Table of contents

Thin-film composites comprised of NiO and NiO/Au nanoparticles in a porous SiO₂ matrix have been prepared using the sol–gel technique. When at elevated temperatures (200 °C< T<350 °C) and exposed to carbon monoxide, the films undergo reversible changes in optical transmittance at wavelengths in the visible–near IR region. For NiO composite films heated at 330 °C and exposed to 1% CO in air, there is an increase in transmittance which approaches 2–4% over most of the visible range. For NiO/Au composite films the transmittance increase exhibits a wavelength dependence, with a maximum change which is close to 6% at λ≈630 nm and which is close to zero in the Au plasmon resonance range (λ≈550 nm).

Microfabricated grippers could be useful for the manipulation of nanoscopic and microscopic samples. A survey is presented of the force requirements for a microgripper to complete pick-and-place nanomanipulation tasks. We then demonstrate in situ pick-and-place operations of nanowires inside a scanning electron microscope using microfabricated electrostatically actuated grippers, and compare the theoretically estimated force requirements with the results of experimental tests of picking up nanowires to evaluate how grippers and strategies for nanomanipulation can be optimized.

We study the effects of nanotransducer fill fraction on the molecular capture efficiency contribution to overall sensor response. Contrary to expectation, we show that the relative capture efficiency can exceed the fill fraction in the transient regime. However, at thermodynamic equilibrium, the relative efficiency equals the fill fraction in the probe-limited case. When the number of target molecules in solution is the limiting factor in capture, then gains in capture efficiency can be obtained even at thermodynamic equilibrium. The important implication of these results is that significant intrinsic nanotransducer enhancement is necessary in order to provide net gain in sensor response, but that nanotransducer enhancement does not need to exceed the inverse fill fraction. In addition, net gain in overall sensor response is more readily achievable at low target concentrations.

This study investigated alkanethiolate self-assembled monolayers (SAMs) of varied chain lengths adsorbed upon novel Au-coated microelectrodes, of which the surface properties were quantitatively evaluated by surface characterization and 3T3 fibroblast cell adhesion, total impedance and cell detachment tests. Thin-film SAMs adsorbed upon Au/PI/Si provided a hydrophobic or passive surface with increased water contact angle and initial total impedance. From cell adhesion tests, we can observe that the film formed as a dense-packed spacer resulted in incomplete cell sealing of 3T3 cells upon the surface-modified microelectrode. Thus the decrease in cell coverage rate and in the slope in association with total impedance as a function of cell–surface reaction time can be found. To study the adhesion force of a comparable single cell attached upon varied modified surfaces, a cell detachment test using a triangular probe tip of a well defined cantilever was carried out in medium containing fibroblast cells. Overall, both the peak force and the work required to detach a comparable single cell from the anchoring domain corresponded well to the increased length of alkyl chains adsorbed upon Au/PI/Si. Both measurements on the SAM modified surfaces demonstrated much smaller values than those on the pristine Au/PI/Si surface. These results concluded that a cell-repulsive characteristic was clearly formed on the SAM modified microelectrode surface. The non-adhering properties of surface-modified microelectrodes should provide better sensitivity for neuromuscular stimulation as well as for the recording of infinitesimal neural signals in future applications of neural prostheses.

Water-soluble multiwalled carbon nanotubes (MWNTs) with temperature-responsive shells were successfully prepared by grafting poly (N-isopropylacrylamide) (PNIPAM) from the sidewalls of MWNTs, via surface reversible addition–fragmentation chain transfer (RAFT) polymerization using RAFT agent functionalized MWNTs as the chain transfer agent. Thermogravimetric analysis (TGA) measurements showed that the weight composition of the as-grown PNIPAM polymers on the MWNTs can be well controlled by the feed ratio (in weight) of NIPAM to RAFT agent functionalized MWNTs (MWNT-SC(S)Ph). The MWNT-g-PNIPAM has good solubility in water, chloroform, and tetrahydrofuran (THF). Transmission electron microscope (TEM) and scanning electron microscope (SEM) images also showed that the MWNT-g-PNIPAM was dispersed individually and eventually bonded with the polymer layer by surface RAFT polymerization. The PNIPAM shell is very sensitive to a change of temperature. This method could find potential applications by grafting other functional polymer chains onto MWNTs.

Since defect rates are expected to be high in nanocircuitry, we analyse the performance of resistor-based demultiplexers in the presence of defects. The defects observed to occur in fabricated nanoscale crossbars are stuck-open, stuck-closed, stuck-short, broken-wire, and adjacent-wire-short defects. We analyse the distribution of voltages on the nanowire output lines of a resistor-logic demultiplexer, based on an arbitrary constant-weight code, when defects occur. These analyses show that resistor-logic demultiplexers can tolerate small numbers of stuck-closed, stuck-open, and broken-wire defects on individual nanowires, at the cost of some degradation in the circuit's worst-case voltage margin. For stuck-short and adjacent-wire-short defects, and for nanowires with too many defects of the other types, the demultiplexer can still achieve error-free performance, but with a smaller set of output lines. This design thus has two layers of defect tolerance: the coding layer improves the yield of usable output lines, and an avoidance layer guarantees that error-free performance is achieved.

