Table of contents

This paper describes the characterization and application of electrically insulated conductive tips mounted on a cantilever for use in an atomic force microscope and operated in liquid. These multifunctional probes were microfabricated and designed for measurements on biological samples in buffer solution, but they can also be employed for electrochemical applications, in particular scanning electrochemical microscopy. The silicon nitride based cantilevers had a spring constant ≤0.1 N m⁻¹ and a conductive tip, which was insulated except at the apex. The conductive core of the tip consisted of a metal, e.g. platinum silicide, and exhibited a typical radius of 15 nm. The mechanical and electrical characterization of the probe is presented and discussed. First measurements on the hexagonally packed intermediate layer of Deinococcus radiodurans demonstrated the possibility to adjust the image contrast by applying a voltage between a support and the conductive tip and to measure variations of less than 1 pA in faradaic current with a lateral resolution of 7.8 nm.

Characterization of industrially important nanophosphors such as ZnS:Mn²⁺, SrAl₂O₄:Eu²⁺, Dy³⁺ and Gd₂O₂S:Pr³⁺ was undertaken with a view to optimize their synthesis methods. To investigate the crystallinity, particle size, efficiency and homogeneity in doping of Mn in ZnS; Eu and Dy in SrAl₂O₄ and Pr in Gd₂O₂S, analytical techniques such as XRD, TEM, PL, TOF-SIMS and laser-SNMS were employed. The XRD and TEM studies revealed the average particle sizes to be between 2 and 15 nm. Photoluminescence (PL) studies carried out for the nanophosphors confirm the effectiveness of doping in the host lattices. TOF-SIMS spectral analysis showed the formation of the crystal (host lattice) with the presence of different dopants. The chemical imaging mode of TOF-SIMS suggested homogeneous doping in ZnS:Mn²⁺ nanophosphor while in the case of SrAl₂O₄:Eu²⁺, Dy³⁺ the degree of homogeneity of doping was found to be considerably less. The broad band of PL in SrAl₂O₄:Eu²⁺, Dy³⁺ nanophosphor may be attributed to such an inhomogeneity to some extent. In the case of Gd₂O₂S:Pr³⁺, the PL was found to be brightest at the higher energy region. But because of very low level doping of Pr³⁺ in the Gd₂O₂S lattice, additional laser-SNMS studies were carried out for analysing the doping distribution using chemical imaging data, which indicated a high degree of homogeneity.

A new technique for producing nanometre scale patterns on thin layers (<30 nm thick) of PMMA on silicon is described. The method consists of inducing the local modification of the PMMA by applying a positive voltage between the silicon and an atomic force microscope (AFM) tip. At voltages larger than 28 V, it is observed that a hole is directly produced on the PMMA. The silicon surface is simultaneously oxidized even in the case where a hole has not been created. Monitoring of the electrical current through the AFM tip during the application of the voltage allows elucidating the mechanism of the PMMA removal. The process is used to define nanometre scale electrodes by combining the AFM lithography with electron beam lithography, metal deposition and lift-off processes.

The gentle control of the nanometric distance between two materials has paved the way for the recent experimental studies on the formation and breaking of metal nanocontacts. In this work, the evolution of Al nanowires along the stretching process up to the final breaking is simulated with density functional calculations. This massive computational work involves the breaking of thick wires (with (111) and (100) orientations and 145 and 136 atoms respectively), and the influence of O, C and H impurities on their mechanical and electrical properties. These simulations show that, close to the breaking point, Al nanowires always develop a dimer geometry irrespective of the initial configuration, crystallographic orientation and the presence of point defects, explaining the universal behaviour of the force and the conductance found in the last stages of the stretching process in all the experiments.

Integrated micrometre scale interpenetrating Au–nanostructured TiO₂ (Au–NST) network nanocomposites have been fabricated using a two-step process. First, NST pad arrays were prepared by reacting patterned Ti surfaces with aqueous H₂O₂. NST formed is porous with pores 50–200 nm in diameter and walls about 75–125 nm thick. Second, Au was infiltrated into pores of NST using electroless deposition to form the nanocomposite. SEM studies indicate that Au was deposited into pores of NST with little void formation. Selective deposition of Au on NST pads was confirmed using XRD and area-mode XPS. This process is a general route to forming micrometre-scale nanocomposite features consisting of NST and metals that are amenable to electroless deposition.

Molecular dynamics (MD) simulations of nanoindentation of multiwalled carbon nanotubes (MWCNTs) are carried out to study the deformation mechanism and the mechanical properties of MWCNTs in the radial direction. The MWCNT is found to be soft in its radial direction, with nanohardness rising slowly from about 6 to 15 GPa. The soft phase persists until all spaces between adjacent layers of the MWCNT are compressed beyond a critical value of about 1.9 Å. Beyond the critical stage the formation of new bonds between different layers starts to increase, producing a super-hard amorphous phase with a hardness of up to 94 GPa. Though locally compressed to a large radial strain of about 63%, the amorphous phase with a mixture of sp³ and sp² bonds is completely reversible upon unloading, showing super-elasticity. Further indentation afterwards leads to permanent sp³ and even sp rehybridization, the MWCNT is badly damaged and the hardness fluctuates with a maximum of about 124 GPa which is comparable to the microhardness of diamond.

The definition of features on the nanometre length scale (NLS) is impossible via conventional lithography, but can be done using extreme ultraviolet, synchrotron-radiation, or electron beam lithography. However, since these techniques are very expensive and still in their infancy, their exploitation in integrated circuit (IC) processing is still highly putative. Geometries on the NLS can however be produced with relative ease using the spacer patterning technique, i.e. transforming vertical features (like film thickness) in the vicinity of a step of a sacrificial layer into horizontal features. The ultimate length that can be produced in this way is controlled by the steepness of the step defining the sacrificial layer, the uniformity of the deposited or grown films, and the anisotropy of its etching. While useful for the preparation of a few devices with special needs, the above trick does not allow by itself the development of a nanotechnology where each layer useful for defining the circuit should be on the NLS and aligned on the underlying geometries with tolerances on the NLS. Setting up such a nanotechnology is a major problem which will involve the IC industry in the post-Roadmap era. Irrespective of the detailed structure of the basic constituents (molecules, supramolecular structures, clusters, etc), ICs with nanoscopic active elements can hardly be prepared without the ability to produce arrays of conductive strips with pitch on the NLS. This work is devoted to describing a scheme (essentially based on the existing microelectronic technology) for their production without the use of advanced lithography and how it can be arranged to host molecular devices.

The effect of oxygen adsorption on a nanotube-based field effect transistor have been controversial as to whether it induces p-type doping of the nanotube body or the work function increase in the metal electrode. Here we report a transport measurement showing that a long individual single-walled nanotube can be doped as p-type upon oxygen adsorption. We discuss that, despite the fact that the charge transfer between the nanotube and O₂ adsorbator has not been agreed to date, the effect of oxygen adsorption should still be interpreted as inducing p-type doping in the nanotube body. The n-type doping by NH₃ adsorption is also measured for the purpose of comparison. Based on these observations, we suggest that, while the Schottky barrier management could be more effective for the transistor with a short nanotube, the doping effect could be more influential in devices with longer nanotubes.

