Table of contents

We present a family of demultiplexer circuit designs based on linear error-correcting codes, which can be laid out on nanoelectronic crossbar structures. The crossbars are assumed to have configurable resistors at the crosspoint junctions, and the demultiplexer circuits are therefore implemented using resistor logic. In general, resistor logic offers poor voltage margins when implementing digital circuits, but the circuit construction we present allows us to circumvent this problem by capitalizing on the minimum-distance property of codes to avoid certain problem cases, and thus achieve a much larger voltage margin. For each linear code, there is a corresponding demultiplexer circuit prescribed by this construction, and thus a large family of demultiplexer circuits is defined. When a demultiplexer of a given size is needed in a system, this circuit family offers to the designer a set of alternative demultiplexer circuit designs, in which increasing voltage margins can be achieved, but at the cost of increasing circuit area. We analyse a demultiplexer circuit based on an arbitrary linear code. For this general case, we give the encoding computation prescribed by the code, give the configuration pattern prescribed by the code for the crossbar part of the circuit, calculate the output voltage on each of the demux output lines as a function of the current input signal, calculate the worst-case voltage margin, and calculate cost parameters measuring the increased area consumed by the circuit. This code-based demultiplexer circuit design makes it possible to handle the voltage-margin problem of resistor logic, and thus makes it feasible to build relatively large demultiplexers using nano-scale crossbars with configurable resistors at the crossbar junctions.

Developments within the electronics industry have led to the fabrication of surfaces with in-plane nanofeatures for use in biological investigations. An inexpensive, high throughput and accessible method has evolved, where a natural lithography technique utilizes off-the-shelf colloidal particles within the nanometric range to produce a variety of patterned substrates. Imaging of cell interactions with respect to underlying nanotopography (sub-100 nm) requires high resolution microscopy techniques. When utilizing field emission scanning electron microscopy (FESEM), operation is restricted to low voltage conditions in an attempt to image fine surface detail while limiting radiation damage, charging and carbon deposition with respect to biological material. The maximum number of backscattered electrons (BSEs) produced from biological specimens is achieved using low accelerating voltages while the number of BSEs emitted from high atomic number materials increases over the accelerating voltage range of 2–16 keV. By increasing the emission current, the number of electrons present in the primary beam is elevated, increasing BSE production at the low voltages utilized. Through the careful selection of high atomic number materials composing the colloids or similar topographical features, secondary electron (SE) and BSE detection can be utilized as complementary imaging techniques. This allows for the surface morphology of cell membranes to be imaged by SE detection in relation to the underlying high contrast nanotopography where BSEs are collected. Furthermore, cytoskeletal features of varying density can also be identified in relation to cells and colloidal nanofeatures when detecting BSEs.

We propose a novel technique to fabricate a free-standing three-dimensional colloidal crystal by self-assembling the colloidal microspheres with controllable thickness from the air–liquid interface. Highly ordered three-dimensional colloidal crystals are formed by polymethylmethacrylate or polystyrene monodisperse microspheres. We also demonstrate the fabrication technique of the free-standing inversed opals by removing the microspheres using calcination. The free-standing colloidal crystal structures can be used for nano-photonic circuits, white-light LEDs or as a photocatalyst.

We report a self-modulated taper-drawing process for fabricating silica nanowires with diameters down to 20 nm. Long amorphous silica nanowires obtained with this top-down approach present extraordinary uniformities that have not been achieved by any other means. The measured sidewall roughness of the wires goes down to the intrinsic value of 0.2 nm, along with a diameter uniformity better than 0.1%. The wires also show high strength and pliability for patterning under optical microscopes. The ability to prepare and manipulate highly uniform silica nanowires may open up new opportunities for studying and using low-dimensional silica material on a nanometre scale.

Titanium oxide (TiO₂) nanowires were prepared for an electrolytic capacitor application by the automatic dipping technique using a porous alumina template. The automatic dipping technique allows us to exactly control the dipping rate so that we can obtain homogenous infiltration of nanowires in the porous alumina membrane, even though the solution is very acidic. From the TEM, SEM and XRD measurements, we confirmed that anatase phase TiO₂ nanowires are highly infiltrated into the porous alumina template. In addition, the electrostatic capacitance of nanowires was measured and compared with a theoretical calculation using an effective thickness (δe). We found that the effective thickness corresponds to the mean radius of nanowires and the experimental measurements were in good agreement with the calculations.

Pure phase CeO₂ nanorods (about 40–50 nm in diameter and 0.3–2 µm in length) were synthesized through a solvothermal synthesis method. The addition of ethylenediamine is critical to obtain CeO₂ nanorods. Other experimental conditions, such as the solvent composition, surfactant and the cerium source precursor were of importance in the final product morphology. The reaction temperature and reaction time also had significant influence on the yield of CeO₂ nanorods. A possible formation mechanism of CeO₂ nanorods was discussed mainly based on the dependences of controlling parameters on the final morphologies. In addition, the optical properties of CeO₂ nanorods were investigated. The UV–visible adsorption spectrum and photoluminescence spectrum of the CeO₂ nanorods showed unusual red-shift and enhanced light emission, respectively.

We report on Raman scattering measurements on Si-capped Ge quantum structures grown by molecular beam epitaxy on Si(001) at low temperatures. We find a double band structure in the Ge–Ge frequency range for nanoislands grown at substrate temperatures ranging in the interval 300–500 °C. Complementary information has been obtained from performing Raman scattering experiments on annealed samples. The results are interpreted in terms of a model that considers quantum structures (hut clusters) composed of a strained Ge core and a more relaxed SiGe shell.

Precursor ZnS nanoparticles, synthesized from the precipitation reaction of zinc acetate and sodium sulfide, were annealed at 700 °C for the fabrication of shuttle-like ZnO nanoparticles. The structural characteristics, morphology, and chemical compositions of the as-prepared ZnO nanoparticles were investigated by x-ray powder diffraction (XRD), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS). It was revealed that the shuttle-like ZnO nanoparticles are pure and single crystalline, with lengths of up to 500 nm, stem diameters of 30–80 nm, and tip diameters of only a few nanometres. In addition, a possible growth mechanism for the obtained shuttle-like nanostructures is also discussed.

Colloidal iron oxide magnetic nanoparticles were synthesized from high temperature reaction of Fe(acac)₃ solution. The size of particles was easily tunable from 4 to 22 nm in only one step in the synthesis process. From TEM images the particles showed cubic–faceted shape with good homogeneity and narrow size distribution. Preliminary magnetic measurements show the usual superparamagnetic and blocked regimes depending on temperature.

Time-resolved and time-integrated microphotoluminescence spectrometry of exciton and biexciton transitions in a single self-assembled InGaN quantum dot gives sharp peaks, with the biexciton 41 meV higher in energy. Theoretical modelling in the Hartree approximation (using a self-consistent finite difference method) predicts a splitting of up to 51 meV. Time-resolved microphotoluminescence measurements yield a radiative recombination lifetime of 1.0 ± 0.1 ns for the exciton and 1.4 ± 0.1 ns for the biexciton. The data can be fitted to a coupled DE rate equation model, confirming that the exciton state is refilled as biexcitons undergo radiative decay.

Silicon nanowire field-effect transistors (SiNWFETs) have been fabricated with a highly simplified integration scheme to function as Schottky barrier transistors with excellent enhancement-mode characteristics and a high on/off current ratio ∼10⁷. SiNWFETs show significant improvement in the thermal emission leakage (∼6 × 10⁻¹³ A µm⁻¹) compared to reference FETs with a larger channel width (∼7 × 10⁻¹⁰ A µm⁻¹). The drain current level depends substantially on the contact metal work function as determined by examining devices with different source/drain contacts of Ti (≈4.33 eV) and Cr (≈4.50 eV). The different conduction mechanisms for accumulation- and inversion-mode operation are discussed and compared with two-dimensional numerical simulation results.

CNT (carbon nanotube)/Fe₃O₄ nanocomposites were prepared. The diameter of the CNT/Fe₃O₄ composites prepared was about 60 nm, while the diameter of the CNTs was about 20 nm according to the results of transmission electron microscopy (TEM) measurements. The average apparent density of the CNT/Fe₃O₄ nanoparticles was about 1.8 g cm⁻³, which is only a quarter of that normally used for magnetic particles. The sedimentation and magnetorheological properties of magnetorheological (MR) fluids based on CNT/Fe₃O₄ nanocomposites were studied. The MR fluids based on CNT/Fe₃O₄ nanocomposites exhibit high sedimentation stability and obvious magnetorheological behaviours such as an apparent viscosity depending on the applied field. These predominant properties are mainly due to the special structure of the soft magnetic layer covering the outside of the hollow CNTs and the large length–diameter ratio of the nanocomposites.

