via the complete oxidation pathway. In the presence of oxygen vacancies, on the other hand, the formed methyl (CH3) prefers to migrate onto the vacancy site while the H from CH4 dehydrogenation remains on the original Fe atop site, and evolves into CO via the partial oxidation pathway. The oxygen vacancies created in the oxidation process can be healed by lattice oxygen diffusion from the subsurface to the surface vacancy sites, and it is found that the outward diffusion of lattice oxygen atoms is more favorable than the horizontal diffusion on the same layer. Based on the proposed mechanism and energy profile, we identify the rate-limiting steps of the partial oxidation and complete oxidation pathways. Also, we find that increasing the oxygen vacancy concentration not only lowers the barriers of CH4 dehydrogenation but also the cleavage energy of Fe-C bonds. However, the barrier of the rate-limiting step cannot further decrease when the oxygen vacancy concentration reaches 2.5%. The fundamental insight into the oxygen vacancy effect on CH4 oxidation with iron oxide oxygen carriers can help guide the design and development of more efficient oxygen carriers and CLPO processes.
View details for DOI 10.1039/c6cp06264d
View details for Web of Science ID 000390436800046
View details for PubMedID 27869258
Epidermal radio frequency electronics for wireless power transfer.
Microsystems & nanoengineering
2016; 2: 16052
Epidermal electronic systems feature physical properties that approximate those of the skin, to enable intimate, long-lived skin interfaces for physiological measurements, human-machine interfaces and other applications that cannot be addressed by wearable hardware that is commercially available today. A primary challenge is power supply; the physical bulk, large mass and high mechanical modulus associated with conventional battery technologies can hinder efforts to achieve epidermal characteristics, and near-field power transfer schemes offer only a limited operating distance. Here we introduce an epidermal, far-field radio frequency (RF) power harvester built using a modularized collection of ultrathin antennas, rectifiers and voltage doublers. These components, separately fabricated and tested, can be integrated together via methods involving soft contact lamination. Systematic studies of the individual components and the overall performance in various dielectric environments highlight the key operational features of these systems and strategies for their optimization. The results suggest robust capabilities for battery-free RF power, with relevance to many emerging epidermal technologies.
View details for PubMedID 31057838
View details for PubMedCentralID PMC6444737
Optics and Nonlinear Buckling Mechanics in Large-Area, Highly Stretchable Arrays of Plasmonic Nano structures
2015; 9 (6): 5968-5975
Large-scale, dense arrays of plasmonic nanodisks on low-modulus, high-elongation elastomeric substrates represent a class of tunable optical systems, with reversible ability to shift key optical resonances over a range of nearly 600 nm at near-infrared wavelengths. At the most extreme levels of mechanical deformation (strains >100%), nonlinear buckling processes transform initially planar arrays into three-dimensional configurations, in which the nanodisks rotate out of the plane to form linear arrays with "wavy" geometries. Analytical, finite-element, and finite-difference time-domain models capture not only the physics of these buckling processes, including all of the observed modes, but also the quantitative effects of these deformations on the plasmonic responses. The results have relevance to mechanically tunable optical systems, particularly to soft optical sensors that integrate on or in the human body.
View details for DOI 10.1021/acsnano.5b00716
View details for Web of Science ID 000356988500037
View details for PubMedID 25906085
Materials and Fractal Designs for 3D Multifunctional Integumentary Membranes with Capabilities in Cardiac Electrotherapy
2015; 27 (10): 1731-?
Advanced materials and fractal design concepts form the basis of a 3D conformal electronic platform with unique capabilities in cardiac electrotherapies. Fractal geometries, advanced electrode materials, and thin, elastomeric membranes yield a class of device capable of integration with the entire 3D surface of the heart, with unique operational capabilities in low power defibrillation. Co-integrated collections of sensors allow simultaneous monitoring of physiological responses. Animal experiments on Langendorff-perfused rabbit hearts demonstrate the key features of these systems.
