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The dynamics of anomalous changes in the microstructure, as well as optical and electrical properties of microcrystalline VO 2 thin films on Si substrates during a reversible temperature-induced metal-insulator phase transition (MIT), were studied by high-resolution X-ray diffractometry (XRD), micro-Raman spectroscopy, and resistivity measurements. Temperature-dependent XRD studies of microcrystalline VO 2 films revealed the coexistence of monoclinic VO 2 (M1) and tetragonal VO 2 (R) structural phases near the MIT, attributable to deformation inhomogeneities and grain size variations. It was determined that inhomogeneous microstructural distortion is the primary factor influencing the MIT in strained VO 2 films. Concurrently, significant variations in the resistivity hysteresis were observed in association with the phase transitions. The structural phase transition (SPT) in VO 2 films was investigated via temperature-dependent micro-Raman spectroscopy, which elucidated the microstructural influence on the MIT. As the VO 2 (M1) temperature approached the critical SPT temperature (340 K), the narrow Raman spectrum of the insulating phase transitioned into a broadband spectrum characteristic of the metallic VO 2 (R) phase, marked by four pronounced peaks at approximately 230 cm−1 (B 1g), 400 cm−1 (E g), 550 cm−1 (A 1g), and 635 cm−1 (B 2g). The analysis of the V–V and V–O vibrational modes in VO 2 indicates that alterations in the V–V and V–O bond lengths are crucial to the temperature-driven SPT from the low-temperature monoclinic VO 2 (M1) phase to the high-temperature tetragonal VO 2 (R) phase. The observed hysteretic temperature dependence of the Raman intensities for V–V and V–O modes shows a quantitative correlation with the resistivity measurements of the VO 2 films, providing insights into the interplay between the SPT and the MIT. The results obtained are pivotal for comprehending the structural and electronic behaviors of nanoscale films and hold significant implications for their application in functional devices. [Display omitted] • Temperature-dependent characterization of Raman, XRD, and resistivity of microcrystalline VO 2 thin films was carried out. • The transformation of the VO 2 from M1 to the mixture M1 + R and further to the R phase was observed. • The correspondence of the V–V and V–O vibrations to the vibrational modes of VO 2 (M1) was found. [ABSTRACT FROM AUTHOR]

The Co-doped ZnO microwires (MWs) were grown using the optical furnace method. We used Scanning electron microscopy (SEM), polarized micro-Raman spectroscopy, photoluminescence (PL) and optical absorption spectroscopy to systematic investigation of the optical and structural properties of Co-doped ZnO MWs. The SEM analysis reveals that Co-doped ZnO MWs has hexagonal facets and cavity inside. The EDS results confirmed the presence and non-uniform distribution of Co impurities in the samples. Co doping of ZnO MWs leads to the decreased intensity, drastically broadening and high-energy shift of the NBE PL band. The red emission band at 1.85 eV originates from 2 E( 2 G) → 4 A 2 ( 4 F) intra-3d-transition of Co 2+ in the ZnO lattice has been observed. The intense structured absorption bands within the near infrared ranges 3800–4800 and 5500–9000 cm −1 are caused by electronic spin-allowed transitions 4 T 2 (F) ← 4 A 2 (F) and 4 T 1 (F) ← 4 A 2 (F) of the tetrahedrally coordinated Co 2+ (3 d 7 ) ions substituting Zn 2+ ions in Co-doped ZnO MWs. Micro-Raman studies of Co doped ZnO MWs show doping/disorder induced additional modes as compared to the undoped sample. The resonant enhancement of the additional local Co-related A 1 -symmetry Raman mode is observed in the parallel polarization geometry y ( z , z ) y ¯ . For the Co doped ZnO MWs, the enhancement of the additional Co-related local vibration mode with an increase in the excitation photon energy is also observed in the Raman spectra. [ABSTRACT FROM AUTHOR]

Abstract: Two-period structures with and without vertical coupling between indirect and direct bandgap InAs quantum dots (QDs) both with type I band alignment, grown by molecular-beam epitaxy, were investigated by confocal Raman and photoluminescence (PL) microspectroscopy. The observed blue shift of PL band of the indirect (direct) bandgap QD by 20 (80)meV with decrease of thickness of Ga(Al)As intermediate layer between two InAs QD layers from 30 to 8nm is considered as caused by increase of elastic strains (decrease of QDs sizes) in QD layers and by coupling between QDs electronic states. Scanning confocal resonant Raman microspectroscopy was applied for non-destructive evaluation of composition at various depths along the thickness of vertical coupling of the upper InAs/AlGaAs and lower InAs/AlAs QDs layers of the sandwich structures. Based on the analysis of determined from the in-depth Raman spectra optical phonons frequencies, the depth distribution of composition in InAlAs and GaAlAs alloy layers formed as a result of strain-driven enhanced interdiffusion was determined. [Copyright &y& Elsevier]

