Optical Extinction Research Articles

Gate-tunable optical extinction of graphene nanoribbon nanoclusters

We investigate the optical response of graphene nanoribbons (GNRs) using the broadband nonlinear generation and detection capabilities of nanoscale junctions created at the LaAlO3/SrTiO3 interface. GNR nanoclusters measured to be as small as 1–2 GNRs in size are deposited on the LaAlO3 surface with an atomic force microscope tip. Time-resolved nonlinear optical probes of GNR nanoclusters reveal a strong, gate-tunable second and third harmonic response, as well as strong extinction of visible to near-infrared light at distinct wavelengths, similar to previous reports with graphene.

Au@Ag Dendritic Nanoforests for Surface-Enhanced Raman Scattering Sensing.

The effects of Au cores in Ag shells in enhancing surface-enhanced Raman scattering (SERS) were evaluated with samples of various Au/Ag ratios. High-density Ag shell/Au core dendritic nanoforests (Au@Ag-DNFs) on silicon (Au@Ag-DNFs/Si) were synthesized using the fluoride-assisted Galvanic replacement reaction method. The synthesized Au@Ag-DNFs/Si samples were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, reflection spectroscopy, X-ray diffraction, and Raman spectroscopy. The ultraviolet-visible extinction spectrum exhibited increased extinction induced by the addition of Ag when creating the metal DNFs layer. The pure Ag DNFs exhibited high optical extinction of visible light, but low SERS response compared with Au@Ag DNFs. The Au core (with high refractive index real part) in Au@Ag DNFs maintained a long-leaf structure that focused the illumination light, resulting in the apparent SERS enhancement of the Ag coverage.

City-level variations in aerosol optical properties and aerosol type identification derived from long-term MODIS/Aqua observations in the Sichuan Basin, China

In recent decades, the Sichuan Basin (SCB) has suffered from severe aerosol pollution. Based on the long-term (2003–2018) aerosol optical properties dataset derived from the Moderate Resolution Imaging Spectroradiometer (MODIS), this study investigated the spatial distribution and interannual variation of aerosol optical depth (AOD) and fine-mode fraction (FMF) as well as the aerosol type at city-level in the SCB. The spatial distribution of AOD exhibited a decreasing trend from the centre of SCB to surrounding areas with high AOD approximately 1.0. The high FMF value was approximately 0.9 in surrounding southern areas. The frequency of occurrence of AOD < 0.2 was approximately 30%–40%. AOD in SCB exhibited a negative trend of approximately −0.03/year and FMF showed a significant positive trend of approximately 0.01–0.02/year. The proportion of continental background aerosols was higher in surrounding areas of SCB. The BB/UI (biomass burning/urban-industrial) aerosols in the central urban area increased significantly to approximately 50%. Mix aerosols were mainly distributed in the north, accounting for approximately 35%–45%. A large proportion of dust aerosols (30%–35%) was noted in the east SCB. The results of this study are of great scientific significance for the analysis of aerosol optical extinction at city level in the SCB of China.

Ternary quarter wavelength coatings for gravitational wave detector mirrors: Design optimization via exhaustive search

Multimaterial optical coatings are a promising viable option to meet the challenging requirements (in terms of transmittance, absorbance and thermal noise) of next generation gravitational wave detector mirrors. In this paper we focus on ternary coatings consisting of quarter-wavelength thick layers, where a third material (H') is added to the two presently in use, namely Silica (L) and Titania-doped Tantala (H), featuring higher dielectric contrast (against Silica), and lower thermal noise (compared to Titania-doped Tantala), but higher optical losses. We seek the optimal material sequences, featuring minimal thermal (Brownian) noise under prescribed transmittance and absorbance constraints, by exhaustive simulation over all possible configurations, for different values (in a meaningful range) of the optical density and extinction coefficient of the third material. In all cases studied, the optimal designs consist of a stack of (H'|L) doublets topped by a stack of (H|L) doublets, confirming previous heuristic assumptions, and the achievable coating noise power spectral density reduction factor is \sim 0.5. The robustness of the found optimal designs against layer thickness deposition errors and uncertainties and/or fluctuations in the optical losses of the third material is also investigated. Possible margins for further thermal noise reduction by layer thickness optimization, and strategies to implement it, are discussed.

