Table of contents

We review the results of the synthesis of IrO₂ nanocrystals (NCs) on different substrates via metal-organic chemical vapour deposition (MOCVD) using (MeCp)(COD)Ir as the source reagent. The surface morphology, structural and spectroscopic properties of the as-deposited NCs were characterized using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffractometry (SAD), x-ray diffractometry (XRD), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The roles of different substrates for the formation of various textures of nanocrystalline IrO₂ are studied. Several one-dimensional (1D) nanostructures have evolved by decreasing the degree of interface instability. The morphological evolution occurs from triangular/wedged nanorods via incomplete/scrolled nanotubes to square nanotubes and square nanorods (NRs), with increasing morphological stability. The results show that the three-dimensional (3D) grains composing traditional film belong to the most stable form as compared to all the 1D NCs, and the sequential shape evolution has been found to be highly correlated to a morphological phase diagram based on the growth kinetics. In addition, area selective growth of IrO₂ NRs has been demonstrated on sapphire(012) and sapphire(100) substrates which consist of patterned SiO₂ as the nongrowth surface. The initial growth of IrO₂ nuclei is studied. Selectivity, rod orientation, and other morphological features of the nanorod forest can find their origins in the nucleation behaviour during initial growth. XPS analyses show the coexistence of higher oxidation states of iridium in the as-grown IrO₂ NCs. The usefulness of the experimental Raman scattering together with the modified spatial correlation (MSC) model analysis as a residual stress and structural characterization technique for 1D IrO₂ NCs has been demonstrated. The field emission properties of the vertically aligned IrO₂ NRs are studied and demonstrated as a high-performance and robust field emitter material owing to its low work function, low resistivity and excellent stability against oxygen.

An approach to fabrication of a patterned magnetic recording medium for next generation data storage systems is presented. (Co/Pd)_n magnetic multilayers are evaluated as candidates for patterned medium materials for their high and easily controllable magnetic anisotropy. The multilayer films deposited on a Ta seed layer enable high intergranular exchange coupling—an essential feature of a patterned magnetic recording medium. The quality of (Co/Pd)_n superlattices was optimized via deposition conditions and monitored using low-angle x-ray diffraction. An estimated in-plane (hard-axis) magnetization saturation field in excess of 40 000 Oe was observed. Vertical (easy-axis) hysteresis loops for as-deposited continuous magnetic multilayers exhibited a low coercivity of 930 Oe, indicating highly uniform (magnetically) films with weak domain wall pinning. Ion-beam proximity lithography was used to pattern magnetic multilayers into 43 nm islands on a 135 nm pitch. Following patterning, easy-axis coercivity increased nearly 15-fold to 12.7 kOe.

The photostability of thiol-capped CdTe quantum dots (QDs) in Euglena gracilis (EG 277) and human embryonic kidney (HEK 293) cells was studied. The photobleaching for the cellular QDs is dependent both on the irradiation power density and the QD local concentration. The photostability of cellular QDs is better than that of chlorophyll in EG 277 cells and of green fluorescence protein (GFP) in HEK 293 cells, and is much better than that of FITC when the local concentration of QDs is not too low. The photobleaching of cellular QDs was remarkably reduced in the nitrogen treated EG 277 cells, indicating that photobleaching in living cells mainly results from photo-oxidation. The effect of photo-oxidation on QD photobleaching was further confirmed by comparing the situations in oxygen treated and nitrogen treated QD aqueous solutions. The photobleaching rate is related to the irradiation power density and the local density of QDs. The higher irradiation power density and oxygen abundance and lower QD concentration will result in a higher photobleaching rate.

Micro/nano-composite TiO₂ porous films are prepared in a nutshell by the electro-hydrodynamic (EHD) method, and are applied to dye sensitized solar cells (DSSCs) successfully. Considering that micro/nano-composite structures based on the EHD technique are better for the filling of ionic liquid and quasi-solid-state electrolytes than liquid state electrolytes, a fill factor (ff) of 78.9% and a total photoelectric conversion efficiency (η) of 6.4% for ionic liquid electrolyte and an ff of 75.3% and an η of 5.3% for quasi-solid-state electrolyte are obtained. Moreover, this kind of composite hierarchical structure may be of benefit for light collection because of strong light scattering. In order to obtain optimized devices, we probe into the influence of adding an amount of polymer on the photovoltaic performance, and find that by changing the concentration of the polymer during the EHD process the specific surface area of the films changes, which leads to different photovoltaic behaviour of solar cells.

