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The salient feature of a supercapacitor is its ability to deliver much higher power density than a battery. A hierarchical design and a cost-effective approach to fabricate high performance supercapacitors using functional carbon nano-particles is reported. A special arc synthesis method is used to produce amorphous/crystalline composite with nitrogen and boron co-doped high charge density carbon nanoparticles. Upon etch removal of the amorphous phase in the composite nanoparticle, a crystalline carbon framework emerges, consisting of a mixture of nano-graphitic sheets mostly in the middle and single nanohorns distributed around the surface of the nanoparticle. These nanoparticles have large internal/external surfaces with subnano channels and sharp nano-tips for high speed charge transport and local charge accumulation. To deliver high power density, the internal resistance of the device is reduced by assembling the nanoparticles via electro-spraying and compacting them into dense films (without any binder) under 700 MPa of pressure before supercapacitor assembly. Taken together, the hierarchical processed supercapacitor has a very high (compared to literature values) power density of nearly 4.5 kW cm−3 and a respectable energy density of 2.45 mWh cm−3. Combining these carbon nanoparticles with large area spraying coating, it can lead to a cost-effective production of high performance supercapacitors.

The salient feature of a supercapacitor is its ability to deliver much higher power density than a battery. A hierarchical design and a cost-effective approach to fabricate high performance supercapacitors using functional carbon nano-particles is reported. A special arc synthesis method is used to produce amorphous/crystalline composite with nitrogen and boron co-doped high charge density carbon nanoparticles. Upon etch removal of the amorphous phase in the composite nanoparticle, a crystalline carbon framework emerges, consisting of a mixture of nano-graphitic sheets mostly in the middle and single nanohorns distributed around the surface of the nanoparticle. These nanoparticles have large internal/external surfaces with subnano channels and sharp nano-tips for high speed charge transport and local charge accumulation. To deliver high power density, the internal resistance of the device is reduced by assembling the nanoparticles via electro-spraying and compacting them into dense films (without any binder) under 700 MPa of pressure before supercapacitor assembly. Taken together, the hierarchical processed supercapacitor has a very high (compared to literature values) power density of nearly 4.5 kW cm−3 and a respectable energy density of 2.45 mWh cm−3. Combining these carbon nanoparticles with large area spraying coating, it can lead to a cost-effective production of high performance supercapacitors.

The salient feature of a supercapacitor is its ability to deliver much higher power density than a battery. A hierarchical design and a cost-effective approach to fabricate high performance supercapacitors using functional carbon nano-particles is reported. A special arc synthesis method is used to produce amorphous/crystalline composite with nitrogen and boron co-doped high charge density carbon nanoparticles. Upon etch removal of the amorphous phase in the composite nanoparticle, a crystalline carbon framework emerges, consisting of a mixture of nano-graphitic sheets mostly in the middle and single nanohorns distributed around the surface of the nanoparticle. These nanoparticles have large internal/external surfaces with subnano channels and sharp nano-tips for high speed charge transport and local charge accumulation. To deliver high power density, the internal resistance of the device is reduced by assembling the nanoparticles via electro-spraying and compacting them into dense films (without any binder) under 700 MPa of pressure before supercapacitor assembly. Taken together, the hierarchical processed supercapacitor has a very high (compared to literature values) power density of nearly 4.5 kW cm−3 and a respectable energy density of 2.45 mWh cm−3. Combining these carbon nanoparticles with large area spraying coating, it can lead to a cost-effective production of high performance supercapacitors.

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.

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.

The salient feature of a supercapacitor is its ability to deliver much higher power density than a battery. A hierarchical design and a cost-effective approach to fabricate high performance supercapacitors using functional carbon nano-particles is reported. A special arc synthesis method is used to produce amorphous/crystalline composite with nitrogen and boron co-doped high charge density carbon nanoparticles. Upon etch removal of the amorphous phase in the composite nanoparticle, a crystalline carbon framework emerges, consisting of a mixture of nano-graphitic sheets mostly in the middle and single nanohorns distributed around the surface of the nanoparticle. These nanoparticles have large internal/external surfaces with subnano channels and sharp nano-tips for high speed charge transport and local charge accumulation. To deliver high power density, the internal resistance of the device is reduced by assembling the nanoparticles via electro-spraying and compacting them into dense films (without any binder) under 700 MPa of pressure before supercapacitor assembly. Taken together, the hierarchical processed supercapacitor has a very high (compared to literature values) power density of nearly 4.5 kW cm−3 and a respectable energy density of 2.45 mWh cm−3. Combining these carbon nanoparticles with large area spraying coating, it can lead to a cost-effective production of high performance supercapacitors.

Au-Pd core-shell nanocubes and triangular nanoparticles were systematically synthesized from a few Pd layers up to fully grown morphologies by a modified seed-mediated growth method. The shape evolution of Au-Pd core-shell nanoparticles from single crystal and singly twinned seed to final concave nanocube and triangular plates are presented at atomic level by Cs-corrected scanning transmission electron microscopy (STEM). The growth mechanism of both morphologies was studied throughout different sizes. It was found that the concave nanocubes grew from octahedral Au seeds due to fast growth along h111i directions; while the triangular nanoparticles grew from singly twinned Au seeds, growing twice as fast in h110i directions along the twin boundary; compared to the h111i direction perpendicular to the twin boundary. Both the concave nanocubes and triangular nanoparticles presented high index facet (HIF) surfaces that will increase the catalytic activity of different reactions.

