We study the optical and vibrational properties of InAlAs alloy films on high-index InP (311)A/B substrate at a wide range of V/III flux ratio (25–125).The crystallinity, vibrational and optical ...characteristics of InAlAs/InP structures are determined using a combination of photoluminescence (PL) and micro-Raman spectroscopies. Raman studies of InAlAs layer grown on traditional (100)InP substrates show a strong dependence of the optical phonons on V/III molar ratio (Sayari et al. in J Raman Spectrosc 40:1023–1027, 2009). Analysis of PL spectra shows the formation of InAs
x
P
1−
x
graded layer located at the inverted interface and a broadening of the InAlAs PL band suggests that a clustering effect. Also, a strong dependence of these PL bands on the V/III ratio and substrate polarity is observed and attributed to the clustering effect and to the presence of a strain-induced piezoelectric field. In addition, micro-Raman spectra show a line shape broadening and wave number shift of the Raman peaks for various V/III molar ratios. Furthermore, we discuss the effect laser excitation wavelength on the Raman spectrum. Then, micro-Raman investigations show the presence of an LO mode related to LO-like InAs in InAsP alloy at the inverted interface in our samples. At lower frequencies, disorder-activated longitudinal acoustic phonons are also observed, which considers the presence of potential fluctuations (cluster effect). Finally, by using the modified random-element-iso-displacement theory, we have explained the alloying effect in the In
x
Al
1−
x
As layers. A good consistency between calculated and measured InAs and AlAs-like phonon frequencies is obtained. Using the AlAs-like LO phonon frequency shifts, we have calculated the residual strain in the In
x
Al
1−
x
As layer. The lower residual strain value is obtained for the (311)A orientation with the lowest V/III ratio and for the (311)B orientation with the largest V/III ratio.
In this article we focus on the optical properties of a luminescent two-dimensional organic–inorganic material (thiopheneethyl ammonium lead iodide) with the formula (C4H3SC2H4NH3)2PbI4. This ...compound exhibits a self-assembled nano-layered structure, forming a multi-quantum wells (QWs) structure. X-ray diffraction patterns revealed that thin films deposited by a spin coating method were highly oriented with the c-axis perpendicular to the substrate surface. The optical properties were investigated by, absorption, ellipsometry and photoluminescence spectroscopy. At room temperature a strong photoluminescence, due to exciton confined in the PbI quantum well, is found around 2.32eV. The Stokes shift was determined and compared with those found for homologous materials. The exciton-phonon interaction was also investigated by studying the temperature dependence of photoluminescence. The exciton-phonon coupling constants for both acoustic and optical phonons were extracted using a phenomenological model are more than one order of magnitude larger than in conventional QWs.
The synthesis and the optical properties of a new organic–inorganic hybrid material (C6H22N4)Pb2Br8 (abbreviated as TETAPb2Br8) is reported here. Its ladder‐like crystal structure is built up from ...infinite 1D chains of corner‐sharing Pb2Br84− bi‐octahedra surrounded by tetra‐protonated triethylenetetramine (abbreviated as TETA4+) organic cations. Under UV excitation, this hybrid organic–inorganic compound emits white light due to radiative recombinations of self‐trapped excitons associated with a structural distortion of the PbBr6 octahedra. Thin films of TETAPb2Br8 show a photoluminescence (PL) quantum yield of ≈11% and exhibit a Commission Internationale de l'Eclairage coordinates of (0.32, 0.37). In the low‐temperature range, the PL intensity increases with increasing temperature. This negative thermal quenching of white‐light emission is interpreted in terms of transitions between excitonic states involving an exciton–phonon interaction. The interpretations are supported by the temperature dependence of the resonant Raman scattering and by density functional theory calculations.
TETAPb2Br8, a 1D ladder‐like organic–inorganic hybrid compound, emits white light due to radiative recombinations of self‐trapped excitons (STEs). In the low‐temperature range, the photoluminescence intensity as well as the STE lifetime increase with increasing temperature. This negative thermal quenching of emission is due to transitions between polaronic states involving exciton–phonon interaction.
We show that the interaction between localized surface plasmons sustained by a metallic nano-antenna and delocalized phonons lying at the surface of an heteropolar semiconductor can generate a new ...class of hybrid electromagnetic modes. These plasphonic modes are investigated using an analytical model completed by accurate Green dyadic numerical simulations. When surface plasmon and surface phonon frequencies match, the optical resonances exhibit a large Rabi splitting typical of strongly interacting two-level systems. Based on numerical simulations of the electric near-field maps, we investigate the nature of the plaphonic excitations. In particular, we point out a strong local field enhancement boosted by the phononic surface. This effect is interpreted in terms of light harvesting by the plasmonic antenna from the phononic surface. We thus introduce the concept of active phononic surfaces that may be exploited for far-infared optoelectronic devices and sensors.
