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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.

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.

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.

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.

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).

Subwavelength rainbow trapping metamaterial nano-gratings provide a unique means for high sensitivity and multiplexed molecular detection through localized and propagating surface plasmon polaritons. Herein we report on the viability of width-graded, depth-graded and chirped plasmonic nano-gratings for high sensitivity multiwavelength light localization. In addition, we introduce two classes of metal-insulator-metal (MIM) width-graded, i.e. formed in a semiconductor (SMIMS) and entirely in a metal (MIM). We show feasibility of SMIMS and MIM width-graded nano-gratings as unique SERS platforms in detecting human phospholipid and propylene glycol sample molecules.

In this work, significant enhancement in absorption, especially in the near infra-red region, is achieved for ultra-thin crystalline silicon of various thicknesses using a photonic crystal structure. This is realized by patterning the silicon with close-packed inverted pyramid structuring, wherein the lattice spacing is comparable to the wavelength of the near infra-red light, which results in strong wave-interference-based light trapping. Absorption enhancement of more than a factor of two in the spectral range of 1000–1100 nm is achieved without any other optical enhancments. Details on the techniques used to realize the ultra-thin silicon, the fabrication of the inverted pyramids using standard photolithography and a complete optical analysis are reported in this work.

One of the most significant losses in luminescent solar concentrators (LSCs) is via the escape cone. In order to reduce this loss, in recent years, the concept of using a seed laser to induce stimulated emission has been proposed. This new concept is called a stimulated emission luminescent solar concentrator (SELSCs). However, a working SELSC has yet to be demonstrated, due to demanding material requirements. In this work, we show through numerical simulations that using a circular SELSC geometry would result in improved performance over a slab geometry, with significant reductions in threshold material requirements.

High minority carrier lifetime of more than 8 ms is achieved by depositing high quality hydrogenated amorphous silicon films on crystalline silicon using the triode plasma enhanced chemical vapor deposition (PECVD) technique. High quality surface passivation is made possible by virtue of introducing a biased grid between the two electrodes of an rf diode. In particular, by choosing an appropriate grid-substrate distance and applying a large negative DC bias on the grid, the passivation quality is substantially enhanced leading to a surface recombination velocity of 2.4 cm/s. In addition, the quality of doped amorphous silicon using the triode PECVD is also improved. An implied open circuit voltage of 710 mV is demonstrated from first silicon heterojunction solar cell devices.

We delineate the four principal surface plasmon polariton coupling and interaction mechanisms in subwavelength gratings, and demonstrate their significant roles in shaping the optical response of plasmonic gratings. Within the framework of width-graded metal-insulator-metal nano-gratings, mode confinement and wave guiding result in multiwavelength light localization provided conditions of adiabatic mode transformation are satisfied. The field is enhanced further through fine tuning of the groove-width (w), groove-depth (L) and groove-to-groove-separation (d). By juxtaposing the resonance modes of width-graded and non-graded gratings and defining the adiabaticity condition, we demonstrate the criticality of w and d in achieving adiabatic mode transformation among the grooves. We observe that the resonant wavelength of a graded grating corresponds to the properties of a single groove when the grooves are adiabatically coupled. We show that L plays an important function in defining the span of localized wavelengths. We show that multiwavelength resonant modes with intensity enhancement exceeding 3 orders of magnitude are possible with w < 30nm and 300nm < d < 900nm for a range of fixed values of L. This study presents a novel paradigm of deep-subwavelength adiabatically-coupled width-graded gratings - illustrating its versatility in design, hence its viability for applications ranging from surface enhanced Raman spectroscopy to multispectral imaging., Submitted to Nanophotonics, 33 pages, 6 figures, Supplementary material uploaded to: https://drive.google.com/open?id=12HKwMvutPqiiAstknDw-owJnONidri2H , and one animation file uploaded to: https://drive.google.com/open?id=1f9TEbGcobhHf3EeDhMHn_9ax5taHs1_4

