Table of contents

Structures of the so-called super-carbon nanotubes are proposed. These structures are built from single walled carbon nanotubes connected by Y-like junctions forming a 'super'-sheet that is then rolled into a seamless cylinder. Such a procedure can be repeated several times, generating a fractal structure. This procedure is not limited to carbon nanotubes, and can be easily modified for application to other systems. Tight binding total energy and density of states calculations showed that the 'super'-sheets and tubes are stable and predicted to present metallic and semiconducting behaviour.

A multi-scale/multi-material computational model for simulation of the electric signal detected on the electrodes of a metal–oxide–semiconductor (MOS) capacitor forming a nanoscale artificial membrane, and containing a nanopore with translocating DNA, is presented. The multi-scale approach is based on the incorporation of a molecular dynamics description of a translocating DNA molecule in the nanopore within a three-dimensional Poisson equation self-consistent scheme involving electrolytic and semiconductor charges for the electrostatic potential calculation. The voltage signal obtained from the simulation supports the possibility for single nucleotide resolution with a nanopore device. The electric signal predicted on the capacitor electrodes complements ongoing experiments exploring the use of nanopores in a MOS capacitor membrane for DNA sequencing.

This paper describes an effective method for quantifying the length and length distribution of large populations of single-wall carbon nanotubes using atomic force microscopy and SIMAGIS software. The results of the measurements were modelled with the Weibull distribution, resulting in a statistically confirmed fit. The fitted Weibull distribution was used to predict the length effect factor and elastic modulus as functions of nanotube properties in composite materials. The prediction shows that the length factor for the elastic modulus tends to increase with enhanced loading but decrease with rising rope diameter. The statistical characterization presented indicates a pathway for the future theoretical modelling and related experimental investigation of carbon nanotube application.

Core/shell structured iron(Fe)/gold(Au) nanoparticles have been prepared by a reverse micelle method, and their potential application as magnetic resonance (MR) contrast agent investigated. The average nanoparticle size is 19 nm, as determined by x-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Magnetic properties and relaxivities of nanoparticles are presented and compared. The saturation magnetization is 81 emu g⁻¹ Fe for freshly prepared nanoparticles and the particles have high r₁(6.87 mM⁻¹ s⁻¹) when the Fe core is kept from oxidation. These nanoparticles may be used as T₁ agents in the unoxidized form.

A new approach has been developed for the preparation of tellurium with various morphologies by a simple hydrothermal method using TeO₂ and poly(vinylpyrrolidone) (PVP). In this method, PVP acts not only as a surfactant but also as a reducing reagent, thus no additional reductants are needed. By control of the reaction conditions, tellurium nanorods, nanowires, and tubes have been prepared. Our experiments showed that pyrrole and polyethylene glycol (PEG) can also be used as reducing reagents.

Gold films with various nanostructures on porous silicon substrates have been created in one step by using a galvanic exchange reaction approach. In this approach, the formation of gold films is initiated by the formation of metal nuclei via an exchange reaction in which both the oxidation of silicon and reduction of gold complex occur simultaneously. Results show that the deposition of gold film is diffusion controlled, and its apparent activation energy was determined to be 28.57 kJ mol⁻¹. Therefore, gold nanostructures with text structure, clusters, and dendrites with leaf-like or branch-like structure can be prepared by adjusting the diffusion conditions such as system temperature, concentration of gold salt, ultrasonic vibration, and addition of additives. The SERS activity of the various porous silicon supported gold nanostructures was evaluated using pyridine and adenine as molecular probes. Amongst the various porous silicon supported gold nanostructures, the gold films with leaf-like structures show the highest SERS activity due to the presence of surface active sites in the nanostructures. The present method is promising for the fabrication of stable gold nanostructures for ultrasensitive analytical measurements.

ZnO thin films were prepared from metallic zinc and metallic zinc + zinc nitride mixture by thermal oxidation. The DC-magnetron sputtering technique was used to deposit the films under argon and argon + nitrogen atmosphere, respectively. The oxide thin films prepared by this method have wurtzite structure without any preferential orientation. Compared to ZnO films grown from metallic zinc that were deposited under Ar only (ZA), ZnO films grown from metallic zinc under nitrogen-rich atmosphere (ZAN) showed a considerably lower average grain size, and growth of abundant nanorods. XPS analysis failed to detect any remaining nitrogen in the prepared films. However, the analyses suggest that nitrogen used in this process can lead to an enhancement of film densification. Room temperature photoluminescence (PL) spectra of both films revealed five emission bands located at the same positions: a predominant exciton ultraviolet (UV) (396 nm), a green (530 nm), a violet (422 nm), a blue (484 nm), and a band to band emission at 354 nm. In addition, ZAN displayed another intense UV emission band peaked at 377 nm.

