Optical Properties Of Nanostructures Research Articles

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.

Green synthesis of Co3O4 nanoparticles using spent coffee: Application in catalytic and photocatalytic dye degradation

Clean water is vital for societal progress, however, the pollution caused by dyes presents a significant global challenge. Dye-contaminated industrial effluent overwhelms wastewater treatment facilities, causing harm to water bodies and ecosystems. This study demonstrates the synthesis of Co3O4 nanoparticles using spent coffee extract as a bioreducing agent and its application in dye degradation. The structural and optical properties of nanostructures were confirmed using X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), and UV–vis spectroscopy. The Co3O4-activated peroxymonosulfate (PMS) system exhibited exceptional catalytic efficiency by attaining a degradation rate of 89.27 % for Tartrazine dye within a 30-minute timeframe, even in the absence of illumination. When exposed to simulated visible light, the degradation kinetic rate increased by 37.60 %, highlighting the excellent photocatalytic activity of Co3O4 nanoparticles. Furthermore, leveraging natural sunlight led to a notable Tartrazine degradation rate of 97.11 %, signifying a substantial 45.41 % enhancement in reaction efficiency when contrasted with the conventional Co3O4/PMS system. Lastly, the Co3O4 nanoparticles illustrated remarkable degradation of synthetic industrial dye effluents (Tartrazine, Methyl Orange, and Remazol Brilliant Red), reaching up to 92.77 % removal, indicating its potential for use in real-world scenarios.

Permittivity Model Selection Based on Size and Quantum-Size Effects in Gold Films

The article is focused on optical properties of nanostructures containing spherical gold nanoparticles of various radii. We explore correlation between the particle radius and the choice of permittivity model applied to describe optical absorption spectra of gold granules. The experiments show splitting of the absorption band of granular gold films to form a second absorption peak. The first peak is associated with the phenomenon of plasmon resonance, while the second one reflects quantum hybridization of energy levels in gold. Quantum effects are shown to prevail over size effects at a granule diameter of about 5-6 nm. The Mie theory gives a rigorous solution for the scattered electromagnetic field on a sphere taking into account optical properties of the latter, however, it does not specify the criteria for selecting a model to calculate dielectric permittivity. Both calculations and experiments confirm the limiting diameter of gold nanoparticles where the Hampe-Shklyarevsky model is applied. Meanwhile, this model is still unable to predict the splitting of the plasma absorption band. The data presented in the article can be used for a predetermined local field enhancement in composite media consisting of a biolayer and metal nanoparticles. The conducted research provides a deeper understanding of the influence of a terahertz high-intensity electromagnetic field localized in the space on quantum dots.

Tailoring of structural and optical properties of electrosprayed β-Ga2O3 nanostructures via self-assembly

The present article demonstrates the fabrication of various β-Gallium Oxide (Ga2O3) nanostructures (NSs) by low-cost and scalable electrospraying (ES) methods via self-assembly (SA). The effect of the annealing sequences on the self-assembled β-Ga2O3 NSs has been detailed. The comparative studies of NSs and nanoflakes (NFs) growth with annealing effect at different stages of self-assembly time (SAT) have been explored further. The fabricated NSs and NFs have been investigated using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The comparative study of categorized growth samples shows better crystalline quality when moving from the category 1 (C1) sample to the category 3 (C3) sample. The annealing sequences with SAT play a significant role in crystal formation and its quality, optical properties, and morphology of the Ga2O3 NSs. The optical properties of NSs have been derived from the normal incidence of absorbance measurements. The maximum observed energy band gap is ~ 5.40 eV. Traps and impurities play a critical role in the formation and deformation of energy bands in crystals. The photoluminescence spectra further reveal the variation in the intensity of luminescence of different emission bands due to the variation in the number of defect states and impurities in the NSs.

