Table of contents

Hierarchically mesoporous silica materials with a bimodal distribution were template-prepared from uniaxially stretched polypropylene membrane in the presence of a surfactant via a sol–gel process. Their regularity and morphologies were characterized by transmission electron microscopy (TEM), x-ray diffraction and Brunauer–Emmett–Teller (BET) surface area analysis. The larger channel pores formed by removing the microfibrils of uniaxially stretched polypropylene membrane have a broad pore size distribution, and their size is around 13 nm. In contrast, the smaller mesopores formed by surfactant templates have a narrow distribution; their size is about 3.9 nm. The size of the smaller pores could be tuned from 2 to 6 nm by selecting different surfactants and by changing the concentration of reactants.

Single crystalline ZnO nanorods with a diameter of about 5 nm were synthesized without the presence of any surfactants in ethanol solvent at room temperature. Nanodots and nanorods with different size and shape could be observed by TEM via simply altering NaOH concentration and reaction time. The polar ZnO nanorod growth mechanism was discussed by the 'Ostwald ripening' mechanism. Optical absorption and photoluminescence properties of ZnO nanorods have been characterized. The UV absorption spectrum revealed a clear blue-shift with a single absorption peak centred at 350 nm.

Electron beam-induced deposition (EBID) using organometallic precursors is a promising technique for nanometre-sized fabrication, but the deposits have been mostly limited to carbonaceous materials. In this study, vapours of water and iron pentacarbonyl were mixed with precise control and the mixture used as a precursor for EBID. We have succeeded in achieving direct formation of Fe₃O₄ nanostructures at room temperature. This will contribute to broadening the range of materials that can be produced by EBID.

Using n-butanol released in situ as the cosurfactant, transparent large-pore mesoporous nanocrystalline anatase (meso-nc-TiO₂) thin films with narrow pore size distribution have been successfully synthesized in a Ti(OBuⁿ)₄–P123–EtOH–HCl system. Furthermore, the mesopore size can be easily controlled in the range of 8.3–14.0 nm through adjusting the quantities of Ti(OBuⁿ)₄, corresponding to the amount of n-butanol released in situ. X-ray diffraction, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and nitrogen sorption were used to investigate the relationship between the amount of Ti(OBuⁿ)₄ and the structural parameters of the obtained meso-nc-TiO₂ thin films. A reasonable mechanism is also proposed here to explain the formation of large-pore mesoporous TiO₂ with tunable pore diameters. The hydrophilicity of our obtained films was evaluated by water contact angle measurement in air. It was found that, in the absence of ultraviolet (UV) illumination, the presented transparent large-pore meso-nc-TiO₂ thin films exhibit high hydrophilicity.

Octahedral CuS nanocages were synthesized by a solid–liquid reaction between solid Cu₂O octahedra and thiourea solution at 90 °C. Octahedral Cu₂O particles were used as the sacrificial cores, precursor and shape-controller. The transformation of octahedral Cu₂O to hollow CuS octahedra was monitored by the TEM images and EDX spectra. A mechanism of mass diffusion followed by Ostwald ripening is proposed based on the evidence of electron microscope images. The critical size (d^*) of the precursor for the formation of hollow structured CuS was estimated based on the proposed mechanism and the designed experiments.

We study the self-aligned growth of a single carbon nanotip on a sharp metal tip via the field-emission-induced growth method. Under typical growth conditions, a micron long nanotip can be formed in around 10 s by field emission in the presence of acetylene gas at ∼10⁻² mbar. The tip radius of the carbon nanotip can be as small as 5 nm, while its length is determined by the growth duration. Electron energy loss spectroscopy (EELS) analysis in a transmission electron microscope revealed that the carbon nanotip is amorphous carbon with predominant sp² bonding. The growth mechanism of the carbon nanotip is discussed to explain the formation of the nanotip and its carbon matrix. Field-emission measurements showed that emission from the carbon nanotip follows the Fowler–Nordheim equation, suggesting that the tip shows metallic behaviour as far as field emission is concerned. A high emission current stress cycle is found to improve the emission current stability significantly.

Here we report a novel hybrid organic–inorganic anode for organic light-emitting diodes (LEDs) and photovoltaic (PV) cells. This hybrid anode structure is realized from a composite of poly(3,4-ethylene dioxythiophene) doped with polystyrenesulfonic acid (PEDOT:PSS) and indium tin oxide (ITO) nanoparticles. Owing to the phase separation, this anodic structure leads to a graded work function from patterned ITO to the photoactive polymer, which in turn reduces the barrier height for holes by ∼70%. The resulting devices based on this design show up to 67% reduction in turn-on voltage (for polymer LEDs) and up to 40% increase in short-circuit current and power conversion efficiency (for PV cells). Current–voltage characteristics, Fowler–Nordheim analysis, SEM imaging and energy band diagram analysis are employed to characterize the improved performance of our devices. The reported approach is expected to be immensely useful for the molecular design of next-generation efficient organic devices.

SnO₂ thin films were deposited by RF inductively coupled plasma enhanced chemical vapour deposition and then the as-deposited SnO₂ thin films were immersed in the plasma for plasma post-treatment. Uniform SnO₂ nanorods were grown in situ from the SnO₂ thin films during plasma treatment and formed a hybrid structure of SnO₂ nanorod thin films consisting of one-dimensional SnO₂ nanorods embedded in the two-dimensional SnO₂ thin film matrix. The growth of SnO₂ nanorods follows a sputtering redeposition mechanism. Due to the intrinsically small grain size and high surface-to-volume ratios associated with the nanorods, the SnO₂ nanorod thin films showed much higher sensitivity at lower operating temperatures together with faster response and shorter recovery time compared with the as-deposited SnO₂ thin films.

