We determine the effect of defects induced by ion bombardment on the Raman spectrum of single-layer molybdenum disulfide. The evolution of both the linewidths and frequency shifts of the first-order Raman bands with the density of defects is explained with a phonon confinement model, using density functional theory to calculate the phonon dispersion curves. We identify several defect-induced Raman scattering peaks arising from zone-edge phonon modes. Among these, the most prominent is the LA(M) peak at ∼227 cm −1 and its intensity, relative to the one of first-order Raman bands, is found to be proportional to the density of defects. These results provide a practical route to quantify defects in single-layer MoS 2 using Raman spectroscopy and highlight an analogy between the LA(M) peak in MoS 2 and the D peak in graphene.

The interplay between phase separation in polyfluorene blends which show photoinduced charge transfer and photovoltaic performance in photodiodes has been investigated. Phase separation length scales have been varied from several microns to tens of nanometers by limiting the time allowed for solvent-enhanced self-organization through several different processing routes. Concurrent with the decrease in feature size, an increase in maximum photovoltaic efficiency of nearly 1 order of magnitude was observed in photodiodes incorporating the phase-separated blends as the active layer. The structure of the blend films was investigated using fluorescence microscopy, fluorescence scanning near-field optical microscopy, and atomic force microscopy. In some cases, a hierarchy of micron-and nanometer-scale phase separation was observed which may explain the unexpectedly high photoresponse in devices with up to micron-scale phase separation structure. This result along with in situ fluorescence microscopy studies of the transformation process highlights the complex, multistage nature of the conjugated polymer blend formation process which generally exhibits spinodal behavior.

We demonstrate by Raman scattering that the spin splitting in the conduction band of a GaAs/ Ga, "Al As asymmetric quantum well is anisotropic and inequivalent along the [11]and [11]directions. This agrees with the results of tight-binding calculations. The Rashba contribution to the spin orientation induced by the asymmetric potential is of comparable magnitude to the bulk inversion-asymmetry-induced term. Hence, we obtain quantitative information on the origin of the spin orientation at the GaAsiGa& Al As interface.

We report on the resonant coupling between localized surface plasmon resonances (LSPRs) in nanostructured Ag films, and an adsorbed monolayer of Rhodamine 6G dye. Hybridization of the plasmons and molecular excitons creates new coupled polaritonic modes, which have been tuned by varying the LSPR wavelength. The resulting polariton dispersion curve shows an anticrossing behavior which is very well fit by a simple coupled-oscillator Hamiltonian, giving a giant Rabisplitting energy of ∼400 meV. The strength of this coupling is shown to be proportional to the square root of the molecular density. The Raman spectra of R6G on these films show an enhancement of many orders of magnitude due to surface enhanced scattering mechanisms; we find a maximum signal when a polariton mode lies in the middle of the Stokes shifted emission band.PACS numbers: 71.36.+c,73.20.Mf, There is currently considerable interest in the interaction between excitonic and photonic states, as a means of modifying the photophysical properties of a system. Potential novel applications include lasers, 1 optical switches, 2 and sensors.3 In microcavities, mixing of exciton and photon modes leads to the formation of new polaritonic states, and has been observed in both organic 4,5,6 and inorganic systems. 7 More recently, coupling has been observed between excitonic and plasmonic states for semiconductor heterostructures.8,9 Localized plasmons are the subject of many current investigations, as they can dramatically alter the optical properties of a locally situated molecule: enhancement and confinement of the excitation field has important consequences in surface enhanced Raman scattering (SERS).10 Furthermore, localized surface plasmon resonances (LSPRs) can be engineered to produce large modifications in fluorescence intensity and lifetime.11,12 Due to this, the interaction between localized plasmon modes and excitonic states has been studied recently for a variety of nanostructured systems: these include nanoparticles, 13,14 nanorods, 15 nanovoids, 16 and subwavelength hole arrays. 17 For all these systems, strong coupling is manifested as an anticrossing behavior in the dispersion curve of the plasmon mode at the energy of the uncoupled exciton mode, indicating the formation of a hybridized exciton-plasmon polariton state; the resulting mode splitting is determined by the coupling strength of the two systems.In this work, we report on the resonant coupling between LSPRs in nanostructured silver films (NSFs), and two different excitonic states in an adsorbed dye, and we demonstrate the importance of this mechanism for SERS. The coupling strength was tuned by varying the LSPR wavelength from 450 to 750 nm; the resulting excitonplasmon polariton peak positions are very well fit by a three-coupled-oscillator Hamiltonian, which gives a Rabisplitting energy comparable to the largest values reported to date. Raman spectra have been taken for each film at two different wavelengths, and in both cases we find a maximum signal enhancement when the middle of t...

Light–matter interactions can be strongly modified by the surrounding environment. Here, we report on the first experimental observation of molecular spontaneous emission inside a highly non-local metamaterial based on a plasmonic nanorod assembly. We show that the emission process is dominated not only by the topology of its local effective medium dispersion, but also by the non-local response of the composite, so that metamaterials with different geometric parameters but the same local effective medium properties exhibit different Purcell factors. A record-high enhancement of a decay rate is observed, in agreement with the developed quantitative description of the Purcell effect in a non-local medium. An engineered material non-locality introduces an additional degree of freedom into quantum electrodynamics, enabling new applications in quantum information processing, photochemistry, imaging and sensing with macroscopic composites.