| 1. |
- Alarcon, Alvaro, et al.
(författare)
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All-in-Fiber Dynamically Reconfigurable Orbital Angular Momentum Mode Sorting
- 2023
-
Ingår i: ACS Photonics. - : AMER CHEMICAL SOC. - 2330-4022. ; 10:10, s. 3700-3707
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Tidskriftsartikel (refereegranskat)abstract
- The orbital angular momentum (OAM) spatial degree of freedom of light has been widely explored in many applications, including telecommunications, quantum information, and light-based micromanipulation. The ability to separate and distinguish between the different transverse spatial modes is called mode sorting or mode demultiplexing, and it is essential to recover the encoded information in such applications. An ideal d mode sorter should be able to faithfully distinguish between the different d spatial modes, with minimal losses, and have d outputs and fast response times. All previous mode sorters rely on bulk optical elements, such as spatial light modulators, which cannot be quickly tuned and have additional losses if they are to be integrated with optical fiber systems. Here, we propose and experimentally demonstrate, to the best of our knowledge, the first all-in-fiber method for OAM mode sorting with ultrafast dynamic reconfigurability. Our scheme first decomposes the OAM mode in-fiber-optical linearly polarized (LP) modes and then interferometrically recombines them to determine the topological charge, thus correctly sorting the OAM mode. In addition, our setup can also be used to perform ultrafast routing of the OAM modes. These results show a novel and fiber-integrated form of optical spatial mode sorting that can be readily used for many new applications in classical and quantum information processing.
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| 2. |
- Alekseeva, Svetlana, 1987, et al.
(författare)
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Single Particle Plasmonics for Materials Science and Single Particle Catalysis
- 2019
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 6:6, s. 1319-1330
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Forskningsöversikt (refereegranskat)abstract
- Single particle nanoplasmonic sensing and spectroscopy is a powerful and at the same time relatively easy-to-implement research method that allows monitoring of changes in the structure and properties of metal nanoparticles in real time and with only few restrictions in terms of surrounding medium, temperature and pressure. Consequently, it has been successfully used in materials science applications to, for instance, reveal the impact of size and shape of single metal nanoparticles on the thermodynamics of metal hydride formation and decomposition. In this Perspective, we review and discuss the research efforts that have spurred key advances in the development of single particle nanoplasmonic sensing and spectroscopy as a research tool in materials science. On this background we then assess the prospects and challenges toward its application in single particle catalysis, with the aim to enable operando studies of the relationship between metal nanoparticle structure or oxidation state and catalytic performance.
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| 3. |
- Andrén, Daniel, 1991, et al.
(författare)
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Large-Scale Metasurfaces Made by an Exposed Resist
- 2020
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 7:4, s. 885-892
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Tidskriftsartikel (refereegranskat)abstract
- Phase-gradient metasurfaces have the potential to revolutionize photonics by offering ultrathin alternatives to a wide range of common optical elements, including bulky refractive optics, waveplates, and axicons. However, the fabrication of state-of-the-art metasurfaces typically involves several expensive, time-consuming, and potentially hazardous processing steps. To address this limitation, a facile methodology to construct phase-gradient metasurfaces from an exposed standard electron beam resist is developed. The method dramatically cuts the required processing time and cost as well as reduces safety hazards. The advantages of the method are demonstrated by constructing high-performance flat optics based on the Pancharatnam-Berry phase gradient concept for the entire visible wavelength range. Manufactured devices include macroscopic (1 cm diameter) positive lenses, gratings exhibiting anomalous reflection, and cylindrical metalenses on flexible plastic substrates.
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| 4. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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Localized Surface Plasmon Decay Pathways in Disordered Two-Dimensional Nanoparticle Arrays
- 2015
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 2:12, s. 1732-1738
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Tidskriftsartikel (refereegranskat)abstract
- The size and shape of a metal nanoparticle determine its optical properties. When placed in an array the single particle response is further modified by the scattered fields, which for a random array are unique to each scatterer. However, at the array level scattering and absorption retain single-particle-like spectra. Using T-Matrix calculations and an analytical model of intra-array coupling in amorphous arrays we show how the branching ratio of the localized plasmon decay depends on disorder and particle density. We calculate the effective polarizability and demonstrate its effects on scattering and absorption. The scattering-to-absorption ratio is a function of particle separation in the disordered array and can significantly deviate from the inherent single particle ratio. We trace the period of this oscillatory dependence of the ratio to the single particle plasmon resonance wavelength. This effect has implications for applications in which one of the decay channels has to be dominant, for example, absorption for hot electron hole pair generation in the metal particles or scattering into a nearby semiconductor.
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| 5. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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Plasmon-Exciton Interactions in a Core-Shell Geometry: From Enhanced Absorption to Strong Coupling
- 2014
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 1:5, s. 454-463
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed Mie theory, finite-difference time-domain, and quasi-static study of plasmon-exciton interactions in a spherical core shell geometry. In particular, we report absorption, scattering, and extinction cross sections of a hybrid core-shell system and identify several important interaction regimes that are determined by the electromagnetic field enhancement and the oscillator strength of electronic excitations. We assign these regimes to enhanced-absorption, exciton-induced transparency and strong coupling, depending on the nature of the observed spectra of the coupled plasmon-exciton resonances. We also show the relevance of performing single-particle absorption or extinction measurements in addition to scattering to validate the interaction regime. Furthermore, at relatively high, yet realistic oscillator strengths we observe emergence of a third mode, which is not predicted by a classical coupled harmonic oscillator model and is attributed to the geometrical resonance of the structure as a whole.
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| 6. |
- Anttu, Nicklas
(författare)
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Shockley-Queisser Detailed Balance Efficiency Limit for Nanowire Solar Cells
- 2015
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 2:3, s. 446-453
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Tidskriftsartikel (refereegranskat)abstract
- III-V semiconductor nanowire arrays show promise as a platform for next-generation solar cells. However, the theoretical efficiency limit for converting the energy of sunlight into electrical energy in such solar cells is unknown. Here, we calculate through electromagnetic modeling the Shockley-Queisser efficiency limit for an InP nanowire array solar cell. In this analysis, we calculate first from the absorption of sunlight the short-circuit current. Next, we calculate the voltage-dependent emission characteristics of the nanowire array. From these processes, we identify how much current we can extract at a given voltage. Finally, after constructing this current-voltage (IV) curve of the nanowire solar cell, we identify from the maximum power output the maximum efficiency. We compare this efficiency of the nanowire array with the 31.0% efficiency limit of the conventional InP bulk solar cell with an inactive substrate underneath. We consider a nanowire array of 400 nm in period, which shows a high short-circuit current. We optimize both the nanowire length and diameter in our analysis. For example, nanowires of 4 mu m in length and 170 nm in diameter produce 96% of the short-circuit current obtainable in the perfectly absorbing InP bulk cell. However, the nanowire solar cell emits fewer photons than the bulk cell at thermal equilibrium, especially into the substrate. This weaker emission allows for a higher open circuit-voltage for the nanowire cell. As an end result, nanowires longer than 4 mu m can actually show, despite producing a lower short-circuit current, a higher efficiency limit, of up to 32.5%, than the bulk cell.
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| 7. |
- Bahsoun, H., et al.
(författare)
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Electronic Light-Matter Strong Coupling in Nanofluidic Fabry-Pérot Cavities
- 2018
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 5:1, s. 225-232
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Tidskriftsartikel (refereegranskat)abstract
- Electronic light-matter strong coupling has been limited to solid molecular films due to the challenge of preparing optical cavities with nanoscale dimensions. Here we report a technique to fabricate such Fabry-Pérot nanocavities in which solutions can be introduced such that light-molecule interactions can be studied at will in the liquid phase. We illustrate the versatility of these cavities by studying the emission properties of Chlorin e6 solutions in both the weak and strong coupling regimes as a function of cavity detuning. Liquid nanocavities will broaden the investigation of strong coupling to many solution-based molecular processes. © 2017 American Chemical Society.