The specific heat of an aligned bulk multiwalled carbon nanotube sample made by the chemical vapour deposition method was measured from 250 to 1.8 K. The specific heat curve gradually decreased, showing one-dimensional (1D) behaviour down to 40 K. Below 40 K it showed a rapid decrease due to the dimensional change from 1D to 3D behaviour, indicated by different temperature dependences at low temperature. Interestingly, a T⁻² term was observed below 5 K, suggesting a nuclear hyperfine component due to magnetic impurities which were confirmed to be present by thermogravimetric analysis and microscopy observations.

Fe_0.32Ni_0.68 alloy nanotubes have been successfully synthesized by electrochemical deposition using a polycarbonate membrane template. The transmission electron microscope and scanning electron microscope observations reveal that the nanotubes have a conical morphology with two ends stuffed and a hollow structure. The length and diameter of the nanotubes are 7–8 µm and 200 nm, respectively. The aspect ratio (length to diameter) is as large as 40. Magnetic measurements show that the coercivities of the nanotubes for an applied parallel and perpendicular field are about 21 and 55 Oe, respectively. The hysteresis loops indicate that the nanotubes were more easily magnetized in applied parallel field than in applied perpendicular field. The mechanism of nucleation and growth of these nanotubes is also discussed.

Gold nanowires have been synthesized by template electrodeposition with an alternating field in porous aluminium oxide membranes. The use of dielectrophoresis to manipulate nanowires between electrodes has been investigated. Assembly was optimized by modelling the dielectrophoretic force, on the basis of the interaction between an alternating applied field and the induced dipole moment of gold nanowires. Results confirm the expected assembly characteristics, but also demonstrate how an understanding of the assembly process, and electrical behaviour of the electrode, is necessary for successfully assembling nanowires bridging the electrode gap.

Electrical characterization of nanowires assembled between electrodes has been conducted to determine the transport properties of these systems. Single nanowires displayed an Ohmic response with 35 Ω resistance values predominantly due to contact resistance between the electrode and nanowire. By optimizing the assembly and cleaning procedures the contribution of the contact resistance to the measured resistance has been reduced below those reported in the literature.

A conductive atomic force microscope (CAFM) has been used to study, at the nanometre scale, the dependence of the electrical behaviour on the post-deposition annealing temperature (T_A) and the dielectric reliability of ultrathin high-dielectric-constant/SiO₂ MOS gate stacks. It has been observed that for high enough T_A the conduction becomes more inhomogeneous, leading to the formation of leaky spots that could be a problem for the integration of these layers in a standard CMOS microelectronic process. The CAFM has also revealed that the values of some parameters related to the dielectric reliability, such as the area of the breakdown spot (i.e. a region that has lost its insulating properties owing to electrical stress), are of the same order for SiO₂ layers and high-dielectric-constant/SiO₂ stacks. Moreover, different conduction regimes, which cannot be detected by standard electrical characterization techniques, have been observed.

A liquid-cell-based cantilever sensor system operating in the dynamic mode has been developed and characterized, and the frequency spectra of commercial micrometre-scale silicon cantilevers in aqueous solutions have been studied. We report data demonstrating measurements of the resonance frequency shift induced upon phospholipid vesicle adsorption on an oscillating cantilever immersed in a liquid. A resonance frequency shift corresponding to an added mass of 450 pg has been measured, which is in good agreement with the estimated mass of 400 pg. In addition, the effect of varying the liquid volume in the cell on the frequency response has been investigated.

Recombination dynamics of photoluminescence (PL) in colloidal CdSe/ZnS quantum dots (QDs) were studied using time-resolved PL measurements. The PL intensity shows a biexponential decay at 9 K, consisting of a fast component (∼1 ns) and a slow component (∼6.3 ns). Based on the emission-energy and temperature dependence of carrier lifetimes, we suggest that the fast and slow PL decay of colloidal CdSe/ZnS QDs originates from recombination of the delocalized carriers in the internal core states and the localized carriers at the interface, respectively.

Carbon nanotube-based microcapsules with integral shells of cross-linked multi-walled carbon nanotubes (MWNTs) have been prepared and characterized. Shells of amine-functionalized MWNTs can be obtained by heterocoagulating nanotubes on latex particles. Cross-linking and dissolving latex particles resulted in hollow shell microstructures with a shell of nanotubes. The average size of the microcapsules is controlled by the average size of the latex particles.

The role of ion flux in Si(100) nanostructuring by normal-incidence Ar⁺ ion sputtering has been studied. The measured relationships of the Si lateral dot size versus ion flux, the surface roughness versus ion flux, and the surface roughness versus sample temperature with ion fluxes of 20 and 380 µA cm⁻² all indicate that the value of the ion flux is decisive for the validity of the Bradley–Harper (BH) model in the nanostructuring of semiconductor single crystals. In this work, for Ar⁺ ion sputtering of Si(100) with ion energy of 1.5 keV, it is found that only beyond ∼220 µA cm⁻² is the BH model well applicable, while below that the Ehrlich–Schwoebel (ES) one tends to be involved. Our results suggest that the ES barrier effect is negligible under relatively high flux conditions, while it is substantial in the case of relatively low flux; for the BH model, the situation is just the reverse. Hence, caution should be exercised as regards the value of the ion flux when one tries to tune the semiconductor nanodot size following the BH model.

We have investigated the carrier capture and relaxation processes in InAs/GaAs self-assembled quantum dots at room temperature by time-resolved photoluminescence techniques with a high time resolution of ∼200 fs. Following the initial fast relaxation in GaAs barriers, we have observed rising processes in time-resolved PL intensity at the energies of quantum dot confined states and the wetting layer. The rising processes are assigned to the carrier capture from the barriers into the wetting layer and confined states in InAs dots and subsequent relaxation in each detected energy level. We found that the carrier capture rate is faster than the intra-dot relaxation within the range of excitation densities that we investigated. Under high excitation intensity, the electronic states in the dots were populated mainly by carriers directly captured from the barrier. However, at low excitation densities, the PL rise times were influenced by the carrier diffusion.

Cs atom beams, transversely collimated and cooled, passing through material masks in the form of arrays of reactive-ion-etched hollow Si pyramidal tips and optical masks formed by intense standing light waves, write submicron features on self-assembled monolayers (SAMs). Features with widths as narrow as 43 ± 6 nm and spatial resolution limited only by the grain boundaries of the substrate have been realized in SAMs of alkanethiols. The material masks write two-dimensional arrays of submicron holes; the optical masks result in parallel lines spaced by half the optical wavelength. Both types of feature are written to the substrate by exposure of the masked SAM to the Cs flux and a subsequent wet chemical etch. For the arrays of pyramidal tips, acting as passive shadow masks, the resolution and size of the resultant feature depends on the distance of the mask array from the SAM, an effect caused by the residual divergence of the Cs atom beam. The standing wave optical mask acts as an array of microlenses focusing the atom flux onto the substrate. Atom 'pencils' writing on SAMs have the potential to create arbitrary submicron figures in massively parallel arrays. The smallest features and highest resolutions were realized with SAMs grown on smooth, sputtered gold substrates.

A detailed theory for enhanced optical absorption in thin silicon with a distribution of nanovoids has been worked out in this paper. It is demonstrated that significant enhancement of the effective optical absorption coefficient (by a factor of about two to more than four) in a thin Si layer can be achieved by optimizing the dimensions and distribution of nanovoids. In this work, the absorption in a thin Si layer has been modelled taking into account the diffraction of light by the nanocrystallites between the voids as well as the scattering of light by the voids. This modelling is supposed to be applicable to any semiconductor film having a distribution of nanovoids since the modelling incorporates scattering phenomena due to Rayleigh scattering for small voids and the gradual transition from Rayleigh scattering to diffraction phenomena in the case of large voids including multiple-and back-scattering effects. The consideration of the diffraction of light instead of Mie scattering greatly simplifies the calculation and still predicts the correct behaviour of absorption phenomena in such films. The simulated results obtained using this modelling agree excellently with Brendel's recently reported experimental results. This enhancement of the optical absorptance in a thin Si film with nanovoids has potential application in different devices, e.g. thin Si solar cells. The realization of nanovoids can be achieved by high temperature annealing of double-layer porous silicon, i.e. a quasi-monocrystalline porous silicon (QMPS) layer.

Silicon and aluminium are the substrates of choice for various micro/nanoelectromechanical systems (MEMS/NEMS) including digital micromirror devices (DMD^®). For efficient and failure-proof operation of these devices, ultrathin lubricant films of self-assembled monolayers (SAMs) are increasingly being employed. In this study, we investigate friction, adhesion and wear properties of various SAMs. Surface properties such as contact angle, adhesive force, friction force and coefficient of friction are compared for SAMs with hydrocarbon and fluorocarbon backbone chains with different chemical structures, chain lengths and end groups. The influence of relative humidity, temperature and sliding velocity on the friction and adhesion behaviour is studied for various SAMs. Failure mechanisms of SAMs are investigated by wear tests and the potential mechanisms involved are discussed. These studies are expected to aid the design and selection of proper lubricants for MEMS/NEMS.