Tuning Hierarchical Order and Plasmonic Coupling of Large-Area, Polymer-Grafted Gold Nanorod Assemblies via Flow-Coating.

Solution-based printing of anisotropic nanostructures is foundational to many emerging technologies, such as energy storage devices, photonic elements, and sensors. Methods to rapidly (>mm/s) manufacture large area assemblies (≫cm2) with simultaneous control of thickness (<10 nm), nanoparticle spacing (<5 nm), surface roughness (<5 nm), and global and local orientational order are still lacking. Herein, we demonstrate such capability using flow-coating to fabricate robust, self-supporting mono- and bilayer films of polystyrene-grafted gold nanorods (PS-AuNRs) onto solid substrates. The relationship among solvent evaporation, deposition speed, substrate surface energy, concentration, and film thickness for solutions of such hairy hybrid nanoparticles spans the Landau-Levich and evaporative film formation regimes. In the Landau-Levich regime, solvent evaporation rapidly concentrates the PS-AuNRs, leading to the formation of thin films with distinct, randomized side-by-side domains. Alternatively, processing at slower velocities in the evaporative regime results in the global alignment of PS-AuNRs. Processing speed and substrate surface energy afford tuning of the film's optical extinction of a given PS-AuNR via fine control of inter-rod distance and subsequent plasmonic coupling between neighboring nanorods. Because the concept of the polymer-grafted nanorod can be expanded to a variety of different polymer canopies, shapes, and core materials, the processing-structure relationships established in this work will have important implications on the future development of anisotropic nanostructure-based applications.

(Invited) Backside Absorbing Layer Microscopy: A New Tool to Study the Optical, Chemical and Electrochemical Properties of 2D Materials

Optical microscopy based on anti-reflective coatings is a simple yet powerful characterization tool, which notably allowed the first observation of graphene in 2004 and of other single-layered materials in the following years. Since then, the field of two-dimensional materials has developed rapidly both at the fundamental and applied levels. Yet, these ultrathin materials present inhomogeneities (edges, grain boundaries, defects, multilayers...) which strongly impact their intrinsic (physical, chemical) properties and their performances as electronic, optoelectronic and energy-conversion devices. The use of local characterization techniques (spectroscopy mapping, scanning probe techniques...) is thus essential. Recently, D. Ausserré et al. introduced a new enhanced-contrast optical microscopy technique, named BALM (Backside Absorbing Layer Microscopy), based on ultrathin (2-5 nm) and strongly light-absorbing (metallic) anti-reflective layers. This talk aims at presenting the remarkable assets of this technique for the study of 2D materials. BALM notably allows observing mono-layered materials with very strong contrast, even for the case of highly transparent ones such as graphene oxide [1]. The inverted microscope geometry allows imaging in solvents so that it is possible to investigate molecular adsorption dynamics on 2D materials in real-time and with extreme sensitivity.[1-2] With its wavelength sensitivity, BALM can also be used as a precise technique to determine the optical refractive index and extinction coefficient of TMDCs (MoS2...). One of the most interesting benefits of BALM is its combination with other techniques. In particular, we considered the coupling of optical measurements and electrochemistry for which the anti-reflective substrate serves as a working electrode. We investigated optically the dynamic of the electrochemical reduction of Graphene Oxide (GO), the electro-grafting of organic layers by diazonium salts reduction on GO and its reduced form (rGO),[3] as well as the intercalation of metallic ions within stacked GO sheets. By combining versatility and high contrast, BALM is established as a promising tool for the study of 2D materials, especially for the local and in situ characterization of their optical, chemical and electrochemical properties.[1] S. Campidelli, R. Abou Khachfe, K. Jaouen, J. Monteiller, C. Amra, M. Zerrad, R. Cornut, V. Derycke, D. Ausserré, Backside absorbing layer microscopy: Watching graphene chemistry, Science Advances 3, e1601724 (2017).[2] K. Jaouen, R. Cornut, D. Ausserré, S. Campidelli, V. Derycke, Ideal optical contrast for 2D materials observation using bi-layer antireflection absorbing substrates, Nanoscale 11, 6129 (2019).[3] K. Jaouen, F. Lebon, B. Jousselme, S. Campidelli, R. Cornut, V. Derycke, Optical monitoring of diazonium electrografting on gold and graphene oxide using Backside Absorbing Layer Microscopy, submitted.