The effect of Mn-doping on the structural, morphological, optical and magnetic properties of the ZnO:Mn nanorods (NRs) synthesized by aqueous chemical process is reported. Grown ZnO:Mn NRs are shown to have hexagonal end facets and the diameters increasing with nominal Mn content. Optical absorption measurements show a decrease in optical band gap with increase of Mn concentration. Raman spectroscopy revealed significant modification of the lattice vibrational properties of the ZnO matrix upon Mn doping. The additional Mn-related vibrational mode, intensity of which increases with amount of Mn can be regarded as an evidence of Mn incorporation into the host lattice of the ZnO. At high Mn concentrations, coexistence of hexagonal Zn 1 − x Mn x O phase along with the secondary phases of ZnMn 2 O 4 cubic spinel is revealed. Magnetic properties of ZnO:Mn NRs are studied by combinatorial atomic force microscopy and magnetic force microscopy imaging, and obtained clear magnetic contrast at room temperature provides a strong evidence of ferromagnetic behavior. [ABSTRACT FROM AUTHOR]

Abstract: The aging of the photoluminescence (PL) in bio-conjugated and non-conjugated CdSeTe–ZnS core–shell quantum dots (QDs) is studied by the micro-PL, micro-Raman and X-ray diffraction (XRD) in the samples of buffered QD solution dried on a crystalline Si wafer and stored in the atmospheric ambience for about 2years. The aging of the PL consists in a “blue” spectral shift of the PL band, an increase in PL band half-width and the decrease in the PL intensity. These changes are more pronounced in the conjugated QD samples. The XRD analysis of the aged samples revealed that the QD core diameter is reduced by ∼1.5nm in the conjugated QDs as compared to the non-conjugated ones. The possible mechanism of PL spectrum aging is the oxidation that decreases the QD core dimension. It is concluded that the bio-conjugation promotes QD oxidation and the mechanism of the effect is proposed. [Copyright &y& Elsevier]

In this paper we investigate the doping effect of FeO and Fe 2 O 3 on the structural, optical and magnetic properties of ZnO layers prepared by a new stencil-free technique. Samples were characterized by X-ray diffraction (XRD), atom force and magnetic force microscopy, photoluminescence and Raman spectroscopy. A quite high quality of the printed Fe-doped ZnO layers was demonstrated. It was shown that the incorporated Fe2+ or Fe3+ ions substitute Zn2+ ions in ZnO lattice and, unlike the doped layers prepared by other technological methods, were uniformly distributed in the Zn2+ sites. The levels of doping with different impurities that make it possible to obtain layers free of second phase inclusions were established. The printed ZnO:Fe layers illustrated pronounced ferromagnetic behavior at ambient conditions. The values of the magnetic field correlated with the impurity content. The value of magnetization of the ZnO:Fe3+ layers was shown to be approximately twice that of the printed ZnO:Fe2+ layers. At the same time, magnetization of ZnO:Fe2+ layers was approximately the same as of the printed ZnO:Co2+ and ZnO:Mn2+ layers studied by us previously. The higher magnetization observed in ZnO:Fe3+ layers was supposed to be due to the carrier-mediated mechanism of magnetization in these layers. • Polycrystalline layers of ZnO doped with Fe2+and Fe3+ ions are manufactured by a method of stencil-free printing developed. • The printed Fe-doped ZnO layers exhibit ferromagnetic behavior at room temperature. • The value of magnetization in the ZnO:Fe3+ layers is twice that in the printed layers of ZnO:Fe2+, ZnO:Co2+ and ZnO:Mn2+. • A simple and cheap method for stencil-free printing of DMS layers is promising for fabricating the spintronics elements. [ABSTRACT FROM AUTHOR]

