Publications
129 results found
Tirole R, Tilmann B, Menezes LDS, et al., 2024, Nonlinear dielectric epsilon near‐zero hybrid nanogap antennas, Advanced Optical Materials, Vol: 12, ISSN: 2195-1071
High-index Mie-resonant dielectric nanostructures provide a new framework to manipulate light at the nanoscale. In particular their local field confinement together with their inherently low losses at frequencies below their bandgap energy allows to efficiently boost and control linear and nonlinear optical processes. Here, nanoantennas composed of a thin indium-tin oxide (ITO) layer in the center of a dielectric gallium phosphide (GaP) nanodisc are investigated. While the linear response is similar to that of a pure GaP nanodisc, it is shown that second harmonic generation is enhanced across a broadband wavelength range. On the other hand, third harmonic generation is only marginally enhanced around the epsilon-near-zero wavelength of ITO. Linear and nonlinear finite-difference time-domain simulations show that despite the high refractive index contrast leading to strong field confinement inside the antenna's ITO layer, the nanogap enhancement effect is mitigated by the low nonlinear volume of the nanogap layer and the antenna's behavior at the harmonic wavelength. Measurement of ITO and GaP nonlinear susceptibilities additionally show a comparative advantage for harmonic generation in GaP. These investigations deliver insights on the mechanisms at play in nonlinear nanogap antennas and their potential applications as nanoscale devices.
Vidal C, Tilmann B, Tiwari S, et al., 2024, Fluorescence enhancement in topologically optimized gallium phosphide all-dielectric nanoantennas, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 24, Pages: 2437-2443, ISSN: 1530-6984
Nanoantennas capable of large fluorescence enhancement with minimal absorption are crucial for future optical technologies from single-photon sources to biosensing. Efficient dielectric nanoantennas have been designed, however, evaluating their performance at the individual emitter level is challenging due to the complexity of combining high-resolution nanofabrication, spectroscopy and nanoscale positioning of the emitter. Here, we study the fluorescence enhancement in infinity-shaped gallium phosphide (GaP) nanoantennas based on a topologically optimized design. Using fluorescence correlation spectroscopy (FCS), we probe the nanoantennas enhancement factor and observe an average of 63-fold fluorescence brightness enhancement with a maximum of 93-fold for dye molecules in nanogaps between 20 and 50 nm. The experimentally determined fluorescence enhancement of the nanoantennas is confirmed by numerical simulations of the local density of optical states (LDOS). Furthermore, we show that beyond design optimization of dielectric nanoantennas, increased performances can be achieved via tailoring of nanoantenna fabrication.
Córdova-Castro RM, van Dam B, Lauri A, et al., 2024, Single-emitter super-resolved imaging of radiative decay rate enhancement in dielectric gap nanoantennas, Light: Science & Applications, Vol: 13, ISSN: 2095-5545
High refractive index dielectric nanoantennas strongly modify the decay rate via the Purcell effect through the design of radiative channels. Due to their dielectric nature, the field is mainly confined inside the nanostructure and in the gap, which is hard to probe with scanning probe techniques. Here we use single-molecule fluorescence lifetime imaging microscopy (smFLIM) to map the decay rate enhancement in dielectric GaP nanoantenna dimers with a median localization precision of 14 nm. We measure, in the gap of the nanoantenna, decay rates that are almost 30 times larger than on a glass substrate. By comparing experimental results with numerical simulations we show that this large enhancement is essentially radiative, contrary to the case of plasmonic nanoantennas, and therefore has great potential for applications such as quantum optics and biosensing.
Wang XS, Savo R, Maeder A, et al., 2023, Graph model for multiple scattering in lithium niobate on insulator integrated photonic networks, Optics Express, Vol: 31, Pages: 42255-42270, ISSN: 1094-4087
We present a graph-based model for multiple scattering of light in integrated lithium niobate on insulator (LNOI) networks, which describes an open network of single-mode integrated waveguides with tunable scattering at the network nodes. We first validate the model at small scale with experimental LNOI resonator devices and show consistent agreement between simulated and measured spectral data. Then, the model is used to demonstrate a novel platform for on-chip multiple scattering in large-scale optical networks up to few hundred nodes, with tunable scattering behaviour and tailored disorder. Combining our simple graph-based model with material properties of LNOI, this platform creates new opportunities to control randomness in large optical networks.
