Table of contents

Detailed, single-molecule AFM mapping can further structural studies of polymeric biomolecules by pinpointing discrete changes in subunits or subunit concatenation. This study explored the binding of purified (ocular) mucins, polymers composed of genetically identical subunits, to controlled surfaces. This process was followed in situ, in real time, as were the effects of the disulfide bond reducing agent dithiothreitol (DTT), a reagent routinely used to depolymerize mucins. The addition of this reagent, while mucins were bound to gold surfaces by thiol-type binding, suggested a way of assessing the strength and extent of this gold–molecule bond formation relative to other forms of mucin–substrate interactions. Real-time AFM has allowed us to visualize the cleavage of in-chain disulfide bonds in a single mucin molecule, and subsequent removal from the substrate of mucin subunits between disulfide sites. In contrast, mucins that were covalently bound via amine groups to a self-assembled succinimide monolayer were not observed to move from the point of their initial attachment to the substrate and the addition of dithiothreitol was not followed by the loss of any sections of molecules from the substrate, emphasizing the different immobilization bond types. This demonstration of the ability to follow the structural changes to a single molecule as a result of a series of chemical processes points to new approaches to single-molecule mapping, and localization of specific chemical moieties.

High-quality single-crystalline GaP nanowires were grown by a simple vapour deposition method and their electrical and opto-electric transport properties were studied. Structural studies showed that the GaP nanowires consisted of a core–shell structure with a single-crystalline GaP core and an outer gallium oxide (GaO_x) layer of thickness  nm. The individual GaP nanowires exhibited n-type field effects with an on/off ratio as high as 10⁵ and their carrier mobilities are in the range of about 10–22 cm² V⁻¹ s⁻¹ at room temperature. When the devices were exposed to an ultraviolet (UV) light source, the current in the nanowires increased abruptly to more than 10³ times, and this was possibly due to carrier generation in the nanowires and de-adsorption of adsorbed O₂⁻ ions on the GaO_x surface shell. The nanowires also showed good reversible switching actions between the high- and low-resistance states.

The self-assembled growth of ordered ZnO nanowires on GaN/Si layers has been observed at the low temperature of 500 °C through Zn evaporation and oxidation. The nanowires have a nearly uniform diameter of 40 nm and length of  nm. No metal catalyst was used. Interestingly, the nanowires grow on a wetting film of an interconnected vortex-like structure. An empirical model is proposed to explain the growth process. Spatially resolved cathodoluminescence (CL) measurements show a sharp and intense emission (I₈ line) from the nanowires, while weak and redshifted luminescence from the wetting layer. The CL indicates the existence of tensile stress in the wetting layer while the nanowires are fully relaxed.

Process engineering design relies on a host of mechanical devices that enable transport phenomena to take place under controlled conditions. These devices include pipes, valves, pumps, chemical reactors, heat exchangers, packed columns, etc. Mass, energy, and momentum transfer will also be essential phenomena in nanoprocess engineering, particularly at the interface between micro- and nanodevices. Control valves are one of the most fundamental components. In this paper we explore the design of a silicon cantilever valve for fluid transport control at the molecular level (34.5–70 nm in length). We utilize design elements that can be synthesized with existing or emerging chemical and solid state fabrication methods. Thus, the valve is constructed with functionalized silicon surfaces, single-wall carbon nanotubes, and organic monolayers. While molecular mechanics design limitations were overcome with help from classical engineering approximations, nonlinear effects, such as nanotube crimping (for an in-line valve design), are accounted for through full-physics atomistic simulations. Optimal design geometries and operating deflection ranges have been estimated for a device containing over 75 000 atoms.

Nanomechanical properties of single-walled carbon nanotube (SWNT) reinforced epoxy composites with varying weight percentage (0, 1, 3, and 5 wt%) of nanotubes were measured by nanoindentation and nanoscratch techniques. Hardness and elastic modulus were measured using a nanoindenter. Scratch resistance and scratch damage were studied using the AFM tip sliding against the SWNT reinforced sample surfaces. Nanoindentation/nanoscratch deformation and fracture behaviour was studied by in situ imaging of the indentation impressions/scratch tracks. Viscoelastic properties of the nanocomposites were measured using nanoindentation dynamic mechanical analysis tests. The reinforcing mechanisms are discussed with reference to the nanotube dispersion, interfacial bonding, and load transfer in the SWNT reinforced polymer composites.

Rod-shaped and wire-shaped SnO₂ nanowhiskers were synthesized by thermal evaporating of tin powders at 900 °C. Three Raman peaks (474, 632, 774 cm⁻¹) showed the typical feature of the rutile phase of as-synthesized SnO₂ nanowhiskers, which was consistent with the result of x-ray diffraction. A relatively low turn-on field of 1.37 V µm⁻¹ at a current density of 0.1 µA cm⁻² was obtained. The dependence of emission current density on the electric field followed a Fowler–Nordheim relationship. Our results indicated that SnO₂ nanowhiskers had an interesting FE property as a wide band gap semiconductor.

CuO nanodendrites have been synthesized by a simple and novel hydrothermal method. Their morphology, structure, and composition have been also characterized. The results show that an as-prepared nanodendrite is composed of a main branch-like nanorod near upon a micrometre in length and about 100 nm in diameter and the sub-branch nanorods several hundred nanometres in length and 20–60 nm in diameter. The dendrite-like CuO nanostructures are of monoclinic phase and single crystalline in nature. The investigation of the hydrothermal process assisted by different quantities of ethylene glycol (EG) indicates that EG plays a critical role in the formation of dendrite-like CuO nanostructures. A possible mechanism for the formation of such CuO nanostructures is discussed. Furthermore, the correlation between the optical spectrum and the different morphologies of copper oxides nanomaterials is also discussed.

