Papers by Sergio Javier Manzi
Se analizan las propiedades de equilibrio y la cinética de dímeros interactuantes sobre redes cua... more Se analizan las propiedades de equilibrio y la cinética de dímeros interactuantes sobre redes cuadradas utilizando métodos estadísticos y cinéticos. Se introduce un nuevo modelo de adsorción de dímeros, el cual permite que los dímeros homonucleares sólo se adsorban paralelos a una de las orientaciones de la red (dímeros alineados). Se implementan simulaciones de Monte Carlo, cálculo exacto de la función de partición en clusters finitos, y la solución exacta de las ecuaciones de movimiento en un cluster finito para obtener las propiedades de equilibrio (isotermas de adsorción) y la cinética a través de los espectros de desorción térmica. La presencia de estructuras ordenadas para interacciones laterales repulsivas puede observarse en las isotermas de adsorción y los espectros de DTP.
Adsorption Science & Technology, Apr 1, 1997
Electrophoresis, Nov 8, 2023
The equilibrium and kinetics properties of interacting dimmers adsorbed on square lattice are ana... more The equilibrium and kinetics properties of interacting dimmers adsorbed on square lattice are analyzed by using statistical and kinetic methods. A new adsorption model is introduced, the homonuclear dimmers only are adsorbed parallel to one of the lattice orientations (aligned dimmers). Monte Carlo simulation, exact calculation of the partition function on finite cluster, and the exact solution of the equations of motion in a finite cluster are implemented to obtain the equilibrium (adsorption isotherms) and kinetics throughout the study of the thermal desorption spectra. The presence of structural order for repulsive lateral interactions can be observed in the adsorption isotherms and TPD spectra.
In this work we have analyzed the adsorption-desorption kinetics in the framework of the lattice ... more In this work we have analyzed the adsorption-desorption kinetics in the framework of the lattice gas model. We have shown that the coefficients representing the transition probabilities must be carefully chosen even when they fulfill the principle of detailed balance, otherwise the observables arising from the kinetics present anomalous behavior. We have demonstrated that when the adsorption $A_i$ and desorption $D_i$ coefficients are linearly related through a parameter $\gamma$, there are values of lateral interaction, $V$, that lead to bad behavior in the kinetics. We have shown a phase diagram for the allowed values of $V$ and $\gamma$, concluding that detailed balance does not guarantee a correct physical behavior of the observables obtained from the rate equations like adsorption isotherms, sticking coefficients and thermal desorption spectra. Alternatively, we have introduced a description of the adsorption-desorption processes based in a simple but consistent energetic argum...
The Journal of Physical Chemistry C, 2021
Oxygen adsorption was studied on a Au/Pd(100) single crystal as a model for single-atom-alloy cat... more Oxygen adsorption was studied on a Au/Pd(100) single crystal as a model for single-atom-alloy catalysts since the surface contains isolated palladium atoms surrounded by gold at high gold coverages...
SSRN Electronic Journal, 2022
Small, 2021
Xenon (Xe) is a valuable and scarce noble gas used in various applications, including lighting, e... more Xenon (Xe) is a valuable and scarce noble gas used in various applications, including lighting, electronics, and anesthetics, among many others. It is also a volatile byproduct of the nuclear fission of uranium. A novel material architecture consisting of silicate nanocages in contact with a metal surface and an approach for trapping single Xe atoms in these cages is presented. The trapping is done at low Xe pressures and temperatures between 400 and 600 K, and the process is monitored in situ using synchrotron-based ambient pressure X-ray photoelectron spectroscopy. Release of the Xe from the cages occurs only when heating to temperatures above 750 K. A model that explains the experimental trapping kinetics is proposed and tested using Monte Carlo methods. Density functional theory calculations show activation energies for Xe exiting the cages consistent with experiments. This work can have significant implications in various fields, including Xe production, nuclear power, nuclear waste remediation, and nonproliferation of nuclear weapons. The results are also expected to apply to argon, krypton, and radon, opening an even more comprehensive range of applications.