Lattice mismatch in a bimetallic core–shell nanoparticle will cause strain in the epitaxial shell layer, and if it reaches the critical layer thickness misfit dislocations will appear in order to release the increasing strain. These defects are relevant since they will directly impact the atomic and electronic structures thereby changing the physical and chemical properties of the nanoparticles. Here we report the direct observation and evolution through aberration-corrected scanning transmission electron microscopy of dislocations in AuPd core– shell nanoparticles. Our results show that first Shockley partial dislocations (SPD) combined with stacking faults (SF) appear at the last Pd layer; then, as the shell grows the SPDs and SFs appear at the interface and combine with misfit dislocations, which finally diffuse to the free surfaces due to the alloying of Au into the Pd shell. The critical layer thickness was found to be at least 50% greater than in thin films, confirming that shell growth on nanoparticles can sustain more strain due to the tridimensional nature of the nanoparticles.

Au-Pd core-shell nanocubes and triangular nanoparticles were systematically synthesized from a few Pd layers up to fully grown morphologies by a modified seed-mediated growth method. The shape evolution of Au-Pd core-shell nanoparticles from single crystal and singly twinned seed to final concave nanocube and triangular plates are presented at atomic level by Cs-corrected scanning transmission electron microscopy (STEM). The growth mechanism of both morphologies was studied throughout different sizes. It was found that the concave nanocubes grew from octahedral Au seeds due to fast growth along h111i directions; while the triangular nanoparticles grew from singly twinned Au seeds, growing twice as fast in h110i directions along the twin boundary; compared to the h111i direction perpendicular to the twin boundary. Both the concave nanocubes and triangular nanoparticles presented high index facet (HIF) surfaces that will increase the catalytic activity of different reactions.

Lattice mismatch in a bimetallic core–shell nanoparticle will cause strain in the epitaxial shell layer, and if it reaches the critical layer thickness misfit dislocations will appear in order to release the increasing strain. These defects are relevant since they will directly impact the atomic and electronic structures thereby changing the physical and chemical properties of the nanoparticles. Here we report the direct observation and evolution through aberration-corrected scanning transmission electron microscopy of dislocations in AuPd core– shell nanoparticles. Our results show that first Shockley partial dislocations (SPD) combined with stacking faults (SF) appear at the last Pd layer; then, as the shell grows the SPDs and SFs appear at the interface and combine with misfit dislocations, which finally diffuse to the free surfaces due to the alloying of Au into the Pd shell. The critical layer thickness was found to be at least 50% greater than in thin films, confirming that shell growth on nanoparticles can sustain more strain due to the tridimensional nature of the nanoparticles.

This paper reports the decoration of single wall carbon nanotubes (SWCNTs) with platinum (Pt) nanoparticles using an electrochemical technique, rotating disk slurry electrode (RoDSE). Pt/SWCNTs were electrochemically characterized by cyclic voltammetry technique (CV) and physically characterized through the use of transmission electron microscopy (TEM), energy dispersive spectroscopy - X-ray florescence (EDS-XRF) and X-ray diffraction (XRD). After characterization it was found that electrodeposited nanoparticles had an average particle size of 4.1 ± 0.8 nm. Pt/SWCNTs were used as sensing material for methane (CH4) detection and showed improved sensing properties in a range of concentration from 50 ppm to 200 ppm parts per million (ppm) at room temperature, when compared to other Pt/CNTs-based sensors. The use of this technique for the preparation of Pt/SWCNTs opens a new possibility in the bulk preparation of samples using an electrochemical method and thus their potential use in a wide variety of applications in chemical sensing, fuel cell and others.

This paper reports the decoration of single wall carbon nanotubes (SWCNTs) with platinum (Pt) nanoparticles using an electrochemical technique, rotating disk slurry electrode (RoDSE). Pt/SWCNTs were electrochemically characterized by cyclic voltammetry technique (CV) and physically characterized through the use of transmission electron microscopy (TEM), energy dispersive spectroscopy - X-ray florescence (EDS-XRF) and X-ray diffraction (XRD). After characterization it was found that electrodeposited nanoparticles had an average particle size of 4.1 ± 0.8 nm. Pt/SWCNTs were used as sensing material for methane (CH4) detection and showed improved sensing properties in a range of concentration from 50 ppm to 200 ppm parts per million (ppm) at room temperature, when compared to other Pt/CNTs-based sensors. The use of this technique for the preparation of Pt/SWCNTs opens a new possibility in the bulk preparation of samples using an electrochemical method and thus their potential use in a wide variety of applications in chemical sensing, fuel cell and others.

