The early stages of nanocrystal nucleation and growth are still an active field of research and r... more The early stages of nanocrystal nucleation and growth are still an active field of research and remain unrevealed. In this work, by the combination of aberrationcorrected transmission electron microscopy (TEM) and electrochemical characterization of the electrodeposition of different metals, we provide a complete reformulation of the Volmer−Weber 3D island growth mechanism, which has always been accepted to explain the early stages of metal electrodeposition and thin-film growth on low-energy substrates. We have developed a Generalized Electrochemical Aggregative Growth Mechanism which mimics the atomistic processes during the early stages of thin-film growth, by incorporating nanoclusters as building blocks. We discuss the influence of new processes such as nanocluster self-limiting growth, surface diffusion, aggregation, and coalescence on the growth mechanism and morphology of the resulting nanostructures. Self-limiting growth mechanisms hinder nanocluster growth and favor coalescence driven growth. The size of the primary nanoclusters is independent of the applied potential and deposition time. The balance between nucleation, nanocluster surface diffusion, and coalescence depends on the material and the overpotential, and influences strongly the morphology of the deposits. A small extent of coalescence leads to ultraporous dendritic structures, large surface coverage, and small particle size. Contrarily, full recrystallization leads to larger hemispherical monocrystalline islands and smaller particle density. The mechanism we propose represents a scientific breakthrough from the fundamental point of view and indicates that achieving the right balance between nucleation, self-limiting growth, cluster surface diffusion, and coalescence is essential and opens new, exciting possibilities to build up enhanced supported nanostructures using nanoclusters as building blocks.
Type III deep eutectic solvents (DES) have attracted significant interest as both environmentally... more Type III deep eutectic solvents (DES) have attracted significant interest as both environmentally friendly and functional solvents that are, in some ways, advantageous to traditional aqueous systems. While these solvents continue to produce remarkable thin films and nanoparticle assemblies, their interactions with metallic surfaces are complex and difficult to manipulate. In this study, the near-surface region (2−600 nm) of a carbon surface is investigated immediately following silver nanoparticle nucleation and growth. This is accomplished, in situ, using a novel grazing transmission small-angle X-ray scattering approach with simultaneous voltammetry and electrochemical impedance spectroscopy. With this physical and electrochemical approach, the time evolution of three distinct surface interaction phenomena is observed: aggregation and coalescence of Ag nanoparticles, multilayer perturbations induced by nonaggregated Ag nanoparticles, and a stepwise transport of dissolved Ag species from the carbon surface. The multilayer perturbations contain charge-separated regions of positively charged choline-ethaline and negatively charged Ag and Cl species. Both aggregation-coalescence and the stepwise decrease in Ag precursor near the surface are observed to be very slow (∼2 h) processes, as both ion and particle transport are significantly impeded in a DES as compared to aqueous electrolytes. Altogether, this study shows how the unique chemistry of the DES changes near the surface and in the presence of nanoparticles that adsorb the constituent species.
... size distribution function. Size distributions are then obtained by fitting the data to a max... more ... size distribution function. Size distributions are then obtained by fitting the data to a maximum entropy model using the Irena package for Igor Pro. Josh Explains ... 1996, 100, 837–844. (12)Grujicic, D.; Pesic, B. Electrochimica Acta 2002, 47, 2901–2912. ...
In this work the nature of gas transport through different Al(OH) 3 gels (smut) formed during the... more In this work the nature of gas transport through different Al(OH) 3 gels (smut) formed during the AC electrograining process is characterized. A new in situ approach that combines small angle X-ray scattering (SAXS) with the electrochemical response is used to show that gas transport through the smut is different with and without additives. We conclude that gas transport occurs, predominantly, through temporary passageways when no additives are used and through permanent pores with additives, indicating a difference in the gel (smut) rheological properties in each case. Gas transport, through the smut, is therefore considered to be a phenomenon that depends on the electrolyte composition, which is expected to alter the gel properties. These changes in the gas transport away from the metal surface correlate with changes in the potential response of the system. The uniquely lower overpotential, associated with temporary passageways results in an etched-like morphology, suggesting that the gas permeability of the surface gel is a factor that affects the final pit morphology.
