Table of contents

The idea of electronic transport in molecular-scale systems dates back to the original theoretical proposals of the 1970s of unimolecular transport, and over the last decade has gained experimental verification by the realization in a variety of systems. The special section in this issue of Nanotechnology surveys the progress in this rapidly evolving field of molecular and atomic scale electronic transport.

The paper by Datta (page S433) discusses the theoretical basis of electronic conductance from an atomistic point of view, and presents the methods and challenges to developing a full predictive theory of these systems. The paper by Di Ventra et al (page S459) elaborates on this, presenting theoretical results on shot noise in these types of systems. A nice comparison of these studies with experimental results is presented by Schönenberger et al (page S479).

Experimental papers are presented in a number of diverse systems in this regime. In the field of organic and molecular transport, Hersam et al (page S452) present results of scanning tunnelling spectroscopy of organic monolayers, and Kushmerick et al (page S489) present results on molecular junction transport and rectification. To test theoretical models of molecular transport, Mayer et al (page S483) present thermal activation studies of molecular junctions.

A valuable tool for the study of molecular and atomic transport is the mechanically controllable break junction, presented in two papers here. The work by van Ruitenbeek et al (page S472) presents results on atomic chains of atoms, and Scheeret al (S465) present a study of this technique for measuring molecular junctions.

The tremendous progress seen within the last decade in this nascent field bodes well for the understanding of molecular scale electronic systems. The papers presented here, written by leading experts in the field, introduce some of the most important breakthroughs in molecular nanoelectronic technologies under development today.

This tutorial article presents a 'bottom-up' view of electrical resistance starting from something really small, like a molecule, and then discussing the issues that arise as we move to bigger conductors. Remarkably, no serious quantum mechanics is needed to understand electrical conduction through something really small, except for unusual things like the Kondo effect that are seen only for a special range of parameters. This article starts with energy level diagrams (section 2), shows that the broadening that accompanies coupling limits the conductance to a maximum of q²/h per level (sections 3, 4), describes how a change in the shape of the self-consistent potential profile can turn a symmetric current–voltage characteristic into a rectifying one (sections 5, 6), shows that many interesting effects in molecular electronics can be understood in terms of a simple model (section 7), introduces the non-equilibrium Green function (NEGF) formalism as a sophisticated version of this simple model with ordinary numbers replaced by appropriate matrices (section 8) and ends with a personal view of unsolved problems in the field of nanoscale electron transport (section 9). Appendix A discusses the Coulomb blockade regime of transport, while appendix B presents a formal derivation of the NEGF equations. MATLAB codes for numerical examples are listed in appendix C. (The appendices are available in the online version only.)

The ultrahigh vacuum scanning tunnelling microscope was used to probe charge transport through two different organic monolayers adsorbed on the Si(100) substrate at room temperature. I–V measurements were taken on monolayers of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and cyclopentene for degenerately doped n-type and p-type substrates. Initial I–V measurements for transport through the TEMPO monolayer exhibited a suppression of negative differential resistance (NDR) relative to previously reported charge transport through isolated molecules. I–V measurements were also performed on isolated cyclopentene molecules and cyclopentene monolayers. Similarly to TEMPO monolayers, the cyclopentene monolayers exhibited attenuated NDR behaviour relative to isolated molecules. The observed NDR suppression suggests that the high packing density of organic monolayers influences charge transport through molecule–semiconductor junctions.

We report first-principles calculations of shot noise properties of parallel carbon wires in the regime in which the interwire distance is much smaller than the inelastic mean free path. We find that, with increasing interwire distance, the current rapidly approaches a value close to twice the current of each wire, while the Fano factor, for the same distances, is still larger than the Fano factor of a single wire. This enhanced Fano factor is the signature of the correlation between electron waves travelling along the two different wires. In addition, we find that the Fano factor is very sensitive to bonding between the wires, and can vary by orders of magnitudes on changing the interwire spacing by less than 0.5 Å. While these findings confirm that shot noise is a very sensitive tool for probing electron transport properties in nanoscale conductors, they also suggest that considerable experimental control of these structures is required to employ them in electronics.

We discuss the use of mechanically controllable break-junctions (MCBs) as electrodes for contacting individual objects such as clusters or molecules. A big advantage of MCB electrodes is the possibility of varying the contact geometry and, accordingly, the contact resistances and the quantum coherent transport properties between the object under study and the electrodes. We compare the suitability of single-atom contacts of different elements as electrode material. Finally, we present preliminary results on electronic transport through individual (or a few) fullerene molecules contacted by gold MCB electrodes. The typical resistances are in the order of the quantum of conductance. The circuits sustain voltages of the order of 1 V and are mechanically more stable than single-atom contacts between the gold electrodes alone.

For the metals Au, Pt and Ir it is possible to form freely suspended monatomic chains between bulk electrodes. The atomic chains sustain very large current densities, but finally fail at high bias. We investigate the breaking mechanism, that involves current-induced heating of the atomic wires and electromigration forces. We find good agreement of the observations for Au based on models due to Todorov and co-workers. The high-bias breaking of atomic chains for Pt can also be described by the models, although here the parameters have not been obtained independently. In the limit of long chains the breaking voltage decreases inversely proportional to the length.

We report on electrical transport measurements in a carbon nanotube quantum dot coupled to a normal and a superconducting lead. Depending on the ratio of Kondo temperature T_K and superconducting gap Δ, the zero bias conductance resonance either is split into two side-peaks or persists. We also compare our data with a simple model of a resonant level–superconductor interface.

The measured effect of temperature on charge transport through individual chemisorbed 1-nitro-2,5-di(phenylethynyl--mercapto)benzene molecules spanning a gold electrode gap is reported for the range of 10–300 K. Conduction is dominated by coherent superexchange at low temperatures and shifts to an incoherent hopping process above bias-dependent temperature thresholds. The results are consistent with proposed theoretical mechanisms in which bias-dependent heat dissipation from inelastic vibrational scattering within the molecule raises the temperature of the junction above that of the surrounding system, which in turn leads to the shift in the prevailing conduction process with increasing bias.

We demonstrate the ability to tune the current rectification in metal–molecule–metal junctions through control of the interaction strength of one of the two metal–molecule contacts. Current–voltage characteristics of thiolate bound molecular wires with a nitro or pyridine termination show that the extent of current rectification in a molecular junction correlates well with the extent of coupling between the chemical linker and metal electrode.

Site-specific deposition of nanoparticles and DNA onto micro-patterned aminoterpolymer films is reported. The chemical patterning of the film surface is accomplished by an easy-to-handle, one-step procedure. Photolabile protection groups are locally removed by applying UV light through an optical mask. This causes exposure of amino groups to the surface to which charged nanoparticles can then associate. End-specific binding of DNA at the surface-exposed amino groups is obtained at optimum pH conditions. This allows a site-specific attachment and stretching of single DNA molecules at the patterned polymer film surface.

GaN nanowires were synthesized by ammoniating Ga₂O₃/Al₂O₃ thin films deposited on Si(111) with radio frequency magnetron sputtering. The cylindrical structures were as long as several micrometres, with diameters ranging between 5 and 40 nm. X-ray diffraction (XRD, Rigaku D/max-rB Cu Kα), scanning electronic microscope (SEM, HitachiH-8010) and high-resolution TEM (HRTEM) results show that most of the GaN nanowires have a single-crystal hexagonal wurtzite structure with major axis [001] alignment. A minority of them are polycrystalline, composed of micrograins with different growth orientations.

An extended vapour–liquid–solid (VLS) growth method, which is the reaction of a mixture of nitrogen and ammonia gas over nanoscale Fe–B 'catalyst' particles at 1100 °C, has been developed. With this method, BN nanotubes of diameter about 20 nm have been prepared and well characterized by high-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy. In contrast to traditional VLS growth, the boron component in the BN nanotubes comes from the Fe–B 'catalyst' itself, rather than from the vapour precursor. A growing mechanism has been discussed accordingly.

The torsional resonance mode (TR mode) is an innovative technique recently introduced for scanning probe microscopes (SPMs). In the TR mode, a cantilever tip vibrates laterally as compared to vibrating vertically in the tapping mode (TM). The tip in the TR mode remains at an almost constant height and interacts aggressively with the surface and/or the near surface because of very high torsional stiffness. In this paper, a comparative study of TM and TR modes is presented for further understanding of the mechanism of the phase angle data produced during the different tip–surface interaction modes. Topography and phase angle measurements were made on a self-assembled monolayer (SAM) sample with a two-phase structure and metal particle (MP) tapes. It is found that although surface topography images are similar using both techniques, the TR mode phase angle image provides more detailed contrast than that obtained using the TM phase technique. The experimental evidence showed that viscoelastic deformation was primarily responsible for the phase contrast and not the friction process. Next, statistical analysis of the phase angle on the MP tapes suggests that the technique can be used for evaluating the particle concentration and the uniformity of viscoelasticity and thus screening of the magnetic tapes. The reasons for the improved contrast in the phase angle imaging in the TR mode are also discussed in this paper.

A novel nanostructured sandwich PAA/Al/PAA (PAA: porous anodic alumina) was successfully designed and fabricated by anodic oxidation on both sides of an Al foil. The pore size of the PAA membranes was controlled by choosing appropriate voltage, length of anodic oxidization time, temperature and electrolytes. The thickness of the central Al layer was varied by changing the anodic oxidization time. We show that the nanostructured sandwich PAA/Al/PAA can be used as a template in fabricating homogeneous or heterogeneous nanostructured sandwiches by depositing the same kind of material or different materials into the PAA membranes of the sandwich. We also show that it can be used to prepare nanowires and bipolar electrodes. In addition, Al nanosheets or Al nanowalls were produced by removing the PAA films completely or partially. Nanogaps between the PAA films were also formed by etching away the centre Al layer of the sandwich structures. The thickness of these nanosheets, nanowalls and nanogaps was controlled by choosing appropriate electrolytes and electrochemical parameters during the anodic oxidation of Al. All these nanostructures offer novel opportunities for both fundamental research and technological applications of low dimensional nanostructure systems.

Scale effects in tribology at the macroscale to nanoscale are considered. The coefficient of dry friction depends on the real area of contact and the shear strength due to adhesion and two- and three-body deformation. The real area of contact depends on the surface topography and elastic modulus for elastic contact, and on the hardness for plastic contact. The surface topography is scale dependent, on the basis of a fractal model or an empirical rule. The hardness is scale dependent on the basis of the strain gradient plasticity. The adhesional shear strength is scale dependent on the basis of a dislocation-assisted sliding model. The two-body deformation component of the coefficient of friction is scale dependent due to the scale dependence of the average asperity slope. The real area of three-body contact is scale dependent due to the scale dependence of the probability for a particle to be trapped at the interface and shear strength. In the presence of a liquid film the measured value of the coefficient of friction is different from the coefficient of dry friction due to the meniscus contribution. The meniscus force is scale dependent, since it depends on the number of contacts and summit radius of the asperities, which are scale dependent, on the basis of the surface topography. The scale dependence of other parameters of tribological importance, such as the wear coefficient, which depends on the scale dependent hardness, and the interface temperature rise, which depends on the scale dependent mean contact size, is also considered.

This paper describes a simple surfactant-assisted solvothermal approach to the large-scale synthesis of one-dimensional Sb₂O₃ nanorods, needle-like fibres, nanobelts and nanotubes. The shape of Sb₂O₃ nanomaterials can be controlled by the concentration of the reactants and CTAB. The growth mechanism and the factors that affect the shapes of 1D Sb₂O₃ nanomaterials are briefly discussed.

