Table of contents

In this first issue of Nanotechnology for 2007 the journal has taken another step forward in its extraordinary growth and development of the past 5 years. The reader will notice two important changes that have been introduced primarily in response to the exponential rise in submissions to the journal: the contents have been restructured into sections and publication will now be weekly. These latest changes, however, are not the only ones that have been made to the journal and its service to authors and readers.

A modern journal has many tools at its disposal that journals of even 10 years ago simply did not. Electronic submission and refereeing, web-based publication, author services such as free electronic reprints and an email alerting service, to name but a few. Published by a learned society, Nanotechnology has constantly responded to the needs of authors and readers alike drawing upon the extensive experience and tools of IOP Publishing. Nanotechnology is of course an exploding field and it is therefore perhaps unsurprising to see a growth in the number of submissions to the journal. However, an inspection of the data surrounding submissions over the past 4 years reveals a disproportionate growth in the success of the journal itself. In 2002 there were 419 submitted papers of which 208 were accepted and published in 6 issues. In 2005 we received 75% more submissions over 2002, had a reduced acceptance rate of 44% and published 12 issues. 2006 showed, in just one year, a growth over 2005 of greater than 50% in the number of submissions. This growth of course does present challenges. The paper issues of the journal have been increasing in mass, hence a move to weekly publishing, and the sheer number of papers means that finding an article on a specific topic can be difficult for readers and authors, hence the move to sections. Sections will also help the Editorial Board in ensuring that the journal has a balanced portfolio of papers reflecting the broad relevance and impact of nanotechnology in general.

With all this growth and change there are always some constant factors that specifically concern authors. Prominent amongst these is the speed of publication. Remarkably, our current publication times are among the most competitive internationally with current receipt to publication times of less than three months. Although this time will be shortened by weekly publication, it will be further reduced by the introduction of an article numbering system as opposed to page numbering. Here, an accepted article is assigned a number and published immediately; there is no need to wait for other articles to form a complete issue. Articles will be published on the web as soon as they are available.

The number of nano-related journals continues to grow, making for a highly congested and competitive market. The fact that Nanotechnology, the longest established journal in the field, continues to grow in size, is able to dynamically change in response to authors and readers alike, and can draw on the renowned academic publishing capabilities of IOP Publishing, means that we look forward to an exciting and productive future. As we strive to deliver the best possible service to our authors and readers we aim to attract the very best of international nanoscience and nanotechnology so that Nanotechnology becomes the pre-eminent journal for reporting research in the field.

Functionalized tetrapodal ZnO nanostructures are tested in plasmid DNA experiments (1) as a solid-phase adsorbent for plasmid DNA purification, (2) as improving reagents in a polymerase chain reaction (PCR) and (3) as novel carriers for gene delivery. The amino-modification, the tetrapod-like shape of the nanostructure and its high biocompatibility all contribute to measurements showing promise for applications. A sol–gel method is used for silica coating and amino-modification. Plasmid DNA is purified through reversible conjugations of amino-modified ZnO tetrapods with DNA. Also, as additional reagents, functionalized tetrapods are shown to improve the amount of PCR product. For transfection, ZnO tetrapods provide some protection against deoxyribonuclease cleavage of plasmid DNA and deliver plasmid DNA into cells with little cytotoxicity.

The assembly and characterization of gold nanoparticle-based binary and ternary structures are reported. Two strategies were used to assemble gold nanoparticles into ordered nanoscale architectures: in strategy 1, gold nanoparticles were functionalized with single-strand DNA (ssDNA) first, and then hybridized with complementary ssDNA-labelled nanoparticles to assemble designed architectures. In strategy 2, the designed architectures were constructed through hybridization between complementary ssDNA first, then by assembling gold nanoparticles to the scaffolding through gold–sulfur bonds. Both TEM measurements and agarose gel electrophoresis confirmed that the latter strategy is more efficient in generating the designed nanostructures.

