Table of contents

DNA computing is a discipline that aims at harnessing individual molecules at the nanoscopic level for computational purposes. Computation with DNA molecules possesses an inherent interest for researchers in computers and biology. Given its vast parallelism and high-density storage, DNA computing approaches are employed to solve many combinatorial problems. However, the exponential scaling of the solution space prevents applying an exhaustive search method to problem instances of realistic size, and therefore artificial intelligence models are used in designing methods that are more efficient. DNA has also been explored as an excellent material and a fundamental building block for building large-scale nanostructures, constructing individual nanomechanical devices, and performing computations. Molecular-scale autonomous programmable computers are demonstrated allowing both input and output information to be in molecular form. This paper presents a review of recent advances in DNA computing and presents major achievements and challenges for researchers in the foreseeable future.

Microtubule shuttles propelled by the motor protein kinesin embedded in self-assembled monolayers are being developed for active transport functions in artificial microfluidic systems. As a model system, biotinylated microtubules have been laden with streptavidin-coated particles as cargo. The behaviour of cargo-laden microtubules has been observed using fluorescence microscopy upon activation of kinesin-driven transport processes. Collisions between mobile microtubules and their particulate cargo result in six distinct behaviours: bypass, microtubule bending, particle knock-off, particle transfers between microtubules, co-joining of microtubules to a common particle, and particle-induced severing of microtubules. The distribution of observed events can be described qualitatively on the basis of the mechanics of motor proteins and microtubules, the geometry of the collision events, and the loading rate dependence of the strength of microtubule–particle binding. Implications of the results for the use of motor proteins in active transport and cargo-handling systems for nanomaterials are described.

We report the first direct observation of the formation process of an alumina nanowire (ANW) array from a porous anodic alumina (PAA) membrane employing a simple droplet etching method, not a general immersion etching method, using field emission scanning electron spectroscopy (FESEM). The PAA membrane is prepared by the two-step anodization method and subsequent lift-off process. The surface view SEM images of the PAA membrane show an array of highly ordered hexagonal pore distribution within the domains of 1–2 µm size, which are separated from neighbouring domains with different orientations of the pore lattice by grain boundaries. The FESEM analysis of the formation process of the alumina nanowire reveals that the formation process consists of three critical steps. The first step involves an image revealing that the outer parts of pore walls are dissolved. The image can be described by the different etching rates of oxide layers in the PAA membrane. Differences in the etching rate can be explained in terms of the different anion impurity concentration in the oxide layer of the PAA membrane. The second step produces an image of the PAA membrane with triangular triple points, surrounded by three adjacent pores. This image can be interpreted as the combined effects of the thickness difference of pore walls and the thermal annealing of the PAA membrane. The last step shows images where the triangular cross section ANWs transform into circular cross section ones as further etching occurs. This can result from the crystallization of the triple points during the annealing process.

Self-organized patterning of supported nanoclusters by virtue of low cost and readiness for mass production is considered as one of the most promising methods; however, this approach is challenging, since the capability of controlling the patterns relies on a suitable combination of clusters and templates. In this paper we demonstrate that Co nanoclusters grown from vapour deposition over Al₂O₃ thin films on NiAl(100) substrate make a perfect combination for self-organized patterning. Uniform and sizeable Co nanoclusters are formed only on crystalline Al₂O₃ films and they are highly aligned by protrusion structures of the crystalline Al₂O₃. Through simple thermal treatments we can pattern the crystalline Al₂O₃ films and consequently the grown Co nanoclusters. The patterns are robust as they are sustained even when the Co nanoclusters are flashed to 750 K, exposed to atmosphere or the coverage is increased to coalescence. Moreover, the patterns can be further refined by using STM tips. The results imply potential applications in both fundamental and applied researches for electronic and magnetic nanodevices as well as catalysis.

Tin (Sn) nanowires, with 15 and 60 nm average diameter and up to 10 µm in length, were fabricated by an injection process using a hydraulic pressure method. The Sn melt was injected into an anodic aluminium oxide (AAO) template and solidified to form nanowires. By back etching the aluminium substrate and barrier layer, the nanowire array ends were partially exposed from the bottom face of the AAO template. The filling ratio of nanowires inside and through the thickness of the AAO template was found to be close to 100%. The nanowires were also found to be dense and continuous with uniform diameter throughout their length. Transmission electron microscope (TEM) and x-ray diffraction (XRD) studies on the 60 nm diameter nanowires revealed that the nanowires were single crystals with body-centred-tetragonal (bct) structure predominantly growing along the [100] direction. The current method of synthesizing nanowires is straightforward, low-cost and suitable for low-melting point (<650 °C) metals including low-melting point alloys with stoichiometric composition.

Aqueous dispersions of chiral polyaniline nanobundles (C-PANI-NB) were prepared by simple interfacial polymerization using immiscible organic/aqueous biphasic systems. C-PANI-NB arise from the intertwining of PANI chains over interconnected units of cyclodextrin sulfate. Formation of C-PANI-NB was witnessed only in the aqueous phase, irrespective of the organic solvent used in the interfacial polymerization. The PANI that formed in the aqueous phase existed in the C-PANI-NB form. This was evident from field emission transmission microscopy. The chiro-optical properties of C-PANI-NB are strikingly different from those of simple chiral polyaniline. C-PANI-NB exhibit size selective enantioseparation. C-PANI-NB are expected to find applications as modifiers in capillary electrophoresis, as catalysts for size selective asymmetric synthesis and in biological sensors. Also, the method adopted here for the preparation of C-PANI-NB could be extended to other conducting polymers.

Ordered arrays of ZnO nanodots were fabricated by pulsed laser deposition (PLD) using an anodic aluminium oxide (AAO) nanopore membrane. Hexagonal-shaped ZnO nanodots with an average diameter of 60 nm and a periodicity of 100 nm were uniformly assembled into hexagonally ordered nanopores of the AAO membrane. Control of the oxygen pressure used in PLD resulted in a preferential photoluminescence (PL) at 380 nm from the ZnO nanodots: keeping the higher O₂ pressure gave a dominant PL peak in the UV range over the visible range, which is attributed to the reduction of the number of oxygen vacancies.

Recently, the biomolecule-assisted synthesis method has been a new and promising focus in the preparation of various nanomaterials. But current works mainly focus on the synthesis of metal nanoparticles and nanowires using macro-biomolecules (e.g. virus, protein and DNA) as templates in the presence of a reducing agent. Beta-carotene, one of the most common bio-antioxidants, can be oxidized to form species with both hydrophilic and hydrophobic ends, which can provide an in situ soft template for the synthesis of nanomaterials. Herein, a simple beta-carotene-assisted method was developed for the first time to synthesize t-Se nanowires and nanoribbons with high crystallinity. We demonstrate that beta-carotene serves as not only the reducing agent, but also an in situ template in the preparation of Se one-dimensional nanostructures. It is found that the growth mechanism of Se nanomaterials is different from the familiar sphere–wire process. A novel flake-cracking mechanism is proposed. By this biomolecule-assisted route, Te one-dimensional nanostructures and Pd nanowires were also fabricated. The assisted-biomolecule in our method may be spread to carotenoids and other antioxidants, and thus broaden the application fields of biomolecules. Our preliminary investigations have shown that the facile, solution-phase biomolecule-assisted method can be potentially extended to the preparation of other low-dimensional nanostructures. The synthesized t-Se nanowires and nanoribbons may serve as templates to generate other tubular functional nanomaterials and find applications in the studies of structure–property relationships as well as in the fabrication of nanoscale optoelectronic devices.

Purified carbon nanotubes are new carbon allotropes, sharing similarities with graphite, that have recently been proposed for their potential use with biological systems as probes for in vitro research and for diagnostic and clinical purposes. However the biocompatibility of carbon nanotubes with cells represents an important problem that, so far, remains largely uninvestigated.

The objective of this in vitro study is to explore the cytocompatibility properties of purified carbon nanofibres with cardiomyocytes.

Cardiac muscle cells from a rat heart cell line H9c2 (2-1) have been used. Highly purified single-walled nanotubes (SWNTs) were suspended at the concentration of 0.2 mg ml⁻¹ by ultrasound in complete Dulbecco's modified Eagle's medium, and administered to cells to evaluate cell proliferation and shape changes by light microscopy, cell viability by trypan blue exclusion, and apoptosis, determined flow cytometrically by annexin/PI staining.

Microscopic observation evidenced that carbon nanotubes bind to the cell membrane, causing a slight modification in cell shape and in cell count only after three days of treatment. Cell viability was not affected by carbon nanotubes in the first three days of culture, while after this time, cell death was slightly higher in nanotube-treated cells (p = ns). Accordingly, nanotube treatment induced little and non-significant change in the apoptotic cell number at day 1 and 3.

The effect of nanotubes bound to cells was tested by reseeding treated cardiomyocytes. Cells from a trypsinized nanotube-treated sample showed a limited ability to proliferate, and a definite difference in shape, with a high degree of cell death: compared to reseeded untreated ones, in SWNT-treated samples the annexin-positive/PI-negative cells increased from 2.9% to 9.3% in SWNT (p<0.05, where p<0.05 defines a statistically significant difference with a probability above 95%), and the annexin-positive/PI-positive cells increased from 5.2% to 18.7% (p<0.05). However, overtime cells from a trypsinized nanotube-treated sample continued to grow, and partially recovered the original shape.

