Table of contents

Molecular dynamics simulations are performed to characterize the response of zinc oxide (ZnO) nanobelts to tensile loading. The ultimate tensile strength (UTS) and Young's modulus are obtained as functions of size and growth orientation. Nanobelts in three growth orientations are generated by assembling the unit wurtzite cell along the [0001], , and crystalline axes. Following the geometric construction, dynamic relaxation is carried out to yield free-standing nanobelts at 300 K. Two distinct configurations are observed in the [0001] and orientations. When the lateral dimensions are above 10 Å, nanobelts with rectangular cross-sections are seen. Below this critical size, tubular structures involving two concentric shells similar to double-walled carbon nanotubes are obtained. Quasi-static deformations of belts with and orientations consist of three stages, including initial elastic stretching, wurtzite-ZnO to graphitic-ZnO structural transformation, and cleavage fracture. On the other hand, [0001] belts do not undergo any structural transformation and fail through cleavage along (0001) planes. Calculations show that the UTS and Young's modulus of the belts are size dependent and are higher than the corresponding values for bulk ZnO. Specifically, as the lateral dimensions increase from 10 to 40 Å, decreases between 38–76% and 24–63% are observed for the UTS and Young's modulus, respectively. This effect is attributed to the size-dependent compressive stress induced by tensile surface stress in the nanobelts. and nanobelts with multi-walled tubular structures are seen to have higher values of elastic moduli (∼340 GPa) and UTS (∼36 GPa) compared to their wurtzite counterparts, echoing a similar trend in multi-walled carbon nanotubes.

Understanding the interfacial interactions between the nanofiller and polymer matrix is important to improve the design and manufacture of polymer nanocomposites. This paper reports a molecular dynamic study on the interfacial interactions and structure of a clay-based polyurethane intercalated nanocomposite. The results show that the intercalation of surfactant (i.e. dioctadecyldimethyl ammonium) and polyurethane (PU) into the nanoconfined gallery of clay leads to the multilayer structure for both surfactant and PU, and the absence of phase separation for PU chains. Such structural characteristics are attributed to the result of competitive interactions among the surfactant, PU and the clay surface, including van der Waals, electrostatic and hydrogen bonding.

The formation of voids and bubbles in the energetic ion implantation process is an important issue in material science research, involving swelling induced embrittlement of materials in nuclear reactors, catalytic activities in the nanopores of the bubble, etc. We report here the formation and in situ dynamics of metallic nanoblisters in GaN nanowires under self-ion implantation using a Ga⁺ focused ion beam. High-resolution transmission electron microscopes equipped with electron energy loss spectroscopy and energy filtering are used to identify the constituents of the blister. In situ monitoring, with focused ion beam imaging, revealed the translation and rotation dynamics of the blisters.

Large-quantity single-crystal SnO₂ nanowires coated with ZnO nanocrystals (nc-ZnO/SnO₂ nanowires) were directly synthesized by a one-step thermal evaporation process. SnO₂ nanowires were single-crystalline tetragonal structures with the diameters and lengths of 50–100 nm and several tens of micrometres, respectively. ZnO nanocrystals were single-crystalline wurtzite structures with average diameters less than 5 nm, which coated the whole SnO₂ nanowires uniformly. Photoluminescence measurements showed that the nc-ZnO/SnO₂ nanowires had a much stronger near-band UV emission (at 393 nm) than pure SnO₂ nanowires. The Sn doping into ZnO nanocrystals may be a most possible reason for the redshift and broadening of UV emission peaks from nc-ZnO/SnO₂ nanowires. The microstructure and photoluminescence properties of the nc-ZnO/SnO₂ nanowires are discussed.

InAs was deposited by molecular beam epitaxy (MBE) on a GaAs substrate with an intentional temperature gradient from centre to edge. Two-dimensional (2D) to three-dimensional (3D) morphology evolution was found along the direction in which the substrate temperature was decreasing. Quantum dots (QDs) with density as low as ∼8 × 10⁶ cm⁻² were formed in some regions. We attribute the morphological evolution to the temperature-dependent desorption of deposited indium and the intermixing between deposited indium and gallium from the buffer.

This paper describes a negative nanoimprint lithography (N-NIL) technique for fabricating metallic nanostructures via combining conventional nanoimprint lithography (NIL) with wet chemical etching. Various metallic nanostructures such as gold grating, gold/chromium alternate bimetallic grating and gold nanoelectrode arrays, which are negative replications of the stamp pattern, have been fabricated with N-NIL. This method has demonstrated its advantages on varying the feature size of obtained metallic nanostructures with a single stamp as well as on fabricating bimetallic nanostructures. In addition, it offers a unique path to fabricate micro–nano complex structures in a single imprint process, which compensates the limitation of conventional nanoimprint lithography and maintains the advantages of conventional nanoimprint lithography such as high throughput, low cost and sub-100 nm resolution.

The interband and intraband photocurrent properties of InAs/InAlAs/InP nanostructures have been studied. The doping effect on the photoluminescence properties of the quantum dots and the anisotropy of the quantum wire interband photocurrent properties are presented and discussed. With the help of interband excitation, an intraband photocurrent signal of the InAs nanostructures is observed. With the increase of the interband excitation power, the intraband photocurrent signal first increases and then decreases, which can be explained by the variance of the ground state occupation of the InAs nanostructures and the change of the mobility and lifetime of the electrons. The temperature dependence of the intraband photocurrent signal of the InAs nanostructures is also investigated.

This paper presents an alternative method based on the metal–organic chemical vapour deposition technique to obtain new nanowire structures. Here, the metal–organic precursor acts as a catalyst and interacts with a metallic substrate to produce 3D structures such as nanowires. In the present case, trimethyl gallium interacts with a copper metallic substrate to build a single-crystalline CuGa_xO_y wire structure. Electronic microscopy techniques on image or diffraction modes have provided the structural and chemical characterization of the obtained nanowires.