Inspired by the lotus effect, we fabricate new microscale and nanoscale hierarchical structured copper mesh films by a simple electrochemical deposition. After modification of the long-chain fatty acid monolayer, these films show superhydrophobic and superoleophilic properties, which could be used for the effective separation of oil and water. The length of the fatty acid chain strongly influences the surface wettability of as-prepared films. It is confirmed that the cooperative effect of the hierarchical structure of the copper film and the nature of the long-chain fatty acid contribute to this unique surface wettability.

Polyaniline (PANI) nanofibre films were fabricated on an indium–tin oxide (ITO) glass substrate through a controlled electropolymerization process. The PANI nanofibres grow vertically on an ITO substrate and are tapered, with average diameters of 20 and 15 nm for the base and top, respectively. The influence of the electrochemical conditions on the nanostructural formation of the PANI films was investigated and the optimized parameters of the electrodeposition were obtained. The optical and electrical properties of the PANI nanofibre electrodes were studied. Employing these PANI nanofibre films as the electrochromic electrode, we fabricated an electrochromic display (ECD) and a self-powered photoelectrochromic cell. The electrochromic and photoelectric properties of the ECD and photoelectrochromic cell are discussed in this paper. The PANI nanofibre based ECD and photoelectrochromic cells have a rapid response compared to conventional thin films due to the high aspect ratio of the nanostructured PANI film.

The diameter dependent magnetoresistance of a single Ni nanowire (i.e. 200 and 30 nm diameter) bridging microfabricated Ni electrodes was investigated at temperatures ranging from 10 to 300 K. Overall, the magnetotransport behaviour of single Ni nanowires was similar to the results for thin films, except that the magnitudes of transverse magnetoresistance and longitudinal magnetoresistance differed from the values for thin films when the diameter of the nanowire was small. The difference might be attributed to a change in the stress anisotropy of the nanowire from a tensile stress induced by a thermal expansion mismatch between the nanowire and the Si substrate or different magnetocrystalline anisotropy. Based on the angle dependent switching field, the magnetization reversal mechanism of 30 and 200 nm nanowires at 10 K was determined to be the curling mode, and the size of the curling nucleation is smaller than the diameter of the nanowire.

We report the observation of periodical negative differential conductivity (NDC) in hydrogenated nanocrystalline silicon/crystalline silicon diode heterostructures by low-temperature current–voltage measurements. The NDC-related series of spike-like current peaks is found to result from the accumulation and depletion of electrons tunnelling through the nanodot layers in the neutral region. The observation has been further supported by the facts of onset-voltage blueshift, number variation in current peaks, and inter-Landau-level tunnelling in the temperature- and magnetic field-dependent experiments. We also discuss the differences between the present periodical NDC and the electric field domain in superlattice structures.

We report here on the self-patterned growth of nanostructured epitaxial oxide thin films using a bottom-up approach. Different stepped (0001) sapphire surfaces have been used as templates to grow different nanostructured thin films of yttria-stabilized zirconia elaborated by a chemical solution deposition technique, namely sol–gel dip-coating. For such films, a morphological instability occurs during post-deposition thermal annealing that forces the film to split into isolated islands. Taking advantage of this effect, three distinct types of nanostructures have been produced depending on the step morphology of the substrate surface, and depending on the relative magnitude of the mean island diameter (D) and the mean terrace length (L). Flat-top islands, dome-shaped islands, tilted flat-top islands or self-organized arrays of nano-islands can be generated. Atomic force microscopy was used to observe nanostructures and quantitative characterizations of crystallographic and nanostructural aspects were carried out by high-resolution x-ray diffraction reciprocal space mapping.

