Anisotropic Optical Properties Research Articles

Universal production of anisotropic bilayer WSe2 nanoscrolls for high-performance photodetector

Abstract Transition metal dichalcogenide nanoscrolls (NSs) exhibit unique optoelectronic properties due to their spiral tubular structures. In this study, we successfully fabricated WSe2 NSs with various morphologies, illustrating the evolution from planar to NS via an internal strain-driven rolling process. The anisotropic optical properties of the NSs were systematically analyzed by angle-resolve polarized Raman spectroscopy. For NSs with different rollup angles, the strain distribution is manifested by the variation of Raman intensity on the linear axis. In addition, the on/off ratio and detectivity of device based on bilayer NS reach 5.3 × 104 and 2.63 × 109 Jones, caused by the ultralow dark photocurrent. In summary, our study demonstrates a universal method for producing polymorphic products, demonstrating that bilayer WSe2 NSs hold significant potential as a platform for fundamental research and technological applications.

A macroscopic magneto-optical response resulting from local effects in ferronematic liquid crystals.

This study investigates the magneto-optical response of liquid crystals (LCs) with planar anchoring in the presence of γ-Fe2O3 magnetic nanoparticles (MNPs). This research demonstrates the formation of novel magnetic composite chains of LCs wrapped around γ-Fe2O3 MNP chains within the LC matrix under an applied magnetic field. These composite chains exhibit a distinct magneto-optical response, characterized by changes in birefringence and dichroism as the magnetic field direction is altered. Based on experimental findings, a two-subsystem model and an effective volume fraction of composite chains are proposed to describe the magneto-optical behavior of the γ-Fe2O3 MNP-doped LCs. The first subsystem comprises the LC matrix, which retains its inherent anisotropic optical properties and does not respond to the applied magnetic field. The second subsystem consists of the magnetic composite chains, which exhibit a distinct magneto-optical response due to their rotational alignment with the magnetic field. The difference in absorbance, 2αdd, which corresponds to dichroism, decreases with increasing magnetic field angle Θ, indicating a corresponding change in dichroism. This interplay between the two subsystems leads to the macroscopic magneto-optical response observed in the γ-Fe2O3 MNP-doped LCs. Due to the stability of the composite chains, the magneto-optical response is stable and can be reversed.

Unveiling the optoelectronic features and physical stability of novel Cs2HgPdI6: Computational insights

In recent years, researchers have been devoted to search for novel stable halide perovskite materials with outstanding photovoltaic performance. Herein, through density functional theory (DFT) calculations, we uncover for the first time the crystal stability, structural parameters, optoelectronic features, and photovolatic performance of Cs2HgPdI6. The Jahn−Teller-distorted Cs2HgPdI6 is detected by its structural feature. The stability of novel Cs2HgPdI6 is completely ensured by means of the DFT calculations. Accurate electronic structure calculations show that Cs2HgPdI6 exhibits an appropriate fundamental gap (1.278 eV). This band gap is mainly determined by the interaction between the I-5p and Pd-4d orbitals. Additionally, Cs2HgPdI6 has good carrier mobility and an ultra-low exciton binding energy. Meanwhile, it also exhibits relatively weak anisotropic optical properties and strong visible-light absorption. The large theoretical conversion efficiency of 31.7 % is illustrated for Cs2HgPdI6. Overall, our research highlights the great potential of this novel compound for photovoltaic applications.

Unveiling the DFT perspectives on structural, elastic, electronic, optical and thermal properties of XMn2As2 (X = Ca, Sr)

A comprehensive first-principles investigation of XMn2As2 (X = Ca, Sr) materials using Density Functional Theory (DFT) have used in this study. Variety of physical attributes, including thermal, mechanical, electronic, optical and elastic anisotropic properties are explored. Lattice parameters and crystal structures showed excellent agreement with previous experimental data. The findings reveal that CaMn2As2 and SrMn2As2 exhibit notable elastic anisotropy, and satisfy the Born criteria for mechanical stability. The calculated elastic moduli are consistent with previously published values. The metallic nature of these compounds is demonstrated through band structure and density of states (DOS) analyses. Optical property analyses, including energy loss function, electrical conductivity, reflectivity, dielectric constant, refractive index, and absorption coefficient, highlight the potential of these materials for optoelectronic and photovoltaic applications. Notably, SrMn2As2 displays an exceptionally low minimum thermal conductivity compared to CaMn2As2, indicating its potential as a superior Thermal Barrier Coating (TBC) material.

