Nanophotonics ,
nano-optics ,
materials for optical and opto-electronic devices ,
Metasurfaces and metamaterials, including hyperbolic metamaterials ,
Near-field microscopy, s-SNOM ,
Hot electron photoemission
We investigate the tunability of metasurface resonances through an electro-optic mechanism based on the Pockels effect. By integrating an electro-optic material with a designed multi-resonant nanoantenna array, we demonstrate control and wide-range tunability of the metasurface resonances. The applied electric field enables dynamic modulation of the optical properties, allowing for the adjustment of the metasurface response. This approach offers a versatile platform for developing tunable photonic devices, with potential applications in optical communication and sensing.
Refractory materials, known for their exceptional thermal stability and robustness in extreme high-temperature conditions, have gained attention in recent years. These materials, including high-melting-point metals, such as titanium, tungsten, chromium, molybdenum, and tantalum, are ideal for applications demanding high-temperature resistance and durability. Here, we present the design of polyatomic refractory metastructures capable of achieving perfect absorptivity as well as near-unity emissivity. We design arrays of clustered refractory-metal nanodisks (tungsten and titanium) coupled to a same-metal backplane with dielectric spacers between the nanodisks and the backplane. Similarly, the spacer is made of refractory materials, silicon nitride and titania, respectively. By tuning the thickness of this spacer, our polyatomic metastructures achieve near-perfect absorptivity and nearunity emissivity across visible and near-infrared spectral ranges (0.4−2 μm). This work highlights the potential of refractory materials for high-performance absorbers and thermal emitters that are capable of withstanding extreme temperatures without compromising performance, thus paving the way for advancements in energy applications and high-temperature sensing.
A periodic array of nanoparticles scatters electromagnetic waves in different diffraction orders, and such periodic arrangements of nanoparticles result in significant field enhancements compared to a single nanoparticle. We investigate multipole Mie resonances in MXene antennas, uncovering absorption enhancement, reflection suppression, and phase variation through analytical models, simulations, and experiments. We study lattice resonances of lossy materials, such as transition metals nickel, titanium, and tungsten, as well as metalloid germanium. We study the impact of substrate and superstrate on Rayleigh anomaly dependency, showing that the resonance peak shifts according to the surrounding medium refractive index. Exploiting these resonances can enable metasurfaces for efficient, broad-spectrum light absorption in large-scale sensing, photodetectors, and energy harvesting applications.
Efficiently confining light at the nanoscale within optical antennas facilitates its precise manipulation and enables the creation of nanostructures with innovative photonic functionalities. We present results of utilizing the iron pyrite antennas to precisely engineer the emissivity of mid-infrared thermal emitters. We also explore multipole Mie resonances within arrays of transition metal carbides and nitrides, specifically focusing on MXene materials. This engineering is achieved by strategically manipulating multipole resonance effects and non-radiative dissipation processes.
Nanoparticles of high-refractive-index materials like semiconductors enable strong confinement of light at the subwavelength scale because of the strong reflection from material boundaries and excitation of Mie resonances within the nanoscale-size particle. Recently, transition metal dichalcogenides (TMDCs) from the family of van der Waals layered materials have been shown to exhibit tailorable optical properties along with strong nonlinearity, high refractive index, and anisotropy originating from layered structure of the material. We envision that TMDCs are a promising material platform for designing metasurfaces and ultra-thin optical elements: these van der Waals materials show a strong spectral response on light excitations in visible and near-infrared ranges, and nanostructure characteristics can be controlled by nanoantenna dimensions and their arrangement [1]. Here, we investigate a periodic array of disk-shaped nanoantennas made of a TMDC material, tungsten disulfide, placed on top of a thin intermediate layer of high-index material such as silicon and low-index oxide substrate. Planar photonics with efficient subwavelength light control can be designed based on transdimensional lattices that operate in the translational regime between 2D and 3D [2]. Such transdimensional lattices include 3D-engineered nanoantennas supporting multipole Mie resonances and arranged in the 2D arrays with collective effects. The periodic arrangement of the nanoantenna array facilitates the strong coupling of light into the thin high-index layer. We show that the nanostructure resonances and coupling between nanoantennas and substrate in TMDC disk-shaped nanoantenna array can be controlled by the variation in silicon layer thickness and have a dependence on the presence of index-match superstrate cover.
