Broadband Optical Absorption Research Articles

Silver Nanowires Deposited on Cellulose Nanofibers/Graphene Oxide Hybrid Membranes as Sandwich-Structured Films for Optoelectronic and SERS Applications

Flexible conductive films with high surface conductivity, broadband optical absorption, and excellent chemical and thermal stabilities are desired for optoelectronic applications. Herein, a facile ...

Solar Steam Generation and Desalination Using Ultra-Broadband Absorption in Plasmonic Alumina Nanowire Haze Structure-Graphene Oxide-Gold Nanoparticle Composite.

Solar steam generation is a promising solar energy harvesting technology to address the global clean energy and water deficiency cost-effectively. In this work, we present a compact plasmonic nanostructure-nanoparticle composite based on haze/GO-rGO/Au enabling multiple purposes such as broadband solar absorption, solar steam generation, and solar desalination. The graphene oxide-reduced GO (GO-rGO) combination allows broadband optical absorption, and the presence of 5 nm Au nanoparticles creates high-density localized hotspots for enhanced photothermal effect as evidenced through Raman signal enhancement studies. Anodized aluminum oxide-based haze nanostructures provide maximum light interaction volume through multiple nanogaps and porosity through vertically aligned nanowires of 20-26 nm width and 5-10 μm depth for water channelization. The haze sample coated with GO-rGO/Au shows high solar absorbance of 92.5% over the 300-2500 nm wavelength range covering the whole solar spectrum (ultraviolet-visible-near-infrared). We have achieved 50 and 71.1% of solar-to-thermal conversion efficiencies in a single-layer microscale sample for saline and freshwater, respectively, with a maximum surface temperature of 95.7 °C. The efficiencies increase to 64 and 77% for two layers of the sample at 5 suns (5 kW m-2) illumination.

Photonic integration of uniform GaAs nanowires in hexagonal and honeycomb lattice for broadband optical absorption

We present an experimental approach toward the realization of GaAs nanowires in the form of square, hexagonal, and honeycomb lattices for photonic integration toward enhanced optical properties. We have carried out a design and fabrication process on GaAs wafers using electron beam lithography patterning, reactive ion etching for hard mask removal, and inductively coupled plasma etching of the material. The resulting photonic crystals are analyzed by field emission scanning electron microscopy. Nanowire array designs in a square, hexagonal, and honeycomb lattice with a variable height of nanowires have been studied. Using finite-difference time-domain simulation, we can derive the comparative optical absorption properties of these nanowire arrays. A very high broadband absorbance of >94% over the 400 nm–1000 nm wavelength range is studied for hexagonal and honeycomb arrays, while a square lattice array shows only a maximum of 85% absorption. We report a minimum of 2% reflectance, or 98% optical absorbance, over 450 nm–700 nm and over a wide angle of 45° through hexagonal and honeycomb lattice integration in GaAs. These results will have potential applications toward broadband optical absorption or light trapping in solar energy harvesting.

Quantitative diffuse optical spectroscopy for noninvasive measurements of the malaria pigment hemozoin.

Hemozoin (Hz) is a crystal by-product of hemoglobin consumption by malaria parasites. There are currently no in vivo deep tissue sensing methods that can quantify Hz presence noninvasively, which would be advantageous for malaria research and treatment. In this work, we describe the broadband near-infrared optical characterization of synthetic Hz in static and dynamic tissue-simulating phantoms. Using hybrid frequency domain and continuous-wave near-infrared spectroscopy, we quantified the broadband optical absorption and scattering spectra of Hz and identified the presence of Hz at a minimum tissue-equivalent concentration of 0.014 µg/mL in static lipid emulsion phantoms simulating human adipose. We then constructed a whole blood-containing tissue-simulating phantom and demonstrated the detection of Hz at physiologically-relevant tissue oxygen saturations ranging from 70-90%. Our results suggest that quantitative diffuse optical spectroscopy may be useful for detecting deep tissue Hz in vivo.

