Table of contents

Dense BaTiO₃ ceramics with 50 nm average grain size obtained by spark plasma sintering were investigated. The dielectric data show a broad ferro–para phase transition with a maximum permittivity of at 390 K and 1 kHz. The local ferroelectric switching behaviour was investigated by piezoresponse force microscopy. Typical piezoelectric hysteresis loops were recorded at different positions of the sample. The present results provide experimental evidence for polarization switching at the local scale, indicating that the critical grain size for the disappearance of ferroelectric behaviour in dense, bulk BaTiO₃ nanocrystalline ceramics is below 50 nm.

Piezo-induced picosecond nonlinear optical effects are investigated in polyvinyl alcohol photopolymer doped by YAB:Cr nanocrystallites of 10–40 nm size. The second harmonic generation (SHG) is studied versus the applied uniaxial mechanical stress up to 20 GPa. The observed phenomena are explained within a framework of fifth-order nonlinear optical susceptibilities with the inclusion of piezo-induced phonons, which favour the observed non-centrosymmetric electron–phonon anharmonicity. The substantial role of the nanocrystalline confinement effect in the observed phenomenon is demonstrated through the size-dependent behaviour of the effective second-order susceptibility. Quantum chemical and molecular dynamics simulations of the observed phenomenon are carried out.

Flower-like Bi₂S₃ nanostructures consisting of nanorods with a lateral size of about 30 nm have been prepared via a thioglycolic acid (HSCH₂COOH, TGA) assisted hydrothermal method. The x-ray diffraction (XRD) pattern shows that the obtained flower-like Bi₂S₃ nanostructures are of orthorhombic phase. High-resolution transmission electron microscopy (HRTEM) identifies that the flower-like Bi₂S₃ nanostructures are single crystalline in nature. It is believed that the sodium thiosulfate (STS) as the sulfur source could facilitate the formation of flower-like embryos and the TGA could enhance the anisotropic growth of Bi₂S₃ nanorods initiated from the embryos. STS and TGA play the key roles in the formation of flower-like Bi₂S₃ nanostructures during the hydrothermal process.

Carbon nanotube-attached atomic force microscope probes were successfully used without nanotube bending to make simultaneous precision nano-oxidation and faradaic current measurements in the dynamic mode. Probe oxidation on H-passivated Si(001) surfaces was carried out by two methods involving vector-scan and raster-scan with a much higher resolution and precision compared to the nanofabrication by standard cantilevers. Faradaic current of the order of a sub-picoampere was detected during nano-oxidation using a carbon nanotube probe, accurately reflecting the subtle difference in the oxidation reaction. The minute current detection through the AFM tip is sensitive enough for the detection of very thin oxides and small-sized features. The dimension of the meniscus during nano-oxidation, which is indispensable for establishing the mechanism model, was evaluated, based on the in situ faradaic current detection and edge broadening.

We present an automation technique for the growth of electron beam deposited tips on whole wafers of atomic force microscope cantilevers. This technique uses pattern recognition on scanning electron microscope images of successive magnifications to precisely place the tips on the cantilevers. We demonstrate the capabilities of the working system on a four-inch wafer of microfabricated small cantilevers with a total of approximately 2100 levers per week.

A real-time scanning algorithm is suggested which uses features of the surface as reference points at relative movements. Generally defined hill- or pit-like topography elements are taken as the features. The operation of the algorithm is based upon local recognition of the features and their connection to each other. The permissible class of surfaces includes ordered, partially ordered, or disordered surfaces if their features have comparable extents in the scan plane. The method allows one to exclude the negative influence of thermodrift, creep, and hysteresis over the performance of a scanning probe microscope. Owing to the possibility of carrying out an unlimited number of averages, the precision of measurements can be considerably increased. The distinctive feature of the method is its ability of topography reconstruction when the ultimate details are smaller than those detectable by a conventional microscope scan. The suggested approach eliminates the restrictions on scan size. Nonlinearity, nonorthogonality, cross coupling of manipulators as well as the Abbé offset error are corrected with the use of scan-space-distributed calibration coefficients which are determined automatically in the course of measuring a standard surface by the given method. The ways of precise probe positioning by local surface features within the fine manipulator field and the coarse manipulator field, automatic probe return into the operational zone after sample dismounting, automatic determination of exact relative position of the probes in multiprobe instruments, as well as automatic successive application of the whole set of probes to the same object on the surface are proposed. The possibility of performing accurately localized low-noise spectroscopy is demonstrated. The developed methodology is applicable for any scanning probe devices.

