Showing papers on "Absorption (electromagnetic radiation) published in 2012"
TL;DR: It is demonstrated that 100% light absorption can take place in a single patterned sheet of doped graphene, relevant for infrared light detectors and sources, which can be made tunable via electrostatic doping of graphene.
Abstract: We demonstrate that 100% light absorption can take place in a single patterned sheet of doped graphene. General analysis shows that a planar array of small particles with losses exhibits full absorption under critical-coupling conditions provided the cross section of each individual particle is comparable to the area of the lattice unit cell. Specifically, arrays of doped graphene nanodisks display full absorption when supported on a substrate under total internal reflection and also when lying on a dielectric layer coating a metal. Our results are relevant for infrared light detectors and sources, which can be made tunable via electrostatic doping of graphene.
1,153 citations
TL;DR: In this paper, the authors show that a great solar cell also needs to be a great light-emitting diode, which is a necessity for approaching the Shockley-Queisser (SQ) efficiency limit.
Abstract: Absorbed sunlight in a solar cell produces electrons and holes. However, at the open-circuit condition, the carriers have no place to go. They build up in density, and ideally, they emit external luminescence that exactly balances the incoming sunlight. Any additional nonradiative recombination impairs the carrier density buildup, limiting the open-circuit voltage. At open circuit, efficient external luminescence is an indicator of low internal optical losses. Thus, efficient external luminescence is, counterintuitively, a necessity for approaching the Shockley–Queisser (SQ) efficiency limit. A great solar cell also needs to be a great light-emitting diode. Owing to the narrow escape cone for light, efficient external emission requires repeated attempts and demands an internal luminescence efficiency 90%.
896 citations
TL;DR: In this article, an organic near-infrared dye is used as an antenna for the b-NaYF4:Yb,Er nanoparticles in which the upconversion occurs.
Abstract: Photon upconversion of near-infrared photons is a promising way to overcome the Shockley–Queisser efficiency limit of 32% of a single-junction solar cell. However, the practical applicability of the most efficient known upconversion materials at moderate light intensities is limited by their extremely weak and narrowband near-infrared absorption. Here, we introduce the concept of an upconversion material where an organic near-infrared dye is used as an antenna for the b-NaYF4:Yb,Er nanoparticles in which the upconversion occurs. The overall upconversion by the dye-sensitized nanoparticles is dramatically enhanced (by a factor of ∼3,300) as a result of increased absorptivity and overall broadening of the absorption spectrum of the upconverter. The proposed concept can be extended to cover any part of the solar spectrum by using a set of dye molecules with overlapping absorption spectra acting as an extremely broadband antenna system, connected to suitable upconverters.
832 citations
TL;DR: An ultrabroadband thin-film infrared absorber made of sawtoothed anisotropic metamaterial waveguide that can be applied in the field of designing photovoltaic devices and thermal emitters.
Abstract: We present an ultrabroadband thin-film infrared absorber made of sawtoothed anisotropic metamaterial. Absorptivity of higher than 95% at normal incidence is supported in a wide range of frequencies, where the full absorption width at half-maximum is about 86%. Such property is retained well at a very wide range of incident angles too. Light of shorter wavelengths are harvested at upper parts of the sawteeth of smaller widths, while light of longer wavelengths are trapped at lower parts of larger tooth widths. This phenomenon is explained by the slowlight modes in anisotropic metamaterial waveguide. Our study can be applied in the field of designing photovoltaic devices and thermal emitters.
826 citations
TL;DR: In this article, a microwave ultra-broadband polarization-independent metamaterial absorber is demonstrated, which is composed of a periodic array of metal-dielectric multilayered quadrangular frustum pyramids.
Abstract: A microwave ultra-broadband polarization-independent metamaterial absorber is demonstrated. It is composed of a periodic array of metal-dielectric multilayered quadrangular frustum pyramids. These pyramids possess resonant absorption modes at multi-frequencies, of which the overlapping leads to the total absorption of the incident wave over an ultra-wide spectral band. The experimental absorption at normal incidence is above 90% in the frequency range of 7.8–14.7 GHz, and the absorption is kept large when the incident angle is smaller than 60°. The experimental results agree well with the numerical simulation.