Nanoparticles (NPs) have shown their efficiency in increasing the oral bioavailability of macromolecular drugs, among them heparin. However, mechanisms of absorption are still unclear. Here, heparin-loaded NPs were prepared from different polymers (Eudragit^® RS, poly(lactic-co-glycolic acid) (PLGA), and their respective mixtures) and analysed for their mucoadhesive properties using a resonant mirror system. Subsequent binding and drug transport studies of the free heparin and heparin-loaded NPs were carried out on Caco-2 cells. Cationic NPs were found to be mucoadhesive, while pure drug and polyester NPs were not. The adsorption of anionic heparin masked the positive surface charge of the particles, thus partially diminishing the adhesiveness to mucin. Increased binding to Caco-2 cells was found for all NP formulation, with RS/PLGA NPs showing maximum binding. However, the transport of heparin was the same for the RS/PLGA NPs and the PLGA NPs and slightly higher than for the free drug. In all cases, no NP transport across the cell layer was observed. When Caco-2 cells were coated with an additional mucin layer, cell binding of RS NPs and RS/PLGA NPs was further increased. Transport across Caco-2 cells demonstrated similar tendencies to results obtained without mucin. In contrast, cationic NPs led to higher heparin transport in the presence of mucin. The mechanism of drug absorption associated with RS NPs was concluded to be independent of typical transcellular NP transport.

This work presents an oxidation-assisted approach to measurement of temperatures with carbon nanotubes that contain liquid gallium (Ga). When a Ga-filled carbon nanotube is heated in air for an appropriate length of time, an oxide marker is formed on the inner wall of the carbon nanotube due to partial oxidation of the Ga. Thus, the temperature to which the nanotube was exposed can be retrieved by progressively heating the carbon nanotube until the liquid Ga reaches the oxide marker. Compared with previous methods, this novel approach provides a simpler and, importantly, a far more reliable way to measure temperatures over a moderate temperature range at the nanometre scale.

We have found a procedure for generating novel two-dimensional (2D) nanowebs in three-dimensional (3D) fibrous mats by optimization of various processing parameters during electrospinning. The electrospun fibres act as a support for the 'fishnet-like' nanowebs comprising interlinked one-dimensional (1D) nanowires. The average diameter of the nanowires contained in typical nanowebs is about one order of magnitude less than that of conventional electrospun fibres. The formation of the nanowebs of poly(acrylic acid) (PAA) and nylon-6 is considered to be due to the electrically forced fast phase separation of the charged droplets which move at high speed between the capillary tip and the collector. The formation, morphology and area density of the nanowebs in electrospun fibrous mats are strongly affected by the applied voltage, ambient relative humidity, kinds of solvents, solution concentration and distance between the capillary tip and the collector.

Several suspensions containing different types of multi-walled carbon nanotubes (MWCNTs) with different dispersion states were prepared, including homogeneous solutions of MWCNT/polymer composites in an organic solvent. The ultraviolet–visible (UV–vis) absorption spectra from 350 to 750 nm were measured, which showed that the absorbance agreed well with Beer's law and an apparent absorption coefficient was calculated. For mono-dispersed MWCNTs, the apparent absorption coefficient was independent of the diameter and length of the MWCNT. The coefficient can be used to determine the concentration of well-dispersed MWCNTs. For poly-dispersed MWCNTs, large dense agglomerates of MWCNTs caused an obvious decrease in the apparent absorption coefficient. A simple method for characterizing the concentration and dispersion state of MWCNTs in suspension or polymer composites quantitatively by spectrophotometry was developed.

The optical properties of polymer nanospheres were tuned by in situ transformation of metal structures on their surfaces. Silver nanoparticles (NPs) deposited on the polystyrene nanospheres were transformed into metal hollows made of gold/silver alloy by a galvanic replacement reaction. The metal hollows made of gold/silver alloy were finally changed into solid gold nanoparticles by the additional treatment of chloroauric acid. Through the transformation process, the optical resonance peak of metal-coated polystyrene (PS) nanospheres was tuned in the 410 to 820 nm region. The transformation of metal nanostructures on the surface of PS nanospheres was monitored and characterized by UV–visible–near infrared (NIR) spectroscopy and transmission electron microscopy. The described protocols should be applied to prepare the metal-coated polymer nanospheres with tunable surface plasmon resonance (from 450 to 820 nm) which would be very useful for biological assays.

We describe a novel colour-tunable light-emitting diode whose operation is based on direct band-gap emission from coupled configurations of InP quantum dots and quantum wells embedded in GaP. The control of the emission colour stems from a marked difference in the current dependence of intensities of two different emission processes. At lower currents, the emission is dominated by the 720 nm luminescence from the quantum dots and appears red; at higher currents, the emission is dominated by the 550 nm quantum-well luminescence and the perceived colour is green. Thus, we are able to tune the colour of such diodes from red to green by means of drive current. A multi-colour pixel can be realized by a single diode, with rapid switching between colour states to provide a range of colour mix.

Proton implantation followed by rapid thermal annealing (RTA) has been employed for the post-growth tuning of the band gap of molecular beam epitaxy grown InAs/GaAs quantum dots (QDs). To enhance QD intermixing, point defects are created by proton implantation at different doses (5 × 10¹⁰–10¹⁴ cm⁻²) followed by rapid thermal annealing at 675 °C for 30 s. Low-temperature photoluminescence (PL) measurements have shown that the proton-implantation-induced intermixing alters both the optical transition energies and the PL full width at half maximum (FWHM). A purely proton-implantation induced band gap tuning limit of 131 meV has been achieved for an implantation dose of 5 × 10¹³ cm⁻², keeping both the QDs' character and around 46% of the initial integrated PL intensity.

Lipid bilayer membranes have been extensively utilized to examine membrane channel and pore proteins and are the subjects of study in their own right. There has been considerable recent interest in developing technologies to substitute or strengthen lipid bilayer membranes for a number of applications, including sensing or drug delivery. In particular, biomimetic amphiphilic block co-polymers have been shown to have the capacity to form membrane structures and to contain membrane proteins within them. In this work, we describe the creation of biomimetic membranes from a 5.7 nm thick tri-block co-polymer and the investigation of the effects of the polymer environment on incorporated channel proteins (α-haemolysin, OmpG, and alamethicin) with single molecule transport measurements. We found that the polymer membranes consistently have seal resistances of tens of GΩ and greater, and that the conductance of single channels is reduced by approximately 10% from that measured in diphytanoyl phosphatidylcholine lipid membranes, possibly as a result of increased cohesion of the polymer compared to lipid. The voltage gating ability and threshold voltages of voltage gated channels were also found to be very similar in the lipid and polymer environments.

Chitosan was added to PVA aqueous solutions as a thickener to improve the electrospinning process. The presence of a small amount of chitosan considerably improved the uniformity of as-spun nanofibres. This improvement is attributed to its significant effect on the solution viscosity and conductivity, with only a slight impact on the surface tension. The concentration of the PVA required to produce bead-free and uniform nanofibres was reduced with the increase in chitosan concentration. The chitosan thickener suppressed the jet break-up and facilitated the jet stretching so that fine and uniform fibres could be electrospun even from a dilute PVA solution.