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| 8. |
- Balla, N. K., et al.
(författare)
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Polarized Nonlinear Nanoscopy of Metal Nanostructures
- 2017
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 4:2, s. 292-301
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Tidskriftsartikel (refereegranskat)abstract
- Nonlinear signals from metal nanostructures are known to be highly polarization-dependent, due to the intrinsic vectorial nature of nonlinear optical coupling. Nonlinear optical polarization responses contain important information on the near-field properties of nanostructures;, however, they remain complex to monitor and to model at the nanoscale. Polarization resolved nonlinear optical microscopy can potentially address this question; however, the recorded signals are generally averaged over the diffraction-limited size of a few hundreds of nanometers, thus, missing the spatial specificity of the nanostructure's optical response. Here we present a form of polarization resolved microscopy, named polarization nonlinear nanoscopy, which reveals subdiffraction scale vectorial variations of electromagnetic fields, even though the intensity image is diffraction-limited. We show that by exploiting, at a single subdiffraction pixel level, the information gained by the polarization-induced modulation, it is possible to spatially map the vectorial nature of plasmonic nonlinear optical interactions in nanostructures, revealing in particular surface contributions, retardation effects, and anisotropic spatial confinements.
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| 9. |
- Baranov, Denis, 1990, et al.
(författare)
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Anapole-Enhanced Intrinsic Raman Scattering from Silicon Nanodisks
- 2018
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 5:7, s. 2730-2736
-
Tidskriftsartikel (refereegranskat)abstract
- Enhancement of inelastic light emission processes through resonant excitation usually correlates with enhanced scattering of the excitation light, as is for example typically the case for surface-enhanced fluorescence and Raman scattering from plasmonic nanostructures. Here, we demonstrate an unusual case where a reverse correlation is instead observed, that is, we measure a multifold enhancement of Raman emission along with suppressed elastic scattering. The system enabling this peculiar effect is composed of silicon nanodisks excited in the so-called anapole state, for which electric and toroidal dipoles interfere destructively in the far-field, thereby preventing elastic scattering, while the optical fields in the core of the silicon particles are enhanced, thus, amplifying light-matter interaction and Raman scattering at the Stokes-shifted emission wavelength. Our results demonstrate an unusual relation between resonances in elastic and inelastic scattering from nanostructures and suggest a route toward background-free frequency conversion devices.
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| 10. |
- Baranov, Denis G., et al.
(författare)
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Toward Molecular Chiral Polaritons
- 2023
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Ingår i: ACS Photonics. - 2330-4022. ; 10:8, s. 2440-2455
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Tidskriftsartikel (refereegranskat)abstract
- Coupling between light and material excitations underliesa widerange of optical phenomena. Polaritons are eigenstates of a coupledsystem with a hybridized wave function. Owing to their hybrid composition,polaritons exhibit at the same time properties typical for photonicand electronic excitations, thus offering new ways for controllingelectronic transport and even chemical kinetics. While most theoreticaland experimental efforts have been focused on polaritons with electric-dipolecoupling between light and matter, in chiral quantum emitters, electronictransitions are characterized by simultaneously nonzero electric andmagnetic dipole moments. Thus, it is natural to wonder what kindsof novel effects chirality may enable in the realm of strong light-mattercoupling. Right now, this field located at the intersection of nanophotonics,quantum optics, and chemistry is in its infancy. In this Perspective,we offer our view toward chiral polaritons. We review basic physicalconcepts underlying chirality of matter and electromagnetic field,discuss the main theoretical and experimental challenges that needto be solved, and consider novel effects that could be enabled bystrong coupling between chiral light and matter.
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| 11. |
- Baranov, Denis, 1990, et al.
(författare)
-
Novel Nanostructures and Materials for Strong Light-Matter Interactions
- 2018
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 5:1, s. 24-42
-
Forskningsöversikt (refereegranskat)abstract
- Quantum mechanical interactions between electromagnetic radiation and matter underlie a broad spectrum of optical phenomena. Strong light-matter interactions result in the well-known vacuum Rabi splitting and emergence of new polaritonic eigenmodes of the coupled system. Thanks to recent progress in nanofabrication, observation of strong coupling has become possible in a great variety of optical nanostructures. Here, we review recently studied and emerging materials for realization of strong light-matter interactions. We present general theoretical formalism describing strong coupling and give an overview of various photonic structures and materials allowing for realization of this regime, including plasmonic and dielectric nanoantennas, novel two-dimensional materials, carbon nanotubes, and molecular vibrational transitions. In addition, we discuss practical applications that can benefit from these effects and give an outlook on unsettled questions that remain open for future research.
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| 12. |
- Becker, Christiane, et al.
(författare)
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Nanophotonic-Enhanced Two-Photon-Excited Photoluminescence of Perovskite Quantum Dots
- 2018
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 5:11, s. 4668-4676
-
Tidskriftsartikel (refereegranskat)abstract
- All-inorganic CsPbBr3 perovskite colloidal quantum dots have recently emerged as a promising material for a variety of optoelectronic applications, among others for multiphoton-pumped lasing. Nevertheless, high irradiance levels are generally required for such multiphoton processes. One strategy to enhance the multiphoton absorption is taking advantage of high local light intensities using photonic nanostructures. Here, we investigate two-photon-excited photoluminescence of CsPbBr3 perovskite quantum dots on a silicon photonic crystal slab. By systematic excitation of optical resonances using a pulsed near-infrared laser beam, we observe an enhancement of two-photon-pumped photoluminescence by more than 1 order of magnitude when comparing to using a bulk silicon film. Experimental and numerical analyses allow relating these findings to near-field enhancement effects on the nanostructured silicon surface. The results reveal a promising approach for significantly decreasing the required irradiance levels for multiphoton processes being of advantage in applications such as biomedical imaging, lighting, and solar energy.
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| 13. |
- Belkadi, Amina, et al.
(författare)
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Demonstration of Thermoradiative Power Generation Using Compensated Infrared Rectennas
- 2023
-
Ingår i: ACS Photonics. - 2330-4022. ; 10:11, s. 3866-3874
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Tidskriftsartikel (refereegranskat)abstract
- Thermoradiative devices convert low-temperature waste heat to electricity. These devices harvest heat and generate energy using deep space as a heat sink by radiating through the 8 to 13 μm atmospheric window. Infrared rectennas, which consist of ultrahigh speed diodes coupled to micrometer-scale antennas, can be tuned to these frequencies and are a good candidate for thermoradiative power generation at room temperature, if certain challenges can be circumvented. Practical optical rectennas require a high diode conversion efficiency, a high coupling efficiency between the diode and antenna, and a large array of devices sufficient to produce significant power. The novelty of our approach lies in designing and building a diode compensation structure at terahertz and arraying 250000 diodes, two approaches that have never been reported before. We demonstrate that a Ni/NiO/Al2O3/Cr/Au metal-double insulator-metal (MI2M) diode-based infrared rectenna with a 2.5 μm transmission line compensation structure in a staggered array can produce power from a temperature difference, and with development, it has the potential to produce competitive power outputs.
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| 14. |
- Bergmann, Michael Alexander, 1989, et al.
(författare)
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Increased Light Extraction of Thin-Film Flip-Chip UVB LEDs by Surface Texturing
- 2023
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 10:2, s. 368-373
-
Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet light-emitting diodes (LEDs) suffer from a low wall-plug efficiency, which is to a large extent limited by the poor light extraction efficiency (LEE). A thin-film flip-chip (TFFC) design with a roughened N-polar AlGaN surface can substantially improve this. We here demonstrate an enabling technology to realize TFFC LEDs emitting in the UVB range (280-320 nm), which includes standard LED processing in combination with electrochemical etching to remove the substrate. The integration of the electrochemical etching is achieved by epitaxial sacrificial and etch block layers in combination with encapsulation of the LED. The LEE was enhanced by around 25% when the N-polar AlGaN side of the TFFC LEDs was chemically roughened, reaching an external quantum efficiency of 2.25%. By further optimizing the surface structure, our ray-tracing simulations predict a higher LEE from the TFFC LEDs than flip-chip LEDs and a resulting higher wall-plug efficiency.