In conclusion our results demonstrate that highly purified carbon nanotubes possess no evident short-term toxicity and can be considered biocompatible with cardiomyocytes in culture, while the long-term negative effects, that are evidenced after reseeding, are probably due to physical rather than chemical interactions.

A highly ordered array of micron-length undoped titania nanotubes exhibits an unprecedented variation in electrical resistance of about 8.7 orders of magnitude (50 000 000 000%), at room temperature, when exposed to alternating atmospheres of nitrogen containing 1000 ppm hydrogen and air. This represents the largest known change in electrical properties of any material, to any gas, at any temperature. The nanotube arrays were fabricated using anodic oxidation of titanium foil in a pH 4.0 electrolyte containing potassium fluoride, sodium hydrogen sulfate monohydrate and sodium citrate tribasic dihydrate. The dramatic change in resistance is believed to be due to the highly active surface states on the nanoscale walls of the tubes, high surface area of the nanotube architecture, and the well-ordered geometry allowing for hydrogen-sensitive tube-to-tube electrical connections.

Nanocomposites were prepared from acrylonitrile–butadiene rubber (NBR), vinyl groups containing organically modified montmorillonite and additives, such as zinc oxide, stearic acid, and sulfur. The organically modified montmorillonites used in these nanocomposites were prepared by ion exchange reactions of N,N'-dimethylalkyl-(p-vinylbenzyl)-ammonium chlorides (DAVBAs, alkyl =  octyl, dodecyl, and octadecyl) with sodium montmorillonite (Na⁺-MMT). NBR nanocomposites were obtained by controlling both the mixing and vulcanization conditions, by using a Brabender mixer and hot-press process. X-ray diffraction (XRD) analysis shows that, depending on the amount of montmorillonite that is added, both exfoliated and intercalated nanocomposite structures are formed. The NBR/DAVBA-MMT nanocomposites exhibit much higher mechanical properties (e.g., tensile strength, Young's modulus, 300% modulus, and hardness) as well as gas barrier properties as compared to NBR Na⁺-MMT or NBR composites generated from modified montmorillonites without vinyl groups. Consistent with the results of XRD, transmission electron microscopy (TEM) reveals that the intercalation and exfoliation structures of the nanocomposites coexist and that the DAVBA-MMT layers are well dispersed in NBR.

This paper investigates the effect of mechanical deformation of a single-walled carbon nanotube (SWNT) on its reactivity with hydrogen and alkyl radicals. The influence of individual loading modes was explored with the aid of molecular dynamics simulation for deformation and quantum mechanics analysis for reaction. The study discovered that the radicals bind to the deformation-induced ridges tightly with high binding energies, but at the deformation-flattened surface the binding energy becomes even lower than that of a non-deformed nanotube. At a low strain energy of ∼2 kJ mol⁻¹ a nanotube deformed by central loading gives a stronger binding with a hydrogen atom to the ridge, while at a little higher strain energy pure bending and torsion give rise to a better binding. The above findings show that mechanical deformation of carbon nanotubes can strongly promote their reactivity and form stronger covalent bonds with radicals.

In this paper, the sensitivity, stability and selectivity of nanoparticle engineered tin oxide (SnO₂) are reported, for microhotplate chemical sensing applications. 16 Å of metals such as nickel, cobalt, iron, copper and silver were selectively evaporated onto each column of the microhotplate array. Following evaporation, the microhotplates were heated to 500 °C and SnO₂ was deposited on top of the microhotplates using a self-aligned chemical vapour deposition process. Scanning electron microscopy characterization revealed control of SnO₂ nanostructures in the range of 20–121 nm. Gas sensing in seven different hydrocarbons revealed that metal nanoparticles that helped in producing faster nucleation of SnO₂ resulted in smaller grain size and higher sensitivity. Sensitivity as a function of concentration and grain size is addressed for tin oxide nanostructures. Smaller grain sizes resulted in higher sensitivity of tin oxide nanostructures. Temperature programmed sensing of the devices yielded shape differences in the response between air and methanol, illustrating selectivity. Spiderweb plots were used to monitor the materials programmed selectivity. The shape differences between different gases in spiderweb plots illustrate materials selectivity as a powerful mapping approach for monitoring selectivity in various gases. Continuous monitoring in 80 ppm methanol yielded stable sensor response for more than 200 h. This comprehensive study illustrates the use of a nanoparticle engineering approach for sensitive, selective and stable gas sensing applications.

