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Series of BODIPY dyads featuring both through-space and through-bond electronic coupling is reported. The degree of electronic interactions depends on the linker used and the strongest one is achieved for diethynylmaleimide linker.

Time-resolved optical measurements of vibrating metal nanoparticles have been used extensively to probe the ultrafast mechanical properties of the nanoparticles and of the surrounding liquid, but nearly all investigations so far have been limited to the linear regime. Here, we report the observation of a low-frequency oscillating signal in transient-absorption measurements of nanoparticles with octahedral gold cores and cubic silver shells; the signal appears at the difference of two mechanical vibrational frequencies in the particles, suggesting a nonlinear mixing process. We tentatively attribute this proposed mixing to a nonlinear coupling between a vibrational mode of the nanoparticle and its optical-frequency plasmon resonance. The optimization of this nonlinear transduction may enable high-efficiency opto-mechanical frequency mixing in the GHz-THz frequency regime.

Background and Aims COVID-19 vaccine hesitancy varies across the USA. Data on COVID-19 vaccine hesitancy in patients with inflammatory bowel disease (IBD) are lacking. We assessed COVID-19 vaccine hesitancy and its associated variables in patients with IBD. Methods We evaluated voluntary patient survey responses during routine clinical visits to our IBD center. Data collected included demographic and clinical characteristics. Descriptive statistics, univariate and multivariate analyses were performed to evaluate significant associations with COVID-19 vaccine hesitancy. Results A total of 239 individuals completed the survey. Over a third of respondents (35.6%) expressed hesitancy toward receiving the COVID-19 vaccine due to vaccine safety concerns (49.4%) and efficacy (23.5%), while others reported non-specific concerns (34.1%). On univariate analysis, Crohn’s disease (OR 2.33 CI 1.28–4.25 p = 0.0056), use of biologic medications (OR 1.93 CI 1.16–3.23, p = 0.012), previous self-reported vaccine refusal (OR 8.13 CI 2.90–22.82 p = 0.0001), earlier date of survey administration (OR 2.01 CI 1.17–3.44 p = 0.011), and self-reported COVID infection (OR 2.55 CI 1.16–5.61 p = 0.0056) were more likely to be associated with COVID-19 vaccine hesitancy. On multivariate analysis, patient age, previous vaccine refusal and date of survey administration were more likely to be associated with COVID-19 vaccine hesitancy. Conclusions Over one-third of patients with IBD expressed COVID-19 vaccine hesitancy. Vaccine safety and efficacy were the most common reasons. Younger age, previous vaccine refusal and earlier date of survey were more likely to be associated with hesitancy. Our findings suggest that there is room for targeted education to improve COVID-19 vaccine uptake in patients with IBD. Supplementary Information The online version contains supplementary material available at 10.1007/s10620-021-07377-5.

Dyads containing two near-infrared absorbing and emitting bacteriochlorins with distinct spectral properties have been prepared and characterized by absorption, emission, and transient-absorption spectroscopies. The dyads exhibit ultrafast ([Formula: see text]3 ps) energy transfer from the bacteriochlorin with the higher-energy S1 state to the bacteriochlorin emitting at the longer wavelength. The dyads exhibit strong fluorescence and relatively long excited state lifetimes ([Formula: see text]4 ns) in both non-polar and polar solvents, which indicates negligible photoinduced electron transfer between the two bacteriochlorins in the dyads. These dyads are thus attractive for the development of light-harvesting arrays and fluorophores for in vivo bioimaging.

Simple liquids are conventionally described by Newtonian fluid mechanics, based on the assumption that relaxation processes in the flow occur much faster than the rate at which the fluid is driven. Nanoscale solids, however, have characteristic mechanical response times on the picosecond scale, which are comparable to mechanical relaxation times in simple liquids; as a result, viscoelastic effects in the liquid must be considered. These effects have been observed using time-resolved optical measurements of vibrating nanoparticles, but interpretation has often been complicated by finite velocity slip at the liquid-solid interface. Here, we use highly spherical gold nanoparticles to drive flows that are theoretically modeled without the use of the no-slip boundary condition at the particle surface. We obtain excellent agreement with this analytical theory that considers both the compression and shear relaxation properties of the liquid.

The interaction between flowing liquids and solid surfaces underpins many physical phenomena and technologies, such as the ability of an airfoil to generate lift and the mixing of liquids for industrial applications. These phenomena are often described using the Navier-Stokes equations and the no-slip boundary condition: the assumption that the liquid immediately adjacent to a solid surface does not move relative to the surface. Herein, we observe violation of the no-slip condition with strong enhancement of slip due to intrinsic viscoelasticity of the bulk liquid. This is achieved by measuring the 20 GHz acoustic vibrations of gold nanoparticles in glycerol/water mixtures, for which the underlying physics is explored using rigorous, theoretical models. The reported enhancement of slip revises current understanding of ultrafast liquid flows, with implications for technologies ranging from membrane filtration to nanofluidic devices and biomolecular sensing.