Polarization Multiplexing Bifunctional Metalens Designed by Deep Neural Networks

AbstractAs planar optical elements, metasurfaces confer an unprecedented potential to manipulate light, which benefits from the deep control of the interactions between nanostructures and light. In the past decade, considerable progress has been made in various metasurfaces for on‐demand functions, drawing great interest from the scientific community. However, it is a great challenge to integrate different functions into a single metasurface, due to the incapability of manipulating light at different dimensions and the lack of universal intelligent design strategy. Here, an intelligent design platform based on deep neural networks is proposed, which can map between structure parameters and optical response. The well‐trained network model can intelligently retrieve nanostructures to meet multidimensional optical requirements of metasurfaces. Four metalenses for chiral focusing are realized by the design platform and the simulation results are highly consistent with the design target. In addition, metalenses based on arbitrary polarization at various working wavelength are also demonstrated, showing that the method has powerful design ability. Various optical properties of nanostructures, such as phase shift and polarization, are manipulated by deep neural networks, which can greatly promote the development of multifunctional devices and further pave the way for optical display, communication, computing, sensing, and other applications.

Seed-free synthesis of ZnO nanorods through egg white/glycerol medium for photocatalyst applications

In this present work, zinc oxide nanorods (ZnO NRs) were synthesized using a simple, inexpensive, seed-free sol-gel method. Three different glycerol concentrations were used as coordinators for the morphologically controlled growth of ZnO NRs in the protein (egg white) medium. The impact of different glycerol concentrations on the structural and optical properties of nanostructures was investigated through X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), ultraviolet-visible (UV–vis) spectroscopy, photoluminescence (PL), and Brunauer–Emmett–Teller (BET) analyses. The obtained XRD patterns showed hexagonal wurtzite structures for ZnO NRs and exhibited a remarkable change along the (002) plane. The ZnO NRs related to the utilization of 2 mL glycerol exhibited the crystallite size of 53.12 nm, diameter size of about 55 nm, energy bandgap of 2.75 eV, and BET surface area (10.68 m2 g−1), which exhibited remarkably superior photoconductivity and photoluminescence at room temperature under sunlight irradiation in comparison to P25-TiO2 as criterion sample material. The enhancement of the photocatalytic performance is mainly attributed to the synergistic effects of mesoporous structure, increased surface area, reduced energy band gap, extended solar light utilization, and surface modification of ZnO NRs. This present work provides a simple, high-performance, and seed-free approach to the large-scale production of ZnO photocatalyst for water treatment applications.

A Comparative Study of Structural, Morphological and Optical Properties of Pure and Tellurium-Doped ZnO Nanostructures

Pure and tellurium-doped ZnO nanostructure films were prepared on microscopic glass substrates using the sol-gel method and investigated the relationship between the structural, morphological, roughness, and optical properties. The X-ray diffraction (XRD) spectra revealed that the nanostructure films have a hexagonal Wurtzite structure. The field emission scanning electron microscope (FESEM) images showed that the surface morphology of the nanostructure films was modified due to the Te dopant. The atomic force microscopy (AFM) technique was used to study the surface roughness of the pure ZnO and Te-doped ZnO deposited films. The optical properties of the nanostructure films were obtained using the ultraviolet-visible spectrophotometer. The effects of Te dopant elements on the optical characteristics and the samples’ energy band gaps were calculated and discussed.

Study on the Plasmonic Properties of Ag-coated Spherical Dielectric Nanoparticles by Finite-Difference Time-Domain Calculations

The optical properties of nanostructures are rather important for designing plasmonic devices. In this work, the plasmonic properties of Ag-coated spherical dielectric nanoparticles (NPs), namely, Ag-SiO2-NPs, Ag-ZnO-NPs, and Ag-TiO2-NPs, were studied using a method of finite-difference time-domain calculations. It was found that the Ag-coated dielectric NPs start to exhibit unique plasmonic properties different from Ag-NPs as the thickness of Ag shells is reduced to be less than a critical value, which is basically determined by the penetration depth of light in silver. On the other hand, the core–shell structures of Ag-coated dielectric NPs were found to be of benefit to the plasmonic resonance high-efficiently coupled with the incident light. In the extinction spectra of Ag-coated dielectric NPs with sufficient thin Ag shells, the dipole plasmonic resonance is predominant and exhibits a pronounced red-shift up to infrared band with increasing the NP sizes. In addition to the electromagnetic waves of emission towards the outside, the electromagnetic field in the dielectric NP inside is uniformly enhanced as well and both of dipole and quadrupole plasmonic resonances are identified. The Ag-coated dielectric NPs are suggested to have great potential in the plasmonic devices working in infrared band, such as the light emitters and SERS substrates for biosensing.Graphical abstract

