Turning off Hydrogen To Realize Seeded Growth of Subcentimeter Single-Crystal Graphene Grains on Copper

Subcentimeter single-crystalline graphene grains, with diameter up to 5.9 mm, have been successfully synthesized by tuning the nucleation density during atmospheric pressure chemical vapor deposition. Morphology studies show the existence of a single large nanoparticle (>∼20 nm in diameter) at the geometric center of those graphene grains. Similar size particles were produced by slightly oxidizing the copper surface to obtain oxide nanoparticles in Ar-only environments, followed by reduction into large copper nanoparticles under H₂/Ar environment, and are thus explained to be the main constituent nuclei for graphene growth. On this basis, we were able to control the nanoparticle density by adjusting the degree of oxidation and hydrogen annealing duration, thereby controlling nucleation density and consequently controlling graphene grain sizes. In addition, we found that hydrogen plays dual roles on copper morphology during the whole growth process, that is, removing surface irregularities and, at the same time, etching the copper surface to produce small nanoparticles that have only limited effect on nucleation for graphene growth. Our reported approach provides a highly efficient method for production of graphene film with long-range electronic connectivity and structure coherence

Polarizability of Six-Helix Bundle and Triangle DNA Origami and Their Escape Characteristics from a Dielectrophoretic Trap

DNA nanoassemblies, such as DNA origamis, hold promise in biosensing, drug delivery, nanoelectronic circuits, and biological computing, which require suitable methods for migration and precision positioning. Insulator-based dielectrophoresis (iDEP) has been demonstrated as a powerful migration and trapping tool for μm- and nm-sized colloids as well as DNA origamis. However, little is known about the polarizability of origami species, which is responsible for their dielectrophoretic migration. Here, we report the experimentally determined polarizabilities of the six-helix bundle origami (6HxB) and triangle origami by measuring the migration times through a potential landscape exhibiting dielectrophoretic barriers. The resulting migration times correlate to the depth of the dielectrophoretic potential barrier and the escape characteristics of the origami according to an adapted Kramer’s rate model, allowing their polarizabilities to be determined. We found that the 6HxB polarizability is larger than that of the triangle origami, which correlates with the variations in charge density of both origamis. Further, we discuss the orientation of both origami species in the dielectrophoretic trap and discuss the influence of diffusion during the escape process. Our study provides detailed insight into the factors contributing to the migration through dielectrophoretic potential landscapes, which can be exploited for applications with DNA and other nanoassemblies based on dielectrophoresis

Core–Shell Compositional Fine Structures of Dealloyed Pt_<i>x</i>Ni_1–<i>x</i> Nanoparticles and Their Impact on Oxygen Reduction Catalysis

Using aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy line profiles with Ångstrom resolution, we uncover novel core–shell fine structures in a series of catalytically active dealloyed Pt_<i>x</i>Ni_1–<i>x</i> core–shell nanoparticles, showing the formation of unusual near-surface Ni-enriched inner shells. The radial location and the composition of the Ni-enriched inner shells were sensitively dependent on the initial alloy compositions. We further discuss how these self-organized Ni-enriched inner shells play a key role in maintaining surface lattice strain and thus control the surface catalytic activity for oxygen reduction

Six-Helix Bundle and Triangle DNA Origami Insulator-Based Dielectrophoresis

Self-assembled DNA nanostructures have large potential for nanoelectronic circuitry, targeted drug delivery, and intelligent sensing. Their applications require suitable methods for manipulation and nanoscale assembly as well as adequate concentration, purification, and separation methods. Insulator-based dielectrophoresis (iDEP) provides an efficient and matrix-free approach for manipulation of micro- and nanometer-sized objects. In order to exploit iDEP for DNA nanoassemblies, a detailed understanding of the underlying polarization and dielectrophoretic migration is essential. Here, we explore the dielectrophoretic behavior of six-helix bundle and triangle DNA origamis with identical sequence but large topological difference and reveal a characteristic frequency range of iDEP trapping. Moreover, the confinement of triangle origami in the iDEP trap required larger applied electric fields. To elucidate the observed DEP migration and trapping, we discuss polarizability models for the two species according to their structural difference complemented by numerical simulations, revealing a contribution of the electrophoretic transport of the DNA origami species in the iDEP trapping regions. The numerical model showed reasonable agreement with experiments at lower frequency. However, the extension of the iDEP trapping regions observed experimentally deviated considerably at higher frequencies. Our study demonstrates for the first time that DNA origami species can be successfully trapped and manipulated by iDEP and reveals distinctive iDEP behavior of the two DNA origamis. The experimentally observed trapping regimes will facilitate future exploration of DNA origami manipulation and assembly at the nano- and microscale as well as other applications of these nanoassemblies with iDEP