Single-crystalline metallic nanowires, Ni, Ag, and Zn, were successfully fabricated using an anodic aluminium oxide (AAO) template by electro-deposition. The single-crystalline Ni and Ag nanowires showed face-centred cubic (fcc) structure with a preferred orientation along the [220] direction. Zn nanowires with hexagonal close-packed (hcp) structure also had preferred orientation along [220]. The structure of metallic nanowires depended on the deposition conditions and can be controlled by the conditions. Thermodynamics and electrochemistry were employed to analyse the growth mechanism. The competition among the nuclei and subsequent coalescence contributed to the formation of columnar structure within the nanopores of AAO, and H-adsorption led to the preferred orientation and single crystallinity.

We provide a fabrication method for silver nano-particles with a uniform particle size using vacuum deposition. The size uniformity was controlled by a small amount of neodymium–copper (Nd–Cu) as a co-sputtered material. Particles with a size of 20 ± 7 nm dispersed in a SiO₂ matrix have been obtained. The full width at half maximum of the plasmon resonance in the optical spectrum by the silver–neodymium–copper (Ag–Nd–Cu) nano-particles was only half of the size compared with the spectral width of a pure Ag nano-particle system. The effect is attributed to an increased uniformity in the particle size.

A single-phase β-sialon nanoceramic, Si₅AlON₇, has been prepared by high-energy mechanical milling, followed by spark plasma sintering. After milling, the starting powder mixture (Si₃N₄, AlN, Al₂O₃) was mostly transformed into an amorphous phase that contains a large number of well-dispersed nanocrystalline β-Si₃N₄ particles. Milling promoted the mixing and reaction among the starting powders; β-sialon grains with the designed composition were formed directly through precipitation from the homogeneous amorphous phase on the nanocrystalline β-Si₃N₄ particles. Milling also improved the sintering ability of the starting powders, so the densification temperature was lowered by about 100 °C compared with that for as-received powders. Particle rearrangement was the main densification mechanism for the milled powders. A homogeneous microstructure composed of equiaxed β-sialon grains with a diameter of about 50 nm was obtained after sintering at 1550 °C for 5 min.

We demonstrate the use of rolling circle replication to template linear DNA arrays whose sizes bridge the gap between nanometre-scale self-assembly and top-down lithographic fabrication. Using rolling circle replication we have produced an oligonucleotide containing several hundred repeats of a short sequence motif. On this template we have constructed, by self-assembly, an array consisting of two parallel duplexes periodically linked by antiparallel Holliday junctions. We have observed arrays up to 10 µm in length by atomic force microscopy.

Moybdenum-based subnanometre diameter nanowires are easy to synthesize and disperse, and they exhibit a variety of functional properties in which they are superior to other one-dimensional materials. However, further progress in the understanding of physical properties and the development of new and specific applications have so far been impeded by the fact that their structure was not accurately known. Here we report on a combination of systematic x-ray diffraction and extended x-ray absorption fine structure experiments, and first-principles theoretical structure calculations, which are used to determine the atomic skeletal structure of individual Mo₆S_9−xI_x (MoSI_x) nanowires, their packing arrangement within bundles and their electronic band structure. From this work we conclude that the variations in functional properties appear to arise from different stoichiometry, not skeletal structure. A supplementary data file is available from http://stacks.iop.org/0957-4484/16/1578

Ultrathin magnetic Fe₃O₄ nanodiscs with thicknesses of ∼20 nm and diameters ranging from 500 to 1000 nm have been obtained on a large scale by a surfactant-assisted solvothermal process. Transmission electron microscopy characterizations show that the nanodiscs grow along the [110] direction. NaOH and PEG-20000 (PEG stands for polyethylene glycol) have key effects on the morphology of the nanodiscs. In addition, the magnetic hysteresis loop of the ultrathin nanodiscs is obtained at room temperature.

We describe our efforts towards constructing a hybrid protein–polymer vesicle device based on the photoactive protein, bacteriorhodopsin (BR), for applications in the area of biosensors and biofuel cells. Successful protein incorporation into biomimetic polymer vesicles is a prerequisite for developing hybrid 'nano–bio' integrated devices. We suggest a systematic procedure for creating energy transducing, protein-incorporating, functional vesicles, based on the morphological ternary diagram. First, we constructed the morphological ternary diagram of the water/ethanol/polymer system with a size distribution of vesicles. The polymer used was an ABA triblock copolymer, PEtOz–PDMS–PEtOz [poly(2-ethyl-2-oxazoline)-b-poly(dimethylsiloxane)-b-poly(2-ethyl-2-oxazoline)]. Second, we incorporated BR in the form of purple membrane (PM) into polymer vesicle membranes under several different conditions, based on the morphological ternary diagram. Generation of electrochemical energy by BR proton pumping was checked by monitoring the pH change in parallel with transmission electron microscope analysis. The morphology of the polymer vesicles changed very little with the addition of PM. This work shows that the morphological ternary diagram provides a systematic method for constructing successful hybrid BR-incorporating biomimetic polymer vesicles.

The fabrication and characterization of tungsten nanoelectrodes insulated with cathodic electrophoretic paint is described together with their application within the field of neurophysiology. The tip of a 127 µm diameter tungsten wire was etched down to less than 100 nm and then insulated with cathodic electrophoretic paint. Focused ion beam (FIB) polishing was employed to remove the insulation at the electrode's apex, leaving a nanoscale sized conductive tip of 100–1000 nm. The nanoelectrodes were examined by scanning electron microscopy (SEM) and their electrochemical properties characterized by steady state linear sweep voltammetry. Electrode impedance at 1 kHz was measured too. The ability of a 700 nm tipped electrode to record well-isolated action potentials extracellularly from single visual neurons in vivo was demonstrated. Such electrodes have the potential to open new populations of neurons to study.

The fabrication of ∼3 nm FePt nanoparticles and detailed studies of the effect of the annealing conditions (temperature and time) on the formation of the face-centred tetragonal phase and on the magnetic properties are described. Additionally, the effect of the precursor molar ratio on the final product and the composition of the as-prepared samples were studied. The main criteria for the determination of the best alloy are the properties desired for applications in the field of magnetic recording media.

Tungsten oxide is one of the most important transition metal oxide materials, which possesses some unique properties such as electrochromic, optochromic, and gaschromic properties. In this paper, we report a simple method for synthesizing high quantity tungsten oxide nanoribbons by oxidizing a tungsten plate under moist conditions. Using potassium iodide as the catalyst, tungsten oxide nanoribbons with a thickness of 40–100 nm, width up to 1 µm and length up to hundreds of micrometres are obtained on a large scale. The morphology, composition and crystal structure of the nanoribbons are characterized by various methods, such as scanning electron microscopy, transmission electron microscopy and x-ray diffraction. The nanoribbons comprise mainly monoclinic tungsten trioxide (WO₃) growing along the [001] direction and the orthorhombic WO₃(H₂O)_0.33. The measured lattice parameters are β = 89.93°, a = 0.7274 nm, b = 0.7501 nm, c = 0.3824 nm for WO₃ and a = 0.7359 nm, b = 1.251 nm, c = 0.7704 nm for WO₃(H₂O)_0.33, respectively.

A fast and simple technique that produces self-aligned gold nanoparticles on a silicon substrate, covering a large area, is described. This technique involves three consecutive steps: first, the substrate is laser-irradiated to produce a periodic nanorippled structure; second, a thin film of gold is grown using ion-beam sputter deposition; and third, a thermal treatment is conducted to produce the formation and self-alignment of nanoparticles. The nanoparticles form along strips parallel to the nanoripple lines. The strip spacing equals the nanoripple spacing and the strip width depends on the angle of deposition and the divergence of the ion beam. The nanoparticle diameter is a function of the annealing temperature and time. It was found that deposition of the film at a very shallow grazing angle (0°) induces, upon thermal annealing in air at 800 °C, the formation of single nanoparticle rows aligned along the ripple ridges. In order to obtain the single-particle lines, a beam collimator, aimed at reducing the angular spread of the incident ion beam, was employed during deposition.

This technique is general and could be used in a large number of substrate/film combinations. Studies of other substrates would provide optimum conditions to obtain similar results, as laser-induced periodic structures are a fairly universal phenomenon.