Nanoscale, 2021
Ring size distribution in silicate bilayers obtained from Monte Carlo simulations using a bond-sw... more Ring size distribution in silicate bilayers obtained from Monte Carlo simulations using a bond-switching algorithm (compared to experimental data) when a temperature gradient is introduced to mimic a crystalline to vitreous domain boundary.
The Journal of Physical Chemistry C, 2019
The design of molecular electronic circuits will require the development of strategies for making... more The design of molecular electronic circuits will require the development of strategies for making controlled interconnections between nanoelectrodes. The simplest example of a molecular electronic component consists of aryl rings with para-anchoring functionalities, commonly isocyanide or thiol groups. In particular, 1,4-phenylene diisocyanobenzene (1,4-PDI) has been shown to form conductive one-dimensional, oligomeric chains that are composed of alternating gold and 1,4-PDI units in which a gold adatom is linked to two trans isocyanide groups. Density functional theory (DFT) calculations of the oligomerization pathway reveal that growth occurs via a vertical, mobile Au− PDI adatom complex that forms by binding to the gold substrate and oligomerizes by the gold adatom attaching to the isocyanide terminus of a growing chain. In this case, the gold atoms in the oligomer derive from the gold substrate. In principle, bridging between adjacent electrodes could be tuned by controlling the 1,4-PDI dose. However, because both nucleation of the adatom complex and the subsequent oligomerization reactions occur at the periphery of gold nanoparticles, it is postulated that oligomer growth is inherently self-limiting. An analytical model is developed for this process that demonstrates the existence of self-limiting growth. This is modeled in greater detail using kinetic Monte Carlo simulations with the energy parameters derived from DFT calculation on gold that confirm that the growth is self-limiting and predicts that bridging between nanoelectrodes should only occur for spacings less than ∼12 nm.
The Journal of Physical Chemistry C, 2019
The atomic distribution on the surface of alloys dictates the nature of the ensembles available a... more The atomic distribution on the surface of alloys dictates the nature of the ensembles available as possible active sites during catalytic reactions. In the present work, an infrared spectroscopic study of carbon monoxide adsorption on the surface of AuPd/Pd(111) alloys, combined with Monte Carlo simulations of the surface and bulk atomic distribution, identifies the correct distribution of available surface adsorption sites. For gold coverages > 0.9 monolayers (ML), CO adsorbs weakly on top of Au atoms and with higher adsorption energy on top of Pd atoms (CO top), distributed mostly as monomers on the surface. For Au = 0.8-0.4 ML, Pd-CO top is the predominant species, even though several other sites with multiple coordination are available. The simulations show no perfect ordering of the surface but a slight tendency to form lines of Pd atoms, thus favoring the appearance of bridge, but not 3-fold hollow sites. Using 13 CO: 12 CO isotopic mixtures, the frequency shifts due to chemical and intermolecular coupling effects has been determined for the CO top IR signal. These effects mostly cancel each other out, so that only small frequency shifts are seen, implying the presence of significant electronic/ligand effects. At Au < 0.5 ML, hollow sites are experimentally observed in agreement to the simulated model surfaces. Their IR absorption bands are tentatively distinguished as fcc and hcp hollow sites by correlating with the simulated distribution of Au and Pd atoms on subsurface sites, where for Au < 0.5 ML an enrichment by Au atoms is seen in the near-surface region.
Physica A: Statistical Mechanics and its Applications, 2017
Physica A: Statistical Mechanics and its Applications, 2017
Monte Carlo simulation is used to study the adsorption-desorption kinetics in the framework of th... more Monte Carlo simulation is used to study the adsorption-desorption kinetics in the framework of the kinetic lattice-gas model. Three schemes of the so-called hard dynamics and five schemes of the so called soft dynamics were used for this purpose. It is observed that for the hard dynamic schemes, the equilibrium and non-equilibrium observable, such as adsorption isotherms, sticking coefficients, and thermal desorption spectra, have a normal or physical sustainable behavior. While for the soft dynamics schemes, with the exception of the transition state theory, the equilibrium and non-equilibrium observables have several problems.