Monolayer transition metal dichalcogenides, coupled to metal plasmonic nanocavities, have recently emerged as new platforms for strong light-matter interactions. These systems are expected to have nonlinear-optical properties that will enable them to be used as entangled photon sources, compact wave-mixing devices, and other elements for classical and quantum photonic technologies. Here, we report the first experimental investigation of the nonlinear properties of these strongly coupled systems, by observing second harmonic generation from a WSe2 monolayer strongly coupled to a single gold nanorod. The pump-frequency dependence of the second-harmonic signal displays a pronounced splitting that can be explained by a coupled-oscillator model with second-order nonlinearities. Rigorous numerical simulations utilizing a nonperturbative nonlinear hydrodynamic model of conduction electrons support this interpretation and reproduce experimental results. Our study thus lays the groundwork for understanding the nonlinear properties of strongly coupled nanoscale systems.

Vibrational ultrastrong coupling, where the light–matter coupling strength is comparable to the vibrational frequency of molecules, presents new opportunities to probe the interactions between molecules and zero-point fluctuations, harness cavity-modified chemical reactions and develop novel devices in the mid-infrared spectral range. Here we use epsilon-near-zero nanocavities filled with a model polar medium (SiO2) to demonstrate ultrastrong coupling between phonons and gap plasmons. We present classical and quantum-mechanical models to quantitatively describe the observed plasmon–phonon ultrastrong coupling phenomena and demonstrate a modal splitting of up to 50% of the resonant frequency (normalized coupling strength η > 0.25). Our wafer-scale nanocavity platform will enable a broad range of vibrational transitions to be harnessed for ultrastrong coupling applications., This research was supported by grants from the US National Science Foundation (ECCS 1809240 to D.Y., D.A.M., S.-H.O.; ECCS 1809723 to I.-H.L., S.-H.O.) and the Samsung Global Research Outreach (GRO) Program (to S.-H.O.). F.d.L.-P. and L.M.-M. acknowledge financial support from the Spanish Ministry of Economy and Competitivity through projects MAT2017-88358-C3-1-R and MAT2017-88358-C3-2-R and the Aragón Government project Q-MAD. M.P. acknowledges support from the US National Science Foundation (NSF DMR-1905135). M.B.R. acknowledges funding from the US National Science Foundation (NSF CHE-1709822). J.D.C. was supported by the Office of Naval Research Grant N00014-18-12107. S.-H.O. further acknowledges support from the Sanford P. Bordeau Chair in Electrical Engineering at the University of Minnesota.

Highlights • Health professional students can effectively implement a contact tracing initiative • A replicable workflow and onboarding system aids in efficient contact tracing • Testing capacity, community buy-in, and sparse resources can impact contact tracing, Background The Centers for Disease Control and Prevention recommends aggressive contact tracing to control the COVID-19 pandemic. In this work, we (1) describe the development of a COVID-19 contact tracing initiative that includes medical, nursing, and public health students, and is led by clinicians and infectious disease epidemiologists within our health system, and, (2) articulate process steps for contact tracing including workflows and telephone scripts, and, (3) highlight the key challenges and strategies to overcome these challenges. Methods A single academic institution-based contact tracing initiative was rapidly scaled to 110 health professional students, four physicians, two epidemiologists, and a research team. Following training, students called patients who were COVID-19 positive and the individuals they were in contact with to ensure proper isolation and quarantine measures. Students also assisted those who faced barriers to quarantine. Implications In total, between March 24 and May 28 – this initiative completed contact tracing for 536 confirmed cases, which resulted in the identification of 953 contacts. We aim to disseminate this process, including telephone scripts and workflow, to other health systems for use in their initiatives to respond to the COVID-19 pandemic and future public health emergencies.

We show that the self-assembly of monodisperse CdSe nanocrystals synthesized at lower temperature (∼310 °C) into three-dimensional supercrystals results in the formation of separate regions within the supercrystals that display photoluminescence at two distinctly different wavelengths. Specifically, the central portions of the supercrystals display photoluminescence and absorption in the orange region of the spectrum, around 585 nm, compared to the 575 nm photoluminescence maximum for the nanocrystals dispersed in toluene. Distinct domains on the surfaces and edges of the supercrystals, by contrast, display photoluminescence and absorption in the green region of the spectrum, around 570 nm. We attribute the different-colored domains to two subpopulations of NCs in the monodisperse ensemble: the nanocrystals in the "orange" regions are chemically stable, whereas the nanocrystals in the "green" regions are partially oxidized. The susceptibility of the "green" nanocrystals to oxidation indicates a lower coverage of capping molecules on these nanocrystals. We propose that the two subpopulations correspond to nanocrystals with different surfaces that we attribute to the polytypism of CdSe.