Rare-earth- (Eu³⁺- or Er³⁺-) doped Gd₂O₃ nanocrystals were prepared using hot solution chemistry. The growth reaction proceeds as a result of the pyrolysis of Gd³⁺/Eu³⁺ oleate complexes in a hot organic solvent mixture. Nanocrystals of Gd₂O₃, regardless of the rare earth activator, exhibited an anisotropic two-dimensional growth, leading to square-shaped nanoplates with 11–16 nm edge length and 1.05 nm edge thickness. The Gd₂O₃ nanoplates were found to crystallize as a metastable monoclinic phase based upon x-ray diffraction and Eu^3+ 5D₀–⁷F₂ transition photoluminescence emission data. Gd₂O₃:Er nanocrystals that show the characteristic Er³⁺ near infrared emissions at 1450–1650 nm due to ⁴I_13/2–⁴I_15/2 transition are also reported.

The length of carbon nanotubes has a dramatic impact on their electron transport properties. Transport through short (<300 nm) nanotubes is free of acoustic phonon scattering and thus favours ballistic transport, which is highly desirable for memory and logic devices. Production of uniformly short and pristine nanotubes can lead to high-performance nanotube electronics. We have modified the lithography-based technique for cutting nanostructures to efficiently produce solutions of individual nanotubes with average lengths as small as 50 nm. The formation of uniform aqueous films of singly dispersed nanotubes flanked by top and bottom silicon dioxide layers on patternable substrates allows protection of the sidewalls of the nanotubes. Upon plasma etching the cut nanotubes are recovered by water rinsing of the substrates. This method does not alter the optical absorption of the nanotubes, indicating the preservation of their intrinsic properties. This technology offers an affordable alternative to produce bulk quantities of short, singly dispersed and pristine nanotubes for a vast number of applications other than nanoelectronics.

We investigate the characteristic spin dynamics corresponding to semiconductor quantum dots within the multiband envelope function approximation (EFA). By numerically solving an 8 × 8 k·p Hamiltonian we treat systems based on different III–V semiconductor materials. It is shown that, even in the absence of an applied magnetic field, these systems show intrinsic spin dynamics governed by intraband and interband transitions leading to characteristic spin frequencies ranging from THz to optical frequencies.

Zinc silicate/silica modulated ZnO nanowires have been successfully prepared by a chemical vapour deposition route. The nanowires have a uniform diameter of ∼30 nm and length of 1 µm. Photoluminescence spectra show four peaks at 382, 398, 478 and 520 nm. Two new additional peaks at 398 and 478 nm are assigned to modulation between ZnO and SiO₂. The formation mechanism of the surface modified ZnO-based nanowires is also proposed.

The size trend for the pressure-induced γ-Fe₂O₃ (maghemite) to α-Fe₂O₃ (haematite) structural phase transition in nanocrystals has been observed. The transition pressure was found to increase with decreasing nanocrystal size: 7 nm nanocrystals transformed at 27 ± 2 GPa, 5 nm ones at 34 ± 3 GPa and 3 nm ones at 37 ± 2 GPa. Annealing of a bulk sample of γ-Fe₂O₃ was found to reduce the transition pressure from 35 ± 2 to 24 ± 2 GPa. The bulk modulus was determined as 262 ± 6 GPa for 7 nm nanocrystals of γ-Fe₂O₃, which is significantly higher than the value of 190 ± 6 GPa that we measured for bulk samples. For α-Fe₂O₃, the bulk moduli for 7 nm nanocrystals (336 ± 5) and the bulk (300 ± 30) were found to be almost the same within error. The bulk modulus for the γ phase was found to decrease with decreasing particle size between 10 and 3.2 nm particle size. Values for the ambient pressure molar volume were found within 1% to be: 33.0 cm³ mol⁻¹ for bulk γ-Fe₂O₃; 32.8 cm³ mol⁻¹ for 7 nm diameter γ-Fe₂O₃ nanocrystals; 30.7 cm³ mol⁻¹ for bulk α-Fe₂O₃; and 30.6 cm³ mol⁻¹ for α-Fe₂O₃ nanocrystals.

Nanosizing of poorly water soluble drugs or incorporating them into nanoparticles to increase their solubility and thereby the bioavailability has become a favoured approach today. This work describes a novel method for encapsulating poorly water soluble phytochemical ellagic acid that is also sparingly soluble/insoluble in routine solvents used to prepare nanoparticles.

Ultrafine FePt nanoparticles have been synthesized via a novel chemical solution synthesis route. Without using a reducing agent, the stoichiometric FePt nanoparticles were produced by the decomposition of iron acetylacetonate and platinum acetylacetonate in octyl ether in the presence of oleic acid and oleyl amine as the surfactants. The particle size was found to be around 2 nm with a narrow size distribution. The particles were then deposited on substrates and heat treated afterwards. Upon annealing, the nanoparticles sintered together to form continuous thin films and at the same time to transform from disordered face centred cubic (fcc) structure to the highly anisotropic ordered face centred tetragonal (fct) structure and therefore magnetic hardening was realized in the thin films. Coercivity up to 27 000 Oe at room temperature has been obtained in the annealed samples. The very high coercivity indicates a highly completed fcc–fct phase transition which may be related to the very fine original particle size.

Polyaniline (PANI) nanofibres or nanotubes (180–200 nm in diameter) containing Fe₃O₄ nanoparticles (diameter ≈10 nm) and PANI-coated γ-Fe₂O₃ nanoneedles (40–80 nm in diameter and 500–600 nm in length) were prepared by in situ doping polymerization in the presence of H₃PO₄ as a dopant. The composite nanostructures exhibited electrical–magnetic properties that are dependent on the structure and the content of the magnetic nanoparticles used. The formation mechanism of the self-assembled composite nanostructures is discussed.

Thin films of polyaniline nanofibres were synthesized using ultraviolet irradiation of aqueous solutions of aniline, nitric acid, and ammonium peroxydisulfate. The parent solution was spin coated on a planar substrate, and allowed to polymerize in the dark for 4–5 min. The substrate was then exposed to ultraviolet light for 6–10 min. Irradiation was carried out either with a frequency-tripled Nd:YAG laser, or with a mercury vapour lamp. The polyaniline fibres and films were characterized with scanning and transmission electron microscopy, and with Fourier transform infrared spectroscopy. Fibres had typical diameters between 20 and 150 nm, and lengths of the order of microns. Bulk polyaniline formed in the unirradiated portion of the samples. Using a masking technique, alternating stripes of bulk polyaniline and polyaniline nanofibres were produced.