View details for DOI 10.1002/adma.201405017
View details for Web of Science ID 000350754100013
View details for PubMedID 25641076
View details for PubMedCentralID PMC4527319
Elasticity of Fractal Inspired Interconnects
2015; 11 (3): 367-373
The use of fractal-inspired geometric designs in electrical interconnects represents an important approach to simultaneously achieve large stretchability and high aerial coverage of active devices for stretchable electronics. The elastic stiffness of fractal interconnects is determined analytically in this paper. Specifically, the elastic energy and the tensile stiffness for an order n fractal interconnect of arbitrary shape are obtained, and are verified by the finite element analysis and experiments.
View details for DOI 10.1002/smll.201401181
View details for Web of Science ID 000348139800013
View details for PubMedID 25183293
- Nanostructure formation mechanism and ion diffusion in iron-titanium composite materials with chemical looping redox reactions JOURNAL OF MATERIALS CHEMISTRY A 2015; 3 (21): 11302-11312
- A hierarchical computational model for stretchable interconnects with fractal-inspired designs JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2014; 72: 115–30
- Evolution of nanoscale morphology in single and binary metal oxide microparticles during reduction and oxidation processes JOURNAL OF MATERIALS CHEMISTRY A 2014; 2 (41): 17511-17520
Multifunctional Skin-Like Electronics for Quantitative, Clinical Monitoring of Cutaneous Wound Healing
ADVANCED HEALTHCARE MATERIALS
2014; 3 (10): 1597–1607
Non-invasive, biomedical devices have the potential to provide important, quantitative data for the assessment of skin diseases and wound healing. Traditional methods either rely on qualitative visual and tactile judgments of a professional and/or data obtained using instrumentation with forms that do not readily allow intimate integration with sensitive skin near a wound site. Here, an electronic sensor platform that can softly and reversibly laminate perilesionally at wounds to provide highly accurate, quantitative data of relevance to the management of surgical wound healing is reported. Clinical studies on patients using thermal sensors and actuators in fractal layouts provide precise time-dependent mapping of temperature and thermal conductivity of the skin near the wounds. Analytical and simulation results establish the fundamentals of the sensing modalities, the mechanics of the system, and strategies for optimized design. The use of this type of "epidermal" electronics system in a realistic clinical setting with human subjects establishes a set of practical procedures in disinfection, reuse, and protocols for quantitative measurement. The results have the potential to address important unmet needs in chronic wound management.
View details for DOI 10.1002/adhm.201400073
View details for Web of Science ID 000343798800009
View details for PubMedID 24668927
View details for PubMedCentralID PMC4177017
- Materials and Designs for Wireless Epidermal Sensors of Hydration and Strain ADVANCED FUNCTIONAL MATERIALS 2014; 24 (25): 3846–54
- Experimental and Theoretical Studies of Serpentine Microstructures Bonded To Prestrained Elastomers for Stretchable Electronics ADVANCED FUNCTIONAL MATERIALS 2014; 24 (14): 2028-2037
Fractal design concepts for stretchable electronics
Stretchable electronics provide a foundation for applications that exceed the scope of conventional wafer and circuit board technologies due to their unique capacity to integrate with soft materials and curvilinear surfaces. The range of possibilities is predicated on the development of device architectures that simultaneously offer advanced electronic function and compliant mechanics. Here we report that thin films of hard electronic materials patterned in deterministic fractal motifs and bonded to elastomers enable unusual mechanics with important implications in stretchable device design. In particular, we demonstrate the utility of Peano, Greek cross, Vicsek and other fractal constructs to yield space-filling structures of electronic materials, including monocrystalline silicon, for electrophysiological sensors, precision monitors and actuators, and radio frequency antennas. These devices support conformal mounting on the skin and have unique properties such as invisibility under magnetic resonance imaging. The results suggest that fractal-based layouts represent important strategies for hard-soft materials integration.
View details for DOI 10.1038/ncomms4266
View details for Web of Science ID 000332667600013
View details for PubMedID 24509865
Spectrally selective chiral silicon metasurfaces based on infrared Fano resonances.
2014; 5: 3892-?
