Table of contents

A number of protein complexes have been developed as nanoscale templates. These can be functionalized using peptide sequences that bind inorganic materials or by fusion to binding or catalytic proteins. In order to integrate peptides and proteins into specific positions in a protein template, we used circular permutation to relocate the amino and carboxy termini of the polypeptide chain. Additional sequences can then be joined to the protein termini. This minimizes disruption of the protein structure and reduces restrictions on size and conformation of the added sequence. We relocated the termini of a Sulfolobus shibatae chaperonin subunit to five different locations across the outside surface of the chaperonin complex (after residues 153, 267, 316, 480 and 499). These changes place the termini on the outside surface of the chaperonin complex. The permutants formed double rings and higher-order assemblies similar to those observed in the natural protein. When enhanced yellow fluorescent protein was fused to two chaperonin subunits permuted at positions 267 and 480, the resulting fusion protein was fluorescent and formed assembled double rings and higher-order structure. This approach is applicable to other nanoscale protein templates.

Peptide nucleic acid (PNA) is an analogue of deoxyribonucleic acid (DNA) and possesses a neutral backbone that affords stronger hybridization, greater stability and higher specificity in base pairing. However, it has not been explored as much as DNA in self-assembling functional nanostructures or nanoelectronic devices. We report here for the first time the metallization of PNA with platinum (Pt) nanoparticles via chemical binding, reduction and deposition. Pt ions from a precursor salt solution are allowed to bind over the PNA fragments followed by a reduction and then growth into metal nanoparticles. PNA–Pt complexes form chains several hundred nanometres in length and by varying the duration of chemical reduction step, the dimension of the Pt nanoparticles can be controlled. The structural features and chemical composition of PNA–Pt nanoparticles have been characterized via scanning electron microscopy, transmission electron microscopy and Fourier transform-infrared spectroscopy. These results are also supported by modelling and analysis of the nature of high-lying molecular orbitals on PNA using density functional theory (DFT) method.

This study reports a novel approach, based on the method of laser induced pattern transfer, that can deposit patterned carbon nanotube (CNT) field emission cathodes on a variety of substrates at room temperature and in an ambient environment. Tests of emission characteristics of the fabricated cathodes present favourable emission current flux, low threshold electrical field, 1 mA cm⁻² current density at 3.3 V µm⁻¹ for the 8 µm thick film and good emission focusing. Well-defined CNT patterns with a feature size down to 10 µm were produced using a mask. Compared with CNT film produced by printing based methods, higher density and better adhesion were achieved, without any post-treatment. Control of the film thickness can plainly be accomplished by adjusting the coated CNT film thickness on the support and the number of laser pulses. The fast deposition rate and high degree of feasibility of using the substrate, as well as the fabrication environment, render the proposed approach a potential method for low cost fabrication of precision patterns for CNT.

In spite of encouraging progress in recent years, the development of magnetic nanoparticles that can be used as drug delivery vectors remains a significant challenge for materials scientists. Among the multiple hurdles that must be overcome are the provision of a sufficiently high magnetic response, a high loading capacity for therapeutic or diagnosis materials and a sufficient degree of biocompatibility. In this work we describe the preparation of encapsulated magnetic nanoparticles consisting of a metallic iron core and an amorphous silica shell by using a modification of the arc-discharge method. This is a simple and inexpensive way to produce well-coated iron nanoparticles. The particles thus obtained present a much stronger magnetic response than any composite material produced up to now involving magnetic nanoparticles encapsulated in inorganic matrices, and the rich chemistry and easy functionalization of the silica outer surface make them promising materials for their application as magnetic carriers.

In a previous paper, we reported that large gold particles (about 100 nm) could be synthesized in onion-type multilamellar vesicles, but with consecutive onion destruction (Regev et al 2004 Chem. Mater.16 5280). Here, we modified the experimental synthesis process to produce stable phosphatidylcholine- (PC-) based onions containing 3–10 nm size gold particles. Direct hydration of the sheared lamellar phase with a 10⁻² M KAuCl₄ solution was used. Insertion of octadecylamine into PC–monoolein onion bilayers results in a decrease of gold particle size from 45 nm down to 5 nm. A reduction process is proposed, which notably enlightens gold formation kinetics. Monoolein is shown to act as the chemical reductant by FT-IR analysis, while a photon-induced reduction is assumed for bilayers depleted in monoolein. The effect of gold particles on lamellar arrangement is tackled by small angle x-ray diffraction experiments, while the stability of particle-containing onion-type multilamellar vesicles is discussed using cryo-TEM imaging.

The memory effect and retention characteristics of a Ge nanocrystal (NC) floating gate memory structure consisting of Hf-aluminate (HfAlO) tunnelling and control oxides have been investigated by means of high-frequency capacitance–voltage (C–V) and capacitance–time (C–t) measurements. The trilayer structure (HfAlO/Ge-NC/HfAlO) on Si was fabricated by pulsed-laser deposition at a relatively low temperature. A high-resolution transmission electron microscopy study revealed that the Ge nanocrystals are about 5 nm in diameter and are well distributed within the amorphous HfAlO matrix. The memory effect was revealed by the counter-clockwise hysteresis loop in the C–V curves and a high storage charge density of about 1 × 10¹³ cm⁻² and a large flat-band voltage shift of 3.6 V have been achieved. An 8% decay in capacitance after 10⁴ s in the C–t measurement suggests a promising retention property of Ge NC charge storage. The effects of size/density of the Ge NC, the tunnelling and control oxide layer thicknesses and their growth oxygen partial pressure to the charge storage and charge retention characteristics have been studied.

Two-dimensional 'single-crystal' hafnia networks were synthesized by the high temperature gas–solid reaction method. Transmission electron microscopy investigation shows that these networks exhibit micrometre-scale external dimensions and nanometre-scale holes and frame width. The formation of these novel structures is based on the vapour–solid growth mechanism, and the boron nitride deposited on the networks' surface plays a key role in the growth procedure by selectively influencing the growth rate of the crystal faces. This process involves the control of crystal surface properties and adsorption of the growth unit, and is extendable to the fabrication of nanosystems either in two dimensions or in three dimensions.

A fluorinated methacryl hybrid material, with low surface tension, was used as an imprinting material for easy de-moulding in a UV-based nano-imprint process. Specifically, a method to measure the adhesive force between the poly(dimethylsiloxane) (PDMS) mould and the imprinting material, using the force–distance curve of PDMS, was suggested to represent the de-mouldability of the PDMS mould in a UV-based nano-imprint process. The fluorinated methacryl hybrid material exhibited a low adhesive force to PDMS, as well as low surface tension, and could be nano-imprinted without using an anti-sticking treatment on the PDMS mould.

