Table of contents

Finite element analysis (FEA) is used to model the nanoindentation process for a rigid, spherically shaped indenter acting on an elastic two-phase system of an elastic layer that is more compliant than the underlying elastic substrate. A review of current analytical equations to model this process is made and compared to FEA. The FEA results may be expressed analytically by a simple function that describes the reduced modulus value obtained with Oliver and Pharr's method for any modulus value, thickness of layer or radius of the indenter tip. This function is used to investigate Bückle's rule, that to measure the properties of a layer, the indentation depth should be 10% or less of the total layer thickness. The results show that Bückle's rule is invalid for layer thicknesses below 5 µm and a new rule is developed which depends on the layer thickness, the indenter radius and the ratio of the reduced moduli of the substrate and overlayer. This rule is based on FEA data. We present a guide to the analysis of the maximum depth that may be indented in order to keep the uncertainty in the reduced modulus for the layer to better than 10%.

Nano-sized TiNi powder with an average size of 50 nm was consolidated using spark plasma sintering (SPS) at 800 °C for 5 min. A layer of anatase TiO₂ coating was formed on the sintered TiNi by chemical reaction with a hydrogen peroxide (H₂O₂) solution at 60 °C followed by heat treatment at 400 °C to enhance the bioactivity of the metal surface. Cell culture using osteoblast cells and a biomimetic test in simulated body fluid proved the biocompatibility of the chemically treated SPS TiNi.

This paper presents a novel, cost-effective and single-step technique for the synthesis of single-walled carbon nanotubes (SWNTs), multi-walled carbon nanotubes (MWNTs) and magnetic metal-filled MWNTs using a fixed bed reaction thermal chemical vapour deposition (CVD) using alloy hydride catalyst. The single-step method involves the pyrolysis of methane at suitable temperatures over fine powders of certain Mischmetal-based AB₃ alloy hydride catalysts, prepared through the hydrogen decrepitation technique. These carbon nanostructures have been characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray analysis (EDAX), thermo-gravimetric analysis (TGA) and Raman spectroscopy. The magnetic properties of these metal-filled MWNTs have been studied by vibrating sample magnetometry, and the results are discussed.

In this paper we focus on the electrochromic property of a multicolour film containing transition metal ion doped hexagonal tungsten bronze (TM-HTB), Fe_0.20-HTB, and Cu_0.15-HTB. Compared with the HTB or Mo-HTB films, the colour range of the TM-HTB films was greatly extended, while the switching speed, colour contrast and electrochromic efficiency were almost unchanged. The Fe_0.20-HTB film could change colour from orange to blue. Its colour contrast and coloration efficiency are 46.6% and 38.1, respectively. And the Cu_0.15-HTB film changes from yellow-green to dark blue under the control of an electric signal. Its colour contrast and coloration efficiency are 38.7% and 54.2, respectively. The switching speed for Fe_0.20-HTB and Cu_0.15-HTB film is 8 s(reduction)/2 s(oxidation) and 8.5 s(reduction)/2 s(oxidation).

Carbon nanotube thin films have been successfully fabricated by the electrophoretic deposition technique. The supercapacitors built from such thin film electrodes have a very small equivalent series resistance, and a high specific power density over 20 kW kg⁻¹ was thus obtained. More importantly, the supercapacitors showed superior frequency response. Our study also demonstrated that these carbon nanotube thin films can serve as coating layers over ordinary current collectors to drastically enhance the electrode performance, indicating a huge potential in supercapacitor and battery manufacturing.

A layer-by-layer (LbL) self-assembly of poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT–PSS) on lignocellulose wood microfibres was used to make conductive fibres and paper. Polycations such as poly(allylamine hydrochloride) (PAH), and poly(ethyleneimine) (PEI) were used in alternate deposition with anionic conductive polythiophene (PEDOT–PSS) to construct the multilayer nanofilms on wood microfibres. Current–voltage characterization was measured on single fibres using a Keithley probe measurement system after deposition of every PEDOT–PSS monolayer to study the electrical properties of the coating. The conductivity of the microfibres increased linearly with increasing number of bilayers of PEDOT–PSS/polycation. The measured conductivities of the coated microfibres ranged from 1 to 10 S cm⁻¹. It was also observed that the conductivity of the fibres (i.e., coating of PEDOT–PSS) depends upon the type of polycations used to alternate with the polythiophene. In this work we have demonstrated successful scale integration from nano to micro and macroscale (nanocoating–microfibres–macropaper) in developing new paper material. The conductive paper that has been produced (and its fabrication method) can be used for the development of smart paper technology on monitoring of electrical, and optical/electrical signals.

