Shedding light on the crystallographic etching of multi-layer graphene at the atomic scale

The controlled etching of graphite and graphene by catalytic hydrogenation is potentially a key engineering route for the fabrication of graphene nanoribbons with atomic precision. The hydrogenation mechanism, though, remains poorly understood. In this study we exploit the benefits of aberration-corrected high-resolution transmission electron microscopy to gain insight to the hydrogenation reaction. The etch tracks are found to be commensurate with the graphite lattice. Catalyst particles at the head of an etch channel are shown to be faceted and the angles between facets are multiples of 30°. Thus, the angles between facets are also commensurate with the graphite lattice. In addition, the results of a post-annealing step suggest that all catalyst particles—even if they are not involved in etching—are actively forming methane during the hydrogenation reaction. Furthermore, the data point against carbon dissolution being a key mechanism during the hydrogenation process.      

Au-Ag alloy nanoporous nanotubes

Metallic nanostructures with hollow interiors or tailored porosity represent a special class of attractive materials with intriguing chemicophysical properties. This paper presents the fabrication of a new type of metallic nanoporous nanotube structure based on a facile and effective combination of nanocrystal growth and surface modification. By controlling the individual steps involved in this process, such as nanowire growth, surface modification, thermal diffusion, and dealloying, one-dimensional (1-D) metallic nanostructures can be prepared with tailored structural features and pre-designed functionalities. These tubular and porous nanostructures show distinct optical properties, such as tunable absorption in the near-infrared region, and enhanced capability for electrochemiluminescence signal amplification, which make them particularly desirable as novel 1-D nanocarriers for biomedical, drug delivery and sensing applications. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Exploring the transferability of large supramolecular assemblies to the vacuum-solid interface

We present an interplay of high-resolution scanning tunneling microscopy imaging and the corresponding theoretical calculations based on elastic scattering quantum chemistry techniques of the adsorption of a gold-functionalized rosette assembly and its building blocks on a Au(111) surface with the goal of exploring how to fabricate functional 3-D molecular nanostructures on surfaces. The supramolecular rosette assembly stabilized by multiple hydrogen bonds has been sublimed onto the Au(111) surface under ultra-high vacuum conditions; the resulting surface nanostructures are distinctly different from those formed by the individual molecular building blocks of the rosette assembly, suggesting that the assembly itself can be transferred intact to the surface by in situ thermal sublimation. This unanticipated result will open up new perspectives for growth of complex 3-D supramolecular nanostructures at the vacuum-solid interface. This article is published with open access at Springerlink.com     

Holed nanostructures formed by aluminum droplets on a GaAs substrate

We have studied the morphology evolution of holed nanostructures formed by aluminum droplet epitaxy on a GaAs surface. Unique outer rings with concentric inner holed rings were observed. Further, an empirical equation to describe the size distribution of the outer rings in the holed nanostructures has been established. The contour line generated by the equation provides physical insights into quantum ring formation by droplets of group III materials on III–V substrates.      

Synthesis and Ex situ doping of ZnTe and ZnSe nanostructures with extreme aspect ratios

We report synthesis windows for growth of millimeter-long ZnTe nanoribbons and ZnSe nanowires using vapor transport. By tuning the local conditions at the growth substrate, high aspect ratio nanostructures can be synthesized. A Cu-ion immersion doping method was applied, producing strongly p-type conduction in ZnTe and ionic conduction in ZnSe. These extreme aspect ratio wide-bandgap semiconductors have great potential for high density nanostructured optoelectronic circuits.      

Superhydrophobic surfaces produced by applying a self-assembled monolayer to silicon micro/nano-textured surfaces

A novel way of producing superhydrophobic surfaces by applying a self-assembled monolayer (SAM) to silicon micro/nano-textured surfaces is presented in this paper. The micro/nano-textured surfaces on silicon substrates were generated by the aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) technique. Octadecyltrichlorosilane (OTS) SAMs were then applied to the textured surfaces by dip coating. The topography and wetting properties of the resulting surfaces were characterized using scanning electron microscopy (SEM) and a video-based contact angle measurement system. The results show that by introducing OTS SAMs on the silicon micro/nano-textured surfaces, superhydrophobic surfaces with water contact angles (WCAs) of 155° were obtained, as compared to the WCAs of OTS-modified smooth silicon surfaces of about 112°. Surface topography was found to directly influence the WCA as predicted by the Cassie-Baxter model.      