This paper reports the decoration of single wall carbon nanotubes (SWCNTs) with platinum (Pt) nanoparticles using an electrochemical technique, rotating disk slurry electrode (RoDSE). Pt/SWCNTs were electrochemically characterized by cyclic voltammetry technique (CV) and physically characterized through the use of transmission electron microscopy (TEM), energy dispersive spectroscopy - X-ray florescence (EDS-XRF) and X-ray diffraction (XRD). After characterization it was found that electrodeposited nanoparticles had an average particle size of 4.1 ± 0.8 nm. Pt/SWCNTs were used as sensing material for methane (CH4) detection and showed improved sensing properties in a range of concentration from 50 ppm to 200 ppm parts per million (ppm) at room temperature, when compared to other Pt/CNTs-based sensors. The use of this technique for the preparation of Pt/SWCNTs opens a new possibility in the bulk preparation of samples using an electrochemical method and thus their potential use in a wide variety of applications in chemical sensing, fuel cell and others.

Au-Pd core-shell nanocubes and triangular nanoparticles were systematically synthesized from a few Pd layers up to fully grown morphologies by a modified seed-mediated growth method. The shape evolution of Au-Pd core-shell nanoparticles from single crystal and singly twinned seed to final concave nanocube and triangular plates are presented at atomic level by Cs-corrected scanning transmission electron microscopy (STEM). The growth mechanism of both morphologies was studied throughout different sizes. It was found that the concave nanocubes grew from octahedral Au seeds due to fast growth along h111i directions; while the triangular nanoparticles grew from singly twinned Au seeds, growing twice as fast in h110i directions along the twin boundary; compared to the h111i direction perpendicular to the twin boundary. Both the concave nanocubes and triangular nanoparticles presented high index facet (HIF) surfaces that will increase the catalytic activity of different reactions.

Lattice mismatch in a bimetallic core–shell nanoparticle will cause strain in the epitaxial shell layer, and if it reaches the critical layer thickness misfit dislocations will appear in order to release the increasing strain. These defects are relevant since they will directly impact the atomic and electronic structures thereby changing the physical and chemical properties of the nanoparticles. Here we report the direct observation and evolution through aberration-corrected scanning transmission electron microscopy of dislocations in AuPd core– shell nanoparticles. Our results show that first Shockley partial dislocations (SPD) combined with stacking faults (SF) appear at the last Pd layer; then, as the shell grows the SPDs and SFs appear at the interface and combine with misfit dislocations, which finally diffuse to the free surfaces due to the alloying of Au into the Pd shell. The critical layer thickness was found to be at least 50% greater than in thin films, confirming that shell growth on nanoparticles can sustain more strain due to the tridimensional nature of the nanoparticles.

Au-Pd core-shell nanocubes and triangular nanoparticles were systematically synthesized from a few Pd layers up to fully grown morphologies by a modified seed-mediated growth method. The shape evolution of Au-Pd core-shell nanoparticles from single crystal and singly twinned seed to final concave nanocube and triangular plates are presented at atomic level by Cs-corrected scanning transmission electron microscopy (STEM). The growth mechanism of both morphologies was studied throughout different sizes. It was found that the concave nanocubes grew from octahedral Au seeds due to fast growth along h111i directions; while the triangular nanoparticles grew from singly twinned Au seeds, growing twice as fast in h110i directions along the twin boundary; compared to the h111i direction perpendicular to the twin boundary. Both the concave nanocubes and triangular nanoparticles presented high index facet (HIF) surfaces that will increase the catalytic activity of different reactions.

Lattice mismatch in a bimetallic core–shell nanoparticle will cause strain in the epitaxial shell layer, and if it reaches the critical layer thickness misfit dislocations will appear in order to release the increasing strain. These defects are relevant since they will directly impact the atomic and electronic structures thereby changing the physical and chemical properties of the nanoparticles. Here we report the direct observation and evolution through aberration-corrected scanning transmission electron microscopy of dislocations in AuPd core– shell nanoparticles. Our results show that first Shockley partial dislocations (SPD) combined with stacking faults (SF) appear at the last Pd layer; then, as the shell grows the SPDs and SFs appear at the interface and combine with misfit dislocations, which finally diffuse to the free surfaces due to the alloying of Au into the Pd shell. The critical layer thickness was found to be at least 50% greater than in thin films, confirming that shell growth on nanoparticles can sustain more strain due to the tridimensional nature of the nanoparticles.

This paper reports the decoration of single wall carbon nanotubes (SWCNTs) with platinum (Pt) nanoparticles using an electrochemical technique, rotating disk slurry electrode (RoDSE). Pt/SWCNTs were electrochemically characterized by cyclic voltammetry technique (CV) and physically characterized through the use of transmission electron microscopy (TEM), energy dispersive spectroscopy - X-ray florescence (EDS-XRF) and X-ray diffraction (XRD). After characterization it was found that electrodeposited nanoparticles had an average particle size of 4.1 ± 0.8 nm. Pt/SWCNTs were used as sensing material for methane (CH4) detection and showed improved sensing properties in a range of concentration from 50 ppm to 200 ppm parts per million (ppm) at room temperature, when compared to other Pt/CNTs-based sensors. The use of this technique for the preparation of Pt/SWCNTs opens a new possibility in the bulk preparation of samples using an electrochemical method and thus their potential use in a wide variety of applications in chemical sensing, fuel cell and others.

