Table of contents

The electron spin g- and hyperfine tensors of the endohedral metallofullerene Sc@C₈₂ are anisotropic. Using electron spin resonance (ESR) and density functional theory (DFT), we can relate their principal axes to the coordinate frame of the molecule, finding that the g-tensor is not axially symmetric. The Sc bond with the cage is partly covalent and partly ionic. Most of the electron spin density is distributed around the carbon cage, but 5% is associated with the scandium d_yz orbital, and this drives the observed anisotropy.

Microelectrical mechanical systems (MEMS) devices coated with a thin film of ionic liquid showed significant improvement in wear life. These promising tribological findings led to the current study of the micro–nano behaviour of an ionic liquid, 1,2-dimethyl–3-butyl imidazolium hexafluorophosphate (DMBI-PF₆), when applied as a thin film on a polished silicon surface. The films remain as microdroplets in ambient conditions but undergo drastic changes when agitated by an atomic force microscope (AFM) contact scan or touched with a biased AFM tip. The nanotribological characteristics including mobility, diffusion and scratch resistance are studied. In the case of DMBI-PF₆, it was observed that the imidazolium ion is a mobile phase while PF₆ is attached to the silicon surface. Crystallites are formed as a result of tip contact and depend on the tip bias and environmental conditions. Crystallization of DMBI-PF₆ from the liquid phase with no tip bias showed substantial variation in crystal shape compared to those formed under the influence of an electric bias.

Dynamic atomic force microscopy (dynamic AFM) with carbon nanotube tips has been suggested as an enabling tool for high precision nanometrology of critical dimension features of semiconductor surfaces. We investigate the performance of oscillating AFM microcantilevers with multi-walled carbon nanotube (multi-walled CNT) tips interacting with high aspect ratio structures while in the attractive regime of dynamic AFM. We present experimental results on SiO₂ gratings and tungsten nanorods, which show two distinct imaging artefacts, namely the formation of divots and large ringing artefacts that are inherent to CNT AFM probe operation. Through meticulous adjustment of operating parameters, the connection of these artefacts to CNT bending, adhesion, and stiction is described qualitatively and explained.

We report on the precise positioning of a carbon nanotube on an atomic force microscope (AFM) tip. By using a nanomanipulator inside a scanning electron microscope, an individual nanotube was retrieved from a metal foil by the AFM tip. The electron beam allows us to control the nanotube length and to sharpen its end. The performance of these tips for AFM imaging is demonstrated by improved lateral resolution of DNA molecules.

Amorphous silica films deposited by combustion chemical vapour deposition (CCVD) were modified by lithium addition in the precursor solution. The modified films were characterized by x-ray diffraction and scanning and transmission electron microscopy. The addition of lithium promoted the crystallization of Li₂O–SiO₂ compounds, mainly crystalline phases like Li₂SiO₃, Li₂Si₂O₅, quartz and cristobalite. Besides this, the morphology of the film was modified, leading to the formation of acicular structures and nanowires. Selected area electron diffraction (SAED) and microprobe EDS analysis indicated that the nanowires are amorphous and probably constituted of silica.

Single-crystalline CeOHCO₃ rods with an orthorhombic structure have been successfully synthesized by the sonochemical method from aqueous solution containing CeCl₃ and urea. Polycrystalline CeO₂ rods have been prepared by thermal conversion of single-crystalline CeOHCO₃ rods at 500 °C in air. CeOHCO₃ and CeO₂ rods were characterized by x-ray powder diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TG) and differential scanning calorimetric analysis (DSC).

We report on a new technique for the fast fabrication of well defined arrays of Si islands by means of a stigmated Ga⁺ focused ion beam without masks, resists or etching. Stigmating and defocusing the ion beam resulted in the direct formation of Si islands of different shape and size. The ordering of the island arrays was determined by the pattern of the beam scanning, and in this way nanometre-sized Si island arrays with hexagonal symmetry were accordingly produced. The effects of beam spot distortion and broadening on the milled structure are also examined by scanning electron microscopy imaging. With this technique, not only is the fabrication time shorter, but also the arrangement of the island arrays is possibly controllable.

