Julia Tagüeña

• Doctor of Philosophy
• Senior Researcher at National Autonomous University of Mexico

The 2030 Agenda for Sustainable Development of the United Nations outlines 17 goals for countries of the world to address global challenges in their development. However, the progress of countries towards these goal has been slower than expected and, consequently, there is a need to investigate the reasons behind this fact. In this study, we have u...

In this scientometric review, we characterize the evolution of polaritonics research during the last 60 years. We explore how the understanding and utilization of polaritons lead to the development of advanced technologies. By employing networks, bibliometric analysis, and artificial intelligence techniques, we identify research trends, patterns of...

The United Nations 2030 Agenda for Sustainable Development outlines 17 goals to address global challenges. However, progress has been slower than expected and, consequently, there is a need to investigate the reasons behind this fact. In this study, we used a novel data-driven methodology to analyze data from 107 countries (2000$-$2022) using unsup...

Ecotechnology, quintessential for crafting sustainable socio-environmental strategies, remains tantalizingly uncharted. Our analysis, steered by the nuances of machine learning and augmented by bibliometric insights, delineates the expansive terrain of this domain, elucidates pivotal research themes and conundrums, and discerns the vanguard nations...

This paper analyzes the research performance evolution of a scientific institute, from its genesis through various stages of development. The main aim is to obtain, and visually represent, bibliometric evidence of the correlation of organizational changes on the development of its scientific performance; particularly, structural and leadership chan...

In this article, we will describe a model to examine the influence of differently organized institutions on their scientific productivity. We take two extreme cases, on one hand, an institution divided in departments with no collaboration between people in different departments. These could be disciplines or merely projects. On the other hand, we c...

En este libro se plantean y discuten aspectos que contribuyen a responder algunas preguntas que se hace la juventud sobre estudiar Energías Renovables. Estas preguntas son respondidas por los propios estudiantes que han terminado el primer semestre de la carrera de Ingeniería en Energías Renovables. Este texto además da elementos para que la juvent...

Se analizan los objetivos de desarrollo sostenible establecidos por Naciones Unidas en 2015, que se pactaron después de una discusión exhaustiva con todos los países del mundo, en la búsqueda del desarrollo sustentable. Se utiliza la versión trabajada en la Cumbre de Género de ese mismo año que incluye la dimensión de género. Se plantea aquí que la...

This updated review summarizes the main theoretical approaches to model porous silicon electronic band structure, comparing effective mass theory, semiempirical and first-principles methods. In order to model its complex porous morphology, supercell, nanowire, and nanocrystal approaches are widely used. In particular, calculations of strain, doping...

This updated review summarizes the main theoretical approaches to model porous silicon electronic band structure, comparing effective mass theory, semiempirical and first-principles methods. In order to model its complex porous morphology, supercell, nanowire, and nanocrystal approaches are widely used. In particular, calculations of strain, doping...

Current research on porous silicon includes the construction of complex structures with luminescent and/or photonic properties. However, their preparation with both characteristics is still challenging. Recently, our group reported a possible method to achieve that by adding an oxidant mixture to the electrolyte used to produce porous silicon. This...

High reflective mirrors are commonly used in solar concentration devices. It has been shown that photonic mirrors are suitable for this purpose. However, despite their high reflectivity, they absorb radiation and heat up showing degradation. To overcome this problem here we propose to enhance the reflectivity of the mirrors. We report an improved a...

This chapter summarizes the main theoretical approaches to model the porous silicon electronic band structure, comparing effective mass theory, semiempirical, and first-principles methods. In order to model its complex porous morphology, supercell, nanowire, and nanocrystal approaches are widely used. In particular, calculations of strain, doping,...

In this article, we offer an analysis of the evolution of the professional field of public communication of science in Mexico, particularly at the National Autonomous University of Mexico, the influences it has received from other countries, the impact it has on Mexican society and some of its relationships with other Latin American countries. We p...

