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Nanoscale ; 11(31): 14540-14552, 2019 Aug 08.
Artigo em Inglês | MEDLINE | ID: mdl-31364684


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).

Sci Adv ; 5(7): eaav5931, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31309142


Optical cavities can enhance and control light-matter interactions. This level of control has recently been extended to the nanoscale with single emitter strong coupling even at room temperature using plasmonic nanostructures. However, emitters in static geometries, limit the ability to tune the coupling strength or to couple different emitters to the same cavity. Here, we present tip-enhanced strong coupling (TESC) with a nanocavity formed between a scanning plasmonic antenna tip and the substrate. By reversibly and dynamically addressing single quantum dots, we observe mode splitting up to 160 meV and anticrossing over a detuning range of ~100 meV, and with subnanometer precision over the deep subdiffraction-limited mode volume. Thus, TESC enables previously inaccessible control over emitter-nanocavity coupling and mode volume based on near-field microscopy. This opens pathways to induce, probe, and control single-emitter plasmon hybrid quantum states for applications from optoelectronics to quantum information science at room temperature.

Nat Commun ; 9(1): 4012, 2018 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-30275446


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.

Nanoscale ; 10(35): 16830-16838, 2018 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-30167608


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.

Nano Lett ; 17(11): 6900-6906, 2017 11 08.
Artigo em Inglês | MEDLINE | ID: mdl-28994296


Nonradiative Auger recombination limits the efficiency with which colloidal semiconductor nanocrystals can emit light when they are subjected to strong excitation, with important implications for the application of the nanocrystals in light-emitting diodes and lasers. This has motivated attempts to engineer the structure of the nanocrystals to minimize Auger rates. Here, we study Auger recombination rates in CdSe/CdS core/shell nanoplatelets, or colloidal quantum wells. Using time-resolved photoluminescence measurements, we show that the rate of biexcitonic Auger recombination has a nonmonotonic dependence on the shell thickness, initially decreasing, reaching a minimum for shells with thickness of 2-4 monolayers, and then increasing with further increases in the shell thickness. This nonmonotonic behavior has not been observed previously for biexcitonic recombination in quantum dots, most likely due to inhomogeneous broadening that is not present for the nanoplatelets.

J Phys Chem Lett ; 8(15): 3607-3612, 2017 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-28722415


Studies of the plasmon resonances in individual and coupled metal nanoparticles often involve imaging of the nanostructures of interest in an electron microscope. We show that this process can dramatically modify the optical spectra of coupled plasmonic nanoparticles, illustrated here with the case of gold nanorod-nanosphere dimers. The spectral changes are due to the thin, partially conductive carbonaceous layer that deposits onto the particles during imaging. These changes are particularly significant for coupled nanoparticles with subnanometer interparticle gaps but have largely been neglected in previous studies of such structures, including studies intended to probe quantum-mechanical effects in plasmon coupling. Accounting for the effects of the carbonaceous layer will lead to a more accurate understanding of such systems.