We employed mechanical patterning methods, including soft hot embossing and nanoimprinting lithography, to fabricate planar photonic crystal structures in organic materials, including both optically inert polymer matrices and light-emitting compounds exhibiting optical gain. The mechanical lithography processes allow a high-fidelity pattern transfer without reducing the emission yield, thus opening the way to the one-step realization of organic-based optoelectronic devices. Our demonstrators, presenting periodicities comprised between 250 and 600 nm, include solid-state distributed feedback cavities, exhibiting lasing emission at 630 nm, with a linewidth of about 1 nm and a pump threshold of 650 µJ cm⁻² at room temperature. The potentiality of these techniques for the realization of two-dimensional planar photonic crystal structures is also presented and discussed.

The concept, design and fabrication of a cantilever-based sensor operating in liquid for biochemical applications are reported. A novel approach for detecting the deflection of a functionalized cantilever is proposed. It consists of detecting the change of the electrochemical current level when a voltage is applied between a deflecting cantilever, acting as one of the electrodes, and a reference fixed electrode placed in close proximity to the free extreme of the cantilever. The detection is possible since the distance between the two electrodes is smaller than 50 nm. The sensor is fabricated by using a combination of MEMS technology and AFM-based lithography.

Na_0.5Bi_0.5TiO₃ (NBT) nanowhiskers with diameters of 20 nm and lengths of 300 nm have been prepared at low temperature by using a sol–gel–hydrothermal technique, which combined the conventional sol–gel process and the hydrothermal method. The reaction conditions such as alkali concentration and temperature were investigated. The powders were characterized by x-ray diffraction (XRD), Fourier transform infrared (FTIR) absorption spectroscopy, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). It is believed that the gel precursor and hydrothermal environment play an important role in the formation of the nanowhiskers.

In this paper, the chemical functionalization of multi-walled carbon nanotubes by a fluorinated trichlorosilane ((tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane) is investigated. The chlorosilane has been shown to react with carboxylic acid moieties, created by an oxidative process on the nanotube walls, as well as with alcohol groups obtained by a reductive reaction of these previous oxidized nanotubes. The derivatizations were directly confirmed by x-ray photoelectron spectroscopy and thermogravimetry analyses. Little difference in the functionalization was observed for the oxidized or reduced nanotubes. However, the amount of grafted silane seems to be slightly more important when the silanization is carried out with reduced nanotubes.

We report the fabrication of sub-micron cross-bridge Kelvin resistors from planar device heterostructures, utilizing a three-dimensional focused ion beam etching technique. By means of a conventional spin valve multilayer, we demonstrate that this geometry eliminates the parasitic resistances of the interconnects, permitting direct probing of device resistances in nanoscale dimensions. It is anticipated that such a technique can be applied to resistance measurements with current-perpendicular-to-plane device geometry in various material systems.

Via a Frenkel–Kontorova (FK) model approach, we study, in the context of solid friction phenomena, the role of the substrate potential geometry on the underdamped dynamics of a chain of interacting atoms. The choice of an on-site potential defined by the sum of two sinusoidal functions with different periodicity allows us to simulate microscopic sliding over simply periodic, multiple-well periodic and quasiperiodic substrates. We analyse the mobility–force characteristics and the related static friction, commenting on the nature of the particle dynamics in the vicinity of the pinning–depinning transition point and considering the role played by the coverage variable on the depinning mechanism. For the quasiperiodic cases, we also examine the hysteretic behaviour of the chain mobility as a function of the adiabatically varying force at zero temperature. For multiple-well periodic potentials, we observe the possible formation of commensurate dynamical structures during sliding.

The occurrence of wear between two unlubricated surfaces in relative motion one against the other presents several open questions, both on the macroscale and nanoscale. This paper takes as a starting point some experiments of wear tests on ionic crystals that have recently been presented. Two different wear mechanisms are discussed for the interaction of an atomic force microscopy probe tip with a flat atomic surface making use of a 2D system. The effects of shear forces and the Van der Waals force are analysed with a numerical model in order to give the occurrence of abrasive- and/or adhesive-wear mechanisms. The idea underlying the work is that adhesive or abrasive contributions to wear are critically dependent on the potential conformation of surfaces and the Lennard-Jones potential between the probe tip and flat atomic surface. The atoms involved in the wear processes can be subject to adherance to the probe tip if the vertical forces are most prominent with respect to shear forces that, in contrast, would involve atoms in an abrasive mechanism. The numerical results are based on a diffusive model both for adhesive- and abrasive-wear mechanisms. This diffusive model allows wear volume quantification by making use of a simple formula. Due to its simplicity, the model adopted could be helpful to understand the occurrence of different wear mechanisms on the nanoscale.