In this study, a novel concept is proposed for molecular electronics that uses vertically aligned multiwall carbon nanotubes as nonvolatile memory elements. Nanotubes grown on a patterned substrate may be opened by partially deleting the outer molecular layer or layers, so that the inner core is able to move along the vertical tube axis. Mounting another dielectric plate above the nanotube forest at a specific distance from the tube caps can provide two stable van der Waals states of the inner core, providing for nonvolatile data storage. A device built using this architecture can function as a two-dimensional memory array. At each cross point in the array, a multiwall carbon nanotube exists in either the separated off-state or in the contact on-state, and can be switched between these states by applying voltage pulses at the corresponding electrodes. A theoretical memory density as high as 10¹³ memory elements per square centimetre is possible, with an operation frequency exceeding 100 GHz. Significant physical characteristics of such a device are bi-stability and reversibility. Such a device can function both as nonvolatile random access memory and as terabit solid-state storage.

An in situ repetitive divergent polymerization strategy was employed to grow multi-amine poly(amidoamine) dendritic macromolecules on the surfaces of multiwalled carbon nanotubes (MWNTs), affording novel three-dimensional (3D) molecular nanocomposites. The crude MWNTs were oxidized using H₂SO₄/HNO₃ = 3:1 (v/v) and then reacted with thionyl chloride, resulting in MWNTs functionalized with chlorocarbonyl groups (MWNT-COCl). MWNT-COCl, when reacted with an excess of ethylenediamine, produced amine-functionalized MWNT supported initiators (MWNT-NH₂). Using the MWNT-NH₂ as the growth supporter and methylacrylate/ethylenediamine as building blocks, multi-amine dendritic poly(amidoamine) macromolecules were covalently grafted onto the sidewalls and ends of MWNTs via Michael addition reaction and amidation. Thermal gravimetric analysis (TGA) measurements showed that the weight ratio of the as-grown dendritic polymers on the MWNT surfaces lay in the 10%–50% range. The products were also characterized by Fourier transform infrared (FTIR), Raman, nuclear magnetic resonance (NMR), and transmission electron microscopy (TEM) analysis. The results indicate that the dendrimers are grafted onto the surface of MWNTs. The as-prepared nanocomposites exhibit excellent dispersibility in water.

Ultraviolet- and visible-light-responsive titania-based photocatalysts were synthesized and employed in the photocatalytic oxidation of NO_x. Sol–gel processes using tetrabutyl orthotitanate and ethanol under acid catalyzed condition and controlled calcination were performed to synthesize titanium dioxide with a mixed crystal lattice of anatase, brookite and rutile phases. The TiO₂ prepared under calcination at 200 °C exhibited high photocatalytic activity for degradation of NO_x under both ultraviolet (UV) and visible-light illumination. The experimental results showed that up to 70% removal of NO_x could be obtained in a continuous flow type reaction system under irradiation with visible light. The calcination temperature has an important influence on the particle size and lattice structure of TiO₂. It is also found that the peculiar mixed-phase structure of TiO₂, evidenced from Raman, x-ray diffractometry (XRD), and UV–vis spectroscopy, was inferred to be an important factor for visible-light absorption and NO_x removal activity under a wide range of visible-light illumination.

Using surface micromachining technology, we fabricated nanofluidic devices with channels down to 10 nm deep, 200 nm wide and up to 8 cm long. We demonstrated that different materials, such as silicon nitride, polysilicon and silicon dioxide, combined with variations of the fabrication procedure, could be used to make channels both on silicon and glass substrates. Critical channel design parameters were also examined. With the channels as the basis, we integrated equivalent elements which are found on micro total analysis (μTAS) chips for electrokinetic separations. On-chip platinum electrodes enabled electrokinetic liquid actuation. Micro-moulded polydimethylsiloxane (PDMS) structures bonded to the devices served as liquid reservoirs for buffers and sample. Ionic conductance measurements showed Ohmic behaviour at ion concentrations above 10 mM, and surface charge governed ion transport below 5 mM. Low device to device conductance variation (1%) indicated excellent channel uniformity on the wafer level. As proof of concept, we demonstrated electrokinetic injections using an injection cross with volume below 50 attolitres (10⁻¹⁸ l).