We report a simple but efficient nanofabrication method to create a dense (nanoscale pitch) array of silicon nanostructures (post and grate) of varying height and shape over a large sample area. By coupling interference lithography with deep reactive ion etching (DRIE) in one process flow, we achieved silicon nanostructures of excellent regularity, currently with a pitch (i.e., period) of 230 nm, and uniform coverage, currently over 2 × 2 cm². The new nanofabrication practice of coupling interference lithography with DRIE not only simplified the nanofabrication process but also produced high-aspect-ratio (higher than 10) nanostructures. By regulating etching parameters, the nanoscopic scalloping problem typical in Bosch DRIE was not only controlled but also utilized to realize sophisticated sidewall profiles, such as tips with a pointed or a re-entrant profile. We showed the tips could be further sharpened by thermal oxidation and subsequent removal of the oxide. Well-defined nanostructures over a large area with controllable sidewall profiles and tip shapes open new application possibilities in areas beyond nanoelectronics, such as microfluidics and tissue engineering.

Bias-induced local heating in Au atom-sized contacts (ASCs) has been studied at 4.2 K by measuring the frequency ν of the conductance two-level fluctuations (TLFs) under high biases of 0.60–0.95 V. The measured logν shows a broad single-peak distribution with the peak frequency logν_m shifting to higher values with increasing bias. The logν_m–V plot is nonlinear at 4.2 K in contrast to the linear behaviour observed at 77 K. The difference in the bias dependence of logν_m manifests a bias-induced overheating in Au ASCs at 4.2 K, which renders the effective contact temperature T_eff much higher than 4.2 K. Our experimental results suggest that .

We report here a simple synthesis method for monodisperse Ge nanocrystals by thermal decomposition of precursor TOG at 360 °C, which is obtained by a reaction of GeCl₄ with oleylamine at room temperature. The effect of refluxing time on the average dimension of Ge nanocrystals is discussed. Fundamental characterizations including HRTEM and XRD were performed on these Ge nanocrystals. FTIR, DSC and TG were used to explain the mechanism of formation of Ge nanocrystals by thermal decomposition of TOG. Ge nanocrystals with average grain sizes clearly exhibit blue emission, which might result from the hydrocarbon absorbed on the surface Ge nanocrystals, the amorphous oxide layer on the surface of Ge nanocrystals and/or defects in Ge nanocrystals.

Weakly coupled quantum dots in the Pauli spin blockade regime are considered with respect to spin-dependent transport. By attaching one half-metallic and one non-magnetic lead, the Pauli spin blockade is formed by a pure triplet state with spin moment S_z = 1 or −1. Furthermore, additional spin blockade regimes emerge because of full occupation in states with opposite spin to that of the half-metallic lead.

We report on the effect of high temperature annealing on the reflection spectra of synthetic opals. The analysis of conditions for simultaneous diffraction on the (111) planes parallel and inclined to the sample surface has shown that both annealed and unannealed opals are compressed along the growth [111] axis and the shape of the SiO₂ balls forming the opals' close packed structure can be described as spheroidal. The structure parameters were evaluated from the analysis of the angular dependences of the peak positions in the Bragg reflection spectra of unfilled and glycerol-filled samples. The major effect of annealing is due to the sintering (interpenetration) of the structural elements of opals. The maximum temperature of 1050 °C leads to a 10-fold increase in the degree of spheroid sintering. As a result, the interspheroid spacing decreases by over 10%, while the filling factor increases from 0.75 to 0.96 together with the effective dielectric constant of the opal as a whole (from 1.74 to 2.08). Sintering takes place not only between spheroids, but also inside spheroids between the α-SiO₂ nanoparticles constituting them. This results in a noticeable (by ∼7%) increase in the dielectric constant of opal spheroids.

