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We report on a combined atomic force microscopy, Raman spectroscopy, and transmission electron microscopy study of InAs/Al(Ga)As and AlAs/InAs quantum dot nanostructures grown by molecular beam epitaxy in the Stranski–Krastanov growth mode on (001)-oriented GaAs substrates. Structure periods of 50 nm and 100 nm were determined by atomic force microscopy of cleaved as well as ion-milled sample surfaces and were confirmed by high resolution transmission electron microscopy. Spatially resolved Raman spectroscopy analysis of a beveled surface allows profiling the Raman intensity of phonon modes. An optimal access to the spatially dependent changes in the phonon spectra is achieved by polishing the samples at an angle of 5–7 degrees with respect to the original sample surface plane. Such analysis allowed the localization of individual quantum dot layers. This opens a way to the structural characterization of quantum dot multilayers by the combination of atomic force microscopy and Raman spectroscopy.

A study is reported of optical vibrational modes in [311]-grown GaAs/AlAs superlattices. An analysis of the TO and LO localized modes observed in IR reflectance spectra showed that the difference between the TO and LO mode frequencies in superlattices grown on (311)A and (311)B surfaces is due to the different localization lengths of these modes. The dispersion of transverse optical phonons in GaAs derived from IR reflectance spectra is in a good agreement with Raman scattering data.

Periodical structures with InAs quantum dots in an (Al,Ga)As matrix and AlAs dots embedded in InAs were studied by Raman spectroscopy focusing on the interface phonons. Experiments on asymmetric GaAs/InAs/AlAs quantum dot structures allowed distinguishing between the phonons of corrugated dot/matrix interfaces and those of planar wetting layer/matrix interfaces. The observed positions of the interface phonons are compared with the dielectric continuum model calculations taking into account the preferential dot shape derived from transmission electron microscopy.

Raman spectroscopy indicates the formation of extended intermixture alloy regions at the interfaces in the GaSb/AlSb superlatttices, which suppress the optical confined modes. A misfit strain was found to be responsible for the high‐frequency shift of the optical phonons confined in the AlSb layers. It turned out that, in the ultrathin layer GaSb/AlSb superlattices with layer thicknesses less than 7 monolayers, the strain was completely relaxed in the alloy interface regions.

We present an experimental study of $\mathrm{In}\mathrm{As}∕\mathrm{Al}\mathrm{As}(\mathrm{Ga}\mathrm{As})$ periodical structures with InAs and AlAs quantum dots by means of Raman spectroscopy. Experiments on the asymmetric $\mathrm{Ga}\mathrm{As}∕\mathrm{In}\mathrm{As}∕\mathrm{Al}\mathrm{As}$ quantum dot structures allowed us to investigate the interface phonons localized in the vicinity of corrugated dot/matrix interface and planar interface between the matrix and wetting layer. The interface phonon frequencies in the quantum dot structures determined from the experiment are compared to those calculated in the framework of the dielectric continuum model. A good agreement is obtained, especially if the preferential shape of the quantum dots determined from transmission electron microscopy is taken into account.

measured from non-oxidized area reveal asymmetric lineshape of LO phonons in InAs QDs and demonstrate its low-frequency shift with increasing excitation energy that is explained by QD size distribution and phonon confinement insmaller-size dots. Raman spectra taken from oxidized area show an increase ofthe LO peak intensity and the shift of thephonon line position towards higher frequency. The first effect is explained by formation of wide bandgap aluminium

Raman spectroscopy which provides valuable information on the structural parameters of QDs was used for monitoring of the lateral oxidation of InAs/AlAs QD structures and study of the phonon properties of InAs QDs in aluminium oxide matrix. Optical phonons of InAs QD's were found to be affected by both strain and confinement. Raman spectra measured from non-oxidized area reveal asymmetric lineshape of LO phonons in InAs QDs and demonstrate its low-frequency shift with increasing excitation energy that is explained by QD size distribution and phonon confinement in smaller-size dots. Raman spectra taken from oxidized area show an increase of the LO peak intensity and the shift of the phonon line position towards higher frequency. The first effect is explained by formation of wide bandgap aluminium oxide matrix that leads to the shift of confined electronic states in InAs QDs closer to the resonance with the laser excitation energy. The latter is caused by increasing mechanical strain in InAs QDs due to a shrinkage of the aluminium oxide layers. At the boundaries of oxidized/non-oxidized areas the presence of amorphous and crystalline As clusters is evident.

Fundamental vibrations in Ge/Si structures with strained and relaxed Ge quantum dots (QDs) grown by molecular beam epitaxy were investigated using resonant Raman spectroscopy. Transmission electron microscopy experiments show that the strained Ge QDs are typical “hut clusters” with base size of 15nm and a height of 2nm. A two mode distribution in size (100–200nm and 3–6nm) is found for relaxed QDs. The Raman efficiencies of the Ge optical phonons as a function of excitation energy reveal maxima at 2.35–2.41eV attributed to the E0 resonance in Ge QDs due to electronic confinement. The frequency positions of optical phonons localized in Ge “hut clusters” under non-resonant conditions correspond to fully strained Ge QDs while the frequency position of optical phonons in relaxed Ge QDs corresponds to the value in bulk Ge. With increasing excitation energy (2.5–2.7eV) the position of the Ge optical phonons shifts downwards due to size-confinement effect of optical phonons in strained and relaxed Ge QDs, indicating the presence of a QD size distribution in Ge dot structures.

