Search

The far-infrared spectroscopy was used to analyze optical properties of PbTe single crystals doped with different amounts of Si. A dielectric function that takes into account the plasmon-phonon interaction was employed in the measured data manipulation. Two frequencies of plasmon-phonon coupled modes were obtained with the best-fit method, whereas the values for LO mode and plasma frequency (ωP) were calculated. The best-fit to the experimentally obtained spectra agrees very well with the theoretical prediction.

In this paper, we describe synthesis and characterization of YVO 4 and Eu 3+ -doped YVO 4 nanopowders. Two methods of preparation were used—solution combustion synthesis (SCS) and classical ceramic method (CCM)—and compared. Morphology and structure of all samples were characterized with atomic-force microscopy (AFM), X-ray diffraction (XRD), and field-emission scanning electron microscopy (SEM). Raman spectroscopy was used to discuss the isotope-like effect. It is confirmed that doping with Eu ions results in a change of Raman spectra of doped samples—new modes arise, and intensity of existing ones change. Influence of different preparation methods on isotope-like effect is presented with detailed calculations of shifted modes. © 2019 John Wiley & Sons, Ltd.

In the present work experimental study of the ZnO@ZnS core-shell nanostructure with an active layer obtained by conversion of zinc oxide powders with H2S is reported. Тhe prepared structures were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and far-infrared spectroscopy. Top surface optical phonon (TSO) in ZnO, characteristic for the cylindrical nano-objects, the surface optical phonon (SOP) mode of ZnS, and SOP modes in ZnO@ZnS core-shell nanostructure are registered. Local mode of oxygen in ZnS and gap mode of sulfur in ZnO are also registered. This result is due to the existence of an active layer in the space between ZnO core and ZnS shell, which is very important for the application of these materials as thermoelectrics. © 2020 John Wiley & Sons, Ltd.

Structural and optical properties of CdTe thin films were investigated applying atomic force microscopy (AFM), XRD powder technique, Raman spectroscopy and far–infrared spectroscopy. CdTe thin films were prepared by using thermal evaporation technique. In the analysis of the far – infrared reflection spectra, numerical model for calculating the reflectivity coefficient for system which includes films and substrate has been applied. Effective permittivity of film mixture (CdTe and air) was modeled by Maxwell – Garnet approximation. We reveal the existence of surface optical phonon (SOP) mode and coupled plasmon-SOP modes (CPSOPM).

The analysis of the optical properties of mechanochemically synthesized stannite Cu2FeSnS4 nanocrystals has been performed using far-infrared spectroscopy. The Cu2FeSnS4 stannite nanocrystals were synthesized mechanochemically from elemental precursors Cu, Fe, Sn, and S. Milling time was 45, 60, 90 and 120 min. Reflectivity spectra were analyzed using the classical form of the dielectric function, which includes the phonon and the free carrier contribution. The influence of milling time on synthesis of stannite Cu2FeSnS4 is observed. Among the modes that are characteristic for the stannite Cu2FeSnS4, we registered the modes of binary phases of FeS and SnS. The total disappearance of the binary phases of FeS and SnS and forming pure Cu2FeSnS4 is observed when the milling time is 120 min. Effective permittivity of Cu2FeSnS4 and binary phases of FeS and SnS were modeled by Maxwell – Garnet approximation.

We have studied the magnetic properties of nanocrystals of ZnO :MnO prepared by traditional wet chemistry method. The detailed structural and morphological characterization was performed. The results of systematic measurements of AC magnetic susceptibility as a function of temperature and frequency as well as DC magnetization are reported. We observed two different types of magnetic behavior depending on the concentration doping. For samples with low nominal content (up to 30 wt% of MnO), superparamagnetic behavior was observed. We attribute the observed superparamagnetism to the presence of nanosized ZnMnO 3 phase. For nanocrystals doped above nominal 60 wt% of MnO ferrimagnetism was detected with TC at around 42 K. This magnetic behavior we assign to the presence of nanosized Mn3O4 phase.

The Solution Combustion Synthesis (SCS) method was used to prepare nanopowders of europium doped cubic Gd2Zr2O7 nanopowders. The surface of the samples have been investigated using atomic force spectroscopy (AFM) and far-infrared spectroscopy (FIR). Far-infrared reflectivity spectra of Eu3+ doped Gd2Zr2O7 nanopowders were measured at room temperature in spectral region between 80 and 650 cm−1. The Maxwell–Garnet formula was used to model dielectric function of Eu3+ doped Gd2Zr2O7 nanopowders as mixtures of homogenous spherical inclusions in air.

