Table of contents

Carbon nanotubes (CNTs) have been grown directly on metallic wires by a powerful but simple technique, which we call cold-plasma chemical vapour deposition. The growth occurs on an Fe catalyst supported by kanthal wires while heating under a hydrocarbon precursor gas and plasma created by a bias. A possible application for such nanotubes on metallic wires is in luminescent tubes. To realize such devices, it is important to grow the nanotubes with controlled density, length, and alignment. In the present investigation we have made a systematic scanning electron microscopy study of these nanotubes. The growth rate for the CNTs is found to be very high. Just a few seconds is sufficient for covering a large surface area. Increased growth time leads to enhanced site density of the nanotubes. The diameter of the nanotubes increases with the growth temperature. CNTs are not always straight; spiral behaviour is quite often observed. We observed, probably for the first time, increase in the spiral periodicity of the nanotubes with increasing temperature. On applying a high bias to the wire (creating plasma), the number of spiral structures was reduced; instead, mostly aligned and self-supporting nanotubes were formed, with lengths as high as 45 μm.

Statistical conductance properties of gold elongating nanowires at room temperature are studied experimentally. The measured conductance histogram, built with thousands of consecutive nanocontact breakage experiments, exhibits a rich structure of low-intensity peaks at high-conductance quanta values. Their position as a function of a peak index number suggests two markedly different regimes for electronic and atomic shell structures in these nanowires, as observed previously for alkali metal nanowires.

By using a semi-classical two-dimensional Monte Carlo simulation, simple devices (T-branch junctions (TBJs) and rectifying diodes) based on AlInAs/InGaAs ballistic channels are analysed. Initially, the model is validated by means of Hall-effect measurements of mobility and electron concentration in long (diffusive) channels. Then, quasi-ballistic transport at room temperature is confirmed in a 100 nm channel. Our simulations qualitatively reproduce the experimental results of electric potential measured in a TBJ appearing as a result of electron ballistic transport, and in close relation with the presence of space charge inside the structure. As examples of devices exploiting the ballistic transport of electrons, preliminary simulations of a multiplexor/demultiplexor and a rectifying diode are presented, demonstrating their capability for terahertz operation.

Research on DNA has been widely carried out as a promising material for nanoelectronics, medicine development and disease diagnosis, using experiment, simulation and theory. We have carried out molecular dynamics simulation coupled with the linear response theory, based on the time-correlation function of an observable, in order to extract the frequency-dependent electrical characteristics of DNA. We observe a dielectric relaxation at around 50 MHz in the case of octamers-DNA, which corresponds to a delta-relaxation. We also observe dielectric relaxation in the case of mixtures of DNA, water molecules and ions, given by the superposition of the individual dielectric relaxations of the DNA and the bulk-like water, at frequencies of about 50 MHz and 10 GHz, respectively.

Modified DNA species have attracted the interest of the scientific community in the last years in a search for an appropriate molecular wire for the incoming nanotechnology. M-DNA, a complex of DNA with divalent metallic ions, is one of the candidates for a molecular wire. In this paper we describe the procedure to fabricate M-DNA using NiCl₂ and CoCl₂, and a simple test to check the production of the modified biomolecule. We present atomic force microscope (AFM) images of nickel and cobalt M-DNA. Our results show that the DNA modified with these metal ions suffers a fivefold reduction in length and an increment of almost one order of magnitude in height as compared to the length and height of regular B-DNA. This type of condensation of the DNA is fully reversible upon the addition of EDTA. AFM images of reversed M-DNA show no differences from regular B-DNA. Two types of electrostatic experiment performed on this modified molecule show no evidence for metallic or semiconductor behaviour.

In this work we present two scanning force microscopy (SFM) techniques applied to the electrical characterization of V₂O₅ nanofibres with one end connected to a metallic electrode: first a non-contact imaging technique combined with the acquisition of current versus voltage curves in a selected spot, and second jumping mode SFM that allows simultaneous acquisition of topograhic images and current maps with nanometric resolution.

Both the conductivity (∼20 S cm⁻¹) and the contact resistance (∼ 62 MΩ) of the fibres are determined. A non-linear behaviour of the conductivity is observed for large applied electrical fields (E > 10⁵ V cm⁻¹) as found previously for V₂O₅ films.

We present a scheme for a molecular memory, which is based on the influence of the positions of chemical side-groups attached to aromatic molecules on the paths for electrons propagating through these molecules in the ballistic and tunnelling transport regimes. Using the elastic scattering quantum chemistry technique in a topological Hückel implementation, we show how it is possible to represent four different output states with a benzene molecule attached to one input and three output electrodes. To achieve this we choose single atomic orbitals as side-groups and by varying their number and positions the desired output pattern is met, at least in the ballistic regime. This case is also compared to the situation where only two electrodes are attached; the differences with respect to the tunnelling regime are analysed in detail. Since our scheme is based on path and therefore phase differences in electronic wave propagation, we also compare its properties with those of other interference-based concepts for information processing, such as quantum computing or photonics.

We present the application of scanning force microscopy using the jumping mode to investigate microtubules adsorbed to glass in air and in liquid. To fix the microtubules the glass surfaces were silanized with aminopropyl-triethoxy-silane. The observed structures ranged from disrupted microtubules in air to intact microtubules in liquid. Intact microtubules show heights between 20 and 24 nm confirming the diameter found in electron microscopy studies. The force applied by the tip was critical for the microtubule height, indicating deformation by the tip. Internal structure, corresponding to protofilaments, was found.

We report the development of an efficient and sophisticated procedure for calculating the first-principles electronic structure and current flow of a nanometre-scale system (e.g. nanowire) sandwiched by two truly semi-infinite bulks. The solution of the Kohn–Sham equation of this system is so constructed as to joint generalized Bloch functions inside the left and right bulks together by matching them across the interfacial region between the bulks. The formalism is described quite simply in the real-space finite-difference approach within the framework of the density functional theory, and thus the wavefunction-matching scheme is easily realized without any troublesome process. The efficiency and accuracy of the method are illustrated by evaluating the electric conductance of a single-row gold nanowire attached to the semi-infinite Au(100) electrodes.

We study the pumping of spin-polarized electrons in a double quantum dot system with up to two electrons per dot, via an applied AC field and a constant magnetic field. The behaviour of the current through the double-dot system is studied as a function of the AC field and coupling to the leads, using a Markov master equation approach for the time evolution of the reduced density matrix. For up to two electrons in the system, we find that the formation of a spin-triplet state blocks the current through the device, and analyse possible solutions. When we incorporate three-and four-particle states, with up to two opposite spin electrons per dot, we find a regime where the pumping of spin-polarized electrons is realized through double occupancy states in each dot. This property is robust against spin-relaxation and decoherence processes which are taken into account phenomenologically. Finally we study the effects of applying a pulsed AC field and the possibility of the resolution of Rabi oscillations.

Future quantum devices may exploit arrays of dopants positioned with nanoscale precision in an intrinsic semiconductor matrix. One proposal for the fabrication of such an array is by the implantation of single low-energy dopant ions into prefabricated cells within the device, the arrival of each dopant being detected electrically. With the aid of technology computer-aided design (TCAD) modelling, we outline an electrical registration process which makes use of appropriately biased electrodes incorporated within the device to detect the space charge induced within the near-intrinsic substrate by a single-ion implant.

A series of simulations aimed at optimizing the charge detection efficiency in such detectors are described, and found to be in good agreement with experimental measurements conducted to characterize fabricated test structures via high-energy He-ion implantation. We demonstrate this fabrication strategy to offer the potential of creating scalable arrangements of dopants for extended nanoscale device applications. Our interest in this scheme is the development of the Kane solid-state quantum computer (Kane B E 1998 Nature393 133), which exploits as qubits³¹P atoms embedded with nanoscale precision in an array, within a pure²⁸Si MOS architecture.

The Kane (Kane B E 1998 Nature393 133) solid-state quantum computer aims to exploit as qubits an array of³¹P nuclear spins embedded in a silicon matrix. A proposed scheme for readout of a qubit spin state relies on measurement of the associated spin state of its donor electron, by attempting to induce and detect, using a single-electron transistor (SET), spin-polarized motion of the electron to an adjacent donor site. The sensitivity required of a SET for detection of sub-surface electronic charge motion in a MOS architecture is examined by simulation of the capacitive coupling of the buried charge to the SET device. It is shown that the SET can support readout of the qubit electronic charge states within the appropriate electron spin relaxation time. This paper presents a novel application of Technology Computer Aided Design, which presents itself as a valuable tool for the design of nanoscale device architectures employing precision electrometry for readout of quantum logic states.