735 citations
TL;DR: It is shown that the film-coupled nanocubes provide a reflectance spectrum that can be tailored by varying the geometry (the size of the cubes and/or the thickness of the spacer) and can be controlled at scales out of reach of lithographic approaches that are otherwise required to manipulate matter on the nanoscale.
Abstract: Efficient and tunable absorption is essential for a variety of applications, such as designing controlled-emissivity surfaces for thermophotovoltaic devices, tailoring an infrared spectrum for controlled thermal dissipation and producing detector elements for imaging. Metamaterials based on metallic elements are particularly efficient as absorbing media, because both the electrical and the magnetic properties of a metamaterial can be tuned by structured design. So far, metamaterial absorbers in the infrared or visible range have been fabricated using lithographically patterned metallic structures, making them inherently difficult to produce over large areas and hence reducing their applicability. Here we demonstrate a simple method to create a metamaterial absorber by randomly adsorbing chemically synthesized silver nanocubes onto a nanoscale-thick polymer spacer layer on a gold film, making no effort to control the spatial arrangement of the cubes on the film. We show that the film-coupled nanocubes provide a reflectance spectrum that can be tailored by varying the geometry (the size of the cubes and/or the thickness of the spacer). Each nanocube is the optical analogue of a grounded patch antenna, with a nearly identical local field structure that is modified by the plasmonic response of the metal's dielectric function, and with an anomalously large absorption efficiency that can be partly attributed to an interferometric effect. The absorptivity of large surface areas can be controlled using this method, at scales out of reach of lithographic approaches (such as electron-beam lithography) that are otherwise required to manipulate matter on the nanoscale.
658 citations
TL;DR: In this article, the authors outline the current understanding of two general aspects of optical response of graphene: optical absorption and light emission, and show that optical absorption in graphene is dominated by intraband transitions at low photon energies and by interband transitions at higher energies (from mid-infrared to ultraviolet).
643 citations
TL;DR: The wavelength range of 650-1450 nm falls in the region of the spectrum with the lowest absorption in tissue and therefore enables the deepest tissue penetration and is the wavelength range focused on with this review.
Abstract: The importance of long wavelength and near-infrared (NIR) imaging has dramatically increased due to the desire to perform whole animal and deep tissue imaging. The adoption of NIR imaging is also growing rapidly due to the availability of targeted biological agents for diagnosis and basic medical research that can be imaged in vivo. The wavelength range of 650–1450 nm falls in the region of the spectrum with the lowest absorption in tissue and therefore enables the deepest tissue penetration. This is the wavelength range we focus on with this review. To operate effectively, the imaging agents must both be excited and must emit in this long-wavelength window. We review the agents used for imaging by absorption, scattering, and excitation (such as fluorescence). Imaging agents comprise both aqueous soluble and insoluble species, both organic and inorganic, and unimolecular and supramolecular constructs. The interest in multimodal imaging, which involves delivery of actives, targeting, and imaging, requires ...
610 citations
TL;DR: A double-sided grating design is introduced, where the front and back surfaces of the cell are separately optimized for antireflection and light trapping, respectively, which yields a photocurrent close to the Yablonovitch limit.
Abstract: Enhancing the light absorption in ultrathin-film silicon solar cells is important for improving efficiency and reducing cost We introduce a double-sided grating design, where the front and back surfaces of the cell are separately optimized for antireflection and light trapping, respectively The optimized structure yields a photocurrent of 346 mA/cm(2) at an equivalent thickness of 2 μm, close to the Yablonovitch limit This approach is applicable to various thicknesses and is robust against metallic loss in the back reflector
604 citations
TL;DR: It is found that the nonlinear refractive index decreases with increasing excitation flux but slower than the absorption, suggesting that graphene may be a very promising nonlinear medium, paving the way for graphene-based nonlinear photonics.
Abstract: Under strong laser illumination, few-layer graphene exhibits both a transmittance increase due to saturable absorption and a nonlinear phase shift. Here, we unambiguously distinguish these two nonlinear optical effects and identify both real and imaginary parts of the complex nonlinear refractive index of graphene. We show that graphene possesses a giant nonlinear refractive index n2≃10−7 cm2 W−1, almost 9 orders of magnitude larger than bulk dielectrics. We find that the nonlinear refractive index decreases with increasing excitation flux but slower than the absorption. This suggests that graphene may be a very promising nonlinear medium, paving the way for graphene-based nonlinear photonics.