Standard continuum assumptions commonly used to describe the fluid mechanics of simple liquids have the potential to break down when considering flows at the nanometer scale. Two common assumptions for simple molecular liquids are that (1) they exhibit a Newtonian response, where the viscosity uniquely specifies the linear relationship between the stress and strain rate, and (2) the liquid moves in tandem with the solid at any solid–liquid interface, known as the no-slip condition. However, even simple molecular liquids can exhibit a non-Newtonian, viscoelastic response at the picosecond time scales that are characteristic of the motion of many nanoscale objects; this viscoelasticity arises because these time scales can be comparable to those of molecular relaxation in the liquid. In addition, even liquids that wet solid surfaces can exhibit nanometer-scale slip at those surfaces. It has recently become possible to interrogate the viscoelastic response of simple liquids and associated nanoscale slip using optical measurements of the mechanical vibrations of metal nanoparticles. Plasmon resonances in metal nanoparticles provide strong optical signals that can be accessed by several spectroscopies, most notably ultrafast transient-absorption spectroscopy. These spectroscopies have been used to measure the frequency and damping rate of acoustic oscillations in the nanoparticles, providing quantitative information about mechanical coupling and exchange of mechanical energy between the solid particle and its surrounding liquid. This information, in turn, has been used to elucidate the rheology of viscoelastic simple liquids at the nanoscale in terms of their constitutive relations, taking into account separate viscoelastic responses for both shear and compressible flows. The nanoparticle vibrations have also been used to provide quantitative measurements of slip lengths on the single-nanometer scale. Viscoelasticity has been shown to amplify nanoscale slip, illustrating the interplay between different aspects of the unconventional fluid dynamics of simple liquids at nanometer length scales and picosecond time scales.

We present time-resolved photoluminescence (PL) spectroscopy of a series of colloidal CdSe/CdS core/shell nanoplatelets with different core and shell thicknesses. Exciton numbers are determined fro...

Strong coupling between plasmons in metal nanoparticles and single excitons in molecules or semiconductor nanomaterials has recently attracted considerable experimental effort for potential applications in quantum-mechanical and classical optical information processing and for fundamental studies of light-matter interaction. Here, we review the theory behind strong plasmon-exciton coupling and provide analytical expressions that can be used for fitting experimental data, particularly the commonly measured scattering spectra. We re-analyze published data using these expressions, providing a uniform method for evaluating and quantifying claims of strong coupling that avoids ambiguities in distinguishing between Rabi splitting and exciton-induced transparency (or Fano-like interference between plasmons and excitons).

The assembly of inorganic nanoparticles often leads to collective properties that are different from the combined properties of the individual components. In particular, coupling plasmonic and excitonic nanoparticles has been shown to modify their optical properties, including absorption, emission, and scattering. Because of this, these coupled assemblies have potential applications in a wide range of areas, including sensing, light harvesting, and photocatalysis. More recently, unique properties, including Fano interference and Rabi splitting, have been observed by increasing the coupling strength. However, the behavior of coupled nanoparticles is highly dependent on the exact organization of the components, including the number of particles coupled, the distance separating them, and their spatial orientation. This is especially true in the case of strongly coupled particles. Because of this, it is important to achieve synthetic techniques that not only can link particles together but also offer good control over how the particles are connected. In this review, assemblies of plasmonic and excitonic nanoparticles are reviewed, including the various methods that have been used for their construction, the properties that these systems have been predicted to possess as well as the ones that have been observed, and their current applications along with current challenges in the field and potential future applications.

Vibrational strong coupling of molecules to optical cavities based on plasmonic resonances has been explored recently, because plasmonic near-fields can provide strong coupling in sub-diffraction limited volumes. Such field localization maximizes coupling strength, which is crucial for modifying the vibrational response of molecules and, thereby, manipulating chemical reactions. Here, we demonstrate an angle-independent plasmonic nanodisk substrate that overcomes limitations of traditional Fabry-Perot optical cavities, because the design can strongly couple with all molecules on the surface of the substrate regardless of molecular orientation. We demonstrate that the plasmonic substrate provides strong coupling with the C=O vibrational stretch of deposited films of PMMA. We also show that the large linewidths of the plasmon resonance allows for simultaneous strong coupling to two, orthogonal water symmetric and asymmetric vibrational modes in a thin film of copper sulfate monohydrate deposited on the substrate surface. A three-coupled-oscillator model is developed to analyze the coupling strength of the plasmon resonance with these two water modes. With precise control over the nanodisk diameter, the plasmon resonance is tuned systematically through the modes, with the coupling strength to both modes varying as a function of the plasmon frequency, and with strong coupling to both modes achieved simultaneously for a range of diameters. This work may aid further studies into manipulation of the ground-state chemical landscape of molecules by perturbing multiple vibrational modes simultaneously and increasing the coupling strength in sub-diffraction limited volumes., Comment: Supplementary information is attached at the end of the main manuscript