In the very active area of molecular electronics, individual molecules or self-assembled molecules have been shown to behave as microscopic switches in transistor and diode architectures. In particular, it has been demonstrated that molecular wires inserted into nanopores and positioned between two metallic electrodes can be used as active elements for the fabrication of resonant tunnelling diodes (RTDs), whose I/V characteristics reveal a negative differential resistance (NDR) behaviour (i.e. a negative slope in the I/V curve). In this paper, we describe at the quantum chemical level a possible mechanism, based on conformational effects, rationalizing the experimental observation of an NDR signal in phenylene ethynylene oligomers. We will demonstrate that the origin of the peak profile in the I/V curves can be described on a qualitative basis from the evolution of the one-electron structure of the wires upon application of a static electric field aligned along the molecular axis, which simulates the driving voltage applied between the two electrodes in the RTD devices.

We present a semiclassical kinetic theory for the electronic transport and noise properties of ballistic n⁺ – n– n⁺ semiconductor nanodiodes. The theory is based on an exact solution of the Vlasov–Langevin kinetic equation self-consistently coupled to the Poisson equation, and takes into account the Pauli exclusion principle. The current–voltage characteristics calculated from the present theory perfectly agree with existing theoretical predictions. Concerning the noise properties, the theory offers the possibility of computing the current noise under all current regimes, thus overcoming the inherent limitations of existing theories.

We describe two different approaches to efficiently analyse the optical properties of defect structures embedded in photonic crystals (PCs). The first one is based on an expansion of the electromagnetic field into optimally localized photonic Wannier functions and thus efficiently utilizes the information of the underlying PCs. The second is based on the recently developed multipole method and is specially suited to deal with finite-size structures. We demonstrate the efficiency of these approaches by considering several defect structures for TM-polarized radiation in two-dimensional PCs.

Multiwalled carbon nanotubes (MWNTs) were incorporated into SiO₂ matrices for the first time by means of partial matrix melting caused by a Nd:YAG laser. Due to the rapid very short heating cycle of the laser MWNTs were detected being well incorporated in the silica matrix although temperatures well above 1200^ºC are reached. It was found that mainly the ability of heat absorption and heat conduction of the MWNTs are responsible for the sample heating. The composites were characterized using scanning electron microscopy, scanning transmission electron microscopy and high resolution electron energy-loss spectroscopy.

We describe the fabrication and digital logic operation of superconducting nanotransistors. The nanotransistor is a superconducting weak-link device that has integrated hot-phonon injector heaters to control its switching critical current. The fabrication process utilizes a self-aligned method, where the heater acts as a mask for reactive ion etching to define the device pattern. This device is much simpler to fabricate than previously reported controllable superconducting transistors and the principle of operation makes it possible to use a single nanotransistor connected to a load resistor as a NOT logic gate, allowing lower power consumption and improved levels of integration.

We report on the fabrication and field emission of carbon nanotube lateral field emitters. Due to its high aspect ratio and mechanical strength, we use vertically aligned multi-wall carbon nanotubes prepared by plasma-enhanced chemical vapour deposition as cathodes, which makes the fabrication of cantilever type lateral field emitters possible. The emission characteristics show that the field emission initiates at 11–17 V. The device has high geometrical enhancement factors (9.3 × 10⁶ cm⁻¹) compared to standard Spindt tips, which may be due to increased field concentration at the nanotube tip and the close proximity of the anode (<1μm). The relative ease of fabrication compared to vertical field emitters and enhanced field emission characteristics observed makes the carbon nanotube lateral field emitter a good candidate for future integrated nano-electronic devices.

Nanocrystalline HITPERM alloys Fe_44.6Co_43.3X_7.4B_3.7Cu₁ (X = Nb, Zr, Hf) prepared by crystallization of amorphous precursors are studied by magnetization and electrical resistivity measurements for the first time. Structural and magnetic components of the electrical resistivity are separated. The electrical resistivity of the nanocrystalline α' (FeCo) phase calculated using the Maxwell–Garnett relation proves strong electron scattering on the grain boundaries. The temperature variation of the crystalline fraction during the first crystallization stage is calculated for the Hf based alloy.

A quantum partition noise with spectral density significantly smaller than the Schottky value 2qI (with q the elementary charge and I the mean current) is predicted to occur in nanoscale electron emitters under the action of strong applied electric fields. The noise suppression effect appears whenever the transmission probabilities for highly occupied states are not small with respect to 1. We show that in two limiting cases: the Fowler–Nordheim regime and the Richardson–Laue–Dushman regime of electron emission, the noise recovers the full Schottky noise without the suppression effect.