Enhancing the light absorption in dye-sensitized solar cell by using bilayer composite materials based photo-anode

In solar conversion devices, photon absorption is the key factor to get useful output power. The energy band-gap of photo-anode material in dye-sensitized solar cells (DSSCs) must match with the dye so that electron transfer between dyes to semiconductor material is easy. The photo-anode based on titanium oxide, graphene oxide, and their bilayer composite were modeled by the finite element method. The absorption capacity of the bilayer photoanode was studied in the range between 300 to 750 nm before and after introducing the silver nanoparticle. The shell thickness and size of core–shell Ag@oxides and silver nanoparticles were 5 and 70 nm, respectively. The results showed that the narrow bandgap energy of photoanode based on composite GO/TiO2resulted in 29.4 and 39.1% absorption enhancement efficiency as compared to pure TiO2 and GO, respectively. However, the strongly localized electric field intensity of Ag embedded oxide nanoparticle further leads to broad band optical absorption. The photoanode based on Ag@GO/Ag@TiO2 composite has 37 and 48% absorption enhancement as compared to Ag@TiO2 and Ag@GO NPs respectively. This novel approach improves the light-harvesting ability thereby achieving high photo-conversion efficiency.

2D GeP-based photonic device for near-infrared and mid-infrared ultrafast photonics

Abstract Germanium phosphide (GeP), a rising star of novel two-dimensional (2D) material composed of Group IV–V elements, has been extensively studied and applied in photonics thanks to its broadband optical absorption, strong light–matter interaction and flexible bandgap structure. Here, we show the strong nonlinear optical (NLO) properties of 2D GeP nanoflakes in the broadband range with open-aperture Z-scan technique to explore the performance of 2D GeP microfiber photonic devices (GMPDs) in near-infrared (near-IR) and mid-infrared (mid-IR) ultrafast photonics. Our results suggest that employing the GMPD as an optical device in an erbium-doped fiber laser (EDFL) system results in ultrashort pulses and rogue waves (RWs) at 1.55 μm. Likewise, by the incorporation of GMPD into a thulium-doped fiber laser (TDFL) system, stable ultrashort pulse operation is also achieved at 2.0 μm. We expect these findings to be an excellent GMPD that can be applied in mode-locked fiber lasers to open up new avenues for its development and application in ultrafast photonics.

A near-ideal solar selective absorber with strong broadband optical absorption from UV to NIR

A near-ideal solar absorber, which is composed of a metal nanowire array and a planar multilayer system, is proposed and investigated. Both numerical and analytical results show that the proposed nanostructure can achieve over 90% optical absorption throughout the wavelength range of 300–1909 nm due to the coupled effect of multiple resonance modes, and can maintain a good absorption stability over a wide incident angle regardless of the polarization states. Meanwhile, for practical applications, the total photothermal conversion efficiency can reach 95.57% at operating temperature of 373.15 K, which is particularly useful in solar energy harvesting. The absorption performance is also strongly dependent on the diameter and height of nanowire as well as the thicknesses of dielectric layers, enabling the further improvement of both the operating bandwidth and absorption efficiency. Moreover, by adjusting the period of the multilayer or nanowire materials, the selective absorption properties of this nanostructure can be flexibly controlled to satisfy more spectral requirements. These features make the presented designs hold promise for a series of solar-dependent optical applications, such as photothermal energy generation and thermal emitters.

Broadband photocatalysts enabled by 0D/2D heterojunctions of near-infrared quantum dots/graphitic carbon nitride nanosheets

A heterojunction made of 0D near-infrared (NIR)-responsive PbS@CdS@ZnS core@shell@shell quantum dots (PCZ QDs) and 2D graphitic carbon nitride (g-C3N4) nanosheets was rationally constructed herein. In addition to some typical advantages of 0D/2D composites, such as short required charge-diffusion distance and high charge mobility, our designed PCZ QDs/g-C3N4 photocatalysts offer additional beneficial features. The broadband optical absorption of high-quality PCZ QDs highly dispersed on g-C3N4 nanosheets and their strong interaction yield efficient charge transfer between them and endow PCZ QDs/g-C3N4 with high photocatalytic activity from ultraviolet to NIR regions. With the optimized QDs loading level, the achieved, normalized rate constant is higher than the best-reported value for NIR-driven photocatalysis. PCZ QDs/g-C3N4 possesses good recycling performance and no metal release was detected in the solution after photocatalysis. This work highlights the great potential of QDs/g-C3N4 0D/2D photocatalysts in realizing high-efficiency broadband photocatalysis and functional optoelectronic devices for full solar spectrum exploitation.