Nanocrystals: Solution-based synthesis and applications as nanocatalysts

Nanocrystals are emerging as key materials due to their novel shape- and size-dependent chemical and physical properties that differ drastically from their bulk counterparts. The main challenges in this field remain rationally controlled synthesis and large scale production. This article reviews recent progress in our laboratory related to solution-based synthesis of various nanostructures, including zero-dimensional (0-D) nanocrystals, 1-D nanowires and nanorods, hollow structures, and superlattice materials. On the other hand, the essential goal for nanoresearchers is to achieve industrial applications of nanostructured materials. In the past decades, these fascinating materials have been widely used in many promising fields such as nanofabrication, nanodevices, nanobiology, and nanocatalysis. Herein, we focus on their applications as nanocatalysts and try to illustrate the main problems and future directions in this area based on our recent endeavors in catalytic applications of nanocrystals. This article is published with open access at Springerlink.com     

On the growth mechanism of nickel and cobalt nanowires and comparison of their magnetic properties

Magnetic nanowires (NWs) are ideal materials for the fabrication of various multifunctional nanostructures which can be manipulated by an external magnetic field. Highly crystalline and textured nanowires of nickel (Ni NWs) and cobalt (Co NWs) with high aspect ratio (∼330) and high coercivity have been synthesized by electrodeposition using nickel sulphate hexahydrate (NiSO₄·6H₂O) and cobalt sulphate heptahydrate (CoSO₄·7H₂O) respectively on nanoporous alumina membranes. They exhibit a preferential growth along 〈110〉. A general mobility assisted growth mechanism for the formation of Ni and Co NWs is proposed. The role of the hydration layer on the resulting one-dimensional geometry in the case of potentiostatic electrodeposition is verified. A very high interwire interaction resulting from magnetostatic dipolar interactions between the nanowires is observed. An unusual low-temperature magnetisation switching for field parallel to the wire axis is evident from the peculiar high field M(T) curve.      

Synthesis of high magnetic moment CoFe nanoparticles via interfacial diffusion in core/shell structured Co/Fe nanoparticles

We report the synthesis of high magnetic moment CoFe nanoparticles via the diffusion of Co and Fe in core/shell structured Co/Fe nanoparticles. In an organic solution, Co nanoparticles were coated with a layer of Fe to form a Co/Fe core/shell structure. Further raising the solution temperature led to inter-diffusion of Co and Fe and formation of CoFe alloy nanoparticles. These nanoparticles have high saturation magnetization of up to 192 emu/g CoFe and can be further stabilized by thermal annealing at 600 °C. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. These two authors made an equal contribution to the work.     

Magnetic field-induced solvothermal synthesis of one-dimensional assemblies of Ni-Co alloy microstructures

One-dimensional magnetic Ni-Co alloy microwires with different microstructures and differently shaped building blocks including spherical particles, multilayer stacked alloy plates, and alloy flowers, have been synthesized by an external magnetic field-assisted solvothermal reaction of mixtures of cobalt(II) chloride and nickel(II) chloride in 1, 2-propanediol with different NaOH concentrations. By adjusting the experimental parameters, such as precursor concentration and Ni/Co ratio, Ni-Co alloy chains with uniform diameters in the range 500 nm to 1.3 μm and lengths ranging from several micrometers to hundreds of micrometers can be obtained. A mechanism of formation of the one-dimensional assemblies of magnetic Ni-Co microparticles in a weak external magnetic field is proposed. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Growth of serpentine carbon nanotubes on quartz substrates and their electrical properties

A simple method for high-yield, chemical vapor deposition (CVD) synthesis of serpentine carbon nanotubes, employing quartz substrates and a molecular cluster catalyst, is described. The growth mechanism is analyzed by controlled addition of nanoscale barriers, and by mechanical analysis of the curved sections. The serpentine structures are used to study the electrical transport properties of parallel arrays of identical nanotubes, which show three-terminal conductance that scales linearly with the number of nanotube segments. This article is published with open access at Springerlink.com     

InAs/InP/ZnSe core/shell/shell quantum dots as near-infrared emitters: Bright, narrow-band, non-cadmium containing, and biocompatible

High quality InAs/InP/ZnSe core/shell/shell quantum dots have been grown by a one-pot approach. This engineered quantum dots with unique near-infrared (NIR) fluorescence, possessing outstanding optical properties, and the biocompatibility desired for in vivo applications. The resulting quantum dots have significantly lower intrinsic toxicity compared to NIR emissive dots containing elements such as cadmium, mercury, or lead. Also, these newly developed ultrasmall non-Cd containing and NIR-emitting quantum dots showed significantly improved circulation half-life and minimal reticuloendothelial system (RES) uptake.      

Controllable nanostructural transitions in grafted nanoparticle-block copolymer composites

We report a theoretical investigation of self-assembled nanostructures of polymer-grafted nanoparticles in a block copolymer and explore underlying physical mechanisms by employing the self-consistent field method. By varying the particle concentration or the chain length and density of the grafted polymer, one can not only create various ordered morphologies (e.g., lamellar or hexagonally packed patterns) but also control the positions of nanoparticles either at the copolymer interfaces or in the center of one-block domains. The nanostructural transitions we here report are mainly attributed to the competition between entropy and enthalpy.      