A 16-pair GaN/AlN structure with GaN nano-structures at the hetero-interface was grown by a metallorganic chemical vapour deposition (MOCVD) system. From the atomic force microscopy (AFM) analysis of the AlN surface grown on the GaN/sapphire template, there are many nano-trenches and nano-holes with a density of about 5 × 10⁸ cm⁻². These GaN nano-structures fill the AlN nano-holes with a dimension of 40 × 40 nm² in width and depth, and with a line density of 6 × 10⁴ cm⁻¹. Furthermore, these GaN nano-structures will be propagated and self-aligned in the growth direction. The photoluminescence (PL) measurement showed that there are bright and dark emission areas on the surface of the 16-pair GaN/AlN structure; the PL intensity at the bright region was ten times stronger than the dark region, and this stronger GaN peak has the blue-shift property caused by a quantum confined effect. In the end, we concluded that the V-shape GaN nano-structures filling the AlN nano-hole structure have a strongly quantum confined effect depending on the temperature and the power dependent PL results.

Triton X-100 is used as a surfactant to disperse carbon nanotube (CNT) bundles. Its influence on the transfer characteristics of carbon nanotube field-effect transistors (CNTFETs) fabricated with the dispersed CNTs by the AC dielectrophoresis technique has been studied. We find that the surfactant at the interface between the CNTs and Au electrodes can change the work function of the electrodes and therefore convert the CNTFETs from typical p-type to having ambipolar characteristics. The adsorbed surfactant between the CNTs and SiO₂ results in a significant hysteresis in the transfer characteristics of the CNTFETs.

A general approach is presented for the controlled synthesis of large-scale Se/Te alloy nanowires (NWs) with sodium dodecylbenzene sulfonate (SDBS) as surfactant. It is found that SDBS acting as surfactant plays an important role in controlling the morphology of Se/Te products. The diameter of Se/Te NWs can be successfully controlled by changing the concentration of SDBS surfactant agents and by adjusting the dynamics of the reaction process. Uniform Se/Te nanoparticles (NCs) can be partly self-assembled into two-dimensional arrays when the SDBS concentration is up to 1.5 wt%. The reaction temperature and concentration of Se⁶⁺ and Te⁶⁺ in starting materials are also important parameters influencing the morphologies and phases of the final products. Phase structures, morphologies and optical properties of the Se/Te products are investigated by XRD, TEM, HRTEM and UV absorption spectroscopy. The formation mechanisms of the NWs and NCs are investigated and discussed on the basis of the experimental results.

The transparent wings of some cicada species present ordered arrays of papillary structures with a spacing of approximately 200 nm. These structures serve an antireflection function, with optical transmission peaking at a value of approximately 98% and rising above 90% over a broad band from 450 to 2500 nm. The dimensions of the papillae are comparable to the roughness scale of surface-enhanced Raman scattering (SERS) substrates. SERS measurements performed on silver- and gold-coated wings display enhancement factors of approximately 10⁶ with no apparent background contribution from the wing.

Nanoparticles of the ferrimagnetic ε-Fe₂O₃ oxide have been synthesized by the sol–gel method. Here we report on the measurement of the dielectric permittivity as a function of temperature, frequency and magnetic field. It is found that, coinciding with the transition from collinear ferrimagnetic ordering to an incommensurate magnetic state occurring at about 100 K, there is an abrupt change (about 30%) of permittivity, suggesting the existence of magnetoelectric coupling in this material. Indeed, magnetic field-dependent measurements at 100 K have revealed an increase in the permittivity of about 0.3% in 6 T. Possible advantages of ε-Fe₂O₃ as a magnetoelectric material are discussed.

Mechanochemical processing of anhydrous chloride precursors with Na₂CO₃ has been investigated as a means of manufacturing nanocrystalline SnO₂ doped ZnO photocatalysts. High-energy milling and heat-treatment of a 0.1SnCl₂+0.9ZnCl₂+Na₂CO₃+4NaCl reactant mixture was found to result in the formation of a composite powder consisting of oxide grains embedded within a matrix of NaCl. Subsequent washing with deionized water resulted in removal of the NaCl matrix phase and partial hydration of the oxide reaction product with the consequent formation of ZnSn(OH)₆. The extent of this hydration reaction was found to decrease in a linear fashion with the temperature of the post-milling heat-treatment over the range of 400–700 °C. For a heat-treatment temperature of 700 °C, the SnO₂ doped ZnO powder was found to exhibit significantly higher photocatalytic activity than either single-phase SnO₂ or ZnO powders that were synthesized using similar processing conditions. The heightened photocatalytic activity of the SnO₂ doped ZnO was attributed to its higher specific surface area and the enhanced charge separation arising from the coupling of ZnO with SnO₂.