The analysis of the vibrational properties of mechanochemically synthesized stannite Cu2FeSnS4 nanocrystals has been performed. X-ray diffraction (XRD) and Raman spectroscopy are techniques used to characterize the crystal structure and compositional purity of stannite Cu2FeSnS4 nanoparticles. The detailed analysis of the experimental spectra has allowed us to determine the frequency and symmetry assignment of the main and weaker peaks. The milling time influence on synthesis stannite Cu2FeSnS4 from elemental precursors Cu, Fe, Sn and S is observed. Among the peaks that are characteristic for the stannite Cu2FeSnS4, we registered the modes of binary phases of FeS and SnS. The total disappearance of the binary phases of FeS and SnS is observed when the milling time is longer than 90 min.

The Raman spectra of Eu3+ doped Gd2Zr2O7 nanopowders were measured. We registered three phonons at 177 cm−1, 268 cm−1, and 592 cm−1, as well as their overtones at 354 cm−1, 445 cm−1, 708 cm−1, 1062 cm−1, 1184 cm−1, ∼1530 cm−1, and ∼1720 cm−1. The phonon at 592 cm−1 is known to be characteristic for Gd2Zr2O7 fluorite-type structure; however, the other two have not been registered so far. We found that the position of the newly detected phonons agrees well with the observed electron-phonon interaction. On the other hand, the registered multiphonon processes were a consequence of miniaturization that further induced changes in electronic structure of Eu3+ doped Gd2Zr2O7 nanopowders.

Thin films of CuSe2 nanoparticles embedded in selenium matrix were prepared by vacuum evaporation method on a glass substrate at room temperature. The optical properties of the films were investigated by photoluminescence spectroscopy (T=20-300K) and UV-VIS spectroscopy (T = 300K). Surface morphology was investigated by scanning electron microscopy. The band gap for direct transition in CuSe2 was found to be in the range of 2.72-2.75 eV and that for indirect transition is in the range of 1.71-1.75 eV determined by UV-VIS spectroscopy. On the other hand, selenium exhibits direct band gap in the range of 2.33-2.36 eV. All estimated band gaps slightly decrease with the increase of the film thickness. Photoluminescence spectra of the thin films clearly show emission bands at about 1.63 and 2.32 eV at room temperature, with no shift observed with decreasing temperature. A model was proposed for explaining such anomaly.

The polymer nanocomposite ZnS/Poly (methylmethacrylate) was prepared by the solution casting method and its structural and optical properties were investigated using XRD, SEM, TEM, HRTEM , and Raman spectroscopy . The basic material, ZnS , has the cubic structure and its crystallite size was estimated to be 2.3 nm, which implies that a strong confinement regime is in effect. Analysis of Raman spectra was performed using the fitting procedure based on effective medium theory. As a result, the surface optical phonon (SOP) mode was detected. It was found that the shape and position of the SOP mode depend on the type of the composite.

Copper selenide thin films of three different thicknesses have been prepared by vacuum evaporation method on a glass substrate at room temperature. The optical properties of the films were investigated by UV-VIS-NIR spectroscopy and photoluminescence spectroscopy. Surface morphology was investigated by field-emission scanning electron microscopy. Copper selenide exhibits both direct and indirect transitions. The band gap for direct transition is found to be ~2.7 eV and that for indirect transition it is ~1.70 eV. Photoluminescence spectra of copper selenide thin films have also been analyzed, which show emission peaks at 530, 550, and 760 nm. The latter corresponds to indirect transition in investigated material. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III45003]

CdGeAs 2 is a promising material for optical applications. It has the wide transparency range between 2.3 and 18 μm except harmful absorption region at 5.5 μm. Its presence is related to the crystal lattice quality. The measurements of Raman and far infrared reflectivity spectra of the series of Cd 1− x Mn x GeAs 2 samples (0 ≤ x ≤ 0.037) were carried out in spectral range from 60 to 400 cm −1 , at room temperature. Beside all expected optical modes three defect modes are registered at about 125, 170 and 235 cm −1 . Their intensities are related to tetragonal distortion of lattice (Δ) so we connected them with lattice defects Ge As , usually formed in this material, and CdAs 2 and Cd 3 As 2 clusters whose characteristic frequencies match these values. Antisite defects Ge As are connected to energy level at about 200 meV and to absorption at 5.5 μm. Based on obtained results we can conclude that doping with small amount of manganese ( x = 0.004) results in slight deformation of CdGeAs 2 crystal lattice and consequently considerably reducing the formation of antisite defects Ge As .