Using non-equilibrium molecular dynamics, argon nanojet injection was simulated under vacuum conditions. A series of simulations with different shapes of solid platinum injectors was conducted. Observed droplet sizes and jet break-up characteristics resemble the Rayleigh break-up theory. However, the different injector shapes did not cause a significant change in the nanojet break-up behaviour. The liquid temperature inside the injector was found to be a controlling factor in determining the subsequent break-up characteristics. A higher liquid temperature is preferred for the faster nanojet break-up with the shorter break-up length.

We have investigated the formation and electrical properties of nanowire bridges formed when nanowires modified with the biomolecule biotin span across a gap between gold microelectrodes functionalized with the complementary biomolecule, avidin. Dielectrophoretic manipulation with a 1 MHz AC voltage is used to manipulate biotin-modified nanowires into the inter-electrode gap. Biomolecular recognition between the biotin-modified nanowires and the avidin-modified gold microelectrodes then holds the nanowires securely in place. By simultaneously applying a second, lower-frequency AC voltage and using lock-in detection, we are able to monitor individual bridging events in real time and to characterize the change in electrical response associated with individual nanowire bridges. The combined use of physical manipulation with biomolecular recognition can be used for selective assembly of nanoscale materials, as well as analytical application as a biologically activated switch in which an electrical contact is controlled by a biomolecular recognition process.

Ultra-fine fibrous membranes were prepared by electrospinning of aqueous mixtures of poly(acrylic acid) and poly(vinyl alcohol) at 17%–83% PAA or 0.14–3.5 COOH/OH molar ratios and cross-linked by heat-induced (140 °C, 5 min) esterification. The fibre diameters increased from 270 to 450 nm with increasing PAA contents. The swelling ratio of the fibrous hydrogels increased up to 31 times their dry weight with increasing pH from 2 to 7, and most significantly between pH 4 and pH 5. The liquid uptake of the fibrous hydrogels was attributed to both the liquid diffused into the fibres and that held in the inter-fibre pores. About 53%, 35%, 43% and 37% of the swelling was contributed by the liquid in the inter-fibre pores when the fibrous hydrogels were swollen at pH 2, 4, 5 and 7, respectively. The fully swollen fibrous membranes could be triggered by an applied electric field to swell further. Such additional swelling was dependent upon the polymer compositions, strength of electric field and pH, and was reversible.

The luminescence efficiency of polymer light-emitting diodes is enhanced to more than double by doping ZnO nanorods into the poly-(3,4-ethylenedioxythiophene):poly-(styrenesulphonic acid) (PEDOT:PSS) hole buffer layer. It was demonstrated, by means of the optical and electrical characteristics and Raman spectroscopy, that there is a certain interaction between the thiophene of PEDOT and the ZnO nanorods, which decreased the amount of defect states at the interface between the PEDOT hole buffer layer and the poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) emitting layer and thus increased the device efficiency and stability.

High-k ZrO₂ films were prepared by nitrogen-assisted direct current reactive magnetron sputtering on n-type silicon (100). The microstructure and optical properties in relation to thermal budgets were investigated. X-ray photoelectron spectroscopy (XPS) was used to determine the chemical states. Atomic force microscopy (AFM) analysis indicated that the annealing temperature had significant effects on surface roughness. By using Fourier transform infrared spectroscopy (FTIR), the resistance to the interface growth after the additional thermal budgets was observed. The thickness and pseudodielectric constants of ZrO₂ thin films correlating to annealing temperature were determined by Tauc–Lorentz spectroscopic ellipsometry (SE) dispersion model fitting. Optical band gaps (E_g) were also obtained based on the extracted absorption edge.

The formation of platinum nanoparticles from a supersaturated vapour phase is investigated by molecular dynamics simulations. Argon is added as carrier gas, removing the condensation heat from the nucleating system. The interactions between the platinum atoms are modelled by the multi-body embedded atom method. The nucleation rates in highly supersaturated systems are estimated as well as properties of the critical clusters from the nucleation theorems. Furthermore, the coalescence of platinum nanoparticles is investigated and a coalescence activated structural transition in platinum nanoparticles is described.

A highly porous and nanostructured CuO–ZnO composite has been synthesized for the sensing electrode of a solid-state electrochemical sensor for the high-temperature detection of carbon monoxide. The sensing electrode is made of ZnO nanotetrapod supported CuO nanoparticles. The ZnO nanotetrapods form a three-dimensional interconnected network, leading to a highly porous electrode. The ZnO nanotetrapods on which the CuO nanoparticles are highly dispersedly supported have a high surface-to-volume ratio while maintaining thermal stability at high temperature. Our approach provides an inexpensive route for large-scale production of porous and nanostructured electrodes, which increases the sensitivity of solid-state electrochemical sensors for on-line gas detection at high temperature.

Vertically well-aligned ZnO nanorods were synthesized without employing any metal catalysts on various substrates including glass, Si(111), 6H-SiC(0001) and sapphire (0001), which were pre-coated with c-oriented ZnO buffer layers, by simple physical vapour deposition. The alignments of the ZnO nanorods on the different substrates depend on the crystallographic alignments of the pre-coated ZnO buffer layers. The ZnO nanorods grown on glass and Si(111) are vertically aligned but randomly oriented in the in-plane direction. In contrast, the vertically aligned ZnO nanorods on 6H-SiC(0001) and sapphire (0001) show an in-plane alignment with azimuthally sixfold symmetry, which indicates the epitaxial relationship between ZnO and the substrate. Similarly, photoluminescence measurements show the distinct appearance of ZnO nanorods on different substrates. Besides the UV band, which was attributed to the recombination of free excitons near the band edge, defect-related visible emissions were also observed for the samples grown on both glass and Si(111) substrates. However, the ZnO nanorods exhibit only strong band edge emission peaks with no noticeable deep level emissions when grown on the 6H-SiC(0001) and sapphire (0001) substrates, which confirms the good crystalline and optical quality of the epitaxial ZnO nanorods.

Metal Sn nanobelts have been fabricated by a substitution reaction using pure Zn powders and SnO₂ nanopowders as starting material. The morphology and structural properties of Sn nanobelts were measured by scanning electron microscopy and high-resolution transmission electron microscopy. The products consist of a large number of beltlike nanostructures with typical lengths in the range of several tens to several hundreds of micrometres and the typical widths of Sn nanobelts are in the range of several tens to several hundreds of nanometres. Sn nanobelts are pure, structurally uniform, and single crystalline. The synthesis of single-crystalline metal Sn nanobelts may open up new possibilities for experimental and theoretical understanding of dimensionally confined transport phenomena of quasi-one-dimensional metal nanomaterials.