Sapienza R, Shcherbakov M, Faccio D, et al., 2023, APL special topic: time modulated metamaterials, Applied Physics Letters, Vol: 123, ISSN: 0003-6951
Tilmann B, Huq T, Possmayer T, et al., 2023, Comparison of harmonic generation from crystalline and amorphous gallium phosphide nanofilms, Advanced Optical Materials, Vol: 11, ISSN: 2195-1071
Gallium phosphide (GaP) is a promising material for nanophotonics, given its large refractive index and a transparency over most of the visible spectrum. However, since easy phase-matching is not possible with bulk GaP, a comprehensive study of its nonlinear optical properties for harmonic generation, especially when grown as thin films, is still missing. Here, second harmonic generation is studied from epitaxially grown GaP thin films, demonstrating that the absolute conversion efficiencies are comparable to a bulk wafer over the pump wavelength range from 1060 to 1370 nm. Furthermore, the results are compared to nonlinear simulations, and the second order nonlinear susceptibility is extracted, showing a similar dispersion and magnitude to that of the bulk material. Furthermore, the third order nonlinear susceptibility of amorphous GaP thin films is extracted from third harmonic generation to be more than one order of magnitude larger than that of the crystalline material, and generation of up to the fifth harmonic is reported. The results show the potential of crystalline and amorphous thin films for nonlinear optics with nanoantennas and metasurfaces, particularly in the visible to near infrared part of the spectrum.
Zotev PG, Wang Y, Andres-Penares D, et al., 2023, Van der Waals materials for applications in nanophotonics, Laser and Photonics Reviews, Vol: 17, ISSN: 1863-8880
Numerous optical phenomena and applications have been enabled by nanophotonic structures. Their current fabrication from high refractive index dielectrics, such as silicon (Si) or gallium phosphide (GaP), pose restricting fabrication challenges while metals, relying on plasmons and thus exhibiting high ohmic losses, limit the achievable applications. An emerging class of layered, so-called van der Waals (vdW), crystals is presented as a viable nanophotonics platform in this work. The dielectric response of 11 mechanically exfoliated thin-film (20–200 nm) vdW crystals is extracted, revealing high refractive indices up to n = 5, pronounced birefringence up to Δn = 3, sharp absorption resonances, and a range of transparency windows from ultraviolet to near-infrared. Nanoantennas are subsequently fabricated on silicon dioxide (SiO2) and gold, utilizing the compatibility of vdW thin films with a variety of substrates. Pronounced Mie resonances are observed due to the high refractive index contrast on SiO2, leading to a strong exciton-photon coupling regime as well as largely unexplored high-quality-factor, hybrid Mie-plasmon modes on gold. Additional vdW-material-specific degrees of freedom in fabrication are further demonstrated by realizing nanoantennas from stacked twisted crystalline thin-films, enabling control of nonlinear optical properties, and post-fabrication nanostructure transfer, important for nano-optics with sensitive materials.
Tirole R, Vezzoli S, Galiffi E, et al., 2023, Double-slit time diffraction at optical frequencies, Nature Physics, Vol: 19, Pages: 999-1002, ISSN: 1745-2473
Double-slit experiments—where a wave is transmitted through a thin double aperture in space—have confirmed the wave–particle duality of quantum objects, such as single photons, electrons, neutrons, atoms and large molecules. Yet, the temporal counterpart of Young’s double-slit experiment—a wave interacting with a double temporal modulation of an interface—remains elusive. Here we report such a time-domain version of the classic Young’s double-slit experiment: a beam of light twice gated in time produces an interference in the frequency spectrum. The ‘time slits’, narrow enough to produce diffraction at optical frequencies, are generated from the optical excitation of a thin film of indium tin oxide near its epsilon-near-zero point. The separation between time slits determines the period of oscillations in the frequency spectrum, whereas the decay of fringe visibility in frequency reveals the shape of the time slits. Surprisingly, many more oscillations are visible than expected from existing theory, implying a rise time that approaches an optical cycle. This result enables the further exploration of time-varying physics, towards the spectral synthesis of waves and applications such as signal processing and neuromorphic computation.
Dranczewski J, Fischer A, Tiwari P, et al., 2023, Plasma etching for fabrication of complex nanophotonic lasers from bonded InP semiconductor layers, Micro and Nano Engineering, Vol: 19, ISSN: 2590-0072
Integrating optically active III-V materials on silicon/insulator platforms is one potential path towards improving the energy efficiency and performance of modern computing. Here we demonstrate the applicability of direct wafer bonding combined with plasma etching to the fabrication of complex nanophotonic systems out of InP layers. We explore and optimise the plasma etching of InP, validating existing processes and developing improved ones. We explore the use of microdisk lasing as a way to evaluate fabrication fidelity, and demonstrate that we can create complex lasing systems of interest to us: coupled disk cavities and random network lasers.
