Table of contents

Starting with crystalline silicon nanoparticles, which were produced by CO₂ laser pyrolysis of silane in a gas flow reactor, we have synthesized amorphous silica nanoparticles via oxidation. Upon excitation with UV light, the novel nanostructured material gives rise to an intense red photoluminescence (PL) which resembles that of some silicon nanostructures. Transmission electron microscopy studies and electron energy loss spectroscopy confirm that the nanoparticles are composed of amorphous silica and that the majority of them are hollow. The strong red PL is attributed to defects or molecular species located at the inner and outer surfaces of the hollow nanoparticles. Its similarity to the PL of nanostructured silicon seems fortuitous.

In this tutorial, focused-ion-beam (FIB)-based fabrication is considered from a very unconventional angle. FIB is considered not as a fabrication tool that can be used for mass production of electronic devices, similar to optical and E-beam—based lithography, but rather as a powerful tool to rapidly fabricate individual nanoscale magnetic devices for prototyping future electronic applications. Among the effects of FIB-based fabrication of magnetic devices, the influence of Ga⁺-ion implantation on magnetic properties is presented. With help of magnetic force microscopy (MFM), it is shown that there is a critical doze of ions that a magnetic material can be exposed to without experiencing a change in the magnetic properties. Exploiting FIB from such an unconventional perspective is especially favourable today when the future of so many novel technologies depends on the ability to rapidly fabricate prototype nanoscale magnetic devices. As one of the most illustrative examples, the multi-billion-dollar data storage industry is analysed as the technology field that strongly benefited from implementing FIB in the above-described role. The essential role of FIB in the most recent trend of the industry towards perpendicular magnetic recording is presented. Moreover, other emerging and fast-growing technologies are considered as examples of nanoscale technologies whose future could strongly depend on the implementation of FIB in the role of a nanoscale fabrication tool for rapid prototyping. Among the other described technologies are 'ballistic' magnetoresistance, patterned magnetic media, magnetoresistive RAM (MRAM), and magnetic force microscopy.

The nanometric scale ploughing friction and wear behaviour of a pyramidal diamond indenter sliding against a face-centred cubic silver (100) surface is investigated by means of parallel molecular dynamic (MD) simulations of nanoindentation followed by nanoscratching. The relationship between the friction coefficient, the hardness and the indenter orientation is studied. The simulations were performed using three different indenter orientations. For each orientation, simulations were performed at an indentation depth of 5 and 10 Å, and a scratching length of 210 Å. In order to study the behaviour of the friction coefficient and the hardness as a function of depth we performed the simulations for one of the orientations at depths of 5, 10 and 30 Å. The simulations show that the friction coefficient is dependent on both the orientation of the indenter and the indentation depth. The results also show that the friction coefficient increases as the depth increases, whereas the contact pressure decreases and the scratch hardness decreases slightly. With a shallow indent of 5 Å, no sub-surface defects were observed beneath the scratch groove, but with the deeper indents of 10 and 30 Å dislocations in the {111} planes are observed beneath the scratch groove. These dislocations propagate in the direction; each dislocation consists of the intersection of stacking faults on two {111} planes and each stacking fault is bounded by two Shockley partial dislocations.

The electron transport process in DNA-doped polypyrrole (PPY) nanocomposite film deposited on tin oxide coated glass by a simple electrodeposition technique is demonstrated here. Optical absorbance spectra clearly exhibited features corresponding to doped PPY nanocomposite film. The I–V characteristics of the films were non-ohmic and showed a significant change when illuminated with light. Photoinduced I–V profiles suggested carrier hopping to be the dominant transport mechanism in the nanocomposite PPY film. The temperature-dependent dc electrical conductivity data showed a crossover from variable-range hopping to thermally activated hopping of electrons with the increase in temperature. The ac electrical transport properties displayed a frequency-independent region below a characteristic frequency of  kHz, above which the conductivity showed a strong frequency-dependent behaviour.