In this contribution we present the visible and near IR photoluminescence (PL) analysis of Er doped nanocrystalline silicon thin films produced by the rf magnetron sputtering method. Efficient photoluminescence was observed in these structures in both the visible and 1.54 µm wavelength regions. We show the strong influence of the presence of a nanocrystalline phase in films on their luminescence efficiency at 1.54 µm, which has been studied for a series of specially prepared samples with different crystallinities, i.e. percentages and sizes of Si nanocrystals. The mechanism involved in the visible photoluminescence of a highly crystalline nc-Si:H sample consisting of about 7 nm silicon nanocrystals embedded in an amorphous matrix is discussed.

The typical size of a single molecule is of the order of a few nanometres; for this reason metal electrodes separated by a nanometre-scale channel are required to make molecule-based electronic devices. In this work, we report on the fabrication of metallic (Cr/Au, Ti/Au or Ti/Pt) arrow-shaped electrodes on Si/SiO₂ substrates, with tip separation between 100 and less than 10 nm. They can be used to implement two and three terminal molecular devices, just by connecting them by the chosen molecules and adding an Ag electrode on the back of the Si substrate. Electron beam lithography (EBL) allowed us to obtain electrodes with separation around 40 nm. In order to reduce the tip separation down to 20 nm, before the EBL process, we used a defocused e-beam to brush the poly(methyl methacrylate) (PMMA) layer for a short time (from 10 to 40 s). The smallest gap between the electrodes (less than 10 nm) was obtained with standard EBL and lift-off followed by Au electroplating deposition. The fabricated devices were inspected by plan-view scanning electron microscopy (SEM) and electrically tested by I/V measurements in the range ± 2 V. Open-circuit characteristics gave very low currents (in the range −10 to 10 pA) and a resistance . As a typical example, we demonstrate a field effect transistor (FET) based on a deoxyguanosine derivative (a DNA base) placed between the fabricated planar electrodes by room temperature (RT) cast deposition. The FET device tested at RT and ambient pressure exhibited a maximum voltage gain as high as 0.76.

Nanocrystalline undoped and Mn doped zinc sulphide (ZnS) thin films were synthesized by a wet chemical route without using any capping agent. The x-ray diffraction pattern showed the typical interplanar spacings corresponding to the cubic phase of ZnS. Transmission electron microscopy (TEM) studies confirmed the nanocrystalline nature with an average particle size  nm. Compositional information was obtained from the energy dispersive x-ray studies. A UV–visible optical spectroscopy study was carried out to determine the bandgap of the nanocrystalline ZnS and it showed a blue-shift with respect to the bulk value. Variation of bandgap energies with annealing temperature was also studied in detail. A photoluminescence (PL) study of the ZnS and ZnS:Mn films at room temperature (300 K) indicated a strong luminescence band at energy 2.07 eV.

Due to the shadowing effect, the oblique angle deposition technique can produce nanorods tilted toward the incident deposition flux. Periodic posts serving as seeds on a substrate allow the fabrication of nanorod arrays with controllable separations. However, in a conventional oblique angle deposition with no substrate rotation, nanorods grow faster along their widths in the direction perpendicular to the plane of incident flux. This anisotropic growth can result in 'fan-out' shapes of nanorods that touch each other due to the faster growing widths. Asymmetric two-phase substrate rotation was designed to eliminate the side growth in oblique angle deposition. In this method, the growing rods are exposed to the deposition flux from all angles with some portion of a rod surface receiving more flux than the rest. We fabricated well-aligned Si nanorod arrays with uniform sizes from templates arranged in square and triangular lattices using this two-phase substrate rotation method.