Rainbow light trapping in plasmonic devices allows for field enhancement of multiple wavelengths within a single device. However, many of these devices lack precise control over spatial and spectral enhancement profiles and cannot provide extremely high localised field strengths. Here we present a versatile, analytical design paradigm for rainbow trapping in nanogroove arrays by utilising both the groove-width and groove-length as tuning parameters. We couple this design technique with fabrication through multilayer thin-film deposition and focused ion beam milling, which enables the realisation of unprecedented feature sizes down to 5 nm and corresponding extreme normalised local field enhancements up to 103. We demonstrate rainbow trapping within the devices through hyperspectral microscopy and show agreement between the experimental results and simulation. The combination of expeditious design and precise fabrication underpins the implementation of these nanogroove arrays for manifold applications in sensing and nanoscale optics., Plasmonics: Trapping a rainbow with nanogrooves A new approach facilitates the fast and versatile design and easy fabrication of nanogroove arrays that can trap the full spectrum of visible light, with potential applications in sensing and nanoscale optics. Katelyn Dixon of the University of Toronto and colleagues conducted mathematical analyses followed by software simulations to determine the wavelengths of visible light that elicit ‘resonance’ within a single metal-insulator-metal nanogroove depending on its width and length. When designed within an array, each nanogroove will have a specific optical response depending on the wavelength of light that causes it to resonate. The team used a unique technique to fabricate devices made of arrays of nanogrooves with different lengths and widths. The narrowest reached five nanometres; ten times smaller than previously designed grooves. The rainbow-trapping arrays overcome limitations in previous designs.

One of the key performance parameters for any energy efficient window product is the center of glass U-value or thermal transmittance. This paper presents a new methodology to compute the thermal performance of fenestration systems incorporating partitioning radiant energy veils™ between two panes of a window. A conduction heat transfer model is used for glazing layers coupled with radiation and convection models at the layer boundary surfaces. Partitioning radiant energy veils™ are treated as individual layers with effective radiative properties. The effect of a wide range of optical properties, pane thicknesses, pane distances and different gas fill types on thermal transmittance of the window are considered. The novel use of partitioning radiant energy veils™, having application specific properties, between two panes of a window allows to customize the thermal performance of a triple or quadruple window. It is shown that using one or two internal partitioning layers, with appropriate pane/inter-layer distances and high spectrally reflective metallo-dielectric coated layers, results in highly enhanced U-Values.

A novel thin film anodized aluminum oxide templating process was developed and applied to make nanopores with anisotropic etching on crystalline silicon through reactive ion etching, with the purpose of enhancing the anti-reflection of silicon substrates. A unique two-step anodizing method was introduced to create high quality nano-channels and it was demonstrated that this process is superior over a one-step anodization approach. It was found that pore to pore distance and pore density can be tuned by changing the applied potential within a range of 10–80 V. Optical characterization of the nanopatterned silicon showed an average 10% reduction in reflection in the UV–Vis wavelength range.

Metal-dielectric multilayers are versatile optical devices that can be designed to combine the visible transmittance of dielectrics with the electronic properties of metals for plasmonic and meta-material applications. However, their performances are limited by an interfacial optical absorption often attributed entirely to the metal surface roughness. Here, we show that during deposition of AlN/Ag/AlN and SiNx/Ag/SiNx multilayers, significant diffusion of Ag into the top dielectric layer form Ag nanoparticles which excite localized surface plasmon resonances that are primarily responsible for the interfacial optical absorption. Based on experimental depth profiles, we model the multilayer’s silver concentration profile as two complementary error functions: one for the diffused Ag nanoparticles and one for the interface roughness. We apply the Maxwell-Garnett and Bruggeman effective medium theories to determine that diffusion characteristics dominate the experimental absorption spectra. The newfound metal nanoparticle diffusion phenomenon effectively creates a hybrid structure characteristic of both metal-dielectric multilayer and metal-dielectric composite.

Surface-enhanced Raman scattering (SERS) substrates with multiwavelength rainbow-trapping properties hold the potential for a one-size-fits-all platform for rapid and multiplexed disease detection. We present the first report on the utilization of rainbow-trapping width-graded nano-gratings, a new class of chirped metamaterials, to detect protein biomarkers. Using cytochrome c (Cc), a charged analyte with inherent difficulty in adsorbing onto sputtered silver films, we investigated methods of binding Cc on the silver nano-grating in order to improve the SERS signal strength at both 532 and 638 nm excitation. Cc was not detectable on the Ag nano-gratings without surface functionalization at 1μM concentration. Upon charge reversal functionalization of the Ag nano-gratings, 1μM Cc was detectable albeit not reliably. By further crosslinking 1μM Cc to the functionalized Ag nano-gratings, the analyte-capture detection scheme greatly improved the SERS signal strength and reliability at both excitation wavelengths and allowed for quantification of their coefficients of variation with values down to 27%.

