Deposition and stripping processes of tin on gold film electrodes studied by surface conductance

The CV and surface conductance (SC) responses of tin species adsorbed on evaporated gold film electrodes were studied as a function of the potential window and the potential sweep rate. Sn adatoms were generated either, by reducing Sn(II) present in the solution (u p d) or by first irreversibly adsorbing Sn(II) and then reducing it in the supporting electrolyte alone. The experimental results show that at potentials about E ≈ −0.25 V(versus SCE), all the Sn(II) is reduced to Sn(0) and this species is adsorbed on the electrode surface. The subsequent oxidation of Sn(0) leads to Sn(II)ad, adsorbed on the electrode. This species desorbs only when the Sn(II)ad is further oxidised to soluble Sn(IV). The number of electrons involved in the reduction of Sn(II) to Sn(0) and vice versa is two. On the other hand, the analysis of the resistance measurements at low coverage is made by applying the surface Linde’s rule. This leads to the conclusion that the Sn(0) behaves as an interstitial impurity. SC experiments, made in the potential region corresponding to Sn bulk deposition, suggest the formation of a bulk Sn–Au alloy.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Radiation Damage Mechanisms of Monolayer-Protected Nanoparticles via TEM Analysis

In this work, it is shown that thiol-protected Au nanoparticles (AuNPs@SR) of approximately 3.4 nm size suffered unexpectedly high radiation damage under standard transmission electron microscopy (TEM) operating conditions. For metallic systems (conducting sample), it is expected that the greatest contribution to the damage comes from knock-on displacement, but radiolysis is the most probable radiation damage mechanism for organic samples. The radiation damage of the electron beam produces huge changes in AuNPs' structure, leading to coalescence of the Au cores when their {100} surfaces are facing each other. The complete coalescence process involve thiol desoprtion, AuNPs' reorientation, and surface diffusion of Au adatoms, which produce the oriented attachment of the Au cores. The knock-on displacement cannot explain by itself the time taken by the entire process. Through a rigorous analysis, we rationalize the results considering that because of the small size of AuNPs they have a lower electron density than the bulk material which favors radiolytic damage.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Radiation Damage Mechanisms of Monolayer-Protected Nanoparticles via TEM Analysis

In this work, it is shown that thiol-protected Au nanoparticles (AuNPs@SR) of approximately 3.4 nm size suffered unexpectedly high radiation damage under standard transmission electron microscopy (TEM) operating conditions. For metallic systems (conducting sample), it is expected that the greatest contribution to the damage comes from knock-on displacement, but radiolysis is the most probable radiation damage mechanism for organic samples. The radiation damage of the electron beam produces huge changes in AuNPs' structure, leading to coalescence of the Au cores when their {100} surfaces are facing each other. The complete coalescence process involve thiol desoprtion, AuNPs' reorientation, and surface diffusion of Au adatoms, which produce the oriented attachment of the Au cores. The knock-on displacement cannot explain by itself the time taken by the entire process. Through a rigorous analysis, we rationalize the results considering that because of the small size of AuNPs they have a lower electron density than the bulk material which favors radiolytic damage.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Radiation Damage Mechanisms of Monolayer-Protected Nanoparticles via TEM Analysis

In this work, it is shown that thiol-protected Au nanoparticles (AuNPs@SR) of approximately 3.4 nm size suffered unexpectedly high radiation damage under standard transmission electron microscopy (TEM) operating conditions. For metallic systems (conducting sample), it is expected that the greatest contribution to the damage comes from knock-on displacement, but radiolysis is the most probable radiation damage mechanism for organic samples. The radiation damage of the electron beam produces huge changes in AuNPs' structure, leading to coalescence of the Au cores when their {100} surfaces are facing each other. The complete coalescence process involve thiol desoprtion, AuNPs' reorientation, and surface diffusion of Au adatoms, which produce the oriented attachment of the Au cores. The knock-on displacement cannot explain by itself the time taken by the entire process. Through a rigorous analysis, we rationalize the results considering that because of the small size of AuNPs they have a lower electron density than the bulk material which favors radiolytic damage.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Pattern preserving deposition: Experimental results and modeling

In this work we discuss pattern-preserving growth during metal deposition from the vapor on micro/nano-structured metal substrates. Experimental results for Cu deposition on patterned Cu substrates show pattern preserving growth or pattern destruction depending on the incident angle. We introduce a mesoscopic 1+1 dimensional model including deposition flow (directed and isotropic), surface diffusion and shadowing effects that account for the experimental growth data. Moreover, simulations on post-deposition annealing, for high aspect-ratio patterns show departures from the predictions of the linear theory for surface diffusion.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Deposition and stripping processes of tin on gold film electrodes studied by surface conductance