The results of studies of printed ZnO:Co polycrystalline layers are first described. The layers with Co concentration of 0.78, 2.09 and 5.42 at.% were printed by a new stencil-free method developed by the authors and then were recrystallized at a temperature 1000–1100 °C. It was shown that the layers were polycrystalline with a typical grain size about 500 nm, were densely packed and had a rather uniform single-phase wurtzite structure. The influence of Co doping on the structure, composition, photoluminescence, optical absorption, confocal micro-Raman spectra and the magnetic properties of the layers was investigated. It was shown that Co ions substituted Zn2+ ions and were uniformly distributed in the ZnO lattice whereas in previous publications on ZnO:Co only the statistical average distribution of Co in ZnO films was reported. In was also found that, with increasing Co contamination, Raman spectra showed systematic frequency shift and broadening of the E 2 (high) and E 2 (low) phonon modes. The optical band gap of the layers decreased with increasing Co contamination and the lattice parameters a and c were found to depend slightly on the Co content. At cryogenic temperatures the donor bound excitons dominated in the photoluminescence spectra of ZnO:Co layers which indicated that the layers were of a good crystalline quality and had a n-type conductivity. Magnetization measurements made by the method of magnetic force microscopy (MFM) revealed a clear magnetic contrast in 2D magnetization maps, providing the evidence of in-plane ferromagnetic magnetization at room temperature. Magnetization was shown to be increased with increasing Co content. The direct correlation between the magnetic behavior of ZnO:Сo polycrystalline layers and their microstructure was identified. In particular, it was shown that secondary Co-related spinel phases, if any, were localized at the grain boundaries of the ZnO:Co microcrystallites. • Сo-doped ZnO polycrystalline layers with a different cobalt content have been printed by the developed stencil-free technique. • Cobalt ions are shown to be uniformly distributed in the Zn sites of the ZnO lattice. • The printed ZnO:Co layers exhibit inplane magnetization at room temperature. [ABSTRACT FROM AUTHOR]

• Mn-doped nanosized titanium dioxide powders were synthesized by a sol–gel method. • Mn doping leads to the predominance of the paramagnetic contribution to the magnetization over the diamagnetic contribution and a small increase in the number of the ferromagnetic clusters. • The linear part along with the diamagnetic contribution typical for metal oxides is due to the contribution of two types of paramagnetic centers. • These regions do not interact magnetically, and the powder as a whole exhibits superparamagnetic behavior. Studies of magnetization of undoped and Mn-doped nanosized titanium dioxide powders showed that its dependence on the magnetic field can be approximated by the function that is a linear combination of two Langevin functions with different parameters. The linear part along with the diamagnetic contribution typical for metal oxides is due to the contribution of two types of paramagnetic centers. The first one is present in both undoped and doped powders. As follows from the published models, the centers are complex lattice defects Ti+3 ions + O− vacancies. The second is the vast majority of the manganese ions (and related oxide vacancies) in the doped powders that are uniformly distributed over all nanoparticles. The nonlinear part, even present in the undoped samples, is caused by the contribution of a small number of regions with a high magnetic moment (ferromagnetic clusters). These regions do not interact magnetically, and the powder as a whole exhibits superparamagnetic behavior. According to our estimates, the introduction of Mn into the TiO 2 lattice mainly leads to the predominance of the paramagnetic contribution to the magnetization over the diamagnetic contribution characteristic of the TiO 2 lattice and a small increase in the number of the ferromagnetic clusters. [ABSTRACT FROM AUTHOR]

The influence of argon and oxygen partial pressure on the structure, morphology, and optical properties of NiO films deposited on glass substrate by radio-frequency magnetron sputtering in layer-by-layer growth regime are presented. The argon and oxygen partial pressures were varied in the range of 0.4–4 Pa. XRD measurements reveal the formation of NiO films without preferred orientation of crystallites. The average transmittance of the deposited NiO films was found to be in the range 33–73 % while the optical band gap, calculated from absorption spectra, varied from 2.9 to 3.3 eV. AFM measurements revealed that the grain size and surface roughness changed in the range of 24–55 nm and 1.4–4.3 nm, respectively. The electrical resistivity of NiO films varied from 2.4 to 880 Ohm·cm. The NiO films deposited by layer-by-layer growth regime in magnetron sputtering demonstrate a suitable structure and good optical properties for various applications. [ABSTRACT FROM AUTHOR]

Novel stable ZnO photocatalyst prepared via simple high-thermal processing of resorcinol-formaldehyde/zinc acetate mixture was synthesized for photocatalytic purposes. As a reference, pure ZnO was obtained using Zn(CH 3 CO 2 ) 2 . The UV–vis spectra demonstrate an intensive absorption of composite ZnO within the visible region, in contrast to pure ZnO (white). The kinetic parameters of the diclofenac sodium photodecomposition reaction reflect higher activity of composite ZnO unlike pure ZnO and P25 (Evonik). Comparative study of bisphenol A degradation during Advanced Oxidation Processes involving ZnO and visible light irradiation demonstrated outstanding role of synthesized photocatalyst. [ABSTRACT FROM AUTHOR]

Quantum-chemical modeling of the geometry of PVC molecules and the calculation of Raman scattering spectra were performed. The calculated spectra are in good agreement with the experimental ones, including the extraction of adjacent Cl atoms. The Raman spectra of PVC-MWCNT nanocomposites with various filler content with functionalization during electron irradiation with an absorption dose of 1 Mrad were obtained. It was shown that with the change of MWCNT content in irradiated samples there is a complex rearrangement of the molecular structure of PVC and conjugate sequences due to the influence of nanotubes and irradiation, as well as to the aggregation of MWCNT. [ABSTRACT FROM AUTHOR]