Multi-walled carbon nanotubes (MWNTs) were functionalized via oxidative polymerization of 3-3'(vinylcarbazole) (PVK). Thin films of PVK-functionalized MWNTs (PVK-MWNTs) were fabricated by the Langmuir–Schaefer (LS) technique and characterized by spectroscopic, microscopic, electrical and electrochemical techniques before and after doping with iodine. I/V characterization showed an increase in the conductivity of the PVK-MWNTs and I₂-doped PVK-MWNTs compared with the PVK and I₂-doped PVK, respectively. The electrochemical characterization showed the formation of an I₂-doped PVK-MWNT complex. These nanostructured PVK-MWNT films revealed an increase in the current density under illumination of about 500 nA cm⁻².

A titanium dioxide porous network structure was synthesized using a poly(styrene-block-polyethylene oxide) diblock copolymer template. The influence of the titanium precursor concentration and annealing temperature on the obtained morphology was studied. Heterojunction solar cells consisting of TiO₂ porous network structure and poly(2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV) were fabricated. The influence of the MEH-PPV layer thickness and device architecture on the solar cell performance was investigated. For an optimized device structure, a short-circuit current as high as 3.3 mA cm⁻² is obtained under simulated solar illumination with an air mass AM 1.5 filter. The improved higher short-circuit current compared to other reports on MEH-PPV /TiO₂ heterojunction cells can be attributed to improved morphology of the TiO₂ layer.

We report the fabrication of Prussian blue nanotubes and nanowires via a novel technique wherein a liquid metal surface is nano-patterned with a porous polycarbonate membrane used as a hard mask. Prussian blue as 1D nanowires and nanotubes is an excellent candidate for ultra-low level sensing, optical waveguides and model systems to test the one-dimensional Ising model. One of the most feasible techniques for nanowire fabrication is to use a porous template. However, Prussian blue dissolves in strong acids and decomposes in strong bases. Conventional procedures which use porous alumina blocked with a back side metal contact require strong acid and base treatment in the various steps of the nanowire fabrication. We report a novel technique which will pave a new route for the facile synthesis of nanowires and nanotubes of materials that are sensitive to strong acidic or basic treatment. Hence, nano-patterning of a liquid metal (Hg, which functions as a top-side metal contact) with polycarbonate membrane instead of porous alumina membrane excludes the necessity of both strong acid and base during the fabrication of nanowires. By attempting this innovative technique, we report the synthesis of novel organic Prussian blue nanotubes and nanowires.

The metal-organic chemical vapour deposition (MOCVD) method has been used to grow Cu nanorods without metal catalysts. Pentagonal bat-shaped Cu nanorods (Cu nanobats) with five-fold symmetry were successfully synthesized by MOCVD without capping reagents. The average diameters of the head and tail of the Cu nanobats are 100 and 50 nm, respectively. The Cu nanobats are evolved from multiply twinned particles with a decahedral shape. Both elongation along the five-fold symmetry axis and lateral growth of exterior twins were found to be important in the growth of pentagonal Cu nanobats. The Cu nanobats possess strong field emission characteristics.

The possibility of selectively assembling three-dimensional structures along bundles of single-walled carbon nanotubes (SWCNTs) will pave the way to using SWCNTs as nanoconducting templates that can spontaneously integrate into a conductive probe or pathway in a nano device. In the past 2 years, ZnO microcages have attracted interest due to their potential application in the remote coupling of electromagnetic signals into nanoscale machines or devices. We report here, for the first time, highly selective self-assembly of ZnO cages on bundles of conducting SWCNT templates. For the selective Zn nucleation we use electrostatic coordination of carboxyl groups on the SWCNTs to Zn atoms. Bundles of SWCNTs perform a dual function as templates for growth and as scaffolds providing structural integrity to the hollow ZnO spheres (20 nm wall thickness).

Coating multiwall carbon nanotubes (MWCNTs) with a fluorescent poly(triphenylamine) related copolymer (referred to as PTPA), which has both hole-transportation moiety of triphenylamine and conjugated aromatic units of 4,4'-biphenylene vinylene in the chain backbone, can be realized via a facile phase separation strategy. The morphology of the nanohybrids was demonstrated by transmission electron microscopy and the aggregate structure of the copolymer on the MWCNTs was investigated by x-ray diffraction. The weight ratio of the PTPA to MWCNT in the nanohybrids was studied by thermogravimetric analysis. The UV–vis and fluorescence spectra indicated electron interaction between the PTPA and MWCNTs. The enhancement of the photosensitivity of PTPA was also observed. These copolymer-coated MWCNT nanohybrids might then act as a fluorescent probe or a single-layer photoreceptor.