Nanocolumnar Metamaterial Platforms: Scaling Rules for Structural Parameters Revealed from Optical Anisotropy

AbstractNanostructures represent a frontier where meticulous attention to the control and assessment of structural dimensions becomes a linchpin for their seamless integration into diverse technological applications. However, determining the critical dimensions and optical properties of nanostructures with precision still remains a challenging task. In this study, by using an integrative and comprehensive methodical series of studies, the evolution of the depolarization factors in the anisotropic Bruggeman effective medium approximation (AB‐EMA) is investigated. It is found that these anisotropic factors are extremely sensitive to the changes in critical dimensions of the nanostructure platforms. In order to perform a systematic characterization of these parameters, spatially coherent, highly‐ordered slanted nanocolumns are fabricated from zirconia, silicon, titanium, and permalloy on silicon substrates with varying column lengths using glancing angle deposition (GLAD). In tandem, broad‐spectral range Mueller matrix spectroscopic ellipsometry data, spanning from the near‐infrared to the vacuum UV (0.72–6.5 eV), is analyzed with a best‐match model approach based on the anisotropic Bruggeman effective medium theory. The anisotropic optical properties, including complex dielectric function, birefringence, and dichroism, are thereby extracted. Most notably, the research unveils a generalized, material‐independent inverse relationship between depolarization factors and column length. It is envisioned that the presented scaling rules will permit accurate prediction of optical properties of nanocolumnar thin films improving their integration and optimization for optoelectronic and photonic device applications. As an outlook, the highly porous nature and extreme birefringence properties of the fabricated columnar metamaterial platforms are further explored in the detection of nanoparticles from the cross‐polarized integrated spectral color variations.

In situ tracking anisotropic photocarrier dynamics in two-dimensional ternary Ta2NiSe5 via digital micromirror device-based pump-probe microscopy

In two-dimensional (2D) material studies, tracking the anisotropic ultrafast carrier dynamics is essential for the development of optoelectronic nano-devices. Conventionally, the anisotropic optical and electronic properties are investigated via either polarization-dependent Raman spectroscopy or field-effect transistors measurements. However, study of the anisotropic transient carrier behaviors is still challenging, due largely to the lack of picosecond-resolved acquisition or programmable scanning capabilities in the current characterization systems. In this work, we select Ta2NiSe5 as a model system to investigate the ultrafast anisotropic transportation properties of photo-excited carriers and transient polarized responses via a digital micromirror device (DMD)-based pump-probe microscope, where the probe beam scans along the armchair and zigzag directions of a crystal structure via binary holography to obtain distinct carrier diffusion coefficients, respectively. The results reveal the nonlinear diffusion behaviors of Ta2NiSe5 in tens of picoseconds, which are attributed to the interplay between excited electrons and phonons. The trend of the measured local polarization-dependent transient reflectivity is consistent with the polarized Raman spectra results. These results show that the DMD-based pump-probe microscope is an effective and versatile tool to study the optoelectronic properties of 2D materials.