The stability of decahedral shaped nanoparticles depends upon size. Ino and Marks introduced new mechanisms for the stabilization of decahedra nanoparticles that involves the faceting and formation of surfaces different from {111}. These mechanisms have relevance for small size nanoparticles; however, they do not thoroughly explain how decahedral particles can grow up to 300 nm or more. Here, we report new mechanisms that help stabilize very large decahedra. With the use of aberration-corrected scanning transmission electron microscopy, we observed the formation of high index facets, determined to be of the {511} family, on all five sides of the particles. Surface dislocations strings are also observed. In addition, surface reconstruction of the {001} surfaces can also be observed in two different orientations: with hexagonal strings along the [110] and [410] directions.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Recently, rutile nanotwins were synthesized using high temperature organic solvent methods, yielding two kinds of common high-quality rutile twinned nanocrystals, (101) and (301) twins, accompanied by minor rutile nanorods (Lu et al 2012 CrystEngComm 14 3120-4). In this report, the atomic structures of the rutile and anatase nanocrystals are directly resolved with no need for calculation or image simulation using atomic resolution STEM techniques. The locations of the oxygen rows in the rutile twins' boundaries are directly determined from both HAADF images and ABF images. To the best of our knowledge, this is the first time oxygen columns have been distinguished in rutile twin boundaries using HAADF and BF imaging.

Recently, rutile nanotwins were synthesized using high temperature organic solvent methods, yielding two kinds of common high-quality rutile twinned nanocrystals, (101) and (301) twins, accompanied by minor rutile nanorods (Lu et al 2012 CrystEngComm 14 3120-4). In this report, the atomic structures of the rutile and anatase nanocrystals are directly resolved with no need for calculation or image simulation using atomic resolution STEM techniques. The locations of the oxygen rows in the rutile twins' boundaries are directly determined from both HAADF images and ABF images. To the best of our knowledge, this is the first time oxygen columns have been distinguished in rutile twin boundaries using HAADF and BF imaging.

In the present paper we report the experimental and theoretical analysis of uniaxial loading to study mechanical properties of nanoparticles by direct compression inside a TEM. These experiments are sensitive to the sample and tip geometry limiting the accuracy of the measurements. Nevertheless, very valuable quantitative information can be obtained. It is found that an outstandingly high plasticity near to 100% present on some metal nanoparticles. Molecular dynamics (MD) calculations with as much as possible the same experimental conditions were carried out in order to understand the mechanism at the atomic level of the deformation process of the nanoparticles, and good agreement has been found among them. Three different particles containing twins, decahedral (Dh) and icosahedral (Ic) nanoparticles, and one single twinned (Ts) nanoparticle. The deformation process involves a displacement of the cantilever of about 1000 nm; therefore the experiments are watched at fairly low magnifications to avoid losing sight of the particles. Figure 1 shows two different decahedra before and after deformation. In Figure 1A-B the deformation was very slow to avoid tilting the particle. We can observe how the top part of the particle is flattened compared with the bottom part, which retains some pyramidal shape. The amount of true compressive strain was 80%. Figures 1C-F show an experimental sequence of a Dh nanoparticle while recording the force measurements (true stress vs. true strain is shown in Fig. 3).

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

V-shaped rutile twinned nanorods (VRTNs) with different aspect ratios were synthesized on large scale using a one-pot organic solvothermal method. Although several different types of VRTNs were produced, (101) twinned nanorods were the major product with minor amounts of (301) twins and straight nanorods. STEM, TEM and XRD characterizations show that [001] is the growth direction of VRTNs, with surfaces dominated by {110} facets. Intermediate formation of both brookite and anatase nanorods provides dual pathways to VRTNs’ growth: one path in which anatase seeds trigger and promote brookite nanorod growth; and a second path in which anatase nanorods are formed by oriented attachment. Subsequent dissolution of both brookite and anatase nanorods provides titania to support VRTNs growth.

In the present manuscript we present the feasibility of two different routes to obtain metal nanoparticles: (1) inert gas deposition technique (IGC) and (2) chemical routes. These two routes can enable the production of metal nanoparticles with a well-controlled size and shape distribution. In addition, Co/Au and Pd/Au nanoparticles have been deposited on three different grids with the aim of studying the coalescence of the different metals. The as-synthesized materials, that initially were forming isolated, core-shell, were sintered by thermal treatment (Co/Au) or by strong electron beam irradiation and the subsequent characterization was carried out in situ in an aberration corrected STEM.

Bimetallic nanoparticles present different properties than their monometallic counterparts, opening a wide range of possibilities for different applications. PtPd nanoparticles have raised interest for their many applications in fuel cells, ethanol and methanol oxidation reactions, hydrogen storage, and so on. However, the cost of Pt makes it unpractical to use in big quantities; therefore, one of the big challenges is to synthesize very small catalysts in order to maximize the efficiency in their use. In this work, we synthesized polyhedral PtPd core−shell nanoparticles under 20 nm and characterized them by Cs-corrected scanning transmission electron microscopy. This technique allowed us to probe the structure at the atomic level of these nanoparticles revealing new structural information. We determined the structure of the three main polyhedral morphologies obtained in the synthesis: octahedral, decahedral, and triangular plates. Decahedral PtPd core−shell nanoparticles are novel morphologies for this system. Morphology and defects present in the nanoparticles are shown and discussed.

Graphene oxide nanoribbons (GONRs) are wide bandgap semiconductors that can be reduced to metallic graphene nanoribbons. The transformation of GONRs from their semiconductive to the metallic state by annealing has attracted significant interest due to its simplicity. However, the detailed process by which GONRs transform from widebandgap semiconductors to semimetals with a near zero bandgap is unclear. As a result, precise control of the bandgap between these two states is not currently achievable. Here, we quantitatively examine the removal of oxygen-containing groups and changes in the bandgap during thermal annealing of GONRs. X-ray photoelectron spectroscopy measurements show the progressive removal of oxygen-containing functional groups. Aberration-corrected scanning transmission electron microscopy reveals that initially small graphene regions in GONRs become large stacked graphitic layers during thermal annealing. These structural and chemical changes are correlated with progressive changes in the electrochemical bandgap, monitored by cyclic voltammetry. These results show that small changes in the thermal annealing temperature result in significant changes to the bandgap and chemical composition of GONRs and provide a straightforward method for tuning the bandgap in oxidized graphene structures.

Bimetallic (BM) nanoparticles exhibit different properties depending upon the variation of composition and structure. In this work, we report the detailed analysis of core-shell Au-Pd nanocubes obtained by seed mediated growth process, investigated by means of aberration-corrected scanning transmission electron microscopy (STEM), conventional transmission electron microscopy (TEM), tomography 3D reconstruction and strain mapping. Strain mapping and 3D reconstruction showed for the first time that the nanocube is distorted inwards at all faces. The nano-tripod analysis showed the presence of an incomplete FCC layer only in the surface that acts as an HCP layer. The study showed that there is no loss of crystallinity by the presence of two metals in both the structures. The characterization revealed that nanocubes are formed by concave high index facets of the {410} family with all six faces distorted. The distortion of all faces of nanocube is demonstrated using tomography 3D reconstruction. Detailed analysis of nano-beam electron diffraction (NBD) and high resolution STEM images showed that Pd atoms grow epitaxially on the Au core in both structures. The stability of the nanostructure is provided by the strain. The nano-tripod analysis showed the presence of an incomplete FCC layer in the surface that acts as an HCP layer. The study showed that there is no loss of crystallinity by the presence of two metals in both the structures.

Graphene oxide nanoribbons (GONRs) are wide bandgap semiconductors that can be reduced to metallic graphene nanoribbons. The transformation of GONRs from their semiconductive to the metallic state by annealing has attracted significant interest due to its simplicity. However, the detailed process by which GONRs transform from widebandgap semiconductors to semimetals with a near zero bandgap is unclear. As a result, precise control of the bandgap between these two states is not currently achievable. Here, we quantitatively examine the removal of oxygen-containing groups and changes in the bandgap during thermal annealing of GONRs. X-ray photoelectron spectroscopy measurements show the progressive removal of oxygen-containing functional groups. Aberration-corrected scanning transmission electron microscopy reveals that initially small graphene regions in GONRs become large stacked graphitic layers during thermal annealing. These structural and chemical changes are correlated with progressive changes in the electrochemical bandgap, monitored by cyclic voltammetry. These results show that small changes in the thermal annealing temperature result in significant changes to the bandgap and chemical composition of GONRs and provide a straightforward method for tuning the bandgap in oxidized graphene structures.

Bimetallic nanoparticles present different properties than their monometallic counterparts, opening a wide range of possibilities for different applications. PtPd nanoparticles have raised interest for their many applications in fuel cells, ethanol and methanol oxidation reactions, hydrogen storage, and so on. However, the cost of Pt makes it unpractical to use in big quantities; therefore, one of the big challenges is to synthesize very small catalysts in order to maximize the efficiency in their use. In this work, we synthesized polyhedral PtPd core−shell nanoparticles under 20 nm and characterized them by Cs-corrected scanning transmission electron microscopy. This technique allowed us to probe the structure at the atomic level of these nanoparticles revealing new structural information. We determined the structure of the three main polyhedral morphologies obtained in the synthesis: octahedral, decahedral, and triangular plates. Decahedral PtPd core−shell nanoparticles are novel morphologies for this system. Morphology and defects present in the nanoparticles are shown and discussed.

In the present manuscript we present the feasibility of two different routes to obtain metal nanoparticles: (1) inert gas deposition technique (IGC) and (2) chemical routes. These two routes can enable the production of metal nanoparticles with a well-controlled size and shape distribution. In addition, Co/Au and Pd/Au nanoparticles have been deposited on three different grids with the aim of studying the coalescence of the different metals. The as-synthesized materials, that initially were forming isolated, core-shell, were sintered by thermal treatment (Co/Au) or by strong electron beam irradiation and the subsequent characterization was carried out in situ in an aberration corrected STEM.

