Table of contents

Multiwalled carbon nanotube (MWNT)/ZrO₂ nanocomposites were successfully prepared by hydrothermal treatment of MWNTs in ZrOCl₂·8H₂O aqueous solution at 150 °C, by which stronger bonds of Zr–O–C are formed between the MWNTs and ZrO₂. The composites were characterized by XRD, TEM, XPS, and IR analysis. It was found that ZrO₂ nanoparticles homogeneously distributed on the sidewall of the MWNTs. By adjusting the experimental parameters, ZrO₂ /MWNT composites with ZrO₂ existing in a different phase were obtained. The composites could find potential applications as catalysts, fuel cells, and ideal reinforcements in other composites.

We have developed a technique for fabricating arrays of gaps as small as 3 nm between metal electrodes using a shadow-evaporation technique. These small gaps are fairly reliable and reproducible, and can in principle be made in large quantities, for example across a whole silicon wafer. The gaps can be used to measure the electrical properties of nanoelectronic systems, such as nanocrystals. Our electrical measurements of CdSe nanocrystals 4.2 nm in diameter at 4.2 K show steps in the current–voltage characteristics related to the filling of electronic shells in the nanocrystal and to Coulomb charging.

Ab initio calculations reveal distinct electronic properties associated with functionalized single-wall carbon nanotubes (SWNTs) with monovalent sidewall additions. The metallic tubes are found to be more reactive than the semiconducting ones. The hybridization between the addend and the tube induces unique impurity states near the Fermi level. For semiconducting tubes the state is localized near the functionalized site with a characteristic length of 15 Å. In contrast, the impurity state is extended and acts as a strong scattering centre in metallic tubes. This effect greatly hinders the ballistic transport of electrons along the metallic nanotubes. The characteristic dependence of the electronic states and the conductance on functional molecules provides possible pathways for chemical sensor applications and the band structure engineering.

A thermal reduction (TR) technique is used to purify single-walled carbon nanotubes (SWNTs) and to reduce chemical defects from their lattice structure. This technique is mainly comprised of two processes, high-temperature reactions of raw SWNTs in a pressurized hydrogen chamber followed by a slow annealing under vacuum. Analyses by TEM, TGA, XRF, and XRD of SWNT samples before and after the purification reveal that over 90% of the carbonaceous impurities formed during the syntheses of SWNTs (by carbon arc, laser ablation, and HiPCO) are eliminated. Post-purification IR spectroscopic analyses show no evidence of hydrogen in the SWNT samples and AFM studies suggest that the samples contain very few chemical defects. In addition, analyses by TEM and Raman spectroscopy do not reveal any significant structural damage of the SWNTs purified by the TR technique.

Uniform FeCo magnetic nanoneedles of  nm in width and axial ratio have been obtained by Co-coating haematite and subsequent hydrogen reduction in two steps. By this method, FeCo needle-like nanoparticles were obtained with Co contents up to 10% evenly distributed inside the particles. Higher Co contents up to 30% were incorporated by coating the Co-doped magnetite nanoneedles. No segregation of a secondary phase was observed in any case and the morphology of the particles was preserved without adding any extra element. Structural changes during the reduction process have been followed by several techniques. Although protected by an oxide layer, the final metal nanoparticles behave as single crystals, but they are composed of sub-crystals with the same crystallographic orientation and a mean diameter that decreases as the Co content increases. We found the highest reported saturation magnetization values for samples of similar size (180 emu g⁻¹). The evolution of the coercivity with the cobalt modification could arise from the changes of the microstructure and the contributions of shape and crystalline anisotropies. Time dependence magnetization measurements showed the thermal activation to be related to the presence of crystallographic sub-units within the nanoneedles.

Helical nanobelts of SiGe/Si and SiGe/Si/Cr are fabricated by rolling up strained thin heterostructures. The fabrication involved electron beam lithography, reactive ion etching, and wet chemical etching steps followed by a drying procedure. All parameters of the helical nanobelts, namely their helical angle, chirality, pitch and diameter, are controllable in a reproducible fashion. The ease of fabrication of SiGe/Si and hybrid helical nanobelts opens new paths for the fabrication technology of micro- or nanoscale sensors, transducers, resonators and cylindrical shaped micro-capacitors.

We present a method to calculate the thermal noise in an atomic force microscope (AFM) that employs the optical beam deflection ('optical lever') detection technique with a finite focused optical spot size. This method is based on optical diffraction theory and extends the formulation by Butt and Jaschke (1995 Nanotechnology6 1), who assumed a spot of infinitesimal size. We consider multiple flexural vibration modes of the cantilever and show that the measured thermal noise strongly depends on the spot size. In general, larger focused spots result in less measured thermal noise, while this dependence is more pronounced for a cantilever with a pinned tip than for a cantilever with a free tip. We analyse the amount of thermal noise that appears in contact mode and force spectroscopy measurements, and discuss how to reduce it by selecting beneficial experimental conditions.

Mesoporous crystalline ZnO nanowires have been successfully fabricated by a simple in situ precipitation method combined with porous anodic alumina membranes as the templates. XRD, TEM, and HRTEM analysis shows that the as-synthesized samples are mesoporous ZnO nanowires with a hexagonal structure, which consist of ZnO nanocrystals and pores. The growth mechanism of mesoporous nanowires was discussed.