(Invited) Exploring in the Near Infrared: Multifunctional Nanoplatforms for Biomedical Applications

Near-infrared (NIR) absorbing and emitting nanomaterials attract significant attention in bioimaging, which shows great potential for disease detection due to its high sensitivity at the subcellular level and low cost of related imaging facilities. However, currently available optical probes are mainly based on visible-emitting materials. The tissue-induced optical extinction and autofluorescence in the visible range result in limited penetration depth and ambiguous photoluminescence signal, which restricts their in vivo use. To address this issue, photoluminescent probes, with both absorption and emission wavelengths operating in the biological windows in the NIR range, in which tissues are optically transparent, are highly desired. Their integration with superparamagnetic nanomaterials to make a multifunctional platform further opens a wide range of promising applications, including bimodal imaging (photoluminescence and magnetic resonance imaging), synergistic hyperthermia (magnetothermal and photothermal), magnetic confinement of trace amounts of biospecies for ultra high-sensitivity biodetection, etc. In this talk, I will present our most recent work on the synthesis of NIR-emitting water soluble, stable core/shell/shell quantum dots (QDs) and multifunctional (NIR photoluminescent and superparamagnetic) nanoparticles and their use in biomedicine. For instance, in one case, multifunctional particles contain single superparamagnetic nanoparticles as cores and NIR-luminescent nanomaterials as shells. In another case, the multifunctional nanoplatform is compose of multiple superparamagnetic nanoparticles and NIR quantum dots in single particles. These different types of multifunctional particles are designed for different biomedical applications.

Optical switch with ultra high extinction ratio using electrically controlled metal diffusion.

An optical switch with ultra high extinction ratio is proposed. Optical switching is realized using the resistive switching effect through the lateral coupling between the input nanophotonic waveguide and output waveguide at a wavelength of 1550 nm. The coupled waveguide system is engineered to increase the number of mode beats in a unit length of the device. An increase in the number of mode beats and controlled diffusion of metal ions through a thin dielectric layer with an applied electric field is responsible for a high optical extinction ratio of 27 dB for a 20 µm long device. Compared to electrical control by plasma dispersion in silicon, the resistive switching effect enables a reduction in the coupling length and an increase in the waveguide absorption, leading to an almost 100 times higher extinction ratio. The proposed compact on-chip silicon-based nanophotonic resistive device is a potential candidate for a large-scale integrated photonic circuit for applications in optical switching, modulation, memory, and computation.

Halloysite Nanotubes with Immobilized Plasmonic Nanoparticles for Biophotonic Applications

Halloysite nanotubes (HNTs) with immobilized gold (Au) and silver (Ag) nanoparticles (NPs) belong to a class of nanocomposite materials whose physical properties and applications depend on the geometry of arrangements of the plasmonic nanoparticles on HNT’ surfaces. We explore HNTs:(Au, Ag)-NPs as potential nano-templates for surface-enhanced Raman scattering (SERS). The structure and plasmonic properties of nanocomposites based on HNTs and Au- and Ag-NPs are studied by means of the transmission electron microscopy and optical spectroscopy. The optical extinction spectra of aqueous suspensions of HNTs:(Au, Ag)-NPs and spatial distributions of the electric fields are simulated, and the simulation results demonstrate the corresponding localized plasmonic resonances and numerous “hot spots” of the electric field nearby those NPs. In vitro experiments reveal an enhancement of the protein SERS in fibroblast cells with added HNTs:Ag-NPs. The observed optical properties and SERS activity of the nanocomposites based on HNTs and plasmonic NPs are promising for their applications in biosensorics and biophotonics.