Nanocrystalline samples of ZnO(Mn) were synthesized by hydrothermal method. The morphology of the samples was studied by HRTEM and SEM. X-ray diffraction was used to determine composition of the samples (ZnO and ZnMn2O4) and the mean crystalline size (from 16 to 99 nm). In this paper we report the experimental spectra of Raman scattering (from 100 to 1600 cm−1) with surface optical phonons (SOP) in range of 497–538 cm−1 as well as formation of new phases MnO, Mn3O4 and ZnMnO3. The phonon of registered phase's exhibit effects connected to phase concentration, while the SOP phonon mode exhibit significant confinement effect.

ZnS nanoparticles were synthesized mechanochemically by high-energy milling, with three different milling times (5 min, 10 min and 20 min). Nitrogen adsorption method was used for examining specific surface area and texture of obtained powders. It was found that all samples are completely mesoporous. The optical properties were studied by far-infrared spectroscopy at room temperature in spectral region of 50-600 cm(-1). The analysis of the far-infrared reflectivity spectra was made by the fitting procedure. The dielectric function of ZnS nanoparticles is modeled as a mixture of homogenous spherical inclusions in air by the Maxwell-Garnet formula. In the analysis of the far-infrared reflection spectra, appearance of combined plasmon-LO phonon modes (CPPMs) with high phonon damping are observed, which causes decrease of coupled plasmon-phonon frequencies. (C) 2016 Elsevier B.V. All rights reserved.

Semiconductors of II-IV-V2 type with chalcopyrite structure have been studied for several decades. Due to advances in materials synthesis technologies, and doping with various elements, the possibilities of their application have expanded. In this paper, polycrystalline ZnSnSb2 + Mn was examined with the aim to explain the connection of its high free carrier concentration with the material structure and influence on optical properties. Two samples of Zn1-xMnxSnSb2 with different compositions (x = 0.027 and x = 0.076) and significant difference in carrier concentrations were analyzed. Their structural properties were examined by x-ray diffraction, optical microscopy, and AFM. The existence of several different phases - ZnSnSb2, ZnSb, SnSb, and small amounts of Sn and MnSb, as well as very complex microstructures, were registered. It was found that the high free carrier concentrations are caused by a large number of defects, especially zinc vacancies. Optical properties were analyzed using IR spectroscopy at room temperature. Based on the analysis of IR reflection spectra, the presence of plasmon - phonons interaction was registered. It was determined that three ZnSnSb2 phonons of B2 symmetry interact with plasma, which then leads to the change of their positions. A detailed analysis of this interaction provides insight into the behavior of some other material parameters. Also, vibration modes of ZnSb and SnSb phases were registered on the spectra. Knowledge of phonon behavior and their interaction with plasma is important for possible applications, especially as a thermoelectric material.

The nanopowders of (ZnO)1–x(Al2O3)x, where x ranges from 0 to 0.7, were obtained by two chemical methods: the co-precipitation/calcination and hydrothermal synthesis. The first assessment of structural and optical properties of the obtained nanopowders was undertaken by the SEM, XRD, Raman and far-infrared spectroscopy, which was followed by the photoluminescence spectroscopy at room temperature. The obtained far-infrared reflectivity spectra were analyzed using the fitting procedure. The dielectric function of ZnO–Al2O3 nanopowders was modeled by the Maxwell-Garnet formula under the assumption that the nanopowders are a mixture of homogenous spherical inclusions in air. The combined plasmon-LO phonon modes (CPPM) were observed in the far-infrared reflection spectra. The photoluminescence spectra contain emissions related to the presence of ZnO, ZnAl2O4, and AlOOH phases in the nanomaterial, which is in agreement with the results obtained by other experiments.

