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We demonstrate local phonon analysis of single AlN nanocrystals by two complementary imaging spectroscopic techniques: tip-enhanced Raman scattering (TERS) and nano-Fourier transform infrared (nano-FTIR) spectroscopy.

A review of recent results and new data on the study of the optical response from semiconductor nanocrystals obtained using plasmon-enhanced optical spectroscopy, including surface enhanced Raman scattering (SERS) and plasmon-enhanced IR absorption, is presented. These methods are based on the amplification of the phonon response of semiconductor nanocrystals located in the field of localized surface plasmon resonance (LSPR) of metal nanostructures. Owing to the choice of a specific morphology of metal nanostructures, coincidence of the LSPR energy with the laser excitation energy and / or the energy of optical phonons in nanocrystals is provided. Resonant conditions ensure a significant increase in local electric fields and, as a result, a sharp increase in the Raman signal and IR absorption at the frequencies of surface optical phonons of nanocrystals. Amplification of the optical response makes it possible not only to detect monolayer coatings of nanocrystals, but also to study their crystal structure, phase and element compositions, and internal mechanical stresses. Application of Raman scattering (RS) in combination with atomic force microscopy with the use of a metallized probe has opened up new possibilities for analyzing the vibrational and electronic spectra of nanocrystals with nanometer spatial resolution

We report on the resonant plasmon enhancement Raman scattering (RS), photoluminescence (PL), and IR absorption by colloidal CdSe-based nanocrystals deposited on Au nanodisk and nanoantenna arrays. Numerical simulations were applied to calculate structural parameters of nanodisks and nanoantennas for which local surface plasmon resonance (LSPR) energy coincides with interband transition energies and surface optical (SO) phonon energies in NCs, correspondingly. The enhancement factors of RS and PL depend resonantly on the nanodisk size. Tip-Enhanced Raman Scattering (TERS) imaging allowed us to carry out the local spectral analysis of CdSe NCs with nanometer spatial resolution. A design of H-type nanoantennas was chosen to achieve maximal enhanced absorption by SO phonons from 1 monolayer of NCs.

Multicomponent semiconductor nanostructures were studied by local spectral analysis based on surface-enhanced Raman scattering by semiconductor nanostructures located on the surface of an array of Au nanoclusters near the metallized tip of an atomic force microscope. In the gap between the metal nanoclusters and the tip, where a semiconductor nanostructure is located, there is a strong increase in the local electric field (hot spot), resulting in a dramatic enhancement of the Raman scattering signal. An unprecedented enhancement of the Raman scattering signal by two-dimensional (over 108 for MoS2) and zero-dimensional (106 for CdSe nanocrystals) semiconductor nanostructures was achieved. The use of the method for mapping the Raman scattering response of a multicomponent system of MoS2 and CdSe made it possible to identify components with a spatial resolution far exceeding the diffraction limit.

We report on the investigation of the localized surface plasmon resonance (LSPR) in periodical Au nanostructures. The arrays of Au nanoclusters and dimers were fabricated on Si and Si/SiO2 surfaces by electron beam lithography. Diameters and periods of nanoclusters with disk shape vary in the range of 30–150 and 130–200 nm, respectively. Because of the opaque nature of the substrates, optical reflection spectroscopy was chosen to probe the plasmonic properties of the metal nanostructures. From a comparison of experimental reflection spectra with those numerically simulated by the Finite Difference Time Domain (FDTD) method, we determined the model structural parameters of the plasmonic nanostructures. These parameters were further used for the calculation of absorptance spectra of the plasmonic structures for which absorptance in the substrate was subtracted. LSPR positions were determined from the maxima of the absorptance spectra. This study reveals a strong dependence of the LSPR position on nanocluster size, distance between nanoclusters, as well as on the SiO2 layer thickness in the nanometer range. In the case of dimer arrays, the plasmon anisotropy in the dimers leads to a splitting of the LSPR plasmon into two modes with orthogonal polarizations. The absorptance spectra reveal a transverse LSPR mode corresponding to the excitation of plasmons in nanoclusters induced by scattered fields from the neighboring ones. This research provides a pathway for a fast and cost-effective determination of the LSPR position from optical reflection spectra. A broad field of potential applications of metal structures with well-controlled plasmonic properties includes surface-enhanced infrared absorption, photoluminescence, and Raman scattering as well as signal transmission in silicon photonics.