A facile spinning approach towards the continuous production of aligned nanocellulose films

In this work, we present an alternative approach to cellulose nanofibril film (CNF) production, taking inspiration from the wet spinning of fibers to wet spin films. During the spinning process, a CNF suspension is injected into a coagulation bath, where the partially aligned CNF network is locked. The CNF alignment of the dry films is then detected by wide angle X-ray scattering (WAXS). The comparison between the ultimate strengths and strengths at breaks of the films produced with different process parameters, including the suspension injection rate, bath pH, and bath flow rate, indicated no significant change in mechanical properties, suggesting a reliable and constant outcome for large-scale film fabrication. Furthermore, the produced films demonstrated high total light transmittance of 93 % at the wavelength of 550 nm, making them suitable for optoelectronic applications. Polarized optical microscopy revealed that even a low degree of CNF alignment can lead to anisotropic optical properties. Moreover, an anisotropic response to humidity was observed, in which the films preferentially bend in the perpendicular direction of the CNF orientation, thus opening a way for humidity-driven actuators.

First-Principles Study of Penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) Monolayer with Highly Anisotropic Electronic and Optical Properties.

Two-dimensional (2D) semiconducting materials with anisotropic physical properties have induced lively interest due to their application in the field of polarizing devices. Herein, we have designed a family of penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) monolayers and predicted the electronic and optical properties based on the first-principles calculation. The results suggest that the penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) monolayers are indirect-gap semiconductors with a medium bandgap of 2.29-2.66 eV. The penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) monolayers own a remarkable mechanical anisotropy with a high Young's modulus anisotropic ratio (3.0). In addition, the penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) monolayers exhibit a high anisotropy ratio of hole/electron mobility in the x and y directions (1.16-3.54). The results calculated by the G0W0+BSE method indicate that the single-layers also bear a salient optical anisotropy ratio (1.56-2.11). The integration of the anisotropic electronic, optical, and mechanical properties entitles penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) monolayers as potential candidates in multifunctional polarized nanodevices.

Impact of quantum point defects on the electronic and optical properties of NbOX[formula omitted] (X: Cl, Br, I) monolayers

Monolayer niobium oxychloride (NbOCl2), synthesized as reported in Guo et al. (2023), exhibits potential as a quantum light source. Our density functional theory (DFT) study assesses niobium oxyhalide monolayers (NbOX2, X = Cl, Br, I), focusing on quantum point defects’ impact on electronic behavior. Vacancy-induced magnetism is observed in these monolayers; oxygen and niobium vacancies trigger magnetism, contrasting with non-magnetic halogen vacancies. The energy difference between magnetic and non-magnetic states is contingent on vacancy type and halogen mass, with oxygen vacancies showing an energy increase and niobium vacancies a decrease as halogen mass rises. Doping effects are notable; halogen and oxygen vacancies result in n-type doping, while niobium vacancies lead to p-type. In the NbOI2 monolayer, the Nb+1 vacancy is found to be more stable than the neutral vacancy. Conversely, for other charge states and vacancies, the neutral state remains the most stable. Magnetization is significantly enhanced by oxygen and halogen bivacancies, with spin energy difference and magnetization scaling with the halogen’s atomic number. The optical spectrum analysis shows that defects can extend absorption into the infrared, with anisotropic optical properties dependent on light polarization direction. These findings highlight the tunability of niobium oxyhalide monolayers for quantum technology applications, emphasizing the role of defects in modulating electronic and optical characteristics.

Homoatomic Polychalcogenide Nonlinear Optical Anionic Groups with Ultra-Large Optical Anisotropy.

Functional assembly of nonlinear optical (NLO) motifs with a large optical anisotropy is vital to the development of advanced NLO and birefringent materials. In this work, we highlight that, in addition to heteroatomic NLO motifs, homoatomic anionic clusters formed by aggregated anions (S, Se, Te) exhibit diverse chain-, ring-, and cage-like chemical structures as well as one-, two-, and three-dimensional motif alignments. The rich structural chemistry enables homoatomic polychalcogenides (HAPCs) to exhibit asymmetric structural features and anisotropic optical properties, with great potential for NLO and birefringent performance. Focusing on totally 55 binary HAPCs A2Qn (n = 2, 3, 4, 5; A = Na, K, Rb, Cs; Q = S, Se, Te) and their ternary analogues, we employ the state-of-the-art first-principles approach to systematically investigate the modulation evolution of their NLO and birefringent properties. Remarkably, Rb2Te3 and Na2TeSe2 exhibit rarely colossal birefringence (>1.0@10 μm) and NLO effects (>20 × AgGaS2), much larger than conventional NLO chalcogenides. Na2Te3 presents the largest birefringence to date (∼3.48@1, 2.72@2, 2.34@10 μm), indicating the unique structural superiority of HAPC in terms of ultra-large birefringence. By mining the intrinsic mechanism, the HAPC anionic groups are identified as novel mid-infrared NLO "material genes", furnishing unique NLO and birefringent performance for the design of novel optoelectronic materials.