ZnS nanowire arrays have been prepared for the first time by direct-current electrodeposition into the nanopores of porous anodic alumina membranes (AAMs), and the growth mechanism is that metal cations are firstly reduced and then react with elemental S to form ZnS nanowire arrays in the nanopores of AAMs. The nanopores of AAMs are of benefit to the formation of sulfide nanowires.

1D indium islands have been formed by epitaxial growth on a self-assembled template. The templates are formed from Bi nanolines, which are 1.5 nm wide, and can be over 500 nm in length. The islands conform to the template width and are over 100 nm long. The first layer of the island forms a novel chain structure of In and Bi atoms, which accounts for the epitaxial growth of the nanocrystals on the template. The second layer shows a hexagonal structure 19 Å or 2.5 dimer rows wide. Epitaxial growth saturates after two layers of In have been deposited. With further deposition, a transition to the growth of 3D In droplets is observed.

We have fabricated ordered arrays of nanoscale torsional actuators consisting of metal mirrors bonded to precisely oriented multiwall carbon nanotubes. The fabrication is facilitated by a new nanotube positioning method which employs localized electron beam activation of polymer residue on a silicon oxide surface.

Without polymer additives, ultrafine titania fibres were successfully prepared via the electrospinning technique in combination with the sol–gel process. The viscosity of titania precursor sol for electrospinning was controlled by the evaporation of solvent and contact with moisture in air. The morphology of the electrospun titania fibres was characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD) and transmission electron microscopy (TEM). The surface morphology and crystallinity of titania fibres were dependent on the calcination temperature. In particular, the titania fibres showed pure anatase crystalline structure when they were calcined at temperature as low as 250 °C for 3 h. Also, the titania fibres calcined at 1300 °C for 3 h showed rutile crystalline structure and burl-like wavy surfaces. This wavy surface seemed to be formed by aggregation of crystalline titania particles, which favours the round shape to minimize the surface area.

Water-soluble CdSe nanoparticles with cubic phase and narrow photoluminescent emission have been synthesized in aqueous solution with the assistance of citric acid (CA) molecules by a microwave irradiation method. This synthesis process was so rapid that the CdSe nanoparticles were obtained within just a few minutes. The size and optical properties of the CdSe nanoparticles were well controlled by the CA molecules.

We have demonstrated micropatterning of a single layer of nanoparticles by combining a self-assembly of diblock copolymer micelles with conventional and soft lithographical methods. On a photoresist micropattern fabricated by conventional photolithography, a single layer of diblock copolymer micelles containing precursors of nanoparticles was spin-coated. By plasma and lift-off processes, nanoparticles with the preservation of a pseudo-hexagonal order of micelles were synthesized in the micropattern without their aggregation. In addition, soft lithography of the microcontact printing technique was combined with the process of diblock copolymer micelles to produce micropatterns of nanoparticles. As an ink of the microcontact printing process, a single-layered film of diblock copolymer micelles was spin-coated directly onto the stamp and then transferred on the substrate by stamping. Formation of a single layer of nanoparticles in the micropattern was carried out by plasma treatment.

In order to fabricate nanoscale oxide patterns on an InP(001) surface, local anodization by atomic force microscopy (AFM) contact and intermittent contact modes has been performed. Contact mode results are similar to those obtained with the local anodization of silicon, and mainly limited by the effect of space charge that occurs during the oxide growth. The existence of this space charge associated with the poor dielectric quality of the obtained oxide has been verified by performing scanning capacitance microscopy (SCM) measurements. Results for oxidation using intermittent AFM contact mode associated with a modulated voltage are more specific. For a more than two decade variation of probe velocity (0.01–5 µm s⁻¹), the AFM oxidation introduces no significant changes in the oxide pattern. Experiments on the influence of oxidation time give rise to two regimes. First, for times shorter than 100 ms, a high growth rate is found. Second, for oxidation times longer than 100 ms, we observe an oxide height saturation and a significant decrease of lateral growth rate. These results provide a way to easily control the oxide shape. The space charge neutralization in this mode has also been investigated by SCM. The interesting results for intermittent contact oxidation confirm the capability of this technique to modify a nanoscale InP surface.

A kind of nanocomposite with hydrophobic nanogold as the core and an absorption layer of poly-N-vinyl-2-pyrrolidone (PVP) molecules surrounding it has been prepared. The nanocomposite can be dispersed well in both water and organic solvent. In water media it disperses over a pH range from 1 to 14, while in organic media the desorption of PVP results in the nanoparticles becoming hydrophobic; the enhancement of the viscosity caused by the PVP solution causes the hydrophobic sol to have very good kinetic stability. The particles can be switched repeatedly between hydrophobic and hydrophilic states. Transmission electron microscopy, Fourier transform infrared spectroscopy and energy dispersive x-ray analysis have been used to study the multilayer protection mechanism.