Contact mode scanning force microscopy was employed to produce permanent deformation in polystyrene films of molecular weight ranging from 5 to 483 kg mol⁻¹. Operating in a regime of small loads and a low number of scan cycles, a variety of wear types was observed, including the formation of grooves and bundles. These differences could be explained in terms of the entanglement density at the film surface. For completely disentangled films, long parallel grooves formed at the lateral edges of the scanned area as a consequence of molecular displacement. In the central region, wide bundles formed after only a few passages. For fully entangled films, discontinuous ridges were immediately generated with a much reduced spacing. A transition in wear behaviour occurred when, for molecular weight between 13 and 64 kg mol⁻¹, entanglement was not fully developed. In this regime, the entanglement degree could be evaluated via measuring the threshold load at which fragments of material were torn off from the surface. Nanowear induced in such a controlled fashion on unknown polymeric surfaces can yield important insights into surface molecular organization.

We report a method for fabricating ordered spatial arrangements of pre-synthesized CdS nanoparticles in thin block copolymer templates by first selectively dispersing these nanoparticles in one particular block of a diblock copolymer, in bulk, by means of dipole–dipole interactions and then using solvent selectivity to sequester CdS nanoparticles in the block copolymer thin film. A long-range, ordered morphology of CdS nanoclusters can be obtained by using patterned substrates with 400 nm shallow grooves. The incorporated nanoparticles retain the same luminescence characteristics as in the pure state.

Flat-surfaced, rod-like materials were obtained by synthesizing long one-dimensional SnO₂ structures using a new spray pyrolysis method. The structure and growing mechanisms were evaluated by using scanning and transmission electron microscopy and atomic force microscopy. Molecular simulation tools and high resolution transmission electron microscopy images allowed the analysis of a dynamic behaviour for energy release which determines how the structures are formed by searching for an axial energy release direction.

We have studied the electronic changes caused by light-induced isomerization of a photochromic molecule between an open state (that absorbs in the UV to become closed) and a closed state (that absorbs in the visible to become open). Data obtained using a newly developed repetitive break junction method are interpreted in terms of single-molecule resistances of 526 ± 90 MΩ in the open form and 4 ± 1 MΩ in the closed form when the molecule is bound between two gold contacts via dithiol linkages. The corresponding ratio of open to closed resistance is in close agreement with the results of ab initio calculations, though the measured resistances are about half of the calculated values. Optical spectroscopy indicates that the photoisomerization occurs in both directions on small gold particles, evaporated thin gold films, and in the break junction experiments. http://stacks.iop.org/0957-4484/16/695

Atomic force acoustic microscopy (AFAM), an emerging technique that affords nanoscale lateral and depth resolution, was employed to measure the elastic properties of ultrathin films. We measured the indentation modulus M of three nickel films approximately 50, 200, and 800 nm thick. In contrast to conventional methods such as nanoindentation, the AFAM results remained free of any influence of the silicon substrate, even for the 50 nm film. X-ray diffraction and scanning electron microscopy results indicated that the films were nanocrystalline with a strong preferred (111) orientation. Values of M ranged from 210 to 223 GPa, lower than expected from values for bulk nickel. The reduced values of the elastic modulus may be attributed to grain-size effects in the nanocrystalline films.

We report on the design and fabrication of a channel structure for high precision guidance and achieving excellent confinement properties for motor-propelled molecular shuttles. The techniques used to manufacture the channel structure are mainly e-beam lithography and selective monolayer functionalization. The structure consists of two lateral layers of concentric channels on a SiO₂ surface made biocompatible with the molecular motors. The quality and advantages of the design are demonstrated by experiments using the motor proteins actin and myosin. The special channel geometry leads to stable biochemical conditions with full motor protein functionality. ATP is sufficiently supplied to all parts of the structure by dedicated service channels, as is the venting of ADP and P_i (inorganic phosphorus). Channels of different widths (100–700 nm) and shapes are fabricated and measurements made on them.

A multilayer nanocomposite consisting of Au nanoparticles separated by layers of amorphous Al₂O₃ was prepared by pulsed laser deposition. The laser energy density used to deposit the Al₂O₃ layers was varied to investigate the effects on the resulting microstructure. When Al₂O₃ is deposited on the Au it results in resputtering and interfacial mixing of the Au nanoparticles into the Al₂O₃ matrix being deposited onto them. This leads to a reshaping of the nanoparticles, elongating them in the growth direction and in some cases forming cavities in the nanoparticles. These effects become more pronounced with increasing laser energy density. The high kinetic energies of the species involved also result in implantation of Au into the Al₂O₃ where it forms nanoparticles of about 1 nm mean diameter.

In this study, we present the results of the influence of surface modification of TiO₂ nanoparticles on the short-term breakdown strength and space charge distribution of low-density polyethylene (LDPE). A polar silane coupling agent N-(2-aminoethyl) 3-aminopropyl-trimethoxysilane (AEAPS) was used for the nanoparticle surface modification. Despite agglomeration and a poor interface compared to untreated nanoparticles, it was found that the incorporation of polar groups onto the nanoparticle surface improved both the dielectric breakdown strength and space charge distribution as compared to samples filled with untreated nanoparticles. Microstructure studies showed that the presence of polar groups on the TiO₂ nanoparticle surface did not evidently affect the degree of crystallinity, crystalline morphology (except for internal spherulitic order), and chemical structure of the polymer matrix. The improved dielectric breakdown strength was therefore concluded to be directly due to beneficial effects related to the variation of the electrical features at the particle surface due to introduction of polar groups. For the same reason, with the use of surface modified nanoparticles, formation of space charge was suppressed.

A convenient one-step synthesis of silicon nanoparticles from thermal reduction of -di-tert-butyl-1, 3-diaza-2, 2-dichloro-2-silacyclopentane in the presence of trioctylphosphine oxide and Li metal is discussed. Transmission electron microscopy, energy dispersive x-ray analysis, UV/visible and IR spectroscopy, fluorescence spectrophotometry and nuclear magnetic resonance were employed to characterize the nanoparticles with an average size of 5.2 ± 1.2 nm.