The CV and surface conductance (SC) responses of tin species adsorbed on evaporated gold film electrodes were studied as a function of the potential window and the potential sweep rate. Sn adatoms were generated either, by reducing Sn(II) present in the solution (u p d) or by first irreversibly adsorbing Sn(II) and then reducing it in the supporting electrolyte alone. The experimental results show that at potentials about E ≈ −0.25 V(versus SCE), all the Sn(II) is reduced to Sn(0) and this species is adsorbed on the electrode surface. The subsequent oxidation of Sn(0) leads to Sn(II)ad, adsorbed on the electrode. This species desorbs only when the Sn(II)ad is further oxidised to soluble Sn(IV). The number of electrons involved in the reduction of Sn(II) to Sn(0) and vice versa is two. On the other hand, the analysis of the resistance measurements at low coverage is made by applying the surface Linde’s rule. This leads to the conclusion that the Sn(0) behaves as an interstitial impurity. SC experiments, made in the potential region corresponding to Sn bulk deposition, suggest the formation of a bulk Sn–Au alloy.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Pattern preserving deposition: Experimental results and modeling

In this work we discuss pattern-preserving growth during metal deposition from the vapor on micro/nano-structured metal substrates. Experimental results for Cu deposition on patterned Cu substrates show pattern preserving growth or pattern destruction depending on the incident angle. We introduce a mesoscopic 1+1 dimensional model including deposition flow (directed and isotropic), surface diffusion and shadowing effects that account for the experimental growth data. Moreover, simulations on post-deposition annealing, for high aspect-ratio patterns show departures from the predictions of the linear theory for surface diffusion.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Análisis del potencial a circuito abierto durante la síntesis de nanopartículas de oro

Se describen estudios sobre mezclas de reacción a las que se adiciona NaBH4 para la síntesis de nanopartículas metálicas. Se midió el potencial a circuito abierto de las soluciones utilizando diferentes electrodos y composiciones de las mezclas. Estos estudios permitieron determinar cuáles fenómenos pueden dificultar la reducción total de especies metálicas solubles, un aspecto de relevancia que ha sido informado. Se determinó que la síntesis debe llevarse utilizando (i) medios ligeramente alcalinos de pH regulado, para evitar la hidrólisis de los aniones borohidruro; (ii) soluciones con baja concentración de oxígeno molecular, de manera de evitar un consumo del reductor por parte del O2; (iii) fuerzas iónicas moderadas, para evitar la aglomeración de las nanopartículas formadas.Facultad de Ciencias Exacta

Análisis del potencial a circuito abierto durante la síntesis de nanopartículas de oro

Se describen estudios sobre mezclas de reacción a las que se adiciona NaBH4 para la síntesis de nanopartículas metálicas. Se midió el potencial a circuito abierto de las soluciones utilizando diferentes electrodos y composiciones de las mezclas. Estos estudios permitieron determinar cuáles fenómenos pueden dificultar la reducción total de especies metálicas solubles, un aspecto de relevancia que ha sido informado. Se determinó que la síntesis debe llevarse utilizando (i) medios ligeramente alcalinos de pH regulado, para evitar la hidrólisis de los aniones borohidruro; (ii) soluciones con baja concentración de oxígeno molecular, de manera de evitar un consumo del reductor por parte del O2; (iii) fuerzas iónicas moderadas, para evitar la aglomeración de las nanopartículas formadas.Facultad de Ciencias Exacta

Atomic Sulfur Formation Mechanism on 3‑Mercaptopropanoic Acid Derivative Self-Assembled Monolayers: Understanding the C–SBond Cleavage

Self-assembled monolayers (SAMs) of ω-carboxylic acid thiols are very important in the surface modification of metals, especially on gold surfaces. Indeed, the 3-mercaptopropanoic acid (MPA) and its ester or amide derivatives are widely used for SAM-based sensor design. It was already shown that MPA does not suffer C−S bond scission when adsorbed on Au. On the other hand, in this work we demonstrate that its simplest derivative, methyl 3-mercapto propionate (Me-MPA), is prone to form significant amounts of atomic sulfur when adsorbed on Au. The MPA derivatives are more sensible than MPA itself to alkaline solutions, and its SAM-based sensors will rapidly degrade given atomic sulfur. In this work, we study the simplest MPA derivative Me-MPA SAMs on preferentially oriented Au(111) surfaces by XPS and electrochemical measurements. It was found that the desulfuration of Me-MPA depends on its preparation conditions (grown from ethanol or toluene solution) and on its post-treatment with alkaline solution. In order to explain the S−C bond scission on Me-MPA SAMs, we discuss different reaction mechanisms. We concluded that the reaction mechanism involves an E1cB elimination pathway (β-elimination). This reaction mechanism also explains the desulfuration behavior of other important related molecules like L-cysteine and glutathione.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada