| 1. |
- Biswas, Rabindra, et al.
(författare)
-
Enhanced sum frequency generation using vertically stacked Mie resonators
- 2024
-
Ingår i: Ultrafast Phenomena and Nanophotonics XXVIII. - : SPIE-Intl Soc Optical Eng.
-
Konferensbidrag (refereegranskat)abstract
- III-V semiconductors, such as Aluminium Gallium Arsenide (AlGaAs), are known for their high refractive index and strong non-resonant second-order optical nonlinearity making them useful for building active nonlinear photonic devices. AlGaAs-based nanophotonic structures supporting anapole resonances can significantly boost the internal electric fields resulting in enhanced nonlinear optical response. However, low-quality factors of these anapolar resonances can result in poor conversion efficiency for the nonlinear optical process. Here we report enhanced sum frequency generation (SFG) from vertically stacked three-disk AlGaAs-based nanoresonators supporting anapole type resonance that exhibit an order of magnitude increase in field enhancement compared to a single-disk resonator system at the SFG wavelength. The vertically stacked resonators consist of three individual AlGaAs layers separated vertically by an under-cut Gallium Arsenide (GaAs) stem. Finite difference time domain (FDTD) simulations of the scattering cross sections were performed to optimize the dimensions of AlGaAs resonator. The optimal structure consists of three vertically stacked AlGaAs nanodisks (550 nm diameter, 50 nm height) separated by a 100 nm GaAs stem. This design ensures anapole type resonance overlap at SFG wavelength (600-670 nm). Multi-spectral SFG images were acquired by varying the input signal wavelength in the range of 1400-1800 nm, keeping the pump wavelength fixed at 1040 nm. The experimental results show a maximum SFG enhancement of approximately 50-times near the resonance wavelength of 645 nm in comparison to unpatterned multilayer samples. Optical nanostructures based on stacked AlGaAs resonators provide a very exciting platform to tailor the light-matter interactions for linear and non-linear optical applications.
|
|
| 2. |
- Kjellberg, Mikko Erik, et al.
(författare)
-
Enhanced Absorption in InP Nanodisk Arrays on Ultra-Thin-Film Silicon for Solar Cell Applications
- 2022
-
Ingår i: Photonics. - : MDPI AG. - 2304-6732. ; 9:3
-
Tidskriftsartikel (refereegranskat)abstract
- The photovoltaic (PV) market today is dominated by silicon (Si)-based solar cells, which, however, can be improved in performance and cost by developing technologies that use less material. We propose an indium phosphide (InP) nanoresonator array on silicon ultra-thin film with a combined thickness of 0.5 mu m to 2 mu m as a solution to minimize cost and maximize power efficiency. This paper focuses on simultaneously achieving broadband antireflection and enhanced absorption in thin-film Si with integrated InP nanodisk arrays. Electromagnetic simulations are used to design and optimize the reflectance and absorption of the proposed design. By varying the height and radius of the InP nanodisks on the Si substrate, together with the array pitch, a weighted reflectance minimum, with respect to the AM1.5 solar spectrum, of 2.9% is obtained in the wavelength range of 400 nm to 1100 nm. The antireflective properties are found to be a combination of a Mie-resonance-induced strong forward-scattering into the structure and an effective index-matching to the Si substrate. In terms of absorption, even up to 2 mu m from the Si surface the InP nanodisk/Si structure consistently shows superior performance compared to plain Si as well as a Si nanodisk/Si structure. At a depth of 500 nm from the surface of the substrate, the absorption values were found to be 47.5% for the InP nanodisk/Si structure compared to only 18.2% for a plain Si substrate. This shows that direct bandgap InP nanoresonator arrays on thin-film Si solar cells can be a novel design to enhance the absorption efficiency of the cell.
|
|
| 3. |
- Nunes, P., et al.
