Table of contents

High-resolution electron microscopy and energy-filtered imaging methods were used to examine single-wall carbon nanotubes and nanotube reinforced polyimide composites. The nanotubes were studied alone, in a polyimide matrix composite, and after deposition of composite material previously dissolved in a solvent. Energy-filtered images based on nitrogen core loss excitations were used to discern the presence of polyimide. Elemental maps of nanotubes extracted from the composite revealed good wetting of the nanotube surfaces by the polyimide.

Ideally, computational modelling techniques for nanoscopic physics would be able to perform free of limitations on the type and number of elements, while providing comparable accuracy when dealing with bulk or surface problems. Computational efficiency is also desirable, if not mandatory, for properly dealing with the complexity of typical nanostructured systems. A quantum approximate technique, the Bozzolo–Ferrante–Smith method for alloys, which attempts to meet these demands, is introduced for calculation of the energetics of nanostructures. The versatility of the technique is demonstrated through analysis of diverse systems, including multiphase precipitation in a five-element Ni–Al–Ti–Cr–Cu alloy and the formation of mixed composition Co–Cu islands on a metallic Cu(111) substrate.

We discuss the optimization aspects of nanofocusing recording probes. In this paper we also research all of the technological aberrations affecting the nanofocused spots. The probe numerical aperture (NA) has been elevated about threefold from 0.72 to 2.15 optimizing the diffraction functions under the full width at half maximum (FWHM) size of 130 nm. The microlens (ML) physical light efficiency is about nine times higher than the values published in previous works. The nanofocused spot is calculated as 25 nm for a micro-laser beam of 8 µm and the diffraction limit is 150 nm using NA = 2.153 for an entire ML diameter over 13 µm. We have obtained nanofocused spots from 20 nm at the geometrical limit and up to 130 nm at the diffraction FWHM size using anti-reflection coatings on both surfaces of the fabricated GaP ML array. The optical power throughput of the nanofocusing probe has been raised 4.0–4.75-fold applying antireflection optimization.

Nanostructured tungsten carbides were synthesized, for the first time, with a size distribution of 5–12 nm on ultrahigh surface area carbon material, by carbothermal hydrogen reduction (CHR) at 850°C and metal Ni promoted CHR at 650°C.

Charge trapping effect in silicon-rich oxide (SRO) films was investigated using capacitance versus voltage (C–V), current versus voltage (I–V) and current versus time (I–t) measurements in an Al/SRO/Si MOS-like structure. SRO layers with different thicknesses were deposited. The trapped charge density was found to depend on the thickness of the SRO layers. It was shown that the total trapped charges can be divided into two parts: one part is correlated with the Si nanoclusters located near the SRO/Si interface (interface-NCs); another one is correlated with the Si nanoclusters distributed in the bulk of the SRO layers (bulk-NC). A current peak was observed in the I–V curves in the surface inversion condition. The peak position voltage varies with the thickness of the SRO layers. The current peak is attributed to the charging/discharging of the interface-NCs. The charging/discharging process of interface-NCs was evidenced by a fast decay of current in I–t measurements at the current peak voltage. I–t curves recorded at a large positive voltage are associated with the charge trapping effect of the bulk-NCs. The Coulomb blockade effect was suggested to be the reason of current decay at constant voltage.

The electron mobility is calculated for Ga_0.5In_0.5P/GaAs quantum wells at 77 K. Deformation potential acoustic phonon and alloy scattering are assumed to be effective. Account has been taken of the energy band nonparabolicity and extension of the wavefunction into the Ga_0.5In_0.5P barrier layer. Calculated results for Al_0.3Ga_0.7As/GaAs quantum wells are also presented for comparison.