Interfacial phenomena occurring during high metal dissolution rates, in an environment with diffu... more Interfacial phenomena occurring during high metal dissolution rates, in an environment with diffusion-limited transport of dissolution products, have been investigated using time-resolved X-ray diffraction (XRD), small-angle X-ray scattering (SAXS) and fast radiography. Time resolved SAXS data reveal that highly anisotropic interfacial X-ray scattering always precedes salt nucleation. The correlation between the interfacial scattering the presence of salt crystals indicates that the interface is between the metal electrode and the concentrated NiCl2 electrolyte and can therefore be interpreted as reflectivity or Porod scattering. Using fast radiography, we show that continued crystal nucleation and growth results in formation of a crystal-containing salt layer, which initially extends far from the interface (>20 μm), until the NiCl2 concentration decreases below saturation. Dissolution of this thick salt layer occurs mainly at the furthest boundary from the interface until, the salt layer thickness decreases to a steady state value, resulting in a steady state limiting current. These results show that the presence of a crystalline salt layer at a dissolving interface causes microscopic roughening which has implications for understanding both the role of salt films in pitting corrosion and electrochemical processing.
Nanothermites composed of aluminum and molybdenum trioxide (MoO(3)) have a high energy density an... more Nanothermites composed of aluminum and molybdenum trioxide (MoO(3)) have a high energy density and are attractive energetic materials. To enhance the surface contact between the spherical Al nanoparticles and the sheet-like MoO(3) particles, the mixture can be cold-pressed into a pelleted composite. However, it was found that the burn rate of the pellets decreased as the density of the pellets increased, contrary to expectation. Ultra-small angle X-ray scattering (USAXS) data and scanning electron microscopy (SEM) were used to elucidate the internal structure of the Al nanoparticles, and nanoparticle aggregate in the composite. Results from both SEM imaging and USAXS analysis indicate that as the density of the pellet increased, a fraction of the Al nanoparticles are compressed into sintered aggregates. The sintered Al nanoparticles lost contrast after forming the larger aggregates and no longer scattered X-rays as individual particles. The sintered aggregates hinder the burn rate, since the Al nanoparticles that make them up can no longer diffuse freely as individual particles during combustion. Results suggest a qualitative relationship for the probability that nanoparticles will sinter, based on the particle sizes and the initial structure of their respective agglomerates, as characterized by the mass fractal dimension.
The early stages of nanocrystal nucleation and growth are still an active field of research and r... more The early stages of nanocrystal nucleation and growth are still an active field of research and remain unrevealed. In this work, by the combination of aberrationcorrected transmission electron microscopy (TEM) and electrochemical characterization of the electrodeposition of different metals, we provide a complete reformulation of the Volmer−Weber 3D island growth mechanism, which has always been accepted to explain the early stages of metal electrodeposition and thin-film growth on low-energy substrates. We have developed a Generalized Electrochemical Aggregative Growth Mechanism which mimics the atomistic processes during the early stages of thin-film growth, by incorporating nanoclusters as building blocks. We discuss the influence of new processes such as nanocluster self-limiting growth, surface diffusion, aggregation, and coalescence on the growth mechanism and morphology of the resulting nanostructures. Self-limiting growth mechanisms hinder nanocluster growth and favor coalescence driven growth. The size of the primary nanoclusters is independent of the applied potential and deposition time. The balance between nucleation, nanocluster surface diffusion, and coalescence depends on the material and the overpotential, and influences strongly the morphology of the deposits. A small extent of coalescence leads to ultraporous dendritic structures, large surface coverage, and small particle size. Contrarily, full recrystallization leads to larger hemispherical monocrystalline islands and smaller particle density. The mechanism we propose represents a scientific breakthrough from the fundamental point of view and indicates that achieving the right balance between nucleation, self-limiting growth, cluster surface diffusion, and coalescence is essential and opens new, exciting possibilities to build up enhanced supported nanostructures using nanoclusters as building blocks.
ABSTRACT The chemistry of molybdenum species in artificial corrosion pits on 316L stainless steel... more ABSTRACT The chemistry of molybdenum species in artificial corrosion pits on 316L stainless steel was investigated using X-ray absorption spectroscopy (XANES). It was found that the K-edge spectra are consistent with the presence of an Mo(III) species. The presence of Mo(VI) polymolybdates as been proposed to explain the well-known beneficial effects of Mo in decreasing the susceptibility of stainless steel to localised corrosion, but no evidence of these species was found. High resolution measurements (with a spatial resolution of 3.5 mu m in the vertical direction) through the dissolving metal interface did not detect the presence of any different Mo-containing species in the vicinity of the salt film. However, the spatial resolution was insufficient to detect the presence of submonolayer species on the dissolving metal surface that have been proposed to block active dissolution.