We demonstrate the bulk synthesis of single crystalline Cu-doped ZnO nanowires using (CuI+ZnI₂) powders at 600 °C. These mass nanowires are characterized through x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction, and high-resolution TEM; they have uniform diameters of about 65 nm and are several tens of microns in length. The growth of ZnCuO nanowires is suggested for self-catalyzed vapour–liquid–solid. In particular, the PL spectra of these nanowires show emission peaks that strongly shift to long wavelength with increasing Cu, and the doping quantity is found to be responsible for the different characteristics; the PL mechanism is explained in detail.

The properties of organic/inorganic poly(3-hexylthiophene) (P3HT):TiO₂ nanocomposite films and nanocomposite based solar cells as a function of TiO₂ concentration and the solvent used for the film fabrication were studied. For low nanoparticle concentration (20–30%) the device performance was worse compared to pure P3HT, while for nanoparticle concentration of 50% and 60% significant improvements were obtained. P3HT photoluminescence quenching in 600–800 nm spectral region changes by a factor of two for the increase in TiO₂ concentration from 20% to 60%, while the AM1 power conversion efficiency increases times. Photoluminescence quenching and solar cell efficiency were found to be strongly dependent not only on nanoparticle concentration but also on the solvent used for spin-coating. The changes in the film and device properties were explained by the change in the film morphology. For optimal fabrication conditions, external quantum efficiency up to 15% and AM1 power conversion efficiency of 0.42% were obtained.

Titania–surfactant inorganic–organic nanocomposites with wormhole-like framework mesostructure were synthesized based on self-assembly between a neutral amine surfactant (dodecylamine) and a neutral inorganic precursor (tetrabutyl titanate). The prepared nanocomposites were characterized by x-ray diffraction (XRD), Fourier transformed infrared spectra (FTIR) and x-ray photoelectron spectroscopy (XPS). The optical absorption and photoluminescence spectra have been measured. It has been found that TiO₂–surfactant inorganic–organic nanocomposites have a significant red shift of the optical absorption band edge in contrast to that of bulk TiO₂, and an unusual room temperature photoluminescence (RTPL). The results obtained indicate that the interfacial effect between the titanium dioxide and the surfactant plays an important role in the optical properties.

Superconducting Pb nanowire arrays with diameters of about 45 nm have been fabricated by electrodeposition using anodic porous alumina templates. The Pb nanowires were of crystalline face-centre cubic structure and structurally uniform. The temperature dependence of their magnetic behaviour was investigated. The Pb nanowire arrays exhibit anisotropy, and the Meissner effect of the nanowires is entirely different from that of the bulk Pb; irreversible type II superconductor behaviour has been observed in the Pb nanowires at 5 K.

Molecular dynamics simulations of nanoscratching are performed with emphasis on the correlation between the scratching conditions and the defect mechanism in the substrate. More than six million atoms are described by the embedded atom method (EAM) potential. The scratching process is simulated by high-speed ploughing on the Al(111) surface with an atomic force microscope (AFM) tip that is geometrically modelled to be of a smoothed conical shape. A repulsive model potential is employed to represent the interaction between the AFM tip and the Al atoms. Through the visualization technique of atomic coordination number, dislocations and vacancies are identified as the two major defect types prevailing under nanoscratching. Their structures and movements are investigated for understanding the mechanisms of defect generation and evolution under various scratching conditions. The glide patterns of Shockley partial dislocation loops are obviously dependent upon the scratching directions in conjunction with the slip system of face-centred cubic (fcc) single crystals. It is shown that the shape of the AFM tip directly influences the facet formation on the scratched groove. The penetration depth into the substrate during scratching is further verified to affect both surface pile-up and residual defect generations that are important in assessing the change of material properties after scratching.

We present the microfabrication of silicon nitride membrane supports ('windows') for transmission electron microscopy (TEM) and illustrate their usefulness for direct preparation and studies of nanostructures. These membrane 'windows' enable TEM to be incorporated as an affordable diagnostic tool in nanostructure fabrication and applications thereof, in an iterative fashion, both during and after preparation as well as subsequent experimental steps with the nanostructures, and even for real time in situ TEM observations. Several examples are shown, including protein adsorption and nanofabrication for applications in heterogeneous catalysis.