Large-scale fabrication of high-purity and uniform Zn nanowires was obtained via thermal evaporation. The resulting Zn nanowires were characterized and confirmed by means of an x-ray diffractometer, scanning electron microscope, transmission electron microscope and energy-dispersive x-ray spectroscope. An analysis of the characterization indicates that the high yield uniform zinc nanowires have serpentine geometries, with lengths up to several micrometres and diameters about 50 nm. The selected area electron diffraction pattern and high-resolution transmission electron microscopy image demonstrate perfect crystallinity with the growth direction of [0001]. Owing to the low content of oxygen in the as-prepared products, their photoluminescence spectrum was measured; it exhibits a significant blue shift. Up to now, such optical properties from zinc nanowires have been little reported.

Reversible electrical modification of a conductive polymer is studied for ultrahigh density data storage based on a scanning probe microscope (SPM). Using a surface-initiated polymerization (SIP) method, a thin polyaniline film is formed from a self-assembled monolayer (SAM) on an Au surface. The conductivity of the film is reversibly changed by applying a voltage between a SPM probe and the film, depending on the polarity of the applied voltage. This reversible electrical modification is considered to originate in the oxidation–reduction reaction or protonation–deprotonation reaction of PANI from x-ray photoelectron spectroscopy (XPS) measurement.

Thermal treatment of compacted GeO₂ powder under argon flow leads to the growth of a dense distribution of microwires and nanowires on the sample surface. Extended treatment causes the formation of more complex structures, including arrays of nanoneedles. Enhanced cathodoluminescence emission is associated with the wires and needles, which show a component at 2.72 eV not observed for the untreated material.

This paper investigates the simulation of charging a semiconductor quantum-dot cellular automata (QCA) cell in the presence of impurity atoms. The complete configuration space of the cell and the impurities is analysed using the canonical partition function. Limits on the size and location of the impurity region are determined. Within these limits, it is shown that the semiconductor QCA cell can be controllably charged. Using these results, it is shown that a short wire consisting of three QCA cells can operate with high logical correctness at cryogenic temperatures.

In this paper we describe a biopolymer-assisted hydrothermal approach to the synthesis of gold sponges. This is carried out by transferring a hyaluronic acid potassium salt/HAuCl₄ aqueous solution into a stainless steel autoclave with a Teflon liner and heating in an oven at 180 °C for 6 h. Here, hyaluronic acid potassium salt plays three roles in the synthesis, namely, stabilization, reduction, and as a soft template. Field emission scanning electron microscopy images, energy-dispersive x-ray spectroscopy, and x-ray diffraction reveal that the materials obtained consist of an interconnected framework of face-centred cubic metallic gold filaments, which is approximately 0.6 µm in width and composed of fused micrometre-sized particles that enclose pores 1–4 µm in size. The test of surface-enhanced Raman scattering (SERS) from 4-mercaptobenzoic acid shows that the prepared gold sponges are an active SERS substrate. This is largely because they had an increased number of particle junctions, which are SERS active sites. This route can also be extended to the fabrication of silver sponges, which are composed of fused crystallites with diameters of 200–400 nm that enclosed pores 0.4–2 µm in size. The test of SERS from Rhodamine 6G also reveals that the prepared silver sponges are likewise an excellent SERS substrate.

Carbon nanotube coated acoustic and optical sensors have been successfully studied for volatile organic compound (VOC) sensing applications, at room temperature. Here, Langmuir–Blodgett (LB) films consisting of tangled bundles of single-walled carbon nanotubes (SWCNTs) have been transferred onto different transducing sensors by using a linker–buffer LB multilayered material of cadmium arachidate pre-deposited on the sensor surface to promote adhesion of SWCNTs. Two different kinds of sensors have been designed, fabricated and utilized: quartz crystal microbalance 10 MHz AT-cut quartz resonators and standard silica optical fibre sensors based on light reflectometry at a wavelength of 1310 nm. The proposed detection techniques are focused on two key parameters in gas sensing applications: mass and refractive index, and their changes induced by gas molecule absorption. The results indicate high sensitivity, good repeatability and reversibility. Signals from each sensor type have been analysed and processed by using pattern recognition techniques such as principal component analysis and use of artificial neural networks. The recognition of the hybrid system is successfully performed, improving the data fusion from acoustic and optical sensors with SWCNT-functionalized sensors that are highly discriminating. To our knowledge, this is the first reported study of combined hybrid integration of acoustic sensors with optical fibre sensors using nanostructured materials as single-walled carbon nanotubes for VOC detection, at room temperature.