Well-dispersed gold nanodumbbells (GNDs) in an aqueous phase have been successfully fabricated by an electrochemical method using a micelle template formed by two surfactants with the addition of acetone solvent during electrolysis, the primary surfactant being cetyltrimethylammonium bromide (CTABr) and the cosurfactant being tetradecyltrimethylammonium bromide (TTABr). The role of acetone solvent is found to change the gold nanoparticles' shape from a rod to a dumbbell. The shape of the GNDs is fatter at the two ends and thinner in the middle section. The GNDs have been determined to be pure gold with a single-crystalline face-centred cubic (FCC) structure from selected area electron diffraction (SAED) patterns. Morphology features of GNDs in cross-section have also been investigated by dark field (DF) transmission electron microscopy (TEM) images. These GNDs exhibit octagonal structure in cross-section and an aspect ratio of around 3.

This paper reports on an alternative nanolithographic technique for bulk micromachining of silicon. We show how to selectively etch Si(110) in aqueous KOH solutions using electron-beam-induced nanomasking. Already nanometre thin carbonaceous films can completely suppress the wet anisotropic chemical etching of Si performed in alkaline solution (10 wt% KOH+5 wt% isopropanol). It is shown that under optimized conditions, this approach can be exploited for the fabrication of three-dimensional micro- and nanostructures.

Vertically aligned ZnO nanorods were synthesized on a lattice-mismatched cubic-phase Mg_0.6Zn_0.4O thin-film-coated Si substrate through thermal evaporation of the mixture of carbon and ZnO powders in Ar flow with an atmospheric pressure. X-ray diffraction (XRD) and Raman scattering spectrum results confirmed that the ZnO nanorods have a wurtzite structure. Transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and high-resolution TEM (HRTEM) studies indicated that the nanorods grow along the [0001] orientation. The room-temperature photoluminescence of a strong ultraviolet (UV) emission at 379 nm and a very weak deep-level emission at 510 nm implied the high optical quality of ZnO nanorods. The influence of growth time and substrate temperature on the morphologies of the nanorods was also investigated. It was found that the growth of ZnO nanorods was assisted by thermally induced phase segregation. A possible growth mechanism is proposed.

The recombination properties of directly doped InGaAs/GaAs quantum dots (QDs) for application in quantum dot infrared photodetectors (QDIPs) have been investigated by time-resolved photoluminescence. Compared with undoped and barrier-doped samples, the overall effect of direct dot doping is found to be small, resulting in only slight deterioration of dot homogeneity. Low-temperature photoluminescence decay times decrease very little, indicating that direct doping does not cause a significant increase of nonradiative recombination. In addition, directly doped quantum dots show a significantly weaker quenching of the photoluminescence intensity with temperature. At the same time, barrier doping causes the formation of more and smaller dots, which results in high photoluminescence intensity at low temperatures but an early onset of thermal carrier emission from the dots. The results suggest that direct QD doping is more prospective for realizing room-temperature operation in QDIPs.

Both bare and self-assembled monolayer (SAM) protected gold substrate could be etched by allyl bromide according to atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometric (ICPMS) analysis results. With this allyl bromide ink material, negative nanopatterns could be fabricated directly by dip-pen nanolithography (DPN) on SAMs of 16-mercaptohexadecanoic acid (MHA) on Au(111) substrate. A tip-promoted etching mechanism was proposed where the gold-reactive ink could penetrate the MHA resist film through tip-induced defects resulting in local corrosive removal of the gold substrate. The fabrication mechanism was also confirmed by electrochemical characterization, energy dispersive spectroscopy (EDS) analysis and fabrication of positive nanopatterns via a used DPN tip.

This is a study of hybrid photovoltaic devices based on TiO₂ nanorods and poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV). We use TiO₂ nanorods as the electron acceptors and conduction pathways. Here we describe how to develop a large interconnecting network within the photovoltaic device fabricated by inserting a layer of TiO₂ nanorods between the MEH-PPV:TiO₂ nanorod hybrid active layer and the aluminium electrode. The formation of a large interconnecting network provides better connectivity to the electrode, leading to a 2.5-fold improvement in external quantum efficiency as compared to the reference device without the TiO₂ nanorod layer. A power conversion efficiency of 2.2% under illumination at 565 nm and a maximum external quantum efficiency of 24% at 430 nm are achieved. A power conversion efficiency of 0.49% is obtained under Air Mass 1.5 illumination.

This study demonstrates the influence of strain on the surface wettability in crystalline films. The strain was induced in chemically grown crystalline HgCr₂S₄ films by varying the thickness. Our study revealed that the wetting properties of the crystalline surface can be systematically controlled by changing strain energy. Therefore this could provide a good basis for designing materials for applications in crystalline anti-reflection, optically transparent, super-hydrophobic and biologically compatible surfaces.

Electron bombardment from a filament as well as voltage pulses from a scanning tunnelling microscope tip have been employed to modify the surface of TiO₂(110). Individual H atoms are selectively desorbed with electrical pulses of +3 V from the scanning tunnelling microscope tip, whilst leaving the oxygen vacancies intact. This allows us to distinguish between oxygen vacancies and hydroxyl groups, which have a similar appearance in scanning tunnelling microscopy images. This then allows the oxygen vacancy-promoted dissociation of water and O₂ to be followed with the microscope. Electrical pulses between +5 and +10 V induce local TiO₂(110)1 × 2 reconstructions centred around the pulse. As for electron bombardment of the surface, relatively low fluxes increase the density of oxygen vacancies whilst higher fluxes lead to the 1 × 2 and other 1 × n reconstructions.

A new type of GdAl₂ nanocapsule with single-phase intermetallic compound GdAl₂ as the core and amorphous Al₂O₃ as the shell has been synthesized by the arc-discharge technique with modified strategies. Meanwhile, novel three-dimensional coral-like hierarchical branching macro-aggregates were self-assembled by disordered nanocapsules synthesized simultaneously in the arc-discharge process. The GdAl₂ nanocapsules display superparamagnetic properties between their blocking temperature of 100 K and Curie temperature of 162 K. The magnetocaloric effect of the GdAl₂ nanocapsules was measured between 5 and 165 K. The absolute value of the change of magnetic entropy of the GdAl₂ nanocapsules sharply increases with decreasing temperature and reaches 14.5 J kg⁻¹ K⁻¹ at 5 K in magnetic fields varying from 0 to 50 kOe. As a result, this new type of nanocapsule can prospectively be applied in cryogenic magnetic refrigerator devices.

Excimer laser irradiation is used to crystallize hydrogenated amorphous silicon thin films. The resulting films show a stratified microstructure with a crystalline volume fraction of up to 90%. There is a range of excimer laser energy that can produce stratified nanocrystalline silicon with a Tauc gap as high as 2.2 eV. This value is greater than that of amorphous or crystalline silicon and is contrary to that predicted from the theoretical analysis of mixed-phase silicon thin films. The phenomenon is explained by employing transmission electron microscopy and spectroscopic ellipsometry, and the observed bandgap enhancement is associated with quantum confinement effects within the nanocrystalline silicon layers, rather than an impurity variation.

We have investigated the structural, electrical and mechanical properties of multi-walled carbon nanotube (MWNT)–polyethylene oxide (PEO) composites. Composites with different wt% (between 0 and 50 wt% of MWNTs) were prepared and characterized by the scanning electron microscopic technique. Enhanced electrical conductivity and mechanical strength were observed for the MWNT–PEO composites. The conductivity measurements on the MWNT–PEO composite films with highest concentration of MWNTs (∼50 wt%) showed an increase of eight orders (∼7.5 × 10⁻⁸ to 6.52 S cm⁻¹) of magnitude in conductivity from bare PEO film. The temperature dependence of the conductivity for MWNT (∼50 wt%)–PEO composite showed predominantly semiconducting behaviour. The elastic modulus and tensile strength of an MWNT (∼50 wt%)–PEO film were increased by about five- and tenfold respectively, as compared to the corresponding values for a PEO film.