Semiconducting nanoplatelets (NPLs) have attracted great attention due to the superior photophysical properties compared to their quantum dot analogs. Understanding and tuning the optical and electronic properties of NPLs in a plasmonic environment is a new paradigm in the field of optoelectronics. Here, we report on the resonant plasmon enhancement of light emission including Raman scattering and photoluminescence from colloidal CdSe/CdS nanoplatelets deposited on arrays of Au nanodisks fabricated by electron beam lithography. The localized surface plasmon resonance (LSPR) of the Au nanodisk arrays can be tuned by varying the diameter of the disks. In the case of surface-enhanced Raman scattering (SERS), the Raman intensity profile follows a symmetric Gaussian shape matching the LSPR of the Au nanodisk arrays. The surface-enhanced photoluminescence (SEPL) profile of NPLs, however, follows an asymmetric Gaussian distribution highlighting a compromise between the excitation and emission enhancement mechanisms originating from energy transfer and Purcell effects. The SERS and SEPL enhancement factors depend on the nanodisk size and reach maximal values at 75 and 7, respectively, for the sizes, for which the LSPR energy of Au nanodisks coincides with interband transition energies in the semiconductor platelets. Finally, to explain the origin of the resonant enhancement behavior of SERS and SEPL, we apply a numerical simulation to calculate plasmon energies in Au nanodisk arrays and emission spectra from NPLs in such a plasmonic environment.

The intensity of the line of antisymmetric vibrations of CH2 in the Raman spectrum of molecular layers of fatty acids and phospholipids is sensitive both to the molecular order in the layer (lateral order) and to the conformational order of the hydrocarbon chain of the molecule. Though the intensity of this line is widely used as an indicator of order in molecular layers containing hydrocarbon tails, the nature of sensitivity of the line of antisymmetric vibrations to the order is still disputable. This issue has been experimentally studied, and it has been demonstrated that disordering leads to redistribution of vibrational modes and to changes in polarizability of antisymmetric vibrations. A hypothesis is proposed that the intensity of the line of the Raman scattering of antisymmetric vibrations of CH2 is determined to a large extent by their interaction with electron excitation of the hydrocarbon chain.

We report a study of the infrared response by localized surface plasmon resonance (LSPR) modes in gold micro- and nanoantenna arrays with various morphologies and surface-enhanced infrared absorption (SEIRA) by optical phonons of semiconductor nanocrystals (NCs) deposited on the arrays. The arrays of nano- and microantennas fabricated with nano- and photolithography reveal infrared-active LSPR modes of energy ranging from the mid to far-infrared that allow the IR response from very low concentrations of organic and inorganic materials deposited onto the arrays to be analyzed. The Langmuir–Blodgett technology was used for homogeneous deposition of CdSe, CdS, and PbS NC monolayers on the antenna arrays. The structural parameters of the arrays were confirmed by scanning electron microscopy. 3D full-wave electromagnetic simulations of the electromagnetic field distribution around the micro- and nanoantennas were employed to realize the maximal SEIRA enhancement for structural parameters of the arrays whereby the LSPR and the NC optical phonon energies coincide. The SEIRA experiments quantitatively confirmed the computational results. The maximum SEIRA enhancement was observed for linear nanoantennas with optimized structural parameters determined from the electromagnetic simulations. The frequency position of the feature’s absorption seen in the SEIRA response evidences that the NC surface and transverse optical phonons are activated in the infrared spectra.

In this article, we present the results of a gap-plasmon tip-enhanced Raman scattering study of MoS2 monolayers deposited on a periodic array of Au nanostructures on a silicon substrate forming a two dimensional (2D) crystal/plasmonic heterostructure. We observe a giant Raman enhancement of the phonon modes in the MoS2 monolayer located in the plasmonic gap between the Au tip apex and Au nanoclusters. Tip-enhanced Raman mapping allows us to determine the gap-plasmon field distribution responsible for the formation of hot spots. These hot spots provide an unprecedented giant Raman enhancement of 5.6 × 108 and a spatial resolution as small as 2.3 nm under ambient conditions. Moreover, due to strong hot electron doping in the order of 1.8 × 1013 cm−2, we observe a structural change of MoS2 from the 2H to the 1T phase. Owing to the very good spatial resolution, we are able to spatially resolve those doping sites. To the best of our knowledge, this is the first time reporting of such a phenomenon with nm spatial resolution. Our results will open the perspectives of optical diagnostics with nanometer resolution for many other 2D materials.