578 citations
TL;DR: In this paper, the authors show that perfect absorption can be achieved in a system comprising a single lossy dielectric layer of thickness much smaller than the incident wavelength on an opaque substrate by utilizing the nontrivial phase shifts at interfaces between lossy media.
Abstract: We show that perfect absorption can be achieved in a system comprising a single lossy dielectric layer of thickness much smaller than the incident wavelength on an opaque substrate by utilizing the nontrivial phase shifts at interfaces between lossy media. This design is implemented with an ultra-thin (∼λ/65) vanadium dioxide (VO2) layer on sapphire, temperature tuned in the vicinity of the VO2 insulator-to-metal phase transition, leading to 99.75% absorption at λ = 11.6 μm. The structural simplicity and large tuning range (from ∼80% to 0.25% in reflectivity) are promising for thermal emitters, modulators, and bolometers.
TL;DR: In this article, the dispersion and absorption properties in the visible and near-infrared wavelength region have been determined for distilled water, heavy water, chloroform, carbon tetrachloride, toluene, ethanol, carbon disulfide, and nitrobenzene at a temperature of 20 °C.
Abstract: Liquid-filled photonic crystal fibers and optofluidic devices require infiltration with a variety of liquids whose linear optical properties are still not well known over a broad spectral range, particularly in the near infrared. Hence, dispersion and absorption properties in the visible and near-infrared wavelength region have been determined for distilled water, heavy water, chloroform, carbon tetrachloride, toluene, ethanol, carbon disulfide, and nitrobenzene at a temperature of 20 °C. For the refractive index measurement a standard Abbe refractometer in combination with a white light laser and a technique to calculate correction terms to compensate for the dispersion of the glass prism has been used. New refractive index data and derived dispersion formulas between a wavelength of 500 nm and 1600 nm are presented in good agreement with sparsely existing reference data in this wavelength range. The absorption coefficient has been deduced from the difference of the losses of several identically prepared liquid filled glass cells or tubes of different lengths. We present absorption data in the wavelength region between 500 nm and 1750 nm.
TL;DR: In this article, the Fabry-Perot model was used to explain the functionality of a perfect absorber based on a molecular monolayer placed at an appropriate distance from a metallic ground plate.
Abstract: Metamaterial-based perfect absorbers promise many applications. Perfect absorption is characterized by the complete suppression of transmission and reflection and complete dissipation of the incident energy by the absorptive meta-atoms. A certain absorption spectrum is usually assigned to a bulk medium and serves as a signature of the respective material. Here we show how to use graphene flakes as building blocks for perfect absorbers. Then, an absorbing meta-atom only consists of a molecular monolayer placed at an appropriate distance from a metallic ground plate. We show that the functionality of such device is intuitively and correctly explained by a Fabry-Perot model.
TL;DR: In this paper, the authors show that few-layer graphene exhibits both a transmittance increase due to saturable absorption and a nonlinear phase shift, and they unambiguously distinguish these two nonlinear optical effects and identify both real and imaginary parts of the complex nonlinear refractive index of graphene.
Abstract: Under strong laser illumination, few-layer graphene exhibits both a transmittance increase due to saturable absorption and a nonlinear phase shift. Here, we unambiguously distinguish these two nonlinear optical effects and identify both real and imaginary parts of the complex nonlinear refractive index of graphene. We show that graphene possesses a giant nonlinear refractive index n2=10-7cm2W-1, almost nine orders of magnitude larger than bulk dielectrics. We find that the nonlinear refractive index decreases with increasing excitation flux but slower than the absorption. This suggests that graphene may be a very promising nonlinear medium, paving the way for graphene-based nonlinear photonics.
TL;DR: A dual-band perfect absorber based on a gold nanocross structure with two bands of maximum absorption of 94% is introduced and can be readily tuned throughout the mid-infrared with their associated resonances giving rise to large near-field enhancements.
