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Photocarriers predominantly recombine at semiconductor surfaces and interfaces, assuming high bulk carrier lifetime. Consequently, understanding the extraction of photocarriers via surfaces is critical to optoelectronics. Here, we propose Haynes-Shockley experiment analogs to investigate photocarrier surface extraction. A Schottky junction is used to tune the silicon near-surface electric field strength that varies over several orders of magnitude and simultaneously observe variations in broadband photocarrier extraction. Schottky barrier height and surface potential are both modulated. Work function tunable indium tin oxide (ITO) is developed to precisely regulate the barrier height and collect photocarriers at 0 V bias, thus avoiding the photocurrent gain effect. All experiments demonstrate >98% broadband internal quantum efficiency. The experiments are further extended to wave interference photonic crystals and random pyramids, paving a way to estimate the photogeneration rate of diverse surface light-trapping topologies by collecting nearly all photocarriers. The insights reported here provide a systematic experimental basis to investigate interfacial effects on photocarrier spatial generation and collection.

Metamaterials are a new class of artificial materials that can achieve electromagnetic properties that do not occur naturally, and as such they can also be a new class of photocatalytic structures. We show that metal-based catalysts can achieve electromagnetic field amplification and broadband absorption by decoupling optical properties from the material composition as exemplified with a ZnO/Cu metamaterial surface comprising periodically arranged nanocubes. Through refractive index engineering close to the index of air, the metamaterial exhibits near-perfect 98% absorption. The combination of plasmonics and broadband absorption elevates the weak electric field intensities across the nonplasmonic absorption range. This feedback between optical excitation and plasmonic excitation dramatically enhances light-to-dark catalytic rates by up to a factor of 181 times, compared to a 3 times photoenhancement of ZnO/Cu nanoparticles or films, and with angular invariance. These results show that metamaterial catalysts can act as a singular light harvesting device that substantially enhances photocatalysis of important reactions.

The hydrogenation of CO2 to hydrocarbon fuels via solar radiation offers a sustainable pathway towards a carbon-neutral energy cycle. However, the reaction is hindered by the intermittent availability of sunlight. This critical issue could be mitigated by engineering a materials system, known as persistent photocatalysis, that prolongs solar fuel production during overcast periods and into the evenings. During illumination, charge can be stored in a suitable capacitor or battery-like material that interfaces with the photocatalyst, while discharging occurs postillumination to continue driving the catalytic reaction. We discuss emerging trends and materials strategies to develop these catalyst systems and prolong the operation of photocatalysis. The photocatalytic conversion of CO2 to fuels could contribute to a carbon-neutral energy cycle, but it works only when sunlight is available. Here the authors propose a persistent photocatalyst system that prolongs solar fuel production and discuss emerging trends and design strategies.

A conventional light management approach on a photo-catalyst is to concentrate photo-intensity to enhance the catalytic rate. We present a counter-intuitive approach where light intensity is distributed below the electronic photo-saturation limit under the principle of light maximization. By operating below the saturation point of the photo-intensity induced hydroxide growth under reactant gaseous H2+CO2 atmosphere, a coating of defect engineered In2O3-x(OH)y nanorod Reverse Water Gas Shift solar-fuel catalyst on an optical waveguide outperforms a coated plane by a factor of 2.2. Further, light distribution along the length of the waveguide increases optical pathlengths of the weakly absorptive green and yellow wavelengths, which increases CO product rate by a factor of 8.1-8.7 in the visible. Synergistically pairing with thinly doped silicon on the waveguide enhances the CO production rate by 27% over the visible. In addition, the persistent photoconductivity behavior of the In2O3-x(OH)y system enables CO production at a comparable rate for 2 h after turning off photo-illumination, enhancing yield with 44-62% over thermal only yield. The practical utility of persistent photocatalysis was demonstrated through outdoor solar concentrator tests, which after a day-and-night cycle showed CO yield increase of 19% over a day-light only period., Concentrating photo-intensities on photocatalyst has diminishing returns. Here the authors show the catalyst on glass rod waveguide at optimal low intensity results in high efficiency in the gas phase reverse water gas shift reaction in an annular glass cylindrical rod photoreactor.

Catalytic reduction of carbon dioxide is a promising strategy for mitigating global carbon emissions. In particular, the abundant and nontoxic material hydroxyapatite demonstrates high activity at ...

Optimizing kinetic barriers of ammonia synthesis to reduce the energy intensity has recently attracted significant research interest. The motivation for the research is to discover means by which a...