The effect of diverse gases on the field emission (FE) properties of ZnO nanorods was investigated. The FE properties of nanorods were fully recovered after evacuating to the initial pressure, even after an abrupt current drop under severe vacuum conditions of Torr induced by the presence of O₂, N₂, Ar and air. The reversible and sensitive response of the FE of the nanorods with variation in pressure was found for all gases tested except for H₂. Exposure of H₂ causes a permanent increase in the FE current and a decrease in the turn-on field. The pressure-dependent field emission behaviour of nanorods must be considered when field emission data are compared and characterized.

The Cu nanowires were prepared in alumina membranes with ordered pore arrays by an electrochemical deposition. X-ray diffraction and scan electron microscopy were employed to characterize the nanowires. The results show that the nanowires are located in the channels of the alumina membrane with a diameter of about 40 nm along the [110] direction. The thermal expansion coefficients of the nanowires were measured by in situ high-resolution x-ray diffraction in the temperature range from 298 to 693 K. The results show that the Cu nanowires possess larger lattice parameters and smaller thermal expansion coefficient compared with the conventional bulk Cu. This is because the nanowires consist of a crystalline component and grain boundaries. The grain boundaries usually contain vacancies and vacancy clusters, so they have a larger thermal expansion coefficient than the crystalline component. With elevating temperature, the vacancies and vacancy clusters disappeared and a small thermal expansion coefficient of the Cu nanowires was observed. The high thermal stability of the Cu nanowires is very important for designing nanoelectronic devices and reforming properties of the cermet.

ZnO nanowires were grown on Si(001) substrates by catalyst-free thermal evaporation of ZnO powders in a lateral quartz tube without using a carrier gas. In the first phase of the vapour deposition process, film-like structures were formed on the substrate surface in three-dimensional island growth mode and then rod-like nanostructures nucleated at the vertices of these ZnO islands. The rod-like structures grew further into slender needle-like structures that finally evolved into straight hexagonal prismatic ZnO nanowires having c-axis oriented single-crystalline wurtzite structure. Morphological evolution of the ZnO nanostructures accompanied improvement in the crystal qualities as reflected in the emission characteristics investigated by photoluminescence (PL) spectroscopy, where intensified near-band-edge (NBE) emission was observed as compared with previously reported cases.

The optical controllability of single-electron tunnelling using an organic molecular Coulomb island consisting of a porphyrin derivative was examined. A double-barrier tunnelling junction (DBTJ) consisting of a Si/SiO₂/molecule/SiO₂/Au multilayer exhibited the current–voltage (I–V) characteristics of a Coulomb staircase. Light irradiation was found to induce a reversible change in the threshold voltage of the Coulomb blockade. That is, optical switching of the tunnelling current was achieved under a certain bias voltage. It is believed that the light-induced switching behaviour was due to a change in the charge distribution in the areas near the molecular Coulomb islands. These results demonstrate a potential use for organic molecules in optically functional single-electron devices.

Very thin films of oriented and densely packed single-walled carbon nanotubes (SWNTs) can be self-assembled on substrates from surfactant sodium dodecyl sulfate (SDS-) coated SWNT suspensions at ambient conditions. The evaporation of water causes a concentration of the SDS-coated nanotubes above critical micelle concentrations for SDS, and it is believed that self-organization of the SDS molecules serves as a driving force for the oriented and dense assembly of the nanotubes. The high degree of alignment in the SWNT thin films was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and polarized Raman spectroscopy.

BaF₂ nanocubes were prepared from quaternary reverse micelles of cetyl trimethyl ammonium bromide (CTAB), n-butanol, n-octane, and water. Interestingly, there are arching sheet-like dendrites growing between two neighbouring sides of these cubes. X-ray powder diffraction (XRD) analysis showed that the products were BaF₂ single phase. Scanning electron microscopy (SEM) or transition electron microscopy (TEM) was used to estimate the size of the final products. The results showed that the shape and size of particles were strongly dependent on the reaction conditions, such as the temperature and reaction time. When the reaction temperature was 25 °C, we obtained cuboid-like particles with 'clean' surfaces (no dendrites growing on them), and when the temperature was 35 °C, we obtained nanocubes with dendrites growing from them between the neighbouring sides. The influence of reaction time at a temperature of 35 °C is also discussed.

Nanotechnology is an area receiving increasing attention as progress is made towards tailoring the morphology of polymeric biomaterial for a variety of applications. In the present study an attempt was made to electrospin poly(L-lactide-co-glycolide) biodegradable polymer nanofibres. In this process, polymer fibres with diameters down to the nanometre range are formed by subjecting a fluid jet to a high electric field. The nanofibres were collected on to a rotating Teflon mandrel and fabricated to tubes or conduits, to function as nerve guidance channels. The feasibility of in vivo nerve regeneration was investigated through several of these conduits. The biological performance of the conduits were examined in the rat sciatic nerve model with a 10 mm gap length. After implantation of the nanofibre nerve guidance conduit to the right sciatic nerve of the rat, there was no inflammatory response. One month after implantation five out of eleven rats showed successful nerve regeneration. None of the implanted tubes showed tube breakage. The nanofibre nerve guidance conduits were flexible, permeable and showed no swelling. Thus, these new poly(L-lactide-co-glycolide) nanofibre conduits can be effective aids for nerve regeneration and repair. Improvements could be done by impregnating nerve growth factors or Schwann cells and may lead to clinical applications.

Nanometre CaP/Al₂O₃–Ti biocomposites for implant applications were successfully fabricated using a hybrid technique of anodization and hydrothermal treatment, in which CaP/Al₂O₃ formed a double-layer coating on titanium with porous CaP as the top layer and anodic Al₂O₃ film as the intermediate layer. Techniques, such as x-ray diffraction (XRD), electron scanning microscopy and energy disperse x-ray analysis (SEM + EDX), transmission electron microscopy (TEM) and atomic force microscopy (AFM), were used to investigate the composition, microstructure and morphology of the fabricated CaP/Al₂O₃ composite coating and the CaP/Al₂O₃–Ti biocomposites. XRD results showed that the fabricated composite coating contained Al₂O₃ and various calcium phosphate phases. SEM and TEM micrographs confirmed that CaP crystals were in nanometres, embedded in situ in the walls of the cylindrical structure of anodic alumina, and finally formed a thin and porous top layer on the anodic alumina intermediate layer. The nanometre and T-shape effects of the CaP top layer, and the porous and cylindrical microstructure of CaP/Al₂O₃ composite coating could produce an excellent combination of bioactivity and mechanical integrity of the CaP/Al₂O₃–Ti biocomposites.

It was also found that the anodization voltage of the anodization process played an important role on the composition and microstructure of the fabricated CaP/Al₂O₃–Ti biocomposites. The contents of Ca and P incorporated in anodic alumina depended strongly on the anodization voltage. Their variations could result in different CaP phases, CaP crystal shapes and sizes, and topography of the CaP/Al₂O₃–Ti biocomposites. The optimal anodization voltage in this study was found to be in the range 40–60 V.

We have fabricated MOS memory devices based on coil–rod–coil triblock molecules acting as quantum dots. Uniform molecular dots result in a discrete shift in the threshold voltage at room temperature, which is indicative of single-electron effects. Molecular scalability and low-power operation make the silicon-molecular hybrid device an attractive candidate for next-generation electronic devices.

We have successfully fabricated devices with isolated single-walled carbon nanotubes (SWNTs) using exclusively standard i-line (365 nm) photolithography. Catalyst islands were patterned with an SU-8-photoresist-based process. This method provides well-defined islands, down to 1 µm in size. The islands are clearly visible with an optical microscope and are used as alignment marks for optical alignment of subsequent layers. SWNTs were grown by chemical vapour deposition (CVD). Contacts to the nanotubes were fabricated by standard photolithography.

Cobalt oxide (Co₃O₄) nanotubes were synthesized by calcining cobalt nanowires embedded in an anodic alumina template (AAT) in air. The morphologies and phases of the nanowires/nanotubes were studied by transmission electron microscope (TEM) and x-ray diffraction (XRD) respectively. A hypothesis of the tube formation process is presented and illustrated by experimental results. According to the experimental results, it is concluded that competition between the oxidation and the evaporation of cobalt nanocrystals plays a crucial role in the formation of such tube-like nanostructures of Co₃O₄.

Many soft materials, such as block copolymers and micelles, are characterized by a tunable organization that can be exploited for formation of nanostructures. In this work, drying patterns, formed when nanoparticle solutions are spin coated on ultrathin films of the block copolymer poly[styrene-b-ethylenepropylene] (PS-PEP), are investigated as a function of the film's organization. Prior to particle deposition, thermal annealing was used to adjust the polymer film organization between a layer of PS-PEP micelles (no annealing) and a bilayer with a uniform PEP 'polymer brush' layer on top of an underlying layer of PS (extensive annealing). For intermediately annealed films, ring-shaped drying patterns consisting of as few as 5 or as many as 30 nanoparticles are observed. The nanorings are polydisperse with a diameter between 15 and 50 nm, and cover macroscopic surface areas of the film. It is suggested that these rings form as a consequence of inhomogeneous drying of particle solutions due to heterogeneities in the film structure, as deposition of nanoparticles on extensively annealed, uniform films did not produce rings.

Rectangular cross-section bismuth nanowires with dimensions of 50 nm by 70–200 nm (thickness by width) were fabricated using an electron beam writing technique. Individual nanowire measurement is possible using this method. The resistivities of the 50 nm thick nanowires were dependent on line width. The measured resistivity of 70, 120 and 200 nm wide nanowires was 4.05 × 10⁻³, 2.87 × 10⁻³ and 2.30 × 10⁻³ Ω cm at 300 K respectively. Temperature-dependent resistance measurements indicated that the electrical conductivity of the Bi nanowires was carrier dependent, and the carrier density decreased at low temperature, showing that the all the Bi nanowires exhibited semiconductor behaviour. The size-dependent resistivity of the Bi nanowires was an indication of the ordinary size effect in the one-dimensional nanowire, where the carrier mobility was grain boundary scattering dominated.

In this study, single-walled carbon nanotube-based sensors are proposed for measuring strain and pressure at the nanoscale. The principle of sensing is based on the resonant frequency shift of a carbon nanotube resonator when it is subjected to a strain resulting from external loading. The carbon nanotube in a bridged configuration is simulated by atomistic modelling, the molecular structural mechanics method. The resonant frequency shifts are shown to be linearly dependent on the applied axial strain and the applied pressure. The sensitivities of nanotube-based sensors are enhanced with the reduction of tube length and tube diameter, respectively, for axial strain and pressure sensing.

