Table of contents

We report the synthesis of self-organized nanoporous iron (III) oxide (haematite) via potentiostatic anodization of iron foil. Dependent upon the applied potential and electrolytic composition, the pore diameters range from 50 to 250 nm with a pore depth of approximately 500 nm. We examine the effect of electrolytic composition, anodization bath temperature and applied potential on the dimensions of the as-synthesized nanoporous structure. Crystallization and structural retention of the synthesized structure are achieved upon annealing the initial amorphous sample in a nitrogen atmosphere at 400 °C. The crystallized nanoporous film, having a 2.2 eV bandgap, exhibited a net photocurrent density of 0.51 mA cm⁻² in 0.5 M H₂O₂+1 M NaOH at 0.6 V versus Ag/AgCl under simulated AM 1.5 sunlight. Factors limiting the photoresponse and strategies of improvement are discussed.

Sulfur is introduced as an additive in CVD processes for the production of carbon nanotubes over Co–Mo/MgO sol–gel catalysts employing two different approaches: for the first time as sulfonated Co–Mo/MgO sol–gel catalysts and, alternatively, as thiophene vapour during the CVD reaction process. On one hand, the use of sulfur compounds during the sol–gel catalyst preparation process generally leads to a significant modification of the matrix composition and the matrix–catalyst interaction. When employing a catalyst here containing sulfur compounds the induced matrix modifications yield enhanced growth of helical carbon nanotubes (HCNTs). On the other hand, adding sulfur in the form of thiophene vapour over non-sulfonated sol–gel catalysts, the growth of Y-shaped carbon nanotubes (YCNTs) is favoured depending on the flow conditions of the hydrocarbon source employed. The obtained results underline the general importance of the nature of the sol–gel matrix for the formation of HCNTs as well as of the local fluctuations in the gas phase for the growth of YCNTs. The findings are of importance for the fabrication of nanotube-based electronic devices.

The effect of barrier growth temperatures on blue InGaN (2 nm)/GaN (12 nm) multiple quantum wells was studied with samples grown by metallorganic chemical vapour deposition. It was found that InGaN active layers composed of InGaN quasi-dots of 2 ± 0.2 nm in diameter, changing from their homogeneous nature, could be obtained by elevating the barrier growth temperature from 700 to 800 °C based on the results of energy-filtered high resolution transmission electron microscopy. These dots may have formed during the ramping process by in situ annealing. Strong piezoelectric field, 'S-shape-like' carrier transition and high internal quantum efficiency of 71.3% were observed in the sample with a higher barrier growth temperature closely related to the dot formation. Furthermore, the forward voltage and the light output power at 20 mA of light emitting diodes from the sample with dots were 0.3 V lower and 11% higher than that from the homogeneous multiple quantum wells.

To avoid high energy consumption, intensive use of hardware and high cost in the manufacture of nanoparticles encapsulated in carbon, a simple, efficient and economical solution-phase method for the fabrication of FeNi@C nanostructures has been explored. The reaction to the magnetic metal@C structures here is conducted at a relatively low temperature (160 °C) and this strategy can be transferred to prepare other transition metal@C core–shell nanostructures. The saturation magnetization of metal in metal@C nanostructures is similar to those of the corresponding buck metals. Magnetic metal@C nanostructures with magnetic metal nanoparticles inside and a functionalized carbon surface outside may not only provide the opportunity to tailor the magnetic properties for magnetic storage devices and therapeutics but also make possible the loading of other functional molecules (e.g. enzymes, antigens) for clinic diagnostics, molecular biology, bioengineering, and catalysis.

A novel approach for the synthesis of cobalt-doped ZnO single-crystalline nanorods based on a wet chemical reaction has been developed. The as-doped ZnO nanorods have a length between 0.3 and 0.6 µm and a diameter between 30 and 60 nm. Structure and composition analyses indicate that the cobalt is incorporated into the ZnO lattice, forming a solid solution without any precipitation. Magnetic property measurements reveal that there is room-temperature ferromagnetism in the Zn_1−xCo_xO nanorods with T_c higher than 300 K.