We propose a radio frequency (RF) and visibly transparent composite metasurface design comprising newly developed transparent multilayer conductive coatings. Detailed experimental and theoretical analysis of the RF/visible transparency of the proposed meta-glass is provided. The proposed nature-inspired symmetrical honeycomb-shaped meta-glass design, alters the electromagnetic properties of the glass substrate in the RF spectrum by utilizing visibly transparent Ag-based conductive coatings on each side. Furthermore, the competing effect of the Ag thickness on optical and RF transparency is discussed. We show that using multilayer dielectric-metal coatings, specifically 5-layered spectrally selective coatings, RF transparency of the meta-glass can be enhanced while preserving visible transparency. Herein we demonstrate high transparency meta-glass with 83% and 78% peak RF and optical transmission at 28 GHz and 550 nm, respectively. The meta-glass yields enhanced RF transmission by 80% and 10% when compared to low-emissivity glass and bare glass, respectively. The meta-glass design presented here is amenable to a variety of 5G applications including automobile radar systems. This work provides a superior alternative to the standard indium-tin-oxide (ITO) transparent material which is becoming scarce. Moreover, this study paves the way for the design of new visibly transparent metamaterials and artificial dielectrics.

Nanostructured forms of stoichiometric In2O3 are proving to be efficacious catalysts for the gas-phase hydrogenation of CO2. These conversions can be facilitated using either heat or light; however, until now, the limited optical absorption intensity evidenced by the pale-yellow color of In2O3 has prevented the use of both together. To take advantage of the heat and light content of solar energy, it would be advantageous to make indium oxide black. Herein, we present a synthetic route to tune the color of In2O3 to pitch black by controlling its degree of non-stoichiometry. Black indium oxide comprises amorphous non-stoichiometric domains of In2O3-x on a core of crystalline stoichiometric In2O3, and has 100% selectivity towards the hydrogenation of CO2 to CO with a turnover frequency of 2.44 s−1., The utilization of white-colored, wide-bandgap CO2 hydrogenation photocatalysts has been hindered by their limited light-harvesting ability. By making stoichiometric white indium oxide non-stoichiometric and black, it is transformed from a highly inactive to a highly active photothermal catalyst.

Solar-driven evaporation is a promising technology with many potential applications including desalination, power generation, purification, sterilization and phase separation. Recently, much resear...

In this study, we present the effect of silver diffusion into a dielectric medium and its consequent effect on the optical spectra on thin metal-dielectric structures. We show that on a grating pattern, reactive sputter deposition of aluminum nitride immediately following the sputter deposition of a thin layer of silver results in a broadening of the absorption peak of the AlN/Ag gratings which is directly related to diffusion of Ag ions into the overlying AlN layer. Time of Flight Secondary Ion Mass spectroscopy shows that the sample with broadened optical absorption has a significant concentration of Ag within the AlN layer and that the concentration profile follows the error function consistent with Fick’s second law of diffusion. Plasma emission spectroscopy reveal that the use of N2/Ar mixture instead of an Ar only plasma during RF sputtering reduces the emission of neutral silver atoms, implying that the density of singly ionized silver increases in a nitrogen-containing plasma. However, sputter deposition of AlN following exposure of the underlying silver grating film to ambient atmosphere does not give rise to the same broadening effect in the optical spectra for the AlN/Ag gratings due to the increased concentration of oxygen within the AlN and Ag layers, indicating that oxidation at the AlN/Ag interface inhibits silver migration into the dielectric.

Photo-Induced Transient Current Spectroscopy (PICTS) is a versatile technique for measurements of defect state energies and densities in photo-active materials. It is suitable for investigating the surface-gas adsorbate behavior and the defect characteristics of defect laden In2O3-x(OH)y nanorods, having oxygen vacancies and hydroxide surface groups, under in situ reactor conditions of dark ambient temperature, dark 150 °C and photo-illuminated 150 °C, for the photo-assisted Reverse Water Gas Shift reaction. From glovebox-protected X-ray Photoelectron Spectroscopy and in situ PICTS measurements we determined that the reduction of CO2 is associated with heterolytic dissociation of H2 into In-H§- and HO-H§+ centres accompanied by an increase in average carrier trap energies; increased carbonate formation in a photo/thermal reactor state of H2 + CO2, and an average trap energy decrease of 0.11 eV from H2 to a CO2 + H2 mixture, which correlates with binding energy shifts of the OH shoulder of the O1s spectra. These results show the reactivity link between the various OH groups, oxygen vacancies and trap energies of In2O3-x(OH)y in the reactant gas atmosphere components.

The photocatalytic activity of nanostructured In2O3–x(OH)y for the reverse water gas shift (RWGS) reaction CO2 + H2 → CO + H2O can be greatly enhanced by substitution of Bi(III) for In(III) in the ...