The large scale formation of uniform Sb₂S₃ nanorod-bundles has been achieved via a simple and mild hydrothermal approach with the assistance of polyvinylpyrrolidone. By closely inspecting the growth process and the crystallographic analysis of as-synthesized products, conclusive evidence has been provided to show that the growth mechanism of such nanorod-bundles is imperfect oriented attachment. The anisotropic adsorption of polyvinylpyrrolidone at the different surfaces of Sb₂S₃ nanocrystals assists the one-dimensional preferential growth; it is just the misorientations that result in the nanorod-based superstructures. Moreover, the hydrothermal treatment time plays a crucial role, and can be used as the parameter to control the size and morphology of the bundles. This simple approach promises future large-scale controlled synthesis of various nanobody-based superstructures for many important applications in nanotechnology.

Hall magnetometers with active areas down to 100 × 100 nm² were fabricated patterning gold and Si-doped GaAs films by focused ion beam. For GaAs probes, electrical characterization shows that the magnetic flux sensitivity is better than 10⁻²Φ₀ at room temperature. Hall nano-probes made of gold can work down to liquid helium temperature with magnetic flux sensitivity 10⁻¹Φ₀.

ZnO nanorods have been prepared with sol–gel methods using zinc acetate dihydrate in ethanol in the presence of lithium hydroxide via alkaline hydrolysis. The electron transfer behaviour at the surface and interface in ZnO nanorods was investigated by means of the surface photovoltage technique. The influence of adsorbed oxygen on the surface photovoltage (SPV) response of ZnO nanorods was studied by surface photovoltage spectroscopy (SPS) and field-induced surface photovoltage spectroscopy (FISPS). The results of SPS demonstrate that for ZnO nanorods the built-in electric field should be a main driving force for the separation of the photogenerated electron–hole pairs and its ensuing SPV response. The method of photogenerated charge recombination was also studied with the aid of PL spectroscopy. It is shown that the two methods of energy relaxation in light-excited ZnO nanorods are competitive. When oxygen is adsorbed at the surface and the built-in electric field is formed, the SPV response should be the leading one. Nevertheless, when oxygen is absent, the energy relaxation is mostly carried out by radiative emission.

The effects of different annealing atmospheres on the chemical surface structure of HfO₂ gate dielectric layers have been evaluated in terms of the improvement in the transconductance (g_m), current on/off ratio (I_on/I_off), and carrier mobility (μ_e) of a back-gated ZnO nanowire field-effect transistor (FET). Compared to O₂ and N₂ annealed HfO₂-gated transistors, the H₂ annealed HfO₂-gated ZnO nanowire FET exhibited a higher transconductance of 1.77 × 10⁻⁷ A V⁻¹, on/off current ratio of ∼1.2 × 10⁴, and electron mobility of 11.90 cm² V⁻¹ s⁻¹.

Ordered gold nanoparticle arrays with high lateral density of 6.87 × 10¹⁰ nanoparticles cm⁻², which are stable up to temperatures of 600 °C, were fabricated. To this end, nanoparticles formed by thermal vacuum evaporation of Au were immobilized within the pores of nanoporous silicon wafers prepared by block copolymer lithography coupled with dry plasma etching. Even after high-temperature treatment the degree of order imposed by the block copolymer template was retained. Optionally, a nanoporous silicon nitride mask can cover the nanoporous silicon.

A nanoelectromechanical model based on atomistic simulations including charge transfer was investigated. Classical molecular dynamics simulations combined with continuum electric models were applied to a carbon-nanotube nanoelectromechanical memory device that was characterized by carbon-nanotube bending performance. For a suspended (5, 5) carbon-nanotube bridge with a length of 11.567 nm (L_CNT) and a trench depth of 0.9–1.5 nm (H), molecular dynamics results showed that the threshold voltage increased linearly as H increased and the transition time decreased exponentially at each trench depth as the applied bias increased. When H/L_CNT was below 0.13, the carbon-nanotube nanoelectromechanical memories acted as nonvolatile memory devices, whereas they were volatile memory or switching devices when H/L_CNT was above 0.14.