We report that the storage and clearing of multi-digital data, that is, the photoluminescence (PL) intensity of CdSe/ZnS core/shell nanocrystal (NC) thin film, can be operated by a single excitation wavelength. First, a 7.4 µm-square area on the NC film was irradiated by strong light ranging in intensity from 2.64 to 1370 nW. Then, a 60 µm-square area including the pre-irradiated region was scanned with weak light (about 0.6 nW) to visualize the PL intensity difference between pre- and non-irradiated regions (I and I₀, respectively). The normalized PL intensity, I/I₀, increased with total pre-irradiation energy, until reaching saturation. The level of I/I₀ at which the PL intensity becomes saturated reversibly increased with decreasing light intensity at pre-irradiation. The results imply that Auger ionization becomes dominant and suppresses the enhancement of the emission efficiency with higher irradiation intensities.

MX₂ nanoparticles, with M =  Mo, W and X =  S or Se, were synthesized via a chemical reaction between molybdenum carbonyl (or tungsten carbonyl) and chalcogen dissolved in para-xylene solution. X-ray diffraction and high-resolution transmission electron microscopy analysis showed that the MoS₂, WS₂, MoSe₂ and WSe₂ powders were constituted of rounded amorphous nanoparticles. Upon annealing at 550 °C the nanoparticles crystallized, losing their round shape. The four materials synthesized under similar conditions showed that the annealed selenide nanoparticles (MoSe₂ and WSe₂) are well crystallized, with aligned stacks of 5–10 layers (002 van der Waals (vdW) planes), while the annealed sulfide nanoparticles (MoS₂ and WS₂) exhibit curved and tangled 002 planes, randomly distributed in the particle.

Alumina nanotemplates integrated on silicon substrate with pore diameters of 12–100 nm were prepared by galvanostatic (constant current) anodization. High current density (e.g. 100 mA cm⁻²) promoted a highly ordered hexagonal pore structure with fast formation rate independent of anodizing solution. Alumina formation rates of 2000 and 1000 nm min⁻¹ were achieved at current densities of 100 and 50 mA cm⁻², respectively. These rates were approximately two orders of magnitude greater than other reports in the literature.

Different electrolytes of sulfuric acid (1.8–7.2 M), oxalic acid (0.3 M) and mixed solutions of sulfuric and oxalic acids were evaluated as anodizing solutions. At fixed current density, sulfuric acid promoted smaller pore diameter with lower porosity than mixed acids and oxalic acid. The I–V characteristics of aluminium anodization show the measured voltages at given current densities strongly depend on solution composition, operating temperature, and bath agitation.

The pore diameter of the silicon-integrated alumina nanotemplate varied linearly with measured voltage with a slope of 2.1 nm V⁻¹, which is slightly smaller than reported data.

Using zinc chloride as source material, zinc oxide nanowires and nanorods were fabricated by a vapour-phase transport method at low temperature. The nanowires grown on gold-coated silicon showed a uniform diameter of about 40 nm, and the nanorods on copper-coated silicon grew upwards to form flower-like arrays. The x-ray diffraction and transmission electron microscopy analyses demonstrated that the nanostructural zinc oxide grew along the [0001] direction. The growth process was attributed to a vapour–liquid–solid mechanism. Distinct photoluminescent behaviours were observed for zinc oxide nanostructures grown on gold-coated and copper-coated silicon wafers.

Nanostructured ceria, zirconia and ceria–zirconia solid solutions have been synthesized via an easy route and characterized by XRD, nitrogen physorption, Raman spectroscopy and TEM. The route involves two steps: the impregnation of ultrahigh surface area carbon materials with nitrate solutions of ceria and/or zirconia and burn-off to remove the carbon materials in a controlled oxidation atmosphere. The results show that the particle sizes of ceria, zirconia and ceria–zirconia solid solutions are about 5–10 nm. The results also show that zirconia is in the monoclinic phase and tetragonal phase and ceria is in a cubic phase with a fluorite structure.

