Table of contents

Although there are many methods of fabricating nanofibres, electrospinning is perhaps the most versatile process. Materials such as polymer, composites, ceramic and metal nanofibres have been fabricated using electrospinning directly or through post-spinning processes. However, what makes electrospinning different from other nanofibre fabrication processes is its ability to form various fibre assemblies. This will certainly enhance the performance of products made from nanofibres and allow application specific modifications. It is therefore vital for us to understand the various parameters and processes that allow us to fabricate the desired fibre assemblies. Fibre assemblies that can be fabricated include nonwoven fibre mesh, aligned fibre mesh, patterned fibre mesh, random three-dimensional structures and sub-micron spring and convoluted fibres. Nevertheless, more studies are required to understand and precisely control the actual mechanics in the formation of various electrospun fibrous assemblies.

We report here on the fabrication of a three-dimensional array of nanoparticles which bridges the gap between lithographically defined gold electrode contacts separated by 20 nm. The nanoparticle assemblies are formed from about 5 nm gold nanoparticles and benzenedimethanethiol (BDMT) bridging ligands. These assemblies are introduced between the contacts using a layer-by-layer protocol with successive BDMT self-assembly being followed by nanoparticle adsorption until the gap is bridged. The temperature dependent electrical properties of these devices are analysed to establish whether they are consistent with the notion that the networks are built up from molecularly interlinked discrete gold nanoparticles. To aid this analysis the molecular conductance of single bridging molecules is also characterized at room temperature using a recently introduced method based on the scanning tunnelling microscope (STM). From these measurements it is concluded that the room temperature electrical properties of the nanostructured networks are limited by the small interparticle connectivity and the inherent resistance of the linker molecules.

A highly ordered and crystallized titania (TiO₂) nanotube array is fabricated by a low-voltage anodization plus a post-embedding calcination process. Polyoxophosphotungstate–titania (POPTA–TiO₂) composite catalyst is synthesized by embedding POPTA in TiO₂ tubule channels to improve the photoelectrochemical properties. The morphological characteristics and crystal behaviour of POPTA–TiO₂ are examined by field-emission scanning electron microscopy and x-ray diffraction. The stability of the chemical structure has been analysed by Fourier transformed infrared spectroscopy measurements. The photoelectrochemical properties are investigated by means of the polarization current response. Photocatalytic and photoelectrocatalytic reactivities for the degradation of an endocrine disrupting chemical have also been investigated to examine the photoelectrochemical reaction efficiency of POPTA–TiO₂ composite catalyst.

Ordered surfactantless self-assembled, mesoporous SnO₂ adsorbents, consisting of tubular voids of nanometric sizes, are prepared by the sol–gel processing of tin (IV) tetra-tert-amyloxide, Sn(OAm^t)₄, whose molecules have been previously chelated with acetylacetone in the absence of water, to modulate their reactivity and to promote an incipient self-assembling of –O–Sn–O oligomeric species; ultimately, the necessary amount of water to induce the hydrolysis–condensation reactions is added to this aged sol, then producing tubular pore templates within the SnO₂ xerogel network. A collection of mesoporous SnO₂ xerogels of assorted structural properties has been obtained after calcination in air of precursory gels proceeding from an aged mixture of Sn(OAm^t)₄ and acetylacetone at temperatures in the range 200–1000 °C. N₂ sorption isotherms measured on these SnO₂ solids evidence mesoporous structures of diverse textural characteristics (i.e. pore widths of 3–50 nm and surface areas of 10–140 m² g⁻¹) in which voids virtually behave as if they are independent cylindrical pores during capillary condensation and evaporation.

Si(100)/CoFe/AlO_x/CoFe/FeMn/Cu/Ta magnetic tunnelling transistors (MTTs) with differing base thicknesses (W) were investigated. The magneto-transport properties of the MTTs were measured at 77 K and room temperature (RT). We obtained magneto-current ratios of 48.3% and 55.9% for emitter–base bias voltages of 1.45 and 2.0 V, respectively, at 77 K. The transfer ratios are 2.83 × 10⁻⁵ and 1.52 × 10⁻⁴, respectively, corresponding to bias voltages of 1.45 and 2.0 V. Moreover, the highest tunnel magneto-resistance (TMR) ratios turned out to be 12% and 20% for a base thickness of 30 Å at RT and 77 K, respectively. These properties raise not only some fundamental questions regarding the phenomenon of spin-independent tunnelling at low and room temperatures, but also show some promising aspect for magneto-electronic applications. In addition, we attempted to elucidate the reason behind the outstanding TMR effect at low and room temperatures. Finally, the origin of the decrease in the mean free path asymmetry () was clarified by using x-ray photoelectron spectroscopy profile analysis of the elements existing in the interface between Si and the CoFe base (Co, Fe, Al, Si, O).

