Polarization-dependent Optical Properties Research Articles

Lizardite–h-BN heterostructures—Application of clay minerals in technology

Graphene has been a subject of great interest not only due to its fascinating properties but also for being the pioneer among 2D van der Waals (vdW) materials. Hexagonal boron nitride, an isomorph of graphene and a wide gap insulator, is commonly referred to as white graphene. The combination of the insulating hexagonal boron nitride (h-BN) with other crystals to form heterostructures provide a path for engineering and manipulating new physics and device properties. In this work, we investigate the vdW heterostructures formed by assembling h-BN and lizardite, a clay-mineral that is abundant in nature and represents the most stable polymorph of the serpentine family. The optoelectronic properties of three distinct heterostructures are presented to discern the characteristics of the systems. We observe that unlike lizardite and h-BN which are insulators, all the three heterostructures exhibit a semiconducting nature. The direct gap of the heterostructure in which two h-BN sheets are simultaneously placed above and below the octahedral and tetrahedral layers also makes it relevant for optoelectronic devices. Additionally, unlike lizardite, the heterostructures demonstrate a polarization-dependent optical properties. The study of the assembled structures combining the clay-mineral with h-BN not only widens the spectrum of vdW heterostructures but also explores their potential within the context of the serpentine family.

Analysis of lizardite-graphene van der Waals heterostructures: A DFT study

Graphene has garnered significant attention not just for its intriguing properties but also for its role as a pioneer among 2D van der Waals materials. The amalgamation of graphene with other crystals to form heterostructures provide a path for engineering and manipulating new physics and device properties. In this work, we investigate the vdW heterostructures formed by assembling graphene and the clay-mineral lizardite, a clay-mineral that is abundant in nature and represents the most stable polymorph of the serpentine family. The electronic and optical properties of three distinct heterostructures are presented to discern the characteristics of the systems. We observe that all the three heterostructures exhibit a metallic nature. Yet, computations using the Heyd-Scuseria-Ernzerhof hybrid functional (HSE) approach suggest the emergence of an energy gap, unveiling the semiconductor characteristics of the heterostructures. Additionally, unlike lizardite, the heterostructures demonstrate polarization-dependent optical properties. The study of the assembled structures combining the clay-mineral with graphene not only widens the spectrum of vdW heterostructures but also explores their potential within the context of the serpentine family.

Polarization-dependent nonlinear optical properties of the epsilon-near-zero hybrid metasurface

Polarization-dependent nonlinear optical properties of the epsilon-near-zero hybrid metasurface

Chiral Plasmonic Pinwheels Exhibit Orientation-Independent Linear Differential Scattering under Asymmetric Illumination.

Plasmonic nanoantennas have considerably stronger polarization-dependent optical properties than their molecular counterparts, inspiring photonic platforms for enhancing molecular dichroism and providing fundamental insight into light-matter interactions. One such insight is that even achiral nanoparticles can yield strong optical activity when they are asymmetrically illuminated from a single oblique angle instead of evenly illuminated. This effect, called extrinsic chirality, results from the overall chirality of the experimental geometry and strongly depends on the orientation of the incident light. Although extrinsic chirality has been well-characterized, an analogous effect involving linear polarization sensitivity has not yet been discussed. In this study, we investigate the differential scattering of rotationally symmetric chiral plasmonic pinwheels when asymmetrically irradiated with linearly polarized light. Despite their high rotational symmetry, we observe substantial linear differential scattering that is maintained over all pinwheel orientations. We demonstrate that this orientation-independent linear differential scattering arises from the broken mirror and rotational symmetries of our overall experimental geometry. Our results underscore the necessity of considering both the rotational symmetry of the nanoantenna and the experimental setup, including illumination direction and angle, when performing plasmon-enhanced chiroptical characterizations. Our results demonstrate spectroscopic signatures of an effect analogous to extrinsic chirality for linear polarizations.

