Table of contents

Technological growth in the electronics industry has historically been measured by the number of transistors that can be crammed onto a single microchip. Unfortunately, all good things must come to an end; spectacular growth in the number of transistors on a chip requires spectacular reduction of the transistor size. For electrons in semiconductors, the laws of quantum mechanics take over at the nanometre scale, and the conventional wisdom for progress (transistor cramming) must be abandoned. This realization has stimulated extensive research on ways to exploit the spin (in addition to the orbital) degree of freedom of the electron, giving birth to the field of spintronics. Perhaps the most ambitious goal of spintronics is to realize complete control over the quantum mechanical nature of the relevant spins. This prospect has motivated a race to design and build a spintronic device capable of complete control over its quantum mechanical state, and ultimately, performing computations: a quantum computer.

In this tutorial we summarize past and very recent developments which point the way to spin-based quantum computing in the solid state. After introducing a set of basic requirements for any quantum computer proposal, we offer a brief summary of some of the many theoretical proposals for solid-state quantum computers. We then focus on the Loss–DiVincenzo proposal for quantum computing with the spins of electrons confined to quantum dots. There are many obstacles to building such a quantum device. We address these, and survey recent theoretical, and then experimental progress in the field. To conclude the tutorial, we list some as-yet unrealized experiments, which would be crucial for the development of a quantum dot quantum computer.

The synthesis of PbSe nanocrystals by electrodeposition on Au(111) is discussed and it is shown that the characteristics of nucleation and growth determine the electrical and optical properties of the nanocrystals. Electrodeposition of PbSe on gold occurs by a two-dimensional nucleation and growth mechanism. This results in strongly flattened structures. These nanocrystals have a staircase-like electron density of states, typical for a quantum well, and the dielectric function of the PbSe nanocrystals shows a marked dependence on the nanocrystal height. Using electronic structure calculations, we demonstrate that these observations are due to quantum confinement in one direction, in agreement with the shape of the nanocrystals.

A quantitative evaluation of the structure deformation of microfabricated electromechanical systems is important for the design and functional control of microsystems. When the displacement measurement of the microstructure's surface is to be made in a domain smaller than a few microns, both spatial sampling resolution and measuring sensitivity should reach nanoscale levels. In this paper, an atom force microscope (AFM) is used to scan surface topographies of silicon beam structures under electrostatic actuation, and then the AFM images are utilized to evaluate the in-plane deformation field based on digital image correlation (DIC) processing. It is shown that the AFM topographic maps provide a kind of carrier pattern to include the displacement information of the deformed surface, whose high scanning resolution and good image correlation makes it possible to search the in-plane displacement components on the nanometre scale from the images with statistics resembling grey level distributions. By using the proposed DIC algorithms, the deformation fields in the beam-end regions are obtained for the folded silicon flexures actuated by electrostatic comb drives.

A new form of thin films formed by multi-walled carbon nanotubes exhibiting high packing density and local alignment were fabricated using a highly concentrated colloidal suspension of carbon nanotubes. Electrical double layer capacitors built from these film electrodes exhibited a close to rectangular cyclic voltammogram even at a high scan rate of 1000 mV s⁻¹, and produced very high specific power density of about 30 kW kg⁻¹, ideal for surge-power delivery applications. The preparation procedure is very simple, and does not require any binders. It has potential for highly efficient manufacturing of high power density supercapacitors and other similar electronic devices.

The effect of dispersants on particle dispersion and flexural properties of SiC/vinyl ester nanocomposites was studied by factorial and response surface designs. The results show that the coupling agent 'gamma-methacryloxy propyl trimethoxy silane (MPS)' has no adverse side effect on the flexural properties as illustrated by the good correlation between maximizing the flexural strength and minimizing the agglomerates. However, the dispersant 'BYK-W 966' has a slight adverse side effect on the flexural properties although it improves dispersion at higher dosage. With an optimal dosage of MPS and W966, a small amount of SiC in 0.5 wt% results in 8% increase in strength and 14% increase in modulus. The flushing operation using the dispersant '1-octanol/decane' achieves an excellent SiC dispersion but it does not result in improved flexural properties. This confirmed that a better state of nanoparticle dispersion does not necessarily lead to improved flexural properties. A good dispersion coupling with a strong filler/matrix interfacial bonding is the key to obtain enhanced flexural properties.

We propose a new process of fabricating nano-gap electrode pairs using an atomic-layer-deposited (ALD) thin film as a sacrificial layer. In this technique, we can control the width of a gap precisely by varying the number of deposition cycles of the ALD layer, and produce many identical gaps simultaneously. Using ALD Al₂O₃ as a sacrificial layer, we have fabricated poly-Si/Au nano-gaps of 10 nm width successfully. This new approach can provide a useful tool for the massive production of integrated molecular device circuits.