Direct evidence for lip-lip interactions in multi-walled carbon nanotubes

The stability of open edged multi-walled carbon nanotubes has been investigated by using in situ high resolution transmission electron microscopy at elevated temperatures. Formation of inter-shell structures was experimentally observed for the first time and attributed to a robust interaction between adjacent concentric shells (so-called lip-lip interaction). The fl uctuating behavior of the inter-shell structures suggests a mechanism by which the carbon atoms can pass in or out through the inter-shell edges during carbon nanotube growth or shrinkage processes. This article is published with open access at Springerlink.com     

Energy dissipation and transport in nanoscale devices

Understanding energy dissipation and transport in nanoscale structures is of great importance for the design of energy-efficient circuits and energy-conversion systems. This is also a rich domain for fundamental discoveries at the intersection of electron, lattice (phonon), and optical (photon) interactions. This review presents recent progress in understanding and manipulation of energy dissipation and transport in nanoscale solid-state structures. First, the landscape of power usage from nanoscale transistors (∼10⁻⁸ W) to massive data centers (∼10⁹ W) is surveyed. Then, focus is given to energy dissipation in nanoscale circuits, silicon transistors, carbon nanostructures, and semiconductor nanowires. Concepts of steady-state and transient thermal transport are also reviewed in the context of nanoscale devices with sub-nanosecond switching times. Finally, recent directions regarding energy transport are reviewed, including electrical and thermal conductivity of nanostructures, thermal rectification, and the role of ubiquitous material interfaces.      

Facile synthesis and application of Ag-chemically converted graphene nanocomposite

An in situ chemical synthesis approach has been employed to prepare an Ag-chemically converted graphene (CCG) nanocomposite. The reduction of graphene oxide sheets was accompanied by generation of Ag nanoparticles. The structure and composition of the nanocomposites were confirmed by means of transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray diffraction. TEM and AFM results suggest a homogeneous distribution of Ag nanoparticles (5–10 nm in size) on CCG sheets. The intensities of the Raman signals of CCG in such nanocomposites are greatly increased by the attached silver nanoparticles, i.e., there is surface-enhanced Raman scattering activity. In addition, it was found that the antibacterial activity of free Ag nanoparticles is retained in the nanocomposites, which suggests they can be used as graphene-based biomaterials.      

Photoluminescence of CdSe nanowires grown with and without metal catalyst

We present temperature and power dependent photoluminescence measurements on CdSe nanowires synthesized via vapor-phase with and without the use of a metal catalyst. Nanowires produced without a catalyst can be optimized to yield higher quantum efficiency, and narrower and spatially uniform emission, when compared to the catalyst-assisted ones. Emission at energies lower than the band-edge is also found in both cases. By combining spatially-resolved photoluminescence and electron microscopy on the same nanowires, we show that catalyst-free nanowires exhibit a low-energy peak with sharp phonon replica, whereas for catalyst-assisted nanowires low-energy emission is linked to the presence of nanostructures with extended morphological defects.      

Enhanced antibacterial activity of bifunctional Fe3O4-Ag core-shell nanostructures

We describe a simple one-pot thermal decomposition method for the production of a stable colloidal suspension of narrowly dispersed superparamagnetic Fe₃O₄-Ag core-shell nanostructures. These biocompatible nanostructures are highly toxic to microorganisms. Antimicrobial activity studies were carried out on both Gram negative (Escherichia coli and Proteus vulgaris) and Gram positive (Bacillus megaterium and Staphylococcus aureus) bacterial strains. Efforts have been made to understand the underlying molecular mechanism of such antibacterial actions. The effect of the core-shell nanostructures on Gram negative strains was found to be better than that observed for silver nanoparticles. The minimum inhibitory concentration (MIC) values of these nanostructures were found to be considerably lower than those of commercially available antibiotics. We attribute this enhanced antibacterial effect of the nanostructures to their stability as a colloid in the medium, which modulates the phosphotyrosine profile of the bacterial proteins and arrests bacterial growth. We also demonstrate that these core-shell nanostructures can be removed from the medium by means of an external magnetic field which provides a mechanism to prevent uncontrolled waste disposal of these potentially hazardous nanostructures.      

Nanotrains and self-assembled two-dimensional arrays built from carboranes linked by hydrogen bonding of dipyridones

The strong hydrogen bonding ability of 2-pyridones were exploited to build nanotrains on surfaces. Carborane wheels on axles difunctionalized with 2-pyridone hydrogen bonding units were synthesized and displayed spontaneous formation of linear nanotrains by self-assembly on SiO₂ or mica surfaces. Imaging using atomic force microscopy confirmed linear formations with lengths up to 5 μm and heights within the range of the molecular height of the carborance-tipped axles. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Bi<Subscript>2</Subscript>S<Subscript>3</Subscript> nanostructures: A new photocatalyst

Uniform colloidal Bi₂S₃ nanodots and nanorods with different sizes have been prepared in a controllable manner via a hot injection method. X-ray diffraction (XRD) results show that the resulting nanocrystals have an orthorhombic structure. Both the diameter and length of the nanorods increase with increasing concentration of the precursors. All of the prepared Bi₂S₃ nanostructures show high efficiency in the photodegradation of rhodamine B, especially in the case of small sized nanodots—which is possibly due to their high surface area. The dynamics of the photocatalysis is also discussed.