Table of contents

We give evidence on how closely different areas of research in the nanometre range are integrated and on what established and new networks and research programmes at EU level may contribute to the further development of the nanosciences. A Delphi study, participant observation, interviews and informal contacts form the basis of this empirical and sociological study. The analysis shows that the invention of scanning probe techniques and other nanotools is entering a variety of areas of research, which are largely unrelated. The EU networks and research programmes present in the selection environment stimulate the emergence of nanotechnology as one among several technologies which use nanotools, are based on nanometre-long structures and utilize properties which can only be made at a nanoscale.

The electrical transport properties of dodecanethiol (DT) and 2.5''-bis(acetylthio)-5.2'5'.2''-terthienyl (T3) embedded in metal-molecule-metal junctions are investigated. Scannning tunelling microscopy imaging and I- V curves recorded on mechanically breakable junctions allow us to observe a marked difference in the electrical behaviour of these molecules: in particular, steps have been observed in the I- V characteristics of gold-T3-gold junctions, which are not found in the gold-DT-gold ones.

Electronic coupling effects in vertically aligned self-assembled InAs quantum dots are investigated using capacitance and far-infrared (FIR) spectroscopy. Capacitance spectra show distinct shifts of the many-particle ground state energies, which is the result of a strong electrostatic dot-dot interaction. FIR spectroscopy shows that the dynamics of the dot system is only slightly affected by Coulomb interaction. The dots in the second layer are found to have a larger diameter than those in the first.

Atomic layer epitaxy (ALE) is a surface controlled, self-limiting method for depositing thin films from gaseous precursors. In this paper the basic principle of ALE and its potentials for nanotechnology are introduced. From the point of view of nanotechnology the most important benefits of ALE are excellent conformality and easily realized subnanometre level accuracy in controlling film thicknesses, which are discussed in more detail with selected examples from thin-film technology. Studies on ALE preparation of laterally confined structures are also reviewed. The paper concludes with an outlook discussing the capabilities and challenges of using ALE in nanotechnology in depositing materials with one or several dimensions confined to the nanometre level.

A new model for particle growth can predict the well known lognormal particle size distribution from first principles in a physically realistic way. The model is completely different from the usually applied coagulation models; it is based on a residence time approach, where the time available for the particles to grow determines the size distribution. The model is generally relevant in fields such as nanoparticle physics, aerosol science or environmental science, whenever particle growth occurs during transport through a growth zone due to diffusion and drift. Model predictions show excellent agreement with published experimental data obtained with the inert-gas evaporation technique.

The field of micromachines is maturing in terms of fabrication technologies, reproducibility and reliability. Different development principles and applications are investigated for a wide range of dimensions from millimetric to nanometric. One promising approach is to make micromachined tools for sensing, handling and manipulating on the nanoscale with high precision. A few examples are presented, including an integrated scanning tunnelling microscope, a monolithic nanoscanner and a high-frequency atomic force microscope nanocantilever. The integration of nanostructures and micromachines will lead to the development of smart nanosystems allowing for future manufacturability.

Local oxidation of silicon surfaces by scanning probe microscopy is a very promising lithographic approach at nanometre scale. Here, we present two approaches to optimize the oxidation for nanofabrication purposes: (i) we analyse the reproducibility and kinetics of the oxidation of Si(100) surfaces when there is no tip and sample mechanical contact and (ii) we study the effect of modulating the voltage in the aspect ratio of the oxide structures grown. The finite tip-sample separation has remarkable practical consequences: the same tip can be used to perform thousands of modifications without any sign of wear. In addition, the structures generated do not show any degradation over long periods (months). It is also found that the kinetics is independent of the force microscopy mode used (contact or non-contact). On the other hand, the application of an AC voltage to induce the oxidation significantly modifies the aspect ratio of the structures. A detailed description of the oxidation mechanism is proposed to account for both results.

Using the nanofibres obtained from a colloidal gold solution as model objects, we test different methods of manipulation at the nanometre scale. The atomic force microscope can be used to deform, cut and move nanofibres with a diameter larger than 2 nm. For smaller fibres, we show that a `soft' manipulation can be performed using wet processes: a capillary flow brings the fibres to a targeted location of the surface while a molecular combing flow stretches and aligns the fibre. This mechanism is used to position sub-nanofibres between the two electrodes of a coplanar nanojunction.

Focused ion-beam milling with a sub-10 nm diameter beam of gallium ions has been used to fabricate field-ion specimens from a multilayer film nanostructure containing 100 repetitions of a bilayer deposited directly onto a planar substrate. Successful field-ion specimen preparation has allowed the observation of these layers on the atomic scale by both field-ion imaging and atom probe compositional analysis.