Optical constants of crystalline Bi2Sr2CaCu2O by Brillouin light scattering spectroscopy

Room-temperature optical constants of crystalline Bi2Sr2CaCu2O were determined using data extracted from Brillouin light scattering spectra. Optical extinction coefficient-to-refractive index ratios at a wavelength of 532 nm were obtained from bulk phonon peak linewidth and frequency shift measurements and range from for directions close to the crystallographic c-axis. These ratios, and optical extinction coefficients, absorption coefficients, and imaginary parts of the dielectric function determined from these ratios and known refractive index, are in general agreement with values found in optical reflectance studies, but are 5–7 times larger than those extracted from optical interference measurements.

Structural, Optical and Acoustical Characterization of Polyvinyl Alcohol Dispersed Cadmium Selenide Nanocomposites

Nanosized semiconducting cadmium selenide particles were successfully distributed within the polymer matrix of polyvinyl alcohol (PVA) utilizing the method of heat induced chemical synthesis. The structural characterization of the prepared nanocomposite was conducted using X-ray diffraction for the phase analysis of the nanocrystallites, Transmission electron microscopy (TEM) was used for size and shape determination of the nanoparticles and Fourier transform infrared (FTIR) spectroscopy for identification of the various chemical functional groups possessed by the PVA/CdSe nanocomposites. Various properties of hybrid nanocomposites have been widely scrutinized by researchers during the past few decades because of their unique properties and versatility. The present study involved the behavioral analysis of various optical properties, such as optical absorbance (A), transmittance (T), optical band gap (Eg), refractive index (n), extinction coefficient (k), real and imaginary dielectric constants (ε1 and ε2) and optical conductivity (σopt), of nanocomposite thin films produced by solution casting at temperatures ranging from 303 K to 343 K. The present study also deals with the evaluation of various ultrasonic acoustical properties, like adiabatic compressibility (βad), acoustic impedance (Z), intermolecular free length (Lf), relaxation time (τ) and attenuation coefficient, α, as a function of the square of the frequency (ƒ 1 ), i.e., (α/ƒ 1 ), to permit detailed understanding of behavioral changes in particle-fluid interactions with variation in the solution temperature of the nanocomposite.

Optical properties of [Ta2O5]1-x[TiO2]x, (x = 0.08) thin films

Thin films of [Ta2O5]1-x-[TiO2]x, with x = 0.08, were deposited on quartz substrates (for optical study) and p- type mono- crystalline silicon (100) surfaces (for structural characterization and electrical measurements) by RF magnetron sputtering of [Ta2O5]0.92-[TiO2]0.08, ceramic target, using argon as sputtering gas and oxygen as reactive gas. Films were deposited at room temperature and further annealed at 400, 500, 600 and 700 0C, at ambient atmosphere. The observed XRD patterns show that the as- deposited and annealed films have crystalline structure. The spectral transmissions of the [Ta2O5]1-x-[TiO2]x (x = 0.08) films were measured in UV-visible range. The low optical transmittance in as-deposited films may be due to the presence of unreacted tantalum along with Ta2O5 in the films. From the observed transmission spectra, refractive index, optical band gap, absorption coefficient, extinction coefficient, and thickness of prepared [Ta2O5]0.92-[TiO2]0.08 films, have been calculated by Swanepoel’s envelope technique.

Tunability of optical constants of Se-Ge-Ag thin films based on change in resistivity with temperature for solar cells