Wurtzite ZnS nanowires were produced by a vapour–liquid–solid process. The growth mechanism of the ZnS nanowires was studied by scanning electron microscopic observations at different stages of the nanowire growth. The produced nanowires were characterized by x-ray diffraction, scanning and transmission electron microscopy and photoluminescence measurements. The ZnS nanowires were perfectly single crystalline and possess a very high aspect ratio. A photoluminescence study shows UV–blue emission from the ZnS nanowires due to the sulfur vacancy and surface states.

A solution-phase reaction under hydrothermal conditions at relatively low temperature is first put forward for the preparation of γ-AlOOH nanotubes and nanorods, on the basis of the possible strategy that the 2D framework structure of γ-AlOOH containing lamellae could provide orientation for the growth of 1D nanostructures. X-ray diffraction (XRD) patterns, transmission electronic microscope (TEM) images, Fourier transform infrared (FTIR) spectra, and photoluminescence (PL) spectra were used to characterize the products. A possible formation mechanism of nanotubes and nanorods from lamellar precursor is proposed.

ZnO nanowires were synthesized by chemical vapour deposition (CVD). The dc electrical conductivity of a single ZnO nanowire was investigated over a wide temperature range from 300 to 6 K. It is found that the temperature dependence of conductivity follows the relation . The conductivity data suggest that the dominant conduction mechanism is Efros–Shklovskii variable-range hopping conduction. The strong electron–electron interaction in the nanowire is also proved by the I–V and d I/d V curves, on which there emerges a Coulomb gap-like structure at low temperatures.

We demonstrate that multiwalled carbon nanotubes can be used as etch masks in a reactive ion etch, yielding silicon structures defined by the size and orientation of the carbon nanotube. The relationship between etch profile and reactive ion etch parameters is optimized to yield an anisotropic etch with vertical sidewalls, supporting carbon nanotubes of diameters down to 25 nm, without apparent damage to the nanotube. We demonstrate that the etched structures can be used as thermal nanoimprint stamps and that the carbon nanotube remains on the etched ridge after imprinting. The method is a route for creating nanoscale structures with a resolution defined by the smoothness and width of a macromolecular structure.

Optical lithography based on microfabrication techniques was employed to fabricate one-dimensional nanogaps with micrometre edge lengths in silicon. These one-dimensional nanogaps served as a platform on which organic/nanoparticle films were assembled. Characterization of the gaps was performed with high-resolution TEM, SEM, and electrical measurements. Novel self-assembling attachment chemistry, based on the interaction of silicon with a diazonium salt, was used to iteratively build a multi-layer nanoparticle film across a 7 nm gap. By using nanoparticles capped with an easily displaced ligand, a variable conductive path was created across the 1D nanogap. Electrical measurements of the gap showed a dramatic change in the I(V) characteristics after assembly of the nanoparticle film.

The statistical variations in the properties of carbon nanotubes and their contacts to metallic electrodes can be averaged by using networks of single-walled carbon nanotubes as sensing devices. Carbon nanotube networks have been assembled on microstructures with dielectrophoresis, using an inhomogeneous alternating electric field to attract carbon nanotubes onto the microelectrodes. The networks were assembled on identical microstructures using four different frequencies in the range 10 kHz–10 MHz. From structural and electrical characterization of the assembled structures, we found that at higher frequencies the assembled nanotubes align better with the electric field and are more free of impurities. We also found consistently lower resistances for networks assembled at higher frequencies, suggesting that a high assembly frequency may lead to better quality networks with low contact resistances.

Arsenic doping of ZnO nanowires for building blocks of potential nanoscale photonic devices is reported. It was demonstrated in high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy that arsenic could be doped into the substitutional sites in ZnO lattice by post-annealing samples grown on GaAs substrates without degradation of the crystalline and optical qualities. In a series of photoluminescence (PL) spectroscopy observations, arsenic-doped ZnO nanowires exhibited emission due to acceptor-bound excitons at room temperature. The observed emission characteristics implied that the dopant arsenic formed a hydrogen-like acceptor, suggesting the feasibility of producing possibly p-type ZnO nanowires via a simple route.

The effects of CeF₃ doping on the photoluminescence (PL) of Si nanocrystals embedded in a SiO₂ matrix, assigned as nc-Si:SiO₂, have been studied. The nc-Si:SiO₂ sample was prepared by means of reactive evaporation followed by thermal annealing, and CeF₃ doping was conducted via thermal diffusion. It is found that the doping of CeF₃ is able to enhance the PL intensity of nc-Si by a factor as large as 3.7. With the increasing doping concentration, the degree of PL intensity enhancement increases until a maximum is reached, and then it drops down. This trend also holds for the PL intensity enhancement versus the diffusion annealing temperature. A continuous redshift of the PL peak was observed with the increasing doping concentration and diffusion annealing temperature. Beyond a certain concentration or temperature, the PL peak starts to shift back towards shorter wavelengths. The doping effects on the PL intensity were explained by a model of electron transfer from Ce ions to nc-Si, while the trends of PL peak shift were accounted for with the help of a previous model referring to the size distribution of nc-Si crystallites versus nc-Si:SiO₂ film thickness (Fang et al 2004 Nanotechnology 15 494); the peak shift was also related to the chemical reaction between Ce and Si.

A combination of new organic photoresist films based on naphthoquinone with a conventional AFM using a tapered fibre tip as a near-field source enables the development of 'real time' dry process nano-lithography. The methodology of the adaptation of these films as well as the system configuration for a nano-scale fabrication will be described. Using these materials the exposure can be performed either by the optical near field or nano-thermal effect to achieve positive or negative lithography. Sub-wavelength gratings fabricated using this system with a variable line width down to 45 nm will be demonstrated.