We use epitaxial Ge islands on silicon-on-insulator (001) to initiate and drive the dewetting of the ultrathin (<8 nm) Si template layer. The process exposes the underlying SiO₂ layer and transforms the Ge islands into oxide-supported, electrically isolated, Ge-rich nanocrystals. We investigate the process of dewetting and demonstrate that it can be used for the controlled assembly of nanocrystals—from isolated single ones to dense arrays.

Due to the finite scanning probe microscopy (SPM) tip radius and the resulting geometric convolution between the tip and the sample surface, nano-resolution surface potential (SP) or electric force measurement (EFM) cannot be free from topographic artefacts. For conventional Kelvin probe microscopy (KPM), only the first harmonic component of the tip oscillation signal (either oscillation amplitude for amplitude-modulated AM-KPM or frequency shift for frequency-modulated FM-KPM) induced by the applied ac voltage is typically used. However, the first harmonic signal depends not only on tip–sample potential difference, but also on the capacitance gradient (AM-KPM) or the second-order gradient (FM-KPM), the main cause of topographical artefacts. Since the second-order harmonic component is proportional only to the capacitance gradient or second-order gradient, we are able to extract true potential difference signals, free of geometric artefacts, by dividing the first- and second-order harmonics. Surface potential mapping on an equipotential surface verifies that this alternative method significantly reduces the magnitude of topological artefacts. In addition, adoption of the proposed imaging method reduces the dependence of the measured potential on the tip–sample separation by more than an order of magnitude.

Green-light-emitting InGaN/GaN multiple quantum wells (MQWs) with high luminescent efficiency were grown by metalorganic chemical vapour deposition (MOCVD). The microstructure of the sample was studied by high-resolution transmission electron microscopy (HRTEM) and high-resolution x-ray diffraction, while its optical behaviour was analysed in great detail by a variety of photoluminescence methods. Two InGaN-related peaks that were clearly found in the photoluminescence (PL) spectrum are assigned to quasi-quantum dots (516 nm) and the InGaN matrix (450 nm), respectively, due to a strong phase separation observed by HRTEM. Except for the strong indium aggregation regions (511 meV of Stokes shift), slight composition fluctuations were also observed in the InGaN matrix, which were speculated from an 'S-shaped' transition and a Stokes shift of 341 meV. Stronger carrier localization and an internal quantum efficiency of the dot-related emission (21.5%), higher than the InGaN-matrix related emission (7.5%), was demonstrated. Additionally, a shorter lifetime and 'two-component' PL decay were found for the low-indium-content regions (matrix). Thus, the carrier transport process within quantum wells is suggested to drift from the low-In-content matrix to the high-In-content dots, resulting in the enhanced luminescence efficiency of the green light emission.

Arrays of vertically well-aligned ZnO nanorod–nanowall junctions have been synthesized on an undoped ZnO-coated silicon substrate by a carbothermal reduction and vapour phase transport method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the nanostructures are well-oriented with the c-axis perpendicular to the substrate. The room temperature photoluminescence (PL) spectrum of the as-prepared ZnO nanostructure reveals a dominant near-band-edge (NBE) emission peak and a weak deep level (DL) emission, which demonstrates its good optical properties. Temperature-dependent PL spectra show that both the intensity of NBE and DL emissions increased with decreasing temperature. The NBE emission at 3.27 eV is identified to originate from the radiative free exciton recombination. The possible growth mechanism of ZnO nanorod–nanowall junctions is also proposed.

Photoluminescent germanium nanocrystals were synthesized in solution using hydride reducing agents. The surface of the Ge nanocrystals was modified with allylamine to produce water-soluble photoluminescent Ge nanocrystals. When the reducing agent was added slowly, the particles were 5 nm in size with a narrow size distribution. However, when the reducing agent was injected rapidly, the Ge nanocrystals formed large (50 nm) triangles that were too large to exhibit the effects of quantum confinement and thus did not fluoresce. Characterization of the Ge nanocrystals is performed using transmission electron microscopy, selected-area electron diffraction, energy-dispersive x-ray spectroscopy and optical spectroscopy.

Hexagonal close-packed (hcp) Ni particles were prepared in the nanosize range (13–25 nm) by reduction of Ni(NO₃)₂ in polyethylene glycol (PEG) with various molecular weights. The reaction occurred in the presence of an equimolecular mixture of oleic acid and oleyl amine, which plays the role of a stabilizer and gives solubility to the nanoparticles in non-polar solvents. The crystal structure of Ni particles seems to be controlled by the molecular weight of the PEG molecule and subsequently the reaction temperature. The magnetic properties of the hcp Ni nanoparticles are also studied.

Spherical amorphous Alq₃ nanoparticles of various diameters could be obtained under a cold trap by adjusting the He pressure in a vapour condensation system. The growth of nanoparticles is related to the collisions between the sublimed Alq₃ molecules and gaseous He atoms. Both the diameter and size distribution of nanoparticles decrease with a decreased He pressure. Smaller nanoparticles have no spectral blue shift but lead to stronger photoluminescence because of the increased optical absorption that results from the larger specific surface area. With a larger surface-to-volume ratio, smaller nanoparticles exhibit higher surface energy and require less enthalpy for phase transition, resulting in decreased temperatures for α–δ phase and melting transitions.

A fast and cheap nanofabrication process for a titania (TiO₂) nanostructured nanowire array with a lateral section ranging from 90 to 180 nm and 1.4 mm in length is presented. As an alternative to typical pattern transfer techniques for submicron fabrication, this work focused on a standard 365 nm ultraviolet (UV) photolithographic process that is able to fabricate sol–gel nanostructured titania nanowires from a solid thin film onto a silicon oxide mesa. Useful process parameters like anisotropy and bias have been calculated. Finally, in order to carry out electrical characterization, the TiO₂ nanowire-based array was electrically contacted by platinum electrodes and tested with EtOH pulses to validate enhanced gas sensor device performance and to verify electrical conductivity of these nanostructures.