(författare)
-
The leaf of Agapanthus africanus (L.) Hoffm. : A physical-chemical perspective of terrestrialization in the cuticle
- 2023
-
Ingår i: Environmental and Experimental Botany. - : Elsevier BV. - 0098-8472 .- 1873-7307. ; 208
-
Tidskriftsartikel (refereegranskat)abstract
- Although Agapanthus africanus (L.) Hoffm. is one of the most popular ornamental species in both hemispheres, it has an extremely restricted wild occurrence (Cape province, South Africa). This contradiction between gener-alized ornamental application and natural distribution was the basis for the analytical approach adopted in the present work. We hypothesized that characteristic features of the cuticular waxes were adopted by this species to help it cope with severe dehydration associated with marine salinity on account of the short distance of the wild populations to the sea. A comprehensive morpho-anatomical, histological and physical-chemical analysis was performed on the epicuticular and intracuticular layers of the adaxial and abaxial surfaces of leaves of specimens of A. africanus. The adaxial epicuticular surface is hydrophilic and the abaxial epicuticular surface exhibits globally hydrophobic behavior. The main chemical compounds detected in the wax layers of both surfaces of the leaf are the short-chain monocaprylin monoglyceride (C8), and very long-chain 1-hexacosanol (C26) and 1-octa-cosanol (C28) alcohols. While monocaprylin is particularly abundant in the intracuticular layers, the epicuticular adaxial surface revealed the highest concentration of both alcohols. We demonstrate that the smart combination of these two classes of molecules with opposite water affinity endows the A. africanus leaf cuticle with a unique water management system combining the efficient entrapment of water in the disordered alpha-gel phase formed by monocaprylin and the high resistance to water transport provided by ordered domains composed of tightly packed, all-trans alkyl chains of the above pair of alcohols. The remarkable structural similarity existing between the monocaprylin alpha-gel and the mucilage of algae is an evidence of the terrestrialization process.
|
|
| 4. |
- Nunes, Silvia C., et al.
(författare)
-
Leaf surfaces and neolithization-the case of Arundo donax L
- 2022
-
Ingår i: Frontiers in Plant Science. - : Frontiers Media SA. - 1664-462X. ; 13
-
Tidskriftsartikel (refereegranskat)abstract
- Arundo donax L. (Arundinoideae subfamily, Poaceae family) is a sub-tropical and temperate climate reed that grows in arid and semi-arid environmental conditions, from eastern China to the Mediterranean basin, suggesting potential adaptations at the epicuticular level. A thorough physical-chemical examination of the adaxial and abaxial surfaces of A. donax leaf was performed herein in an attempt to track such chemophenetic adaptations. This sort of approach is of the utmost importance for the current debate about the hypothetical invasiveness of this species in the Mediterranean basin versus its natural colonization along the Plio-Pleistocene period. We concluded that the leaf surfaces contain, apart from stomata, prickles, and long, thin trichomes, and silicon-rich tetralobate phytolits. Chemically, the dominating elements in the leaf ashes are oxygen and potassium; minor amounts of calcium, silicon, magnesium, phosphorous, sulphur, and chlorine were also detected. In both surfaces the epicuticular waxes (whose density is higher in the adaxial surface than in the abaxial surface) form randomly orientated platelets, with irregular shape and variable size, and aggregated rodlets with variable diameter around the stomata. In the case of green mature leaves, the dominating organic compounds of the epicuticular waxes of both surfaces are triterpenoids. Both surfaces feature identical hydrophobic behaviour, and exhibit the same total transmittance, total reflectance, and absorption of incident light. The above findings suggest easy growth of the plant, remarkable epidermic robustness of the leaf, and control of water loss. These chemophenetic characteristics and human influence support a neolithization process of this species along the Mediterranean basin.
|
|
| 5. |
- Peralta Amores, Albert, et al.
(författare)
-
Design and Modelling of Metal-Oxide Nanodisk Arrays for Structural Colors and UV-Blocking Functions in Solar Cell Glass Covers
- 2022
-
Ingår i: Photonics. - : MDPI AG. - 2304-6732. ; 9:5
-
Tidskriftsartikel (refereegranskat)abstract
- We present a multifunctional structural coloration strategy for solar cell glass covers based on all-dielectric nanoscatterer arrays. Titanium dioxide (TiO2) nanostructures are designed to efficiently scatter in the visible and absorb in the UV region, making them suitable candidates as UV absorptive color coatings. Results from finite difference time domain (FDTD) simulations on a square lattice of TiO2 nanocylinders show that a rich palette in the reflected colors can be obtained by varying the period of the lattice. The reflected colors are narrow-banded, with a typical FWHM similar to 11-17 nm, leading to a minimal penalty on the amount of transmitted light. This narrow band reflectance is attributed to the interaction of Mie resonances between individual scatterers with their neighbors in the lattice. The color appearance, with viewing angles of similar to 45 degrees, is maintained for incidence angles up to similar to 70 degrees. With TiO2 being transparent for a major part of silicon solar cells spectral response (400-1100 nm), a loss of similar to 4.5-9.2% in the short-circuit current has been estimated in the specified wavelength range, primarily due to the loss of photons in the reflected light. Furthermore, due to the inherent UV-absorption properties of TiO2, the proposed color-cover designs reduce the transmittance of UV radiation (320-400 nm) by up to similar to 63.70%, potentially preventing the degradation of the encapsulation materials and thus increasing the lifetime expectancy of a solar panel.
|
|
| 6. |
- Pereira, Rui F. P., et al.