We theoretically study the conducting electronic contribution to the cohesive force in a metallic nanowire irradiated under a transversely polarized external electromagnetic field at low temperatures and in the ballistic regime. In the framework of the free-electron model, we have obtained a time-dependent two-level electronic wavefunction by means of a unitary transformation. Using a thermodynamic statistical approach with this wavefunction, we have calculated the cohesive force in the nanowire. We show that the cohesive force can be divided into two components, one of which is independent of the electromagnetic field (static component), which is consistent with the existing results in the literature. The magnitude of the other component is proportional to the electromagnetic field strength. This extra component of the cohesive force is originally from the coherent coupling between the two lateral energy levels of the wire and the electromagnetic field.

The in vitro release behaviour of indomethacin (IMC, 1-[p-chlorobenzoyl]-2-methyl-5-methoxy-3-indoleacetic acid) encapsulated in poly(lactic acid-co-ethylene oxide) (PLA–PEO) nanospheres is investigated based on two mathematical models: the diffusion model derived from Fick's law and the dissolution model from the mass balance of IMC. A dual chamber transport system (DCTS) is designed and used for the in vitro experiment. The release behaviour of IMC from the PLA–PEO drug delivery systems (DDSs) is compared to the mathematical models suggested in this work. The synthesis of PLA–PEO and the fabrication of the IMC-loaded PLA–PEO DDSs are discussed and characterized by¹H NMR, transmission electron microscopy (TEM) and quasi-elastic light scattering (QELS) spectroscopy. Spherical PLA–PEO nanospheres are well prepared as a model DDS as suggested by the characterization results. The overall releasing behaviour of the model drug can be manipulated by varying several key parameters including the volumetric ratio between the organic and the aqueous phase (V_r), the partition coefficient (K_p) and the encapsulation efficiency (EE). Modelling results show that the releasing mechanism is different depending on the particle size. When large PLA–PEO nanospheres are fabricated, the dissolution mechanism can be effective, as the dissolution of IMC can be a rate-determining step due to its high hydrophobicity in an aqueous surrounding medium. In this manner, the optimum DDS can be suitably designed and the releasing profile can be also estimated by considering several major factors for a specific type of substance and its purpose.

Scanning electron microscopy (SEM) is widely used for the inspection of nanostructures such as nanocrystallites and nanotubes as well as quantum wells and many other sub-micrometre devices. Some published papers show that the apparent size of small details in SEM images appear larger than their real dimension as obtained from transmission electron microscopy, for instance. A possible explanation is deduced here from the use of two simple models for the radial distribution of the emitted secondary electrons to simulate SEM intensity profiles across stripes of increasing widths, D, with respect to the incident probe diameter, d. Supported by a comparison to published data obtained on quantum wells of increasing widths, the results show that the apparent size of small details appears to be larger than their real dimension and the apparent distance between small details may appear less than their real dimension. The same approach permits us to define strategies to minimize the errors when the dimension of details is of the order of or less than the effective resolution of the operated SEM.

In this paper we study the properties of microring resonator structures fabricated with high-index-of-refraction dielectric material. These structures concentrate light and can produce very strong optical potential gradients. They are of great interest for the trapping, manipulation and transport of cold atoms near surfaces. The study consists of two parts: in the first part we investigate the symmetry properties of the resonator response for simple models of the microring structures. In the second part we present detailed numerical calculations of the actual spectra for realistic microfabricated structures. We employ the direct space integral equation method (DSIEM). This method, based on a volume integral solving procedure, has already been found to cope successfully with nonresonant dielectric nanostructures. Such ab initio investigations of the optical near-field distributions only require a specification of the frequency-dependent dielectric constant and the precise shape of the fabricated structures. Consequently, these calculations can stand alone, or complement and inform anticipated experimental studies.

Interest in using electrostatics for active nano-assembly has grown significantly over the last five years. One common electret structure for such electrostatic constructs is the silicon–silicon dioxide interface. In this paper, an experimental and mathematical analysis of the process of writing negative charge spots in Si–SiO₂ is presented. It is demonstrated that controlling the spread of the charge can reduce the spot size and the drop in written potential. Simulation results of a one-dimensional charging model that assumes tunnelling of electrons through the oxide and trapping within SiO₂ are presented and compared with the experimental data. The model assumes charge trapping at the Si–SiO₂ interface and none at the oxide–air interface or within the oxide bulk. Conducted experiments also show that although the lateral spread of charge places a lower limit on the minimum spot size in silicon–silicon dioxide structures, the use of a hydrophobic hexamethyldisilazane layer can be effective in improving the size stability of the written electrical spots.

