Table of contents

We have investigated the changes in the morphology and microstructure of carbon nanotubes (CNTs) brought about by acetylene in the buffer gas of helium in arc discharge. Observations using scanning electron microscopy and transmission electron microscopy indicate that, with the introduction of acetylene, on the one hand, the diameters of spots in the central pattern region decrease markedly and CNTs are embellished with nanoparticles on the top surface of cathode deposit; and, on the other hand, the outer and inner diameters of CNTs decrease evidently. These results indicate that the outer diameter and innermost empty space of the nanotubes are related to growth conditions such as the density of carbon species and temperature in the growth region. This suggests that the outer and inner diameters of CNTs are adjustable by controlling the growth conditions in the growth region.

Nanomedicine in a broad sense is the application of nano-scale technologies to the practice of medicine. The creation of nanodevices such as nanobots capable of performing therapeutic functions in vivo is a destination within the emerging field of nanomedicine. On the journey to that destination, significant technological advances across multiple scientific disciplines continue to be proposed, validated and commercialized. Advances in delivering therapy, miniaturization of analytical tools, improved computational and memory capabilities and developments in remote communications will be integrated allowing for the development of such nanobots. Nanomedicine is both a destination and a journey. The journey will cross new frontiers, uncover new knowledge and bring new horizons to the understanding and practice of medicine.

The effects of bias voltage and cladding layer thickness on the surface photovoltage in the semiconductor/electrolyte system (PSE) of InAs/GaAs quantum dot (QD) structures grown by atmospheric-pressure metal organic vapour phase epitaxy have been investigated. It was shown that the effect of compensation of the normal component of the photovoltage by the lateral component in the structures with an asymmetric point ohmic contact may help to reveal details of the energy spectrum of the QDs. Using this effect, it was shown that emission of electrons and holes from the QDs to the barrier at strong electric field occurs directly from the excited levels, without relaxation to the ground state. The observed broadening of the optical transition lines in QDs in a strong electric field was related to the lifetime of the carriers in the excited levels in QDs, according to the uncertainty relation. The lifetime of the carriers in QDs was limited by the carrier emission rate from QDs to the matrix through a triangle barrier at strong electric field. The possibility of in situ investigation of the processes of formation and passivation of the surface traps resulting from electrochemical reactions in the electrolytic cell by PSE spectroscopy has been demonstrated.

The hardness and Young's modulus of barrier-type, amorphous anodic oxides have been determined by nanoindentation. The procedure used shallow indents, of 55 nm depth, with alumina, tantala and alumina/tantala `mixed oxide' films of about 500 nm thickness. The results revealed respective hardnesses of approximately 7.0, 5.3 and 6.5 GPa, and respective Young's moduli of approximately 122, 140 and 130 GPa. Thus, the hardness and Young's modulus followed opposite trends, with alumina having the highest hardness and lowest modulus, and the `mixed oxide' having intermediate properties. The hardness and Young's modulus of amorphous alumina are factors of about 3.1-3.7 times lower than those of crystalline aluminas.

Piezoforce microscopy (PFM) has been used to determine the domain structure of lead zirconate titanate (PZT) (30/70) on an indium tin oxide (ITO)/glass substrate with a TiO₂ boundary layer. The PZT nucleates into the perovskite form in a random crystallographic manner, which leads to a random domain structure in the final film. Using PFM it has been possible to visualize the domain structure of the PZT and determine that the domain structure has features as fine as 8 nm herringbone patterns. The possible impact of these structures for future devices utilizing nanoscale features of PZT and especially FeRAM developments is highlighted.

A new method of protein crystallization based on a homologous Langmuir-Schaefer (LS) protein thin-film template proves to successfully stimulate crystal nucleation and growth of the four different proteins being studied, under different crystallization conditions including those failing to lead to crystal formation in solution. Protein microcrystals were obtained by a modified vapour diffusion hanging drop method. This report is focused on recombinant bovine cytochrome P-450scc crystallization and subsequent crystal characterization by atomic force microscopy in an appropriate chamber. The results are discussed in terms of a possible transition in protein crystallization from art to science by means of LS thin-film nanotechnology.

Thin films consisting of layers of Ag nanocrystals (NCs) embedded in amorphous Al₂O₃ were grown by pulsed laser deposition. High-resolution electron microscopy was used to characterize the structure of the films. The growth kinetics of the NCs were studied by varying the Ag content of the films between 0.8 and 12.4×10¹⁵ atoms cm^-2 which produced NCs with average diameters of between 1.1 and 9.6 nm. At low Ag content the NCs have a spherical in-plane shape with a narrow size distribution but they become more elongated with a broader size distribution as the Ag content increases due to coarsening and coalescence of the NCs. Underneath each layer of NCs there is a continuous layer of what is believed to be Ag implanted into the amorphous Al₂O₃ due to the high kinetic energy, of the order of 100 eV, of the Ag species produced during laser ablation.