Metamaterials and metasurfaces represent a remarkably versatile platform for light manipulation, biological and chemical sensing, and nonlinear optics. Many of these applications rely on the resonant nature of metamaterials, which is the basis for extreme spectrally selective concentration of optical energy in the near field. In addition, metamaterial-based optical devices lend themselves to considerable miniaturization because of their subwavelength features. This additional advantage sets metamaterials apart from their predecessors, photonic crystals, which achieve spectral selectivity through their long-range periodicity. Unfortunately, spectral selectivity of the overwhelming majority of metamaterials that are made of metals is severely limited by high plasmonic losses. Here we propose and demonstrate Fano-resonant all-dielectric metasurfaces supporting optical resonances with quality factors Q>100 that are based on CMOS-compatible materials: silicon and its oxide. We also demonstrate that these infrared metasurfaces exhibit extreme planar chirality, opening exciting possibilities for efficient ultrathin circular polarizers and narrow-band thermal emitters of circularly polarized radiation.
View details for DOI 10.1038/ncomms4892
View details for PubMedID 24861488
Ultrasmooth, Highly Spherical Monocrystalline Gold Particles for Precision Plasmonics
2013; 7 (12): 11064-11070
Ultrasmooth, highly spherical monocrystalline gold particles were prepared by a cyclic process of slow growth followed by slow chemical etching, which selectively removes edges and vertices. The etching process effectively makes the surface tension isotropic, so that spheres are favored under quasi-static conditions. It is scalable up to particle sizes of 200 nm or more. The resulting spherical crystals display uniform scattering spectra and consistent optical coupling at small separations, even showing Fano-like resonances in small clusters. The high monodispersity of the particles we demonstrate should facilitate the self-assembly of nanoparticle clusters with uniform optical resonances, which could in turn be used to fabricate optical metafluids. Narrow size distributions are required to control not only the spectral features but also the morphology and yield of clusters in certain assembly schemes.
View details for DOI 10.1021/nn404765w
View details for Web of Science ID 000329137100067
View details for PubMedID 24219591
- Mechanics of ultra-stretchable self-similar serpentine interconnects ACTA MATERIALIA 2013; 61 (20): 7816–27
- Tetrahedral Colloidal Clusters from Random Parking of Bidisperse Spheres PHYSICAL REVIEW LETTERS 2013; 110 (14)
Stretchable batteries with self-similar serpentine interconnects and integrated wireless recharging systems
An important trend in electronics involves the development of materials, mechanical designs and manufacturing strategies that enable the use of unconventional substrates, such as polymer films, metal foils, paper sheets or rubber slabs. The last possibility is particularly challenging because the systems must accommodate not only bending but also stretching. Although several approaches are available for the electronics, a persistent difficulty is in power supplies that have similar mechanical properties, to allow their co-integration with the electronics. Here we introduce a set of materials and design concepts for a rechargeable lithium ion battery technology that exploits thin, low modulus silicone elastomers as substrates, with a segmented design in the active materials, and unusual 'self-similar' interconnect structures between them. The result enables reversible levels of stretchability up to 300%, while maintaining capacity densities of ~1.1 mAh cm(-2). Stretchable wireless power transmission systems provide the means to charge these types of batteries, without direct physical contact.
View details for DOI 10.1038/ncomms2553
View details for Web of Science ID 000316616400111
View details for PubMedID 23443571
Plasmonic Mode Engineering with Templated Self-Assembled Nanoclusters
2012; 12 (10): 5318-5324
Plasmonic nanoparticle assemblies are a materials platform in which optical modes, resonant frequencies, and near-field intensities can be specified by the number and position of nanoparticles in a cluster. A current challenge is to achieve clusters with higher yields and new types of shapes. In this Letter, we show that a broad range of plasmonic nanoshell nanoclusters can be assembled onto a lithographically defined elastomeric substrate with relatively high yields using templated assembly. We assemble and measure the optical properties of three cluster types: Fano-resonant heptamers, linear chains, and rings of nanoparticles. The yield of heptamer clusters is measured to be over 30%. The assembly of plasmonic nanoclusters on an elastomer paves the way for new classes of plasmonic nanocircuits and colloidal metamaterials that can be transfer-printed onto various substrate media.