The vapour–liquid–solid (VLS) growth of TiO₂ nanowires (NWs) was performed using a thermally evaporated Ti source and sputter-deposited Au catalysts under an O₂ gas flow. High-density single-crystalline TiO₂ NWs having the rutile structure were successfully grown on sapphire (single-crystal α-Al₂O₃) and quartz (amorphous SiO₂) substrates. Ti buffer layers, deposited on the substrates to prevent undesirable reactions between the Ti vapour and substrates, were identified to promote the TiO₂ NW growth by providing supplementary Ti vapour to the Au catalysts. Crystallinity of TiO₂ NWs was investigated by x-ray diffraction (XRD) and their morphological features were characterized by field emission scanning electron microscopy (FESEM). High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) analyses reveal growth of the rutile NWs having twofold twin structures along the growth direction on Ti/sapphire and the defect-free single-crystalline rutile NWs on Ti/quartz substrates. TiO₂ NWs grown on Ti/quartz showed a short-wavelength (∼402 nm) and high-intensity photoluminescence (PL) emission compared to those grown on Ti/sapphire substrates. By introducing a Ti buffer layer and using quartz substrates, the crystallinity and PL properties were successfully improved for VLS-grown TiO₂ NWs.

A high-aspect-ratio cone-shaped carbon nanotube (CNT), which we refer to as a carbon nanocone (CNC), was fabricated for scanning probe microscopy (SPM) by a novel and reliable patterning technique and dc plasma chemical vapour deposition. Carbon dots from electron beam induced deposition (EBID) were utilized as convenient chemical-etch masks to create catalyst patterns for the growth of a single CNC probe on a tipless cantilever and an array of CNC probes on a silicon substrate. This resist-free EBID process is an efficient way of preparing a patterned catalyst and resultant nanoprobe on the specific edge location of the cantilever. The CNC probe produces high-resolution images of specimens in air as well as in liquid. No degradation in imaging performance was observed after a period of continuous scanning. The CNC bed-of-nails array imaged in contact mode by a commercial Si₃N₄ probe demonstrates the mechanical toughness/sturdiness of the CNC tip. This also indicates the possibility of using the CNC bed-of-nails as a convenient means for the characterization of SPM tips.

Nanocrystalline Y₂O₃:Eu phosphors have been successfully synthesized by a novel combustion method using sucrose as a chelating agent and fuel. The sucrose hydrolysation and complexing mechanisms are discussed. X-ray diffraction analysis showed that the cubic phase can be formed at a low temperature of 400 °C, and transmission electron microscopy observations revealed that the phosphor particles were 30–50 nm annealed at 1000 °C. The post-treated Y₂O₃:Eu nanophosphors yield intense red emission at 610 nm, corresponding to the ⁵D₀–⁷F₂ transitions. The luminescence properties of the Y₂O₃:Eu particles were strongly affected by the annealing temperatures and the sucrose to metal ion ratios. This work demonstrates that the sucrose combustion process can be a quasi-universal medium for the preparation of nanoscale phosphors.

We report a new approach to convert an electrospun nanofibrous cellulose acetate mat surface from super-hydrophilic to super-hydrophobic. Super-hydrophilic cellulose acetate nanofibrous mats can be obtained by electrospinning hydrophilic cellulose acetate. The surface properties of the fibrous mats were modified from super-hydrophilic to super-hydrophobic with a simple sol–gel coating of decyltrimethoxysilane (DTMS) and tetraethyl orthosilicate (TEOS). The resultant samples were characterized by field emission scanning electron microscopy (FE-SEM), x-ray photoelectron spectroscopy (XPS), water contact angle, Brunauer–Emmett–Teller (BET) surface area, atomic force microscopy (AFM), and UV–visible measurements. The results of FE-SEM and XPS showed that the sol–gel (I) films were formed on the rough fibrous mats only after immersion in sol–gel. After the sol–gel (I) coating, the cellulose acetate fibrous mats formed in both 8 and 10 wt% cellulose acetate solutions showed the super-hydrophobic surface property. Additionally, the average sol–gel film thickness coated on 10 wt% cellulose acetate fibrous mats was calculated to be 80 nm. The super-hydrophobicity of fibrous mats was attributed to the combined effects of the high surface roughness of the electrospun nanofibrous mats and the hydrophobic DTMS sol–gel coating. Additionally, hydrophobic sol–gel nanofilms were found to be transparent according to UV–visible measurements.