The optical transmittance and the electrical capacitance as a function of the externally applied dc voltage are obtained for a twisted nematic cell composed of inorganic clay; i.e., sodium montmorillonite, as an additive to the organic liquid crystal E7. Higher loaded nematic, with smectite clay content of over 3 wt%, exhibits wider voltage–transmittance and voltage–capacitance hystereses, indicating that such cells suffer from more serious ion-charge effects and the orientation barrier of the liquid crystal. Experimental evidence suggests that the addition of merely 0.5–1% by weight of clay substantially rectifies the electro-optical characteristics of the pristine nematic, leading to an apparent lowering of the dc threshold voltage.

A key issue in nanoimprint lithography (NIL) is determining the ultimate pitch resolution achievable for various pattern shapes and their critical dimensional control. To this end, we demonstrated the fabrication of 6 nm half-pitch gratings and 0.04 µm² cell area SRAM metal interconnects with 20 nm line half-pitch in resist by NIL. The mould for the 6 nm half-pitch grating was fabricated by cleaving a GaAs /Al_0.7Ga_0.3As superlattice grown on GaAs with molecular beam epitaxy, and selectively etching away the Al_0.7Ga_0.3As layers in dilute hydrofluoric acid. The mould for the 0.04 µm² SRAM metal interconnects was fabricated in silicon dioxide using 35 kV electron beam lithography with polystyrene as a negative resist and a reactive ion etch with the resist as mask. Imprints from both moulds showed excellent fidelity and critical dimension control.

A novel assay of protein delivery to a surface with nanoscale precision was established. This was achieved by combining recent advancements in atomic force microscopy (AFM) and bioconjugation. We utilized a heterobifunctional photocleavable cross linker to functionalize an AFM tip with proteins. Upon irradiation, the proteins were released from the tip due to a photolytic reaction of the cross linker. These proteins bound tightly to their binding partners on a substrate. When tip functionalization is carefully controlled, proteins can be locally delivered to a desired area. Importantly, the result of protein delivery can be examined immediately by high-resolution imaging in the same area using the protein-free tip. Successful protein delivery was also confirmed by fluorescence imaging and was proved to be reproducible. The approach allows protein delivery and subsequent imaging to be performed in the same local area with the same AFM tip, thus opening up the possibility of monitoring protein functions in living cells in real time.

High-density, well aligned, -oriented wurtzite ZnO nanorod arrays with significantly different tip shapes were controllably fabricated by evaporating zinc powders at temperatures varying from 450 to 600 °C. It is found that the tip shape depends not only on the substrate but also on the substrate direction relative to the auxiliary gas flow, and the radius of curvature at these tips can be less than 2 nm. These nanorods exhibit good rectification characteristics in conductive atomic force microscopy (CAFM) measurements; the current rectification can be as large as ∼10³ at 1 V. The conductance of these 'nanotips' can be tuned readily by simple air-annealing.

Nanobelts are quasi-one-dimensional nanostructures with a high ratio of width to thickness and a thickness of several tens of nanometres. Their nanomechanical behaviour determines the applications in nanodevices and nanosystems. In this work, the nanomechanical deformation of ZnS nanobelts was characterized by nanoindentation. It is found that the contact stiffness is proportional to the indentation load, while there is no size effect on the elastic deformation of the ZnS nanobelts. Indentation-induced fracture in the nanoindentation of the ZnS nanobelts is observed, which provides a potential approach to nanomanipulate nanobelts for the fabrication of nanodevices.

Co-sputtering from two independent magnetron sources was used to prepare polymer–metal nanocomposite films. Both gradient films with increasing metal fraction and homogeneous composite films were produced from polytetrafluoroethylene (PTFE) and silver targets using a rotatable sample holder. The structure of the pure sputtered polymer as well as the composite structure was studied. Electrical properties of the composite material near the percolation threshold show the expected, sharp change in the resistivity from 10⁷ Ω cm atsmall silver content to 10⁻³ Ω cm after percolation. The optical absorption in the visible region due to surface plasmon resonances also has a strong dependence on the metal content, showing a red shift of the absorption peak from 405 nm to more than 500 nm at higher silver content.

A technique for highly reproducible deposition of nanoscale sized gold dots in an atomic force microscopy (AFM) configuration is described. This is achieved by precisely controlling the tip–sample separation, using feedback control enabled by the application of an external electrostatic servo force. Application of a voltage pulse of either polarity to a gold coated oscillating cantilever tip leads to the deposition of the Au dot. Dimensions for the fabricated dots are 6–100 nm in width, and <1–10 nm in height. The well controlled deposition process allowed the study of dot formation and the obtaining of relevant statistics. We found that the deposition process is the field emission of Au ions. Nevertheless, threshold values obtained are higher than previously reported ones and were found to be dependent on the tip shape. Depositions are independent of substrate morphology and lithographically patterned lines formed by overlapping Au nanodots as long as 55 µm have been fabricated.

A novel micromachined silicon displacement sensor based on the conduction of heat between two surfaces through the ambient air is described. A displacement resolution of less than 1 nm and a dynamic range of more than 100 µm was achieved in a 10 kHz bandwidth. To minimize drift, the sensors are operated in pairs, using a differential measurement configuration. The power consumption of these devices is on the order of 10 mW per sensor, and the measured time response is described by a simple exponential with a time constant of approximately 100 µs.

We have used scanned electrospinning to deposit oriented polyethylene oxide and silica glass fibres over trenches etched in silicon. We measured the Young's moduli of the fibres using an atomic force microscope. The Young's moduli of the glass fibres agree with values calculated from previously measured mechanical resonance frequencies of similar fibres. The Young's moduli of the polyethylene oxide fibres are significantly larger than those reported for polyethylene oxide bulk and films, suggesting molecular orientation in the fibres.

The mechanism of induced nucleation of nearly monodisperse haematite nanoparticles, obtained after two hours of ageing via a novel solution-based chemical route, was clarified on the basis of x-ray diffractometry, Fourier transform infrared spectroscopy, transmission electron microscopy and x-ray photoelectron spectroscopy analysis. Due to the induction of acetic anions, the amounts of OH⁻ groups on the ferrihydrite surface increased and thereby accelerated the transformation of ferrihydrite to haematite. Moreover, the complexes of acetic anions and Fe³⁺ ions controlled the solution supersaturation during the formation of monodisperse haematite nanoparticles. Superconducting quantum interference device (SQUID) measurements revealed superparamagnetic behaviour of as-prepared haematite nanoparticles above their blocking temperature of 45 K when the field of 50 Oe was applied.

Single-crystalline Mg_xZn_1−xO (0≤x≤0.25) nanowires (MZO NWs) were synthesized on glass substrates by a hydrothermal method using a mixture of an aqueous solution of zinc nitrate hexahydrate, magnesium nitrate hexahydrate and diethylenetriamine at temperatures that ranged from 75 to 105 °C. X-ray diffraction, scanning electron microscopy and transmission electron microscopy investigations were carried out to characterize the crystallinity, surface morphologies and orientations of these nanowires, respectively. These nanowires with direct band gaps ranging from 3.21 to 3.95 eV emitted ultraviolet photoluminescence from 406 to 397 nm at room temperature as the Mg content increased. Field emission measurements revealed that the turn-on electric field and threshold electric field (current density of 1 mA cm⁻²) of ZnO NWs are 1.6 and 2.1 V µm⁻¹ with the β value of 3340. Therefore, low temperature synthesized MZO NWs (0≤x≤0.25) with modulated band gaps may be applied in solar cells, light emission devices and other nanoheterojunction devices in the future.