Barelli M, Vidal C, Fiorito S, et al., 2023, Single-photon emitting arrays by capillary assembly of colloidal semiconductor CdSe/CdS/SiO2 nanocrystals, ACS Photonics, Vol: 10, Pages: 1662-1670, ISSN: 2330-4022
The controlled placement of colloidal semiconductor nanocrystals (NCs) onto planar surfaces is crucial for scalable fabrication of single-photon emitters on-chip, which are critical elements of optical quantum computing, communication, and encryption. The positioning of colloidal semiconductor NCs such as metal chalcogenides or perovskites is still challenging, as it requires a nonaggressive fabrication process to preserve the optical properties of the NCs. In this work, periodic arrays of 2500 nanoholes are patterned by electron beam lithography in a poly(methyl methacrylate) (PMMA) thin film on indium tin oxide/glass substrates. Colloidal core/shell CdSe/CdS NCs, functionalized with a SiO2 capping layer to increase their size and facilitate deposition into 100 nm holes, are trapped with a close to optimal Poisson distribution into the PMMA nanoholes via a capillary assembly method. The resulting arrays of NCs contain hundreds of single-photon emitters each. We believe this work paves the way to an affordable, fast, and practical method for the fabrication of nanodevices, such as single-photon-emitting light-emitting diodes based on colloidal semiconductor NCs.
Granchi N, Lodde M, Stokkereit K, et al., 2023, Near-field imaging of optical nanocavities in hyperuniform disordered materials, PHYSICAL REVIEW B, Vol: 107, ISSN: 2469-9950
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Kalinic B, Cesca T, Balasa IG, et al., 2023, Quasi-BIC modes in all-dielectric slotted nanoantennas for enhanced Er3+ emission, ACS Photonics, Vol: 10, Pages: 534-543, ISSN: 2330-4022
In the quest for new and increasingly efficient photon sources, the engineering of the photonic environment at the subwavelength scale is fundamental for controlling the properties of quantum emitters. A high refractive index particle can be exploited to enhance the optical properties of nearby emitters without decreasing their quantum efficiency, but the relatively modest Q-factors (Q ∼ 5–10) limit the local density of optical states (LDOS) amplification achievable. On the other hand, ultrahigh Q-factors (up to Q ∼ 109) have been reported for quasi-BIC modes in all-dielectric nanostructures. In the present work, we demonstrate that the combination of quasi-BIC modes with high spectral confinement and nanogaps with spacial confinement in silicon slotted nanoantennas lead to a significant boosting of the electromagnetic LDOS in the optically active region of the nanoantenna array. We observe an enhancement of up to 3 orders of magnitude in the photoluminescence intensity and 2 orders of magnitude in the decay rate of the Er3+ emission at room temperature and telecom wavelengths. Moreover, the nanoantenna directivity is increased, proving that strong beaming effects can be obtained when the emitted radiation couples to the high Q-factor modes. Finally, via tuning the nanoanntenna aspect ratio, a selective control of the Er3+ electric and magnetic radiative transitions can be obtained, keeping the quantum efficiency almost unitary.
Vidal C, Tilmann B, Tiwari S, et al., 2023, Performance of gallium phosphide nanoantennas from optimised design
Over the last years, various numerical algorithms have been used to predict the design of a dielectric nanoantenna which maximises the local density of optical states (LDOS) [1-4]. As simulation techniques have evolved and improved in speed and accuracy, the ultimate design for dielectric nanoantennas to enhance a single emitter has to combine resonant modes with nanoscale enhancement. Experiments evaluation of the performance of such antennas is challenging due to the complexity of combining high-resolution nanofabrication and nanoscale positioning of the emitter [5].