This three-dimensional exploratory study on vertical silicon wire MOS transistors with metal gates and undoped bodies demonstrates that these transistors dissipate less power and occupy less layout area while producing comparable transient response with respect to the state-of-the-art bulk and SOI technologies. The study selects a single metal gate work function for both NMOS and PMOS transistors to alleviate fabrication difficulties and then determines a common device geometry to produce an OFF current smaller than 1 pA for each transistor. Once an optimum wire radius and effective channel length is determined, DC characteristics including threshold voltage roll-off, drain-induced barrier lowering and sub-threshold slope of each transistor are measured. Simple CMOS gates such as an inverter, two- and three-input NAND, NOR and XOR gates and a full adder, composed of the optimum NMOS and PMOS transistors, are built to measure transient performance, power dissipation and layout area. Simulation results indicate that worst-case transient time and worst-case delay are 1.63 and 1.46 ps, respectively, for a two-input NAND gate and 7.51 and 7.43 ps, respectively, for a full adder for a fan-out of six transistor gates (24 aF). Worst-case power dissipation is 62.1 nW for a two-input NAND gate and 118.1 nW for a full adder at 1 GHz for the same output capacitance. The layout areas are 0.0066 µm² for the two-input NAND gate and 0.049 µm² for the full adder circuits.

The ability to manipulate the orientation of nanoscale materials is of great importance for applications in advanced devices. Here, we describe the controlled growth of aligned carbon nanofibres (CNFs) in a hollow cathode discharge (HCD) set-up. Instead of vertical alignment well demonstrated in other plasma-based chemical vapour deposition, CNFs with specific and symmetrically aligned configurations are grown on a flat surface during HCD. Experimental evidence shows that the alignment is not the result of the edge or flow effect, but results from a unique electric field distribution imposed on the substrate surface in the HCD environment. Due to the field reversal characteristic of the HCD, two alignment trends simultaneously occur. For the transverse direction of the channel, the grown CNFs on the substrate appear in a convergent manner, while those along the longitudinal direction exhibit a radiative arrangement. These results will open up the possibility of both tuning the electric fields on the basis of plasma design and tailoring the spatial orientations of CNFs using HCDs.

A digital nano-moiré method with wavelet transformation is explored to measure nanoscale in-plane displacement fields. By applying e-beam lithography, a periodic PMMA nanostructure array is fabricated directly on the specimen and used as the specimen grating. Moiré patterns are generated by overlapping the images of the PMMA specimen grating obtained from AFM scanning and the virtual reference grating produced by a digital image generating process. Then, the overlapped images are filtered by the 2D wavelet transformation (WT) to capture the target moiré patterns. Existing methods, by overlapping the monitor-generated scanning lines with the image of the specimen grating, cause a mismatch problem. Previously, the carrier moiré method was explored with the aim of curing the mismatch problem. Unfortunately, the carrier moiré method, in addition to suffering from increased complexity of mathematical calculations, is incapable of directly obtaining the displacement field. Thus, the mismatch problem will result in inconveniences and restrictions in the practical application. Instead of using monitor-generated scanning lines, the proposed method applies the virtual reference grating, and thus puts the mismatch problem to rest. Nevertheless, the resultant moiré image suffers from low contrast which, if left untreated, might distort the measurement result. Therefore, the WT, known for its sharpened abilities of characteristic and edge detection, is used to capture the target moiré patterns and improve the measurement accuracy. The proposed method has been carried out in the laboratory. Experimental results have shown that the proposed method is convenient and efficient for nanoscale displacement measurement.

The remanent magnetic states of rows of electrodeposited nanoscale Ni pillars with diameters of 57–120 nm and aspect ratios of up to 2 have been characterized using off-axis electron holography, which measures the magnetic induction within the pillars and the stray field surrounding them. Inhomogeneities in the Ni, resulting from its grain structure, significantly perturb the axial uniformity of the magnetization. The magnetization is reduced from that of pure Ni due to surface oxidation and the co-deposition of impurities. Interactions between the pillars can be deduced from the external field distribution, and vary with the pillar size and spacing.