Conventional window technologies tend to have poor thermal transmittance coefficients (U-values) which cause significant heat loss during the winter season and undesired heat gain in the summer. This study reports a new procedure to calculate center glass U-values of triple and quadruple windows which include low-emissive radiant energy veils – shades and blinds with spectrally selective coatings – between the outermost glass panes. A numerical zonal model is developed to simulate a net radiation system coupled with finite difference and ray tracing methods using validated derived experimental equations. A parametric investigation is carried out wherein the influence of different parameters such as optical properties, inter-pane distances and slat angles of the blinds on the thermal performance of the glazing system are analyzed. Three different gas fill types are examined under realistic boundary conditions. It is shown that this window system has a compelling U-value compared to ordinary multilayer glazing products.

Micromanipulation techniques that are capable of assembling nano/micromaterials into usable structures such as topographical micropatterns (TMPs) have proliferated rapidly in recent years, holding great promise in building artificial electronic and photonic microstructures. Here, a method is reported for forming TMPs based on optoelectronic tweezers in either "bottom-up" or "top-down" modes, combined with in situ photopolymerization to form permanent structures. This work demonstrates that the assembled/cured TMPs can be harvested and transferred to alternate substrates, and illustrates that how permanent conductive traces and capacitive circuits can be formed, paving the way toward applications in microelectronics. The integrated, optical assembly/preservation method described here is accessible, versatile, and applicable for a wide range of materials and structures, suggesting utility for myriad microassembly and microfabrication applications in the future.

Calcium hydroxyphosphate, Ca10(PO4)6(OH)2, is commonly known as hydroxyapatite (HAP). The acidic calcium and basic phosphate/hydroxide sites in HAP can be modified via isomorphous substitution of calcium and/or hydroxide ions to enable a cornucopia of catalyzed reactions. Herein, isomorphic substitution of Ca2+ ions by Cu2+ ions especially at very low levels of exchange created new analogs of molecular surface frustrated Lewis pairs (SFLPs) in CuxCa10− x(PO4)6(OH)2, thereby boosting its performance metrics in heterogeneous CO2 photocatalytic hydrogenation. In situ Fourier transform infrared spectroscopy characterization and density functional theory calculations provided fundamental insights into the catalytically active SFLPs defined as proximal Lewis acidic Cu2+ and Lewis basic OH−. The photocatalytic pathway proceeds through a formate reaction intermediate, which is generated by the reaction of CO2 with heterolytically dissociated H2 on the SFLPs. Given the wealth of information thus uncovered, it is highly likely that this work will spur the further development of similar classes of materials, leading to the advancement and, ultimately, large‐scale application of photocatalytic CO2 reduction technologies., Complementary DRIFTS, UPS, in situ XPS, 1H MAS NMR, and DFT calculations provided insight into a new kind of SFLPs in low Cu2+ exchange CuxCa10− x(PO4)6(OH)2. A formate reaction intermediate is identified, which is generated by the reaction of CO2 with heterolytically dissociated H2 on Ca─OH···Cu lattice pairs to form Ca─OH2 +···CuH−.

Laser cooling of matter through anti-Stokes photoluminescence, where the emitted frequency of light exceeds that of the impinging laser by virtue of absorption of thermal vibrational energy, has been successfully realized in condensed media, and in particular with rare earth doped systems achieving sub-100K solid state optical refrigeration. Studies suggest that laser cooling in semiconductors has the potential of achieving temperatures down to ~10K and that its direct integration can usher unique high-performance nanostructured semiconductor devices. While laser cooling of nanostructured II-VI semiconductors has been reported recently, laser cooling of indirect bandgap semiconductors such as group IV silicon and germanium remains a major challenge. Here we report on the anomalous observation of dominant anti-Stokes photoluminescence in germanium nanocrystals principally associated with plasmon coupling. Specifically, we attribute this Raman anomaly to the confluence of ultra-high purity nanocrystal germanium, generation of high density of electron-hole plasma, the inherent degeneracy of longitudinal and transverse optical phonons in non-polar indirect bandgap semiconductors, and commensurate spatial confinement effects. At high laser intensities, plasmon-assisted laser cooling with lattice temperature as low as ~50K is inferred.

We use photoconductivity time, optical absorption, and electron quantum efficiency measurements under in situ reactant CO2 + H2 atmospheres to determine the role of surface trap states during photoreduction of CO2 to CO using In2O3- xOH y nanorods of varied annealing times. Photocurrent decay trends show an asymmetric energy distribution of surface barrier potentials with increased asymmetry from vacuum to CO2 + H2. Urbach analysis shows crystalline disorder parameters of 0.35-0.40 under vacuum and 0.45-0.6 under CO2 + H2. Quantum efficiency spectra show that under H2 + CO2 average tail state energies are similar to those under vacuum but with increased densities of photoconductive gap states. Photoelectro-paramagnetic-resonance measurements show the creation of new paramagnetic centers. Overall, enhanced activity is associated with a lower maximum barrier potential of 0.39 eV than that of 0.41 eV, lower average trap energies of 2.58 eV compared to 2.69 eV, with higher disorder due to increased surface state densities. These techniques pave the way for facile in situ probing of gas-phase photocatalysts, providing simple macrolevel understanding of adsorbed reactants on surface band bending, thus correlating to catalytic efficacy.