We have theoretically investigated the high frequency properties of a carbon-nanotube-based three-terminal nanoelectromechanical relay. The intrinsic mechanical frequency of the relay is in the GHz regime, and the electromechanical coupling shows a non-linear resonant behaviour in this frequency range. We discuss how these resonances may be detected and show that the resonance frequencies can be tuned by the bias voltage. Also, we show that the influence of external electromagnetic fields on the relay is negligible at all frequencies.

Hydrogen adsorption measurements on mixed carbon material containing single-walled carbon nanotubes (SWNTs) obtained by the electric-arc method were carried out by three different techniques: a volumetric system, a gravimetric system and an electrochemical method. The found H₂ gas adsorption capacity (volumetric and gravimetric) is very low, around 0.01 wt% at room temperature and pressure, increasing to 0.1 wt% at 20 bar. Electrochemical measurements show a slightly higher capacity (0.1–0.3 wt%) than volumetric and gravimetric data. The results obtained by the three different techniques are compatible within each other and they are also in good agreement with other previously reported data from different researchers.

A rigid body boundary layer interface force (RIF) model for stress calculation on the nanoscale is proposed in this paper for calculating stress based on molecular dynamics. The RIF model is used to study the stress–stain behaviour when nanoscale single crystal copper is under uniaxial tension, and is used for 15 tensile simulations each with different strain rate. The stress–strain curve established from simulation was first converted into a true stress–strain curve; a regression analysis was then applied in order to find the flow curve.

From simulation results, it is found that the strain rate has large influence on both K and n values of the flow curve. At low strain rate (less than 1 × 10¹² s⁻¹), both K and n values decrease with the increase of strain rate. When the strain rate exceeds 1 × 10¹² s⁻¹, the strain rate against the K and n values of the flow curve approaches a constant. Flow curve equations considering the influence of strain rate are derived; both complete and simplified forms of flow curve equations are also derived. It is observed that the lower the strain rates, the higher the fluctuations of the stress–strain curve. Furthermore, the increase of strain rate resulting in a smoother stress–strain curve is also found.

A suspension containing 20 nm silica particles in ethylene glycol was subjected to electrohydrodynamic atomization (EHDA) in the stable cone-jet mode using a ring-shaped ground electrode. The droplets produced were sized by laser diffraction and were in the range 0.5–20 µm. Immediately after deposition, droplet relics were analysed by optical microscopy and were found to be in the size range 1–80 µm. Subsequently, using a pointed rod-electrode (rather than a ring), and by increasing the intensity of the electric field and by reducing the flow rate of suspension subjected to EHDA, relics of in size were deposited using a patterning device. In both of the above instances, the relics contained two distinct zones, an outer ring of ethylene glycol and a much smaller dense inner region of silica nanoparticles. These results show that, by using EHDA, a novel controlled deposition method of nanosuspensions has been developed.

DNA-templated polyaniline nanowires and networks are synthesized using three different methods. The resulting DNA/polyaniline hybrids are fully characterized using atomic force microscopy, UV–vis spectroscopy and current–voltage measurements. Oxidative polymerization of polyaniline at moderate pH values is accomplished using ammonium persulfate as an oxidant, or alternatively in an enzymatic oxidation by hydrogen peroxide using horseradish peroxidase, or by photo-oxidation using a ruthenium complex as photo-oxidant. Atomic force microscopy shows that all three methods lead to the preferential growth of polyaniline along DNA templates. With ammonium persulfate, polyaniline can be grown on DNA templates already immobilized on a surface. Current–voltage measurements are successfully conducted on DNA/polyaniline networks synthesized by the enzymatic method and the photo-oxidation method. The conductance is found to be consistent with values measured for undoped polyaniline films.

A facile and selective self-sacrificing template-like conversion process has been developed to produce both high-quality flower-like patterns of radially aligned Bi₂(Se,S)₃ nanorods and Bi₂Se₃ nanoflakes at low temperature. In this process, the patterns of radially aligned Bi₂S₃ nanorod precursors act as both the source materials and template to confine the growth of final products. The possible growth mechanism was discussed based on the experiments. This novel radially aligned morphology may find uses in a variety of areas such as the fabrication of advanced electronic and opto-electronic nanodevices.

Al₁₃-pillared anatase TiO₂ is used as a cathode of a lithium battery for the first time. First, a layered titanium dioxide with cationic surfactant ions of cetyltrimethylammonium (CTA⁺) in the interlayers is synthesized by self-assembly. Then, pillared TiO₂ is obtained by exchange of polyoxo cations of aluminium, [Al₁₃O₄(OH)₂₄(H₂O)₁₂]⁷⁺, with CTA⁺ and subsequent calcination at 300 °C for 1 h in the air. Powder x-ray diffraction (XRD), transmission electron microscopy (TEM) and surface area (BET) methods are used to characterize the layered and pillared forms of titanium dioxide. A lithium battery with the Al₁₃-pillared TiO₂ as the cathode and Li metal foil as the anode is studied within the 1–2.2 V voltage range. The specific capacity of the closed button cell (size 2025) that is delivered on the initial discharge reached 191.4 mA h g⁻¹ at the rate of 25 mA g⁻¹. The cell shows good cycling performance over 50 cycles.