Background and Purpose: Cerebrovascular prevalence is high in patients with coronavirus disease 2019 (COVID-19). However, racial disparities have not been systematically explored in this population. Methods: We performed a retrospective, observational study of stroke prevalence in all patients with COVID-19 who visited emergency department (ED) up to August 13, 2020 in the United States. We used multivariable logistic regression to compare the odds of stroke in black patients with COVID-19 compared to their non-black counterpart while adjusting for the major confounders. Results: Among 8815 patients with ED visits with COVID-19, 77 (0.87 %) had ischemic stroke. The median age of patients with stroke was 64 years (SD: 2 years); 28 (43%) were men, 55 (71%) had hypertension, and 29 (50%) were black. After adjustment for age, sex, hypertension, diabetes, obesity, drinking and smoking, the likelihood of stroke was higher in black than non-black patients (adjusted odds ratio, 2.76; 95% CI, 1.13-7.15, p=0.03). Conclusions: Racial disparities in the prevalence of stroke among patients with COVID-19 exist, with blacks carrying greatest burden.

We have demonstrated induced transparency and strong coupling between a single colloidal quantum dot and plasmonic metal nanocavities at room temperature. These structures have the potential to serve as ultrafast, low-power, nanoscale optical modulators.

Monolayer transition metal dichalcogenides, coupled to metal plasmonic nanocavities, have recently emerged as new platforms for strong light-matter interactions. These systems are expected to have nonlinear optical properties that will enable them to be used as entangled photon sources, compact wave-mixing devices, and other elements for classical and quantum photonic technologies. Here we report the first experimental investigation of the nonlinear properties of these strongly coupled systems, by observing second harmonic generation from a WSe2 monolayer strongly coupled to a single gold nanorod. The pump frequency dependence of the second harmonic signal displays a pronounced splitting that can be explained by a coupled oscillator model with second-order nonlinearities. Rigorous numerical simulations utilizing a nonperturbative nonlinear hydrodynamic model of conduction electrons support this interpretation and reproduce experimental results. Our study thus lays the groundwork for understanding the nonlinear properties of strongly coupled nanoscale systems.

We demonstrate room temperature strong coupling of a single quantum emitter to a configurable plasmonic pico-cavity formed by a nano-tip. Through atomic scale control of mode volume we demonstrate switching and modulation of coupling strength.

On-chip integration of plasmonics and electronics can benefit a broad range of applications in biosensing, signal processing, and optoelectronics. A key requirement is a chip-scale manufacturing method. Here, we demonstrate a split-trench resonator platform that combines a high-quality-factor resonant plasmonic biosensor with radio frequency (RF) nanogap tweezers. The split-trench resonator can simultaneously serve as a dielectrophoretic trap and a nanoplasmonic sensor. Trapping is accomplished by applying an RF electrical bias across a 10 nm gap, thereby either attracting or repelling analytes. Trapped analytes are detected in a label-free manner using refractive-index sensing, enabled by interference between surface-plasmon standing waves in the trench and light transmitted through the gap. This active sample concentration mechanism enables detection of nanoparticles and proteins at a concentration as low as 10 pM. We can manufacture centimeter-long split-trench cavity resonators with high throughput via photolithography and atomic layer deposition, toward practical applications in biosensing, spectroscopy, and optoelectronics., D.Y., A.B., D.A.M., and S.-H.O. acknowledge support from the U.S. National Science Foundation (NSF ECCS 1809723 and ECCS 1809240). D.Y. and S.-H.O. acknowledge partial support provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR). F.d.L.P. and L.M.-M. acknowledge financial support from Spanish Ministry of Economy and Competitivity through projects MAT2017-88358-C3-1-R and MAT2017-88358-C3-2-R and the Aragón Government project Q-MAD. M.P. acknowledges support from the U.S. National Science Foundation (NSF DMR-1905135). S.-H.O. further acknowledges support from the Sanford P. Bordeau Endowed Chair at the University of Minnesota and the McKnight Foundation.

