Revista Mexicana de Física

New CaRbNaZ (Z=Si and Ge) semiconductor compounds suitable for photovoltaic and thermoelectric devices

2024-09-03T14:10:26+00:00

Semiconductor compounds are a fascinating type of materials that have attracted the attention of scientists because of their ability to enhance green technology by efficiently converting, storing, and transmitting waste heat into electrical energy. This research aimed to investigate the structural, electronic, elastic, optical, and thermoelectric characteristics of newly developed Quaternary Heusler alloys (QHAs) CaRbNaZ (where Z represents Si and Ge). This was achieved using the generalized gradient approximation (GGA) and the Tran-Blaha modified Becke-Johnson (TB-mBJ) potential. For both approximations, CaRbNaSi and CaRbNaGe are found to be nonmagnetic semiconductors with band gaps varying in the range from 0.49 to 1.00 eV. The studied alloys additionally conform to the Slater-Pauling rule, exhibiting a specific magnetic moment of Mtot = 8 − Ztot for nonmagnetic behavior and, therefore, having a total magnetic of 0.00 µB. They possess an optical band gap comparable to the electronic band gap, along with significant absorption properties (90 × 104 and 103 × 104 cm−1 ) in visible and UV regions, respectively, proving that these compounds are promising materials for photovoltaic cells and UV radiation shields. The high merit factor values (0.76 and 0.80) at 300K confirm that CaRbNaZ (Z= Si and Ge) are suitable candidates for thermoelectric devices.

Zn-QDs Synthesis applying simultaneously the techniques of colloidal synthesis and sol gel and phenomenon at Zn2+ → Zn3+ + e−charge transfer

2024-08-10T20:08:16+00:00

ZnO-QD thin solid films are drop deposited on glass substrates and calcined in the air atmosphere at temperatures of 60°C, 100°C, 140°C, 160°C and 210°C, respectively. The samples are examined applying the techniques: Scanning Electron Microscopy (SEM), xRay Diffraction (XRD), Fourier transforms in the Infrared (FTIR), Photoluminescence (PL), Transmittance (% T), and absorbance (α). Tauc model, the band gap (Eg) energy is evaluated. The electrical measurements of Current-Voltage (I-V), the concentration of charge carriers, mobility and Resistance, are registered by Hall Effect. The morphology of the layers shows a structural configuration with stacked compact plates and flakes-like crystalline conglomerates with a fibrous appearance. The films show a Wurtzite-type crystalline phase according to the XRD diffractograms. The grain size increased by 3.6-6.9 nm. The dislocation density (δ) presents a gradual increase with the calcination temperatura δ ( lines /m²) ∼ 1.57×10¹⁵ −2.22×10¹⁵. On FT-IR spectroscopy analysis, various vibrational bands are associated with the CO²₃ ion and by-products generated by the hydrolysis of zinc acetate di-hydrate discussed. The Eg undergoes oscillatory and disorderly shifting towards higher photon energy, caused by faults at crystalline lattice of Eg ∼ 3.7 − 3.87 eV. In optical analysis, the discontinuity located at UV-Vis region is associated in principle at Zn²⁺ → Zn³⁺ + e⁻charge transfer. PL spectra at UV − Vis region records the emission bands with different relative intensity. The asymmetric Gaussian curve is associated with intrinsic defects in the crystal lattice. The deconvolution of the Gaussian curve generates different emission bands assigned to: red (RE) at ∼ 770 nm, blue (BE), green (GE) at 492-520 nm and yellow (YE) at 570-600 nm. The systematic construction of the Schottky diode is done by placing the corresponding thin film on ITO, then PEDOT: PSS was placed, then the silver contact and finally the P − n junction was identified.