Multiwall carbon nanotube array/silicone elastomer composite films have been fabricated with an in situ injection modelling method. The transverse conductivity of the composite films is larger than the lateral conductivity because the aligned carbon nanotube array is embedded into the polymer matrix. The nonlinear I–V curve has been analysed and the temperature-dependent transport behaviour has been investigated.

The microstructure of plasma-nitrided high-k ZrO₂ thin films is found to continuously transform and larger size nano-crystals are formed during electron bombardment. Real-time high-resolution transmission electron microscopy (HRTEM) studies show that the plasma-nitrided nano-size particles can self-crystallize and regrow, whereas this phenomenon is not observed in amorphous ZrO₂ without N incorporation. Similar results are observed in plasma-nitrided HfO₂ samples and fine-scale polycrystalline nano-arrays are obtained by electron irradiation. Our results show that incorporation of N is crucial for inducing microstructural evolution as well as polycrystalline nano-array formation in high-k oxide under electron irradiation.

In this paper we experimentally demonstrate the fabrication and operation of a rapidly prototyped optical cylindrical micro-waveguide based biosensor. This device works on the principle of variation to the light intensity and path of coupled input light due to the binding of protein bio-molecules onto the micro-waveguide surface as a method of physical transduction. The variation to the coupled light intensity and path is dependent on the nature of the bio-molecule and the density of the bio-molecules. This technique has been used to identify protein biomarkers for inflammation and thrombosis, namely myeloperoxidase (MPO) and C-reactive protein (CRP). The detection limit that has been demonstrated is pg ml⁻¹. The detection speed is of the order of seconds from the time of injection of the bio-molecule. The optical signature that is obtained to identify a protein bio-molecule is entirely dependent on the nature of adsorption of the bio-molecule on to the cylindrical cavity surfaces. This in turn is dependent on the protein conformation and the surface charge of the bio-molecules. Hence a specific protein bio-molecule generates a unique optical identifier based on the nature of binding/adsorption to the cavity surface. This physical phenomenon is exploited to identify individual proteins. This technique is a demonstration of detection of nano-scale protein bio-molecules using the optical biosensor technique with unprecedented sensitivity.

By the formation of ZnO and Pt nanocomposites, it is found that the bandgap emission can be greatly enhanced, while the defect emission is suppressed to the noise level. The photoluminescence intensity ratio between the bandgap and defect emission can be improved by up to 10³ times. The underlying mechanism behind enhancement of the bandgap emission and quenching of the defect emission is a combination of the energy transfer between defects and surface plasmon resonance in Pt nanoparticles, as well as electron–hole pair generation and recombination in the ZnO nanorods. Our results will be very useful to manufacturers of highly efficient optoelectronic devices.

In this study we manufactured highly porous graphite nanofibres (GNFs) by physical activation in order to develop promising energy storage materials. The activation was performed at activation temperatures in the range of 800–1050 °C. The pore structures of the porous GNFs were analysed using N₂/77 K adsorption isotherms. After the activation, the porous GNFs showed a decrease in diameter and scratches on their surfaces, resulting from surface oxidation and the opening of the graphitic layers, respectively. It was found that the specific surface area of the porous GNFs prepared at 1050 °C was more than 2000 m² g⁻¹ without loss of their fibre shape or serious increase in electrical resistivity. This result indicates that porous GNFs prepared under optimal conditions can have a much higher specific surface area and are promising materials for energy storage technologies.

A dual functional and water soluble spin-coatable lanthanum strontium manganese oxide (LSMO) resist has been developed that consists of lanthanum nitrate, strontium nitrate, manganese nitrate, polyvinyl alcohol and water. Energetic nitrates plus polyvinyl alcohol fuel promote autoignition and produce nanopatterns (<60 nm) upon mild electron beam exposure (<2 mC cm⁻²). The formation of cubic perovskite LSMO has been confirmed by micro-IR spectroscopy, elemental analysis, x-ray diffraction and transmission electron microscopy. The patterned LSMO film can be developed using nontoxic and environmentally friendly pure water, and the resist can fabricate active magnetic patterns directly by electron beam exposure. The spin-coatable LSMO resist can be fabricated into either positive or negative patterns easily by varying the electron doses. It can change from negative resist to positive resist and then finally negative resist with the increase of electron dose. The positive and negative dual functional mechanism of spin-coatable LSMO resist is reported. A resist with simultaneous positive and negative capabilities patterning will benefit the direct writing technology of an electron beam. The active magnetic characteristics and high refractive index of the material are useful for the direct fabrication of magnetic and optical devices.