A convenient method for the fabrication of metal nanowires by a combination of atomic force microscopy nanoscratching on a single-layer resist and lift-off process is reported. Various metal nanowires, including Au, Cu, Ni, Al, and Ti, with widths as small as 50 nm are successfully created. The electrical resistivities of the nanowires have also been obtained and found to be in good agreement with reported results.

We present a new method, using amorphous selenium, for inducing a well-controlled 2D–3D transition of a strained CdSe/ZnSe layer, i.e. for initiating self-organization of CdSe quantum dots that does not occur spontaneously during epitaxial growth. X-ray diffraction results evidence the very good crystal quality of the samples obtained using this technique. Optical characterizations by photoluminescence and time-resolved photoluminescence show the interest of this process in the growth of CdSe/ZnSe quantum dots.

In this paper, we report a study on time-domain capacitance characterization of metal–oxide–semiconductor (MOS) structures with Si nanocrystals (nc-Si) distributing throughout the gate oxide. A drastic reduction of MOS capacitance can be observed by charge trapping in nc-Si, while release of the charges leads to the recovery of the capacitance. Such capacitance modulation is explained by an equivalent circuit in terms of the change of nc-Si capacitance as a result of charging/discharging. As the capacitance modulation represents a change in the electrical states of MOS structure, it could be used for memory applications.

Single-wall carbon nanotubes (SWNTs) were functionalized with biotin at the ends and sidewalls of the nanotubes in a series of chemical reactions. Streptavidin-coated gold nanoparticles were attached to the biotin-modified SWNTs in solution in a self-assembly process. Gold nanoparticles which connected two SWNTs were selected and contacted for transport measurements. At low temperatures, Coulomb blockade oscillations were observed as a function of gate voltage. The size of the nanoparticles can be enlarged by catalytic deposition of gold leading to current increase through the SWNT–nanoparticle–SWNT junction.

We report a simple low-temperature inverse micelle solvothermal route for the synthesis of a large quantity of single-crystalline germanium nanocrystals. X-ray diffraction measurement indicates that the as-prepared nanocrystals are composed of pure Ge with a cubic structure. The morphology, size, chemical composition, crystallinity, and structural features of the as-prepared nanocrystals were characterized by transmission electron microscopy and energy-dispersive x-ray spectroscopy.

We report the hierarchical self-assembly of ZnO nanoparticles on single-walled carbon nanotubes (SWCNT–ZnO) and multi-walled carbon nanotubes (MWCNT–ZnO) by utilizing an electrostatic coordination approach. The affinity for Zn atoms to the oxygen of the C = O in the carboxyl groups is utilized to decorate oxidized single-walled and multi-walled carbon nanotubes with ZnO nanoparticles. The CNT–ZnO structures are indicative of the carboxyl group distribution along the carbon nanotubes (CNTs). By this technique we have achieved complex design architecture such as T- and Y-junctions that would be useful for device applications. The ZnO conjugation is a reversible process; that is, the ZnO nanoparticles can be washed off from the CNTs by dissolving in NaOH or H₂SO₄. The conjugation leaves the suspension with carbon nanotubes of smaller lengths compared to the average lengths of the material that we started with. Scanning and transmission electron microscopy along with energy dispersive spectroscopy (EDS) were used to characterize the conjugation.

Single-step synthesis of ultra-fine barium titanate powder with a crystallinity as high as 90% and without barium carbonate contamination has been successfully performed under supercritical conditions using a continuous-flow reactor in the temperature range 150–380 °C at 16 MPa. To synthesize this bimetallic oxide, alkoxides, ethanol and water were used. The influence of the synthesis parameters on the BaTiO₃ powder characteristics was investigated. The results show that the water to alkoxide precursor ratio, the reactor temperature and the Ba:Ti molar ratio of alkoxide precursor play a major role in the crystallization of pure and well-crystallized BaTiO₃ nanoparticles. The continuous mode of operation without post-treatments for powder washing, drying or crystallization increase the industrial interest.

The effects of photoadsorbed H₂, N₂, O₂ and Ar on the photoluminescence (PL) of ZnSe nanowires are studied. The nanowires were grown by metalorganic chemical vapour deposition. Passivation and cleaning by photodesorption in vacuum serve to sensitize the surface of the nanowires to adsorbed gases. The PL intensity of the near band edge emissions is enhanced after each sensitizing step. When different gases are photoadsorbed, different responses in the intensity are observed; it increases for H₂ while it decreases for N₂, O₂ and Ar. While the effects of other gases can be reversed by photodesorption, that of O₂ cannot. Once oxidized, the nanowires are no longer sensitive to the ambient gases. Only above band gap photons are found to induce the adsorption, desorption and oxidation, below band gap photons are found to be ineffective. The results are understood from a picture of surface states and band bending and may form the basis of using nanowires to fabricate re-useable, multi-gas sensors.

A multi-layered nanocomposite thin film was fabricated to increase the density of PbSe quantum dots. It consisted of low-loss polymer layers and multi-stacked PbSe quantum dot layers in series. The solutions of a UV-curable low-loss polymer and PbSe quantum dots were spin-coated layer-by-layer. An arrayed and multi-stacked PbSe quantum dot layer was self-assembled by spin-coating and solvent evaporation. The multi-stacked layers of PbSe quantum dots have a face-centred cubic structure with an average {111} plane distance of ∼6.1 nm, determined by small-angle x-ray scattering. The average diameter of PbSe quantum dots is ∼5 nm and the average interparticle spacing distance is ∼2.5 nm, characterized by transmission electron microscopy. The density of PbSe quantum dots in the single-arrayed layer is ∼1.8 × 10¹² cm⁻² and the density in the three-layered thin film of multi-stacked PbSe QDs is >1.6 × 10¹³ cm⁻². The peak intensities of absorption and photoluminescence were increased with increasing number of PbSe quantum dot layers. The time of luminescence decay to e⁻¹ is 138 ns at room temperature. We investigated the structures of multi-layered and multi-stacked PbSe quantum dot thin films as well as their optical properties, and then suggested their photonic applications.

Tin(0) nanoparticles have been prepared by a new low temperature chemical reduction of SnCl₄ with t-BuONa activated NaH in THF. The size and the crystallinity of the particles can be controlled by adjusting the reaction time. Subnanometrical and amorphous Sn(0) particles were produced after 1 h reaction at 65 °C. Tetragonal Sn(0) particles with diameters of 3.2 and 40.0 nm were respectively prepared by further heating for 1 and 3.5 h. The colloidal solutions thus produced are stable at room temperature for long periods of time. Sn nanoparticles were characterized by transmission electron microscopy, XPS and EDS analyses and x-ray powder diffraction.