Synthesis and characterizaton of silver/silver oxide thin film via chemical bath deposition

2024-08-26T00:05:48+00:00

The chemical bath deposition technique was used to deposit Ag/AgO films on a glass substrate using silver nitrate (AgNO3) and triethanolamine (a polymer matrix) as the complexing agent. X-ray diffraction (XRD) was used to study the crystalline structure of the films, scanning electron microscopy (SEM) was used to study the micrograph/morphology, and energy dispersive spectroscopy (EDS) was used for elemental composition analysis. Four peaks at 2θ values of 38.05°, 44.15°, 64.31°, and 77.41° matched the (111), (200), (220), and (311) peaks, respectively, indicating that the obtained films were crystalline. The Ag/AgO films had a relatively low transmittance value of approximately 12% in the wavelength range of 300 to 1100 nm, a band gap energy of less than 2 eV, and a high absorbance of ≥ 80%, suggesting applications in photothermal, photoelectronic devices/systems, architectural coatings, and other areas where spectrally selective films are of interest.

Theoretical study of the adsorption modes of a process control agent in the growth of PbTe

2024-07-11T23:50:18+00:00

The effect of formaldehyde (CH₂O) as a surface modifier of PbTe is evaluated. Global descriptors are calculated through density functional theory to delve into the nature of the interaction between CH₂O and the PbTe surface. The CH₂O molecule is structurally optimized using the PBE exchange-correlation functional and ultrasoft pseudopotentials. Subsequently, vertical ionization energies and vertical electron affinities are calculated to elucidate how the CH₂O molecule behaves energetically with respect to electron removal and gain, respectively. In order to determine regions with higher and lower charge accumulation, the electrostatic potential on the van der Waals isosurface is mapped. It is inferred that the theoretical knowledge generated is useful for proposing modes of CH₂O adsorption on the PbTe surface, results that rationalize the faces exposed by PbTe after surface treatment. The optimized structures of the composite systems showed a close correlation between the change in surface energy (Δγ) and the exposed faces of PbTe. Finally, through Wulff construction, the morphology of PbTe interacting with CH₂O as a process control agent is determined. It was found that formaldehyde helps decrease the surface energy of the exposed faces of PbTe, leading to decahedra and faceted morphologies.

Radiation-responsive polymers: a novel spectral approach to investigate ultrahigh molecular weight polyethylene modifications using Grunwald-Letnikov and Caputo fractional order derivatives

2024-08-03T00:50:18+00:00

The impact of gamma radiation on Ultrahigh Molecular Weight Polyethylene (UHMWPE) using fractional differential transformations of FTIR spectra has been probed during the current study. The gamma irradiated samples of UHMWPE for doses of 0, 25, and 50 kGy have been tested with FTIR spectroscopy, and subsequent to testing each spectrum has been analyzed with fraction order differentiation ranging from 0.5 to 1. The exhibited significant shifts in absorbance due to radiation-induced physical and chemical changes, including C=C unsaturation, C=O carbonyl absorption, and variations in CH2 bending and stretching frequencies are clearly evident even at the lowest order of applied transformation. The weak bands in spectral regions 800 − 1100 cm−1 because of gamma radiation caused peak splitting in the 800 − 1100 cm−1 region, attributed to the conversion of vinyl groups into vinylidene and trans-vinylene groups, have also been observed at all orders of applied transformations. It is, therefore, fractional differential transformations thus proved to be a potential methodology for in depth spectra analysis of radiation responsive polymers like UHMWPE with a minimal information loss during the transformation. This is also confirmed by sensitivity and specificity analysis that demonstrated that lower-order transformations are effective for accurate spectral characterization.

Wind tunnel measurements of indoor air quality in a building with natural cross-ventilation

2024-07-08T18:36:44+00:00

In recent years, there has been an increase in indoor air quality studies in buildings, which examine minimum requirements to reduce the probability of respiratory disease transmission. These studies are primarily conducted in existing buildings, with fewer evaluations of generic geometry buildings in wind tunnels. These experimental studies are valuable, among other things, for validating numerical models of Computational Fluid Dynamics (CFD). This study employs the experimental technique of electron capture detection to obtain the distribution of a tracer gas throughout the interior volume of a scaled building with cross-ventilation in a modelled atmospheric boundary layer flow. The building is considered isolated (without neighbors) and features windows at the same bottom height of the windward and leeward facades. A facade porosity (the ratio of area between the window and the facade) of 10% is considered. Maintaining geometric and dynamic similarity, the results are scaled based on a building height of 2.8 m and an incident wind velocity at the building height of 0.85 m/s. Under these conditions, the values of air exchange rate I = 0.0167 s −1 , nominal time τn = 60 s, and 60 air changes per hour (ACH) are calculated. It is anticipated that the concentration results presented in this study will be utilized in future validations of CFD models.