Metallic nanoparticles were incorporated into the core of standard telecommunication grade optical fibres. This creates a simple, yet robust, platform which can be used to investigate the properties of nanoparticles, for sensing, spectroscopy, and optical switching applications. The optical response of gold nanoparticles embedded in the optical fibre matrix was evaluated as a function of temperature and the use of the structure as an inline fibre-optic temperature sensor is described. A redshift in the localized surface plasmon (LSP) resonance related peak, as well as broadening of the plasmon resonance, was observed upon increasing the temperature of the nanoparticle containing fibre. The shift and broadening of the plasmon resonance were attributed to the temperature dependence of dielectric constants of metallic nanoparticles and the silica matrix and to plasmon–phonon interactions.

Facile, cost-effective, and manufacturable techniques to create single-nanowire based devices with good electrical interconnects is demonstrated by combining template directed electrodeposition, magnetic assembly, and a post-annealing in a reducing environment. Nickel nanowires with a diameter of approximately 30 nm were electrodeposited from low-stress nickel sulfamate baths at room temperature using in-house made anodized alumina as a nanotemplate. After electrodeposition, nanowires were released from the template, efficiently positioned, trapped, and assembled on ferromagnetic electrodes using the magnetic interaction between the nanowires and the electrodes. By annealing the interconnect in a reducing environment of 5%H₂+95%N₂ at 300 °C for 30 min, the interconnect's resistance was dramatically reduced from >10 M Ω to 835 Ω. Magnetotransport studies at 300 K on a single nickel interconnect with diameters ranging from 30 to 200 nm show a strong diameter dependent magnetoresistance, which might be attributed to different domain structure within the interconnect.

The formation of nanocolumns of C clusters in thin films of a Si based inorganic polymer, allylhydridopolycarbosilane (HPCS), as a result of irradiation of the films with 100 MeV Au ions at fluences of 2 × 10¹² and 5 × 10¹² ions cm⁻² is demonstrated. The evolution and arrangement of the C clusters while subjected to the irradiation fluence is investigated by energy filtered cross-sectional transmission electron microscopy. Irradiation results in evolution of C clusters of sizes ≤5 nm, and their alignment along channels of ∼10 nm diameter, which are essentially the latent tracks created by the Au ions in the polymer. At the fluence of 5 × 10¹² ions cm⁻², these clusters become densely packed in the channels. The growth of such C cluster filled nanocolumns is shown to be a consequence of two simultaneous diffusion processes taking place during the transient molten phase of the latent tracks.

This paper investigates the change in contact angle of droplets of fluid containing dispersed nanoparticles (nanofluid) functionalized with thioglycolic acid molecules as a function of the concentration and size of nanoparticles, and the quality and composition of the substrate material. Bismuth telluride nanoparticles with an average size ranging from 2.5 to 10.4 nm and functionalized with thioglycolic acid groups were grown by a microemulsion method and dispersed in water. Experimental measurements of the contact angle of nanofluid droplets cast on smooth glass and silicon substrates show that the contact angle depends strongly on nanoparticle concentration. Moreover, smaller size nanoparticles lead to larger changes in contact angle at the same mass concentration. These findings contribute to understanding the role of functionalized nanoparticles in surface wettability.

Co₃O₄ nanoparticles have been produced by mechanochemical reactions involving cobalt carbonate, sodium oxide and sodium carbonate. The mechanochemical reactions are carried out during milling at room temperature and the nanoparticles have been obtained without the need for any thermal treatment after the milling operation. The CoO phase is produced in the first 30 min of the mechanochemical process, followed by a second stage of oxidation to Co₃O₄ which lasts for several hours. Under proper milling conditions the final products were soft agglomerates of ultrafine particles with average sizes between 15 and 20 nm.

A variety of patterns of well-ordered perovskite-type complex oxide nanostructures were obtained by pulsed laser deposition (PLD) on conductive single crystalline substrates through latex sphere monolayer and double-layer masks. Patterns obtained via deposition through hexagonally close packed (hcp) latex sphere monolayers include the usual arrays of hexagonally ordered nanoislands, hexagonal arrays of nanorings of much lower height coexisting with hexagonal nanoislands, hcp shell-like structures, and hexagonally interconnected nanocrown arrays. The formation of the nanopatterns depends on the ambient gas pressure during PLD, with well-separated nanoislands obtained at low pressures, and interconnected nanocrowns formed at high pressures. After annealing, the obtained BaTiO₃ and SrBi₂Ta₂O₉ nanopatterns were examined by piezoresponse force microscopy using conductive scanning probes. Under an external biasing electric field, polarization domain reversal was observed in the nanopatterns with deep submicron lateral dimensions. BaTiO₃ nanocrowns ∼9 nm high are ferroelectric, while SrBi₂Ta₂O₉ nanorings of ∼5 nm thickness show at least piezoelectric activity. In addition to the patterns of hexagonally ordered nanostructure arrays, a pattern of rhombohedrally ordered nanostructure arrays was also fabricated by deposition through latex sphere double layers.