A large number of alumina nanofibres with strong photoluminescence was obtained in treated porous anodic alumina (PAA) film. The treatment includes three steps: doping the Cr into the high-purity aluminium by melting, anodizing the Cr-doped Al sheet to produce PAA followed by an etching process, and calcination. This routine yields a large number of alumina nanofibres with diameter about 80–150 nm, which were characterized by a scanning electron microscope and a transparent electron microscope. The obtained alumina nanofibres reveal very strong and sharp peaks in the photoluminescence spectrum, indicating their potential applications in nano-optics.

Here we investigate the formation of superficial micro- and nanostructures in poly(ethylene-2,6-naphthalate) (PEN), with a view to their use in biomedical device applications, and compare its performance with a polymer commonly used for the fabrication of these devices, poly(methyl methacrylate) (PMMA). The PEN is found to replicate both micro- and nanostructures in its surface, albeit requiring more forceful replication conditions than PMMA, producing a slight increase in surface hydrophilicity. This ability to form micro/nanostructures, allied to biocompatibility and good optical transparency, suggests that PEN could be a useful material for production of, or for incorporation into, transparent devices for biomedical applications. Such devices will be able to be autoclaved, due to the polymer's high temperature stability, and will be useful for applications where forceful experimental conditions are required, due to a superior chemical resistance over PMMA.

Luminescent CdS nanoparticles immobilized on copolymer microspheres were produced by the chemical precipitation of poly(St-co-GMA-IDA)–Cd²⁺ (PSG–Cd²⁺) complexes. PSG latex was prepared by the soap-free emulsion copolymerization of styrene (St) and 2-methacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester (GMA-IDA). GMA-IDA chelating groups within copolymer latex have coordination sites for chelating metal ions, at which CdS particles were grown. The presence of ethanol as a cosolvent improved both the particle monodispersity and the surface charge. Fourier transform infrared (FT-IR) spectroscopy spectra were obtained to elucidate the characteristics of GMA-IDA in the PSG latex. The size distribution, morphology and structure of CdS nanoparticles were measured by transmission electron microscope (TEM) and x-ray diffraction (XRD) analysis. The growth kinetics of CdS nanoparticles were studied by TEM and obtaining photoluminescence (PL) spectra. The size and morphology of CdS particles were influenced by the amount of the chelating, iminodiacetic acid group on the surface of the copolymer microsphere, the concentration of Cd²⁺ ions and the pH. The PSG-A3–CdS sample with [Cd²⁺]/[GMA-IDA] = 1/6, pH = 3.5, which was formed from ultrafine CdS particles with mean diameters below 5 nm immobilized on the surface of copolymer microspheres, emitted photons with a higher energy than other samples in this investigation.

Carbon nanotubes (CNTs) can be usefully applied to composites for extremely high strength, and thermal and electrical conductivity. Longer CNTs are better fitted for the implementation, and the syntheses have been reported. However, a detailed synthesis process has not yet been discovered to optimize the CNT quality and production yield. In this report, the synthesis temperature, composition of the source solution, source feed rate, etc, have been examined for production of high quality long strands of single-wall CNTs using scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and thermo-gravimetric analysis. It has been revealed that the higher synthesis temperature can produce higher quality CNTs, but only when the process parameters are optimized. Therefore, different optimum conditions exist at different synthesis temperatures. The best quality CNTs were obtained at 1100 °C, the highest temperature among the conditions tested.

The combination of a key element of soft lithography, namely the elastomeric stamp, with the operation principle of step and flash imprint lithography results in a moulding procedure allowing high throughput and remarkable operational simplicity. 100 nm scale dense features can be fabricated via in situ polymerization of a polyurethane fluid, simultaneous to the capillary penetration into the recessed regions of high-resolution elastomeric elements. Excellent pattern definition has been obtained for features down to 200 nm, with aspect ratio of around unity over areas of the order of cm². The physical principles of the fluidic motion within the sub-µm channels are also discussed, to estimate the maximum aspect ratio achievable before the complete curing of the employed photopolymer.

Depositions of Ni clusters on a Cu(001) surface have been simulated by molecular dynamics in order to produce magnetic nanostructures. Two arrangements of the atoms at the interface between the Ni clusters (a few monolayers) and the Cu substrate, overlapped and non-overlapped, have been analysed. The difference between Ni and Cu lattice parameters (2.6%) gives rise to strain at the interface, which is the cause of magnetoelastic anisotropy. We have focused our interest especially on matching effects. The bombardment energy was varied between 0 and 1 eV/atom. Differences in the nanocluster morphology due to this have been discussed. Lattice defects which develop in the deposited clusters have been analysed. Final atomic distances, especially mean changes in lattice parameters, have been quantified at the interface. A study of atomic mixing and of its influence in spacing between layers has been also accomplished.