Solar-pumped lasers and optical amplifiers continue to draw research interest with advances in nanomaterials science and technology. Establishing accurate detailed balance limits for inversion in these systems is essential. In this Letter, we re-examine the threshold limits for inversion in broadband-pumped lasers, with reference to those provided by Roxlo and Yablonvitch [Opt. Lett. 8, 271 (1983)OPLEDP0146-959210.1364/OL.8.000271], where they determined the minimum Stokes shift and the minimum ratio of pump band to emission band absorption constants—based on independent consideration of the emission at pump and emission frequencies. In contrast, the derivation here simultaneously accounts for emission in both the pump and emission bands, which in turn leads to a single consolidated inequality that serves to establish the revised threshold requirements for inversion. Upon applying this new unified relationship to solar-pumped devices, a large increase in the minimum required Stokes shifts for 1-sun devices, particularly at larger pump energies and smaller ratios of α p 0 / α e 0 , is found. The maximum possible efficiencies of solar-pumped devices are calculated using this new relation.

Rapid advances in metamaterial technology are enabling the engineering of wave-matter interactions heretofore not realized and functionalities with potentially far-reaching implications for major challenges in the fields of energy conservation and radio frequency (RF) communication. We propose a visibly and RF transparent composite metasurface utilizing dielectric-metal spectrally selective coatings with high NIR control and low thermal emissivity, thus achieving a multi-functional metasurface capable of enhancing 5G communication efficiency and exhibiting energy conservation features. The proposed meta-glass yields 92% peak RF transmission at 30 GHz which corresponds to 20% and 90% enhancement when compared to plain glass and low-emissive glass substrates. This meta-glass possesses 86% peak optical transparency at $\lambda=550 nm$, $>$60% near-IR reflection, and $>$ 80% mid-IR reflection which corresponds to $\approx$ 0.2 thermal emissivity. The proposed metasurface design is highly flexible and can be tuned to operate over different frequency ranges owing to its frequency scalability. This study provides a better alternative using earth-abundant materials compared to low-emissive glass based on indium tin oxide (ITO) while boosting the efficiency of 5G communication amenable to window systems demanding simultaneous functionalities for emergent smart/energy-efficient buildings/cities and autonomous transportation applications.

A periodically structured surface or grating has been used to demonstrate state-of-the-art high efficiency crystalline silicon photovoltaic cells. However, until now the understanding of the complete relationship between the grating periodicity, silicon thickness, and absorption enhancement in silicon solar cell with an inverted pyramidal texture is still unclear. In this paper, we simulate front surface inverted pyramidal grating texture on 2–400-μm thick silicon and optimize it to derive maximum photocurrent density from the cell. We identify a “one-size-fits-all” front grating period of 1000 nm that leads to maximum photo-absorption of normally incident AM1.5g solar spectrum in silicon (configured with a back surface reflector) irrespective of the thickness of the crystalline silicon absorbing layer. With the identification of such universally optimized periodicity for the case of an inverted pyramidal grating texture, a common fabrication process can be designed to manufacture high-efficiency devices on crystalline silicon regardless of the wafer thickness. The measured reflectance from submicron and wavelength scale periodic textures also verifies simulation results.

A unidirectional photonic wire laser has been developed by integrating reflectors into terahertz quantum cascade lasers. The transverse dimension is much smaller than the lasing wavelength (80 μm). A record wall-plug power efficiency of 1% is achieved.