AC electrochemical processes have found applications in controlled surface roughening of aluminiu... more AC electrochemical processes have found applications in controlled surface roughening of aluminium (AC electrograining), fine-tip sharpening for field ion microscopy (AC machining) and thin film anodising (AC anodising). The formation of a surface layer and copious amounts of hydrogen gas are inherent in these AC processes. The presence of a resistance is observed in these processes but it is the source of the resistance that is important to the understanding of ionic transport through the surface film. The AC electrograining process is chosen here, as the annual worldwide production of aluminium plate for high quality lithographic printing and for energy storage super-capacitors is in excess of 800 km 2 . In this study, a method to detect gas in the surface layer (smut) in-situ with Small Angle X-ray Scattering (SAXS) is proposed. The total scattering from the in-situ SAXS is used with knowledge of the total volume of smut to explain how a gas fraction can be determined by comparing two samples. Results suggest that a gas fraction can be retained in smut during AC electrograining, the degree to which varies with smut properties.
A new experimental approach to study nanoparticle size distributions in electrochemical depositio... more A new experimental approach to study nanoparticle size distributions in electrochemical deposition processes by in-situ Small Angle X-ray Scattering (SAXS) is presented. A specifically designed flow cell was used to acquire SAXS frames after different nucleation and growth pulses in a potentiostatic multiple pulse approach. Measurements show that after a correct background subtraction, scattered intensity variations are only caused by electrodeposited silver nanoparticles and that size distribution evolution derived after modeling the SAXS data is in agreement with electrochemical particle growth.
ABSTRACT Pitting corrosion of stainless steel has been investigated with high-resolution in situ ... more ABSTRACT Pitting corrosion of stainless steel has been investigated with high-resolution in situ X-ray microtomography. The growth of pits at the tip of stainless steel pins has been observed with 3D microtomography under different conditions of applied current and cell potential. The results demonstrate how pits evolve in stainless steel, forming a characteristic “lacy” cover of perforated metal. In addition, it is shown how the shape of pits becomes modified by MnS inclusions.
The early stages of nanocrystal nucleation and growth are still an active field of research and r... more The early stages of nanocrystal nucleation and growth are still an active field of research and remain unrevealed. In this work, by the combination of aberrationcorrected transmission electron microscopy (TEM) and electrochemical characterization of the electrodeposition of different metals, we provide a complete reformulation of the Volmer−Weber 3D island growth mechanism, which has always been accepted to explain the early stages of metal electrodeposition and thin-film growth on low-energy substrates. We have developed a Generalized Electrochemical Aggregative Growth Mechanism which mimics the atomistic processes during the early stages of thin-film growth, by incorporating nanoclusters as building blocks. We discuss the influence of new processes such as nanocluster self-limiting growth, surface diffusion, aggregation, and coalescence on the growth mechanism and morphology of the resulting nanostructures. Self-limiting growth mechanisms hinder nanocluster growth and favor coalescence driven growth. The size of the primary nanoclusters is independent of the applied potential and deposition time. The balance between nucleation, nanocluster surface diffusion, and coalescence depends on the material and the overpotential, and influences strongly the morphology of the deposits. A small extent of coalescence leads to ultraporous dendritic structures, large surface coverage, and small particle size. Contrarily, full recrystallization leads to larger hemispherical monocrystalline islands and smaller particle density. The mechanism we propose represents a scientific breakthrough from the fundamental point of view and indicates that achieving the right balance between nucleation, self-limiting growth, cluster surface diffusion, and coalescence is essential and opens new, exciting possibilities to build up enhanced supported nanostructures using nanoclusters as building blocks.