The noise performance of piezoresistive atomic force microscopy (AFM) devices is investigated. The total deflection noise of a piezoresistive AFM device comprises vibrational noise from the cantilever, and Johnson and flicker noise from the piezoresistor. The vibrational deflection noise is found to have a minimum when the length of the piezoresistor is of the cantilever length. The minimum vibrational deflection noise is for a free cantilever, whereas a supported cantilever has a minimum vibrational noise of , where K is the spring constant of the device. Taking self-heating of the device into account, it is shown that an optimum power level exists at which the total equivalent displacement noise of a device is minimized. This minimum deflection noise is, for a fixed value of the spring constant, approximately proportional to the cantilever thickness, whereas it varies rather slowly with the length of the piezoresistor.

A novel concept for the fabrication of nanostructured probe tips for application in scanning near-field optical microscopy (SNOM) based on micromachining and thin-film technology is presented. This concept allows for the reproducible batch fabrication of aperture probe tips consisting of a transparent silicon nitride cone with a sharp tip apex surrounded by a metallic coating. Furthermore, the concept can be extended to the fabrication of probe tips with a coaxial nanostructure or a single nanoelectrode. The tip fabrication can be integrated into micromachining processes for the batch fabrication of scanning probe microscopy sensors and therefore leads to new types of multifunctional probes. Here the integration of the SNOM probe tip into an AFM cantilever equipped with an integrated optical waveguide designed for simultaneous AFM/SNOM operation is described.

In this paper we analyse the transport properties of Josephson junctions embedded in an electromagnetic environment caused by pads and leads near to the junctions. At sufficiently low temperatures we find that the conductivity of the Josephson junctions at low bias is strongly suppressed due to the Coulomb blockade of Cooper pair tunnelling. At high enough temperatures, the conductivity of the Josephson junctions is also reduced due to thermal activated phase slip processes. As a consequence, transport of supercurrent with maximal conductivity is reached at an intermediate temperature. The dependence of various transport regimes on the Josephson energy and the charging energy is discussed.

The inclusion compounds (ICs) of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) with several small molecules have been studied, for the first time, by ¹³C magic angle spinning NMR. The channel-type structure of TPP ICs (about 5 Å wide) provides an aromatic environment to trap some molecules such as benzene, tetrahydrofurane and p-xylene. ¹³C solid state NMR shows that the high symmetry of the adducts is consistent with an hexagonal crystal cell. The dynamic behaviour of the guest and host molecules has been studied by the measurement of ¹³C T_i relaxation times and compared with structures containing 10 Å diameter channels. The release of the guest molecules has been followed by differential scanning calorimetry and by solid state NMR. There exist two crystal structures of the guest-free TPP molecule: the former is monoclinic and the latter retains the channel-type structure and hexagonal packing. ¹³C CP MAS spectra and relaxation times of guest-free TPP structures demonstrate the existence of empty nanotubes stable up to 150 °C. These structures are easily available for uptaking guest molecules by a phenomenon which is quite unusual for molecular architectures. The peak multiplicity of ³¹P CP MAS spectra reflect the symmetry of the crystal cells together with residual dipolar coupling with ¹⁴N.

Micrometre long nanoribbons have been grown from solutions of functionalized poly( para-phenyleneethynylene)s (PPE)s on noncrystalline insulating substrates including glass and carbon coated copper grids. Tapping mode scanning force microscopy (SFM) and transmission electron microscopy (TEM) revealed that these nanostructures possess a molecular cross section with a typical thickness of 2-3 molecular layers and a width which reflects the distribution of macromolecular lengths. The ribbons are therefore quite similar to the ones found on the crystalline mica substrate except that they are not oriented within the surface plane. This indicates that the growth of these architectures from solution is mainly governed by intermolecular interactions between the π-conjugated macromolecules. The possibility to self-assemble these nanoribbons also on amorphous silica opens a prospect for their application as molecular nanowires bridging gold nanoelectrodes grown on oxidized silicon wafers.

Nanocrystalline ferroelectric thin films are obtained by pulsed laser deposition from a target prepared by sintering at approximately 700 °C nanosized powders of Pb(Zr_0.52Ti_0.48)O₃ (PZT) with 1% weight addition of Nb₂O₂. The powder was prepared by spray-drying and it was calcinated at 500 °C. Film deposition is performed on Si(100) and Au/Si(100) substrates in a reactive oxygen atmosphere using a pulsed Nd-YAG laser with energy 0.3 J/pulse, wavelength 1064 nm, pulse duration 10 ns and frequency 10 Hz. The film samples are investigated by scanning electron microscopy (SEM), x-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and dielectric measurements. The crystallite dimension of PZT films has been found through morphological analysis to be about 30-40 nm. A broadening of the dielectric constant peak at the ferroelectric transition temperature due to finite-size effects is observed. The critical coefficient γ in the Curie-Weiss law is found to be 1.85 which is indicative of a partially diffused phase transition.

