Journal of Applied Spectroscopy最新文献

Formation and dispersion processes of monoclinic and hexagonal molybdenum-trioxide phases during thermally induced polycondensation of molybdic acid in aqueous medium at 100°C were investigated using dynamic light scattering. Programmed variation of the reaction medium concentration made it possible to control effectively particle nucleation and growth in the solution. Right prismatic crystallites of metastable hexagonal molybdenum trioxide with an average size from 200–500 nm to 10 μm could be obtained.

Nanostructured thin films on a silicon substrate were obtained by the action of high-frequency repetitively pulsed f ~ 10–13 kHz laser radiation with wavelength λ = 1.064 μm and power density q = 57 MW/cm² on an La_0.13Bi_0.87FeO₃ target at a pressure in the vacuum chamber p = 4.6 Pa. The morphology of the La_0.13Bi_0.87FeO₃ thin films was studied using atomic force microscopy. Transmission spectra of the films in the visible and near- and mid-IR regions were obtained. The electrophysical characteristics of the La_0.13Bi_0.87FeO₃ structures were analyzed.

A novel technique was developed for the preparation of bilayer sandwich-type structures containing monolayers or laterally-oriented silver nanoplates electrostatically deposited onto thin polymer films. The surface-enhanced Raman scattering (SERS) signal of 4-mercaptobenzoic acid in the ligand layer of the silver nanoplates was found to depend on the surface concentration of the deposited silver nanoplates in the monolayer. A two-fold enhancement was found for the surface-enhanced Raman scattering signal of the analyte located in the gaps between the silver nanoplate monolayers compared to the signal from a single silver nanoplate monolayer with identical surface concentration of the analyte molecules.

A chemiluminescence technique was used to establish that, in contrast to TiO₂ photocatalysts, TiO₂:MoO₃ composite photocatalysts suppress the photogeneration of superoxide ions, while the capture of photoelectrons in the MoO₃ phase to give reduced Mo(V) states creates conditions for the long-term generation of hydrogen peroxide capable of acting as a biocide. The TiO₂:MoO₃ accumulating photocatalysts were shown to be fully reusable and the cycle of photocharging followed hydrogen peroxide generation can be repeated multiple times.

The surface of hydroxyapatite (HA) was functionalized with silver nanoparticles by reducing silver nitrate in the presence of glucose or hydrazine hydrochloride. Two types of (HA)Ag nanocomposite were obtained presumably possessing excess negative charge ((HA)Ag-I) or positive charge ((HA)Ag-II). Plasmonic coatings of (HA)Ag-I and (HA)Ag-II nanoparticles were formed on the surface of glass substrates using the droplet deposition method and their structural and spectral properties were studied. A comparative study of the intensity of surface-enhanced Raman scattering (SERS) spectra of cationic and anionic porphyrins CuTMpyP4 and CuTPPS4 as well as rhodamine 6G adsorbed on the surface of both types of nanocomposites was carried out. Plasmonic structures (HA)Ag-I provide the greatest enhancement of the SERS signal for the cationic porphyrin CuTMpyP4, while high spectral intensity is observed for the anionic porphyrin CuTPPS4 adsorbed on films of the (HA)Ag-II composite, which is almost forty times higher than for (HA)Ag-I. For Rh6G molecules with charge +1, the efficiency of the SERS signal amplification by (HA)Ag-II nanostructures is several times higher than by plasmonic films of (HA)Ag-I. Hence, feasibility was demonstrated for obtaining various SERS-active substrates with highly-efficient SERS enhancement for both anionic and cationic analyte molecules by changing the synthesis conditions.

The electronic structure of cylindrical conjugated macromolecules of boron and nitrogen atoms modeling short open nanotubes of zigzag (n,0) and armchair types (n,n) was calculated using density functional theory with the B3LYP hybrid functional in the 6–31G basis set. Their stability as a function of diameter and length was studied. It was shown that a constant electric fi eld applied along the tubes led to a compression of the energy gap in the electron energy spectrum of the nanotubes up to ≈0.2 eV. The threshold of fi eld electron emission from boron-nitride nanotubes was calculated in the framework of the emission molecular orbitals theory. It was shown that, despite conjugated systems of boron-nitride and carbon nanotubes being isoelectronic, substitution of carbon atoms in the nanotube framework of nitrogen and boron atoms led to a decrease in the threshold fi eld strength of the fi eld emission. It was found that the diameter of boron-nitride nanotubes had virtually no eff ect on the emission molecular orbital.

Techniques developed at the Institute of Physics of the National Academy of Sciences of Belarus for increasing the sensitivity of atomic and molecular spectroscopy in studies of microsamples taken from paintings (more than 200 artworks) are reviewed. A microscopic sample of a paint layer from the painting "The Birth of Venus" studied using laser-induced breakdown spectroscopy, Fourier transform infrared spectroscopy, and surface enhanced Raman scattering is presented as an example of the multi-analytical approach. The results of the study allow one to conclude that the work was created in the glue tempera technique. Chrome orange, lithopone, and iron oxide pigments (like red or yellow ochers, for example) were identified. This determined that the artwork could have been created no earlier than the last quarter of the 19th century.

Optically detectable magnetic resonance spectra were measured for ensembles of NV-centers in CVD diamonds with different ¹³C contents. The obtained spectra were described using a model based on the spin Hamiltonian. The magnitude of the magnetic field applied to the sample was estimated using the constructed model and experimental data.

Magnetically induced (MI) transitions of ⁸⁵Rb atoms, D₂-lines 5S_1/2 → 5P_3/2, F_g = 3 → F_e = 1 with circular polarization σ^–, the intensities of which are zero in a zero magnetic field, have been studied experimentally and theoretically. However, their intensities increase significantly in magnetic fields of 0.5–1 kG. The MI transition F_g = 3 → F_e = 1 was used for the first time at the probe radiation frequency to implement the process of electromagnetically induced transparency (EIT). The frequency of the coupling radiation was resonant with the F_g = 2 → F_e = 1 transition. The generated EIT resonance was located on the low-frequency tail of the spectrum. It was shown that EIT resonance was formed only when the probe and coupling radiations had the same circular polarization σ^–. This was true for MI transitions F_e – F_g = ΔF = –2.

Peculiarities of absorption spectra formation of porphine derivatives upon attachment of an NO₂ group to the C_m-position of the tetrapyrrole macrocycle have been studied. The molecular conformation of the substituted porphine molecule was optimized using quantum chemistry methods. The energies of molecular orbitals were determined. Absorption spectra were calculated. It was found that the electronic interaction between the macrocycle and the NO₂ group is determined by the orientation of the nitro group relative to the macrocycle mean plane. It has been established that the energies of the LUMO and HOMO–1 orbitals depend significantly on the dihedral angle θ between the macrocycle mean plane and the nitro group plane, while the energies of the LUMO+1 and HOMO orbitals vary slightly. As a result, the S₀ → S₁ and S₀ → S₂ absorption bands have bathochromic shifts, the magnitudes of which are different and depend on the configurational composition of the transitions. The oscillator strength of the S₀ → S₁ transition turns out to be greatest in the coplanar conformer, which has minimal configuration interaction. The oscillator strength of the S₀ → S₁ transition increases sharply in the orthogonal conformer, in which the LUMO and LUMO+1 are quasi-degenerate. All spectral characteristics can be presented as functions of the weighted sum of cos² θ and cos²2θ, taking into account the configuration composition of the electronic transitions.