We have developed a large area technique for fabricating magnetic nanostructures. This technique is based on deep ultraviolet lithography followed by a lift-off process. A phase shift mask is used to create nanoscale patterns of very high density. By varying the focus and exposure doses we have synthesized multiple patterns using the same mask. Arrays of Ni₈₀Fe₂₀ nanostructures of different shapes and sizes were fabricated using this technique. Scanning electron microscopy was used to verify the lateral dimensions and uniformity of the structures. We have used a vibrating sample magnetometer to characterize the magnetic properties of the fabricated structures. We observed a marked increase in both the coercivity and the switching field of the patterned nanomagnets compared with the reference film due to the magnetic shape anisotropy.

Carbon nanofibre–polystyrene (PS) composites were fabricated by ultrasonic dispersion in a solution followed by spraying to cast films. These films were then hot-pressed to form thicker structures. Direct current conductivity measurement results show that the conductivity of the composite reaches 2.6 × 10⁻⁵ S m⁻¹ at 3 wt% carbon nanofibre loading, which is an increase of ten orders of magnitude over the pure PS matrix, indicating that the composite is electrically conductive at a very low nanofibre loading. The dielectric properties of carbon nanofibre–PS composites were investigated at room temperature within the Ku-band (frequency range: 12.4–18 GHz). The results reveal that the dielectric constants of the composites are slightly dependent on the frequency but increase rapidly with increasing carbon nanofibre loading in the composite. The experimental data show that the dielectric constant of carbon nanofibre–PS composite can reach more than 80 at a frequency of 15 GHz.

Europium-doped yttrium silicate nanoparticles were grown inside a porous silicon oxide matrix by chemical impregnation of porous silicon layers, followed by heat treatments. The average size of the nanoparticles is 50 nm and they are dispersed almost uniformly within the whole porous layer. Local composition measurements demonstrate that Y and Eu are found only in nanoparticles, indicating a good phase separation efficiency. There is indirect evidence that yttrium silicate nanoparticles are nucleated around Eu ions. The crystalline phase of the particles is pure α-Y₂Si₂O₇, with no trace of Y₂O₃ or Y₂SiO₅ or other Y₂Si₂O₇ polymorphs. Structural purity is an advantage for this method, as in the case of powder or sol–gel methods single-phase yttrium silicate formation is hardly possible, even at high firing temperatures.

Si nanocrystals were formed by the implantation of Si⁺ into a SiO₂ film, deposited on (100) Si, followed by high-temperature annealing. Transmission electron microscopy (TEM) was used to examine the effect of implantation dose on the microstructure of the Si nanocrystals (Si nc) in the SiO₂ film. The size and spatial distribution and concentration of the Si nc in four passivated samples with different implantation doses were investigated using the dark-field imaging technique. The thickness of all the samples was determined by electron energy-loss spectroscopy (EELS). The structure of the Si nc in all the samples was determined using selected area electron diffraction. It was found that the average diameter of the Si nc changes from 2.7 to 3 and to 3.3 nm for the samples with implantation doses of 6 × 10¹⁶, 8 × 10¹⁶ and 1 × 10¹⁷ cm⁻²; however, it ranges from 2 to 22 nm in the sample with an implantation dose of 3 × 10¹⁷ cm⁻². The size of the Si nc is comparatively homogeneous throughout the whole implanted layer in the samples with implantation doses of 6 × 10¹⁶ and 8 × 10¹⁶ cm⁻², while in the samples with implantation doses of 1 × 10¹⁷ and 3 × 10¹⁷ cm⁻², the Si nc in the middle region of the implanted layer are bigger than those near the surface or the bottom of the layer. From TEM experimental results, the concentration of the Si nc is estimated to be 6 × 10¹⁸, 4 × 10¹⁸ and 4 × 10¹⁸ cm⁻³ for the samples with implantation doses of 6 × 10¹⁶, 8 × 10¹⁶ and 1 × 10¹⁷ cm⁻², respectively. For the sample with an implantation dose of 3 × 10¹⁷ cm⁻², the concentration for the Si nc of 3 nm is around 5 × 10¹⁸ cm⁻³; the concentration for Si nc of 6 nm is around 2 × 10¹⁸ cm⁻³; and the concentration for the 12 nm group is about 1 × 10¹⁸ cm⁻³. In addition, the concentration determined from TEM experiments is compared with the calculated one. Combining the TEM results with a Monte Carlo simulation, we also discuss the sputtering effect and the depth distribution of the Si ions implanted in SiO₂.

Scale dependence of micro/nanotribological properties is studied for various materials, coatings and lubricants used in micro/nanoelectromechanical systems (MEMS/NEMS). The adhesive force and friction force dependence on rest time and sliding velocity and the effect of relative humidity and temperature on the scale dependence of these properties is studied. The scale dependence of the coefficient of friction is attributable to the sample surface roughness and the scan size. For larger scan sizes the sliding interface encounters larger asperities and so friction force is higher. The adhesive force is higher on the microscale although on the nanoscale surface forces such as electrostatic attraction that are generally negligible on the microscale can become dominant. The difference in the adhesive force on the micro- and nanoscale for different rest times, relative humidities and temperatures is due to the meniscus force dependence on the sample surface roughness. The velocity dependence of the friction force shows significant scale dependence due to the scale dependent roughness and the higher contact pressures that are encountered on the nanoscale.

The conditions for single wall carbon nanotube formation in the arc discharge method of nanotube production are described. Carbon nanotube seed formation and charging in the interelectrode gap are found to be very important effects that may alter carbon nanotube formation on the cathode surface. The model predicts that the long carbon nanotubes formed in the relatively dense plasma region can be deposited on the cathode surface. The nanotubes in the cathode deposit are primarily oriented in the cathode surface plane and not along the electric field. This prediction is qualitatively confirmed by an SEM analysis of the cathode deposit.