The ability to grow carbon nanotubes/nanofibres (CNs) with a high degree of uniformity is desirable in many applications. In this paper, the structural uniformity of CNs produced by plasma enhanced chemical vapour deposition is evaluated for field emission applications. When single isolated CNs were deposited using this technology, the structures exhibited remarkable uniformity in terms of diameter and height (standard deviations were 4.1 and 6.3% respectively of the average diameter and height). The lithographic conditions to achieve a high yield of single CNs are also discussed. Using the height and diameter uniformity statistics, we show that it is indeed possible to accurately predict the average field enhancement factor and the distribution of enhancement factors of the structures, which was confirmed by electrical emission measurements on individual CNs in an array.

In this paper we present some of the most important magnetic and transport properties of mixed-valence manganite nanoparticles. The samples were prepared by a sol–gel method, which allows us to control particle size and, in this way, to obtain new properties of the archetypal ferromagnetic- metallic compound La_2/3Ca_1/3MnO₃. Magnetic properties allow us to present a model for the nanoparticles based on an ideal inner core and an outer shell in which the magnetism is modified by oxygen non-stoichiometry, vacancies and stress. The experimental results obtained from the electrical transport properties, namely increasing intergranular magnetoresistance (MR) with reducing particle size, tuning of intrinsic colossal MR and low-temperature electrostatic blocking effects, seem to support the proposed model.

We investigated a focused ion beam nanofabrication technique as a high-resolution patterning method suitable for nanocontact imprinting. Different ion beam currents, milling times, and dwell times are exploited to optimize focused ion beam milling conditions. Single-pixel lines are milled on a silicon master and replicated on polydimethylsiloxane through replica moulding. The profile of the grooves (the depth-to-width aspect ratio) was found to be depth dependent regardless of the beam current and dwell time. The depth of the line cuts was strongly dependent upon beam current and dwell time at a given dose. This technique holds great promise for mass production of nanostructures due to its simplicity and high reproducibility.

Both von Neumann's NAND multiplexing, based on a massive duplication of imperfect devices and randomized imperfect interconnects, and reconfigurable architectures have been investigated to come up with solutions for integrations of highly unreliable nanometre-scale devices. In this paper, we review these two techniques, and present a defect- and fault-tolerant architecture in which von Neumann's NAND multiplexing is combined with a massively reconfigurable architecture. The system performance of this architecture is evaluated by studying its reliability, i.e. the probability of system survival. Our evaluation shows that the suggested architecture can tolerate a device error rate of up to 10⁻², with multiple redundant components; the structure is efficiently robust against both permanent and transient faults for an ultra-large integration of highly unreliable nanometre-scale devices.

Nanostructured Fe-based alloys have softer magnetic properties, such as larger saturation polarizations and magnetic permeabilities, smaller anisotropies and coercive fields and vanishing magnetostrictions, than their precursor alloys in the amorphous state. The softest magnetic properties are obtained for the smallest nanocrystalline grain sizes (between 10 and 20 nm), and these nanostructured materials are very suitable for use as high-frequency electronic components in magnetic devices or magnetic sensors based on the magnetoimpedance (MI) effect. In this work we study the correlation between the structural, electrical and magnetic properties together with the MI effect response in some heat-treated Finemet type and FeZrB ribbons. We show that the maximum MI ratio of around 130% and a sensitivity to the applied magnetic field of 0.07% (A m⁻¹)⁻¹ is obtained in the heat-treated samples that show an optimum nanocrystalline state and exhibit softer magnetic properties.

Magneto-optic diffraction by a periodic domain structure is reported. The periodic domain structure is generated in a flat ferromagnetic metal by coupling it magnetically to an array of magnetic elements. Both exchange and magnetostatic couplings are effective, creating a modulation of the magnetization, although the effect is somewhat larger for magnetostatic coupling, since it favours an antiparallel alignment of adjacent domains. Micromagnetic simulations agree qualitatively with the experimental findings.

The advantages/limitations obtained by working in dynamic scanning force microscopy (DSFM) at different levels of tip/sample interaction forces (from the net attractive to the hard repulsive regime) are experimentally shown by imaging monolayers containing novel fibre-like supramolecular nanostructures wrapped up in spiral-like domains. The structures have been obtained by using the Langmuir–Blodgett technique and transferring onto mica monolayers of quercetin-3-O-palmitate molecules mixed with a fraction of about 25% of dimyristoylphosphatidylcholine. The measurements in the attractive regime allowed us to reveal morphological features of the supramolecular structures that cannot be demonstrated by the conventional repulsive regime. In particular, by attractive dynamic scanning force microscopy (DSFMA) the height of the fibre-like structures was a factor of two to three higher and peculiar nano-ruptures along the wrapped fibres have been observed. The influence of the tip/sample contact interaction was investigated by recording images in hard tapping and successively imaging the same region in DSFMA as well as by comparing the images in DSFMA with those obtained in negative lift mode force modulation microscopy, phase imaging and friction force microscopy.