Chemistry of Materials, 2015
The influence of directing agents in the self-assembly of molecular wires to produce twodimension... more The influence of directing agents in the self-assembly of molecular wires to produce twodimensional electronic nanoarchitectures is studied here using a Monte Carlo approach to simulate the effect of arbitrarily locating nodal points on a surface, from which the growth of self-assembled molecular wires can be nucleated. This is compared to experimental results reported for the self-assembly of molecular wires when 1,4-phenylenediisocyanide (PDI) is adsorbed on Au(111). The latter results in the formation of (Au-PDI) n organometallic chains, which were shown to be conductive when linked between gold nanoparticles on an insulating substrate. The present study analyzes, by means of stochastic methods, the influence of variables that affect the growth and design of self-assembled conductive nano-architectures, such as the distance between nodes, coverage of the monomeric units that leads to the formation of the desired architectures and the interaction between the monomeric units. This work proposes an approach and sets the stage for the production of complex 2D nanoarchitectures using a bottom-up strategy but including the use of current state-of-the-art top-down technology as an integral part of the self-assembly strategy.
En este trabajo se estudia en forma teórica la cinética de adsorción-desorción con múltiple ocupa... more En este trabajo se estudia en forma teórica la cinética de adsorción-desorción con múltiple ocupación de sitios. El problema se formula en el marco del modelo de gas de red cinético para una red unidimensional. Por medio de las llamadas reglas de evolución local se obtiene el conjunto de ecuaciones diferenciales acopladas que describen la evolución para las funciones de correlación. Mediante el uso de clausuras de campo medio (m, n), que permiten el truncamiento del sistema de ecuaciones, se obtiene el comportamiento cinético de los observables. Como resultado de esto se analizan las propiedades de equilibrio, la aproximación al equilibrio y las propiedades de no-equilibrio para la especie adsorbida, a través de las isotermas de adsorción y los espectros de desorción térmica programada (DTP) para adsorbatos móviles e inmóviles. Descriptores: Modelos de cinética de superficie; cinética de adsorción; difusión superficial; espectrometría de desorción térmica. The adsorption-desorption kinetics with multiple site occupation in a one-dimensional network is formulated in the framework of the kinetic lattice gas model. The kinetic equations that describe the time evolution of the correlators are obtained by use of the so called Local Evolution Rules, that take into account the adsorption, desorption, and diffusion of the adsorbed molecules. After truncating the infinite hierarchy of equations, different cases are analyzed. Equilibrium solutions are obtained and the exact expression for adsorption isotherms as well as the nearest-neighbor correlations are presented. The asymptotic approach to the equilibrium is also discussed. Finally, we analyzed the desorption kinetics throughout the thermal desorption spectra.
Surface Science, 2003
A theoretical approach, based on exact calculation of the partition function on finite rectangula... more A theoretical approach, based on exact calculation of the partition function on finite rectangular clusters, is introduced to study the adsorption of interacting homonuclear dimers on square lattices. An efficient algorithm allows us to calculate the detailed structure of the configuration space for m ¼ ðk  lÞ clusters with m varying from 8 to 48. The adsorption process has been monitored by following thermodynamic properties such as coverage versus chemical potential, internal energy and specific heat of the adlayer, etc. The analytical results are compared with those in [Surf. Sci. 411 (1998) 294], which were obtained by using Monte Carlo simulation and finite-size scaling techniques. The theoretical adsorption isotherms and phase diagrams (critical temperature versus coverage) for both attractive and repulsive lateral interactions are in good qualitative agreement with the computational data. This agreement between simulated and theoretical results supports the validity of the cluster-exact approximation proposed in this paper.
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Papers by Sergio Javier Manzi