By adjusting the rotating speed and colloidal concentration in the spin coating of silver nanoparticles onto a glass substrate, the coating density could be varied from 1.5 × 10⁻⁶ to 1.1 × 10⁻⁴ g cm⁻², or in other words from a dispersed distribution to multi-layered close packed films. The coating density was found to be proportional to the volume fraction of silver colloids and inversely to the rotating speed to the 0.442 power. The multi-layered films were further investigated for sintering behaviour. Our results indicated that the film started to exhibit a noticeable sintering effect at about 100 °C, and at the same time it became electrically conductive. As the treatment temperature increased further, the film resistivity reached a minimum value at 250 °C and finally became insulating again when the temperature was over 400 °C due to silver coalescence into large particles and breaking up of the conductive paths. Smaller silver nanoparticles, however, would exhibit a similar phenomenon but at lower temperatures.

We have recently fabricated Keggin-type polyoxometalate (H₄SiW₁₂O₄₀) nanotubes by calcining layer-by-layer (LBL) structured ultrathin hybrid film coated electrospun fibrous mats. The hybrid film coated electrospun fibrous mats were obtained from the alternate deposition of positively charged poly(allylamine hydrochloride) (PAH) and negatively charged H₄SiW₁₂O₄₀ on the surface of negatively charged cellulose acetate (CA) nanofibres using the electrostatic LBL self-assembly technique. The fibrous mats were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared (FT-IR) spectroscopy, and wide-angle x-ray diffraction (WAXD). It was found that the morphology of hybrid PAH/H₄SiW₁₂O₄₀ film coated fibrous mats was strongly influenced by the number of deposition bilayers and the pH of dipping solutions. The fibrous mats were contracted and H₄SiW₁₂O₄₀ nanotubes with a wall thickness of about 50 nm can be fabricated after calcination at high temperature. Additionally, the FT-IR and WAXD results indicated that the pure H₄SiW₁₂O₄₀ nanotubes were obtained with a Keggin structure.

Two-dimensional staggered silver nanosheets (NSs) immobilized on a flat aluminium foil have been synthesized by keeping the underside surface of the foil in contact with the solution of normal silver mirror reaction. The NSs are hundreds of nanometres to several micrometres in dimensions and tens of nanometres in thickness. The effects of the aluminium foil, a chemically active substrate, on the orientation growth of silver nanosheets has been revealed. The results demonstrated that the growth and the morphology control of the silver nanostructure were simply realized in one process by the introduction of a chemically active substrate.

We have investigated the sintering behaviour of cubic BaTiO₃ nanoparticles obtained under supercritical conditions. The ferroelectric properties of samples sintered between 950 and 1300 °C were measured from room temperature up to 200 °C and in the frequency range 100 Hz–10 kHz. The influence of the initial powder characteristics on the microstructure and dielectric properties of ceramics have been investigated. The ferroelectric transition temperature was used as an intrinsic probe for the ceramic characterization and was then found to be dependent on the Ba:Ti ratio of the initial powder. Understanding the role of the key parameters at different scales (bulk and nanoscale composition, tetragonal distortion, microstructure) on the permittivity, losses and transition temperature would lead to a possible modulation of ferroelectric properties.

ZnO nanoparticles and nanorods as anode active materials were investigated by charge–discharge cycle measurements. The ZnO nanomaterials with larger specific surface area exhibited higher electrochemical activity than conventional ZnO particles. The discharge capacity delivered by ZnO nanorods exceeded 500 mA h g⁻¹ until the 175th cycle. It also exhibited higher midpoint discharge voltage than conventional ZnO. The morphologies of ZnO had a significant effect on the electrochemical properties of the anodes. In the initial cycles, the morphologies of ZnO did not essentially change due to the extension effect, and the electrochemical performance of the electrodes was relatively stable. When increasing the cycles, according to the texture growth mechanism, the large flaky ZnO parallel to the substrate surface predominated to reduce the electrochemical performance. Due to the intensive extension effect, the growth mode of ZnO nanorods changed. The eventual morphology was erect small flaky ZnO crystals that suppressed the production of Zn dendrite and enhanced the capacity maintenance.

In this paper, we address the problems associated with the identification and compensation of adverse dynamic effects (magnitude and phase distortions) that limit the operating speed in currently available scanning tunnelling microscopes (STMs). To minimize errors caused by dynamic effects, current STM systems are operated at relatively low speeds (scan frequencies) when compared to the first resonant frequency of the system. Low operating speed limits the temporal resolution of STMs, which in turn limits the STM's ability to observe fast surface phenomena, and reduces the throughput of STM-based applications such as nanofabrication. Our main contribution is the development of an image-based approach that exploits the extant imaging capabilities of the STM to identify and compensate for errors caused by unwanted dynamic effects, thereby enabling high-speed STM operation. The proposed image-based method is illustrated by applying it to an experimental STM.

A two-step masking technique has been developed to prepare large-scale triangular lattice arrays of uniform sub-micron islands on substrates at room temperature and at low cost by utilizing self-assembly of polystyrene microspheres. As an example, fabrication of large arrays of nickel islands with long-range periodicity and morphological uniformity is demonstrated, which is also ready to apply to fabricate periodic sub-micron islands of other materials on flat substrates in general. The islands so prepared resemble the shape of a hexagonal disc with its size determined by the size of the polystyrene spheres and its thickness variable in a wide range. These islands of various materials on different kinds of substrates can be used in a variety of applications such as catalysts to grow aligned carbon nanotubes and nanowires for 2D photonic crystals, nanoelectrode arrays for molecular devices, nanostructure building blocks for nanofabrications, etc.