White light emission was obtained from a light-emitting diode prepared from polymer/quantum dot nanocomposites consisting of poly(9,-dihexylfluorene-2,7-divinylene- m-phenylenevinylene-stat-p-phenylenevinylene) (PDHFPPV) and two kinds of CdSe nanoparticles with different particle size. Blue emission from the polymer, green emission from the  nm CdSe and red emission from the  nm CdSe, which is triggered by partial excitation energy transfer from the polymer, jointly contribute to white emission of the organic–inorganic hybrid device. Also, the blue-emitting matrix polymer makes the device preparation process simpler due to its high processability. By controlling the blend ratio, we could obtain a pure white colour from the hybrid device.

A molecular dynamics simulation of ultrathin gold nanowires for tensile behaviour has been carried out. Ultrathin nanowires, unlike the bulk FCC structure, have a multi-shell helical structure. This work compares the mechanical properties of the 7-1 multi-shell helical structure with those of the FCC structure. The results reveal that the temperature and the strain rate influence the yielding stress. One atom chain was detected before the nanowire broke when the temperature was near absolute zero. At room temperature, severe interaction between atoms caused successive yielding and a cluster of three atoms in cross-section was formed before the nanowire broke.

A thiol linkage designed to act as a 'conducting flange' between a carbon nanotube and a gold(111) surface is investigated computationally. Such a flange could be used to anchor long nanotubes in nanotube-based devices or, using short nanotubes, to build controlled interfaces between electrodes and molecular electronic devices for use in electronic circuits on the 1 nm scale. Density-functional calculations indicate that, even though the nanotube considered is of the 'metallic type', a Schottky barrier forms at the interface which restricts charge flow to and from short-length nanotubes. In fact, at realistic applied field strengths, sufficient charge cannot be forced onto short nanotubes for them to be useful as part of a gate electrode in a 1 nm sized field-effect device. However, the electronic density of states of short flanged nanotubes is calculated to be significant at the metal Fermi energy. Hence, adequate electrical conductivity is expected through the flange under a conductance tunnelling scenario, making the junction useful in purely nanotube-based devices. Principles of mechanically sound flange design are also considered through high-temperature molecular dynamics studies. The need to establish proper gold–sulfur binding is stressed, with strained junctions involving five thiol linkages shown to lead to lower barriers to translation than one single, fully relaxed, junction.

Two-dimensional arrays of silicon nanocrystals embedded in ultrathin SiO₂ layers for application in silicon nanocrystal memories were fabricated by a three-step process: (a) growth of a tunnelling silicon oxide, (b) low pressure chemical vapour deposition (LPCVD) of a thin layer of amorphous silicon (α-Si), and (c) solid phase crystallization of the α-Si layer in a high temperature furnace under nitrogen flow, followed by thermal oxidation in the same furnace. Transmission electron microscopy (TEM) was used for the structural characterization of the three-layer structure and the determination of layer thicknesses and silicon nanocrystal size, while capacitance–voltage (C–V) and current–voltage (I–V) measurements were used to investigate the charging properties of the silicon nanocrystal layer. In an attempt to increase the silicon nanocrystal density, as suggested in the literature, a dip of the oxidized wafer in diluted HF before LPCVD deposition was used, but this step was found to seriously affect the charging properties of the structure.

The shift in technology away from silicon complementary metal–oxide semiconductors (CMOS) to novel nanoscale technologies requires new design tools. In this paper, we explore one particular nanotechnology: carbon nanotube transistors that are self-assembled into circuits by using DNA. We develop design tools and demonstrate how to use them to develop circuitry based on this nanotechnology.

Fatigue of nanostructures is one of the important issues that can affect the reliable operation of micro/nanoelectromechanical systems (MEMS/NEMS). Nanoscale bending and fatigue test methodologies were developed using an atomic force microscope (AFM) to measure the elastic modulus and fatigue properties of the nanoscale hinge directly on a digital micromirror device (DMD) chip. The bending and fatigue test methodologies performed on the nanoscale could potentially be applied to other MEMS/NEMS devices.