ZnO nano-rods were grown on polycrystalline Zn foil by cathodic electrodeposition in an aqueous zinc chloride/calcium chloride solution at 80°C. Variations in the solution concentration and substrate surface preparation were explored to shed light on the nucleation of the nano-rods. It was found that the nano-rod diameter increased with increasing solution concentration. Rolling striations and native ZnO on the surface of the Zn appeared to enhance nucleation and allowed more highly aligned, dense structures to be grown. By using low solution concentrations (5.0 × 10⁻⁴ M ZnCl ₂) and non-electropolished Zn substrates, well faceted, hexagonal nano-rod structures of dimension ∼80 nm diameter and >1 µm length were obtained. X-ray studies showed the samples to be highly aligned but containing a Zn-oxychloride impurity phase. Annealing caused the impurity phase to disappear and resulted in the films having a sharp photoluminescence double peak at 380/396 nm.

Long Bi₂S₃ nanowires have been prepared via the thioglyolic acid (HSCH₂COOH, TGA) assisted hydrothermal method. The x-ray diffraction pattern shows that the Bi₂S₃ nanowires obtained are of orthorhombic phase. High resolution transmission electron microscopy identifies that the Bi₂S₃ nanowires are single crystalline in nature. Furthermore, we give a preliminary presentation of the mechanism for the TGA-assisted hydrothermal synthesis of Bi₂S₃ nanowires.

Current perpendicular to the plane, giant magnetoresistance (GMR) and the spin-valve effect were observed in Co/Cu multilayered nanowires electrodeposited into self-organized nanoporous anodized aluminium templates grown at the surface of bulk aluminium. Pores as short as 2000 nm could be used. The pore bottom oxide layer was removed or thinned by chemical etching. Alternating Co and Cu layers of 10 nm in thickness were synthesized by pulse plating. 20% of GMR was observed in 100 Co/Cu bilayer nanowires at room temperature. Co/Cu/Co tri-layered nanowires clearly showed the typical resistance switching of spin-valves.

A low-temperature chemical vapour deposition method has been successfully developed for synthesizing single-crystalline Te nanobelts in bulk quantity from Al₂Te₃ powder and H₂O. The nanobelts had a uniform single-crystal hexagonal structure with width ranging from 50 to 300 nm, thickness about 10–20 nm, and lengths up to several tens of micrometres. The growth of Te nanobelts is controlled by a vapour–solid crystal growth mechanism. The method is very simple and the as-synthesized products are pure, so it represents a practical approach to large-scale synthesis of pure single-crystal Te nanobelts.

The diffraction efficiency as a function of the externally applied voltage exhibits an unusual trend for a holographic grating written in a nanotube-doped liquid-crystal cell composed of two glass substrates with asymmetric patterns of filmy transparent indium–tin oxide. Experimental evidence suggests that output energy redistributes among multiple orders of diffraction at various dc biases.

Strong photoluminescent emission has been obtained from 3 nm PbS nanocrystals in aqueous colloidal solution, following treatment with CdS precursors. The observed emission can extend across the entire visible spectrum and usually includes a peak near 1.95 eV. We show that much of the visible emission results from absorption by higher-lying excited states above 3.0 eV with subsequent relaxation to and emission from states lying above the observed band-edge of the PbS nanocrystals. The fluorescent lifetimes for this emission are in the nanosecond regime, characteristic of exciton recombination.

We present low-temperature heat capacity measurements performed on two different kinds of single-walled carbon nanotube bundles which essentially differ in their mean number of tubes (N_T) per bundle. For temperatures below a few kelvin, the vibrational heat capacity can be analysed as the sum of two contributions. The first one is a regular T³ phononic one, characteristic of the three-dimensional (3D) elastic character of the bundle for long-wavelength phonons. A crossover to a lower effective dimensionality appears at a few kelvin. From the 3D contribution, we estimate a mean sound velocity, and hence a mean shear modulus of the bundle. The difference in amplitude of the acoustic term and in the crossover temperature between the two samples is ascribed to the different bundle topology (i.e. N_T). The second contribution, of similar amplitude in both kinds of samples, shows a peculiar power law T^α variation (α < 1) indicative of localized excitations, very probably due to intrinsic structural defects of the nanotubes.

