Computer simulations applied to the study of electrochemically

E. P. M. LEIVA; S. A. DASSIE; N. LUQUE; P. VÉLEZ; M. MARISCAL; M. ROJAS; O. OVIEDO

Shanghai, China

Congreso; Internacional Symposium on Funcional Materials & Interfacial Electrochemistry; 2006

Nanoscale electrochemistry appears as a promising field in which scientists are beginning to generate structures at the atomic and molecular scales in order to obtain surfaces and systems with novel properties. In the particular case of electrochemistry, nanostructuring on solid surfaces has been undertaken using different types of techniques, that share a common instrument for their implementation - a scanning tunnelling microscope (STM). The exponential dependence of the tunneling current on the tip-surface distance makes this device very sensitive to the topology of the surface in the z direction. For this reason, in the origin of the STM techniques, the most popular application was to get topological information, but soon an alternative application was developed, consisting in the possibility of manipulation of matter at the atomic level. Electrochemists have managed to employ the STM in several ways to nanostructure surfaces. In one of them, denominated tip induced local metal deposition (TILMD), nanoclusters are generated on the surface of a substrate by transfer of matter from the tip of the STM. The material on the tip is continuously renewed by deposition from a solution containing ions of the metal to be deposited (1). In a second method defects are generated on a metal surface, and the holes obtained in this way are later decorated through deposition of the foreign metal (2,3). In a third method the tip of an STM was used as an electrochemical nanoelectrode to generate supersaturation conditions with respect to the bulk metal equilibrium potential, and nucleation and growth of a single clusters is achieved (4,5). A fourth application of the STM consists in the generation of nanowires. Moving a STM Au tip into and out of contact with a Au substrate in the presence of molecules that interact strongly with gold, Xu and Tao (6) were able to generate monomolecular junctions. While many facts could be explained for the nanostructuring processes mentioned above, an important number of question arose, leaving a fruitful field for theoretical modelling. Although statistical mechanics cannot be applied directly due to the complexity of the problems mentioned, computer simulations provide an alternative way towards the understanding of the atomistic processes involved. In those cases where the electronic structure of the system plays an important role, quantum mechanical calculations are required. On the other hand, for those system where the behavior is the result of the collective interaction of the particles, some approximated potential can be employed to describe the interacion between the constituents particles. It these cases, a more complete statistical description of the system can be made. In the present talk we will discuss on the application of quantum mechanical calculations and classical simulation methods (molecular dynamics, Monte Carlo) to the problems mentioned above. Some of the question to be addressed wll be the generation mechanisms of the nanostructures and their stability, in relation to the nature of the materials involved.- a scanning tunnelling microscope (STM). The exponential dependence of the tunneling current on the tip-surface distance makes this device very sensitive to the topology of the surface in the z direction. For this reason, in the origin of the STM techniques, the most popular application was to get topological information, but soon an alternative application was developed, consisting in the possibility of manipulation of matter at the atomic level. Electrochemists have managed to employ the STM in several ways to nanostructure surfaces. In one of them, denominated tip induced local metal deposition (TILMD), nanoclusters are generated on the surface of a substrate by transfer of matter from the tip of the STM. The material on the tip is continuously renewed by deposition from a solution containing ions of the metal to be deposited (1). In a second method defects are generated on a metal surface, and the holes obtained in this way are later decorated through deposition of the foreign metal (2,3). In a third method the tip of an STM was used as an electrochemical nanoelectrode to generate supersaturation conditions with respect to the bulk metal equilibrium potential, and nucleation and growth of a single clusters is achieved (4,5). A fourth application of the STM consists in the generation of nanowires. Moving a STM Au tip into and out of contact with a Au substrate in the presence of molecules that interact strongly with gold, Xu and Tao (6) were able to generate monomolecular junctions. While many facts could be explained for the nanostructuring processes mentioned above, an important number of question arose, leaving a fruitful field for theoretical modelling. Although statistical mechanics cannot be applied directly due to the complexity of the problems mentioned, computer simulations provide an alternative way towards the understanding of the atomistic processes involved. In those cases where the electronic structure of the system plays an important role, quantum mechanical calculations are required. On the other hand, for those system where the behavior is the result of the collective interaction of the particles, some approximated potential can be employed to describe the interacion between the constituents particles. It these cases, a more complete statistical description of the system can be made. In the present talk we will discuss on the application of quantum mechanical calculations and classical simulation methods (molecular dynamics, Monte Carlo) to the problems mentioned above. Some of the question to be addressed wll be the generation mechanisms of the nanostructures and their stability, in relation to the nature of the materials involved.z direction. For this reason, in the origin of the STM techniques, the most popular application was to get topological information, but soon an alternative application was developed, consisting in the possibility of manipulation of matter at the atomic level. Electrochemists have managed to employ the STM in several ways to nanostructure surfaces. In one of them, denominated tip induced local metal deposition (TILMD), nanoclusters are generated on the surface of a substrate by transfer of matter from the tip of the STM. The material on the tip is continuously renewed by deposition from a solution containing ions of the metal to be deposited (1). In a second method defects are generated on a metal surface, and the holes obtained in this way are later decorated through deposition of the foreign metal (2,3). In a third method the tip of an STM was used as an electrochemical nanoelectrode to generate supersaturation conditions with respect to the bulk metal equilibrium potential, and nucleation and growth of a single clusters is achieved (4,5). A fourth application of the STM consists in the generation of nanowires. Moving a STM Au tip into and out of contact with a Au substrate in the presence of molecules that interact strongly with gold, Xu and Tao (6) were able to generate monomolecular junctions. While many facts could be explained for the nanostructuring processes mentioned above, an important number of question arose, leaving a fruitful field for theoretical modelling. Although statistical mechanics cannot be applied directly due to the complexity of the problems mentioned, computer simulations provide an alternative way towards the understanding of the atomistic processes involved. In those cases where the electronic structure of the system plays an important role, quantum mechanical calculations are required. On the other hand, for those system where the behavior is the result of the collective interaction of the particles, some approximated potential can be employed to describe the interacion between the constituents particles. It these cases, a more complete statistical description of the system can be made. In the present talk we will discuss on the application of quantum mechanical calculations and classical simulation methods (molecular dynamics, Monte Carlo) to the problems mentioned above. Some of the question to be addressed wll be the generation mechanisms of the nanostructures and their stability, in relation to the nature of the materials involved. Acknowledgement The authors acknowledge financial support from CONICET, Agencia Córdoba Ciencia, Secyt U.N.C., Program BID 1201/OC-AR PICT No. 06-12485