In this paper, uniform hydroxyapatite (HA) nanowires of width 60 nm and length 1 µm are synthesized by solvothermal synthesis. The formation process of the nanowires has been elaborated from the structure within the reverse micelles by the time-resolved fluorescence quenching technique. The results reveal that the formation of amorphous nuclear/surfactant complex and the electrostatic field within the reverse micelles maintain the unidirectional, irreversible fusion of reverse micelles, leading to the growth of nanowires in one direction. In the solvothermal synthesis, the pressure generated in the autoclave is estimated. The results suggest that the products are prepared under stable conditions without intense shearing stress where it is favourable for the formation of long and uniform HA nanowires.

Ge growth on a Si(111)-7 × 7 surface at room temperature was studied by in situ scanning tunnelling microscopy. The Ge hexagonal meshwork film composed of Ge nanoclusters located on the centre of the half-unit-cells of Si(111)-7 × 7 grows in the 'monolayer mode': the first layer is 0.22 nm thick, and then increases in thickness by 0.11 nm, forming the 0.33 nm bilayer. This growth mode leads to a simple stacking sequence. However, the Stranski–Krastanov growth mode was still found for the thick meshwork films.

The concept of phase separation was coupled with electrospinning to generate polyacrylonitrile (PAN) and poly(ethylene oxide) (PEO) bicomponent fibres that, upon removal of the phase-separated PEO domains, became nanoporous. Electrospinning of PAN (150 kDa) with 15–50% w/w PEO (10 kDa) at a 8% w/w total concentration in N,N-dimethylformamide produced fibres with decreasing averaged diameters from 390 to 130 nm. Evidence of phase separation between PAN and PEO in the bicomponent fibres was indicated by the characteristic PAN and PEO peaks by Fourier transform infrared (FTIR) spectroscopy and solid-state nuclear magnetic resonance (NMR) imaging, and confirmed by the co-existence of PAN cyclization and PEO melting by differential scanning calorimetry (DSC) and the presence of PEO crystalline diffraction by wide-angle x-ray scattering (WAXS). Removal of PEO by dissolution in water was confirmed by the matched mass loss to PEO fraction and the absence of PEO by FTIR and DSC. The water-treated bicomponent fibres appeared slightly larger in diameter and contained internal pores of nanometre scale. The nanoporous fibres generated from 50/50 PAN/PEO bicomponent precursor contained internal pores of a few nanometres to tens of nanometres in size and had 50% higher pore volume and 2.5-fold higher specific surface.

We investigated the impact of the growth morphology of single-walled carbon nanotubes (SWNTs) on gas sensing performance. An SWNT film was directly synthesized on alumina substrate by thermal chemical vapour deposition. Different morphologies of the SWNTs in terms of density, diameter distribution and orientation were obtained by varying the growth temperature. Vertically aligned SWNTs with a high density were grown at 750 °C, while horizontally lying SWNT networks with a low density were grown in the temperature range 800–950 °C. The sensor response of the resultant SWNTs to NO₂ was characterized at room temperature. It was found that the density of SWNTs strongly dominates sensor performance; the SWNT networks with the lowest density exhibited the highest sensor sensitivity. This was evidenced by characterization of density-controlled SWNTs synthesized using different thicknesses of an Fe/Al multilayer catalyst. The high sensor sensitivity for low-density SWNT networks is likely to be attributed to suppression of the formation of SWNT bundles and reduction of narrow-band-gap conduction paths, resulting in the enhancement of the adsorption probability and chemical gating efficiency of gas molecules on SWNTs.

The combined use of phosphatidylcholine passivated gold nanorods (PC-NRs) and pulsed near-infrared (near-IR) irradiation resulted in cell death. Pulsed near-IR laser irradiation also induced reshaping of PC-NRs into spherical nanoparticles. Since reshaped particles showed no absorption in the near-IR region, successive laser irradiation did not affect cells. Photo-reshaping of PC-NRs is expected to be advantageous in preventing unwanted cell damage following destruction of target cells.