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| 15. |
- Bergqvist, Jonas, et al.
(författare)
-
Uniaxial Anisotropy in PEDOT:PSS Electrodes Enhances the Photocurrent at Oblique Incidence in Organic Solar Cells
- 2018
-
Ingår i: ACS Photonics. - : AMER CHEMICAL SOC. - 2330-4022. ; 5:8, s. 3023-3030
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Tidskriftsartikel (refereegranskat)abstract
- PEDOT:PSS is a well studied organic conductor, commonly used as a transparent electrode material in printed organic devices such as organic solar cells. PEDOT:PSS thin films are known to be uniaxially anisotropic and exhibit a lower extinction coefficient and lower refractive index in the out of plane direction. To determine the maximum attainable photocurrent in thin film solar cells, the optical power dissipation can be calculated by the transfer matrix method. However, until now the anisotropic properties of PEDOT:PSS films have not been included in the model. In this work we have included an uniaxial anisotropic treatment of PEDOT:PSS films. We investigate reversed and semitransparent solar cells, with aluminum and PEDOT:PSS respectively as the second electrode and PEDOT:PSS as the top electrode, as compared to devices with isotropic PEDOT:PSS electrodes. For p-polarized light at large oblique incidence the inclusion of anisotropy shows a gain of over 7% for the maximum photocurrent in reversed solar cells. In semitransparent solar cells the photocurrent enhancement reaches 4-5% for p-polarized light. However, an enhancement of optical power dissipation and thus photocurrent generation of close to 40% is calculated for wavelengths close to the absorber bandgap. This work shows that for correct calculations of optical power dissipation in devices with PEDOT:PSS electrodes anisotropy should be included in the optical model. This will be especially important to determine the daily energy output of organic solar cells as their expected first markets are on building facades and indoor applications with larger fractions of diffuse light at large oblique incidence.
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| 16. |
- Bi, Dongqin, et al.
(författare)
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Unraveling the Effect of PbI2 Concentration on Charge Recombination Kinetics in Perovskite Solar Cells
- 2015
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 2:5, s. 589-594
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Tidskriftsartikel (refereegranskat)abstract
- CH3NH3PbI3 perovskite solar cells have rapidly risen to the forefront of emerging photovoltaic technologies. A solution-based, two-step method was reported to enhance the reproducibility of these solar cells. In this method, first a coating of PbI2 is applied by spin-coating onto a TiO2-coated substrate, followed by a dip in a methylammonium iodide solution, leading to conversion to CH3NH3PbI3. The concentration of PbI2 in the spin-coating solution is a very important factor that affects the infiltration of the perovskite and the amount deposited. The best solar cell performance of 13.9% was obtained by devices prepared using 1.0 M of PbI2 in dimethylformamide. These devices also had the longest electron lifetime and shortest carrier transport time, yielding lowest recombination losses. Rapid quenching of the perovskite emission is found in device-like structures, suggesting reasonably good efficient carrier extraction at the TiO2 interface and quantitative extraction at the spiro-OMeTAD interface.
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| 17. |
- Bosio, Noemi, 1993, et al.
(författare)
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Plasmonic versus All-Dielectric Nanoantennas for Refractometric Sensing: A Direct Comparison
- 2019
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 6:6, s. 1556-1564
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Tidskriftsartikel (refereegranskat)abstract
- In comparison to nanoplasmonic structures, resonant high-index dielectric nanoantennas hold several advantages that may benefit nanophotonic applications, including CMOS compatibility and low ohmic losses. One such application area might be label-free refractometric sensing, where changes in individual antenna resonance properties are used to quantify changes in the surrounding refractive index, for example, due to biomolecular binding. Here, we analyze and compare the sensing performance of silicon and gold nanodisks using a common and unbiased testing framework. We find that the all-dielectric system is fully capable of effectively monitoring small changes in bulk refractive index and biomolecular coverage, but the sensitivity is five to ten times lower than the plasmonic counterpart. However, this drawback is partly compensated for by a more linear response to adsorbate layer thickness changes and an approximately four times smaller susceptibility to photothermal heating. Finally, dielectric sensors may show promise if certain strategies are employed to improve their performance, which could thus bridge the gap between the two systems.
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| 18. |
- Bresolí-Obach, Roger, et al.
(författare)
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Resonantly Enhanced Optical Trapping of Single Dye-Doped Particles at an Interface
- 2021
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 8:6, s. 1832-1839
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Tidskriftsartikel (refereegranskat)abstract
- The optical resonance between an absorbing particle and the trapping laser can enhance the radiation force exerted on micro/nanoscale objects. However, the exact mechanism behind this resonance is still elusive. To unravel the phenomenon, we studied the resonance between a single dye-doped polystyrene particle and a 1064 nm trapping laser under specifically designed optical conditions. The dye-doped particle was trapped at a water-glass interface while simultaneously being excited by a 488 nm widefield laser. In contrast with former reports (â 10-35% trapping stiffness enhancement), we obtained an unprecedented 4-fold trapping stiffness enhancement due to resonant excitation. When we photobleached the embedded dyes as a control, the trapping stiffness enhancement was no longer observed. Based on nonlinear resonant radiation force theory and the experimental data obtained with a three-dimensional multiplane microscope, we propose that the widefield laser excites the dye to S1 and the trapping laser induces a simultaneous ultrafast S1-S2-S1 cyclic transition, resonantly enhancing the induced dye polarization and, consequently, the radiation force. The elucidation of the optical resonance effect is expected to ultimately enable single molecule manipulation in solution at room temperature.
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| 19. |
- Brodu, Annalisa, et al.
(författare)
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Exciton Fine Structure and Lattice Dynamics in InP/ZnSe Core/Shell Quantum Dots
- 2018
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 5:8, s. 3353-3362
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Tidskriftsartikel (refereegranskat)abstract
- Nanocrystalline InP quantum dots (QDs) hold promise for heavy-metal-free optoelectronic applications due to their bright and size tunable emission in the visible range. Photochemical stability and high photoluminescence (PL) quantum yield are obtained by a diversity of epitaxial shells around the InP core. To understand and optimize the emission line shapes, the exciton fine structure of InP core/shell QD systems needs be investigated. Here, we study the exciton fine structure of InP/ZnSe core/shell QDs with core diameters ranging from 2.9 to 3.6 nm (PL peak from 2.3 to 1.95 eV at 4 K). PL decay measurements as a function of temperature in the 10 mK to 300 K range show that the lowest exciton fine structure state is a dark state, from which radiative recombination is assisted by coupling to confined acoustic phonons with energies ranging from 4 to 7 meV, depending on the core diameter. Circularly polarized fluorescence line-narrowing (FLN) spectroscopy at 4 K under high magnetic fields (up to 30 T) demonstrates that radiative recombination from the dark F = +/- 2 state involves acoustic and optical phonons, from both the InP core and the ZnSe shell. Our data indicate that the highest intensity FLN peak is an acoustic phonon replica rather than a zero-phonon line, implying that the energy separation observed between the F = +/- 1 state and the highest intensity peak in the FLN spectra (6 to 16 meV, depending on the InP core size) is larger than the splitting between the dark and bright fine structure exciton states.
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| 20. |
- Bronte Ciriza, David, et al.