Thin films of semiconductor Se80Ge20-xAgx (x = 0, 3, 6, 9, 12 and 15 at.%) were deposited by the thermal evaporation technology. Through optical and electrical characterization, the influence of the Ag ratio on the photoelectric parameters of Se–Ge thin film was studied. The X-ray diffraction pattern showed the amorphous nature of the deposited films as well as the polycrystalline state when the films were annealed at the maximum crystallization temperature (415 K), which was determined by the first derivative of the resistivity curve with respect to temperature. The crystallization kinetics of the film was extracted from the electrical analysis by measuring the change in resistivity with temperature. The electrical results of the thin film showed three regions; namely, amorphous, extended (crystalline) and hopping. In the extended and hopping states, the activation energy and pre-exponential factors were calculated. The optical constants, extinction coefficient and refractive index were calculated using the transmittance and reflectance of the grown Se80Ge20-xAgx films. The energy gaps of the films were estimated in the strong absorption regions. The changes in the bandgap energy of the film by thermal annealing can help to produce materials with acceptable band gaps for use as absorber layers in solar cell applications. Also, the results provide microscopic insights and studies on the structure, electr-othermal and optical properties of Ag metal-doped GeSe as a back contact of solar cells.

Edge, confinement effects, and measurement of the number of layers of MoS2 nanosheets by liquid-exfoliated method assisted by different solvents

A liquid exfoliation method is an indispensable productive approach, inhibited by our breakdown to measure nanosheet concentration, estimation, and thickness. The light scattered by MoS2 nanosheets in liquid solvents, viz., dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone, and ethanol results in optical extinction spectra which determines the optoelectronic properties. All samples were characterized by X-ray diffraction, scanning electron microscopy, and UV–Vis spectroscopy for determining their structure, morphology, and optical properties, respectively. The minimum estimated number of layers was found to be 15 in DMSO as solvent. The liquid-phase method can be employed to a wide range of 2D material including MoSe2, WS2, and WSe2.

Interparticle Distance Effect on the Optical Response of Platinum Dimer Nanoparticles

This article describes the plasmonic coupling effect on the Localized Surface Plasmon Resonance (LSPR) of Platinum (Pt) dimer nanoparticles. The effect of the dielectric medium on the optical response is also calculated for the Pt dimer. The optical extinction spectra have been investigated over a broad spectral range (from the visible to the near infra-red). Measurements were performed using a numerical method based on Finite Element Method (FEM) which permits the determination of both the interparticle distance and the polarization effects on the LSPR. A clear enhancement of LSPR has been appeared for a longitudinal polarization compared to a transversal one. Furthermore, plasmonic coupling induces a tunable red-shifting and broadening of LSPR in dimers by decreasing the interparticle distance.

Effect of Al doping on optical properties of ZnO thin films: theory and experiment

The structural, electronic, and optical properties of zinc oxide thin films with Al-doping have been investigated experimentally and with density functional theory (DFT) calculations. Changes in properties of doped thin films, which are deposited on a glass substrate by a high-frequency magnetron sputtering method, are monitored using X-ray diffraction data and UV measurements. Our theoretical calculations show that the electronic structure of ZnO: Al can be well described by the DFT+U method. The XRD measurements demonstrated the formation of a pure single ZnO phase and Al atoms is well incorporated in the ZnO lattice. Also, we determine the optical constants such as optical dielectric function, refractive index, optical band gap values, extinction coefficient, and optical conductivity of the doping films through transmittance spectra. The calculated results show the change of lattice parameters Al-doped ZnO. The optical band gap of ZnO: Al is increased compared with pure ZnO. Besides, around the Fermi level of Al-doped ZnO was emerged the shallow donor states from mainly 3s-Al states. Our DFT calculations of optical properties Al-doped ZnO agree satisfactorily with the experimentally measured transmittance values.

Optical properties of multi-stacked BaTiO3/SrTiO3 thin films synthesized via chemical method

In this work, the BaTiO3 and SrTiO3 thin films as well as BaTiO3/SrTiO3 lamellar composites are synthesized via sol-gel spin-coating method. The formation of corresponding phases from their sols is investigated by virtue of X-ray diffraction on their powders, which confirms the formation of tetragonal structure for BaTiO3, but cubic structure for SrTiO3. The field emission scanning electron microscopy images show that crack-free films with different morphologies are formed in each sample. Likewise, by changing periodicity of the samples, the morphology of the composite samples is changed. As the number of layers increases from 1 to 20, the band gap reduces from 4.38 eV to 4.10 eV for BaTiO3 samples and from 4.13 eV to 3.80 eV for SrTiO3 samples confirmed by UV–Vis spectra. The band gap of periodicity = 1 sample is higher than that of BaTiO3, while band gaps of periodicity = 2 and 5 composites mount between those of BaTiO3 and SrTiO3. In addition, the refractive indices of multi-stacked composites are about 0.2 lesser than refractive indices of BaTiO3 sample in high wavelengths. The periodicity dependence of optical frequency dielectric constant, dielectric loss, impedance, Urbach tail, extinction coefficient, and electric modulus of multi-stacked composites are also studied.