Light incident on nanoscale metal-insulator-metal (MIM) plasmonic gratings generates surface plasmon polaritons (SPPs) which resonate and propagate within the grating structure. The SPP resonant wavelength can be altered by introducing a gradient in the width of the MIM grooves. Specifically, a symmetrically graded grating with a narrow central groove leads to a gradient in the effective refractive index such that the index increases in the direction of the central groove. This index gradient guides non-localized SPP waves towards the grating center. This waveguiding of SPPs along with localized SPP modes within the narrow central grooves give rise to multi-wavelength electric field enhancement at the grating center. SPP coupling across the grooves leads to an increase in electromagnetic field strength with decreasing groove width. However, standard nanofabrication techniques limit the minimum width of the grooves to approximately 50nm, preventing maximum field enhancement. Herein we report on the development of a novel nanoplasmonic graded grating with a 10 nm central groove flanked by increasingly wider grooves on either side, which are fabricated using thin film RF magnetron sputter deposition technique. These structures are studied using COMSOL Multiphysics modelling in which we vary the groove width, groove separation and groove depth, and thus demonstrate localization of broadband incident light. Raman spectroscopy and fluorescence microscopy are used to demonstrate field enhancement at several visible wavelengths.

Herein we propose an analytically formulated novel asymmetrical meta-atom for the control of electromagnetic wave shaping. We show that the proposed meta-cylinder is highly versatile and well capable of achieving exotic electromagnetic responses.

Herein quantum efficiency enhancements are demonstrated in multi-junction solar cells with one-dimensional Selectively Transparent and Conducting Photonic Crystal (STCPC) intermediate Bragg reflectors. Specifically, the modelling, design and fabrication of series-connected multi-junction cells comprising a top amorphous-silicon cell and a bottom crystalline-silicon heterojunction cell with spectrally tunable STCPC intermediate reflectors (IR) is presented. Wave-optics modeling analysis shows current density gains of up to 17.4% and 10.4% compared to multi-junction cells without an IR and with an industry standard IR comprising a ZnO film, respectively. Fabricated multi-junction cells based on these modelled structures demonstrate that the STCPC IR enhances cell currents by 17.1% and 13.2% compared to the reference cases without an IR and with a ZnO film IR, respectively. From an efficiency standpoint, the STCPC IR improved cell performance by 7.9% over reference cells without an IR, but was 8.9% less efficient relative to the reference cells with a ZnO IR. The lower overall efficiency of the tandem cell with the STCPC IR with respect to that of the cell with the ZnO IR is primarily due to non-optimal electrical performance of the STCPC compared to the single ZnO layer. Methods for improving the electrical properties are discussed.

Thermophotovoltaics (TPV) is concerned with the application of photovoltaic diodes to harvest electricity from thermal radiation. This is achieved through the use of appropriately designed thermal emitters which are typically heated to temperatures of more than 800 ° C. Merits of thermophotovoltaics include the prospect of delivering high power density compared to solar photovoltaics, fuel versatility, portability and capability of around-the-clock operation. The key challenges en route to commercialization of TPV technology include low heat-to-electricity conversion efficiency, mechanical and thermostructural reliability at high temperatures, and cost. Recent advances which include the development of photonic crystal emitters, miniaturization of TPV systems, and improvement of rare earth oxide emitters have contributed to enhancing the performance of TPV systems. Further, current research on ultra-low bandgap photovoltaic materials, thin film monolithic system design, and global system optimization promise additional advances. This article presents an overview of the fundamental principles of thermophotovoltaics followed by a review of the development of all the main components comprising combustion thermophotovoltaic systems. This review also scrutinizes state-of-the-art developments, discusses the fundamental and technical challenges facing commercial adoption of TPV, and prospects of TPV.

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, In2 O3- x (OH)y , is a semiconducting material capable of photocatalyzing the hydrogenation of gaseous CO2 ; however, its wide electronic bandgap limits its absorption of photons to the ultraviolet region of the solar spectrum. Herein, the benefits of both nanomaterials in a ternary heterostructure: TiN@TiO2 @In2 O3- x (OH)y are combined. This heterostructured material synergistically couples the metallic TiN and semiconducting In2 O3- x (OH)y phases via an interfacial semiconducting TiO2 layer, allowing it to drive the light-assisted reverse water gas shift reaction at a conversion rate greatly surpassing that of its individual components or any binary combinations thereof.