We discuss the optical aspects of nanofocusing recording probes. In this paper we also consider the aberration conditions for a higher-density disk memory. Optical modules, comprising a micro-lens with a nano-probe, have been designed. The obtained design configurations are shown using ray-trace modelling and wave-optics analysis. The optical recording head discussed in this paper is a module of convex micro-lenses aligned with a pyramidal prism probe array which is under fabrication on both sides of a thin GaP substrate using the same production method. We present the technological and residual aberrations with computed tolerances. The results obtained in this research are intended for near-field optical heads. These nanofocusing data are quite similar to the published values of the previous optical memory system.

The structures formed by atomic force microscopic tip scanning on a 133 nm thick poly(tert-butyl acrylate) (PtBuA) film were examined at temperatures ranging from room temperature to 58 °C with various scanning velocities from 1 to 20 µm s^-1. It was observed that bumps were created at low temperatures and high scanning velocities. As the temperature was increased and the scanning velocity was decreased, bundles were produced through aggregation of the bumps. The width of the bundles was about 100 nm. As the temperature was further increased to higher than the glassy-rubbery phase transition temperature, T_g~50 °C, of the PtBuA polymer, no bundle structures were formed at low scanning velocities. Our results clearly indicate that the formation of bumps and bundles occurs from the interplay of polymer peeling and relaxation. With polymer peeling taking place on soft polymer surfaces, slower relaxation favours the accumulation of polymer coil displacement and the formation of the bump and bundle structures, while fast relaxation results in the recovery of the polymer perturbation and no formation of surface structures.

Positive pressure infusion of Y₂O₃:Eu³⁺ particles 8-12 nm in size was carried out in 75 cm³ samples of 0.6% agarose gels that have internal mass transport properties similar to those of in vivo mammalian brain tissue. The purpose of the study was to investigate the nature of the porous-like structure of the gels at distance scales of the order of ≈10 nm. Fluorescence of the particles under UV excitation was used to observe their time-dependent distribution pattern, with the result that the convection-enhanced flow provided by the infusion process caused the particles to permeate the gel's interstitial structure, thus revealing a porosity scale size commensurate with that of the particle size.

We present transconductance measurements on gated V-groove GaAs/AlGaAs quantum wire heterostructures grown by metal-organic chemical vapour deposition. The results show anomalously large negative magnetoresistance for a magnetic field perpendicular to the current, and oscillations in conductance with the field oriented along the width of the wire. Clear steps in conductance versus gate voltage are also observed and these are consistent with the charging of a nearby `droplet' with each step corresponding to a change in the occupation of a single electron.

We have realized highly doped suspended silicon nanowires with lateral dimensions down to 20 nm for studying electron transport and dissipation phenomena in these wires. Random dopant fluctuations lead to the formation of multiple tunnel junctions, showing Coulomb blockade phenomena at low drain-source bias. In the finite-bias regime we observe relaxation of hot electrons via phonons. Melting of the wires then occurs at high bias values at an extremely large current density of the order of 10⁶ A cm^-2.

A novel chemical functionalization method for multiwalled carbon nanotubes (MWNTs), through an oxidation and silanization process, is presented. The method allows us to have different organo-functional groups attached to the MWNTs, which improves their chemical compatibility with specific polymers for producing new nanotube-based composites. The corresponding moieties were characterized by infrared, Raman and energy dispersion spectroscopies.

The limits of pushing storage density to the atomic scale are explored with a memory that stores a bit by the presence or absence of one silicon atom. These atoms are positioned at lattice sites along self-assembled tracks with a pitch of five atom rows. The memory can be initialized and reformatted by controlled deposition of silicon. The writing process involves the transfer of Si atoms to the tip of a scanning tunnelling microscope. The constraints on speed and reliability are compared with data storage in magnetic hard disks and DNA.

We have investigated several ultra-thin copper nanobridges between supporting layers using a classical molecular dynamics simulation and a many-body potential function of the second-moment approximation of the tight-binding scheme. When the nanobridge has a well-defined structure, the resonance frequency of the nanobridge is defined and the resonance phenomenon is in common with classical oscillation systems. The caloric curve and the diffusivity of the nanobridge have shown information on the melting and the breaking of the nanobridge. The supporting layers of the nanobridge play an important role in the dynamics and thermal properties of nanobridges.

