Table of contents

Embedded carbon nanotubes delay polymer film cracking via tube stretching and pulling out. Tube breaking is not observed in our experiments, which contradicts a previous report.

Aluminium nitride (AlN) nanopowder was successfully synthesized from transition alumina nanopowder via a new single-step nitridation process. A gas mixture of NH₃–C₃H₈ was employed as a reduction–nitridation agent, which enables direct nitridation of transition alumina at processing temperatures of 1200–1400 ^°C. AlN powder prepared under typical reaction conditions was found to be phase-pure and nanocrystalline, with a specific surface area of 36.4 m² g⁻¹ and a mean particle size around 50 nm. The AlN nanopowders produced could be densified to a pore-free state in conventional processing, without resort to the use of sintering aids. SEM observation revealed markedly small grain sizes in the sintered specimens compared with the commonly processed AlN.

Arrays of epitaxial Fe/MgO/Fe planar tunnel junction elements have been fabricated with square or rectangular shape, micrometric sizes and nanometric interdistances in order to study the role of element shape geometry in the magnetic behaviour of these small structures. The elements are patterned from a continuous fully epitaxial trilayer by electron beam lithography. Magneto-optical measurements show that the patterning drastically modifies the magnetization reversal behaviour which can be tailored with the particular shape dimensions of the junction elements. In square elements, hysteresis loops with two stages and a remanence M_r ∼ 0 are observed, revealing the antiparallel alignment due to top–bottom magnetostatic interaction. On the other hand, rectangular elements of a similar area present M_r ∼ 1 and a two step reversal process when the field sign is changed, so that the magnetic state can be switched from parallel to antiparallel layer magnetization just by applying a small magnetic field.

In this work, we have fabricated a triode field emitter using directly grown carbon nanotubes (CNTs) as an electron emission source. Vertically aligned CNTs have been grown in the centre of the gate hole, to the size of 1.5µm in diameter, using thermal chemical vapour deposition. A comparison of the field emission characteristics of two types of microgated nanotube emitter with and without a sidewall protector for the gate hole is made. A sidewall protector formed by the method of tilting the substrate can enhance the electrical characteristics by suppressing the problem of short circuits between the gate and the CNTs. The leakage current of an emitter with a sidewall protector is approximately sevenfold lower than that of an emitter without a sidewall protector at a gate voltage of 100 V.

The quantum transport properties of ultrathin silver nanowires are investigated. For a perfect crystalline nanowire with four atoms per unit cell, three conduction channels are found, corresponding to three s bands crossing the Fermi level. One conductance channel is disrupted by a single-atom defect, either adding or removing one atom. The quantum interference effect leads to oscillation of conductance versus the inter-defect distance. In the presence of a multiple-atom defect, one conduction channel remains robust at the Fermi level regardless the details of defect configuration. The histogram of conductance calculated for a finite nanowire (seven atoms per cross section) with a large number of random defect configurations agrees well with recent experiments.

We report on a method that allows direct, massively parallel nanopatterning of a silicon surface using ultraviolet (UV) lasers. Silica or polystyrene nanospheres with diameters of the order of the laser wavelength were deposited on the silicon surface. Spheres arranged themselves into hexagonally close-packed form due to capillary force. The nanosphere array was irradiated with 248 and 355 nm UV lasers. The silicon surface was locally melted due to enhancement of the optical field between the nanosphere and the substrate. Redistribution of molten material due to surface tension forces leads to the formation of a nanodent array. These nanodents vary their shape from bowl-like to 'sombrero-like' with the increase of laser energy as a result of competition between the thermocapillary force and the chemicapillary force.

In this paper the electrical properties of InAs/InP nanostructures (wires and dots) were investigated using Kelvin probe electrostatic force microscopy and conductive atomic force microscopy techniques. Surface potential measurements were strongly affected by the presence of the thin InAs film at the top surface of the undoped InP buffer layer. These results and the electrical images suggest the suppression of the surface depletion region due to electron accumulation in InAs wires and dots. I–V spectroscopy shows the formation of a Schottky-type junction between the metal-coated Si tip and the semiconductor surface exposed to air. Larger conductances and different threshold voltages for current onset for the two types of nanostructure analysed here can be related to the particular electronic structure of InAs wires and dots.