Optically driven actuators have been fabricated from single-wall carbon nanotube–polymer composite sheets. Like natural muscles, the millimetre-scale actuators are assemblies of millions of individual nanotube actuators processed into macroscopic length scales and bonded to an acrylic elastomer sheet to form an actuator that have been shown to generate higher stress than natural muscles and higher strains than high-modulus piezoelectric materials. Strain measurements revealed 0.01%–0.3% elastic strain generated due to electrostatic and thermal effects under visible light intensities of 5–120 mW cm⁻². An optically actuated nanotube gripper is demonstrated to show manipulation of small objects. This actuation technology overcomes some of the fundamental limitations such as the use of high voltages or electrochemical solutions for actuation, opening up possibilities for remote light-induced actuation technologies.

Fine control of gold nanoparticle shape can be achieved by varying the pH of the reaction medium in the presence of gold nanorods, which acted as seeds. Under various pH (3.6–9.6) values of the reaction medium, different shapes of gold nanostructural architectures, from rectangle-, 'dogbone'- and peanut-like outlines to branched multipods with corrugated surface, can be fabricated in high yield from gold nanorods with aspect ratio 2.9 and 2.1. These shape changes of gold nanorods directly influence their optical properties.

ZnO nanostructures with different morphologies have been achieved by simple thermal evaporation of mixed powders of ZnS, graphite and SnO₂ at 1050 °C in a flowing Ar atmosphere. Branched nanobelts and wide nanosheets of ZnO were formed on Si wafers at a temperature of 700 and 500 °C, respectively. As for the branched nanobelts, there exist nanotwins along the axial direction of the stem belts, and a definite included angle about 70° between the stem and the branch. In contrast, the wide nanosheets have a rectangle-like cross-section with typical widths of 200 nm to several micrometres and lengths of up to tens of micrometres. Photoluminescence measurements reveal that the branched nanobelts and wide nanosheets have visible green emission bands at about 530 and 510 nm, respectively. The branched ZnO nanobelts have potential for building optoelectronic nanodevices with special configurations, and the ZnO nanosheets might be used in nanoscale sensors.

We report a soft and template-free electrochemical deposition method for preparing wafer-scale ZnO nanoneedle arrays on an oriented gold film coated silicon substrate. It has been shown that the ZnO nanoneedles possess single-crystal wurtzite structure and grow along the c-axis perpendicularly on the substrate. Raman and resonant Raman scattering studies have confirmed that the ZnO nanoneedles are of good crystal quality. The room temperature photoluminescence spectrum of such ZnO nanoneedle arrays exhibits a strong ultraviolet emission but negligible visible emission. The time-resolved photoluminescence spectral analysis discloses the excitonic origin of the ultraviolet emission. The field electron emission study, showing notable emission current in a moderate turn-on field, demonstrates potential applications of such ZnO nanoneedle arrays in field emission display devices. The formation of such a ZnO nanoneedle array is attributed to the formation of {0001}-oriented ZnO nuclei on the oriented gold coated silicon substrate and preferential growth along .

Pd(0) nanoclusters were dispersed by using the metal vapour synthesis technique in organometallic polymers of chemical structure (M = Pd,Pt), namely Pd-DEBP and Pt-DEBP. The hybrids were characterized by means of solid state ¹³C and ³¹P nuclear magnetic resonance, which highlighted the chain organization and the plasticizing effect of the nanoparticles on the polymers. Scanning electron microscopy images of the pristine organometallic polymers, and of their hybrids containing Pd(0), exhibited a growth of nanosized fibrils on glass substrates. High resolution transmission electron microscopy measurements showed a narrow distribution of Pd(0) nanoparticles which have dimensions in the range 1.0–5.0 nm in the case of Pd/Pd-DEBP hybrids and 0.5–2.0 nm in the case of Pd/Pt-DEBP hybrids.

A simple and effective means for fabricating gold hollow spheres with controllable gold particle size is presented, where polydiacetylene vesicles terminated with –NH₂ were synthesized and used as templates for the fast combination of gold nanoparticles. The combination process of gold to the hollow ball and the subsequent particle reductive growth have been investigated using a quartz crystal microbalance, and the morphology and stability of these hollow spheres are characterized using transmission electron microscopy and ultraviolet–visible spectroscopy. This shows that different sizes of gold particles and a variety of coverage of gold nanoparticles on –NH₂-terminated spheres could be easily controlled. The as-prepared gold hollow ball has an excellent ability against mechanical disturbance and the nanogolds on it have very high stability against aggregation and ageing. The immobilization effect of a single-strand DNA probe shows that gold nanoparticles on the surface of this kind of sphere have a great advantage over their counterparts on a planar substrate surface.