The polyol process including the introduction of preformed seeds and the inducement of poly(vinyl pyrrolidone) (PVP) has been developed as a powerful approach for synthesizing silver nanowires. Here, silver nanowires without other metal elements as impurities were synthesized through a silver seeding polyol process in a shielding gas atmosphere. It is demonstrated that the first seeding step is critical in obtaining silver nanowires as the principal product, and we also observe that the shielding gas atmosphere not only improves the repeatability of experiments but also affects the morphology of the final product. We obtained nanocubes with hydrogen gas shielding in a short reaction time; these would scarcely appear with argon or air shielding. Our work supplies new evidence to explain the actual growth mechanism of silver nanowires.

We study apertureless field enhancing optical probes beyond the spherical approximation in a smooth transition towards up to 3 µm long conical silicon tips. Such tips are used in apertureless scanning near field optical microscopy, which holds the promise of sub 10 nm lateral resolution. A fully three-dimensional numerical solution to the Maxwell equations is obtained with the multiple multipole method giving simultaneously both near fields and scattered far fields. The significance of focused beam excitation for work with long tips is illustrated and the relative influence of relevant length scales such as tip length, excitation wavelength, and beam waist radius is discussed. In the limit of vanishing tip apex radius, the near field grows without bounds, whereas the far field remains finite. We verify that for small apex radii the near field confinement at the tip apex, which is related to the achievable lateral resolution, scales with the inverse of the radius. We find, however, that long tips exhibit a markedly lower confinement than spherical or very short tips. Relevant for experimental studies, we demonstrate how scanning the excitation field with long conical tips can be a useful technique for mapping the focal volume. We show that the normalized near field at the tip apex is robustly tolerant against small misalignments or misorientations of illumination focus and tip apex.

Uniformly distributed ZnO nanorods with diameter 80–120 nm and length 2 µm have been grown at low temperatures on GaN by a catalyst-free and inexpensive aqueous solution method. The formation of the ZnO nanorods and the growth parameters are controlled by reactant concentration, temperature and pH. XRD and TEM studies show that the ZnO nanorods are single crystals and are well oriented along the c-axis of the crystal plane. The room-temperature photoluminescence measurements have shown a dominant ultraviolet peak at 3.23 eV with high intensity, which are comparable to those found in high-quality ZnO films. Through the photoluminescence measurement at a low temperature, the ZnO nanorods show a strong near band edge emission with weak deep level emission and also a free-to-bound transition with its phonon replicas. The temperature dependence of these excitonic emission and multiple phonon replicas from 4 to 250 K have been observed and their origins have been identified.

We derive a general expression for the current noise for an 'N–QD–S' system by using the non-equilibrium Green's function approach. We apply our formula to investigate the shot noise of a finite carbon nanotube sandwiched by a normal metal electrode and a superconducting electrode. By adjusting the gate voltage, the transparency of the system can be changed substantially and the Fano factor can be tuned from zero to nearly one. For asymmetric coupling, the Fano factor with a small gate voltage versus the bias voltage gives an anomalous peak around zero bias voltage.

The electrical transport and chemical sensing properties of single-walled carbon nanotube field effect transistors (SWNT-FETs) coated with metal clusters have been investigated. The source–drain current passing through an SWNT-FET coated with Pd nanoparticles showed no change over a range of gate voltages. Nevertheless, the magnitude of the current was still sensitive towards NO₂, NH₃ and H₂ exposure. The Pd nanoparticles coating on the nanotube generated hole carriers, which either became diluted upon NH₃ or H₂ adsorption, or enhanced upon NO₂ adsorption. Unlike the ohmic behaviour demonstrated by SWNT-FETs coated with Pd nanoparticles, the transfer characteristics of SWNT-FETs coated with Al nanoparticles revealed Schottky barrier formations at the metal–nanotube contacts. Here, the conductance through the nanotube decreased, while the device sensitivity towards NO₂ and NH₃ gases improved greatly. We suggest that coating SWNT-FETs with metal nanoparticles could be exploited for the development of highly sensitive nanotube-based molecular sensors.

Plasma intensity during the growth of vertically aligned carbon nanofibres by direct-current plasma-enhanced chemical vapour deposition has been greatly reduced to avoid the associated detrimental overetching and overheating effects due to intense ion flux bombardment. With the plasma current significantly decreased, the plasma configuration undergoes an abrupt change, which is qualitatively identified as a state transition from glow to dark discharge region. A plasma current density (<6.2 µA cm⁻²), 2–3 orders of magnitude lower than values ever reported, is shown to be effective for growing large-scale well-aligned carbon nanofibres at 400 °C. This low-energy dark discharge regime enables the growth of large arrays of small-diameter (down to 5 nm) carbon nanofibre field emitters with a reduced site density on soda-lime glass for flat panel displays, and direct carbon nanofibre growth on transparent conducting oxides for optoelectronic applications.

