Table of contents

The formation of nanometre-scale silicon dots with a germanium core on an ultrathin SiO₂ layer has been studied by controlling the early stages of low-pressure chemical vapour deposition (LPCVD) alternately using pure monosilane and 5% germane diluted with helium. From atomic force microscope observations and x-ray photoelectron spectroscopy measurements, the selective growth of Ge on pregrown Si dots and subsequent complete coverage with a Si cap have been confirmed. Cross-sectional transmission electron microscope images have shown the formation of isolated spherical nanocrystallites with Ge cores in contrast with hemispherical pregrown Si dots, implying a high structural strain at the interface between cladding Si and the Ge core. For multiply stacked structures of the dots with a Ge core, Raman-scattering spectra indicate that compositional mixing occurs partly at the Si/Ge-core interface during LPCVD.

Examination was made of the optimum performance of thermal ionization, field ionization and electron ionization sources, using permalloy (Ni₈₁Fe₁₉) and aluminium as source materials. Discussion is made of the possible use of these to give direct deposition sources, for low-cost nanoscale device production. Fabrication of field emitter tips using focused ion beam milling was used to try to enhance the ion emission current of field ionization sources. Electron ionization produced the largest ion current, but field ionization gave enhanced stability.

A sol–gel process and a nanochannel aluminium template were employed to fabricate an orderly array of ZnO nanowires. The ZnO nanowires, with a hexagonal structure, were identified by means of x-ray diffraction and selected-area electron diffraction. The arrays of ZnO nanowires were characterized by scanning electron microscopy. Transmission electron microscopy (TEM) shows that the diameters of the ZnO nanowires are very uniform, at about 60 nm. Furthermore, high-resolution TEM provides lattice images of {100}, {002} and {101} planes in the nanowires, indicating that the nanowires are well crystallized.

Lateral force microscopy appears as an attractive field for its applications as well as for the study of the physical nature of tip–sample interaction. We present a dynamic-mode lateral force microscope based on an amplitude-controlled oscillator whose frequency-selective element is a modified quartz tuning fork. The instrument is very compact and cheap and has high vertical sensitivity, while lateral resolution is limited by the oscillation amplitude of the prongs of the tuning fork. Experimental data on the oscillator itself are reported. Friction force operation has been demonstrated by use of approaching curves and open-loop imaging of the metal foil peeled off a compact disc.

We develop a simple to implement, inherently parallel and high throughput technique for the fabrication of large areas of patterned aligned multi-wall carbon nanotube (CNT) arrays deposited on silicon or quartz substrate. This technique makes use of a parallel or converging laser beam from a high power pulsed laser for the destruction of aligned CNTs with a copper grid as lithography mask to define patterned aligned CNT arrays. The wavelength of the laser beam used is 248 nm and the average energy per pulse is 500 mJ. Using this technique, an extensive area of patterned CNT arrays as large as 3 × 5 mm² can be fabricated without the use of any pre-patterned substrate. In addition, we were able to control the size of the features created by (1) using different copper grids and (2) using a converging beam. Exposing the sample to different numbers of laser pulses allows us to generate families of CNTs with different uniform lengths. Furthermore, using two overlapping grids as a lithography mask, we managed to create a regular array of features with sizes as small as 2.5 μm.

Size-dependent solution phase diagrams for binary systems are established based on models of size-dependent melting temperature and melting enthalpy of components and a newly developed model for the size-dependent interaction energy. The results show that as the size of the components decreases, the temperatures of solidus and liquidus curves drop and the two-phase zone becomes small. As the size of the components decreases to a critical size, the two-phase zone deteriorates into a curve where the liquid phase and the solid phase are indistinguishable in structure and thus the phase numbers transform from two to one.

PbS nanocrystals were prepared using water/C₁₂E₉/cyclohexane microemulsions as nanoreactors. The sizes and morphologies of the cubic PbS nanocrystals can be modified by controlling the concentration of ions, the volume ratio of water to surfactant and the reaction temperature. The shuttle-like nanoparticles consisting of PbS nanocrystals were obtained by reaction at the temperature of 150^°C.

We describe the self-assembly in solution of a nanoscale architecture from DNA and gold nanoparticles. Also described is the characterization of this nanoscale architecture by transmission electron microscopy, atomic force microscopy and near-field scanning optical microscopy. A key finding is that it is possible to image both the DNA and nanoparticle components of the nanoscale architecture.

Metal–oxide–semiconductor-capacitor arrays are fabricated on both P and N type silicon wafers using layer-by-layer (LbL) self-assembled insulating layers. The vertical dimension of the self-assembled thin film can be precisely controlled as well as the molecular order. Unlike the conventional process, the LbL self-assembly allows one to obtain the thin films for a semiconductor device with a dramatically lower temperature, lower cost and shorter processing time. The deposited thin film is stable and can grow on any substrate other than silicon. The conventional lithographic technique is employed to pattern the self-assembled thin films, resulting in an extremely high reproducibility. This enables the possibility of industrial applications to fabricate devices with this simplified and versatile technique. A CCD camera was used to produce the image of the pattern, and a white light interferometric microscope was used to measure the dimension and surface roughness of the produced device. The quartz crystal microbalance served to monitor the growth of the self-assembled thin films.

In this work, NiO thin film was prepared by the sol–gel technique and analysed by thermogravimetry, x-ray diffractometry and x-ray photoelectron spectroscopy. The electrochromic characteristics were studied by ultraviolet spectroscopy. NiO thin film shows electrochromic characteristics. Its colour changes from transparent to brown when a voltage is applied. The transmittance of the film can shift from 90 to 40%. Deterioration of the film caused by colouring and discolouring was not observed for up to 100 cycles.

Molecular electronics offer an alternative pathway to construct nanoscale circuits in which the critical dimension is naturally associated with molecular sizes. We describe the fabrication and testing of nanoscale molecular-electronic circuits that comprise a molecular monolayer of [2]rotaxanes sandwiched between metal nanowires to form an 8 × 8 crossbar within a 1 µm² area. The resistance at each cross point of the crossbar can be switched reversibly. By using each cross point as an active memory cell, crossbar circuits were operated as rewritable, nonvolatile memory with a density of 6.4 Gbits cm⁻². By setting the resistances at specific cross points, two 4 × 4 subarrays of the crossbar were configured to be a nanoscale demultiplexer and multiplexer that were used to read memory bits in a third subarray.

Opinions differ widely as to the type of architecture most suitable for achieving the tremendous performance gains expected with computers built by nanotechnology. In this context little research effort has gone into asynchronous cellular arrays, an architecture that is promising for nanocomputers due to (1) its regular structure of locally interconnected cells, and (2) its asynchronous mode of timing. The first facilitates bottom-up manufacturing techniques like directed self-assembly. The second allows the cells' operations to be timed randomly and independently of each other, mitigating the problems accompanying a central clock, like high power consumption and heat dissipation. The advantages of asynchronous timing notwithstanding, it makes computation less straightforward. Attempts to compute on asynchronous cellular arrays have therefore focused on simulating synchronous operation on them, at the price of more complex cells. Here we advance a more effective approach based on the configuration on an asynchronous cellular array of delay-insensitive circuits, a type of asynchronous circuit that is robust to arbitrary delays in signals. Our results may be a step towards future nanocomputers with a huge number of autonomously operating cells organized in homogeneous arrays that can be programmed by configuring them as delay-insensitive circuits.