The wetting properties of silicon nanotips (SiNTs) are discussed. SiNTs were prepared by single step dry etching of silicon wafers in an electron cyclotron resonance plasma of silane, methane, argon and hydrogen and water contact angles were measured as a function of their aspect ratio (α) and the inter-tip distance. The hydrophilic nature of the SiNTs is tunable with α and the inter-tip distance. Super-hydrophilicity with water contact angles close to 2° was observed with α>12 (length ∼1500 nm). Upon coating a 1500 nm long SiNT with TiO₂, the water contact angle jumped from 2° to ∼140°, demonstrating a switchover from super-hydrophilic to hydrophobic surface properties.

Selective fluorogenic probes for the labelling of intracellular reduced glutathione (GSH), i.e. ortho-phthaldialdehyde (OPA) and naphthalene-2,3-dicarboxaldehyde (NDA), have been encapsulated in polymeric nanoparticles (NPs) and the ability of the NPs to enhance uptake of the probe by microbial cells has been evaluated. Preparation of the probe-loaded NPs composed of Eudragit^® E was based on an oil-in-water emulsification solvent evaporation method using an ultrasonic probe and polyvinyl alcohol as the surfactant. The encapsulation efficiency of the probes in lyophilized NPs was determined using high performance liquid chromatography (HPLC). A higher encapsulation rate of NDA than OPA was found: 47.6 ± 9.9 (n = 6) and 2.1 ± 0.2% (n = 3), respectively. The NDA-loaded particle diameter and zeta potential were 224.6 ± 14.7 nm and +40.9 ± 6.5 mV, respectively. After 20 min incubation of cultured Candida albicans yeast cells with either free NDA or NDA-loaded NPs (final NDA concentration 100 µM), cells were harvested and corresponding lysates were analysed using HPLC coupled with spectrofluorimetric detection. Incubation of cells with NDA-loaded NPs increased intracellular levels of NDA-GSH adduct by about nine-fold in comparison with the free probe. Adhesion on the cells and the penetration behaviour of NPs loaded with either NDA or fluorescent label (Nile Red) were characterized qualitatively by confocal laser scanning microscopy.

Different methods of synthesis for the production of electroactive nanocrystals (NCs) for use as labels in DNA sensing systems are presented. They are based on two general ways of controlling the formation and growth of the nanoparticles: (a) physical restriction of the volume available for the growth of the individual nanoparticles by using templates such as reverse micelles; (b) arrested precipitation that depends on exhaustion of one of the reactants. The water dispersed nanocrystals thus obtained are then characterized by optical or electrochemical techniques so as to evaluate the quality of the prepared NCs. A novel direct electrochemical stripping detection protocol that involves the use of a bismuth modified graphite epoxy composite electrode is developed and applied so as to quantify the CdS NCs. The electrochemical study revealed a linear dependency of the stripping current upon the concentration of CdS NCs with a detection limit of around 10¹⁵ CdS NCs cm⁻³. The obtained NCs are of great interest for future applications in electrochemical genosensors.

Uniform V₂O₅· xH₂O nanobelts with high aspect ratios and ultra-long V₂O₅· xH₂O nanorolls with novel scroll-like structures were synthesized on a large scale by a simple hydrothermal growth route using NH₄VO₃ as the raw material in the presence of different acids at 180 °C for 24 h. Their morphologies were observed by scanning electron microscopy (SEM). X-ray powder diffraction measurement and thermal gravimetric analysis revealed the composition of nanobelts and nanorolls to be V₂O₅·0.9H₂O and V₂O₅·0.6H₂O, respectively. The possible mechanisms of formation of the nanobelts and nanorolls were schematically elucidated based on the layered structure of vanadium pentoxide. In addition, corresponding anhydrous V₂O₅ nanostructures with better crystallinity were obtained by calcining the precursors of V₂O₅·0.9H₂O nanobelts or V₂O₅·0.6H₂O nanorolls. Furthermore, we have investigated the electrochemical intercalation properties with Li⁺ and the photocatalytic activities of the synthesized V₂O₅·0.9H₂O nanobelts, V₂O₅·0.6H₂O nanorolls and their corresponding post-annealing products. It was observed that the morphologies and compositions of the synthesized products had an evident influence on the electrochemical intercalation properties with Li⁺ and photocatalytic activities.