V-shaped rutile twinned nanorods (VRTNs) with different aspect ratios were synthesized on large scale using a one-pot organic solvothermal method. Although several different types of VRTNs were produced, (101) twinned nanorods were the major product with minor amounts of (301) twins and straight nanorods. STEM, TEM and XRD characterizations show that [001] is the growth direction of VRTNs, with surfaces dominated by {110} facets. Intermediate formation of both brookite and anatase nanorods provides dual pathways to VRTNs’ growth: one path in which anatase seeds trigger and promote brookite nanorod growth; and a second path in which anatase nanorods are formed by oriented attachment. Subsequent dissolution of both brookite and anatase nanorods provides titania to support VRTNs growth.

Bimetallic (BM) nanoparticles exhibit different properties depending upon the variation of composition and structure. In this work, we report the detailed analysis of core-shell Au-Pd nanocubes obtained by seed mediated growth process, investigated by means of aberration-corrected scanning transmission electron microscopy (STEM), conventional transmission electron microscopy (TEM), tomography 3D reconstruction and strain mapping. Strain mapping and 3D reconstruction showed for the first time that the nanocube is distorted inwards at all faces. The nano-tripod analysis showed the presence of an incomplete FCC layer only in the surface that acts as an HCP layer. The study showed that there is no loss of crystallinity by the presence of two metals in both the structures. The characterization revealed that nanocubes are formed by concave high index facets of the {410} family with all six faces distorted. The distortion of all faces of nanocube is demonstrated using tomography 3D reconstruction. Detailed analysis of nano-beam electron diffraction (NBD) and high resolution STEM images showed that Pd atoms grow epitaxially on the Au core in both structures. The stability of the nanostructure is provided by the strain. The nano-tripod analysis showed the presence of an incomplete FCC layer in the surface that acts as an HCP layer. The study showed that there is no loss of crystallinity by the presence of two metals in both the structures.

This paper establishes the chemical nature of Pd nanoparticles protected by alkanethiolates that were prepared through a ligand placeexchange approach and the two-phase method, first developed for Au nanoparticles by Brust and Schiffrin. After 10 years since the first study on this kind of Pd nanoparticles was published, the surface composition of the particles is a matter of debate in the literature and it has not been unambiguously assessed. The nanoparticles were studied by means of several techniques: UV−visible spectroscopy, scanning transmission electron microscopy, Fourier-transform infrared spectroscopy, extended X-ray absorption fine structure, and X-ray photoelectron spectroscopy. The experimental data, obtained for the 3 nm diameter Pd particles, prepared by both synthetic routes, are consistent with nanoparticles composed by Pd(0) cores surrounded by a submonolayer of sulfide species, which are protected by alkanethiolates. Also, we unambiguously demonstrate that the chemical nature of these particles is very similar to that experimentally found for alkanethiolate-modified bulk Pd. The results from this paper are important not only for handling thiolate-protected Pd nanoparticles in catalysis and sensing, but also for the basic comprehension of metallic nanoparticles and the relation of their surface structure with the synthesis method.

This paper establishes the chemical nature of Pd nanoparticles protected by alkanethiolates that were prepared through a ligand placeexchange approach and the two-phase method, first developed for Au nanoparticles by Brust and Schiffrin. After 10 years since the first study on this kind of Pd nanoparticles was published, the surface composition of the particles is a matter of debate in the literature and it has not been unambiguously assessed. The nanoparticles were studied by means of several techniques: UV−visible spectroscopy, scanning transmission electron microscopy, Fourier-transform infrared spectroscopy, extended X-ray absorption fine structure, and X-ray photoelectron spectroscopy. The experimental data, obtained for the 3 nm diameter Pd particles, prepared by both synthetic routes, are consistent with nanoparticles composed by Pd(0) cores surrounded by a submonolayer of sulfide species, which are protected by alkanethiolates. Also, we unambiguously demonstrate that the chemical nature of these particles is very similar to that experimentally found for alkanethiolate-modified bulk Pd. The results from this paper are important not only for handling thiolate-protected Pd nanoparticles in catalysis and sensing, but also for the basic comprehension of metallic nanoparticles and the relation of their surface structure with the synthesis method.

This paper establishes the chemical nature of Pd nanoparticles protected by alkanethiolates that were prepared through a ligand placeexchange approach and the two-phase method, first developed for Au nanoparticles by Brust and Schiffrin. After 10 years since the first study on this kind of Pd nanoparticles was published, the surface composition of the particles is a matter of debate in the literature and it has not been unambiguously assessed. The nanoparticles were studied by means of several techniques: UV−visible spectroscopy, scanning transmission electron microscopy, Fourier-transform infrared spectroscopy, extended X-ray absorption fine structure, and X-ray photoelectron spectroscopy. The experimental data, obtained for the 3 nm diameter Pd particles, prepared by both synthetic routes, are consistent with nanoparticles composed by Pd(0) cores surrounded by a submonolayer of sulfide species, which are protected by alkanethiolates. Also, we unambiguously demonstrate that the chemical nature of these particles is very similar to that experimentally found for alkanethiolate-modified bulk Pd. The results from this paper are important not only for handling thiolate-protected Pd nanoparticles in catalysis and sensing, but also for the basic comprehension of metallic nanoparticles and the relation of their surface structure with the synthesis method.