Rational manipulation of lattice strain to tailor the electronic and optical properties of nanostructures

Optoelectronic devices with different energy ranges requires materials with different band gaps, sometimes even within the same device. Structural distortions within the nanostructures produce lattice strains, which can change physical properties. However, the detailed knowledge of lattice strains in nanostructures remains confusing. Here, we rationally design and employ a simple and effective scheme to fabricate strained BiVO4/ZnS nanostructures. Lattice strain originates from lattice distortion caused by the intentional incorporation of metal ions into the inner layer of nanostructures. Experimental findings show that the maximum and minimum band gap energies of BiVO4/ZnS nanostructures are 2.87 and 2.79 eV under the tensile strain, which are increased by 4.4% and 1.4%, respectively, compared with that of the reference sample (2.75 eV). Impressively, BiVO4/ZnS nanostructures exhibit tunable dual emission behavior, and lattice strain significantly changes the electron band structure of the nanostructures. In addition, we identify the composite structure of BiVO4/ZnS nanomaterials and elucidate the mechanistic origin of regulation of the optical and electronic properties by lattice strain in combination with experimental and density functional theory calculations. These results provide a deep understanding of the relationship between lattice strain and optical properties and indicate that strain engineering can be potentially used in the design of nanostructures.

Polarization-dependent mode coupling in hyperbolic nanospheres

Abstract Hyperbolic materials offer much wider freedom in designing optical properties of nanostructures than ones with isotropic and elliptical dispersion, both metallic or dielectric. Here, we present a detailed theoretical and numerical study on the unique optical properties of spherical nanoantennas composed of such materials. Hyperbolic nanospheres exhibit a rich modal structure that, depending on the polarization and direction of incident light, can exhibit either a full plasmonic-like response with multiple electric resonances, a single, dominant electric dipole or one with mixed magnetic and electric modes with an atypical reversed modal order. We derive conditions for observing these resonances in the dipolar approximation and offer insight into how the modal response evolves with the size, material composition, and illumination. Specifically, the origin of the magnetic dipole mode lies in the hyperbolic dispersion and its existence is determined by two diagonal permittivity components of different sign. Our analysis shows that the origin of this unusual behavior stems from complex coupling between electric and magnetic multipoles, which leads to very strong scattering or absorbing modes. These observations assert that hyperbolic nanoantennas offer a promising route towards novel light–matter interaction regimes.

Significance of nanostructure morphologies in photoelectrochemical water splitting cells: A brief review

The main component in photoelectrochemical (PEC) water splitting technology is the semiconductor, which its electronic structure has an essential effect on the final performance of the cell. Morphology plays a significant role in the electronic properties of semiconductors. The relationship between the electron and optical properties of nanostructures and their surface morphology is a subject that is less addressed in scientific papers. This review attempts to detail the impact of morphology on nanostructures' properties, such as light absorption and charge carrier transport. Creating a direct path for electron transport, reducing charge recombination, and increasing light scattering are some of the things that are directly related to the surface morphology of nanostructures. The present review aims to provide general information about synthesized nanostructures and their advantages and disadvantages to help readers create new ideas and innovate in this field.

Formation features, morphology and optical properties of nanostructures via anodizing Al/Nb on Si and glass

Using the method of niobia electrochemical anodizing via the porous alumina, three types of nanostructures: skittle-, medusa- and goblet-like niobia embryos were formed. Their morphology and formation boundary conditions were investigated. Established up to 37 V embryos are formed like skittles, in the region from 53 to 100 V medusa-like are formed, and above 150 V – goblet-like. To research the optical column-like niobia nanostructure properties inside porous alumina, embryos 53 V like medusa were formed on a glass substrate and re-anodized to a voltage of 230 V not to leave the metallic niobium. Investigations have shown the complete absorbance of the ultraviolet range and the presence of transmittance, reflectance and absorbance in the visible and infrared range with significant oscillations, which indicates the presence of Fabry-Perot interference.