A large number of single-crystalline Ag₂V₄O₁₁ nanobelts with thickness of 10–30 nm, width of 70–200 nm, and lengths of 2–5 µm have been successfully synthesized by a hydrothermal method. The morphologies and structures of the nanobelts were characterized by x-ray powder diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and thermal gravimetric analysis. The magnetic measurement data showed that Ag₂V₄O₁₁ nanobelts are paramagnetic materials. The nanobelts exhibited an electronic emission turn-on field of 28.9 V µm⁻¹, which is the expected macroscopic field required to produce a current density of 10 µA cm⁻². On the basis of the analytical data, it was observed that Ag₂V₄O₁₁ nanobelts could serve as a novel candidate for a future field emitter.

This paper describes a new and facile method, 'solvent capillary contact printing (SCCP)', that fabricates micro-patterned hydrophilic/hydrophobic surface caused by the selective manipulation of nanometre-scale block copolymer micelles. The method is based on using capillary injection and evaporation of a solvent, which is preferential to a core block of micelles, through poly(dimethylsiloxane) (PDMS) microchannels placed on a pre-formed block copolymer micelle monolayer. We produced well-defined surface micropatterns where a nanostructure consisting of core-opened micelles gave rise to hydrophilic surface property in the regions in contact with solvent while one consisting of hemispherical micelles remained hydrophobic in the regions contacted by the PDMS mould. Our method allows repetitive micropatterning; a surface micropattern previously formed is simply erased by exposure of preferential solvent vapour due to reversible structure modification of micelles. Furthermore, SCCP with various metal salts, precursors of metal nanoparticles, enables us to fabricate micropatterned arrays of well-separated metal nanoparticles which can be used as a catalyst for synthesizing nanowires. The micropatterned arrays of GaN nanowires are demonstrated, fabricated by SCCP.

We report on the systematically controlled growth of InP nanowire arrays by catalyst-free selective area metalorganic vapour phase epitaxy on partially masked InP(111)A substrates. The length, diameter, shape and position of the nanowires were precisely controlled by careful choice of the growth conditions and mask patterning. Manipulation of the growth conditions also enabled us to deliberately define the nanowire growth along either the axial or the radial direction, which has significant potential for the realization of novel nanostructures. Transmission electron microscopy studies revealed that the InP nanowires grown were single-crystalline with wurtzite crystal structure and the photoluminescence studies carried out at 4 K on InP nanowire arrays revealed a single intense emission peak with a significant blueshift. The controlled fabrication thus enabled the nanowires to be realized in a highly uniform manner as reproducibly identical structures and with perfect positioning in predetermined configurations, making them highly suitable for practical integration into nanodevices.

In the current paper, we report a facile template-free route for 'mass production' of ZnS hollow spheres with nano- and submicro-sizes, employing thiocarbamide, (CH₃COO)₂Zn·2H₂O and water as the raw materials. ZnS hollow spheres were obtained via hydrothermal reaction at 140 °C for 5 h. XRD analysis showed that the as-prepared ZnS hollow spheres were of hexagonal phase structure. To the best of our knowledge, there were few reports on the preparation of hexagonal ZnS crystals under low temperature (<300 °C) in the literature. Furthermore, there is no report on the hollow structure of hexagonal phase ZnS under such low temperature (140 °C). Experimental results showed that the amount of thiocarbamide in the reaction system had a great impact on the size, shape, and structure of the final product. On the basis of the experimental results and our previous work, a possible formation mechanism was suggested.

The technique of transferring Au nanowire onto HSQ by using nanoimprinting was studied. The Au nanowires were fabricated by immersion plating and investigated by SEM, AFM, and TEM analysis. The concentration of HF in the electroplating solution affects the nucleation and growth of the Au. The process of imprinting HSQ was also investigated. The Au wire transfer results were also investigated by using SEM photography and an optical microscope. Nanowires with width ∼197 nm and microwires with width ∼2 µm can be successfully transferred onto HSQ substrates.

Silicon nanocone arrays are formed on porous silicon substrates by plasma etching in a hot filament chemical vapour deposition system. The as-formed Si nanocones were characterized by means of scanning electron microscopy, high resolution transmission electron microscopy, energy dispersive x-ray analysis, and Raman spectroscopy. The results indicate that the nanocone is composed of a silicon core coated with a thin amorphous carbon (a-C) layer produced by carbon-bearing plasma etching. Plasma etching is a key factor in the formation of the nanocone arrays, while re-condensation of evaporated silicon atoms on the tip of the as-etched cone also occurs. Field emission measurements show that the a-C coating can effectively enhance the field emission ability of the nanocone arrays due to the decrease of the surface work function from 4.15 to 2.37 eV.

Nanoscale patterning was accomplished for octadecylphosphonic acid (OPA) self-assembled monolayers (SAMs) on mica using a novel electro-mechanical process based on scanning probe microscopy (SPM) techniques. In such a process, the combination of a mechanical force, applied by the SPM cantilever, and a strong electric field, generated at the SPM tip apex, is employed to create permanent or temporary patterns on OPA SAMs. The absence of electrical current enables the application of this electro-mechanical patterning process on any SAMs supported by insulating substrates.

Single-crystalline Zn₂SnO₄ (ZTO) nanowires have been successfully synthesized using a simple thermal evaporation method by heating Zn and Sn powders directly without catalysts under a temperature lower than 800 °C. The synthesized ZTO nanowires are ribbon-like, and have an average width of 100–200 nm and thickness of 50 nm. These nanowires are ultra-long, up to 0.5–1 mm. Further analyses indicate that the synthesized products are ZTO nanowires with a fairly high purity. These nanowires are highly single crystalline in the face-centred-cubic spinel structure, and grow along the direction. It is believed that the growth process of the nanowires follows a vapour–solid mechanism. Photoluminescence properties of the nanowires were measured, showing two green peaks at 529 and 544 nm and two yellow–orange emission peaks at 572 and 613 nm, which have not been reported before, besides the known blue–green peak (485 nm).

By using a simple and low-cost arc-discharge method in deionized water, high purity SiC/SiOx nanocables have been synthesized in large-scale. The synthesized SiC/SiOx nanocables consist of an uniform cubic β-SiC core and an amorphous silicon oxide shell. They are about several hundred nanometres to several microns in length and the smallest average diameter of the β-SiC core is only about 5 nm, which may be attributed to the arc-discharge in deionized water approach and to the constraint of the outer sheath. The diameters of the as-grown nanocables can be controlled through adjusting the processing parameters. The SiC/SiOx nanocables emit stable violet-blue light at wavelengths of about 315 nm and 360–400 nm. Compared to the reported results in β-SiC nanowires or nanocables, the photoluminescence of the synthesized nanocables shows significant blueshift, which is resulted from the small diameter of the β-SiC core. The photoluminescence intensity can be enhanced by annealing the as-prepared SiC/SiOx nanocables.

A reliable method enabling electrical measurements on single nanowires prepared by electrodeposition in an alumina template is described. This technique is based on electrically controlled nanoindentation of a thin insulating resist deposited on the top face of the template filled by the nanowires. We show that this method is very flexible, allowing us to electrically address single nanowires of controlled length down to 100 nm and of desired composition. Using this approach, current densities as large as 10⁹ A cm⁻² were successfully injected through a point contact on a single magnetic multilayered nanowire. This demonstrates that the technique is very promising for the exploration of electrical spin injection in magnetic nanostructures.

In this paper a statistically significant study of 1096 individual GaN nanowire (NW) devices is presented. We have correlated the effects of changing growth parameters for hot-wall chemically-vapour-deposited (HW-CVD) NWs fabricated via the vapour–liquid–solid mechanism. We first describe an optical lithographic method for creating Ohmic contacts to NW field effect transistors with both top and bottom electrostatic gates to characterize carrier density and mobility. Multiprobe measurements show that carrier modulation occurs in the channel and is not a contact effect. We then show that NW fabrication runs with nominally identical growth parameters yield similar electrical results across sample populations of >50 devices. By systematically altering the growth parameters we were able to decrease the average carrier concentration for these as-grown GaN NWs ∼10-fold, from 2.29 × 10²⁰ to 2.45 × 10¹⁹ cm⁻³, and successfully elucidate the parameters that exert the strongest influence on wire quality. Furthermore, this study shows that nitrogen vacancies, and not oxygen impurities, are the dominant intrinsic dopant in HW-CVD GaN NWs.

GaAs hexagonal air-hole arrays fabricated by selective-area metal-organic vapour phase epitaxy (SA-MOVPE) on patterned GaAs(111)B substrates are promising for applications to hexagonal air-hole-type two-dimensional photonic crystal (2D-PhC) slabs, because the grown structures exhibit smooth flat surfaces surrounded by crystal facets. In this paper, we describe SA-MOVPE carried out under various gas-flow sequences in order to reduce the growth temperature, and to obtain uniform air-hole arrays without lateral over-growth (LOG). We found that the growth rate in the pattern region and LOG were closely related to the effective As coverage and the desorption rate of the source materials. By optimizing SA-MOVPE, we obtained uniform hexagonal air-hole arrays with almost no LOG for arrays with 500–400 nm periodicity using alternate supply of the source materials (flow-rate modulation epitaxy mode). Finally, we successfully fabricated air-bridge-type hole arrays using selective etching of a sacrificial layer for vertical confinement of light in 2D-PhCs.

Nanobelts of hexagonal close-packed cobalt have been synthesized by a hydrothermal reduction process at 160 °C. The as-synthesized nanobelts, with a rectangular cross section, are 200–500 nm in diameter, 50–80 nm in thickness and a few hundreds of micrometres in length. The Co nanobelts are single crystalline and grow preferentially along the [001] direction. Furthermore, the coexisting nanosheets with zigzag edges are 2–4 µm in diameter and several tens of nanometres in thickness. The hysteresis loop at room temperature of the as-obtained product shows a ferromagnetic behaviour. In addition, some influential factors as regards the morphologies of the final products were also discussed.

A sandblasting and annealing process was utilized to modify the surface structure of aluminium. The modified surface structure was examined by x-ray diffraction (XRD) profile analysis and transmission electron microscopy (TEM). It was demonstrated that the grain size of the sandblast–annealed surface layer was in the range 50–70 nm. Mechanical and tribological properties of the nanocrystalline surface were investigated using micro-indentation, nano/micro-scratch, scanning Kelvin probe (SKP), and atomic force microscope (AFM) techniques. It was observed that the micro-hardness and wear resistance of the surface were considerably increased due to the formation of a nanocrystalline layer. In addition, a close correlation between the electron work function (EWF) and the adhesive force was observed; higher EWF corresponded to lower adhesive force and thus lower friction under light loads.

The deformation behaviour of Au nanowires subjected to uniaxial tension at high strain-rate under different temperatures is studied by molecular dynamics simulation along [001], [011], and [111] elongation directions, respectively. The stress distributions and the radial distribution functions of the structure of the nanowires are evaluated and discussed. It is seen that the stress–strain curves are quite different from those of the bulk material. Moreover, the microstructures of nanowires are transformed first from FCC to face-centred-orthorhombic-like crystalline, and then changed to the amorphous state. The first neighbouring distance in the radial distribution functions along the [001] direction is clearly split into two peaks. It appears that the ductility of the nanowires at high strain-rate is higher than the corresponding macroscopic cases. The magnitudes of Young's modulus and the maximum strength along different crystalline directions are evaluated and compared with each other. They tend to decrease as the temperature increases. It may be predicted from our simulations that the conductance at high strain-rate deformation may be a continuous function of elongation due to the smooth reduction of area.

We demonstrate irreversible blocking of ion channels using single-wall carbon nanotubes (SWNTs) functionalized with 2-aminoethylmethane thiosulfonate (MTSET). In contrast, as-produced and purified SWNTs exhibit reversible blocking, indicating that the MTSET molecule attached to SWNTs chemically interacts with the cysteine groups in the ion channels. Functionalization of SWNTs with MTSET is inferred from Fourier transform infrared (FTIR) spectroscopy, which clearly shows absorptions due to –CH stretching and deformation modes, and decrease in intensity of the –COOH line due to reaction of acid functionalized SWNTs with the basic N–CH₃ end of the MTSET molecule.