The brightness enhancement of liquid crystal displays (LCD) through polarization recycling was investigated by placing a nano-wire grid polarizer (NWGP) between an LCD panel and a backlight unit. NWGPs with a period of 200 nm were fabricated using laser interference lithography and oblique deposition of aluminium. We optimized the fabrication process and achieved a high transmission of above 90% and a contrast ratio of above 12.5 for the range of wavelengths corresponding to visible light. This condition led to a strong enhancement of the brightness in an LCD with NWGP, which was 1.3 times higher than that without NWGP.

Ag nanorod electrodes with different nanorod lengths are fabricated by a simple vacuum deposition technique, oblique angle deposition (OAD). The as-grown Ag nanorods are aligned on the substrate and have a diameter of ∼60–70 nm, a density of ∼200–300 × 10⁷ cm⁻², and a tilting angle of ∼70°–80° with respect to the surface normal. The electrochemical behaviours of the Ag nanorod electrode are characterized by cyclic voltammetry at various scan rates with comparison to an Ag thin-film electrode. The capacitive current is found to be proportional to the actual surface area, and the faradic redox current also increases monotonically with the surface area of the nanorod electrodes, but the increase is not as significant as that of the capacitive current due to the diffusion layer overlapping for the highly compacted nanorods. This indicates that the Ag nanorod electrode could improve the electrolytic sensor for amperometric response measurements, especially for the bimolecular measurements due to the biocompatibility of Ag. The high capacitance also suggests a promising usage of the developed nanostructures for battery and energy storage applications.

In this study, a fabrication of ordered ZnO hierarchical structures with nano- and microscale pores is presented. Tunable ordered hollow and solid nanostructures of dots and networks have been obtained utilizing the effect of surface-charge coupling between the latex particles and the oxide nanoparticles deposited in the electrophoretic deposition process. The force induced by an electrical field can move the charged particles towards an electrode, and the surface-charge coupling force can efficiently fine-tune the relative position of the neighbouring particles and thus result in the formation of various ordered assemblies.

We investigate the fundamental mechanism by which self-assembled Ge islands can be nucleated at specific sites on Si(001) using ultra-low-dose focused ion beam (FIB) pre-patterning. Island nucleation is controlled by a nanotopography that forms after the implantation of Ga ions during subsequent thermal annealing of the substrate. This nanotopography evolves during the annealing stage, changing from a nanoscale annular depression associated with each focused ion beam spot to a nanoscale pit, and eventually disappearing (planarizing). The correspondence of Ge quantum dot nucleation sites to the focused ion beam features requires a growth surface upon which the nanotopography is preserved. A further key observation is that the Ge wetting layer thickness is reduced in patterned regions, allowing the formation of islands on the templated regions without nucleation elsewhere. These results provide routes to the greatly enhanced design and control of quantum dot distributions and dimensions.

ZnO–SiO₂ lamellar nanocomposites with high zinc content (5≤Si/Zn≤50) have been synthesized through a one-pot surfactant-assisted procedure from aqueous solution and starting from molecular atrane complexes of Zn and Si as inorganic hydrolytic precursors. This approach allows optimization of the dispersion of the ZnO nanodomains in the silica sheets. The nature of the layered silica materials has been confirmed by x-ray diffraction. Spectroscopic (ultraviolet–visible and photoluminescence) study of these layered silica materials shows that, regardless of the Si/Zn ratio, Zn atoms are organized in well-dispersed, uniform ZnO nanodomains (about 1.2 nm) partially embedded within the silica sheets. Quantum confinement effects have been observed in the optical response of the ZnO nanoparticles included in these nanocomposites.

