The surface structure of dodecanethiolate self-assembled monolayers (SAMs) on Au(111) surfaces, f... more The surface structure of dodecanethiolate self-assembled monolayers (SAMs) on Au(111) surfaces, formed from the liquid phase, have been studied by grazing incidence X-ray diffraction (GIXRD), scanning tunneling microscopy (STM), and electrochemical techniques. STM images show that the surface structure consists of (square root 3 x square root 3)-R30 degrees domains with only a few domains of the c(4 x 2) lattice. The best fitting of GIXRD data for the (square root 3 x square root 3)-R30 degrees lattice is obtained with alkanethiolate adsorption at the top sites, although good fittings are also obtained for the fcc and hcp hollow sites. On the basis of this observation, STM data, electrochemical measurements, and previously reported data, we propose a two-site model that implies the formation of incoherent domains of alkanethiolate molecules at top and fcc hollow sites. This model largely improves the fitting of the GIXRD data with respect to those observed for single adsorption sites and, also, for the other possible two-site combinations. The presence of alkanethiolate molecules adsorbed at the less favorable top sites could result from the adsorption pathway that involves an initial physisorption step which, for steric reasons, takes place at on top sites. Once the molecules are chemisorbed, the presence of energy barriers for alkanethiolate surface diffusion, arising mostly from chain-chain interactions, "freezes" some of them at the on top sites, hindering their movement toward fcc hollow sites. By considering the length of the hydrocarbon chain and the adsorption time, the two-site model could be a tool to explain most of the controversial results on this matter reported in the literature.
ABSTRACT Metallic nanoparticles (NPs) appear as promising materials to be used in biomedicine, as... more ABSTRACT Metallic nanoparticles (NPs) appear as promising materials to be used in biomedicine, as efficient catalysts and electrocatalysts, and as active elements in electronic and sensing devices. The most common strategy to protect these NPs is by using thiolate self-assembled monolayers (SAMs), a strategy that has proved to be useful to control the physical and chemical properties of extended solid surfaces. However, the knowledge of the structure and chemistry of thiol?metal interfaces yet remains elusive, although it is crucial for understanding how NPs interact with molecules, biomolecules, and living cells and also for a better design of NP-based devices. This Perspective strives to show the complexity of the thiol?metal NP interface chemistry and how this changes with the nature of the metallic core.
The immobilization of methylene blue (MB) on iodine-covered Au(111) is studied by electrochemical... more The immobilization of methylene blue (MB) on iodine-covered Au(111) is studied by electrochemical techniques, scanning tunneling microscopy (STM), Auger Electron Spectroscopy (AES), and Raman spectroscopy. Results show that MB species are efficiently adsorbed on the square root of 3 x square root of 3 R30 degrees I lattice on Au(111). The electrochemical behavior of the adsorbed MB molecules is reversible, indicating a relatively fast electron transfer from the Au(111) surface to the immobilized MB species through the iodine layer. STM images with molecular resolution are consistent with adsorption of MB dimers on a square root of 3 x square root of 3 R30 degrees I lattice placed atop of the Au(111) substrate. Results are compared to those obtained for MB immobilized on Au(111) covered by S(n) (n = 3-8) surface structures.
ABSTRACT Electrodesorption potentials for alkanethiolate self-assembled monolayers (SAMs) on poly... more ABSTRACT Electrodesorption potentials for alkanethiolate self-assembled monolayers (SAMs) on polycrystalline Cu and Cu(111) surfaces were determined by using electrochemical techniques combined with Auger electron spectroscopy. For a given alkanethiolate SAM, the electrodesorption potentials from Cu are shifted 0.6 V in the negative direction with respect to those found on An. Calculations based on density funtional theory for methanethiolate desorption from Cu(111) show that these potential differences reflect differences in the energy for introducing an electron into the alkanethiolate-metal system and also in the energy to break the alkanethiolate S-head-metal bond. On the other hand, the alkanethiolate-alkanethiol ate interaction energies at SAMs remain practically independent of the substrate.
The surface structure of dodecanethiolate self-assembled monolayers (SAMs) on Au (111) surfaces, ... more The surface structure of dodecanethiolate self-assembled monolayers (SAMs) on Au (111) surfaces, formed from the liquid phase, have been studied by grazing incidence X-ray diffraction (GIXRD), scanning tunneling microscopy (STM), and electrochemical ...