(författare)
-
Vicariance Between Cercis siliquastrum L. and Ceratonia siliqua L. Unveiled by the Physical-Chemical Properties of the Leaves' Epicuticular Waxes
- 2022
-
Ingår i: Frontiers in Plant Science. - : Frontiers Media SA. - 1664-462X. ; 13
-
Tidskriftsartikel (refereegranskat)abstract
- Classically, vicariant phenomena have been essentially identified on the basis of biogeographical and ecological data. Here, we report unequivocal evidences that demonstrate that a physical-chemical characterization of the epicuticular waxes of the surface of plant leaves represents a very powerful strategy to get rich insight into vicariant events. We found vicariant similarity between Cercis siliquastrum L. (family Fabaceae, subfamily Cercidoideae) and Ceratonia siliqua L. (family Fabaceae, subfamily Caesalpinoideae). Both taxa converge in the Mediterranean basin (C. siliquastrum on the north and C. siliqua across the south), in similar habitats (sclerophyll communities of maquis) and climatic profiles. These species are the current representation of their subfamilies in the Mediterranean basin, where they overlap. Because of this biogeographic and ecological similarity, the environmental pattern of both taxa was found to be very significant. The physical-chemical analysis performed on the epicuticular waxes of C. siliquastrum and C. siliqua leaves provided relevant data that confirm the functional proximity between them. A striking resemblance was found in the epicuticular waxes of the abaxial surfaces of C. siliquastrum and C. siliqua leaves in terms of the dominant chemical compounds (1-triacontanol (C30) and 1-octacosanol (C28), respectively), morphology (intricate network of randomly organized nanometer-thick and micrometer-long plates), wettability (superhydrophobic character, with water contact angle values of 167.5 +/- 0.5 degrees and 162 +/- 3 degrees, respectively), and optical properties (in both species the light reflectance/absorptance of the abaxial surface is significantly higher/lower than that of the adaxial surface, but the overall trend in reflectance is qualitatively similar). These results enable us to include for the first time C. siliqua in the vicariant process exhibited by C. canadensis L., C. griffithii L., and C. siliquastrum.
|
|
| 7. |
- Ravishankar, Ajith Padyana, et al.
(författare)
-
Fabrication of self-organized InP nanopillars by ion-bombardment for optoelectronic applications
- 2019
-
Ingår i: 2019 IEEE 14th Nanotechnology Materials and Devices Conference, NMDC 2019. - : Institute of Electrical and Electronics Engineers Inc.. - 9781728126371
-
Konferensbidrag (refereegranskat)abstract
- In this work, we investigate a wafer-scale, lithography-free, self-assembled indium phosphide (InP) nanopillars fabrication method based on ion bombardment. The influence of process conditions, such as the substrate temperature, ion beam energy, ion beam incidence angle, and processing time, were investigated with regard to the geometry (shape, diameter and height) and density of the fabricated nanopillars. For optimized process conditions, we show that by controlling the ion beam incidence angle (while rotating the sample), the shape (tapered to cylindrical) and average diameter (~75-150 nm) can be tuned and where InP nanopillar heights of ~600 nm were realized. It is shown that by modifying the shapes of the InP nanopillars, broadband anti-reflection can be obtained with average reflectance as low as ~4% in the wavelength range of 400-900 nm.
|
|
| 8. |
- Ravishankar, Ajith Padyana, et al.
(författare)
-
Strong Coupling in Metallo-dielectric Hybrid Metasurfaces
- 2021
-
Ingår i: The 11th International Conference on Metamaterials, Photonic Crystals and Plasmonics, META 2021. - : META Conference. ; , s. 146-147
-
Konferensbidrag (refereegranskat)abstract
- The presented work involves designing a hybrid metasurfaces by incorporating merits of two different types of resonator system (metal and dielectric) and investigating novel optical features emerging from the metasurface. The metasurface design consists of a high-index resonator array on top of thick metal film with a spacer layer. Simulation studies on the metasurface shows that a strong coupling can be achieved between the anapole mode in the disk and a surface plasmon polariton (SPP) mode at the metaldielectric interface.
|
|
| 9. |
- Ravishankar, Ajith Padyana, et al.