Vynck K, Pierrat R, Carminati R, et al., 2023, Light in correlated disordered media, Reviews of Modern Physics, Vol: 95, ISSN: 0034-6861
The optics of correlated disordered media is a conceptually rich research topic emerging at the interface between the physics of waves in complex media and nanophotonics. Inspired by photonic structures in nature and enabled by advances in nanofabrication processes, recent investigations have unveiled how the design of structural correlations down to the subwavelength scale could be exploited to control the scattering, transport, and localization of light in matter. From optical transparency to superdiffusive light transport to photonic gaps, the optics of correlated disordered media challenges our physical intuition and offers new perspectives for applications. This review examines the theoretical foundations, state-of-the-art experimental techniques, and major achievements in the study of light interaction with correlated disorder, covering a wide range of systems: from short-range correlated photonic liquids to Lévy glasses containing fractal heterogeneities to hyperuniform disordered photonic materials. The mechanisms underlying light scattering and transport phenomena are elucidated on the basis of rigorous theoretical arguments. Ongoing research on mesoscopic phenomena such as transport phase transitions and speckle statistics and the current development of disorder engineering for applications such as light-energy management and visual appearance design are overviewed. Finally, special efforts are made to identify the main theoretical and experimental challenges to address in the near future.
Cordova-Castro RM, Cabriel C, Jonker D, et al., 2023, Controlling Spontaneous Emission with Nanomaterials at the Single-Emitter Level, Pages: 1481-1482
The direct measurement of a single emitter decay rate and the simultaneous knowledge of its position is a powerful tool for the study of light-matter interaction at the nanometer scale. We use single-molecule fluorescence lifetime imaging microscopy (smFLIM) to map at the nanometer scale the decay rate enhancement of single emitters coupled to new nanomaterials platforms that significantly modified the electromagnetic environment.
Fischer A, Raziman TV, Dranczewski J, et al., 2023, Spectral Control of Coupled InP Nanolasers around Exceptional Points through Selective Excitation
Tunable on-chip nanolaser sources are indispensable for advances in optical data transmission and computing. One way to tune emission wavelength is through use of coupling between two nanolasers, and to exploit their non-Hermitian properties, such as single mode emission and exceptional points as a function of non-uniform gain distribution [1]. We experimentally study mode interactions between coupled, epitaxially-grown InP microdisks, with diameters in the micron range that support resonant whispering gallery modes (Fig. 1a) [2]. Through selective excitation, via a digital micromirror device (DMD), arbitrary pumping powers on each disk (P1, P2) can be reached (Fig. 1b). This enables the full exploration of the coupled mode landscape that is theoretically described by coupled mode theory [3] and includes PT-symmetric and PT-broken regimes, lasing gaps, and exceptional points. In specific regions of the mode landscape, a reversed pump dependence is observed, resulting in a counter-intuitive lasing gap [3]. When one of the microdisks is pumped above threshold (P1) and the pump on the second disk (P2) is increased from zero, hence increasing the total pump power, the lasing intensity decreases until the system is below threshold and in the lasing gap (Fig. 1c). Further increase in P2 is needed to close the lasing gap and drive the system above threshold at a shifted wavelength. When the power on the constantly pumped disk (P1) is increased, the lasing gap closes and the system reaches a virtual exceptional point.
Sapienza R, Pendry J, Maier S, et al., 2022, Saturable time-varying mirror based on an epsilon-near-zero material, Physical Review Applied, Vol: 18, ISSN: 2331-7019
We report a switchable time-varying mirror, composed of an indium-tin-oxide–gold bilayer, displaying a tenfold modulation of reflectivity (ΔR≈0.6), which saturates for a driving-pump intensity Ipump≈100GW/cm2. Upon interacting with the saturated time-varying mirror, the frequency content of a reflected pulse is extended up to 31 THz, well beyond the pump spectral content (2.8 THz). We interpret the spectral broadening as a progressive shortening of the mirror rise time from 110 fs to below 30 fs with increasing pump power, which is confirmed by four-wave-mixing experiments and partially captured by a linear time-varying model of the mirror. A temporal response unbounded by the pump bandwidth enables applications for spectral manipulation from time-varying systems with impact for communication networks, optical switching, and computing.
Sapienza R, Barahona M, Saxena D, et al., 2022, Sensitivity and spectral control of network lasers, Nature Communications, Vol: 13, Pages: 1-7, ISSN: 2041-1723
Recently, random lasing in complex networks has shown efficient lasing over more than 50 localised modes, promoted by multiple scattering over the underlying graph. If controlled, these network lasers can lead to fast-switching multifunctional light sources with synthesised spectrum. Here, we observe both in experiment and theory high sensitivity of the network laser spectrum to the spatial shape of the pump profile, with some modes for example increasing in intensity by 280% when switching off 7% of the pump beam. We solve the nonlinear equations within the steady state ab-initio laser theory (SALT) approximation over a graph and we show selective lasing of around 90% of the strongest intensity modes, effectively programming the spectrum of the lasing networks. In our experiments with polymer networks, this high sensitivity enables control of the lasing spectrum through non-uniform pump patterns. We propose the underlying complexity of the network modes as the key element behind efficient spectral control opening the way for the development of optical devices with wide impact for on-chip photonics for communication, sensing, and computation.