Silver nanodots and nanoripples have been grown on nanocavity-patterned polycrystalline Au templa... more Silver nanodots and nanoripples have been grown on nanocavity-patterned polycrystalline Au templates by controlled electrodeposition. The initial step is the growth of a first continuous Ag monolayer followed by preferential deposition at nanocavities. The Ag-coated nanocavities act as preferred sites for instantaneous nucleation and growth of the three-dimensional metallic centres. By controlling the amount of deposited Ag, dots of approximately 50 nm average size and approximately 4 nm average height can be grown with spatial and size distributions dictated by the template. The dots are in a metastable state. Further Ag deposition drives the dot surface structure to nanoripple formation. Results show that electrodeposition on nanopatterned electrodes can be used to prepare a high density of nanostructures with a narrow size distribution and spatial order.
Nanostructuring of metallic and semiconductor surfaces in the sub-100 nm range is a key point in ... more Nanostructuring of metallic and semiconductor surfaces in the sub-100 nm range is a key point in the development of future technologies. In this work we describe a simple and low-cost method for metal nanostructuring with 50 nm lateral and 6 nm vertical resolutions based on metal film deposition on a silane-derivatized nanostructured silicon master. The silane monolayer anti-sticking properties allow nanopattern transfer from the master to the deposited metal films as well as easy film detachment. The method is non-destructive, allowing the use of the derivatized master several times without damaging. Potential applications of the method are in the field of high-density data storage, heterogeneous catalysis and electrocatalysis, microanalysis (sensors and biosensors) and new optical devices.
ABSTRACT Metallic nanoparticles (NPs) appear as promising materials to be used in biomedicine, as... more ABSTRACT Metallic nanoparticles (NPs) appear as promising materials to be used in biomedicine, as efficient catalysts and electrocatalysts, and as active elements in electronic and sensing devices. The most common strategy to protect these NPs is by using thiolate self-assembled monolayers (SAMs), a strategy that has proved to be useful to control the physical and chemical properties of extended solid surfaces. However, the knowledge of the structure and chemistry of thiol?metal interfaces yet remains elusive, although it is crucial for understanding how NPs interact with molecules, biomolecules, and living cells and also for a better design of NP-based devices. This Perspective strives to show the complexity of the thiol?metal NP interface chemistry and how this changes with the nature of the metallic core.
The immobilization of methylene blue (MB) on iodine-covered Au(111) is studied by electrochemical... more The immobilization of methylene blue (MB) on iodine-covered Au(111) is studied by electrochemical techniques, scanning tunneling microscopy (STM), Auger Electron Spectroscopy (AES), and Raman spectroscopy. Results show that MB species are efficiently adsorbed on the square root of 3 x square root of 3 R30 degrees I lattice on Au(111). The electrochemical behavior of the adsorbed MB molecules is reversible, indicating a relatively fast electron transfer from the Au(111) surface to the immobilized MB species through the iodine layer. STM images with molecular resolution are consistent with adsorption of MB dimers on a square root of 3 x square root of 3 R30 degrees I lattice placed atop of the Au(111) substrate. Results are compared to those obtained for MB immobilized on Au(111) covered by S(n) (n = 3-8) surface structures.
ABSTRACT Thiolate-protected platinum nanoparticles have become promising for applications in hete... more ABSTRACT Thiolate-protected platinum nanoparticles have become promising for applications in heterogeneous catalysis and the fabrication of new materials for hydrogen storage. Once nanoparticles have been synthesized and conveniently grafted onto a particular support, thiol removal might be required before its use. Here, thiolate and sulfur electrodesorption from nanoparticle and planar platinum surfaces are comparatively studied by combining ex-situ X-ray photoelectron spectroscopy (XPS) and electrochemical techniques. We show that alkanethiolates and sulfur adsorbed on Pt surfaces are more stable against reductive desorption than these species on Au substrates. Furthermore, for short-chain thiol-capped platinum nanoparticles we observe complete removal of sulfur-containing species. Hence, these results make this procedure suitable for its use in electrocatalysis. As an example, we demonstrate that 2 nm thiomalic acid-protected platinum nanoparticles markedly improve the performance of a hydrogen storage alloy material, with no additional steps in the preparation of the electrodes.