Magnesium hydroxide nanoparticles with different morphological structures of needle-, lamellar- and rod-like nanocrystals have been synthesized by solution precipitation reactions of alkaline with magnesium chloride in the presence of complex dispersants and characterized in terms of morphology, particle size, crystal habits and thermal behaviour by transmission electron microscopy, x-ray diffraction and thermogravimetric analysis. The sizes and morphologies of magnesium hydroxide nanocrystals can be controlled mainly by the reaction conditions of temperature, alkaline-injection rate and the concentrations of reactants. The data show that the needle-like morphology is of size 10 × 100 nm², the lamellar shape 50 nm in diameter and estimated 10 nm in thickness, and the rod-like nanoparticles 4 µm in length and 95 nm in diameter, respectively. All three kinds of nanoparticles are of hexagonal structures. The needle- and lamellar-like nanoparticles can be obtained by the reactions of alkaline injected into magnesium chloride solution at about 2 and 20 °C, respectively, while the rod-like nanoparticles can be prepared by a slower alkaline-injection rate and lower aqueous ammonia concentration at about 10 °C. The results obtained from the ethylene–vinyl acetate nanocomposites blended with the lamellar-like nanoparticles show that magnesium hydroxide nanocrystals possess higher flame retardant efficiency and mechanical reinforcing effect by comparison with common micrometre grade magnesium hydroxide particles.

Experimental techniques based on the atomic force microscope (AFM) have been developed for characterizing mechanical properties at the nanoscale and applied to a variety of materials and structures. Atomic force acoustic microscopy (AFAM) is one such technique that uses spectral information of the AFM cantilever as it vibrates in contact with a sample. In this paper, the dynamic behaviour of AFM cantilevers that have a dagger shape is investigated using a power-series method. Dagger-shaped cantilevers have plan-view geometry consisting of a rectangular section at the clamped end and a triangular section at the tip. Their geometry precludes modelling using closed-form expressions. The convergence of the series is demonstrated and the convergence radius is shown to be related to the given geometry. The accuracy and efficiency of the method are investigated by comparison with finite element results for several different cases. AFAM experiments are modelled by including a linear spring at the tip that represents the contact stiffness. The technique developed is shown to be very effective for inversion of experimental frequency information into contact stiffness results for AFAM. In addition, the sensitivities of the frequencies to the contact stiffness are discussed in terms of the various geometric parameters of the problem including the slope, the ratio of the rectangular to triangular lengths and the tip location. Calculations of contact stiffness from experimental data using this model are shown to be very good in comparison with other models. It is anticipated that this approach may be useful for other cantilever geometries as well, such that AFAM accuracy may be improved.

We report on the growth of FePt nanostructures by self-assembling on the van der Waals surface of WSe₂(0001) under ultra-high vacuum conditions. The morphology and crystalline structure of nanostructures were investigated by reflection high energy electron diffraction (RHEED), scanning tunnelling microscopy (STM) and x-ray diffraction. The FePt nanostructures grow with the (111) plane azimuthally aligned to the WSe₂(0001) plane with a narrow size distribution centred around 4.5 nm showing a rounded shape for deposition temperatures in the 300–500 °C range. They develop the L1₀-type structure starting at a relatively low deposition temperature of about 200 °C with the occurrence of three possible variants. Moreover, segregation of Se at the growing surface was observed even in films deposited at room temperature. However, such a surfactant effect does not prevent the L1₀ ordering and could explain the perpendicular magnetic anisotropy observed in previously studied CoPt₃ films grown at room temperature on WSe₂. Magnetic measurements in 3 nm thick FePt(111) deposits have revealed an easy axis of magnetization in the film plane, with a coercivity strongly enhanced with L1₀ order.

This paper presents a new approach to gas sensing using a multi-walled carbon nanotube (MWCNT) subject to electrical breakdown. The electrical resistances of large-diameter MWCNTs were found to decrease in the presence of air after experiencing electrical breakdown, while pristine MWCNTs were not appreciably sensitive. The sensitivity could be controlled by manipulating the level of the electrical breakdown, and larger-diameter MWCNTs showed better sensitivity because they possess more damaged shells that can create more adsorption sites for oxygen molecules. It was suggested by theoretical calculations that the oxygen sensitivity might be associated with an oxidized junction that exists between the outer and inner shells of the nanotubes.

Selective self-assembly properties of the thio and methoxy functional groups are utilized to micropattern (3-mercaptopropyl) trimethoxysilane molecules on a gold coated glass target starting with a nano-structured silicon grating template. Further modifications of the target surface are introduced by self-assembled monolayers of mercaptoacetic acid sodium salt molecules. The anisotropy in reflection properties is observed from the spectroscopic ellipsometric measurements in relation to the orientation of the plane of incidence. Conformations of spun adenine base and zinc oxide nanocomposite films on the gold substrate are found to depend upon its surface modifications due to the self-assembled monolayer.

Nanocrystalline diamond (NCD) films were deposited using CH₄ and H₂ gas mixtures by the electron assisted chemical vapour deposition (EACVD) method at 640 and 400 °C, and microcrystalline diamond film was simultaneously synthesized at 890 °C. The size of NCD was estimated as about 8–100 nm according to electron micrographs and the full width at half maximum of diamond features of x-ray diffraction spectra. We have investigated the local gas environments where diamond films were deposited using a quadrupole mass spectrometer. It shows that the growth temperature and local gas environment are two important factors influencing diamond grain size.