Nanocrystalline CaWO₄ and Eu³⁺ (Tb³⁺)-doped CaWO₄ phosphor layers were coated on non-aggregated, monodisperse and spherical SiO₂ particles by the Pechini sol–gel method, resulting in the formation of SiO₂@CaWO₄, SiO₂@CaWO₄:Eu³⁺/Tb³⁺ core–shell structured particles. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), time-resolved PL spectra and lifetimes were used to characterize the core–shell structured materials. Both XRD and FT-IR indicate that CaWO₄ layers have been successfully coated on the SiO₂ particles, which can be further verified by the FESEM and TEM images. The PL and CL demonstrate that the SiO₂@CaWO₄ sample exhibits blue emission band with a maximum at 420 nm (lifetime = 12.8 µs) originated from the WO₄²⁻ groups, while SiO₂@CaWO₄:Eu³⁺ and SiO₂@CaWO₄:Tb³⁺ show additional red emission dominated by 614 nm (Eu³⁺:⁵D₀–⁷F₂ transition, lifetime = 1.04 ms) and green emission at 544 nm (Tb³⁺:⁵D₄–⁷F₅ transition, lifetime = 1.38 ms), respectively. The PL excitation, emission and time-resolved spectra suggest that there exists an energy transfer from WO₄²⁻ to Eu³⁺ and Tb³⁺ in SiO₂@CaWO₄:Eu³⁺ and SiO₂@CaWO₄:Tb³⁺, respectively. The energy transfer from WO₄²⁻ to Tb³⁺ in SiO₂@CaWO₄:Tb³⁺ is more efficient than that from WO₄²⁻ to Eu³⁺ in SiO₂@CaWO₄:Eu³⁺.

SnO₂ thin films have been deposited by radio-frequency inductively coupled plasma-enhanced chemical vapour deposition using dibutyltin diacetate as the precursor. The as-deposited SnO₂ thin films were post-treated in the inductively coupled plasma. After plasma treatment, uniform SnO₂ nanorods were grown on the SnO₂ thin films. The nanorods were formed by a sputtering–redeposition mechanism. The effects of the conditions of the plasma treatment on the morphology of plasma-treated SnO₂ thin films were studied. The plasma power and the gaseous composition of the plasma had a great effect on the growth of SnO₂ nanorods from SnO₂ thin films. The type of plasma was also very critical, and no nanorods were grown on the SnO₂ thin films treated in capacitively coupled plasma.

Using nonresonant bond-polarization theory, Raman spectra of periodic double-walled carbon nanotubes are calculated. Although the symmetry of these tubes is highly reduced in comparison with the symmetry of the layers, the intensities of Raman active modes do not show significant changes. In ZZ polarization, modes related to radial breathing and high energy modes of individual layers remain the most intensive ones, even though the number of totally symmetric modes could be quite high. The shift of all Raman active modes with notable intensity is discussed and special attention is given to the possibility of tube identification from Raman data. In the case of breathing-like modes, the frequency of the out of phase mode is found to be chirality dependent, while the in phase one remains only diameter dependent as in the case of individual layers.

Single-crystalline conic ZnO nanotubes were synthesized on Si(001) without catalysts by thermal chemical vapour deposition at 475 °C. The nanotubes grown along the ZnO [0001] direction are sharp open-ended tips consisting of planar defects revealed by transmission electron microscopy and scanning electron microscopy. The nanotubes were formed by self-assembly of numerous six-radiated branches of hexagram nanosheets. The diameters and the wall thicknesses of the nanotubes are in the ranges 30–100 and 15–30 nm, respectively. The lengths and areal densities of the nanotubes are around 0.5 µm and 1–9 × 10⁸ cm⁻², respectively. Field-emission measurements on the conic nanotubes show a low turn-on field of 3.5 V µm⁻¹ at 10 µA cm⁻². The field-emission properties related to the nanotube density and geometry and the nonlinearity in the Fowler–Nordheim (FN) plot at lower field region are discussed.

InGaAs/AlGaAs V-groove quantum-wire (QWR) arrays were fabricated by holographic lithography and one-time metalorganic chemical vapour deposition (MOCVD) to evaluate gain-coupled distributed-feedback (GC-DFB) effects in the InGaAs/AlGaAs materials. Using a finite-element method (FEM), mode analysis of the actual cross-sectional structure verified the modal gain of the QWR DFB structure, in which the gain was identified by a single peak at the Bragg wavelength of the grating. In addition, we observed a large gain anisotropy due to the gain/loss coupling in the DFB structure at a wavelength of 914 nm in the emission spectra from the 430 nm pitch QWR grating at room temperature.

Silica films containing various concentrations of Ag nanoparticles were deposited on glass slides using a sol–gel process and then heat-treated in air at different temperatures. The films were analysed by using UV–visible spectrophotometry, atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) for their optical, surface morphological as well as structural, and chemical properties. After heat-treatment, the optical absorption peaks of Ag nanoparticles show a blueshift and an intensity reduction due to particle size reduction and AgO_x nanoparticle formation, respectively. The particle size reduction and surface morphology changes in the films were observed by AFM and TEM as a function of heat-treatment temperature and Ag concentration. Using AFM and XPS analyses, we have found that the Ag nanoparticles accumulated on the surface diffuse into the substrate as the heat-treatment temperature increases. XPS analysis also showed that the silver oxidation occurs during the heat-treatment, causing the reduction of absorption intensity. By controlling the Ag concentration and the heat-treatment temperature, we could change the silica structure, and tailor the average size of the silver nanoparticles down to less than 4 nm.