(författare)
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Faster and More Accurate Geometrical-Optics Optical Force Calculation Using Neural Networks
- 2022
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 10:1, s. 234-41
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Tidskriftsartikel (refereegranskat)abstract
- Optical forces are often calculated by discretizing the trapping light beam into a set of rays and using geometrical optics to compute the exchange of momentum. However, the number of rays sets a trade-off between calculation speed and accuracy. Here, we show that using neural networks permits overcoming this limitation, obtaining not only faster but also more accurate simulations. We demonstrate this using an optically trapped spherical particle for which we obtain an analytical solution to use as ground truth. Then, we take advantage of the acceleration provided by neural networks to study the dynamics of ellipsoidal particles in a double trap, which would be computationally impossible otherwise.
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| 21. |
- Bronte Ciriza, David, et al.
(författare)
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Optically Driven Janus Microengine with Full Orbital Motion Control
- 2023
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Ingår i: ACS PHOTONICS. - 2330-4022. ; 10:9, s. 3223-3232
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Tidskriftsartikel (refereegranskat)abstract
- Microengines have shown promise for a variety of applications in nanotechnology, microfluidics, and nanomedicine, including targeted drug delivery, microscale pumping, and environmental remediation. However, achieving precise control over their dynamics remains a significant challenge. In this study, we introduce a microengine that exploits both optical and thermal effects to achieve a high degree of controllability. We find that in the presence of a strongly focused light beam, a gold-silica Janus particle becomes confined at the stationary point where the optical and thermal forces balance. By using circularly polarized light, we can transfer angular momentum to the particle, breaking the symmetry between the two forces and resulting in a tangential force that drives directed orbital motion. We can simultaneously control the velocity and direction of rotation of the particle changing the ellipticity of the incoming light beam while tuning the radius of the orbit with laser power. Our experimental results are validated using a geometrical optics phenomenological model that considers the optical force, the absorption of optical power, and the resulting heating of the particle. The demonstrated enhanced flexibility in the control of microengines opens up new possibilities for their utilization in a wide range of applications, including microscale transport, sensing, and actuation.
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| 22. |
- Chang, Tsu Chi, et al.
(författare)
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Electrically Injected GaN-Based Vertical-Cavity Surface-Emitting Lasers with TiO2 High-Index-Contrast Grating Reflectors
- 2020
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 7:4, s. 861-866
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the first electrically injected GaN-based vertical-cavity surface-emitting lasers (VCSELs) with a TiO2 high-index-contrast grating (HCG) as the top mirror. Replacing the top distributed Bragg reflector (DBR) with an HCG offers substantial thickness reduction, polarization-pinning, and setting of the resonance wavelength by the grating parameters. Conventional HCGs are usually suspended in the low refractive index material, such as air, in order to create the largest refractive index contrast. However, the mechanical stability of such structures can be questioned and creating free-hanging GaN-membrane on top of GaN is problematic. We have therefore fabricated TiO2-HCGs resting directly on GaN without an air-gap. No DBR layers are used below the HCG to boost the reflectivity. A VCSEL with an aperture diameter of 10 μm shows a threshold current of 25 mA under pulsed operation at room temperature. The lasing modes locate around 400 nm and are transversely electrically -polarized with a line width of 0.5 nm. The full-width half-maximum beam divergence is 10°. This demonstration of a TiO2-HCG VCSEL offers a new route to achieve polarization pinning and could also allow additional benefits such as postgrowth setting of the resonance wavelength.
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| 23. |
- Chen, Junsheng, et al.
(författare)
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Evidence of High-Order Nonlinearities in Supercontinuum White-Light Generation from a Gold Nanofilm
- 2018
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 5:5, s. 1927-1932
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Tidskriftsartikel (refereegranskat)abstract
- White-light supercontinuum generation can be readily observed when gold nanostructures are irradiated with short pulses of light. It is believed that the nanostructures enhance the optical fields, which facilitates the supercontinuum white-light generation from the surrounding environment or the substrate. Here, we investigate the different nonlinear processes that contribute to the generation of the supercontinuum from plasmonic nanostructures themselves using a technique that isolates the different nonlinear contributions. By exciting a gold nanofilm with a pair of frequency shifted optical frequency combs, we demonstrate multiple modulation frequencies in the supercontinuum. Their dependence on the excitation intensity reveals that the supercontinuum originates from different orders of nonlinear light-matter interactions. This contrasts with the supercontinuum generation by a cascaded third-order optical nonlinear response in traditional dielectric-based white-light sources. The while-light emission from the gold nanofilm is efficient even under relatively weak excitation indicating that nonlocal effects in nanostructures may facilitate the supercontinuum generation by adding new pathways in the nonlinear interactions. The results provide experimental basis for the understanding of the collective nonlinear response of free-electrons in the metallic nanostructures and associated nonlinear processes, which are crucial in development of nonlinear metasurfaces and nanophotonic devices.
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| 24. |
- Chen, Shangzhi, et al.
(författare)
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Dynamic Conducting Polymer Plasmonics and Metasurfaces
- 2023
-
Ingår i: ACS Photonics. - : AMER CHEMICAL SOC. - 2330-4022. ; 10:3, s. 571-581
-
Tidskriftsartikel (refereegranskat)abstract
- Metals have been the dominant plasmonic materials for decades, but they suffer from limited tunability. By contrast, conducting polymers offer exceptional tunability and were recently introduced as a new category of dynamic plasmonic materials. Their charge carrier density can be drastically modulated via their redox state, offering reversible and gradual transitions between optically metallic and dielectric behavior. Nanoantennas made from conducting polymers can therefore be reversibly turned off and on again. This enables phase gradient metasurfaces with tunable functionalities, holding promise for applications such as video holograms. In this Perspective, we discuss the emergence of dynamic conducting polymer plasmonics as a new research direction, including recent developments, remaining challenges, and opportunities for future research. We hope that this Perspective will encourage more researchers to join the journey and contribute toward a rapid development of this interdisciplinary field.
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| 25. |
- Chung, Nguyen Xuan, et al.
(författare)
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Toward Practical Carrier Multiplication : Donor/Acceptor Codoped Si Nanocrystals in SiO2
- 2018
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 5:7, s. 2843-2849
-
Tidskriftsartikel (refereegranskat)abstract
- Carrier multiplication (CM) is an interesting fundamental phenomenon with application potential in optoelectronics and photovoltaics, and it has been shown to be promoted by quantum confinement effects in nanostructures. However, mostly due to the short lifetimes of additional electronhole (e-h) pairs generated by CM, major improvements of quantum dot devices that exploit CM are limited. Here we investigate CM in SiO2 solid state dispersions of phosphorus and boron codoped Si nanocrystals (NCs): an exotic variant of Si NCs whose photoluminescence (PL) emission energy, the optical bandgap, is significantly red-shifted in comparison to undoped Si NCs. By combining the results obtained by ultrafast induced absorption (IA) with PL quantum yield (PL QY) measurements, we demonstrate CM with a long (around 100 mu s) lifetime of the additional e-h pairs created by the process, similar as previously reported for undoped Si NCs, but with a significantly lower CM threshold energy. This constitutes a significant step toward the practical implementation of Si-based NCs in optoelectronic devices: we demonstrate efficient CM at the energy bandgap optimal for photovoltaic conversion.
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| 26. |
- de Amorim Ferreira, Beatriz, 1996, et al.
(författare)
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Revealing Dark Exciton Signatures in Polariton Spectra of 2D Materials
- 2024
-
Ingår i: ACS Photonics. - 2330-4022. ; 11:6, s. 2215-2220
-
Tidskriftsartikel (refereegranskat)abstract
- Dark excitons in transition metal dichalcogenides (TMDs) have been so far neglected in the context of polariton physics due to their lack of oscillator strength. However, in tungsten-based TMDs, dark excitons are known to be the energetically lowest states and could thus provide important scattering partners for polaritons. In this joint theoretical-experimental work, we investigate the impact of the full exciton energy landscape on polariton absorption and reflectance. By changing the cavity detuning, we vary the polariton energy relative to the unaffected dark excitons in such a way that we open or close specific phonon-driven scattering channels. We demonstrate both in theory and experiment that this controlled switching of scattering channels manifests in characteristic sharp changes in the optical spectra of polaritons. These spectral features can be exploited to extract the position of dark excitons. Our work suggests new possibilities for exploiting polaritons for fingerprinting nanomaterials via their unique exciton landscape.