A method involving dry deposition plus wet chemical etching was devised to fabricate silicon nanowire (SiNW) arrays and to study silver catalysis during fabrication. Through investigation of the track of catalyst particles, it was shown that Ag really catalyses the etching of silicon underneath Ag, which clarifies doubts about the formation of SiNW arrays during wet chemical etching. The intrinsic properties of Ag and the network structure of Ag clusters during etching facilitate the etching process. The etching product, i.e. vertical SiNW arrays containing an Ag nanocluster mesh, could be considered as a prototype secondary composite nanostructured catalyst with promise for future applications.

The synthesis of CdS_xSe_1−x (0<x<1) ternary alloy nanowires on an Au-coated Si substrate by a pulsed laser ablation process in a hot-wall-type chamber was studied. The diameter and length of the synthesized alloyed nanowires were 50–100 nm and several tens of micrometres, respectively. X-ray diffraction analysis showed that the resulting nanowires have a hexagonal wurtzite crystalline structure. The diffraction peaks were shifted toward the higher value of 2θ as the value of x increases, which indicates that the lattice constant and unit cell volume scales linearly with the composition. Based on the photoluminescence analysis, we found that the direct band gap of the nanowires also changes linearly with the composition, which means that the energy band gap could be systematically modulated in the spectral region from 1.74 to 2.45 eV.

The technique of electron-beam-induced deposition (EBID), when performed with organic precursors, typically results in relatively low metal content due to the partial decomposition of the organic precursor, leaving carbon-rich remnants in the deposition. Here we describe a method applied to noble-metal structures deposited using EBID, consisting of a post-treatment step of heating in a reactive atmosphere of oxygen, whereby the amount of carbon in the structure is strongly reduced. As a result, we have been able to increase the purity of platinum deposits from 15 at.% to nearly 70 at.%, and gold similarly from 8 at.% to nearly 60 at.%. The resistivity of these structures has also been improved by up to four orders of magnitude, to achieve (1.4 ± 0.2) × 10⁴ µΩ cm in the case of platinum.

We report on a novel, in situ approach toward connecting and electrically contacting vertically aligned nanowire arrays using conductive nanoparticles. The utility of the approach is demonstrated by development of a gas sensing device employing this nano-architecture. Well-aligned, single-crystalline zinc oxide nanowires were grown through a direct thermal evaporation process at 550 °C on gold catalyst layers. Electrical contact to the top of the nanowire array was established by creating a contiguous nanoparticle film through electrostatic attachment of conductive gold nanoparticles exclusively onto the tips of nanowires. A gas sensing device was constructed using such an arrangement and the nanowire assembly was found to be sensitive to both reducing (methanol) and oxidizing (nitrous oxides) gases. This assembly approach is amenable to any nanowire array for which a top contact electrode is needed.

Films of octadecyl-capped Si nanoparticles (NPs) (diameter, 3.4 ± 0.7 nm) prepared by drop-coating on indium tin oxide (ITO) showed electrogenerated chemiluminescence (ECL) for both cathodic and anodic potential sweeps in KOH solutions containing peroxydisulfate. The redox potentials of the Si NPs can be estimated as approximately −0.9 and +0.95 V (versus Ag|AgCl) based on the anodic potential for the onset of ECL minus the ECL peak energy. The ECL exhibits a relatively broad spectrum (FWHM = 160 nm) with a peak wavelength of ∼670 nm (1.85 eV), similar to the photoluminescence spectra. In electrochemical studies in KOH solution in the absence of peroxydisulfate, an anodic current peak appears at about −1 V (versus Ag|AgCl) following a scan to negative potentials. A similar peak has been observed during the etching of a bulk single crystal Si electrode in alkaline aqueous solution. Unpassivated surface sites of Si NPs seem to be etched at potentials negative of the anodic oxidation peak.

The field enhancement factor of a carbon nanotube (CNT) placed in a cluster of CNTs is smaller than an isolated CNT because the electric field on one tube is screened by neighbouring tubes. This screening depends on the length of the CNTs and the spacing between them. We have derived an expression to compute the field enhancement factor of CNTs under any positional distribution of CNTs using a model of a floating sphere between parallel anode and cathode plates. Using this expression we can compute the field enhancement factor of a CNT in a cluster (non-uniformly distributed CNTs). This expression is used to compute the field enhancement factor of a CNT in an array (uniformly distributed CNTs). Comparison has been shown with experimental results and existing models.

We report the fabrication of ultrafine structures consisting of regular arrays of nanoemitters through the self-assembly of luminescent nanoparticles on a silicon wafer. Nanoparticles of yttrium aluminium garnet (YAG) doped with Eu³⁺ ions were synthesized by a sonochemical technique. These particles, suspended in ethanol, are introduced onto a pre-patterned silicon wafer, covered with a thin oxide layer. On annealing the sample in an ultrahigh-vacuum chamber, the nanoparticles self-assemble along the pattern. We demonstrate this 'chemical lithography' by assembling the nanoparticles along a variety of patterns. We believe that such self-organized nanopatterning of functional structures is important for the realization of nanodevices.

This paper describes a polyethylene glycol (PEG)-assisted approach to the large-scale hollow organization of bismuth sulfide nanorods, formed by a hydrothermal reaction between Bi-PEG complexes and thiourea. Field-emission scanning electron microscopy studies indicate that these microspheric assemblies have a hollow central cavity. The constituent Bi₂S₃ nanorods possess a diameter of tens of nanometres with lengths of ∼1.5 µm. High-resolution transmission electron microscopy and selective-area electron diffraction studies reveal that each Bi₂S₃ nanorod is a single crystal along the direction. The mechanism for the hollow organization is proposed. The bismuth species added to the PEG solution convert the PEG polymer coils to Bi(III)-PEG globules and the initial transparent solution of Bi(III)-PEG globules turns to pale yellow Bi^III(Tu)_x/PEG when thiourea is added. The decomposition of Bi^III(Tu)_x/PEG and the deposition of Bi₂S₃ on the flexible structures of the globules, which are the templates for the growth of Bi₂S₃ nanorods, results in the observed structure of interest. The Bi₂S₃ nanorods grow via the very tiny units of bismuth sulfide attaching to the template during the hydrothermal process.