Arrays of hydroporphyrins with boron complexes of dipyrromethene (BODIPY) are a promising platform for biomedical imaging or solar energy conversion, but their photophysical properties have been relatively unexplored. In this paper, we use time-resolved fluorescence, femtosecond transient absorption spectroscopy, and density-functional-theory calculations to elucidate solvent-dependent energy and electron-transfer processes in a series of chlorin- and bacteriochlorin-BODIPY arrays. Excitation of the BODIPY moiety results in ultrafast energy transfer to the hydroporphyrin moiety, regardless of the solvent. In toluene, energy is most likely transferred via the through-space Forster mechanism from the S1 state of BODIPY to the S2 state of hydroporphyrin. In DMF, substantially faster energy transfer is observed, which implies a contribution of the through-bond Dexter mechanism. In toluene, excited hydroporphyrin components show bright fluorescence, with quantum yield and fluorescence lifetime comparable to those of the benchmark monomer, whereas in DMF, moderate to significant reduction of both quantum yield and fluorescence lifetime are observed. We attribute this quenching to photoinduced charge transfer from hydroporphyrin to BODIPY. No direct spectral signature of the charge-separated state is observed, which suggests that either (1) the charge-separated state decays very quickly to the ground state or (2) virtual charge-separated states, close in energy to S1 of hydroporphyrin, promote ultrafast internal conversion.

Strong quantum-mechanical coupling between single emitters and cavity modes enables quantum transduction between photons and excitations in the solid state. However, previous experiments have been limited to cryogenic temperatures. By coupling single colloidal quantum dots to plasmonic nanocavities, we have demonstrated strong coupling at room temperature for single solid-state emitters.

Strong quantum-mechanical coupling between single emitters and plasmonic nanocavities has the potential to enable new classical and quantum photonic technologies at room temperature. Through a new technique of tip-enhanced strong coupling, we have demonstrated the ability to systematically study and dynamically control strong coupling between plasmons and single quantum dots at room temperature.

We have demonstrated induced transparency (Fano interference) and strong coupling (Rabi splitting) between a single colloidal quantum dot and a plasmonic metal nano-cavity at room temperature. These structures have the potential to serve as ultrafast, low-power optical modulators on the nanoscale.

Aims Epilepsy exacts substantial adverse economic and quality of life (QoL) costs. Clarifying the quantitative and qualitative relationships between total and out-of-pocket (OOP) healthcare expenditures and QoL could shed insights into how they influence each other, and have done so over recent times. Methods We used the Medical Expenditure Household Components 2003–2014 to identify a total of 2450 adults with epilepsy, representing a weighted population of 1,942,413. Quality of life was assessed using the Physical Component Summary (PCS) and the Mental Component Summary (MCS) derived from the Short-form 12 Version 2 (SF-12 V2), converted into quartiles of equal distribution, with higher quartiles indicating a better QoL. We computed unadjusted mean and adjusted (through a generalized linear model (GLM)) total and OOP healthcare expenditures by QoL categories among adults with epilepsy (reported as dollars in 2016). Results The pooled estimates of total healthcare expenditures decreased as PCS and MCS quartiles of QoL increased [PCS: costs for quartile 1 = $21,792 (95% confidence interval (CI): $18,416–$25,168 vs. costs for quartile 4 = $6057 (95% CI: $4648–$7466) and MCS: costs for quartile 1 = $19,040 (95% CI: $15,544–$22,535) vs. quartile 4 = $12,939 (95% CI: $8450–$17,429)]. Similarly, the pooled estimates of OOP healthcare expenditures and QoL were inversely related [PCS: costs for quartile 1 = $1849 (95% CI: $1583–$2114) vs. costs for quartile 4 = $948 ($709–$1187) and MCS: costs for quartile 1 = 1812 (95% CI: $1483–2141) vs. quartile 4 = $1317 (95% CI: $982–$1652)]. The association between QoL and total and OOP healthcare expenditures was unchanged after adjusting for socioeconomic and healthcare system related confounders in the GLM. Overall, healthcare expenditures were stable across years independently of the QoL; only OOP expenditures decreased between 2003–2006 and 2011–2014 for quartile 1 of PCS and MCS. Conclusion Quality of life and OOP health expenditures are independently and inversely related to each other among adults with epilepsy. Over the decade studied in the United States, there was a decrease in OOP health expenditures among those patients with epilepsy with the lowest QoL, possibly reflecting a rise in insurance coverage after the Affordable Care Act.

Semiconductor nanoplatelets, or colloidal quantum wells, may enable low-cost, high-efficiency lasers at colors throughout the visible spectrum, with potential applications to solid-state lighting.

The most recent class of semiconductor nanocrystal to be synthesized colloidally is the quantum well, in which carriers are confined quantum mechanically in only one dimension. Electrons and holes in colloidal quantum wells undergo different dynamics than in either colloidal quantum dots or epitaxially grown quantum wells, providing new opportunities for applications. The opportunities presented by cadmium chalcogenide nanoplatelets are particularly exciting, because they can be grown with control over their thickness down to the single atomic layer and with all nanoplatelets in an ensemble having the same thickness. This Feature Article reviews the relaxation and recombination dynamics of electrons and holes, which are tightly bound into excitons, in nanoplatelets. These dynamics are favorable for optical gain and lasing, and this Article reviews the progress that has been made toward practical realization of nanoplatelet lasers, including the demonstration of low thresholds for room-temperature gain and...