Single-wall carbon nanotubes (SWNTs) were examined as catalysts for improving the hydrogen absorption and desorption properties of Ti/Zr-doped NaAlH₄ hydride, proposed as a reversible hydrogen storage material. We studied the hydrogen charge and discharge characteristics and stability of sodium aluminium composites ball milled with carbon additives such as SWNTs, graphite or activated carbon (AX-21). The SWNT–NaAlH₄ system was tested at 160 °C for up to 200 cycles, and the sorption kinetics were enhanced by a factor of four. Also, the catalyzed NaAlH₄ hydride with graphite and activated carbon additives shows fast absorption and desorption kinetics. Our results indicate that by creating new hydrogen transition sites, the structure of carbon in the composites plays an important role in enhancing the hydrogen absorption and release rates.

For the next-generation optical disc, electron beam mastering has been considered as a high-potential technique to fabricate a high-density optical disc. However, for electron beam mastering, the proximity effect caused by electron backscattering is an important problem. In this study, the influence of the proximity effect on the linewidth (full width at half magnitude, FWHM) and thickness of the residual resist is discussed. Some methods are presented to solve the proximity effect for optical disc mastering, i.e., by raising the electron beam voltage and depositing thin film material with low atomic number on a silicon substrate. In the study, thin film materials such as Al, Ni, SiO₂, and Si₃N₄ are deposited on a silicon wafer to explore the proximity effect. The preliminary experimental results show that raising the electron beam voltage and depositing SiO₂ or Si₃N₄ thin film on a silicon substrate can efficiently solve this problem. Later, the resist with a nano-pattern is transferred into a metal Ni–Co (nickel–cobalt) mould by electroplating. The technique of the Ni–Co electroplating process with hardness at least Vicker hardness (Hv) 650 and residual stress below 1.5 kg mm⁻² is developed. Then, with the Ni–Co mould, a modified LIGA process is applied to produce a high-density optical disc. The Ni–Co mould serves as the master for the hot embossing process to replicate the nano-pattern onto the PMMA sheet. Since the feature size is down to the nanometre range, the study presents an innovative demoulding mechanism to demould the master from the PMMA sheet without damaging the nanometre patterns.

Si nanowires have been produced in high yield on Si substrate with the absence of a catalyst by thermal evaporation at high temperature. The self-induced growth of Si nanowires suggests that a catalyst should be not essential. Transmission electron microscopic investigation shows that the nanowires, with a diameter ranging from 10 to 100 nm and length up to a few hundred microns, are crystalline or amorphous. The self-induced solid–liquid–solid model and oxygen-assisted vapour–solid mode are employed to explain the results. Raman spectroscopy shows an asymmetric peak around 512 cm⁻¹, with a deviation of 9 cm⁻¹ from that of the bulk crystalline Si. XRD and TEM were used to characterize the Si nanowires. The effects of growth conditions on quality and production were investigated.

A rational approach is described for fabricating multilevel silicon-based nanostructures via scanning probe oxidation (SPO) and anisotropic wet etching. Using silicon oxide nanopatterns on Si(100) and Si(110) surfaces created by SPO as masks, two-dimensional (2D) nanostructures with high aspect ratio and a variety of patterns can be formed by anisotropic wet etching with KOH. By employing a mixture of KOH solutions and isopropyl alcohol (IPA) as an alternative to KOH alone, control of the morphology of the etched silicon surfaces, crucial for further fabrication, was greatly improved. The SPO and etching processes can be continually repeated on the 2D nanostructures, permitting the formation of various multilevel silicon-based nanostructures, including a T-gate structure useful for electronic circuitry. In addition, these multilevel silicon structures can be used as nanoimprint moulds for their rapid replication.

Highly ordered Fe₄₈Co₅₂ nanowire arrays with various interpore distances and diameters were fabricated by electrochemical deposition. The change of their magnetic properties after annealing has great dependences on the interpore distance and the wire diameter. The model of the prolate ellipsoid chain modified with the magnetostatic interaction is employed to explain this geometry dependence of the annealing effect. After annealing at 550 °C in H₂ atmosphere, good hard magnetic properties (at room temperature, coercivity H_c = 3.89 kOe, squareness M_r/M_s = 0.954; at 78 K, H_c = 4.55 kOe, M_r/M_s = 0.954) were obtained in the arrays with a diameter of about 22 nm and an interpore distance of about 50 nm.

Morphology-controlled, ordered poly(vinyl pyrrolidone) (PVP) nanotubes and nanowires have been prepared on porous alumina templates with hydrophilic or hydrophobic pore surfaces. The nanostructures were about 270 nm in diameter with a narrow size distribution and up to 10 µm in length. The fluorescence spectrum was used to characterize the pore surface of AAO templates with different polarities. The mechanism of the formation of PVP nanotubes or nanowires was discussed.