This study reports new three-dimensional (3D) micromachined magnetic tweezers consisting of micro-electromagnets and a ring-trap structure, fabricated using MEMS (micro-electro-mechanical systems) technology, for manipulating a single 2 nm diameter DNA molecule. The new apparatus uses magnetic forces to exert over 20 pN with less heating, allowing the extension of the DNA molecule over its whole contour length to investigate its entropic and elastic regions. To improve the localized DNA immobilization efficiency, a novel ring-trapper structure was used to handle the vertical movement of magnetic beads which were adhered to the DNA molecules. One extremity of the DNA molecule, which was bound to the thiol-modified magnetic bead, could be immobilized covalently on a gold surface. The other extremity, which was bound to another unmodified magnetic bead, could be manipulated under a magnetic field generated by micro-electromagnets. The important elastic modulus of DNA has been explored to be 453 pN at a low ionic strength. This result reveals that DNA becomes more susceptible to elastic elongation at a low ionic strength due to electrostatic repulsion. The force–extension curve for DNA molecules is found to be consistent with theoretical models. In addition to a single DNA stretching, this study also successfully demonstrates the stretching of two parallel DNA molecules.

We report a systematic investigation of the effect of different inert gases on chemical vapour deposition (CVD) of nano-crystalline diamond. The surface morphology and growth rate of the nano-structure CVD films were characterized by Raman spectroscopy and different microscopic techniques. In situ optical emission measurement was employed to monitor the plasma chemistry, which possibly influences the film growth. Our result indicates that C₂ is not necessarily the key growth species for nano-crystalline diamond and we demonstrate here that the nano-crystalline diamond film can be grown under conditions where the C₂ concentration is very small. Modelling results support the trend in number density changes for intermediate radicals with the volume percentage of argon variation for CH₄/H₂/Ar plasma.

In this work, we propose a combined photochemical–chemical method that enables us to grow CdS nanoparticles with ångström precision. CdS nanoparticles were formed through a photo-induced reaction between CdSO₄ and Na₂S₂O₃. Thioglycerol (C₃H₈O₂S) was used as the capping agent. Fine tuning of the size was subsequently carried out by controlling the pH of the solution. Optical absorption spectroscopy was mainly used to monitor the process of particle formation, and to measure the bandgap and size. X-ray diffraction spectra confirmed the optical sizes and demonstrated crystalline nanoparticles. In the presence of the capping agent there was a dark growth that was completely dependent on the pH of the solution. The rate of dark growth decreased when the pH of the solution increased to 7.0. In pHs of 7.5 and 8, we observed a boundary situation where the number of particles was constant and only the existing particles grew in size. We proposed a model to explain this effect. The model is based on the formation of a local higher H⁺ concentration near the nanoparticle's surface. Finally, in pHs higher than 8.3 there was no dark growth. In a typical procedure, we showed that fine tuning of the size with ångström precision is possible, i.e. a 1.6 Å change in size was obtained in 45 min reaction time.

Nanorods of zinc oxalate dihydrate have been synthesized using the reverse micellar route. These nanorods were decomposed at 450 °C in air to obtain nanoparticles of zinc oxide. Transmission electron microscopy shows the nanorods to be 120 nm in diameter and 600 nm in length. The ZnO nanoparticles are 55 nm in diameter. The photoluminescence studies show two peaks at 370 and 403 nm which can be ascribed to free excitonic transition and donor–acceptor pair transition respectively. The temperature dependent PL intensity shows an anomalous non-monotonous temperature dependence probably due to two different optical processes.

This paper describes the design and implementation of a tunable beam splitter for fabricating three-dimensional low-index-contrast photonic crystals using four-beam interference. Here, a central console is used to split a single laser beam into four beams that are focused onto the sample in an umbrella-like configuration using three adjustable mirrors. The design facilitates simple and precise adjustments of the beam angles and polarization, which can be used to readily optimize fabrication conditions for different photosensitive materials and lattice structures. Structures fabricated using this tunable beam splitter at two different incident angles of 18.5° and 27° resulted in lattices with hexagonal symmetries having well-defined nanometre-scale features that are in close agreement with the feature sizes predicted theoretically.

Microwave-induced plasmas (MIPs) of H₂S and N₂/H₂ have been used to sulfidize and reduce WO₃ and MS₃ (where M = Zr and Hf) phases respectively. Characterization by powder x-ray diffraction and electron microscopy techniques shows that inorganic fullerene structures of WS₂ and nanorods/nanotubes of ZrS₂ can be synthesized. In all cases the structures appear to exhibit a higher concentration of defects and final morphologies are reflective of the precursor used. Furthermore, for ZrS₂ and HfS₂ phases significant post-synthesis oxidation is observed.

The temperature dependence of the formation of nano-scale indium clusters in InAlGaN quaternary alloys, which are grown by metalorganic chemical vapour deposition on GaN/Si(111) epilayers, is investigated. Firm evidence is provided to support the existence of phase separation, or nano-scale In-rich clusters, by the combined results of high-resolution transmission electron microscopy (HRTEM), high-resolution x-ray diffraction (HRXRD) and micro-Raman spectra. The results of HRXRD and Raman spectra indicate that the degree of phase separation is strong and the number of In clusters in the InAlGaN layers on silicon substrate is higher at lower growth temperatures than that at higher growth temperatures, which limits the In and Al incorporated into the InAlGaN quaternary alloys. The detailed mechanism of luminescence in this system is studied by low temperature photoluminescence (LT-PL). We conclude that the ultraviolet (UV) emission observed in the quaternary InAlGaN alloys arises from the matrix of a random alloy, and the second emission peak in the blue–green region results from the nano-scale indium clusters.

The electrical transport properties of high quality ZnO nanorods, synthesized by catalyst-free metalorganic chemical vapour deposition, were studied as a function of temperature by fabricating field effect transistors based on single ZnO nanorods. The thermally activated Schottky emission was found to be a ruling transport mechanism in the temperature regime of 70–293 K over a wide range of electric fields with an effective barrier height of ∼120 meV. In contrast, the Fowler–Nordheim tunnelling dominated at low temperatures (<70 K) under very high electric fields.