In this paper, a simple route to the fabrication of palladium nanosheets is described. The interaction of palladium chloride (PdCl₂) and n-octylamine salt resulted in the formation of a quasi-perovskite-type composite with a layered structure on a molecular scale. This composite can be employed as a template for preparing ultrathin Pd nanosheets when a {PdCl₄}²⁻ network is reduced in situ by hydrogen in toluene. The x-ray diffraction results indicate that the resulting Pd nanosheets are highly ordered, and they are confined inside the organic matrix as evidenced by high resolution transmission electron microscopy. These Pd nanosheets can be reorganized into layered structures in non-polarized organic solvent when the ordered structure is destroyed. This method of preparing Pd nanosheets is expected to be applicable to other layered organic/inorganic perovskite systems for obtaining the corresponding metal nanosheets.

We report the preparation of low density self-assembled InGaAs on GaAs grown by metal–organic chemical vapour deposition for single photon sources. Through using a set of optimized growth parameters, including the arsine partial pressure, total coverage of quantum dots, and growth temperature, high optical quality quantum dots with density as low as 5 × 10⁶ cm⁻² have been obtained. Using local optical excitation through a sub-micron aperture of a single quantum dot, its spectral lines associated with the exciton, biexciton, multi-exciton, and charged exciton have been resolved and identified. Photon correlation measurements show that the single quantum dot can successfully emit antibunched photons.

We report the synthesis of well aligned, high density, vertical single-crystal ZnO nanowires on ITO-buffered Si substrate (ITO is indium tin oxide) at 550 °C for 30 min. It was found that the average length and diameter of the ZnO nanowires were around 3.5 µm and 30 nm, respectively. It was also found that the ZnO nanowires were oriented in the (002) direction with extremely good crystal quality. Furthermore, it was found that In diffusion occurred at the bottom of the ZnO nanowires.

TiO₂ nanofibres were prepared using a templating method with tetraisopropylorthotitanate (TiPT) as a precursor. The preparation comprises liquid phase deposition on cellulose fibres followed by thermal removal of the cellulose template. The obtained TiO₂ fibrous substance consists of micron-size fibres with a microstructure of nanofibres. It was demonstrated that nanofibres are basically formed through the aggregation of TiO₂ nanoparticles and nanorods into chain structures during the thermal treatment process. The measured surface area of the TiO₂ fibres was about 250 m² g⁻¹. It was shown that the pore size distribution is multi-scale and a fractal morphology was demonstrated with two fractal regimes with dimensions of 1.78 and 2.97 for sizes below and above 7.5 nm, respectively. The crystalline phase of the TiO₂ nanofibres, as well as the nanoparticles in the solution, could be controlled by the pH of the solution. A pH of 1.2 resulted in rutile phase, while a pH of 1.8 resulted in anatase phase.

Three-dimensional (3D) ZnO hybrid nanostructures, composed of a bottom ZnO film, ZnO nanowire arrays, and a top ZnO film, are continuously fabricated by adjusting the supersaturation conditions, using metal–organic chemical vapour deposition, to utilize the vertically aligned ZnO nanowires as an active element in oxygen sensing applications. The oxygen sensing characteristics of the different 3D hybrid nanostructures, fabricated to have different average values of radius and length of the ZnO nanowire arrays, are studied comparatively without complicated nanowire manipulation processes. The decrease of the current flow through the ZnO nanowire arrays with increasing ambient oxygen concentration indicates that the 3D hybrid nanostructures can be applied in oxygen sensors. In addition, the 3D hybrid nanostructure having thinner radius of the nanowire arrays exhibits higher oxygen sensitivity.

We report the use of nanostructured TiO₂ (NST) as porous cellular adhesion interfaces for microsystems. Integrated NST films and pad arrays with sponge-like morphology were fabricated by aqueous oxidation of Ti films followed by thermal annealing. Cell culture studies indicate significantly (t<0.02 from the student's t-test) greater initial attachment of mouse fibroblast cells on porous NST than on silicon dioxide and nitride films for up to 18 h seeding time. Fibroblasts seeded on NST have flat morphology with numerous processes attaching to walls of NST. These results indicate the potential of using NST as porous cell adhesion films and membranes for bioMEMS applications.