The photoluminescence from epitaxially grown GaN/AlN quantum dots (QDs) has been engineered by capping the surface either with a nanoscale thin silver layer or silver nanoshell structures. The spontaneous emission rate in strained and large QDs is enhanced due to resonant surface-plasmon interaction at the continuous Ag nanolayer–semiconductor interface as observed by the decrease (typically 3–5 times) in the photoluminescence (PL) intensity. The photoluminescence from strained QDs can also be dramatically enhanced by patterning the AlN-capped GaN dots layers with Ag nanoparticles. The enhancement depends on the size and distribution of the Ag nanoparticles at the surface of the QDs. The Ag nanoparticles act as radiating dipole sources and the emission from the QDs is resonantly coupled into these Ag particles, resulting in a relative enhancement of the PL emission compared to the off-resonant GaN buffer layer. The changes in luminescence in the ultraviolet regime (both quenching or enhancement) due to the modification of the emission rate in the QDs are comparable to the near-infrared regime based GaAs or InP quantum wells.

We present an overview of ab initio plane-wave density functional theory calculations performed on DNA-based model complexes and realistic helices. After elucidating the predictions concerning the effects of hydrogen pairing and stacking interactions on the formation of dispersive energy bands and delocalized orbitals, we focus our attention on metal–nucleotide coupling and hybridization. The latter effects are currently explored as a factor that may enhance DNA conductivity.

Dynamic scanning force microscopy (dynamic SFM) images of (001) surfaces of KBr which have been prepared by cleavage and further decorated by nanometre-sized gold clusters in UHV are presented. During scanning we could achieve atomic resolution on the KBr substrate surface; however, the clusters mostly appeared as hemisphere-like or fuzzy objects exhibiting only a few details of their internal structure. We performed force spectroscopy measurements above single clusters which might point to a charging of the clusters. We anticipate that mainly a long-range electrostatic interaction between the cluster and the macroscopic tip apex determines the appearance of the clusters. Information on the interior of the clusters can be gained only for short tip–cluster distances in the presence of a short-range, chemical interaction between the cluster and the tip atoms closest to the surface.

Solvothermal synthesis of La(OH)₃ sol and microwave radiation drying of La(OH)₃ nanorods were employed for the first time to synthesize La₂O₃ nanorods with diameters around 10 nm and lengths up to 200 nm. The resulting products were characterized with XRD, TEM and HRTEM. Microwave radiation drying was found to be more effective to maintain the morphologies of nanorods than conventional drying.

Nanocomposites of polyaniline (PANI)–titanium dioxide (PANI–TiO₂) are prepared from a colloidal sol of TiO₂ nanoparticles. The dc and ac conductivities of samples with different concentrations of PANI have been investigated as a function of frequency and temperature. The dc conductivity follows three-dimensional variable range hopping. The ac conductivity has been interpreted as a power law of frequency. The temperature variation of the frequency exponent suggests a correlated barrier hopping conduction process in the nanocomposites. A very large dielectric constant of about 3700 at room temperature has been observed. An electric modulus presentation is used to interpret the dielectric spectra. The interface between polyaniline and TiO₂ plays an important role in yielding a large dielectric constant in the nanocomposite.

In this paper, the humidity sensing properties of multi-walled carbon nanotubes modified with LiClO₄ are investigated. The new sensing material is characterized by FESEM, FTIR, Raman, ICP and XPS. For comparison, the humidity sensing characteristics of the four conventional materials MnWO₄ (hubnerite), BaTiO₃ (perovskite), NiWO₄ (huberite), and ZnCr₂O₄ (spinel) are also discussed. The selectivity of the new humidity sensing material is studied. Finally, the response to water vapour of the new sensing material is discussed by using a dynamic testing method.

This paper illustrates the use of computer simulation in understanding the interaction of nano-scale synthetic molecules with cellular membranes, which are themselves a few nanometres thick. Specifically, the interaction of a membrane-bound synthetic molecule with a model membrane has been studied using so-called coarse-grain (CG) molecular dynamics (MD). The reported CG-MD simulations have been carried out for a pore-promoting hydraphile molecule in a dimyristoylphosphatidylcholine (DMPC) lipid bilayer. Analysis of the CG-MD simulation provides insights into the nature of the interaction of the hydraphile with the lipid molecules and how an initially fully extended trans-membrane hydraphile adjusts its end-to-end distance to match the bilayer thickness. The equilibrium membrane-bound hydraphile conformation observed in the CG-MD simulation agrees well with deductions based on experimental observations. The success of the CG-MD approach in the present example suggests that the methodology could be used as a design tool in related nano-science and engineering applications.