The effects of charging and single-electron tunnelling in a metal cluster structure are investigated theoretically. In the framework of the particle-in-a-box model for spherical and disc-shaped gold clusters, the electron spectrum and the temperature dependence of the electron chemical potential are calculated. The difference between the electron chemical potentials of massive electrodes and islands leads to the noticeable charging of the electrode. We show that the effective residual charge is equal to the non-integer value of the elementary charge e and depends on the shape of the cluster. The equations for the analysis of the current–voltage characteristic are used under the conditions of conservation of the total energy of the structure, taking into account the contact potential difference. Restrictions associated with the Coulomb instability of a cluster are introduced into the theory in a simple way. It is shown that the critical charge of the cluster in an open electron system is close to the effective residual charge. For single-electron molecular transistors based on small gold clusters the current gap and its voltage asymmetry are computed. We demonstrate that the current gap exhibits non-monotonic size dependences which are related to the quantization of the electron spectrum and the Coulomb blockade.

A facile technique was demonstrated for the controlled assembly and alignment of multi-segment nanowires using bioengineered polypeptides. An elastin-like-polypeptide (ELP)-based biopolymer consisting of a hexahistine cluster at each end (His₆-ELP-His₆) was generated and purified by taking advantage of the reversible phase transition property of ELP. The affinity between the His₆ domain of biopolymers and the nickel segment of multi-segment nickel/gold/nickel nanowires was exploited for the directed assembly of nanowires onto peptide-functionalized electrode surfaces. The presence of the ferromagnetic nickel segments on the nanowires allowed the control of directionality by an external magnetic field. Using this method, the directed assembly and positioning of multi-segment nanowires across two microfabricated nickel electrodes in a controlled manner was accomplished with the expected ohmic contact.

Nano-onions are ellipsoidal or spherical particles consisting of a core surrounded by concentric shells of nanometre size. Nano-onions produced by self-assembly and colloidal techniques have different structures and compositions, and thus differ in the state of strains. The mismatch of the thermal expansion coefficients and lattice constants between neighbouring shells induces stress/strain fields in the core and shells, which in turn affect their physical/mechanical properties and/or the properties of the composites containing them. In this paper, the strains in embedded and free-standing nano-onions with uniform and non-uniform compositions are studied in detail. It is found that the strains in the nano-onions can be modified by adjusting their compositions and structures. The results are useful for the band structure engineering of semiconductor nano-onions.

We report the assembly and characterization of individually suspended Ag, GaN, SnO₂, and Ga₂O₃ nanowires (NWs) using dielectrophoresis. The four kinds of NWs were individually assembled using an experimental approach based on the dielectrophoretic force equation. To freely suspend the individual NWs, we controlled the thickness of the bottom electrode. After depositing a Pt top electrode using a focused ion beam, we investigated the I–V curves of NW devices according to the change in the bottom electrode metal as well as the free suspension height from the insulator. We found that their conductivity for four kinds of NWs was remarkably increased along with the increase in the suspension height, while the gate effect in GaN was reduced.

We report on a simple and effective ac and dc dielectrophoresis (DEP) method that can be used to align and manipulate semiconductor gallium nitride (GaN) nanowires (NWs) with variations in the type of electrical fields as well as variations of frequency. We observed that the ability of the alignment and the formation of the assembling nanowires (single or a bundle configuration) strongly depend on the magnitude of both the ac and dc electric fields. The yield results indicate that the GaN NWs, using ac DEP, are better aligned with a higher yield rate of approximately 80% over the entire array in the chip than by using dc DEP. In addition, we first demonstrated the simple hybrid p–n junction structures assembled by n-type GaN nanowires together with a p-type silicon substrate (n-GaN NW/p-Si substrate) using dielectrophoresis. From the transport measurements, the p–n junction structures show well-defined current rectifying behaviour with a low reverse leakage current of approximately 3 × 10⁻⁴ A at −25 V. We believe that our unique p–n junction structures can be useful for electronic and optoelectronic nanodevices such as rectifiers and UV nano-LEDs.

Scanning probe-based ferroelectric domain imaging and patterning has attracted broad attention for use in the characterization of ferroelectric materials, ultrahigh density data storage, and nanofabrication. The viability of these applications is limited by the minimal domain size that can be fabricated and reliably detected by scanning probe microscopy. Here, the contrast transfer mechanism in piezoresponse force microscopy (PFM) of ferroelectric materials is analysed in detail. A consistent definition of resolution is developed both for the writing and the imaging processes, and the concept of an information limit in PFM is established. Experimental determination of the object transfer function and the subsequent reconstruction of an 'ideal image' is demonstrated. This contrast transfer theory provides a quantitative basis for image interpretation and allows for the comparison of different instruments in PFM. It is shown that experimentally observed domain sizes can be limited by the resolution of the scanning probe microscope to the order of tens of nanometres even though smaller domains, of the order of several nanometres, can be created.