Molding Process Retaining Gold Nanoparticle Assembly Structures during Transfer to a Polycarbonate Surface.

The immobilization of gold nanoparticle (AuNP) linear surface assemblies on polycarbonate (PC) melt surface via molding is investigated. The order of the particle assemblies is preserved during the molding process. The assemblies on PC exhibit plasmonic coupling features and dichroic properties. The structure of the assemblies is quantified based on Scanning Electron Microscopy (SEM) and image analysis data using an orientational order parameter. The transfer process from mold to melt shows high structural fidelity. The order parameter of around 0.98 reflects the orientation of the lines and remains unaffected, independent of the injection direction of the melt relative to the particle lines. This is discussed in the frame of fountain flow during injection molding. The particles were permanently fixed and withstood the injection molding process, detachment of the substrate, and extraction in boiling ethanol. The plasmonic particles coupled strongly within the dense nanoparticle lines to produce anisotropic optical properties, as quantified by dichroic ratios of 0.28 and 0.52 using ultraviolet-visible-near-infrared (UV-Vis-NIR) spectroscopy. AuNP line assemblies on a polymer surface may be a basis for plasmonic devices like surface-enhanced Raman scattering (SERS) sensors or a precursor for nanowires. Their embedding via injection molding constitutes an important link between particle-self-assembly approaches for optically functional surfaces and polymer processing techniques.

Signature of excitonic insulators in phosphorene nanoribbons

Phosphorene is a recently developed two-dimensional (2D) material that has attracted tremendous attention because of its unique anisotropic optical properties and quasi-one-dimensional (1D) excitons. We use first-principles calculations combined with the maximally localized Wannier function tight binding Hamiltonian and Bethe–Salpeter equation (BSE) formalism to investigate quasiparticle effects of 2D and quasi-1D blue and black phosphorene nanoribbons. Our electronic structure calculations shows that both blue and black monolayered phases are semiconductors. On the other hand black phosphorene zigzag nanoribbons are metallic. Similar behavior is found for very thin blue phosphorene zig-zag and armchair nanoribbon. As a general behavior, the exciton binding energy decreases as the ribbon width increases, which highlights the importance of quantum confinement effects. The solution of the BSE shows that the blue phosphorene monolayer has an exciton binding energy four times higher than that of the black phosphorene counterpart. Furthermore, both monolayers show a different linear optical response with respect to light polarization, as black phosphorene is highly anisotropic. We find a similar, but less pronounced, optical anisotropy for blue phosphorene monolayer, caused exclusively by the quasi-particle effects. Finally, we show that some of the investigated nanoribbons show a spin-triplet excitonic insulator behavior, thus revealing exciting features of these nanoribbons and therefore provides important advances in the understanding of quasi-one dimensional phosphorus-based materials.

Degrading effect on electrical properties of printed gallium sulfide based photodetector

Layered GaS structures have been attracting increasing research interest due to their highly anisotropic structural, electrical, optical, and mechanical properties. However, the investigation of the performance based on the responsivity, external quantum efficiency, and detectivity of printed GaS based photodetector on a flexible PET substrate with respect to a period of time under the environmental conditions have not been reported so far. This experimental study shows that the printed GaS based photodetector stored in ambient conditions undergoes a change in terms of performance in a few weeks after the fabrication. This work also holds an importance being premier study experimentally investigating the printed III–VI group monochalcogenide based photodetector stored under the environmental conditions and contributing the literature to improve the printed device performance in further applications.

