[en] The sublimation and van der Waals (vdW) epitaxy on Bi₂Se₃(0001) surface have been first visualized using in situ reflection electron microscopy. When Bi₂Se₃(0001) surface was exposed to a Se molecular beam (up to 0.1 nm/s) and heated to ∼400°C, we observed ascending motion of atomic steps corresponding to congruent Bi₂Se₃ sublimation. During the sublimation, grooves made by probe lithography act as sources of atomic steps: groove depth increases and generates atomic steps that move in the ascending direction away from the source. We used this phenomenon to create self-organized regularly-spaced zigzag atomic steps having 1 nm height on the Bi₂Se₃(0001) surface. The deposition of Bi (up to ∼0.01 nm/s) onto the Bi₂Se₃(0001) surface at constant Se flux (up to ∼0.1 nm/s) reversed the direction of the step flow, and vdW epitaxy was observed. The deposition of In and Se onto the Bi₂Se₃(0001) surface at ∼400°C led to the epitaxial growth of layered In₂Se₃. This vdW heteroepitaxy started with 2D island nucleation and, after 3–5 nm growth, continued with a screw-dislocation-driven formation of 3D islands. Ex situ Raman scattering measurements have shown that the grown 20-nm-thick In₂Se₃ film exhibits vibrational modes that originate from the β-In₂Se₃ crystal phase. (paper)

[en] We report on the study of surface enhanced infrared absorption (SEIRA) by steroid hormone cortisol molecules with different concentrations deposited on linear Au nanoantenna arrays. Localized surface plasmon resonances (LSPRs) arise in the nanoantennas under the influence of external electromagnetic radiation. LSPR frequency depends mainly on the nanoantenna length and can vary from the visible to the terahertz range. We establish the ratio between the structural parameters of nanoantenna arrays and LSPR frequencies based on the results of 3D electrodynamic simulations. Using nanolithography we fabricate nanoantenna arrays having LSPR frequencies close to the frequencies of the most intense absorption modes of steroid hormone cortisol. We deposit cortisol molecules onto the surface of nanoantenna arrays by drop– coating. SEIRA spectra of the nanoantenna arrays make it possible the determination of the presence of cortisol and establishing the sensitivity limit of this method. Thus, we show possibility of SEIRA application for cortisol concentration analysis. (paper)

[en] A review of recent applications of Raman spectroscopy as a fast, sensitive, and non-destructive technique for exploring II–VI semiconductor nanocrystals fabricated by various methods (colloidal chemistry, Langmuir–Blodgett method, diffusion-limited growth) is presented. Specific size-related features revealed in the nanocrystal Raman spectra (phonon confinement, surface phonons) are analysed, as well as more complicated size effects for ultrasmall nanocrystals (NCs) related to the activation of the phonon density of states modified by surface reconstruction. Similarities and differences of the Raman scattering in II–VI and III–V or elemental (Si) semiconductor NCs are briefly analysed. Implementation of resonant conditions and application of infrared absorption analysis, complementary to the Raman spectroscopy—resulting in the observation of phonon modes ‘silent’ in conventional Raman scattering processes—are discussed. Furthermore, Raman spectroscopy is employed for fast and efficient assessment of the composition of matrix-embedded ternary II–VI nanocrystals, as well as more complicated multimode quaternary II–VI systems. Selective probing of electronic and vibrational spectra of different parts of heterogeneous NCs (such as core–shell systems) by tuning the excitation wavelength in resonant Raman scattering is considered. The analysis of phonon spectra is applied to the quantitative estimation of strain in the core and shell, and degree of interface intermixing, as well as to checking the surface oxidation. The above approaches and phenomena are further explored in more complex compound NCs beyond II–VI, such as CuInS₂/ZnS. Recent results in the field of surface- and tip-enhanced Raman spectroscopy and surface-enhanced infrared absorption are analysed showing the perspectives of Raman spectroscopy as a tool for investigation of single-nanocrystal phonon spectra. (topical review)

[en] 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.

No abstract available

[en] Resonant Raman scattering spectra of glass-embedded CdS_1-xSe_x nanocrystals are measured and complemented with TEM and optical absorption as well as photoluminescence data. The selectivity of the resonant Raman process not only for the size, but also for the composition of nanocrystals within the ensemble, is directly observed in the dependence of phonon band frequency, linewidth and shape on the excitation wavelength

[en] 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, E₂(high) and A₁(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.

[en] GaN nanocolumnar structures were grown by plasma-assisted molecular beam epitaxy (PAMBE) and also fabricated by electron cyclotron resonance reactive ion etching (ECR-RIE) of a compact GaN film parallel to the [111] direction of the Si(111) substrates. Scanning electron microscopy shows that the nanocolumns fabricated by PAMBE have a length of about 300-500 nm with diameters ranging from 20 to 150 nm while nanowhiskers formed by RIE have diameters of 40-80 nm and a height between 1.4 and 1.7 μm. A comparative study of the vibrational spectrum (including optical and interface phonons) of the nanostructures using conventional macro-Raman and micro-Raman scattering as well as surface-enhanced Raman scattering is presented