We report on a new class of plasmonic nanogratings in which the gradient in the groove-width enables facile fabrication of multiwavelength surface-enhanced Raman spectroscopy (SERS) substrates. These substrates have the potential of achieving unprecedented detection sensitivity, specificity and speed. The structure of these nano-gratings consist of metal-insulator-metal grooves with a 40 nm central groove width flanked by a series of grooves on either side with gradually increasing width. Groove widths increase in steps of 5 nm up to a maximum width of 200 nm positioned farthest from the central groove on either side. The gradient in groove width in turn produces a gradient in the effective refractive index of the grating determined by the groove width at each location. Together, multiple laser wavelengths can be simultaneously confined to the centrally situated narrow grooves, with the neighbouring larger grooves guiding the nonlocalized waves toward the grating center from both directions. This generates a maximally enhanced plasmonic field over a broad range of wavelengths on the surface of the nanograting which can be used to increase the Raman scattering efficiency of a sample molecule distributed over the structure. The structures were fabricated using electron beam lithography, reactive ion etching, and sputter-deposition techniques. Experimental results demonstrated up to four orders of magnitude enhancement in the SERS intensity of 1 mM phospholipid samples deposited over the graded nano-gratings. In addition, characterization of the phospholipids in aqueous phase flowing over the nano-gratings integrated within a microfluidic device revealed that the Raman peaks were only detectable with the enhancement introduced by the grating. These results were obtained using 532, 638, and 785 nm lasers, demonstrating the multispectral sensing capability of the graded gratings for static and dynamic characterization of low concentration species.

Optoelectronic tweezers (OET) are a microsystem actuation technology capable of moving microparticles at mm s−1 velocities with nN forces. In this work, we analyze the behavior of particles manipulated by negative dielectrophoresis (DEP) forces in an OET trap. A user-friendly computer interface was developed to generate a circular rotating light pattern to control the movement of the particles, allowing their force profiles to be conveniently measured. Three-dimensional simulations were carried out to clarify the experimental results, and the DEP forces acting on the particles were simulated by integrating the Maxwell stress tensor. The simulations matched the experimental results and enabled the determination of a new “hopping” mechanism for particle-escape from the trap. As indicated by the simulations, there exists a vertical DEP force at the edge of the light pattern that pushes up particles to a region with a smaller horizontal DEP force. We propose that this phenomenon will be important to consider for the design of OET micromanipulation experiments for a wide range of applications.

The behavior of composite nanostructures depends on both size and elemental composition. Accordingly, concurrent control of size, shape, and composition of nanoparticles is key to tuning their functionality. In typical core-shell nanoparticles, the high degree of symmetry during shell formation results in fully encapsulated cores with severed access to the surroundings. We commingle light parameters (wavelength, intensity, and pulse duration) with the physical properties of nanoparticles (size, shape, and composition) to form hitherto unrealized core-vest composite nanostructures (CVNs). Unlike typical core-shells, the plasmonic core of the resulting CVNs selectively maintains physical access to its surrounding. Tunable variations in local temperature profiles ≳50 °C are plasmonically induced over starburst-shaped nanoparticles as small as 50-100 nm. These temperature variations result in CVNs where the shell coverage mirrors the temperature variations. The precision thus offered individually tailors access pathways of the core and the shell.

Photocarrier radiometry (PCR) with 355 nm laser excitation was used for the study of c-Si covered with intrinsic thin hydrogenated amorphous Si (i-a-Si:H) on one, or both, sides, with thicknesses ranging from 10 nm to 90 nm. Short wave- length excitation allows one to resolve the contribution of the upper i-a-S layer to the PCR signal due to the very small absorption depth (tens of nm) of the excitation beam. As a result, fundamental transport parameters of the composite structure can be evaluated from the PCR frequency dependence. A theoretical model has been devel- oped to describe the diffuse carrier density wave (CDW) in this two-layer system. The model of the one-dimensional CDW fields for composite electronic solids involves front, interface, and back surface recombination velocities, the diffusion coefficient, recombinationlifetimesintheupper andlowerlayers,andtheunoccupied trapdensity at the interface. Simulations of the transport parameter influence on the PCR signal were performed, and the theoretical model was able to describe the experimental data accurately, therefore, making it possible to evaluate the transport parameters of i-a- Si:H and c-Si as well as to elucidate the role of interface electronic traps in the PCR frequency dependence under short wavelength excitation.