Measurement of atomic force microscope cantilever spring constants (k) is essential for many of the applications of this versatile instrument. Numerous techniques to measure k have been proposed. Among these, we found the thermal noise and Sader methods to be commonly applicable and relatively user-friendly, providing an in situ, non-destructive, fast measurement of k for a cantilever independent of its material or coating. Such advantages recommend these methods for widespread use. An impediment thereto is the significant complication involved in the initial implementation of the methods. Some details of the implementation are discussed in publications, while others are left unsaid. Here we present a complete, cohesive, and practically oriented discussion of the implementation of both the thermal noise and Sader methods of measuring cantilever spring constants. We review the relevant theory and discuss practical experimental means for determining the required quantities. We then present results that compare measurements of k by these two methods over nearly two orders of magnitude, and we discuss the likely origins of both statistical and systematic errors for both methods. In conclusion, we find that the two methods agree to within an average of 4% over the wide range of cantilevers measured. Given that the methods derive from distinct physics we find the agreement a compelling argument in favour of the accuracy of both, suggesting them as practical standards for the field.

In this work, we present the fabrication and full characterization of stoichiometric SiO₂ nanoisland arrays (dots) on silicon, grown through an anodic porous alumina template. Atomic force and transmission electron microscopy (AFM, TEM) were used to characterize the morphology, size, size distribution and density of the dots as a function of the anodization time used. It was found that dot density is lower for very short anodization times, and it stabilizes after a certain time. The dot height increases rapidly after nucleation, reaching values of 8–10 nm. With prolonged oxidation the dots continue to nucleate to fill the available area on the silicon surface underneath the porous alumina, while the well developed dots grow in height and width, reaching saturation values at 14 and 55 nm respectively. X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) were used to investigate the stoichiometry and surface coverage of the dots.

We propose a novel approach to the synthesis of photoluminescent Ge nanoparticles using reactive laser ablation. The deposition of germanium under low oxygen pressure (2–100 mTorr) yields Ge nanoparticles embedded in a Ge oxide matrix. Ge nanostructures were characterized by transmission electron microscopy, x-ray photoelectron spectroscopy and photoluminescence (PL) spectroscopy. The oxygen pressure determines the degree of oxidation of GeO_x films (0≤x≤2). A strong PL signal depending on oxygen pressure was observed. The PL maximum is detected for 10 mTorr of oxygen corresponding to a nanoparticle size of 1.8 ± 0.5 nm.

A new triode-type field emitter structure using carbon nanotubes synthesized on an anodic aluminium oxide template is demonstrated. The emitter structure is characterized by uniform diameters and heights, as well as by high mechanical stability. The structure is proven to be advantageous in mass production. In the structure, the leakage current to the gate can be reduced to near zero by coating the insulator on the gate. Through this, a very high current density of 5 mA cm⁻² is achieved. The very high field enhancement factor of 1.5 × 10⁶ cm⁻¹ illustrates the high performance of the triode structure, which is realized by freely using well developed semiconductor processing technologies.

A simple approach to the self-assembly production of palladium nanowires by electroless deposition on a porous stainless steel template is reported. Various arrays of self-assembled palladium nanowires in the form of single wire, parallel and curved wires, intersections and network structures are illustrated. This experimental result demonstrates that metal nanowires can be built in a self-assembled manner by the assembly of nanoparticles generated in the initial stages of the deposition without any external field except the chemical reaction. Such self-assembled nanowires may attract engineering applications because the electroless deposition process and the preparation of the substrate are simple and inexpensive.

In this paper, nanoporous platinum films with an enhanced surface area were obtained through a facile route by selective anodic dissolution of Cu from PtCu alloy. A homogeneous PtCu alloy was electrochemically deposited at a glassy carbon electrode at room temperature, then Cu was electrochemically etched from the PtCu alloy resulting in the fabrication of a nanoporous platinum film with a much higher surface area. The surface area of the dealloyed nanoporous platinum film was highly enhanced by up to 500 times compared with that of a polycrystalline platinum electrode. This nanoporous platinum film exhibited high stability and remarkable catalytic activity for oxygen electro-reduction and methanol electro-oxidation, with promising applications in fuel cells and biosensors, etc.