We have investigated the relation between the conduction property and the work function of the contact metal in carbon nanotube field-effect transistors (NTFETs). The conduction type and the drain current are dependent on the work function. In contrast to NTFETs with Ti and Pd contact electrodes, which showed p-type conduction behaviour, devices with Mg contact electrodes showed ambipolar characteristics and most of the devices with Ca contact electrodes showed n-type conduction behaviour. This indicates that the barrier height of the metal/nanotube contact is dependent on the work function of the contact metal, which suggests that the Fermi-level pinning is weak at the interface, in contrast to conventional semiconductors such as Si and GaAs. We have also demonstrated nonlinear rectification current–voltage characteristics in a nanotube quasi-pn diode with no impurity doping, in which different contact metals with different work functions are used for the anode and the cathode.

InAs nanowires with diameters of 7–70 nm and lengths of up to several micrometres were synthesized by a new modified solvothermal method. The x-ray diffraction pattern showed that the InAs nanowires that were prepared had zinc blende and wurtzite structures. A combination of concentration-driven and ligand-aided solution–solid (LSS) growth mechanisms was used to explain the morphology evolution of the InAs nanowires. The preparation method features a low temperature (120–180 °C) and economical mass-production and is free of catalyst nanoparticles. It was believed that we have explored a promising path towards the synthesis of other morphology-controllable one-dimensional (1D) III–V group nano-materials. The structural stability of InAs nanowires during annealing was also studied.

A novel technique for the preparation of water-soluble carbon nanotubes was demonstrated using a pulsed streamer discharge generated in water. The technique involved chemical reactions between radicals generated by the pulsed streamer discharge and carbon nanotubes. The pulsed streamer-treated carbon nanotubes were homogeneously dispersed and well solubilized in water for a month or longer. The mechanism of solubilization of carbon nanotubes by the pulsed streamer discharge is discussed based on FTIR spectroscopy and optical emission spectra measurements. FTIR spectroscopy revealed that –OH groups, which are known to impart a hydrophilic nature to carbon material, were introduced on the carbon nanotube surface. Optical emission spectra from the pulsed streamer plasma showed that highly oxidative O^* and H^* radicals were generated in water. These results suggest that the functionalization of the carbon nanotube surface by –OH group can be attributed to the O^* and H^* radicals. An advantage of the proposed method is that there is no need for any chemical agents or additives for solubilization. Chemical agents for solubilization are generated from the water itself by the electrochemical reactions induced by the pulsed streamer discharge.

Silver nanodots and nanoripples have been grown on nanocavity-patterned polycrystalline Au templates by controlled electrodeposition. The initial step is the growth of a first continuous Ag monolayer followed by preferential deposition at nanocavities. The Ag-coated nanocavities act as preferred sites for instantaneous nucleation and growth of the three-dimensional metallic centres. By controlling the amount of deposited Ag, dots of ∼50 nm average size and ∼4 nm average height can be grown with spatial and size distributions dictated by the template. The dots are in a metastable state. Further Ag deposition drives the dot surface structure to nanoripple formation. Results show that electrodeposition on nanopatterned electrodes can be used to prepare a high density of nanostructures with a narrow size distribution and spatial order.

Atomic force microscopy in the non-contact mode (nc-AFM) can provide atom-resolved images of the surface of, in principle, any material independent of its conductivity. Due to the complex mechanisms involved in the contrast formation in nc-AFM imaging, it is, however, far from trivial to identify individual surface atoms or adsorbates from AFM images. In this work, we successfully demonstrate how to extract detailed information about defects and the chemical identity of adsorbates on a metal oxide surface from nc-AFM images. We make use of the observation that the apex of the AFM tip can be altered to expose either a positive or negative tip termination. The complementary set of images recorded with the two tip terminations unambiguously define the ionic sub-lattices and reveal the exact positions of oxygen vacancies and hydroxyl (OH) defects on a TiO₂ surface. Chemical specificity is extracted by comparing the characteristic contrast patterns of the defects with results from comprehensive AFM simulations. Our methodology of analysis is generally applicable and may be pivotal for uncovering surface defects and adsorbates on other transition metal oxides designed for heterogeneous catalysis, photo-electrolysis or biocompatibility.