An extrusion method, using anodic aluminium oxide (AAO) membranes as templates, has been developed to fabricate Nafion^®-115 nanowire arrays. Surface decoration of the templates plays an important role in the synthesis of the Nafion^®-115 nanowire arrays. By using sodium dodecyl sulfate (SDS) as a surfactant in the surface decoration, the filling rate of the Nafion^®-115 nanowires in the corresponding template exceeds 95%, compared with the filling rate of 42% in an undecorated template, while on using cetyltrimethylammonium bromide (CTAB) as a surfactant, the filling rate is only about 20%. Systematical investigations show that the effect of surface decoration is induced by the combination of surface tension and electrostatic force (radial component), of which the radial component of the electrostatic force is more important. This effect is significant in organic nanowire fabrication; furthermore, the as-synthesized organic nanowires would have potential application such as in organic electronics, optoelectronic devices, and nanoscale proton exchange membrane fuel cells.

A three-step method combining physical vapour deposition, grazing ion milling and thermal annealing techniques for large-area fabrication of nanodot arrays in anodic alumina oxide (AAO) templates is demonstrated. By this method, ordered arrays of Ni and Au nanodots with highly uniform diameters and a density of 1.2 × 10¹⁰ cm⁻² were fabricated. The diameter and packing density of the nanodots can be controlled by the cell parameters of the AAO template. The fabrication method presented here can be extended to many other materials and allows further investigation of the size related characteristics of nanodot structures.

We developed a method to precisely control the locations and orientations of deposited divanadium pentoxide (V₂O₅) nanowires on SiO₂ surfaces using chemically functionalized patterns. The nanowires were deposited onto the substrates either from solution or via the edge transfer mechanism of micro-contact printing. In both cases, negatively charged V₂O₅ nanowires showed a strong adsorption selectivity onto 3-aminopropyltriethoxysilane (APS) self-assembled monolayers (SAMs) with positively charged functional groups, whereas the SAMs with non-polar and neutral terminal groups of octadecyltrichlorosilane (OTS) worked as perfect passivation layers. In particular, directional alignment of nanowires inside the chemically patterned area, depending upon the shapes of the patterns, was observed. The wires were aligned along the long axis of the pattern when the width of the APS pattern was as small as 1 µm. This strategy allows us to control the adsorption and alignment of V₂O₅ nanowires on the substrates, which could be used for various nano-device applications such as interconnection of electronic circuits.

This work systematically investigated the optical and structural properties of multilayer electronic vertically coupled InAs/GaAs quantum dot (QDs) structures grown by molecular beam epitaxy for long-wavelength applications. A significant energy blue-shift in the photoluminescence (PL) spectra from 30-period InAs/GaAs QDs structures was observed as the GaAs spacer thickness was decreased. Transmission electron microscopy (TEM) and PL measurements indicated that the abnormal blue-shift can be attributed to the strain-driven In/Ga intermixing between QDs and spacer layers, which overcompensates for the effects of electronic and structural couplings between QD layers. Moreover, this study demonstrates that increasing the growth rate of InAs QDs can prevent intermixing. A PL emission wavelength of 1320 nm with strong luminescence at room temperature, which corresponds to an energy red-shift of 50 meV from that of the single QD layer sample, was achieved in a 10-period InAs/GaAs QD superlattice with a spacer thickness of 16 nm.

Low indium content InGaN/AlGaN multiple quantum wells (MQWs) have been grown on Si(111) substrate by metal–organic chemical vapour deposition (MOCVD). A new method of using an isoelectronic indium-doped AlGaN barrier has been found to be very effective in improving the crystalline quality and interfacial abruptness of InGaN quantum well layers. We grew five periods of In_0.06Ga_0.94N/Al_0.20Ga_0.80N:In MQWs with In-doped barrier layers and obtained strong near-ultraviolet (UV) emission (∼400 nm) at room temperature. An In-doped AlGaN barrier improves the room-temperature PL intensity of InGaN/AlGaN MQWs, making it a candidate barrier for a near-UV source on Si substrate.