Two-dimensional ZnO nanosheet networks composed of many thin and uniform hexagonal-shaped ZnO nanosheets and ZnO nanodiscs were prepared in a large scale on silicon substrate through thermal evaporation using ZnCl₂ and O₂ as source materials for Zn and oxygen, respectively, without the use of metal catalysts or additives. Detailed structural studies indicated that the synthesized products are single crystalline with wurtzite hexagonal structure. Raman scattering of the synthesized products confirmed that the as-grown structures have good crystal quality with a hexagonal wurtzite phase. Room temperature photoluminescence spectra showed a strong green band with a suppressed UV emission from the ZnO nanosheet networks, but on the other hand a dominant and strong near band edge emission with a much suppressed deep level emission was observed in the nanodiscs. The growth mechanism of these structures is also discussed in detail.

The carrier dynamics in strain-induced InGaAsP/InP quantum dots (QDs) is investigated by time-resolved photoluminescence and continuous-wave photoluminescence. The stressor QDs are fabricated by depositing self-assembled InAs islands (or stressor islands) on top of a near-surface InGaAsP/InP quantum well (QW). The temporal behaviour of the QD photoluminescence transients are observed to exhibit a two-phase decay. Rate equation analyses reveal that by increasing the distance of the QW from the surface the surface capture time constant is increased considerably while the capture time constant of an electron from the QW to the QD is decreased.

The thermal stability of multi-walled carbon nanotubes (MWCNTs) was assessed under various spark plasma sintering (SPS) conditions. Our experimental results show that the MWCNTs transform into micrometre-sized diamonds at 1500 °C and only 80 MPa during SPS. The resulting diamonds are single or agglomerated crystalline particles, with diameters up to 100 µm, and are sheathed with an amorphous carbon layer and a residue of a few CNT layers. The SPS-assisted transition from MWCNTs to diamond was investigated, and a model for CNT breakage is proposed to describe the initial diamond growth. Taking into account the rapid and simple operating features of SPS, we believe that this process exhibits great potential for diamond synthesis on a large scale.

A simple ultrasonic nanowelding technique has been developed to reliably bond single-wall carbon nanotubes (SWCNTs) onto metal electrodes, by pressing SWCNTs against electrodes under a vibrating force at ultrasonic frequency. The bonds formed have been demonstrated to be mechanically robust. Using this technique, a stable low-Ohmic contact between SWCNTs and metal electrodes was achieved, with resistances in the range of 8–24 kΩ for a 1 µm long metallic SWCNT at room temperature. The performance of carbon nanotube field-effect transistors (FETs) fabricated using this ultrasonic nanowelding method has also been greatly improved. Transconductance as high as 3.6 µS among the solid-state back-gate individual nanotube FETs has been achieved.

Sub-cellular compartmentalization is critical to life; it minimizes diffusion effects and enables locally high concentrations of biochemicals for improved reaction kinetics. We demonstrate an example of in vitro biochemical synthesis inside the water channels of foam using engineered artificial organelles (bacteriorhodopsin and F₀F₁-ATP synthase reconstituted polymer vesicles) as functional units to produce ATP. These results show that the interstitial space of bubbles serves as a metaphor for sub-cellular structure, providing a new platform for both investigating cellular metabolism and the engineering of biofunctional materials and systems.

GaN nanowire field-effect transistors were fabricated using single-crystalline GaN nanowires synthesized by thermal evaporation of GaN powder with NH₃. They were found to be depletion mode transistors with an electron concentration of ∼10⁷ cm⁻¹, electron mobility of 50 cm² V⁻¹ s⁻¹, and on/off current ratio of ∼10². Using the transmission line method, the resistivity of the GaN nanowires and specific contact resistivity were estimated to be 7.8 × 10⁻² Ω cm and 1.7 × 10⁻⁵ Ω cm², respectively. The current transport at contacts was described by the thermionic emission with a barrier height of 68 meV. The contact characteristics were improved by supplying excess carriers in the nanowires. These results will enable GaN nanowires to be used in reliable nanoscale devices.

The wetting layer (WL) in InAs/GaAs quantum-dot systems has been studied by reflectance difference spectroscopy (RDS). Two structures related to the heavy-hole (HH) and light-hole (LH) related transitions in the WL have been observed. On the basis of a calculation model that takes into account the segregation effect and exciton binding energies, the amount of InAs in the WL (t_WL) and its segregation coefficient (R) have been determined from the HH and LH transition energies. The evolutions of t_WL and R exhibit a close relation to the growth modes. Before the formation of InAs dots, t_WL increases linearly from ∼1 to ∼1.6 monolayer (ML), while R increases almost linearly from ∼0.8 to ∼0.85. After the onset of dot formation, t_WL is saturated at ∼1.6 ML and R decreases slightly from 0.85 to 0.825. The variation of t_WL can be interpreted by using an equilibrium model. Different variations of in-plane optical anisotropy before and after dot formation have been observed.