We utilized a Monte Carlo optimization algorithm on an array of metallic nanoslits of uniform width to maximize the normalized electric field at a focal point. The results indicate optimal hyperspectral focusing of light in the far-field.

We present an overview of the design potential of nano-porous anti-reflection coatings (ARCs) and the associated challenges in its fabrication. Genetic algorithm optimization for the most effective ARCs on glass for normal and all incident angles is carried out and an admittance loci-based pictorial is used to visualize their performance. We then describe the advantages of using nano-porous multi-layers vis-a-vis other types of moth-eye type nano-grating films: Principally trading high performance and high cost of fabrication for good performance and lower cost facile synthesis. We describe some of the issues involved in the fabrication of such multi-layer stacks on glass and polymeric substrates and provide suggestions for overcoming these limitations.

This article reports on the integration of facile native oxide-based passivation of crystalline silicon surfaces within the back amorphous-crystalline silicon heterojunction solar cell concept. The new passivation scheme consists of 1-nm thick native oxide and nominally 70-nm thick PECVD silicon nitride. The low temperature passivation scheme provides uniform high quality surface passivation and low parasitic optical absorption. The interdigitated doped hydrogenated amorphous silicon layers were deposited on the rear side of the silicon wafer using the direct current saddle field PECVD technique. A systematic analysis of a series of back amorphous-crystalline silicon heterojunction cells is carried out in order to examine the influence of the various cell parameters (interdigital gap, n-doped region width, ratio of widths of p, and n-doped regions) on cell performance. A photovoltaic conversion efficiency of 16.7 % is obtained for an untextured cell illuminated under AM 1.5 global spectrum (cell parameters: VOC of 641 mV, JSC of 33.7 mA-cm − 2 and fill factor of 77.3 %). Copyright © 2014 John Wiley & Sons, Ltd.

This article presents the design, fabrication and characterization of a micromachined energy harvester utilizing aluminium nitride (AlN) as a piezoelectric thin film material for energy conversion of random vibrational excitations. The harvester was designed and fabricated using silicon micromachining technology where AlN is sandwiched between two electrodes on top of a silicon cantilever beam which is terminated by a silicon seismic mass. The harvester generates electric power when subjected to mechanical vibrations. The generated electrical response of the device was experimentally evaluated at various acceleration levels. A maximum power of 34.78 μW was obtained for the device with a seismic mass of 5.6 × 5.6 mm2 at an acceleration value of 2 g. Various fabricated devices were tested and evaluated in terms of the generated electrical power as well as the resonant frequency.

We use energy methods and lumped-element modelling in the analysis and optimization of a miniaturized aluminum nitride based piezoelectric energy harvester which utilizes tritiated silicon as an uninterrupted energy source. Tritiated silicon serves as a radioisotope source which emits energetic β particles that results in an electrostatic force between the radioactive source and collector that traps the emitted particles. The generated electrostatic force will drive the charging and actuating cycles of the piezoelectric cantilever leading to a continuous charge---discharge cycles, thus inducing vibrations in the piezoelectric cantilever. The energy generated from the piezoelectric thin-film is appropriately rectified and stored to provide continuous and uninterrupted electrical power to a low-power devices. The modelled results have been benchmarked against available experimental data for a unimorph piezoelectric harvester with very good agreement. Furthermore, the model was applied to a bimorph piezoelectric harvester, showing that the output power can be doubled in relation to a unimorph design. Moreover, the model accounts for the entire range of design and operating factors such as the ambient medium and associated damping losses, current leakage, and device scaling.

We report on the fabrication of 15-nm Ag films with 0.6 nm RMS roughness and only 3 times the bulk electrical resistivity using a transparent AlN seed layer and Ar/N2 (60% N2) based sputtering of Ag. Either AlN-seeding or Ar/N2 sputtering alone reduces the percolation threshold of Ag thin films and smoothens their surface. However, significant reduction in localized surface plasmon resonance was observed only through the use of Ar/N2 sputtering. As a demonstration of its application as a transparent conductive film, we construct a transparent heat-regulating metallo-dielectric coating using our ultrathin ultrasmooth Ag films with minimal optical absorption loss.