Ferroelectric random access memories are non-volatile, low voltage, high read/write speed devices which have been introduced into the market in recent years and which show the clear potential of future gigabit scale universal non-volatile memories. The ultimate limit of this concept will depend on the ferroelectric limit (synonymous superparaelectric limit), i.e. the size limit below which the ferroelectricity is quenched. While there are clear indications that 2D ferroelectric oxide films may sustain their ferroelectric polarization below 4 nm in thickness (Tybell T, Ahn C H and Triscone J M 1999 Appl. Phys. Lett.75 856), the limit will be quite different for isolated 3D nanostructures (nanograins, nanoclusters).

To investigate scaling effects of ferroelectric nanograins on Si wafers, we studied PbTiO₃ (PTO) and Pb(Zr_xTi_1−x)O₃ grown by a self-assembly chemical solution deposition method. Preparing highly diluted precursor solutions we achieved single separated ferroelectric grains with grain sizes ranging from 200 nm down to less than 20 nm.

For grains smaller than 20 nm, no piezoresponse was observed and we suppose this could be due to the transition from the ferroelectric to the paraelectric phase which has no spontaneous polarization. Recent calculations (Zhong W L, Wang Y G, Zhang P L and Qu B D 1994 Phys. Rev. B 50 698) and experiments (Jiang B, Peng J L, Zhong W L and Bursill L A 2000 J. Appl. Phys.87 3462) showed that the ferroelectricity of fine ferroelectric particles decrease with decreasing particle size. From these experiments the extrapolated critical size of PTO particles was found to be around 4.2–20 nm.

A new method of fabricating small metal–molecule–metal junctions is developed, approaching the single-molecule limit. The conductance of different conjugated molecules in a broad temperature, source–drain and gate voltage regime is reported. At low temperature, all investigated molecules display sharp conductance steps periodic in source–drain voltage. The positions of these steps can be controlled by a gate potential. The spacing corresponds to the energy of the lowest molecular vibrations. These results show that the low bias conductance of molecules is dominated by resonant tunnelling through coupled electronic and vibration levels.

The motion of single conjugated molecules inserted in a self-assembled monolayer (SAM) matrix composed of a spherical bicyclo[2.2.2]octane derivative was observed using scanning tunnelling microscopy at room temperature. Two kinds of conjugated molecules, i.e. benzenemethanethiol and 4-biphenylmethanethiol, were inserted in the SAM matrix. It was revealed that the isolated single molecules exhibited two types of motions. One was the change in tilt of the molecular axis at a fixed position, and the other was lateral motion in the SAM matrix. These motions of the single molecules due to thermal energy at room temperature were most likely caused by large and mobile vacancies of single molecular defects in the SAM matrix.

We show that well-defined arrays of self-assembled Ge dots on Si(001) can be grown after pre-patterning the Si surface by means of an electron beam. The electron beam produces C-containing growth masks. The overgrowth of these masks with Si results in pits at the Si surface, in and around which Ge dots nucleate selectively. A manifold of different arrays can be obtained. Almost perfect arrays of quadruples of dots nucleate in the intersections of the four {11n} facets. This way of producing quantum dot arrays is very promising for producing dot structures suitable for use in the study of, for instance, dot–dot tunnelling and related effects.

Uniform fine Co₈₀Ni₂₀ particles with diameters between 18 and 540 nm have been synthesized by polyol reduction of metallic salts. Their magnetic properties have been studied as a function of the particle size at 10 and 300 K. From the analysis of the experimental results at room temperature, a transition from polydomain structure to single-domain structure with the reduction of the particle size to around 40 nm is deduced. A considerable decrease of the saturation magnetization with respect to the bulk value has been found as the particle size decreases at both measuring temperatures. At low temperature, a strong increase of coercivity has been observed which is ascribed to an enhancement of the effective magnetic anisotropy induced by the surface layer.

Two types of hybrid CMOS-molecular memories with large scaling potential are discussed; resistive memories based on functional molecular layers and charge trapping devices with integrated nanotubes. For the first type, the resistive memory, crossbar cell and transistor cell architectures are compared. In the crossbar geometry the advantage of a dense cell geometry comes at the cost of more complex circuitry and complicated process technology, whereas the transistor cell has, in general, a lower area density, but enhanced read–write performance and reduced disturbance. However, using a specially designed vertical transistor architecture a cell size similar to that in the crossbar cell can be realized. The other concept for a highly scalable non-volatile memory is based on the integration of nanowires or nanotubes into standard silicon technology. In this memory cell, charges in the trapping layer shift the threshold voltages of nanotube-based transistors, while controlling and readout can be done by conventional CMOS electronics.