CdS nanoparticles were grown using CdSO₄ and Na₂S₂O₃ as the precursors and thioglycerol (TG) as the capping agent. TG was shown to exhibit a catalytic role in the reaction and also acted as a capping agent. It was demonstrated that size growth is linearly related to the temperature of the reaction, i.e. the sizes can be controllably adjusted by temperature. The crystalline phase of the nanocrystals was also dependent on the temperature of growth: higher temperature favours the cubic phase. The pH also plays an important role in nanoparticle growth, as lower pH leads to a higher release rate of sulfur species. At pH as high as 10, the growth rate remains slow even at boiling temperature. This provides a way to controllably grow nanoparticles at high temperatures and/or control the nucleation growth processes.

The carbon nanotube (CNT) is a promising reinforcement material for manufacturing metal-or ceramic-based composites. However, CNTs are prone to interact with the matrix in a reactive atmosphere that often alters the structure and properties of CNTs and depresses their reinforcing effect. To overcome this problem, a protective silicon layer has been deposited on multi-walled carbon nanotubes (MWNTs) using cycled vacuum-feeding chemical vapour deposition by the in situ decomposition of gaseous SiH₄. The silicon coating is well covered and continuous with a cubic-phase structure. It effectively improves the thermal stability of MWNTs by acting as a protective film, which inhibits and delays the onset of oxidation. Thermogravimetric analysis (TGA) reveals that the oxidation of Si-coated MWNTs occurs at a temperature of 676.3 °C, which is 105.1 °C higher than that of uncoated MWNTs, and the weight loss decreases with the increasing thickness of silicon coating.

Suspended single-walled carbon nanotubes (SWNTs) have been synthesized on Si inverse-opal structures by laser-assisted chemical vapour deposition (LCVD). A CW CO₂ laser at 10.6 µm was used to directly irradiate the substrates during the LCVD process. At a laser power density of 14.3 MW m⁻², suspended SWNT networks were found predominantly rooted at the sharp edges in the Si inverse-opal structures. Raman spectroscopy indicated that the SWNT networks were composed of high-quality defect-free SWNTs with an average diameter of 1.3 nm. At a lower laser power density (6.4 MW m⁻²), multi-walled carbon nanotubes (MWNTs) were grown on the entire surface of the substrates. The preference for the synthesis of SWNTs or MWNTs was attributed to the difference in the catalyst sizes as well as the growth temperature in the LCVD process.

High yields of Mo/MoS₂ inorganic fullerene-like and actinomorphic nanospheres with a core–shell structure have been successfully synthesized by the one-step reaction of sulfur and molybdenum nanospheres under a hydrogen atmosphere, in which the Mo nanospheres were prepared by the wire electrical explosion method. The shell thickness of MoS₂ is about 4–10 nm and exhibit an expansion of about 4.2–1% along the c-axis. Observed from high-resolution transmission electron microscopy images, unreacted molybdenum lying between the (002) layers of MoS₂ contributes to the larger expansion besides the strain in the bent layer and the crystal defects; the preferred growth orientations for MoS₂ on the surface of Mo have two directions under different annealing temperatures: parallel to the (110) plane of Mo, presenting an actinomorphic phase, and perpendicular or having certain angles to the (110) plane, showing a fullerene-like phase. The actinomorphic Mo/MoS₂ can be used for catalysis and intercalation. The fullerene-like phase can be applied as a solid lubricant to enhance the structural rigidity and load bearing capacity of hollow MoS₂. In addition, the core–shell nanospheres exhibit a little higher onset temperature and a narrow temperature range against oxidation with a weaker exothermic peak than conventional 2H-MoS₂.

The in situ growth of a deposit in electron-beam-induced deposition (EBID) was studied by dynamic Monte Carlo simulation, showing first the preferential growth of deposit along the incident direction of the electron beam. The effects of electron energy, probe size, substrate thickness, and deposit (or substrate) composition on EBID were investigated and discussed, considering the electron scattering of not only secondary electrons but also primary and backscattered electrons in solids. By including the depositions at not only the top but also the bottom surfaces of the substrate, the growth model of the deposit in EBID was modified. Concerning the resolution of EBID, a small lateral size can be achieved on the deposit (or substrate) containing light atoms using a high-energy electron beam with a fine probe size.

The nanometre-scale oxidation characteristics of a p-GaAs(100) surface are investigated by atomic force microscope (AFM) electrochemical nanolithography with a multiwalled carbon nanotube (MWCNT) probe. The electrochemical parameters, such as anodizing voltages, scanning rate and modulated voltages, and how they affect the creation and growth of the oxide nanostructures are explored. The present results reveal that the initial growth rate (∼600 nm s⁻¹ for 10 V) decreases rapidly as the electric field strength is decreased. The oxide practically ceases to grow as the electric field is reduced to the order of ∼1.2 × 10⁷ V cm⁻¹. Also, the oxide growth rate depends not only on the electric field strength but also on the applied anodizing voltage. The present results show that the height of the oxide structures can be significantly improved at an applied anodizing voltage of 10 V by using a CNT probe. In addition, Auger electron spectroscopy (AES) measurements performed in the present work confirm that modified structures replace the form of anodizing p-GaAs(100).

We carry out systematic molecular mechanics (MM) analyses to study the effect of the displacement increment on the critical buckling strain of single-walled carbon nanotubes (SWCNTs) under axial compression. The SWCNT geometric parameters, such as the tube length, diameter, and chirality, are varied in the numerical studies. The results show that the critical buckling strain of the SWCNTs deduced from the atomistic analyses is highly sensitive to the displacement increment used in the numerical simulation, and such an effect is more obvious for tubes with smaller diameters. Therefore, a reasonable compressive displacement increment should be selected in the atomistic simulations in order to obtain the intrinsic values of the critical buckling strain, which is suggested in this paper. The studies in this paper may be used to explain the contradicting results of the critical compressive buckling strains computed by other MM analyses in the literature.

The hydrogen desorption properties of commercial nanocrystalline magnesium hydride (Tego Magnan^® from Degussa–Goldschmidt) processed by controlled mechanical milling (CMM) are investigated. A profound effect of the powder particle size on the hydrogen desorption characteristics has been observed. The onset (T_ON) and peak hydrogen desorption temperatures measured by differential scanning calorimetry (DSC) decrease initially slowly with decreasing mean particle size of hydride, and when the particle size reaches a certain critical threshold value, the desorption temperatures start decreasing more rapidly with further decrease of particle size. The total drop of desorption temperature from its initial value for the as-received MgH₂ to the value attained for the milled MgH₂ having a particle size of ∼500–600 nm is within the range 40–60 °C. The metastable γ-MgH₂ hydride coexists with the stable nanocrystalline β-MgH₂ in the microstructure of the MgH₂ powders ball milled for 10 h and longer. Quantitative evidence shows that two factors, namely the refined powder particle size and the γ-MgH₂ phase residing within the powder particles, acting additively, are responsible for a substantial reduction of the hydrogen desorption temperature of MgH₂ hydride.