Very high effective minority carrier lifetime (6.3 ms) and very low surface recombination velocity (2.6 cm/s) have been demonstrated on float-zone 1–2 Ω cm crystalline silicon (c-Si) wafers by depositing a-Si:H films using grid-biased remote radio-frequency plasma enhanced chemical vapor deposition (RF PECVD). This method employs a semi-transparent DC biased-grid within the conventional RF PECVD configuration. The DC-biased grid is positioned between the RF electrodes in order to develop a remote plasma and thus allow control of the flux and type of precursors involved in the growth of hydrogenated amorphous silicon (a-Si:H) film. It is shown that compared to conventional RF diode, the grid-biased remote RF PECVD method produces a-Si:H films with superior passivating properties as well as significantly lower concentrations of void and SiH 2 bonding and a lower overall hydrogen content, all of which contribute to a higher quality a-Si:H–c-Si heterostructure.

It is shown here that rendering the width of nano-grooves into a tunable parameter presents a new means of light trapping in subwavelength gratings. Particularly, in gratings with groove-widths below 150 nm, the plasmon coupling between the perimeter walls of the groove becomes dominant and thus turns groove width into the principle geometric parameter in determining light trapping. Using this parameter, we investigate the prospect of tunable optical functionalities. An analytical formula is derived by treating each nano-groove as a plasmonic waveguide resonator. The resulting change in the cavity effective mode index is examined; these results are in close agreement with numerical simulations. It is shown that the tunable nano-groove resonator presented here accurately defines waveguiding, slow-light, and light-trapping regimes., 5 Pages, 5 Figures, Submitted prior to CLEO 2014

The development of strategies for increasing the lifetime of photoexcited charge carriers in nanostructured metal oxide semiconductors is important for enhancing their photocatalytic activity. Intensive efforts have been made in tailoring the properties of the nanostructured photocatalysts through different ways, mainly including band-structure engineering, doping, catalyst-support interaction, and loading cocatalysts. In liquid-phase photocatalytic dye degradation and water splitting, it was recently found that nanocrystal superstructure based semiconductors exhibited improved spatial separation of photoexcited charge carriers and enhanced photocatalytic performance. Nevertheless, it remains unknown whether this strategy is applicable in gas-phase photocatalysis. Using porous indium oxide nanorods in catalyzing the reverse water-gas shift reaction as a model system, we demonstrate here that assembling semiconductor nanocrystals into superstructures can also promote gas-phase photocatalytic processes. Transient absorption studies prove that the improved activity is a result of prolonged photoexcited charge carrier lifetimes due to the charge transfer within the nanocrystal network comprising the nanorods. Our study reveals that the spatial charge separation within the nanocrystal networks could also benefit gas-phase photocatalysis and sheds light on the design principles of efficient nanocrystal superstructure based photocatalysts.

Two common methods for recording absolute photoluminescence quantum yields using integrating spheres are discussed. These methods are developed from a theoretical standpoint, with a discussion of the assumptions made in each and their principle differences, and practical comparisons between the two are made using a range of different materials and sample types. It is shown that despite the underlying theoretical differences both methods ultimately yield very similar experimental results. Additionally, the concept of a time-dependent quantum yield is examined and preliminary studies along these lines are presented in the form of an investigation into the photo-oxidation of a luminescent polymer film.