Anisotropic optical property of ferroelectric Bi2O2X(X = S,Se,Te) monolayer and strain engineering

Based on the first-principles calculations, ferroelectric Bi2O2X(X = S,Se,Te) monolayers with unequivalent in-plane lattice constants are confirmed to be the ground state, which is consistent with the experiment result (Ghosh et al 2019 Nano Lett. 19 5703–09), and the anisotropic optical property is firstly investigated. We find that the polarizations of Bi2O2X monolayers points along the direction of a-axis, and Bi2O2Te monolayer process the largest polarization. Furthermore, both the biaxial and uniaxial strains are favor for the enhancement of polarization of Bi2O2X monolayers. It should be mentioned that the type of band gap will convert from indirect to direct for Bi2O2Te monolayer when the a-axial tensile strain is larger than 2%. At last, the optical absorption coefficient for Bi2O2X monolayers are calculated, and we obtain that Bi2O2Te monolayer has the strongest optical absorption within the range of visible light, the anisotropy and possible strain engineering to improve the optical absorption are discussed in detail. Our findings are significant in fields of optoelectronics and photovoltaics.

Optical tunability with superlattice hyperbolic metamaterial coatings

Optical tunability is demonstrated with multi-metal hyperbolic metamaterial (HMM) structures on varying substrate surfaces. A systematic uniaxial modeling methodology is adapted from classical approaches to extract the anisotropic permittivity of the films to identify epsilon-near-zero (ENZ) behavior over a wide range of metal volume fractions (φ). The anisotropic model accuracy is quantified by a mean squared error (MSE) with the presented modeling routine resulting in a MSE < 35 for all samples. The optical model thicknesses were verified with transmission electron microscopy (TEM) imaging and measurements. This study also demonstrates the ability to tune the optical responses in the visible-to-infrared frequencies with surface microtexturing and applied strain with HMM coatings on flexible Kapton substrates. Furthermore, the structured films and modeling procedure lay the groundwork for future studies on coupling the anisotropic optical and thermal properties for control over advanced multifunctional thin-film coatings.

Controlling the broadband enhanced light chirality with L-shaped dielectric metamaterials

The inherently weak chiroptical responses of natural materials limit their usage for controlling and enhancing chiral light-matter interactions. Recently, several nanostructures with subwavelength scale dimensions were demonstrated, mainly due to the advent of nanofabrication technologies, as a potential alternative to efficiently enhance chirality. However, the intrinsic lossy nature of metals and the inherent narrowband response of dielectric planar thin films or metasurface structures pose severe limitations toward the practical realization of broadband and tailorable chiral systems. Here, we tackle these problems by designing all-dielectric silicon-based L-shaped optical metamaterials based on tilted nanopillars that exhibit broadband and enhanced chiroptical response in transmission operation. We use an emerging bottom-up fabrication approach, named glancing angle deposition, to assemble these dielectric metamaterials on a wafer scale. The reported strong chirality and optical anisotropic properties are controllable in terms of both amplitude and operating frequency by simply varying the shape and dimensions of the nanopillars. The presented nanostructures can be used in a plethora of emerging nanophotonic applications, such as chiral sensors, polarization filters, and spin-locked nanowaveguides.

Contactless and nondestructive evaluation of residual stress distribution in modified and pure HDPE materials using a novel terahertz method and line-scan thermographic technique

Optical-stress properties were always studied at the elastic stage and at wavelengths shorter than terahertz (THz) radiation. Until present, the relationship between plastic strain and refractive index has not been fully understood. In this work, a novel THz method and line-scan thermographic technique are used for quantitative evaluation of the residual stress in the pure HDPE, as well as in the HDPE mixed with 5% by weight of wastepaper plus 5% by weight of chopped basalt as fillers. A new theory considering both influences from the sample thickness and the refractive index difference is proposed, thus allowing to improve the measurement accuracy. For the first time, the stress-optic constant and thermal diffusivity have been applied to characterize the residual stress.. The experiments suggest that, after stretching, the initial isotropic material transits into a material with highly anisotropic optical properties in THz band. This observation is useful when describing the conventional bi-refringence phenomenon. Finally, the residual stress distribution was calculated based on the proposed techniques.

