Single-crystal silicon nanowires with diameters approaching molecular dimensions were synthesized using gold nanocluster-catalyzed 1D growth. High-resolution transmission electron microscopy studies show that silicon nanowires grown with silane reactant in hydrogen are single crystal with little or no visible amorphous oxide down to diameters as small as 3 nm. Structural characterization of a large number of samples shows that the smallest-diameter nanowires grow primarily along the 〈110〉 direction, whereas larger nanowires grow along the 〈111〉 direction. In addition, cross-sectional transmission electron microscopy was used to address the importance of surface energetics in determining the growth direction of the smallest nanowires. The ability to prepare well-defined molecular-scale single-crystal silicon nanowires opens up new opportunities for both fundamental studies and nanodevice applications.

The kagome lattice is a two-dimensional network of corner-sharing triangles that is known to host exotic quantum magnetic states. Theoretical work has predicted that kagome lattices may also host Dirac electronic states that could lead to topological and Chern insulating phases, but these states have so far not been detected in experiments. Here we study the d-electron kagome metal FeSn, which is designed to support bulk massive Dirac fermions in the presence of ferromagnetic order. We observe a temperature-independent intrinsic anomalous Hall conductivity that persists above room temperature, which is suggestive of prominent Berry curvature from the time-reversal-symmetry-breaking electronic bands of the kagome plane. Using angle-resolved photoemission spectroscopy, we observe a pair of quasi-two-dimensional Dirac cones near the Fermi level with a mass gap of 30 millielectronvolts, which correspond to massive Dirac fermions that generate Berry-curvature-induced Hall conductivity. We show that this behaviour is a consequence of the underlying symmetry properties of the bilayer kagome lattice in the ferromagnetic state and the atomic spin-orbit coupling. This work provides evidence for a ferromagnetic kagome metal and an example of emergent topological electronic properties in a correlated electron system. Our results provide insight into the recent discoveries of exotic electronic behaviour in kagome-lattice antiferromagnets and may enable lattice-model realizations of fractional topological quantum states.

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We report that alkali ions (sodium or potassium) added in small amounts activate platinum adsorbed on alumina or silica for the low-temperature water-gas shift (WGS) reaction (H(2)O + CO → H(2) + CO(2)) used for producing H(2). The alkali ion-associated surface OH groups are activated by CO at low temperatures (~100°C) in the presence of atomically dispersed platinum. Both experimental evidence and density functional theory calculations suggest that a partially oxidized Pt-alkali-O(x)(OH)(y) species is the active site for the low-temperature Pt-catalyzed WGS reaction. These findings are useful for the design of highly active and stable WGS catalysts that contain only trace amounts of a precious metal without the need for a reducible oxide support such as ceria.

The ability to control and modulate the composition1–4, doping1,3–5, crystal structure6–8 and morphology9,10 of semiconductor nanowires during the synthesis process has allowed researchers to explore various applications of nanowires11–15. However, despite advances in nanowire synthesis, progress towards the ab initio design and growth of hierarchical nanostructures has been limited. Here we demonstrate a ‘nanotectonic’ approach that provides iterative control over the nucleation and growth of nanowires and use it to grow kinked or zigzag nanowires in which the straight sections are separated by triangular joints. Moreover, the lengths of the straight sections can be controlled and the growth direction remains coherent along the nanowire. We also grow dopant-modulated structures in which specific device functions, including p-n diodes and field-effect transistors, can be precisely localized at the kinked junctions in the nanowires.

Nanometer-sized pores can be used to detect and characterize biopolymers, such as DNA, RNA, and polypeptides, with single-molecule resolution. Experiments performed with the 1.5 nm pore a-hemolysin (a-HL) [1] demonstrated that singlestranded DNA and RNA molecules can be electrophoretically threaded through a pore, and that the ion current flowing through the pore contains information about the biopolymer sequence: its type, length, and secondary structure. [2,3] The a-HL nanopore has been used to study the unzipping kinetics of DNA hairpin molecules under stationary or time-varying forces, [4] to detect DNA hybridization kinetics, [5] and to study the interaction of DNA with bound proteins using nanopore force spectroscopy. [6] In addition, a-HL can be biochemically modified for various sensing tasks, such as analyte detection and ligand-receptor interactions.[7]Solid-state nanopores can be fabricated in thin Si 3 N 4 and SiO 2 membranes, using either an Ar + beam [8,9] or an electronbeam (e-beam) in a transmission electron microscope (TEM), [10] as well as in a variety of materials using other techniques.[11] Solid-state nanopores offer several advantages over phospholipid-embedded protein channels, namely, their size can be tuned with nanometer precision and they exhibit an increased mechanical, chemical, and electrical stability. Recent studies using solid-state pores have begun to emerge, demonstrating the detection of single-stranded and double-stranded DNA molecules. [12,13] A major advantage of solid-state nanopores is that they can, in principle, be integrated into devices compatible with other detection schemes in addition to ion current measurements. In particular, optical-based methods offer straightforward parallelism through the simultaneous probing of many nanopores. Optical methods for sensing single molecules can be implemented by labeling the biomolecules and/or the nanopores. Although protein pores embedded in a phospholipid bilayer can be interrogated optically to detect single molecules, [14] a stable, long-timescale probing is very complicated since the pores readily diffuse in the bilayer, leading to aggregation and destabilization of the membrane. In contrast, nanopores fabricated in solid-state materials are static, and are therefore more compatible with optical probing.In this paper, we extend state-of-the-art techniques by demonstrating the rapid fabrication of finely tuned nanopores and nanopore arrays. The nanopores were fabricated in thin Si 3 N 4 films using the intense e-beam of a field-emission TEM. By maximizing the e-beam density at the specimen we achieved a nearly fivefold decrease in the fabrication time of a single nanopore (ca. 30 s). [15,16] Investigation of pore contraction/expansion dynamics [17] under different irradiation conditions enabled nanopore fabrication in the range of 2-20 nm with exceptional size control (<0.5 nm variability). Since the nanopores were fabricated sequentially (i.e., using one e-beam), both the reduction in fabrication time and size control were...

Iron doping of nickel oxide films results in enhanced activity for promoting the oxygen evolution reaction (OER). Whereas this enhanced activity has been ascribed to a unique iron site within the nickel oxide matrix, we show here that Fe doping influences the Ni valency. The percent of Fe 3+ doping promotes the formation of formal Ni 4+ , which in turn directly correlates with an enhanced activity of the catalyst in promoting OER. The role of Fe 3+ is consistent with its behavior as a superior Lewis acid.water splitting | renewable energy | electrocatalysis | oxygen evolution reaction | catalysis

We have developed a technique so that both transmission electron microscopy and microphotoluminescence can be performed on the same semiconductor nanowire over a large range of optical power, thus allowing us to directly correlate structural and optical properties of rotationally twinned zinc blende InP nanowires. We have constructed the energy band diagram of the resulting multiquantum well heterostructure and have performed detailed quantum mechanical calculations of the electron and hole wave functions. The excitation power dependent blue-shift of the photoluminescence can be explained in terms of the predicted staggered band alignment of the rotationally twinned zinc blende/wurzite InP heterostructure and of the concomitant diagonal transitions between localized electron and hole states responsible for radiative recombination. The ability of rotational twinning to introduce a heterostructure in a chemically homogeneous nanowire material and alter in a major way its optical properties opens new possibilities for band-structure engineering.