CFD simulation and implementation of a griddle-type biomass stove for rural communities

2024-08-09T16:55:23+00:00

This work focuses on the design of a new griddle-type biomass stove with an internal cross-flow configuration. For this purpose, numerical simulations of the heat transfer and fluid flow in the stove have been carried out. In particular, the equations corresponding to the momentum, energy, and chemical species are solved to determine the influence of the geometrical design. Temperature and isothermal contours on the surface of the griddle were presented. Various stove designs with firepower settings ranging from 10 to 16 kW were investigated. The findings revealed a decrease in thermal efficiency with increasing firepower, which was attributed to higher convective losses. Based on the numerical results, a cookstove prototype was manufactured. Furthermore, the thermal efficiency of the stove was evaluated using the WBT protocol. The goal of this research is not only to assess the thermal performance of the developed technology but also to provide a real-world example of the adoption process of a new technology designed for rural communities.

Numerical simulation of electromagnetically driven flow and temperature distribution inside an electric arc furnace with two non-parallel electrodes

2024-03-09T20:22:19+00:00

In this study, numerical simulations were performed for a three-dimensional computational fluid dynamics model to investigate the fluid dynamic, thermal, and magnetohydrodynamic behavior inside an electric arc furnace. Simulations consider the interaction of the multiphase flow involving steel, slag, and air, along with the induction of electric current through two non-parallel graphite electrodes. It accounts for heat transfer resulting from the Joule effect and the impact of the Lorentz force on the fluid dynamic pattern of steel. To validate the magnetic flux density generated by the electric current, experiments were conducted using a gaussmeter during the operation of an electric arc furnace. Results provide comprehensive insights into temperature, velocity, Joule heat, and Lorentz force fields to characterize the flow. The Lorentz force, arising from the interaction between electric current density and magnetic flux density has a maximum value of 164 N · m⁻³, and it was observed to counteract the movement of convective flow induced by buoyancy forces. This counteraction led to a reduction in velocity within the liquid steel of about 4%, consequently resulting in a more uniform temperature distribution throughout the liquid steel with a maximum temperature value significantly lower compared to the case that does not consider the contribution of the Lorentz force.

Theoretical investigation of the effects of solvents and para-substituents

2024-06-05T01:09:16+00:00

The effects of halogens (F, Br, and Cl) and solvent media (acetone, ethanol, and toluene) on the structural and electronic properties of nitrobenzene compounds were investigated by combination the DFT/B3LYP and MP2 methods with 6-31 + G (d,p) basis set. The results indicate that the bond lengths between carbon-halogen atoms are increased with increased atomic size and decreased electronegativity, whereas some bond angle magnitudes are reduced than those with substitution halogens. Also, various solvent effects of studied compounds were performed with the conductor-like polarizable continuum model (CPCM) method, showing a reduction of the dipole moment by the substitution of a hydrogen atom for a ring with halogen atoms in para-position over the ring. In addition, natural bond orbitals (NBA), chemical reactivity descriptors, and the frontier molecular orbitals (FMOs) of substituted nitrobenzene were calculated. NBO analysis showed the strong interactions within a cyclic system and the fluorine atom in P-FNB is considered the best donor. Moreover, FMO analysis showed that energy band gap is related to the nature of the substituents (halogen atoms) in the para-position of the nitrobenzene compound.