Pb (Zr_xTi_1−x)O₃ (PZT) thin films with (111) texture were deposited onto commercially available Pt/Ti/SiO₂/Si substrates via the sol–gel technique. Piezoforce microscopy (PFM) was then used to analyse the evolution of domain populations as a function of the Zr content x. Domain structures of virgin films, local piezoelectric properties of individual grains and piezoelectric histograms were studied in films with different compositions (x = 0.2–0.6), which cover both the tetragonal and rhombohedral sides of the phase diagram. In films with low Zr content mainly single-domain grains were observed. As the Zr content increased, a larger fraction of polydomain grains was found. The local piezoelectric response measured inside sufficiently big grains indicated that the strongest piezoelectric effect occurs in PZT30/70 (x = 0.3) films. This was attributed to two different effects: high out-of-plane polarization achieved due to the (111) texture and influence of the dielectric constant. In tetragonal films with their lower dielectric constants the electric field seen by a ferroelectric is higher as compared to other compositions, giving rise to an apparent increase of the effective piezoelectric response measured by PFM. The analysis of the domain images indicated that sol–gel derived PZT films are slightly self-polarized near the free surface. With increasing Zr/Ti ratio, the variation of domain populations resulted in reversing the sign of the average piezoelectric response at x≈0.3. It is demonstrated that PFM histograms are extremely sensitive to PZT composition and can be used as a signature of complex domain structures in ferroelectric thin films.

Overlayers of a fatty acid (palmitic and lauric acid) formed at the interface between a solution of this molecule in phenyloctane and the basal plane of graphite are studied by in situ scanning tunnelling microscopy. The layers organize into lamellae, which are formed by a close packing arrangement of molecules parallel to the graphite surface. Chemical modification of the STM tips used allowed identification of the functional group. Indeed, the gold tips used are functionalized with 4-mercaptobenzoic acid (4-MBA) and 4-mercaptotoluene (4-MT). The same functional group on a sample is then 'seen' as a dark and a bright spot when imaged with 4-MBA and 4-MT modified tips, respectively. This contrast distinction is related to interactions (or a lack of them) between the carboxyl group on the sample and molecules on the tip, which can facilitate (or hinder) the electron tunnelling.

We demonstrate the use of optical patterns, produced by resonant Rayleigh scattering from gold nanorods, as markers by which local deformations can be measured using image correlation techniques. While the use of optical data, in this case from dark-field microscopy, to generate deformational field information (displacements and strains) is not new, the use of the light scattered from gold nanorods as the correlated pattern is new, and has the potential to enable smaller scale measurements even over large deformations. We find excellent agreement between the measured and theoretical deformation and strain fields for two sample polymers with gold nanorod markers. The gold nanorod surface can be modified to make biocompatible nanomaterials, which will be useful for examining mechanical effects in biological tissue.

In situ real-time spectroscopic ellipsometry is used to monitor the growth of magnetron sputtered silver nanoparticles on SiO₂ substrates, through the percolation threshold and into the bulk film regime. The plasmon polariton resonances in the nanoparticulate regime are effectively modelled by a Lorentz oscillator. The resonance energy of the oscillator is observed to reduce to zero shortly after the percolation threshold, whereby the oscillation is described by Drude free electron theory. From the Drude theory, the electronic mean free path is observed to increase dramatically at the percolation threshold, to a value of 16 nm in the bulk regime, in good agreement with x-ray diffraction and transmission electron microscope measurements of the crystallite size in the films. Shortly before the percolation threshold the data is better modelled by two Lorentz oscillators, attributed to coupling between the plasmon polaritons. The onset of the coupling is determined to occur at a surface area coverage of 52%.

Ethylcyanoacrylate nanoparticles (40–100 nm) were synthesized to act as potential skin drug carriers. A novel multiscale non-linear model, based on an oscillatory mechanism, which includes polymerization, de-polymerization, re-polymerization and cluster dynamics, is shown to fit the kinetics experimental data and it is used to estimate the amount of potentially histotoxic by-products (i.e. residual monomers or very low molecular weight oligomers).