View details for DOI 10.1021/nl302650t
View details for Web of Science ID 000309615000041
View details for PubMedID 22947109
Near-Normal Incidence Dark-Field Microscopy: Applications to Nanoplasmonic Spectroscopy
2012; 12 (6): 2817-2821
The spectroscopic characterization of individual nanostructures is of fundamental importance to understanding a broad range of physical and chemical processes. One general and powerful technique that addresses this aim is dark-field microscopy, with which the scattered light from an individual structure can be analyzed with minimal background noise. We present the spectroscopic analysis of individual plasmonic nanostructures using dark-field illumination with incidence nearly normal to the substrate. We show that, compared to large incidence angle approaches, the near-normal incidence approach provides significantly higher signal-to-background ratios and reduced retardation field effects. To demonstrate the utility of this technique, we characterize an individual chemically synthesized gold nanoshell and a lithographically defined heptamer exhibiting a pronounced Fano-like resonance. We show that the line shape of the latter strongly depends on the incidence angle. Near-normal incidence dark-field microscopy can be used to characterize a broad range of molecules and nanostructures and can be adapted to most microscopy setups.
View details for DOI 10.1021/nl300160y
View details for Web of Science ID 000305106400028
View details for PubMedID 22524322
DNA-Enabled Self-Assembly of Plasmonic Nanoclusters
2011; 11 (11): 4859-4864
DNA nanotechnology provides a versatile foundation for the chemical assembly of nanostructures. Plasmonic nanoparticle assemblies are of particular interest because they can be tailored to exhibit a broad range of electromagnetic phenomena. In this Letter, we report the assembly of DNA-functionalized nanoparticles into heteropentamer clusters, which consist of a smaller gold sphere surrounded by a ring of four larger spheres. Magnetic and Fano-like resonances are observed in individual clusters. The DNA plays a dual role: it selectively assembles the clusters in solution and functions as an insulating spacer between the conductive nanoparticles. These particle assemblies can be generalized to a new class of DNA-enabled plasmonic heterostructures that comprise various active and passive materials and other forms of DNA scaffolding.
View details for DOI 10.1021/nl203194m
View details for Web of Science ID 000296674700062
View details for PubMedID 22007607
- Dipolar modeling and experimental demonstration of multi-beam plasmonic collimators NEW JOURNAL OF PHYSICS 2011; 13
- Terahertz plasmonics ELECTRONICS LETTERS 2010; 46 (26): S52–S57
Fano-like Interference in Self-Assembled Plasmonic Quadrumer Clusters
2010; 10 (11): 4680-4685
Assemblies of strongly interacting metallic nanoparticles are the basis for plasmonic nanostructure engineering. We demonstrate that clusters of four identical spherical particles self-assembled into a close-packed asymmetric quadrumer support strong Fano-like interference. This feature is highly sensitive to the polarization of the incident electric field due to orientation-dependent coupling between particles in the cluster. This structure demonstrates how careful design of self-assembled colloidal systems can lead to the creation of new plasmonic modes and the enabling of interference effects in plasmonic systems.
View details for DOI 10.1021/nl1029732
View details for Web of Science ID 000283907600065
View details for PubMedID 20923179
- GaAs/Al0.15Ga0.85As terahertz quantum cascade lasers with double-phonon resonant depopulation operating up to 172 K APPLIED PHYSICS LETTERS 2010; 97 (13)
Designer spoof surface plasmon structures collimate terahertz laser beams
2010; 9 (9): 730-735
Surface plasmons have found a broad range of applications in photonic devices at visible and near-infrared wavelengths. In contrast, longer-wavelength surface electromagnetic waves, known as Sommerfeld or Zenneck waves, are characterized by poor confinement to surfaces and are therefore difficult to control using conventional metallo-dielectric plasmonic structures. However, patterning the surface with subwavelength periodic features can markedly reduce the asymptotic surface plasmon frequency, leading to 'spoof' surface plasmons with subwavelength confinement at infrared wavelengths and beyond, which mimic surface plasmons at much shorter wavelengths. We demonstrate that by directly sculpting designer spoof surface plasmon structures that tailor the dispersion of terahertz surface plasmon polaritons on the highly doped semiconductor facets of terahertz quantum cascade lasers, the performance of the lasers can be markedly enhanced. Using a simple one-dimensional grating design, the beam divergence of the lasers was reduced from approximately 180 degrees to approximately 10 degrees, the directivity was improved by over 10 decibels and the power collection efficiency was increased by a factor of about six compared with the original unpatterned devices. We achieve these improvements without compromising high-temperature performance of the lasers.