The stability of decahedral shaped nanoparticles depends upon size. Ino and Marks introduced new mechanisms for the stabilization of decahedra nanoparticles that involves the faceting and formation of surfaces different from {111}. These mechanisms have relevance for small size nanoparticles; however, they do not thoroughly explain how decahedral particles can grow up to 300 nm or more. Here, we report new mechanisms that help stabilize very large decahedra. With the use of aberration-corrected scanning transmission electron microscopy, we observed the formation of high index facets, determined to be of the {511} family, on all five sides of the particles. Surface dislocations strings are also observed. In addition, surface reconstruction of the {001} surfaces can also be observed in two different orientations: with hexagonal strings along the [110] and [410] directions.

This paper establishes the chemical nature of Pd nanoparticles protected by alkanethiolates that were prepared through a ligand placeexchange approach and the two-phase method, first developed for Au nanoparticles by Brust and Schiffrin. After 10 years since the first study on this kind of Pd nanoparticles was published, the surface composition of the particles is a matter of debate in the literature and it has not been unambiguously assessed. The nanoparticles were studied by means of several techniques: UV−visible spectroscopy, scanning transmission electron microscopy, Fourier-transform infrared spectroscopy, extended X-ray absorption fine structure, and X-ray photoelectron spectroscopy. The experimental data, obtained for the 3 nm diameter Pd particles, prepared by both synthetic routes, are consistent with nanoparticles composed by Pd(0) cores surrounded by a submonolayer of sulfide species, which are protected by alkanethiolates. Also, we unambiguously demonstrate that the chemical nature of these particles is very similar to that experimentally found for alkanethiolate-modified bulk Pd. The results from this paper are important not only for handling thiolate-protected Pd nanoparticles in catalysis and sensing, but also for the basic comprehension of metallic nanoparticles and the relation of their surface structure with the synthesis method.

Using graphene as an ultrathin support, highresolution transmission and scanning transmission electron microscopy (TEM and STEM) images of organic ligandstabilized silicon (Si) nanocrystals with unprecedented clarity were obtained. TEM images of Si nanocrystals are usually obscured on conventional amorphous carbon TEM supports because of low atomic number (Z) contrast. The atomically thin graphene supports enabled clear images of the crystalline Si cores and, for the first time, organic capping ligands. Various twin defects were observed, often accompanied by very significant lattice distortion and anisotropic strain.

The stability of decahedral shaped nanoparticles depends upon size. Ino and Marks introduced new mechanisms for the stabilization of decahedra nanoparticles that involves the faceting and formation of surfaces different from {111}. These mechanisms have relevance for small size nanoparticles; however, they do not thoroughly explain how decahedral particles can grow up to 300 nm or more. Here, we report new mechanisms that help stabilize very large decahedra. With the use of aberration-corrected scanning transmission electron microscopy, we observed the formation of high index facets, determined to be of the {511} family, on all five sides of the particles. Surface dislocations strings are also observed. In addition, surface reconstruction of the {001} surfaces can also be observed in two different orientations: with hexagonal strings along the [110] and [410] directions.

In the present manuscript we present the feasibility of two different routes to obtain metal nanoparticles: (1) inert gas deposition technique (IGC) and (2) chemical routes. These two routes can enable the production of metal nanoparticles with a well-controlled size and shape distribution. In addition, Co/Au and Pd/Au nanoparticles have been deposited on three different grids with the aim of studying the coalescence of the different metals. The as-synthesized materials, that initially were forming isolated, core-shell, were sintered by thermal treatment (Co/Au) or by strong electron beam irradiation and the subsequent characterization was carried out in situ in an aberration corrected STEM.

Bimetallic nanoparticles present different properties than their monometallic counterparts, opening a wide range of possibilities for different applications. PtPd nanoparticles have raised interest for their many applications in fuel cells, ethanol and methanol oxidation reactions, hydrogen storage, and so on. However, the cost of Pt makes it unpractical to use in big quantities; therefore, one of the big challenges is to synthesize very small catalysts in order to maximize the efficiency in their use. In this work, we synthesized polyhedral PtPd core−shell nanoparticles under 20 nm and characterized them by Cs-corrected scanning transmission electron microscopy. This technique allowed us to probe the structure at the atomic level of these nanoparticles revealing new structural information. We determined the structure of the three main polyhedral morphologies obtained in the synthesis: octahedral, decahedral, and triangular plates. Decahedral PtPd core−shell nanoparticles are novel morphologies for this system. Morphology and defects present in the nanoparticles are shown and discussed.