The mechanisms of exciton dissociation and migration in the conjugated polymer (poly(2-methoxy-5-(2'-ethyl)(hexyloxy)1,4-phenylenevinylene))(MEH-PPV)/CdSe nanoparticle hybrid materials were investigated by steady-state and time-resolved photoluminescence spectroscopy. Rapid exciton dissociation at the nanoparticle/polymer interfaces, leading to quenching of the photoluminescence efficiency η and shortening of the measured lifetime τ_PL, is observed. The excitons which contribute to the remaining luminescence in the polymer migrate to the lower energy sites with longer conjugated sequences in the composites. The result is further evident from the observation of a redshift of the photoluminescence peak positions, a progressive decrease of the Huang–Rhys factor S and an increase in the natural radiative lifetime τ_R with increasing CdSe nanoparticle content.

We report on the fabrication of gallium nitride (GaN) nanowire field-effect transistors (FETs) with both bottom-gate and top-gate structures, with very high yield using a unique pre-alignment process. The catalyst positions were chosen to be aligned with the source/drain position, and Ni catalysts with a diameter of 200 nm were deposited selectively at these pre-determined positions. Electrostatic analysis was performed for the bottom-gate devices to estimate the nanowire's electrical characteristics. Comparison of the bottom-gate and the top-gate structures indicated that better performance, in terms of saturation and breakdown characteristics, can be obtained using the top-gate structure. For the top-gate nanowire FETs, temperature-dependent characteristics were investigated up to the current saturation regime, and memory effects were observed at room temperature.

The transport properties of metal–molecule–metal junctions containing a monolayer of conjugated and saturated molecules with characteristic dimensions in the range 30–300 nm are correlated with microscopic topography, stress and chemical bonding at the metal–molecule interfaces. Our statistically significant dataset allows us to conclude that the conductivity of organic molecules ∼1.5 nm long is at least four orders of magnitude lower than is commonly believed.

We report the synthesis of nominal 2 and 5 at.% Mn-doped ZnO nanocrystalline particles by a co-precipitation method. Rietveld refinement of x-ray diffraction data revealed that Mn-doped ZnO crystallizes in the monophasic wurtzite structure and the unit cell volume increases with increasing Mn concentration. DC magnetization measurements showed ferromagnetic ordering above room temperature with H_c∼150 Oe for nominal 2 at.% Mn-doped ZnO nanoparticles annealed at 675 K. A distinct ferromagnetic resonance (FMR) signal was observed in the EPR spectra of the 2 at.% Mn-doped ZnO nanoparticles annealed at 675 K. EPR measurements were used to estimate the number of spins participating in ferromagnetic ordering. Of the total Mn present in the 2 at.% Mn ZnO lattice, 25% of the Mn²⁺ ions were responsible for ferromagnetic ordering, whereas nearly 5% of the Mn²⁺ ions remained uncoupled (isolated spins). A well resolved EPR spectrum of 5% Mn-doped ZnO samples annealed at 875–1275 K (g = 2.007, A = 80 G, D = 210 G and E = 15 G) confirmed that Mn was substitutionally incorporated into the ZnO lattice as Mn²⁺. On increasing the temperature of annealing beyond 1075 K an impurity phase emerges in both the 2 and 5 at.% Mn-doped ZnO samples, which has been identified as a variant of (Zn_1−XMn(II)_X)Mn(III)₂O₄ with T_c∼15 K. Our results indicate that the observed room temperature ferromagnetism in Mn-doped ZnO can be attributed to the substitutional incorporation of Mn at Zn-sites rather than due to the formation of any metastable secondary phases.

The temporal evolution of an electron in a double rectangular quantum dot in the presence of an electric field pulse is explored in this work. In the framework of the effective mass approximation, first-order scattering rates for electron–electron and electron–longitudinal acoustic phonon interaction at room temperature are calculated in the high tunnelling regime, and used to evaluate the dynamics of the population and coherence of the first three confined levels under an electric field pulse. Small values of these rates dependent upon the coupling barrier make feasible the emission of coherent radiation near 0.1 THz.

Using an explicit empirical potential and a combination of Monte Carlo and molecular dynamics simulations, we investigate the energetic, thermal and dynamical stability of hydrogenated palladium nanoclusters containing a few hundred atoms. At zero temperature, icosahedral clusters favour tetrahedral absorption sites, while cubic clusters preferentially absorb at octahedral sites. As a consequence, icosahedra can absorb a larger quantity of hydrogen than cubic clusters. However, even a moderate amount of absorbed hydrogen is found to favour cubic structures. There are two distinct effects of temperature. First, thermal desorption of hydrogen atoms can take place spontaneously even at low temperatures. Second, hydrogen rich cubic particles undergo a structural transition toward icosahedra before melting occurs. A simplified diagram is proposed to account for the observed behaviour. Finally, the coalescence between two clusters is studied dynamically for several clusters at various temperatures, both in the gas phase and for particles embedded in a simple model solvent. The heat produced from coalescence results in the desorption of hydrogen molecules. This leads to a significant cooling of the nanoparticle, thereby contributing to its stabilization.

Nanoscale globular platinum dendrites were synthesized by chemical reduction of platinum complexes with ascorbic acid in aqueous micellar solutions. The dendritic platinum nanostructures can be reproducibly prepared on a gram scale, allowing their characterization by N₂ adsorption as well as transmission electron microscopy (TEM), cross-section TEM, scanning TEM (STEM), scanning electron microscopy (SEM), and x-ray diffraction (XRD). Because of the high surface area, these nanoporous Pt dendrites have potential applications as catalysts and electrocatalysts. Control over the size of these platinum dendrites was realized by seeding their autocatalytic growth at the beginning of the reaction either by addition of platinum nanoparticles or by growing the seed particles using a porphyrin photocatalyst. The results support a mechanism based on dendritic growth from the seeds by an autocatalytic metal-reduction reaction occurring at the surface of the platinum dendrites rather than a mechanism based on formation of nanoparticles that subsequently aggregate.

The extinction spectra of spherical gold nanoparticles suspended in a homogeneous media were measured and the results were adjusted with Mie's theory together with an appropriate modification of the optical properties of bulk material considering the limitation that introduces the size of nanoparticles on the dielectric function. Usually, the contribution of free electrons to the dielectric function is modified for particle size, while the contribution of bound electrons is assumed to be independent of size. This work discusses the separated contribution of free and bound electrons on the optical properties of particles and their variation with size for gold nanoparticles. The effects of dielectric function and its changes with size on extinction spectra near plasmon resonance are considered. The damping constant for free electrons was changed with size as usual and a scattering constant of C = 0.8 was used. For the bound electron contribution, two different models were analysed to fit the extinction spectra: on the one hand, the damping constant for interband transitions and the gap energy were used as fitting parameters and on the other, the electronic density of states in the conduction band was made size-dependent. For the first model, extinction spectra corresponding to particles with radius R = 0.7 nm were fitted using two sets of values of the energy gap and damping constant: E_g = 2.3 eV and or E_g = 2.1 eV and . For the second model, a simple assumption for the electronic density of states and its contribution to the dielectric function in terms of size allowed to adjust extinction spectra for all samples explored (from 0.3 to 1.6 nm radius). This last model uses only one parameter, a scale factor R₀ = 0.35 nm, that controls the contribution of the bound electrons in nanoparticles. Contrast between the maximum and the minimum in the extinction spectra near the resonance at 520 nm or alternatively the broadening of the plasmon band can be used to determine the size of gold nanoparticles with radius smaller than 2 nm.