Understanding and Controlling Nanoporosity Formation for Improving the Stability of Bimetallic Fuel Cell Catalysts

Nanoporosity is a frequently reported phenomenon in bimetallic particle ensembles used as electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. It is generally considered a favorable characteristic, because it increases the catalytically active surface area. However, the effect of nanoporosity on the intrinsic activity and stability of a nanoparticle electrocatalyst has remained unclear. Here, we present a facile atmosphere-controlled acid leaching technique to control the formation of nanoporosity in Pt–Ni bimetallic nanoparticles. By statistical analysis of particle size, composition, nanoporosity, and atomic-scale core–shell fine structures before and after electrochemical stability test, we uncover that nanoporosity formation in particles larger than ca. 10 nm is intrinsically tied to a drastic dissolution of Ni and, as a result of this, a rapid drop in intrinsic catalytic activity during ORR testing, translating into severe catalyst performance degradation. In contrast, O₂-free acid leaching enabled the suppression of nanoporosity resulting in more solid core–shell particle architectures with thin Pt-enriched shells; surprisingly, such particles maintained high intrinsic activity and improved catalytic durability under otherwise identical ORR tests. On the basis of these findings, we suggest that catalytic stability could further improve by controlling the particle size below ca. 10 nm to avoid nanoporosity. Our findings provide an explanation for the degradation of bimetallic particle ensembles and show an easy to implement pathway toward more durable fuel cell cathode catalysts

Interface-Confined FeO_<i>x</i> Adlayers Induced by Metal Support Interaction in Pt/FeO_<i>x</i> Catalysts

Active oxide nanolayers can be stabilized on noble metal surfaces through interface confinement effect in oxide/metal inverse catalysts. Here, using normal metal/oxide catalysts we show that Fe oxide nanolayers can be confined on Pt nanoparticles (NPs) when treating a Pt/FeO_<i>x</i> catalyst in Ar or H₂/O₂ atmospheres at elevated temperatures. Pt NPs partially covered with Fe oxide nanopatches are more active in CO oxidation than bare Pt NPs, while those with fully encapsulated Fe oxide shells in strong metal–support interaction (SMSI) state show much lower activity. Characterization results indicate that three steps play an important role in the formation of Fe oxide overlayers: Pt-aided reduction of interfacial Fe oxide, Pt alloying of interfacial Fe atoms, and surface segregation of alloyed Fe atoms onto surface of Pt NPs. Active surface oxides in so-called support–metal interface confinement (SMIC) state and fully encapsulated oxide layers in the SMSI state can be sequentially produced which depend on the treatment conditions