Polarization-dependent photoluminescence properties of fab-compatible nanowire-based nanophotonic structures

Semiconductor nanowires show great potential for controlling light–matter interactions. Moreover, their polarization-dependent optical properties, primarily enabled by their dielectric mismatch, are a significant requisite for a plethora of emerging applications spanning from polarized photodetection to quantum photonics and quantum communication. Herein, we study the polarization dependence of photoluminescence (PL) properties from fab-compatible nanophotonic structures, comprising arrays of ultrathin (20 nm) silicon carbide nanowires (NWs) doped with oxygen and erbium ions. Polarization-resolved PL studies demonstrate a significant excitation polarization anisotropy (∼0.7) of the visible NW PL for light polarized parallel and perpendicular to the NWs' long axis. This anisotropic behavior agrees with our simulations and with the classical dielectric contrast model and is consistent across the investigated periodicity range of the NW arrays. Furthermore, the effect of this anisotropy on the NW carrier dynamics is explored through power-dependence and transient PL measurements. We have observed a faster carrier lifetime for light polarized parallel to the NWs than the perpendicular polarization. Finally, we demonstrate a translation of this polarization dependence to the technologically significant erbium-induced 1540 nm emission from the erbium centers in the NW arrays. The ability to engineer emission polarization and placement of these centers in the NW array offers a promising platform for emission enhancement of telecom emitters through effective coupling to optical nanocavities for applications in chip-scale photonics and quantum photonics.

Large-Area Fabrication of Complex Nanohole Arrays with Highly Tunable Plasmonic Properties.

By combining nanosphere lithography with oblique angle deposition, large-area asymmetric compound Ag nanohole arrays with nanorods inside the hole were patterned on substrates. The technique enabled the production of complex nanohole arrays with controlled hole diameter, thickness, and rod structure inside the hole. The compound asymmetric Ag nanohole structures showed strong polarization-dependent optical properties, and a new extraordinary optical transmission (EOT) mode with tunable resonance wavelength at the near-IR region was observed. The transmission at the new EOT wavelength region can increase from 27% of nanohole to 69% of the compound structure, and these structures can achieve a refractive index sensitivity as high as 847 nm RIU-1. The tunable EOT wavelength and strong polarization-dependent optical properties make the structure ideal for ultrathin optical filters, polarizers, surface-enhanced spectroscopies, etc.

Visualizing Orbital Content of Electronic Bands in Anisotropic 2D Semiconducting ReSe2.

Many properties of layered materials change as they are thinned from their bulk forms down to single layers, with examples including indirect-to-direct band gap transition in 2H semiconducting transition metal dichalcogenides as well as thickness-dependent changes in the valence band structure in post-transition-metal monochalcogenides and black phosphorus. Here, we use angle-resolved photoemission spectroscopy to study the electronic band structure of monolayer ReSe2, a semiconductor with a distorted 1T structure and in-plane anisotropy. By changing the polarization of incoming photons, we demonstrate that for ReSe2, in contrast to the 2H materials, the out-of-plane transition metal dz2 and chalcogen pz orbitals do not contribute significantly to the top of the valence band, which explains the reported weak changes in the electronic structure of this compound as a function of layer number. We estimate a band gap of 1.7 eV in pristine ReSe2 using scanning tunneling spectroscopy and explore the implications on the gap following surface doping with potassium. A lower bound of 1.4 eV is estimated for the gap in the fully doped case, suggesting that doping-dependent many-body effects significantly affect the electronic properties of ReSe2. Our results, supported by density functional theory calculations, provide insight into the mechanisms behind polarization-dependent optical properties of rhenium dichalcogenides and highlight their place among two-dimensional crystals.

Coupling between plasmonic nanohole array and nanorod array: the emerging of a new extraordinary optical transmission mode and epsilon-near-zero property

The compound Ag nanohole structures with an Ag nanorod in the middle of an Ag nanohole are investigated by finite-difference-time-domain calculations. The structure shows strong polarization-dependent optical properties. A new extraordinary optical transmission (EOT) mode is observed when the polarization direction is aligned with the long axis of the nanorods, and its resonance wavelength red-shifts exponentially with the nanorod length. Around this resonance wavelength, the real part of the effective permittivity also becomes zero, demonstrating the epsilon-near-zero (ENZ) property. The new EOT mode is found to be the result of the enhanced local radiation of the nanorods as well as the electromagnetic coupling to the nanoholes to produce the enhanced transmission. The tunable resonance wavelength, EOT, strong near-field enhancement, and ENZ properties make the structure ideal for many potential applications, such as ultrathin optical filter, polarizers, surface-enhanced spectroscopies, etc.