The effects of phonon confinement on the excited state dynamics of Eu³⁺ in Gd₂O₃ nanotubes are investigated. Anomalous thermalization appears due to elimination of low-energy phonon modes in this highly efficient nanophosphor of many potential applications. It is observed that in the low-temperature excitation spectrum hot bands with fine structures originate from the lowest sublevel of ⁷F₁ at 217 cm⁻¹ above the ground state. The intensity of the hot bands hardly changes below 50 K, but it increases and exhibits normal Boltzmann thermalization above 50 K. The fluorescence lifetime of ⁵D₀ (2.19 ms at 10 K) is found to be unusually longer than that of the bulk counterparts, indicating a small filling factor of 0.55 for the nanotubes. These luminescent properties are attributed to the morphology and to the lack of low-energy phonon modes in the nanotubes.

This work examines the influence of post-growth phosphorus implantation followed by rapid thermal annealing on the photoluminescence (PL) emission from self-assembled InAs/InP(001) quantum dots (QDs). Upon annealing, the spectra reveal an atypical evolution, showing an increase in the emission bandwidth and the rise of a InAsP quantum-well-like peak. The overall emission exhibit a blueshift whose magnitude increases with annealing temperature and fluence up to ∼325 meV. The temperature threshold for a detectable PL shift, 400 °C, is considerably lower than the 725 °C value for unimplanted samples, thereby demonstrating the potential of ion-implantation-induced intermixing for spatially selective band gap tuning of InAs/InP QDs.

Optical signals measured in apertureless scanning near field optical microscopy (ASNOM) under ambient conditions are found to be affected significantly by the thin water layer absorbed on the surface under investigation, the presence of which is detected through measurements of the shear force experienced by the tip. This water layer also results in a large hysteresis between optical signals measured during approach and withdrawal of the tip to the sample surface. The role of this effect in ASNOM is anticipated to be significant, with the possibility of resultant topographically induced artefacts for ASNOM involving intermittent contact of tip and sample, but also providing a potential mechanism for nanoscale optical resolution.

Specific metal deposition on nanoparticles is of outstanding importance in molecular construction as well as for signal enhancement in bioanalytics. To characterize the growth mechanism we studied the enhancement process of immobilized gold nanoparticle ensembles at single particle level by atomic force microscopy, monitoring the very same particle arrangements after each enhancement step. The particles grew linearly and a dependence of the growth rate on the seed diameter was found. The findings may help us to understand the underlying growth mechanism.

A model of deflection–voltage curves in atomic force microscopy and its use in DC electrostatic nanomanipulation experiments are presented. The proposed model predicts the deflection of the atomic force microscope probe as a function of the applied probe–substrate voltage, as well as the distance and voltage at which the tip collapses irreversibly onto the substrate due to electrostatic forces. The model is verified experimentally and its use in DC electrostatic manipulation of 25 nm radius gold nanoparticles is demonstrated.

The strain distribution in heterostructured wurtzite InAs/InP nanowires is measured by a peak finding technique using high resolution transmission electron microscopy images. We find that nanowires with a diameter of about 20 nm show a 10 nm strained area over the InAs/InP interface and the rest of the wire has a relaxed lattice structure. The lattice parameters and elastic properties for the wurtzite structure of InAs and InP are calculated and a nanowire interface is simulated using finite element calculations. Both the method and the experimental results are validated using a combination of finite element calculations and image simulations.

We report the growth of single-walled carbon nanotubes (SWNTs) on glass substrate using water-assisted plasma CVD. Highly pure SWNTs are successfully grown on glass at 550 °C, below the strain point of the glass. The growth behaviour of SWNTs on glass is not only influenced by the growth temperature, but is also highly dependent on the buffer layer. Two different buffer layers are studied: Al₂O₃ and SiO₂. Detailed effects on the grown nanotubes are discussed through Raman spectroscopy. This work suggests that the application area of SWNTs may extend to thin film transistors (TFTs) in micro-electronics for opto-electronics with a flexible choice of substrates.