The field emission (FE) properties of nanowires made from the recently synthesized nanowire material Mo₆S₃I₆ are reported. A single nanowire was mounted on an indium-coated nickel holder by dielectrophoresis in isopropyl alcohol. A careful activation or conditioning in a vacuum of 10⁻⁷ mbar was shown to be indispensable in order to extract relatively stable FE currents in excess of 1 µA originating from only a few sites at the end of the nanowire. Measurements were performed in an FE microscope with an additional plane mesh, which enables us to record I–U characteristics in diode mode, or to observe the emission patterns in triode mode. With FE currents around 5–7 µA the emitter degrades gradually, and to some extent irreversibly. The degradation mechanism is not a reversal of the instant site build-up.

We report a comparative study of structural, morphological and magnetic properties of freshly prepared and aged Cu(OH)₂ nanoribbons. Microscopy studies, performed with a transmission electron microscope, a scanning electron microscope and an atomic force microscope, demonstrate that the average length of the Cu(OH)₂ nanoribbons decreases with ageing. The basic Cu(OH)₂ structure is, however, still preserved at this stage, as confirmed by x-ray diffraction measurements. Morphological changes are reflected also in the magnetic properties. For instance, we found that Cu(OH)₂ nanoribbons with ageing gradually lose their one-dimensional antiferromagnetic character as the defects, which form during the ageing process, tend to cut the Cu–(OH)₂–Cu chains into increasingly shorter segments. These defects in aged samples completely change the spectrum of magnetic excitations and make aged samples much more three-dimensional from the point of view of magnetism.

We report modified self-assembly of InAs islands acting as stressors for strain-induced InGaAs(P) quantum dots (SIQDs). The quantum dots are fabricated by growing InAs islands on top of a near-surface InGaAs(P)/InP quantum well (QW). The compressively strained QW affects the size and density of the InAs islands, as compared to islands grown on a plain InP buffer. By adjusting the growth conditions, the height of the InAs stressors is tuned from 15 to 30 nm while the areal density varies around 10⁹ cm⁻². The confinement of carriers in the SIQDs is characterized by low-temperature photoluminescence. Increasing the size of the InAs stressor is shown to enhance the depth of the lateral confinement potential and reduce the level splitting of excited QD states. However, the small inhomogeneous broadening of the SIQD transitions, as narrow as 11 meV, shows no correlation with the height dispersion of the stressor islands.

Applications of carbon nanotubes such as field emission or microelectrode sensor arrays require a patterning of vertically aligned carbon nanotubes over large areas. A highly purified and concentrated monodisperse cobalt colloid was produced for use as a catalyst for growth of carbon nanotubes. Nanocontact printing was employed to deposit the cobalt nanoparticles in regular patterns with feature sizes at the 100 nm scale onto silicon wafers at low cost over large areas. Vertically aligned carbon nanotubes were grown by direct current plasma enhanced chemical vapour deposition at temperatures ranging from 300 to 640 °C.

High dielectric constant ZrO₂ gate dielectric thin films have been prepared by means of in situ thermal oxidation of sputtered metallic Zr films. XRD reveals that the as-oxidized samples are amorphous, but can be made polycrystalline with a highly ()-preferential orientation by increasing the annealing temperature. AFM measurements confirm that high temperature annealing results in increase of the roughness root mean square value of the films. The growth and properties of the interfacial SiO₂ layer formed at the ZrO₂/Si interface are observed by using Fourier transform infrared spectroscopy. It has been found that the formation of the interfacial layer depends on the post-deposition annealing temperature. On the basis of a parametrized Tauc–Lorentz dispersion model, the optical properties of the as-oxidized and annealed films related to the annealing temperature are systematically investigated by spectroscopic ellipsometry. The increase in the refractive index and decrease in extinction coefficient with increase of the annealing temperature are discussed in detail.

The growth of SiO₂ nanowires (SiONWs) via carbothermal reduction of CuO powders as functions of the Ar flow rate, the carbon concentration in the CuO/carbon powders, and the oxygen concentration in the Ar/O₂ flow was studied. Significant amounts of SiONWs were grown on the Si substrate without a catalyst from CuO/carbon powders at a temperature of 1000–1100 °C in flowing Ar with the flow rate of 100 sccm. Without using CuO/carbon powders SiONWs could not be readily grown. A small amount of SiC associated with SiONWs was grown from CuO/carbon powders with a higher proportion of carbon. The minimum Ar flow rate required for the growth of SiONWs was about 10 sccm and the amount as well as the diameter of the SiONWs increased with increase of the Ar flow rate, revealing that vapour transport assisted by Ar flow is an important mechanism for the nucleation and growth of SiONWs. The growth of SiONWs mainly originated in the cracks which were formed in the Si substrate due to the generation of SiO(g) from the reaction between CO₂ and the Si substrate. The introduction of O₂ into the Ar flow could generate a significant amount of CO and thereby suppress the growth of SiONWs. The present studies reveal that the growth of SiONWs via carbothermal reduction of CuO powders mainly follows the vapour–solid mechanism.

We describe the preparation of a tungsten pillar nanoimprint stamp without the use of lithography and etching techniques. Structures with heights of 15 nm were prepared on the basis of self-ordered porous alumina templates and this was followed by DC sputtering of tungsten. The stamp was successfully used to prepare an aluminium surface to obtain highly ordered porous anodic alumina films after a single anodization step. The preparation efficiency for highly ordered porous alumina was dramatically improved as compared to the more conventional two-step anodization–strip-anodization method, as a sacrificial layer with a thickness of a few hundred micrometres was not required. In addition, by fractal calculations, we have evaluated the degree of ordering of the asperities on the nanoimprint master stamp.

Polyaniline (PANI)–Fe₃O₄ nanoparticles were obtained using a novel method: aniline dimer–COOH assisted polymerization. The synthetic strategy involved two steps: first, the composite of magnetic nanoparticles modified with aniline dimer–COOH was synthesized by a chemical precipitation method. Then aniline monomer and oxidant were added to create PANI–Fe₃O₄ nanoparticles. The structure of Fe₃O₄ nanoparticles capped with aniline dimer–COOH was characterized by Fourier transform infrared, ultraviolet–visible, x-ray photoelectron spectroscopy and x-ray diffraction analyses. Transmission electron microscope images of the PANI–Fe₃O₄ nanocomposite showed that the Fe₃O₄ nanoparticles were well dispersed in PANI matrices. The PANI–Fe₃O₄ composite was characterized by means of FTIR, XPS and XRD analyses. The PANI–Fe₃O₄ nanoparticles were found to be superparamagnetic. The hysteresis loop at room temperature showed high saturated magnetization (M_s = 21 emu g⁻¹) and a low coercive force (μ_c = 0).

Many papers have been published on methods to determine the normal spring constant, k_z, of atomic force microscope (AFM) cantilevers. This is necessary to calibrate force measurements in the AFM, which then lead to a wide variety of applications from measuring the rupture force of protein bonds to determining the Young's modulus of materials such as polymers at surfaces. Manufacturers' nominal values of k_z have been found to be up a factor of two in error, therefore practical methods to calibrate k_z are required. There are three main categories of methods, with some overlap, which we call: (1) dimensional, (2) static experimental and (3) dynamic experimental. Here, we consider the dimensional aspects of these methods involving the cantilever material properties and geometry. We do this via reviewing the analytical equations of seven publications and comparing them with finite element analysis (FEA) calculations. It is shown that the best analytical equations are those of Neumeister and Ducker but that these need a revision for the bending of the triangular portion of the V-shaped cantilever. This is done and the correlation with FEA is then excellent. Equations are also provided for the effect of a metallized layer and the imaging tip not being at the cantilever apex; these also agree with FEA. We evaluate the relevant uncertainties and provide recommendations as to the best equations to use together with relevant correction parameters based on the assumption that the FEA calculations are valid. We test this assumption elsewhere.

In this paper, we propose a technique to remove the fringe distortion and measurement error of AFM moiré due to the non-linear scan and creep of the probe. In this technique, the scanned AFM image of a standard holography grating and a virtual grating were used to generate the AFM moiré fringe pattern. Two sets of moiré fringe patterns, i.e. the initial fringe pattern prior to loading and the subsequent fringe pattern after uniform 'loading', were achieved in this way. Fringe pattern distortion can be found due to the non-linear scan and creep of the AFM probe. Then, phase shifting is precisely realized to AFM moiré fringe patterns with the aid of a virtual grating and a logical moiré technique. Wrapped and unwrapped phase maps of the two fringe patterns were calculated respectively. Finally, the unwrapped phase map of the initial fringe pattern was subtracted from that of the fringe pattern after loading and a new fringe pattern free from distortion was reconstructed; this corresponded to the uniform 'loading'. In this way, the fringe distortion and measurement errors due to the non-linear scan and creep of the AFM probe were removed.