A simple and cost-effective method of patterning photonic crystal (PhC) or similar structures by electron beam lithography is demonstrated. Instead of using fine resolution and a multitude of small-sized beam spots to write a single hole, the combination of a single electron-beam spot having the size of the hole and a position resolution equal to the period of the PhC is used. This single-spot exposure scheme typically shows an order-of-magnitude reduction in the required job time compared to that for the conventional multi-spot exposure scheme. In addition, the inherently circular shape of the electron-beam spot is directly transferred into the UV3 resist used in this work, leaving uniform circular holes after development. A cross-sectional view of the holes shows a very good verticality in the sidewalls of the resist. A modified scheme using four spots is also demonstrated which alleviates some limitations encountered in the single-spot exposure scheme.

Metal nanoclusters can be produced cheaply and precisely in an electrochemical environment. Experimentally this method works in some systems, but not in others, and the unusual stability of the clusters has remained a mystery. We have simulated the deposition of the clusters using classical molecular dynamics and studied their stability by grand-canonical Monte Carlo simulations. We find that electrochemically stable clusters occur only in those cases where the two metals involved form stable alloys.

Coupling agents have been widely used to retard the sintering of silver paste and minimize co-firing defects due to densification mismatch between silver and dielectrics. The thermal-decomposition and crystallization behaviour of the coupling agent is a subject of great concern. Formation of the coupling agent layer is achieved by coating an Ag powder surface with Zr, Al or Ti organometallic compounds. Differential thermal analysis (DTA) detected an exothermic peak in Ag powder surfaces coated with Zr, Al or Ti which was absent in the uncoated silver powder. The exothermic peak clearly indicates the presence of the organic coupling agent on the Ag powder surface. The exothermic peak is absent when the sample is analysed in an N₂ atmosphere, which suggests that the exothermic peak is related to oxidation of the coupling agent. To elucidate what is responsible for the oxidation, Ti organometallic compounds were calcined to different temperatures (350, 400, 500, 600 °C) for 2 h and the crystallization behaviour determined by x-ray diffraction (XRD). This demonstrated the presence of an anatase phase until a temperature of greater than 350 °C, and the intensity of the crystalline peak of (101) at 2θ = 25.3° increased continuously with the dwell time. Combining the results of DTA and XRD, it was found that formation of nanocrystallized titania accompanied the combustion of organometallic compounds.

In this paper we describe how the effect of irradiation-and strain-induced surface processing of elastomer surfaces (Katzenberg  2001 Macromol. Mater. Eng.286  26) can be exploited for production of highly regular nanostructured metallization layers. Poly(dimethyl siloxane) elastomer was treated under one-dimensional strain by an argon plasma to exhibit highly oriented surface undulations with nearly uniform periods and amplitudes. The microstructured silicone surface topography was evaporated under a tilt angle of 45° with platinum and subsequently mechanically strained up to 30%. This treatment results in the formation of platinum ribbons or rods with a width which is similar to the wavelength of the silicone surface undulations. The gaps between the rods can be reproducibly tuned by strain of the silicone substrate between a few nm up to some 100 nm. To fix a special gap width between a set of nanorods arranged in parallel, the metallization on top of the silicone can be transferred completely to another polymer support.

Our ability to analyse charge transport through a biological macromolecule, pertinent to our understanding not only of biological redox processes but also, for example, to our interpretation of tunnelling imaging, remains a significant practical and theoretical issue. Though much information can be gained by carrying out such examinations at a molecular level, there exist few methods where such controlled analyses are, in fact, feasible. Here we report on the electron transport characteristics of a blue copper metalloprotein as characterized at a refined level by conductive-probe atomic force microscopy. The modulation of this conductance with compressional force has also been examined. Though highly resistive, observations are consistent with the ability of the protein matrix to mediate appreciable tunnelling current. This work, then, paves the way for designed implementation of biomacromolecules into electronic devices.