Construction of luminescent single- and bilayer polymer arrays in micron and submicron scales through dewetting on a heterogeneous conducting polymer surface is demonstrated. We study the influence of the pattern geometry and film thickness of polymer dewetting upon annealing, and the morphology of created polymer arrays on the heterogeneous surface. The materials used for patterning are an insulating poly(methyl methacrylate) (PMMA) or a conjugated fluorescent polymer, poly(dioctylphenylthiophene) (PDOPT). The substrate used is the conducting polymer poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT–PSS), with modified heterogeneous surface energy obtained by application of a bare polydimethylsiloxane (PDMS) stamp.

Micro-photoluminescence spectroscopy measurements have been performed on single self-organized InAs/InP quantum dashes, either on sub-micron mesas made on the sample surface or through sub-micron apertures realized in a gold mask deposited on the surface. The emission wavelength of the quantum dashes is centred around 1.5 µm at room temperature. The micro-photoluminescence measurements on sub-micron mesas, at low temperature and with low excitation power density, show PL spectra consisting of a few single sharp exciton lines with a rather large full width at half maximum (FWHM) in the 0.8–1.8 meV range, whereas peak broadening is found to be much smaller for the spectra recorded through the sub-micron apertures with an FWHM below 300 µeV. When the excitation power density is increased, new lines arise which are interpreted as emission coming from excited states of single InAs/InP quantum dashes and from bi-exciton recombination.

The fabrication of In_0.3Ga_0.7N/GaN multiple-quantum-well nanorods with diameters of 60–100 nm and their optical characteristics performed by micro-photoluminescence measurements are presented. The nanorods were fabricated by inductively coupled plasma dry etching from a light-emitting diode wafer. The structure and surface properties of fabricated nanorods were verified by the field emission scanning electron microscopy and the transmission electron microscopy. The photoluminescence (PL) spectra with sharp linewidths of typically 1.5 nm were observed at 4 K. The excitation-power-dependent spectra show that no energy shift was observed for these sharp peaks. Moreover, increasing the excitation power instead leads to an occurrence of new, sharp PL peaks at the higher energy tail of the PL spectra, which suggest that excitons are strongly confined in quantum-dot-like regions or localization centres.

Selective, well controlled and directionally grown Sn doped In₂O₃ nanowires (In₂O₃: Sn nanowires, SIO NWs) were synthesized at a low fabrication temperature () through a vapour–liquid–solid (VLS) process under a precise carrier gas flow. The majority of the SIO NWs are grown along [222], with [400] and [440] as minority forming directions, which implies a nearly epitaxial crystal structure. There are fewer physical defects, such as line or planar defects and contaminations, in the SIO NWs than in pure In₂O₃ nanowires seen through high resolution transmission electron microscopy (HR-TEM) observations. The spectrum of photoluminescence (PL) emission indicates a stable strong blue light peak located at  nm with an excited wavelength of 275 nm at room temperature. The Sn dopant in the SIO NWs can enhance the conductivity of the nanowires leading to the lowering of the turn-on electric-field to 0.66 V µm⁻¹ undera current density of up to 1.0 mA cm⁻² based on their field emission characteristics. Furthermore, the field emission enhancement coefficient, β, is also increased to 1.48 × 10⁵, which is very close to the carbon nanotube, (CNT) level. SIO NWs fabricated by a VLS process offer a potential application in flat panel displays as demonstrated in this study.

One important requirement for future applications of carbon nanotube electronic devices is the ability to controllably grow carbon nanotubes on metal electrodes. Here we show that it is possible to grow small diameter (<10 nm) vertically aligned carbon nanotubes on different metal underlayers using plasma-enhanced chemical vapour deposition. A crucial component is the insertion of a thin silicon layer between the metal and the catalyst particle. The electrical integrity of the metal electrode layer after plasma treatment and the quality of the metals as interconnects are also investigated.

Tribological issues in micro/nanoelectromechanical systems (MEMS/NEMS) and BioMEMS/NEMS are one of the concerns for the reliability of these devices. Silicon based components for MEMS/NEMS devices have been the standard, but new materials, such as polymers, are gaining use due to their advantages over silicon in the area of BioMEMS. Adhesion and friction properties of two polymers of interest, poly(methyl methacrylate) (PMMA) and polydimethylsiloxane (PDMS), along with a single-crystal silicon substrate, Si(100), are investigated by using a novel microtriboapparatus capable of adopting BioMEMS components used in microfluidic devices. The adhesion and friction properties of PMMA and PDMS are dependent upon the surrounding environment, and to study these issues three different liquids are applied to the interface of the contacts in two different forms, a drop and a film. Other environmental effects are also investigated in this study by looking at relative humidity, temperature, rest time and different gaseous environments such as nitrogen gas and reduced pressure.