Wide-gap semiconductors with nanostructures such as nanoparticles, nanorods, nanowires are promising as a new type of UV photosensor. Recently, ZnO (zinc oxide) nanowires have been extensively investigated for electronic and optoelectronic device applications. ZnO nanowires are expected to have good UV response due to their large surface area to volume ratio, and they might enhance the performance of UV photosensors. In this paper, a new fabrication method of a UV photosensor based on ZnO nanowires using dielectrophoresis is demonstrated. Dielectrophoresis (DEP) is the electrokinetic motion of dielectrically polarized materials in non-uniform electric fields. ZnO nanowires, which were synthesized by nanoparticle-assisted pulsed-laser deposition (NAPLD) and suspended in ethanol, were trapped in the microelectrode gap where the electric field became higher. The trapped ZnO nanowires were aligned along the electric field line and bridged the electrode gap. Under UV irradiation, the conductance of the DEP-trapped ZnO nanowires exponentially increased with a time constant of a few minutes. The slow UV response of ZnO nanowires was similar to that observed with ZnO thin films and might be attributed to adsorption and photodesorption of ambient gas molecules such as O₂ or H₂O. At higher UV intensity, the conductance response became larger. The DEP-fabricated ZnO nanowire UV photosensor could detect UV light down to 10 nW cm⁻² intensity, indicating a higher UV sensitivity than ZnO thin films or ZnO nanowires assembled by other methods.

A new concept of multi-level assemblies of nanorod-based structures has been proposed, which could give new insight into the construction of nanorod-based complex structures from the bottom up. Multi-level architectures of complex lead sulphide (PbS) nanorod-based structures have been realized by a simple and general amino acid-mediated approach. First-level structure (multi-arm horn-like structure), second-level structure (bi-pyramid structure formed by several horn-like structures), and third-level structure (multi-pyramid structure formed by several pyramid-like structures) can be synthesized with the assistance of different amino acids: aspartic acid, serine, and histidine, respectively. The amino acids have several functional groups, such as –NH₂ and –COOH, which have strong abilities for coordination with the metal ions, and might provide reaction sites by coordinating with metal ions to initiate and then confine the assemblies of the PbS nanorods. This amino acid-mediated method provides a possibility of studying the formation and assembly mechanisms from the bottom up and might open a door to constructing complex nanorod-based structures at different levels.

It has been demonstrated that it is possible to create laterally differentiated frictional patterning and three-dimensional structures using an atomic force microscope (AFM) probe on the surface of a soft elastic polymer, poly(dimethylsiloxane) (PDMS). The resulting effect of contact mode imaging at low loading forces (<100 nN), observed in the lateral force mode, revealed a homogeneous pattern on the PDMS surface exhibiting higher friction. With higher loading forces ( nN) the effect is non-uniform, resulting in structures with depths on the nanometre scale. The topographic and frictional data revealed stick–slip responses in both the fast (orthogonal to the long axis of the lever) and slow (parallel to the long axis of the lever) directions of probe travel from scanning in a raster pattern. The stick–slip events are manifested in the form of a series of shallow channels spaced evenly apart on the polymer surface. Detailed friction loop analysis acquired during the manipulation process showed that the lateral force changed according to the strength of trapping of the tip with the polymer surface exhibiting significant in-plane deformation due to lateral forces being imposed. An incremental increase in the initial loading force resulted in an increase in in-plane displacement and a greater spacing between the stick lines/channels in the slow-scan direction. A decrease in channel length in the fast-scan direction is also observed as a result of an increase in static friction with normal force, resulting in greater surface deformation and shorter track length for sliding friction.

The arrangement of nanostructures into desired well-ordered architectures is crucial for the realization of functional nanodevices and has been the focus of current nanotechnology. Existing physical and chemical approaches have the ability to assemble nanostructures, but it is still a challenge to arrange basic nanostructures into a highly ordered designed pattern. Here, we report a novel method to integrate tin-doped indium oxide single-crystalline nanocolumns into highly ordered two-dimensional nanopore patterns through radio-frequency magnetron sputtering by the aid of porous alumina membranes (PAMs). We have further demonstrated that the morphology of the assembled nanopore arrays is controllable by adjusting either the PAM configurations or sputtering conditions. Our present method provides the possibility of a general approach for nanounit integration, and these assembled regular nanopore arrays pave the way for the application of novel filters and sensors.

Luminescent materials have been utilized widely in applications from lighting to sensing. The new development of technologies based on luminescence requires the materials to have high luminescence efficiency and mechanical strength. In this paper, we report the fabrication of luminescent materials possessing high mechanical strength by nanofabrication with polyvinyl alcohol used as a stabilizer or coupling agent. X-ray diffraction and high-resolution transmission microscope observations reveal that the nanocomposite sample contains ZnS and ZnO nanoparticles as well as kozoite and sodium nitrate. The mechanical strength and hardness of these nanocomposites are reasonably high, higher than polycarbonate and some carbon nanotube reinforced nanocomposites. Strong luminescence is observed in the new nanocomposites and the luminescence intensity does not degrade following up to 30 min of x-ray irradiation. Our results indicate that nanofabrication may provide a good method to improve the mechanical strength of luminescent materials for some applications in which high-strength luminescent materials are needed.