TiO₂/apatite coating on metal implants is an effective method to enhance the biological properties of the metal surface. In this study, porous NiTi with a banded structure of channels and an average porosity of 45 vol% was prepared by self-propagating high-temperature synthesis. Samples were subjected to chemical treatment in H₂O₂/HCl to form a layer of nanocrystallite TiO₂ coating. A biomimetic process of soaking the samples in a simulated body fluid (SBF) was subsequently employed to deposit a nanocrystallite apatite coating on the surface of the TiO₂ coating. Analysis of the coatings showed that a nanocrystallite TiO₂ coating with anatase phase was formed on the surface of porous NiTi. A carbonated and non-stoichiometric nanocrystallite apatite coating with Ca/P ratio of 1.49 was biomimetically deposited on the surface of TiO₂, which has similar mineral composition to that of natural bone. The thickness of the TiO₂ and apatite coatings increased with increasing chemical treatment time and the immersion period in SBF, respectively. The growth kinetics and mechanism are also discussed. Results suggested that the TiO₂/apatite nanocomposite coatings can be deposited on porous NiTi by chemical treatment and a subsequent biomimetic process.

We prepared a standard resist pattern to evaluate critical-dimension atomic-force microscopy (CD-AFM) by photo-nanoimprint lithography using a trilayer resist system. Standard patterns require low line-edge roughness (LER), which is an important factor in the accuracy of high-precision CD-AFM. However, LER can easily be increased during the dry etching necessary in the trilayer resist process. The LER of final standard patterns was 2.5 nm (1 sigma), which was made using a mould of which the LER is 2.2 nm. We thermally treated the standard resist patterns to reduce the LER; the LER improved from 2.5 to 1.2 nm with the thermal treatment.

Isolated freestanding single-walled carbon nanotubes (SWNTs) have been successfully produced on silicon-based flat substrates using diffusion plasma-enhanced chemical vapour deposition. The quantitative effects of plasma parameters, such as ion density and sheath electric field, on the growth and tube alignments of freestanding SWNTs are discussed on the basis of Langmuir probe measurements and simple calculations.

The reason behind the majority of difficulties encountered in the integration of nanoscale objects with microelectromechanical systems can almost always be traced back to the lack of batch-compatible fabrication techniques at the nanoscale. On the one hand, self-assembly products do not allow a high level of control on their orientation and numbers, and hence, their attachment to a micro device is problematic. On the other hand, top-down approaches, such as e-beam lithography, are far from satisfying the needs of mass fabrication due to their expensive and serial working principle. To overcome the difficulties in micro–nano integration, a batch-compatible nanowire fabrication technique is presented, which is based on fabricating nanowires using simple lithographic techniques and relying on guided self-assembly. The technique is based on creating cracks with a predetermined number and orientation in a thin SiO₂ coating on Si substrate, and then filling the cracks with an appropriate material of choice. After the SiO₂ coating is removed, nanowires remain on the Si surface as a replica of the crack network. The technique, previously confined to electroless deposition, is now extended to include electroplating, enabling the fabrication of nanowires of various alloys. As an example, arrays of NiFe nanowires are introduced and their magnetic behaviour is verified.

In this work, the synthesis of Eu-doped titania nanotubes was studied via a two-step hydrothermal treatment method. The first hydrothermal treatment was to obtain Eu-doped TiO₂ nanopowders with good dispersity. The second treatment was to produce the corresponding nanotubes. X-ray diffraction confirmed that the nanotubes were made of hydrated titania. Scanning electron microscope and transmission electron microscope analyses showed that the multilayered nanotubes had an outer diameter of 12 nm and inner diameter of 4 nm, with length up to a few microns. The Eu-doped nanotubes exhibited strong emission lines associated with the transition of Eu³⁺. The nanotubes prepared by the two-step hydrothermal treatment exhibited better photoluminescence properties than the corresponding nanopowders and nanotubes prepared directly by the one-step hydrothermal treatment. The effect of the heat treatment of nanotubes was also studied.