The nonlinear optical properties of gold nanoparticles with different densities of particles on indium–tin oxide (ITO) substrates of different origins are investigated. The coherent photoinduced nonlinear optical effect at 1.32 µm reveals a marked dependence on the interparticle distance and density. The decrease of the interparticle distance with the increase of Au nanoparticle density favours the photoinduced optical second harmonic generation. The maximal second-order optical susceptibility attained at a wavelength of 1.32 µm corresponds to the value of about 4.56 pm V⁻¹. The predominant role of the interface between the Au nanoparticles and the ITO substrate is shown.

The deformation of 'soft' polystyrene spheres is found to limit the usefulness of nanosphere lithography in high-density applications because of the eventual closure of the void areas between the self-assembled nanospheres which function as channels for material deposition. We have used a plasma etching technique to reopen and enlarge these channels in the template in a controlled manner. This enables the controlled fabrication of a range of nanoarrays of very high density and variable sizes. The resulting shape of the nanodots produced can be understood by considering the etching-induced surface diffusion of the polystyrene in the plasma treatment.

This paper demonstrates the fabrication of a membrane permeated by a silicon dioxide nanocapillary array for manipulating highly charged ions at the nanoscale. The fabrication method involves (i) the formation of pores at the nanoscale on lithographically patterned, n-type silicon using photo-assisted electrochemical etching, followed by (ii) thermal oxidation, (iii) bulk silicon back etching and (iv) oxide etching using silicon micromachining technology. The electrochemical etching parameters were chosen to form arrays of straight pores with a diameter of about 250 nm, a length of 30 µm and interpore distances of 1 and 1.4 µm. The back side of the pore arrays was etched in potassium hydroxide and tetramethyl ammonium hydroxide. Finally, the inside of the pores was thermally oxidized to yield SiO₂ capillary arrays. The present method could allow the fabrication of capillaries with further smaller dimensions by increasing the thermally grown oxide thickness.

Fe₂₀Ni₈₀@Au core–shell nanoparticles have been prepared by a multi-step microemulsion technique and the influence of annealing from 200 to 500 °C on the particles' size, morphology and magnetic properties is reported. After annealing under dilute H₂ at 300 °C and above, FeNi₃-structured Permalloy nanoparticles were observed in the XRD patterns with a lattice parameter of a = 3.560(2) Å. The sizes of the nanocomposites increased non-linearly with increasing annealing temperature, accompanied by a decrease in the expansive strain in the shells and cores. The samples were found to exhibit superparamagnetic behaviour with a ferromagnetic component that became dominant at high annealing temperatures due to an increase in the average particle diameter over the critical radius required for superparamagnetic behaviour. The saturation magnetization (M_S) of the samples taken at 300 K increased from 19 emu g⁻¹ for the as-prepared sample to 100 emu g⁻¹ for the sample annealed at 500 °C.

We demonstrate the feasibility of in situ manipulation and characterization of individual carbon nanotubes using a nano-manipulation system operating inside a scanning electron microscope, which can also act as an electrical probing system. Transport characteristics of an individual multi-walled carbon nanotube in free space can be reversibly changed between linear and non-linear transport behaviour and are a result of changes in nanotube resistance.

A two-step process was developed to prepare a direct heteronanojunction of ZnO nanorods on SiC nanowires, using a simple heating method and metal–organic chemical vapour deposition (MOCVD). First, an SiC nanowire substrate was prepared by heating NiO catalysed Si wafer at 1050 °C. Subsequently, diethylzinc was used as metal–organic source to grow ZnO nanorods on SiC nanowires at 450 °C. High-resolution TEM images showed that the heteronanojunction has an atomically abrupt interface with no interfacial layers formed between ZnO nanorods and SiC nanowires. The epitaxial relationship between ZnO nanorods and SiC nanowires was ZnO[0001] ⊥ SiC[111].

Slanted nano-columns and square nano-springs made of amorphous silicon (a-Si) were fabricated on bare Si and patterned substrates by oblique angle deposition with a back–forth substrate swing rotation mode. Scanning electron microscopy was used to characterize the grown nanostructures. The tilt angle of slanted nano-rods is determined by the incident angle of deposition flux and the azimuthal swing rotation angle of a substrate. The controlled substrate rotation affects the uniformity and the shape of the nanostructures. On the patterned substrate, the broadening of the size of individual nano-columns is greatly reduced and the nano-columns are not connected as they grow. A simple model based on decomposing the deposition flux is used to describe the effect of substrate rotation on tilt angle, uniformity, and the top-end shape of nanostructures. The feasibility of fabricating separated and well aligned nanostructures by our swing rotation method provides an effective and controllable way to fabricate nano-devices.

Peculiarities of kinetics of the solid–solid phase transition between single-phase and two-phase states in a nanopowder are considered here. We present a numerical assessment of the time-dependent behaviour of a supersaturated nanosystem undergoing temperature cycling. We demonstrate a distinct size-induced hysteresis and its peculiarities. The analysis indicates that as the system size decreases the hysteresis loop narrows, showing a tendency to disappearance. The model predictions are demonstrated for a sample system with general hypothetical properties. The results are found to depend on such thermodynamic and kinetic constraints as the size, the rate of temperature cycling, energy barriers for nucleation and diffusion, mechanisms of nucleation, and scatter in particle sizes of a nanopowder. The newly obtained results may be used for the achievement of an alternative method of information recording in present-day and future technologies.

Two-dimensional polar-surface-dominated ZnO nanosheets (nanodiscs) with dimensions of several microns and thickness of tens of nanometres were synthesized in bulk quantity at low temperature (∼70 °C) by a simple and environmentally benign chemical bath deposition (CBD) method. These ZnO nanosheets are of single-crystal wurtzite structure; they grow along the crystallographic directions within polar {0001} planes. This is different from previous reported films or nanowire arrays prepared by the CBD method. Raman scattering spectrum studies confirm that the as-synthesized nanosheets are of high crystal quality and indicate an optical phonon confinement effect in such ZnO nanosheets. These nanosheets show a sharp intrinsic ultraviolet excitonic emission peak centred at 380 nm at room temperature, have large surface area exposed to the gaseous environment, and could be an ideal ultraviolet light source or objects for the fabrication of nanoscaled devices.

The spherical curvature induced by pentagons in corannulenes and hexagonal sheets is shown to be the basic constituent that controls the growth of fullerenes and single-walled carbon nanotubes (SWNTs) in soot forming and carbon vapour environments. Formation of the initial ring of five or six atoms is the essential step which with the addition of further pentagons and hexagons determines whether a spinning fullerene is to be formed or the cap that lifts up and leads to the formation of an SWNT. A continuum elastic model is developed to determine the criteria for the growth of these structures. The observed dominance of the growth of 14 Å diameter armchair SWNTs in sooting and carbonaceous environments is explained by using the nanoelastic model of C shells.

In an attempt to mimic the bamboo's architecture, bamboo-like polymer/silicon nanocomposites were synthesized by filling silicon nanopores with two conjugated polymers, namely poly(p-phenylene vinylene) (PPV) and its derivative poly(2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene) (MEHPPV). The microstructure, elastic modulus, hardness, nanoscratch resistance, and fracture toughness of the bamboo-like polymer/nanoporous silicon (PS) films were investigated using different functions of an atomic force microscope and nanoindentation techniques. The fracture toughness of MEHPPV- and PPV-filled PS films is 2 and 1.6 times higher than that of PS, respectively, although their elastic modulus and hardness decrease compared to PS. Strengthening and deformation mechanisms are discussed in conjunction with nanocomposite structure, hardness, elastic modulus and nanoscratch resistance.

X-ray nanodiffraction was developed to study individual crystalline nano-objects at the Advanced Photon Source (APS). This technique allows nondestructive structural characterization of individual nano-objects with the advantages of high structural sensitivity and high penetration. Using the extremely high brightness of a third-generation synchrotron radiation source and hard x-ray phase zone-plate optics, we have focused hard x-rays to a microbeam of less than 200 nm during routine operation so that significant diffraction can be measured from a single tin oxide nanowire (cross section down to 24 nm × 10 nm). In this paper, we will describe the experimental technique in detail and present the results of a structural study of a few tin oxide nanowires.

Here we present a new concept to determine tensile properties of nanofilms and materials via nanoindentation. The proposed methodology utilizes a conical or truncated conical indenter and requires the fabrication of an upwardly obtruded well shaped tube from the substrate. The downward stroke of the indenter along the centreline of the tube mainly produces tensile hoop stress in the upper region of the tube where the nanofilm exists. In the present work, the feasibility of the proposed method has been demonstrated through finite element analysis, as the first stage of a longer project on the topic. It has been demonstrated that Young's modulus and the yield strength of the nanofilm can be suitably determined in tensile mode from the load–stroke relation.