Polarization-Dependent Optical Properties and Optoelectronic Devices of 2D Materials.

The development of optoelectronic devices requires breakthroughs in new material systems and novel device mechanisms, and the demand recently changes from the detection of signal intensity and responsivity to the exploration of sensitivity of polarized state information. Two-dimensional (2D) materials are a rich family exhibiting diverse physical and electronic properties for polarization device applications, including anisotropic materials, valleytronic materials, and other hybrid heterostructures. In this review, we first review the polarized-light-dependent physical mechanism in 2D materials, then present detailed descriptions in optical and optoelectronic properties, involving Raman shift, optical absorption, and light emission and functional optoelectronic devices. Finally, a comment is made on future developments and challenges. The plethora of 2D materials and their heterostructures offers the promise of polarization-dependent scientific discovery and optoelectronic device application.

Antimonene/bismuthene vertical Van-der Waals heterostructure: A computational study

In this paper, the structural, electronic, mechanical and optical properties of antimonene-bismuthene Van-der Waals heterostructure (Sb-Bi HS) were calculated based on the first principle density functional theory. We explored different stacks of Sb-Bi HS to find the most and the least stable staking for this heterostructure. At the GGA level of theory, the most stable model is a semiconductor with an indirect band gap of 159 meV. However, when the spin-orbit (SO) interaction is considered, the VBM and CBM touch the Fermi level and the HS becomes a semimetal. Our results also show that the electronic properties of the HS are robust against the external electric field and biaxial strain. Young modulus was calculated as 64.3N/M which predicts this HS as a resistant material against being stretched or compressed. The calculated optical properties, similar to monolayer antimonene, are completely dependent on the polarization of incident light and differ when parallel or perpendicular polarization is considered. Moreover, the absorption coefficient for perpendicular polarization in the visible region is significantly increased in comparison with the monolayer antimonene. High structural stability, electronic and mechanical robustness against electric field and strain, along with polarization-dependent optical properties of this HS, promise for its applications in beam splitters and nano-scale mirrors.

Study of Oxidation and Polarization-Dependent Optical Properties of Environmentally Stable Layered GaTe Using a Novel Passivation Approach.

Emerging two-dimensional gallium chalcogenides, such as gallium telluride (GaTe), are considered promising layered semiconductors that can serve as vital building blocks towards the implementation of nanodevices in the fields of nanoelectronics, optoelectronics, and quantum photonics. However, oxidation-induced electronic, structural, and optical changes observed in ambient-exposed gallium chalcogenides need to be further investigated and addressed. Herein, we report on the thickness-dependent effect of air exposure on the Raman and photoluminescence (PL) properties of GaTe flakes, with thicknesses spanning in the range of a few layers to 100 nm. We have developed a novel chemical passivation that results in complete encapsulation of the as-exfoliated GaTe flakes in ultrathin hydrogen–silsesquioxane (HSQ) film. A combination of correlation and comparison of Raman and PL studies reveal that the HSQ-capped GaTe flakes are effectively protected from oxidation in air ambient over the studied-period of one year, and thus, preserving their structural and optical characteristics. This contrasts with the behavior of uncapped GaTe, where we observe a significant reduction of the GaTe-related PL (~100×) and Raman (~4×) peak intensities for the few-layered flakes over a period of few days. The time-evolution of the Raman spectra in uncapped GaTe is accompanied by the appearance of two new prominent broad peaks at ~130 cm−1 and ~146 cm−1, which are attributed to the formation of polycrystalline tellurium, due to oxidation of ambient-exposed GaTe. Furthermore, and by leveraging this novel passivation, we were able to explore the optical anisotropy of HSQ-capped GaTe flakes. This is caused by the one-dimensional-like nature of the GaTe layer, as the layer comprises Ga–Ga chains extending along the b-axis direction. In concurrence with high-resolution transmission electron microscopy analysis, polarization-dependent PL spectroscopy was used to identify the b-axis crystal direction in HSQ-capped GaTe flakes with various thicknesses over a range of wavelengths (458 nm–633 nm). Thus, our novel surface-passivation offers a new approach to explore and reveal the physical properties of the layered GaTe, with the potential of fabricating reliable polarization-dependent nanophotonics with structural and optical stability.

