Thin films (~ 150 nm) of amorphous As30Te70−xGax (where x = 0, 1, 3, 6, and 10 at%) are prepared through thermal evaporation of As30Te70−xGax bulk samples on glass substrates. X-ray powder diffraction (XRD) analysis reveals the amorphous nature of the as-prepared As30Te70−xGax thin films. The influence of Ga content on the As30Te70−xGax thin films’ linear and nonlinear optical properties is determined based on the optical reflectance and transmittance spectra. The estimated (direct or indirect) optical bandgap decreases with an increase in Ga content up to 3 at% and then increases, whereas the Urbach energy exhibits an opposite trend. The linear and nonlinear refractive indices, extension coefficient, optical conductivity, electrical conductivity and nonlinear susceptibility, optical density, inter-band transition strength, etc., are found to be significantly influenced by Ga content and the energy of incident waves. The As30Te67Ga3 composition can be considered as a puzzling compound as most of the investigated parameters in As30Te70−xGax alloys demonstrate opposite behaviors around that composition. Moreover, the optical surface resistance and thermal emission of As30Te70−xGax thin films are estimated from the investigated optical parameters and it was found that they are dependent on Ga content. The obtained results enhanced basic understanding and showed that the As–Te–Ga system qualifies for various optoelectronic applications.

In the present study, hybrid organic–inorganic composites were fabricated from epoxy–TEOS (tetraethyl orthosilicate, Si(OC2H5)4) with various ratios (0–10 wt%) of multiwall carbon nanotubes (MWCNTs) as reinforcing nanofillers by the sol–gel method. The effect of the MWCNTs ratios on the structural, optical and mechanical characteristics and the thermal conductivity of the epoxy–TEOS/MWCNTs composites is investigated. The X-ray diffraction (XRD) analysis reveals that the pure epoxy-TEOS is amorphous, while epoxy–TEOS/MWCNTs composites are crystalline with an orthorhombic crystal structure that has an average crystallite size of 3.9 ± 0.15 nm. In addition, thermal stability and thermal conductivity were improved by adding TEOS and MWCNTs, whereas the exothermic peak temperature decreases compared with pure epoxy-TEOS. Similarly, the hardness Shore-D and tensile strength reach the optimum value at 4 wt% MWCNTs content. The significant improvement in the mechanical and thermal properties of the prepared composites could be attributed to the synergistic effect of MWCNTs and epoxy–TEOS which was emphasized by Fourier transform infrared (FTIR) spectroscopy. Moreover, epoxy-TEOS sample has high optical transmittance (T) within the visible region, but the composites samples are transparent at λ  800 nm and have a lower value of T. The indirect optical band gap decreases from 3.59 to 2.91 eV with an increase in MWCNTs fractions from 0 to 10 wt%, respectively. However, the glass transition reflects the onset of decomposition temperatures was also considerably increased. The acquired outcomes such as a large increase in thermal conductivity and tensile stress coupled with reduced T make the composites readily applicable for a variety of applications.

In the present study, hybrid organic–inorganic composites were fabricated from epoxy–TEOS (tetraethyl orthosilicate, Si(OC2H5)4) with various ratios (0–10 wt%) of multiwall carbon nanotubes (MWCNTs) as reinforcing nanofillers by the sol–gel method. The effect of the MWCNTs ratios on the structural, optical and mechanical characteristics and the thermal conductivity of the epoxy–TEOS/MWCNTs composites is investigated. The X-ray diffraction (XRD) analysis reveals that the pure epoxy-TEOS is amorphous, while epoxy–TEOS/MWCNTs composites are crystalline with an orthorhombic crystal structure that has an average crystallite size of 3.9 ± 0.15 nm. In addition, thermal stability and thermal conductivity were improved by adding TEOS and MWCNTs, whereas the exothermic peak temperature decreases compared with pure epoxy-TEOS. Similarly, the hardness Shore-D and tensile strength reach the optimum value at 4 wt% MWCNTs content. The significant improvement in the mechanical and thermal properties of the prepared composites could be attributed to the synergistic effect of MWCNTs and epoxy–TEOS which was emphasized by Fourier transform infrared (FTIR) spectroscopy. Moreover, epoxy-TEOS sample has high optical transmittance (T) within the visible region, but the composites samples are transparent at λ  800 nm and have a lower value of T. The indirect optical band gap decreases from 3.59 to 2.91 eV with an increase in MWCNTs fractions from 0 to 10 wt%, respectively. However, the glass transition reflects the onset of decomposition temperatures was also considerably increased. The acquired outcomes such as a large increase in thermal conductivity and tensile stress coupled with reduced T make the composites readily applicable for a variety of applications.