In this paper we present photoluminescence measurements of CdSe nanoparticles embedded in transparent glass. Sample is prepared using an original technique, which combines both heat treatment and ultraviolet laser irradiation. Photoluminescence spectra displayed one main emission band at 2.14 eV. We identify this bands energy as basic interband transition in CdSe nanoparticle. We calculated energy of basic (1sh–1se) transition in spherical CdSe quantum dot (QD), within infinite potential barrier, in effective-mass approximation. On the basis of this model, average radius of synthesized CdSe QDs is about 3 nm, which is in consistence with AFM measurements and UV–VIS absorption measurements.

The interest in thorough description of Zn 1– x Mn x GeAs 2 arises from its suitability for application in the field of non-linear optics. The room temperature far-infrared reflectivity spectra of single crystals Zn 1– x Mn x GeAs 2 , where 0 ≤ x ≤ 0.078, were measured in the spectral range from 80 cm −1 to 500 cm −1 . The spectra were analyzed by fitting procedure using a dielectric function which includes interaction between a plasmon and two different phonons. The detected phonons are in excellent agreement with the theoretical predictions. The MnAs cluster phonons are detected, as well.

Nanocrystaline samples of ZnO(Fe) were synthesized by traditional wet chemical method followed by calcinations. Samples were characterized by X-ray diffraction to determine composition of the samples (ZnO, ZnFe 2 O 4 and Fe 2 O 3 ) and the mean crystalline size (from 8 to 51 nm). In this paper we report the experimental spectra of Raman scattering (from 200 to 1600 cm −1 ) with surface optical phonons (SOP) in range of 500–550 cm −1 . The phonon of registered phase’s exhibit effects connected to phase concentration, while the SOP phonon mode exhibit significant confinement effect.

Properties of CdS thin films were investigated applying atomic force microscopy (AFM) and Raman spectroscopy. CdS thin films were prepared by using thermal evaporation technique under base pressure 2 x 10-5 torr. The quality of these films was investigated by AFM spectroscopy. We apply Raman scattering to investigate optical properties of CdS thin films, and reveal existence of surface optical phonon (SOP) mode at 297 cm-1. Effective permittivity of mixture were modeled by Maxwell - Garnet approximation. [Projekat Ministarstva nauke Republike Srbije, br. 45003]

The far-infrared reflectivity spectra of CdTe 0.97 Se 0.03 and CdTe 0.97 Se 0.03 (In) single crystals were measured at different temperatures. The analysis of the far-infrared spectra was carried out by a fitting procedure based on the dielectric function which includes spatial distribution of free carriers as well as their influence on the plasmon–phonon interaction. We found that the long wavelength optical phonon modes of CdTe 1 − x Se x mixed crystals exhibit a two-mode behavior. The local In mode at about 160 cm −1 is observed. In both sample, a surface layer with a low concentration of free carriers (depleted region) are formed.

Behavior of PbTe samples doped with different amount of Cr, prepared by two methods of synthesis is analyzed using galvanomagnetic measurements and far-infrared spectroscopy. The far-infrared reflectivity spectra of PbTe(Cr) alloys were measured in the 50–650 cm −1 spectral range at different temperatures and analyzed using a numerical fitting procedure based on the plasmon–phonon interaction model. The two local Cr modes at about 260 cm −1 and 480 cm −1 together with the strong plasmon–phonon coupling are observed. The persistent photoconductivity is registered. Using results of galvanomagnetic measurements the carrier concentrations is determined and hence we obtained the Fermi level temperature dependence.

Nanocrystalline samples of ZnO(Mn) were characterized by X-ray diffraction to determine composition of the samples (ZnO, Mn3O4, ZnMn2O4 and ZnMnO3) and the mean crystalline size (between 9 and 13 nm for ZnMnO3 phases, from 24 to 47 nm for Mn3O4 phases and above 100 nm for ZnO and ZnMn2O4 phases). In this paper we report the experimental spectra of Raman scattering (from 200 to 1600 cm−1) with surface optical phonons (SOP) in range of 520–575 cm−1. The phonon of registered phases exhibits effects connected to phase concentration, while the SOP phonon mode exhibits significant confinement effect.