Nanostructures of high-refractive-index materials such as semiconductors can support Mie resonances due to confinement of light at the nanoscale and have been investigated both theoretically and experimentally for a range of nanophotonic applications. Transition metal dichalcogenides (TMDCs) from the family of van der Waals layered materials have high refractive index and strong optical anisotropy. Recently, it has been shown that due to the tunable optical properties of TMDCs, they possess enormous potential for designing metasurfaces and various ultra-thin optical elements. Periodically arranged nanoantennas of van der Waals layered materials can exhibit strong spectral resonances in the visible and near-infrared frequencies. In this work, we investigate the scattering and transmission properties of a periodic array of disk-shaped nanoantennas of a TMDC material, tungsten disulfide WS2. We show the dependence of the reflection and transmission spectra from the TMDC nanoantenna array and investigate the spectral features for various thicknesses of the supporting layers positioned between the antenna array and glass substrate.
Planar optical elements with efficient light control at the nanoscale can be designed based on transdimensional photonic lattices that include 3D-engineered nanoantennas supporting multipole Mie resonances and arranged in the 2D arrays to harness collective effects in the nanostructure. Periodic arrays of nanoparticles have gained special attention because of extraordinary lattice resonances in proximity to the wavelength of diffraction, the so-called wavelength of Rayleigh anomaly. We show the possibility of exciting strong periodic nanoparticle resonances not only in plasmonic arrays but also in the nanoparticle lattices with the high refractive index. We perform the calculation for tungsten disulfides, which belongs to the families of van der Waals materials and transition metal dichalcogenides. Nanoparticles arrangement in a periodic array plays a crucial role resulting in collective array resonances and pronounces features in spectra.
Optical antennas made out of van der Waals material with naturally occurring hyperbolic dispersion is a promising alternative to plasmonic and high-refractive-index dielectric structures in the practical realization of nanoscale photonic elements and optical components. Here we show that antenna made out of hexagonal boron nitride (hBN) possesses different resonances enabled by the supporting high-k modes and their reflection from the antenna boundaries. Multipole resonances cause the decrease in the reflection from antenna array to zero, which can be ascribed to resonant Kerker effect satisfying generalized zero back-scattering condition for particles in the array. Reflection and transmission through the van der Waals heterostructure with hBN antennas array can be tailored and actively switched by tuning optical properties of two-dimensional materials. Transdimensional photonic lattices consisting of resonant hBN antennas in the engineered periodic arrays have great potential to serve as functional elements in ultra-thin optical components and photonic devices.
The effective multipole decomposition approach is applied to study the optical features of the silicon metasurface in the near-infrared. The spectral regions of perfect transmission and reflection have been analyzed using the Cartesian multipole decomposition. It is shown that transmission peaks appear due to the mutual interaction of multipole moments up to the third order, while reflection peaks are due to the dominant contribution of one of the multipole moments. The results of this work can be broadly applied to design novel metasurfaces, sensors, and optical filters.
High-refractive-index (HRI) dielectric metasurfaces have attracted a lot of attention recently due to their advantages of low non-radiative losses and high melting temperatures. Silicon is one of feasible HRI materials that has been widely used in solar cells, photonic waveguides, and photon detectors. However, the band-gap ~ 1 eV makes the quantum efficiency of silicon low at near-infrared (NIR) wavelengths. In this work, a high absorptance device is proposed and realized by using amorphous silicon nanoantenna arrays (a-Si NA arrays) that suppress backward and forward scattering with engineered lattice resonance with Kerker effect. The overlap of electric dipole and magnetic dipole resonances is experimentally demonstrated. The absorptance of a-Si NA arrays increases 3-fold in the near-infrared (NIR) range in comparison to unpatterned silicon films. Nonradiating a-Si NA arrays can achieve high absorptance with a small resonance bandwidth (Q = 11.89) at wavelength 785 nm.