The sensitivity of flexural vibration modes for the rectangular cantilever of an atomic force microscope (AFM) has been derived by taking into account the cantilever slope, and a closed-form expression is obtained. As expected, the results show that each mode has a different sensitivity and that the first mode is the most sensitive mode for the AFM cantilever. The sensitivity of flexural modes is greater for a lower normal contact stiffness between the material surface and the cantilever tip. The high-order flexural modes are more sensitive than the low-order modes as the contact stiffness increases. The sensitivities of the first four vibration modes for a sloped cantilever have been compared to those of a level cantilever. The effects of various cantilever slopes on the sensitivity have also been compared. Increasing the cantilever slope apparently decreases the sensitivity as the contact stiffness becomes small. As the contact stiffness becomes large, the increasing tip length increases the sensitivity of the vibration modes.

Stress analysis facilitates the optimal design of micro/nanoelectromechanical system (MEMS/NEMS) devices for reliability. A finite element method was used to study nanostructures with different geometries and materials. By comparing the load-displacement responses obtained from the modelling and the actual experiments, it was concluded that an elastic model can be used. The numerical model was used to analyse the effect of surface roughness and scratches on stresses. Bending stresses as a function of beam geometry and load location, which is useful for beam design, were obtained. Beams with surface roughness in the form of semicircular and grooved asperities and scratches with various aspect ratios were modelled with the load present at the centre of the beam as well as at different offsets. Asperity and scratch locations were also varied so as to ascertain their effect on bending stresses. It was observed that the asperities and scratches increase the bending tensile stresses which could lead to failure of MEMS/NEMS devices. The loading was varied on the beams and the material was assumed to be pure elastic, elastic-plastic and elastic-perfectly plastic to observe the variations in the bending stresses and displacements. The results of the analysis can be useful to designers to develop the most suitable geometry for nanostructures.

We have investigated the structure and properties of copper nanorods composed of a central atomic strand and polygonal tubes, using a classical molecular dynamics simulation with a well-fitted many-body potential function of the second-moment approximation of the tight-binding scheme. The ultra-thin multi-shell nanorods possessed a hexagonal surface lattice and had needle-like edges. The structure of pentagonal multi-shell nanorods was that of a square surface lattice for diameters of several nanometres. The properties were close to those of a face-centred-cubic lattice, as the sub-units were composed of both triangular- and quadrangular-pyramid shapes oriented along the ⟨100⟩ direction. Our investigation showed the relationship between ultra-thin multi-shell nanorods and a tetrahedron, and revealed that pentagonal copper nanorods can be classified by three types of needle-like nanorods: (i) icosahedral, (ii) decahedral and (iii) decagonal discus.

We have measured the dielectric response of monolayer films of surface mounted chloromethyl-and dichloromethylsilyl dipolar rotors on fused silica at frequencies in the 1 kHz range and temperatures from 4 to 300 K. The torsional potentials, calculated from molecular mechanics, show an asymmetrical three-fold barrier to rotation with a barrier height sufficient to hinder motion of the rotor at experimental temperatures. A broad distribution of barrier heights is observed experimentally, consistent with calculated results showing that the intrinsic barrier of the rotor is modified by interactions with the underlying substrate. For a series of samples with differing concentrations of the rotor, the observed signal strength varies in proportion to the rotor coverage measured by Auger spectroscopy; however, the absolute strength of the signal is about three times larger than expected.

We describe the design and production of a tobacco mosiac virus mutant that provides for specific and stoichiometric attachment of a wide variety of ligand-linker groups. As a result, specific ligands could be chemoselectively linked to the virion to produce highly diverse nanomolecular materials. These included semi-crystalline protein arrays and metallic 'nanopipes', as well as nanomolecular 'light sticks'. The method described is facile and inexpensive with potential uses in such diverse areas as nanofabrication and biomolecular structure determination.

Self-assembled electronic devices, such as quantum dots or switchable molecules, need self-assembled nanowires as connections. We explore the growth of Gd disilicide nanowires at step arrays on Si(111). Atomically smooth wires with large aspect ratios are formed at low coverage and high growth rate (length ≥ 1 μ m, width 10 nm, height 0.6 nm). They grow parallel to the steps in the [1 0] direction, which is consistent with a lattice match of 0.8% with the a-axis of the hexagonal silicide, together with a large mismatch in all other directions. This mechanism is similar to that observed previously on Si(100). In contrast to Si(100), the wires are always attached to step edges on Si(111) and can thus be grown selectively on regular step arrays.