The nature of the interaction between plant cell wall polysaccharides was investigated by force spectroscopy and computer simulations. Single xyloglucan molecules were tethered between a cellulose substrate and an atomic force microscope tip, which was cycled at rates from 0.1 to 7 Hz. The force–extension curves showed force plateaux of tens of piconewtons, in some cases multiple, with no clear rate dependence. Similar force plateaux were predicted by simulations of polymer chains adsorbed to a flat surface and a virtual cantilever, using a coarse-grained Monte Carlo approach. The simulated plateaux were five to ten times smaller than those obtained by experiment. The experimental plateau energies suggest that at least one hydrogen bond per backbone glucose residue is involved in the interaction. Multiple plateaux always decrease in height with extension, implying a self-tensioning system. This behaviour in a biological nanocomposite could have applications in the manufacture of novel synthetic nanocomposites.

Electrically insulating tips prepared by carbon deposition are used as sensitive detectors of nanoscale charge patterns on cleaved insulating surfaces. Dynamic scanning force microscopy images recorded with a neutral carbon tip reveal the surface topography and strong local charging at step edges while images taken with a charged tip exhibit subtle contrast features resulting from charges located at or beneath the surface of flat terraces. Analysing dynamic phenomena during imaging allows a determination of charge polarity and identifies sub-surface charges as trapping centres for charges exchanged between the tip and the surface. A density of a few hundred charged sub-surface defects per μm² is determined on while the defect density is one order of magnitude smaller on CaF₂(111). The method allows the detection of elementary charges at room temperature.

Large-scale and uniform Dy(OH)₃ nanorods have been successfully prepared by a simple hydrothermal method. Subsequent thermal decomposition of the as-prepared Dy(OH)₃ nanorods produced Dy₂O₃ nanorods. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA) and differential thermal analysis (DTA) have been employed to characterize the products. XRD and SAED patterns showed the Dy(OH)₃ nanorods were a pure hexagonal phase and single-crystal in nature. FMSEM and TEM images showed that the diameters of the Dy(OH)₃ nanorods ranged from 40 to 50 nm and the lengths ranged from 300 to 500 nm. The Dy₂O₃ nanorods inherited their parents' morphology, but their size is slightly shrunk in comparison with the Dy(OH)₃ nanorods. The formation mechanism of Dy(OH)₃ nanorods is discussed. Photoluminescence measurement shows that the nanorods have two emission peaks around 490 and 575 nm, which should come from the electron transition from ⁴F_9/2 to ⁶H_15/2 levels and ⁴F_9/2 to ⁶H_13/2 levels, respectively.

We report the growth of oriented nanowires of manganites within the pores of anodic alumina (AAO) templates. The processing of stoichiometric nanowires of La_0.67Sr_0.33MnO₃ (LSMO) at relatively low temperatures (870 K) is greatly aided by the linear chain polymer cation complex formed by ethylene glycol. The nanowires were found to grow preferentially along the direction of cubic LSMO. The growth of oriented nanowires was achieved by: (a) electrostatically confining the sol particles to the core regions of the cylindrical pores of the template—this avoids heterogeneous nucleation of LSMO on amorphous pore walls and (b) introducing a polymer matrix that serves as a backbone structure to the growing crystallites—this facilitates reorientation of the grains during heat treatment. The nanowires are ferromagnetic at room temperature and exhibit a ferromagnetic transition temperature (T_c) of 370 K.

Composites of conjugated poly(3-hexylthiophene) (P3HT) and the fullerene derivative [6,6]-phenyl-C₆₁ butyric acid methyl ester (PCBM) demonstrate an efficient photogeneration of mobile charge carriers. Thermal annealing of P3HT:PCBM based devices gives rise to a significant increase of the photovoltaic efficiency, as follows from measurements of the external quantum efficiency and the current–voltage characteristics. Upon annealing, the absorption spectrum of the P3HT:PCBM composite undergoes a strong modification, whereas in the pure components it remains unchanged. The absorption of the annealed blends becomes stronger and red shifted in the wavelength region ascribed to P3HT, while the absorption due to the PCBM contribution does not change. Atomic force microscope measurements on P3HT:PCBM disclose some variation in morphology due to the crystallization of PCBM. The concentration of the PCBM clusters and their size (up to 500 nm) were found to be correlated with the amount of PCBM in the blend. We have studied the performance of photovoltaic devices with different weight ratios of P3HT:PCBM, namely, 1:3, 1:2, 1:1.5, 1:1, 1:0.9, 1:0.8, and 1:0.7. The photocurrent and the power conversion efficiency showed a maximum between 1:1 and 1:0.9. We conclude the variation in the absorption spectrum and the red shift to result from molecular diffusion of PCBM out of the polymer matrix upon annealing. The growth of the PCBM clusters leads to formation of percolation paths and, therefore, improves the photocurrent. Above a certain concentration, the PCBM crystals provide mechanical stress on the metal electrode, therefore possibly damaging the interface. Optimization of the composite weight ratio reveals the important role played by morphology for the transport properties of bulk heterojunction P3HT:PCBM based solar cells.