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| 27. |
- De Zuani, Stefano, et al.
(författare)
-
High-Order Hilbert Curves: Fractal Structures with Isotropic, Tailorable Optical Properties
- 2015
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 2:12, s. 1719-1724
-
Tidskriftsartikel (refereegranskat)abstract
- © 2015 American Chemical Society. Fractals are promising candidates as nonperiodic, nonresonant structures exhibiting a homogeneous, isotropic, and frequency-independent effective optical response. We present a comprehensive optical investigation of a metallic Hilbert curve of fractal order N = 9 in the visible and near-infrared spectral range. Our experiments show that high-order fractal nanostructures exhibit a nearly frequency independent reflectance and an in-plane isotropic optical response. The response can be simulated in the framework of a simple effective medium approximation model with a limited number of parameters. It is shown that high-order Hilbert structures can be considered as a transparent in-plane metal, the dielectric function of which is modified by the filling factor f, hence creating a tunable conductive effective metal with tailorable plasma frequency and variable reflectance without going through an insulator-to-metal transition.
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| 28. |
- De Zuani, Stefano, et al.
(författare)
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Suppressed Percolation in Nearly Closed Gold Films
- 2016
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 3:6, s. 1109-1115
-
Tidskriftsartikel (refereegranskat)abstract
- Metal-dielectric composites exhibit remarkable properties at the percolation threshold. A small variation of the filling factor can lead to a huge variation in the dc conductivity from an insulator-like to a metal-like behavior while the real part of the permittivity diverges. This behavior can, in principle, be described by percolation theories at low frequencies and by effective medium approximations at higher frequencies. These theories assume a random distribution of the metallic inclusions inside the insulating matrix. But what happens in ordered structures when the percolation is deliberately suppressed? Even though a simple, nanometer-wide scratch can deteriorate the dc conductivity of a thin metal film, can it influence the mirror-like reflectivity? To address this question, we perform a systematic ellipsometric investigation on nearly closed Au films interrupted only by a two-dimensional periodic mesh of 20 nm wide lines. These nanostructured films have metal filling factors close to unity, but exhibit no dc conductivity. In the infrared, they show an antireflective behavior that can be tuned through the mesh periodicity. Surprisingly, the optical response of these structures can be modeled quite well by simple effective medium approximations. Increasing the size of the squares leads to a tunable, diverging, real part of the permittivity: A maximum of the real part of the permittivity of 1420 is found for the largest investigated squares in this study.
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| 29. |
- Descamps, Thomas, et al.
(författare)
-
Dynamic Strain Modulation of a Nanowire Quantum Dot Compatible with a Thin-Film Lithium Niobate Photonic Platform
- 2023
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 10:10, s. 3691-3699
-
Tidskriftsartikel (refereegranskat)abstract
- The integration of indistinguishable single photon sources in photonic circuits is a major prerequisite for on-chip quantum applications. Among the various high-quality sources, nanowire quantum dots can be efficiently coupled to optical waveguides because of their preferred emission direction along their growth direction. However, local tuning of the emission properties remains challenging. In this work, we transfer a nanowire quantum dot onto a bulk lithium niobate substrate and show that its emission can be dynamically tuned by acousto-optical coupling with surface acoustic waves. The purity of the single photon source is preserved during the strain modulation. We further demonstrate that the transduction is maintained even with a SiO2 encapsulation layer deposited on top of the nanowire acting as the cladding of a photonic circuit. Based on these experimental findings and numerical simulations, we introduce a device architecture consisting of a nanowire quantum dot efficiently coupled to a thin-film lithium niobate rib waveguide and strain-tunable by surface acoustic waves.
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| 30. |
- Errando-Herranz, Carlos, 1989-, et al.
(författare)
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Resonance Fluorescence from Waveguide-Coupled, Strain-Localized, Two-Dimensional Quantum Emitters
- 2021
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 8:4, s. 1069-1076
-
Tidskriftsartikel (refereegranskat)abstract
- Efficient on-chip integration of single-photon emitters imposes a major bottleneck for applications of photonic integrated circuits in quantum technologies. Resonantly excited solid-state emitters are emerging as near-optimal quantum light sources, if not for the lack of scalability of current devices. Current integration approaches rely on cost-inefficient individual emitter placement in photonic integrated circuits, rendering applications impossible. A promising scalable platform is based on two-dimensional (2D) semiconductors. However, resonant excitation and single-photon emission of waveguide-coupled 2D emitters have proven to be elusive. Here, we show a scalable approach using a silicon nitride photonic waveguide to simultaneously strain-localize single-photon emitters from a tungsten diselenide (WSe2) monolayer and to couple them into a waveguide mode. We demonstrate the guiding of single photons in the photonic circuit by measuring second-order autocorrelation of g((2))(0) = 0.150 +/- 0.093 and perform on-chip resonant excitation, yielding a g((2))(0) = 0.377 +/- 0.081. Our results are an important step to enable coherent control of quantum states and multiplexing of high-quality single photons in a scalable photonic quantum circuit.
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| 31. |
- Faggiani, Rémi, et al.
(författare)
-
Modal Analysis of the Ultrafast Dynamics of Optical Nanoresonators
- 2017
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 4:4, s. 897-904
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a semianalytical formalism based on a time-domain resonant-mode-expansion theory to analyze the ultrafast temporal dynamics of optical nanoresonators. We compare the theoretical predictions with numerical data obtained with the FDTD method, which is commonly used to analyze experiments in the field. The comparison reveals that the present formalism (i) provides deeper physical insight onto the temporal response and (ii) is much more computationally efficient. Since its numerical implementation is easy, the formalism, albeit approximate, can be advantageously used to both analyze and design ultrafast nano-optics experiments.
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| 32. |
- Fognini, A., et al.
(författare)
-
Dephasing Free Photon Entanglement with a Quantum Dot
- 2019
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 6:7, s. 1656-1663
-
Tidskriftsartikel (refereegranskat)abstract
- Generation of photon pairs from quantum dots with near-unity entanglement fidelity has been a long-standing scientific challenge. It is generally thought that the nuclear spins limit the entanglement fidelity through spin flip dephasing processes. However, this assumption lacks experimental support. Here, we show two-photon entanglement with negligible dephasing from an indium rich single quantum dot comprising a nuclear spin of 9/2 when excited quasi-resonantly. This finding is based on a significantly close match between our entanglement measurements and our model that assumes no dephasing and takes into account the detection system's timing jitter and dark counts. We suggest that neglecting the detection system is responsible for the degradation of the measured entanglement fidelity in the past and not the nuclear spins. Therefore, the key to unity entanglement from quantum dots comprises a resonant excitation scheme and a detection system with ultralow timing jitter and dark counts.
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| 33. |
- Friese, D. H., et al.
(författare)
-
Five-photon absorption and selective enhancement of multiphoton absorption processes
- 2015
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 2:5, s. 572-577
-
Tidskriftsartikel (refereegranskat)abstract
- We study one-, two-, three-, four-, and five-photon absorption of three centrosymmetric molecules using density functional theory. These calculations are the first ab initio calculations of five-photon absorption. Even- and odd-order absorption processes show different trends in the absorption cross sections. The behavior of all even- and odd-photon absorption properties shows a semiquantitative similarity, which can be explained using few-state models. This analysis shows that odd-photon absorption processes are largely determined by the one-photon absorption strength, whereas all even-photon absorption strengths are largely dominated by the two-photon absorption strength, in both cases modulated by powers of the polarizability of the final excited state. We demonstrate how to selectively enhance a specific multiphoton absorption process.