The surface structure of dodecanethiolate self-assembled monolayers (SAMs) on Au(111) surfaces, f... more The surface structure of dodecanethiolate self-assembled monolayers (SAMs) on Au(111) surfaces, formed from the liquid phase, have been studied by grazing incidence X-ray diffraction (GIXRD), scanning tunneling microscopy (STM), and electrochemical techniques. STM images show that the surface structure consists of (square root 3 x square root 3)-R30 degrees domains with only a few domains of the c(4 x 2) lattice. The best fitting of GIXRD data for the (square root 3 x square root 3)-R30 degrees lattice is obtained with alkanethiolate adsorption at the top sites, although good fittings are also obtained for the fcc and hcp hollow sites. On the basis of this observation, STM data, electrochemical measurements, and previously reported data, we propose a two-site model that implies the formation of incoherent domains of alkanethiolate molecules at top and fcc hollow sites. This model largely improves the fitting of the GIXRD data with respect to those observed for single adsorption sites and, also, for the other possible two-site combinations. The presence of alkanethiolate molecules adsorbed at the less favorable top sites could result from the adsorption pathway that involves an initial physisorption step which, for steric reasons, takes place at on top sites. Once the molecules are chemisorbed, the presence of energy barriers for alkanethiolate surface diffusion, arising mostly from chain-chain interactions, "freezes" some of them at the on top sites, hindering their movement toward fcc hollow sites. By considering the length of the hydrocarbon chain and the adsorption time, the two-site model could be a tool to explain most of the controversial results on this matter reported in the literature.
ABSTRACT Metallic nanoparticles (NPs) appear as promising materials to be used in biomedicine, as... more ABSTRACT Metallic nanoparticles (NPs) appear as promising materials to be used in biomedicine, as efficient catalysts and electrocatalysts, and as active elements in electronic and sensing devices. The most common strategy to protect these NPs is by using thiolate self-assembled monolayers (SAMs), a strategy that has proved to be useful to control the physical and chemical properties of extended solid surfaces. However, the knowledge of the structure and chemistry of thiol?metal interfaces yet remains elusive, although it is crucial for understanding how NPs interact with molecules, biomolecules, and living cells and also for a better design of NP-based devices. This Perspective strives to show the complexity of the thiol?metal NP interface chemistry and how this changes with the nature of the metallic core.
The immobilization of methylene blue (MB) on iodine-covered Au(111) is studied by electrochemical... more The immobilization of methylene blue (MB) on iodine-covered Au(111) is studied by electrochemical techniques, scanning tunneling microscopy (STM), Auger Electron Spectroscopy (AES), and Raman spectroscopy. Results show that MB species are efficiently adsorbed on the square root of 3 x square root of 3 R30 degrees I lattice on Au(111). The electrochemical behavior of the adsorbed MB molecules is reversible, indicating a relatively fast electron transfer from the Au(111) surface to the immobilized MB species through the iodine layer. STM images with molecular resolution are consistent with adsorption of MB dimers on a square root of 3 x square root of 3 R30 degrees I lattice placed atop of the Au(111) substrate. Results are compared to those obtained for MB immobilized on Au(111) covered by S(n) (n = 3-8) surface structures.
ABSTRACT Electrodesorption potentials for alkanethiolate self-assembled monolayers (SAMs) on poly... more ABSTRACT Electrodesorption potentials for alkanethiolate self-assembled monolayers (SAMs) on polycrystalline Cu and Cu(111) surfaces were determined by using electrochemical techniques combined with Auger electron spectroscopy. For a given alkanethiolate SAM, the electrodesorption potentials from Cu are shifted 0.6 V in the negative direction with respect to those found on An. Calculations based on density funtional theory for methanethiolate desorption from Cu(111) show that these potential differences reflect differences in the energy for introducing an electron into the alkanethiolate-metal system and also in the energy to break the alkanethiolate S-head-metal bond. On the other hand, the alkanethiolate-alkanethiol ate interaction energies at SAMs remain practically independent of the substrate.
The surface structure of dodecanethiolate self-assembled monolayers (SAMs) on Au (111) surfaces, ... more The surface structure of dodecanethiolate self-assembled monolayers (SAMs) on Au (111) surfaces, formed from the liquid phase, have been studied by grazing incidence X-ray diffraction (GIXRD), scanning tunneling microscopy (STM), and electrochemical ...