We report on mid-infrared photoconductivity of Be-doped p-type lateral conduction quantum dot infrared photodetectors and electronic states of the valence band in InAs self-assembled quantum dots. We have observed a broad photocurrent signal in a photon energy range of 100–400 meV (λ∼3–10 µm) due to bound-to-continuum intersublevel absorption of normal incidence radiation in the valence band of InAs self-assembled quantum dots, showing a peak sensitivity around hν = 190 meV (λ∼6.5 µm). The observed responsivity was as high as 16 A W⁻¹ at T = 10 K. Furthermore, the activation energy from ground state in the quantum dot to the valence band of GaAs was estimated to be around 100 meV.

The mechanical properties of TiO₂-derived nanoribbons were investigated by using a three-point bending method. Thin nanoribbons (cross-section dimension ∼30 nm) have an average Young's modulus of 260 ± 55 GPa. For thicker nanoribbons, which are composed of several thinner nanostrips, the bending modulus rapidly decreases with increasing cross-section. In analogy with carbon nanotube ropes we argue that shear deformations become important and the shear modulus is G = 0.07–0.4 GPa. The present results together with our previous work suggest that TiO₂-derived nanoribbons and nanotubes may undertake a dual function in polymer composites: they could reinforce the polymer matrix while at the same time they could provide a large active surface area.

Silicon micro cantilevers are used as transducers for a wide range of physical, chemical and biochemical stimuli, where they exhibit exquisite sensitivity (10⁻¹⁸ g, 10⁻¹⁵ J, 10⁻⁹ M, etc) over a wide range of temperatures (100 mK–1300 K). This is accomplished by inducing static bending in the cantilever structure or by changing the cantilever's resonant behaviour, both easily measurable responses. There is increasing interest in using higher-order resonant modes to achieve extra sensitivity; however, this raises the question of exactly which modes are excited in the cantilever. Using strobed interferometric microscopy we are able to probe the dynamic behaviour of individual (100 × 500 × 1 µm³) cantilevers in an eight cantilever array over frequencies from 0 to 1 MHz. We present data that enable spatial visualization of 16 cantilever modes with nanometre-scale amplitudes; combined with finite element analysis calculations we directly assign mode indices. We discuss the reversal of specific modes between experiment and theory, the uniformity of individual cantilevers in the array and the clear relationship between boundary conditions and resonant behaviour. Our conclusion is that the assignment of a resonant frequency spectrum is fairly complex and does not necessarily follow simple intuition.

The mechanical and structural properties of a surface play an important role in determining the morphology of attached cells, and ultimately their cellular functions. As such, mechanical and structural integrity are important design parameters for a tissue scaffold. Electrospun fibrous meshes are widely used in tissue engineering. When in contact with electrospun scaffolds, cells see the individual micro- or nanofibres as their immediate microenvironment. In this study, tensile testing of single electrospun nanofibres composed of poly(ε-caprolactone) (PCL), and its copolymer, poly(caprolactone-co-ethyl ethylene phosphate) (PCLEEP), revealed a size effect in the Young's modulus, E, and tensile strength, σ_T. Both strength and stiffness increase as the fibre diameter decreases from bulk (∼5 µm) into the nanometre region (200–300 nm). In particular, E and σ_T of individual PCL nanofibres were at least two-fold and an order of magnitude higher than that of PCL film, respectively. PCL films were observed to have more pronounced crystallographic texture than the nanofibres; however no difference in crystalline fraction, perfection, or texture was detected among the various fibres. When drugs were encapsulated into single PCLEEP fibres, mechanical properties were enhanced with 1–20 wt% of loaded retinoic acid, but weakened by 10–20 wt% of encapsulated bovine serum albumin. This understanding of the effect of size and drug and protein encapsulation on the mechanical properties of electrospun fibres may help in the optimization of tissue scaffold design that combines biochemical and biomechanical cues for tissue regeneration.

We synthesized CdSe/CdS/ZnS core/multi-shell nanocrystals through a single coating step by using different growth rates of CdS and ZnS crystalline layers on CdSe cores. The resulting nanocrystals exhibited a controlled redshift from the initial photoluminescent (PL) emission of CdSe cores with much improved quantum yield (QY above 70%).

Muscovite mica is commonly used to immobilize DNA molecules onto a flat surface. This method, however, requires either the use of divalent cations in the buffer solution or the chemical modification of the surface. Here we show that DNA molecules have different binding affinities and assume different conformations when adsorbed to different layered minerals. In particular, the effect of biotite, muscovite, talc, brucite and chlorite upon DNA binding is investigated. Using atomic force microscopy it is possible to quantify the amount of DNA deposited onto a flat surface and it is experimentally confirmed that biotite, talc and brucite have a much higher affinity than muscovite (7-, 20- and 25-fold more volume of DNA deposited, respectively). The deposition of DNA onto chlorite presents areas (brucite-like) with high DNA coverage and areas (mica-like) where DNA molecules are absent. We regularly observed isolated DNA molecules that became stretched across these regions of low affinity. The stretching is not induced by the deposition procedure but is driven by the surface potential gradient between brucite-like and mica-like regions in chlorite. The active stretching of DNA on chlorite is a clear indication of the technological potential carried by these materials when used as substrates for biomolecules.

We report on the fabrication process of SiO₂ templates with periodic sub-100 nm patterns by electron-beam (e-beam) lithography followed by reactive ion etching. One-dimensional and two-dimensional periodic patterns were defined in 350 nm polymethylmethacrylate resist by e-beam lithography, and then transferred into 100 nm SiO₂ layers which were coated on GaAs or GaN/sapphire substrate. Patterns including line arrays and square/hexagonal hole arrays were obtained in the SiO₂ layers with sizes ranging from 100 nm to 52 nm in width or diameter. A pattern size deviation of less than 4% in a hole array of 100 µm by 100 µm was achieved. The patterned SiO₂ layers can serve as templates for the growth of periodic III–V semiconductor nanostructures. In this work, periodic InGaN nanowires and nanodots with high optical quality have been fabricated successfully by using the SiO₂ templates on GaN/sapphire.