A new and efficient Tx-100/cyclohexanol/H₂O micellar system has been developed to synthesize rectangular single-crystalline PbCrO₄ nanotubes and nanorods through a self-seeding template growth (SSTG) process at room temperature. Studies found that the whole procedure involves the nucleation of nanoparticles, the growth into nanotubes from nanoparticles and the evolution into nanorods from nanotubes, merely by stepwise prolonging the reaction time while keeping other conditions constant. This simple method provides guidance for the morphology control of other nanostructural materials.

We report detailed reflectance studies of the exciton–polariton structure of thin film nanocrystalline ZnO at low temperatures and compare these data to bulk crystal data. The reflectance spectra are modelled using a two-band dielectric response function with a number of different models involving reflected waves in the thin film and/or excitonic dead layers. We present matrix forms for the solution of these models, enabling computation of the reflected intensity and other field components. The reflectance of nanocrystalline ZnO differs substantially from that of bulk material, with Fabry–Perot oscillations at energies below the transverse A exciton and above the longitudinal B exciton. Between these energies we see no evidence of anomalous waves because the strong interaction of the damped exciton with the photon leads to polaritons with substantial damping such that the Fabry–Perot oscillations are eliminated. Good agreement is found between the model and data, and the importance of the polariton viewpoint in understanding the reflectance data for nanocrystalline material is clearly seen. The fits provide parameter values that can be compared to bulk crystal parameters, providing a method for quantitative analysis of the films and their potential for applications such as thin film random lasing or polariton lasing in microcavities.

Novel hollow mesoporous silica spheres (HMSs) with uniform size and morphology have been successfully synthesized in a facile route using poly(vinylpyrrolidone) (PVP) and cetyltrimethylammonium bromide (CTAB) as co-templates at room temperature. XRD, N₂ adsorption–desorption analysis, FE-SEM, and TEM are used for the characterization of the structure. The hexagonally ordered pore channels are formed on the shell. Ibuprofen (IBU) as a model drug is used to examine the storage capacity and the release behaviour of drug molecules. The storage capacity of hollow mesoporous silica spheres can reach 1133 ± 52.4 mg g⁻¹ for ibuprofen, which is three times higher than that of conventional mesoporous materials previously reported (337 mg g⁻¹), and the storage capacity is adjustable in a wide range. Furthermore, this system also shows a sustained-release behaviour. The release rates from the IBU-HMSs system (IBU stored in HMSs) increase with the decrease of pH values and the release process follows a Fick's law.

Highly porous thin films with columnar microstructures are applicable to many optical, chemical, and electronic devices, and can be fabricated using the glancing angle deposition method for physical vapour deposition onto tilted substrates. In a recent advancement of this method, it was shown that decoupling of the vapour incidence direction from the column growth direction provides significant flexibility to engineer the pore structure of the films. Here we elaborate on the decoupling principle by applying it to chiral thin films with a periodic microstructure, and demonstrating how it leads to improved film uniformity and the elimination of column broadening. We also show the effects of such depositions onto substrate seed layers with intentional defects. Substrate based defects normally transfer to thin films as air filled defects, but here we present for the first time that a simple adjustment of the deposition parameters can invert the normally air filled defects to become solid, evaporant filled defects. This defect engineering capability provides new opportunities for the deployment of glancing angle deposition thin films to photonic bandgap crystals and microfluidic devices.

This current work demonstrates the first reported successful synthesis of a novel unique one-dimensional nanostructure of monoclinic W₁₈O₄₉ that exhibits characteristic porous morphologies with the nanosized pores distributed rather regularly along the length of the nanowires. Their microstructures were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectrum. The unique porous structures may be helpful in studies of nanostructure growth mechanisms and find applications in numerous fields.

The spatio-temporal dynamics of molecular motors and the potential of its control are studied on the basis of a spatially dependent Fokker–Planck model. The model considers spatially inhomogeneous excitation coupling the energetic sublevels of the molecules as well as dynamic spatial fluctuations and diffusion. Simulations show that both the spatio-temporal noise in the molecular properties and the spatio-temporal excitation set an upper limit to the efficiency of the motor progression. Moreover, a sufficiently small molecular diffusion, as well as a thorough adjustment of transition rates, leads to a regular forward propagation while for high diffusion and improperly chosen rates spatio-temporally diverging particle distributions may evolve. Suitable excitation conditions for efficient movement control are identified.