Type III deep eutectic solvents (DES) have attracted significant interest as both environmentally... more Type III deep eutectic solvents (DES) have attracted significant interest as both environmentally friendly and functional solvents that are, in some ways, advantageous to traditional aqueous systems. While these solvents continue to produce remarkable thin films and nanoparticle assemblies, their interactions with metallic surfaces are complex and difficult to manipulate. In this study, the near-surface region (2−600 nm) of a carbon surface is investigated immediately following silver nanoparticle nucleation and growth. This is accomplished, in situ, using a novel grazing transmission small-angle X-ray scattering approach with simultaneous voltammetry and electrochemical impedance spectroscopy. With this physical and electrochemical approach, the time evolution of three distinct surface interaction phenomena is observed: aggregation and coalescence of Ag nanoparticles, multilayer perturbations induced by nonaggregated Ag nanoparticles, and a stepwise transport of dissolved Ag species from the carbon surface. The multilayer perturbations contain charge-separated regions of positively charged choline-ethaline and negatively charged Ag and Cl species. Both aggregation-coalescence and the stepwise decrease in Ag precursor near the surface are observed to be very slow (∼2 h) processes, as both ion and particle transport are significantly impeded in a DES as compared to aqueous electrolytes. Altogether, this study shows how the unique chemistry of the DES changes near the surface and in the presence of nanoparticles that adsorb the constituent species.
... size distribution function. Size distributions are then obtained by fitting the data to a max... more ... size distribution function. Size distributions are then obtained by fitting the data to a maximum entropy model using the Irena package for Igor Pro. Josh Explains ... 1996, 100, 837–844. (12)Grujicic, D.; Pesic, B. Electrochimica Acta 2002, 47, 2901–2912. ...
In this work the nature of gas transport through different Al(OH) 3 gels (smut) formed during the... more In this work the nature of gas transport through different Al(OH) 3 gels (smut) formed during the AC electrograining process is characterized. A new in situ approach that combines small angle X-ray scattering (SAXS) with the electrochemical response is used to show that gas transport through the smut is different with and without additives. We conclude that gas transport occurs, predominantly, through temporary passageways when no additives are used and through permanent pores with additives, indicating a difference in the gel (smut) rheological properties in each case. Gas transport, through the smut, is therefore considered to be a phenomenon that depends on the electrolyte composition, which is expected to alter the gel properties. These changes in the gas transport away from the metal surface correlate with changes in the potential response of the system. The uniquely lower overpotential, associated with temporary passageways results in an etched-like morphology, suggesting that the gas permeability of the surface gel is a factor that affects the final pit morphology.
Interfacial phenomena occurring during high metal dissolution rates, in an environment with diffu... more Interfacial phenomena occurring during high metal dissolution rates, in an environment with diffusion-limited transport of dissolution products, have been investigated using time-resolved X-ray diffraction (XRD), small-angle X-ray scattering (SAXS) and fast radiography. Time resolved SAXS data reveal that highly anisotropic interfacial X-ray scattering always precedes salt nucleation. The correlation between the interfacial scattering the presence of salt crystals indicates that the interface is between the metal electrode and the concentrated NiCl2 electrolyte and can therefore be interpreted as reflectivity or Porod scattering. Using fast radiography, we show that continued crystal nucleation and growth results in formation of a crystal-containing salt layer, which initially extends far from the interface (>20 μm), until the NiCl2 concentration decreases below saturation. Dissolution of this thick salt layer occurs mainly at the furthest boundary from the interface until, the salt layer thickness decreases to a steady state value, resulting in a steady state limiting current. These results show that the presence of a crystalline salt layer at a dissolving interface causes microscopic roughening which has implications for understanding both the role of salt films in pitting corrosion and electrochemical processing.
Nanothermites composed of aluminum and molybdenum trioxide (MoO(3)) have a high energy density an... more Nanothermites composed of aluminum and molybdenum trioxide (MoO(3)) have a high energy density and are attractive energetic materials. To enhance the surface contact between the spherical Al nanoparticles and the sheet-like MoO(3) particles, the mixture can be cold-pressed into a pelleted composite. However, it was found that the burn rate of the pellets decreased as the density of the pellets increased, contrary to expectation. Ultra-small angle X-ray scattering (USAXS) data and scanning electron microscopy (SEM) were used to elucidate the internal structure of the Al nanoparticles, and nanoparticle aggregate in the composite. Results from both SEM imaging and USAXS analysis indicate that as the density of the pellet increased, a fraction of the Al nanoparticles are compressed into sintered aggregates. The sintered Al nanoparticles lost contrast after forming the larger aggregates and no longer scattered X-rays as individual particles. The sintered aggregates hinder the burn rate, since the Al nanoparticles that make them up can no longer diffuse freely as individual particles during combustion. Results suggest a qualitative relationship for the probability that nanoparticles will sinter, based on the particle sizes and the initial structure of their respective agglomerates, as characterized by the mass fractal dimension.
