Marcelo M Mariscal

National University of Cordoba, Argentina | UNC · School of Chemical Science

In electrochemical catalysis, parameters such as current, resistance, or capacitance must be referred to the electrochemically exposed area, otherwise they lack physical sense. For this reason it is necessary to know this exposed area as accurately as possible. Although there are several experimental methods to estimate the electrochemically expose...

We report a combined experimental/theoretical approach to study the connection of S-vacancies and wrinkling on MoS2 layers, and how this feature produce significant changes on its electronic structure and reactivity of this 2D material. The MoS2 material, when used as a catalyst in operative conditions, was found to be mainly composed of thin and s...

Magnesium is a promising material for the automotive technology. Avoiding its spontaneous oxidation is, however, mandatory for a feasible industrial application of this metal. We perform computer simulations to demonstrate that a protective graphene layer can successfully avoid the oxidation of a magnesium material. This feature remains true even w...

Abstract We present ab initio simulations of X-ray Absorption Near-Edge Structure (XANES) spectra, performed on model clusters built by fast simulated annealing and optimized by Density Functional Theory (DFT) minimization. As is known, larger stability of Cu clusters with 20 atoms was found in comparison with those with 19 and 21 atoms. Based on t...

Nanotherapeutics is a promising field for numerous diseases and represents the forefront of modern medicine. In the present work, full atomistic computer simulations were applied to study poly(lactic acid) (PLA) nanoparticles conjugated with polyethylene glycol (PEG). The formation of this complex system was simulated using the reactive polarizable...

A novel strategy to synthesize photoluminescent silicon nanocrystals (SiNCs) from a reaction between tetraethylorthosilicate (TEOS) and trimethyl-hexadecyl-ammonium borohydride (CTABH4) in organic solvent is presented. The formation reaction occurs spontaneously at room temperature in homogeneous phase. The produced silicon nanocrystals are charact...

Watching graphene grow The growth of graphene on metal surfaces can be catalyzed by mobile surface metal atoms. Patera et al. used a high-speed scanning tunneling microscope to image the growth of graphene islands on a nickel surface. High temperatures caused carbon to diffuse to the surface, where mobile nickel atoms catalyzed graphene growth on t...

IrAu nanoalloys have been proven to have remarkable reactivity for several reactions. In this work, mixed IrAu nanoalloys of 8, 27, 48 and 64 total atoms were studied in different atomic compositions (Ir m Au n) using Density Functional Theory (DFT). A notable segregation tendency is observed, where Ir atoms are located in the inner part and Au ato...

Interaction with the substrate strongly affects the electronic/chemical properties of supported graphene. So far, graphene deposited by chemical vapor deposition (CVD) on catalytic single crystal transition metal surfaces - mostly 3-fold close-packed - has mainly been studied. Herein, we investigated CVD graphene on a polycrystalline nickel (Ni) su...

In this work, we report on the van der Waals (vdW) interactions of n-alkanethiols (ATs) adsorbed on planar Au (111) and Au (100) surfaces and curved Au nanoparticles of different diameters. By means of electrochemical measurements and molecular dynamic calculations, we show how the increase in the average geometrical curvature of the surface influe...

The scouting of alternative plasmonic materials able to enhance and extend the optical properties of noble metal nanostructures is on the rise. Aluminum is endowed with a set of interesting properties that turn it into an attractive plasmonic material. Here we present the optical and electronic features of different aluminum nanostructures stemming...

In this work, we report on the van der Waals (vdW) interactions of n-alkanethiols (ATs) adsorbed on planar Au (111) and Au (100) surfaces and curved Au nanoparticles of different diameters. By means of electrochemical measurements and molecular dynamic calculations, we show how the increase in the average geometrical curvature of the surface influe...

Atomistic computer simulations on the generation of nanotunnels on graphite and the subsequent immobilization of gold nanoparticles are presented in this work. A Morse potential dependent on the coordination of carbon atoms was parameterized based on density functional theory including long dispersion forces. The set up chosen is such that a direct...

Formation of monoatomic chains by axial stretching of zinc oxide nanowires is investigated by molecular dynamics and supported by density functional calculations. Special focus is made on the mechanical properties of these structures. Using a state-of-the-art force field it was found that O2 species are commonly formed within the chain. This specie...

The mechanical response of zinc oxide nanowires under uniaxial tensile loading is investigated by molecular dynamics and supported by density functional calculations. Previous theoretical works predict a stress-induced phase transition which has not been observed experimentally in zinc oxide nanowires up to date. Here, we report an explanation for...