Single walled carbon nanotubes (SWNTs) exhibit strong Raman signals as well as fluorescence emissions in the near infrared region. Such signals do not blink or photobleach under prolonged excitation, which is an advantage in optical nano-biomarker applications. In this paper, we present single-stranded DNA conjugated SWNT probes to locate a particular sequence of DNA within a complex genome. Chromosomal DNAs of human fibroblasts and Escherichia coli are used as a target and a control, respectively. Southern blotting, which uses photostable Raman signals of nanotubes instead of fluorescent dyes, demonstrates excellent sensitivity and specificity of the probes. The results show that SWNTs may be used as generic nano-biomarkers for the precise detection of specific kinds of genes.

Polypyrrole nanowires have been electrosynthesized by direct oxidation of 0.1 mol l⁻¹ pyrrole in a medium of 75% isopropyl alcohol + 20% boron trifluoride diethyl etherate + 5% poly (ethylene glycol) (by volume) using porous alumina membranes as the templates. The as-prepared nanowires had a smooth surface and uniform diameter and were arranged in an orderly manner in a high density. The conductivity of a single nanowire was measured by the four-electrode technique to be 23.4 S cm⁻¹ at room temperature. The field emission devices based on the nanowire array were fabricated and their operations were explored. The experimental results indicated that the field emission characteristics of the devices fitted well to the Fowler–Nordheim model of emission. The turn-on electric field was only 1.2 V µm⁻¹ and the current density reached 200 µA cm⁻² at 2.6 V µm⁻¹.

Current computational simulations on metallic nanowires are largely focused on ultrathin wires with characteristic sizes smaller than 2 nm. The electronic, thermal and optical properties form the bulk of these studies, with investigations of the mechanical properties centred on the breaking force of monatomic chains, and the structural evolution of small nanowires subjected to axial, shear, bending and torsional forces. This study seeks to build on the wealth of current knowledge for computational simulation on the mechanical properties of metallic nanowires. The simulation scale will be upped to 24 000 atoms to study a larger metallic nanowire with a 6 nm characteristic size scale. The commonly studied Au nanowire is studied in conjunction with the rarely examined Pt nanowire. The effects that size and strain rate have on the stretching behaviour of these nanowires are investigated through the simulation of nanowires with three characteristic sizes of 2, 4 and 6 nm, subjected to three distinct strain rates of 4.0 × 10⁸, 4.0 × 10⁹ and 4.0 × 10¹⁰ s⁻¹. The selected strain rates produce three distinct modes of deformation, namely crystalline-ordered deformation, mixed-mode deformation and amorphous-disordered deformation, respectively. The mechanisms behind the observations of these distinct deformation modes are analysed and explained. A Doppler 'red-shift' effect is observed when the nanowires are strained at the highest strain rate of 4.0 × 10¹⁰ s⁻¹. This effect is most pronounced for the nanowire subjected to the largest stretch velocity. As a result, a constrained dynamic free-vibration phenomenon is observed during stretching, which eventually leads to delocalized multiple necking, instead of a single localized neck when it is strained at a lower rate. This unique phenomenon is discussed and future research effort is in the pipeline for a more detailed investigation into metallic nanowires strained at a supersonic velocity.

Single-crystalline bamboo-like β-SiC nanowires with hexagonal cross-sections were synthesized by thermal evaporation of mixed SiO+C+GaN powders in an Ar atmosphere. The as-synthesized nanowires were studied by x-ray diffraction, scanning electron microscopy and transmission electron microscopy. Studies found that the as-synthesized SiC nanowires are composed of hexagonal stems decorated with larger diameter knots along their whole length with the growth direction. The growth of bamboo-like SiC nanowires is governed by the vapour–liquid–solid mechanism. Field-emission properties of the peculiar nanostructures were also explored, showing a turn-on field of about 10.1 V µm⁻¹.

Partially sulfided nanostructures were synthesized by direct sulfurization of α-MoO₃ nanorods using a mixture of H₂S/H₂, 15 vol%, at several temperatures (400, 500, 600, 700, and 800 °C). These materials were tested as catalysts in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and characterized by specific surface areas using the expression developed by Brunauer, Emmett, and Teller (BET equation), x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The TEM images show a gradual evolution from a smooth surface to a rough material, presenting some type of holes all over the particles, but keeping their rod-like structure throughout sulfidation. The results of evaluating the catalysts in the HDS of DBT showed that the best temperature for sulfidation is 500 °C. In all samples, a higher selectivity for hydrogenation over sulfur removal was observed.