The fine hair adhesive system found in nature is capable of reversibly adhering to just about any surface. This dry adhesive, best demonstrated in the pad of the gecko, makes use of a multilevel conformal structure to greatly increase inelastic surface contact, enhancing short range interactions and producing significant amounts of attractive forces. Recent work has attempted to reproduce and test the terminal submicrometre 'hairs' of the system. Here we report the first batch fabricated multi-scale conformal system to mimic nature's dry adhesive. The approach makes use of massively parallel MEMS processing technology to produce 20–150 µm platforms, supported by single slender pillars, and coated with ∼2 µm long, ∼200 nm diameter, organic looking polymer nanorods, or 'organorods'. To characterize the structures a new mesoscale nanoindenter adhesion test technique has been developed. Experiments indicate significantly improved adhesion with the multiscale system. Additional processing caused a hydrophilic to hydrophobic transformation of the surface and testing indicated further improvement in adhesion.

The synthesis of ZnO nano-needles using unbalanced magnetron sputtering is reported. A multilayer structure comprised of ZnO(50 nm)/Zn(20 nm)/ZnO(2 µm) was grown on a stainless steel substrate without substrate heating. The growth of ZnO nano-needles was observed on the surface of the multilayer structure after post-annealing treatment at 300–400 °C. The nano-needles were distributed randomly over the entire surface and had an average diameter of 20 nm; their length varied from 2 to 5 µm. The ultra-thin Zn layer (20 nm) in the multilayer structure is attributed to act as a nucleating centre and it activates the coalescence process for the growth of ZnO nano-needles. The ZnO nano-needles showed enhanced ultraviolet photoresponse with an initial fast rise and decay. The origin of the photoconductivity is due to the bulk related process. Results show the myriad application of ZnO nano-needles in ultraviolet light detection.

Homogeneous metallic nanowires with diameters below 10 nm are produced by sputter coating suspended DNA molecules and/or carbon nanotubes. A fabrication method is described that allows 'e-beam nanosculpting', i.e. local modification of the shape of nanowires, with a resolution of ∼3 nm. The process is performed with a focused electron beam (e-beam) in a transmission electron microscope, under direct visual control. We also demonstrate that e-beam radiation can induce local crystallization of nanowires. This method could be used to fabricate novel electronic devices, e.g. single-electron tunnelling transistors, with dimensions below 10 nm, possibly operating at room temperature.

Polyaniline (PANI) nanofibres were synthesized using a biocatalyst (recombinant Coprinus cinereus peroxidase) instead of toxic chemical oxidants. Relatively uniform nanofibres with 50–100 nm diameter were easily obtained with this method, and the doping state of the PANI nanofibre could be controlled either with 1N camphorsulfonic acid (CSA) or with 30% NH₄OH. Doped (or dedoped) PANI nanofibres were deposited on pre-patterned Au electrodes for electrical characterization. Completely dedoped PANI behaves as an insulator, while a larger current, by more than four orders of magnitude, was observed from doped PANI nanofibres. A weak p-type gate effect was observed for PANI nanofibre devices as well. As one could expect from the easy doping nature of PANI, PANI nanofibre devices show high sensitivity toward dedoping (NH₃) gases, thereby demonstrating the possibility of using enzyme-synthesized PANI nanofibre devices as sensitive chemical sensors.

We present a novel technique for fabricating nanometre spaced metal electrodes on a smooth crystal cleavage plane with precisely predetermined spacing. Our method does not require any high-resolution nanolithography tools, all lateral patterning being based on conventional optical lithography. Using molecular beam epitaxy we embedded a thin gallium arsenide (GaAs) layer in between two aluminium gallium arsenide (AlGaAs) layers with monolayer precision. By cleaving the substrate an atomically flat surface is obtained exposing the AlGaAs–GaAs sandwich structure. After selectively etching the GaAs layer, the remaining AlGaAs layers are used as a support for deposited thin film metal electrodes. We characterized these coplanar electrodes by atomic force microscopy and scanning electron microscopy; this revealed clean, symmetric and macroscopically flat surfaces with a maximum corrugation of less than 1.2 nm. In the case of a device with a 20 nm thick GaAs layer the measured electrode distance was 22.5 nm with a maximum deviation of less than 2.1 nm. To demonstrate the electrical functionality of our device we positioned single colloidal gold nanoparticles between the electrodes by an alternating voltage trapping method; this resulted in a drop of electrical resistance from ∼11 G Ω to ∼1.5 k Ω at 4.2 K. The device structure has large potential for the manipulation of nanosized objects like molecules or more complex aggregates on flat surfaces and the investigation of their electrical properties in a freely suspended configuration.

In the present paper, we report on the processing of titanate nanotubes using the hot filament chemical vapour deposition (HF-CVD) method to synthesize titania–carbon nanotube–wire composites. The titanate nanotubes are prepared using a chemical route, and then deposited on silicon using an electrodeposition method. The HF-CVD is used to process these coatings at different temperatures in vacuum as well as in different concentrations of hydrogen (H₂) and methane (CH₄) gas mixtures. The evolutions of the surface and precipitation for various phases have been monitored using different characterization techniques. It is observed that titanate nanotubes start disintegrating above T_s∼500 °C, and exhibit different types of phase precipitation depending upon the temperature and gas ambient. Under appropriate conditions, the presence of activated hydrogen and carbon radicals leads to the formation of novel architectures of mixtures of nanophases such as carbide, nonstoichiometric titania, carbon nanotubes, and titania decorated carbon nanowires. The results are discussed in terms of reduction in the thermal reaction barrier due to the presence of atomic hydrogen, and the formation of energetic sites during disintegration of titania nanotubes to facilitate nucleation of nanotube and nanowire structures.

Multi-walled carbon nanotubes (MCNTs) can be obtained by heating grass in the presence of a suitable amount of oxygen. Grass contains a large amount of vascular bundles in the stem and nervation. The major compositions of them are cellulose, hemicellulose and lignin. In the present approach, a rapid heat treatment (at about 600 °C) and the participation of oxygen make the vascular bundles become dehydrated and turn into carbon nanotubes. The diameters of the carbon nanotubes obtained are between 30 and 50 nm.

Digital computers use binary states, typically represented by 0 and 5 V, to store and process information at all stages of a calculation. If more states (ideally a continuum) were available in between, density of information could be dramatically increased. Here we show that self-assembled nanoparticle films can feature such continuous state or analogue information storage. Information provided by an arbitrary gate voltage is 'written' by trapping charges in local, gate-modified potentials when films are cooled below 175 K. The information is 'read' using the film's built-in ability to sense charge via Coulomb blockade. Application of a time-dependent, multi-step writing gate voltage generates conductance maps corresponding to multi-valued continuous information. As a proof of concept, we exploit this technique to store 'UT' in Morse code.

Room temperature synthesis of nano-carbons, i.e., whiskers, wires, onions and tubes, has been achieved by an electrochemical process under a liquid phase of organic solution with a metal catalyst. The electrochemical method supplies athermal energy to the reactants contrary to ordinary methods, i.e., this method creates nano-carbons directly transferring electrons at the electrode in the condensed phase, and the temperature does not increase during the synthesis. The nano-carbons with various structures were obtained by using C₂H₅OH with solution under a high electric field. The metal catalyst plays an important role in the nano-carbon growth in the present method, in a similar way to the usual methods. By virtue of the low temperature synthesis, this technique has great advantages in nano-scale interconnections and large area field emission cathodes of nano-carbons in next-generation devices on a thermally unstable substrate.