We have studied the epitaxial growth of self-assembled Ge quantum dots when a submonolayer of carbon is deposited on a Ge wetting layer (WL) prior to the growth of the dots. Using atomic-force microscopy combined with optical techniques like Raman and ellipsometry, we performed a systematic study of the role played by thermally activated Si interdiffusion on dot density, composition and morphology, by changing only the growth temperature T_WL of the WL. Strikingly, we observe that higher dot densities and a narrower size distribution are achieved by increasing the deposition temperature T_WL, i.e. by enhancing Si interdiffusion from the substrate. We suggest a two-stage growth procedure for fine tuning of dot topography (density, shape and size) useful for possible optoelectronic applications.

GaN quantum dots were grown on an Al_0.11Ga_0.89N buffer layer by using flow rate modulation epitaxy. The Stranski–Krastanov growth mode was identified by an atomic force microscopy study. The thickness of the wetting layer is about 7.2 monolayers. The temperature dependent photoluminescence studies showed that at low temperature the localization energy, which accounts for de-trapping of excitons, decreases with the reducing dot size. The decrease in emission efficiency at high temperature is attributed to the activation of carriers from the GaN dot to the nitrogen vacancy (V_N) state of the Al_0.11Ga_0.89N barrier layer. The activation energy decreases with reducing dot size.

Lead tungstate single crystals with dendritic, flowery and star-like structures have been prepared via a facile, ethylene glycol (EG)-assisted sonochemical method. The concentrations of EG and ultrasound irradiation were found to play crucial roles in the morphology control of the final products. The growth process was investigated by carefully following time-dependent experiments, and the oriented attachment process accompanying Ostwald ripening was proposed for the possible formation mechanism. The optical properties, such as the Raman spectra and photoluminescence (PL) spectra, of the obtained PbWO₄ crystals were studied.

Experimental studies of Ge nanocrystals embedded in SiO₂ films doped with Er and Yb deposited by rf-magnetron sputtering are presented. Although inter-band photoluminescence (PL) from the Ge nanocrystals is not observed, it is nevertheless found that the presence of Ge nanocrystals is crucial for obtaining light emission from Er³⁺ and Yb³⁺. For both kinds of rare earth ions, the intensity of the related PL line has a maximum after heat treatment at 800 °C, and the PL excitation spectra for the two cases are very similar. This suggests that the presence and the structure of the nanocrystals are important for the efficiency of PL from Er³⁺ and Yb³⁺. Experiments performed with multilayer structures of Ge nanocrystals and SiO₂ show that the optically active rare earth ions are located in the SiO₂ layers, and not inside the Ge nanocrystals. The mechanism of energy transfer from Ge nanocrystals to the rare earth ions is found to be non-optical.

A potential driven self-assembly of sodium dodecyl sulfate/tungsten oxide aggregates at the electrolyte–electrode interface followed by template extraction and annealing yielded mesoporous thin films of electrochromic tungsten oxide (WO₃). Electron microscopy images revealed that the films are characterized by a hitherto unreported hybrid structure comprising nanoparticles and nanorods with a tetragonal crystalline phase of WO₃ with the measured lattice parameters: a = 0.53 nm and c = 0.37 nm. In addition to pentagonal voids characteristic of the tetragonal WO₃ phase at the lattice scale, open channels and pores of 5–10 nm in diameter lie between the nanoparticles, which cumulatively promote rapid charge transport through the film. This resulted in colouration efficiency (η_max∼90 cm² C⁻¹ at λ = 900 nm) and switching kinetics (colouration time =  3 s and bleaching time =  2 s for a 50% change in transmittance) higher and faster than previously reported values for mesoporous WO₃ films. Repetitive cycling between the clear and blue states has no deleterious effect on the electrochromic performance of the film, which is suggestive of its potential as a cathode in practical electrochromic windows.

We present a simple solvent-assisted capillary molding method to fabricate zinc oxide (ZnO) nanostructures using an ultraviolet (UV) curable polyurethane acrylate (PUA) mold. A thin film of the ZnO sol–gel precursor solution in methyl alcohol was prepared by spin coating on a solid substrate and subsequently a nanopatterned PUA mold was brought into conformal contact with the substrate under slight physical pressure (∼3.5 bar). After annealing at 230 °C for 4 h, well-defined ZnO nanostructures formed with feature size down to ∼50 nm, aided by capillary rise and solvent evaporation. It was found that the height of capillary rise depended highly on the applied pressure. A simple experimental setup was devised to examine the effects of pressure, revealing that the optimum pressure ranged from 3.5 bar to 5 bar. Also, ZnO nanorods could be selectively grown on patterned regions using the seed layer as a pseudocatalyst when the width of the seed layer was larger than ∼200 nm.