A simple hydrothermal procedure is developed for incorporating Fe into H₂Ti₃O₇ nanotubes. Detailed characterizations have been carried out using scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, electron energy loss spectroscopy and x-ray diffractometry, and results showed that the specimens have the same structural framework as H₂Ti₃O₇, into which Fe atoms are successfully incorporated. Ultraviolet–visible absorption spectra show that the Fe-incorporated H₂Ti₃O₇ nanotube has a much improved photon absorption efficiency in the visible region compared with the pure H₂Ti₃O₇ nanotube. Other metals have also been incorporated into H₂Ti₃O₇ nanotubes, and similar improvements are observed in some of these metal-incorporated nanotubes.

We report in this paper the growth of PbS shells over colloidal PbSe nanocrystal quantum dots (NQDs) with monolayer-precision. The technique of successive ion layer adsorption and reaction (SILAR) has been adapted to the growth of high-quality core–shell nanocrystals. The core–shell infrared NQDs were ligand-exchanged with short-chain octylamine, and the photoluminescence efficiency of the surface-engineered core–shell nanoparticles was substantially higher than that of the plain core structures undergoing the same surface processing, which reveals less ligand dependence and enhanced chemical robustness in the core–shell NQDs. The reported results open up the possibility of incorporating semiconductor infrared NQDs in the silicon matrix to develop all-inorganic light-emitting heterojunctions on silicon substrates.

Nanoshells are a novel class of optically tunable nanoparticles that consist of alternating dielectric and metal layers. They can potentially be used as contrast agents for multi-label molecular imaging, provided that the shell thicknesses are tuned to specific ratios. Sub-100 nm multi-layer nanoshells can potentially have improved tissue penetration, generate a strong surface plasmon resonance, and may exhibit absorption peaks in the visible–near-infrared (NIR) spectrum. Herein we describe the synthesis and characterization of bilayered concentric nanoshells with an overall diameter of around 50 nm consisting of a gold core, a tunable silica spacer layer and an outermost gold shell, which is approximately 16 times smaller than previously described multi-layered nanoparticles. The structured nanoshells were visualized by transmission electron microscopy (TEM) at each step of preparation. The absorption spectra of the gold–silica bilayered nanoshells are in good agreement with Mie's prediction and their resonance peak position is a function of the relative thickness of silica and gold layers.

A capacitive humidity sensor is presented for moisture detection at room temperature. The sensor is fabricated by depositing multi-wall carbon nanotubes (MWCNTs) on one of the stainless-steel substrates. When compared to a sensor without CNTs, a CNT-enhanced sensor has an increase of 60–200% in capacitance response when the humidity is under 70% relative humidity (RH), and 300–3000% if the RH level goes over 70%. The performance is comparable to a commercial sensor from Honeywell, which is used as a benchmark throughout the experiments. Our results demonstrate that nano-materials like MWCNTs can naturally form networks of porous nano-structures, which can potentially realize a miniature capacitive humidity sensor with a higher sensitivity. The gain in performance is attributed to the capillary condensation effect.

We studied the efficacy of five generations of polypropyleneimine (PPI) dendrimer to provoke nanostructure formation from a 21-nucleotide antisense oligodeoxynucleotide (ODN). Nanostructure formation was observed with all generations of dendrimer by light scattering and microscopic techniques. The efficacy of the dendrimers increased with generation number. Atomic force microscopy (AFM) was used to study the morphology of the structures at different condensation stages. Based on the observed nanostructures, we propose a zipping condensation mechanism, which is very different from the condensation pathways of high molecular weight DNA polymers. Electron microscopy showed the presence of toroidal nanoparticles. Confocal microscopic analysis showed that the nanostructures formed with G-4 and G-5 dendrimers could undergo facile cellular uptake in a breast cancer cell line, MDA-MB-231, whereas nanostructures formed with G-1 to G-3 dendrimers lacked this ability. Nanoparticles formed with G-1 to G-3 dendrimers showed significantly lower zeta potential (5.2–6.5 mV) than those (12–18 mV) of particles formed with G-4 and G-5 dendrimers. These results show that the structure and charge density of the dendrimers are important in ODN nanoparticle formation and cellular transport and that G-4 and G-5 dendrimers are useful in cellular delivery of antisense ODN.