El presente trabajo parte de tres ideas, la primera es la noción de obstáculos epistemológicos (OE), explicaciones del mundo que, de acuerdo con Bachelard, limitan la comprensión de los conocimientos científicos durante su enseñanza. La segunda es que la nanociencia y la nanotecnología se han convertido en aspectos comunes de la vida diaria a los q...

This chapter summarizes the main theoretical approaches to model the porous silicon electronic band structure, comparing effective mass theory, semiempirical, and first-principles methods. In order to model its complex porous morphology, supercell, nanowire, and nanocrystal approaches are widely used. In particular, calculations of strain, doping,...

The morphology of porous silicon (p-Si) depends on several parameters such as the doping type and the carriers’ concentration of the crystalline silicon substrate. The electrolytes used in the p-Si fabrication also have an important role. The final structure determines if p-Si is luminescent or suitable for photonic applications. Experimental resul...

A demás de la escuela, la apropiación de la ciencia puede darse en espacios y con medios muy diversos, desde leyen-do una revista hasta disfrutando los juguetes in-fantiles. Simplemente el observar los fenómenos que suceden en la naturaleza y preguntarse sobre ellos, acerca a los seres humanos a la ciencia. Este proceso de divulgación científica, e...

Porous silicon (p−Si)(p−Si) morphology depends on several parameters of the crystalline silicon substrate such as doping type and carriers concentration. Experimental results on (p−Si)(p−Si) show that although in the porous samples carriers are greatly reduced, boron atoms remain in the bulk. The study of p-type silicon crystals substrates by means...

As scientists we like to think that modern societies and their members base their views, opinions and behaviour on scientific facts. This is not necessarily the case, even though we are all (over-) exposed to information flow through various channels of media, i.e. newspapers, television, radio, internet, and web. It is thought that this is mainly...

Based on very recent experimental evidence about magnetic transitions in high-Tc superconductors the role of superconductivity and magnetism is analyzed. A model of interacting electrons in a one-dimensional system is constructed, taking into account that antiferromagnetic interactions in the underlying lattice are present. The origin of this antif...

The use of porous silicon (PS) in fabricating optoelectronic devices is in progress. However, the performance of such applications still needs to be improved. In particular, in solar cells heat must be dissipated to avoid a decay in their efficiency and one of the properties of PS that must be evaluated is the effective thermal conductivity. It is...

Porous silicon (PS) has been extensively studied in recent years. The origin of its luminescence has been a subject of debate. This work attempts to give some insight towards the understanding of this phenomenon, studying the behaviour of the energy band structure of PS as a function of the pore morphology and distribution, for a given porosity. Th...

Micro and nano-structures have opened a new area in materials research since they present interesting phenomena such as efficient luminescence and localization of carriers. An important example of these new materials is porous silicon (PS). It is considered that the quantum confinement is an essential cause of the opto-electronic properties of PS [...

In this work, the imaginary part of the dielectric function of porous silicon is studied by means of both the tight-binding and the effective medium approaches, in the latter exact result is obtained for the case of 50% porosity. Within the tight-binding approximation, the dielectric function is calculated by using the interconnected and chessboard...

Semi-empirical tight-binding techniques have been extensively used during the last six decades to study local and extended defects as well as aperiodic systems. In this work we propose a tight-binding model capable of describing optical properties of disordered porous materials in a novel way. Besides discussing the details of this approach, we app...

Chemically deposited thin films have multiple applications, in particular for low cost solar cells production. However, due to their inhomogeneous structure, it is very difficult to predict their physical properties. In this work we present a mean field approximation to model the effective electrical conductivity of the polycrystalline ZnO chemical...

In previous works we have obtained an expression for the effective electrical conductivity of a columnar model simulating porous silicon. We used the averaging volume method that has proven to be successful in treating fluid transport in porous media. With this method we can calculate the bulk and the surface contribution to an effective transport...

Far-field secondary emission spectra of free standing samples of one-dimensional porous silicon photonic crystals show characteristic co-focal rings centered close to the structure normal plane. The rings appear when the frequency of picoseconds excitation laser pulses is tuned into the edges of the fourth photonic band gap. They can be clearly dis...