We report on a study of surface-enhanced infrared absorption (SEIRA) by optical phonons in monolayers (MLs) of CdSe, CdS, and PbS nanocrystals (NCs) deposited on arrays of linear nanoantennas the optimized structural parameters of which allow coupling between the localized surface plasmon resonance (LSPR) and diffraction modes in the far-infrared spectral region. The Langmuir–Blodgett technique was used for homogeneous deposition of the NCs. The structural parameters of the arrays and the NC MLs were determined by scanning electron microscopy. According to the three-dimensional electrodynamic simulations of the electromagnetic field distribution around the antennas, the maximal SEIRA enhancement is realized for an array period of about 15 μm when the energy of a diffraction mode coincides with that of the LSPR mode. SEIRA experimental results are in perfect quantitative agreement with the simulation. The maximal SEIRA enhancement is observed for the nanoantenna length and transverse periodicity predicted ...

Tip-enhanced Raman spectroscopy (TERS) allows the chemical analysis with a spatial resolution at the nanoscale, well beyond what the diffraction limit of light makes possible. We can further boost the TERS sensitivity by using a metallic substrate in the so-called gap-mode TERS. In this context, the goal of this work is to provide a generalized view of imaging artifacts in TERS and near-field imaging that occur due to tip-sample coupling. Contrary to the case of gap-mode with a flat substrate where the size of the enhanced region is smaller than the tip size when visualizing 3D nanostructures the tip convolution effect may broaden the observed dimensions due to the local curvature of the sample. This effect is particularly critical considering that most works on gap-mode TERS consider a perfectly flat substrate which is rarely the case in actual experiments. We investigate a range of substrates to evidence these geometrical effects and to obtain an understanding of the nanoscale curvature role in TERS imaging. Our experimental results are complemented by numerical simulations and an analogy with atomic force microscopy artifacts is introduced. As a result, this work offers a useful analysis of gap-mode TERS imaging with tip- and substrate-related artifacts furthering our understanding and the reliability of near-field optical nanospectroscopy.

Since the first report in the early 2000s, there have been several experimental configurations that have demonstrated enhancement and spatial resolution of tip-enhanced Raman spectroscopy (TERS). The combination of a plasmonic substrate and a metallic tip is one suitable approach to achieve even higher enhancement and lateral resolution. In this contribution, we demonstrate TERS on a monolayer of MoS2 on an array of Au nanodisks. The Au nanodisks were prepared by electron beam writing. Thereafter, MoS2 was transferred onto the plasmonic substrate via the exfoliation technique. We witness an unprecedented enhancement and spatial resolution in the experiments. In the TERS image a ring-like shape is observed that matches the edges of the nanodisks. TERS enhancement at the edges is about 170 times stronger than at the center of the nanodisks. For a better understanding of the experimental results, finite element method (FEM) simulations were employed to simulate the TERS image of the MoS2/plasmonic heterostructure. Our calculations show a higher electric field concentration at the edges that exponentially decays to the center. Therefore, it reproduces the ring-like shape of the experimental image. Moreover, the calculations suggest a TERS enhancement of 135 at the edges compared to the center, which is in very good agreement with the experimental data. According to our calculations, the spatial resolution is also increased at the edges. For comparison, FEM simulations of a tip-flat metal substrate system (conventional gap-mode TERS) were carried out. The calculations confirmed a 110 times stronger enhancement at the edges of the nanodisks than that of conventional gap-mode TERS and explained the experimental maps. Our results provide not only a deeper understanding of the TERS mechanism of this heterostructure, but can also help in realizing highly efficient TERS experiments using similar systems.

The study of infrared absorption by linear gold nanoantennas fabricated on a Si surface with underlying SiO2 layers of various thicknesses allowed the penetration depth of localized surface plasmons into SiO2 to be determined. The value of the penetration depth derived experimentally (20 ± 10 nm) corresponds to that obtained from electromagnetic simulations (12.9–30.0 nm). Coupling between plasmonic excitations of gold nanoantennas and optical phonons in SiO2 leads to the appearance of new plasmon–phonon modes observed in the infrared transmission spectra the frequencies of which are well predicted by the simulations.