We herein report a facile one-pot synthesis, stabilization, redispersion and Cu–S interaction of L-cysteine and dodecanethiol (DDT) protected copper organosol in toluene from precursor copper stearate using sodium borohydride in toluene under a nitrogen atmosphere. Surface modification of the synthesized copper organosol with an amino acid L-cysteine and an alkanethiol (dodecanethiol, DDT) is accomplished by a thiolate bond between the used ligands and nanoparticle surface. The cysteine molecule binds the copper surface via a thiolate and amine linkage but not through electrostatic interaction with the carboxylate group due to the solvent polarity and dielectric medium. Fourier transform infrared (FTIR) analysis was performed to confirm the surface functionalization of the amino acid and DDT to the copper surface. Copper organosol has been characterized by optical spectroscopy (UV/vis), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD). The as-synthesized particles are spherical in shape and exhibit a Mie scattering profile with an absorption maxima in the visible range. Copper nanoparticles capped by cysteine and/or DDT in non-aqueous media are found to represent an interesting catalytic approach for the synthesis of octylphenyl ether.

We have developed a fast and facile CO₂ laser assisted chemical vapour deposition LA-CVD synthesis route for carbon nanotubes, which requires no supplementary hydrocarbon feedstock. The technique yields a broad range of carbon nanostructures due to the sharp thermal gradient afforded by the laser. This in turn provides useful information on the changes in nanostructure formation with temperature. A distinct and unusual aspect of this route is that, unlike other synthesis approaches, the obtained single wall carbon nanotube diameters show no dependence on the synthesis parameters and this is attributed to their nucleation via fullerenes and fullerene caps. The results suggest fullerene nucleation may also be active in other CVD synthesis routes.

Low-wavenumber (≤20 cm⁻¹) acoustic vibrations of the M13 phage have been studied using Raman spectroscopy. The dominant acoustic vibrational mode has been found to be at 8.5 cm⁻¹. The experimental results are compared with theoretical calculations based on an elastic continuum model and appropriate Raman selection rules derived from a bond polarizability model. The observed Raman mode has been shown to belong to one of the Raman-active axial torsion modes of the M13 phage protein coat. It is expected that the detection and characterization of this low-frequency vibrational mode can be used for applications in nanotechnology such as for monitoring the process of virus functionalization and self-assembly.

In this paper, we evaluate the strength, toughness and stiffness of super-nanotubes, just recently discovered, and of the related fibre-reinforced composites. The prediction of huge toughening mechanisms suggests the feasibility of 'super-composites'. We found the optimum for super-nanotubes with a number of ∼2 hierarchal levels, similar to the optimization done by Nature in nacre.

A double-walled carbon nanotube (CNT) oscillator encapsulating a copper nanowire has been investigated using molecular dynamics simulations. Our simulation results show that the excess energy due to the interactions between the copper nanowire and the outer CNT were around 1% of the excess of van der Waals energy between the inner and the outer CNTs. The classical oscillation theory and the theory given by Zheng et al (2002 Phys. Rev. Lett.88 045503) provide a fairly good estimate of the mass-dependent frequency of a CNT oscillator encapsulating a metal nanowire. The nanotube oscillator encapsulating a metal nanowire is found to be more dependent on the encapsulated metal mass than the metal–carbon interaction.

Quantitative characterization of tip–sample interaction in scanning force microscopy is fundamental for optimum image acquisition as well as data interpretation. In this work we discuss how to characterize the electrostatic and van der Waals contribution to tip–sample interaction in non-contact scanning force microscopy precisely. The spectroscopic technique presented is based on the simultaneous measurement of cantilever deflection, oscillation amplitude and frequency shift as a function of tip–sample voltage and tip–sample distance as well as on advanced data processing. Data are acquired at a fixed lateral position as interaction images, with the bias voltage as fast scan, and tip–sample distance as slow scan. Due to the quadratic dependence of the electrostatic interaction with tip–sample voltage the van der Waals force can be separated from the electrostatic force. Using appropriate data processing, the van der Waals interaction, the capacitance and the contact potential can be determined as a function of tip–sample distance. The measurement of resonance frequency shift yields very high signal to noise ratio and the absolute calibration of the measured quantities, while the acquisition of cantilever deflection allows the determination of the tip–sample distance.