In this paper we report the viability of using porous silicon photonic mirrors (PSPM) as secondary reflectors in solar concentration systems. The PSPM were fabricated with nanostructured porous silicon to reflect light from the visible range to the near infrared region (500–2500 nm), although this range could be tuned for specific wavelength applic...

Two of the most important properties of a porous silicon multilayer for photonic applications are flat interfaces and a relative large refractive index contrast between layers in the optical wavelength range. In this work, we studied the effect of the current density and HF electrolyte concentration on the refractive index of porous silicon. With t...

In this paper we study the propagation of light through an asymmetric array of dielectric multilayers built by joining two porous silicon substructures in a Fibonacci sequence. Each Fibonacci substructure follows the well-known recursive rule but in the second substructure dielectric layers A and B are exchanged. Even without mirror symmetry, this...

This study proposed and experimentally demonstrated a cost-efficient scheme that can deliver 60 GHz millimeter-wave (mm-wave) multi-gigabit wireless services over 125 km long-reach passive optical networks (PONs) without any dispersion compensation. By introducing a remote local exchange (LE) stage with robust signal regeneration and all-optical up...

We simulate a lossless one-dimensional photonic crystals (1D-PC) structure and show that negative refraction could be present near the low frequency edge of at least the second, fourth and sixth bandgaps. We experimentally demonstrate for the first time negative refraction in strongly modulated porous silicon 1D-PC in the visible and near infrared...

La Universidad Nacional Autónoma de México (UNAM, www.unam.mx) es la universidad más importante de México, sobre todo desde el punto de vista de la investigación. Ha sido pionera en muchas áreas y en este momento lo es en el área de comunicación de la ciencia, como una disciplina emergente, fundamental para todas las sociedades modernas. La labor d...

We present a brief review of recent advances in experimental investigations of dielectric relaxation in glass-forming systems, especially with regard to the feature of the excess wing and the applicability of Nagel scaling. Based on the new findings described, we analyze our contributions to the search for microscopic models yielding glass-like rel...

In this work the electronic interband transitions in porous silicon are studied. The calculation is performed using a supercell model with a tight-binding Hamiltonian, where an atomic-orbital sp3s* basis set is used. The pores are modelled as empty columns, digged in a crystalline silicon structure, and then passivated with hydrogen atoms. The effe...

The discovery of, fourteen years ago, the visible luminescence of porous silicon produced many expectations on the possibility of building optoelectronic devices. However, the difficulty in producing stable luminescence forced to look for other applications of this material. The possibility of constructing porous silicon layers with different refra...

Latin America and the Caribbean form a region of great variations yet marked by cultural resemblances. The origins of the region's countries, of their wealth, and also of their problems are quite similar. Indeed, there are clear points of contact in the most basic aspects, such as each society's worldview. Throughout the region there is a very stro...

América Latina y el Caribe constituyen una región muy variada, pero culturalmente afín. Los orígenes de sus países, sus riquezas y también sus problemas son muy semejantes; inclusive se encuentran puntos claros de contacto en aspectos más fundamentales, como la visión del mundo de cada sociedad. En toda esta región existe una corriente democratizad...

An overview is provided of our recent work involving kinetic Ising models for the study of relaxation in quasi one-dimensional chains. The Hamiltonian of the first such model, introduced in 1993, was constructed so as to reduce to the one giving the intramolecular energy of the Gibbs–di Marzio lattice model for polymeric glasses. Variations of this...

DOI:https://doi.org/10.1103/PhysRevE.68.049903

The kinetic Ising model on an inhomogeneous periodic chain, which is composed of N segments with n different bonds, is considered. The model is studied within the Glauber dynamics and the restricted dynamics introduced by the authors for the description of relaxation phenomena in linear polymer chains, and it corresponds to an extension of the alte...