The structure of Si nanocrystals (nc-Si) embedded in SiO₂ is promising for achieving optical gain and waveguiding with the advantage of full compatibility with the matured Si technology. In this paper, we report an approach to optical-constant profiling for such a planar waveguide structure formed by Si ion implantation into a SiO₂ thin film based on spectroscopic ellipsometry (SE). With the nc-Si optical constants calculated from the Forouhi–Bloomer model and the nc-Si depth profile obtained from secondary ion mass spectroscopy (SIMS) measurements, the optical properties at a given depth are simulated with the Maxwell–Garnett effective medium approximation (EMA). Then an SE fitting is carried out, and the optical constants of nc-Si are extracted from the best fitting. Finally, the depth profile of optical constants of the structure is obtained from the EMA calculation. The result also suggests that the structure has a very low optical loss in the visible to infrared spectral range.

A novel approach for positioning InAs islands on GaAs(110) by cleaved-edge overgrowth is reported. The first growth sample contains a strained In_xGa_1−xAs /GaAs superlattice of varying indium fraction and thickness, which acts as a strain nanopattern for the cleaved edge overgrowth. The formation of aligned islands is observed by means of atomic force microscopy. The ordering of the aligned islands and the structure of a single InAs island are found to depend on the properties of the underlying In_xGa_1−xAs /GaAs superlattice and molecular beam epitaxy growth conditions.

We show the success of large-scale growth of ZnO hexagonal nanoprisms on silicon substrates by a two-staged mechanism. In the first stage, the catalyst nanoparticles assisted the nucleation via the vapour–liquid–solid (VLS) mechanism to form polyhedral nanoparticles. In the second stage, the nanoprism was grown up by anisotropic homoepitaxy, layer by layer, on the c-face of the polyhedral nanoparticle. The surface of the nanoprism consists of the ultraflat {0001} and planes. The nanoprism is 200–500 nm in width and controllably sized in length, of high crystalline quality and excellent optical quality. This nanoprism would be an interesting building block for highly efficient nanolasers.

We investigated a carbon nanotube (CNT) oscillator controlled by thermal gas expansion using classical molecular dynamics simulations. When the temperature rapidly increased, the force on the CNT oscillator induced by the thermal gas expansion rapidly increased and pushed out the CNT oscillator. As the CNT oscillator extruded from the outer nanotube, the suction force on the CNT oscillator increased by the excess van der Waals (vdW) energy. When the CNT oscillator reached the maximum extrusion point, the CNT oscillator was encapsulated into the outer nanotube by the suction force. Therefore, the CNT oscillator could be oscillated by both the gas expansion and the excess vdW interaction. As the temperature increased, the amplitude of the CNT oscillator increased. At high temperatures, the CNT oscillator escaped from the outer nanotube, because the force on the CNT oscillator due to the thermal gas expansion was higher than the suction force due to the excess vdW energy. By the appropriate temperature controls, such as the maximum temperature, the heating rate, and the cooling rate, the CNT oscillator could be operated.

Ultrafine β-LiFe₅O₈ nanoparticles were successfully synthesized at the low temperature of 140 °C through a hydrothermal method. The average particle size is about 5 nm with a fairly narrow size distribution. The saturation magnetization (M_s), remanent magnetization (M_r), and coercivity (H_c) could be determined to be 25.23 emu g⁻¹, 3.95 emu g⁻¹, and 301 Oe, respectively. The Teflon cell using the prepared nanoparticles as active cathode material shows an initial discharge capacity of about 162 mA h g⁻¹. The as-prepared ultrafine β-LiFe₅O₈ nanoparticles exhibit higher capacity than any other known lithium ferrites, which may be ascribed to the unique microstructure and smaller particle size achieved by the hydrothermal synthesis procedure.

The interaction between an energetic ion and an atom of the carbon nanotube is approximated as that between a carbon atom and an sp² carbon atom of a graphene sheet and computed using density functional theory utilizing a local density functional. Using the calculated force, molecular dynamics simulation of a low energy carbon ion moving in a single-wall carbon nanotube is conducted. Compared with the simulation using the ZBL potential, the result shows that the motion of the ion is quite different and the range is much shorter. The attractive part of the interatomic interaction is found to play an important role in the channelling of low energy ions in an SWCNT.