Single-crystalline LaFeO₃ nanotubes with rough tube walls have been prepared by a new two-step method: co-precipitation followed by molten-salt synthesis. The as-prepared samples were characterized by x-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM, selected area electron diffraction (SAED) and energy dispersive x-ray spectroscopy (EDS). Gas sensors were fabricated using the as-prepared sample. It was found that the sensors based on the LaFeO₃ nanotubes showed good sensing properties to Cl₂ at room temperature. The detection limit of the sensors reached 1 ppm Cl₂ at room temperature and the sensors showed good selectivity and stability.

Amorphous AlQ₃ thin film and nanoparticles can directly grow into crystalline nanowires by a one-step heat treatment. With appropriate Ar pressure and heating time at 190 °C, growth of α-phase nanowires from the film occurs. Similar growth from amorphous nanoparticles is also demonstrated by heat treatment at 150 °C. The growth is dictated by the anisotropic crystallographic nature of α-AlQ₃. The growth mechanism can be illustrated in terms of nucleation and molecular migration within the film or nanoparticles. Complete structural transformation to nanowires leads to a spectral blue shift and an enhanced intensity of photoluminescence.

Diluted magnetic semiconductor Zn_1−xCo_xO (x≤0.11) nanowires with average diameter of ∼40 nm were prepared by thermal evaporation, followed by high-energy Co ion implantation. Bombardment by Co ions produced a good number of structural defects (stacking faults and orientational variations) in the nanowires. The as-implanted nanowires were paramagnetic. We performed two types of thermal annealing, one in 1 atm argon flow and the other in a high vacuum, at 600 °C, and studied the effects of annealing on the magnetic properties of these nanowires. Argon annealing removed structural defects in the nanowires and the nanowires then revealed ferromagnetic ordering. This result suggests that structure defects are harmful to the occurrence of ferromagnetism in the Co-implanted ZnO. The structure of the as-implanted and the annealed nanowires was inspected in detail by using scanning electron microscopy, energy dispersive x-ray spectroscopy, maps of electron energy loss spectra, x-ray diffraction, and high-resolution transmission electron microscopy. Taken together, these studies suggested that no second phase existed on the scale down to the spatial resolution of ∼0.5 nm. Noticeably, the nanowires even displayed largely enhanced ferromagnetism after annealing in a high vacuum. A subsequent annealing in oxygen has also been performed on those vacuum-annealed nanowires to study the roles played by the O vacancies in determining the ferromagnetic properties of the nanowires. Our results indicate that both the improved structural quality and the increased number of O vacancies are key factors for the occurrence of ferromagnetic ordering in the Zn_1−xCo_xO nanowires.

Scanning tunnelling microscopy (STM) imaging was performed on gold surfaces with a large coverage of monodispersed silver nanoparticles soft-landed on the surface from the gas phase. In both ambient and ultra-high vacuum conditions, STM scanning was found to displace the particles out of the scanning area, due to weak adhesion of the particles to the substrate surface. Calculations based on contact mechanics and electrostatics show that the particles can overcome the force of adhesion to the surface and jump onto the STM tip beyond the tunnelling distance. The observation provides the possibility for patterning or arranging nanoparticles on a surface, which is demonstrated, and offers the potential for a multiplexed approach to create very precise surface patterns and particle arrangements.

The atomic force microscope is used increasingly to investigate the mechanical properties of materials via sample displacement under an applied force. However, both the extent of forces attainable and the accuracy of those forces measurements are significantly limited by the optical lever configuration that is commonly used to infer nanoscale deflection of the cantilever. We present a robust and general approach to characterize and compensate for the nonlinearity of the position-sensitive optical device via data processing, requiring no modification of existing instrumentation. We demonstrate that application of this approach reduced the maximum systematic error on the gradient of a force–displacement response from 50% to 5%, and doubled the calibrated force application range. Finally, we outline an experimental protocol that optimizes the use of the quasi-linear range of the most commonly available optical feedback configurations and also accounts for the residual systematic error, allowing the user to benefit from the full detection range of these indirect force sensors.