Color Changes in Ag Nanoparticle Aggregates Placed in Various Environments: Their Application to Air Monitoring.

Fresh Ag nanoparticles (NPs) dispersed on a transparent SiO2 exhibit an intense optical extinction band originating in localized surface plasmon resonance (LSPR) in the visible range. The intensity of the LSPR band weakened when the Ag NPs was stored in ambient air for two weeks. The rate of the weakening and the LSPR wavelength shift, corresponding to visual chromatic changes, strongly depended on the environment in which Ag NPs were set. The origin of a chromatic change was discussed along with both compositional and morphological changes. In one case, bluish coloring followed by a prompt discoloring was observed for Ag NPs placed near the ventilation fan in our laboratory, resulted from adsorption of large amounts of S and Cl on Ag NP surfaces as well as particle coarsening. Such color changes deduce the presence of significant amounts of S and Cl in the environment. In another case, a remarkable blue-shift of the LSPR band was observed for the Ag NPs stored in the desiccator made of stainless steel, originated in the formation of CN and/or HCN compounds and surface roughening. Their color changed from maroon to reddish, suggesting that such molecules were present inside the desiccator.

Influence of Ni-Co dual doping on structural and optical properties of CdSe thin films prepared by chemical bath deposition method

Pure and Ni-Co dual doped CdSe thin films were deposited on glass substrate by chemical bath deposition (CBD) technique. The deposited thin films were annealed for 1 h at 500 °C. X-ray diffraction (XRD) and UV–vis Spectroscopy were used to study the structural and optical properties of the prepared thin films. XRD studies revealed the hexagonal phase for pure CdSe, CdSe: 0%Ni-8%Co, CdSe: 2%Ni-6%Co, CdSe: 6%Ni-2%Co and CdSe: 8%Ni-0%Co thin films, while CdSe: 4%Ni-4%Co produced the cubic phase. The XRD results revealed that the dual doping affected strongly the preferred orientation of the crystallites. The optical band gap energy, Urbach energy, Extinction coefficient, refractive index, real and imaginary dielectric constants and optical conductivity were calculated for all obtained thin films. The direct optical band gap energy of pure CdSe film was 1.43 eV and it decreased with Ni and Co dual doping. The lowest optical band gap energy was observed for CdSe: 4%Ni-4%Co. The dual doping with Ni and Co increased the efficiency of CdSe thin films to be used as solar cells.

SDSS-IV MaNGA: A Star Formation–Baryonic Mass Relation at Kiloparsec Scales

Abstract Star formation rate density, ΣSFR, has shown a remarkable correlation with both components of the baryonic mass kiloparsec scales (i.e., the stellar mass density and molecular gas mass density, Σ* and Σmol, respectively) for galaxies in the nearby universe. In this study, we propose an empirical relation between ΣSFR and the baryonic mass surface density (Σb = Σmol,Av + Σ*, where Σmol,Av is the molecular gas derived from the optical extinction, A V ) at kiloparsec scales using the spatially resolved properties of the MaNGA survey, the largest sample of galaxies observed via integral field spectroscopy (∼8400 objects). We find that ΣSFR tightly correlates with Σb. Furthermore, we derive an empirical relation between ΣSFR and a second-degree polynomial of Σb, yielding a one-to-one relation between these two observables. Both Σb and its polynomial form show a stronger correlation and smaller scatter with respect to ΣSFR than the relations derived using the individual components of Σb. Our results suggest that these three parameters are indeed physically correlated, suggesting a scenario in which the two components of the baryonic mass regulate the star formation activity at kiloparsec scales.