Here we present the results on an investigation of resonant Stokes and anti- Stokes surface-enhanced Raman scattering (SERS) by optical phonons in colloidal CdSe nanocrystals (NCs) homogeneously deposited on arrays of Au nanoclusters using the Langmuir–Blodgett technology. The thickness of deposited NCs, determined by transmission and scanning electron microscopy, amounts to approximately 1 monolayer. Special attention is paid to the determination of the localized surface plasmon resonance (LSPR) energy in the arrays of Au nanoclusters as a function of the nanocluster size by means of micro-ellipsometry. SERS by optical phonons in CdSe NCs shows a significant enhancement factor with a maximal value of 2 × 103 which depends resonantly on the Au nanocluster size and thus on the LSPR energy. The deposition of CdSe NCs on the arrays of Au nanocluster dimers enabled us to study the polarization dependence of SERS. It was found that a maximal SERS signal is observed for the light polarization along the dimer axis. Finally, SERS by optical phonons was observed for CdSe NCs deposited on the structures with a single Au dimer. A difference of the LO phonon energy is observed for CdSe NCs on different single dimers. This effect is explained as the confinement-induced shift which depends on the CdSe nanocrystal size and indicates quasi-single NC Raman spectra being obtained.

We review our recent results concerning surface-enhanced Raman scattering (SERS) by confined optical and surface optical phonons in semiconductor nanostructures including CdS, CuS, GaN, and ZnO nanocrystals, GaN and ZnO nanorods, and AlN nanowires. Enhancement of Raman scattering by confined optical phonons as well as appearance of new Raman modes with the frequencies different from those in ZnO bulk attributed to surface optical modes is observed in a series of nanostructures having different morphology located in the vicinity of metal nanoclusters (Ag, Au, and Pt). Assignment of surface optical modes is based on calculations performed in the frame of the dielectric continuum model. It is established that SERS by phonons has a resonant character. A maximal enhancement by optical phonons as high as 730 is achieved for CdS nanocrystals in double resonant conditions at the coincidence of laser energy with that of electronic transitions in semiconductor nanocrystals and localized surface plasmon resonance in metal nanoclusters. Even a higher enhancement is observed for SERS by surface optical modes in ZnO nanocrystals (above 104). Surface enhanced Raman scattering is used for studying phonon spectrum in nanocrystal ensembles with an ultra-low areal density on metal plasmonic nanostructures.

A method is proposed for the formation of ZnO nanoparticles (NP) in dimethylformamide, which permits variation of the mean NP diameter from 3.6-3.7 to 6.0 nm by selecting the suitable duration and temperature of the post-synthesis heat treatment. The ZnO nanoparticles in DMF display characteristic photoluminescence, emitting in a broad band with maximum at 2.24-2.25 eV, with a quantum yield up to 13%, and a mean radiative lifetime of ~2 μs. Giant enhancement of Raman scattering on the surface phonons of the ZnO NP is observed upon the photoexcitation of these NP with an island-like silver film deposited on their surface.

We apply Raman spectroscopy to study the phonon spectrum in periodical GeSiSn/Si nanostructures with Sn concentration varied from 0 to 20%. In the optical spectral region, an insignificant shift of the phonon mode positions with a variation of the Sn content prevents determination of Sn concentration relying only on the optical phonons behavior. In the acoustic region, we observe the doublets of the folded acoustic phonons, the spectral positions of which undergo the low-frequency shift with increasing the Sn content. The application of the elastic continuum model with the linear approximation of sound velocity via Sn content in GeSiSn layers fails to explain the experimental results. This indicates a nonlinear Sn concentration dependence of sound velocity in GeSiSn layers which describes well the positions of the folded acoustic phonons.

We report on the study of localized surface plasmon resonances (LSPRs) arising in arrays of metal (Au) nanoclusters, dimers, and nanoantennas under the influence of external electromagnetic radiation. Using nanolithography, the plasmonic arrays with different morphologies including cylindrical nanoclusters and dimers, linear and H-type nanoantennas were fabricated. Their LSPR frequencies were determined from the analysis of optical reflection and IR spectra. LSPR frequency depends strongly on morphology of metal nanostructures and is varied from visible to terahertz spectral range with variation of the structures from cylindrical nanoclusters to the nanoantennas with a high aspect ratio. We established the interconnection between the structural parameters of the plasmonic arrays and their LSPR frequencies based on the results of 3D electrodynamic simulations.

The method of nanostructuring metal surfaces by means of nanolithography was optimized and Au nanoantenna arrays with the controllable parameters on the Si surfaces were formed. The surface-enhanced infrared spectroscopy was used for analysis of steroid hormone cortisol in blood plasma.