Quantum computers are machines that exploit the quantum mechanical properties of physical systems to realize an exponential speed-up in problem-solving capability compared with existing computers. Existing schemes for the realization of such machines occur in diverse areas such as atomic physics, nuclear magnetic resonance, superconductivity, quantum optics and solid state physics. We are concerned here with the experimental realization of various elements needed for quantum information processing using nuclear spin immersed in a confined electronic system in the quantum Hall regime. Some distinguishing characteristics of this approach include the application of the Overhauser effect for dynamic nuclear polarization at relatively high temperatures, spin measurement using relatively simple electrical detection techniques, spin control with microwave/radio frequency methods, the utilization of the electronic spin exciton as a possible mobile spin transfer mechanism for the eventual realization of a logic gate, and the application of semiconductor technology to device integration. Concepts involved in this approach are also illustrated with experimental results.

Adding to the efforts spent to establish localized electrochemical deposition (LECD) as a standard fabrication process; this paper presents an experimental investigation and theoretical modelling of shape formation of high aspect ratio columns and lines fabricated by LECD. The proposed model suggests that transport of depositing ions leading to deposit formation is mainly dominated by migration forces. The deposition model is verified by numerical simulation which utilizes electric field calculation by a boundary element method and a progressive boundary update approach to determine the evolution of deposition profiles. Simulation results are compared against images of copper columns obtained at different formation stages during the deposition process. Both results are in agreement, which demonstrates the potential and capabilities of the proposed model and simulation procedures as an analysis tool to aid in characterizing the deposition process and resulting structures, as well as the understanding of the dynamics and factors influencing object formation in LECD.

Nanofibres of TiO₂–SiO₂  (Ti:Si = 50: 50 mol%) with diameters of 50–400 nm were prepared by calcining electrospun nanofibres of polyvinyl acetate (PVac)/titania–silica composite as precursor. These PVac/titania–silica hybrid nanofibres were obtained from a homogenous solution of PVac with a sol–gel of titanium isopropoxide (TiP) and tetraethoxysilane by using the electrospinning technique. The nanofibres were characterized by scanning electron microscopy (SEM), wide-angle x-ray diffraction (WAXD), Fourier transform infrared (FTIR) spectroscopy and Brunauer–Emmett–Teller (BET) surface area. SEM, WAXD and FTIR results indicated that the morphology and crystalline phase of TiO₂–SiO₂ nanofibres were strongly influenced by the calcination temperature and the content of titania and silica in the nanofibres. Additionally, the BET results showed that the surface area of TiO₂–SiO₂ nanofibres was decreased with increasing calcination temperature and the content of titania and silica in nanofibres.

P-type transparent CuAlO₂ semiconductor films are made by the spin-on technique from nanocrystals. The nanocrystals are synthesized by a hydrothermal metathesis reaction. Scanning electron microscopy, x-ray diffraction and energy dispersive x-ray spectrometry suggest that the films contain nanocrystalline phases of CuAlO₂. Both the Hall technique and Seebeck measurements reveal that the film is p-type and a very high room-temperature conductivity of 2.4S cm⁻¹ is achieved. This success in fabricating a high-conductivity transparent CuAlO₂ film indicates that nanotechnology will be helpful in enhancing the conductivity of p-type transparent semiconductors. The Hall measurement of the film shows a sheet mobility of 3.6 cm² V⁻¹ S⁻¹ and a carrier concentration of 5.4 × 10¹⁸ cm⁻³. The optical band-gap of the film is estimated to be 3.75 eV and the activation energy for the positive hole is 0.14 eV.