In this paper, we have studied the effect of annealing under slightly oxidizing ambient (N₂+O₂) on the structural and electrical characteristics of a limited number of silicon nanoparticles embedded in an ultra-thin SiO₂ layer. These nanoparticles were synthesized by ultra-low-energy (1 keV) ion implantation and annealing. Specific experimental methods have been used to characterize the ncs populations. They include transmission electron microscopy (TEM) Fresnel imaging for evaluating the distances and widths of interest and spatially resolved electron energy loss spectroscopy (EELS) using the spectrum-imaging mode of a scanning transmission electron microscope (STEM) to measure the size distribution and density of the ncs population. To perform electrical measurements of these particles, a nanoscale contact (100 nm × 100 nm) was patterned over the samples by electron-beam nanolithography. Room-temperature I–V characteristics of these nano-MOS structures exhibit discrete current peaks which have been associated with single-electron charging of the nanoparticles and electrostatic interaction of the trapped charges with the tunnelling current. The effect of the progressive oxidation of the Si nanoparticles on these I(V) characteristics has been studied and related to the nanocrystal characteristics.

Tungsten nanodots were reproducibly fabricated on ultrathin SiO₂/Si by a novel technique in which repeatedly large-scale voltage ramps were applied between a scanning tunnelling microscope (STM) tip and samples. These nanodots have a similar geometry with a height of 1.0 ± 0.2 nm and diameter of 4.0 ± 1.0 nm. Nanodot formation processes were inspected simultaneously during the fabrication by means of scanning tunnelling spectroscopy (STS). The appearance of high conductivity I–V curves indicates a nanocontact formed during the nanodot fabrication. The fabrication mechanism is believed to be the sequential process of the field induced tip elongation, nanocontact formation and nanocontact breaking. The behaviour of the electron transport through the nanocontact was scrutinized by fitting the I–V curves to a direct tunnelling model in the low bias range. A tunnelling barrier of 1.2 ± 0.3 eV between tungsten and SiO₂ was deduced. We also present the feasibility of probing the STM tip apex by the nanodots, which could be applied in in situ monitoring of tip apex variation during STM operation.

The existence of a large induced magnetic moment in defected single-walled carbon nanotubes (SWCNTs) is predicted using the Green's function method. Specific to this magnetic moment of defected SWCNT is its magnitude, which is much larger (by several orders of magnitude) than that of perfect SWCNTs. The induced magnetic moment also shows certain remarkable features. Therefore, we suggest that two pair-defect orientations in SWCNTs can be distinguished in experiment through the direction of the induced magnetic moment at some specific energy points.

A novel and facile synthesis route for the manufacture of transparent and uniform nanocrystalline (nc)-TiO₂ thin films on indium–tin oxide (ITO)-coated glass substrates is reported, utilizing TiCl₄ as the titania source and triblock copolymer as the uniform-structure-directing agent through evaporation-induced assembly (EIA). A systematic study of the effect of the calcining temperature on the texture, morphology, and photo-induced hydrophilicity of nc-TiO₂ thin films is provided. X-ray diffraction, atomic force microscopy, transmission electron microscopy, and a contact angle meter were used to study the nc-TiO₂ thin films obtained by calcination at different temperatures. Both the increase of calcination temperature and irradiation by UV light result in a pronounced decrease of water contact angle.

The structural properties of an ultrathin (3 nm) Si layer sandwiched between two thin SiO₂ layers subjected to thermal annealing have been investigated by energy filtered transmission electron microscopy (EFTEM). It has been demonstrated that the first stages of the thermal evolution of the Si layer involve the formation of a highly interconnected Si network, followed by the appearance of well defined nanoclusters (both amorphous and crystalline). The quantitative analysis of the EFTEM data allowed determination of the size and density of the Si nanoclusters, as well as their crystalline fraction. This information has been used to explain the dependence of the system photoluminescence on the annealing temperature.

Ag/cross-linked poly(vinyl alcohol) (PVA) cable-like nanostructures were synthesized with control in an aqueous solution of a hydrolysable amphiphilic block polymer, poly(vinyl acetone) (PVKA) (ketalization degree D_H = 0.533) under γ-ray irradiation, via one-step in situ reduction of Ag⁺ and cross-linking of alcohol units. In the present approach, we try to control the speed of the cross-linking reaction of PVA chains (alcohol units), which are yielded from the hydrolysed PVKA, utilizing the low hydrolysis rate of the PVKA in dilute acidic solution.

A colloidal suspension of hollow aluminium, cap-shaped nanoparticles ('nano-caps') can be conveniently produced by evaporation of aluminium onto a spin-coated layer of polystyrene nanoparticles (PSNPs), followed by sonication and dissolution of the polymer template. Although ordinary spherical aluminium nanoparticles have a plasmon resonance in the ultra-violet, the 'nano-caps' show plasmon absorption between 700 and 1200 nm due to their geometry. The position of their extinction peaks can be tuned by varying the thickness of the aluminium and the shape of the nano-cap. The optical properties of these shapes were modelled using the discrete dipole approximation method, which confirmed that the 'caps' have very significantly red-shifted absorbance and scattering compared to spheres. This finding suggests that aluminium nano-caps might compete with gold and silver nanoparticles in applications requiring absorption in the near infrared.

A method for reproducible site-specific force spectroscopic measurements at room temperature by combining frequency modulation atomic force microscopy and the atom tracking technique is proposed. The atom tracking enables us to compensate the change in the tip–sample relative position induced by the thermal drift as well as to precisely position the tip over the same spot of the surface within sub-Ångström stability. Here, we describe our atom-tracking implementation and the protocol we have followed for the reproducible room-temperature acquisition of series of frequency shift versus tip–sample distance (Δf–Z) curves using this technique. With this acquisition protocol, a large number of equivalent Δf–Z curves can be averaged, resulting in a considerable noise reduction, and therefore avoiding its propagation to the corresponding calculated force curve.

Inorganic nanoparticles with controlled size and shape seem especially technologically important due to the strong correlation between these parameters and their magnetic, electrical, and catalytic properties. Herein we demonstrate that uniform spinel cobalt oxide (Co₃O₄) nanocubes can be successfully synthesized on a large scale via a facile hydrothermal synthetic route under mild conditions. The size and shape of final products can be readily tuned in a wide range by tuning process parameters such as hydrothermal time, reaction temperature, surfactant, concentration, and molar ratios of starting material.

