| 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. |
- Bowallius, Olof, et al.
(författare)
-
Scanning capacitance microscopy investigations of buried heterostructure laser structures
- 1999
-
Ingår i: Applied Surface Science. ; 144-145:0, s. 137-140
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, InP-based buried heterostucture lasers are used to demonstrate the utility of scanning capacitance microscopy (SCM) for characterising complex device structures. The lasers use p-n junctions formed by selective regrowth of p and n doped InP layers around a mesa for current confinement. For comparison, the regrowth was performed by liquid phase epitaxy (LPE) and metal organic vapour phase epitaxy (MOVPE). Our investigations show that scanning capacitance microscopy is capable of detecting the p-n junctions formed at different regions of the device and thereby allows visualisation of the current confinement regions. Variations in the imaged depletion regions are attributed to doping variations due to modification of the regrowth process by the mesa. The SCM data show significant differences between the devices regrown by LPE and MOVPE and the results are consistent with the different regrowth mechanisms. Finally, the implications of the SCM data on device performance are discussed. © 1999 Elsevier Science B.V. All rights reserved.
|
|
| 3. |
- De Luca, Eleonora, et al.
(författare)
-
Modal phase matching in nanostructured zinc-blende semiconductors for second-order nonlinear optical interactions
- 2017
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 96:7
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate enhanced second-harmonic generation in arrays of nanowaveguides satisfying modal-phase-matching condition, both theoretically and experimentally. The overlap of interacting fields defined by the fundamental mode of the pump and the second-order mode of the second-harmonic wave is enhanced by the longitudinal component of the nonlinear polarization density. For guided modes with significant longitudinal electric field components, the overlap of fields is comparable to that obtained in the quasi-phase-matching technique leading to higher conversion efficiencies. Thus, the presented method is preferable to achieve higher conversion efficiency in second-order nonlinear processes in nanowaveguides.
|
|
| 4. |
- Dev Choudhury, Bikash, 1978-, et al.
(författare)
-
Rapid thermal annealing treated spin-on doped antireflective radial junction Si nanopillar solar cell
- 2017
-
Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 25:8, s. A200-A207
-
Tidskriftsartikel (refereegranskat)abstract
- Radial junction nanopillar Si solar cells are interesting for cost effective efficiency improvement. Here, we address a convenient top-down fabrication of Si nanopillar solar cells using spin-on doping and rapid thermal annealing (RTA) for conformal PN junction formation. Broadband suppressed reflection as low as an average of 5% in the 300-1100 nm wavelength range and un-optimized cell efficiency of 7.3% are achieved. The solar cell performance can be improved by optimization of spin-on-doping and suitable surface passivation. Overall, the all RTA processed, spin-on doped nanopillar radial junction solar cell shows a very promising route for low cost and high efficiency thin film solar cell perspectives.
|
|
| 5. |
- Johansson, Wilhelm, et al.
(författare)
-
Transparent TiO2 and ZnO Thin Films on Glass for UV Protection of PV Modules
- 2020
-
Ingår i: American Ceramic Society Bulletin. - : American Ceramic Society Inc.. - 0002-7812 .- 1945-2705. ; 99:4, s. 26-29
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- To stabilize the global temperature and mitigate climate change, the emission of anthropogenic greenhouse gases will have to be greatly reduced. To make it possible, the energy sector will have to transfer from fossil energy to environmentally friendly and carbon neutral sources.
|
|
| 6. |
- 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.
|
|
| 7. |
- 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.
|
|
| 8. |
- 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.
|
|
| 9. |
- 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.
|
|
| 10. |
- 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.
|
|