Sapienza R, 2022, Controlling random lasing action, NATURE PHYSICS, Vol: 18, Pages: 976-979, ISSN: 1745-2473
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Trivedi M, Saxena D, Ng WK, et al., 2022, Self-organized lasers from reconfigurable colloidal assemblies, NATURE PHYSICS, Vol: 18, Pages: 939-+, ISSN: 1745-2473
Tavakoli N, Spalding R, Lambertz A, et al., 2022, Over 65% sunlight absorption in a 1 mu m Si slab with hyperuniform texture, ACS Photonics, Vol: 9, Pages: 1206-1217, ISSN: 2330-4022
Thin, flexible, and invisible solar cells will be a ubiquitous technology in the near future. Ultrathin crystalline silicon (c-Si) cells capitalize on the success of bulk silicon cells while being lightweight and mechanically flexible, but suffer from poor absorption and efficiency. Here we present a new family of surface texturing, based on correlated disordered hyperuniform patterns, capable of efficiently coupling the incident spectrum into the silicon slab optical modes. We experimentally demonstrate 66.5% solar light absorption in free-standing 1 μm c-Si layers by hyperuniform nanostructuring for the spectral range of 400 to 1050 nm. The absorption equivalent photocurrent derived from our measurements is 26.3 mA/cm2, which is far above the highest found in literature for Si of similar thickness. Considering state-of-the-art Si PV technologies, we estimate that the enhanced light trapping can result in a cell efficiency above 15%. The light absorption can potentially be increased up to 33.8 mA/cm2 by incorporating a back-reflector and improved antireflection, for which we estimate a photovoltaic efficiency above 21% for 1 μm thick Si cells.
Granchi N, Spalding R, Lodde M, et al., 2022, Near-field investigation of luminescent hyperuniform disordered materials, Advanced Optical Materials, Vol: 10, Pages: 1-9, ISSN: 2195-1071
Disordered photonic nanostructures have attracted tremendous interest in the past three decades, not only due to the fascinating and complex physics of light transport in random media, but also for peculiar functionalities in a wealth of interesting applications. Recently, the interest in dielectric disordered systems has received new inputs by exploiting the role of long-range correlation within scatterer configurations. Hyperuniform photonic materials, that share features of photonic crystals and random systems, constitute the archetype of systems where light transport can be tailored from diffusive transport to a regime dominated by light localization due to the presence of photonic band gap. Here, advantage is taken of the combination of the hyperuniform disordered (HuD) design in slab photonics, the use of embedded quantum dots for feeding the HuD resonances, and near-field hyperspectral imaging with sub-wavelength resolution in the optical range to explore the transition from localization to diffusive transport. It is shown, theoretically and experimentally, that photonic HuD systems support resonances ranging from strongly localized modes to extended modes. It is demonstrated that Anderson-like modes with high Q/V are created, with small footprint, intrinsically reproducible and resilient to fabrication-induced disorder, paving the way for a novel photonic platform for quantum applications.
Granchi N, Spalding R, Stokkereit K, et al., 2022, Engineering high Q/V photonic modes in correlated disordered systems, Pages: 1155-1156
Hyperuniform disordered (HuD) photonic materials have recently been shown to display several localized states with relatively high Q factors. However, their spatial position is not predictable a priori. Here we experimentally benchmark through near-field spectroscopy the engineering of high Q/V resonant modes in a defect inside a HuD pattern. These deterministic modes, coexisting with Anderson-localized modes, are a valid candidate for implementations in optoelectronic devices due to the spatial isotropy of the HuD environment upon which they are built.
Galiffi E, Tirole R, Yin S, et al., 2022, Photonics of time-varying media, ADVANCED PHOTONICS, Vol: 4
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Molkens K, Tanghe I, Saxena D, et al., 2022, Coupled Micro Ring Lasers based on Hybrid Integration of Colloidal Quantum Dots
Coupled and Random laser require flexible fabrication methods for photonic integration. Series of (random) coupled micro ring resonators were made with colloidal quantum dots and their unique properties investigated in both linear and lasing regimes.
Tirole R, Vezzoli S, Galiffi E, et al., 2022, Single and double slit time diffraction at optical frequencies
In a temporal version of a single slit and Young's double slit experiments, newly generated optical frequencies form a diffraction pattern. The spectral extent of these frequencies is beyond the expected bandwidth of the modulation.