Dielectrophoresis has appeared recently as a non-destructive means to manipulate and sort carbon nanotubes. In order to compute the electrostatic forces that act on carbon nanotubes when subjected to an external field and placed in the vicinity of metallic protrusions, we develop a technique that relies on a monopole–dipole description of the nanotubes and on a dielectric-function model of the metallic elements. The technique proceeds iteratively between these two descriptions in order to determine the nanotube polarization and the resulting counter-polarization of the metallic elements. Specific differentiation schemes as well as a finite-difference formulation of Poisson's equation are given in cartesian and cylindrical coordinates. As an application, we compute the polarization and forces that act on a metallic (5, 5) and a semiconducting (10, 0) nanotube, when placed in the vicinity of a flat metallic support with either a conical or semi-elliptical protrusion. The results quantify the relevant electrostatic forces as well as the contribution of the image interaction to these forces. It is shown that the nanotubes get more polarized and attracted to the protrusion when the latter has a semi-elliptical shape. The differences in the polarization and forces that act on the metallic (5, 5) and semiconducting (10, 0) nanotubes support the idea that dielectrophoresis may be used to separate them.

A novel ferromagnetic/semiconductor oxide nanocomposite formed by arrays of Ni nanocylinders grown by the electrodeposition technique in a semiconductor oxide matrix of self-aligned and randomly disordered titanium dioxide nanotubes has been synthesized. X-ray diffraction, EDX, SEM, AFM, rf-GDOES and VSM magnetometry techniques have been used to investigate the structural, compositional and morphological properties, as well as its specific magnetic behaviour. Titania nanotubes have been grown through a single anodization process, by using HF acidic electrolytes in a potentiostatic mode. The thus-obtained titanium dioxide nanotube outer diameter ranges between 90 and 150 nm, wall thickness about 25–40 nm and 300 nm in depth. The electrodeposited Ni nanocylinders reach above 100 nm diameter and 240 nm length, giving rise to coercive fields of 98 and 200 Oe, well within the hysteresis loops perpendicular or parallel to the nanocylinder axis, respectively, which could be ascribed to the formation of magnetic vortex domain states. It is expected that this novelty nanocomposite, based on ferromagnetic Ni nanocylinders embedded in a semiconductor titanium dioxide nanotube template, will become a promising candidate for many applications in a broad range of scientific and technological areas, such as ultrahigh density magnetic storage media or spin-based electronic devices.

A novel method for designing photonic crystals with high orders of rotational symmetry using an inverse Fourier transform (IFT) method is presented. The IFT of an n-sided polygon is taken and the positions of the peaks are computed in order to obtain a set of discrete points in real space where the scattering centres are to be located. We show, by simulating the diffraction pattern, that although these points appear disordered they possess long range order, which also confirms that the arrangement of points has n-fold rotational symmetry. The designed structures can possess an arbitrary number of rotational symmetries, whilst retaining the sharp diffraction patterns characteristic of known crystal lattices which exhibit wide bandgaps. We present simulation results using the finite difference time domain method (FDTDM) for large non-repeating patterns of scatterers produced by this method. We also present results where around 50 points have been generated in a square unit cell and tiled to produce a lattice. These were simulated using both the finite element method (FEM) and the FDTDM, which were shown to agree. Our results demonstrate that the method is capable of producing crystal structures with wide bandgaps where the scattering centres are either non-repeating with no fundamental unit cell, or consist of a (large) number of points in a unit cell, which may then be tiled to form a lattice.

A simple and versatile one-pot sol–gel synthesis of Eu³⁺-doped nanocrystalline TiO₂ and ZrO₂ nanomaterials is reported in this paper. It consists of the controlled crystallization of Eu³⁺-doped TiO₂ or ZrO₂ nanoparticles from an initial solution containing the metal alkoxide, the lanthanide precursor, a complexing agent and a non-complexing acid. The main interest is that it could be extended to different lanthanide ions and inorganic metal oxides to prepare other multifunctional nanomaterials.

The characterization by XRD, HRTEM and SAED techniques showed that the TiO₂ and ZrO₂ crystallization takes place at very low temperatures (60 °C) and that the crystallite size can be tailored by modifying the synthetic conditions. The optical properties of the resulting materials were studied by emission spectra and decay measurements. Both Eu³⁺:TiO₂ and Eu³⁺:ZrO₂ samples exhibited long lifetime values after removing organic components (τ = 0.7 and 1.3 ms, respectively), but the Eu³⁺:ZrO₂ system is specially promising for photonic applications since its τ value is longer than some reported for other inorganic or hybrid matrices in which Eu³⁺ ions are complexed. This behaviour has been explained through an effective dispersion of the lanthanide ions within the ZrO₂ nanocrystals.