Fe₃Al nanoparticles have been synthesized by the hydrogen plasma–metal reaction method. In order to study the oxidation behaviour of the intermetallic nanoparticles, changes in morphology, particle size and crystal structure during heat treatment in air were investigated by transmission electron microscopy and x-ray diffraction. The as-prepared nanoparticles were stable both in shape and structure at 473 K where the iron nanoparticles were known to be oxidized fully. The high oxidation resistance of intermetallic nanoparticles was attributed to the aluminum oxide layer. The oxidation of Fe₃Al nanoparticles proceeded slowly below 573 K and rapidly above this temperature. The oxides formed between 473 and 673 K were Al₂O₃ and a mixture of iron oxides (α-Fe₂O₃ and γ-Fe₂O₃) changing into single phase α-Fe₂O₃ at 873 K. The nanoparticles started to grow by coalescence at 573 K and the mean particle size was larger than 100 nm above 673 K.

Single-molecule manipulation provides a valuable tool for the characterization of biological processes on the molecular scale. The techniques are usually based on microscopical methods; typical examples are optical tweezers and scanning probe techniques. They need sophisticated equipment and usually handle only one molecule at a time. In contrast to these established serial manipulation methods, techniques for the parallel manipulation of individual molecules are still in development. Here we describe an approach to place single molecules at a defined position on a microstructured surface based on self-assembly steps. Using DNA molecules with lengths in the micrometre range on microstructured surfaces, the defined immobilization of one DNA molecule spanning the gap between microelectrodes is demonstrated by scanning force microscopy. In principle, the described self-aligning approach should also work in a parallel manner. It opens the way for access to the molecular world with high throughput and without the need for ultramicroscopical setups.

We demonstrate the integration of vertically aligned carbon nanofibre (VACNF) elements with the intracellular domains of viable cells for controlled biochemical manipulation. Deterministically synthesized VACNFs were modified with either adsorbed or covalently-linked plasmid DNA and were subsequently inserted into cells. Post insertion viability of the cells was demonstrated by continued proliferation of the interfaced cells and long-term (> 22 day) expression of the introduced plasmid. Adsorbed plasmids were typically desorbed in the intracellular domain and segregated to progeny cells. Covalently bound plasmids remained tethered to nanofibres and were expressed in interfaced cells but were not partitioned into progeny, and gene expression ceased when the nanofibre was no longer retained. This provides a method for achieving a genetic modification that is non-inheritable and whose extent in time can be directly and precisely controlled. These results demonstrate the potential of VACNF arrays as an intracellular interface for monitoring and controlling subcellular and molecular phenomena within viable cells for applications including biosensors, in vivo diagnostics, and in vivo logic devices.

Cytostructural features associated with the invasive characteristics of brain tumour cells have been inspected and measured with atomic force microscopy. In one case the invadopodia extended from a T98 human glioblastoma cell departed from a linear path by 1 mrad for each 240 nm of axial extension from the point where its curvature began. In another cell, diametrically opposed invadopodia were projected over the collagen substrate and were co-aligned to within < 175 mrad (10°) of a common axis. In the latter case, an estimate of the torque that would be needed to overcome the adhesion forces and rotate the cell via moments applied by the invadopodia led to a value of 7 nN µm. From measurements by others of the interactions between glioma cells and collagen, the implied adhesion force for this cell was ≈ 0.5 nN, which was consistent with still other values reported in the literature. The measured mean radius of the cell was roughly 15 µm. The implications of these results for understanding and slowing the invasion of tumour cells through the extracellular matrix of the brain are discussed.

Non-contact electrostatic force microscopy techniques were used to study the open-circuit photovoltage of purple membrane multilayers electrodeposited on indium tin oxide. A humidity-dependent photovoltage response under illumination by a 635 nm photodiode was observed. Peak photovoltages in excess of 2 V at ∼36 W m⁻² were obtained for ∼15% relative humidity.

We have used computer simulations to investigate the potential of triptycene-based rotors mounted on the Si(100)-2 × 1 surface. Two concepts are explored for attaching the triptycene to the Si surface: –COOH and –OH groups. We find the –COOH produces an axle with too many degrees of freedom, creating too flexible a coupling to the substrate. By contrast, the calculations suggest that the –OH coupling should provide a useful stiff axle.