Our work deals with the problem of producing a complex metal-ceramic composite using the processes of internal oxidation (IO) and severe plastic deformation. For this purpose, Cu-Al alloy with 0.4wt.% of Al was used. IO of sample serves in the first step of the processing as a means for attaining a fine dispersion of nanosized oxide particles in the metal matrix. Production technology continues with repeated application of severe plastic deformation (SPD) of the resulting metalmatrix composite to produce the bulk nanoscaled structural material. SPD was carried out with equal channel angular pressing (ECAP), which allowed that the material could be subjected to an intense plastic strain through simple shear. Microstructural characteristics of one phase and multiphase material was studied on internally oxidized Cu with 0.4wt.% of Al sample composed of one phase copper-aluminum solid solution in the core and fine dispersed oxide particles in the same matrix in the mantle region. In this manner AFM, X-ray diffraction and Raman spectroscopy were used. Local structures in plastically deformed samples reflect presence of Cu, CuO, Cu2O, Cu4O3 or Al2O3 structural characteristics, depending on type of sample. [Projekat Ministarstva nauke Republike Srbije, br. III45003]

Currently, complex ferromagnetic semiconductor systems are of significant interest due to their potential applicability in spintronics. A key feature in order to use semiconductor materials in spintronics is the presence of room temperature ferromagnetism. This feature was recently observed and is intensively studied in several Mn-alloyed II-IV-V2 group diluted magnetic semiconductor systems. The paper reviews the origin of room temperature ferromagnetism in II-IV-V2 compounds. In view of our recent reports the room temperature ferromagnetism in Mn-alloyed chalcopyrite semiconductors with more than 5 molar % of Mn is due to the presence of MnAs clusters. The solubility of magnetic impurities in bulk II-IV-V2 materials is of the order of a few percent, depending on the alloy composition. High values of the conducting hole - Mn ion exchange constant Jpd have significant value equal to 0.75 eV for Zn0.997Mn0.003GeAs2. The sample quality has significant effect on the magnetotransport of the alloy. The magnetoresistance of the alloy change main physical mechanism from spin-disorder scattering and weak localization for homogeneous samples to cluster-related geometrical effect observed for nanocomposite samples. The magnetoresistance of the II-IV-V2 alloys can be then tuned up to a few hundreds of percent via changes of the chemical composition of the alloy as well as a degree of disorder present in a material. [Projekat Ministarstva nauke Republike Srbije, br. III45003]

Nano spinel ferrites MFe2O4 (M=Ni, Mn, Zn) were obtained by soft mechanochemical synthesis in a planetary ball mill. The appropriate mixture of oxide and hydroxide powders was used as initial compounds. All of this mixture of powders was mechanically activated, uniaxial pressed and sintered at 1100°C/2h. The phase composition of the powders and sintered samples were analyzed by XRD and Raman spectroscopy. Morphologies were examined by SEM. In this study, the AC-conductivity and DC-resistivity of sintered samples of MFe2O4 (M= Ni, Mn, Zn) ferrites were measured at different frequencies and at room temperature. The values of the electrical conductivities show an increase with increasing temperature, which indicated the semiconducting behavior of the studied ferrites. The conduction phenomenon of the investigated samples could be explained on the basis of hopping model. The complex impedance spectroscopy analysis was used to study the effect of grain and grain boundary on the electrical properties of all three obtained ferrites [Projekat Ministarstva nauke Republike Srbije, br. III 45003]

The properties of 3 monolayers (ml) CdTe self-assembled quantum dot (SAQD) sample are investigated by means of Raman and photoluminescence (PL) spectroscopy. The PL spectrum is characterized by two main emission peaks, both connected with the existence of QDs. One presents direct deexcitation to ground state and the other one is optical phonon ( ω = 204.2 cm −1 ) assisted deexcitation. One-phonon Raman spectra at room temperature show surface-optical phonon at 201 cm −1 . At temperatures below 200 K, multiphonon processes are registered. Multiphonon maximum depends on the temperature, and laser energy.

Two zinc ferrite nanoparticle materials were prepared by the same method – soft mechanochemical synthesis, but starting from different powder mixtures: (1) Zn(OH) 2 /α-Fe 2 O 3 and (2) Zn(OH) 2 /Fe(OH) 3 . In both cases a single phase system was obtained after 18 h of milling. The progress of the synthesis was controlled by X-ray diffractometry (XRD), Raman spectroscopy, TEM and magnetic measurements. Analysis of the XRD patterns by Rietveld refinement allowed determination of the cation inversion degree for both obtained single phase ZnFe 2 O 4 samples. The sample obtained from mixture (1) has the cation inversion degree 0.3482 and the sample obtained from mixture (2) 0.400. Magnetization measurements were confirmed that the degrees of the inversion were well estimated. Comparison with published data shows that used method of synthesis gives nano powder samples with extremely high values of saturation magnetizations: sample (1) 78.3 emu g −1 and sample (2) 91.5 emu g −1 at T = 4.5 K.