In this article, surface relaxation and its effects on the electronic and structural properties of porous silicon are studied by using the total-energy pseudopotential formalism within the density-functional theory. Our model is based on a 32-atom supercell, where columns of atoms are removed and saturated with hydrogen atoms. Samples with 4.4%, 13...

DOI:https://doi.org/10.1103/PhysRevLett.88.089901

A restricted dynamics, previously introduced in a kinetic model for relaxation phenomena in linear polymer chains, is used to study the dynamic critical exponent of one-dimensional Ising models. Both an alternating isotopic chain and an alternating-bond chain are considered. In contrast with what occurs for Glauber dynamics, in these two models the...

The dynamical properties of the S=1/2 Heisenberg ferromagnet are studied using an extension of the RPA method. The effect of temperature is represented by a fixed array of up and down spins, including short-range-order effects. The spin wave excitations are calculated in this disordered array using the coherent-potential approximation (CPA) for a s...

We consider a point charge embedded in an infinite dielectric cylinder and calculate its dielectric function dependent on the charge distribution. This result is used, within the effective medium approximation framework, to study the dielectric function when charged cylindrical inclusions are embedded in a matrix of a different dielectric. The resu...

The kinetic Ising model on an n-isotopic chain is considered in the framework of Glauber dynamics. The chain is composed of N segments with n sites, each one occupied by a different isotope. Due to the isotopic mass difference, the n spins in each segment have different relaxation times in the absence of interactions, and consequently the dynamics...

The method of Kittler and Falicov (1976, 1978) for binary alloys has been extended to the case when one of the components terminates the Bethe lattice. It has been applied to hydrogenated amorphous silicon (a-Si:H) and the results compared with experimental photo-emission spectra. It is shown that complex configurations such as SiH2 and SiH3 are re...

The goal of this work is to model experimental optical data in porous silicon within the framework of the effective medium theories and to analyze the role of including the effect of charges in the nanostructures. The presence of charge produces a blueshift in the optical response similarly to quantum confinement. Also, the intensity of the excitat...

A restricted dynamics, previously introduced in a kinetic model for relaxation phenomena in linear polymer chains, is used to study the dynamic critical exponent of one-dimensional Ising models. Both the alternating isotopic chain and the alternating-bond chain are considered. In contrast with what occurs for the Glauber dynamics, in these two mode...

The dynamic critical exponent and the frequency and wave-vector dependent susceptibility of the kinetic Ising model on an alternating isotopic chain with Glauber dynamics are examined. The analysis provides a connection between a microscopic model and the Nagel scaling curve originally proposed to describe dielectric susceptibility measurements of...

The optical properties of porous silicon (p-Si) are calculated from the electronic band structure obtained by means of an sp3s* tight-binding Hamiltonian and a supercell model, in which the pores are columns detched in crystalline silicon (c-Si). The disorder in the pore sizes and the undulation of the silicon wires are considered by the existence...

The dynamic critical exponent and the frequency and wave-vector dependent susceptibility of the kinetic Ising model with Glauber dynamics on an alternating isotopic chain are examined. The analysis provides to our knowledge the first connection between a microscopic model and the Nagel scaling curve originally proposed to describe dielectric suscep...

We calculate the optical constants of porous silicon (por-Si) from the electronic band structure obtained by means of an sp3s* tight-binding Hamiltonian and a supercell model, in which the pores are columns dug in crystalline Si. The position of the absorption edge of the material is defined by two competing effects: (i) transitions assisted by the...

The electronic properties of porous silicon (p-Si) are studied by means of a supercell model with a tight-binding Hamiltonian and sp 3s* atomic orbitals. The pores are modelled as empty columns digged in a crystalline silicon structure, passivated with hydrogens atoms. In this work, the band structure and the density of sates of p-Si are presented...

We present the calculations of the coefficient of light (photo) absorption in porous silicon (por-Si) using the supercell tight-binding sp(3)s* model, in which the pores are columns digged in crystalline silicon. The disorder in the pore sizes and the undulation of the silicon wires are taken into account by considering nonvertical interband transi...