We demonstrate that a combination of ion sputtering and soft lithography is an alternative and effective way of nanostructuring soft matter. We create self-organized nanoscale structures on a glass template by irradiating the surface with a defocused, low energy Ar ion beam. Capillary force lithography is then used to transfer the pattern, exploiting the glass transition of polymeric layers. In particular, we demonstrate the pattern transfer of a periodic 150 nm ripple structure onto an organic compound. This new, unconventional combination is then a low-cost strategy that opens the way to a variety of applications in the field of organic-based devices.

We have investigated a process for tailoring of epitaxial CoSi₂/Si nanostructures using low temperature wet oxidation. A separation between two CoSi₂ layers on a Si substrate in the range of 60 nm is generated by a self-assembly process. During subsequent low temperature wet oxidation, SiO₂ formation on top of the silicide layers pushes the latter into the substrate. At the edges of the gap, the silicide layers are shifted in both and directions, leading to an effective reduction of the separation width to dimensions below 20 nm and eventually to merging of the two layers. The significantly lower oxidation rate of the silicon in the initial gap compared with the CoSi₂ provides the excess Si for the shift in the direction. The structures were investigated using transmission electron microscopy (TEM) and scanning electron microscopy (SEM).

Large-scale, uniform and regular oxide/sulfide core–shell nanostructures and nonlayered sulfide nanotubes, such as ZnO/ZnS, SnO₂/SnS₂, MnO₂/MnS₂ core–shell nanostructures, as well as ZnS and SnS₂ nanotubes, have been prepared by a versatile approach based on a thioglycolic acid assisted hydrothermal process and subsequent NaOH treatment. The above-mentioned nanostructures have been characterized by x-ray powder diffraction (XRD), transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). Moreover, the role of thioglycolic acid for the formation of oxide/sulfide core–shell and nonlayered sulfide nanotubes has been identified. Finally, the formation mechanism for the derived nanostructures has been phenomenologically presented.

The effect of non-sphericity of the quantum dot on the eigenvalues and eigenfunctions has been investigated for the case when the barrier height at the surface is finite. The ground and excited state energies have been calculated variationally for prolate and oblate spheroids as a function of eccentricity of the spheroid. Analytic wavefunctions giving the admixture of higher angular momentum states have been obtained as a function of eccentricity.

Silicon nitride thin films deposited on silicon substrates are patterned by using atomic force microscopy (AFM) local oxidation nanolithography. The mechanism of the AFM-induced oxidation is studied by analysing the kinetics of the oxidation and by studying the electrical current during the oxidation process. We observe that the silicon substrate and the silicon nitride layer are simultaneously modified. Because of the significant technological relevance of silicon nitride film, the technique is applied for fabricating masks with nanometre-scale features by transferring the pattern to the silicon substrate.

Recent developments in the analysis and the application of DNA often require the stretching of individual DNA molecules to specific surfaces. We propose and demonstrate a method for the positioning of unmodified extended DNA molecules. A local microscopic circular flow is created by a non-uniform AC field and utilized to stretch the λ-DNA on a gold surface or between gold electrodes. The electrical-field amplitude and frequency responses of DNA motion are studied. The method can be applied to position the DNA with accuracy on a microscopic scale while requiring no modification of the DNA for terminal binding. With a diluted DNA solution, the number of DNA molecules across the electrodes is controllable and the positioning of a single extended DNA across electrodes is achievable.

Highly ordered La_0.62Pb_0.38MnO₃ nanowire arrays are successfully fabricated using an improved sol–gel template method. The x-ray diffraction and transmission electron microcopy results reveal that the nanowires are polycrystalline with uniform diameter around 50 nm. Magnetic measurement indicates that the ferromagnetic transition temperature T_C of the nanowires is around 308 K, which is lower than that of the corresponding bulk material. The nanowire arrays demonstrate the perpendicular magnetic anisotropy as a result of shape anisotropy and enhanced coercivity compared with bulk materials and the temperature dependence of the saturation magnetization exhibits a T^1.25 behaviour. The growth mechanism of the nanowires is also briefly discussed.