While gold nanorods (AuNRs) have found many applications due to their unique optical properties, a few challenges persist in their synthesis. Namely, it is often difficult to reproducibly synthesize AuNRs with specific and monodisperse sizes, especially at shorter aspect ratios. Here, we report a method of post-synthesis precise tailoring of AuNRs by etching with cysteamine. Cysteamine selectively etches AuNRs from their ends while preserving the initial rod shape and monodispersity, making this a viable means of obtaining highly monodisperse short AuNRs down to aspect ratio 2.3. Further, we explore the effect of this etching method on two types of silica-coated AuNRs: silica side-coated and silica end-coated AuNRs. We find that the etching process is cysteamine concentration-dependent and can lead to different degrees of sharpening of the silica-coated AuNRs, forming elongated tips. We also find that cysteamine behaves only as a ligand at concentrations above 200 mM, as no etching of the AuNRs is observed in this condition. Simulations show that excitation of plasmon resonances in these sharpened AuNRs produces local electric fields twice as strong as those produced by conventional AuNRs. Thus, cysteamine etching of AuNRs is shown to be an effective means of tailoring both the size and shape of AuNRs along with their corresponding optical properties. At the same time, the resulting cysteamine coating on the etched AuNRs displays terminal amino groups that allow for further functionalization of the nanorods.

Recent measurements on the gigahertz vibration of nanoparticles immersed in simple liquids, such as glycerol, show that the liquid’s viscoelastic properties can significantly affect the nanoparticle’s mechanical response. Here, we theoretically explore the high-frequency (elastic) limit of this phenomenon where the characteristic time scale for molecular relaxation in the liquid far exceeds the nanoparticle’s vibration period. Paradoxically, we find that the effects of liquid elasticity (and viscosity) may not be visible in the nanoparticle’s dynamic response in this high-frequency elastic limit—the response being identical to that of a macroscopic resonator in an inviscid fluid. A comprehensive mechanistic study reveals that the conditions for this unusual behavior are strongly dependent on the nanoparticle’s vibration mode and the liquid’s properties. A judicious choice of vibration mode is essential for interrogating the viscoelastic properties of simple liquids. Our findings explain recent measurement...

Measurements of acoustic vibrations in nanoparticles provide an opportunity to study mechanical phenomena at nanometer length scales and picosecond time scales. Vibrations in noble-metal nanoparticles have attracted particular attention because they couple to plasmon resonances in the nanoparticles, leading to strong modulation of optical absorption and scattering. There are three mechanisms that transduce the mechanical oscillations into changes in the plasmon resonance: (1) changes in the nanoparticle geometry, (2) changes in electron density due to changes in the nanoparticle volume, and (3) changes in the interband transition energies due to compression/expansion of the nanoparticle (deformation potential). These mechanisms have been studied in the past to explain the origin of the experimental signals; however, a thorough quantitative connection between the coupling of phonon and plasmon modes has not yet been made, and the separate contribution of each coupling mechanism has not yet been quantified. Here, we present a numerical method to quantitatively determine the coupling between vibrational and plasmon modes in noble-metal nanoparticles of arbitrary geometries and apply it to silver and gold spheres, shells, rods, and cubes in the context of time-resolved measurements. We separately determine the parts of the optical response that are due to shape changes, changes in electron density, and changes in deformation potential. We further show that coupling is, in general, strongest when the regions of largest electric field (plasmon mode) and largest displacement (phonon mode) overlap. These results clarify reported experimental results and should help guide future experiments and potential applications.

International audience; Quantum state control of two‐level emitters is fundamental for many information processing, metrology, and sensing applications. However, quantum‐coherent photonic control of solid‐state emitters has traditionally been limited to cryogenic environments, which are not compatible with implementation in scalable, broadly distributed technologies. In contrast, plasmonic nano‐cavities with deep sub‐wavelength mode volumes have recently emerged as a path toward room temperature quantum control. However, optimization, control, and modeling of the cavity mode volume are still in their infancy. Here recent demonstrations of plasmonic tip‐enhanced strong coupling (TESC) with a configurable nano‐tip cavity are extended to perform a systematic experimental investigation of the cavity‐emitter interaction strength and its dependence on tip position, augmented by modeling based on both classical electrodynamics and a quasinormal mode framework. Based on this work, a perspective for nano‐cavity optics is provided as a promising tool for room temperature control of quantum coherent interactions that could spark new innovations in fields from quantum information and quantum sensing to quantum chemistry and molecular opto‐mechanics.