We present the results of an investigation of surface-enhanced Raman scattering (SERS) by optical phonons in colloidal CdSe nanocrystals (NCs) homogeneously deposited on both arrays of Au nanoclusters and Au dimers using the Langmuir–Blodgett technique. The coverage of the deposited NCs was less than one monolayer, as determined by transmission and scanning electron microscopy. SERS by optical phonons in CdSe nanocrystals showed a significant enhancement that depends resonantly on the Au nanocluster and dimer size, and thus on the localized surface plasmon resonance (LSPR) energy. The deposition of CdSe nanocrystals on the Au dimer nanocluster arrays enabled us to study the polarization dependence of SERS. The maximal SERS signal was observed for light polarization parallel to the dimer axis. The polarization ratio of the SERS signal parallel and perpendicular to the dimer axis was 20. The SERS signal intensity was also investigated as a function of the distance between nanoclusters in a dimer. Here the maximal SERS enhancement was observed for the minimal distance studied (about 10 nm), confirming the formation of SERS “hot spots”.

We present the results of a Raman study of optical phonons in CuS nanocrystals (NCs) with a low areal density fabricated through the Langmuir–Blodgett technology on nanopatterned Au nanocluster arrays using a combination of surface- and interference-enhanced Raman scattering (SERS and IERS, respectively). Micro-Raman spectra of one monolayer of CuS NCs deposited on a bare Si substrate reveal only features corresponding to crystalline Si. However, a new relatively strong peak occurs in the Raman spectrum of CuS NCs on Au nanocluster arrays at 474 cm−1. This feature is related to the optical phonon mode in CuS NCs and manifests the SERS effect. For CuS NCs deposited on a SiO2 layer this phonon mode is also observed due to the IERS effect. Its intensity changes periodically with increasing SiO2 layer thickness for different laser excitation lines and is enhanced by a factor of about 30. CuS NCs formed on Au nanocluster arrays fabricated on IERS substrates combine the advantages of SERS and IERS and demonstrate stronger SERS enhancement allowing for the observation of Raman signals from CuS NCs with an ultra-low areal density.

Surface- and tip-enhanced resonant Raman scattering (resonant SERS and TERS) by optical phonons in a monolayer of CdSe quantum dots (QDs) is demonstrated. The SERS enhancement was achieved by employing plasmonically active substrates consisting of gold arrays with varying nanocluster diameters prepared by electron-beam lithography. The magnitude of the SERS enhancement depends on the localized surface plasmon resonance (LSPR) energy, which is determined by the structural parameters. The LSPR positions as a function of nanocluster diameter were experimentally determined from spectroscopic micro-ellipsometry, and compared to numerical simulations showing good qualitative agreement. The monolayer of CdSe QDs was deposited by the Langmuir-Blodgett-based technique on the SERS substrates. By tuning the excitation energy close to the band gap of the CdSe QDs and to the LSPR energy, resonant SERS by longitudinal optical (LO) phonons of CdSe QDs was realized. A SERS enhancement factor of 2 × 10(3) was achieved. This allowed the detection of higher order LO modes of CdSe QDs, evidencing the high crystalline quality of QDs. The dependence of LO phonon mode intensity on the size of Au nanoclusters reveals a resonant character, suggesting that the electromagnetic mechanism of the SERS enhancement is dominant. Finally, the resonant TERS spectrum from CdSe QDs was obtained using electrochemically etched gold tips providing an enhancement on the order of 10(4). This is an important step towards the detection of the phonon spectrum from a single QD.

This chapter presents the results of phonon study of semiconductor superlattices and quantum dots using Raman scattering and Infrared spectroscopy. The combination of these methods allows the spectrum of confined, surface optical, and folded acoustic phonons, as well as plasmon–phonon modes in semiconductor nanostructures, to be studied in detail. The analysis of the energy position of the phonon modes, their intensity, and their spectral width provides information on electronic spectrum and structural parameters such as layer thickness, quantum dot size, shape, and composition, as well as in-built mechanical strain. We discuss here possibilities and perspectives for establishing the phonon spectrum of single nanostructures using surface-enhanced Raman scattering.

Here, we present the results on the investigation of structural and vibrational properties of CuxS (x = 1–2) nanocrystals formed using the Langmuir–Blodgett technique. The synthesis requires deposition of high quality Langmuir–Blodgett films of copper behenates on a solid substrate (Si, Au, and Pt). The Langmuir–Blodgett film is then sulfidized, what results in the formation of the copper sulfide nanocrystals embedded in behenic acid matrix. Finally, free-standing CuxS nanocrystals are obtained after temperature annealing at 120–400 °C in an Ar atmosphere. Morphology (size, shape, and areal density) and the crystal structure of nanocrystals were determined by direct structural methods including scanning and transmission electron microscopies and high-energy electron diffraction. Surface-enhanced Raman scattering (SERS) by optical phonons in CuxS nanocrystals in the vicinity of metal nanoclusters provided a significant enhancement factor (about 25) and allowed the fine structure of their phonon spectrum to...