Theoretical study on the optoelectronic properties of GaAs nanostructures with Al component gradient change

In order to improve the photoemission characteristics of the GaAs photocathode, GaAs nanostructures (nanoholes and nanowires) with three sublayers and Al component of gradient distribution are designed in this article. Finite element method was used to study the effects of Al component gradient interval, component range, height, diameter, and other parameters on light absorption of nanostructures. And the quantum efficiency of these nanostructures was calculated. The results show that the wide band absorption can be achieved with small gradient interval and component variation range, and the nanostructure can enhance the light capture ability with certain angle inclination. In the gradient component nanostructures, the thickness of the top most layer has a great influence on the quantum efficiency. Highlights The nanohole and nanowire structures with three sublayers and Al component gradient distribution were designed. The effects of gradient interval, range of Al components, and geometric parameters on the optical properties of nanostructures are discussed.

Effect of doping and surfactant on the structural and Fenton-like catalytic activity of digenite structures synthesized by a solvothermal method

Pure, Co, and Ho-doped digenite (Cu9S5 or Cu1.8S) nanostructures were synthesized through simple solvothermal approaches. The effect of surfactant) Tween 20, polyethylene glycol, and oleic acid) on the morphology and optical properties of nanostructures was investigated in detail. The plasmonic band of samples synthesized in the presence of Tween 20 and oleic acid was reduced because of trapping of Cu vacancies by the carboxylate groups of surfactants. In addition, the surfactants adsorbed on the nanostructure surface have a negative impact on catalytic activity of particles, while the Fenton-like activity of doped catalysts yielded good performance in terms of methylene blue (MB) decolorization (98% and 90% for Ho and Co doping Cu1.8S, respectively). Ho improves redox cycling of Cu2+ to Cu+ and Co improves reactivity with H2O2 accelerate MB decolorization.

Interfacial strain and shell thickness effect on core squeeze/stretch in core/shell quantum dots

Large surface to volume ratio in zero dimension core/shell quantum dots makes lattice mismatch induced interfacial strain vital in determining structural and optical properties of nanostructures. In this study, changes in lattice mismatch induced strain from different compressive shell (CdS–ZnS) with different thicknesses (thin and thick) are evaluated and its effect on capped core diameter is theoretically calculated. Capped core squeeze amount is compared with its initial (bare) diameter obtained from transmission electron microscopy. The capped core diameter is first calculated theoretically using effective mass approximation. Then, same diameter is obtained from modified version of effective mass approximation method that considers interfacial strain amount. Comparison of the results with bare core size obtained from transmission electron microscopy revealed effect of shell thickness imposed on capped core diameter. Results show, larger lattice mismatch between core and shell induces higher strain amount on the core thereby larger squeezes the core. At the meantime, it is shown that, thicker compressive shell enforces lower stress on core as it widens its distance from core due to lattice relaxation. Hence, core is squeezes less under thicker shell.

Influence of the size, shape and concentration of magnetic particles on the optical properties of nano-dispersive structures

In the present paper, using the discontinuous Ni films and magnetite magnetic fluids as examples we consider theoretically and experimentally the influence of the structural parameters on the optical properties of the ultrafine structures. The optical properties of nanostructures are represented within the theoretical Maxwell-Garnett model. The behavior of the optical spectra of thin Ni films and magnetite magnetic fluids was explained in the framework of the effective medium approximation in two cases: q < 0.5 and 0.5 < q < 1. In this model an effective refractive index (n+ik) of the nanostructures can be calculated as a function of the εm, q, and particle shapes. This approach demonstrated a good accordance between the experimental results and the theoretical calculations.

Investigation of laser wavelength effect on optical properties of graphene oxide colloidal nanostructures prepared by pulsed laser ablation

In this work we prepared graphene oxide nanostructures (GONE) in a liquid environment using pulsed laser ablation technique. We used for the synthesis Nd: YAG pulsed laser operatating at 1064 nm and 532 nm of wavelength, we study the effect of wavelength of the laser on the optical properties of Nanostructures (NE) synthesized. The aim was determining the optical bandgap and the characteristic peak related by bond transitions using the absorbance UV-Vis spectra. Both samples show high absorption in the ultraviolet region in the UV-Vis spectra. Using Tauc’s plot method we compute the bandgap energy for GONEs assuming indirect bandgap. In addition, we observe characteristic peak formation 1 hour after synthesized NPs at 256 nm for NPs prepared at 1064 nm and for NPs prepared at 532 nm the peak with less intensity is observed at a wavelength of 218 nm. The characteristic peak for both samples increase of intensity 24 hours after preparation.