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| 34. |
- Frigerio, Jacopo, et al.
(författare)
-
Second Harmonic Generation in Germanium Quantum Wells for Nonlinear Silicon Photonics
- 2021
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 8:12, s. 3573-3582
-
Tidskriftsartikel (refereegranskat)abstract
- Second-harmonic generation (SHG) is a direct measure of the strength of second-order nonlinear optical effects, which also include frequency mixing and parametric oscillations. Natural and artificial materials with broken center-of-inversion symmetry in their unit cell display high SHG efficiency, however, the silicon-foundry compatible group IV semiconductors (Si, Ge) are centrosymmetric, thereby preventing full integration of second-order nonlinearity in silicon photonics platforms. Here we demonstrate strong SHG in Ge-rich quantum wells grown on Si wafers. Unlike Si-rich epilayers, Ge-rich epilayers allow for waveguiding on a Si substrate. The symmetry breaking is artificially realized with a pair of asymmetric coupled quantum wells (ACQW), in which three of the quantum-confined states are equidistant in energy, resulting in a double resonance for SHG. Laser spectroscopy experiments demonstrate a giant second-order nonlinearity at mid-infrared pump wavelengths between 9 and 12 μm. Leveraging on the strong intersubband dipoles, the nonlinear susceptibility χ(2) almost reaches 105 pm/V, 4 orders of magnitude larger than bulk nonlinear materials for which, by the Miller's rule, the range of 10 pm/V is the norm.
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| 35. |
- Gedeon, Johannes, et al.
(författare)
-
Time-domain topology optimization of arbitrary dispersive materials for broadband 3D nanophotonics inverse design
- 2023
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 10:11, s. 3875-3887
-
Tidskriftsartikel (refereegranskat)abstract
- In the last decades, nanostructures have unlocked myriads of functionalities in nanophotonics by engineering light–matter interaction beyond what is possible with conventional bulk optics. The space of parameters available for design is practically unlimited due to the large variety of optical materials and nanofabrication techniques. Thus, computational approaches are necessary to efficiently search for the optimal solutions. In this paper, we enable the free-form inverse design in 3D of linear optical materials with arbitrary dispersion and anisotropy. This is achieved by (1) deriving an analytical adjoint scheme based on the complex-conjugate pole-residue pair model in the time domain and (2) its implementation in a parallel finite-difference time-domain framework with a topology optimization routine, efficiently running on high-performance computing systems. Our method is tested on the design problem of field confinement using dispersive nanostructures. The obtained designs satisfy the fundamental curiosity of how free-form metallic and dielectric nanostructures perform when optimized in 3D, also in comparison to fabrication-constrained designs. Unconventional free-form designs revealed by computational methods, although may be challenging or unfeasible to realize with current technology, bring new insights into how light can more efficiently interact with nanostructures and provide new ideas for forward design.
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| 36. |
- Gugole, Marika, 1993, et al.
(författare)
-
High-Contrast Switching of Plasmonic Structural Colors: Inorganic versus Organic Electrochromism
- 2020
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 7:7, s. 1762-1772
-
Tidskriftsartikel (refereegranskat)abstract
- Plasmonic structural colors have recently received a lot of attention. For many applications there is a need to actively tune the colors after preparing the nanostructures, preferably with as strong changes in the optical response as possible. However, to date, there is a lack of systematic investigations on how to enhance contrast in electrically induced color modulation. In this work we implement electrochromic films with plasmonic metasurfaces and compare systematically organic and inorganic materials, with the primary aim to maximize brightness and contrast in a reflective color display. We show nanostructures with good chromaticity and high polarization-insensitive reflectivity (-90%) that are electrochemically stable in a nonaqueous solvent. Methods are evaluated for reliable and uniform electropolymerization of the conductive polymer dimethylpropylenedioxythiophene (PProDOTMe2) on gold. The resulting organic films are well-described by Lambert-Beer formalism, and the highest achievable contrast is easily determined in transmission mode. The optical properties of the inorganic option (WO3) require full Fresnel models due to thin film interference, and the film thickness must be carefully selected in order to maintain the chromaticity of the metasurfaces. Still, the optimized fully inorganic device reaches the highest contrast of approximately 60% reflectivity change for all primary colors. The switching time is about an order of magnitude faster for the organic films (hundreds of ms). The bistability is very long (hours) for the inorganic devices and comparable for the polymers, which makes the power consumption essentially zero for maintaining the same state. Finally, we show that switching of the primary colors in optimized devices (both organic and inorganic) provides almost twice as high brightness and contrast compared to existing reflective display technologies with RGB subpixels created by color filters.
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| 37. |
- Hanczyc, Piotr, 1985, et al.
(författare)
-
Stimulated Emission from Rhodamine 6G Aggregates Self-Assembled on Amyloid Protein Fibrils
- 2015
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 2:12, s. 1755-1762
-
Tidskriftsartikel (refereegranskat)abstract
- Amyloid fibrils are excellent bioderived nanotemplates for controlling molecular and optical properties of small molecules such as organic dyes. Here we demonstrate that two representative fibril-forming proteins, lysozyme and insulin, from the amyloids family can determine the optical signature of rhodamine 6G. Their structural variety leads to a unique molecular arrangement of dye aggregates on the biotemplate surface. This significantly influences the light amplification threshold as well as the stimulated emission profiles, which show remarkable broadband wavelength tunability. We show in addition that amyloid fibrils can be potentially used in constructing broadband emission biolasers.
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| 38. |
- Hassaan, Muhammad Umair, et al.
(författare)
-
Highly Efficient Energy Transfer in Light Emissive Poly(9,9-dioctylfluorene) and Poly(p-phenylenevinylene) Blend System
- 2018
-
Ingår i: ACS Photonics. - : AMER CHEMICAL SOC. - 2330-4022. ; 5:2, s. 607-613
-
Tidskriftsartikel (refereegranskat)abstract
- A polymer blend system F8(1-x):SYx based on poly(9,9-dioctylfluorene) (F8) from the family of polyfluorenes (PFO) and a poly(para-phenylenevinylene) (PPV) derivative superyellow (SY) shows highly efficient energy transfer from F8 host to SY guest molecules. This has been realized due to a strong overlap between F8 photoemission and SY photoabsorption spectra and negligibly low self-absorption. The steady-state and time-correlated spectroscopic measurements show an increased photo-luminescence quantum efficiency (PLQE) and lifetime (tau) of SY, with an opposite trend of decreasing PLQE and tau of F8 excitons with increasing SY concentration, suggesting the Forster resonance energy transfer (FRET) to be the main decay pathway in the proposed system. The systematic study of the exciton dynamics shows a complete energy transfer at 10% of SY in the F8 host matrix and a Forster radius of similar to 6.3 nm. The polymer blend system exhibits low laser and amplified spontaneous emission thresholds. An ultrahigh efficiency (27 cd.A(-1)) in F8(1-x):SYx based light emitting diodes (LED) has been realized due to the intrinsic property of a well-balanced charge transport within the emissive layer. The dual pathway, that is, the efficient energy transfer between the blended molecules via resonance energy transfer, and the charge-traps-assisted balanced transport makes the system promising for achieving highly efficient devices and a potential candidate for lasing applications.
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| 39. |
- He, Nan, et al.
(författare)
-
High-Speed Duplex Free Space Optical Communication System Assisted by a Wide-Field-of-View Metalens
- 2023
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 10:9, s. 3052-3059
-
Tidskriftsartikel (refereegranskat)abstract
- Free space optical communication (FSO) has gained significant attention due to the growing demand for a high information capacity. For FSO between multiple or moving targets, a receiver with a wide angle of acquisition capability is necessary. Traditionally, gimbals and fast steering mirrors have been used, but they are often difficult to make both compact and wide-angle. Here, a novel duplex FSO system is demonstrated, which utilizes a highly compact fiber coupling metalens to receive and transmit signals in a large field of view up to 80°. High coupling efficiency up to 48.8% at a wavelength of 1550 nm is experimentally achieved. The small coupling loss enables the user to modulate and direct the downstream power from the base station back along the same path, saving energy and leaving only one source in the FSO system. The low bit error rate and the open and clear eye diagram results validate the excellent downlink/uplink communication performance of a 10 Gbps FSO system empowered by the metalens. The system exhibits a large field of view, high data rate, compact size, and low power consumption, which meets the size, weight, and power requirement of smart devices.