Fusarium oxysporum fungal strain was screened and found to be successful for the inter- and extracellular production of platinum nanoparticles. Nanoparticle formation was visually observed, over time, by the colour of the extracellular solution and/or the fungal biomass turning from yellow to dark brown, and their concentration was determined from the amount of residual hexachloroplatinic acid measured from a standard curve at 456 nm. The extracellular nanoparticles were characterized by transmission electron microscopy. Nanoparticles of varying size (10–100 nm) and shape (hexagons, pentagons, circles, squares, rectangles) were produced at both extracellular and intercellular levels by the Fusarium oxysporum. The particles precipitate out of solution and bioaccumulate by nucleation either intercellularly, on the cell wall/membrane, or extracellularly in the surrounding medium. The importance of pH, temperature and hexachloroplatinic acid (H₂PtCl₆) concentration in nanoparticle formation was examined through the use of a statistical response surface methodology. Only the extracellular production of nanoparticles proved to be statistically significant, with a concentration yield of 4.85 mg l⁻¹ estimated by a first-order regression model. From a second-order polynomial regression, the predicted yield of nanoparticles increased to 5.66 mg l⁻¹ and, after a backward step, regression gave a final model with a yield of 6.59 mg l⁻¹.

The miscibility and the mechanism for thermal nanopore templating in films prepared from spin-coating and subsequent drying of homogenous solutions of curable polymethylsilsesquioxane dielectric precursor and thermally labile, reactive triethoxysilyl-terminated four-armed poly(ε-caprolactone) porogen were investigated in detail by in situ two-dimensional grazing incidence small-angle x-ray scattering analysis. The dielectric precursor and porogen components in the film were fully miscible. On heating, limited aggregations of the porogen, however, took place in only a small temperature range of 100–140 °C as a result of phase separation induced by the competition of the curing and hybridization reactions of the dielectric precursor and porogen; higher porogen loading resulted in relatively large porogen aggregates and a greater size distribution. The developed porogen aggregates underwent thermal firing above 300 °C without further growth and movement, and ultimately left their individual footprints in the film as spherical nanopores.

Nanocomposite films containing Ag nanoparticles embedded in a polymer matrix of Teflon AF, poly(methyl methacrylate) (PMMA) and Nylon 6 were prepared by vapour phase co-deposition in high vacuum. A large variation of the particle plasmon resonance frequency in the visible region was obtained by increasing the Ag volume fraction from 4–80%. The metal volume fraction was measured by energy dispersive x-ray spectrometry (EDX) and the film thickness was measured by surface profilometry. The position, width and strength of the plasmon resonance depend strongly on the metal filling factor, cluster size and interparticle distance. The microstructure of the nanocomposites (shape, size, size distribution and interparticle separation of metal clusters) was determined by transmission electron microscopy. The effect of the surrounding dielectric medium on the optical properties of nanocomposites was investigated by comparing the Teflon AF/Ag, PMMA/Ag and Nylon/Ag composites.

The field emissive, electrical, magnetic, and structural characteristics of nickel (Ni) nanowires synthesized using the electrochemical deposition method with an alumina nanoporous template are reported. The synthesis and formation of Ni nanowires were confirmed by XRD, SEM, and HR-TEM experiments. Ferromagnetic hysteresis curves and the metallic temperature dependence of the current–voltage characteristics were observed for the Ni nanowire systems. The nanotip emitters of the field emission cells of the Ni nanowires after O₂ plasma treatment were easily patterned using the solution drop casting (SDC) method, in which the Ni nanowires were homogeneously dispersed in organic solvents, and then dropped and dried on an n-type doped Si substrate as the cathode. For the O₂ plasma treated Ni nanowires, we observed that the inhomogeneous oxidized layer on their surface was reduced, that the current density of the field emission cell increased from ∼3.0 × 10⁻⁹ to ∼1.0 × 10⁻³ A cm⁻² due to field emission, and that the lowest threshold electric field was ∼4 V µm⁻¹. The field enhancement factor was estimated as ∼1300 for the O₂ plasma treated Ni nanowires. The evolution of the field emission obtained from the phosphor screen was observed at different applied electric fields.

Porous cobalt nanowall arrays have been prepared by electrochemical deposition of mono-precursor [Co(NH₃)₅Cl]Cl₂ on copper substrates. Brunauer–Emmett–Teller (BET) and Barret–Joyner–Halenda (BJH) investigations of the surface properties indicate that the resulting porous nanomaterials possess high surface area and uniform pore size distribution, which implies potential applications in some fields, such as catalysis, energy, and magnetic data storage devices. The magnetism measurements of the porous cobalt nanowall arrays take on a good ferromagnetic behaviour with enhanced coercivity (H_c).

Ag–TiO₂ nanofibres (about three µm long and 30–150 nm thick) formed by a single-crystalline silver wire (20–30 nm thick) and an external layer of amorphous TiO₂ of variable thickness are prepared at 403 K by oxygen plasma activation of a silver substrate followed by plasma deposition of TiO₂. Thicker fibres of anatase crystallites surrounding the silver wire were prepared when plasma deposition was carried out at 523 K. The fibres have been analysed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray photoemission spectroscopy (XPS). The plasmon losses of the silver core wire have been characterized by electron energy loss spectroscopy in the TEM microscope. Based on the experimental evidence, a new volcano-type mechanism of formation of these core–shell fibres is proposed, whereby the effect of the plasma and the high mobility of the silver would be key factors determining their morphology and dimensions.

We report a large-scale synthesis of micron and nanosized tin-doped indium oxide (ITO) octahedrons via an ultrasonic spray assisted chemical vapour deposition, in which no catalyst is involved. The single crystalline nature of the ITO octahedrons was revealed by high-resolution transmission electron microscopy. The formation of ITO octahedrons, which are bounded by eight {111} facets, is due to the lowest surface energy of the {111} facet. The size of the octahedron was found to be strongly dependent on deposition temperature and the concentration of the precursor solution, with perfectly shaped ITO octahedrons being synthesized at a temperature between 400 and 550 °C. By simply changing the concentration of the precursor solution, we can produce well-dispersed ITO octahedral particles, dense ITO films with octahedral grains, or clusters of octahedral.

In this study we show that pure and well crystallized nanoparticles of Ba_xSr_1−xTiO₃ (BST) can be synthesized over the entire range of composition through the hydrolysis and further crystallization of alkoxide precursors under supercritical conditions. To our knowledge, this is the first time that the whole ferroelectric solid solution has been produced in a continuous way, using the same experimental conditions. The composition of the powder can be easily controlled by adjusting the feed solution composition. The powders consist of soft-aggregated monocrystalline nanoparticles with an average particle size ranging from ∼20 to 40 nm. Ferroelectric ceramics with accurately adjustable Curie temperature (100–390 K) can thus be obtained by sintering.

Poly(vinyl pyrrolidone)-capped multiple twinned gold (Au) particles with decahedral shape have been synthesized by a simple and convenient solvothermal wet chemical method. In the process, hydrogen tetrachloroauric acid (HAuCl₄·3H₂O) was reduced by ethylene glycol (EG) to form the multiple twinned Au nanocrystals in the presence of poly(vinyl pyrrolidone) (PVP) molecules at 200 °C under the extra condition of autogenous pressure. The decahedral nanoparticles take up about 10% of the total amount and have the usual size distribution from several tens to hundreds of nanometres. Some larger microsized five-twinned Au particles with perfect decahedral shape have also been observed in the final product. Furthermore, x-ray photoelectron spectroscopy (XPS) measurements verified that PVP molecules are adsorbed on the surface of the Au particles. Based on the experimental results, a growth mechanism has been suggested to elucidate the formation of the small decahedral Au nanoparticles as well as their evolution into perfect large decahedral Au particles with the size of several micrometres.

Colloidal CdSe/ZnSe core/shell nanocrystals were prepared via the conventional TOP/TOPO process and their shell thickness was controlled varying the ZnSe precursor concentration. X-ray diffraction (XRD) on the nanocrystals showed gradual peak shifts to high two-theta angles due to a decrease in the lattice parameter of CdSe cores with an increase in the ZnSe shell thickness. High-resolution transmission electron microscopy (HRTEM) images of the CdSe/ZnSe nanocrystals show a c-axis elongation with an increase in ZnSe precursor concentration and crystalline defect formation in some of the nanocrystals with 2.0 mM ZnSe precursor concentration, possibly due to high compressive strain. Photoluminescence (PL) spectra of the CdSe/ZnSe nanocrystals showed an increase in the peak intensity up to 1.0 mM ZnSe precursor concentration due to the surface passivation effect, and a decrease beyond this value, possibly due to the formation of crystalline defects such as stacking faults. The PL wavelength showed red-shifts up to 1.0 mM ZnSe precursor concentration due to the partial leakage of an electron wavefunction of CdSe cores into the ZnSe shells and blue-shifts beyond this value due to the high compressive strain from the ZnSe shells.

The dynamics of nanostructured surface phases on SrTiO₃(001) have been analysed using in situ scanning tunnelling microscopy (STM) above 800 °C. During high-temperature annealing, the formation, growth and ordering of the nanostructures has been observed. Dilines, with a width of ∼1 nm, are formed from a TiO₂-rich intermediary at 800 °C. STM during annealing at 825 °C has enabled us to follow both the growth and dissolution of dilines. Following extended annealing, trilines with a width of ∼2 nm and ordered two-dimensional (2D) nano-arrays form from the diline domains. Our observations of diline dissolution implies random nucleation and growth, followed by rearrangement at elevated temperature to form domains.