This study reports the use of surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS), both independent and in combination, to investigate Raman enhancement of films under different confinement geometries. The experiments are performed on ultrathin cobalt phthalocyanine (CoPc) films deposited on specially designed SERS structures. The SERS structures are fabricated by electron-beam lithography and contain nanostructured gold films and gold dimer arrays with controlled size and internanocluster distance. Such structures allow investigation of the effects of nanocluster size and internanocluster distance, excitation wavelength, and polarization of light upon the electromagnetic SERS enhancement. Significant enhancement of the Raman scattering by CoPc is observed under 632.8 nm excitation because of the double resonance originating from the energy match between the laser excitation and the localized surface plasmon and electronic transitions in CoPc. The SERS signal of CoPc is further enhanced by decreasing the internanocluster distance. Maximum SERS enhancement occurs when the polarization of the incident light is perpendicular to the dimer axis. Under 514.5 nm excitation, nanostructured gold films give greater enhancement than any of the nanocluster arrays, with the highest enhancement realized using the so-called “gap-mode TERS” wherein the SERS structures are probed in the TERS condition. The TERS experiment is performed using a customized TERS setup and all-metal atomic force microscopy tips custom fabricated. In terms of obtaining the ultimate sensitivity in Raman spectroscopy, further enhancement is achieved by confining the electromagnetic field in a gap between two metallic nanostructures either by using SERS or by combining SERS and TERS.

CdZnS quantum dots (QDs) with systematically varied Zn content (from 0 to 100%) are formed in an organic matrix using the Langmuir–Blodgett technique. Annealing of the QD structures leads to a removal of the organic matrix and an increase in the Zn content for free-standing CdZnS QDs. After annealing, the size of QDs as determined from UV–vis absorption experiments is in good agreement with electron microscopy measurements. Analysis of UV–vis absorption and Raman scattering data demonstrates strong changes in the content of the CdZnS QDs upon annealing. A model of the process of QD formation is developed using the precipitation model and is found to adequately describe the experimental results.

The enhancement of Raman scattering by optical phonon modes in quantum dots was achieved in resonant and surface-enhanced Raman scattering experiments by approaching the laser energy to the energy of either the interband transitions or the localized surface plasmons in silver nanoclusters deposited onto the nanostructures. Resonant Raman scattering by TO, LO, and SO phonons as well as their overtones was observed for PbS, ZnS, and ZnO quantum dots while enhancement for LO and SO modes in CdS quantum dots with a factor of about 700 was measured in surface enhanced Raman scattering experiments. Multiple phonon Raman scattering observed up to 5th and 7th order for CdS and ZnO, respectively, confirms the high crystalline quality of the grown QDs.

Phonon spectra of CdS, ZnS, PbS, CuS, Ag2S, and ZnO quantum dots formed by using the Langmuir–Blodgett technology are investigated by Raman and infrared spectroscopies. The Raman spectra of structures show peaks corresponding to the scattering by longitudinal and transverse optical (LO and TO) phonons localized in quantum dots that confirm the formation of nanocrystals. In addition to TO and LO phonon modes, the modes observed in the IR spectra between the frequency positions of LO and TO phonons are attributed to the surface optical phonons in quantum dots.

Confined optical phohon modes were observed in reflection spectra of GaAs/AlAs superlattices . It gave the possibility to measure the dispersion of TO-phonons of GaAs and AlAs. 1. iNTRODUCTION By now the confinement of optical phonons in superlattices (SL's) was observed by Raman scatte-ring which Is the second order process with respect to the light. IR-absorbtion or reflection Is thefirst order process and therefore in this case the interpretation of experimental results can be pre-sented in a simpler way. Moreover due to the symmetry selection rules some phonons are forbiddenin Raman but active in 1R measurements. In t his paper we report on the first observation of confinedoptical phonons in SLs GaAs/AlAs by IR-reflection. 2. EXPERIMENTAL The samples under investigation were GaAs/AlAs SL's with different periods grown on GaAs [100]substrates by Molecular Beam Epitaxy. IR-spectra were measured by Fourier-transform spectrometerBruker IFS-113 V at temperature 4.2 K.