For measuring nanoscale displacements, air/vacuum tunnelling is the most sensitive method. However, the alignment mechanism is difficult to scale down for integrated devices. Here, we present a tunnelling displacement sensor based on a squeezable molecular bilayer, which was built from two stacked self-assembled monolayers of mercaptohexadecanoic acid. The bilayer provides an inherent vertical alignment between the tunnelling electrodes. Squeezing of the bilayer leads to an exponential change in the tunnel current. Nanometre displacement sensitivity was achieved.

Whole device printing is presented for realizing full colour displays with red (R), green (G) and blue (B) organic light emitting diodes (OLEDs). In this process, the whole OLED structure is transferred from a patterned mould to a glass substrate. Therefore, a simple step and repeat of the transfer of each of R, G and B OLED for RGB pixels completes the fabrication of the full colour display over a given area. A difference in the work of adhesion at two interfaces enables the transfer. A 'rigiflex' mould is used for the printing. It is rigid enough to allow sub-100 nm resolution and yet flexible enough for intimate contact with the glass substrate, which permits large area application.

Carbon nanotube (CNT) oscillators based on a single-walled CNT bundle were investigated using classical molecular dynamics simulations. We present the schematics of a CNT bundle oscillator that could be initiated by an electrostatic capacitive force. While the capacitive force acting on a CNT oscillator extruded it, the force exerted on the CNT oscillator by the excess van der Waals energy sucked it into the bundle. Therefore, the CNT oscillator could be oscillated by both Coulomb and the van der Waals interactions. The operation frequency of a CNT bundle oscillator could be controlled by both the size and the length of the bundle. Our molecular dynamics simulation results showed unique features of the CNT bundle oscillators such as chaotic signature and high damping rate. CNT oscillation in the bundle showed the coupled motion to be dependent on other CNTs rather than a collective motion of the bundle. As the number of CNTs in the bundle oscillator increased, the chaotic signature of the CNT bundle oscillator increased with the increasing of coupled CNTs.

Structural phase transformations of silicon during nanoindentation were investigated in detail at the atomic level. The molecular dynamics simulations of nanoindentation on the (100) and (111) surface of single crystalline silicon were simulated, and this supported the theoretical prediction of the anisotropic behaviour of structural phase transformations. Simulations showed that microscopic aspects of phase transformation varied according to the crystallographic orientation of the contact surface and were directly linked to the slip system of silicon. In the transformed region along the centreline, the crystalline structure of Si-II and the amorphous structure were observed when silicon was loaded in the [100] and [111] directions, respectively. Simultaneously, metastable phases with fourfold coordination, such as Si-III and Si-XII, were formed by the inhomogeneous distortion in the slip direction of silicon and observed along the direction. Additionally, our results indicated that the deviatoric stress added to the hydrostatic pressure induced by loading was an indispensable factor for the structural phase transformation to Si-II during nanoindentation on the (100) surface.

ZnO nano-rods are prepared by one-step solid-state reaction of zinc acetate dihydrate, sodium hydroxide and cetyltrimethylammonium bromide (CTAB) at room temperature. The samples are characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The gas-sensing properties of the prepared material have been investigated. The results indicate that the as-prepared ZnO nano-rods are uniform with diameters of 10–30 nm and lengths of about 150–250 nm. The relatively high sensor signal and stability of sensors made from ZnO nano-rods demonstrate the potential for developing a new class of sensitive sensors.

We report on the fabrication and electroluminescence of an n-ZnO nanorod/p-Si heterojunction. ZnO nanorods were grown on p-type Si substrates employing an easy low-temperature aqueous solution method. As-grown ZnO nanorods showed good crystallinity and a preferable c axial orientation. Electroluminescent devices were constructed using high-molecular-weight polymers as the fill-in, and the I–V characteristics were diode-like. A typical electroluminescent spectrum of such an n-ZnO/p-Si heterojunction under forward bias was composed of a narrow ultraviolet peak centred at 387 nm and a broad green band at 535 nm, consistent with the photoluminescent spectrum. The intensity of the ultraviolet light grew more quickly than that of the green light with the increasing of bias.

Self-organized InGaAs quantum dot chains grown by molecular beam epitaxy were investigated using vertical stacking techniques on pre-patterned GaAs(100) substrates. The results demonstrate the formation of quantum dot (QD) chains only on desired spatial regions. In addition to QD chains, the results show that almost any shape of lines of QDs are possible depending on the faceted pre-patterned substrate. The experimental results suggest that this approach has the potential to be used to fabricate single QD chains or necklaces or almost any pattern.