Atomically resolved scanning tunnelling microscope (STM) images of low-dimensional structures of titanium oxides grown on Ni(110) have been recorded. The overlayers were prepared by vapour phase deposition of Ti followed by oxidation in 1 × 10⁻⁷ mbar O₂ at 800 K. Arrays of self-assembled TiO nanodots of about 8 Å in diameter are observed, which appear to contain five Ti atoms. In addition, rutile TiO₂(110) islands are observed, along with TiO(001) terraces and a previously reported quasi-hexagonal overlayer.

The production of hierarchical nanopatterns (using a top-down microfabrication approach combined with a subsequent bottom-up self-assembly process) will be an important tool in many research areas. We report the fabrication of silica nanoparticle arrays on lithographically pre-patterned substrates suitable for applications in the field of nanobiotechnology. Two different approaches to reach this goal are presented and discussed: in the first approach, we use capillary forces to self-assemble silica nanoparticles on a wettability contrast pattern by controlled drying and evaporation. This allows the efficient patterning of a variety of nanoparticle systems and—under certain conditions—leads to the formation of novel branched structures of colloidal lines, that might help to elucidate the formation process of these nanoparticle arrays. The second approach uses a recently developed chemical patterning method that allows for the selective immobilization of functionalized sub-100 nm particles at distinct locations on the surface. In addition, it is shown how these nanocolloidal micro-arrays offer the potential to increase the sensitivity of existing biosensing devices. The well-defined surface chemistry (of particle and substrate) and the increased surface area at the microspots, where the nanoparticles self-assemble, make this patterning method an interesting candidate for micro-array biosensing.

Nanocrystalline titanium nitride thin films have been deposited by reactive dc magnetron sputtering in pure N₂, Ar–N₂ and He–N₂ gas mixtures. The influence of the nature of the sputtering gas on the structural, optical and the electronic properties of the nanocrystalline TiN films has been studied. Structural properties were investigated by using x-ray diffraction and an atomic force microscope, optical ones by using a UV–visible spectrophotometer and electronic properties by means of dc four-probe resistivity measurements. The films deposited in an He–N₂ gas mixture exhibited a strong (111) texture, while for those deposited in an Ar–N₂ mixture under identical conditions, the texture of the films changed from (111) to (200).

A self-consistent ab initio approach for calculating electron transport through molecular electronic devices is developed. It is based on density functional theory (DFT) calculations and the Green's function technique employing a finite basis of local orbitals. The device is rigorously separated into the extended molecule region and the electrode region. In the DFT part calculating the Hamiltonian matrix of the extended molecule from its density matrix, the electrostatic correction induced by electrodes and the exchange–correlation correction due to the spatial diffuseness of localized basis functions are included. Our approach is efficient and accurate, with a controllable error to deal with such open systems. A one-dimensional infinite gold monatomic chain, whose electronic structure can be known from conventional DFT calculations with periodic boundary conditions (PBCs), is employed to validate the accuracy of our approach. With both corrections, our result for the gold chain at equilibrium is in excellent agreement with the PBC DFT result. We find that, for the gold chain, the exchange–correlation correction is more significant than the electrostatic correction.

We report the confirmed occurrence of Fowler–Nordheim (FN) electron tunnelling in p⁺ Si (SiO_x)/self-assembled monolayers of 3-mercaptopropyltrimethoxysilane (MPTMS)/Au structures. The statistically favoured values of the effective mass and energy barrier heights for electrons are determined to be in the ranges 0.15–0.18 m_e and 1.3–1.5 eV, respectively. The electrically stressed breakdown of the monolayers is observed to take place at very high fields, i.e. 16–50 MV cm⁻¹. Prior to the breakdown, switching of FN currents between different conduction states was observed; this is found to be related to a change in the electrical properties of monolayers owing to the creation of field-induced defects.

We report the synthesis of aligned wurtzite InN nanofingers by the ion-beam assisted filtered cathodic vacuum arc technique. InN nanofingers exhibit a polycrystalline structure. Photoluminescence (PL) and field emission properties of the InN nanofingers were studied. The PL emission peak was centred at ∼1.1 eV with a full width at half maximum of 105 meV. The field emission characteristic was observed from the InN nanofingers with turn-on field of 9.7 V µm⁻¹ at a current density of 10 µA cm⁻². The formation of InN nanofingers was attributed to the Volmer–Weber growth mode.

ZnS nanoribbons with variable widths ranging from a few nanometres to micrometre order have been fabricated in a controlled way. The ultra-long nanoribbons were single crystalline, smooth and uniform throughout their lengths. Growth of the nanoribbons was initiated by the vapour–liquid–solid process and subsequently their widths were regulated by the influence of the vapour–solid process. These nanoribbons possessed a bulk-like bandgap as determined from the optical absorption spectra. Room temperature photoluminescence was observed in the UV–visible region from the ZnS nanoribbons with the emission peaks at 398 and 458 nm attributed to the transitions from the sulfur vacancy related defect states and surface states respectively.

This paper presents a novel method for the preparation of copper nanoparticles by reducing CuSO₄ with hydrazine in ethylene glycol under microwave irradiation. The influences of reaction parameters such as molar ratios of N₂H₄·H₂O /CuSO₄ and NaOH/CuSO₄, heating method and reaction temperature on the particle size and composition of powder were investigated by x-ray diffractometry (XRD), transmission electron microscopy (TEM) and particle size analysis. Well-dispersed copper nanopowder with a diameter of about 15 nm was obtained in the absence of a protective polymer.

We compared the nano-structures of three samples of ZnO thin films grown on GaN with different growth temperature conditions. Although disconnected spiral domain structures (of the order of 100 nm in width) were observed in the samples of high-temperature growth, their crystal qualities are generally better than the one grown at low temperature, either near the GaN interface or far away from the interface. In the sample of high-temperature growth through the whole process, the domain structures extend from the interface with a smaller scale and almost vertical sharp boundaries. The sample grown at the low temperature showed a generally continuous structure from the interface. However, its crystal quality is quite poor. In the sample with initial low-temperature growth and then high-temperature growth, the ZnO layer started with a continuous structure, like the sample of low-temperature growth. However, it evolved into domain structures similar to the sample of high-temperature growth beyond about 200 nm in thickness. The samples of high-temperature growth generally have higher photon emission efficiencies. The sample grown at the high temperature through the whole growth process has the highest emission quantum efficiency.