We present a detailed experimental study of magnetic relaxation on a single crystal of Mn₁₂ 2Cl-benzoate and compare with results obtained on a single crystal of Mn₁₂ acetate. Relaxation times obtained from a.c. susceptibility experiments for both samples show sharp minima at the same resonant fields. Although magnetic relaxation of Mn₁₂ 2-Cl benzoate is faster at any field and temperature, activation energies in zero field are approximately equal. This is an indication that a small increase of the transverse fields magnitude (arising from dipole-dipole interactions) does not modify appreciably tunnelling rates between spin states which are degenerate at zero field. This result agrees with the predictions of a new theoretical model recently developed by some of the authors.

The influence of surface nanotopography of ceramic powders on their sintering behaviour was studied. ZrO₂-3 mol% Y₂O₃ powders were prepared by sol-gel techniques and calcined at different temperature in order to obtain powders showing different nanostructural properties. After compaction and sintering, strong differences in microstructure and mechanical properties were found in the sintered bodies. In order to correlate the powders' different sintering behaviour to their nanostructural properties, HRTEM and FTIR analyses were carried out. It is suggested that the temperature of calcination strongly influences the distribution of surface crystallographic configurations (i.e. surface nanotopography) which, in turn, have a predominant role in the microstructural development during sintering.

Noise can be a unique probe of electron-electron correlations in nanoscale electron devices. While stationary or small signal transport can often be simply understood in terms of single particle behaviour, noise can be extremely sensitive to many-body effects (Landauer L 1996 Physica B 227 156).

We present a new collective phenomenon emerging in electron transport in a resonant tunnelling diode, due to Coulomb repulsion dramatically magnified by the particular shape of the density of states in the quantum well. This phenomenon, for which the name of Coulomb breach is proposed, reveals itself by making shot noise several times greater than that expected in the absence of correlated electron motion. Experimental results showing shot noise enhancement of a factor 6.6 are reported.

As manufacturing technology has improved over the past few years, it is inevitable that the size of components to be manufactured has been affected, and the desire to reduce the size of such components is the driving force behind the move towards micro- and nanotechnology. One of the problems is the electrode breakdown at electrode separations for less than a millimetre separation. At large separation, the behaviour of the electrodes has been widely studied and is reasonably well understood. However, some fundamental problems have not been properly addressed such as maximum safe operating voltages and critical dimensions required at the small separations between the different types of materials. A systematic study of electrical breakdown at sub-millimetre separations using materials commonly used in the fabrication of microdevices is being undertaken. Specimens for examination at electrode separations from 500 nm to 25 µm have been made with different electrode configurations, such as flat to flat and flat to point.

Using a photon scanning tunnelling microscope combined with a shear-force feedback system, we image both topographical and near-field optical images (at the wavelengths of 633 and 594 nm) of silver colloid fractals. Near-field optical imaging is calibrated with a standing evanescent wave pattern. Near-field optical images exhibit spatially localized (within 150-250 nm) intensity enhancement (by up to 20 times) in the form of round bright spots, whose positions and brightness are found to be sensitive to the light wavelength, polarization and angle of incidence. The observed phenomenon is related to the localization of resonant dipolar eigenmodes in random surface nanostructures.

In this issue of Nanotechnology a number of papers are collected as they were presented at the TMR conference `Nanoscience for Nanotechnology' in May 1998 (http://www.cismi.dk/nano.htm). The motivation for the series of conferences, with this being the first, has been to identify the nanoscience community in Europe. Several committees have previously been formed to discuss the definition of nanoscience, however a unanimous definition has failed to emerge.

According to the observation made by Ineke Malsch [1] that `nanoscience encompasses all traditional scientific disciplines in natural sciences where systems of nanometre scale are investigated'. In a sense this leaves the field open for everyone. Nanoscience in Europe will therefore be what scientists in Europe are shaping by their joint effort in the field. Nanotechnology is different. To qualify as a technology an activity has to aim at a specific problem or class of problems. The activity has to be refined for repeated use in terms of instrumentation. Social, ecological and ethical aspects have to be evaluated as well. There has to be a market willing to sustain the technology through the pricing of the product. Many basic research areas in biology and chemistry have dealt with nanoscale objects for years. They may be re-labelled as nanoscience, but not as nanotechnology .

New nanotechnologies have emerged such as for example scanning probe instrumentation. This is a technology in which the results are often interpreted based on empirical rules. Here nanoscience is urgently needed to underpin the methods. This will allow us to refine the interpretation of the results and spur new experiments and new knowledge.

The public and politicians are always hunting for new buzzwords. Nanotechnology has been gaining interest over the last two years. It is likely that the public and politicians in the next ten years will see nanotechnology as the new `thing' destined to save society and the economy. Hopefully the scientists will remain honest and focused on the extensive and fascinating subject of the nanoworld.

E Shabanova, K Schaumburg and W Göpel