The effects of a SiO₂ layer grown on a Si substrate and the CuO additive in GeO₂ powders for the enhanced growth of Ge–Si_1−xGe_xO_y and GeO₂–Si_1−xGe_xO_y core–shell nanowires (hereafter referred to as Ge–Si_1−xGe_xO_y and GeO₂–Si_1−xGe_xO_y nanowires, respectively) via carbothermal reduction at 1050–1100 °C in flowing Ar were studied. Using GeO₂ powders as the feedstock alone, nanowires having a composition of Ge–Si_1−xGe_xO_y were grown on a SiO₂/Si substrate, whereas the same nanowires could not be grown on a Si substrate. Adding CuO into GeO₂ powders enhanced the growth of GeO₂–Si_1−xGe_xO_y and Ge–Si_1−xGe_xO_y nanowires on the Si substrate as well as that of GeO₂–Si_1−xGe_xO_y nanowires on the SiO₂/Si substrate. The crystal growth mechanism seems to follow the vapour–solid process. The present study reveals that the oxidation of the Si substrate plays an important role in enhancing the growth of Ge–Si_1−xGe_xO_y and GeO₂–Si_1−xGe_xO_y nanowires via carbothermal reduction of GeO₂ powders. The mechanisms for the precipitation of the Ge or GeO₂ core inside the Si_1−xGe_xO_y shell on Si and SiO₂/Si substrates are discussed, respectively.

Photophysical properties of semiconductor nanocrystal quantum dots (QDs) are primary determinants of their efficacy as fluorescence probes in biological systems. Our minimally passivated core/shell/shell QDs are smaller than the QDs with thick polymer coats that are often used for cellular probes, permitting less restricted access to intracellular compartments and at the same time a greater sensitivity to environmental conditions. We report here a reversible photoinduced fluorescence enhancement (photoactivation) of endocytosed mercaptoacetic-acid-capped CdSe quantum dots (MAA QDs) and the pH dependence of MAA QD photoluminescence in SKOV-3 human ovarian cancer cells. The fluorescence emission of MAA QDs taken up directly by SKOV-3 cells without the need for extra capping ligands or permeabilization steps remains bright and stable for at least 14 days. These intracellular fluorescent nanocrystals do not colocalize with low-pH lysosomes, and the emission of the MAA QDs in fixed cell preparations is quenched by acidic buffer, suggesting that a low-pH environment in cellular vesicles quenches QD fluorescence. Photoactivation of intracellular MAA QD luminescence is dependent on the excitation energy and is related to the metabolic activity of the cells. These active interactions between cells and nanocrystals demonstrate the potential of MAA QDs as intracellular environmental sensors.

Highly luminescent Si quantum dot embedded SiO_x films were studied as down-converting emitters for solid-state lighting applications. Strong red photoluminescence was observed from these Si nanocrystal embedded films prepared by thermal evaporation of SiO in vacuum or an O₂ atmosphere followed by anneal at 1100 °C. The stoichiometry (1.0<x<1.9) and refractive indices (1.5–1.75) of these films could be well controlled by varying the oxygen flow rate and the deposition rate. The emission peak shifted from 840 to 745 nm with increasing O₂ flow rate due to a decrease in the size of the Si QDs. Two excitation bands, peaked at 280 and 370 nm, were observed from these samples. The 370 nm band was much stronger than the 280 nm band, which is near the UV LED emission range required for solid-state lighting applications. Blue and green emissions were also observed from samples annealed at a lower temperature.

A facile method was developed for completely transferring high quality monodisperse iron oxide nanocrystals from organic solvents to water. The as-prepared aqueous dispersions of iron oxide nanocrystals were extremely stable and could be functionalized for bioconjugation with biomolecules. These iron oxide nanocrystals showed negligible cytotoxicity to human breast cancer cells (SK-BR-3) and human dermal fibroblast cells. This method is general and versatile for many organic solvent-synthesized nanoparticles, including fluorescent semiconductor nanocrystals.

A polyaniline/In₂O₃ nanofibre composite based layered surface acoustic wave (SAW) sensor has been developed and investigated for different gases. Chemical oxidative polymerization of aniline in the presence of finely divided In₂O₃ was employed to synthesize a polyaniline nanofibre/In₂O₃ nanoparticle composite. The nanocomposite was deposited onto a layered ZnO/64° YX LiNbO₃ SAW transducer. The novel sensor was exposed to H₂, NO₂ and CO gases. Fast response and recovery times with good repeatability were observed at room temperature.