The aim of the present work is to study the magnetic properties of nanocrystals of ZnO(Co) prepared by two methods of synthesis. We used the microwave assisted hydrothermal synthesis and traditional wet chemistry method followed by calcination. The detailed structural characterization was performed by means of X-ray diffraction and micro-Raman spectroscopy measurements. The magnetic properties were studied by means of AC susceptibility χ. All samples demonstrated Curie–Weiss behavior at higher temperatures. For calcination process, the negative values of the Curie–Weiss θ temperature were observed indicating the predominance of antiferromagnetic interactions. For samples prepared by hydrothermal synthesis, we observed the breakdown of predominance of antiferromagnetic interactions.

The properties of CdS thin films were investigated by applying atomic force microscopy (AFM), Raman and far-infrared spectroscopy. CdS thin films were prepared by using the thermal evaporation technique under base pressure 2 × 10 −5 torr. The quality of these films was investigated by AFM spectroscopy. We applied Raman scattering and far-infrared spectroscopy to investigate the optical properties of CdS thin films, and reveal the existence of Surface Optical Phonon (SOP) mode at 297 cm −1 . Effective permittivity of mixture was modeled by Maxwell–Garnet approximation. In the analysis of the far-infrared reflection spectra, a numerical model for calculating the reflectivity coefficient for a system which includes films and substrate was applied.

Bismuth germanium oxide Bi12GeO20 (BGO) has very interesting electrical, optical and magnetic properties. In order to make devices based on this material more flexible, its powder was used for preparing polymer composites. This study reports investigation of the effects of using different solvents and polymers in preparation of BGO composite on the microstructural and optical behaviour of the resulting material. Preparation of such composites by a solution casting method is described. Poly (methyl methacrylate) (PMMA) and polystyrene (PS)) were used as matrix materials and acetone and chloroform as solvents. Their microstructure and the quality of BGO dispersion and deaggregation in polymer matrix were analyzed by SEM, Raman, XRD and optical spectroscopy. The influence of particle size distribution, their shapes, and concentration on the optical transmission is calculated based on Mie scattering theory and discussed, too. This is the peer-reviewed version of the article: Brajovic, L.M., Stojanovic, D.B., Mihailovic, P., Markovic, S.B., Romcevic, M., Mitric, M., Lazovic, V., Dramlic, D., Petricevic, S., Romcevic, N., 2017. Preparation and characterization of bismuth germanium oxide (BGO) polymer composites. Journal of Alloys and Compounds 695, 841–849. [https://doi.org/10.1016/j.jallcom.2016.10.140]

This paper describes the structural and optical properties of Cu-Se-CuSe2 thin films. The surface morphology of thin films was investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Formation of thin films is concluded to proceed unevenly, in the form of islands which later grew into agglomerates. The structural characterization of Cu-Se-CuSe2 thin film was investigated using X-ray diffraction pattern (XRD). The presence of two-phase system is observed. One is the solid solution of Cu in Se and the other is low-pressure modification of CuSe2. The Raman spectroscopy was used to identify and quantify the individual phases present in the films. Red shift and asymmetry of Raman mode characteristic for CuSe2 enable us to estimate nanocrystal dimension. In the analysis of the far-infrared reflection spectra, numerical model for calculating the reflectivity coefficient of layered system, which includes film with nanocrystallite inclusions (modeled by Maxwell–Garnet approximation) and substrate, has been applied. UV–VIS spectroscopy and photoluminescence spectroscopy are employed to estimate direct and indirect band gap of CuSe2.