Cd₄Cl₃(OH)₅ is a good precursor compound that can be easily converted into Cd(OH)₂ or functional compounds CdS and CdSe. Novel 3D nanostructured Cd₄Cl₃(OH)₅ nanoflower arrays were controllably synthesized through a simple low temperature hydrothermal process. The morphology was characterized by scanning electron microscopy, x-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The cadmium precursor, solution concentration, solvent, reaction temperature and reaction time are of great importance on the flower-like structure. The formation mechanism of the flower-like structure is also discussed. The Cd₄Cl₃(OH)₅ nanoflowers as template compounds were further transformed into Cd(OH)₂ and CdS nanoflowers by an anion-exchange reaction.

Hydrogen adsorption on the recently discovered boron nanotubes, BNTs, and on boron sheets is investigated by density functional calculations. Both molecular physisorption and dissociative atomic chemisorption are considered. The geometric and electronic structures of BNTs and boron sheets have been elucidated. These two novel boron structures present buckled surfaces with alternating up and down rows of B atoms, with a large buckling height of about 0.8 Å. The buckled structures are about 0.20 eV/atom more stable than the corresponding flat ones. However, the helicity of some BNTs does not allow for the formation of alternating up and down B rows in the surface and, therefore, these nanotubes have flat surfaces. The buckled and flat nanostructures have different geometric and bonding characteristics, but both are metallic. Molecular hydrogen physisorption energies are about 30–60 meV/molecule on boron sheets and nanotubes, actually lower than in graphene and in carbon nanotubes and far from the energies of 300–400 meV/molecule necessary for efficient hydrogen storage at room temperature and moderate pressures for onboard automotive applications. Chemisorption binding energies on BNTs are about 2.4–2.9 eV/H atom, similar to the ones obtained in CNTs. Finally, the energy barrier from molecular physisorption to dissociative chemisorption of hydrogen is about 1.0 eV /molecule. Therefore, the calculations predict physisorption as the leading adsorption mechanism of hydrogen at moderate temperatures and pressures. The expected hydrogen adsorption capacity of these novel B materials is even smaller than that of CNTs.

A thick layer of pure boron nitride (BN) nanowires with a uniform diameter of 20 nm was synthesized for the first time using a CVD process with a new precursor of boron triiodide (BI₃). Transmission electron microscopy revealed a nanocrystalline structure in the BN nanowires and the absence of any catalyst particle. Some BN nanowires self-assembled into thick threads up to several hundred micrometres long on top of the nanowire layer. The nitriding reactions and lack of catalyst suggest new formation mechanisms of the BN nanowires.

Carbon nanofibres (CNFs) of controlled diameter and length were grown on different metal substrates using plasma-enhanced chemical vapour deposition (PECVD). The diameter control of catalyst dots (and hence CNF diameter) was obtained by using the shot modulation technique in electron beam lithography. Catalyst dots of different sizes within arrays of different pitch were prepared and the dependence of the growth of vertically aligned CNFs on these parameters was studied for different metal underlayers. Good quality vertically aligned CNFs with a narrow length distribution were grown on Mo and W substrates. The structures grown on Nb substrates were significantly shorter for identical growth conditions and showed a lower nucleation rate. We demonstrate that through the shot modulation technique it is possible to control the diameter variation of CNFs from a single design geometry for the catalyst deposition. Individual VACNFs can be grown down to a pitch within the range 100–500 nm.

This paper describes a nanoporous substrate for applications in biomedical diagnostics. A photolithographic microstructuring technique for an ordered nanopore array fabrication is reported. The process uses a negative resist with hydrophobic properties increasing specificity to biomolecule linking. Nanoporous alumina is formed by an anodic process and yields straight holes with high aspect ratio: its use as substrates for DNA-microarray or protein-chip application offers several advantages over conventional supports, making them very attractive to use as supports for biological sample microarray application.

The selected-control synthesis of uniform α-Fe₂O₃ nanoparticles with morphologies of rhombohedra, rods, and cubes was successfully achieved in large quantities by the capping agent–cationic surfactant–CTAB-mediated hydrolysis of FeCl₃. The nanoparticles were obtained when the concentration of FeCl₃ ranged from 0.01 to 0.05 M at 120 °C. The growth mechanisms of α-Fe₂O₃ nanorhombohedra, nanorods, and nanocubes were analysed in detail, based on the topotactic transformation of the precursor β-FeOOH with different morphologies under the capping agent mediation. The concentration of FeCl₃, the reaction temperature, and the concentration of CTAB are all responsible for the final crystalline morphologies of the α-Fe₂O₃ nanoparticles. This result may facilitate not only the exploration of controlled approaches of preparing α-Fe₂O₃ nanoparticles for potential technical applications but also a deeper understanding of the fundamental physical and chemical processes of hydrothermal methods. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and field-emission scanning electron microscopy (FE-SEM) were used to characterize the products.