Colloidal PbS nanocrystals over-coated with CdS are prepared in aqueous solutions and exhibit strong photoluminescence with two distinct peaks in the visible regime. A photoluminescence peak is observed at 640 nm, which is attributed to the band edge recombination in the PbS nanocrystals, and another peak at 510 nm, which is above the band edge of the PbS nanocrystals. The two PL peaks are isolated by extracting separate species of nanocrystal based upon their surface morphology. Micro-emulsions of hexane:PVA are used to remove the species containing the PL peak at 640 nm from the solution, leaving a singular peak at 510 nm. We show conclusively that the double-peaked structure observed in the photoluminescence spectra of PbS nanocrystals over-coated with CdS is due to the presence of two distinctly different nanocrystal species.

Immune responses from Au/Ni nanorods prepared by electrochemical deposition in alumina templates are evaluated in C57BL/6 mice. When the nanorods are bombarded into skin, they generate a strong CD8 T-cell and antibody response. When pcDNA3 is bound to the Ni segment of the nanorod, it provides a strong immunostimulatory adjuvant effect to the antigen bound on the Au segment.

Materials with exceptionally high contents of carbon are used in technologies with various degrees of added value, from quasi-amorphous materials for carbon electrodes used in e.g. lithium batteries to highly organized materials comprising e.g. nanotubes and fullerenes. The present study aims to test the feasibility of predicting the properties of carbon based materials using (i) molecular modelling and simulation techniques; (ii) application to fullerene as an idealized model of nano-pores in carbon materials; and (iii) available experimental data regarding the behaviour of carbon materials for lithium batteries as validation data. It has been found that the increase in the H/C atomic ratio has an ambivalent impact on the structural stability of lithium-doped carbon materials, with the ultimate lithium-doped material being the result of the 'tug of war' between the folding of the 'house-of-cards' structure due to increased flexibility of the idealized pore scaffold and the pore expansion due to the doping process coupled with the increase in structural flexibility. With regard to molecular motors, the simulations demonstrate that small numbers of hydrogenated defects may induce large enough structural changes to damage the smoothness of the surface of the nanogears, but the insertion of lithium atoms may stabilize this deleterious effect.

Conductance of nanoscale junctions consisting of a molecular monolayer in contact with different metal electrodes is studied. The characteristic energy scales of conductance are determined from the temperature dependence and from the non-linear current–voltage characteristics. Conductance measured at small bias follows Arrhenius behaviour. The effective activation energies are dependent on the metal contacts. The activation energies, typically in the range of 5–150 meV, are small compared to the expected molecular energy level spacings. The nature of the low-energy states remains unclear; however, some mechanisms, such as doping of the molecular layer by metal atoms, can be excluded. For certain metal pairs, the energies extracted from the onset of the non-linearity correspond to the low-bias activation energies, while for other metals this is not observed. These differences are probably caused by the differences in the relative topography of metal electrodes defining the effective conducting paths through the molecular layer.

We report a simple and general approach for the preparation of SiO₂-sheathed semiconducting nanowires. We provide conclusive evidence to illustrate the growth mechanism of SiO₂-sheathed semiconducting nanowires by taking ZnS/SiO₂ nanocables as an example. ZnS/SiO₂ nanocables were synthesized via a thermal evaporation process. The growth of the nanocables is initiated by the formation of ZnS nanowires, and the subsequent (most possibly by a synergic way) formation of the SiO₂ sheath. The results revealed that the ZnS/SiO₂ nanocables consisted of ZnS nanowires as the core and SiO₂ as the sheath. The photoluminescence measurements showed that the ZnS/SiO₂ nanocables had strong visible-light emission bands located at 460 and 592 nm, which were attributed to the surface state of the ZnS nanowires and the defects induced by SiO₂ sheaths, respectively.

We demonstrate here the wet chemical synthesis of cobalt doped γ-Fe₂O₃ nanoparticles and the subsequent effect on magnetic properties with the variation in dopant concentration. It is observed that cobalt can be homogeneously doped into the γ-Fe₂O₃ lattice up to 5 mol% without any appreciable change in the particle size ( nm). Further increase in cobalt concentration (10 mol% here) resulted in an increase in particle size ( nm) due to possible adsorption of a cobalt layer on the surface of γ-Fe₂O₃ nanoparticles rather than complete doping in the iron oxide lattice. The ac susceptibility measurements revealed an increase in blocking temperature (T_B) with percentage variation in cobalt doping (2–10%), indicating substitution of Fe³⁺ ions by Co²⁺ ions in the γ-Fe₂O₃ lattice. The dc magnetization measurements showed an increase in saturation magnetization only up to 5%, beyond which it significantly diminished. The reduction in saturation magnetization is attributed to the contribution from surface anisotropy in cobalt coated γ-Fe₂O₃ nanoparticles.