ZnO nanowires were grown on GaAs(002) single-crystal substrates using metal–organic chemical vapour deposition. X-ray diffraction analysis, scanning electron microscopy and photoluminescence spectroscopy were carried out to characterize their crystallinity, orientations, dimensions and optical properties. It was demonstrated that well aligned arrays of single-crystalline ZnO nanowires with sharp tips could be grown on GaAs substrates using a typical thin film deposition technique without catalysts. The application potential of the nanowires as probes of atomic force microscopes (AFMs) was then discussed by predicting their structural compatibility with AFM cantilevers based on continuum elasticity and finite element analysis. Theoretically estimated mechanical properties of the ZnO nanowires suggested that they are structurally compatible with typical AFM cantilevers while maintaining mechanical stability during operation and they are therefore promising candidates for high aspect ratio probes.

The study of the properties of nanostructures in an electric field is very important not only from the fundamental point of view but also for practical applications. According to classical physics, an insulating system will be broken down in a large electric field. Can we predict such a behaviour for nanostructures using ab initio calculation? Such an attempt is made in this paper. The electronic structure and charge distributions of the thinnest (SiO₂)_n wire in electric field are studied in detail with a first-principles method. It is found that the HOMO–LUMO gap increases with size and saturates at large values of 6.4 eV when , suggesting that the SiO₂ chain can be a very good insulating nanowire. However, when the wire is in an applied electric field, the HOMO and LUMO energies of the wire decrease linearly at different speeds, and the gap approaches zero, at which point the insulating wire is broken down by the electric field.

We have synthesized carbon nanofibres (CNFs) in an ethylene–air flame on a stainless steel substrate. Ten-minute specimens consisted of both nodules and carbon micro- and nanofibres of various diameters up to . There are two kinds of primary fibres. The first are of  nm thickness and show numerous kinks along their length. The second variety can have thicknesses of the order of and can grow to a length of . Nanofibre branching is also evident. The inclusion of periodic metal deposits in the nanofibres reveals a strategy by which it might be possible to encapsulate metal particles in order to form connected CNF networks.

In this work we investigated the hydrogen storage properties of stoichiometric Mg₂Ni intermetallic nanoparticles produced from Mg and Ni nanoparticles. The mean size of the Mg₂Ni particles is about 30–50 nm and the lattice constants of the Mg₂Ni compound are a = 5.22 Å, c = 13.29 Å. The Mg₂Ni compound showed excellent hydrogen storage properties without activation. It can absorb 2.77, 2.93 and 3.03 wt% hydrogen at 523, 573 and 623 K respectively. After one simple activation process, the obtained Mg₂Ni absorbed 1.74, 2.07, 2.31 and 2.82 wt% hydrogen at 293, 348, 426 and 493 K respectively. The absorption and desorption plateau hydrogen pressures are about 2.5 and 0.8 bar at 523 K, 5.9 and 3.4 bar at 573 K and 12.7 and 9.7 bar at 623 K. The resulting van't Hoff equation is log(P/bar) = −3464/T+6.541 and the formation enthalpy (ΔH) and entropy (ΔS) for the Mg₂NiH₄ are −66.32 kJ/mol H₂ and −125.3 J K⁻¹/mol H₂.

A two-step method for constructing nanometre-scale architectural structures of nanoparticles on a solid surface is demonstrated. The method depends on physical processes between a colloid of nanoparticles and a hydrophobic surface that contains recess patterns. The effects of sedimentation of particles and of dewetting of the surface result in deposition of nanoparticles only within the patterns. This method has been used to generate spatially confined monolayers of nanoparticles, to assemble a small number of particles to each point of a 2D array and to construct 1D chains of interconnected particles on a surface. This versatile method can be used to generate architectural structures on a solid surface on various length scales.

Nanocrystalline BaTiO₃ powders were prepared via a chemical process. This process involved the addition of aqueous barium nitrate, titanyl nitrate, triethanolamine (TEA) and sucrose to produce a homogeneous complex solution. After the complete evaporation of homogenous solution, the Ba–Ti–TEA–sucrose complex decomposed and produced black, fluffy precursor materials. The precursor materials on calcinations to 700 °C for 2 h produced nanocrystalline BaTiO₃ with the corresponding average x-ray and TEM particle size  nm. BaTiO₃ powders modified with SrTiO₃ [Ba_1−xSr_xTi_1−yZr_yO₃ (x = 0.03, y = 0)] and BaZrO₃ [Ba_1−xSr_xTi_1−yZr_yO₃ (x = 0, y = 0.03)] were also prepared using this route and investigated through x-ray diffraction and energy dispersive x-ray analysis.