A 3D ZnO nanostructure with sisal-like morphology has been synthesized in the temperature range 120–220 °C by a rapid hydrothermal route (30 min) via the assembly of CTA⁺ and Zn(OH)₄²⁻. The obtained samples are hexagonal wurtzite structures and they exhibit special optical properties with a red-shift of about 20 nm compared to the corresponding nanorods and nanowires. The sisal, constructed of many nanorods, possesses typical tapering features with tip size 80–100 nm. The effects of CTAB, NaOH, reaction time and temperature were investigated. Results show that the concentration of CTAB and Zn²⁺/OH⁻ molar ratio play important roles in the fabrication of uniform and pure ZnO samples. On the basis of structural information provided by XRD, SEM, TEM, and HRTEM, a growth mechanism is proposed for the formation of sisal-like 3D ZnO nanostructures.

Carbon nanotubes (CNTs) are known to possess extraordinary strength, stiffness and ductility properties. Their fracture resistance is an important issue from the perspective of durability and reliability of CNT-based materials and devices. According to existing studies, brittle fracture is one of the important failure modes of single-walled carbon nanotube (SWNT) failure due to mechanical loading. However, based on the authors' knowledge, the fracture resistance of CNTs has not been quantified so far. In this paper, the fracture resistance of zigzag SWNTs with preexisting defects is calculated using fracture mechanics concepts based on atomistic simulations. The interatomic forces are modelled with a modified Morse potential; the Anderson thermostat is used for temperature control. The problem of unstable crack growth at finite temperature, presumably caused by the lattice trapping effect, is circumvented by computing the strain energy release rate through a series of displacement-controlled tensile loading of SWNTs (applied through moving the outermost layer of atoms at one end at constant strain rate of 9.4 × 10⁻⁴ ps⁻¹) with pre-existing crack-like defects of various lengths. The strain energy release rate, G, is computed for (17, 0), (28, 0) and (35, 0) SWNTs (each with aspect ratio 4) with pre-existing cracks up to 29.5 Å long. The fracture resistance, G_c, is determined as a function of crack length for each tube at three different temperatures (1, 300 and 500 K). A significant dependence of G_c on crack length is observed, reminiscent of the rising R curve behaviour of metals at the macroscale: for the zigzag nanotubes G_c increases with crack length at small length, and tends to reach a constant value if the tube diameter is large enough. We suspect that the lattice trapping effect plays the role of crack tip plasticity at the atomic scale. For example, at 300 K, G_c for the (35, 0) tube with aspect ratio 4 converges to 6 J m⁻² as the crack length exceeds 20 Å. This value is comparable with the fracture toughness of graphite and silicon. The fracture resistance of the tubes is found to decrease significantly as the temperature increases. To study the length effects, the computations are repeated for zigzag nanotubes with the same three chiralities but with aspect ratio 8 at 1 K. The fracture resistances of the longer nanotubes are found to be comparable to those of the shorter nanotubes.

This work presents a photomask lithography for mass manufacture of 100 nm photonic bandgap structures with designed defects. The photomask is composed of 300 nm thick dielectric rod arrays in order to generate edge diffracted beams. As the rod sizes are smaller than one wavelength, diffracted beams from the edges merge together and form subwavelength beaming arrays at rod regions. Theoretical calculations and optical near-field measurements verify the existence of subwavelength focused beams. Furthermore, the focused beams are not affected by the neighbouring defects in the near-field region. Using the transparent photomask, a simple laser exposure system and reactive dry etching method, we demonstrate the fabrication of subwavelength photonic bandgap structures with designed channel defects in a silicon substrate.

A low cost nanosphere lithography method for patterning and generation of semiconductor nanostructures provides a potential alternative to the conventional top-down fabrication techniques. Forests of silicon pillars of sub-500 nm diameter and with an aspect ratio up to 10 were fabricated using a combination of the nanosphere lithography and deep reactive ion etching techniques. The nanosphere etch mask coated silicon substrates were etched using oxygen plasma and a time-multiplexed 'Bosch' process to produce nanopillars of different length, diameter and separation. Scanning electron microscopy data indicate that the silicon etch rates with the nanoscale etch masks decrease linearly with increasing aspect ratio of the resulting etch structures.

Au nanoparticles are commonly used as seeds for epitaxial growth of III–V semiconductor nanowires. However, the interaction between Au and In-containing III–V materials makes it difficult to control the growth of more complex nanowire structures in materials such as InAs. Here we report the growth of InAs nanowires and branched nanotrees using Au and Au–In nanoparticles. We show that the initial composition of the particle does not affect the morphology of the first-generation nanowires, nor does it affect the final composition of the particle after growth. However, when the Au–In particles were used to seed a second generation of nanowires, producing nanotrees, the branches exhibited a 2–3 times higher growth rate and more regular shape than those seeded by pure Au particles. This result is attributed to the decreased interaction between the seed particle and the trunk nanowires when Au–In particles are used. Thus the incorporation of In into the seed particle during particle production allows for modification of the particle–wire interaction.

Ultrathin films of Eu³⁺ doped Y₂O₃ were deposited onto alumina nanoparticles using a unique solution synthesis method. The surface structure, composition, and morphology of the thin films deposited were analysed using high resolution transmission electron microscopy (TEM) and high angle annular dark field scanning TEM imaging and energy dispersive x-ray measurements. The films deposited were extremely thin, on the order of 3–5 nm, and uniformly covered all the alumina nanoparticles. X-ray diffraction was used to investigate the phases and structures of the thin films deposited. At the heat treatment temperature of 600 °C, cubic Y₂O₃ nanocrystals were found in the film while as-coated layers exhibited mainly amorphous features. As the heat treatment temperature increased to 750 °C, the amorphous thin film became well crystallized. Optical properties of Eu³⁺ doped Y₂O₃ films were characterized by fluorescence spectroscopy. Strong photoluminescence was observed in the sample annealed at 750 °C, from the fluorescence of Eu³⁺ ions in a well-crystallized film, consistent with the x-ray diffraction and TEM observations.