Raman and infrared phonon spectra of ultrasmall (1.8 nm) colloidal CdS nanoparticles (usNPs) are presented. Multiphonon scattering by optical phonons up to the third order is observed in the Raman spectra at low temperature and resonant (325 nm) excitation. The first-order optical phonon peak is a superposition of several components, two of which can be assigned to surface optical (SO) and longitudinal optical (LO) modes, respectively. The LO mode, being markedly broadened compared to that of spectra of regular (>2 nm) NPs, is related to phonon confinement and bond distortion induced by a significant structural relaxation in usNPs. A shoulder observed above the LO frequency is either due to the density of phonon states induced by distorted surface bonds or due to higher-order scattering processes involving optical and acoustic phonons. The Raman peaks of usNPs do not reveal the upward shift and narrowing upon decreasing temperature from 300 K down to 85 K typical for crystalline semiconductors, even thoug...

The properties of an artificial anisotropic structure formed by microhelices have been numerically simulated by the example of a specially designed sample. The sample contains paired helices with right- and left-handed twisting directions, due to which the metamaterial chirality is compensated for. Helices are characterized by precalculated optimal parameters; as a result, the permittivity and permeability of metamaterial are approximately equal. Therefore, the wave impedance of the structure is close to the impedance of free space in the frequency range near 2 THz and the reflection of normally incident electromagnetic waves is weak. A boundary problem is solved and an analytical expression is obtained for the reflection and transmission coefficients of an electromagnetic wave passing through the structure. The simulated properties of the structure are compared with experimental results.

We studied phonon modes propagating along the [3 1 1] direction in highly ordered, stacked InAs QDs embedded in an InGaAlAs matrix grown on InP(3 1 1) substrate by Raman spectroscopy. The Raman spectra showed clear doublets of folded quasi-longitudinal modes which have mixed transverse and longitudinal character. A broad feature observed in the Raman spectra was attributed to superposition of densely folded and/or confined phonon modes that is with agreement with our previous theoretical calculation. The phonon gap was observed and compared with our theoretical calculations.

Deposition of silica shells onto ZnO nanoparticles (NPs) in dimethyl sulfoxide was found to be an efficient tool for terminating the growth of ZnO NPs during thermal treatment and producing stable core–shell ZnO NPs with core sizes of 3.5–5.8 nm. The core–shell ZnO–SiO2 NPs emit two photoluminescence (PL) bands centred at ∼370 and ∼550 nm originating from the direct radiative electron–hole recombination and defect-mediated electron–hole recombination, respectively. An increase of the ZnO NP size from 3.5 to 5.8 nm is accompanied by a decrease of the intensity of the defect PL band and growth of its radiative life-time from 0.78 to 1.49 μs. FTIR spectroscopy reveals no size dependence of the FTIR-active spectral features of ZnO–SiO2 NPs in the ZnO core size range of 3.5–5.8 nm, while in the Raman spectra a shift of the LO frequency from 577 cm−1 for the 3.5 nm ZnO core to 573 cm−1 for the 5.8 nm core is observed, which can indicate a larger compressive stress in smaller ZnO cores induced by the SiO2 shell. Simultaneous hydrolysis of zinc(II) acetate and tetraethyl orthosilicate also results in the formation of ZnO–SiO2 NPs with the ZnO core size varying from 3.1 to 3.8 nm. However, unlike the case of the SiO2 shell deposition onto the pre-formed ZnO NPs, individual core–shell NPs are not formed but loosely aggregated constellations of ZnO–SiO2 NPs with a size of 20–30 nm are. The variation of the synthetic procedures in the latter method proposed here allows the size of both the ZnO core and SiO2 host particles to be tuned.