Magnetic films were produced by ultrashort pulsed laser deposition (uPLD) using a rotating multitarget of terfenol-D (nominal composition: Tb_0.3Dy_0.7Fe₂) and iron. The composite films obtained have a nanoparticle morphology typical of material produced by the uPLD technique, where each particle retains the stoichiometry of the parent target material. The co-deposition allows the production of (Tb_0.3Dy_0.7Fe₂)_100−xFe_x films, where x can range from 0% to 100%. Unlike films obtained by standard nanosecond PLD, pure terfenol-D layers (x = 0) are amorphous, while the addition of iron induces the formation of Fe crystalline nanoparticles inside an amorphous nanogranular matrix of terfenol-D. The magnetic properties depend on the nanoparticle morphology and more strictly on the fraction of iron particles. In particular, it was demonstrated that the exchange interaction between hard magnetic terfenol-D nanoparticles and iron nanoparticles is active in the uPLD films, giving a cumulative magnetic response resulting from an averaging of the properties of the two component phases.

The carbon concentration in catalytic metal particles during the initial stages of single-walled carbon nanotube (SWNT) nucleation is studied by thermodynamics modelling and molecular dynamics simulation. Highly supersaturated carbon concentrations are necessary for nucleating the initial small carbon structures (e.g., islands) on the particle surface. A lower, but still supersaturated, concentration is required to enlarge the carbon island, with the required carbon concentration decreasing with increasing island size. This decrease in carbon concentration explains the widely observed phenomenon that only one carbon nanotube is nucleated per catalyst particle in catalytic chemical vapour deposition experiments. It is also shown that an inhomogeneous distribution of carbon in the catalyst particle can lead to the formation of several SWNTs from each particle, as formed in arc discharge and laser ablation experiments.

We have studied the photoluminescence (PL) of individual single-walled carbon nanotubes (SWNTs) placed in field-effect transistor structures. The SWNTs were suspended in the air so that strong PL was obtained. When an external bias voltage was applied to the device, no spectral changes could be detected, but the intensity drastically increased or decreased. This behaviour is explained by the injection/extraction of carriers from/to the electrodes by the electric field. In the case of p-type FETs in the air, PL intensity increased due to hole injection by applying a small negative gate bias. After the device was heated in vacuum, the maximum PL intensity was obtained at zero gate bias. This can be explained by the change in the interface between the SWNT and contact electrodes. The drain field dependence of the PL intensity shows a monotonic decrease, which is explained by a competition between the recombination lifetime and transit time of photo-excited carriers in the SWNT. Using analytical steady-state rate equations on carrier density in the SWNT, the relation between the recombination lifetime and carrier transit time has been evaluated. The carrier saturation velocity has also been estimated.

Boron nitride armchair and zigzag nanoarch surfaces have been studied through first principles density functional calculations. The results show marked differences as regards the electronic band structure, including a wider energy gap for the zigzag than for the armchair nanoarch. An isolated band was observed in the density of states exclusively for the armchair arrangement, well below the remaining broad band at energies above the Fermi level. The calculations indicate a change in the sp² bonding of a BN graphitic sheet occurring in both types of arch. This fact may be of help in understanding the cBN nucleation in vapour deposition processes, as well as in the BN fullerene formation mechanism itself.

Silver nanowire arrays with high aspect ratios have been prepared using potentiostatic electrodeposition within the confined nanochannels of a commercial porous anodic aluminium oxide template. The nucleation and growth processes are intensively studied by current versus time transients. Scanning electron microscopy results show that the nanowires have a highly anisotropic structure with diameters and lengths of 170 nm and 58 µm, respectively, which coincide with the dimensions of the template used. Structural characterization using x-ray diffraction shows that the Ag nanowires are highly crystalline, and those obtained at higher overpotentials present a very strong [220] preferred crystallographic orientation. The optical properties of the silver nanowires embedded in the alumina template show a clear edge close to 320 nm, that is an expected value for a silver–alumina composite material.

Carbon nanotubes (CNTs) coated with MoS₂ were produced by hydrothermal reaction using Na₂MoO₄ as the Mo source and CS(NH₂)₂ as the reducing agent and S source, with CNTs present. The product was characterized by high resolution transmission electron microscopy, energy-dispersive spectroscopy, Raman and x-ray diffraction methods. The effects of CNTs on the formation of the tubular MoS₂ layers were discussed. It was found that CNTs provide a topological and structural template favouring nucleation and growth of tubular MoS₂ layers on the surface of CNTs. The tubular MoS₂ layers had a high crystallinity. Heteronanostructural MoS₂/CNTs composite nanotubes could be obtained in this facile way.

Gibbs' condition of material equilibrium for a dissolving particle is generalized in three aspects: mobile components are included, the general case of an anisotropic surrounding medium is considered, and the dependence of the thermodynamic surface tension on the particle size is taken into account. The latter dependence is directly calculated for the case of dispersion forces to show the significance of the corrections introduced for nanoparticles whose size is comparable with molecular dimensions.