We report on techniques for catalytic synthesis of rigid, high-aspect-ratio, vertically aligned carbon nanofibres by dc plasma enhanced chemical vapour deposition that are tailored for applications that require arrays of individual fibres that feature long fibre lengths (up to 20 µm) such as scanning probe microscopy, penetrant cell and tissue probing arrays and mechanical insertion approaches for gene delivery to cell cultures. We demonstrate that the definition of catalyst nanoparticles is the critical step that enables growth of individual, long-length fibres and discuss methods for catalyst particle preparation that allow the growth of individual isolated nanofibres from catalyst dots with diameters as large as 500 nm. This development enables photolithographic definition of catalyst and therefore the inexpensive, large-scale production of such arrays.

A precise experimental investigation of the amplitude and phase resonance curves of a driven dynamic force microscope (DFM) cantilever interacting with an Al₂O₃(0001) surface in ultra-high vacuum is reported. The large amplitude (a few tens of nanometres), high cantilever stiffness (25 N m⁻¹) and high quality factor (a few 10⁴) characterizing these experiments are typical of the frequency modulation (FM) mode of DFM. The whole range of tip–substrate distances where a stationary oscillation of the cantilever can be maintained is explored. It covers two different regimes: a large distance regime where only long range conservative van der Waals interactions contribute and a small distance regime where short range interactions play a significant role. A comparison is made with frequency shift and excitation amplitude curves as a function of the distance acquired in the FM mode. It is also shown that approach–retract amplitude and phase curves usually obtained in the amplitude modulation mode can be extracted from these data. These experimental results are compared with analytical predictions reported in the literature. An excellent agreement is found in the van der Waals domain, allowing us to evaluate the Hamaker constant for the alumina–vacuum–silicon system.

We report on a study of the electrical-transport properties of monolayers of phthalocyaninepolysiloxane (PcPS) polymers, and evaluate their potential for use as molecular wires. Monolayers have been deposited with the Langmuir–Blodgett technique on top of Si/SiO₂ substrates with interdigitated electrodes. Current–voltage curves have been measured as a function of temperature for samples with varying electrode distance and number of monolayers. In the undoped state, the conduction is well described by the space-charge-limited-current model. From the data we obtain material characteristics such as the density of trap states within the gap and an estimate of the charge-carrier mobility. It appears that the conductivity is too low to yield a measurable current through a single PcPS polymer. Chemical doping and a field effect have been investigated. Oxygen is effective in doping the PcPS layers, resulting in a two orders of magnitude increase of the conductivity. Iodine is not effective as a dopant. By application of a voltage on a back-gate, we observe a field-effect-induced increase of the conductivity by three orders of magnitude. The effect however decays rapidly in time.

We have demonstrated the electrical modification of a conductive polymer for data storage using a scanning probe microscope (SPM). A blend of polyaniline and polymethyl-methacrylate as the conductive polymer was spun on a silicon substrate to make a test specimen. The tip of a conductive SPM probe was placed in contact with the conductive polymer and electrical modification was carried out by applying a voltage between the SPM probe and the conductive polymer. The conductance image and a simultaneous topographic image were taken with the SPM. It was found that the electrical conductivity was decreased more than 20 times by this modification. Measurement of the topographic image shows no obvious change to the surface topography in the modified area. Measurement of the I–V characteristics suggests that a chemical reaction occurred at an applied voltage of about 3.2 V.

We would like to acknowledge the contribution of R Seidel, M Mertig and W Pompe to this work by adding their names as co-authors of the published article. The correct list of authors for the paper `Controlled positioning of a DNA molecule in an electrode setup based on self-assembly and microstructuring' is

G Maubach¹, A Csáki¹, R Seidel², M Mertig², W Pompe², D Born¹ and W Fritzsche¹

¹Institute for Physical High Technology, PO Box 100239, 07702 Jena, Germany ²Max-Bergmann-Center of Biomaterials and Institute of Materials Science, Technical University Dresden, D-01169 Dresden, Germany.