Mechanistic Framework for the Formation of Different Sulfur Species by Electron Irradiation of n-Dodecanethiol Self-Assembled Monolayers on Au(111) and Au(100)

The electron-induced damage in self-assembled monolayers (SAMs) of n-dodecanethiolate on Au(111) and Au(100) single-crystalline surfaces is investigated in situ by X-ray photoelectron spectroscopy. The same irradiation dose produced different adsorbed groups. The damage at the headgroup–substrate interface leads to find dialkyl sulfide (RS–R′) on Au(111), while dialkyl disulfide (RS–SR) and/or thiol (RSH) were produced on Au(100). With regard to C species, significant amounts of C═C are generated on Au(111) but not on Au(100), showing that double bond formation is not triggered through the same pathways on these surfaces. Detailed analysis of a variety of mechanisms, which involved cationic (RS+), anionic (RS–), or thiyl radical (RS•) species, in combination with ab initio density functional theory (DFT) calculation, leads to the conclusion that the radical pathways successfully explain the experimental results. Molecular dynamics simulations show that the n-dodecanethiolate SAMs on both surfaces are equivalent with regard to the van der Waals interactions. The breakage of the S–Au bonds is studied by means of DFT calculations. The thiyl radical would form close to the Au(100) surface, making it likely to react with another thiyl radical or thiolate to form the RS–SR species. On the other hand, for Au(111), the thiyl radical would form farther from the surface, reacting with the alkyl chains of neighboring molecules to form RS–R′ species. The mechanistic framework proposed here is very useful to explain the behavior of related systems.This work was supported in part by CONICET (PIP 0333), ANPCyT (PICT 2017-4519), Universidad Nacional de La Plata (UNLP X786) of Argentina, and Universidad Nacional de Cuyo. J.O.-A. and M.M.M. acknowledge financial support from CONICET through Grant PIP 11220150100141CO, FONCyT PICT-2015-2191, and SeCyT UNC. This work has used computational resources from CCAD, Universidad Nacional de Córdoba (http://ccad.unc.edu.ar/) and resources provided by the CYTED co-funded Thematic Network RICAP (517RT0529)

ESIPT and FRET probes for monitoring nanoparticle polymer coating stability

Coating strategies of inorganic nanoparticles (NPs) can provide properties unavailable to the NP core alone, such as targeting, specific sensing, and increased biocompatibility. Non-covalent amphiphilic NP capping polymers function via hydrophobic interactions with surface ligands and are extensively used to transfer NPs to aqueous media. For applications of coated NPs as actuators (sensors, markers, or for drug delivery) in a complex environment, such as biological systems, it is important to achieve a deep understanding of the factors affecting coating stability and behavior. We have designed a system that tests the coating stability of amphiphilic polymers through a simple fluorescent readout using either polarity sensing ESIPT (excited state intramolecular proton transfer) dyes or NP FRET (Förster resonance energy transfer). The stability of the coating was determined in response to changes in polarity, pH and ionic strength in the medium. Using the ESIPT system we observed linear changes in signal up to ∼20-25% v/v of co-solvent addition, constituting a break point. Based on such data, we propose a model for coating instability and the important adjustable parameters, such as the electrical charge distribution. FRET data provided confirmatory evidence for the model. The ESIPT dyes and FRET based methods represent new, simple tools for testing NP coating stability in complex environments.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

ESIPT and FRET probes for monitoring nanoparticle polymer coating stability

Coating strategies of inorganic nanoparticles (NPs) can provide properties unavailable to the NP core alone, such as targeting, specific sensing, and increased biocompatibility. Non-covalent amphiphilic NP capping polymers function via hydrophobic interactions with surface ligands and are extensively used to transfer NPs to aqueous media. For applications of coated NPs as actuators (sensors, markers, or for drug delivery) in a complex environment, such as biological systems, it is important to achieve a deep understanding of the factors affecting coating stability and behavior. We have designed a system that tests the coating stability of amphiphilic polymers through a simple fluorescent readout using either polarity sensing ESIPT (excited state intramolecular proton transfer) dyes or NP FRET (Förster resonance energy transfer). The stability of the coating was determined in response to changes in polarity, pH and ionic strength in the medium. Using the ESIPT system we observed linear changes in signal up to ∼20-25% v/v of co-solvent addition, constituting a break point. Based on such data, we propose a model for coating instability and the important adjustable parameters, such as the electrical charge distribution. FRET data provided confirmatory evidence for the model. The ESIPT dyes and FRET based methods represent new, simple tools for testing NP coating stability in complex environments.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Surface nanopatterning of metal thin films by physical vapour deposition onto surface-modified silicon nanodots

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.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Surface nanopatterning of metal thin films by physical vapour deposition onto surface-modified silicon nanodots

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.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Molding and Replication of Ceramic Surfaces with Nanoscale Resolution

The design of reproducible and more efficient nanofabrication routes has become a very active research field in recent years. In particular, the development of new methods for micro- and nanopatterning materials surfaces has attracted the attention of many researchers in industry and academia as a consequence of the growing relevance of patterned surfaces in many technological fields, ranging from optoelectronics to biotechnology. In this work we explore, discuss, and demonstrate the possibility of extending the well-known molding and replication strategy for patterning ceramic materials with nanoscale resolution. To achieve this goal we have combined physical deposition methods, molecule-thick antisticking coatings, and nanostructured substrates as master surfaces. This new perspective on an “old technology”, as molding is, provides an interesting alternative for high-resolution, direct surface-relief patterning of materials that currently requires expensive and time-consuming lithographic approaches.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Influence of capping on the atomistic arrangement in palladium nanoparticles at room temperature

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 images and atomistic Langevin dynamics simulations. It was found that the arrangement of Pd atoms is less ordered in thiolate-protected nanoparticles than in amine-protected ones. The experimental and theoretical data showed that the disorder in ∼3 nm thiolate-protected particles is promoted by the strong S–Pd bond in the sulfide layer that surrounds the nanoparticles.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada