Table of contents

We demonstrate that exchange interactions between antiferromagnetic nanoparticles of ⁵⁷Fe-doped NiO can be varied by simple macroscopic treatments. Mössbauer spectroscopy studies of the superparamagnetic relaxation behaviour show that grinding or suspension in water of nanoparticles of NiO can significantly reduce interparticle interactions. Slow drying of aqueous suspensions of NiO nanoparticles did not lead to enhanced interparticle interactions. This is opposite to the behaviour of α-Fe₂O₃ (hematite) nanoparticles.

A process for transferring carbon nanotube (CNT) arrays from a silicon wafer to an alumina substrate coated with Ag paste is proposed. A current density of up to 325 mA cm⁻² at an electric field of 2.4 V µm⁻¹ was achieved. The influence of the patterned size and the length of carbon nanotubes on the field emission properties were investigated. Through this transfer method, the adhesion between the CNTs and the substrate is enhanced and the current density and turn-on voltage are improved. The effects of the microstructure of the emitting sites at the CNT tip on the current density were also studied.

A non-conjugated polymeric poly(acrylic acid) (PAA) is shown to efficiently form a stable composite with multi-walled carbon nanotubes (MWNTs). The prepared PAA-wrapped MWNTs composite is readily soluble and stable in water. The PAA–MWNTs composite exhibits interesting optical properties. FT-IR spectra show that the characteristic peaks for MWNTs are unchanged, and new chemical bonds are not formed in PAA–MWNTs, indicating that the electronic structures of the MWNTs are still intact after polymer wrapping. The obvious blue-shift of the peak at 266 nm for the C = C double bonds of pristine MWNTs upon polymer-wrapping, the systematic upshift in peak position and the enhancement in the band intensities of characteristic Raman bands of MWNTs after winding with PAA as well as the disappearance of ¹H NMR spectra for the wrapped polymer in PAA-MWNTs composite were observed, which indicate that there is strong binding of PAA to MWNTs surface via the hydropholic attraction between PAA and MWNTs. The as-prepared PAA-MWNTs dispersions could facilitate the processing of the nanotubes into composites with high nanotube loading for bioelectronic devices and biological applications where a water-based environment is needed.

Fe₃O₄/CdSe/ZnS magnetic fluorescent bifunctional nanocomposites were obtained by depositing heterogeneous semiconductor on magnetic nanoparticles. The structure and properties of the Fe₃O₄/CdSe/ZnS nanocomposites were fully characterized by TEM, XPS, XRD, SQUID and PL. The results indicate that the Fe₃O₄/CdSe/ZnS nanocomposites are superparamagnetic and are about 8 nm in size. The quantum yield of the nanocomposites increases from 2–3% in Fe₃O₄/CdSe to 10–15% in Fe₃O₄/CdSe/ZnS, together with a red shift of both the absorption peak and PL band. The increase of quantum yield is due to the passivation of the surface of magnetic-CdSe nanocomposites with a ZnS layer.

Four different hierarchical ZnO nanostructures, including nanosleeve-fishes, radial nanowire arrays, nanocombs and nanoflowers, have been successfully fabricated through thermal chemical vapour deposition by adjusting the source temperature and the gas flow rate. Field emission measurements of these nanostructures showed a high emission current density and a low turn-on field of 1.3, 1.9, 2.5 and 3.4 V μm⁻¹ in sequence, which is comparable to that of one-dimensional ZnO nanostructures and carbon nanotubes. The good performance for field emission makes the hierarchical ZnO nanostructures promising candidates for further applications in field emission microelectronic devices.

We report the successful synthesis of 30 wt% In₂O₃/SnO₂ nanocomposites by heating the precursor obtained via a mechanochemical reaction, and investigate their gas-sensing properties. The samples were characterized by means of x-ray diffraction, scanning electron microscopy and x-ray photoelectron spectroscopy. Subsequent thermal treatment of the precursor for 2 h in air at 700 °C resulted in the formation of In₂O₃/SnO₂ nanocomposites with an average crystal size of about 22 nm. In comparison to pure SnO₂, the gas sensor fabricated from the as-synthesized In₂O₃/SnO₂ nanocomposites has an excellent gas-sensing performance, such as high sensitivity (93 for 1000 ppm C₂H₅OH), a rapid response rate (within 5 s for 90% response and recovery times) and high selectivity to ethanol. To explain the enhanced sensitivity of the In₂O₃/SnO₂ gas sensor, the gas-sensing mechanism is discussed.

Electrodeposition of RuO₂ on electrospun TiO₂ nanorods using cyclic voltammetry is shown to increase the capacitance of RuO₂. This phenomenon can be attributed to the large surface areas of the nanorods. Among several ranges of deposition, the range from 0.25 to 1.45 V with respect to Ag/AgCl was effective. The electrode deposited with this range exhibited a specific capacitance of 534 F g⁻¹ after deposition for 10 cycles with a scan rate of 50 mV s⁻¹. The structural water content in RuO₂ was quite different depending on the deposition potential range. Higher amounts of structural water increased the charge storage capability. The stability of the electrode was tested using cyclic voltammetry over 300 cycles.

Novel silicon carbide nanostructures, beaded nanochains, are prepared from the carbothermal reduction of a carbonaceous silica xerogel with cetyltrimethylammonium bromide and lanthanum nitrate as additives. The nanochains consist of a stem with a diameter of about 50 nm and uniform beads with diameters of 100–200 nm. It is demonstrated that the tensile strength of an epoxy composite filled with the SiC nanochains improves significantly due to the unusual morphology of the nanochains.

We report that engineered nanoscale zinc oxide structures can be effectively used for the identification of the biothreat agent, Bacillus anthracis by successfully discriminating its DNA sequence from other genetically related species. We explore both covalent and non-covalent linking schemes in order to couple probe DNA strands to the zinc oxide nanostructures. Hybridization reactions are performed with various concentrations of target DNA strands whose sequence is unique to Bacillus anthracis. The use of zinc oxide nanomaterials greatly enhances the fluorescence signal collected after carrying out duplex formation reaction. Specifically, the covalent strategy allows detection of the target species at sample concentrations at a level as low as a few femtomolar as compared to the detection sensitivity in the tens of nanomolar range when using the non-covalent scheme. The presence of the underlying zinc oxide nanomaterials is critical in achieving increased fluorescence detection of hybridized DNA and, therefore, accomplishing rapid and extremely sensitive identification of the biothreat agent. We also demonstrate the easy integration potential of nanoscale zinc oxide into high density arrays by using various types of zinc oxide sensor prototypes in the DNA sequence detection. When combined with conventional automatic sample handling apparatus and computerized fluorescence detection equipment, our approach can greatly promote the use of zinc oxide nanomaterials as signal enhancing platforms for rapid, multiplexed, high-throughput, highly sensitive, DNA sensor arrays.

A facile and efficient aqueous phase-based strategy to synthesize carbon nanotube (CNT)/silver nanocrystal nanohybrids at room temperature is reported. In the presence of carboxyl group functionalized or poly(acrylic acid)- (PAA-) grafted CNTs, silver nanoparticles were in situ generated from AgNO₃ aqueous solution, without any additional reducing agent or irradiation treatment, and readily attached to the CNT convex surfaces, leading to the CNT/Ag nanohybrids. The produced silver nanoparticles were determined to be face-centred cubic silver nanocrystals by scanning transmission electron microscopy (STEM), electron diffraction (ED) and x-ray powder diffraction (XRD) analyses. Detailed experiments showed that this strategy can also be applied to different CNTs, including single-walled carbon nanotubes (SWNTs), double-walled carbon nanotubes (DWNTs), multiwalled carbon nanotubes (MWNTs), and polymer-functionalized CNTs. The nanoparticle sizes can be controlled from 2 nm to 10–20 nm and the amount of metal deposited on CNT surfaces can be as high as 82 wt%. Furthermore, large-scale (10 g or more) CNT/Ag nanohybrids can be prepared via this approach without the decrease of efficiency and quality. This approach can also be extended to prepare Au single crystals by CNTs. The facile, efficient and large-scale availability of the nanohybrids makes their tremendous potential realizable and developable.

We present an efficient gas-phase route to decorate both single-walled and multiwalled carbon nanotubes with nanoparticles based on electrostatic force directed assembly. We show that, in addition to an intrinsic nanoparticle size selection, the packing density and the final size distribution of nanoparticles docking on nanotubes can be controlled during the assembly process. Our method enables in situ coating of nanotubes with nanoparticles. Due to the inherent material-independent nature of the electrostatic force, various compositions of such nanoparticle–nanotube structures can be produced using this new technique. These novel structures will enable new opportunities for exploring nanoscience, nanotechnology, and biotechnology.

Silicon nanowires (SiNWs) were synthesized by the vapour–liquid–solid (VLS) growth mechanism using gold implanted silicon substrates. Implantation of high ion fluences leads to an amorphized silicon layer at the wafer surface. During annealing the Au in the implanted region agglomerates and yields Au droplets at the surface upon recrystallization of the amorphous layer. The structural quality of nanowires grown from implanted substrates is comparable to those grown on wafers with evaporated gold films. This opens up new possibilities for local growth of SiNWs by implanting through masks or using a focused ion beam technique.

Photopolymer nanocomposite films were prepared by dispersing an aromatic methacrylate monomer in a hybrid sol of alkoxy silanes that contained an organically modified sol–gel precursor, using the sol–gel process. Triethoxysilylpropyl, poly(ethyleneglycol)carbamate (TSPEG) was introduced to examine its effect as a side-chain in the sol–gel processed film on monomer diffusion and polymerization, to achieve holographic recording. The glass transition temperature (T_g) of the photopolymer films was shifted to a lower value as the TSPEG content was increased in the photopolymer composition. The maximum value and the evolution of the diffraction efficiency (η) of the photopolymer films under a holographic recording condition were significantly affected by the TSPEG content, indicating that the organic part of the hybrid photopolymer affected the polymerization and diffusion of the monomer during the holographic recording. Under an optimized composition (T025), the films showed a high diffraction efficiency of 0.98 under a 532 nm laser with a light power of 2.1 mW.

In this work, a new capping agent, cinnamic acid (CA) was used to synthesize Au nanoparticles (NPs) under ambient conditions. The size of the NPs can be controlled by adjusting the concentration of reductant (in our experiment sodium borohydride was used) or CA. The CA-stabilized Au NPs can self-assemble into 'nanowire-like' or 'pearl-necklace-like' nanostructures by adjusting the molar ratio of CA to HAuCl₄ or by tuning the pH value of the Au colloidal solution. The process of Au NPs self-assembly was investigated by UV–vis spectroscopy and transmission electron microscopy. The results reveal that the induced dipole–dipole interaction is the driving force of Au NP linear assemblies.

ZnS nanowires with heterocrystal and bicrystal structures were successfully synthesized using the DC-plasma chemical vapour deposition (CVD) method. The heterocrystalline ZnS nanowires have the zinc blende (ZB) and wurtzite (WZ) zones aligned alternately in the transverse direction but without an obvious period. The bicrystal ZnS nanowires are composed of two ZB fractions separated by a clear grain boundary along the length. Significantly, the grain boundaries in both the heterocrystal and bicrystal structures are atomically sharp without any visible lattice distortion. The effects of plasma species, ion bombardment, and silicon impurities in the formation of these distinctive structures are discussed. A defect-induced red-shift and broadening of the band-gap emission are revealed in photoluminescence (PL) and cathodoluminescence (CL) measurements.

Unusual 3D flower-shaped SnS₂ nanostructures have been synthesized using a mild hydrothermal treatment in the presence of octyl-phenol-ethoxylate (Triton X-100) at 160 °C. The nanostructures have an average size of 1 µm, and consist of interconnected nanosheets with thicknesses of about 40 nm. Based on time-dependent experimental results, we ascribe the oriented attachment mechanism to the growth of the SnS₂ nanostructures. The nonionic surfactant Triton X-100 plays a key role in the formation of the flower-like morphology. Room temperature gas-sensing measurements show that the 3D SnS₂ nanostructures could serve as sensor materials for the detection of NH₃ molecules.

Germanium nanowires (GeNWs) have been synthesized by the thermal evaporation of Ge powder at 950 °C onto silicon wafer and ceramic (alumina) substrate using Au nanoparticles as a catalyst via a vapour–liquid–solid (VLS) process. The morphology, crystal structure and growth direction of the as-prepared GeNWs have been characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), and transmission electron microscopy (TEM). GeNWs are uniform with a diameter of ∼30 nm and lengths of tens of micrometres. High-resolution TEM shows that an individual GeNW is a single crystal with a diamond structure and a preferred growth along the direction. Au nanoparticles are found at the tip of GeNWs indicating that the growth of GeNWs follows a VLS mechanism. The electronic and local structures of the as-prepared GeNWs have also been investigated by x-ray absorption fine structure spectroscopy (XAFS). The results and the implications will be discussed.

PbS nanobelts and nanowires were successfully synthesized through a carbothermal reduction/sulfidation method, in which a powder mixture of sulfur, PbCl₂ and active carbon was heated to 600 °C under ambient pressure. Structural characterizations show that the one-dimensional nanostructures grow with a [110] orientation. The nanobelts do not have any crystal defects but the nanowires have deformations, dislocations and grain boundaries, including Σ17 [001] tilt grain boundaries, Σ17 [001] symmetric grain boundaries and Σ5 [001] tilt grain boundaries. According to coincidence site lattice theory, the models for the fitted atoms in Σ17 [001] tilt grain boundaries and Σ17 [001] symmetric grain boundaries are established. The growth mechanism has also been discussed. This first report on PbS microstructures, especially on defects, might be beneficial in studying their synthesis, characterization and applications in the near future.

We have developed a method for fabricating a carbon nanotube (CNT) tip for an atomic force microscope (AFM). To attach a CNT to the tip apex, we used dielectrophoresis (DEP) with a non-uniform electric field. After inserting a drop of CNT solution and applying an AC electric field between a metal-coated AFM tip and an electrode plate, CNTs were deposited directly on the tip so that they protruded from the tip. We fabricated tips with individual multi-walled carbon nanotubes and found the experimental conditions that gave high fabrication yields. From AFM measurements of the nanoscale anodized aluminium oxide (AAO) structure, we have shown that a CNT tip assembled using DEP can produce high-resolution images and have a good wear resistance.

When growing one-dimensional (1D) nanomaterials via the vapour–liquid–solid (VLS) model, the substrates usually need to be coated with a layer of catalyst film. In this study, however, an effective approach for the synthesis of boron nitride (BN) nanowires directly onto commercial stainless-steel foils has been demonstrated. Growth occurs by heating boron and zinc oxide (ZnO) powders at 1100 °C under a mixture of nitrogen and hydrogen gas flow (200 ml min⁻¹). The stainless-steel foils played an additional role of catalyst besides substrate during the VLS growth of these BN nanowires. The as-synthesized nanowires emit strong photoluminescence (PL) bands at 515, 535 and 728 nm. In addition, we found that the gas flow rate and the hydrogen content in the gas mixture strongly affected the diameter and yield of the nanowires by changing the relative concentration of the nanowire growth species in the chamber.

A catalyst for the detoxification of nerve agents is synthesized from β-cyclodextrin (β-CD) and o-iodosobenzoic acid (IBA). Functionalized polymer nanofibre membranes from PVC polymer are fabricated with β-CD, IBA, a blend of β-CD+IBA, and the synthesized catalyst. These functionalized nanofibres are then tested for the decontamination of paraoxon, a nerve agent stimulant, and it is observed that the stimulant gets hydrolysed. The kinetics of hydrolysis is investigated using UV spectroscopy. The rates of hydrolysis for different organophosphate hydrolyzing agents are compared. The reactivity and amount of adsorption of these catalysts are of higher capacity than the conventionally used activated charcoal. A new design for protective wear is proposed based on the functionalized nanofibre membrane.

Self-assembled monolayers (SAMs) are very useful for the systematic modification of the physical, chemical and structural properties of a surface by varying the chain length, tail group and composition. Many of these properties can be studied making use of atomic force microscopy (AFM), and the interaction between the AFM probe tip and the SAMs can also be considered an excellent reference to study the fundamental properties of dissipation phenomena and onset wear for viscoelastic materials on the nanoscale. We have performed a numerical study showing that the fundamental mechanism for the onset wear is a process of nucleation of domains starting from initial defects. An SAM surface repeatedly sheared by an AFM probe tip with enough applied loads shows the formation of progressive damages nucleating in domains. The AFM induced surface damages involve primarily the formation of radicals from the carbon chain backbones, but the deformations of the chains resulting in changes of period lattice also have to be taken into consideration. The nucleation of the wear domains generally starts at the initial surface defects where the energy cohesion between chains is lower. Moreover, the presence of surface defects is consistent with the changes in lateral force increasing the probability of the activation for the removal of carbon debris from the chain backbone. The quantification of the progressive worn area is performed making use of the Kolmogorov–Johnson–Mehl–Avrami (KJMA) theory for phase transition kinetic processes. The advantage of knowing the general conditions for onset wear on the SAM surfaces can help in studying the fundamental mechanisms for the tribological properties of viscoelastic materials, in solid lubrication applications and biopolymer mechanics.

ZnO nanowires without or with Mg doping were produced by thermally oxidizing pure Zn or (Zn + Mg) powders. X-ray diffraction (XRD) patterns indicated that ZnO nanowires with and without Mg doping were crystalline with wurzite structure. The highest hydrogen uptake capability was 2.79 wt% at room temperature and 860 psi for Mg-doped ZnO nanowires. 70.1% of the stored hydrogen can be released at ambient pressure. 2.57 wt% uptake and 68.3% release were measured for ZnO nanowires. Fourier transform infrared spectroscopy (FTIR) showed the formation of O–H bonds, while temperature programmed desorption (TPD) suggested that chemisorbed hydrogen could be released only at 100–250 °C. The H₂ absorption mechanism on ZnO is discussed.

In this study, the use of a CO₂ supercritical fluid (SCF) and silver (Ag) nanoparticles is shown to improve the electrical contact between a metal and porous silicon (PS). Earlier problems concerning surface roughness are not observed. Scanning electron microscopy (SEM) showed that SCF processing at 100 °C with Ag nanoparticles of a diameter of about 100 nm filled the pores of PS. Separate experiments using different concentrations of the silver precursor in the process showed that the size and morphology of the nanoparticles could be controlled. Because of the large reduction in contact resistance that is produced, it is possible to observe a nonlinear current–voltage characteristic at room temperature.

Highly fluorescent CdTe quantum dots (Q-dots) stabilized by 3-mercaptopropionic acid (MPA) were prepared by an aqueous solution approach and used as fluorescent labels in detecting a cancer marker, carcinoembryonic antigen (CEA), expressed on human colon carcinoma cell line LS 180. Nonspecific adsorptions of CdTe Q-dots on carcinoma cells were observed and effectively eliminated by replacing MPA with a thiolated PEG (poly(ethylene glycol), Mn = 750) synthesized according to literature. It was unexpectedly found out that the PEG-coated CdTe Q-dots exhibited very strong and specific affinity to anti-CEA monoclonal antibody rch 24 (rch 24 mAb). The resultant CdTe–(rch 24 mAb) conjugates were successfully used in detections of CEA expressed on the surface of cell line LS 180. Further experiments demonstrated that the fluorescent CdTe Q-dots exhibited much better photostability and a brighter fluorescence than FITC, which consequently led to a higher efficiency in the cancer marker detection.

We study quasi-ballistic heat transfer through air between a hot nanometre-scale tip and a sample. The hot tip/surface configuration is widely used to perform non-intrusive confined heating. Using a Monte Carlo simulation, we find that the thermal conductance reaches 0.8 MW m⁻² K⁻¹ on the surface under the tip and show the shape of the heat flux density distribution (nanometre-scale thermal spot). These results show that a surface can be efficiently heated locally without contact. The temporal resolution of the heat transfer is a few tens of picoseconds.

Eu³⁺-doped zinc aluminate (ZnAl₂O₄) nanorods with a spinel structure were successfully synthesized via an annealing transformation of layered precursors obtained by a homogeneous coprecipitation method combined with surfactant assembly. These spinel nanorods, which consist of much finer nanofibres together with large quantities of irregular mesopores and which possess a large surface area of 93.2 m² g⁻¹ and a relatively narrow pore size distribution in the range of 6–20 nm, are an ideal optical host for Eu³⁺ luminescent centres. In this nanostructure, rather disordered surroundings induce the typical electric-dipole emission of Eu³⁺ to predominate and broaden.

Large-scale morphology-controlled SWCNT/polymeric microsphere arrays can be obtained by a wet chemical self-assembly technique. The loading of SWCNTs, the length of SWCNTs, and the size and nature of polymeric microspheres can easily be controlled. Similar results can also be reached using this method for MWCNTs. In both types of CNTs, they form an interesting interactive 'net' structure on spheres and sphere joints. The SWCNT/PS-modified Au electrode was used for detection of uric acid by cyclic voltammetry and single-potential time-based techniques. The preliminary results show that the modified electrode presents good sensitivity and stability to uric acid.

Here we report an aggregation-driven growth of highly oriented and densely packed ZnO nanorod arrays through a simple natural oxidation process of pure metal zinc in formamide/water solution at low temperature. Very intense orange emission was observed in the resulting nanoparticle-built ZnO nanorods with numerous interfacial defects among their primary nanoparticles.

This investigation describes the development of a InGaN/GaN light-emitting diode (LED) with textured sidewalls using natural lithography with polystyrene spheres (PSs) as the etching mask and dry etching the epitaxial layers of LEDs to achieve nano-scale textured sidewalls. The LED with textured sidewalls increased the output power of the InGaN–GaN multiple quantum well (MQW) LEDs by a factor of 1.3, indicating that the LED with nano-scale textured sidewalls had larger light extraction efficiency. The wall-plug efficiency of nitride-based LEDs was increased by 30% using textured sidewalls.

We report on a theoretical study pointing out the fundamental role of the backbone energetics in the charge transfer efficiency of polyG–polyC and polyA–polyT chains. The double-strand DNA (ds-DNA) molecules are modelled in terms of a single channel effective Hamiltonian. By introducing a two-step renormalization scheme analytical results for the energy spectrum and transmission coefficient are derived, and current–voltage characteristics are numerically investigated. Significant modulations of the main I–V features (voltage threshold, current amplitude) are reported and their physical origin is traced back to backbone-induced electronic effects. These results open new perspectives for experimental work aimed at controlling the charge transfer efficiency in nanodevices based on synthetic DNA.

Ag/C nanostructures (core–shell nanoparticles and nanocables) were obtained through the reduction of Ag⁺ with ascorbic acid in the presence of cetyltrimethylammonium bromide (CTAB) under hydrothermal conditions. It was found that the final morphology of the product was determined by the CTAB concentration. The formation process of both nanostructures included two evolution stages: (1) the synthesis of the Ag nanoparticles in the restriction of CTAB, (2) the carbonization of ascorbic acid and the formation of an amorphous carbon layer on Ag nanoparticles surface. The present study offers a possible new route to prepare new nanostructures.

Multi-walled carbon nanotubes/SnO₂ (CNT/SnO₂) core/shell nanostructures were synthesized by a simple wet-chemical method. The thickness of the SnO₂ shell was about 10 nm and the diameters of the SnO₂ particles were 2–8 nm. Sensors based on the core/shell heterostructures exhibited enhanced ethanol sensing properties. The sensitivity to 50 ppm ethanol was up to 24.5, and the response time and recovery time were about 1 and 10 s, respectively. In addition, the fluctuation of the sensitivity was less than ± 3% on remeasurement after 3 months. These results indicate that the core/shell nanostructures are potentially new sensing materials for fabricating gas sensors.

We propose a rational fabrication method for nanoimprinting moulds by scanning probe lithography. By wet chemical etching, different kinds of moulds are realized on Si(110) and Si(100) surfaces according to the Si crystalline orientation. The structures have line widths of about 200 nm with a high aspect ratio. By reactive ion etching, moulds with patterns free from the limitation of Si crystalline orientation are also obtained. With closed-loop scan control of a scanning probe microscope, the length of patterned lines is more than 100 µm by integrating several steps of patterning. The fabrication process is optimized in order to produce a mould pattern with a line width about 10 nm. The structures on the mould are further duplicated into PMMA resists through the nanoimprinting process. The method of combining scanning probe lithography with wet chemical etching or reactive ion etching (RIE) provides a resistless route for the fabrication of nanoimprinting moulds.

In this paper we report that a single nanowire was successfully grown by controlling the distance between the emitter and substrates with a nanorobotic manipulator moving at a speed of 15 nm s⁻¹. A tree-like nanowire was grown on the tip of an individual carbon nanotube (CNT) without interelectrode control. These nanowires were induced by field emission, with tungsten hexacarbonyl (W(CO)₆) as precursor. The nanowire's geometric properties were characterized with transmission electron microscopy (TEM) and its composition was obtained with TEM energy dispersive x-ray spectrometry (EDS). The EDS results showed that the nanowires are mainly made of tungsten and carbon. Degradation of the CNT emitter is an important problem and influences the device's stability and lifetime. We propose that the growth of nanowires can be used for modifying degraded emitters.

We describe herein a new facile approach to control the size and morphology of polypyrrole (PPy) nanotubular/wire structures in the presence of a cationic surfactant. The fibrillar complex of FeCl₃ and methyl orange (MO), acting as a reactive self-degraded template for the formation of polypyrrole nanotubules, was modified by cetyltrimethylammonium bromide (CTAB), which plays a dual role of adjusting the size of the seed template and providing an expanded region for the growth of polypyrrole. The modified template itself reacted oxidatively with pyrrole monomers to effectively construct nanotubular/wire structures with high yield. The effect of the concentration of CTAB on the initial template and subsequent polymerization process of pyrrole was investigated systematically. In the case of introducing anionic surfactant sodium dodecyl sulfate (SDS) into the system, the MO–FeCl₃ template was etched, resulting in a congregation of polypyrrole nanotubes and granules.

Highly ordered 3D superlattices comprised of monodisperse CdS nanocrystals are formed rapidly in solution using a simple procedure. Control over the instigation of the superlattice crystallization process is demonstrated by adjusting the concentration of sulfur in solution. Transmission electron microscopy shows that the CdS nanocrystals are 7 nm in size and form well-ordered structures. Selected area electron diffraction of the superlattices reveals that the CdS nanocrystals have their crystal axes partially aligned. This is further confirmed using a fast Fourier transform analysis of high-resolution transmission electron micrographs.

At the nanoscale, zirconium dioxide may form in a number of different polymorphs, depending in part upon the size of the particles. Although considerable attention has been given to finding methods for controlling the phase of zirconium dioxide nanocrystals, the role of nanomorphology in affecting the size-dependent phase transition has been largely ignored. To address this issue, we have used a shape-dependent thermodynamic model to investigate the relationship between nanomorphology and phase stability. Our results provide the free energy of formation for tetragonal and monoclinic nanocrystals with a variety of shapes, and show that the transition size is strongly dependent on the prevalence of particular surface facets. From these results we suggest that variations in the thermochemical results reported in the literature may also be partially attributed to variations in nanocrystal shapes.

Polyvinyl alcohol (PVA)/polyoxotungstoeuropate composite fibres were successfully prepared by a facile method called the electrospinning technique. Scanning electron microscopy (SEM) analysis revealed the fibre morphology of the composite. Transmission electron microscopy (TEM) showed spherical nanoparticles of the polyoxotungstoeuropate component with an average particle size of several nanometres to tens of nanometres and good dispersion. The electrospinning process prevented the polyoxometalate (POM) turning to an inhomogeneous microphase and large aggregation, so it is an effective and facile method for avoiding the phase separation of POM in the polymer matrices. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and ultraviolet–visible (UV–vis) spectra were used to characterize the structure of PVA/polyoxotungstoeuropate composite fibres. The fluorescence properties of the composite fibres were also investigated.

We synthesized nanoporous silica thin films on solid substrates through chemical bath deposition and investigated their structural properties using small-angle x-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The nanoporous silica is made of organic and inorganic molecules, interacting through a sol–gel process. The as-deposited films appear to grow in a continuous way as the bath deposition time elapses and consequently cubic ordering can be found in the nanostructured silica films. Through a properly controlled synthesis and annealing process, the present cubic nanoporous materials are expected to have a wide range of applications such as molecular detectors, a nanoscale reaction matrix, and molecular transport channels.

In₂O₃ nanostructures such as aligned nanocolumn arrays, nanowires and nanopyramids were fabricated using a simple physical evaporation technique. Nanocolumn arrays and the nanowires were produced using an Au catalysed vapour–liquid–solid (VLS) technique and the nanopyramid structures were prepared using a non-catalytic approach. Field-emission studies revealed that the morphologies of these In₂O₃ nanoforms have considerable effects on the field-emission properties. Among these nanoforms, nanocolumn arrays have the lowest turn-on voltage and the highest field enhancement factor. The results indicated that the In₂O₃ nanoforms could be used as cathode materials for the fabrication of devices based on field-emission properties.

We have fabricated fully released nano-electro-mechanical system (NEMS) cantilevers of various geometries from metallic alloy nanocomposite films. At thicknesses of 4.3 and 20.0 nm, these are the thinnest released metal cantilevers reported in the literature to date. Such device dimensions are very difficult to achieve using conventional metal films. We were able to overcome this limitation by using room-temperature co-sputtering to synthesize nanocomposite alloy films of Al–Mo. A systematic investigation of microstructure and properties as a function of Mo content resulted in an optimum film composition of Al–32 at.%Mo with a unique microstructure comprising a dense distribution of nano-scale Mo crystallites dispersed in an amorphous Al-rich matrix. These films were found to exhibit unusually high nanoindentation hardness and a very significant reduction in roughness compared with pure Al, while maintaining resistivity in the metallic range. A single-anchored cantilever 5 µm long, 800 nm wide and 20 nm thick showed a resonance frequency of 608 kHz, yielding a Young's modulus of 112 GPa, in good agreement with a reduced modulus of 138 GPa measured by nanoindentation.

Dynamic force microscopy (DFM) with the self-oscillator (SO) method is not generally subjected to the instability effects typical of tapping-mode DFM, as confirmed experimentally. The inherent stability of SO-DFM is related to phase locking of the cantilever oscillation to the excitation signal. Such phase locking determines univocally the oscillation state (i.e. amplitude and frequency) on the resonance curve, even when multiple amplitude values are compatible with a given frequency. By modelling the behaviour of an air-operated DFM system, it is found that, while stabilizing tip/surface distance for DFM imaging at constant frequency shift, and beyond a certain critical phase value, instabilities are possible in the SO constant-excitation amplitude mode. However, such instabilities cannot affect dynamic force spectroscopy approach curves, because of phase locking. By extension to vacuum operation, this result can confirm the origin of jumps in frequency shift found on some experimental DFM approach curves, for instance between non-passivated silicon tips to specific surface atomic sites of reconstructed silicon, since instrumental effects of the SO method can be ruled out.

Single-walled carbon nanotubes (SWCNTs) were added to aluminium using friction stir processing (FSP). The SWCNTs survived the thermal and stress cycles involved with friction stir processing. The Raman spectroscopy and SEM results are presented. Potential applications of nanotubes inserted into metals by this method are discussed.