The strong absorption characteristics of ternary one-dimensional photonic crystals with silver layer

In order to achieve broadband and efficient optical absorption, the multiple silver nanolayer was introduced into the photonic crystals to form a one-dimensional ternary periodic symmetric structure. The effects of thickness of each layer on the band range, absorption bandwidth, absorbance and absorption energy field distribution of the solar spectrum high absorption band were studied by the transfer matrix method. The absorption band with wavelength range from 724 ran to 1 188 nm, spectral width of 464 nm, and average absorbance of 0.78 was obtained by structural adjustment. The absorbed energy is mainly distributed in the first half of the symmetrical structure of the photonic crystal. When the thickness of the silver layer decreased from 30 nm to 15 nm, the local energy in each period increased significantly. At the same time, the distribution and transfer of energy in silicon and MgF2 layers can be controlled. The results of this paper can be used to improve the absorption of solar radiation, and provide an important basis for the design of photonic crystal and their application in solar energy utilization.

A Skin‐Inspired, Interactive, and Flexible Optoelectronic Device with Hydrated Melanin Nanoparticles in a Protein Hydrogel–Elastomer Hybrid

AbstractMelanin, a biologically occurring pigment featuring broadband optical absorption, ion‐binding affinity including antioxidative and radical‐scavenging properties, and hydration‐dependent electrical conductivity is an ideal natural semiconducting material for interfacing electronics with biological systems. Here, a skin‐mimicking optoelectronic device with a melanin nanoparticle (MNP) dispersion in a protein hydrogel–elastomer hybrid (a mimic of epidermis/dermis layers with melanin) and its application as a dopamine sensor and a UV index meter are reported. MNPs dispersed in water are placed in the elastomer reservoir with integrated silver nanowire electrodes and a transparent silk hydrogel window cover; they exhibit n‐type semiconducting behavior with increased conductivities compared with those of dehydrated MNPs. Enhanced generation of free radicals by light illumination results in an increase of the electrical conductivity. In addition, the artificial optoelectronic skin interacts with its environment through the silk hydrogel window. Applications of the device, including its use as a dopamine sensor and a UV index meter to detect dopamine and UV light passing through the window, are demonstrated. The sensitivity of the dopamine sensor is enhanced by the light illumination.

Tungsten-Coated Silicon Nanopillars as Ultra-Broadband and Thermally Robust Solar Harvesting Materials

Solar harvesting materials or structures, with broadband optical absorption, high-temperature tolerance, and scalable fabrication processes, have attracted much attention for real-life optical appl...

Melanin.

Melanins are a unique class of pigments found throughout the biosphere with a wide variety of functions, structures, and presentations. Cordero and Casadevall highlight the wide range of places melanins are found and the diverse functions they play in nature.

Fabrication of Ag-modified hollow titania spheres via controlled silver diffusion in Ag-TiO2 core-shell nanostructures.

Inorganic hollow spheres find a growing number of applications in many fields, including catalysis and solar cells. Hence, a simple fabrication method with a low number of simple steps is desired, which would allow for good control over the structural features and physicochemical properties of titania hollow spheres modified with noble metal nanoparticles. A simple method employing sol–gel coating of nanoparticles with titania followed by controlled silver diffusion was developed and applied for the synthesis of Ag-modified hollow TiO2 spheres. The morphology of the synthesized structures and their chemical composition was investigated using SEM and X-ray photoelectron spectroscopy, respectively. The optical properties of the synthesized structures were characterized using UV–vis spectroscopy. Ag–TiO2 hollow nanostructures with different optical properties were prepared simply by a change of the annealing time in the last fabrication step. The synthesized nanostructures exhibit a broadband optical absorption in the UV–vis range.