Precise control the microstructural, optical, photocatalytic, and photoelectrochemical properties of TiO2 nanoarrays through changing with growth substrate via hydrothermal method

A series of TiO2 nanostructures with rutile phase were synthesized on arbitrary substrates of conductive transparent fluorine-doped tin oxide (FTO), tin-doped indium oxide (ITO), and glass at the low temperature of 150 °C by the hydrothermal method. The samples were characterized by XRD, SEM, TEM, XPS, UV–Vis absorption, and micro-Raman spectroscopy. The effects of growth substrates on the morphologies and optical properties of nanostructures were investigated. TiO2 nanorods were grown on the FTO substrate, while TiO2 nanoflowers were grown on the ITO and glass substrates, and the growth mechanism for these different nanostructures is discussed in detail. The results show that the TiO2 nanorods can improve photocatalytic properties and photoelctrochemical (PEC) performance for its unique structure and optical properties. The TiO2 nanorods exhibited a maximal photocatalytic rate of 4.42 min−1 and photocurrent density of 0.049 mA/cm2, which is about 1.52 and 3.03 times higher than those of TiO2 nanoflowers grown on the ITO substrates, respectively. These findings are quite promising and encouraging for the use of TiO2 nanoarrays in photocatalysis and energy applications.

Symmetry-breaking induced magnetic Fano resonances in densely packed arrays of symmetric nanotrimers

Due to unique properties and great design flexibilities, Fano resonances represent one of the most promising optical features mediated by metallic nanostructures, while the excitation of some Fano modes is impossible due to symmetry reasons. The aim of this work is to show that dense lattice arrangements can have a profound impact on the optical properties of nanostructures and, in particular, can enable the excitation of otherwise dark modes. Here, we demonstrate this concept using the example of rectangular arrays of symmetric trimers packed so densely that the coupling between neighbouring unit cells imposes a symmetry break, enabling the excitation of magnetic Fano resonances. We found that in experiments as well as in simulations, electric and magnetic Fano resonances can be simultaneously formed in cases where the inter-trimer distances are sufficiently small. By analysing the transition from an isolated trimer mode into a regime of strong near-field coupling, we show that by modifying the rectangular unit cell lengths due to the symmetry mismatch between lattice and trimer, two types of Fano resonances can be found, especially magnetic Fano resonances with loop-type magnetic field distributions within the centre of each trimer, which can be either enhanced or suppressed. In addition, the influence of the refractive index environment was measured, showing sensitivity values of approximately 300 nm/RIU. Our work provides fundamental insights into the interaction of the lattice and nanostructure response and paves the way towards the observation of novel optical excitations.

Joint effect of electric and magnetic field on electron energy spectrum in spherical nanostructure ZnS/CdSe/ZnS

The electron energy spectrum in inverted core-shell quantum dot driven by magnetic and electric fields is studied. The parallel and perpendicular electric and magnetic fields are considered. The Schödinger equation is solved using the method of expansion of the electron wave function on the basis of wave functions in the nanostructure without the external fields.The formation of the electron ground state under the influence of the electric and magnetic field is researched. It is shown that this state is successively formed by the states with m ≤ 0 (Aharonov-Bohm effect) when the magnetic field induction increases. This effect vanishes when the electric field intensity increases and if the magnetic field is parallel to the electric one. The electron ground state is characterized only by quantum number m = 0 in the whole range of magnetic field induction when the electric field intensity is bigger than certain critical magnitude. When the electric field intensity increases, being perpendicular to the magnetic one, the cylindrical symmetry of problem is broken and the wave function of electron ground state is obtained as a series, containing the states with different values of magnetic quantum number. Their partial contributions essentially depend on the magnitudes of electric field intensity and magnetic field induction. The effect of magnetic field on electron ground state energy decreases when the external fields are perpendicular.The peculiarities of the formation of electron energy spectrum due to the electric and magnetic field should be displayed on the selection rules and the energies of quantum transitions and, thus, on the optical properties of nanostructure.