The aim of the present work is to study influence of preparation method on samples characteristics, creation and behavior of surface optical phonons (SOP) modes with change of concentration of doping elements by micro Raman spectroscopy. Nanocrystalline samples of ZnO(Co) were prepared by use of traditional wet chemistry method followed by calcinations and the microwave assisted hydrothermal synthesis. The phase composition of the samples (ZnO, Co3O4, ZnCo2O4) and the mean crystalline size (14–300 nm) were determined using X-ray diffraction measurements. In this paper we report the experimental spectra of Raman scattering (from 100 to 1600 cm−1) for both type of samples. Main characteristic of experimental Raman spectrum are: sharp peak at 436 cm−1 and broad multi phonon structure at ~1150 cm−1, typical for ZnO; sharp peaks at 194, 482, 521, 618 and 691 cm−1 typical for Co3O4 and sharp peaks at 185, 475, 520, 610 and 690 cm−1 typical for ZnCo2O4 nanoparticles. The phonon of registered phase’s exhibit effects connected to phase concentration, while the SOP phonon mode exhibit significant confinement effect.

On Raman scattering spectra of nanocrystaline samples ZnO(Co) prepared by use of the microwave assisted hydrothermal synthesis, surface optical phonons (SOP) where observed in the range of 519 - 572 cm-1. The mean crystalline size (33 - 300 nm) as well as the phase composition of obtained samples (ZnO, ZnCo2O4) where determinate with X - ray diffraction measurements. These measurements aloud us to study the change of SOP modes position with crystalline size and how change in concentration of doping element CoO influence the change of SOP modes intensity.

Optical properties of p-type Zn1−xMnxGeAs2 for 0 ⩽ x ⩽ 0.078 were investigated by Raman spectroscopy at room temperature. Phonons of ZnGeAs2 are experimentally determined and they are in excellent agreement with those theoretically predicted. Existence of MnAs clusters was confirmed in the sample with the highest concentration of Mn. MnAs was found in α and β phases and their vibrational frequencies are obtained experimentally. Plasmon – two different phonons interaction in Zn1−xMnxGeAs2 is registered and analyzed.

Currently, wide-gap ZnO nanoparticles bear important potential application in electro-optical devices, transparent ultraviolet protection films, and spintronic devices. We have studied the magnetic properties of nanocrystals of ZnO(Fe, Co, Mn) prepared by two methods of synthesis. We have used the microwave assisted hydrothermal synthesis and traditional wet chemistry method followed by calcination. The detailed structural characterization was performed by means of X-ray diffraction and micro-Raman spectroscopy measurements. The morphology of the samples was studied by means of SEM and TEM microscopy. The results of systematic measurements of AC magnetic susceptibility as a function of temperature and frequency as well as SQUID magnetization are presented. The SQUID magnetization measurements revealed a clear bifurcation of the FC and ZFC plots. Such behavior suggested superparamagnetic behavior above the blocking temperature. The dynamic magnetic measurements were performed at small AC magnetic field with amplitude not exceeding 5 Oe and different frequency values (from 7 Hz to 9970 Hz). For ZnO(Fe) and ZnO(Mn), the AC susceptibility maxima has been found for in-phase susceptibility Re(χ) and for out of phase susceptibility Im(χ). We analyzed the observed frequency dependence of the peak temperature in the AC susceptibility curve using the empirical parameter Φ that is a quantitative measure of the frequency shift and is given by the relative shift of the peak temperature per decade shift in frequency, as well as Vogel- Fulcher law. We observed two different types of magnetic behavior, spin-glasslike behavior or superparamagnetic behavior, depending on the synthesis process. For ZnO(Co) nanocrystalline samples high temperature Curie-Weiss behavior in AC magnetic susceptibility was observed. We observed that the determined negative values of the Curie- Weiss temperature θ depend strongly on the nominal content of cobalt oxide. It was shown that for calcination method the values of θ increase with the increase of magnetic ion content indicating enhancement of predominance of antiferromagnetic interactions. For hydrothermal method the opposite effect was observed indicating the breakdown of predominance of aniferromagnetic coupling with the increase of nominal magnetic ion content. This paper gives an in-depth discussion of the structural and magnetic properties of ZnO nanocrystals in addition to the technological issues such as different methods of wet chemical synthesis.

Surface optical phonons (SOP) were observed in the range of 496–572 cm−1 on Raman scattering spectra of nanocrystalline samples of ZnO(Co) prepared by use of the microwave assisted hydrothermal synthesis and traditional wet chemistry method followed by calcinations. The phase composition of the samples (ZnO, Co3O4, ZnCo2O4) and the mean crystalline size (14–300 nm) were determined using X-ray diffraction measurements. The SOP phonon mode exhibit significant size confinement effect, while the phonons of registered phases exhibit effects connected to phase concentration.