Highly oriented ZnSe nanorods were grown on a ZnSe epilayer on GaAs(001) substrate by metalorganic chemical vapour deposition without any introduced catalysts. Cathodoluminescence spectra and images of individual nanorods, projecting from the buffer layer, were obtained at various temperatures down to 4.5 K in a scanning electron microscope. They show that the luminescence of the nanorods is localized, with the near band edge and deep level related emissions originating predominantly from their interior and surface, respectively. The luminescence is also not uniform along the length of the nanorods. We attribute the strong surface luminescence to the post-growth oxidization of the nanorods when they were exposed in air. The temperature dependence of the cathodoluminescence spectra was also measured to study the energy gap of the nanorods, which was found to behave similarly to that of bulk ZnSe.

When rain falls on lotus leaves water beads up with a high contact angle. The water drops promptly roll off the leaves, collecting dirt along the way. This self-cleaning ability or lotus effect has, in recent years, stimulated much research effort worldwide for a variety of applications ranging from self-cleaning window glasses, paints, and fabrics to low friction surfaces. What are the mechanisms giving rise to the lotus effect? Although chemical composition and surface structure are believed important, a systematic experimental investigation of their effects is still lacking. By altering the surface structure of the leaves while keeping their chemical composition approximately the same, we report in this study the influence of micro- and nano-scale structures on the wetting behaviour of lotus leaves. The findings of this work may help design self-cleaning surfaces and improve our understanding of wetting mechanisms.

Wormhole-like mesoporous nanocrystalline anatase (meso-nc-TiO₂) has been synthesized by using tetrabutyl titanate as the inorganic precursor and triblock copolymer as the structure-directing agent. The obtained materials were characterized in detail by x-ray diffraction, atomic force microscopy, N₂ sorption, ellipsometry, measurements of the contact angle, and UV–visible spectrophotometry. The effect of calcination temperatures (the as-synthesized samples were calcined at different temperatures) on the physical parameters, photo-induced hydrophilicity, and photocatalytic activity of wormhole-like meso-nc-TiO₂ was also investigated in this study.

Temperature control in non-equilibrium nano-electromechanical systems is a vital issue to both scientific and engineering fields. The effect of temperature control in a specific dynamic system is studied using the concepts of thermodynamic temperature and kinetic temperature in a molecular dynamic model. It is demonstrated that isothermal simulations can be realized by constant thermodynamic temperature control of the system, but a constant kinetic temperature control scheme yields misleading results for the mechanical movements of the system. The isothermal simulations yield similar trends as an adiabatic approximation, at least at low temperature.

Vanadium pentoxide (V₂O₅) nanowires were directly transferred to desired patterns on SiO₂ substrates using the microcontact printing (MCP) technique. The hydrophilicity of the poly(dimethylsiloxane) (PDMS) stamp exerted a strong influence on the mechanism of transfer of polar V₂O₅ nanowires onto the substrate. The V₂O₅ nanowires were transferred from the relief side of the hydrophilic stamp, whereas they were transferred from the recess edges of the hydrophobic one forming agglomerated nanowire patterns on the substrate. When the hydrophobic stamp was used, the width of the agglomerated nanowire patterns could be controlled by the concentration of the nanowire solution as well as by the width of the recess area of the PDMS stamp. This method allows us to generate nanowire patterns with a submicrometre line width, which is much smaller than a the few-micrometre sizes of PDMS stamp patterns. When the hydrophilic stamp with a small-sized (≤ the average length of V₂O₅ nanowires) pattern was used, alignment of individual nanowires in the direction of the boundary of the line pattern was obtained. These results suggest that the transfer mechanism in the MCP process strongly depends on the wetting interaction between the stamp and the nanowire ink.

We have investigated a new process for the fabrication of nanocomposite cups by electrospraying blended polymer–sol–gel solutions followed by calcination. Due to the low viscosity and high surface tension of the blended polymer–sol–gel solutions, the electrostatically extruded continuous liquid jet from the spray source became tiny droplets with diameters of less than 1 µm. These droplets dried in transit and were collected at the counter electrode. To eliminate polymers, as well as cross-link sol–gel material, they were calcined at 850 °C for 3 h. We also investigated a probable method to control the morphology of the nanocups by changing the ionic concentration of the polymer solution. This is a simple and efficient approach for producing nanocomposite cups, which cannot be made by the aggregation method. These nanocomposite cups may find applications in drug delivery and filtration media.

A facile nonaqueous route has been developed for the preparation of tetragonal CoMn₂O₄ nanocrystals. In a simple reaction process, cobalt (II) acetylacetonate and manganese (II) acetylacetonate were dissolved in oleylamine and allowed to decompose at 230 °C. This process led to nearly monodisperse nanocrystals with sizes ranging from 5.3 to 12 nm, as shown by x-ray diffraction analysis and transmission electron microscopy. An x-ray photoelectron spectroscopy study revealed that the lower oxidation state Mn²⁺ ions increased with decreasing particle size, accompanied by an increase in higher oxidation state cations (such as: Mn⁴⁺, Co³⁺ and Co⁴⁺ ions) due to charge balancing. The broad metastable cation distribution reveals that the nanoparticles have potential applications for catalysts. Magnetic measurements revealed that the nanoparticles were ferrimagnetic at low temperature and paramagnetic at room temperature, and possess blocking temperatures of 30–40 K. The blocking temperature did not increase when the samples' size increased from 6.7 to 9.0 nm, partly because of the broad metastable cation distribution and partly due to the dipolar interactions between the nanoparticles. In addition, the nanoparticles showed exchange bias behaviour due to the ferrimagnetic–ferromagnetic exchange coupling between the ferrimagnetic core and ferromagnetic shell.

We developed a new method to dissect and recover nanometre-scale chromosome fragments from specific regions of a chromosome by atomic-force microscopy (AFM) with a novel AFM cantilever control. Recovery of the chromosome fragments using this method was highly reproducible, with a success rate greater than 90%. The width of the dissection depended on the cantilever-tip diameter; similar widths (240 ± 92 nm on average) were obtained when a standard silicon cantilever was used. We also achieved successive dissection and recovery of five fragments located on a specific region of a chromosome. Rinsing the specimen with a biological buffer, such as PBS, facilitated the recovery. This treatment may cause the chromosome structures to be more relaxed. The method, called the 'scratch method', will be a useful tool to easily obtain nucleotide sequences with positional information on a specific region of a chromosome and will contribute to various fields of genetic investigations.