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Determining paleomagnetic field intensity (paleointensity: PI) for lavas with high reliability and low measurement uncertainty is still difficult to achieve. Some of the factors on which the PI used methods depends are the non-ideal physical and magnetic characteristics of lava sample, grain size, cooling rate effect and thermal stability. Xitle volcano (SW Mexico City) is a good example to illustrate and discuss this problem because several previous PI studies that were carried out on its evolved flow units, have commonly resulted in different mean values with large dispersions. Indeed, 211 published PI data obtained by use of Thellier and microwave experiments gave a mean of 64. 1 μT with a standard deviation of 11. 0 μT. After a careful evaluation, we found that only 134 of these data can be considered reliable, as they meet a set of selection criteria designed in this study. These evaluated data gave an average mean …

Our knowledge of the Earth's magnetic field intensity changes over the past few thousand years is still limited because of the uneven spatial and temporal distribution of data, which also includes the Americas. The present study reports 41 new palaeointensity data covering the past 3600 years which, together with 38 previously published data of similar quality, are used to construct a palaeointensity secular variation curve for Central Mexico. These new data are an important contribution to the global intensity database and will also improve the application of palaeomagnetic dating in Mexico, which is of interest because of the many Holocene monogenetic volcanoes within the Trans-Mexican Volcanic Belt, and of its archaeological heritage. The most conspicuous feature of the new intensity curve is the rapid increase between 400 and 250 BCE, from about 45 to 65 μT. Other relative intensity highs of ≈45–55 μT …

We present 32 new paleomagnetic directions and 21 absolute paleomagnetic intensities (PI) from 33 volcanoes, sampled at 66 sites and covering the last 46 ka. Of these, 29 were radiocarbon-dated, 3 by thermo-luminescence, and one is of historical age (AD 1793). Rock magnetic experiments show that the dominant minerals are magnetite and titanomagnetite of low to intermediate titanium content, and of pseudo single domain size. Paleodirections were determined using stepwise demagnetization protocols, and PI by the IZZI or Thellier-Coe protocols, and strict selection criteria were applied to ensure the reliability of the data. Previously published data were evaluated to fulfill similar quality criteria as our data, resulting in: 65 directional data point; 18 paleointensity entries from lavas; 59 archeointensities are found to be acceptable. All accepted data come from a region within an 860 km radius around Mexico City …

Copper nanoparticles were fabricated and deposited on a glass substrate by spark discharge of copper electrode under different atmospheric conditions for SERS application. An interesting dependence of the deposition process and the formation of different particle structures on the deposition atmospheres were observed. Static air atmosphere ensured the deposition of the Cu particles on the glass surface by avoiding the repulsion between charged Cu particles and the surface of the glass through the formation of CuO, which acts as a seed mediated for nanorods formation. The average diameter of the as-deposited Cu rods was measured by the TEM to be 39 nm. Thermal annealing of the film up to 200 °C resulted in a reduction in the diameter of the nanorods as well as an increase in the rod density. A water solution of dye molecule (crystal violet) with a concentration of 1 × 10–6 to 1 × 10–9 M was dropped on the prepared Cu substrate. Raman signals from dye molecule were detected and their intensities changed according to deposition time, post-annealing temperature and dye concentration. A significant increase in the Raman scattering signal of a dye molecule was observed in the film fabricated at 30 min of deposition time and post-annealed temperature of 200 °C for 1 h. This substrate provides a maximum SERS intensity with a detection limit of 1 × 10–8 M, with an enhancement factor of 3.9 × 103. The SERS performance of the substrates was correlated well with the change in their surface morphologies.

Nanostructured Au33Pd67 alloy films were fabricated on glass using one-step air plasma DC magnetron sputtering. The films exhibited highly sensitive detection of dye molecules (RhB and CV) by the surface-enhanced Raman scattering (SERS). The synthesized films also showed good catalytic properties for the reduction in 4-nitrophenol at pH ≈ 9.8. Such unique characteristic of the films was linked to the evolution of nanostructure, which can be controlled simply by the sputtering time. At the shorter sputtering time (10 and 20 s), the film was composed of isolated particles. By increasing the sputtering time (30 and 40 s), agglomeration of such nanoparticles resulted in the formation of the partially connected island nanostructures (about 38 nm) which can be confirmed by TEM and electrical resistivity measurement. The detection limit of 1 × 10–12 M RhB and 1 × 10–8 M CV with an enhancement factor of 7 × 107 and 3.3 × 104, respectively, was achieved over the film synthesized at the sputtering time of 30 s. The high sensitivity of this film can be ascribed to the strong electromagnetic field at the junction spots formed between the two adjacent islands. Moreover, this film has a slightly lower SERS, and better catalytic properties, in contrast to Au (30 s) film. Finally, the film providing efficient SERS enhancement is not the most active catalyst. Unlike the SERS, the catalytic activity depends highly on the amount of AuPd deposited.

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