Acoustic oscillations of metal nanoparticles can be used to study the properties of liquids at GHz frequencies and nanometer length scales. We use time-resolved spectroscopy to probe the dynamics of the metal nanoparticle oscillations utilizing a pump-probe technique. The incident pump laser pulse heats the nanoparticles leading to expansion and impulsive excitation of vibrations of the nanoparticles. The oscillations produce shifts in the plasmon resonance, which are monitored by measuring the change in absorption of a second weak broadband probe pulse. In our experiment, we immersed a sample of highly monodisperse gold bipyramids in water-glycerol mixtures from which we determined the damping resulting from the structure-liquid interactions. Performing these measurements over a range of temperatures provides a means to vary the fluid properties of a given water-glycerol mixture. Viscous damping could account for the measured results at low glycerol concentrations and sufficiently high temperatures but failed to describe the damping for high glycerol concentrations and sufficiently low temperatures. Accounting for the viscoelastic nature of the liquid mixtures mostly resolved the discrepancies, but consistently overestimated the degree of damping. Ultimately, allowing for a finite slip length produced good agreement with the measured damping rates. Our results show that standard assumptions in the fluid mechanics of simple liquids – a purely viscous response and the no-slip boundary condition – must be revisited at short length scales and fast time scales.

Optical cavities can enhance and control light-matter interactions. This has recently been extended to the nanoscale, and with single emitter strong coupling regime even at room temperature using plasmonic nano-cavities with deep sub-diffraction-limited mode volumes. However, with emitters in static nano-cavities, this limits the ability to tune coupling strength or to couple different emitters to the same cavity. Here, we present tip-enhanced strong coupling (TESC) spectroscopy, imaging, and control. Based on a nano-cavity formed between a scanning plasmonic antenna-tip and the substrate, by reversibly and dynamically addressing single quantum dots (QDs) we observe mode splitting > 160 meV and anticrossing over a detuning range of ~100 meV, and with sub-nm precision control over the mode volume in the ~1000 nm^3 regime. Our approach, as a new paradigm of nano-cavity quantum-electrodynamics near-field microscopy to induce, probe, and control single-emitter plasmon hybrid quantum states, opens new pathways from opto-electronics to quantum information science., 4 figures

Achieving room-temperature quantum-mechanical strong coupling, or vacuum Rabi splitting, between a single emitter and a plasmon resonance has been a longstanding goal. Recently, two peaks have been observed in the scattering spectra of plasmonic metal nanostructures coupled to single molecules and single quantum dots, and this was taken as evidence of strong coupling. However, a two-peak scattering structure can also arise at intermediate coupling strengths, below the strong-coupling threshold, due to Fano interference between the plasmon and emitter dipole. We unambiguously distinguish between intermediate and strong coupling by measuring both the scattering spectra and the photoluminescence spectra of coupled plasmon-emitter structures. Specifically, we couple single colloidal quantum dots to a plasmon resonator by placing them in the gap between a gold nanoparticle and a silver film. We observe weak, intermediate, and strong coupling in these hybrid metal-semiconductor structures at room temperature, depending on the detailed nanoscale structure of the metal nanoparticle. These structures have the potential to serve as ultrafast, low-power plasmonic modulators on the nanoscale. Both induced transparency and strong coupling can be canceled by absorbing a photon in the quantum dot, leading to a strong change in extinction at the quantum dot transition frequency. Since only a single photon must be absorbed by the QD for this to happen, the energy needed for modulation has the potential to be extremely low, and the structure has the potential to enable all-optical quantum information processing.

Optical trapping has been implemented in many areas of physics and biology as a noncontact sample manipulation technique to study the structure and dynamics of nano- and mesoscale objects. It provides a unique approach for manipulating microscopic objects without inducing undesired changes in structure. Combining optical trapping with hard X-ray microscopy techniques, such as coherent diffraction imaging and crystallography, provides a nonperturbing environment where electronic and structural dynamics of an individual particle in solution can be followed in situ. It was previously shown that optical trapping allows the manipulation of micrometer-sized objects for X-ray fluorescence imaging. However, questions remain over the ability of optical trapping to position objects for X-ray diffraction measurements, which have stringent requirements for angular stability. Our work demonstrates that dynamic holographic optical tweezers are capable of manipulating single micrometer-scale anisotropic particles in a microfluidic environment with the precision and stability required for X-ray Bragg diffraction experiments-thus functioning as an "optical goniometer." The methodology can be extended to a variety of X-ray experiments and the Bragg coherent diffractive imaging of individual particles in solution, as demonstrated here, will be markedly enhanced with the advent of brighter, coherent X-ray sources.

WOS:000455561300035 PubMed: 30539638 Modal gain coefficient is a key figure of merit for a laser material. Previously, net modal gain coefficients larger than a few thousand cm(-1) were achieved in II-VI and III-V semiconductor gain media, but this required operation at cryogenic temperatures. In this work, using pump-fluence-dependent variable-stripe-length measurements, we show that colloidal CdSe nanoplatelets enable giant modal gain coefficients at room temperature up to 6600 cm(-1) under pulsed optical excitation. Furthermore, we show that exceptional gain performance is common to the family of CdSe nanoplatelets, as shown by examining samples having different vertical thicknesses and lateral areas. Overall, colloidal II-VI nanoplatelets with superior optical gain properties are promising for a broad range of applications, including high-speed light amplification and loss compensation in plasmonic photonic circuits.