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| 40. |
- He, N., et al.
(författare)
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Highly Compact All-Solid-State Beam Steering Module Based on a Metafiber
- 2022
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 9:9, s. 3094-3101
-
Tidskriftsartikel (refereegranskat)abstract
- Optical phased arrays occupy the predominant position in the solid-state light detection and ranging; however, their applications are limited by high insertion loss, complex control, and the need for tunable lasers. Here, by assembling a quadratic silicon metalens onto the end face of a single-mode fiber array to form a metafiber, we propose an all-solid-state beam steering module. With the introduction of the flat metalens, the module is highly compact, and the field of view may be extremely wide. A large field of view up to about 60° is testified experimentally based on a one-dimensional module. The application for parking space monitoring is also demonstrated based on a two-dimensional module. The beam steering module can be switched between the scanning mode and the flash mode compatibly and can also be extended to a larger scale with a higher scanning precision by increasing the size of the fiber array and scaling the metalens. The presented scheme featured with high compactness, high performance, and good compatibility provides a distinctive beam steering candidate for light detection and ranging or optical wireless communication applications.
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| 41. |
- Higo, Akio, et al.
(författare)
-
Optical Study of Sub-10 nm In0.3Ga0.7N Quantum Nanodisks in GaN Nanopillars
- 2017
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 4:7, s. 1851-1857
-
Tidskriftsartikel (refereegranskat)abstract
- We have demonstrated the fabrication of homogeneously distributed In0.3Ga0.7N/GaN quantum nanodisks (QNDs) with a high density and average diameter of 10 nm or less in 30-nm-high nanopillars. The scalable top-down nanofabrication process used biotemplates that were spin-coated on an In0.3Ga0.7N/GaN single quantum well (SQW) followed by low-damage dry etching on ferritins with 7 nm diameter iron cores. The photoluminescence measurements at 70 K showed a blue shift of quantum energy of 420 meV from the In0.3Ga0.7N/GaN SQW to the QND. The internal quantum efficiency of the In0.3Ga0.7N/GaN QND was 100 times that of the SQW. A significant reduction in the quantum-confined Stark effect in the QND structure was observed, which concurred with the numerical simulation using a 3D Schrödinger equation. These results pave the way for the fabrication of large-scale III–N quantum devices using nanoprocessing, which is vital for optoelectronic communication devices.
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| 42. |
- Hjelm, Anna, et al.
(författare)
-
Tailoring Escherichia coli for the L-Rhamnose P-BAD Promoter-Based Production of Membrane and Secretory Proteins
- 2017
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 6:6, s. 985-994
-
Tidskriftsartikel (refereegranskat)abstract
- Membrane and secretory protein production in Escherichia coli requires precisely controlled production rates to avoid the deleterious saturation of their biogenesis pathways. On the basis of this requirement, the E. coli L-rhamnose PBAD promoter (PrhaBAD) is often used for membrane and secretory protein production since PrhaBAD is thought to regulate protein production rates in an L-rhamnose concentration-dependent manner. By monitoring protein production in real-time in E. coli wild-type and an L-rhamnose catabolism deficient mutant, we demonstrate that the L-rhamnose concentration-dependent tunability of PrhaBAD-mediated protein production is actually due to L-rhamnose consumption rather than regulating production rates. Using this information, a RhaT-mediated L-rhamnose transport and L-rhamnose catabolism deficient double mutant was constructed. We show that this mutant enables the regulation of PrhaBAD-based protein production rates in an L-rhamnose concentration-dependent manner and that this is critical to optimize membrane and secretory protein production yields. The high precision of protein production rates provided by the PrhaBAD promoter in an L-rhamnose transport and catabolism deficient background could also benefit other applications in synthetic biology.
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| 43. |
- Hjort, Filip, 1991, et al.
(författare)
-
A 310 nm Optically Pumped AlGaN Vertical-Cavity Surface-Emitting Laser
- 2021
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 8:1, s. 135-141
-
Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet light is essential for disinfection, fluorescence excitation, curing, and medical treatment. An ultraviolet light source with the small footprint and excellent optical characteristics of vertical-cavity surface-emitting lasers (VCSELs) may enable new applications in all these areas. Until now, there have only been a few demonstrations of ultraviolet-emitting VCSELs, mainly optically pumped, and all with low Al-content AlGaN cavities and emission near the bandgap of GaN (360 nm). Here, we demonstrate an optically pumped VCSEL emitting in the UVB spectrum (280-320 nm) at room temperature, having an Al0.60Ga0.40N cavity between two dielectric distributed Bragg reflectors. The double dielectric distributed Bragg reflector design was realized by substrate removal using electrochemical etching. Our method is further extendable to even shorter wavelengths, which would establish a technology that enables VCSEL emission from UVA (320-400 nm) to UVC (<280 nm).
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| 44. |
- Huang, Jing, 1987-, et al.
(författare)
-
Large-Area Transparent “Quantum Dot Glass” for Building-Integrated Photovoltaics
- 2022
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 9:7, s. 2499-2509
-
Tidskriftsartikel (refereegranskat)abstract
- A concept of transparent “quantum dot glass”(TQDG) is proposed for a combination of a quantum dot(QD)-based glass luminescent solar concentrator (LSC) and itsedge-attached solar cells, as a type of transparent photovoltaics(TPVs) for building-integrated photovoltaics (BIPVs). Differentfrom conventional LSCs, which typically serve as pure opticaldevices, TQDGs have to fulfill requirements as both powergeneratingcomponents and building construction materials. In thiswork, we demonstrate large-area (400 cm2) TQDGs based onsilicon QDs in a triplex glass configuration. An overall powerconversion efficiency (PCE) of 1.57% was obtained with back-reflection for a transparent TQDG (average visible transmittance of84% with a color rendering index of 88 and a low haze ≤3%), contributing to a light utilization efficiency (LUE) of 1.3%, which isamong the top reported TPVs based on the LSC technology with similar size. Most importantly, these TQDGs are shown to havebetter thermal and sound insulation properties compared to normal float glass, as well as improved mechanical performance andsafety, which significantly pushes the TPV technology toward practical building integration. TQDGs simultaneously exhibit favorablephotovoltaic, aesthetic, and building envelope characteristics and can serve as a multifunctional material for the realization of nearlyzero-energy building concepts.
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| 45. |
- Hägglund, Carl, 1975-, et al.
(författare)
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Strong coupling of plasmon and nanocavity modes for dual-band, near-perfect absorbers and ultrathin photovoltaics
- 2016
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 3:3, s. 456-463
-
Tidskriftsartikel (refereegranskat)abstract
- When optical resonances interact strongly, hybridized modes are formed with mixed properties inherited from the basic modes. Strong coupling therefore tends to equalize properties such as damping and oscillator strength of the spectrally separate resonance modes. This effect is here shown to be very useful for the realization of near perfect dual-band absorption with ultrathin (~10 nm) layers in a simple geometry. Absorber layers are constructed by atomic layer deposition of the heavy-damping semiconductor tin monosulfide (SnS) onto a two-dimensional gold nanodot array. In combination with a thin (55 nm) SiO2 spacer layer and a highly reflective Al film on the back, a semi-open nanocavity is formed. The SnS coated array supports a localized surface plasmon resonance in the vicinity of the lowest order anti-symmetric Fabry-Perot resonance of the nanocavity. Very strong coupling of the two resonances is evident through anti-crossing behavior with a minimum peak splitting of 400 meV, amounting to 24% of the plasmon resonance energy. The mode equalization resulting from this strong interaction enables simultaneous optical impedance matching of the system at both resonances, and thereby two near perfect absorption peaks which together cover a broad spectral range. When paired with the heavy damping from SnS band-to-band transitions, this further enables approximately 60% of normal incident solar photons with energies exceeding the bandgap to be absorbed in the 10 nm SnS coating. Thereby, these results establish a distinct relevance of strong coupling phenomena to efficient, nanoscale photovoltaic absorbers and more generally for fulfilling a specific optical condition at multiple spectral positions.