Far-infrared reflectivity spectra, in spectral region 50-600 cm(-1) and temperature region 80-300 K, of CdS and Cd1-xMnxS nanocrystals embedded in hexametaphosphate, are presented. The analysis of the far-infrared experimental reflectivity spectrum was made by the fitting procedure. The Maxwell-Garnet effective medium theory is used for modeling an effective dielectric function as well as to separate respond from nanoparticles. To analyze spectra in CdS omega(TO)(approximate to 238 cm(-1)) to omega(TO)(approximate to 305 cm(-1)) spectral region, quantized dipolar modes in a spherical isotropic material quantum dot (QD) are considered in the framework of a continuum model. As to the mechanical boundary conditions rigid sphere is concerned. Experimental far-infrared reflectivity spectra of our samples are in general agreement with the predictions of this model. Experimentally registered and through fitting procedure located features for CdS nanoparticles in spectral region below CdS omega(TO) at: approximate to 102 cm(-1), approximate to 135 cm(-1), approximate to 170 cm(-1) and approximate to 210 cm(-1) are associated to defect induced modes, especially to defects located near the surface of CdS QD. In region over CdS omega(LO), modes are identified as multiphonons. In Cd1-xMnxS QD spectra new reflectivity peaks are at: approximate to 85 cm(-1), approximate to 110 cm(-1) and approximate to 180 cm(-1) in spectral region below CdS omega(TO), approximate to 270 cm(-1) inside CdS omega(TO)-omega(LO) spectral region and approximate to 356 cm(-1) and approximate to 376 cm(-1) in region over CdS omega(LO). First two registered modes are associated to both mass and force constant defects at the surface, and rest four modes are consequence of MnS phases present in the sample. (C) 2012 Published by Elsevier B.V.

Nickel ferrite (NiFe2O4) and manganese ferrite (MnFe2O4) have been prepared by a soft mechanochemical route from mixture of (1) Ni(OH)2 and α-Fe2O3 and (2) Mn(OH)2 and α-Fe2O3 powders in a planetary ball mill. The mixture was activated for varying duration. Soft mechanochemical reaction leading to formation of the NiFe2O4 and MnFe2O4 spinel phases were followed by X-ray di raction, Raman and infrared spectroscopy, scanning and transmission microscopy. The spinel phase formation was rst observed after 4 h of milling (case 1) and after 3 h (case 2) and its formation was completed after 25 h in both cases. The synthesized NiFe2O4 and MnFe2O4 ferrites have a nanocrystalline structure with a crystallite size of about 30 and 40 nm for cases (1) and (2), respectively. There are ve Raman and four IR active modes. In order to understand better the whole process of phase formation, the Mossbauer measurements were done.

New semimagnetic semiconductor Hg 0.91 Mn 0.09 Te-MnSe mixture, grown by Bridgman method, was investigate by Atomic Force Microscopy, X-ray and far-infrared spectroscopy, in order to obtain the necessary feedback information to determine the optimal conditions for crystal growth. The investigated mixture consists of MnSe nanoclasters randomly distributed in Hg 0.91 Mn 0.09 Te matrix. Far-infrared reflectivity spectrum of the Hg 0.91 Mn 0.09 Te-MnSe mixture was measured in the 80–500 cm −1 range at a room temperature. The analysis of the far-infrared spectrum was made by the fitting procedure. The Maxwell-Garnett effective medium theory is used for modeling an effective dielectric function, and on that way calculating both electron and phonon response.

Powdery nickel ferrite, NiFe2O4 has been obtained by soft mechanochemical synthesis in a planetary ball mill. Ni(OH)2 and Fe(OH)3 are used as initial compounds. This mixture was mechanically activated for 25h, uniaxial pressed and sintered at 1100°C for 2h. The phase composition of the sintered sample was analyzed by X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and Raman spectroscopy. Morphologies were examined by scanning electron microscopy (SEM). The electrical DC/resistivity/conductivity at different temperatures was measured using a Source Meter Keithley 2410. An Impedance/Gain-Phase Analyzer (HP-4194) was used to measure the impedance spectra (100Hz - 10MHz) at different temperatures. [Projekat Ministarstva nauke Republike Srbije, br. III 45003 i br. III 45015]