In this work, we report a facile synthesis route, structural characterization, and full atomistic simulations of gold-palladium nanoalloys. Through aberration corrected-STEM, UV-vis and EDS chemical analysis, we were able to determine that Au(core)-Pd(shell) bimetallic nanoparticles were formed. Using different computational approaches, we were cap...

The adsorption of very small Rhenium clusters (2 - 13 atoms) supported on graphene was studied with high annular dark field - scanning transmission electron microscopy (HAADF-STEM). The atomic structure of the clusters was fully resolved with the aid of density functional calculations and STEM simulations. It was found that octahedral and tetrahedr...

The role that protecting molecules have on the way that palladium atoms arrange themselves in nanoparticles prepared at room temperature was studied by the analysis of aberration-corrected scanning transmission electron microscopy (STEM) images and atomistic Langevin Dynamics simulations. It was found that the arrangement of Pd atoms is less ordere...

The structural order in ultrathin films of monolayer protected clusters (MPCs) is important in a number of application areas but can be difficult to demonstrate by conventional methods, particularly when the metallic core dimension, d, is in the intermediate size-range, 1.5 < d < 5.0 nm.

Highly monodispersed Cu–Pt bimetallic nanoclusters were synthesized by a facile synthesis approach. Analysis of transmission electron microscopy (TEM) and spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM) images shows that the average diameter of the Cu–Pt nanoclusters is 3.0 ± 1.0 nm. The high angle annular dark...

In this work we present an atomistic simulation study analyzing the effect of ligand molecules on the morphology and crystalline structure of monolayer protected gold nanoparticles (NPs). In particular, we focused on Au NPs covered with alkyl thiolates (-SR), which form a strong covalent bond with the Au surface, and alkyl amines (-NH2R), which phy...

The structural order in ultrathin films of monolayer protected clusters (MPCs) is important in a number of application areas but can be difficult to demonstrate by conventional methods, particularly when the metallic core dimension, d, is in the intermediate size-range, 1.5 o d o 5.0 nm. Here, improved techniques for the synthesis of monodisperse t...

Ultra-smooth, highly spherical monocrystalline gold particles were prepared by a cyclic process of slow growth followed by slow chemical etching, which selectively removes edges and vertices. The etching process effectively makes the surface tension isotropic, so that spheres are favored under quasi-static conditions. It is scalable up to particle...

We report the synthesis, structural characterization, and atomistic simulations of AgPd-Pt trimetallic (TM) nanoparticles. Two types of structure were synthesized using a relatively facile chemical method: multiply twinned core-shell, and hollow particles. The nanoparticles were small in size, with an average diameter of 11 nm and a narrow distribu...

The fabrication of bimetallic magnetic nanoparticles (NPs) smaller than the size of single magnetic domain is very challenging because of the agglomeration, non-uniform size, and possible complex chemistry at nanoscale. In this paper, we present an alloyed ferromagnetic 4 ± 1 nm thiolated Au/Co magnetic NPs with decahedral and icosahedral shape. Th...

Conductance experiments on single molecular junctions are pushing the computational field towards new challenges involving conductance calculations along a large collection of molecular conformations. To tackle this problem, a combination of accelerated dynamics (to enhance sampling) and non-equilibrium Green functions (for conductance computation)...

Systems in the range between 1 and 50 nm have an intermediate size between single molecules and bulk materials. This is why they exhibit unique electronic properties which obey quantum-mechanical rules [1] that strongly depend on particle size and shape, as well as on interparticle interactions and protecting agents, if there were some. In these sm...

Metallic nanoparticles are most promising materials due to their potential applications on different technological areas and human life, ranging from novel building materials to medicine. From the point of view of the industrial and governmental markets ‘‘Nanotechnology’’ became a key word of public interest, since even politicians and economists r...

Accelerated molecular dynamics and quantum conductance calculations are employed to shed light onto the electrochemical properties of the Au|1,8-octanedithiol|Au junction. Widely different contact geometries with varying degrees of roughness are examined. Strikingly, the two extreme situations considered in this work, tip-tip and tip-perfect surfac...

An accelerated dynamics scheme is employed to sample the configurational space of a system consisting of an alkanedithiol molecule confined to the gap between a metal tip and a perfect metal surface. With this information and by means of nonequilibrium green functions techniques (NEGF), conductance calculations are performed. The present results sh...