Morozov S, Vezzoli S, Myslovska A, et al., 2021, Purifying single photon emission from a CdSe/CdS colloidal quantum dot, Publisher: ArXiv
Colloidal quantum dots are robust and flexible single photon emitters forroom-temperature applications, but their purity is strongly reduced at highpump powers, due to multiexcitonic emission which cannot be easily filtered dueto the photo-luminescence spectral broadening at room temperature. Giant-shellquantum dots feature a large blueshift of the biexciton spectrum due toelectron-hole wave function engineering and piezoelectric charge separation,which can be exploited for spectral separation of the single exciton from themultiexciton emission. Here, by spectral filtering, we show that we can recoveran excellent single-photon emission, with $g_2{(0)} < 0.05$ (resolutionlimited), even at high pump powers above saturation of the exciton emission.The bright and pure single-photon generation shown here has importantapplications in quantum information technology and random-number generation.
Glass D, Quesada-Cabrera R, Bardey S, et al., 2021, Probing the role of atomic defects in photocatalytic systems through photoinduced enhanced raman scattering, ACS Energy Letters, Vol: 6, Pages: 4273-4281, ISSN: 2380-8195
Even in ultralow quantities, oxygen vacancies (VO) drastically impact keyproperties of metal oxide semiconductors, such as charge transport, surface adsorption,and reactivity, playing central roles in functional materials performance. Currentmethods used to investigate VO often rely on specialized instrumentation under far fromideal reaction conditions. Hence, the influence of VO generated in situ during catalyticprocesses has yet to be probed. In this work, we assess in situ extrinsic surface VOformation and lifetime under photocatalytic conditions which we compare tophotocatalytic performance. We show for the first time that lifetimes of in situ generatedatomic VO play more significant roles in catalysis than their concentration, with strongcorrelations between longer-lived VO and higher photocatalytic activity. Our resultsindicate that enhanced photocatalytic efficiency correlates with goldilocks VOconcentrations, where VO densities must be just right to encourage carrier transportwhile avoiding charge carrier trapping.
Sortino L, Zotev PG, Phillips CL, et al., 2021, Bright single photon emitters with enhanced quantum efficiency in a two-dimensional semiconductor coupled with dielectric nano-antennas, Nature Communications, Vol: 12, ISSN: 2041-1723
Single photon emitters in atomically-thin semiconductors can be deterministically positioned using strain induced by underlying nano-structures. Here, we couple monolayer WSe2 to high-refractive-index gallium phosphide dielectric nano-antennas providing both optical enhancement and monolayer deformation. For single photon emitters formed on such nano-antennas, we find very low (femto-Joule) saturation pulse energies and up to 104 times brighter photoluminescence than in WSe2 placed on low-refractive-index SiO2 pillars. We show that the key to these observations is the increase on average by a factor of 5 of the quantum efficiency of the emitters coupled to the nano-antennas. This further allows us to gain new insights into their photoluminescence dynamics, revealing the roles of the dark exciton reservoir and Auger processes. We also find that the coherence time of such emitters is limited by intrinsic dephasing processes. Our work establishes dielectric nano-antennas as a platform for high-efficiency quantum light generation in monolayer semiconductors.
Dagdeviren OE, Glass D, Sapienza R, et al., 2021, The effect of photoinduced surface oxygen vacancies on the charge carrier dynamics in TiO2 films, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 21, Pages: 8348-8354, ISSN: 1530-6984
Metal-oxide semiconductors (MOS) are widely utilized for catalytic and photocatalytic applications in which the dynamics of charged carriers (e.g., electrons, holes) play important roles. Under operation conditions, photoinduced surface oxygen vacancies (PI-SOV) can greatly impact the dynamics of charge carriers. However, current knowledge regarding the effect of PI-SOV on the dynamics of hole migration in MOS films, such as titanium dioxide, is solely based upon volume-averaged measurements and/or vacuum conditions. This limits the basic understanding of hole-vacancy interactions, as they are not capable of revealing time-resolved variations during operation. Here, we measured the effect of PI-SOV on the dynamics of hole migration using time-resolved atomic force microscopy. Our findings demonstrate that the time constant associated with hole migration is strongly affected by PI-SOV, in a reversible manner. These results will nucleate an insightful understanding of the physics of hole dynamics and thus enable emerging technologies, facilitated by engineering hole-vacancy interactions.
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