The hydrogen sorption capacity of arc-synthesized single-walled carbon nanotubes (SWNTs) was studied using a specially built high-pressure rig coupled to a Toepler pump capable of directly measuring the desorbed volumes of gas. The samples studied were prepared using the arc-evaporation method and were as-produced SWNT material formed at the cathode (collar), as-produced SWNTs deposited in the soot and a purified sample of SWNTs. The three samples had similar diameter ranges, the major difference between them being the concentration of remaining metal particles from the Ni/Y/C catalyst used in the arc-synthesis. The effect of the presence of these residual catalyst metal particles has been analysed and seen to strongly influence the hydrogen storage capacity of the samples.

Catalytic synthesis of multi-walled carbon nanotubes (MWNTs) by the pyrolysis of acetylene over mischmetal (Mm) based MmNi₂ and MmFe₂ hydride catalysts is reported. The hydrogen decrepitation technique has been used to prepare the catalyst particles of these Mm based hydrogen storage alloys. Large hydrogen decrepitation and low cost make these hydrides potential catalysts for large-scale production of CNTs. The samples were purified by air oxidation and acid treatment and were characterized by XRD, SEM, TEM, HRTEM, Raman spectroscopy and XPS. The yield of MWNTs was estimated to be and the purity of MWNTs thus obtained was more than 90%, as characterized by TGA. In addition, hydrogen adsorption measurements were carried out for as-prepared and purified MWNTs at 125 and 298 K using a high pressure hydrogen adsorption set-up. A maximum hydrogen storage capacity of 3.2 wt% at 60 bar is obtained at 125 K for purified CNTs prepared with MmFe₂ hydride catalysts.

In this paper, the assembly and stability of locally spotted spherical nanoparticles onto various substrates are studied. Arrays of silicon-based microcantilevers, combined with an automated three-stage spotter, are used to deposit picolitre droplets containing 300 nm diameter polyethylene glycol and 150 nm diameter amino conjugated silica nanospheres onto silicon, allylamine and acrylic acid surfaces. Matrices of colloid spots ranging from 10 to 100 µm in diameter have been successfully patterned. SEM characterizations of the nanoparticles' geometry and spatial distribution within the spots were carried out, showing the colloid aggregation at the droplet's rim and the selective stability of the printed patterns. The expected substrate functionalization was assessed by XPS characterizations of the nanoparticles' surfaces. Finally, polyethylene glycol–SiO₂ nanoparticle conjugates were used as masks during a selective reactive ion etching of the silicon substrate, and silicon nanopillars have been obtained. This work opens up possibilities of high spatial resolution nanopatterning with nanoparticle conjugates.

Double-walled carbon nanotubes (DWCNTs) were synthesized by chemical vapour deposition using Fe–Mo catalyst supported on magnesium oxide particles. A mixture of gases of methane and hydrogen was used for the growth. The effect of gas pressure, ratio of methane to hydrogen, and growth temperature on the structure, purity, and yield of DWCNTs has been studied in detail. Transmission electron microscope studies revealed that the growth temperature is the crucial factor determining the size of the catalyst particles. Scanning electron microscope studies were also carried out to provide information on the purity and diameter of DWCNTs synthesized under various conditions.

The room-temperature solid-state reactions occurring in the preparation of nanotubes of zinc sulfide are further investigated by x-ray powder diffractometry (XRD) and infra-red (IR) spectrometry measurements, and the nanotube ZnS product obtained is measured by Z-scan technology to investigate the third-order nonlinear optical (NLO) properties. The XRD result suggests that the reactions leading to the formation of the nanotubules have occurred through reaction-controlled to growth-controlled procedures, and the IR result indicates that the procedures involve a coordination effect of the additive DABCO as ligand on the reactant. The result of NLO measurements shows that the nanotube ZnS products obtained have the behaviours of the third-order nonlinear optical properties of both NLO absorption and NLO refraction with self-focusing effects.

Atomic force acoustic microscopy (AFAM) provides nanometre resolution images reflecting sample elasticity and a possible technique for measuring the elastic modulus of thin films and extremely narrow areas. In AFAM, the resonant frequency of a micro-cantilever equipped with a sensor tip measures the contact stiffness between tip and sample. In the case of stiff samples like metals and ceramics, AFAM exhibits significantly low sensitivity, i.e., the resonant frequency is insensitive to the contact stiffness. The proposed concentrated-mass (CM) cantilever offers a smart solution to the problem without trade-offs. The present study discusses schemes for imaging elastic heterogeneity and evaluating elastic modulus in the case of CM cantilevers. The present experiment employed a flat tip with a metallic coating, namely a Ti/Pt thin film. The adhesive strength and ductility of the coating resulted in a prolonged lifetime. Images of a Ti sheet sample acquired with so-called slope detection clearly revealed nano-grains and slip bands, which would be unachievable by topographic images. The flat tip ensures a constant contact area, rendering contact stiffness independent of the magnitude of the contact force and tip–sample adhesion force, and significantly simplifying evaluation of the elastic modulus.