In the present paper we report the experimental and theoretical analysis of uniaxial loading to study mechanical properties of nanoparticles by direct compression inside a TEM. These experiments are sensitive to the sample and tip geometry limiting the accuracy of the measurements. Nevertheless, very valuable quantitative information can be obtained. It is found that an outstandingly high plasticity near to 100% present on some metal nanoparticles. Molecular dynamics (MD) calculations with as much as possible the same experimental conditions were carried out in order to understand the mechanism at the atomic level of the deformation process of the nanoparticles, and good agreement has been found among them. Three different particles containing twins, decahedral (Dh) and icosahedral (Ic) nanoparticles, and one single twinned (Ts) nanoparticle. The deformation process involves a displacement of the cantilever of about 1000 nm; therefore the experiments are watched at fairly low magnifications to avoid losing sight of the particles. Figure 1 shows two different decahedra before and after deformation. In Figure 1A-B the deformation was very slow to avoid tilting the particle. We can observe how the top part of the particle is flattened compared with the bottom part, which retains some pyramidal shape. The amount of true compressive strain was 80%. Figures 1C-F show an experimental sequence of a Dh nanoparticle while recording the force measurements (true stress vs. true strain is shown in Fig. 3).

Bimetallic (BM) nanoparticles exhibit different properties depending upon the variation of composition and structure. In this work, we report the detailed analysis of core-shell Au-Pd nanocubes obtained by seed mediated growth process, investigated by means of aberration-corrected scanning transmission electron microscopy (STEM), conventional transmission electron microscopy (TEM), tomography 3D reconstruction and strain mapping. Strain mapping and 3D reconstruction showed for the first time that the nanocube is distorted inwards at all faces. The nano-tripod analysis showed the presence of an incomplete FCC layer only in the surface that acts as an HCP layer. The study showed that there is no loss of crystallinity by the presence of two metals in both the structures. The characterization revealed that nanocubes are formed by concave high index facets of the {410} family with all six faces distorted. The distortion of all faces of nanocube is demonstrated using tomography 3D reconstruction. Detailed analysis of nano-beam electron diffraction (NBD) and high resolution STEM images showed that Pd atoms grow epitaxially on the Au core in both structures. The stability of the nanostructure is provided by the strain. The nano-tripod analysis showed the presence of an incomplete FCC layer in the surface that acts as an HCP layer. The study showed that there is no loss of crystallinity by the presence of two metals in both the structures.

Graphene oxide nanoribbons (GONRs) are wide bandgap semiconductors that can be reduced to metallic graphene nanoribbons. The transformation of GONRs from their semiconductive to the metallic state by annealing has attracted significant interest due to its simplicity. However, the detailed process by which GONRs transform from widebandgap semiconductors to semimetals with a near zero bandgap is unclear. As a result, precise control of the bandgap between these two states is not currently achievable. Here, we quantitatively examine the removal of oxygen-containing groups and changes in the bandgap during thermal annealing of GONRs. X-ray photoelectron spectroscopy measurements show the progressive removal of oxygen-containing functional groups. Aberration-corrected scanning transmission electron microscopy reveals that initially small graphene regions in GONRs become large stacked graphitic layers during thermal annealing. These structural and chemical changes are correlated with progressive changes in the electrochemical bandgap, monitored by cyclic voltammetry. These results show that small changes in the thermal annealing temperature result in significant changes to the bandgap and chemical composition of GONRs and provide a straightforward method for tuning the bandgap in oxidized graphene structures.

V-shaped rutile twinned nanorods (VRTNs) with different aspect ratios were synthesized on large scale using a one-pot organic solvothermal method. Although several different types of VRTNs were produced, (101) twinned nanorods were the major product with minor amounts of (301) twins and straight nanorods. STEM, TEM and XRD characterizations show that [001] is the growth direction of VRTNs, with surfaces dominated by {110} facets. Intermediate formation of both brookite and anatase nanorods provides dual pathways to VRTNs’ growth: one path in which anatase seeds trigger and promote brookite nanorod growth; and a second path in which anatase nanorods are formed by oriented attachment. Subsequent dissolution of both brookite and anatase nanorods provides titania to support VRTNs growth.

Recently, rutile nanotwins were synthesized using high temperature organic solvent methods, yielding two kinds of common high-quality rutile twinned nanocrystals, (101) and (301) twins, accompanied by minor rutile nanorods (Lu et al 2012 CrystEngComm 14 3120-4). In this report, the atomic structures of the rutile and anatase nanocrystals are directly resolved with no need for calculation or image simulation using atomic resolution STEM techniques. The locations of the oxygen rows in the rutile twins' boundaries are directly determined from both HAADF images and ABF images. To the best of our knowledge, this is the first time oxygen columns have been distinguished in rutile twin boundaries using HAADF and BF imaging.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Using graphene as an ultrathin support, highresolution transmission and scanning transmission electron microscopy (TEM and STEM) images of organic ligandstabilized silicon (Si) nanocrystals with unprecedented clarity were obtained. TEM images of Si nanocrystals are usually obscured on conventional amorphous carbon TEM supports because of low atomic number (Z) contrast. The atomically thin graphene supports enabled clear images of the crystalline Si cores and, for the first time, organic capping ligands. Various twin defects were observed, often accompanied by very significant lattice distortion and anisotropic strain.