Strong coupling between plasmons in metal nanoparticles and single excitons in molecules or semiconductor nanomaterials has recently attracted considerable experimental effort for potential applications in quantum-mechanical and classical optical information processing and for fundamental studies of light-matter interaction. Here, we review the theory behind strong plasmon-exciton coupling and provide analytical expressions that can be used for fitting experimental data, particularly the commonly measured scattering spectra. We re-analyze published data using these expressions, providing a uniform method for evaluating and quantifying claims of strong coupling that avoids ambiguities in distinguishing between Rabi splitting and exciton-induced transparency (or Fano-like interference between plasmons and excitons).

Noble metal nanoclusters (NCs) play a pivotal role in bridging the gap between molecules and quantum dots. Fundamental understanding of the evolution of the structural, optical, and electronic properties of these materials in various environments is of paramount importance for many applications. Using state-of-the-art spectroscopy, we provide the first decisive experimental evidence that the structural, electronic, and optical properties of Ag44(MNBA)30 NCs can now be tailored by controlling the chemical environment. Infrared and photoelectron spectroscopies clearly indicate that there is a dimerization between two adjacent ligands capping the NCs that takes place upon lowering the pH from 13 to 7.

This Letter reports the measurement of photoinduced electron-transfer rates from individual CdSe/CdS nanocrystals, or quantum dots (QDs), to methyl viologen acceptor molecules adsorbed on the QD surfaces, using time-resolved photoluminescence at the single-nanocrystal level. For each QD measured, the electron-transfer rate is constant over time, and the photoluminescence blinking dynamics are independent of the measured transfer rate. The total electron-transfer rate is distributed in discrete, constant increments, corresponding to discrete numbers of adsorbed molecules on each QD. The results thus validate previous assumptions that viologen molecules adsorb independently on QD surfaces and that the total electron-transfer rate from a single QD to multiple molecules on its surface is simply the sum of the transfer rates to the individual molecules. The measurement provides an optical method to count the number of active acceptor molecules bound to a single nanocrystal and opens up new possibilities for me...

IntroductionIn 2013, peptic ulcer disease (PUD) caused over 300 000 deaths globally. Low-income and middle-income countries are disproportionately affected. However, there is limited information regarding risk factors of perioperative mortality rates in these countries.ObjectiveTo assess perioperative mortality rates from complicated PUD in Africa and associated risk factors.DesignWe performed a systematic review and a random-effect meta-analysis of literature describing surgical management of complicated PUD in Africa. We used subgroup analysis and meta-regression analyses to investigate sources of variations in the mortality rates and to assess the risk factors contributing to mortality.ResultsFrom 95 published reports, 10 037 patients underwent surgery for complicated PUD. The majority of the ulcers (78%) were duodenal, followed by gastric (14%). Forty-one per cent of operations were for perforation, 22% for obstruction and 9% for bleeding. The operations consisted of vagotomy (38%), primary repair (34%), resection and reconstruction (12%), and drainage procedures (6%). The overall PUD mortality rate was 6.6% (95% CI 5.4% to 8.1%). It increased to 9.7% (95% CI 7.1 to 13.0) when we limited the analysis to studies published after the year 2000. The correlation was higher between perforated PUD and mortality rates (r=0.41, pConclusionPerioperative mortality rates from complicated PUD in Africa are substantially high and could be increasing over time, and there are possible regional differences.

Coherent coupling between plasmons and transition dipole moments in emitters can lead to two distinct spectral effects: vacuum Rabi splitting at strong coupling strengths, and induced transparency (also known as Fano interference) at intermediate coupling strengths. Achieving either strong or intermediate coupling between a single emitter and a localized plasmon resonance has the potential to enable single-photon nonlinearities and other extreme light–matter interactions, at room temperature and on the nanometer scale. Both effects produce two peaks in the spectrum of scattering from the plasmon resonance, and can thus be confused if scattering measurements alone are performed. Here we report measurements of scattering and photoluminescence from individual coupled plasmon–emitter systems that consist of a single colloidal quantum dot in the gap between a gold nanoparticle and a silver film. The measurements unambiguously demonstrate weak coupling (the Purcell effect), intermediate coupling (Fano interference), and strong coupling (Rabi splitting) at room temperature., The signatures of strong and intermediate plasmon-emitter coupling can be confused if scattering measurements alone are performed. Here, the authors use scattering and photoluminescence to demonstrate weak, intermediate, and strong coupling between single quantum dots and plasmons at room temperature.