In this work we investigate the performance of several simulation techniques, i.e., Canonical Molecular Dynamics, Canonical Monte Carlo, and the Optimized Multicanonical Monte Carlo, to study melting-like transitions of Co/Au nanoalloys that are compared to those of pure Co and Au clusters of the same size. A surprising enhancement in the thermal s...

This work presents key modeling aspects that are central to the manipulation of the decoration of metallic nanoparticles by a thin shell of a metal of different chemical nature. The concept of underpotential deposition is generalized to nanoparticles. An all-atom model, taking into account many-body interactions by means of the embedded atom potent...

Electropolymerisation is a very useful methodology for conducting polymers synthesis. A total comprehension of this process will help on the designing of new materials with improved optical and electrical properties. In this sense, computational simulations can deliver important information at atomic scale. Within a kinetic Monte Carlo scheme, diff...

Export Date: 26 June 2012, Source: Scopus, CODEN: ECCMF, doi: 10.1016/j.elecom.2011.12.013, Language of Original Document: English, Correspondence Address: Leiva, E.P.M.; Departamento de Matemática y Física, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, X5000HUA, Argentina; email: eleiva@fcq.unc.edu.ar

We report a combined theoretical and experimental study on the growth mechanism of silver and gold nanoparticles. We introduce for the first time the grand-canonical Monte Carlo method to study the growth/dissolution steps of nanoparticle growth mediated by seeds. In particular we found that small changes on the chemical potential, i.e. the activit...

In this work we investigate the performance of several simulation techniques, i.e., Canonical Molecular Dynamics, Canonical Monte Carlo, and the Optimized Multicanonical Monte Carlo, to study melting-like transitions of Co/Au nanoalloys that are compared to those of pure Co and Au clusters of the same size. A surprising enhancement in the thermal s...

Bimetallic nanoparticles constitute a promising type of catalysts, mainly because their physical and chemical properties may be tuned by varying their chemical composition, atomic ordering, and size. Today, the design of novel nanocatalysts is possible through a combination of virtual lab simulations on massive parallel computing and modern electro...

Results of dynamical simulations of collision-induced formation and properties of bimetallic nanoparticles are presented and analyzed. The analysis includes the effects of the collision energy and the impact parameter. For nonzero impact parameters, the formed (in many cases Janus-type) nanoparticles are rotating. The energy of the rotating nanopar...

A new semiempirical potential, based on density functional calculations and a bond-order Morse-like potential, is developed to simulate the adsorption behavior of thiolate molecules on non-planar gold surfaces, including relaxing effects, in a more realistic way. The potential functions include as variables the metal-molecule separation, vibrationa...

Grand Canonical Monte Carlo simulations were used to study the growth of a Na layer onto a O–p(2×2)–Pt(111) surface. At the beginning of the deposition, the film presents a disordered structure which becomes progressively ordered as the coverage increases due to the repulsive lateral interactions between the adsorbates. We found some ordered struct...

In the present work we discuss the statistical mechanical framework for predicting the decoration of metallic nanoparticles using electrochemical methods, in thermodynamic equilibrium. It is found that depending on the interactions between the two metals, controlled decoration may be achieved for core–shell nanoparticles in undersaturation and over...

In the present work new findings on the structure of the S-Au interface are presented. Theoretical calculations using a new semiempirical potential, based on density functional theory and a bond-order Morse potential, are employed to simulate the adsorption process in a more realistic way. The simulation results reveal the formation of gold adatoms...

We report the formation of Au/Co nanoparticles and their characterization by aberration (Cs) corrected scanning transmission electron microscopy (STEM). The nanoparticles were synthesized by inert gas condensation, forming initially core-shell and bimetallic crystals. However, after thermal treatment at normal atmospheric conditions, the Co nanopar...

In this work we present the analysis by aberration corrected electron microscopy of the formation of gold clusters based on the proton irradiation of larger nanoparticles (NP). Pentagonal arrays have been observed and energetic calculations have been performed in order to prove the stability of these materials.

In the present work we show that synthesis of gold nanoparticles (NPs) could be performed by microwave-assisted technique without the need of adding any reducing agent. Only water and the gold salt precursor are necessary to generate the NPs under the influence of microwaves. The produced NPs have been characterized by state-of-art microscopy techn...