Calibrating density functionals with DMol3 applied on lithium oxide battery

2024-08-19T20:50:06+00:00

Density functional theory - based methods constitute part of the computational techniques considered for finding energy, temperature, pressure, density, electronic structure, and more, of materials and other systems. There is not a general density functional for solving either one or another system, rather there are approximations to the exchange-correlation functional designed to apply this theory, and the density functional for the system in study is usually selected through the Jacob’s Ladder. The purpose of this article is to calibrate by means of selecting multiple density functionals, for calculating potential energy curves on a specific system, and comparing these results with literature values to determine the most suitable functional. With this theory, when a calculation becomes cyclical means that it does not converge after thousands of steps or iterations. The use of thermal smearing calculations can achieve the convergence of the molecular systems. The density functional is calibrated at insignificant thermal smearing values (around 0.005 Hartrees), because the calculated minimum energy is still consistent against experimental values. This level of theory allows searching for stable reaction products. Among the interactions developed to find a suitable density functional are Li + O, Li + O₂, Li + CO, 2 LiO^– + C₃₈H₈. We select GGA-PBE-Grimme as the most suitable density functional. The resulting information is for applying it to infer about charge/discharge of a rechargeable battery, according to the porosity of the cathode.

3T Eulerian-radiation description of graphite laser induced plasma under Martian conditions

2024-06-11T01:30:37+00:00

We report the results of a simulation of the laser-induced breakdown spectra of graphite in an atmosphere similar to that of Mars using a non-equilibrium 3T-Eurlian fluid model. In our approach the atomic energy level populations were calculated using a collisional-radiative (CR) NLTE-model taking into account the mixing between the plasma and the ambiant gas. The simulation was performed with the FLASH radiation-hydrodynamics code. We have investigate the effects of laser irradiance and ambient CO2 pressure on the plasma parameters namely the electron and ion temperatures and the electron and ion densities and the temporal variation of the fluid velocity with the laser irradiance at constant pressure which indicate the presence of a shock front associated with the plasma initiation, dynamics, and expansion into the ambient gas.

Variational symmetries in the Hamiltonian formalism

2024-07-08T22:00:59+00:00

We consider the effect on the Hamilton equations of an arbitrary coordinate transformation in the extended configuration space, $q_{i}' = q_{i}'(q_{j}, t)$, $t' = t'(q_{j}, t)$ (which may not be canonical) and we show that when the Hamiltonian is invariant under a one-parameter family of these transformations, there is an associated nontrivial constant of motion.

Local structure modeling of iron doped triglycine sulphate single crystals

2024-08-04T18:08:14+00:00

Zero field splitting parameters of iron doped triglycine sulphate single crystals are evaluated with the help of superposition model and the perturbation theory. These parameters are in reasonable agreement with the experimental values taking local distortion into account. The theoretical result supports the experimental observation that iron occupies interstitial position in triglycine sulphate crystal. Using crystal field analysis program with crystal field parameters from superposition model as input, the optical spectra of the system are computed. A reasonable match between the computed and experimental energy values is obtained. Thus the theoretical investigation supports the experimental conclusion. The present modeling approach may be useful in other ion-host systems to explore crystals for technological and industrial applications.

Raman spectra of thermally excited Brazil nut oil and experimental and theoretical correlation of oleic acid

2024-06-05T17:30:40+00:00

In this study, Raman spectra of Brazil nut oil were collected through a frying process at temperatures ranging from 50 °C to 250 °C, and of oleic acid at room temperature to compare their respective vibrational bands. The theoretical and scaled Raman frequencies of the oleic acid structure were obtained with the Density Functional Theory, employed using the basis set of the 6-311G+(d,p) Gaussian type orbital and the B3LYP functional. Experimental results reveal subtle changes in the spectra of Brazil nut oil from 210 °C onwards, characterized mainly by a decrease in the Raman signal and broadening of certain bands, such as those observed at 1746 cm^-1, 2726 cmcm^-1 and 3012 cmcm^-1. At temperatures around 230 °C to 250 °C, Brazil nut oil undergoes advanced thermal degradation. The linear fit data demonstrate a linear relationship between the Raman signal and temperature increase, with R² values of 0.999 and 0.977, for some bands. The Density Functional Theory method proved to be useful in predicting oleic acid spectra and vibrational signatures were assigned with the help of the VEDA program. This work highlights the potential of Raman spectroscopy to detect changes in Brazil nut oil during frying.