View details for DOI 10.1038/NMAT2822
View details for Web of Science ID 000281178400023
View details for PubMedID 20693995
Fano Resonances in Plasmonic Nanoclusters: Geometrical and Chemical Tunability
2010; 10 (8): 3184–89
Clusters of plasmonic nanoparticles and nanostructures support Fano resonances. Here we show that this spectral feature, produced by the interference between bright and dark modes of the nanoparticle cluster, is strongly dependent upon both geometry and local dielectric environment. This permits a highly sensitive tunability of the Fano dip in both wavelength and amplitude by varying cluster dimensions, geometry, and relative size of the individual nanocluster components. Plasmonic nanoclusters show an unprecedented sensitivity to dielectric environment with a local surface plasmon resonance figure of merit of 5.7, the highest yet reported for localized surface plasmon resonance sensing in a finite nanostructure.
View details for DOI 10.1021/nl102108u
View details for Web of Science ID 000280728900076
View details for PubMedID 20698635
Self-Assembled Plasmonic Nanoparticle Clusters
2010; 328 (5982): 1135-1138
The self-assembly of colloids is an alternative to top-down processing that enables the fabrication of nanostructures. We show that self-assembled clusters of metal-dielectric spheres are the basis for nanophotonic structures. By tailoring the number and position of spheres in close-packed clusters, plasmon modes exhibiting strong magnetic and Fano-like resonances emerge. The use of identical spheres simplifies cluster assembly and facilitates the fabrication of highly symmetric structures. Dielectric spacers are used to tailor the interparticle spacing in these clusters to be approximately 2 nanometers. These types of chemically synthesized nanoparticle clusters can be generalized to other two- and three-dimensional structures and can serve as building blocks for new metamaterials.
View details for DOI 10.1126/science.1187949
View details for Web of Science ID 000278104700037
View details for PubMedID 20508125
Influence of excitation and collection geometry on the dark field spectra of individual plasmonic nanostructures
2010; 18 (3): 2579–87
Dark field microspectroscopy is the primary method for the study of plasmon modes of individual metallic nanostructures. Light from a plasmonic nanostructure typically scatters with a strong angular and modal dependence, resulting in significant variations in the observed spectral response depending on excitation and collection angle and polarization of incident light. Here we examine how spectrally dependent radiation patterns arising from an individual plasmonic nanoparticle, positioned on a dielectric substrate, affect the detection of its plasmon modes. Careful consideration of excitation and collection geometry is of critical concern in quantitative studies of the optical response of these nanoparticle systems.
View details for DOI 10.1364/OE.18.002579
View details for Web of Science ID 000274791200080
View details for PubMedID 20174087
- Layered superconductors as negative-refractive-index metamaterials PHYSICAL REVIEW B 2010; 81 (7)
- Plasmonics for Laser Beam Shaping IEEE TRANSACTIONS ON NANOTECHNOLOGY 2010; 9 (1): 11–29
Quantum cascade lasers with integrated plasmonic antenna-array collimators
2008; 16 (24): 19447–61
We demonstrated in simulations and experiments that by defining a properly designed two-dimensional metallic aperture-grating structure on the facet of quantum cascade lasers, a small beam divergence angle can be achieved in directions both perpendicular and parallel to the laser waveguide layers (denoted as theta perpendicular and theta parallel, respectively). Beam divergence angles as small as theta perpendicular=2.7 degrees and theta parallel=3.7 degrees have been demonstrated. This is a reduction by a factor of approximately 30 and approximately 10, respectively, compared to those of the original lasers emitting at a wavelength of 8.06 microm. The devices preserve good room temperature performance with output power as high as approximately 55% of that of the original unpatterned lasers. We studied in detail the trade-off between beam divergence and power throughput for the fabricated devices. We demonstrated plasmonic collimation for buried heterostructure lasers and ridge lasers; devices with different waveguide structures but with the same plasmonic collimator design showed similar performance. We also studied a device patterned with a "spider's web" pattern, which gives us insight into the distribution of surface plasmons on the laser facet.