Carbon nanotubes (CNTs) and nanofibres (CNFs) are grown on bulk-micromachined silicon surfaces by thermal and plasma-enhanced chemical vapour deposition (PECVD), with catalyst deposition by electron beam evaporation or from a colloidal solution of cobalt nanoparticles. Growth on the peaked topography of plasma-etched silicon 'micrograss' supports, as well as on sidewalls of vertical structures fabricated by deep-reactive ion etching demonstrates the performance of thermal CVD and PECVD in limiting cases of surface topography. In thermal CVD, uniform films of tangled single-walled CNTs (SWNTs) coat the structures despite oblique-angle effects on the thickness of the catalyst layers deposited by e-beam evaporation. In PECVD, forests of aligned CNFs protrude from areas which are favourably wet by the colloidal catalyst, demonstrating selective growth based on surface texture. These surface preparation principles can be used to grow a wide variety of nanostructures on microstructured surfaces having arbitrary topography, giving substrates with hierarchical microscale and nanoscale surface textures. Such substrates could be used to study cell and neuronal growth, influence liquid–solid wetting behaviour, and as functional elements in microelectronic and micromechanical devices.

Epitaxial ZnO nanowires and random-growth-oriented nanobelts were grown on c-plane sapphire with and without a pre-coated ZnO epilayer film. On the pre-coated ZnO epilayer, ZnO nanowires are vertically aligned with good in-plane alignment as a result of homoepitaxy, whereas on the bare c-plane sapphire, besides a few nanowires vertically aligned with , the nanowires were properly aligned with three-fold rotation symmetry. The ZnO nanowires are well-defined hexagonal crystals with diameters of 70–500 nm and lengths of up to several micrometres. In the junction regions between the pre-coated epilayer and the bare sapphire surface, however, ZnO nanobelts (nanoribbons) were found. Cathodoluminescence measurements revealed that the emission at 3.26 eV is correlated with free-exciton recombination and the broad green emission at 2.48 eV is attributed to surface defects. The stronger green emission implies that more surface defects exist on the side walls of nanowires and nanobelts. In Raman scattering, the E1(LO) mode is sensitive to the orientation of nanostructure that is consistent with the cathodoluminescence results.

This study deals with the dispersion of longitudinal waves in a single-walled armchair carbon nanotube, focusing on the effect of the microstructure of the carbon nanotube on the wave dispersion. To reveal the effect analytically, the carbon nanotube is modelled as a non-local elastic cylindrical shell in the study. The dynamic equation of the non-local elastic cylindrical shell is established and the corresponding dispersion relation of longitudinal waves is derived. These analytic results are verified via molecular dynamics simulations, based on the Terroff–Brenner potential, for the propagation of various longitudinal waves in three single-walled armchair carbon nanotubes. The molecular dynamics simulations indicate that the longitudinal wave dispersion predicted by the model of the non-local elastic cylindrical shell shows a good agreement with that of molecular dynamics simulations in a wide frequency range up to the terahertz region. They also show that both the microstructure of the carbon nanotube and the coupling between the longitudinal wave and the radial motion play an important role in the dispersion of longitudinal waves in a single-walled armchair carbon nanotube.

Since nanosized metals exhibit a considerably lower melting point compared to bulk materials, nanometallic particle coated films can be deposited and cured to obtain electric conductors at a relatively low processing temperature. In this study, suspensions with Au nanoparticles of average size 3.9 ± 0.7 nm were prepared and spin-coated onto several commonly used electronic substrates (Cu, Ni and Al), and then thermally processed in a protective atmosphere. Experimental results show that the degree of continuity of the coated film on the Cu substrate was better than that on the Ni substrate, which was in turn better than the Al substrate. It was also found that isothermally heating the suspension at 300 °C, a temperature greater than the melting point of the nanoparticles used, could produce fine Au deposits with acceptable adhesion. Worthy of notice is that, after a proper curing treatment, Au layers deposited with nanoparticle suspension exhibited superior adhesion to those produced by sputtering.

Core–shell acicular nanoparticles of ∼90 nm length and ∼5 axial ratio consisting of an iron core coated with an oxidized layer of different composition have been obtained by thermal reduction with hydrogen of coated goethite precursors. Uniform goethite particles were prepared by oxidation in air of FeSO₄ solutions previously precipitated with Na₂CO₃. Al or Y oxide layers were deposited on the goethite particle surface by heterocoagulation. The efficiencies of both compounds as protecting agents for preventing particle sintering and corrosion and their effects on the magnetic properties of the final α-Fe nanoparticles have been evaluated. Yttrium oxide coating was found to be more effective than alumina coating, giving rise to iron nanoparticles with larger coercivity and higher corrosion resistance. This behaviour is mainly discussed in terms of the observed differences in location of the two sintering prevention agents during the transformation from iron oxide to metal, which give rise to different particle microstructures.

We report the results of a detailed study on the structural, electrical and optical properties of light emitting devices based on amorphous Si nanostructures. Amorphous nanostructures may constitute an interesting system for the monolithic integration of optical and electrical functions in Si ULSI technology. In fact, they exhibit an intense room temperature electroluminescence (EL), with the advantage of being formed at a temperature of 900 °C, while at least 1100 °C is needed for the formation of Si nanocrystals. Optical and electrical properties of amorphous Si nanocluster devices have been studied in the temperature range between 30 and 300 K. The EL is seen to have a bell-shaped trend as a function of temperature with a maximum at around 60 K. The efficiency of these devices is comparable to that found in devices based on Si nanocrystals, although amorphous nanostructures exhibit peculiar working conditions (very high current densities and low applied voltages). Time resolved EL measurements demonstrate the presence of a short lifetime, only partially due to the occurrence of non-radiative phenomena, since the very small amorphous clusters formed at 900 °C are characterized by a short radiative lifetime. By forcing a current through the device a phenomenon of charge trapping in the Si nanostructures has been observed. Trapped charges affect luminescence through an Auger-type non-radiative recombination of excitons. Indeed, it is shown that unbalanced injection of carriers (electrons versus holes) is one of the main processes limiting luminescence efficiency. These data will be reported and the advantages and limitations of this approach will be discussed.