Hydroxyapatite (HAP)/liposome core–shell nanocomposites have been prepared at room temperature. The liposome shells and the precipitate cores ranged in diameter mainly from 80 to 140 nm and from 40 to 120 nm, respectively. Rod-like whiskers ranging in length mainly from 10 to 30 nm were obtained after separating the precipitates from the liposomes. In contrast, the whiskers synthesized without liposomes ranged in length mainly from 70 to 140 nm. The precipitates synthesized both with and without liposomes were poorly crystalline, and had a similar chemical composition to the natural HAP.

We present here our work on nanoscale wear induced by the tip of an atomic force microscope on thin polystyrene films. Under a wide range of conditions, the repeated scanning of the polymer surface leads to the formation of tip-induced wear patterns consisting of ridges oriented perpendicular to the scanning directions. We found that the evolution of the root mean squared roughness follows an exponential saturation law. Tip-induced wear was more extensive at higher applied loads where transition from rippling to rupturing wear was also observed. Analysis of the patterns formed suggests a crazing mechanism for the observed plastic deformation. The degree of wear as well as the type of the patterns formed was found to depend strongly on the density of the scan lines. In particular an overlap between successive scan lines is necessary to obtain a periodic pattern.

Magnetic nanoparticles can be used for a variety of biomedical applications. They can be used in the targeted delivery of therapeutic agents in vivo, in the hyperthermic treatment of cancers, in magnetic resonance (MR) imaging as contrast agents and in the biomagnetic separations of biomolecules. In this study, a characterization of the movement and heating of three different types of magnetic nanoparticles in physiological systems in vitro is made in a known external magnetic field and alternating field respectively. Infra-red (IR) imaging and MR imaging were used to visualize these nanoparticles in vitro. A strong dependence on the size and the suspending medium is observed on the movement and heating of these nanoparticles. First, two of the particles (mean diameter d = 10 nm, uncoated Fe₃O₄ and d = 2.8 µm, polystyrene coated Fe₃O₄+γ-Fe₂O₃) did not move while only a dextran coated nanoparticle (d = 50 nm, γ-Fe₂O₃) moved in type 1 collagen used as an in vitro model system. It is also observed that the time taken by a collection of these nanoparticles to move even a smaller distance (5 mm) in collagen (∼100 min) is almost ten times higher when compared to the time taken to move twice the distance (10 mm) in glycerol (∼10 min) under the same external field. Second, the amount of temperature rise increases with the concentration of nanoparticles regardless of the microenvironments in the heating studies. However, the amount of heating in collagen (maximum change in temperature ΔT_max∼9 °C at 1.9 mg Fe ml⁻¹ and 19 °C at 3.7 mg Fe ml⁻¹) is significantly less than that in water (ΔT_max∼15 °C at 1.9 mg Fe ml⁻¹ and 33 °C at 3.7 mg Fe ml⁻¹) and glycerol (ΔT_max∼13.5 °C at 1.9 mg Fe ml⁻¹ and 30 °C at 3.7 mg Fe ml⁻¹). Further, IR imaging provides at least a ten times improvement in the range of imaging magnetic nanoparticles, whereby a concentration of (0–4 mg Fe ml⁻¹) could bevisualized as compared to (0–0.4 mg Fe ml⁻¹) by MR imaging. Based on these in vitro studies, important issues and parameters that require further understanding and characterization of these nanoparticles in vivo are discussed.

With the recent surge of the use of room-temperature ionic liquids in the syntheses of inorganic nanomaterials, we have successfully integrated the advantages of a thiol-functionalized ionic liquid and the seed growth method to generate palladium nanowires at room temperature. Moreover, the as-prepared palladium nanowires show very high catalytic activity and stability for the Sonogashira coupling reaction.

We report a simple technique that facilitates the micropatterning of an aligned array of CuO nanorods on a substrate as well as the fusion of the nanorods into fused junctions. The technique utilizes a focused laser beam from a He–Ne laser with moderate power to melt away the pointed end of as-grown CuO nanorods resulting in the formation of microballs at the tips of the truncated nanorods. The size of the microballs and the length of the truncated CuO nanorods were found to be dependent on the laser power used during the process. The nature of the microballs formed was investigated by high-resolution transmission electron microscopy and Raman spectroscopy. Such a focused beam provides an effective means to modify the morphology of the as-grown nanorod array and to pattern the aligned CuO nanorod array into interesting and potentially useful configurations. In addition, the focused laser beam was utilized to fuse and join nanorods, which could potentially be useful in the fabrication of nanorod circuits and network repair.

Gain-coupled distributed-feedback (GC-DFB) effects in a V-groove In_0.2Ga_0.8As/Al_0.2Ga_0.8As quantum-wire (QWR) array are investigated by comparison with those in a GaAs/Al_0.2Ga_0.8As QWR array. Temperature-dependent photoluminescence (PL) spectra are measured for both samples, showing that the PL spectra from the QWRs are much stronger than those from the quantum wells (QWs) in the entire temperature region. Then, InGaAs/AlGaAs QWR GC-DFB lasers are fabricated by one-step metallorganic chemical vapour deposition (MOCVD) growth and characterized. As a result, strong nonlinearity in the emission spectra by optical feedback along the DFB directions is clearly observed near the threshold current, indicating that a V-groove InGaAs QWR array is a good candidate for a gain-coupled DFB laser.

This paper presents the first production and demonstration of thermoplastic scanning force microscopy cantilevers with integrated tips fabricated via injection moulding. Their imaging resolution, clarity, and accuracy are equal to conventional silicon-type parts. The tips exhibit acceptable wear and are ready for use upon removal from the injection mould. This work shows the ability to economically mass-produce SFM probes with arbitrary shapes and features, as well as tailorable physical and chemical properties, which until now were limited by the properties of silicon and integrated-circuit processing technology used to make current commercial SFM probes.

We reported in a previous study (Zhao et al 2003 Phys. Rev. Lett.91 175504) that energy transfer from the orderly intertube translational oscillation to intratube vibrational modes for an isolated system of two coaxial carbon nanotubes at low temperatures takes place primarily via two distinct types of collective motion of the carbon nanotubes, i.e., off-axial rocking motion of the inner tube and radial wavy motion of the outer tube, and that these types of motion may or may not occur for such a system, depending upon the amount of the initial extrusion of the inner tube out of the outer tube. Our present study, using micro-canonical molecular dynamics (MD), indicates the existence of an energy threshold, largely independent of system sizes and configurations, for a double-walled nano-oscillator to deviate from the intertube translational oscillation and thus to encounter significant intertube friction. The frictional forces associated with several distinct dissipative mechanisms are all found to exhibit no proportional dependence upon the normal force between the two surfaces in relative sliding, contrary to the conventional understanding resulting from tribological studies of macroscopic systems. Furthermore, simulation has been performed at different initial temperatures, revealing a strong temperature dependence of friction in the early phase of oscillation. Finally, our studies of three-walled nano-oscillators show that an initial extrusion of the middle tube can cause inner-tube off-axial instabilities, leading to strong frictional effects.