Complex rare earth fluoride (NaRF₄, R = Ce,Y,Gd) nanocrystals of 30–50 nm were synthesized by hydrothermal and solvothermal techniques. The size, morphology and phase transition of the complex rare earth fluorides are discussed as the effects of different solvents, reaction time and temperature. Hexagonal phase NaRF₄ nanocrystals with good dispersibility can be prepared in the presence of EDTA using ethanol as the solvent. After doping with Yb³⁺, Er³⁺; Yb³⁺, Tm³⁺, and Eu³⁺, some typical up-conversion and down-conversion photoluminescence was characterized and discussed.

Low-energy atomic impacts on the Ag(110) surface are investigated by molecular dynamics simulations based on reliable many-body semiempirical potentials. Trajectory deflections (steering) caused by the atom–surface interaction are observed, together with impact-following, transient-mobility effects. Such processes are quantitatively analysed and their dependence on the initial kinetic energy and on the impinging direction is discussed. A clear influence of the surface anisotropy on both steering and transient mobility effects is revealed by our simulations for the simple isolated-atom case and in the submonolayer-growth regime. For the latter case, we illustrate how steering and transient mobility affect the film morphology at the nanoscale.

Different ZnO nanostructures have been modified using the layer-by-layer polyelectrolyte deposition process. The polymer multilayers were deposited on free standing ZnO tetrapods, ZnO tetrapods on a substrate and ZnO nanorod arrays. In addition, attachment of metallic (Au) nanoparticles to the ZnO nanostructure surface using layer-by-layer deposition was demonstrated. The properties of the ZnO nanostructures with modified surfaces were investigated by electron microscopy, absorption and photoluminescence measurements. A linear increase in polymer thickness with the number of polymer multilayers was confirmed by absorption and transmission electron microscopy. The technique can be readily extended to different nanoparticles and different morphologies of ZnO.

Self-assembled monolayer (SAM) patterns on electrodes are often utilized to guide the assembly of single-walled carbon nanotubes (SWCNTs) onto the electrodes to form desired device structures. In this case, the SWCNTs are in contact with the electrodes through the SAM which comprises molecular wires. Presumably, it is desirable to use conjugated molecular wires for a low contact resistance because they have been reported as a better electric conductor than non-conjugated ones. However, until now, the directed-assembly of SWCNTs has been driven mostly via molecular wires with alkane backbones which are known to be relatively poor conductors. Herein, we report large-scale directed-assembly of SWCNTs utilizing SAM patterns comprising conjugated molecular wires. We achieved highly selective adsorption and precision alignment of SWCNTs utilizing polar SAM patterns comprising conjugated molecular wires, while SAM patterns with non-polar terminal groups efficiently prevented adsorption of SWCNTs. Furthermore, we developed a process for assembling a SWCNT across two electrodes coated with conjugated molecular wires, and the electrical conduction through the SWCNT was measured via a conducting atomic force microscope. This result could be an important guideline for large-scale directed-assembly of SWCNT-based devices in the future.

Mullite (2SiO₂·3Al₂O₃) nanoribbons, millimetres in length and with a high width-to-thickness ratio, were synthesized at temperatures as low as 1150 °C. This high ratio made it easy to fabricate a single nanoribbon sensor. The I–V relation of the sensor versus concentration of glucose was recorded with a pico-ammeter. The sensor shows good reproducibility and long-term stability. This single nanoribbon sensor may be used as an in situ monitor. The nanoribbons were also characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and x-ray photoemission spectroscopy.

Silver chloride/polyaniline (PANI) core–shell composites were synthesized through a facile one-step process in the presence of polyvinylpyrrolidone (PVP). PVP not only acted as an anchor agent leading to the formation of the core–shell structure but also prevented the aggregation of PANI efficiently. Transmission electron microscopy (TEM) images gave direct evidence of the core–shell structure. Fourier transform infrared (FTIR) confirmed the formation of PANI and x-ray diffraction (XRD) showed the presence of crystal AgCl. Cyclic voltammetric experiments indicated that this kind of material showed excellent redox ability in neutral solution. Based on the excellent electrochemical behaviour of the AgCl/PANI, it was applied to construct a H₂O₂ biosensor. The biosensor exhibited a fast amperometric response to H₂O₂ with the linear range 6 × 10⁻⁴–9 × 10⁻³ mol l⁻¹.