We report a method of depositing individual 'templated carbon nanotubes' (T-CNTs) on opposing electrodes so that they are suspended across 100 µm deep trenches, and in separate experiments across low profile (70 nm thick) opposing electrodes. The geometry of the electrodes with deep trenches was chosen to be essentially identical to that in a micro-electromechanical system (MEMS) testing stage used for mechanical loading of nanostructures. An electric field was used to attract the T-CNTs dispersed in a solvent and critical point drying was employed to protect them from breaking or deforming. The real-time potential change in the circuit was monitored as a means of characterizing the deposition of an individual T-CNT across this deep trench. For the case of sequential deposition on electrodes that are 70 nm above the substrate surface, a method was developed for counting the number of sequentially deposited T-CNTs. Simultaneous video recording of the deposition of T-CNTs confirmed the measured real-time potential changes for both cases. It was found that the resistance of the circuit changed as each new T-CNT was deposited for the sequential deposition; up to five T-CNTs were sequentially detected. This approach allows for controlled deposition of one-dimensional nanostructures for their potential use in NEMS devices, and may be useful for large-scale integration.

The large-scale synthesis of uniform Bi₂S₃ nanowires has been successfully synthesized by a solvothermal method adopting an inorganic-surfactant (BiCl₄⁻–CTA⁺) lamellar structure as precursor. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and electron diffraction (ED) results show that the as-synthesized samples are orthorhombic-structured Bi₂S₃ single-crystal nanowires. The morphologies and structure of the Bi₂S₃ nanowires have been characterized using transmission electron microscopy (TEM). In addition, studies of nanowire growth as a function of growth time have shown that nanowire length is directly proportional to growth time. The efficient method can be used to synthesize other III–VI sulfides. The growth mechanism was also discussed in our paper.

We report end-to-end assembly for tuning the optical properties of a gold nanorod/sphere based on oligonucleotide hybridization. The rationale behind the selection of the mercaptoalkyloligonucleotide molecule is based on the fact that the thiol group binds to the ends of the nanorods, which further assemble in an end-to-end fashion through hybridization with the target oligonucleotide. A highly selective, colorimetric polynucleotide detection method based on mercaptoalkyloligonucleotide-modified gold nanorod/sphere probes is also reported.

The creation of geometrically well-defined submicron structures on insulating substrates by e-beam lithography is hampered by surface charging. This problem becomes crucial when trying to create nanosized protein patterns by selective molecular assembly patterning (SMAP) on transparent glass substrates. In this paper we demonstrate that the use of thin films of conductive indium tin oxide resolves the issue of surface charging during e-beam writing while being compatible with the standard SMAP protocol for surface modification.

Microporous polyvinyl chloride (PVC) with pore size of 0.2–2 µm has been obtained by the foaming of PVC powders using a solution of 2,2'-azo-bis-iso-butyronitrile in a co-solvent of butanone and cyclohexanone. The PVC/CaCO₃ hybrid powders deposited with CaCO₃ nanoparticles have been synthesized using the microporous PVC as reactors of CaCO₃ nanoparticles, i.e., the reaction of Ca(OH)₂ with CO₂ occurs inside the pore of microporous PVC. The in situ PVC/CaCO₃ nanocomposites have been prepared by melt blending in situ PVC/CaCO₃ hybrid powders. The images of SEM and TEM show that the in situ CaCO₃ nanoparticles are uniformly dispersed in the PVC matrix and the sizes of the CaCO₃ nanoparticles are less than 50 nm. TEM images and XRD patterns for the in situ CaCO₃ strongly suggest that pseudo-amorphous crystals and defect-rich crystals are formed. The mechanical properties and DMA data indicate that the in situ PVC/CaCO₃ nanocomposites exhibit much higher strength, toughness, modulus and glass temperature than common PVC/CaCO₃ nanocomposites. This novel nanotechnology has potential applications in preparation of organic–inorganic hybrid nanocomposites.

The use of polymer light-emitting devices is hindered by their poor stability on exposure to oxygen and moisture as well as by their low quantum efficiency. In the case of blue-light-emitting polymers, an additional major concern is the presence of long-wavelength tails in their emission spectra. With the aim of simultaneously overcoming all these drawbacks, a blue-light-emitting polymer/mesoporous silica nanocomposite was prepared by blending poly(9,9-dioctylfluorene) with nanosized MCM-41. This nanocomposite film shows dramatically increased photostability and colour purity, as well as higher electroluminescence output.

Self-assembled monolayers (SAMs) of alkanethiols have been patterned on micrometre and nanometre length scales by exposure to light from a frequency doubled argon ion laser. Friction force microscopy shows that the patterning speed depends on the nature of the terminal group and is in the order COOH> CH₃, the reverse of the order reported previously using a mercury arc lamp, indicating that a different photo-oxidation mechanism is responsible. It is suggested that this involves the creation of hot electrons at the gold surface that initiate oxidation of the adsorbate. Nanostructures have been fabricated using scanning near-field photolithography (SNP), in which the UV laser is coupled to a near-field scanning optical microscope. During SNP, the rates of writing required for complete oxidation correlate closely with oxidation rates measured during micropatterning, suggesting that the mechanism is essentially the same. SAMs on silver have been patterned, yielding linewidths smaller than 50 nm. The selective alkylation of hydrogen passivated Si has been demonstrated, yielding structures that may be used as resists for etching and demonstrating a powerful new capability—fluid-phase nanophotolithography. Patterned SAMs prepared using SNP have been used to selectively attach polymer nanoparticles, demonstrating their utility for the creation of functional molecular nanostructures. Nanopatterns generated by SNP have also been used as resists, enabling the etching of nanostructures into gold and the fabrication of three-dimensional nanostructures in silicon using a two-stage wet etch process.

Tuning the interfacial area is essential for the optimization of nanostructured CeO₂ in a variety of applications. In this work, we investigate the microstructural mechanism of an oxidation-induced transition from a partially oriented, granular and porous nanostructure to a dense epitaxial one in CeO₂ films deposited from chemical solutions. Crystallization under reducing atmospheric conditions results in a nanometric granular microstructure with a high fraction of C decorating grain boundaries and interstitial cavities. Annealing in oxidizing conditions removes C impurities and promotes grain growth, resulting in a fully epitaxial film, as well as stabilizing the otherwise energetically prohibitive polar (001) planes. A mechanism that considers an impurity induced grain boundary blocking mechanism and the stabilization of (001) planes via surface oxidation is proposed.

We report on the photoresponse from large arrays of 40 nm radius nanopillars with sensitivity in the long-wavelength infrared regime. Using photoluminescence techniques, a peak wavelength blue shift of approximately 5 meV was observed at 30 K from GaInAs/InP nanopillar structures, indicating carrier confinement effects. Responsivity measurements at 30 K indicated peak wavelength response at about 8 µm with responsivity of 420 mA W⁻¹ at −2 V bias. We have also measured the noise and estimated the peak detectivity to be 3 × 10⁸ cm Hz^1/2 W⁻¹ at 1 V reverse bias and 30 K. A maximum internal quantum efficiency of 4.5% was derived from experiment. Both the photo and the dark transport have been successfully modelled as processes that involve direct and indirect field-assisted tunnelling as well as thermionic emission. The best agreement with experiment was obtained when allowances were made for the non-uniformity of barrier widths and electric field heating of carriers above the lattice temperature.

A weak polyelectrolyte layer-by-layer self-assembled multilayer has several morphologies depending on solution pH, including the morphology of poly(allylamine hydrochloride) (PAH) pH 7.5/poly(acrylic acid) (PAA) pH 3.5, which is called texture structure. We confirmed the initial growth of a weak polyelectrolyte layer-by-layer (LBL) multilayer in a stepwise adsorption process. The growth states of bilayers from 0.5 to 4.0 and over 4.5 were different when measured by quartz crystal microbalance (QCM), scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and contact angle measurements.

The texture structure appeared in 1.0 bilayer, after PAA adsorption. The initial growth was changed around 4.0 bilayers. In this phenomenon, the LBL layer of PAH pH 7.5/PAA pH 3.5 had two zones at least, similar to a strong polyelectrolyte LBL layer.