A compound with a non-layered structure composed of Cu_2−xSe nanotubes was prepared in a room temperature redox reaction in ethylene diamine solution. The product was characterized by x-ray diffractometry, transmission electron microscopy, high resolution transmission electron microscopy, and x-ray photoelectron spectroscopy. Analysis shows that the nanotubes have a multiwall structure with (002) planes of face-centred cubic Cu_2−xSe and open ends. The Cu_2−xSe nanotubes have length 500 nm, with an inner diameter of 20 nm and an outer diameter of 30 nm on average. Ethylene diamine's ability to achieve strong coordination and the presence of the reducing agent hydrazine hydrate aid the formation of Cu_2−xSe nanotubes with mixed valence.

An easy and convenient technique to fabricate a carbon nanotube (CNT) film on a glassy carbon electrode (GCE) is described. In the presence of a hydrophobic surfactant, insoluble multi-walled carbon nanotubes (MWNTs) were dispersed into water to give a homogeneous and stable suspension. After solvent evaporation, a stable and uniform CNT film was achieved on the GCE surface. The MWNT film was characterized by scanning electron microscopy and transmission electron microscopy images. The electrochemical behaviour of thyroxine at the MWNT film-coated GCE was investigated. It was found that this novel CNT film can remarkably enhance the sensitivity of determination of thyroxine. Consequently, a novel electrochemical method was developed for the determination of thyroxine with simplicity and high sensitivity. The analysis method is demonstrated by using human blood serums.

We investigated In_0.8Ga_0.2As self-assembled quantum dots (SAQDs) and their underlying GaAs wire structures grown by metalorganic vapour phase epitaxy on SiO₂-patterned exact and vicinal (001) GaAs substrates. The directions of the misorientation of the vicinal (001) GaAs substrate and the patterned wire SiO₂ mask were . During the growth of the GaAs layer on SiO₂-patterned vicinal (001) GaAs substrates, {110}, {111}A, and {113}A facets were evolved by the opening layer width of the masks and the misorientation angles of the substrates. The ratio of the growth rate on the {111}A sidewalls to that on the neighbouring facets, (G_{111}A), was increased by using the vicinal substrate having the higher misorientation angle, hence the surface migration of Ga adatoms from the {111}A sidewalls to the top region decreased. In_0.8Ga_0.2As SAQDs having regular periodicity on a narrow (001) top terrace were formed on a SiO₂-patterned 5°-off (001) GaAs substrate.

Faradaic current during anodic oxidation is measured over a relative humidity range of 40–70% using an atomic force microscope with humidity control. The level of detected current during the fabrication of oxide dots on H-passivated Si(001) is in the picoampere (pA) level. Current flow began immediately (within a few milliseconds) after applying an oxidation voltage above a threshold value and decreased with time according to oxide growth. The total charge resulting from the current flow was calculated by integrating the current–time curve and was found to agree well with an estimation of expected current from the volume of the fabricated oxide dots. Actual monitoring of the oxidation process by the Faradaic current is demonstrated during the fabrication of a two-dimensional lattice.

The combination of large thickness (>3 µm), large-area uniformity (75 mm diameter), and high growth rate (up to 0.4 µm min⁻¹) in assemblies of complex-shaped nanowires on lithographically defined patterns has been achieved for the first time. The nanoscale and the microscale have thus been blended together in sculptured thin films with transverse architectures. SiO_x () nanowires were grown by electron-beam evaporation onto silicon substrates both with and without photoresist lines (1D arrays) and checkerboard (2D arrays) patterns. Atomic self-shadowing due to oblique-angle deposition enables the nanowires to grow continuously, to change direction abruptly, and to maintain a constant cross-sectional diameter. The selective growth of nanowire assemblies on the top surfaces of both 1D and 2D arrays can be understood and predicted using simple geometrical shadowing equations.