Synchrotron x-ray diffraction and high temperature SEM examinations were used to study the crystallochemical and morphological evolution of a ZnO–NaCl system during thermal processing. Decomposition of ZnO precursor (Zn₂(OH)₂CO₃* xH₂O) at T<400 °C is accompanied by shrinkage and destruction of its fibre-like particles into nanosized isotropic ZnO crystallites. Intensive intergrowth of ZnO nanoparticles and its interaction with coarse NaCl crystallites leads at T = 650–700 °C to the formation of a continuous sponge-like framework with an elementary unit size which is far below the initial size of NaCl crystallites. The higher temperature processing at is accompanied by the appearance of nanorods. The role of the metastable liquid phase in the formation of ZnO nanorods at T<800 °C is discussed. Luminescence properties of ZnO nanorods synthesized at 500 and 700 °C were demonstrated.

Silicon nanophases are grown in fused silica using an ion implantation technique followed by a thermal and swift heavy ion irradiation induced annealing process. From an estimation of the track cooling time and nanoprecipitation nucleation time for the present experiment, it is inferred that nanoprecipitation occurs inside the swift heavy ion induced latent tracks. The blue shift of the photoluminescence peak as well as the UV/visible absorption band edge for swift heavy ion induced annealing indicate the occurrence of nanoprecipitation inside the track.

Magnesium hydroxide sulfate hydrate nanoribbons have been synthesized by a solution-phase approach, which is based on the treatment of freshly precipitated magnesium hydroxide in an alcohol–water solution containing high concentrations of magnesium sulfate. These nanoribbons had typical lengths up to the micrometre range, widths of 60–300 nm, and thicknesses of 16–50 nm.

Tipless thermoplastic microcantilevers suitable for chemical and biological sensing applications were fabricated by injection moulding. Their stiffnesses and resonant frequencies were each determined by two techniques. Polystyrene beams produced by this method exhibited stiffnesses ranging from 0.01 to 10 N m⁻¹, making them feasible for biosensing applications. The approach proved repeatable with low standard deviations on the parameters measured on 22 microcantilever beams (stiffness and first-mode resonant frequency) made from the same mould. The variations were much lower than those of similar, commercially available, silicon-type beams. The polymeric microcantilevers were shown to be of at least equal calibre to commercially available microcantilevers.

We investigated nanoscale engine schematics composed of a carbon nanotube oscillator, motor, channel, nozzle, etc. For the fluidic gas driven carbon nanotube motor, the origination of the torque was the friction between the carbon nanotube surface and the fluidic gases. The density and flow rate of the working gas or liquid are very important for the carbon nanotube motor. When multi-wall carbon nanotubes with very low rotating energy barriers are used for carbon nanotube motors, the fluidic gas driven carbon nanotube motors can be effectively operated and controlled by the gas flow rates. The variations of the flux were the same as the variations of the carbon nanotube oscillator. Although the carbon nanotube oscillator continually vibrated, since the angular velocity of the motor was saturated at a constant value, the speed of the nanoscale engine could be controlled by the frequency of the carbon nanotube oscillator below the maximum speed.

We have developed a fabrication method for nanogap electrodes without employing photo- or electron-beam lithography to measure the electrical characteristics of nanostructured molecules. This angle-controlled shadow-masking method enables us to construct nanogap electrodes without a wet process after the molecules are positioned on the substrate. The proposed method makes it possible to measure electrical characteristics without structurally deforming or denaturing the molecules due either to the step edge of an electrode or to the organic solvents used in the wet process. The results demonstrate that a gap length between the electrodes of less than 100 nm can be fabricated reproducibly. We have measured the electrical characteristics of lambda DNA (λ-DNA) networks and molecular nanorods made of porphyrin-derivative molecules (TPPS: 5,10,15,20-tetraphenyl-21H,23H-porphyrine tetrasulfonic acid) in which J-aggregates are formed inside. Experimental findings reveal that the electrical conductivity of λ-DNA decreased under a vacuum condition, whereas that of TPPS nanorods decreased under oxygen and nitrogen gas-purged conditions.

Different acid oxidation methods were systematically carried out to purify the SWNTs synthesized by CVD. The results show that the best purification process can produce over 98% pure single-wall carbon nanotubes within 2 h. In this process, it is found by Raman characterization that the amount of nanotubes with small diameters do not diminish within 3 h.

We have functionalized single-walled carbon nanotubes using a CF₄ microwave discharge and characterized the samples through in situ FTIR spectroscopy, UV–VIS–NIR spectroscopy, FT-Raman spectroscopy, SEM and x-ray photoelectron spectroscopy. A high degree of functionalization is achieved in a very short time frame, demonstrating that a microwave plasma scheme is an efficient technique for surface modification of carbon nanotubes. The analysis indicates a fractional surface coverage of 2/3 with fluorination.

Laser-assisted nanopatterning of aluminium (Al) thin films using particle-induced near-field optical enhancement and nanoimprinting has been investigated experimentally and theoretically. It is found that nano pit arrays can be created on Al surfaces by laser irradiation (KrF excimer laser, λ = 248 nm) on an Al surface on which a monolayer of silica particles has been self-assembled. The influence of particle size and laser fluence on the structuring of Al surfaces has been examined. Particles with various diameters of 0.97, 2.34 and 5.06 µm were used in the experiment. Near-field optical enhancement and nanoimprinting were identified to explain the mechanisms for the formation of different structures on Al surfaces under different laser fluences. A high frequency structure simulator (HFSS) was used to simulate the optical field distribution in the particles attached on Al surfaces.