A quasi one-dimensional kinetic Ising-like model is developed to study relaxation phenomena in linear polymer chains. In the case where the number N of bonds in the chain is very large, the model Hamiltonian reduces to the one giving the intramolecular energy of the Gibbs-di Marzio lattice model. The equations governing the dynamics of the differen...

The absorption and emission spectra of the hydrogen atom are explained through a computer game. The idea of electronic energy levels (quantization) is introduced by using the idea of the `right photon' to excite an electron. The software includes many important concepts such as mean lifetime, electrons, photons, spectra, ionization, etc. Deeper inf...

An effective medium approximation which includes surface contributions has been used to model the optical properties of porous silicon (p-Si) [1] as a bundle of parallel c-Si wires covered by different materials. It was previously shown that such an approach may be in the right direction when compared with some experimental measurements, but for ex...

The assumption of constant local coefficients is one of the first restrictions in most of the smoothing theories for transport in porous media. In this paper we present a formal analysis of the effects produced by nonconstant local transport coefficients on the nonlinear behavior of the effective transport properties. In particular, we use the volu...

Porous silicon (PS) presents interesting phenomena such as efficient luminescence and a peculiar transport of carriers. Due to its possible optoelectronic applications, it is important to calculate the dielectric function from interband optical transitions in PS to include quantum effects. In this work, we apply a supercell model for PS within an s...

Porous silicon (PS) presents efficient photoluminescence and electroluminescence with potential applications in the optoelectronic industry, in particular in photovoltaic devices. It is now generally accepted that the interesting optical properties of PS are due to two combined aspects: on the one hand, the quantum confinement and on the other, the...

In this work, we study the electronic and optical properties of porous silicon (PS) using a supercell model, where an sp 3s* tight-binding Hamiltonian is used and empty columns of atoms are produced in an otherwise perfect silicon structure, passivated with hydrogen atoms. As it is considered that quantum confinement is one of the causes of the opt...

In this work, we study an inhomogeneous material, porous silicon (PS), using a supercell model and an s p3 s∗ tight-binding Hamiltonian. The interband non-vertical transitions are studied in two schemes, which consider different contributions within the intra-atomic approximation. The oscillator strength analysis as a function of the porosity revea...

The quasi-confinement concept, where electrons can find ways out through the necks between the pores, is discussed and its consequences in the localization and optical properties of porous silicon are analyzed. The polarized light absorption is studied by observing the oscillator strength behaviour. The localization is quantified using the inverse...

The effective dielectric function, effective absorption coefficient and effective refractive index for a model of porous silicon (PS) are calculated using the volume and surface averaging method. The model consists of periodic Si wires with different surface coverages. This approach allows to obtain analytical results within certain approximations....

The relaxational heat capacity of an infinite linear polymer chain is computed. The result is derived within a kinetic Ising-like model previously introduced to provide for a dynamical generalization of the Gibbs-di Marzio lattice model. The questions of universality of the dynamic responses of the chain and of the existence of more than one relaxa...

Due to a mistake in equation (3), additional conditions have to be imposed in order to obtain the equations of motion presented in the paper. The rule of transition shown in (3) should be so that we can allow for single site excitations, and this means that the transitions are not correlated. Considering the analogous magnetic system, if these tra...

Porous silicon presents a fascinating pore morphology, which could be relevant for its efficient luminescent properties in the visible spectrum. This work attempts to give some insight into the understanding of its optical properties, by studying the electronic band structure. The porous structure is modeled as empty columns of different sizes and...

Porous silicon presents a fascinating pore morphology, which could be relevant for its efficient luminescent properties in the visible spectrum. This work attempts to give some insight into the understanding of its optical properties, by studying the electronic band structure. The porous structure is modeled as empty columns of different sizes and...

From a theoretical point of view, linear transport in homogeneous systems is well understood. However, transport phenomena through porous materials are far more complicated. In fact, there are some materials like porous silicon with a very promising technological impact, where mainly experimental evidence is available and theoretical models have sc...