Recently, the polarizability tensor of metal bispheres located near a plane metal substrate was analytically derived in dipole approximation and was used to calculate the extinction spectra of silver dimers (Pinchuk and Schatz 2005 Nanotechnology16 2209). To evaluate the accuracy of dipole approximation for this problem, we compare the optical properties of silver and gold dimers, embedded in a homogeneous dielectric medium, by using electrostatic and electrodynamic dipole approximations and an exact electrodynamic multipole solution. For longitudinal TM-excitation (the electric field is directed along the bisphere axis), the dipole and multipole absorption and scattering spectra differ dramatically, whereas for transversal TE-excitation the dipolar approximation gives acceptable results. The physical origin of the inaccuracies of the dipole electrostatic solution is related to the highly inhomogeneous electric-field distribution near the contact point of the spheres. Thus, we have to include several multipole orders even in the electrostatic solution for dimer particles that are, individually, well within dipole approximation. Although we do not consider the effects of a plane metal substrate, we believe that the multipole interaction of constituent dimer spheres can also be important in this case. The T-matrix plasmon resonance spectral shifts for randomly oriented 42 nm gold bispheres with various separations are in satisfactory agreement with the experimental measurements by Reinhard et al (2005 Nano Lett.5 2246), whereas the electrostatic dipole approximation gives too underestimated shifts.

Backside illuminated solar cells based on 6 µm long highly-ordered nanotube-array films sensitized by a self-assembled monolayer of bis(tetrabutylammonium)-cis-(dithiocyanato)- N,N'-bis(4-carboxylato-4'-carboxylic acid-2, 2'-bipyridine)ruthenium(II) (commonly called 'N719') show a short-circuit current density of 8.79 mA cm⁻², 841 mV open circuit potential and a 0.57 fill factor yielding a power conversion efficiency of 4.24% under AM 1.5 sun. The solvent used to infiltrate the dye into the nanotube arrays, made by potentiostatic anodization of a titanium foil, was found to significantly influence the electrical characteristics of the resulting solar cell. A superior photoresponse was obtained with acetonitrile as the dye solvent. This is attributed to the improved wetting characteristics of the dye solution in acetonitrile enabling self-assembled monolayers with higher surface coverage to be formed inside the nanotubes. In comparison to nanocrystalline films, the nanotube-array films consistently exhibit larger open circuit photovoltage values; the origins of this enhancement are discussed.

We report on the permanent magnetism exhibited by 1 nm sized thiol-capped palladium nanoparticles, up to temperatures above 300 K. The hysteresis loop does not change appreciably between 5 and 300 K. The local magnetic anisotropy constant was found to be stronger than 2 meV per Pd atom. The localized character of electrons and holes of the 4d residual band, revealed through the structureless plasmon resonance curve, suggests that the origin of the permanent magnetism is associated with localized magnetic moments.

Nanoposts of 10–40 nm top diameter on an InGaN/GaN quantum well structure were fabricated using electron-beam lithography and inductively coupled plasma reactive ion etching. Significant blue shifts up to 130 meV in the photoluminescence (PL) spectrum were observed. The blue-shift range increases with decreasing post diameter. For nanoposts with significant strain relaxation, the PL spectral peak position becomes less sensitive to carrier screening. On the basis of the temperature-dependent PL and time-resolved PL measurements and a numerical calculation of the effect of quantum confinement, we conclude that the optical behaviours of the nanoposts are mainly controlled by the combined effect of 3D quantum confinement and strain relaxation.

Palladium nanoparticles are deposited in the pores of freestanding, mesoporous anodic aluminium oxide (AAO) templates via a chemical route at room temperature. In the precursor, Pd²⁺ ions are complexed with ammonia and reduced to Pd⁰ by adding an excess amount of formaldehyde. To enhance the infiltration of pores with the precursor, 2-propanol is added to the solution. After a few hours of plating at room temperature, crystalline Pd⁰ nanoparticles with an average size of ∼4 nm form on the pore walls of the AAO templates. The effect of heat treatment on the structure of the AAO/Pd system is also studied. The specimens are investigated using FESEM, EFTEM/EDX, and electron and x-ray diffraction techniques. Preliminary catalyst activity analyses reveal good selectivity of ∼90%, but low conversion of ∼1.2% of carbon monoxide to methane in hydrogen flow at 330 °C on AAO/Pd. The oxidized form of the catalyst shows instantaneous oxidation with ∼100% selectivity and conversion of carbon monoxide to carbon dioxide in oxygen flow at 140 °C.

We have developed a new hybrid AFM probe combining an SU-8 polymer body with a full tungsten cantilever having a nanometric tip. The fabrication is based on surface micromachining a silicon wafer, where tungsten is sputter deposited in oxidation sharpened moulds to yield sharp tips with radius below 20 nm. The material properties of tungsten were measured, yielding a hardness of 14 GPa, a specific resistivity of 14.8 µΩ cm and Young's modulus of 380 GPa. Analyses of the probes show a mechanical quality factor of 90 in air, and a low contact resistance of 25 Ω on a gold sample is measured. AFM imaging is demonstrated. As a step in the development of a robust electrically conducting AFM probe, the results are very promising.

A low cost platform made of a silicon nitride window with pre-patterned metallic leads has been fabricated. The platform is compatible for both transmission electron microscopy (TEM) studies and electrical transport measurements. We demonstrated that TEM analyses, in situ local structure modification with a high intensity electron beam and ex situ transport measurements can be performed for the same individual nanowire assembled on this platform. The platform can therefore be used to directly link the transport properties of a testing nanomaterial or a nanodevice to its morphological, structural and chemical properties.

Templated catalytic etching has been developed as an effective method for preparing highly ordered, wafer scale Si_1−xGe_x quantum dot arrays on an Si substrate. Process parameters including etching time, etching temperature, and the diameter and dosage of polystyrene spheres can be independently adjusted to control the dot size, inter-dot space, and dot arrangement mode. Photoluminescence characterization indicates a remarkable enhancement of the luminescence intensity, showing potential for future optoelectronic applications.

The effect of the pit shape on the read-out signal of a super-resolution near-field structure optical memory was investigated with a view to improving the read-out characteristics. Finite difference time domain calculations were carried out in an effort to understand the effect of the pit shape on the optical near-field induced local heating and resulting signal enhancement. Calculations showed an increase in read-out signal intensity with increasing aspect ratio significantly larger than that which can be explained by area increase alone, in excellent agreement with experimental results.

We have used direct, low-frequency scanning capacitance microscopy measurements to characterize variations in thin, dielectric films with up to 1 nm thickness and ∼200 nm lateral resolution. This technique may be used on metallic as well as semiconducting substrates because it does not rely upon d C/d V measurements. We also find that the sensitivity of capacitance to film thickness can be enhanced by an aqueous meniscus that typically forms between the atomic force microscope tip and the sample surface. Further, we quantified the nanometre-scale capacitance of the tip–meniscus–sample system that is sensitive to variations in film thickness by making simultaneous capacitance and cantilever deflection measurements. This capacitance is used along with an average film thickness to quantify variations in film thickness.