The early stages of nanocrystal nucleation and growth are still an active field of research and r... more The early stages of nanocrystal nucleation and growth are still an active field of research and remain unrevealed. In this work, by the combination of aberrationcorrected transmission electron microscopy (TEM) and electrochemical characterization of the electrodeposition of different metals, we provide a complete reformulation of the Volmer−Weber 3D island growth mechanism, which has always been accepted to explain the early stages of metal electrodeposition and thin-film growth on low-energy substrates. We have developed a Generalized Electrochemical Aggregative Growth Mechanism which mimics the atomistic processes during the early stages of thin-film growth, by incorporating nanoclusters as building blocks. We discuss the influence of new processes such as nanocluster self-limiting growth, surface diffusion, aggregation, and coalescence on the growth mechanism and morphology of the resulting nanostructures. Self-limiting growth mechanisms hinder nanocluster growth and favor coalescence driven growth. The size of the primary nanoclusters is independent of the applied potential and deposition time. The balance between nucleation, nanocluster surface diffusion, and coalescence depends on the material and the overpotential, and influences strongly the morphology of the deposits. A small extent of coalescence leads to ultraporous dendritic structures, large surface coverage, and small particle size. Contrarily, full recrystallization leads to larger hemispherical monocrystalline islands and smaller particle density. The mechanism we propose represents a scientific breakthrough from the fundamental point of view and indicates that achieving the right balance between nucleation, self-limiting growth, cluster surface diffusion, and coalescence is essential and opens new, exciting possibilities to build up enhanced supported nanostructures using nanoclusters as building blocks.
ABSTRACT The chemistry of molybdenum species in artificial corrosion pits on 316L stainless steel... more ABSTRACT The chemistry of molybdenum species in artificial corrosion pits on 316L stainless steel was investigated using X-ray absorption spectroscopy (XANES). It was found that the K-edge spectra are consistent with the presence of an Mo(III) species. The presence of Mo(VI) polymolybdates as been proposed to explain the well-known beneficial effects of Mo in decreasing the susceptibility of stainless steel to localised corrosion, but no evidence of these species was found. High resolution measurements (with a spatial resolution of 3.5 mu m in the vertical direction) through the dissolving metal interface did not detect the presence of any different Mo-containing species in the vicinity of the salt film. However, the spatial resolution was insufficient to detect the presence of submonolayer species on the dissolving metal surface that have been proposed to block active dissolution.
AC electrochemical processes have found applications in controlled surface roughening of aluminiu... more AC electrochemical processes have found applications in controlled surface roughening of aluminium (AC electrograining), fine-tip sharpening for field ion microscopy (AC machining) and thin film anodising (AC anodising). The formation of a surface layer and copious amounts of hydrogen gas are inherent in these AC processes. The presence of a resistance is observed in these processes but it is the source of the resistance that is important to the understanding of ionic transport through the surface film. The AC electrograining process is chosen here, as the annual worldwide production of aluminium plate for high quality lithographic printing and for energy storage super-capacitors is in excess of 800 km 2 . In this study, a method to detect gas in the surface layer (smut) in-situ with Small Angle X-ray Scattering (SAXS) is proposed. The total scattering from the in-situ SAXS is used with knowledge of the total volume of smut to explain how a gas fraction can be determined by comparing two samples. Results suggest that a gas fraction can be retained in smut during AC electrograining, the degree to which varies with smut properties.
A new experimental approach to study nanoparticle size distributions in electrochemical depositio... more A new experimental approach to study nanoparticle size distributions in electrochemical deposition processes by in-situ Small Angle X-ray Scattering (SAXS) is presented. A specifically designed flow cell was used to acquire SAXS frames after different nucleation and growth pulses in a potentiostatic multiple pulse approach. Measurements show that after a correct background subtraction, scattered intensity variations are only caused by electrodeposited silver nanoparticles and that size distribution evolution derived after modeling the SAXS data is in agreement with electrochemical particle growth.
ABSTRACT Pitting corrosion of stainless steel has been investigated with high-resolution in situ ... more ABSTRACT Pitting corrosion of stainless steel has been investigated with high-resolution in situ X-ray microtomography. The growth of pits at the tip of stainless steel pins has been observed with 3D microtomography under different conditions of applied current and cell potential. The results demonstrate how pits evolve in stainless steel, forming a characteristic “lacy” cover of perforated metal. In addition, it is shown how the shape of pits becomes modified by MnS inclusions.
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