A simple two-dimensional model of thin film growth based on the ballistic aggregation of hard discs is proposed. In this model the impinging hard discs travel in a straight line and initially 'stick' to the first previously deposited hard disc they contact. Previously (Dirks and Leamy 1977 Thin Solid Films47 219) the criterion for relaxation has been migration of the impinging disc to the nearest pocket formed by two additional discs. In the model proposed here, however, relaxation is dependent on the surrounding geometry of the previously deposited atoms. The deposited disc may 'relax' into a position where it then makes contact with three, two or one previously deposited disc(s). The influences of substrate temperature, deposition rate, angle of incidence, self-shadowing effect and substrate roughness, including amorphous substrates are investigated. Results are qualitatively in good agreement with the structure zone model (SZM) predictions for thin metallic films.

The morphology and optical properties of zinc oxide fibres with diameters in the nanometre to micrometre range are reported. The PVA/zinc acetate organic/inorganic hybrid nanofibres were successfully prepared by electrospinning using polyvinyl alcohol (PVA) and zinc acetate. Pure zinc oxide fibres were obtained by high-temperature calcination of the hybrid fibres in air. The nanofibres were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray diffractometry (XRD) and Raman spectroscopy. The photoluminescence spectra under excitation at 325 nm showed an ultraviolet emission at 3.13 eV and a green emission at 2.21 eV. These nanofibres could be used as light emitting devices in nanoscale optoelectronic applications.

N-trimethylsilyl-7-azanorbornadiene (TMSAN) is synthesized and chemisorbed on the silicon(100)-2 × 1 surface under ultra-high vacuum conditions and the resulting structure is determined using scanning tunnelling microscopy (STM). The binding exhibits poor short-range order, similar to that for norbornadiene. Patterning of the adsorbate is demonstrated following STM electron-stimulated depassivation of a silicon(100)-2 × 1-H surface, indicating that the placement of TMSAN on the surface can be controlled. Density-functional theory (DFT) calculations verify the close analogy between the binding of TMSAN and its much studied parent compound, norbornadiene. This analogue is novel, however, in that it can provide anchor points for construction at the molecular level above the silicon surface. How such construction could proceed is controlled by the topology of the nitrogen atom and the torsional potential for rotation about the N–Si bond. While these key features are not readily apparent from the STM results, DFT predicts that TMSAN above silicon(100) adopts a structure containing an azimuthal rotor: the nitrogen atom is in a planar configuration so that the N–Si bond is normal to the silicon surface, there being also nearly free rotation about the N–Si bond. Further, variants of TMSAN are considered in which a double-well potential for nitrogen inversion is predicted, suggesting that chemical control can be established over the architectural function of this class of compounds.

A new approach to fabricating hemispherical cavity arrays on silicon (Si) substrate using laser-assisted nanoimprinting of self-assembled particles is presented. A monolayer of silica particles, with different diameters of 0.30 and 0.97 µm, was deposited on a Si substrate by self-assembly. A quartz plate was tightly placed on the sample surface to firmly sandwich the self-assembled nanoparticle monolayer. The silica particles were imprinted into Si substrates after laser irradiation (KrF excimer laser, λ = 248 nm) on the quartz/nanoparticle/Si structure with a single pulse. Ultrasonic cleaning and hydrofluoric acid (HF) solution were used to remove the silica particles in the sample surface. Hemispherical cavities were formed on the substrate surface. The influence of laser fluence and particle size on the structuring of the surface has been investigated. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were performed to observe the dimensions of the cavities. One-dimensional thermal calculation was employed to calculate the thermal effects in this process.

The effect of organic additives, including citric acid, PEG (2000) and PEG (200), on the yield and quality of single-wall carbon nanotubes (SWNTs) synthesized by a Fe–Mo catalyst dispersed on an alumina matrix prepared by the sol–gel process in assisted chemical vapour deposition (CVD) has been investigated by transmission electron microscopy (TEM), thermo-gravimetric analysis (TGA) and Raman spectroscopy. Different morphologies of catalyst including big flakes, spherical particles and porous supporting materials were obtained using citric acid, PEG (2000) and PEG (200) as dispersant, respectively. SWNT yields of 10 wt%, 16 wt% and 33 wt% were obtained using citric acid, PEG (2000) and PEG (200) as the dispersants, respectively, which implies that the PEG (200) is the most effective at improving the yield of SWNTs due to the effect of additives on the specific surface area of the catalyst. The as-grown SWNTs are mostly in large bundles with diameters of 0.5–2 nm, but in some cases, isolated tubes with much larger diameters can also be found. Finally a preliminary explanation for the increased SWNT yield using PEG (200) is presented.