There is a great need to design better orthopaedic implant devices by modifying their surface properties. In this respect, one approach that has received much attention of late is the simulation of the surface roughness of bone in synthetic orthopaedic implant materials. Bone has numerous nanometre features due to the presence of nanostructured entities such as collagen and hydroxyapatite. Despite this fact, current orthopaedic implant materials are smooth at the nanoscale. Previous studies have measured increased osteoblast (bone-forming cell) functions on biologically inspired nanophase titania compared to conventional titania formulations. In fact, in vitro calcium deposition by osteoblasts was up to three times higher on nanostructured compared to conventional titania. However, it was unclear in those studies what underlying surface properties (roughness, crystallinity, crystal phase, chemistry, etc) promoted enhanced functions of osteoblasts on nanophase titania. For that reason, the objective of the present in vitro study was to specifically determine the role nanostructured surface roughness of titania had on increasing functions of osteoblasts. To achieve this, the surface roughness of nanophase and conventional titania was transferred to a model tissue engineering polymer: poly-lactic-co-glycolic acid (PLGA). Results of the present study demonstrated greater osteoblast adhesion and proliferation for up to 5 days of culture on PLGA moulds of nanophase compared to conventional titania. In this manner, this study elucidated that the property of nanophase titania which increased osteoblast function was a large degree of nanometre surface features that mimicked bone. For this reason, nanophase materials deserve more attention in improving orthopaedic implant applications.

Sol–gel-prepared nanocrystalline tin (IV) oxide has been characterized by magic angle spinning nuclear magnetic resonance (MAS NMR) in a pure form and also with silica and alumina pinning phases present. The ¹¹⁹Sn MAS NMR lineshape was observed to broaden as the SnO₂ nanocrystal sizes decreased, a reflection of the increasingly important contribution of the more disordered surface region. A second local Sn environment other than the cassiterite phase was observed, probably an orthorhombic phase that has previously been observed in nanoparticles of SnO₂. The silica and alumina pinning particles were characterized by ²⁹Si and ²⁷Al MAS NMR. The silica pinning particles retained a high degree of disorder over the range of annealing temperatures, whereas alumina crystallized at ∼1000 °C. A possible explanation for this difference is that since the alumina pinning particles are less successful at restricting nanocrystal growth than the silica particles, they may aggregate together and combine, hence they are larger, less constrained particles.

This investigation describes the development of an InGaN/GaN light emitting diode (LED) with a nano-roughened top p-GaN surface using an Ni nano-mask and laser etching. The light output of the InGaN/GaN LED with a nano-roughened top p-GaN surface is 1.55 times that of a conventional LED, and the wall-plug efficiency is 68% higher at 20 mA. The series resistance of the InGaN/GaN LED was reduced by 32% by the increase in the contact area of the nano-roughened surface.

It is essential to characterize the nonlinearity in scanning probe microscopes (SPMs) in order to acquire spatial measurements with high levels of accuracy. In this paper, a new characterization method is presented that combines a high-resolution image processing technique used by the experimental mechanics community known as Digital Image Correlation (DIC) with digital images from a standard type of SPM known as an atomic force microscope (AFM). The characterization results using this new method match those from the conventional method using micromachined calibration gratings. However, the new method uses the texture of a specimen surface and not a precisely micromachined calibration grating. As a consequence, the new characterization technique is a more direct method for measuring scanning errors that can be conducted in situ when imaging a specimen surface at any scale within the scanning range of the SPM. It also has the advantage of reconstructing the position error curve more continuously with less noise than the conventional method.

We demonstrate a new assembly method to position metal nanoparticles delivered from the gas phase onto surfaces using the electrostatic force generated by biased p–n junction-patterned substrates. Aligned deposition patterns of metal nanoparticles were observed, and the patterning selectivity quantified. A simple model accounting for the generated electric field, and the electrostatic, van der Waals, and image forces, was used to explain the observed results.

High-field electron transport in multi-walled carbon nanotubes (MWNTs) is studied employing a mechanically controllable break junction (MCBJ) technique. Bridging of MWNTs over Au electrodes is accomplished by repeatedly breaking Au contacts in a nanotube-dispersed solution. Observed conductance versus bias voltage (G–V) characteristics show that the conductance of MWNTs linearly increases with the bias up to 3 V. Also, the important role of the nanotube/electrode contact resistance on the electron transport through MWNTs is pointed out from measurements of G–V characteristics at various electrode distances.

The direct covalent modification of silicon nanowires with DNA oligonucleotides, and the subsequent hybridization properties of the resulting nanowire–DNA adducts, are described. X-ray photoelectron spectroscopy and fluorescence imaging techniques have been used to characterize the covalent photochemical functionalization of hydrogen-terminated silicon nanowires grown on SiO₂ substrates and the subsequent chemistry to form covalent adducts with DNA. XPS measurements show that photochemical reaction of H-terminated Si nanowires with alkenes occurs selectively on the nanowires with no significant reaction with the underlying SiO₂ substrate, and that the resulting molecular layers have a packing density identical to that of planar samples. Functionalization with a protected amine followed by deprotection and use of a bifunctional linker yields covalently linked nanowire–DNA adducts. The biomolecular recognition properties of the nanowires were tested via hybridization with fluorescently tagged complementary and non-complementary DNA oligonucleotides, showing good selectivity and reversibility, with no significant non-specific binding to the incorrect sequences or to the underlying SiO₂ substrate. Our results demonstrate that the selective nature of the photochemical functionalization chemistry permits silicon nanowires to be grown, functionalized, and characterized before being released from the underlying SiO₂ substrate. Compared with solution-phase modification, the ability to perform all chemistry and characterization while still attached to the underlying support makes this a convenient route toward fabrication of well characterized, biologically modified silicon nanowires.

We report the fabrication of a 50 nm half-pitch wire grid polarizer with high performance using nanoimprint lithography. The device is a form of aluminium gratings on a glass substrate whose size of 5.5 cm × 5.5 cm is compatible with a microdisplay panel. A stamp with a pitch of 100 nm was fabricated on a silicon substrate using laser interference lithography and sidewall patterning. The imprint and the aluminium etching processes are optimized to realize uniform aluminium gratings with aspect ratio of 4. The polarization extinction ratio of the fabricated device is over 2000, with transmission of 85% at a wavelength of 450 nm, which is the highest value ever reported. This work demonstrates that nanoimprint lithography is a unique cost-effective solution for nanopatterning requirements in consumer electronics components.

Despite recent advances in electrospinning, creating highly ordered structure through the use of electrospun fibres is not possible. This is due to the chaotic motion of the electrospinning jet which means that the deposition location of the fibres covers a few centimetres radius. As a result, applications for electrospun fibres are restricted to applications where precise positioning is not required. However, through the use of steel blades to control the electric field, it is now possible to create a fibre bundle made of highly aligned nanofibres where the ends of the fibre bundle are fixed during electrospinning. The creation of highly ordered structures made of electrospun fibre bundles is now possible since the fibre bundle is robust enough to be handled, and it is also easy to transfer the fibre bundle onto a substrate. More importantly, with the two ends of the fibre bundle known, automating the transfer of the fibre bundle onto a substrate is a possibility.

The effects of post-thermal treatment and rod diameter on the field emission (FE) properties of RuO₂ nanorod films are reported. The FE properties of RuO₂ nanorods with pyramidal tips have been studied on samples of two average rod diameters, 48 and 35 nm. Both of them exhibit a transient behaviour in emission current under a fixed electric field. Thermal annealing at 400 and 500 °C generally improves the FE characteristics in lowering the emission barriers of nanorods, as manifested by a decrease in the turn-on field, the threshold field, the slope of the Fowler–Nordheim plot, and the time-span of the transient period. Reduction in emission barrier appears to be particularly evident for the 35 nm nanorods. Yet 500 °C annealing also degrades the emission current stability of 35 nm nanorods. The standard deviation of emission current density of 35 nm nanorods after 500 °C annealing is around 44%. On the other hand, both specimens after 400 °C annealing display a much more stable emission current density, whose fluctuations are 26% of their average values. The transient period is regarded as a consequence of gas molecules being desorbed from the RuO₂ tips during emission, resulting in a reduction of the emission barrier. Thermal annealing weakens the bonding between the adsorbed gas and the tip surface, and facilitates the gas desorption and electron tunnelling processes.

One of the unsolved problems in the application of nanoparticle arrays is how to precisely control their macroscopic properties based on the microscopic properties of their basic component—the individual nanoparticle. Thus it is highly desirable to fabricate arrays of perfect iso-nanoparticles, which are defined as particles of the same size, structure, and ambient condition. Here we show that ordered semiconductor (indium oxide) single-crystal nanoparticle arrays can be obtained by oxidation of arrayed metal (indium) nanoparticles. The arrayed semiconductor nanoparticles have similar size, shape, crystalline structure and orientation, and ambient condition. Our work is a step closer towards the goal of achieving iso-nanoparticle arrays.