We demonstrate registration of the location of the impact site of single ions using a thin film polymethyl methacrylate resist on a SiO₂/Si substrate. Carbon nanotube-based atomic force microscopy is used to reveal craters in the surface of chemically developed films, consistent with the development of latent damage induced by single-ion impacts. The responses of thin PMMA films to the implantation of He⁺ and Ga⁺ ions indicate the role of electronic and nuclear energy loss mechanisms at the single-ion level.

Electronic and structural properties of several charge states of vacancies, antisites and carbon substitutional impurities in a (10, 0) BN nanotube are investigated through density functional theory calculations. The formation energies indicate that neutral and simply charged states occur in the range of allowable electronic chemical potential. For carbon substitutional impurities, the most probable states are, besides the neutrals, the positively charged state for carbon at a boron site (C_B⁺), and the negatively charged state for carbon at a nitrogen site (C_N⁻). The charge compensation between neighbouring pairs of C_B⁺ and C_N⁻ defects is suggested to explain the successful experimentally obtained boron carbonitride nanotubes. Vacancies always present high formation energies. The neutral and positively charged states of the nitrogen antisite show low formation energies. The calculated formation energies for all defects studied here can be interpreted as due to two main effects: a tendency to recover the number of electrons of the defect-free BN nanotube and the screening effects due to the perturbative potential of the defects.

The light-emitting properties of Ge nanocrystals on an Si(100) matrix prepared by pulsed laser deposition (PLD) and in situ rapid thermal annealing (RTA) were studied. The photoluminescence (PL) intensity becomes stronger and the FWHM decreases from 100 to 50 meV when the annealing temperature varies from 300 to 600 °C, reflecting that the as-deposited amorphous Ge has been effectively crystallized by high temperature. Also, the PL peak significantly shifts from 0.786 to 0.732 eV and the FWHM of the peaks increases from 30 to 70 meV as deposition time increases from 30 s to 8 min, indicating that the PL of the Ge nanocrystals has a large quantum size effect. In addition, the PL peaks increase initially and then decrease with increasing reversed bias voltage, which is attributed to the tunnelling effect of the carriers.

A continuous impingement mixing process is described that has been used to disperse unpurified single-walled carbon nanotubes (SWNTs) in a Shell EPON-862/EpiCURE system. Composites with up to 0.5 wt% of nanotubes were prepared by this process. Mechanical properties of these samples were compared with those of plain material and with samples prepared by hand-mixing, and they were found to be enhanced by up to 40%. More specifically, tensile stress was increased by 40% at 5% strain in composites prepared by impingement mixing. Recurrent mixing was also found to improve SWNT dispersion. The effect of stabilizing SWNTs with polyvinyl pyrrolidone (PVP) prior to composite preparation is also reported.

Aligned carbon nanotubes with uniform outer diameters, ordered over wafer-scale areas were fabricated using porous alumina templates on silicon. Anodization of aluminium films deposited on corrugated silicon surfaces, patterned using interference lithography, led to periodic pore structures over wafer-scale areas with controlled spacing and symmetry, and with pore sizes independently controlled through the anodization conditions. Nickel deposited at the base of the pores catalysed CNT growth during PECVD. These results demonstrate a wafer-scale approach to the control of the size, pitch, ordering symmetry, and position of nanotubes and nanowires in a rigid insulating scaffold.

Studies on two-photon lithography in negative SU-8 photoresist demonstrate the possibility of obtaining mechanically stable, stress-free, extended nanorods having lateral sizes of about 30 nm (corresponding to λ/25 resolution). The high resolution achievable with the given combination of materials and fabrication techniques demonstrates its potential for the fabrication of large-scale nanostructures, such as photonic crystals with photonic stop gaps at visible wavelengths.

AAO template technology was combined with silicon technology to be directly applied to electronic device fabrication. Thin film anodic aluminium oxide (AAO) templates were fabricated on a silicon wafer by multiple anodizations. No electropolishing was used after the deposition of the aluminium layer on Si wafers. The ordering of the pore arrangement was improved by repeated anodizations, and highly ordered AAO templates could be obtained on Si wafers.

CNT field emitter arrays were made with the AAO templates on Si wafers. Field emission measurement revealed that the emission current density increased with the synthesis temperature of CNTs. The large field enhancement factor in the range of 2440–4000 indicates the potential of the CNT field emitter array based on the AAO template on a Si wafer.

Nanoparticle impacts on an ultra-smooth surface always occur in nano-machining processes, such as polishing of a monocrystalline silicon wafer, which is an important process in the manufacture of semiconductors. A fundamental understanding of nanoparticle impacts on a solid surface is important to control and prevent the deformation of the surface. In this study, a cylindrical liquid jet containing de-ionized water and SiO₂ nanoparticles impacts obliquely on a single crystal silicon surface at a speed of 50 m s⁻¹. The microstructure of the impacted surface was examined using a high resolution transmission electron microscope, an atomic force microscope, etc. Some crystal defects, lattice distortion, grain refinement and rotation of grains in the surface layer of the silicon wafer after exposure for 30 s have been observed. However, when the exposure time is extended to 10 min, an amorphous layer containing crystal grains is exhibited in the subsurface, and many craters, scratches and atom pileups can be found in the surface.