Following the framework established by Hill and Chamberlin [T. L. Hill and R. V. Chamberlin, Proc. Natl. Acad. Sci. U. S. A., 1998, 95, 12779] to analyze the extension of thermodynamics of small systems to metastable states, we have adopted the same basic ideas to study the thermodynamic stability of core-shell nanoparticles. For the first time we...

The structural and mechanical properties of single-and multi-walled carbon nanotubes filled with iron nanowires are studied using a recent parameterization of the modified embedded atom model. We have analyzed the effect of different crystal structures of iron (bcc and fcc) inside carbon nanotubes of different topographies. We have computed strain...

Molecular dynamic simulations in combination with energy minimizations are used in order to understand the basis of the novel experiments reported recently by Haiss et al. (W. Haiss, C. Wang, I. Grace, A.S. Batsanov, D.J. Schiffrin, S.J. Higgins, M.R. Bryce, C.J. Lambert, R.J. Nichols, Nature Mater. 5 (2006) 995). Our model suggests that single-mol...

A stochastic model which may be used to analyze the formation of bonds connecting the interface formed by a substrate surface and a scanning tunneling microscope (STM) tip is presented. The model is tested by means of kinetic Monte Carlo simulations, and analytical predictions are given for some limiting cases. In the case of long time observations...

In this work, the structural and energetic properties of two typical catalytic surfaces, Na/Pt(111) and O/Pt(111), are studied by means of quantum mechanical calculations and Monte Carlo Grand Canonical simulations. The simulations were performed with electrostatic potentials at different truncation schemes. In order to elucidate the modification o...

In the present work a detailed atomic-level analysis of some of the main diffusion mechanisms which take place during cobalt adatom deposition are studied within atom dynamics (AD) and the nudged elastic band (NEB) method. Our computer simulations reveal a very fast exchange between Co and Au atoms when the deposit is a single cobalt adatom. Howeve...

We report on thermodynamic modeling and computer simulations on the electrochemical generation of metallic and bimetallic nanoparticles (NPs) by means of quenched molecular dynamics (QMD). The present results suggest that the spontaneous formation of core-shell NPs depends on several factors, i.e. size and shape of the core, chemical composition of...

Computer simulations on the generation of bimetallic nanoparticles are presented in this work. Two different generation mechanisms are simulated: (a) cluster-cluster collision by means of atom dynamics simulations; and (b) nanoparticle growth from a previous seed through grand canonical Monte Carlo (gcMC) calculations. When two metal nanoparticles...

In the present talk we will show two different approachs to study the generation of bimetallic nanoparticles. Firstly, we report a dynamic method to generate bimetallic nanoparticles by collision of two pure individual nanoparticles at different kinetic energies and impact parameters. Depending on such conditions and the chemical nature of the meta...

First steps are taken towards computer simulation of the atomistic mechanism taking place during the supersaturation induced local metal deposition method, as developed by Schindler and coworkers [D. Hofmann, W. Schindler, J. Kirchner, Appl. Phys. Lett. 73 (1998) 3279]. Using a combination of stochastic Langevin dynamics (LD) and deterministic atom...

A new method for the study of the molecular dynamics of electrochemical systems is presented, which explicitly contains the electrode potential. It is based on a combination of ordinary molecular dynamics, stochastic dynamics, and a grand-canonical ensemble. The method is tested for the deposition of silver on Au(111), and is found to represent the...

IntroductionMolecular Dynamics Simulations GeneralitiesNanostructuring of Metallic SurfacesMonte Carlo Method GeneralitiesOff-lattice Models Stability of Metallic NanostructuresLattice Models IntroductionElectrocrystallizationDynamics of Crystal GrowthSimulation of a Complex Underpotential Deposition SystemBrownian and Langevin Dynamics Simulations...

In this work, the structural and energetic properties of two typical catalytic surfaces, Na/Pt(111) and O/Pt(111), are studied by means of quantum mechanical calculations and Monte Carlo Grand Canonical simulations. The simulations were performed with electrostatic potentials at different truncation schemes. In order to elucidate the modification o...

A new atomistic simulation model for electrochemical systems is presented. It combines microcanonical molecular dynamics for the electrode with stochastic dynamics for the solution, and allows the simulation of electrochemical deposition and dissolution for specific electrode potentials. As first applications the deposition of silver and platinum o...

In the present work we consider two aspects of the deposition of metal clusters on an electrode surface. The formation of such clusters with the tip of a scanning tunneling microscope is simulated by atom dynamics. Subsequently the stability of these clusters is investigated by Monte Carlo simulations in a grand-canonical ensemble. In particular, t...