Using an electron holographic technique, we investigated the charging-up phenomena of BaTiO₃ particles under electron beam irradiation. BaTiO₃ particles were confirmed to be charged up by electron irradiation just after insertion in a transmission electron microscope (TEM). However, the amount of the electric charge induced by electron irradiation was found to decrease by further irradiation in a TEM. After irradiating for 1.5 h, about half of the electrical charge was lost compared with that in the initial state. This implies that the electric resistivity of the particle decreased upon irradiation. In addition, this reduction process of the resistivity due to irradiation was confirmed to be an irreversible reaction. It could be concluded that the reduction of resistivity is attributed to the generation of oxygen vacancies due to the irradiation. The electron irradiation technique can be considered to be a new modification method of conductivity in BaTiO₃-based materials.

Multiple emission peaks have been observed from surface passivated PbS nanocrystals displaying strong quantum confinement. The emission spectra are shown to be strongly dependent on the excited-state parity. We also find that intraband energy relaxation from initial states excited far above the band-edge is nearly three orders of magnitude slower than that found in other nanocrystal quantum dots, providing evidence of inefficient energy relaxation via phonon emission. The initial-state parity dependence of the photoluminescent emission properties suggests that energy relaxation from the higher excited states occurs via a radiative cascade, analogous to energy relaxation in atomic systems. Such radiative cascade emission is possible from ideal zero-dimensional semiconductors, where electronic transitions can be decoupled from phonon modes.

The feasibility of improving polymer composites was investigated using 30 nm SiC nanoparticles in a vinyl ester resin. Even when the particle loading was less than 4% by weight, the viscosity of the nanoparticle suspension was found to increase much higher than that of microparticle suspension. This phenomenon may be the result of association between nanoparticles and polymer molecules, effectively making the nanoparticles larger. The resulting reduction in the mobility of polymer molecules also led to delayed curing. Ultrasonic mixing did not fully disperse the particles. As a result, the composite strength did not improve although the modulus increased. The use of a dispersant, methacryloxy propyl trimethoxy silane (MPS), improved the dispersion quality and hence the composite strength. The paper discusses the issues involved with processing, characterization and properties of SiC/vinyl ester nanocomposites. Methods of improving the nanocomposite quality are proposed in the paper as well.

One of the most popular methods for calibrating the spring constant of an atomic force microscope cantilever is the thermal noise method. The usual implementation of this method has been to position the focused optical spot on or near the end of the cantilever, acquire a force curve on a hard surface to characterize the optical lever sensitivity and to then measure the thermal motion of the cantilever. The equipartition theorem then allows the spring constant to be calculated. In this work, we measured the spring constant as a function of the spot along the length of the cantilever. The observed systematic variation in the spring constant as a function of this position ranged from for a short 60 µm cantilever up to for a 225 µm cantilever we examined. In addition, the thermally calibrated spring constants systematically disagreed with spring constants calibrated using the Sader and Cleveland methods: by for the short 60 µm cantilever and by for the longest, 225 µm cantilever. By using a model that accounts for the spot diameter and position on the cantilever, the thermally measured spring constants were brought into better than 10% agreement with the other methods.

Photoluminescent emission is observed from surface-passivated PbS nanocrystals following the two-photon excitation of high-energy excitonic states. The emission appears directly at the excitation energy with no detectable Stokes-shift for a wide range of excitation energies. The observation of direct emission from states excited by two-photon absorption indicates that the parity of the excited states of surface-passivated PbS nanocrystals is partially mixed.

Atomic beams of argon and neon in excited electronic metastable states have been used to pattern bare and dodecanethiol (DDT) resist coated Au/Si substrates. Positive and negative contrast patterning has been observed for DDT-Au/Si, and negative patterning has been observed for bare Au/Si. Our results provide evidence for the formation of these negative patterns resulting from significant background pump oil contamination, and at significantly lower metastable dosages than previously observed. X-ray photoelectron spectroscopy (XPS) results indicate the growth of a carbonaceous layer as the origin of the negative resists in DDT-Au/Si and bare Au/Si substrates. For DDT-Au/Si, results indicate that the transition from positive to negative resist formation relies both on the metastable dosages and level of background pump oil contamination.