ZnO nanoparticles were fabricated in sapphire (α-Al₂O₃ single crystal) by Zn ion implantation (48 keV) at an ion fluence of 1 × 10¹⁷ cm⁻² and subsequent thermal annealing in a flowing oxygen atmosphere. Transmission electron microscopy (TEM) analysis revealed that metallic Zn nanoparticles of 3–10 nm in dimensions formed in the as-implanted sample and that ZnO nanoparticles of 10–12 nm in dimensions formed after annealing at 600 °C. A broad absorption band, peaked at 280 nm, appeared in the as-implanted crystal, due to surface plasma resonance (SPR) absorption of metallic Zn nanoparticles. After annealing at 600 °C, ZnO nanoparticles resulted in an exciton absorption peak at 360 nm. The photoluminescence (PL) of the as-implanted sample was very weak when using a He–Cd 325 nm line as the excitation source. However, two emission peaks appeared in the PL spectrum of ZnO nanopraticles, i.e., one ultraviolet (UV) peak at 370 nm and the other a green peak at 500 nm. The emission at 500 nm is stronger and has potential applications in green/blue light-emitting devices.

A wet chemical approach is used successfully to produce nanostructured Au material by the reduction of sulfonated polyaniline (SPANI) nanotubes. The Au nanostructures obtained are composed of single crystal Au nanoplates, which are aggregated layer-by-layer into stacks or edge-on-face into clusters at various conditions. The Au nanoplate diameter and thickness can be conveniently controlled in the range of 100 nm to 2 µm and 10 to 30 nm, respectively, with no accompanying single Au nanoparticles being observed. The formation of the Au nanostructures was controlled by the degradation of SPANI. The gradually and slowly released segments of SPANI served as the reductant during the growth of the 2D Au nanostructures.

Biodegradable polymeric nanofibres produced by electrospinning have been used as scaffolds for tissue engineering. Before these nanofibrous scaffolds can be implanted into the human body, it is important to know if the individual nanofibres are strong enough to withstand the forces exerted by the cells as they grow and migrate on the scaffold. However, due to the small size of the nanofibres, it is a challenge to characterize the mechanical properties of individual nanofibres. Therefore, we aim to mechanically characterize a single nanofibre using both a tensile test and a nanoscale three-point bend test. As some scaffolds may be heat-treated by annealing to enhance the stiffness and strength of the nanofibres, we also investigate the effects of annealing on the structural and mechanical properties of single nanofibres. The material properties of as-spun and annealed nanofibres were studied using differential scanning calorimetry and atomic force microscopy. Annealing was found to increase the Young's modulus of the nanofibre mainly due to the increase in crystallinity and the change in morphology from a purely fibrillar structure to a mixture of fibrillar and nano-granular structure with enhanced interfibrillar bonding.

We report the first detailed studies of the electrical transport behaviour of C₇₀ fullerene peapod bundles at various temperatures from 400 K down to 4 K. With electrical breakdown, we have prepared ambipolar (i.e. both p- and n-type) field-effect transistors (FETs) using fullerene peapod bundles with high levels of performance. This paper focuses on the role of the Schottky barrier and the thermal activation energy in the transport behaviour of fullerene bundles. The temperature dependence of our measurements reveals that transport is dominated by thermally assisted tunnelling in fullerene bundles at low temperature.

This paper describes a class of three component hybrid nanowires templated by DNA directed self-assembly. Through the modification of carbon nanotube (CNT) termini with synthetic DNA oligonucleotides, gold nanoparticles are delivered, via DNA hybridization, to CNT tips that then serve as growth sites for zinc oxide (ZnO) nanowires. The structures we have generated using DNA templating represent an advance toward building higher order sequenced one dimensional nanostructures with rational control.

A galvanic technique for the deposition of ZnO thin films is reported. The depositions were carried out on p-type single-crystal silicon substrates at room temperature, from a solution of ZnSO₄, where the Zn rod acted as a sacrificing anode and p-Si was the cathode. The deposition of ZnO by this method is pH sensitive, and a pH between 4 and 5 is found to be optimum for film deposition. This deposition technique is simple, inexpensive and can be carried out at room temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies revealed the nanocrystalline structure of the films. The resistivity of the annealed ZnO films was determined by the Van der Pauw measurement technique.