This paper discusses a novel deposition route of size-selected metal clusters, specifically Ag_N⁺ (where N = 2700), on graphite. The clusters are produced via a magnetron sputtering, gas aggregation cluster beam source and are size selected via a lateral time-of-flight mass filter. These clusters are deposited on a highly oriented pyrolytic graphite (HOPG) target predecorated with surface defects via Ar⁺ sputtering. Scanning tunnelling spectroscopy (STM) reveals a stable, randomly dispersed array of Ag₂₇₀₀ clusters after deposition.

The formation of nanoporous TiO₂ by anodization of titanium films deposited on silicon substrates was investigated. Films with homogeneously distributed pores having an average pore diameter of 25 nm and interpore distance of 40 nm were obtained by anodization in an aqueous HF electrolyte solution after a comprehensive investigation of the anodization conditions. It was shown that the magnitude of the anodization current and voltage have significant roles in the formation of different surface morphologies with different pore dimensions, ranging from big pits to nanosize porous structures. The study showed that the nanoporous structure is formed only in 0.5–1.0 wt% HF solution while keeping the anodizing potential at 3–5 V. The porous TiO₂ films were characterized using scanning electron microscopy and x-ray diffraction techniques, and their formation conditions are discussed. In addition, a growth mechanism model is presented to explain the formation of different surface structures.

This paper reports the results of an investigation into the stability of an individual multi-walled carbon nanotube subjected to combined bending and axial compression loading. The effect of van der Waals forces between two adjacent tubes is taken into account and a multiple-shell model is adopted. According to the ratio of radius to thickness, multi-wall carbon nanotubes discussed here are classified into three cases: thin, thick, and nearly solid. The critical combined loading and the stability mode are calculated for various ratios of radius to thickness. Results carried out show that the stability mode corresponding to the critical combined loading is unique, which is obviously different from the purely axial compression buckling of an individual multi-wall carbon nanotube. It is also seen from numerical examples that the distribution of the maximum critical bending stresses applied on each tube of MWNTs under combined bending and axial compression loading is dependent on the ratio of radius to thickness and the ratio of axial compression loading to bending moment. The new features of the combined stability of multi-walled carbon nanotubes under combined bending and axial compression loading and some meaningful and interesting results in this paper are helpful for the application and the design of nanostructures in which multi-wall carbon nanotubes act as basic elements.

Self-doped polyaniline (PANI) micro-rings have been successfully generated electrochemically. The polymer forming rings were about 100 nm wide, and the ring diameter is tunable from several to dozens of micrometres depending on deferent current densities. The morphology of such nanostructured polyaniline rings was investigated and further confirmed with field-emission scanning electron microscopy (FE-SEM). Furthermore, the film was characterized using UV/visible spectroscopy and cyclic voltammetry. The bubble template formation mechanism of the micro-rings was also proposed. Such nanostructured materials synthesized electrochemically open up a new approach to surface morphology control.

ZnO nanowires with different diameters were grown on Si substrates, then implanted with 80 keV Co⁺ ions at a dose of 3 × 10¹⁶ cm⁻², and subsequently annealed at 700 °C for 5 min. No Co precipitates appeared in the ZnO nanowires according to the results observed using a high-resolution transmission electron microscope, revealing that the magnetism of the ZnO nanowires was independent of the Co precipitates. The RKKY theory could be used to explain the phenomenon. Hysteresis was observed at 10 K for all samples of ZnO nanowires with different sizes. The Curie temperature decreased (from above 300 to 70 K) with the reduction in the ZnO nanowires' diameters. The mechanism of this phenomenon is also discussed with the RKKY theory. It is very valuable to show that the quantum-confined effect appears gradually with decreasing size of the nanowires.

We report the synthesis and characterization of colloidal nanocrystals consisting of ZnO doped with Tb³⁺ cations. Introducing the Tb³⁺ cations in ZnO nanosized hosts led to photoluminescent systems whose wavelength emission depends on the excitation line. Chemical surface modification of the doped ZnO nanocrystals associated with photoluminescence studies allows us to conclude that Tb³⁺ cations are located in the ZnO core.

ZnO microtubes with adjustable arrayed nanopores on the walls are prepared by using butterfly wing scales as natural biotemplates. Flat butterfly wing scales used as templates rolled into tubes during the calcinations; all the windows on the scales were reserved and formed porous walls. Furthermore the density of the pores on the walls is partially determined by experimental conditions, such as temperature and time of treatment. The nano/microstructures obtained have been investigated by means of x-ray diffraction and field emission scanning electron microscopy. The room temperature (T = 300 K) cathodoluminescence of these unique ZnO microtubes is also studied. The spectrum shows a sharp near band edge emission and a broad deep level emission, which are similar to those for other previously synthesized ZnO microtubes.