Abstract: Metamaterial-based perfect absorbers utilize intrinsic loss, with the aid of appropriate structural design, to achieve near unity absorption at a certain wavelength. For most of the reported absorbers, the absorption occurs only at a single wavelength where plasmon resonances are excited in the nanostructures. Here we introduce a dual-band perfect absorber based on a gold nanocross structure. Two bands of maximum absorption of 94% are experimentally accomplished by breaking the symmetry of the cross structure. Furthermore, we demonstrate the two bands can be readily tuned throughout the mid-infrared with their associated resonances giving rise to large near-field enhancements. These features are ideal for multiband surface-enhanced infrared spectroscopy applications. We experimentally demonstrate this application by simultaneously detecting two molecular vibrational modes of a 4 nm thick polymer film utilizing our proposed absorber. Furthermore, in response to variations in the interaction strength betwee...
TL;DR: The ability to obtain spatially resolved IR spectra as well as high-resolution chemical images collected at specific IR wavenumbers was demonstrated and it was shown that by taking advantage of the ability to arbitrarily control the polarization direction of the IR excitation laser, it was possible to obtain important information regarding molecular orientation in electrospun nanofibers.
Abstract: Polymer and life science applications of a technique that combines atomic force microscopy (AFM) and infrared (IR) spectroscopy to obtain nanoscale IR spectra and images are reviewed. The AFM-IR spectra generated from this technique contain the same information with respect to molecular structure as conventional IR spectroscopy measurements, allowing significant leverage of existing expertise in IR spectroscopy. The AFM-IR technique can be used to acquire IR absorption spectra and absorption images with spatial resolution on the 50 to 100 nm scale, versus the scale of many micrometers or more for conventional IR spectroscopy. In the life sciences, experiments have demonstrated the capacity to perform chemical spectroscopy at the sub-cellular level. Specifically, the AFM-IR technique provides a label-free method for mapping IR-absorbing species in biological materials. On the polymer side, AFM-IR was used to map the IR absorption properties of polymer blends, multilayer films, thin films for active devices such as organic photovoltaics, microdomains in a semicrystalline polyhydroxyalkanoate copolymer, as well as model pharmaceutical blend systems. The ability to obtain spatially resolved IR spectra as well as high-resolution chemical images collected at specific IR wavenumbers was demonstrated. Complementary measurements mapping variations in sample stiffness were also obtained by tracking changes in the cantilever contact resonance frequency. Finally, it was shown that by taking advantage of the ability to arbitrarily control the polarization direction of the IR excitation laser, it is possible to obtain important information regarding molecular orientation in electrospun nanofibers.
TL;DR: The unique ability of multi-wavelength photo-acoustic measurements of dry and thermal-denuded absorption to deconstruct this complicated wavelength-dependent system of absorption and mixing of BB particles is reported on.
Abstract: Biomass burning (BB) contributes large amounts of black carbon (BC) and particulate organic matter (POM) to the atmosphere and contributes significantly to the earth’s radiation balance BB particles can be a complicated optical system, with scattering and absorption contributions from BC, internal mixtures of BC and POM, and wavelength-dependent absorption of POM Large amounts of POM can also be externally mixed We report on the unique ability of multi-wavelength photo-acoustic measurements of dry and thermal-denuded absorption to deconstruct this complicated wavelength-dependent system of absorption and mixing Optical measurements of BB particles from the Four Mile Canyon fire near Boulder, Colorado, showed that internal mixtures of BC and POM enhanced absorption by up to 70% The data supports the assumption that the POM was very weakly absorbing at 532 nm Enhanced absorption at 404 nm was in excess of 200% above BC absorption and varied as POM mass changed, indicative of absorbing POM Absorption by internal mixing of BC and POM contributed 19( ± 8)% to total 404-nm absorption, while BC alone contributed 54( ± 16)% Approximately 83% of POM mass was externally mixed, the absorption of which contributed 27( ± 15)% to total particle absorption (at 404 nm) The imaginary refractive index and mass absorption efficiency (MAE) of POM at 404 nm changed throughout the sampling period and were found to be 0007 ± 0005 and 082 ± 043 m2 g-1, respectively Our analysis shows that the MAE of POM can be biased high by up to 50% if absorption from internal mixing of POM and BC is not included
TL;DR: The results presented here reveal the exceptional potential of sulfide-based ion-exchangers for remediating of uranium-containing wastes and groundwater and for extracting uranium from the sea.