We study the effect of doping transition metals (TMs) into single-wall carbon nanotubes by using first-principles calculations. For metallic isolated (3,3) single-wall carbon nanotubes, doping of Mn, Fe and Co makes them semi-metallic, while Ni doping leads to semiconductors. For (3,3) nanotube bundles, a Co atom in the unit cell makes it exhibit semiconductor character. With two or three Co and Ni atoms doped into the bundle, the impurity atoms change the nanotube to semi-metal. In particular, the Mn₂C₁₂ and Mn₃C₁₂ bundle have comparable large magnetic moments, suggesting that such TM-doped nanotubes could be useful as nanomagnets.

CuFe₂O₄ nanowalls with a thickness of 10 nm are directly fabricated from CuFe₂O₄ ceramic grains on the surface of the ceramic at the cathode by an electrochemical method. During this fabrication period, some of the Cu²⁺ will be reduced to Cu metal and released from the lattice; at the same time, some of the Fe³⁺ will be reduced to Fe²⁺ and this will lead to cation rearrangement and a phase transition from tetragonal to cubic structure. Release of copper from the lattice and lattice cell shrinkage during the phase transition are found to be responsible for the imposing of stress in the surface layer of the sample and the formation of the nanowalls.

The ability to control the permeability of a synthetic membrane structure formed by a spatially stochastic forest of vertically aligned carbon nanofibres is demonstrated. Control of membrane pore size and morphology was achieved by varying the thickness of a uniform, conformal coating of SiO₂ on the nanofibre surfaces. Characterization of passive diffusion using fluorescence microscopy and labelled latex beads confirms the ability to alter membrane permeability. Further, statistically reproducible transport regimes are predicted for the spatially stochastic membrane as a function of the nanofibre diameter by a Monte Carlo simulation technique. Realizing predictable nanoscale behaviour in a microscopically random, statistical structure is essential for applications requiring controlled, species specific transport.

Conduction of electro-migration gap junctions coated with various organic molecules is studied to expose the prevalence of different transport processes. The principal comparison made here is between molecules with conjugated versus non-conjugated backbones. Coulomb blockade (CB) is observed in all junctions, including bare junctions and those with non-conjugated molecules, but at significantly lower prevalence than for conjugated molecules. Importantly, CB with high charging energy is seen almost exclusively on junctions with conjugated molecules. These results indicate that CB is ubiquitous in molecular electro-migration junction transport with prevalence that should be characterized using large numbers of samples.

Laurionite nanowires and nanoribbons were successfully synthesized via a rapid mechanochemical solution route by grinding a PbCl₂ powder and NaOH solution mixture for ∼2 min. The x-ray powder diffraction pattern and scanning electron microscopy results show their orthorhombic structure and morphology, respectively. Transmission electron microscopy and high-resolution electron microscopy show that the nanowires and nanoribbons grow along the [001] direction. The growth processes and the influences of experimental conditions on the sample phase and morphologies are also discussed. Furthermore, the solubility and reactivity for PbCl₂ in NaOH solution are studied. The UV–vis absorption and photoluminescence of laurionite nanowires and nanoribbons show their ultraviolet absorption and green emitting behaviour.

This work demonstrates the integration of the energy-transducing proteins bacteriorhodopsin (BR) from Halobacterium halobium and cytochrome c oxidase (COX) from Rhodobacter sphaeroides into block copolymeric vesicles towards the demonstration of coupled protein functionality. An ABA triblock copolymer-based biomimetic membrane possessing UV-curable acrylate endgroups was synthesized to serve as a robust matrix for protein reconstitution. BR-functionalized polymers were shown to generate light-driven transmembrane pH gradients while pH gradient-induced electron release was observed from COX-functionalized polymers. Cooperative behaviour observed from composite membrane functionalized by both proteins revealed the generation of microamp-range currents with no applied voltage. As such, it has been shown that the fruition of technologies based upon bio-functionalizing abiotic materials may contribute to the realization of high power density devices inspired by nature.

Controlled growth of CdSe nanoneedles and nanorods was realized in a metal–organic chemical vapour deposition system by employing sputtered Au as a catalyst. The controls over the morphology, density and structure of the nanostructures were realized by varying the growth parameters independently. By varying the growth temperature, the morphology of the CdSe structures can be changed from tapered nanoneedles to uniform nanorods. Their density can also be controlled by just changing the amount of deposited Au. The changes in morphology and density were characterized by scanning electron microscopy. X-ray diffraction and transmission electron microscopy show that the tapered nanoneedles crystallize in the zinc-blende structure with the growth direction along , and the uniform nanorods in the wurtzite structure with the growth direction along .

We report the effect of applied thermal energy in the fabrication of protruded nanostructures on tantalum (Ta) thin films using atomic force microscope (AFM) lithography and the fabrication of nanopatterns of Ta thin films by a dry etching process of protruded tantalum oxide (Ta₂O₅). Oxidized nanostructures with a high aspect ratio were successfully fabricated at high temperature by applying thermal energy. The lithographic speed of fabrication of protruded nanostructures was dramatically improved by the enhancement of electron transfer depending on the applied thermal energy and directional diffusion of OH⁻ ions depending on the increase of temperature. Nanopatterns of Ta with a high angle slope (over 80°) were fabricated by selective dry etching of Ta₂O₅.

Thermally induced transmission and reflectivity changes are investigated in thin films formed by Bi nanostructures embedded in amorphous Al₂O₃. The Bi nanostructures are formed by coalesced nanoparticles forming a quasi-network close to the percolation threshold. Upon heating above the Bi melting temperature (>574 K), the transmission of the film increases abruptly, up to 18% in respect to the initial value, which is related to Bi melting. Upon cooling, the high transmission state remains up to temperatures as low as 436 K, thus evidencing a wide melting–solidification hysteresis cycle. The existence of transient morphological changes within the embedded nanostructure related to the contraction of Bi upon melting seems to have a significant contribution to the large transmission contrast between the molten and solid states of the Bi nanostructures. This large contrast together with the large width of the cycle makes this nanostructured film promising for a thermally driven optical switch.

The PDF file provided contains web links to all articles in this volume.