The structural features and thermal conductivity of silicon nanoparticles of diameter 2–12 nm are studied in a series of molecular dynamics simulations based on the Stilling–Weber (SW) potential model. The results show that the cohesive energy of the particles increases monotonically with an increasing particle size and is independent of the temperature. It is found that particles with a diameter of 2 nm have a heavily reconstructed geometry which generates lattice imperfections. The thermal conductivity of the nanoscale silicon particles increases linearly with their diameter and is two orders of magnitude lower than that of bulk silicon. The low thermal conductivity of the smallest nanoparticles is thought to be the result of particle boundary and lattice imperfections produced during fabrication, which reduce the phonon mean free path (MFP). Finally, it is found that the influence of the temperature on the thermal conductivity decreases significantly as the temperature increases. Again, this is thought to be the result of a reduced phonon MFP at elevated temperatures.

A highly ordered hexagonally close-packed nanochannels array was prepared using the self-ordering phenomena during a two-step anodization process of a high purity aluminium foil. The anodized aluminium oxide, with pore diameters of about 280 nm and interpore distances of about 450 nm was prepared as a suspended membrane of about 15 µm thickness on the aluminium frame to which it belongs. The Al₂O₃ capillaries were bombarded with 3 keV Ne⁶⁺ ions. The first results unambiguously show the existence of ion guiding observed at 5° and 7.5° tilt angles of the capillaries compared to the beam direction. To the best of our knowledge, such ion guiding effects of slow ions through hexagonally ordered nanochannels in alumina has not been reported previously.

This study uses molecular dynamics simulations to investigate the intrinsic thermal vibrations of a single-walled carbon nanotube (SWNT) modelled as a clamped cantilever. Using an elastic model defined in terms of the tube length, the tube radius and the tube temperature, the standard deviation of the vibrational amplitude of the tube's free end is calculated and the Young's modulus of the SWNT evaluated. The numerical results reveal that the value of the Young's modulus is independent of the tube length, but decreases with increasing tube radius. At large tube radii, the Young's modulus value approaches the in-plane modulus of graphene, which can be regarded as an SWNT of infinitely large radius. The results also indicate that the Young's modulus is insensitive to changes in the tube temperature at temperatures of less than approximately 1100 K, but decreases significantly at higher temperatures.

Vertical single-walled and double-walled carbon nanotube (SWNT and DWNT) arrays have been grown using a catalyst embedded within the pore walls of a porous anodic alumina (PAA) template. The initial film structure consisted of a SiO_x adhesion layer, a Ti layer, a bottom Al layer, a Fe layer, and a top Al layer deposited on a Si wafer. The Al and Fe layers were subsequently anodized to create a vertically oriented pore structure through the film stack. CNTs were synthesized from the catalyst layer by plasma-enhanced chemical vapour deposition (PECVD). The resulting structure is expected to form the basis for development of vertically oriented CNT-based electronics and sensors.

The optical properties of indium nitride nanorods grown by chemical-beam epitaxy are investigated by photoluminescence (PL) and Raman spectroscopy. The PL peaks show a blue shift from 0.69 to 0.79 eV, which is associated with a decrease in the size of the nanorods from 40 to 5 nm. Judging from the Raman spectra and transmission electron diffraction of these nanorods, it can be concluded that the quantum size effect is the most likely factor causing the PL shift, rather than the strain or Moss–Burstein effects.

Silver nanowires with adjustable diameters ranging from 20 to 500 nm have been synthesized by introducing certain control agents into the conventional polyol process. These control agents can be classified into three types: inorganic anions, metal cations, and molecules. The as-synthesized nanowires also exhibit size dependent UV–vis absorption spectra, which are meaningful to the fabrication of nanodevices. It is presumed that the control agents could influence the size of the initial nucleus and therefore the diameters of the final nanowires through forming silver salt colloids or varying the rate of silver reduction. This synthetical strategy may also provide a versatile route to prepare nanomaterials with well-defined diameters.

CuO nanocrystals with different shapes, i.e. irregular nanoparticles, nanobelts and nanoplatelets, have been synthesized by controlling a few critical synthesis parameters to explore their catalytic properties. It was found that the rate of CO oxidation on the nanoplatelets is over six times higher than that on the nanoparticles and about three times higher than that on the nanobelts at 110 °C. Based on combined characterizations, such as BET, XRD, TEM, HRTEM and CO temperature-programmed reduction, the relationship between the catalytic reactivity and the shape as well as the predominantly exposed crystal planes of the CuO nanocrystals has been discussed.

We have developed a spherical aberration corrected transmission electron microscopy (C_s-corrected TEM) technique that allows us to obtain clearer images in real space than ever before. We applied this technique to titanium oxide, in which light elements such as oxygen are difficult to observe using TEM because of its small cross section and electronic damage. In the present study, we successfully observed oxygen atoms in rutile TiO₂. In addition, this direct observation of oxygen atoms enabled us to study the Magnéli structure (Ti_nO_2n−1), which is caused by oxygen vacancies. These vacancies caused an atomic relaxation of the titanium and oxygen atoms. The relaxed atoms formed a characteristic shear structure of rutile titanium dioxide phase. This shear structure of the Magnéli structure (Ti_nO_2n−1) was visualized with a spatial resolution of 0.119 nm. At the same time, the selected area diffraction (SAD) pattern of the defect structure was obtained. Additional spots were shown inside the rutile [110] spot. We made structural models of the shear structure and simulated the diffraction pattern and images using a multi-slice simulation. Additional spots in the simulated diffraction patterns accurately reconstructed the experimental data. We also considered the possibility of the real-space analysis of local structures using spherical aberration corrected transmission electron microscopy.

We have undertaken a systematic investigation of the influence of ethanol on the shape of conical pores produced by the track-etch technique in poly(ethylene terephthalate) films. We have found that the cone angle of the conical nanopore generated is dependent on the amount of ethanol present in an alkaline etching solution. By varying the percentage of ethanol in the etch solution, precise control over the geometry of the conical nanopore and nanomaterials templated within these pores can be attained. We prove this by plating gold nanocones within the various conical nanopores prepared, dissolving the membrane to liberate the nanocones, and imaging the nanocones using scanning electron microscopy. The results of these investigations are reported here.