Abstract: Uranium is the main source for nuclear energy but also one of the most toxic heavy metals. The current methods for uranium removal from water present limitations, such as narrow pH operating range, limited tolerance to high salt concentrations, or/and high cost. We show here that a layered sulfide ion exchanger K2MnSn2S6 (KMS-1) overcomes these limitations and is exceptionally capable in selectively and rapidly sequestering high (ppm) as well as trace (ppb) quantities of UO22+ under a variety of conditions, including seawater. KMS-1 can efficiently absorb the naturally occurring U traces in seawater samples. The results presented here reveal the exceptional potential of sulfide-based ion-exchangers for remediating of uranium-containing wastes and groundwater and for extracting uranium from the sea.
TL;DR: In this article, the authors demonstrate the design, characterization, and interference-theory interpretation of a terahertz triple-band metamaterial absorber (MA) with three distinctive absorption peaks at 0.5, 1.03, and 1.71 THz with absorption rates of 96.4, 96.3, and 96.7%, respectively.
Abstract: We demonstrate the design, characterization, and interference-theory interpretation of a terahertz triple-band metamaterial absorber (MA). The experiments show that the fabricated MA has three distinctive absorption peaks at 0.5, 1.03, and 1.71 THz with absorption rates of 96.4%, 96.3%, and 96.7%, respectively. We use the multi-reflection interference theory to investigate the physical insight of the proposed triple-band terahertz MA, which provides a design guideline for MA of such type. The theoretical predictions of the interference model have excellent agreements with experimental results. The designed multiband absorber is easy to manufacture and insensitive to incident polarizations with high absorption, which is favorable for various applications.
TL;DR: In this paper, the band gap energy of indium sulfide quantum dots is observed to be dependent on the Cu/In ratio, exhibiting a higher band gap from more Cu-deficient QDs.
Abstract: Copper indium sulfide (CIS) quantum dots (QDs) with different Cu/In molar ratios of 1/1, 1/2, and 1/4 are synthesized via a hot colloidal route. The band gap energy of CIS QDs is observed to be dependent on Cu/In ratio, exhibiting a higher band gap from more Cu-deficient QDs. The emission wavelengths of all CIS QDs belong to a deep red region (665–717 nm) with relatively low quantum yields (QYs) of 8.6–12.7%. Compared to respective original core QDs, the absorption peaks of all CIS/ZnS QDs are blue-shifted, and their emission wavelengths move to a higher energy accordingly, showing a quite tunable emission from yellow to red. The effective surface passivation by a ZnS overlayer results in a dramatic increase in QY of CIS/ZnS QDs in the range of 68–78%. All CIS/ZnS QDs are tested as wavelength converters for the fabrication of QD-based light-emitting diodes (LEDs). QD-based white LEDs that consist of only a single type of QD are for the first time realized by applying yellow-emitting CIS/ZnS QDs as a resul...
TL;DR: In this article, an inverted nanopyramid light-trapping scheme for thin-film crystalline silicon (c-Si) solar cells was proposed to enhance light absorption within the semiconductor absorber layer and reduce material usage.
Abstract: Thin-film crystalline silicon (c-Si) solar cells with light-trapping structures can enhance light absorption within the semiconductor absorber layer and reduce material usage. Here we demonstrate that an inverted nanopyramid light-trapping scheme for c-Si thin films, fabricated at wafer scale via a low-cost wet etching process, significantly enhances absorption within the c-Si layer. A broadband enhancement in absorptance that approaches the Yablonovitch limit (Yablonovitch, E. J. Opt. Soc. Am.1987, 72, 899–907 ) is achieved with minimal angle dependence. We also show that c-Si films less than 10 μm in thickness can achieve absorptance values comparable to that of planar c-Si wafers thicker than 300 μm, amounting to an over 30-fold reduction in material usage. Furthermore the surface area increases by a factor of only 1.7, which limits surface recombination losses in comparison with other nanostructured light-trapping schemes. These structures will not only significantly curtail both the material and proc...
TL;DR: The results demonstrate that current climate models that treat OC as nonabsorbing are underestimating the total warming effect of carbonaceous aerosols by neglecting part of the atmospheric heating, particularly over biomass-burning regions that emit BrC.
