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In this paper, the study of Raman signal enhancement due to interaction between ZnO rods and pork spleen DNA is reported. ZnO microstructures were synthesized by the Sol-Gel method and afterward combined with porcine spleen DNA extracted in the previous stages, following standardized cell lysis, deproteinization, and precipitation processes. Raman spectroscopy was used for the characterization of structures of ZnO and ZnO-DNA complex, and the results show the respective bands of ZnO wurtzite hexagonal phase for modes E2 (M), A1(TO), E2(High), E1(LO), and 2LO. Due to the SERS effect in the spectral range from 200 to 1800 cm,-1 Raman bands caused by vibrations of the deoxyribose C-O-C binding were also observed, producing deformation of the ring as shown in the 559 cm-1 peak. The broad band at 782 cm-1, together with the complex vibration of the string 5'-COPO-C3′, is over a wide band of thymine (790 cm-1) or cytosine (780 cm-1). A prominent band near 1098 cm-1 assigned to symmetric stretching vibration phosphodioxy group (PO2-) DNA backbone is most favoured in intensity by the addition of ZnO particles originated by the SERS effect. This effect suggests a possible mechanism for enhancing the Raman signal due to the electromagnetic interaction between a DNA molecule and the flat surface of the ZnO rod. [ABSTRACT FROM AUTHOR]

In this work, powders were prepared Zn1-xCoxO (0.00 ≤ x ≤ 0.05) at temperatures of calcination of 773, 823, and 873 K by sol gel methods (citrate route). In the XRD patterns, all the observed diffraction peaks could be indexed to ZnO wurtzite structure, and no other impurity phase was found, leading to the conclusion that the Co ions in fact entered into ZnO crystal. Rietveld analysis shows that all samples have a hexagonal wurtzite structure with mean lattice constants a = 3.2507 A˚ and c = 5.2073 A˚, and that no important changes of the lattice parameters were observed as a consequence of Co doping or temperature of calcination. The average crystallite size was measured using Scherrer's method, and the results show that when Co concentration increased from 0 to 5%, crystallite size varied depending on the sample calcination temperature (Tc). In general, the lower the Tc, the higher the crystallite size, and at a particular Tc, the higher the Co concentration, the higher the crystallite size. The last one suggests the promotion of crystal growth as a result of Co doping in ZnO at least for the synthesis method used here. Raman spectroscopy results showed an increase of the defect concentration as a consequence of an increase in Co contents. [ABSTRACT FROM AUTHOR]

Abstract: The role of the magnetoelectric effect upon optical reflectivity is studied by adapting an electrodynamic-based model for a system composed by a 2D metallic film in contact with an extended multiferroic material exhibiting weak ferromagnetism. The well-known Nakayama's boundary condition is reformulated by taking into account the magnetoelectric coupling as well as an externally applied magnetic field B in an arbitrary direction. It is found that the reflectance shows strong fluctuations for incident radiation close to the characteristic antiferromagnetic resonance frequency associated with the multiferroic material in the THz regime. These results were verified for a 10nm metallic foil by using a finite element method (FEM) and the Rouard's approach, for a wide range of wavelengths (0.1–5mm), showing good agreement with respect to Nakayama's outcome, for the particular material BaMnF4. [Copyright &y& Elsevier]

Elastic modulus of the radial section of the Guadua angustifolia Kunth variety Bicolor was studied by technique of propagation of acoustic waves; the signal time delay in the samples was used as the control parameter. The studies were carried out in the culm cross-section in radial direction. The results indicate that the elastic modulus and the propagation velocity of the longitudinal wave in each of the cross-sections varied from 2.5 x 107 to 1.6 x 109 Pa and from 1370 to 250 m/s for the inside and outside region of the culm, respectively. This behavior is due to the inhomogeneity, the water concentration, the fiber density, and the silicon concentration. The Raman spectroscopy analysis showed bands associated with hemicellulose, cellulose (carbon-carbon bonds), hydroxides carbon, and lignin. Silicone polymer compounds were identified by gas chromatography/mass spectroscopy. [ABSTRACT FROM AUTHOR]

Small hexagonal-shaped ZnO Nanorods (ZnO-NRs) were synthesized on PET (Polyethylene terephthalate)/ITO substrates through a conventional wet chemical method assisted by ultrasound using Zn(NO3)2 and hexamethylenetetramine (HMT) as precursors. The reaction was carried out in three steps: i) ZnO seeds synthesis, ii) ZnO seeds deposition, and iii) ultrasound-assisted unidirectional growth of ZnO-NRs. Aligned ZnO-NRs were characterized by HRTEM, SAED, EFSEM, UV-Vis and Raman spectroscopy; their lengths and thicknesses ranged 240 - 350 nm and 25 - 80 nm, respectively on PET/ITO substrates. Results indicated that ZnO-NRs were grown on a 200 nm thick ZnO rigid film formed by a dipcoating method which has brittle nature. It could hinder the use of these substrates in the construction of flexible devices. ZnO-NRs/(PET/ITO) transmits a UV-Vis radiation between 50% and 80%, whose variation depends on the synthesis conditions. Optical band-gap of the synthesized material approximately 3.3 [ABSTRACT FROM AUTHOR]

In this study we emphasize on the role of the geometry upon the magnetic and critical properties of ferromagnetic manganite nanoparticles having stoichiometry La2/3 Ca1/3MnO3. To do that, we consider a set of fine particles of different shapes (spherical and polyhedral) containing approximately the same amount of ions (~8000 magnetic Mn ions) and distributed according to a simple cubic structure. The method is based on the standard Monte Carlo-Metropolis technique. Our theoretical framework employs a classical Heisenberg-like Hamiltonian, where different magnetic nearest neighbor superexchange integrals, preserving orbital ordering for this composition, have been considered. Results showed the specific behavior of the Curie temperature and low temperature coercive force. The studies were done depending on the nanoparticle shapes. [ABSTRACT FROM AUTHOR]