ZnSe hollow nanospheres have been hydrothermally synthesized at 140 °C for 24 h starting from the precursor ZnCl₂(N₂H₄)₂ and Na₂SeO₃ by using hydrazine hydrate (N₂H₄·H₂O) as the reducing agent. The sample was characterized by XRD, ICP-AES, FE-SEM, and TEM. The BET surface area of the obtained ZnSe hollow nanospheres is 77.13 m² g⁻¹. Both the transverse optic (TO) and longitudinal optic (LO) phonon peaks in Raman spectra of the ZnSe product showed a obvious shift to lower frequency compared to bulk values; a blue-shift () was observed in PL spectra. It appears that the hollow spheres might be formed by a soft-template of gas bubbles of N₂ produced during the reaction.

The remarkable mechanical properties of carbon nanotubes (CNTs) have generated a lot of interest in recent years. While CNTs are found to have ultra-high stiffness and strength, an enormous scatter is also observed in available laboratory results. This randomness is partly due to the presence of nanoscale defects, heterogeneities etc, and this paper studies the effects of randomly distributed Stone–Wales (SW or 5–7–7–5) defects on the mechanical properties of single-walled nanotubes (SWNTs) using the technique of atomistic simulation (AS). A Matern hard-core random field applied on a finite cylindrical surface is used to describe the spatial distribution of the Stone–Wales defects. We simulate a set of displacement controlled tensile loadings up to fracture of SWNTs with (6, 6) armchair and (10, 0) zigzag configurations and aspect ratio around six. A modified Morse potential is adopted to model the interatomic forces. We find that fracture invariably initiates from a defect if one is present; for a defect-free tube the crack initiates at quite random locations. The force–displacement curve typically behaves almost linearly up to about half way, although there is no obvious yield point. Three mechanical properties—stiffness, ultimate strength and ultimate strain—are calculated from the simulated force and displacement time histories. The randomness in mechanical behaviour resulting only from initial velocity distribution was found to be insignificant at room temperature. The mean values of stiffness, ultimate strength and ultimate strain of the tube decrease as the average number of defects increases, although the coefficients of variation do not show such a monotonic trend. The introduction of an additional defect has the most pronounced effect on the randomness in mechanical properties when the tube is originally defect free. We also find that, for a given mean number of defects in the tube, the zigzag configuration has less strength and less ultimate strain on average, but more uncertainty in its stiffness and ultimate strain, compared with the armchair tube.

Potential biomedical applications for carbon nanofibres include, but are not limited to, biosensors and drug delivery vehicles. For such applications, it is essential to know how carbon nanotubes interact with antibodies and proteins. We report on the successful adsorption of monoclonal CD3 antibodies on two types of carbon nanofibre produced by the same method and having the same average size and shape, but differing in surface structure and chemistry due to dissimilar post-treatments. Binding of proteins to nanofibres is enhanced by poly (L-lysine) (PLL) and improves with increasing disorder and hydrophilicity of the nanofibres' surface. Oxidized and disordered surfaces of pyrolytically stripped nanofibres show improved wetting and attachment of PLL and proteins compared to hydrophobic and well-ordered surfaces of heat-treated nanofibres. These results show that the surface of carbon nanofibres can be tailored for their use in biomedical applications.

We report on a nanoscale patterning method on Si substrates using self-assembled metal islands and low-energy ion-beam irradiation. The Si nanostructures produced on the Si substrate have a one-to-one correspondence with the self-assembled metal (Ag, Au, Pt) nanoislands initially grown on the substrate. The surface morphology and the structure of the irradiated surface were studied by high-resolution transmission electron microscopy (HRTEM). TEM images of ion-beam irradiated samples show the formation of sawtooth-like structures on Si. Removing metal islands and the ion-beam induced amorphous Si by etching, we obtain a crystalline nanostructure of Si. The smallest structures emit red light when exposed to a UV light. The size of the nanostructures on Si is governed by the size of the self-assembled metal nanoparticles grown on the substrate for this replica nanopatterning. The method can easily be extended for tuning the size of the Si nanostructures by the proper choice of the metal nanoparticles and the ion energy in ion irradiation. It is suggested that off-normal irradiation can also be used for tuning the size of the nanostructures.

ZnO tetrapod nanowires were fabricated by evaporation of Zn in a N₂ gas flow. Stimulated emission with a threshold of was observed and the linewidths of individual modes were in the range 0.7–0.9 nm. Time-resolved measurements have been performed at different excitation powers. With an increase of the pump power, the transition from exciton stimulated emission to the electron–hole plasma regime can be clearly observed. Both electron–hole plasma and exciton emission have decay times under 10 ps.