We have prepared LiNi_1−yCo_yO₂ (0 ≤ y ≤ 1) compounds as polycrystalline nanomaterials (d ≈ 400 nm) using a low-temperature sol–gel method. XRD studies indicate that these materials are single phase for 0.2 ≤ y ≤ 1 with an ordered distribution of Li and Ni/Co in the layered structure. Nevertheless, as this technique provides only averaged structural information, it is still possible that locally there are some defects, among them disorder, that could affect the electrochemical behaviour of these materials. In fact, through FTIR spectroscopy we observe for the Li–O band a slight deviation from a linear behaviour for high nickel content (y ≤ 0.2), that is attributed to the presence of Ni cations in the predominantly lithium layers (octahedral interstices). In addition, by means of magnetic measurements, χ_m (T) and M(H), we detect in all the samples a ferrimagnetic signal, that gets smaller and smaller as the Co content increases, but that indeed reveals the presence of some Ni²⁺ ions occupying Li⁺ places, that would lead to the formation of small ferromagnetic islands. From those magnetic measurements we have estimated the size of those nanometric magnetic inhomogenities that decreases upon Co doping from R_{(y = 0)} = 3.5 nm to R_{(y = 0.4)} = 0.5 nm. This result confirms that the addition of Co³⁺ inhibits the presence of interlayer Ni²⁺ and therefore favours a better lamellar structure, only obtained for y > 0.4.

Using the extended Hückel molecular orbital–N elastic scattering quantum chemistry technique, the scattering electronic properties of four-and two-electrode monomolecular Wheatstone bridges are discussed. Simple intramolecular circuit rules are given for the design of an intramolecular electronic circuit integrated in a single molecule. The balancing condition of the four-electrode monomolecular Wheatstone bridge is provided. The value of the tuning resistance of the bridge is the same applying the new tunnel circuit rules and the standard Kirchhoff node and mesh laws. Only the way of reaching the equilibrium of the bridge is different.

We have fabricated self-aligned, side-gated suspended multi-walled carbon nanotubes (MWCNTs), with nanotube-to-gate spacing of less than 10 nm. Evaporated metal forms an island on a suspended MWCNT, the island and the nanotube act as a mask shielding the substrate, and lift-off then removes the metal island, leaving a set of self-aligned side gates. Al, Cr, Au, and Ti were investigated and the best results were obtained with Cr, at a yield of over 90%.

The magnetic behaviour of patterned Ni wires has been studied by magnetotransport measurements to analyse the mechanisms that govern the magnetization reversal in these ordered nanostructures as a function of temperature in the 150–350 K range. These results show reversal processes driven by a temperature-dependent combination of two different mechanisms: coherent rotation and a curling-like irreversible process. When the field is decreased from saturation the magnetization rotates reversibly until it reaches the nanowires' direction where it reverses its sign by an irreversible process at low fields. The amplitude in the magnetoresistance of this irreversible process is reduced as the temperature is increased, with a sharp step at room temperature. In fact, the analysis of the angular dependence reveals that it is compatible with an incoherent curling process up to 300 K in the whole angular range. For higher temperatures, a crossover towards coherent rotation is observed in the irreversible contribution for high angles between the applied field and the wire direction.

We demonstrate a theoretical analysis concerning the geometrical structures and electrical conduction of infinite monatomic gold and aluminium wires in the process of their elongation, based on first-principles molecular-dynamics simulations using the real-space finite-difference method. Our study predicts that the single-row gold wire ruptures up to form a dimer coupling structure when the average interatomic distance increases up to more than 3.0 Å, and that the wire is conductive before breaking but changes to an insulator at the rupturing point. In the case of the aluminium wire, it exhibits a magnetic ordering due to the spin polarization, and even when stretched up to the average interatomic distance of 3.5 Å, a dimerization does not occur and the wire keeps a metallic nature.

The effective anisotropy field and the saturation magnetostriction constant are presented as a function of the annealing parameters for Fe_93−x−yZr₇B_xCu_y (x = 6, 8 and y = 0, 1, 2) samples. The results obtained for these magnetic properties are interpreted in terms of microstructure–magnetization interactions, which lead to an enhancement of the soft magnetic character in the samples. Experimental data on saturation magnetostriction are analysed from the point of view of the surface properties and the magnetostriction constant, which describes the interface between the crystalline grain and the amorphous matrix.