Anodic aluminium oxide (AAO) templates for multi-walled carbon nanotube (MWCNT) growth were produced by anodization of aluminium followed by pulse-reverse electrodeposition of cobalt inside the AAO pores. Cobalt functioned as the catalyst for H₂/C₂H₂ chemical vapour deposition (CVD) growth of fairly well graphitized MWCNTs initiating inside the majority of the AAO pores and quickly growing beyond the pore confines. A technique is introduced for the production of AAO templates that fill evenly during pulsed electrodeposition. The electrodeposition produced an active metallic catalyst in the pore bottoms, with minimal over-filling. This process also eliminates the reduction step necessary when alternating current (AC) electrodeposition is used for filling AAO pores.

In this work, we have synthesized titanium dioxide nanorods ranging in size from 20 to 40 nm by means of the linear plasmid pBR322 and using titanium isopropoxide as a precursor through the sol–gel process. The resulting gels were calcined and the resulting powders were characterized by means of scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, x-ray diffraction, thermogravimetric analysis and differential thermal analysis. The results show that the synthesis in vitro of nanorods in the presence of DNA can be achieved. Thus, we report the synthesis of hybrids made of nucleic acids in inorganic materials that may have several applications as catalytic systems, biomaterials and nanostructured materials.

Synthesis of nanoporous SnO₂ by a surfactant self-assembling sol–gel technique is described in this work. The synthesis was performed at room temperature by employing tin(IV) tetra-tert-amyloxide, Sn (OAm^t)₄, as the porous SnO₂ frame precursor in the presence of the micelles of a cationic surfactant solution of cetyltrimethylammonium bromide (CTAB), which, in turn, acts as the SnO₂ particle nanostructure director. The pH of the Sn alkoxide–CTAB mixture was adjusted to a value of 2 with HCl in order to eventually achieve a finely dispersed SnO₂ gel structure. The final annealed materials were attained after thermal treatment of the above mentioned SnO₂ gel systems between 300 and 500 °C. This annealing procedure burned off different numbers of CTAB micelles and caused some sintering of the substrates depending on the final calcination temperature, thus producing truly mesoporous (cylindrical) SnO₂ skeletons of pore sizes 5–9 nm and surface areas between 60 and 100 m² g⁻¹ as well as some other assorted structural and textural characteristics.

We present detailed information on the fabrication of free-standing ultrathin porous alumina membranes (PAMs) with controllable thickness of 100–1000 nm. The mechanism of the ultrathin PAM formation has been revealed by a combination study of current–time characteristics and microstructure images. At the beginning of the anodization, V-shape nanopores can be observed due to the alumina formation in both the sidewalls and the barrier layers. As a result of the applied electric field effect, part of the alumina in the sidewalls is dissolved, the nanopores gradually become regularly U-shape and finally grow steadily. Ultrathin PAMs with controllable thickness and morphology have been realized by changing the anodization time and the current density. Furthermore, an improved method has been demonstrated to obtain free-standing ultrathin PAMs by removing unoxided aluminium through a nontoxic mixture solution of saturated CuSO₄ and HCl.

It is intriguing that a solid containing ∼10¹ atoms of Ga or IV-A elements (C, Si, Ge, Sn, and Pb) melts at temperatures that are higher than the melting point of the corresponding bulk solid (T_m,b) though the T_m of a solid in the 10^0–2 nm size range drops universally with the sample size. Consistent insight into the phenomenon of T_m oscillation (suppression followed by elevation as the solid size is reduced from bulk to subnanometre size) over the whole range of sizes remains a scientific challenge. Here we show that the T_m oscillation arises from the joint effect of bond order loss and its consequence on bond strength gain of small clusters in particular for Ga and atoms of the IV-A elements.

The formation of gold wires separated by a few nanometres is reported. Such nanometre-separated gaps are formed by ramping, at ambient conditions, a bias voltage across a thin gold wire until the wire breaks or fails. Externally heating the wire does not result in a lowering of the mean bias or current conditions required for creating the break, although electromigration-based models predict rapid decreases in the current required to cause the break. Based on measurements of changes in resistance during the voltage ramp, we determine that the temperature reached in the wires is very large and can approach the melting point of gold. To avoid deleterious effects of such large temperatures on molecules, we recommend here an alternate procedure for utilizing the break protocol in molecular electronics.

The electron field emission from zinc oxide (ZnO) nanoneedles on flexible plastic substrates is reported. ZnO thin films were first deposited on plastic substrates at 200 °C using a filtered cathodic vacuum arc technique; the films were then bombarded by Ar⁺ ion. After ion beam irradiation, high-density ZnO nanoneedle arrays were selectively formed on the thin films. The average diameter and length of the ZnO nanoneedles is around 100 and 700 nm respectively. Field emission measurement showed a fairly low threshold voltage of 4.1 V µm⁻¹ with a current density of 1 µA cm⁻². The emission current density can be as high as 1 mA cm⁻² at 9.6 V µm⁻¹. The result establishes a method of fabricating a flexible field emitter, which should find practical applications in vacuum electronic devices.

Atomistic simulations are performed to investigate the structural, mechanical and electronic properties of a coaxial C/BN nanocable under axial elongation using molecular dynamics. Our results show that the mechanism of the breaking process essentially differs from those for initial single-walled carbon and BN nanotubes. The formation of a carbon as well as a –C–B–N– atomic chain connecting two cable fragments before fracture is obtained, and due to such bridges the cable can be stretched until complete rupture up to ε_max∼29% as compared with ε_max∼23% for a single-walled carbon nanotube. After breakage the opposite tips of cable fragments form different individual atomic morphologies and compositions and can have promising potential as electron emitters. The Young moduli of the C/BN cable and C-NT are comparable. An analysis of the electronic structure shows that during tensile deformation the C/BN cable retains the basic electronic characteristics (metallic-like for the inner carbon nanotube and dielectric for the outer BN tube); however, the bandgap between the highest occupied N 2p and lowest unoccupied B 2p states decreases from 4.0 to 1.2 eV.

Many potential applications in nanotechnology require virtually defect-free arrays of nanometre-scale particles over large areas. Guided self-assembly of colloidal particles on patterned templates has been shown to produce ordered arrays of colloidal particles. However, there is a need to extend this technique to particles measuring much less than 50 nm in size and to develop robust fabrication techniques that would lead to defect-free, large-area arrays. We have investigated the use of the dip-coating technique to assemble one- and zero-dimensional arrays on patterned templates using particles with diameters in the 15–50 nm range. Substrates with high-resolution groove or hole patterns were prepared with extreme-ultraviolet interference lithography (EUV-IL). Particle arrays with low defect density were achieved by adapting the deposition conditions (particle concentration, pH, dip speed and orientation). The experimental findings are explained with a model that describes the relative influences of the contributing forces in the assembly process. The driving force behind the assembly is found to be the capillary forces that organize the particles with respect to the pattern on the substrate and each other. The process does not seem to impose any inherent limitations on the defect density or the size of the particle arrays.

A method for fabricating integrated carbon pipes (nanopipettes) of sub-micron diameters and tens of microns in length is demonstrated. The carbon pipes are formed from a template consisting of the tip of a pulled alumino-silicate glass capillary coated with carbon deposited from a vapour phase. This method renders carbon nanopipettes without the need for ex situ assembly and facilitates parallel production of multiple carbon-pipe devices. An electric-field-driven transfer of ions in a KCl solution through the integrated carbon pipes exhibits nonlinear current–voltage (I–V) curves, markedly different from the Ohmic I–V curves observed in glass pipettes under similar conditions. The filling of the nanopipette with fluorescent suspension is also demonstrated.