Electromagnetic field induced resonance tunneling in a quantum point contact

2024-10-04T17:51:22+00:00

Recently experimental results described electron transport through a quantum point contact irradiated by an electromagnetic wave in the tunneling regime as a photon-stimulated tunneling. In this work, we study electron tunneling through potential barrier in the presence of an intense electromagnetic field. Using the time-dependent unitary transformation method, the electron scattering by the laser-dressed potential barrier is calculated analytically. It is shown that the potential barrier is modified in the presence of the electromagnetic radiation and electron transmission probability is enhanced with increasing the laser-field strength.

Caracterización mecánica de morteros en proceso de fraguado a partir de técnicas de impacto acústico y procesamiento de imágenes

2024-07-29T18:30:00+00:00

En el campo de la ingeniería civil es de suma importancia la determinación de la resistencia a compresión axial de los elementos estructurales de una edificación, así como el diagnóstico de los mismos durante su vida útil, esto es posible con el uso de técnicas invasivas como no invasivas. En este trabajo se presentan los resultados experimentales de pruebas destructivas y no destructivas a especímenes de morteros fabricados a diversas proporciones de agregados pétreos y sometidos a esfuerzos de compresión axial hasta el punto de falla o ruptura. El método destructivo consistió en el uso de una prensa hidráulica para someter las muestras de morteros a esfuerzos de compresión. Los métodos no destructivos considerados fueron pruebas de impacto acústico y de procesamiento de las imágenes digitales mediante patrones de luz dispersada por la superficie del mortero bajo estudio para su caracterización entrópica. Las pruebas se realizaron en muestras cúbicas de mortero a diferentes edades durante su proceso de fraguado o curado durante un periodo de análisis de 28 días. Los resultados muestran una gran afinidad entre los métodos no destructivos para la caracterización mecánica a compresión y los métodos convencionales destructivos.

In the field of civil engineering, the determination of the axial compression resistance of the structural elements of a building is of utmost importance, as well as their diagnosis during its service life. This is possible with the use of both invasive and non-invasive techniques. This work presents the experimental results of destructive and non-destructive tests on mortar specimens manufactured with various proportions of oil aggregates and subjected to axial compression stress up to the point of failure or rupture. The destructive method consisted of using a hydraulic press to subject the mortar samples to compression forces. The non-destructive methods considered were acoustic impact tests and digital image processing using light patterns scattered by the mortar’s surface under study for its entropic characterization. The tests were performed on cubic mortar samples at different ages during their setting or curing process over an analysis period of 28 days. The results show a great affinity between non-destructive methods for compression mechanical characterization and the conventional destructive methods.

Experimental analysis of the scattering light for the wavelength of 532 nm through water cloud by the Monte Carlo-Mie method

2024-08-20T18:47:47+00:00

This paper describes an experimental analysis of the scattering of light through a cloud water. For this goal, an experimental setup to emulate a cloud of water is assembled. This arrangement is composed of an optical source emitting at the wavelength of 532 nm that is driven by a switching interface, a turbid medium, a photodiode, and an optical power meter. The optical source is modulated at the frequency of 1 Hz under Pulse Width Modulation (PWM) format. The modulated beam light travels the turbid medium, recovered by the photodiode that is connected to the power meter. The measured power data are analyzed using a novel Monte Carlo-Mie model to obtain the weighted extinction coefficient ratio probability. Subsequently, by the investment model some physical properties of the turbid medium as the refractive index and water droplet average sizes are obtained.

Exact chirped solutions, stability analysis, chaotic behaviors and dynamical properties of the nonlinear Schrödinger equation with anti-cubic law nonlinearity

2024-07-26T19:54:12+00:00

In this paper, the dynamical properties of the nonlinear Schrödinger equation with anti-cubic law nonlinearity is studied. By using the trial equation method and the complete discrimination system for polynomial method, the exact chirped solutions of the equation are obtained, and the parametric stability of these modes is analyzed. Finally, we study the chaotic behaviors of the equation with perturbation terms.