CdS nanocrystals have been synthesized based on low-temperature thermolysis of one single-source organometallic precursor in noncoordinating (ethanol) or coordinating (oleic acid) solvent. The organometallic precursor was prepared by using cadmium chloride, thiourea and sodium hydroxide in ethanol solution. The products were characterized by high-resolution transmission electron microscopy (HRTEM) and x-ray powder diffraction (XRD). The nucleation and growth stage were investigated by ultraviolet–visible (UV–vis) absorption spectroscopy. CdS nanocrystals prepared in oleic acid have a narrower size distribution than those prepared in ethanol. Phase transformation of CdS nanocrystals from a cubic to hexagonal structure in ethanol solution during the ageing stage was observed. Strong photoluminescence was observed in CdS nanocrystals prepared in oleic acid.

Erbium deposited on vicinal Si(001) at room temperature and postannealed at 630 °C is observed to form self-assembled erbium silicide nanowires with a single orientation. In the same growth conditions, the nanowires formed on the flat Si(001) surface possess two orthogonal orientations. The growths and evolutions of nanowires on vicinal and flat Si(001) are studied by scanning tunnelling microscopy and compared with each other. The nanowires on both vicinal and flat surfaces undergo a ripening process at the late growth stage, which is considered to be affected by coalescence and strain.

Local oxidations of InN and GaN were realized using an atomic force microscope (AFM). InN was oxidized easily by traditional AFM oxidation to ∼40 nm oxide height. The same AFM methodology was applied to GaN, which exhibited only minimum oxidation even at 10 V and high humidity. However, further experimentation led to successful nano-oxidation of GaN by two different techniques. In the first technique, a ∼10 nm gold film was deposited by sputtering onto the clean GaN substrate. The gold film reduced the AFM oxidation circuit resistance and increased the oxyanion driving current (oxidation current), thereby allowing AFM oxidation with heights reaching ∼25 nm at a humidity of 70%, but with a danger of gold contamination of the oxide. To eliminate this danger, additional experiments were performed in which the gold film on the GaN was removed in a small area, after which AFM oxidation was successfully performed in the area with gold removed with oxidation heights comparable to those of the gold-covered GaN. The techniques in this study make possible fast, chemical-free and contamination-free AFM nano-oxidation for metal–oxide–semiconductor field effect transistors based on two important nitrides.

This paper presents a continuum mechanics approach to modelling the elastic deformation of finite graphene sheets based on Brenner's potential. The potential energy of the graphene sheet is minimized for determining the equilibrium configuration. The four edges of the initially rectangular graphene sheet become curved at the equilibrium configuration. The curving of the sides is attributed to smaller coordination number for the atoms at the edges compared to that of the interior atoms. Considering two graphene models, with only two or all four edges constrained to be straight, the continuum Young's moduli of graphene are computed applying the Cauchy–Born rule. The computed elastic constants of the graphene sheet are found to conform to orthotropic material behaviour. The computed constants differ considerably depending on whether a minimized or unminimized configuration is used for computation.

In magnetic resonance force microscopy single spin experiments, forces in the attonewton range have to be measured. Non-commercial, soft single crystalline silicon bar cantilevers with a high quality factor and minimized spring constants have to be used, in order to improve the detection sensitivity. In our low temperature force microscope we obtain force sensitivities of the order of 10⁻¹⁸ N Hz^−1/2 at 10 K (Gysin 2002 Temperaturerverhalten der Elastizität und inneren Reibung mikromechanischer Resonatoren, Thesis Basel).

Micrometre-sized magnetic particles, which generate a magnetic field of 500 G and magnetic field gradients (), are attached on ultrasensitive cantilevers. A severe loss in force sensitivity and a frequency shift are observed while exposing a cantilever with a magnetic tip to a homogeneous magnetic field. To minimize the damping losses of the cantilevers with ferromagnetic particles, various magnetic materials (e.g. SmCo₅, Nd₂Fe₁₄B, and Pr₂Fe₁₄B) with different grain and domain sizes are investigated. The lowest magnetic dissipation is observed with SmCo₅ and Pr₂Fe₁₄B tips. We try to explain the dissipation effect of cantilevers with magnetic tips.

Non-linear distortions caused by thermal drift and hysteresis of piezo-scanners hinder the alignment of a series of two-dimensional scanning probe microscopy (SPM) images for Nanotomography volume images and for movies. We report on a registration method to correct these distortions. To speed up the registration of a complete stack of hundreds of two-dimensional images, the data were registered in a whole block, and a multi-resolution approach was used. Other specific problems of SPM measurements, such as image artefacts and the handling of image boundaries, were solved by introducing a mask with implicit mapping. With this approach we are able to obtain high-resolution Nanotomography images of modern nanostructured materials over large areas (1 µm) with a resolution of 10 nm. Examples are individual crystalline lamellae in a semicrystalline polymer film as well as a 50 nm wide channel in a nickel-based superalloy.