The porphyrin–perylenetetracarboxylic diimide–fullerene triad has been designed to act as an efficient light-to-current converter in molecular devices. Light absorption by the perylenetetracarboxylic diimide–porphyrin dyad occurs in complementary regions, giving extended absorption in the visible light region. This dyad of perylenetetracarboxylic diimide–porphyrin was covalently linked with C₆₀, which can act as an electron acceptor, to construct porphyrin–perylenetetracarboxylic diimide–fullerene (FPP) self-assembled monolayers (SAMs) on the indium tin oxide (ITO) surface. The relative strong photocurrent generation of the ITO/FPP/ methyl viologen (MV²⁺)/Pt system in the continuous visible light region (from 400 to 650 nm) indicated that this system is highly promising as regards light–energy conversion.

The assembly and detailed structural characterization of a Y-shaped DNA template incorporating a central biotin moiety is reported. Also reported is the use of this template to assemble a model protein-functionalized three-electrode architecture. Of particular significance is the finding that a biotin-modified nanoparticle will recognize and selectively bind the central biotin moiety, once functionalized by the protein streptavidin. Potential applications of the above and related DNA templates in the emerging field of nanoelectronics are considered.

The bactericidal action of silver (0) nanoparticles and amoxicillin on Escherichia coli is studied, respectively. Increasing concentration of both amoxicillin (0–0.525 mg ml⁻¹) and silver nanoparticles (0–40 µg ml⁻¹) showed a higher antibacterial effect in Luria–Bertani (LB) medium. Escherichia coli cells have different bactericidal sensitivity to them. When amoxicillin and silver nanoparticles are combined, it results in greater bactericidal efficiency on Escherichia coli cells than when they were applied separately. Dynamic tests on bacterial growth indicated that exponential and stationary phases are greatly decreased and delayed in the synergistic effect of amoxicillin and silver nanoparticles. In addition, the effect induced by a preincubation with silver nanoparticles is examined. The results show that solutions with more silver nanoparticles have better antimicrobial effects. One hypothesized mechanism is proposed to explain this phenomenon.

ZnO nanorods have been synthesized by growth from salt mixtures with a solution-processed Zn-containing precursor at high temperatures. The salt composition and the size of the Zn-containing precursor particles play a key role in the synthesis of ZnO nanorods and define their size and properties. The mechanism of the nanorods' growth is based on the contact melting phenomena at the ZnO nanocrystals–NaCl crystal interface. The resulting nanorods show a strong blue-shifted cathodoluminescence emission due to the quantum confinement effect.

Because of the discrete conductance steps in split-gate GaAs/Al_xGa_1−xAs quantum point contacts and wires they are commonly referred to as one-dimensional (1D) systems. We discuss what is meant by this characterization by analysing the local density of states (DOS). For realistic device parameters we find that the local DOS may deviate substantially from the ideal 1D case, which indicates that the Lieb–Mattis theorem (Lieb and Mattis 1962 Phys. Rev. 125 164), frequently referred to in the present context, does not apply in an obvious way. Spontaneous magnetization due to interactions is therefore feasible, in particular in the vicinity of sublevel thresholds and the associated low electron sub-band densities.

A simple template-based hot-press method has been developed to fabricate metal and polymer nanowires and nanotubes. By using this method, indium, tin, and poly(vinylidene fluoride–trifluoroethylene) copolymer nanowires and nanotubes with diameters ranging from 50 to 300 nm and lengths up to 60 µm were successfully obtained. The effects of the hot-press temperature and the pore size of the template on the formation of nanowires and nanotubes are discussed. The present method is comparatively simple, efficient and low cost, and can be readily extended to prepare other nanowires and nanotubes using a variety of low melting point materials as the starting precursors.

Gram quantities of titania (TiO₂) nanotubes, with a typical outside diameter about 9 nm, wall thickness of about 2.5 nm, and length of about 600 nm, were synthesized from anatase nanopowder and micropowder using the hydrothermal method. The crystallization, structure, and phase stability of the nanotubes at high temperatures were studied. A morphology change from nanotube to nanowire was observed at 650 °C. The as-prepared nanotubes were usually contaminated with sodium impurities and were poorly crystallized, but under optimized synthesis conditions the impurity phase was completely removed, resulting in highly crystallized nanotubes. The volume filling fraction of the autoclave as well as the concentration of the acid treatment were found to be particularly important for controlling the purity and crystallinity of the resulting nanotubes. The various TiO₂-derived nanotube phases (sodium titanate and hydrogen titanate) reported previously by different groups were also observed under different synthesis conditions, resolving the contradiction among the previous results.

This paper presents the use of molecular dynamics (MD) simulations to investigate atomic-scale frictional behaviour between a roller and a slab under rolling–sliding conditions. The simulations consider both abrasive wear and non-abrasive wear during the rolling–sliding process. Different rolling–sliding conditions are simulated by implementing various separation distances between the roller and the slab and by changing the angular velocity of the roller. The frictional and normal forces acting at the interface between the roller and the slab, and the temperature of both operating components, are calculated during the rolling–sliding process. The relationships between the roller–slab friction phenomena and the rolling–sliding conditions are investigated. Finally, the rolling–sliding characteristics associated with a hard-on-soft rolling–sliding system are compared with those of a soft-on-soft rolling–sliding system.

Reactive core–shell nanoparticles are prepared in aqueous media by the addition of a solution of an amphiphilic organic polymer and a metal oxide precursor. The nanoparticles are thought to form by nucleation, with a core–shell structure forming later. Using acid catalysis the precursor is converted to metal oxide by an in situ sol–gel reaction. The hybrid nanoparticles, prepared with 10, 15, and 20 wt% Al(OiPr)₃, are dried and compression moulded, yielding flexible, transparent films (0.5 and 2 mm) that retain a core–shell nanoparticle structure and show well-distributed alumina-rich domains throughout the organic matrix. Preliminary results are given that show relationships between processing variables and film properties (particle diameter, appearance of the core, T_g (glass transition temperature), and storage modulus). The apparent stability of the alumina distribution is also discussed. Nanoparticles prepared using 10 wt% Al(OiPr)₃ (aluminium isopropoxide) gave films that, depending on the nanoparticles' process conditions, possessed core–shell nanoparticles with a median diameter of 45 ± 2 nm and a T_g that was 27 °C above the matrix polymer's T_g, or a median nanoparticle diameter of 161 ± 30 nm and a T_g that was 17 °C above the matrix polymer's T_g.

Cerium oxide, CeO₂, nanoparticles were prepared using reverse micellar synthesis, using cerium nitrate as a starting material, sodium hydroxide as a precipitating agent, n-octane as the oil phase, cetyl trimethyl ammonium bromide (CTAB) as the surfactant, and 1-butanol as the co-surfactant. Using x-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM), the average size of the nanoparticles obtained was found to be around 3.7 nm, and the particles had a well defined polyhedral shape. The particles also showed strong UV absorption and room temperature photoluminescence. The photoluminescence peak was sensitive to the particle concentration and showed a blue-shift upon dilution.

Multi-layered inverse opals were fabricated by laser-assisted imprinting of self-assembled silica particles into silicon substrates. A single pulse (pulse duration 23 ns) of a KrF excimer laser instantaneously melts the silicon substrate, which infiltrates and solidifies over the assembled silica particles on the substrate. By removing silica particles embedded in the silicon surface using hydrofluoric acid, inverse-opal photonic crystals were fabricated. This technique is potentially capable of controlling the photonic crystal properties by flexibly varying the silica particle size and the substrate material.

CdSe/poly(butyl acrylate) nanocomposites were synthesized by in situ miniemulsion polymerization. The hybrid nanomaterial is very stable and presents a bright green photoluminescence at 2.29 eV under ultraviolet excitation. With the excitation conditions used the intensity of the emission band keeps nearly constant from 7 K to room temperature. The morphological, structural and room temperature electrical properties of the CdSe/poly(butyl acrylate) nanocomposite have been investigated.

The phonons of self-assembled InAs/InAlAs/InP quantum wires (QWRs) have been studied by Raman scattering. The QWR LO phonons show an unusual frequency shift with the increase of the InAs deposited thickness due to dislocations. The QWR LO phonons are found to follow the selection rule of the LO phonons in bulk zinc-blende semiconductors. Because of the intermixing of In/Al atoms and the multiplication of dislocations, the post-growth thermal annealing treatment leads to a shift of the QWR LO phonons to lower frequency.

We report on the controlled synthesis of silica nanotubes on a large scale using ZnO nanowires as templates. The ZnO nanowires are first coated with a uniform silica layer by a sol–gel method. Then silica nanotubes are obtained after removal of ZnO nanowires in diluted hydrochloric acid solution. The thickness of the outer walls is tuned from ∼5 to ∼30 nm and the inner diameter is completely dependent on the size of the ZnO nanowires. Moreover, three-dimensional nanotubes such as tetrapod-like silica nanotubes are also synthesized through the same approach. Silica nanotubes with various thicknesses of outer walls and with special morphologies are expected to have potential applications in designing and fabricating novel nanodevices.