We report the modelling and characterization of 2D photonic crystals that we have successfully implemented using a well adapted technical process: focused ion beam etching of multilayer membranes. Devices have been dimensioned to operate as polarizing beam splitters at telecommunication wavelengths. Modelling the experimental observations has allowed us to characterize FIB etching performances and to propose further technological improvements.

Dynamic atomic force microscopy (AFM) is a standard technique for imaging and the analysis of surfaces at the nanometre scale. In order to estimate material properties from the microscope data it is important to understand the nonlinear dynamics in the tip–sample interaction. Here, the system response of a tapping-mode atomic force microscope is investigated with numerical simulations. In the numerical model, the AFM cantilever is treated as a distributed parameter system that is capable of higher eigenmode excitation. With this multiple-degree-of-freedom (MDOF) approach the generation of higher harmonics as well as the generation of subharmonics is analysed. Under typical imaging conditions higher harmonics are generated whereas a closer approach to the specimen surface can lead to a complicated dynamics.

Gold-nanoparticle-coated K₂SO₄ microcrystals were prepared by a recently reported self-assembly process and their organization onto micron-patterned silicon substrates was explored. Electron beam lithography, anisotropic chemical etching and high temperature thermal oxidation were used to fabricate oxidized or non-oxidized V-grooves on a silicon substrate and suspensions of gold-coated microcrystals were spin-coated over the surface. The nanoparticle-coated microcrystals were found to spontaneously deposit within the grooves and to form remarkably coherent structures made up of lines of microcrystals aligned relative to each other. Controls showed that this phenomenon was not observed with bare K₂SO₄ crystals suggesting a catalytic role for the gold nanoparticles in the organization process.

Gold nanoparticles immobilized on a silicon wafer were used to semi-quantitatively study the Raman enhancement from the individual particles and the interparticle coupling, with p-aminothiophenol (p-ATP) molecules as Raman probes. At low coverage of gold nanoparticles on the surface, the gross intensity of the p-ATP Raman peaks was found to be proportional to the number of particles per unit area, suggesting that the spectra could be a sum of contributions from the isolated particles while the interparticle coupling could be neglected. However, a sharp nonlinear increase in the intensity of the p-ATP Raman peaks versus the number of particles per unit area was observed at higher coverages, indicating that the contribution from the interparticle coupling became remarkable at reduced interparticle distances. By comparing the apparent enhancement factors of the isolated particles with that of particles at saturated surface coverage, a 10–20 times extra-enhancement can be derived which could be attributed to the interparticle electromagnetic coupling. The critical centre-to-centre interparticle distance for significant electromagnetic coupling is found to be about twice the particle diameter. Further efforts will be made in quantitatively correlating the present results with the possible alterations in plasmon resonance of the assembled gold nanoparticles by the substrate and the interparticle coupling.

The carrier gas flow rate, a key parameter for controlling the morphology and size in the synthesis of nanomaterials by thermal evaporation—vapour phase transport—condensation processes, can significantly affect the shape and size of the products. Besides nanoscale ZnO dendrites and wires, a uniform tetrapod-shaped ZnO nanostructure has also been successfully synthesized by using a controlled carrier gas flow rate during synthesis. The ZnO nanotetrapod was formed via a vapour–solid process. The special structural character of the nanotetrapods may have interesting physical properties and potential applications in semiconductor electronic devices.

Nanostructures of cubic aluminium nitride were synthesized by DC arc-plasma-induced melting of aluminium in a nitrogen–argon ambient. The material flux ejected from the molten aluminium surface was found to react with nitrogen under highly non-equilibrium conditions and subsequently condense on a water-cooled surface to yield a mixture of nanowires and nanoparticles of crystalline cubic aluminium nitride. Both x-ray diffraction and electron diffraction measurements revealed that the as-synthesized nitrides adopted the cubic phase. Fourier transform infrared spectroscopy was used to understand the bonding configuration. Microstructural features of the synthesized material were best studied by transmission electron microscopy. From these analyses cubic aluminium nitride was found to be the dominating phase for both nanowires and nanoparticles synthesized at low currents. The typical particle size distribution was found to range over 15–80 nm, whereas the wires varied from 30 to 100 nm in diameter and 500 to 700 nm in length, depending upon the process parameters such as arc current and the nitrogen pressure. The reaction products inside the plasma zone were also obtained theoretically by minimization of free energy and the favourable zone temperature necessary for the formation of aluminium nitride was found to be  K. Results are discussed in view of the highly non-equilibrium conditions that prevail during the arc-plasma synthesis.