A new class of single-phase multiferroics: Bismuth-based layered supercell oxide thin films—Current progress and future perspectives

Multiferroic materials, where ferroelectric and magnetic orders coexist, have ignited substantial research interest due to the achievable manipulation of magnetic orders using external electric fields, a feature that has garnered serious interest for memory storage applications. Nonetheless, naturally occurring single-phase multiferroic materials are scarce, thus constraining options for practical use. Over the last decade, bismuth-based layered supercell (LSC) oxides have emerged as novel candidates for multiferroics, catalyzing extensive investigations in this domain. Additionally, these LSC systems are known for their anisotropic structures and optical properties, making them promising for application in optics such as polarizers, beam splitters, and modulators. This thorough review explores the development and current advancements in multiferroic bismuth-based LSC materials. It covers the diverse nature of LSCs, detailing their microstructure, properties, and the mechanics of self-assembly formation. It also highlights the remarkable multifunctional characteristics of LSC-based nanocomposites, with a particular focus on their applications in electronics and optics. Moreover, this review examines the significant potential of LSCs in practical applications, particularly through their integration onto silicon and flexible substrates via heteroepitaxy and film transfer techniques. Finally, it offers insights into potential future research avenues and the broader implications of these versatile LSC materials.

Two-dimensional BxS materials with biphenylene network structure: A first-principles study

Two-dimensional (2D) boron-sulfur (BxSy) materials have garnered significant attention due to their potential applications in optoelectronic devices, catalysis, and energy conversion. In this study, we have innovatively designed a series of 2D-BxS materials (x = 2, 3, 5) with biphenylene (BP) network structures, denoted as BP-like BxS. Density functional theory calculations reveal that, with the exception of B5S, the metallic B2S and B3S exhibit exceptional thermal and mechanical stability, showcasing anisotropic mechanical and optical properties. Furthermore, B2S and B3S demonstrate a broad spectrum of light absorption capabilities, spanning from infrared to ultraviolet and visible light. Remarkably, these materials exhibit promising photocatalytic activity for the hydrogen evolution reaction (HER), with limiting potentials (UL) of 0.55 eV for B2S and 0.94 eV for B3S, respectively. The catalytic behavior is pH-dependent, with B2S favoring acidic conditions and B3S favoring alkaline conditions, where UL for B3S can reach 0.28 eV at pH = 12.58. This work reports BP-like BxS materials for the first time, thereby enriching the BxSy material family and extending their properties and potential applications in the fields of optoelectronics and catalysis.

Exploring van der Waals materials with high anisotropy: geometrical and optical approaches

The emergence of van der Waals (vdW) materials resulted in the discovery of their high optical, mechanical, and electronic anisotropic properties, immediately enabling countless novel phenomena and applications. Such success inspired an intensive search for the highest possible anisotropic properties among vdW materials. Furthermore, the identification of the most promising among the huge family of vdW materials is a challenging quest requiring innovative approaches. Here, we suggest an easy-to-use method for such a survey based on the crystallographic geometrical perspective of vdW materials followed by their optical characterization. Using our approach, we found As2S3 as a highly anisotropic vdW material. It demonstrates high in-plane optical anisotropy that is ~20% larger than for rutile and over two times as large as calcite, high refractive index, and transparency in the visible range, overcoming the century-long record set by rutile. Given these benefits, As2S3 opens a pathway towards next-generation nanophotonics as demonstrated by an ultrathin true zero-order quarter-wave plate that combines classical and the Fabry–Pérot optical phase accumulations. Hence, our approach provides an effective and easy-to-use method to find vdW materials with the utmost anisotropic properties.