ZnO nanoparticles were synthesized and successfully incorporated in Ce³⁺-doped SiO₂ matrix by a sol–gel method. Photoluminescence intensities were compared for ZnO nanoparticles, Ce³⁺-doped SiO₂ (SiO₂:Ce³⁺) and ZnO encapsulated in SiO₂:Ce³⁺ (ZnO–SiO₂:Ce³⁺) fabricated from sol–gels. Green emission from ZnO associated with anionic oxygen vacancies and blue broadband emission due to transitions in Ce³⁺ ions were observed. The photoluminescence intensity of Ce³⁺ was enhanced considerably by the energy transfer from ZnO nanoparticles.

We describe a family of defect-tolerant demultiplexers based on error-correcting codes. A conventional demultiplexer with a k-bit input address and 2^k-bit output may be fortified against certain defect types by widening its address bus to n>k bits to permit an encoded address to be used within the demultiplexer. The redundant address is computed by an encoder that guarantees a minimum Hamming distance d between addresses, which sparsely populate an expanded address space. The increased Hamming distances between addresses are especially tolerant of stuck-open defects (and broken wires, which are equivalent to multiple stuck-open defects). For each address width k, there are a series of demultiplexer designs with increasing internal redundancy, increasing d, and increasing capability for defect tolerance. These circuit designs are especially suitable for nano-scale crossbars; in particular, they may be realized at the interface where the CMOS wires of conventional microelectronics cross nano-wires to form a mixed-scale interconnect crossbar. Thus, a small number (2n) of CMOS wires may be used to control a much larger number (2^k) of nano-wires; the family of encoded demultiplexer designs provides a robust interface to the nano-circuitry, giving significant protection from manufacturing mistakes at the cost of a relatively small amount of area overhead . This is a qualitatively new application of error-correcting codes, the analysis of which combines elements of the conventional coding-theoretic notions of full-error and erasure correction. In particular, a code with minimum distance d guarantees tolerance to up to d−1 defects per nano-wire, in analogy to conventional erasure correction.

Highest purity calcium difluoride crystals having a roughness below 1 nm over large areas were prepared by ultra-precision machining to create technical surfaces for optical applications. High resolution dynamic scanning force microscopy reveals surfaces with close to atomic flatness over areas larger than 10 µm². The residual roughness is due to a high density of pits and protrusions with a height of 0.32 nm corresponding to an F–Ca–F triple-layer that is the smallest possible unit on stoichiometric CaF₂(111). Additionally, imperfections of the machining process may appear as protrusions of typically 1 nm height or a high density of aligned triple-layer steps for surfaces that were apparently slightly inclined with respect to the machining plane. A terraced structure also appears in the vicinity of nanometre-sized defects found for one sample. Machining may also cause a fracture in the form of branched channels of some tens of nanometres in width and some micrometers in length.

This paper describes a digital logic architecture for 'CMOL' hybrid circuits which combine a semiconductor–transistor (CMOS) stack and two levels of parallel nanowires, with molecular-scale nanodevices formed between the nanowires at every crosspoint. This cell-based, field-programmable gate array (FPGA)-like architecture is based on a uniform, reconfigurable CMOL fabric, with four-transistor CMOS cells and two-terminal nanodevices ('latching switches'). The switches play two roles: they provide diode-like I–V curves for logic circuit operation, and allow circuit mapping on CMOL fabric and its reconfiguration around defective nanodevices. Monte Carlo simulations of two simple circuits (a 32-bit integer adder and a 64-bit full crossbar switch) have shown that the reconfiguration allows one to increase the circuit yield above 99% at the fraction of bad nanodevices above 20%. Estimates have shown that at the same time the circuits may have extremely high density (approximately 500 times higher than that of the usual CMOS FPGAs with the same design rules), while operating at higher speed at acceptable power consumption.

The aim of the present work is to extract the conservative and dissipative parts of the tip–sample interaction from the atomic force microscope amplitude modulation mode (AM, often called tapping). To do so, analytical expressions are used to transform the experimental amplitudes and phase variations with tip–sample distance to frequency shift and damping coefficient. The experimental procedure for the separation is detailed. The separated conservative and dissipative parts from the AM mode are compared for two driving frequencies, and then they are compared to the frequency modulation mode (FM, often called resonant non-contact) measurements for two different amplitudes. The conservative parts from the AM measurements are similar to the frequency shifts measured in the FM mode and also the dissipative parts from the AM measurements are very close to the dissipation measured in the FM mode. Experimentally, this good agreement is related to the small amplitude variation in the AM data on a chemically controlled grafted layer.

Those results show experimentally that the AM and FM modes are just two different ways to probe the same tip–sample interaction. They also validate the AM data treatment to separate the conservative and dissipative parts as the only hypothesis needed is that only the fundamental harmonic contributes to the signal.

For the first time, Au/Ti micro- and nanotubes were prepared by rolling initially planar, strained Au/Ti bifilms, freed from the Si substrates by wet selective etching of underlying Al sacrificial layers. Conducting metal tubes with diameters ranging from 20 µm to 40 nm were made from 10 µm wide and 10 cm long metal strips lithographically defined on Si substrates. Also, arrays of tubes rigidly attached to the substrate by unrolled parts of the film were obtained. Fully detached tubes could be bent to form sharp angles or loops without mechanical failure, due to their high plasticity. The shape and electric conductivity of the Au/Ti micro- and nanotubes were found to remain unchanged over a more than two-year long storage in ambient air.

A new template-directed method for large-scale fabrication of hexagonally patterned and vertically aligned ZnO nanowires is demonstrated. The process involves a novel type of metal membrane, gold catalyst templates produced using the membrane as the deposition mask, and catalyst-guided vapour-phase growth of ZnO nanowires. The metal membranes, composed of hexagonal nanotube arrays, are electrochemically replicated from ordered porous alumina. The obtained ZnO nanowires are uniformly aligned perpendicular to the GaN surface and have a distribution according to the pattern defined by the nanotube membrane. We also demonstrate that by modifying the electrochemical parameters and growth conditions, the diameter of the nanowires can be varied in the range 30–110 nm.