A nickel nanoparticle assembly was formed by vapour deposition on various single-crystal supports. The nanoparticle structure, distribution, composition and charge transfer properties were examined simultaneously by atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), mass spectroscopy (MS) and electrochemistry. The data obtained by applied analytical techniques were correlated. X-ray photoelectron spectroscopy (XPS) of nanoparticle assemblies deposited at ambient temperature revealed the Ni(II) oxidation state, while metallic Ni was found in nanoparticles grown at 300 °C. The amount of nickel deposited on highly ordered pyrolytic graphite (HOPG) estimated by AFM was found to be an order of magnitude higher than that obtained from XPS analysis, while AFM and XPS data for silicon agree well. The discrepancy was discussed in terms of differences in support elastic properties and AFM-tip/surface interactions. Current–potential measurements of nanoparticle charge transfer reaction point to the high stability and low resistant Ohmic character of the nanoparticle/HOPG interface.

A wealth of superfine single-crystal hollow cuprous oxide (Cu₂O) spheres with nanoholes have been prepared for the first time with glucose as the reducing agent and gelatin as a soft template. The mechanism of the formation of these hollow crystals with nanoholes has been studied, and the UV–visible absorption spectrum has been used to resolve the excitonic or interband transitions of the hollow Cu₂O spheres. The band gap of the products calculated from the UV–vis spectra is as large as 2.67 eV, which is ascribed to the decrease of the overall crystal size and the hollowing of the Cu₂O spheres with nanoholes.

A highly effective electrothermal tuning method is demonstrated for Al–SiC nanomechanical resonators. Doubly clamped beam devices are actuated and read out using a magnetomotive technique under a moderate vacuum at room temperature. Direct current applied to a beam heats the structure and shifts the resonance frequency downward. Frequency shifts of 10% are easily achievable, and the thermal time constant of these structures is in the submicrosecond range. The initial frequency and frequency tunability are studied for beams of varying Al thickness, and the device performance can be accurately modelled using simple mechanical and thermal models. Because of the different mechanical properties of SiC and Al, both the initial frequency and the frequency tunability can be modified by varying the Al layer thickness. This approach has the potential to become an important tool for effective frequency tuning in deployable SiC-based nanoelectromechanical system devices and systems for applications that would benefit from SiC as the structural material.

A facile, large-scale and low-cost route was used to synthesize inorganic fullerene-like (IF) WS₂ nanoparticles by the reaction of sulfur powder (S) and as-prepared WO₃ nanoparticles in a hydrogen atmosphere at a heating temperature of 500–650 °C. The as-synthesized IF-WS₂ nanoparticles are of a closed hollow cage structure with an average size of about 50 nm. The composition, morphology and structure of the products were characterized by XRD, TEM, FE-SEM, and HRTEM. The influences of the main reaction conditions were investigated and the possible growth mechanism are proposed. It is worth noting that through changing the amount of as-prepared composite powder (WO₃ and S) and the content of hydrogen, yields of IF-WS₂ in larger scales can accordingly be easily obtained, and such a synthetic route may also be used in the synthesis of other transition IF metal dichalcogenides. Furthermore, tribological experiments emphasized the important role played by these as-synthesized IF-WS₂ nanoparticles in providing excellent lubricating performance, which may bring a much brighter future for their applications in the lubricating field, or even arouse great interest of both scientists and industrialists for their many other important applications.

Mn-doped ZnO nanoparticles were synthesized by a rheological phase-reaction–precursor method and the thermal decomposition of the oxalate precursors was studied by thermogravimetry and differential thermal analysis in air. The Mn-doped ZnO obtained at lower temperature crystallizes in a wurtzite structure and a new phase appears at higher temperature. The lattice parameters of Zn_1−xMn_xO (0.09≤x≤0.1) increase gradually with increasing temperature up to 650 °C and then decrease. X-ray photoelectron spectroscopy indicates that there are different Mn valence bonds in Mn-doped ZnO nanoparticles. Furthermore, two additional Raman peaks were observed. One peak is considered to have an origin related to the incorporation of Mn ions into the Zn site of the ZnO lattice; the other may be attributed to the ZnMnO₃ phase. Magnetization measurements under field cooling conditions reveal that the Zn_1−xMn_xO nanoparticles exhibit ferromagnetic behaviour, and the Curie temperatures of some samples are above room temperature. The difference of the ferromagnetic properties of the Mn-doped ZnO nanoparticles is primarily attributed to the Mn²⁺ content.

Lanthanide-based nanocrystals have shown great potential to be used as luminescent materials but their biological applications have been limited because most of the nanocrystals synthesized so far are not water soluble or biocompatible. We report a very straightforward method to synthesize water soluble and biocompatible LaF₃ nanocrystals doped with Eu³⁺ via facile co-precipitation with a natural biopolymer, chitosan. The nanocrystals are very fluorescent and have a small size of about 20 nm. Chitosan is found to cap the nanocrystals during the synthesis process, which renders them water soluble and biocompatible, and provides functional groups such as hydroxyl and amino groups for further attachment of biomolecules. The nanocrystals remain stable in aqueous solution with pH ranging from 2 to 7.4. The nanocrystals are very suitable for use in biological applications, for example, intracellular labelling or measurements, because they are very small in size.

The solvothermal process was employed to grow ZnO nanorods at low temperature on conducting substrate, which is extremely important for making efficient electrical contacts in various applications based on ZnO nanorods. Efforts were made to find the ideal growth parameters for better alignment of the ZnO nanorods with a view to tailor their luminescent properties. The ZnO nanorod arrays were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive analysis of x-rays (EDAX) and x-ray diffraction study. The ZnO nanorod arrays were found to have excellent UV emission properties at room temperature. Aligned ZnO nanorod arrays exhibit good field emission properties, revealing their applicability as cathode materials for field emission based devices.

Previous work by Jensen L, Schmidt O H, Astrand P-O and Mikkelsen K V (2000 J. Phys. Chem. B 104 10462–6) presents the computational method described in Section 2 of this paper. The atomic parameters α_p previously fitted to the full polarizability tensors of quantum mechanical computed molecular polarizabilities of a series of 115 substituted aliphatic and aromatic molecules containing the elements H, C, N, O, F and Cl were reported by Jensen L, Astrand P-O, Sylvester-Hvid K O and Mikkelsen K V (2000 J. Phys. Chem. A 104 1563–9). The values of α_p used in this work were parametrized by ab initio coupled Hartree-Fock for the PhD of C Voisin in 1991 at the Universite de Nancy I (Voisin C, Cartier A and Rivail J L 1992 J. Phys. Chem.96 7966–71, Voisin C and Cartier A 1993 J. Mol. Struct. (THEOCHEM)286 35–45). The values of Φ_p are not used.