Atomic force microscopy (AFM) was used to study the morphology and coagulation of human blood cells in contact with solid surfaces. Blood was extracted from the veins of healthy adult donors and the samples were used immediately after extraction, deposited either on borosilicate glass or diamond substrates. Some blood samples were anti-coagulated by adding heparin for single cell AFM imaging. No chemicals were used for attaching or immobilizing the cells. The diamond substrates were produced by chemical vapour deposition (CVD diamond) using a hot-filament CVD system fed with ethanol highly diluted in hydrogen. AFM imaging of isolated cells (anti-coagulated by heparin) was only possible on the glass substrates due to the lack of adherence of the cells to the diamond surface. The coagulation results suggest that blood clotting on diamond produces a less rough surface than blood clotting on glass.

The formation of iron particles without and with carbon coating was studied in a hot wall flow reactor. The precursors ironpentacarbonyl (IPC, Fe(CO)₅) and ethylene (C₂H₄) both diluted in N₂ were used in a concentric tubular flow arrangement and were heated to temperatures between 570 and 1170 K at pressures between 50 and 500 mbar. In experiments without C₂H₄, either individual iron particles in the size range of or long iron chains composed of several hundreds of individual iron particles were found depending on the reaction conditions. In experiments with C₂H₄ addition, these particles or particle chains were covered by a thin carbon/carbide layer. The size of the primary particles was measured in situ by time-resolved laser-induced incandescence (TR-LII) and ex situ by rapid thermophoretic particle probing and TEM imaging.

A new technique of fluidized-bed metal–organic chemical vapour deposition (FB-MOCVD) is developed as a one-step method to prepare highly dispersed metal-supported catalysts for carbon nanotube synthesis. By using ultrafine powder of gamma-alumina (70 nm Sauter mean in size) as the support with Fe(CO)₅ and Mo(CO)₆ as the metal precursors, Fe/Al₂O₃, Mo/Al₂O₃ and Fe–Mo/Al₂O₃ catalysts have been prepared in an FB-MOCVD reactor. Compared with the conventional catalyst-preparation methods such as impregnation, ion exchange, co-precipitation and co-crystallization, the one-step FB-MOCVD technique is advantageous in many aspects. These include eliminating the solid–liquid separation and the subsequent operations of drying and high-temperature calcination/reduction, thus minimizing the aggregation or the crystalline size-growing problem for the supported metal particles caused by these operations. The metal-supported catalysts obtained by FB-MOCVD are characterized with various techniques including ICP-AES, SEM-EDX, XRD and nitrogen isothermal adsorption. Some catalysts are selected and used for carbon nanotube synthesis by CVD from acetylene (C₂H₂) in a fluidized bed at 650 or 850 °C. The formation of the entangled multi-walled carbon nanotubes (MWNTs), around 50 nm in outer diameter and 10 nm in inner diameter, and several to tens of microns in length, has been confirmed by the TEM and SEM analyses. High CNT selectivity () with the carbon yield ranging widely from about 10% to over 60%, depending on the type of catalyst used and the CNT deposition temperature, has been demonstrated with TGA tests.

SnO₂ nanowhiskers of mass production have been synthesized by evaporating metal tin (Sn) powders at 800 °C. The synthesized products were characterized with scanning electron microscopy, x-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Each SnO₂ nanowhisker was a tetragonal rutile single crystal, with the diameters ranging from 50 to 200 nm and the lengths extending to tens of micrometres. The SnO₂ nanowhiskers exhibited a sensitivity of 23 to 50 ppm ethanol gas at 300 °C. Our results demonstrated that SnO₂ nanowhiskers have a promising application for gas sensor fabrication.

Metastable VO₂ nanowire arrays, designated as VO₂ (B), have been synthesized via an ethylene glycol reduction approach. The samples are characterized by XRD, TEM, HRTEM, SAED, and XPS. The as-prepared VO₂ (B) nanowires have an average diameter of 6 nm and length of up to several micrometres and grow along the [010] direction. The experimental results reveal that the reaction temperature and ethylene glycol are of importance for obtaining pure VO₂ (B) nanowire arrays.

New varieties of computer architectures, capable of solving highly demanding computational problems, are enabled by the large manufacturing scale expected from self-assembling circuit fabrication (10¹²–10¹⁹ devices). However, these fabrication processes are in their infancy and even at maturity are expected to incur heavy yield penalties compared to conventional silicon technologies. To retain the advantages of this manufacturing scale, new architectures must efficiently use large collections of very simple circuits. This paper describes two such architectures that are enabled by self-assembly and examines their performance.

Two-dimensional (2D) arrays of nanometre scale holes were opened in thin SiO₂ layers on silicon by electron beam lithography and chemical etching. Oxidized silicon wafers with a 5 nm thick SiO₂ layer on top were used in this respect. Pattern transfer involved either only removal of SiO₂ or a two-step process of oxide removal and anisotropic silicon chemical etching to form nanometre scale silicon V-grooves. The size of the holes in the photoresist layer varied in the range 40–80 nm, depending on the exposure dose used. The smallest holes in the oxide were about 50 nm in diameter, while in V-grooves the smallest width was  nm. 2D arrays of Ge dots or Ge/Si hetero-nanocrystals were selectively grown on these patterned silicon wafers. In small windows only one Ge island per hole was nucleated.