article i nfo This work is devoted to the investigation of surface-enhanced Raman scattering by vibrational modes of co- balt phthalocyanine ultrathin films and CuS nanocrystals prepared using by organic molecular beam vapor deposition and the Langmuir-Blodgett technique, respectively, on laterally ordered arrays of Au nanoclusters formed by electron beam lithography on Si and GaAs substrates. The surface-enhanced Raman scattering study of cobalt phthalocyanine films demonstrates the strong depen- dence of Raman intensity of vibrational modes in cobalt phthalocyanine on the laser excitation wavelength as well as on the size and period of Au nanoclusters. By tuning the optical resonance conditions a maximal en- hancement factor of 2 × 10 4 is achieved. The investigation of surface-enhanced Raman scattering by cobalt phthalocyanine deposited on laterally ordered arrays of paired Au nanoclusters (dimers) reveals anisotropic enhancement with respect to polarization of the scattered light parallel or perpendicular to the dimer axis. © 2013 Elsevier B.V. All rights reserved.

Surface-enhanced Raman scattering by optical and surface phonons in CdS, GaN, and CuS nanocrystals, and AlN nanowires is detected and studied. It is found that the presence of metal (Ag, Au, and Pt) nanoclusters noticeably modifies the Raman spectra of the nanostructures and results in a resonant increase in the intensity of optical phonon modes in CdS and CuS nanocrystals or in the emergence of surface modes in GaN nanocrystals and AlN nanowires. It is shown that the frequencies of the surface optical phonon modes of the examined nanostructures are in good agreement with the theoretical values calculated within the framework of the dielectric continuum model.

We present the results of micro-Raman scattering study of acoustic phonons of InAs/AlAs quantum dot superlattices grown by molecular beam epitaxy in the Stranski–Krastanow growth mode. Raman scattering from the planar surface and the cleaved (110)-oriented edge of the nanostructures was investigated. Doublets of folded longitudinal acoustic (FLA) phonons up to 7th order were observed in the Raman spectra measured in the z(x,x)-z scattering geometry whose energy positions are well described by the elastic continuum model of Rytov. The in-plane Raman scattering spectra measured in the y′(x′,x′)-y′ geometry reveal the changing energy positions and intensities of the FLA doublet components which are consistent with the changing effective wave vector in the nanostructures induced by the momentum transfer of the light. The Raman selection rules for the FLA phonons with different symmetries are discussed.

Semiconductor core–shell nanocrystals (NCs) have greatly improved luminescent properties including better resistance to photobleaching and ligand exchange. It was suggested that compound alloying at the core/shell interface could play an important role in obtaining bright and stable NCs. Here, we investigate the interface composition and strain evolution in spherical and dot-in-plate CdSe/CdS nanocrystals with shell thickness ranging from 1 to 3 nm, using a combination of Raman and infrared spectroscopy. A slower rate of strain accumulation in the core is observed for dot-in-plate nanocrystals and is linked to the anisotropic shape of the plate-like shell. We resolved the respective contributions of the core, shell, and alloyed interface and observed a drastic change of the shell-related Raman feature with the appearance of the bulk-like optical phonon in the shell thicker than 1 nm. The average composition of the alloy interface is estimated using the frequencies of the alloy modes. Because of the high c...

Silver nanoparticles sprayed onto a crystalline quartz substrate are characterized by means of the low-frequency Raman scattering. Contributions of silver nanoparticles of different sizes to the Raman scattering spectrum are estimated. Data of scanning electron microscopy are used to verify the validity of the results obtained.

Nanoantenna-assisted plasmonic enhancement of IR absorption and Raman scattering was employed for studying the vibrational modes in organic molecules. Ultrathin cobalt phthalocyanine films (3 nm) were deposited on Au nanoantenna arrays with specified structural parameters. The deposited organic films reveal the enhancement of both Raman scattering and IR absorption vibrational modes. To extend the possibility of implementing surface-enhanced infrared absorption (SEIRA) for biological applications, the detection and analysis of the steroid hormone cortisol was demonstrated.

Recently developed two-dimensional colloidal semiconductor nanocrystals, or nanoplatelets (NPLs), extend the palette of solution-processable free-standing 2D nanomaterials of high performance. Growing CdSe and CdS parts subsequently in either side-by-side or stacked manner results in core–crown or core/shell structures, respectively. Both kinds of heterogeneous NPLs find efficient applications and represent interesting materials to study the electronic and lattice excitations and interaction between them under strong one-directional confinement. Here, we investigated by Raman and infrared spectroscopy the phonon spectra and electron–phonon coupling in CdSe/CdS core/shell and core–crown NPLs. A number of distinct spectral features of the two NPL morphologies are observed, which are further modified by tuning the laser excitation energy Eexc between in- and off-resonant conditions. The general difference is the larger number of phonon modes in core/shell NPLs and their spectral shifts with increasing shell thickness, as well as with Eexc. This behaviour is explained by strong mutual influence of the core and shell and formation of combined phonon modes. In the core–crown structure, the CdSe and CdS modes preserve more independent behaviour with only interface modes forming the phonon overtones with phonons of the core.