C₆₀ clustered layers were produced on highly oriented pyrolytic graphite substrates using high-vacuum beam deposition and charge-transfer reduction in a KOH aqueous solution. Electrochemical nanostructuring of the fullerene films is effective: upon electrochemical reduction, nanometre-sized clusters of conductive potassium fullerides are formed in layers at the electrode. The evidence for clustering is illustrated by cyclic voltammetry, x-ray diffraction and scanning tunnelling microscopy.

Aligned piezoelectric (PZT) nanofibres were fabricated by electrospinning using PZT sol–gel as precursor. A pure perovskite phase with an average grain size of 10 nm was obtained at 650 °C. The average diameter of these fibres could be controlled to range from 52 to 150 nm by varying the concentration of poly(vinyl pyrrolidone) (PVP) in the precursor. Special samples of PZT nanofibres were deposited across the microfabricated trenches on a silicon wafer. Atomic force microscopy (AFM) was used to measure the mechanical properties of a single nanofibre. The elastic modulus of an individual PZT nanofibre that was obtained was 42.99 GPa, which was smaller than that of a thin-film PZT. The possible reasons for the reduction in elastic modulus of the nanofibres were discussed.

The stochastic dynamics of micron and nanoscale cantilevers immersed in a viscous fluid are quantified. Analytical results are presented for long slender cantilevers driven by Brownian noise. The spectral density of the noise force is not assumed to be white and the frequency dependence of the noise force is determined from the fluctuation-dissipation theorem. The analytical results are shown to be useful for the micron scale cantilevers that are commonly used in atomic force microscopy. A general thermodynamic approach is developed that is valid for cantilevers of arbitrary geometry as well as for arrays of multiple cantilevers whose stochastic motion is coupled through the fluid. It is shown that the fluctuation-dissipation theorem permits the calculation of stochastic quantities via straightforward deterministic methods. The thermodynamic approach is used with deterministic finite element numerical simulations to quantify the auto-correlation and noise spectrum of cantilever fluctuations for a single micron scale cantilever and the cross-correlations and noise spectra of fluctuations for an array of two experimentally motivated nanoscale cantilevers as a function of cantilever separation. The results are used to quantify the noise reduction possible using correlated measurements with two closely spaced nanoscale cantilevers.

A novel technique for fabricating silicon dioxide (SiO₂) and silicon carbide (SiC) nanostructures on SiC substrates is reported in this paper. The technique involves amorphization of crystalline SiC at the nanoscale using a focused ion beam followed by selective thermal oxidation that results in oxide nanostructures due to the enhanced oxidation rate of amorphous SiC. Selective etching of the oxide results in crystalline SiC nanostructures. Nanostructures (SiO₂ and SiC) with minimum feature sizes of ∼55 nm have been fabricated. Oxide nano-channels with channel widths of less than 20 nm are demonstrated. The physical mechanisms that control the evolution of the structures and limit the resolution have been addressed.

The present contribution reports, for the first time, the successful fabrication of α-chitin whisker-reinforced poly(vinyl alcohol) (PVA) nanocomposite nanofibres by electrospinning. The α-chitin whiskers were prepared from α-chitin flakes from shrimp shells by acid hydrolysis. The as-prepared chitin whiskers exhibited lengths in the range 231–969 nm and widths in the range 12–65 nm, with the average length and width being about 549 and 31 nm, respectively. Successful incorporation of the chitin whiskers within the as-spun PVA/chitin whisker nanocomposite nanofibres was verified by infrared spectroscopic and thermogravimetric methods. The incorporation of chitin whiskers within the as-spun nanocomposite fibre mats increased the Young's modulus by about 4–8 times over that of the neat as-spun PVA fibre mat.

Carbon nanotubes have been deposited and aligned onto the pre-structured metal contacts of a silicon chip. Crucial for the deposition and alignment process are micro-fluidic flow fields combined with electric dipole fields generated by surface acoustic waves within a gap filled with an aqueous carbon nanotube suspension. This gap is formed when the pre-structured silicon chip is flipped onto the piezoelectric lithium niobate substrate, allowing for the generation of surface acoustic waves. The contacting probability of carbon nanotubes on the prestructured metal contacts has been found to be 37%. In combination with back-gates, these structures define three-terminal devices and the first current–voltage characteristics.