Single-particle Correlation Study: Polarization-dependent Differential Interference Contrast Imaging of Two-dimensional Gold Nanoplates

Questions surrounding the optical properties of two-dimensional (2D) triangular single gold nanoplates (AuNPs) remain largely unanswered. Herein, a scanning-electron microscopy-correlated single-particle study was conducted to identify polarization-dependent optical properties of AuNPs under dark-field (DF) and differential interference contrast (DIC) microscopy. AuNPs with an aspect ratio of ∼3 showed a single broad DF scattering spectrum without separation of the two dipole and quadrupole resonance modes present in 2D AuNPs. Polarization-sensitive interference properties of the individual AuNPs were revealed through periodic changes in the intensities and types of DIC images obtained. A dipole resonance mode was found to mainly contribute to the polarization-sensitive interference properties of AuNPs. Furthermore, DIC polarization anisotropy allowed us to track the real-time orientation of a dipole resonance mode of a AuNP rotating on a live cell membrane.

Mechanotunable Surface Lattice Resonances in the Visible Optical Range by Soft Lithography Templates and Directed Self-Assembly.

We demonstrate a novel colloidal self-assembly approach toward obtaining mechanically tunable, cost-efficient, and low-loss plasmonic nanostructures that show pronounced optical anisotropy upon mechanical deformation. Soft lithography and template-assisted colloidal self-assembly are used to fabricate a stretchable periodic square lattice of gold nanoparticles on macroscopic areas. We stress the impact of particle size distribution on the resulting optical properties. To this end, lattices of narrowly distributed particles (∼2% standard deviation in diameter) are compared with those composed of polydisperse ones (∼14% standard deviation). The enhanced particle quality sharpens the collective surface lattice resonances by 40% to achieve a full width at half-maximum as low as 16 nm. This high optical quality approaches the theoretical limit for this system, as revealed by electromagnetic simulations. One hundred stretching cycles demonstrate a reversible transformation from a square to a rectangular lattice, accompanied by polarization-dependent optical properties. On the basis of these findings we envisage the potential applications as strain sensors and mechanically tunable filters.

Stimuli-Responsive DNA-Linked Nanoparticle Arrays as Programmable Surfaces

Self- and directed-assembly approaches have enabled precise control over the composition and geometry of 2D and 3D nanoparticle constructs. However, the resulting structures are typically static, providing only a single structural arrangement of the nanoparticle building blocks. In this work, the power of DNA-linked nanoparticle assembly is coupled to a grayscale patterning technique to create programmable surfaces for assembly and thermally activated reorganization of gold nanoparticle arrays. Direct grayscale patterning of DNA monolayers by electron-beam lithography (DNA-EBL) enables the production of surfaces with nanometer-scale control over the density of functional DNA. This enables tuning of the particle-surface interactions with single-nanoparticle resolution and without the need for a physical template as employed in most directed assembly methods. This technique is applied on suspended membrane structures to achieve high-resolution assembly of 2D nanoparticle arrays with highly mutable architectures. Gold nanorods assembled on grayscale-patterned surfaces exhibit temperature-dependent configurations and ordering behavior that result in tunable polarization-dependent optical properties. In addition, spherical gold particles assembled from a bimodal suspension produce arrays with temperature-dependent configurations of small and large particles. These results have important implications for the design and fabrication of reconfigurable nanoparticle arrays for application as structurally tunable optical metasurfaces.

Elucidating the contribution of dipole resonance mode to polarization-dependent optical properties in single triangular gold nanoplates

We synthesized triangular gold nanoplates (AuNPs) through a one-pot seedless growth method and characterized their optical properties under dark-field (DF) microscopy at the single particle level. We experimentally demonstrated that the dipole resonance is not completely separated from the quadrupole resonance for single AuNPs with an aspect ratio of ∼5. We further used a defocused orientation and position imaging technique to visualize the spatial scattering field distributions from dipole and quadrupole modes. Their optical properties were mainly dominated by the dipole resonance, which resulted in the polarization-dependent, periodic DF defocused images and intensities of single AuNPs.