We review recent experimental work to utilize the size dependence of the luminescence quenching of colloidal semiconductor quantum dots induced by functionalized porphyrin molecules attached to the surface to describe a photoluminescence (PL) quenching process which is different from usual models of charge transfer (CT) or Foerster resonant energy transfer (FRET). Steady-state and picosecond time-resolved measurements were carried out for nanocomposites based on colloidal CdSe/ZnS and CdSe quantum dots (QDs) of various sizes and surfacely attached tetra-mesopyridyl-substituted porphyrin molecules (“Quantum Dot-Porphyrin” nanocomposites), in toluene at 295 K. It was found that the major part of the observed strong quenching of QD PL in “QD-Porphyrin” nanocomposites can neither be assigned to FRET nor to photoinduced charge transfer between the QD and the chromophore. This PL quenching depends on QD size and shell and is stronger for smaller quantum dots: QD PL quenching rate constants scale inversely with the QD diameter. Based on the comparison of experimental data and quantum mechanical calculations, it has been concluded that QD PL quenching in “QD-Porphyrin” nanocomposites can be understood in terms of a tunneling of the electron (of the excited electron-hole pair) followed by a (self-) localization of the electron or formation of trap states. The major contribution to PL quenching is found to be proportional to the calculated quantum-confined exciton wave function at the QD surface. Our findings highlight that single functionalized molecules can be considered as one of the probes for the complex interface physics and dynamics of colloidal semiconductor QD.

We present a study of resonant and surface enhanced Raman scattering by arrays of nanocrystals (cadmium sulfide CdS, lead selenide PbSe, and zinc oxide ZnO) with various areal density fabricated by using the Langmuir−Blodgett technique and colloidal chemistry. Resonant Raman scattering by transverse, longitudinal, and surface optical (TO, LO, and SO) phonons and their overtones up to ninth order was achieved for nanocrystal (NC) arrays by adjusting the laser energy to that of the interband transitions. The resonance enhancement allowed a Raman response from arrays of NCs with a low areal density (down to 10 PbSe NCs per 1 μm 2 ) to be measured. An enhancement of Raman scattering by LO and SO modes in CdS NC arrays with a low areal density by a factor of about 730 was achieved due to the resonant surface enhanced Raman scattering effect.

Raman scattering (including nonresonant, resonant, and surface enhanced scattering) of light by optical and surface phonons of ZnO nanocrystals and nanorods has been investigated. It has been found that the nonresonant and resonant Raman scattering spectra of the nanostructures exhibit typical vibrational modes, E 2(high) and A 1(LO), respectively, which are allowed by the selection rules. The deposition of silver nanoclusters on the surface of nanostructures leads either to an abrupt increase in the intensity (by a factor of 103) of Raman scattering of light by surface optical phonons or to the appearance of new surface modes, which indicates the observation of the phenomenon of surface enhanced Raman light scattering. It has been demonstrated that the frequencies of surface optical phonon modes of the studied nanostructures are in good agreement with the theoretical values obtained from calculations performed within the effective dielectric function model.

A micro-Raman study of optical phonons in GaAs/InGaAs and InGaAs/InAs bilayer microtubes is presented. From the analysis of optical phonon frequencies the built-in mechanical strain in the microtubes was estimated and compared with theoretical predictions. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Raman scattering by surface phonons in CdS1–xSex nanocrystals grown in a borosilicate glass matrix, is studied. CdSe-like and CdS-like surface phonon frequencies are shown to increase with the relevant component content in the nanocrystal composition. No clear size dependence of the surface phonon frequencies has been observed. On the other hand, surface phonons in CdS1–xSex nanocrystals exhibit resonant dependence on the Raman excitation wavelength. It is emphasized that measurements of Raman scattering by surface phonons in CdS1–xSex nanocrystals give no reason to judge upon the nanocrystal shape. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report resonant Raman scattering from InGaAs/AlAs quantum dots with indium content x = 0.3 ÷ 1. The first order Raman spectra reveal resonant behaviour selective to a quantum dot size. Up to third-order multi-phonon processes have been observed in the quantum dot structure. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)