This study shows unique capability of deep-subwavelength metal-insulator-metal (MIM) width-graded nano-gratings in offering high intensity electromagnetic field. The plasmonic field is underpinned by the strong coupling of the surface plasmon polaritons on the sidewalls of the nanogrooves. We present quantitative SERS detection of various biomolecule species at an ultra-low concentration corresponding to detection of single molecule. We report limit of detection of a gold coated bullseye width-graded plasmonic nano-grating as a SERS platform in detecting small molecule (such as propylene glycol) or sepsis biomarkers (such as protein c) at multiple wavelengths of light.

We propose a novel type of bi-anisotropic hybrid metal-dielectric structure comprising dielectric and metallic cylindrical wedges wherein the composite meta-cylinder enables advanced control of electric, magnetic and magnetoelectric resonances. We establish a theoretical framework in which the electromagnetic response of this meta-atom is described through the electric and magneticmultipole moments. The complete dynamic polarizability tensor, expressed in a compact form, is derived as a function of the Mie scattering coefficients. Flexibility in the design makes the proposed meta-cylinder a viable candidate for various applications in the microscopic (single meta-atom) and macroscopic (metasurface) levels. We show that the highly versatile bi-anisotropic meta-atom is amenable to being designed for the desired electromagnetic response, such as electric dipole-free and zero/near-zero (backward and forward) scattering at the microscopic level. In addition, we show that the azimuthal asymmetry gives rise to normal polarizability components which are vital elements in synthesizing asymmetric Optical Transfer Function (OTF) at the macroscopic level.We conduct a precise inspection, from the microscopic to the macroscopic level, of the metasurface synthesis for emphasizing on the role of normal polarizability components for spatial optical signal processing. It is shown that this simple two-dimensional asymmetric meta-atom can perform first-order differentiation and edge detection at normal illumination.The results reported herein contribute toward improving the physical understanding of wave interaction with artificial materials composed of asymmetric elongated metal-dielectric inclusions and open the potential of its application in spatial signal and image processing., Comment: 16 pages, 10 figures

Stimulated emission luminescent solar concentrators (SELSCs) have the potential to reduce escape cone losses in luminescent solar concentrators (LSCs). However, a functional SELSC is yet to be demonstrated. Previous numerical studies and detailed balance limits provide guidance, but they also contradict and likely overestimate performance and underestimate requirements. In this work, we introduce a rate-equation model with inversion requirements compatible with detailed balance limits and apply this model to the numerical modelling of window-sized SELSCs. We find that the optimal pump photon energy for both LSCs and SELSCs is 1.35 eV and the potential improvement of SELSCs over LSCs is found to be 19.3%. The efficiencies found are much lower than those specified in previous work due to the increase in Stokes shift required for a highly luminescent material. We also find that SELSCs are more attractive at higher matrix losses, that emission linewidths

Photo-Induced Transient Current Spectroscopy (PICTS) is a versatile technique for measurements of defect state energies and densities in photo-active materials. It is suitable for investigating the surface-gas adsorbate behavior and the defect characteristics of defect laden In2O3-x(OH)y nanorods, having oxygen vacancies and hydroxide surface groups, under in situ reactor conditions of dark ambient temperature, dark 150 °C and photo-illuminated 150 °C, for the photo-assisted Reverse Water Gas Shift reaction. From glovebox-protected X-ray Photoelectron Spectroscopy and in situ PICTS measurements we determined that the reduction of CO2 is associated with heterolytic dissociation of H2 into In-H§- and HO-H§+ centres accompanied by an increase in average carrier trap energies; increased carbonate formation in a photo/thermal reactor state of H2 + CO2, and an average trap energy decrease of 0.11 eV from H2 to a CO2 + H2 mixture, which correlates with binding energy shifts of the OH shoulder of the O1s spectra. These results show the reactivity link between the various OH groups, oxygen vacancies and trap energies of In2O3-x(OH)y in the reactant gas atmosphere components.

Optimizing kinetic barriers of ammonia synthesis to reduce the energy intensity has recently attracted significant research interest. The motivation for the research is to discover means by which activation barriers of N

Nanoscale titanium nitride TiN is a metallic material that can effectively harvest sunlight over a broad spectral range and produce high local temperatures via the photothermal effect. Nanoscale indium oxide-hydroxide, In

Here, we propose a novel composite metasurface comprising a glass substrate and honeycomb-shaped spectrally selective nano-thin optical coatings. Simultaneously, the proposed structure is transparent in the visible and RF region while being reflective in the IR (low-emissivity).