In this work palladium nanowires have been synthesized by a template nanomanufacturing technique and their electrical properties have been studied. Freshly cleaved highly oriented pyrolytic graphite (HOPG) was exposed to PdCl₂ solution and cyclic voltametry was used to obtain the deposition of the nanowires on the 'V' shaped grooves of HOPG. The morphology of the nanowires was analysed using an atomic force microscope (AFM) in non-contact mode and the diameter of the observed nanowires was measured to be approximately 250 nm. Scanning electron microscope (SEM) images revealed that the nanowires fabricated by this procedure were parallel and continuous. The deposited nanowires were transferred on a polystyrene film. The microelectrodes required to study the electrical properties have been patterned by silver evaporation and by shadow masking using a 60 µm tungsten wire. The electrical resistance measurements have shown that the array of nanowires is conducting and has resistance of the order of kilo-ohms.

Carbon nanotubes change their electronic properties when subjected to strains. In this study, the strain sensing characteristic of carbon nanotubes is used to develop a carbon nanotube film sensor that can be used for strain sensing on the macro scale. The carbon nanotube film is isotropic due to randomly oriented bundles of single-wall carbon nanotubes (SWCNTs). Using experimental results it is shown that there is a nearly linear change in voltage across the film when it is subjected to tensile and compressive stresses. The change in voltage is measured by a movable four-point probe in contact with the film. Multidirectional and multiple location strains can be measured by the isotropic carbon nanotube film.

Bionanotechnology can be viewed as the integration of tools and concepts in nanotechnology with the attributes of biomolecules. We report here on an atomic force microscopy–immunosensor assay (AFMIA) that couples AFM with solid phase affinity capture of biological entities for the rapid detection and identification of group B coxsackievirus particles. Virus identification is based on type-specific immunocapture and the morphological properties of the captured viruses as obtained by the AFM. Representatives of the six group B coxsackieviruses have been specifically captured from 1 µl volumes of clarified cell lysates, body fluids and environmental samples. Concentration and kinetic profiles for capture indicate that detection is possible at 10³ TCID₅₀ µl⁻¹ and the dynamic range of the assay spans three logs. The results demonstrate that the melding of a nanotechnological tool (AFM) with biotechnology (solid phase immunocapture of virus particles) can create a clinically relevant platform, useful for the detection and identification of enterovirus particles in a variety of samples.

Ablation plumes caused by short-pulse laser irradiation provide conditions which are well suited to the formation of nanoclusters. The high saturation ratios and presence of ionization lead to extraordinarily high nucleation rates and small critical radii. We have explored the homogeneous nucleation and heterogeneous growth of condensates from Si targets expanding into a low-pressure He ambient using a Nd:YAG laser with a pulse length of 8 ns, wavelength of 532 nm and intensities in the range of 5 × 10⁷–5 × 10⁹ W cm⁻². Clusters in the range of 5–50 nm have been produced. In the highly dynamic, non-linear regime of short-pulse laser–matter interactions, plume evolution and condensation processes are strongly coupled and difficult to predict accurately from modelling alone. Both numerical predictions and experimental results were used to quantify the competing effects of ionization and supersaturation. The results suggest a dominant influence of ionization for nearly all intensities above the ablation threshold.

ZnO nanowires were grown in gram quantities on graphite flakes (as collector) using the vapour transport and condensation approach. The yield, defined as the weight ratio of ZnO nanowires to the original graphite flakes, has been studied thoroughly by tuning the various growth parameters such as pressure and temperature inside the tube furnace, the amount of graphite powder in the original source, the source to collector ratio, etc. A yield as high as 200% has been achieved, equivalent to a 40% conversion of the ZnO powder in the original source. A study comparing the photoluminescence spectra of the ZnO nanowires grown on both graphite flakes and substrates with commercially available ZnO powder has been carried out.