Silver nanodots and nanoripples have been grown on nanocavity-patterned polycrystalline Au templa... more Silver nanodots and nanoripples have been grown on nanocavity-patterned polycrystalline Au templates by controlled electrodeposition. The initial step is the growth of a first continuous Ag monolayer followed by preferential deposition at nanocavities. The Ag-coated nanocavities act as preferred sites for instantaneous nucleation and growth of the three-dimensional metallic centres. By controlling the amount of deposited Ag, dots of approximately 50 nm average size and approximately 4 nm average height can be grown with spatial and size distributions dictated by the template. The dots are in a metastable state. Further Ag deposition drives the dot surface structure to nanoripple formation. Results show that electrodeposition on nanopatterned electrodes can be used to prepare a high density of nanostructures with a narrow size distribution and spatial order.
Nanostructuring of metallic and semiconductor surfaces in the sub-100 nm range is a key point in ... more Nanostructuring of metallic and semiconductor surfaces in the sub-100 nm range is a key point in the development of future technologies. In this work we describe a simple and low-cost method for metal nanostructuring with 50 nm lateral and 6 nm vertical resolutions based on metal film deposition on a silane-derivatized nanostructured silicon master. The silane monolayer anti-sticking properties allow nanopattern transfer from the master to the deposited metal films as well as easy film detachment. The method is non-destructive, allowing the use of the derivatized master several times without damaging. Potential applications of the method are in the field of high-density data storage, heterogeneous catalysis and electrocatalysis, microanalysis (sensors and biosensors) and new optical devices.
ABSTRACT Metallic nanoparticles (NPs) appear as promising materials to be used in biomedicine, as... more ABSTRACT Metallic nanoparticles (NPs) appear as promising materials to be used in biomedicine, as efficient catalysts and electrocatalysts, and as active elements in electronic and sensing devices. The most common strategy to protect these NPs is by using thiolate self-assembled monolayers (SAMs), a strategy that has proved to be useful to control the physical and chemical properties of extended solid surfaces. However, the knowledge of the structure and chemistry of thiol?metal interfaces yet remains elusive, although it is crucial for understanding how NPs interact with molecules, biomolecules, and living cells and also for a better design of NP-based devices. This Perspective strives to show the complexity of the thiol?metal NP interface chemistry and how this changes with the nature of the metallic core.
The immobilization of methylene blue (MB) on iodine-covered Au(111) is studied by electrochemical... more The immobilization of methylene blue (MB) on iodine-covered Au(111) is studied by electrochemical techniques, scanning tunneling microscopy (STM), Auger Electron Spectroscopy (AES), and Raman spectroscopy. Results show that MB species are efficiently adsorbed on the square root of 3 x square root of 3 R30 degrees I lattice on Au(111). The electrochemical behavior of the adsorbed MB molecules is reversible, indicating a relatively fast electron transfer from the Au(111) surface to the immobilized MB species through the iodine layer. STM images with molecular resolution are consistent with adsorption of MB dimers on a square root of 3 x square root of 3 R30 degrees I lattice placed atop of the Au(111) substrate. Results are compared to those obtained for MB immobilized on Au(111) covered by S(n) (n = 3-8) surface structures.
ABSTRACT Thiolate-protected platinum nanoparticles have become promising for applications in hete... more ABSTRACT Thiolate-protected platinum nanoparticles have become promising for applications in heterogeneous catalysis and the fabrication of new materials for hydrogen storage. Once nanoparticles have been synthesized and conveniently grafted onto a particular support, thiol removal might be required before its use. Here, thiolate and sulfur electrodesorption from nanoparticle and planar platinum surfaces are comparatively studied by combining ex-situ X-ray photoelectron spectroscopy (XPS) and electrochemical techniques. We show that alkanethiolates and sulfur adsorbed on Pt surfaces are more stable against reductive desorption than these species on Au substrates. Furthermore, for short-chain thiol-capped platinum nanoparticles we observe complete removal of sulfur-containing species. Hence, these results make this procedure suitable for its use in electrocatalysis. As an example, we demonstrate that 2 nm thiomalic acid-protected platinum nanoparticles markedly improve the performance of a hydrogen storage alloy material, with no additional steps in the preparation of the electrodes.
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