We have developed an eight-band finite-difference envelope function approximation model capable of reproducing in almost all situations the true D_2d or C_2v symmetry of [001] grown zinc-blende heterostructures. We have used our model to study the relative contributions of the bulk inversion asymmetry (BIA) and structural inversion asymmetry to the spin splitting in the conduction band of asymmetric AlSb/GaSb/InAs/AlSb quantum wells, and clarify apparently contradictory statements about the relative magnitude of the two contributions. We show that, in the system under study, the inclusion of BIA effects changes considerably the angular dependence and the magnitude of the splitting. We also investigate how BIA changes the transmission properties of a resonant tunnelling structure.

Yttria-doped zirconia, lead zirconate titanate (PZT) and barium titanate were successfully obtained using hydrothermal procedures. Based on these results mathematical models describing the correlation between the nanopowders' characteristics and the main synthesis parameters are proposed.

Powders from the systems (Y₂O₃)_0.1 (ZrO₂)_0.9 and (Y₂O₃)_0.04 (ZrO₂)_0.96 obtained from soluble Zr(IV) peroxide precursors show that cubic/tetragonal phases have been formed by controlled crystallization from the solution. With increasing temperature and hydrothermal treatment temperature the mean crystallite sizes increase from a minimum of 5 nm to a maximum of 22 nm. The activation energy shows a diffusion-controlled process.

Barium titanate powders with controlled stoichiometry could also be hydrothermally synthesized in the temperature range 110– 175^°C.

Synthesis of PZT powders with controlled stoichiometry and mean crystallite sizes from 4 to 43 nm is finally presented.

Dense yttria-partial stabilized zirconia with high ionic conductivity and PZT with a good stability of electric–physical parameters for use in the design of materials with improved sensorial characteristics was obtained after sintering the nanopowders.

Cr₂O₃ nanoparticles of controlled particle size were prepared by calcination of a precursor, Cr(OH)₃, obtained by precipitation with sodium hydroxide. Samples were characterized by transmission electron microscopy and x-ray diffraction. Average particle sizes ranged from 20 to 200 nm. The magnetic properties of Cr₂O₃ nanoparticles show the presence of a net magnetic moment at the surface due to the large surface/volume ratio. This fact modifies the classical behaviour expected for bulk antiferromagnetic particles. Below the Néel temperature, magnetization curves as a function of the applied magnetic field show the presence of coercive forces in the low-field range.

The growth of three-dimensional photonic crystals (PhCs) on patterned silicon substrates is reported. It is shown that deep trenches can be uniformly filled by a self-assembly of polymer microspheres, in a close-packed face-centred cubic lattice. The crystalline quality is compared for different channel widths. These observations are confirmed by optical reflectance measurements in the visible range, showing a bandwidth of enhanced reflection. The possibility to detach the PhC, i.e. to use the substrate as a mould, is also demonstrated. The potential of this approach for building PhC-based complex architectures is discussed.

We use a simultaneous flow of ethylene and hydrogen gases to grow single-wall carbon nanotubes by chemical vapour deposition. Strong coupling to the gate is inferred from transport measurements for both metallic and semiconducting tubes. At low temperatures, our samples act as single-electron transistors where the transport mechanism is mainly governed by Coulomb blockade. The measurements reveal very rich quantized energy level spectra spanning from the valence to the conduction band. The Coulomb diamonds have similar addition energies on both sides of the semiconducting gap. Signatures of the subband population have been observed at intermediate temperature.

In the present work the electrostatic interaction of a real scanning force microscopy (SFM) probe with a sample is studied theoretically as well as experimentally. To model the probe, a complex system composed of a macroscopic cantilever, a mesoscopic tip cone and a nanometric tip apex is proposed. The corresponding interaction is calculated analytically by means of an appropriate approximation. In most experimental situations we find that the total interaction is dominated by the cantilever and/or the tip cone and not by the tip apex. Experimental determination of tip–sample interaction supports this model. In addition, we find that a real SFM probe may lead to misinterpretation of experimental data in the so-called Kelvin probe microscopy (KPM). Again, experimental data confirm that the effects described by the model we propose may induce severe errors in KPM. As shown in this work, the resolution in KPM and electrostatic force microscopy is dramatically enhanced and data interpretation simplified if the force gradient rather than the force is used as signal source for the electrostatic interaction.