Highly ordered quasi-nanowires from fluorescent semiconductor CdSe/ZnS spherical (quantum dots) or rod-like (quantum rods) nanoparticles were produced using DNA as a template. Positively charged nanoparticles were fixed along the negatively charged DNA backbone by electrostatic interaction. After incubation of the solution of DNA and nanoparticles at different stoichiometric ratios the complexes were applied to the hydrophobic surface and stretched using the molecular combing technique. Here, we demonstrate that fluorescent patterns with desirable morphology and properties can be formed by varying the nanoparticle charge and shape and their stoichiometry in the complex with DNA.

A simple and low-cost soft route has been developed to the direct large-scale production of highly oriented ZnO nanowire arrays at 60 °C. It has been found that the growth of well-aligned ZnO nanowire arrays is dependent on several parameters, such as the reaction time and the concentration of ammonium ions. The environmentally benign ZnO nanowires obtained, with significant photoluminescence property and interesting photocatalytic activity, are single crystals and have a low defect concentration, which could be expected to find promising potential for optoelectronic and environmental application.

We report on the realization of high electron mobility (over 10³ cm² V⁻¹ s⁻¹) in structure-ordered and lattice-strained hydrogenated nanocrystalline silicon (nc-Si:H) due to the decrease of conduction effective mass and phonon scattering. The nc-Si:H thin films were grown on crystalline silicon substrates by plasma-enhanced chemical vapour deposition through the radio-frequency power to properly control the chemical reactions of H atoms with the Si–Si network. The electron mobility and concentration in the nc-Si:H have been extracted with the aid of magnetic-field-dependent Hall effect measurements. X-ray diffraction, Raman, and infrared transmission experiments have been employed to yield information about the lattice strain and structural order in the Si nanocrystals. The room-temperature experimental mobility has been well explained by a generalized Drude transport model unifying both the diffusive and ballistic transport mechanisms.

We have investigated the patterning of silicon surfaces using ion blistering in conjunction with e-beam lithography. Variable width (150–5000 nm) trenches were first written in 500 nm thick PMMA resist spin coated on silicon, using an electron beam. Next, 10 keV H₂⁺ ions were implanted to various fluences through the masks. The resist was then removed and the samples were rapidly thermally annealed at 900 °C. The resulting surface morphologies were investigated by atomic force microscopy. In the wider trenches, round blisters with 600–900 nm diameter are observed, which are similar to those observed on unmasked surfaces. In submicron trenches, there is a transition in morphology, caused by the proximity to the border. The blisters are smaller and they are densely aligned along the trench direction ('string of pearls' pattern). Unusual blister geometries are observed in the narrowest trenches (150 nm) at higher H doses (≥1 × 10¹⁷ H cm⁻²)—such as tubular blisters aligned along the trench. It was also found that for H doses of ≥6 × 10¹⁶ H cm⁻² the surface swells uniformly, which has implications for the blistering mechanism. The prospects for accomplishing ion cutting, layer transfer and bonding of finely delineated patterns of silicon onto another material are discussed in the light of the above results.

Thermally induced reduction of amorphous Fe₂O₃ nanopowder (2–3 nm) with nanocrystalline Mg (∼20 nm) under a hydrogen atmosphere is presented as a novel route to obtain α-Fe and Fe₃O₄ magnetic nanoparticles dispersed in a MgO matrix. The phase composition, structural and magnetic properties, size and morphology of the nanoparticles were monitored by x-ray diffraction, ⁵⁷Fe Mössbauer spectroscopy at temperatures of 24–300 K, transmission electron microscopy and magnetic measurements. Spherical magnetite nanoparticles prepared at a reaction temperature of 300 °C revealed a well-defined structure, with a ratio of tetrahedral to octahedral Fe sites of 1/2 being common for the bulk material. A narrow particle size distribution (20–30 nm) and high saturation magnetization (95 ± 5 A m² kg⁻¹) predispose the magnetite nanoparticles to various applications, including magnetic separation processes. The Verwey transition of Fe₃O₄ nanocrystals was found to be decreased to about 80 K. The deeper reduction of amorphous ferric oxide at 600 °C allows α-Fe (40–50 nm) nanoparticles to be synthesized with a coercive force of about 30 mT. They have a saturation magnetization 2.2 times higher than that of synthesized magnetite nanoparticles, which corresponds well with the ratio usually found for the pure bulk phases. The magnetic properties of α-Fe nanocrystals combined with the high chemical and thermal stability of the MgO matrix makes the prepared nanocomposite useful for various magnetic applications.