Six-Helix Bundle and Triangle DNA Origami Insulator-Based Dielectrophoresis

Self-assembled DNA nanostructures have large potential for nanoelectronic circuitry, targeted drug delivery, and intelligent sensing. Their applications require suitable methods for manipulation and nanoscale assembly as well as adequate concentration, purification, and separation methods. Insulator-based dielectrophoresis (iDEP) provides an efficient and matrix-free approach for manipulation of micro- and nanometer-sized objects. In order to exploit iDEP for DNA nanoassemblies, a detailed understanding of the underlying polarization and dielectrophoretic migration is essential. Here, we explore the dielectrophoretic behavior of six-helix bundle and triangle DNA origamis with identical sequence but large topological difference and reveal a characteristic frequency range of iDEP trapping. Moreover, the confinement of triangle origami in the iDEP trap required larger applied electric fields. To elucidate the observed DEP migration and trapping, we discuss polarizability models for the two species according to their structural difference complemented by numerical simulations, revealing a contribution of the electrophoretic transport of the DNA origami species in the iDEP trapping regions. The numerical model showed reasonable agreement with experiments at lower frequency. However, the extension of the iDEP trapping regions observed experimentally deviated considerably at higher frequencies. Our study demonstrates for the first time that DNA origami species can be successfully trapped and manipulated by iDEP and reveals distinctive iDEP behavior of the two DNA origamis. The experimentally observed trapping regimes will facilitate future exploration of DNA origami manipulation and assembly at the nano- and microscale as well as other applications of these nanoassemblies with iDEP

Six-Helix Bundle and Triangle DNA Origami Insulator-Based Dielectrophoresis

Self-assembled DNA nanostructures have large potential for nanoelectronic circuitry, targeted drug delivery, and intelligent sensing. Their applications require suitable methods for manipulation and nanoscale assembly as well as adequate concentration, purification, and separation methods. Insulator-based dielectrophoresis (iDEP) provides an efficient and matrix-free approach for manipulation of micro- and nanometer-sized objects. In order to exploit iDEP for DNA nanoassemblies, a detailed understanding of the underlying polarization and dielectrophoretic migration is essential. Here, we explore the dielectrophoretic behavior of six-helix bundle and triangle DNA origamis with identical sequence but large topological difference and reveal a characteristic frequency range of iDEP trapping. Moreover, the confinement of triangle origami in the iDEP trap required larger applied electric fields. To elucidate the observed DEP migration and trapping, we discuss polarizability models for the two species according to their structural difference complemented by numerical simulations, revealing a contribution of the electrophoretic transport of the DNA origami species in the iDEP trapping regions. The numerical model showed reasonable agreement with experiments at lower frequency. However, the extension of the iDEP trapping regions observed experimentally deviated considerably at higher frequencies. Our study demonstrates for the first time that DNA origami species can be successfully trapped and manipulated by iDEP and reveals distinctive iDEP behavior of the two DNA origamis. The experimentally observed trapping regimes will facilitate future exploration of DNA origami manipulation and assembly at the nano- and microscale as well as other applications of these nanoassemblies with iDEP

Lattice Strain Distributions in Individual Dealloyed Pt–Fe Catalyst Nanoparticles

Lattice strain is considered to play an important role in the oxygen reduction catalysis on Pt-based catalysts. However, so far, direct evidence of the lattice strain in the catalyst nanoparticles has not been achieved. By using aberration-corrected high-resolution transmission electron microscopy combined with image simulations, a unique core–shell structure, that is, a percolated lattice-contracted Pt–Fe alloy core and a Pt-rich surface with a gradient compressive strain, was directly demonstrated within individual dealloyed Pt–Fe nanoparticles and thus provides direct evidence for the strain effect on their enhanced oxygen reduction activity

Novel Xylanase from a Holstein Cattle Rumen Metagenomic Library and Its Application in Xylooligosaccharide and Ferulic Acid Production from Wheat Straw

A novel gene fragment containing a xylanase was identified from a Holstein cattle rumen metagenomic library. The novel xylanase (Xyln-SH1) belonged to the glycoside hydrolase family 10 (GH10) and exhibited a maximum of 44% identity to the glycoside hydrolase from Clostridium thermocellum ATCC 27405. Xyln-SH1 was heterologously expressed, purified, and characterized. A high level of activity was obtained under the optimum conditions of pH 6.5 and 40 °C. A substrate utilization study indicated that Xyln-SH1 was cellulase-free and strictly specific to xylan from softwood. The synergistic effects of Xyln-SH1 and feruloyl esterase (FAE-SH1) were observed for the release of xylooligosaccharides (XOS) and ferulic acid (FA) from wheat straw. In addition, a high dose of Xyln-SH1 alone was observed to improve the release of FA from wheat straw. These features suggest that this enzyme has substantial potential to improve biomass degradation and industrial applications