Composite layers Ni–P + Co, Ni–P + W and Ni–P + Ti were obtained in galvanostatic conditions, at j_dep = 0.200 A cm⁻². The x-ray diffraction method was used to determine the phase composition of the layers and atomic absorption spectrometry was applied to specify their chemical composition. A metallographic microscope, stereoscopic microscope and Form Talysurf-type profilograph were used for cross-section and surface morphology characterization of the layers. The behaviour of the obtained layers was investigated in the process of hydrogen evolution reaction from 5 M KOH using classical methods (voltammetry, steady-state polarization) and electrochemical impedance spectroscopy (EIS). Based on recorded steady-state polarization curves, the Tafel equation parameters for this process were determined. EIS was used to study the interfacial properties at electrode overpotential ΔE = −0.200 V. It was found that the investigated Ni–P + Co layer is characterized by increased electrochemical activity for hydrogen evolution compared to Ni–P + W and Ni–P + Ti layers. Greater activity of the Ni–P + Co layer in this process may be attributed to the developed electrode surface. The values of surface roughness factor R_f were also determined.

We study the spin-dependent conductance of ballistic mesoscopic ring systems in the presence of an inhomogeneous magnetic field. We show that, for the set-up proposed, even a small Zeeman splitting can lead to a considerable spin polarization of the current. Making use of a spin-switch effect (Frustaglia et al2001 Phys. Rev. Lett.87 256602) we propose a device of two rings connected in series that in principle allows for both creating and coherently controlling spin polarized currents at low temperatures.

This special issue of Nanotechnology contains contributions presented at the third `Trends in Nanotechnology' (TNT2002) international conference, held in Santiago de Compostela (Spain), 9–13 September 2002. More than 370 scientists from Europe, the United States, Japan and other countries worldwide attended this meeting and contributed talks (77), posters (200) and stimulating discussions about their most recent research.

The rapidly emerging areas of nanoscale science and technology are focused on the design, fabrication and characterization of functional objects having dimensions at the nanometre-length scale. New advances in this emerging area are expected to have long-range implications in a wide variety of different scientific and engineering disciplines. The importance of nanoscale science is growing worldwide and it is now widely recognized as a critical component to the future growth of the world economy.

The aim of the conference was to focus on the applications of nanotechnology and to bring together, in a scientific forum, various groups from throughout the world belonging to industry and public institutions. TNT2002 was particularly effective in transmitting information and establishing contacts among workers in this field. Graduate students attending such conferences quickly learn the importance of interdisciplinary skills and become more effective in their future research. Last year, almost 50 graduate students received a grant (from NASA, PHANTOMS or TNT) to attend the conference and presented their work through a poster (10 prizes to the best posters were awarded by Professor Leo Esaki). The scientific programme, without parallel sessions, covered a wide spectrum of nanotechnology research. The structure of the conference provided an opportunity for broad interaction.

A one-day SRC/TNT nanoelectronics workshop was also organized, as an integrated part of the TNT conference. The workshop was structured to encourage an active interchange of ideas among participants, to highlight the most relevant scientific results and define strategies. Five major nanoelectronics themes were identified, each of which was addressed by a speaker from industry and a speaker from a university. All lecturers were asked to present their opinions on the following questions in a report: (i) What is the most significant achievement in the field in 2001–2002? (ii) What is overall the most significant result in the field? (iii) What are the recommended research vectors?

We would like to thank all the participants for their assistance as well as the authors for their written contributions. We are indebted to the following institutions, companies and government agencies for their help and financial support: Universidad Autónoma de Madrid, Consejo Superior de Investigaciones Científicas, CMP Cientifica, University of Cambridge, University of Purdue, Universidad Complutense de Madrid, Universidad Carlos III de Madrid, Universidad de Santiago de Compostela, PHANTOMS Network (funded by the EU through its IST programme), National Science Foundation, NASA, Riken Institute, Air Force Office of Scientific Research, Donosti International Physics Centre, Xunta de Galicia, Concello de Santiago, Hewlett Packard, Motorola, Carburos Metalicos, World Scientific, Institute of Physics Publishing and the Ministerio Español de Ciencia y Tecnología. We would also like to thank the following companies for their participation as exhibitors: NanoTec, Raith, World Scientific and Institute of Physics Publishing.

We invite readers of this special issue of Nanotechnology to join us in the `Trends in Nanotechnology' conference series. The next conference (TNT2003) is being held in Salamanca (Spain), 15–19 September 2003.

Guest Editors:Antonio CorreiaCMP Cientifica, SpainPedro A SerenaICMM/CSIC, SpainJuan Jose SaenzUniversidad Autónoma de Madrid, SpainMark WellandUniversity of Cambridge, UKRon ReifenbergerPurdue University, USA