Two-dimensional transition metal dichalcogenide (2D-TMD) semiconductors are new class of functional materials with a great promise for optoelectronics. Despite their atomic thickness, they strongly interact with light. This allows 2D-TMDs to become suitable converters of photons into useful electric charges in heterostructures involving 2D-TMDs and metallic nano-plasmonics or semiconductor quantum dots (QDs). In this talk, I will illustrate how femtosecond pump-probe spectroscopy can reveal a sub-45 fs charge transfer at a 2D/QDs heterostructure composed of tungsten disulfide monolayers (2D-WS2) and a single layer of cadmium selenide (CdSe)/zinc sulfide (ZnS) core/shell 0D-QDs. In another heterostructure involving 2D-TMDs and plasmonics, I will describe how plasmons of an array of aluminum (Al) nanoantennas are excited indirectly via energy transfer from photoexcited exciton of 2D-WS2 semiconductor. In particular, femtosecond spectroscopy measurements indicated that the lifetime of the resulting plasmon-induced hot electrons in the Al array continue as long as that of the 2D-WS2 excitons. Conversely, the presence of these excited plasmons almost triples the lifetime of the 2D-WS2 excitons from ~15 to ~44 ps. This exciton-plasmon coupling enabled by such hybrid nanostructures may open new opportunities for optoelectronic applications.
This research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. Synthesis of the two-dimensional materials was supported by the Materials Science and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy.
Photoelectric properties of metamaterials comprising asymmetrically shaped, similarly oriented metallic nanoparticles embedded in a homogeneous semiconductor matrix are theoretically and numerically studied. The asymmetric shape of the nanoparticles is found to result in the existence of a preferred direction where “hot” photoelectrons are emitted from the nanoparticle surface under the action of the localized plasmonic resonance excited in the nanoparticles. The resulting directional photocurrent flow occurring when nanoparticles are uniformly illuminated by a homogeneous plane wave is the direct analogy of the photogalvanic effect known to exist in naturally occurring non-centrosymmetric media. This plasmonic bulk photovoltaic effect is intermediate between the inner photoelectric effect in bulk media and the outer photoelectric effect at macroscopic interfaces. The results obtained are valuable for characterizing photoemission and photoconductive properties of plasmonic nanostructures. They can find many uses for photodetection-related and photovoltaic applications.
We focus on plasmonic modulators with a gain core to be implemented as active nanodevices in photonic integrated circuits. In particular, we analyze metal–semiconductor–metal (MSM) waveguides with InGaAsP-based active material layers. A MSM waveguide enables high field localization and therefore high modulation speed. The modulation is achieved by changing the gain of the core that results in different transmittance through the waveguide. Dependences on the waveguide core size and gain values of various active materials are studied. The effective propagation constants in the MSM waveguides are calculated numerically. We optimize the structure by considering thin metal layers. A thin single metal layer supports an asymmetric mode with a high propagation constant. Implementing such layers as the waveguide claddings allows to achieve several times higher effective indices than in the case of a waveguide with thick (>50 nm) metal layers. In turn, the high effective index leads to enhanced modulation speed. We show that a MSM waveguide with the electrical current control of the gain incorporates compactness and deep modulation along with a reasonable level of transmittance.
A multilayered waveguide, which supports surface plasmon polaritons, is considered as an absorption modulator. The
waveguide core consists of a silicon nitride layer and ultrathin layer with the varied carrier density embedded between
two silver plates, which also serve as electrodes. Under applying voltage to electrodes the carrier density in the
transparent conducting oxide layer (we study indium tin oxide - ITO) changes according to the Thomas-Fermi screening
theory. We employ analytical solutions for a multilayered system as well as numerical simulations with the commercial
software package CST Microwave Studio in the frequency domain. We explore different permittivities of the ITO layer,
which can be achieved by utilizing different anneal conditions. To increase transmittance and enhance modulation depth
or efficiency, we propose to pattern the continuous active layer. Dependence from the pattern size and filling factor of
the active material are analyzed for tuned permittivity of the ITO layer. Direct simulation of the device functionality
validates optimization design.
We explore structures composed of two gratings with subwavelength slits in silver films. We study the extraordinary
transmission of electromagnetic wave in these structures and the conditions at which the transmittance is equal to zero.
Dependences on various geometric parameters are analyzed. We show that the zero of transmittance i.e. the suppression
of the extraordinary transmission is observed at wavelength that corresponds to the excitation of surface plasmon
polariton in a gap between two gratings with subwavelength slits. We also research structures composed of arrays of slits
in thick films set close to continuous thin films. We reveal that an efficiency of the transmission of the slit mode of the
grating into the thin film is greater than an efficiency of the transmission of plane wave into the same film. The
investigations are performed through numerical simulations with the Fourier modal method.
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