The catalytic activity of metal silicide for carbon nanotube (CNT) nucleation and growth is reported by systematically evaluating CNT synthesis on different metal silicide phases compared with pure metal catalysts. Using a combination of high-resolution microscopy, x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS), the influence of various pretreatment annealings on 1, 5 and 10 nm Ni and Co films sputter deposited on pristine Si(100) and SiO₂ substrates has been explored in relation to their ability to catalyse CNT growth under a broad range of synthesis conditions. Under certain pretreatment and growth conditions metal silicide nanoparticles are as catalytically active as pure metal nanoparticles. The impact of these findings is significant. The considerable expertise on metal silicide already existing in silicon technology can be applied and extended for the integration of CNTs in electronics.

We investigated the effect of the buffer layer thickness on the structural and optical properties of ZnO nanorods grown on Si substrates by metalorganic chemical vapour deposition. Increasing the thickness of the buffer layer significantly enhanced the vertical alignment and density of the nanorods. The ZnO nanorods grown on the buffer layer with a thickness exceeding 500 nm were inclined on the substrate surface, due to the formation of a rugged morphology with a pyramidal shape on the surface of the buffer layer, which was attributed to the surface undulation resulting from the increased tensile strain. This inclination also resulted in a decrease in the intensity of the (0002)_ZnO diffraction peak and the ultraviolet emission peak. This paper discusses the microstructural properties and growth mechanism of the ZnO nanorods on buffer layers with various thicknesses.

FeNi₃/(Ni_0.5Zn_0.5)Fe₂O₄ nanocomposite particles were successfully synthesized using the hydrazine reduction combined with ammonia co-precipitation ferrite coating method. The x-ray and transmission electron microscopy analysis showed that face-centred cubic-structured FeNi₃ nanoparticles were coated with spinel Ni–Zn ferrite. The composite particles were nearly spherical with diameters of about 80–200 nm and exhibited typical soft magnetic properties. The saturation magnetization (M_s) of the composite was greatly improved, compared with that of traditional ferrite. With increasing ferrite content, the eddy-current loss was effectively suppressed and a notable high frequency characteristic, in which the real part μ' of the permeability was almost independent of the frequency, was observed. The imaginary part μ'' remained at an extremely low value below the frequency of 300 MHz. The cut-off frequency f_r was estimated to be above 1 GHz. The highest value of μ' reached 13 when the ratio of FeNi₃ to Ni_0.5Zn_0.5Fe₂O₄ was 1:1. Two peaks were observed in the permeability spectra, which may be ascribed to the ferromagnetic resonances of FeNi₃ and Ni–Zn ferrite respectively.

The room-temperature stability of nanometre-sized silver clusters in silica matrices has been investigated by following the temporal evolution of their surface plasmon absorption. Ag clusters in SiO₂ were prepared by either annealing silica samples doped with atomic silver or by co-deposition of preformed clusters of defined size. Clusters were found to be unstable at ambient conditions on a timescale of days to weeks, independent of preparation conditions. The disappearance of the plasmonic resonance is explained by successive oxidation of the clusters even inside the matrix.

A vapour transport route for the in situ fabrication of Eu-doped GaN nanoneedles is reported. The nanoneedles are single crystals of hexagonal structure and they grow in the [100] direction. The typical taper of a nanoneedle (in diameter) varies from 5 nm to 1 µm with a length of up to a few microns. Energy-dispersive x-ray studies indicate that the Eu concentration doped into the GaN nanoneedles is ∼0.2 at.%. Photoluminescence spectra show that the nanoneedles have very strong red emission around 611 nm with a significant blueshift by 11 nm probably due to the nanostructures' small size and the surface states of the nanoneedles. The flow rate of ammonia is shown to have a large effect on the doping rate and photoluminescence of GaN:Eu nanoneedles.