The study of transport in porous materials is a very challenging problem. In particular, the understanding of electric transport in porous silicon is fundamental for its promising technological impact. In a previous work we obtained an analytical expression for the axial effective electrical conductivity of a model simulating porous silicon (PS). W...

The electronic structure of an amorphous Ge-Sn alloy is modelled by an extension of the coherent potential approximation (CPA), which takes into account the chemical order and the absence of Sn dangling bonds found experimentally. In accordance with experiment, the present calculations predict a smooth linear decrease of the band gap with tin conce...

PrBaâCuâO{sub 7-{ital y}} is the only homomorphic member of the entire rare-earth 1:2:3 family which is insulating and not metallic or superconducting. With this unusual behavior in mind, and with an eye to resolving certain questions regarding the widely held notion of otherwise mobile holes held captive in a supratrivalent Pr ionic state as its c...

A molecular calculation of silicon and germanium clusters is used for modelling the amorphous solids formed by these atoms and alloys with group IV substitutional impurities. Care was taken to consider the molecular relaxation needed to avoid spurious strains. The results of the calculations are interpreted in terms of the properties of the solids...

Electron-tunneling measurements were performed in granular and homogeneous samples of Y-Ba-Cu-O, taking advantage of the presence of natural insulating barriers between grains. The results show supercurrents, the superconducting gap and sharp peaks that can be related to a new mechanism for superconductivity. A phenomenological interpretation of th...

Tunneling experiments were performed in Y-Ba-Cu-O samples that show a granular composition that allow the measurements of differential resistance using a conventional modulation technique. Typical tunneling spectra are produced from the samples. These curves show clear structure that could be associated to excitations coupled to the tunneling elect...

A theory to calculate, in real space, the electronic structure of non-periodic systems is developed. The method consists in applying the Hartree-Fock approximation to the cluster-Bethe lattice model. As an example the method is applied to study a model of a-Si:H.

A theory to calculate the electronic structure of non-periodic systems in real space is developed. The method consists on applying the Hartree-Fock approximation to the Cluster-Bethe lattice model. As an example the method is used to investigate a model for a-Si:H.

The phonon density of states is evaluated for the mixed system PdyAg1-xDx. A coherent potential approximation described earlier is used which enables the authors to treat the simultaneous presence of substitutional and interstitial disorder. Their results indicate that the Ag-D force constants are approximately the same as those for Pd-D.

The CNDO method is used to calculate the energy spectra and electron density maps of silicon clusters simulating a-Si, a-Si: H, and a-Si: H: F. In order that the ring topology be taken into account, clusters with a five-atom ring and with a six-atom ring were considered. For the boundary conditions the external bonds were saturated with hydrogen at...

Lattice dynamics of PdDx and PdHx are analysed with reference to the coherent neutron scattering experiments of Rowe et al. (1974) and incoherent neutron scattering lineshape reported by Rahman et al. (1976). Disorder in the octahedral interstitial sublattice is treated within a coherent potential approximation format suitable for treating both 'on...

A general theory of the tunneling solar cells (MIS and SIS structures) is presented. This new theory is valid even at strong illumination when free carriers are stored near to the semiconductor surface and the quasi-Fermi level drops appreciably across the insulator layer. Some numerical calculations of the conversion efficiency at high light conce...

The molecular self-consistent-field method (MOSCFM) together with the cluster model has been proved very successfully to obtain electronic properties of solids (1). The MOSCFM is essentially a tight binding LCAOCNDO type of approximation and the use of the cluster model simplifies enormously the computation in systems without symmetries. In this wo...

The behavior of ITO‐SiO x ‐pSi tunneling solar cell (MIS type) under concentrated light illumination is analyzed theoretically. Conversion efficiency as high as 22.7% is predicted at 75×AM1 illumination. At still higher light concentration the efficiency drops mainly owing to the resistance of the SiO x layer. The numberical calculations show the i...