Finely focused electron beam induced chemical vapour deposition with iron carbonyl gas, Fe(CO)₅, was carried out at room temperature to fabricate desired-shape nanostructures such as dots, rods and rings. The as-formed structures exhibited an amorphous phase containing iron, carbon and oxygen elements in the whole volume and iron oxide nanocrystals existed near their surfaces. A post-deposition heat treatment at about 600 °C resulted in the transformation into a crystalline alpha-iron phase, while their shapes were maintained. The residual magnetic flux density B_r of the as-formed and alpha-iron nanorods was quantitatively measured by electron holography after magnetization, showing that their B_r values were similar to those of iron micro-powders, although the alpha-iron nanorod has a smaller B_r value than the as-formed nanorod.

GaSb/GaAs quantum dot systems are fabricated using MBE under various growth modes. The as-grown samples are studied with in situ synchrotron radiation XPS covering the As 3d, Sb 4d and Ga 3d core levels and the valence band region. The XPS spectra show dramatic changes with the growth modes, reflecting changes in the local electronic structure and chemical environments of the surface and interface atoms in both quantum dots and wetting layer. A quantum dot specific contribution near the valence band maximum is identified and related to the hole accumulation process. Local valence band offsets measured in the GaSb/GaAs systems evolve over the interface region and depend on the growth modes, which adds another degree of freedom to band engineering on the nanoscale.

The development of hybrid organic–inorganic membranes with a low propensity for protein adsorption and highly uniform nanometre size pores is described. Poly(ethylene glycol) (PEG) monolayers were grafted to nanoporous alumina membranes using covalent silane and physical adsorption poly(ethyleneimine) (PEI) immobilization chemistries. X-ray photoelectron spectroscopy (XPS) and electron microscopy were used to investigate the chemical and physical surface properties of the membranes. The adsorption behaviour of a serum albumin on the membranes was characterized with fluorescence spectroscopy and it was determined that the PEG coating reduced nonspecific protein adsorption to a level too small to be measured. The gas and liquid permeabilities of membranes were measured to determine if the surface chemistries changed the functional behaviour of the membranes. Surprisingly, the silane chemistry produced little change in the permeabilities while polymer adsorption resulted in a total loss of water permeability. The diffusion of ovalbumin through the membranes was also measured and compared with a theoretical value. Diffusion of ovalbumin through the silane-PEG-modified membranes was found to be 50% slower than the unmodified membranes, which suggests that the pores are coated with a dense film of PEG. These results suggest that hybrid organic–inorganic membranes can provide significantly improved functional behaviour over existing organic or inorganic membranes.

Highly ordered WO₃/TiO₂ composite nanotubes have been successfully prepared by the combination of the sol–gel chemical method and the anodic aluminium oxide (AAO) templating method. The diameter of the WO₃/TiO₂ composite nanotubes is about 100 nm, which is in good agreement with the pore diameter of the AAO template. The composite nanotubes are composed of mixed oxides of W⁶⁺ and Ti⁴⁺.

This paper is an attempt to clarify the question of the damping signal in non-contact atomic force microscopy. For more than ten years now, the non-contact atomic force has been used as a powerful tool for investigating topography and/or mechanical properties of surfaces at the nanometre scale. In non-contact mode the cantilever is inside a closed loop and the frequency of the loop depends on the tip–surface interaction. Variations of the frequency shift as a function of the tip–surface distance are now well understood, and theoretical models are able to explain experimental results. Besides the frequency shift, there is another signal available, the damping signal, which is the error signal of the automatic gain control used to keep the amplitude of the oscillation constant. This signal gives information about the dissipative forces, and true atomic resolution is also obtained with the damping signal. Various theoretical models have been proposed for explaining the dissipation, but as far as the atomic scale is concerned, most of them predict much smaller dissipation than the ones often observed. In an attempt to clarify the situation, a new fast virtual machine has been built using a coarse graining method. This new machine represents real progress compared to preceding virtual machines because it improves the computing time by more than two orders of magnitude. This machine allows us to extract the contribution of the instrument to the damping signal and thus to propose a method for experimentalists for removing any artefact measurements. On the other hand, it is shown that the damping signal can be strongly enhanced if the gains of the automatic gain control and the scan speed of the tip are chosen close to some critical values. Finally, theoretical results are successfully compared to experimental results.

We propose an on-demand single-photon source for quantum cryptography using a metal–insulator–semiconductor quantum dot capacitor structure. The main component in the semiconductor is a p-doped quantum well, and the cylindrical gate under consideration is only nanometres in diameter. As in conventional metal–insulator–semiconductor capacitors, our system can also be biased into the inversion regime. However, due to the small gate area, at the onset of inversion there are only a few electrons residing in a quantum dot. In addition, because of the strong size quantization and large Coulomb energy, the number of electrons can be precisely controlled by the gate voltage. After holding just one electron in the inversion layer, the capacitor is quickly biased back to the flat-band condition, and the subsequent radiative recombination across the bandgap results in single-photon emission. We present numerical simulation results of a semiconductor heterojunction and discuss the merits of this single-photon source.

Co nanoparticles have been assembled in situ on a template of double-stranded deoxyribonucleic acid (DNA) to form magnetic nanowires. DNA was immobilized on freshly cleaved mica or silanized glass and oriented by molecular combing. Pd(II) ions bound to DNA were reduced to zero-valence nanoclusters, which selectively catalysed deposition of Co(0) in a dimethylamine borane (DMAB)-based reducing bath. Co nanoclusters grew only where Pd nuclei were localized on the DNA template. Material characterization by UV–vis spectroscopy (UVS), atomic force microscopy (AFM), and energy dispersive x-ray (EDX) spectroscopy revealed that the fabrication process resulted in the formation of Co nanowires microns long and 10–20 nm thick.

Single-crystal nanowires of zinc oxide were prepared by a novel self-seeded vapour–liquid–solid (VLS) growth method using ultrasonic spray-assisted chemical vapour deposition, in which liquid Zn droplets were used as 'catalysts'. In this approach, a nanocrystalline seed layer was first deposited, by direct decomposition of a zinc acetate precursor solution, onto a glass substrate at a temperature slightly below the melting point (420 °C) of Zn. ZnO nanowires were subsequently grown at a temperature above the melting point of Zn. From transmission electron microscopy, solidified Zn/ZnO droplets were observed on the ends of the ZnO nanowires. A novel mechanism for self-seeded growth of ZnO by the 'vapour (Zn acetate)–liquid (Zn)–solid (ZnO)' growth mechanism is described. The main advantage of the method is that it is clean, since growth occurs in the absence of a second phase catalyst.

Single-crystalline Ge nanowires covered with amorphous carbon were synthesized by using GeO₂ as the Ge source and reacting it with a mixed gas of C₂H₄ and NH₃ at 750 °C. Electron microscopy studies show that the nanowires have a diameter distribution ranging from 15 to 50 nm and a length up to tens of micrometres. The growth mechanism of the Ge nanowires could be attributed to the well known vapour–liquid–solid (VLS) catalytic growth process promoted by nanoparticles attached at the end of the nanowires.