We report a chemical route to synthesize oriented arrays of conducting polyaniline (PANI) nanotubes (60–150 nm in diameter and a few micrometres in length) by hydrogen-bonding directionality in the presence of a crown ether derivative (CE-SO₃K) and ammonium persulfate (APS) in HCl solution. The morphology of the oriented PANI nanotubes was confirmed by SEM and TEM images. The effects of reaction conditions on the morphology of the resultant PANI nanostructures were studied. The chemical and electronic structures of the PANI nanotubes were also studied by FTIR and UV–vis spectrometry, respectively.

Single electron charging and single electron tunnelling effects were observed in silicon rich oxide (SRO). The devices used in this study have an Al/SRO/Si metal–oxide–semiconductor-like structure, where the SRO layer was deposited using low pressure chemical vapour deposition. Two types of Si nanodots (NDs), interface NDs and bulk NDs, were identified by transmission electron microscopy measurements. Under electric field, charges from the Si substrate are transferred into the interface NDs that locate at the interface, and each interface ND traps only one carrier. As the voltage increases, conduction paths between the Al electrode and the silicon substrate are formed, and the conduction of electrons is via sequential tunnelling through the bulk NDs. Due to the Coulomb blockade effect, only one electron tunnels on each nanodot at a specific electric field. The transport of the electrons through the Si nanodots is due to the Poole–Frenkel mechanism in the voltage regime studied.

A facile and versatile method is reported to fabricate the interwoven tubular hierarchy of SnO₂ films using a biotemplate eggshell membrane (ESM) combined sol–gel approach. In order to promote the crystallization of SnO₂ films, calcination is necessary and can adjust the size of the building units in the range 2.8–26 nm. Under the direction of ESM biomacromolecules, SnO₂ nanocrystallites come into being and assemble into nanotubes, and further pattern porous hierarchical meshworks to faithfully retain the morphology of natural ESM. The sensor performance of as-prepared biomorphic SnO₂ was measured for ethanol, liquefied petroleum gas (LPG), H₂S, and gasoline. It is found that the SnO₂ hierarchical films obtained have a good selectivity for LPG with a working temperature above 300 °C while for ethanol below 270 °C.

The evolution between lattice-matched GaAs/Al_0.3Ga_0.7As single and double ring-like nanostructures is studied, with an emphasis on the construction and destruction of the observed outer ring. Using droplet epitaxy, this was achieved by directly controlling the Ga surface diffusion on GaAs(100). Double ring-like nanostructures were observed at relatively low temperatures under a fixed As₄ flux (beam equivalent pressure (BEP) of 6.4 µTorr) and at a fixed temperature under a high As₄ flux. The construction of the outer ring can be controlled through surface diffusion by varying the substrate temperature or the As₄ flux. Single ring-like nanostructures were realized both at relatively high temperatures under a fixed As₄ flux, and at low temperatures under a relatively low As₄ flux.

A rapid, easy-to-implement, and potentially large-scale production method for fabricating high-aspect-ratio columnar-like nanostructures on poly(dimethylsiloxane) (PDMS) is demonstrated. Plasma treatment of PDMS under appropriate conditions in SF₆ gas, followed by plasma-induced fluorocarbon film deposition, results in PDMS surfaces of fully controlled wetting properties, geometrical characteristics leading to robust superhydrophobic surfaces, and transparency. Potential applications to microfluidic devices are outlined.

Hierarchical wurtzite ZnS architectures assembled from nanosheets and nanorods, such as branched flowers and fluffy solid and hollow spheres, have been synthesized by a facile, template-free, low-temperature solution route. The growth of wurtzite ZnS nanostructures at temperatures as low as 4 °C without any organic additives has been realized by the slow reaction between Zn(NH₃)₄²⁺ and thioacetamide in aqueous (NH₄)₂SO₄–NH₄OH solutions. Branched ZnS flowers made of ultrathin nanosheets ∼6–10 nm in thickness were produced at 4 °C, whereas fluffy ZnS spheres consisting of radially oriented nanorods were fabricated at 60 °C. Prolonged ageing of the fluffy spheres at 60 °C resulted in the formation of unique fluffy hollow ZnS spheres through a spontaneous hollowing process based on Ostwald ripening.

Single-crystalline α-Si₃N₄ nanowires are controlled to grow perpendicular to the wet-etched trenches in the SiO_0.94 film on the plane of the Si substrate without metal catalysis. A detailed characterization is carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photoluminescence at 600 nm from α-Si₃N₄ nanowires is attributed to the recombination at the defect state formed by the Si dangling bond . The growth mechanism is considered to be related to the catalysis and nitridation of SiO nanoclusters preferably re-deposited around the inner corner of the trenches, as well as faster Si diffusion along the slanting side walls of the trenches. This simple direction-controlled growth method is compatible with the CMOS process, and could facilitate the fabrication of α-Si₃N₄ nanoelectronic or nanophotonic devices on the Si platform.

The modification of inorganic polymeric oxides at the surface of carbon nanotubes is of paramount importance for developing new sensors. In this study, molybdenum oxide (MoO_x) film was electrodeposited on the surface of multi-walled carbon nanotubes (MWNTs) by cycling the potential between +0.20 and −0.80 V (versus 3 M KCl–Ag|AgCl) in Na₂MoO₄ solution. The MoO_x-modified nanotube (MoO_x/MWNT) electrode displays well-defined redox transitions in 5 mM H₂SO₄ or in phosphate buffer solution (PBS), which can be attributed to the reductive formation and the re-oxidation of hydrogen molybdenum oxides. X-ray photoelectron spectra (XPS) showed that the deposited MoO_x films are mainly Mo⁶⁺ complexes. Both MWNT and MoO_x/MWNT electrodes have ideal reversibility in 5 mM K₃[Fe(CN)₆] in 1 M KCl as supporting electrolytes at all sweep rates (0.02–1.00 V s⁻¹) by cyclic voltammetry. The negatively charged surface of MoO_x/MWNTs can further attract molecular cations such as Ru(NH₃)₆³⁺. The MoO_x/MWNT electrode exhibited electrocatalytic ability towards the reduction of bromate due to high surface area and the fast electron transfer rate of nanotubes. Thus, electrochemical modification of inorganic polymeric oxides on the carbon nanotube provides a simple method for the preparation of novel sensors.