A new method for fabricating semiconductor quantum rings has been developed. Instead of using the conventional GaAs cap layer, we used the GaAs/AlAs cap layer for the ring formation. The additional AlAs layer impedes the inward diffusion of the Ga and Al atoms and results in nicely formed ring structures with a more relaxed growth condition. Because of this layer, the ring-shaped structure can be maintained with a higher annealing temperature without being washed out by the intermixing of Ga/Al with In in the central region of the dots. The shape and the strain distribution of quantum rings have also been characterized by transmission electron microscopy.

The formation mechanism of stoichiometric MoSi₂ by mechanical alloying (MA) from elemental powders has been investigated. The experimental results demonstrate that molybdenum disilicide can be synthesized by MA through different formation mechanisms, which are governed by the milling energy. MoSi₂ is formed by the mechanism of self-propagating high-temperature synthesis (SHS) at high rotational speeds and most likely by the mechanism of a mechanical collision reaction (MCR) at lower rotational speeds. Nanocrystalline phase transformation of occurs during MA when the crystallite size decreases to approximately 8 nm; the final product of MA is β-MoSi₂.

Copper-doped zinc oxide nanowires were fabricated on copper-coated silicon substrate by sintering a mixture of zinc oxide and graphite powders at high temperature. Copper functioned as a catalyst in the zinc oxide nanowire growth and was incorporated during the growth as a dopant. The size of copper-doped zinc oxide nanowires ranges from 30 to 100 nm in diameter and tens to hundreds of microns in length. The photoluminescent excitation spectra showed multiple absorption peaks in the ultraviolet and blue/green region. Correspondingly, broad and continuous photoluminescence spectra were observed extending from the ultraviolet to the red region with shoulder peaks at room temperature, which is different from that of the bulk. The x-ray photoelectron spectroscopy and low temperature photoluminescence were employed to analyse the luminescent mechanism.

Force spectroscopy curves from a number of oxide surfaces have been recorded. Contact potential difference (CPD) curves recorded from two different areas of an MgO(100) surface are shifted in a manner consistent with local surface charging. This charging is removed by deposition of Fe or Cu. On an NiAl(110) supported alumina film we have investigated the use of frequency shift (Δf) versus distance curves as an analytical tool for chemical identification. Curves recorded from the bare substrate are clearly different to those recorded over adsorbates. This difference is likely to be due to local surface charging, since such differences are not observed in detuning curves recorded from domain boundaries of similar apparent height to the adsorbates.

During 2003, Dr R A Said published essentially duplicate versions of a paper in two archival journals: Nanotechnology and the Journal of The Electrochemical Society. The papers in question were: `Microfabrication by localized electrochemical deposition: experimental investigation and theoretical modelling' (2003 Nanotechnology14 523) and `Shape formation of microstructures fabricated by localized electrochemical deposition' (2003 J. Electrochem. Soc.150 C549). The two papers were submitted, revised, and published at essentially the same time. The papers used the same figures and neither paper referenced the other.

Nanotechnology requires a signed copyright-transfer form assigning copyright in articles published to Institute of Physics Publishing, and the Journal of The Electrochemical Society requires the same for The Electrochemical Society. It is a tradition of long standing, stated in the information for contributors, that submission implies that the work has not been submitted, copyrighted, or accepted for publication elsewhere. Hence, duplicate publication not only raises legal questions and represents a serious breach of scientific ethics, but also leads to an unnecessary imposition on readers', referees', and editors' time. We regard this infraction as a serious matter. An apology from the author for this grave error is printed below.

Author's apology

I have mistakenly published similar results in two manuscripts in Nanotechnology and in the Journal of The Electrochemical Society, as stated above. I am responsible for this error. I agree with the Editors that such a practice should not have occurred, and I would like to sincerely apologize to Nanotechnology and the Journal of The Electrochemical Society, their publishers, and their readers for this matter. I will take actions in the future to prevent the occurrence of similar incidents.

R A Said