Thin-film filters on optical components have been in use for decades and, for those industries utilizing a polymer substrate, the mismatch in mechanical behaviour has caused problems. Surface damage including scratches and cracks induces haze on the optical filter, reducing the transmission of the optical article. An in-mold anti-reflective (AR) filter incorporating 1/4-wavelength thin films based on a polymer nanocomposite is outlined here and compared with a traditional vacuum deposition AR coating. Nanoindentation and nanoscratch techniques are used to evaluate the mechanical properties of the thin films. Scanning electron microscopy (SEM) images of the resulting indentations and scratches are then compared to the force deflection curves to further explain the phenomena. The traditional coatings fractured by brittle mechanisms during testing, increasing the area of failure, whereas the polymer nanocomposite gave ductile failure with less surface damage.

The bending Young's modulus of ZnO nanobelts was measured by performing three-point bending tests directly on individual nanobelts with an atomic force microscope (AFM). The surface-to-volume ratio has no effect on the bending Young's modulus of the ZnO nanobelts for surface-to-volume ratios ranging from 0.017 to 0.035 nm² nm⁻³, with a belt size of 50–140 nm in thickness and 270–700 nm in width. The bending Young's modulus was measured to be 38.2 ± 1.8 GPa, which is about 20% higher than the nanoindentation Young's modulus of 31.1 ± 1.3 GPa. The ZnO nanobelts exhibit brittle fracture failure in bending but some plastic deformation in indentation.

Energies of a certain class of fullerene molecules (elongated, contracted and regular icosahedral fullerenes) are numerically calculated using a microscopic description of carbon–carbon bonding. It is shown how these results can be interpreted and comprehended using the theory of elasticity that describes bending of a graphene plane. Detailed studies of a wide variety of structures constructed by application of the same general principle are performed, and analytical expressions for energies of such structures are derived. Comparison of numerical results with the predictions of a simple implementation of elasticity theory confirms the usefulness of the latter approach.

As-synthesized ZnO nanostructures with a bladed bundle-like architecture have been fabricated from a flower-like precursor ZnO·0.33ZnBr₂·1.74H₂O via a mechanism of dissolution–recrystallization. Experimental conditions, such as initial reactants and reaction time, are examined. The results show that no bladed bundle-like ZnO hierarchical nanostructures can be obtained by using the same molar amount of other zinc salts, such as ZnBr₂, instead of the flower-like ZnO·0.33ZnBr₂·1.74H₂O precursor, and keeping other conditions unchanged. The products were characterized by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The ZnO nanostructures are mainly composed of nanowires with a diameter around 40–50 nm and length up to 1.5–2.5 µm. Meanwhile, ZnO nanoflakes with a thickness of about 4–5 nm attached to the surface of ZnO nanowires with a preferred radially aligned orientation. Furthermore, the photoluminescence (PL) measurements exhibited the unique white-light-emitting characteristic of hierarchical ZnO nanostructures. The emission spectra cover the whole visible region from 380 to 700 nm.

Carbon nanofibres aerosolized by the agitation of as-produced commercial powder have been characterized in situ by using the differential mobility analyser–aerosol particle mass analyser (DMA–APM) method to determine their structural properties such as the effective density and fractal dimension for toxicology study. The effective density of the aerosolized carbon nanofibres decreased from 1.2 to 0.4 g cm⁻³ as the mobility diameters increased from 100 to 700 nm, indicating that the carbon nanofibres had open structures with an overall void that increased with increasing diameter, due to increased agglomeration of the nanofibres. This was confirmed by transmission electron microscopy (TEM) observation, showing that 100 nm mobility diameter nanofibres were predominantly single fibres, while doubly or triply attached fibres were seen at mobility diameters of 200 and 400 nm. Effective densities calculated using Cox's theory were in reasonable agreement with experimental values. The mass fractal dimension of the carbon nanofibres was found to be 2.38 over the size range measured and higher than that of single-walled carbon nanotubes (SWCNTs), suggesting that the carbon nanofibres have more compact structure than SWCNTs.

Three kinds of magnetic nanoparticle, tetraheptylammonium capped nanoparticles of Fe₃O₄, Fe₂O₃ and Ni have been synthesized, and the synergistic effect of these nanoparticles on the drug accumulation of the anticancer drug daunorubicin in leukaemia cells has been explored. Our observations indicate that the enhancement effect of Fe₃O₄ nanoparticles is much stronger than that of Fe₂O₃ and Ni nanoparticles, suggesting that nanoparticle surface chemistry and size as well as the unique properties of the magnetic nanoparticles themselves may contribute to the synergistic enhanced effect of the drug uptake of targeted cancer cells.