Micro four-point probes fabricated using a conventional silicon microfabrication technique were used to measure the resistivity of thin Au and Pt nanowires deposited with the nanostencil evaporation method in both direct and indirect contact modes. We found the resistivity to be an order of magnitude larger than the bulk values for both nanowires. A micrometre-resolution resistivity map was obtained of the Pt nanowires, but could not be obtained of the Au wires due to poor adhesion. We discuss the microprobe as a tool for the characterization of such small structures and the possibilities of further improving the technique.

We describe the basis for an affinity biosensor platform in which enhanced fluorescence transduction occurs through the optical excitation of molecules located within metallic nanocavities. These nanocavities are about 200 nm in diameter, are arranged in periodic or random two-dimensional arrays, and are fabricated in 70 nm thick gold films by e-beam lithography using negative e-beam resist. The experimental results show that both periodic and randomly placed metallic nanocavities can be used to enhance the fluorescence output of molecules within the cavities by about a factor of ten. In addition, the platform provides isolation from fluorescence produced by unbound species, making it suitable for real-time detection. Finally, we demonstrate the use of the platform in the real-time detection of 20-base oligonucleotides in solution.

Polystyrene nanofibres were electrospun with the inclusion of cationic surfactants, dodecyltrimethylammonium bromide (DTAB) or tetrabutylammonium chloride (TBAC), in the polymer solution. A small amount of cationic surfactant effectively stopped the formation of beaded fibres during the electrospinning. The cationic surfactants were also found to improve the solution conductivity, but had no effect on the viscosity. Only DTAB had an effect on the surface tension of the polymer solution, the surface tension decreasing slightly with an increase in the concentration of DTAB.

The formation of beaded fibres was attributed to an insufficient stretch of the filaments during the whipping of the jet, due to a low charge density. Adding the cationic surfactants improved the net charge density that enhanced the whipping instability. The jet was stretched under stronger charge repulsion and at a higher speed, resulting in an exhaustion of the bead structure. In addition, a polymer/surfactant interaction was found in the polystyrene–DTAB solution system, while this interaction was not found in the polystyrene–TBAC system. The polymer/surfactant interaction led to the formation of thinner fibres than those formed in the absence of the interaction.

The effects of a non-ionic surfactant, Triton X-405, on the electrospun fibres were also studied. The addition of Triton X-405 did not eliminate the fibre beads, but reduced the bead numbers and changed the morphology. Triton X-405 slightly improved the solution conductivity, and had a minor effect on the surface tension, but no effect on the viscosity.

Wires with meso- and nanoscale widths have been fabricated using a novel assembly technique based on the deposition of Sb clusters on templated surfaces. The template elements are V-grooves etched into the surface of a Si wafer. It is demonstrated that the clusters bounce or slide to the apex of the V-grooves, without significant fragmentation, and that this motion is the underlying mechanism behind the formation of the wires. The flow rate of inert gas into the cluster growth chamber controls the average velocity of the clusters and the morphology and width of the wires. Sb cluster-assembled wires with lengths over 150 µm and widths down to 100 nm have been assembled from  nm diameter Sb clusters. Electrical contacts to the wires have been achieved via lithographic alignment of NiCr/Au contacts to the V-grooves prior to deposition.

Contradictory claims about synthesized nanoscopic aluminium nitride material have been communicated in the same month to two different journals (Balasubramanian et al 2004 Nanotechnology15 370; 2004 Chem. Phys. Lett.383 188) when citing an article in Applied Physics Letters (Tondare et al 2002 Appl. Phys. Lett.80 4813). The contradiction arises because two different claims have been made about the synthesized nanoscopic material as aluminium nitride nanotubes and as aluminium nitride nanowires. The authors of the article published in Nanotechnology have re-interpreted the results of the field emission micrographs published in the article mentioned above (2002 Appl. Phys. Lett.80 4813). This comment explains in detail that their re-interpretation lacks a scientific basis. It also provides a few prominent articles for the reader to refer to on the synthesis of aluminium nitride nanotubes and nanowires, which have not been cited in the articles mentioned above by Balasubramanian and co-workers.