A Monte Carlo simulation study of the exchange bias properties in ferromagnetic/antiferromagnetic (FMJAFM) bilayers by using a classical Heisenberg model and the Metropolis algorithm is addressed. In our model several contributions including nearest neighbors exchange interactions, two different interface couplings, magnetocrystalline anisotropy, and a Zeeman term were considered. Our study focuses on the influence of FM and AFM layer thicknesses (dF and dA) on hysteresis loops, particularly exchange bias field (HEB) and coercive force (Hc). Results reveal that the influence of dA on the exchange bias phenomenon is negligible, while dF produces an important effect on HEB and Hc. Such behaviors agree with several models and results reported in the literature. Concretely, our model allows inferring a dependence of the exchange bias field with the FM layer thickness proportional to 1/(dF)m characterized by an exponent m = 0.71 ± 0.11. On the Other hand, coercive force exhibits a power law increase with the FM layer thickness when thermal fluctuations become relevant. For completeness, thermal stability of the hysteretic properties is finally presented and discussed. [ABSTRACT FROM AUTHOR]

In this work, we report the calculus the D term in the octahedral sites and tetrahedral positions in presence of a magnetic field of the spinel type ZnCr2S4. In this work, we report the behavior the EPR signal of the system ZnCr2S4as a function of temperature in range between 103 and 293 K. The samples were prepared by heating a mixture of the elements Zn, Cr and S in an evacuated silica tube at 800 °C. The results observed by ESR, where the typical chromium signal is observed in octahedral sites in a center field of 3427 Gauss corresponding to the chromium's configuration in tetrahedral sites when the term Dtetra/ Doct ≅ 9/4. [ABSTRACT FROM AUTHOR]

We show results of conductivity measurements using the spectroscopy of impedance SI, in the frequency range from 5 to 100 kHz under the room temperature for the polycrystalline composite Pr0.5Ca0.5MnO3. The real part of the conductivity in function with the frequency σ(ω) for different temperatures, revealed a dependency of potential type for the high frequency region; a behavior known as Jonscher`s universal law Aωn, where A and n were found to be weakly temperature-dependent. On the other hand, this dependency shows that the conductions in these systems are thermally activated. That is to say, the carrier jump frequency, intervening in the charge transport is a function of temperature ωp(T). In the formalism of the complex dielectrical module it is possible to discern that there is a distribution of relaxation times independent from temperature and they do not follow a Debye behavior type in the temperature range from 210 to 300 K. [ABSTRACT FROM AUTHOR]

Carbon films were grown on Si substrates by the Hot Filament Chemical Vapor Deposition technique (HFCVD), the structural characterization was made by means of X-ray Photoemission Spectroscopy (XPS). The C1s, the valence band, and Si2p1, Si2s and O1s regions were analyze& Hybridization sp² and sp³ was found in both the valence band and the C1s region. The sp²/sp³ ratio is indicative of the presence of a diamond-like carbon (DLC) structure. The information given by the Si2p1, Si2s, and O1s bond energies allows us to detect the presence of SiO2 in the intermediate growth phases. [ABSTRACT FROM AUTHOR]

From the behaviour of the Raman emission spectrum, it is possible to obtain structural and compositional information of the material under study. Analysis of this information is made difficult due to low intensities of the signal, relative to noise in measurement process, and the signals generated by the nature of the compounds. Raman spectra are composed of overlapping emission bands associated with the samples, and the noise generated by fluorescence, which constitutes the baseline. The useful information is screened by the fluorescence, hiding emission peaks, which are assigned to the normal modes of vibration of low intensity. Signal processing techniques, and pattern recognition that allow to reconstruct the Raman spectrum of ZnO by subtracting the fluorescence signal, are presented in this work. In the linearizing, the Huber and the truncated quadratic functions are used, both symmetric and asymmetric, the baseline is adjusted to a lower-order polynomial. [ABSTRACT FROM AUTHOR]

This work presents a comparison in the ZnO films crystalline structure grown by chemical bath on glass substrates by two different Silar methods. The films were grown using zinc sulfate as precursor and ammonium and ammonium hydroxide as complex agent. The employed processes were named as Silar 1 and Silar 2. The films characterization was carry out by XRD to determine their phase and crystallinity, by UV-Vis the gap was found around 3, 3 eV, the vibration modes were analyzed by Raman microscopy. It was study the films behavior in front of the annealing process. It was found that the films grown by Silar 2 present better crystallinity than the Silar 1. The crystallinity improves with annealing temperature increase. [ABSTRACT FROM AUTHOR]

The mixed oxide whit a perovskite structure La 0.5 Sr 0.5 MnO 3 was prepared by the solid reaction method starting from precursors available on the market. The X-ray diffraction analysis to an room temperature, permits to infer that the composite corresponds to a pseudo-cubic crystal structure with lattice parameters of a = 5.4802 ± 0.01322 Å. Magnetic thermogravimetric measures (TMG) showed a continuous and soft decreasing in the magnetic force value (which is proportional to the sample magnetization), as the sample is heated almost up to zero in the value of the Curie temperature (T c ), suggesting that the transition phase is of second order. Calorimetric measures (MDSC) at temperature from 313 to 473 K, showed a small anomaly in the specific heat near the para-ferromagnetic phase transition (PM-FMM). The Curie temperature obtained through the measures MTG and MDSC is about 360 K. [ABSTRACT FROM AUTHOR]