Abstract: Black carbon (BC) is functionally defined as the absorbing component of atmospheric total carbonaceous aerosols (TC) and is typically dominated by soot-like elemental carbon (EC). However, organic carbon (OC) has also been shown to absorb strongly at visible to UV wavelengths and the absorbing organics are referred to as brown carbon (BrC), which is typically not represented in climate models. We propose an observationally based analytical method for rigorously partitioning measured absorption aerosol optical depths (AAOD) and single scattering albedo (SSA) among EC and BrC, using multiwavelength measurements of total (EC, OC, and dust) absorption. EC is found to be strongly absorbing (SSA of 0.38) whereas the BrC SSA varies globally between 0.77 and 0.85. The method is applied to the California region. We find TC (EC + BrC) contributes 81% of the total absorption at 675 nm and 84% at 440 nm. The BrC absorption at 440 nm is about 40% of the EC, whereas at 675 nm it is less than 10% of EC. We find an enhanced absorption due to OC in the summer months and in southern California (related to forest fires and secondary OC). The fractions and trends are broadly consistent with aerosol chemical-transport models as well as with regional emission inventories, implying that we have obtained a representative estimate for BrC absorption. The results demonstrate that current climate models that treat OC as nonabsorbing are underestimating the total warming effect of carbonaceous aerosols by neglecting part of the atmospheric heating, particularly over biomass-burning regions that emit BrC.
TL;DR: In this article, an in-depth study of bilayer cells consisting of a donor/acceptor interface between zinc phthalocyanine (ZnPc) and fullerene (C60) is conducted and devices with the typically deposited standing up (edge-on) orientation are compared to those with ZnPC lying flat (face-on).
Abstract: The anisotropy inherent to many planar organic molecules leads to a high sensitivity of various fundamental processes to the orientation of molecules within films and at heterojunctions. Such processes include absorption, charge and exciton transport, energy levels, and charge transfer, all of which are critical to organic solar cell operation. Here,an in-depth study of bilayer cells consisting of a donor/acceptor interface between zinc phthalocyanine (ZnPc) and fullerene (C60) is conducted and devices with the typically deposited standing up (edge-on) orientation are compared to those with ZnPc lying flat (face-on). The face-on ZnPc-based device allows for an increase in all solar cell parameters, substantially increasing power conversion efficiency from 1.5% to 2.8%. Spectrally resolved photocurrent measurements reveal a >50% increase in ZnPc signal, from which only 12% is accounted for by the increase in absorption associated with the face-on orientation. The increase in internal quantum efficiency is accounted for via an improved charge transfer. The results of this study indicate that proper consideration of the orientation between donor and acceptor needs to be taken in order to fully optimize the numerous processes required for photovoltaic energy conversion.
TL;DR: It is demonstrated experimentally that two-dimensional arrays of sharp convex grooves in gold ensure efficient (>87%) broadband (450-850 nm) absorption of unpolarized light, reaching an average level of 96%.
Abstract: Plasmonic effects can turn reflective metals into strong absorbers, although this is usually realized within narrow wavelength ranges near resonances. Using arrays of ultra-sharp convex grooves, Sondergaard et al. show that nonresonant absorption can lead to effective broadband light absorption.
TL;DR: A novel 3D star-shaped acceptor based on triphenylamine as a core and diketopyrrolopyrrole as arms was synthesized and exhibited excellent thermal stability, strong absorption, and very high open-circuit voltage in solution-processed organic solar cells based on P3HT:S(TPA-DPP).
TL;DR: In this article, a radiating two-oscillator model is proposed to describe both the absorption spectrum and the scattering parameters quantitatively, and the model also predicts metamaterials with a narrow spectral feature in the absorption larger than the background absorption of the radiative element.
Abstract: Several classical analogues of electromagnetically induced transparency in metamaterials have been demonstrated. A simple two-resonator model can describe their absorption spectrum qualitatively, but fails to provide information about the scattering properties-e.g., transmission and group delay. Here we develop an alternative model that rigorously includes the coupling of the radiative resonator to the external electromagnetic fields. This radiating two-oscillator model can describe both the absorption spectrum and the scattering parameters quantitatively. The model also predicts metamaterials with a narrow spectral feature in the absorption larger than the background absorption of the radiative element. This classical analogue of electromagnetically induced absorption is shown to occur when both the dissipative loss of the radiative resonator and the coupling strength are small. These predictions are subsequently demonstrated in experiments.
TL;DR: In this article, an enhanced photocurrent in a thin-film iron oxide photoanode coated on arrays of Au nanopillars was shown, attributed primarily to the increased optical absorption originating from both surface plasmon resonances and photonic-mode light trapping in the nanostructured topography.