Silver nanorods were prepared by a seed-mediated growth approach, and self-assembled into two-dimensional ordered arrays on glass substrates. The polarization-dependent optical responses of the rods were measured, which indicated ordered alignment. These arrays were evaluated as potential surface-enhanced Raman spectroscopy (SERS) substrates using trans-bis(4-pyridyl)ethylene molecules. The SERS signals were observed to be enhanced with the increase of the aspect ratio of the Ag nanorod, and this was mainly attributed to the local field enhancement. The lateral arrangement of the Ag nanorod arrays was also partially responsible for the SERS enhancement.

We report the crystal structure and magnetic properties of Zn_1−xCo_xO (0≤x≤0.10) nanoparticles synthesized by heating metal acetates in organic solvent. The nanoparticles were crystallized in the wurtzite ZnO structure after annealing in air and in a forming gas (Ar95% + H5%). The x-ray diffraction and x-ray photoemission spectroscopy (XPS) data for different Co content show clear evidence for the Co²⁺ ions in tetrahedral symmetry, indicating the substitution of Co²⁺ in the ZnO lattice. However, samples with x = 0.08 and higher cobalt content also indicate the presence of Co metal clusters. Only those samples annealed in the reducing atmosphere of the forming gas, that showed the presence of oxygen vacancies, exhibited ferromagnetism at room temperature. The air annealed samples remained non-magnetic down to 77 K. The essential ingredient in achieving room temperature ferromagnetism in these Zn_1−xCo_xO nanoparticles was found to be the presence of additional carriers generated by the presence of the oxygen vacancies.

Electrical transport through individual solution-grown GaAs nanowires was measured as a function of temperature. The current–voltage (IV) curves are nonlinear and exhibit space charge limited currents. The IV curves become increasingly nonlinear with decreasing temperature and follow the scaling relationship . This scaling indicates that the space charge limited currents are limited by trapped charge. The characteristic energies of the trap states were estimated from the IV data and found to vary from wire to wire, ranging from 0.024 to 0.11 eV below the band edge. In the low bias region of the IV curves, where the curves were ohmic, the activation energy (related to the Fermi energy) was determined and found to be shifted significantly towards the band edge, which indicates either the presence of a large concentration of impurities, such as Si, in the nanowires or charged surface states.

Standing [111]-oriented crystalline gold nanotube (AuNT) and nanorod (AuNR) arrays using electrochemical deposition through template growth are reported. Segments of single crystal and bamboo-like crystalline AuNR arrays with growing direction of [111], having a diameter of 100–150 nm and a length of 10 µm, standing perpendicular to Ti metal foil substrates, are synthesized. The as-synthesized AuNTs and AuNRs are characterized by powder and five circle x-ray diffractometry, UV–visible molecular absorption spectrometry, field emission scanning electron microscopy, and transmission electron microscopy. AuNRs and AuNTs are formed by starting with a tube and the wall of the tube gets progressively thicker and eventually sealed up to form nanorods. Optical absorption at 548 and 578 nm wavelength for gold nanotubes and nanorods, respectively, caused by the transverse (width) mode is identified.

Quasi-one-dimensional semiconductor ZnS hierarchical nanostructures have been fabricated by thermal evaporation of a mixture of ZnS nanopowders and Sn powders. Sn nanoparticles are located at or close to the tips of the nanowires (or nanoneedles) and served as the catalyst for quasi-one-dimensional ZnS nanostructure growth by a vapour–liquid–solid mechanism. The morphology and microstructure of the ZnS hierarchical nanostructures were measured by scanning electron microscopy and high-resolution transmission electron microscopy. The results show that a large number of ZnS nanoneedles were formed on the outer shells of a long and straight ZnS axial nanowire. The ZnS axial nanowires grow along the [001] direction, and ZnS nanoneedles are aligned over the surface of the ZnS nanowire in the radial direction. The room temperature photoluminescence spectrum exhibits a UV weak emission centred at 337 nm and one blue emission centred at 436 nm from the as-synthesized single-crystalline semiconductor ZnS hierarchical nanostructures.

Sub-100 nm resolution on a 200 mm silicon stamp has been hot embossed into commercial Sumitomo NEB 22 resist. A single pattern, exposed with electron beam lithography, has been considered to define the stamp and thus make it possible to point out the impact of stamp design on the printing. These results may be considered as a first attempt to define rules to solve the proximity printing effects (PPEs). Moreover, a large range of initial resist thickness, from 56 to 506 nm, has been spin coated to assess the effect of polymer flow properties for the stamp cavity filling and the printed defects. A detailed analysis of the printed resist in dense hole patterns showed that the application volume conservation is enough to calculate the residual layer thickness as the height of the printed resist feature. Good accordance has been obtained between the theoretical approach and experimental results. Moreover, the impact of the pattern symmetry breakdown on mould deformation is clearly shown in this paper in the printed areas as well as in the unprinted areas.