Electrospinning offers an avenue to produce small diameter tubes made out of nanofibres. However, to date, most tubes from electrospun fibres have been either random fibres or from sheets that were rolled into tubes. Although there have been suggestions of getting tubes made of circumferentially aligned fibres, this is the first time that a method used to create a tube made of diagonally aligned electrospun fibres has been described. This tube was formed by depositing fibres on a rotating tube during electrospinning to give a resultant tube with uniform thickness and superior all round mechanical strength without any line of weakness. A knife-edged auxiliary electrode was given a charge that was opposite to that of the charge given to the needle to create an electrostatic field that encouraged fibre alignment on a rotating tube collector. A tubular structure made of nanofibres aligned in a diagonal direction was produced through electrospinning.

The role of plasma in plasma enhanced chemical vapour deposition of carbon nanotubes and nanofibres is investigated with both experimental and computational diagnostic techniques. A residual gas analysis (RGA) of a 12 mbar dc discharge with a C₂H₂/NH₃ gas mixture is conducted near the Ni catalyst surface employed for carbon nanofibre growth. The results are corroborated with a 1D dc discharge model that solves for species densities, ion momentum, and ion, electron and neutral gas thermal energies. The effect of varying the plasma power from 0 to 200 W on the gas composition is studied. The dissociation efficiency of the plasma is demonstrated where over 50% of the feedstock is converted to a mixture of hydrogen, nitrogen and hydrogen cyanide at 200 W. Finally, the important role that endothermic ion–molecule reactions play in this conversion is, for the first time, established. Of these reactions, dissociative proton abstraction and collision-induced dissociation are of the greatest significance.

Sintering of ZnO pressed powder under Ar flow at temperatures between 1250 and 1300 °C leads to the formation of elongated microstructures and nanostructures, with different morphologies, on the sample surface. Rods and needles with cross-sectional dimensions ranging from tens of nanometres to several tens of microns and up to hundreds of microns in length are obtained. In an advanced stage of growth, nanoneedles are frequently arranged in bundles, forming the walls of tubes with different cross-sectional dimensions. In addition, microcombs and microfeathers consisting of well oriented nanoneedles are observed. Cathodoluminescence (CL) in the scanning electron microscope (SEM) has been used to characterize the structures grown. The formation of the elongated structures causes spectral changes, in particular an enhancement of the green–orange luminescence. High CL emission from the internal surface of the tubes has been observed.

We demonstrate metal organic vapour phase epitaxy growth of GaP/GaAs_1−xP_x/GaP double heterostructure nanowires on GaP(111)B, and report bright photoluminescence at room temperature. By using different PH₃ to AsH₃ flow ratios during growth of the GaAs_1−xP_x segment, we are able to control the composition of the segment, making it feasible to tune the wavelength of the emitted light. A photoluminescence system was employed to characterize the luminescence, and x-ray energy dispersive spectrometry and x-ray diffraction studies were used to investigate the composition of the segment. These double heterostructure nanowires could in the future be used in optoelectronic devices and as multiple-wavelength fluorescent markers for biomedical applications.

Intense photoluminescence in blue was measured in as-deposited Si-in-SiN_x films prepared by plasma-enhanced chemical vapour deposition on cold substrates. The density of the silicon nanoparticles amounts to 1.4 × 10¹³ cm⁻² as calculated from transmission electron microscope images, and the particle size can be well controlled under 2.6 nm. Rapid annealing at 500 °C for two minutes roughly doubles the photoluminescence intensity, while the peak profile suffers only negligible change. In contrast, annealing at 1050 °C results in a broadened spectrum red shifted by about 80 nm. External quantum efficiency for the photoluminescence was estimated to be well above 1.0% by comparing with GaN. This demonstrates that, with appropriate processing parameters, the low-temperature procedure is promising for obtaining applicable light emission from Si-in-SiN_x films.

Amorphous chalcogenides in the form of bulk or thin films are known as photosensitive materials that undergo changes in optical or structural properties upon irradiation. Here we study the optical properties of nanocomposite films of ZnS–SiO₂ illuminated with ultraviolet (UV) light and relate them to the photo-induced evolution of roughness, as well as photo-crystallization effects in these films. We observe that upon UV irradiation a new crystalline phase of ZnSiO₃ is formed in the nanocomposite film. This is accompanied by the evolution of surface roughness on the film.

Ultrafast time-resolved reflectivity investigations are performed on InP-based photonic crystals with a wide range of structural parameters. It is found that the structure plays a critical role in determining the recombination dynamics of the photo-injected charge carriers. For sufficiently large etched sidewall area densities the carrier lifetime is decreased to a level below 100 ps.

We have studied particle size distributions of FePt nanoparticles with analytical ultracentrifugation. The particles were made with the common polyol process by thermal decomposition of iron pentacarbonyl and reduction of platinum (II) acetylacetonate. The size distribution is found to be bimodal (dual) rather than a monomodal distribution as normally reported. The density values for these particles indicates that the smaller particles, ∼7.4 nm diameter, have a density above 4 g cm⁻³ while the larger particles, ∼16 nm, have a density of ∼3.2 g cm⁻³ due to a higher Fe content in the lighter particles.