Extrinsic polarization-controlled optical anisotropy in plasmon-black phosphorus coupled system

Two-dimensional black phosphorus (BP) has drawn extensive research interest due to its promising anisotropic photonic and electronic properties. Here, we study anisotropic optical absorption and photoresponse of exfoliated BP flakes at visible frequencies. We enhance this intrinsic optical anisotropy in BP flakes by coupling plasmonic rectangular nanopatch arrays that support localized surface plasmon resonances. In particular, by combining extrinsic anisotropic plasmonic nanostructures lithographically aligned with intrinsically anisotropic BP flakes, we demonstrate for the first time a combined anisotropic plasmonic-semiconductor coupling that provides significant control over the polarization-dependent optical properties of the plasmon-BP hybrid material system, enhancing polarization-sensitive responses to a larger degree. This hybrid material system not only unveils the plasmon-enhanced mechanisms in BP, but also provides novel controllable functionalities in optoelectronic device applications involving polarization-sensitive optical and electrical responses.

Fabrication of Periodic Gold Nanocup Arrays Using Colloidal Lithography.

Within recent years, the field of plasmonics has exploded as researchers have demonstrated exciting applications related to chemical and optical sensing in combination with new nanofabrication techniques. A plasmon is a quantum of charge density oscillation that lends nanoscale metals such as gold and silver unique optical properties. In particular, gold and silver nanoparticles exhibit localized surface plasmon resonances-collective charge density oscillations on the surface of the nanoparticle-in the visible spectrum. Here, we focus on the fabrication of periodic arrays of anisotropic plasmonic nanostructures. These half-shell (or nanocup) structures can exhibit additional unique light-bending and polarization-dependent optical properties that simple isotropic nanostructures cannot. Researchers are interested in the fabrication of periodic arrays of nanocups for a wide variety of applications such as low-cost optical devices, surface-enhanced Raman scattering, and tamper indication. We present a scalable technique based on colloidal lithography in which it is possible to easily fabricate large periodic arrays of nanocups using spin-coating and self-assembled commercially available polymeric nanospheres. Electron microscopy and optical spectroscopy from the visible to near-infrared (near-IR) was performed to confirm successful nanocup fabrication. We conclude with a demonstration of the transfer of nanocups to a flexible, conformal adhesive film.