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| 46. |
- Jain, Vishal, et al.
(författare)
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InP/InAsP Nanowire-Based Spatially Separate Absorption and Multiplication Avalanche Photodetectors
- 2017
-
Ingår i: ACS Photonics. - Washington : American Chemical Society (ACS). - 2330-4022. ; 4:11, s. 2693-2698
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Tidskriftsartikel (refereegranskat)abstract
- Avalanche photodetectors (APDs) are key components in optical communication systems due to their increased photocurrent gain and short response time as compared to conventional photodetectors. A detector design where the multiplication region is implemented in a large band gap material is desired to avoid detrimental Zener tunneling leakage currents, a concern otherwise in smaller band gap materials required for absorption at 1.3/1.55 μm. Self-assembled III-V semiconductor nanowires offer key advantages such as enhanced absorption due to optical resonance effects, strain-relaxed heterostructures, and compatibility with mainstream silicon technology. Here, we present electrical and optical characteristics of single InP and InP/InAsP nanowire APD structures. Temperature-dependent breakdown characteristics of p+-n-n+ InP nanowire devices were investigated first. A clear trap-induced shift in breakdown voltage was inferred from I-V measurements. An improved contact formation to the p+-InP segment was observed upon annealing, and its effect on breakdown characteristics was investigated. The band gap in the absorption region was subsequently varied from pure InP to InAsP to realize spatially separate absorption and multiplication APDs in heterostructure nanowires. In contrast to the homojunction APDs, no trap-induced shifts were observed for the heterostructure APDs. A gain of 12 was demonstrated for selective optical excitation of the InAsP segment. Additional electron-beam-induced current measurements were carried out to investigate the effect of local excitation along the nanowire on the I-V characteristics. Simulated band profiles and electric field distributions support our interpretation of the experiments. Our results provide important insight for optimization of avalanche photodetector devices based on III-V nanowires.
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| 47. |
- Jash, Asmita, et al.
(författare)
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Excitonic Dynamics at the Type-II Polytype Interface of InP Platelets
- 2023
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Ingår i: ACS Photonics. - 2330-4022. ; 10:9, s. 3143-3148
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Tidskriftsartikel (refereegranskat)abstract
- Indirect excitons are the focus of intense research due to the opportunity of studying degenerate quantum gases and liquids in an excitonic system. To realize such systems, it is highly advantageous to have as little scattering as possible. A polytype type-II interface is formed between wurtzite and zincblende InP due to the band alignment. Electrons gather on the zincblende and holes on the wurtzite side of the interface. Therefore, electrons and holes that are spatially separated by the interface form indirect excitons with aligned dipoles. This polytype type-II interface is perfectly flat, which limits scattering. Here we report that repulsive interaction between the indirect excitons is the driving force behind the long-range transport of indirect excitons along the interface at high exciton densities. This is indicative of less scattering than in conventional type-II heterostructures. The spatial separation of the charge carriers across the interface leads to a low recombination rate of the indirect excitons since the overlap of the electron-hole wavefunction at the interface is small. Emission from the long-lived indirect excitons can be detected even after 40 μs. Our studies have been performed by using spatially and temporally resolved photoluminescence at the low temperature.
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| 48. |
- Jeddi Abdarloo, Hossein, Doktorand, 1992-, et al.
(författare)
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Spectrally Tunable Broadband Gate-All-Around InAsP/InP Quantum Discs-in-Nanowire Array Phototransistors with a High Gain-Bandwidth Product
- 2023
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Ingår i: ACS Photonics. - Washington, DC : American Chemical Society (ACS). - 2330-4022. ; 10:6, s. 1748-1755
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Tidskriftsartikel (refereegranskat)abstract
- High-performance broadband photodetectors offering spectral tunability and a high gain-bandwidth product are crucial in many applications. Here, we report on a detailed experimental and theoretical study of three-terminal phototransistors comprised of three million InP nanowires with 20 embedded InAsP quantum discs in each nanowire. A global, transparent ITO gate all around the nanowires facilitates a radial control of the carrier concentration by more than two orders of magnitude. The transfer characteristics reveal two different transport regimes. In the subthreshold region, the photodetector operates in a diffusion mode with a distinct onset at the bandgap of InP. At larger gate biases, the phototransistor switches to a drift mode with a strong contribution from the InAsP quantum discs. Besides an unexpected spectral tunability, the detector exhibits a state-of-the-art responsivity, reaching around 100 A/W (638 nm/20 μW) @ VGS = 1.0 V/VDS = 0.5 V with a gain-bandwidth product of around 1 MHz, in excellent agreement with a comprehensive real-device model. © 2023 The Authors. Published by American Chemical Society.
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| 49. |
- Jones, Steven, 1990, et al.
(författare)
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Photothermal Heating of Plasmonic Nanoantennas: Influence on Trapped Particle Dynamics and Colloid Distribution
- 2018
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 5:7, s. 2878-2887
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Tidskriftsartikel (refereegranskat)abstract
- Plasmonic antennas are well-known and extremely powerful platforms for optical spectroscopy, sensing, and manipulation of molecules and nanoparticles. However, resistive antenna losses, resulting in highly localized photothermal heat generation, may significantly compromise their applicability. Here we investigate how the interplay between plasmon-enhanced optical and thermal forces affects the dynamics of nanocolloids diffusing in close proximity to gold bowtie nanoantennas. The study is based on an anti-Stokes thermometry technique that can measure the internal antenna temperature with an accuracy of ∼5 K over an extended temperature range. We argue that Kapitza resistances have a significant impact on the local thermal landscape, causing an interface temperature discontinuity of up to ∼20% of the total photothermal temperature increase of the antenna studied. We then use the bowties as plasmonic optical tweezers and quantify how the antenna temperature influences the motion and distribution of nearby fluorescent colloids. We find that colloidal particle motion within the plasmonic trap is primarily dictated by a competition between enhanced optical forces and enhanced heating, resulting in a surprising insensitivity to the specific resonance properties of the antenna. Furthermore, we find that thermophoretic forces inhibit diffusion of particles toward the antenna and drive the formation of a thermal depletion shell that extends several microns. The study highlights the importance of thermal management at the nanoscale and points to both neglected problems and new opportunities associated with plasmonic photothermal effects in the context of nanoscale manipulation and analysis.
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| 50. |
- Kadkhodazadeh, S., et al.
(författare)
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Optical Property-Composition Correlation in Noble Metal Alloy Nanoparticles Studied with EELS
- 2019
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 6:3, s. 779-786
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Tidskriftsartikel (refereegranskat)abstract
- Noble metals are currently the most common building blocks in plasmonics and thus define the available range of optical properties. Their alloying provides a viable strategy to engineer new materials with a tunable range of optical responses. Despite this attractive prospect, the link between composition and optical properties of many noble metal alloys is still not well understood. Here, electron energy-loss spectroscopy is employed to systematically study AuAg and AuPd nanoparticles of varying compositions. The localized surface plasmons, the bulk plasmons, and the permittivity functions of these two sets of alloys are investigated as functions of their composition. In the case of the more widely studied AuAg alloy system, good agreement is found with previous experimental and theoretical studies. The results on the less scrutinized AuPd system provide highly valuable experimental data that complements other experimental investigations and supports the development of theoretical models.
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