Surface acoustic wave (SAW) devices have been used extensively for a variety of applications such as telecommunications, electronic devices, and sensors. The emerging need for high-bit data processing at gigahertz frequencies and the requirement of high-sensitivity sensors demand the development of high-efficiency SAW devices. With the objective of exploiting the high acoustic velocity of diamond, we report on an optimally developed nanodiamond thin film with crystal size of 3-5 nm, embedded in an amorphous carbon matrix with grain boundaries of 1-1.5 nm, that is integrated with aluminum nitride (AlN) to extend the operating frequency of SAW transducers. We utilize this attractive property of diamond through facile synthesis of a bilayer structure consisting of sputtered AlN deposited on an ultrananocrystalline diamond (UNCD) film. We report the realization of a high-frequency SAW resonator, using a device architecture based on an UNCD layer. The UNCD films were synthesized using a microwave plasma-enhanced chemical vapor deposition (MWPECVD) technique and were used to enhance the SAW velocity in the AlN thin film, thus opening the way for the application of CMOS compatible high-frequency SAW devices. The deposition and characterization of UNCD thin films are presented and highlighted for the realization of the SAW resonators. The high velocity associated with the UNCD/AlN bilayered approach together with the high lateral resolution of the interdigital transducers obtained with electron beam lithography is essential for the realization of high-frequency SAW devices. The fabricated devices demonstrate resonance frequencies of 11.3 and 6.2 GHz corresponding to spatial periods of 800 and 1600 nm, respectively, yielding a SAW velocity of 9040 and 10 064 m/s, respectively.

Selectively-transparent and conducting photonic crystals (STCPCs) made of alternating layers of sputtered indium-tin oxide (ITO) and spin-coated silica (SiO 2 ) nanoparticle films exhibit Bragg-reflectance peaks in the visible spectrum of 95% reflectivity and have a full width at half maximum that is greater than 200 nm. At the same time, their conductive properties are comparable to that of solid sputtered ITO films. Moreover, the average transmission of the STCPCs in the pass-band can be increased to ∼88%, or within 3.3% of the bare glass slide they are fabricated on. Furthermore, we also show that these STCPCs can readily be fabricated on textured surfaces similar to those used for micromorph solar cells. In this context wave optics analysis shows that these STCPCs can be utilized as intermediate reflectors that boost the relative photo-current generated in textured micromorph cells by more than 20% over a broad range of incident angles.

Photocarrier radiometry (PCR), microwave photoconductivity decay (μ-PCD) and transient and quasi-steady-state eddy currents were used for the characterization of a crystalline (c-) Si wafer passivated with intrinsic hydrogenated amorphous silicon films on either front or back side, or on both sides of the wafer. All three techniques are capable of measuring recombination lifetimes, however additional fundamental free photoexcited carrier transport parameters (diffusion coefficient, front- and back-surface recombination velocity) can be evaluated from the PCR frequency dependence owing to the free-carrier-density wave's diffusion-length depth-dependence on frequency. The measured recombination lifetimes are compared and differences in values among the three techniques are discussed in terms of the role of surface and interface defects. μ-PCD and eddy currents yield effective or vertically averaged lifetime measurements, as opposed to PCR which yields bulk recombination lifetimes separately from surface recombination effects.

Piezoelectric energy microgenerators are devices that generate continuously electricity when they are subjected to varying mechanical strain due to e.g. ambient vibrations. This paper presents the mathematical analysis, modelling and validation of a miniaturized piezoelectric energy harvester based on ambient random vibrations. Aluminium nitride as piezoelectric material is arranged between two electrodes. The device design includes a silicon cantilever on which AlN film is deposited and which features a seismic mass at the end of the cantilever. Euler–Bernoulli energy approach and Hamilton’s principle are applied for device modeling and analysis of the operation of the device at various acceleration values. The model shows good agreement with the experimental findings, thus giving confidence into model. Both mechanical and electrical characteristics are considered and compared with the experimental data, and good agreement is obtained. The developed analytical model can be applied for the design of piezoelectric microgenerators with enhanced performance.

A novel low-emissive (low-E) coating based on plasma enhanced chemical vapor deposited hydrogenated diamond-like amorphous carbon (DLC) films has been developed. The coating is a three-layer structure comprised of a nano-thin Ag layer sandwiched between DLC layers. The tunable optical properties that the DLC layers afford make it extremely appealing for large-scale, low-cost manufacturing of low-E coatings. We have shown that the refractive index of DLC films can be precisely tuned between 1.55 and 2.15 at a wavelength of 550 nm, while the optical gap can be tuned between 1.7 and 4.0 eV. The tunable optical properties allow greater flexibility and provide an additional parameter for optimization of low-E coatings. The tunability also allows for simple fabrication of multi-layer or graded-layer low-E coatings. Initial results of the DLC based low-E coating have a mid-IR reflectance of approximately 95% and a transmittance of approximately 70% over the visible frequencies.