In this paper, we report that reversible strain amplitudes that are three times higher than commercial piezoceramics can be achieved in metallic nanowire actuators. By self-assembling nanoparticles of platinum on single-wall carbon nanotube templates, hybrid nanowires of platinum were fabricated with extremely high surface area to volume ratio. These nanowires showed reversible strains of 0.3% by modulating the surface electronic charge density through an applied potential relative to an electrolyte. Three regimes of actuation corresponding to different actuation mechanisms at different charge injection levels were identified. A stress of ∼12 MPa was generated, corresponding to the maximum strain of 0.31% at low voltages. These results show the applicability of hybrid metallic nanowire systems for artificial muscle applications.

Using molecular dynamics simulations, we show that a Y-junction carbon nanotube can be used to separate K⁺ and Cl⁻ ions from a KCl solution. The Y-junction nanotube is formed by connecting two smaller carbon nanotube branches of sizes (5, 5) and (6, 6) to a larger (8, 8) carbon nanotube. While uncharged (5, 5) and (6, 6) carbon nanotubes show close to zero occupancy of K⁺ and Cl⁻ ions, we show that a negatively charged (5, 5) carbon nanotube and a positively charged (6, 6) carbon nanotube can be selective to K⁺ and Cl⁻ ions, respectively. By performing molecular dynamics simulations on the entire system comprising the Y-junction carbon nanotube, the KCl solution chamber, the push plate and the receiving chamber, we show that as the electrolyte moves through the (8, 8) carbon nanotube the K⁺ and the Cl⁻ ions can be selectively transported through the (5, 5) and the (6, 6) carbon nanotube, respectively. The formation of ion pairs can affect the separation efficiency and we discuss the conditions under which perfect separation can be obtained.

Immiscible biopolymers of gelatin (Gt) and polycaprolactone (PCL) were first electrospun into a biomimicking composite fibre of Gt/PCL. Based on a phase separation study of the electrospun fibres, a leaching method was employed to generate 3D porous nanofibres by selectively removing the water soluble component of gelatin in a 37 °C aqueous solution of phosphate buffered saline. It was found that leaching treatment gave rise to a unique nanotopography containing grooves, ridges and elliptical pores on the surface as well as inside of the resultant individual nanofibres. Brunauer–Emmett–Teller (BET) area measurement indicated that the formed 3D porous fibres also brought in a pronounced increase of the surface area of fibres. The BET surface area of the porous fibres was observed to be about 2.4 times that of the precursor fibres, up to 15.84 m² g⁻¹ at its relatively large size of 800 nm diameter. The 3D porous fibres herein prepared could have considerable value for uses in developing highly integrated cell–scaffold tissue complexes and other industrial applications.

The energetics and kinetics of carbon nanotube growth are studied using an ab initio method. Specifically, the role of the nitrogen atom is analysed in detail for various pathways to the growth of the nanotube edge. The energy barriers are estimated by identifying transition states and it is found that the growth rate of a zigzag-type edge is significantly enhanced. The underlying physical mechanism is explained based on the electronic structure of nitrogen atoms embedded in the carbon networks.

Magnesium-doped GaN nanorods were grown on Si(111) substrates by plasma-assisted molecular-beam epitaxy. Time-integrated and time-resolved photoluminescence measurements were carried out to study the optical transitions. Two emission lines corresponding to blue emission at about 3.26 and 3.18 eV, with their corresponding phonon replicas, were observed. These peaks are attributed to conduction band to shallow acceptor transitions and to defects associated with column/substrate interface–shallow Mg acceptor complexes, respectively.

A simple method has been demonstrated for the synthesis of single-crystal and controllable sized silver nanoparticles (Ag NPs) homogeneously distributed on the surfaces of polyacrylonitrile (PAN) nanofibres via electrospinning followed by UV irradiation. Keeping the concentration of PAN at 7 wt%, the diameters of the monodisperse single-crystal Ag NPs can be adjusted from 3.5 to 10 nm by varying the molar ratio of silver nitrate to PAN (in terms of the repeating unit: AN). Transmission electron microscopy (TEM), field emitting scanning electron microscopy (FESEM) and x-ray diffraction (XRD) are used to characterize the products.

We demonstrate that a focused ion beam can deposit magnetic coatings on cantilevers used for atomic force microscopy, thereby producing a sensor for magnetic force microscopy. This technique is highly versatile, allowing the convenient deposition of complex or expensive materials, such as Co₇₁Cr₁₇Pt₁₂. A second material chosen for this demonstration was the permalloy (Ni₈₀Fe₂₀). We show magnetic images acquired with these cantilevers to illustrate their excellent properties and the differences between coatings. In principle, multilayer coatings could be easily made with this technique.