View details for DOI 10.1364/OE.16.019447
View details for Web of Science ID 000261561900006
View details for PubMedID 19030032
- Small divergence edge-emitting semiconductor lasers with two-dimensional plasmonic collimators APPLIED PHYSICS LETTERS 2008; 93 (18)
- Small-divergence semiconductor lasers by plasmonic collimation NATURE PHOTONICS 2008; 2 (9): 564-570
Terahertz quantum cascade lasers with copper metal-metal waveguides operating up to 178 K
2008; 16 (5): 3242–48
We report terahertz quantum cascade lasers operating in pulsed mode at an emission frequency of 3 THz and up to a maximum temperature of 178 K. The improvement in the maximum operating temperature is achieved by using a three-quantum-well active region design with resonant-phonon depopulation and by utilizing copper, instead of gold, for the cladding material in the metal-metal waveguides.
View details for DOI 10.1364/OE.16.003242
View details for Web of Science ID 000254121300043
View details for PubMedID 18542411
- Wide-ridge metal-metal terahertz quantum cascade lasers with high-order lateral mode suppression APPLIED PHYSICS LETTERS 2008; 92 (3)
- Double-metal waveguide lambda similar or equal to 19 mu m quantum cascade lasers grown by metal organic vapour phase epitaxy ELECTRONICS LETTERS 2007; 43 (23): 1284–85
Plasmonic nanoclusters: a path towards negative-index metafluids
2007; 15 (21): 14129–45
We introduce the concept of metafluids-liquid metamaterials based on clusters of metallic nanoparticles which we will term Artificial Plasmonic Molecules (APMs). APMs comprising four nanoparticles in a tetrahedral arrangement have isotropic electric and magnetic responses and are analyzed using the plasmon hybridization (PH) method, an electrostatic eigenvalue equation, and vectorial finite element frequency domain (FEFD) electromagnetic simulations. With the aid of group theory, we identify the resonances that provide the strongest electric and magnetic response and study them as a function of separation between spherical nanoparticles. It is demonstrated that a colloidal solution of plasmonic tetrahedral nanoclusters can act as an optical medium with very large, small, or even negative effective permittivity, epsilon(eff), and substantial effective magnetic susceptibility, Chi(eff) = mu(eff) -1, in the visible or near infrared bands. We suggest paths for increasing the magnetic response, decreasing the damping, and developing a metafluid with simultaneously negative epsilon(eff) and mu(eff).
View details for DOI 10.1364/OE.15.014129
View details for Web of Science ID 000251223100071
View details for PubMedID 19550686
- Single-mode laser action in quantum cascade lasers with spiral-shaped chaotic resonators APPLIED PHYSICS LETTERS 2007; 91 (13)
Surface emitting terahertz quantum cascade laser with a double-metal waveguide
2006; 14 (24): 11672–80
We investigate the implementation of surface emission via a second order grating in terahertz quantum cascade lasers with double-metal waveguides. Absorbing edge structures are designed to enforce anti-reflecting boundary conditions, which ensure distributed feedback in the cavity. The grating duty cycle is chosen in order to maximize slope efficiency. Fabricated devices demonstrate surface emission output powers that are comparable to those measured from edge-emitting double metal waveguide structures without gratings. The slope efficiency of surface emitting lasers is twice that of double-metal edge emitting structures. Surface emitting lasers show single mode behavior, with a beam divergence of approximately six degrees.
View details for DOI 10.1364/OE.14.011672
View details for Web of Science ID 000242325700021
View details for PubMedID 19529587