Abstract: Photocatalytic water splitting represents a promising way to produce renewable hydrogen fuel from solar energy. Ultrathin semiconductor electrodes for water splitting are of particular interest because the optical absorption occurs in the region where photogenerated charge carriers can effectively contribute to the chemical reactions on the surface. It is therefore important to manipulate and concentrate the incident light so that more photons can be absorbed within the thin film. Here we show an enhanced photocurrent in a thin-film iron oxide photoanode coated on arrays of Au nanopillars. The enhancement can be attributed primarily to the increased optical absorption originating from both surface plasmon resonances and photonic-mode light trapping in the nanostructured topography. The resonances can be tuned to a desirable wavelength by varying the thickness of the iron oxide layer. A net enhancement as high as 50% was observed over the solar spectrum.
TL;DR: This work develops a facile strategy for synthesizing atomically thick single layers and demonstrates their superior ability to optimize the thermoelectric energy harvesting.
Abstract: Thermoelectric materials can realize significant energy savings by generating electricity from untapped waste heat. However, the coupling of the thermoelectric parameters unfortunately limits their efficiency and practical applications. Here, a single-layer-based (SLB) composite fabricated from atomically thick single layers was proposed to optimize the thermoelectric parameters fully. Freestanding five-atom-thick Bi2Se3 single layers were first synthesized via a scalable interaction/exfoliation strategy. As revealed by X-ray absorption fine structure spectroscopy and first-principles calculations, surface distortion gives them excellent structural stability and a much increased density of states, resulting in a 2-fold higher electrical conductivity relative to the bulk material. Also, the surface disorder and numerous interfaces in the Bi2Se3 SLB composite allow for effective phonon scattering and decreased thermal conductivity, while the 2D electron gas and energy filtering effect increase the Seebeck c...
TL;DR: Experimental results reveal that these Au-BiVO(4) heterogeneous nanostructures exhibit much higher visible-light photocatalytic activities than the individual BiVO( 4) microtubes and nanosheets for both dye degradation and water oxidation.
Abstract: Au-BiVO4 heterogeneous nanostructures have been successfully prepared through in situ growth of gold nanoparticles on BiVO4 microtubes and nanosheets via a cysteine-linking strategy. The experimental results reveal that these Au-BiVO4 heterogeneous nanostructures exhibit much higher visible-light photocatalytic activities than the individual BiVO4 microtubes and nanosheets for both dye degradation and water oxidation. The enhanced photocatalytic efficiencies are attributed to the charge transfer from BiVO4 to the attached gold nanoparticles as well as their surface plasmon resonance (SPR) absorption. These new heteronanostructures are expected to show considerable potential applications in solar-driven wastewater treatment and water splitting.
TL;DR: In this article, a spectroscopic analysis of 115 wintertime particulate matter samples collected in rural California showed that wood smoke absorbs solar radiation with a strong spectral selectivity, consistent with prior work that has demonstrated that organic carbon (OC), in addition to black carbon (BC), appreciably absorb solar radiation in the visible and ultraviolet spectral regions.
Abstract: . A spectroscopic analysis of 115 wintertime particulate matter samples collected in rural California shows that wood smoke absorbs solar radiation with a strong spectral selectivity. This is consistent with prior work that has demonstrated that organic carbon (OC), in addition to black carbon (BC), appreciably absorbs solar radiation in the visible and ultraviolet spectral regions. We apportion light absorption to OC and BC and find that the absorption Angstrom exponent of the light-absorbing OC in these samples ranges from 3.0 to 7.4 and averages 5.0. Further, we calculate that OC would account for 14% and BC would account for 86% of solar radiation absorbed by the wood smoke in the atmosphere (integrated over the solar spectrum from 300 to 2500 nm). OC would contribute 49% of the wood smoke particulate matter absorption of ultraviolet solar radiation at wavelengths below 400 nm and, therefore, may affect tropospheric photochemistry. These results illustrate that BC is the dominant light-absorbing particulate matter species in atmospheres burdened with residential wood smoke and OC absorption is secondary but not insignificant. Further, these results add to the growing body of evidence that light-absorbing OC is ubiquitous in atmospheres influenced by biomass burning and may be important to include when considering particulate matter effects on climate.