SiGe nanoislands grown in a silicon matrix at temperatures of 300 to 600°C are studied using Raman spectroscopy and electroreflectance. For islands grown at relatively low temperatures (300–500°C), phonon bands are observed to have a doublet structure. It is shown that changes in the percentage composition, size, and shape of nanoislands and, hence, in the elastic stresses (depending on the growth temperature of the structures) have a significant effect on the energies of optical electronic interband transitions in the islands. As a consequence, the resonance conditions for Raman scattering also change. It is found that interdiffusion from the silicon substrate and the cover layer (determining the mixed composition of SiGe islands) is of importance even at low growth temperatures of nanostructures (300–400°C).

Properties of the buried silicon oxide layer in Si–Si bonded wafers upon annealing were studied using Infrared (IR) spectroscopy and high resolution transmission electron microscopy (HRTEM). IR spectra of chemically etched Si–Si bonded wafers allow the thickness of the buried oxide layers to be evaluated. The increasing thickness of the buried oxide layer with annealing temperature is determined via a curve fitting procedure of IR spectra measured in the spectral range of longitudinal optical and transversal optical phonons in silicon oxide. The behavior observed is in very good agreement with that obtained from HRTEM measurements.

We present the results of an infrared (IR) spectroscopic investigation of interfaces between two hydrophilic Si wafers bonded at low temperature. Multiple internal transmission IR spectra were recorded of the bonds, with different chemical pretreatments of Si surfaces employed before bonding. The analysis of IR spectra shows that the number of O–H and H–Si–Ox species at the interface depends strongly on the chemical pretreatment type, which determines the bonding energy. The annealing procedure used in the bonding process leads to dissociation of water molecules, oxidation of silicon at the interfaces, and diffusion of hydrogen into silicon oxide layer formed at the interface. The difference in bonding processes is discussed.

Multiple internal reflection and transmission IR spectra of hydrophobic and hydrophilic Si wafers, Si wafers with thermally grown SiO2 layers, and Si wafers bonded at high and room temperature were investigated. It was found that the surface of the as-prepared hydrophobic wafer is terminated by hydrogen and water molecules, while the IR spectra of hydrophilic wafer demonstrate only the presence of water molecules at the surface. IR spectra of Si wafers covered by a thermally grown SiO2 layer exhibit a number of the strong absorption bands assigned to combinational phonon bands in SiO2. The wafer bonding leads to the appearance of siloxane and hydroxyl groups at the buried interface whose absorption bands were observed in IR spectra. A rearrangement of atoms at the buried interface takes place after annealing of Si bonded wafers. IR spectra of room temperature bonds show a large number of water molecules and presence of the hydrogen in the oxide layer at the interface.

The optical phonon modes in short-period GaAs/AlAs superlattices were investigated by means of Raman spectroscopy and far-infrared reflection spectroscopy using a grating coupler technique. Grating couplers provide a wave vector transfer parallel to the layers, enabling study of in-plane dispersion of the phonon modes in the superlattice structure. The mixing of confined and interface optical modes was observed as the in-plane phonon wave vector was varied. The experimental frequencies of the superlattice optical modes obtained from infrared and Raman spectra are in good agreement with calculations performed using a dielectric continuum model.

The vibrational spectrum of ultra-thin layer GaSb/AlSb superlattices was investigated in detail by infrared (IR) and Raman spectroscopies. The effect of confinement of the transverse and longitudinal optical phonons in both types of the layers was studied. The dispersions of optical phonons of the GaSb and the AlSb obtained from the analysis of the Raman and IR spectra are in a good accordance with the theoretical data and results of neutron scattering experiments. First- and second-order Raman spectroscopy indicates the presence of intermixture of atoms at the interfaces in the GaSb/AlSb superlattices.

Vibrational properties of self-assembled InAs quantum dots (QD’s) embedded in AlAs and aluminium oxide were studied by Raman spectroscopy. The InAs/AlAs QD structures were grown by molecular beam epitaxy on GaAs (001) substrates. The following main features of the phonon spectra of InAs/AlAs QD nanostructures were observed: 1) asymmetric lines of QD LO phonons affected by strain, confinement and size inhomogeneity of QD’s; 2) confined phonons of InAs wetting layer (WL); 3) two bands of interface phonons in the AlAs frequency region, attributed to modes associated with the planar interface WL/AlAs matrix and the three-dimensional QD/matrix interface; 4) doublets of folded acoustic phonons caused by periodicity in the multilayer QD structures. The influence of growth temperature, varied from 420 to 550°C, on the morphology of QD’s was investigated. QD’s grown at 420°C are found to have the smallest size. Increasing the temperature up to 480°C leads to the formation of larger InAs islands and improved size homogeneity. Further temperature elevation (above 500°C) causes partial re-evaporation of InAs leading to a decrease of QD size and density, and, finally, their complete disappearance. InAs QD’s embedded in aluminium oxide were fabricated by selective oxidation of the AlAs matrix in self-assembled InAs/AlAs QD’s. Micro-Raman spectroscopy data show that depending on oxidation conditions (humidity, temperature) InAs QD’s in an oxide matrix can be even more strained than before oxidation, or become fully relaxed. At the boundaries of oxidized/non-oxidized areas the presence of amorphous and crystalline As clusters is evident.