Color Contrast of Single-Layer Graphene under White Light Illumination Induced by Broadband Photon Management.

Visualizing and manipulating the optical contrast of single-layer graphene (SLG) and other 2D materials has continuously been an interesting topic to understand fundamental light-matter interaction down to atomic thickness. Because the optical properties of SLG can be tuned by gating, demonstrating and manipulating the color contrast of SLG also has significant potential applications in ultrathin flexible color display. However, previous demonstrations of optical contrast of SLG are mostly limited to reflection intensity contrast under monochromatic illumination using the interference effect. The reported spectral contrast in SLG has mostly been narrow-band or at resonant wavelengths, and it required precise thickness control and/or nanolithography that are hardly scalable to large enough area for display applications. In this paper, we demonstrate novel color contrast optical visibility of SLG under white light using broadband photon management induced by nanoneedle-structured SnOx (x ≤ 1) transparent conductive oxides (TCOs), which is scalable to large-area color display. The low-temperature fabricated, self-assembled, nanoneedle-structured SnOx (x ≤ 1) thin films help to significantly increase the broadband optical absorption in SLG by enhancing the electromagnetic field and increasing the scattering efficiency at the SnOx/SLG interface. With nanoneedle-structured SnOx, the optical absorption in SLG on a fused quartz (SiO2) substrate is drastically increased from ∼1.4 to >10% at λ = 560-990 nm (from yellow to near infrared spectral regimes), leading to a clear color contrast to the surrounding region without SLG. The self-assembly approach, rather than sophisticated and costly nanolithography, allows scalable fabrication of large area 2D photonic devices with a broadband and highly efficient photon management effect. Therefore, this approach can be further extended to color-tunable TCO/dielectric/SLG 2D photonic devices by adjusting the free carrier concentrations/Fermi levels in the TCO and SLG layers via gating-a stepping stone toward ultrathin flexible color display technologies utilizing 2D materials and nanostructured thin films.

Nearly perfect and broadband optical absorption by TMDCs in cover/TMDC/spacer/Au/substrate multilayers

Two-dimensional transition metal dichalcogenides (TMDCs) with direct bandgap and high optical absorption have opened a new horizon in photonics and optoelectronics. Increasing their absorption could greatly benefit their application, a subject still under debate. Thus, this study was focused on the plasmonic effect mediated by a thin gold layer and the role of individual spacer and cover layers or their combination in structures that include TMDC monolayers, namely, cover/TMDC/spacer/Au/substrate multilayers. The optical properties of these structures were investigated via the transfer matrix method in the visible wavelength region, revealing absorption values up to 99%. Such structures could be applied in the design of efficient optical absorbers for high-performance photovoltaic devices.

Spectroscopic properties of Cu2+ in alkaline earth metaphosphate, fluoride-phosphate and fluoride-phosphate-sulfate glasses

Abstract Divalent copper ions (Cu2+) are not only important colorants in consumer glasses. They can also be used as a probe for assessing the local structural arrangement within a solid host. Here, we report on the incorporation of Cu2+ into alkaline earth metaphosphate (MP), fluoride-phosphate (FP) and fluoride-phosphate-sulfate (FPS) glasses. As a d9 transition metal ion, Cu2+ exhibits a broad optical absorption band at wavelengths of 740–880 nm when incorporated into oxide glasses. The specific properties of this band are strongly affected by the local basicity of the host, which reflects in a straightforward dependence of the band position on the mean-field optical basicity in alkaline earth MP. For FP and FPS, however, distinct deviations from this simplistic correlation are found due to selective cation localization on the various oxoanions and/or halogen species. In addition, high basicity favours the formation of monovalent Cu+. Electron paramagnetic resonance indicates a transition from tetragonally distorted octahedral coordination of Cu2+ in MP to rhombohedral distortion in FP and FPS glasses.