The motion of coupled oscillators based on multiwalled carbon nanotubes is studied using rigid-body dynamics simulations. The results show the existence of chaotic and regular behaviours for a given total energy, indicating the manifestation of chaos in nanoscaled mechanical systems based on carbon nanotube oscillators. Different regular motions are observed for different total energies, and they can be obtained by appropriately choosing the initial conditions. This possibility can allow the construction of multi-functional nano-devices based on multiwalled carbon nanotube oscillators.

Transient currents induced by the polarity reversal of an applied dc voltage in nematic liquid crystal hybridized with montmorillonite clay have been studied. Comparative values of the ion-charge concentrations deduced from the experimental data suggest that the clay hybridized into liquid crystal has a great impact on the ion-charge concentration, which can be dramatically reduced to as low as to for a nematic cell containing merely 0.5 wt% clay. Such hybridization suppresses the formation of electric bilayers and the charge-screening effect. Due to the clay and liquid-crystal molecules being aligned to the direction of the field, a higher mobility is observed in hybridized cells. This study demonstrates that montmorillonite clay hybridized into liquid crystal yields many advantages to improve the electro-optical properties of the display device.

Gd(OH)₃ nanorods have been prepared via hydrothermal growth, and their microstructures are characterized by x-ray diffraction, high-resolution transmission electron microscopy and electron energy loss spectroscopy. The diameters of the Gd(OH)₃ nanorods are 15–20 nm and the lengths are 150–250 nm. The nanorods are single crystalline with clean surfaces, and they grow preferentially along the [001] direction.

We present a novel display based on the manipulation of neutral nanoparticles dispersed in an insulating liquid. The operative mechanism is based on dielectric forces and electric field-induced dipolar interactions between neutral nanoparticles, leading to compact aggregates that change the optical characteristics. Such displays can operate either in a diffusive scattering mode or in a written mode, both based on the capacity to have a compact particle storage mode. Owing to the hysteretic behaviour, low-power operation is obtained.

An electrostatic actuation method to generate useful out-of-plane motion of a cantilever structure is described. The critical design feature is to create an asymmetric electric field such that an electrostatic force is generated in a direction perpendicular to the wafer surface. The technical application of the actuation method is to large arrays of microfabricated sensors such as cantilevers and in particular to resonator type sensors. The design approach also overcomes several problems associated with exposure of microfabricated cantilever structures to fluid environments, either during processing or during application of such devices as bio-sensors, e.g. stiction, condensation, squeeze damping, exposure to a biological sample, cleaning and biological activation treatments of the cantilever surfaces. The viability of the technique is demonstrated using microfabricated silicon cantilevers utilizing both optical and piezoresistive detection of the cantilever displacement.

Catalyst-free needle-like ZnO nanowires have been grown on Si(111) substrate at 430 °C via a simple solid–vapour process. The obtained nanowires are found to have a uniform size distribution with sharp tips. The lengths of the nanowires range from 2.8 to 3.2 µm with diameters of about 100 nm for the root and 30 nm for the tip parts. The x-ray diffraction (XRD) result shows the nanowires are c-axis preferentially oriented. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) analysis reveal that every single nanowire is a well developed single crystal. The room temperature photoluminescence (PL) spectrum shows a dominant near-band-edge emission peak. The near-band-edge emission is further identified to originate from the radiative free exciton recombination by the temperature-dependent PL.

We present a method to realize active optical tips for use in near-field optics that can operate at room temperature. A metal-coated optical tip is covered with a thin polymer layer stained with CdSe nanocrystals or nanorods at low density. The time analysis of the emission rate of the active tips and the analysis of their emission spectra reveal that a very small number of particles—possibly down to only one—can be made active at the tip apex. This opens the way to optics with a single inorganic nanoparticle as a light source.

The resonance tunnelling of states at two interfaces are investigated through the three models of two-terminated carbon nanotube heterojunctions: (5, 5)/(10, 0)/(5, 5), (9, 0)/(10, 0)/(9, 0) and (5, 5)/(10, 0)/(9, 0). In (5, 5)/(10, 0)/(5, 5) CNQD, we observed the existence of interface states in LDOS, and the resonant tunnelling peak at the position of interface states also emergent in quantum conductance. With the increase of QDs size, the resonant tunnelling peak gradually disappears. Comparing their quantum conductance for different sizes, when the size of the (5, 5)/(10, 0)/(5, 5) model is larger than 23 layers, there is not a quantum conductance peak at −0.26 eV. Therefore, the largest size for resonant tunnelling occurring between two interface states in (5, 5)/(10, 0)/(5, 5) is about 23 layers (about 45 Å).