We present a unified framework for the description of the interaction of fast electrons with complex nanostructures based on the Green dyadic method. We show that the computation of a generalized ...field propagator yields the electron energy losses and cathodoluminescence of nano-objects of arbitrary morphologies embedded in complex dielectric media. Spectra and maps for both penetrating and non-penetrating electron trajectories are provided. This numerical approach can be extended to describe complex experiments involving fast electrons and optically excited nanostructures.
The optical response of 2D layered perovskites is composed of multiple equally‐spaced spectral features, often interpreted as phonon replicas, separated by an energy Δ ≃ 12 − 40 meV, depending upon ...the compound. Here the authors show that the characteristic energy spacing, seen in both absorption and emission, is correlated with a substantial scattering response above ≃ 200 cm−1 (≃ 25 meV) observed in resonant Raman. This peculiar high‐frequency signal, which dominates both Stokes and anti‐Stokes regions of the scattering spectra, possesses the characteristic spectral fingerprints of polarons. Notably, its spectral position is shifted away from the Rayleigh line, with a tail on the high energy side. The internal structure of the polaron consists of a series of equidistant signals separated by 25–32 cm−1 (3–4 meV), depending upon the compound, forming a polaron vibronic progression. The observed progression is characterized by a large Huang‐Rhys factor (S > 6) for all of the 2D layered perovskites investigated here, indicative of a strong charge carrier – lattice coupling. The polaron binding energy spans a range ≃ 20–35 meV, which is corroborated by the temperature‐dependent Raman scattering data. The investigation provides a complete understanding of the optical response of 2D layered perovskites via the direct observation of polaron vibronic progression. The understanding of polaronic effects in perovskites is essential, as it directly influences the suitability of these materials for future opto‐electronic applications.
The authors observe the distinct fingerprint of polaron formation in 2D layered perovskites using resonant Raman scattering. The dominating scattering response >200 cm−1 is attributed to the polaron vibronic progression with a large Huang‐Rhys factor S>6. Crucially, the observed high‐frequency scattering response is well‐correlated with the characteristic equally separated features in absorption and photoluminescence.
Using numerical simulations, we demonstrate that fine shape details of gold nanoring-disks are responsible for significant modifications of their localized surface plasmon properties. The numerical ...results are supported by optical transmission measurements and by atomic force microscopy. In particular, we found that, depending on the ring wall sharpness, the spectral shift of the ring-like localized surface plasmon resonance can be as large as few hundred nanometers. These results shed the light on the strong sensitivity of the surface plasmon properties to very small deviations of the ring and disk shapes from the ideally flat surfaces and sharp edges. This effect is particularly important for tailoring the surface plasmon properties of metallic nanostructures presenting edges and wedges for applications in bio- and chemical sensing and for enhancement of light scattering.
The integration of transition metal dichalcogenide layers into photonic devices is a current challenge in the field of 2D materials. Based on numerical simulations, this work explores the design of ...devices combining an MoS2 monolayer with planar photonic gratings sustaining localized optical resonances. A special attention is paid to the technological constraints. The optical response of six devices is compared taking into account the limitations imposed by the growth conditions of the MoS2 layer and the processing of the resonant optical gratings. The reported photonic devices composed of grating filters and a backside reflector on silicon and silica substrates exhibit a theoretical absorption by the MoS2 layer between 85 and 99% at 532 nm. The numerical simulations further show that the addition of an Al2O3 encapsulation layer, to protect the MoS2 monolayer, results in an increase of the performance of the devices. These hybrid MoS2 based photonic devices are promising technological platforms for the study of the optical properties of integrated MoS2 monolayers.
This work is devoted to the fundamental understanding of the interaction between acoustic vibrations and surface plasmons in metallic nano-objects. The acoustoplasmonic properties of coupled ...spherical gold nanoparticles and nanodisk trimers are investigated experimentally by optical transmission measurements and resonant Raman scattering experiments. For excitation close to resonance with the localized surface plasmons of the nanodisk trimers, we are able to detect several intense Raman bands generated by the spherical gold nanoparticles. On the basis of both vibrational dynamics calculations and Raman selection rules, the measured Raman bands are assigned to fundamental and overtones of the quadrupolar and breathing vibration modes of the spherical gold nanoparticles. Simulations of the electric near-field intensity maps performed at the Raman probe wavelengths showed strong localization of the optical energy in the vicinity of the nanodisk trimers, thus corroborating the role of the interaction between the acoustic vibrations of the spherical nanoparticles and the surface plasmons of the nanodisk trimers. Acoustic phonons surface enhanced Raman scattering is here demonstrated for the first time for such coupled plasmonic systems. This work paves the way to surface plasmon engineering for sensing the vibrational properties of nanoparticles.
Optical and vibrational properties of novel self-assembled silver nanocolumns are studied experimentally and theoretically. The split of the surface plasmon resonance into transverse and longitudinal ...modes verifies the one-dimensional character of the nanocolumns. In this work, we have identified the acoustic vibration modes of the nanocolumns using Raman scattering, as spheroid-like modes (l = 2, m = +/-2) involving vibrations of the nanocolumns along their minor axes and the existence of surface plasmon-vibration coupling mechanisms.
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