Effect of Various Shapes of Silver Nanoparticles on the Performance of Plasmonic Solar Cells Active Layer

In this work, the enhancement of optical absorption in organic thin film active layer was investigated theoretically. The optical absorption results reveal that the introduction of periodic silver (Ag) nanoparticles (NPs) into the thin film active layer influences the absorption spectra. In this study, copper phthalocyanine (CuPc) as one of the organic solar cell materials has been used. Finite Different Time Domain technique has been used to demonstrate the role of the three different shapes of the silver nanoparticles (SNPs). It has been found that the NPs can result in broadband optical absorption enhancement in the wavelength range (350-550) nm due to the surface plasmonic resonance (SPR) phenomena. Moreover, the investigation has been performed the effect of the few shapes of (Cylinder with radius (R) 20 nm and height (H) 60 nm, radius (R) 30 nm for Sphere NPs, and Ellipse NPs with radius R1, R2 of 20 and 30 nm respectively) on the absorption in the organic thin films.

Breakdown of Native Oxide Enables Multifunctional, Free-Form Carbon Nanotube-Metal Hierarchical Architectures.

Passive oxide layers on metal substrates impose remarkable interfacial resistance for electron and phonon transport. Here, a scalable surface activation process is presented for the breakdown of the passive oxide layer and theformation of nanowire/nanopyramid structured surfaces on metal substrates, which enables high-efficiency catalysis of high-crystallinity carbon nanotubes (CNTs) and the direct integration of the CNT-metal hierarchical architectures withflexible free-form configurations. The CNT-metal hierarchical architecture facilitates a dielectric free-energy-carrier transport pathway and blocks the reformation of passive oxide layer, and thus demonstrates a 5-fold decrease in interfacial electrical resistance with 66% increase in specific surface area compared with those without surface activation. Moreover, the CNT-metal hierarchical architectures demonstrate omnidirectional blackbody photoabsorption with the reflectance of 1 × 10-5 over the range from ultraviolet to terahertz region, which is 1 order of magnitude lower than that of any previously reported broadband absorber material. The synergistically incorporated CNT-metal hierarchical architectures offer record-high broadband optical absorption with excellent electrical and structural properties as well as industrial-scaleproducibility.

All-solution-processed Si films with broadband and omnidirectional light absorption

Silicon photonic structures have attracted a great deal of attention due to their potential benefits of efficient light management in optoelectronic applications. In this paper, we demonstrate broadband optical absorption enhancement in solution-processed amorphous silicon (a-Si) by leveraging the advantages of silicon photonic structures. Graded refractive index silicon multi-layer structures are employed by modulating optical constants with simple process optimization, resulting in significantly improved reflectance over a broad range of visible wavelengths. In addition, nanopatterning flexibility of solution-processed silicon provides benefits for tailoring silicon optical properties. With the incorporation of the two-dimensional submicron pattern into silicon films, the absorptivity of silicon films improves considerably below the wavelength of the bandgap (λ ∼ 800 nm), and the limited bandwidth of absorptivity in silicon films can be extended to near-infrared wavelengths by coating with a thin gold layer. The methodology is generally applicable to a platform for improving the broadband optical absorption of photonic and optoelectronic devices.

Ultrahigh omnidirectional, broadband, and polarization-independent optical absorption over the visible wavelengths by effective dispersion engineering

Achieving perfect light absorption at a subwavelength-scale thickness has various advantageous in terms of cost, flexibility, weight, and performance for many different applications. However, obtaining perfect absorbers covering a wide range of wavelengths regardless of incident angle and input polarization without a complicated patterning process while maintaining a small thickness remains a challenge. In this paper, we demonstrate flat, lithography-free, ultrahigh omnidirectional, polarization-independent, broadband absorbers through effective dispersion engineering. The proposed absorbers show day-integrated solar energy absorption up to 96%, which is 32% better than with lossy semiconductor/metal absorbers. The proposed simple yet effective method can be applied to light absorption thin film structures based on various types of highly lossy semiconductor materials, including emerging 2D materials.