(författare)
-
Strong optical coupling in metallo-dielectric hybrid metasurfaces
- 2022
-
Ingår i: Optics Express. - : Optica Publishing Group. - 1094-4087. ; 30:23, s. 42512-42524
-
Tidskriftsartikel (refereegranskat)abstract
- Metasurfaces consisting of hybrid metal/dielectric nanostructures carry advantages of both material platforms. The hybrid structures can not only confine electromagnetic fields in subwavelength regions, but they may also lower the absorption losses. Such optical characteristics are difficult to realize in metamaterials with only metal or dielectric structures. Hybrid designs also expand the scope of material choices and the types of optical modes that can be excited in a metasurface, thereby allowing novel light matter interactions. Here, we present a metallodielectric hybrid metasurface design consisting of a high-index dielectric (silicon) nanodisk array on top of a metal layer (aluminum) separated by a buffer oxide (silica) layer. The dimensions of Si nanodisks are tuned to support anapole states and the period of the nanodisk array is designed to excite surface plasmon polariton (SPP) at the metal-buffer oxide interface. The physical dimensions of the Si nanodisk and the array periods are optimized to excite the anapole and the SPP at normal incidence of light in the visible-NIR (400-900 nm) wavelength range. Finite difference time domain (FDTD) simulations show that, when the nanodisk grating is placed at a specific height (similar to 200 nm) from the metal surface, the two modes strongly couple at zero detuning of the resonances. The strong coupling is evident from the avoided crossing of the modes observed in the reflectance spectra and in the spectral profile of light absorption inside the Si nanodisk. A vacuum Rabi splitting of up to similar to 129 meV is achievable by optimizing the diameters of Si nanodisk and the nanodisk array grating period. The proposed metasurface design is promising to realize open cavity strongly coupled optical systems operating at room temperatures. Published by Optica Publishing Group under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
|
|
| 10. |
- Rodriguez, S., et al.
(författare)
-
The Surfaces of the Ceratonia siliqua L. (Carob) Leaflet : Insights from Physics and Chemistry
- 2021
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 37:6, s. 2011-2028
-
Tidskriftsartikel (refereegranskat)abstract
- The production of superhydrophobic coatings inspired by the surface of plant leaves is a challenging goal. Such coatings hold a bright technological future in niche markets of the aeronautical, space, naval, building, automobile, and biomedical sectors. This work is focused on the adaxial (top) and abaxial (bottom) surfaces of the leaflet of the Ceratonia silique L. (carob), a high-commercial-value Mediterranean tree cultivated in many regions of the world. The adaxial and abaxial surfaces feature hydrophobic and superhydrophobic behaviors, respectively. Their chemical composition is very simple: monopalmitin ester and palmitic acid are protuberant in the epicuticular and intracuticular wax layers of the adaxial surface, respectively, whereas 1-octacosanol dominates in the abaxial wax layers. In both surfaces, epicuticular wax is organized along a randomly oriented and intricate network of nanometer-thick and micrometer-long plates, whose density and degree of interconnection are significantly higher in the abaxial surface. The measured tilting angles for the abaxial surface (12-70 degrees) reveal unusual variable density and water adhesion of the nanostructured plate-based texture. Optical measurements demonstrate that light reflectance/absorbance of the glaucous abaxial surface is significantly higher/lower than that of the nonglaucous adaxial surface. In both surfaces, diffuse reflectance is dominant, and the absorbance is weakly dependent on the light incidence angle. We show that the highly dense nanostructured platelike texture of the epicuticular abaxial layer of the C. siliqua leaflet works as a sophisticated light and water management system: it reflects solar radiation diffusely to lower the surface temperature, and it has superhydrophobic character to keep the surface dry. Such attributes enable efficient gas exchange (photosynthesis and respiration), transpiration, and evaporation. To mimic for the first time the abaxial surface, a templation approach was adopted using poly(dimethylsiloxane) (PDMS)/poly(methylphenylsiloxane) (PMPS) positive/negative replicas and a soft polymer/siloxane negative replica produced by the sol-gel process. Because high topographical variations of the biotemplate and wax adhesion to the biohybrid film affected the replication quality, the reproduction of the wax texture via the synthesis of 1-octacosanol-grafted siloxane-based hybrid materials is proposed as a suitable route to duplicate the abaxial surface with high fidelity. The natural chemical/physical strategy adopted by the C. siliqua leaflet to face the harsh Mediterranean climate is a powerful source of bioinspiration for the development of diffuse reflecting and superhydrophobic material systems with foreseen applications as dual-functional antiglare and water-repelling coatings.
|
|