In this work we report on the photoluminescence (PL) characteristics of porous silicon (PS) prepared by electrochemical anodization of a p-type Si wafer using chemically metal-dissolved hydrofluoric solutions. Various solid metals, oxidative (Al, Fe, Sn, Ni, Cr) and reductive (Cu), were used for this work. The effects of metals on the PL properties in as-grown, illuminated, and aged states have been studied. It is found that for the as-grown state the PL intensity is reduced by the addition of metal. In particular, the Cu-doped PS reveals a PL intensity lower by one order of magnitude as compared to that of normal PS. The improvement of stability in the PL intensity under illumination was only observed for the Cu-doped PS sample, which is more stable by a factor of 2 as compared to that of normal PS. On the other hand, the improved stability of the PL intensity in the aged state was observed for metal-doped PS samples other than for the Cu-doped sample. From the results, it is suggested that reductive metals are more effective in reducing the PL degradation caused by illumination while oxidative metals are more effective in reducing the PL degradation caused by ageing.

Site-controlled InAs quantum wires were fabricated on cleaved edges of AlGaAs/GaAs superlattices (SLs) by solid source molecular beam epitaxy. The cleaved edge of AlGaAs/GaAs SLs acted as a nanopattern for selective overgrowth after selective etching. By just growing 2.0 ML InAs without high temperature degassing, site-controlled InAs quantum wires were fabricated on the cleaved edge. Furthermore, atomic force microscopy demonstrates the diffusion of In atoms is strong toward the direction on the (110) surface.

We report on various biomedical applications of our deposited nanostructured column–void Si films including respiratory monitoring, quick mass analysis for proteomics, and cell attachment. These applications exploit certain unique attributes of our nanostructured Si material that are not present for bulk Si, such as molecular immobilization, enhanced coupling with electromagnetic radiation, high surface area, and pronounced hydrophobicity. A brief review of morphology and film growth is also given according to our latest understanding. Our capability of controlling columnar separation and porosity by varying film growth conditions allows the tailoring of the properties of our films as well as the optimization of the performance in an application. The fact that these films can be deposited on low processing temperature substrates such as plastics further enhances their versatility.

Anodized aluminium oxide (AAO) with self-organized and ordered nano-hole arrays may be a good candidate for an irradiation mask to modify the properties of a nano-scale region. In order to use AAO as a mask for ion beam patterning, the ion beam transmittance of AAO should first be tested. In an AAO with a high aspect ratio (about 100), anodized from Al bulk foil, the ion beam transmittance was extremely low. However, when AAO with low aspect ratio (about 5), fabricated with thin film Al on SiO₂, was irradiated with 80 keV Co ions, the Co ion transmittance was enormously improved. After selective etching of the unirradiated region, ion beam patterned 80 nm SiO₂ dot arrays have been fabricated. This shows a potential of AAO with a low aspect ratio for an ion beam patterning nano-mask. In order to demonstrate the ion beam nano-patterning, magnetic nano-patterning was performed. A Co/Pt multilayer film with a perpendicular magnetic anisotropy was ion irradiated through an AAO mask with a low aspect ratio, 460 nm height and 50 nm diameter, and the magnetic properties were investigated by MOKE. The formation of a magnetic nano-pattern was confirmed by MFM.

Thermally stable (not sinterable) Pt/SnO₂ (metal/semiconductor) nanocomposite particles were successfully prepared by chemical methods consisting of thermohydrolysis of SnCl₄, hydrothermal processes of resultant SnO₂ nanoparticles and subsequent photo-deposition of Pt using H₂PtCl₆. XRD, HRTEM, EDS and XPS examinations revealed that platinum nanodomains (about 2 nm in size) could be deposited on the surface of nanocrystalline SnO₂ particles (about 8 nm). After annealing the Pt/SnO₂ nanopowders at 500 °C, their specific surface area was found to be still higher than 100 m² g⁻¹, thereby indicating high thermal stability against particle growth and sintering. These results show an important aspect in loading nanomaterials in practical devices without losing the nanocrystalline nature.

We demonstrate here that single-crystal β-Ni(OH)₂ nanosheets can be selectively synthesized in large quantities through a facile hydrothermal synthetic method using aqueous nickel nitrate as the nickel source and sodium hydroxide as alkaline reagent. This attempt is based on the treatment of aqueous nickel nitrate with high concentrations of sodium hydroxide solution under hydrothermal condition. Single-crystal NiO nanorolls can be obtained via a thermal decomposition method using single-crystal β-Ni(OH)₂ nanosheets as the precursor. The influences of alkaline concentration and reaction temperature are carefully investigated in this paper. The morphologies and phase structures of the as-prepared products are investigated in detail by x-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The probable formation mechanism of the NiO nanorolls is proposed on the basis of the experimental results.

Poly-p-phenylenebenzobisoxazole (PBO) and carbon nanotubes have a fully conjugated rod-like backbone entailing excellent mechanical properties, thermo-oxidative stability and solvent resistance. Rigid-rod PBO is commonly processed by dissolving in methanesulfonic acid or Lewis acid. A multi-wall carbon nanotube (MWNT) was dissolved in an isotropic Lewis acid solution of PBO for dispersion of nanotubes and for processing into thin film. The MWNT concentration in the films was up to 5 wt%. Compared to pure PBO film, all PBO + MWNT composite films retained the same but enhanced UV–Vis absorption peaks, showing that MWNT and PBO did not have overlapping electron orbitals affecting their energy gaps. The films were excited at 325 nm using a He–Cd laser for photoluminescence (PL) emission. All PL spectra had the maximum intensity at 540 nm, indicative of a yellow–green light emission. Single-layer light emitting diodes of MWNT doped PBO decreased the threshold voltage by 2 V. Up to 0.1 wt% of MWNTs, the diode emission current increased by about two orders of magnitude over those of the diodes without MWNT. Further increase of MWNT concentration caused a successive decrease in electroluminescence emission intensity, that was attributed to a quench effect from aggregation of MWNTs.

Tribo-nanolithography (TNL) can form an affected layer on a silicon surface that is resistant to corrosion by KOH, and a nanostructure can be fabricated by combination with wet chemical etching. Transmission electron microscope (TEM), Auger electron spectroscopy (AES) and secondary ion mass spectrometry (SIMS) analyses were utilized to investigate the mechanism of the etch stop effect on the machined area. TEM observation revealed that the silicon crystal structure was converted to an amorphous structure measuring approximately 15–20 nm. AES and SIMS analyses indicated that the amorphous layer consisted entirely of silicon. Thus, the mechanism of the etch stop effect on the machined area was determined to result from the formation of an amorphous silicon structure.

Using an oxide right prism attached to the drain electrode of carbon nanotube based field effect transistors (CNTFETs), we have obtained asymmetric transfer characteristics of the CNTFETs based on semiclassical simulation. The calculated results suggest that the slope of the prism and the electrode thickness play important roles in the transfer characteristics of such CNTFETs. Through optimizing them, we can convert the performance of the CNTFETs from ambipolar characteristics to unipolar (p-type or n-type) behaviour with a significant drop in the OFF current or an increase in the ON/OFF current ratio.