Progress in functional 2D ordered arrays based on monolayer colloidal crystals

Two-dimensionally (2D) ordered micro- and nanostructure arrays have attracted considerable attention because of their novel and/or enhanced properties arising from the patterned structures. Monolayer colloidal crystals (MCCs) assembled from colloidal spheres have been widely employed for the controllable fabrication of a variety of 2D ordered micro- and nanostructure arrays because this strategy has been demonstrated to be facile, inexpensive, efficient, and versatile. This review paper summarizes the recent progress in the functional 2D ordered arrays based on MCCs, including their applications in 2D photonic crystal sensors, plasmonic nanostructure arrays, solar energy conversion devices, optic and optoelectronic devices, surface wetting and adhesion, biomedical materials, etc. Particular attention is paid to our recent advances in the controlled fabrication and applications of ZnS nanobowl arrays, heterostructured Ag2S-Ag nanobowl arrays, heterostructured TiO2 nanorod@nanobowl arrays, and single crystal calcite microlens arrays. Firstly, large-area ZnS nanobowl arrays with a monolayer inverse opal structure were synthesized facilely by nanosphere lithography at solution surface through direct solution deposition. Owing to the 2D periodic structure of the hexagonally ordered nanobowl arrays and the high refractive index of ZnS, the obtained ZnS nanobowl arrays showed intensive structural colors and tunable photonic band-gap properties. The as-prepared ZnS nanobowl arrays can be used as a sensitive 2D photonic crystal sensor for fast detection of organic solvents and for visual oil sensing. After surface functionalization, the ZnS nanobowl arrays can be used as an effective 2D photonic crystal biosensor for sensitive detection of avidin molecules. Secondly, unique Ag2S-Ag heterostructured nanobowl arrays consisting of Ag2S nanonets lying on Ag nanobowl arrays were fabricated by two-step nanosphere lithography at the gas-liquid interface. The heterostructured nanobowl arrays exhibited effective resistance switching behaviors, thus showing the potential application in electronic switches and memory devices. Meanwhile, the heterostructured nanobowl arrays exhibited enhanced photocatalytic activity owing to their unique structure when they were used as a photoanode for photoelectrochemical (PEC) water splitting. This result may open up new possibilities for facile and rational synthesis of large-area ordered arrays of semiconductor-noble metal hybrid nanostructures with multifunctions. Thirdly, heterostructured TiO2 nanorod@ nanobowl (NR@NB) arrays consisting of rutile TiO2 nanorods grown on the inner surface of arrayed anatase TiO2 nanobowls were designed and fabricated as a new type of photoanodes for PEC water splitting. The unique heterostructures with a hierarchical architecture were readily fabricated by interfacial nanosphere lithography followed by hydrothermal growth. The heterostructured TiO2 NR@NB arrays on the FTO substrate showed significantly enhanced PEC properties for water splitting because they possessed multiple scattering centers, increased electrolyte accessible surface area, and beneficial anatase-rutile heterojunction. This work may open new avenues towards building complex semiconductor nanostructures with desirable architectures for efficient harvesting and utilization of solar energy. Lastly, unprecedented concave microlens arrays (MLAs) made of calcite single crystals with tunable crystal orientations were readily fabricated by MCC-assisted epitaxial growth in solution without additives under ambient conditions. Calcite single crystal MLAs with two different crystallographic orientations, namely, calcite (104) microlens arrays and calcite (001) microlens arrays, were produced using selected calcite substrates, respectively. While the non-birefringent calcite (001) microlens array showed excellent imaging performance like brittlestar’s microlens arrays, the birefringent calcite (104) microlens array exhibited remarkable polarization-dependent optical properties. In general, this work may open new pathways towards the fabrication of micropatterned single crystals for various optical applications and shed light on fundamental mechanisms in biomineralization. After a brief summary of the recent progress in this research field, the challenges and perspectives for future research are addressed.

External tunability of optical filter in symmetric one-dimensional photonic crystals containing ferroelectric and ITO material defect

This study theoretically investigates the properties of the defect mode with external controllability in a symmetric 1D defective photonic crystal (1DDPC) composed of a ferroelectric layer and two pairs of thin Indium–tin oxide (ITO) as defect layers. The tunability of defect mode was investigated, as a function of the electric field alongside the incident angle. The results reveal that the defect mode wavelength can be tuned by variations of the electric field and the incident angle as well Because of the polarization-dependent optical properties of ferroelectric layer, the shift trend in the defect mode is shown to also rely on the polarization. The proposed structure can be good candidate in designing an externally tunable optical filter with potential applications in electro-optical devices.

Orientation-and polarization-dependent optical properties of the single Ag nanowire/glass substrate system excited by the evanescent wave.

As an important plasmon one-dimensional material, orientation- and polarization-dependent properties of single Ag nanowires/glass substrate system are investigated by a powerful platform consisting of evanescent wave excitation, near-/far-field detection and a micromanipulator. In the case of the nanowire perpendicular or parallel to the incident plane and p- ors-polarized evanescent excitation respectively, optical properties of the nanowire is measured both in far-field and near-field. For the perpendicular situation, scattering light from the nanowire shows strong dependence on the polarization of incident light, and period patterns along the nanowire are observed both in the near- and far-field. The chain of dipole model is used to explain the origin of this pattern. The discrepancy of the period patterns observed in the near- and far-field is due to the different resolution of the near- and far-field detection. For the parallel case, light intensity from the output end also depends on the incident polarization. Both experimental and calculation results show that the polarization dependence effect results from the surface plasmon excitation. These results on the orientation- and polarization-dependent properties of the Ag nanowires detected by the combination of near- and far-field methods would be helpful to understand interactions of one-dimensional plasmonic nanostructures with light.