We demonstrate the successful formation of ferromagnetic nanoclusters in Mn-incorporated GaInAs layers grown by metal–organic vapour phase epitaxy on InP(100) substrates under low growth temperature conditions below 450 °C. We find that MnAs nanoclusters with NiAs-type hexagonal crystallographic structures, which show ferromagnetic characteristics up to a relatively high temperature of about 305 K, are formed near the layer surfaces of Mn-incorporated GaInAs layers grown at 440 °C. After deposition of undoped InP layers on Mn-incorporated GaInAs layers, MnP nanoclusters with orthorhombic cubic crystallographic structures, in which 7% arsenic is incorporated, are formed in InP layers. The samples with MnP nanoclusters show strong ferromagnetic coupling up to about 305 K, although the Curie temperature of MnP bulk compounds is 291 K. Energy dispersive x-ray spectroscopy (EDS) indicates that Mn concentrations in InP and GaInAs layers surrounding MnP nanoclusters are almost negligible. MnAs nanoclusters are also formed in Mn-incorporated GaAs layers grown under low growth temperature conditions of 450 °C on GaAs(100) substrates. From the results of magnetic characterizations with respect to growth temperatures of the samples, we found that all the Mn-incorporated GaAs layers grown at temperatures below 450 °C showed ferromagnetic behaviour.

Atomic force microscopy (AFM) provides three-dimensional images with resolution at or near the atomic level. Many researchers have addressed the metrological aspects of AFM imaging of physical samples, producing a range of recognized standards for calibrated spatial measurements. However, because of the complex interplay of forces between an AFM tip and biological samples, the dynamic environment in which such imaging takes place, and difficulties in immobilization, no satisfactory equivalents exist for the biological AFM community. Here an exploration of the effects of AFM imaging parameters on apparent biomolecular dimensions in aqueous environments is carried out for a three-component system comprising GroEL protein, plasmid DNA and gold nanoparticles. The biomolecules in this system have been chosen to present differing imaging challenges, while gold nanoparticles serve as an internal reference for tip performance. Concurrent immobilization of these entities requires optimization of sample preparation methodology, described here as it is hoped the system may act as a template for future bio-metrological standards. Investigation of differences in measured heights and lateral dimensions of DNA, GroEL and gold spheres under a range of imaging conditions and the implications of these results for accurate imaging of biological samples and as a potential bio-metrological standard are discussed.

The role of the crystalline orientation of the STM tip in the generation of metal clusters is studied by atom dynamics simulations. When a (111) facet is facing the surface, the process is accompanied by a perturbation of the surface stronger than that observed for more open tip structures. This implies a technological application: the possibility of orienting a nanocrystallite deposited on a tip according to the changes observed in the force on the tip.

Nanosized Mn-doped ZnO particles were synthesized by a rheological phase reaction precursor method and the thermal decomposition of the oxalate precursors was studied by thermogravimetry and differential thermal analysis in air atmosphere. X-ray analysis reveals that the Mn-doped ZnO crystallizes in a wurtzite structure. The lattice constants of Zn_1−xMn_xO increase slightly when Mn is doped into ZnO. TEM analysis shows that the average diameter of the nanoparticles is about 10–13 nm. In addition, magnetization measurements under field cooling conditions reveal that the Mn-doped ZnO nanoparticles show ferromagnetic behaviour at room temperature and both the susceptibility and coercive force of Zn_0.95Mn_0.05O are larger than those of Zn_0.97Mn_0.03 and Zn_0.93Mn_0.07. This work demonstrates that Mn can be doped into nanosized ZnO by the method of rheological phase reaction, which represents an important method to synthesize a nanosized diluted magnetic semiconductor.

In this paper, we report an approach to prepare a new type of field emitter made up of ZnO nanowires coated with an amorphous carbon (a-C) or carbon nitride film (a-CN_x). The coated ZnO nanowires form coaxial nanocables. The best field emission properties, which showed a very low turn-on electric field of 1.5 V µm⁻¹ and an emission current density of 1 mA cm⁻² (enough to produce a luminance of 300 cd m⁻² from a VGA FED with a typical high-voltage phosphor screen efficacy of 9 lm W⁻¹) under the field of only 2.5 V µm⁻¹, have been obtained from the a-CN_x coated ZnO nanowire field emitter among three kinds of emitters: a-C coated ZnO nanowires, a-CN_x coated ZnO nanowires and uncoated ZnO nanowires. Microstructures and crystal configuration were investigated by scanning electron microscopy, x-ray diffraction and transmission electron microscopy. Band edge transition without any significant photoluminescence peak relating to intrinsic defects has been observed by photoluminescence measurement. The superior properties of the field emission are attributed to the low work function of the coated carbon nitride film and good electron transport property of the ZnO nanowires with an extremely sharp tip.

Micromachining of magnetic materials is becoming a crucial technology for future magnetic systems/devices such as high-density magnetic recording heads, high-density patterned media, magnetic quantum devices, and micro-magnetic smart systems. NiFe alloy, one of the typical ferromagnetic materials, can be deposited and fabricated using current thin film and micromachining technologies, and it has found various applications in microsensors, microactuators, and microsystems. In our recent work, Ni₄₅Fe₅₅ alloy with the highest saturation magnetic-flux density was selected as the micro-magnet for an all-silicon quantum computer. The micro-magnet was designed to create a large magnetic field gradient and to distinguish ²⁹Si nuclear spins arranged as chains in a ²⁸Si matrix with Larmor frequencies. This paper reports the micromachining of a Ni₄₅Fe₅₅ alloy mesa structure for an all-silicon quantum computer and the preliminary evaluation of its effectiveness using a magnetic force microscope (MFM) and a superconducting quantum interference device (SQUID).

An approximation for the SAW velocity (Rayleigh waves) in dependence on Poisson's ratio, which was misprinted in a former paper (P D Warren et al 1996 Nanotechnology 7 295–301), is corrected. At the same time, the connection of this approximation with the recent history of exact formulae for the Rayleigh-wave velocity is established.