We report the study of charge transport in the conducting polymer MEH-PPV between Au electrodes with nanogaps created by atomic force microscopy nanoscratching. Two different types of charge transport, namely space-charge-limited and Ohmic conductions, are observed. For the former case, a high mobility of around 1 cm² V⁻¹ s⁻¹ at a field of 10⁶ V cm⁻¹ is obtained. For the latter case, a high conductivity of around 10 S cm⁻¹ is obtained and a lower limit mobility of around 5 cm² V⁻¹ s⁻¹ is calculated. The origin of this unusual result is not clear, but it may be due to the formation of single-crystalline domains between the electrodes, that facilitates three-dimensional band transport.

A nanocapacitor with ultra high capacitance (718 ± 0.2 pF) has been fabricated using electro-deposited Au nanowires manipulated between two Au microelectrodes by the dielectrophoresis technique. A high dc resistance value (∼100 MΩ) and nonlinear current–voltage characteristics indicate the formation of a dielectric interface between the nanowires. From frequency dependent conductivity, it is seen that the interface exhibits a giant dielectric permittivity (ε∼1.8 × 10⁷), which shows no frequency dispersion over the range from 30 Hz to 1 MHz. The enhancement of this permittivity value is attributed to the formation of a disordered interface containing gold atoms disrupted from the surface of the Au nanowires.

In this study, we introduce a thin nickel interlayer to enhance the phase separation and silicon nanocrystal (Si-NC) growth in Si-rich silica films. Through TEM analysis, it is observed that the Si-NC density in the sample with a Ni interlayer is 2.6 times higher than that of the sample without Ni after high temperature annealing. The photoluminescence (PL) spectrum of the sample with a Ni interlayer is 2–5 times stronger than the one without Ni according to different silicon excess. By analysing the samples after rapid thermal annealing (RTA) with Fourier transform infrared absorption (FTIR), we find that nickel can induce phase separation in Si-rich silica films during annealing. Thermodynamic and kinetic analysis indicates a reduction of 31.4 kJ mol⁻¹ in the Si-NC nucleation activation free energy by adding the nickel interlayer, which subsequently results in higher Si-NC density.

Reduction of contact resistance is demonstrated at Cu–Cu interfaces using a multiwalled carbon nanotube (MWCNT) layer as an electrically conductive interfacial material. The MWCNTs are grown on a copper substrate using plasma enhanced chemical vapour deposition (PECVD) with nickel as the catalyst material, and methane and hydrogen as feed gases. The MWCNTs showed random growth directions and had a bamboo-like structure. Contact resistance and reaction force were measured for a bare Cu–Cu interface and a Cu–MWCNT–Cu interface as a function of probe position. For an apparent contact area of 0.31 mm², an 80% reduction in contact resistance was observed when the MWCNT layer was used. Resistance decreased with increasing contact force, thereby making it possible to use this arrangement as a small-scale force sensor. Also, the Cu–MWCNT–Cu interface was roughly two times stiffer than the bare Cu–Cu interface. Contact area enlargement and van der Waals interactions are identified as important contributors to the contact resistance reduction and stiffness increase. A model based on compaction of the MWCNT layer is presented and found to be capable of predicting resistance change over the range of measured force.

This paper describes the syntheses of boat-shaped core–shell Au–Ag bimetallic nanoparticles (NPs) and Au–Ag bimetallic nanowires (NWs). Initially, gold nanorods (AuNRs) having lengths and widths of 70 ± 18 and 12 ± 2 nm, respectively, were prepared from gold seeds in the presence of hexadecyltrimethylammonium bromide (CTAB), benzyldimethylammonium chloride (BDAC), NaAuCl₄, AgNO₃, and ascorbic acid. The thus-prepared AuNRs were then used to prepare boat-shaped core–shell Au–Ag bimetallic NPs in a glycine solution (pH 8.0) containing CTAB, AgNO₃, and ascorbic acid. The CTAB/BDAC molar ratio and the AgNO₃ concentration were important parameters affecting the anisotropy of the products. Silver atoms were deposited at both ends of the AuNRs to form the boat-shaped core–shell Au–Ag bimetallic NPs. Upon coalescence of the NPs at 88 ± 2 °C, the boat-shaped core–shell Au–Ag bimetallic NPs assembled into the form of NWs. These NWs, which were stable in solution at room temperature for at least 3 weeks, formed nanomaterials containing AuNRs after being heated at 210 °C for 15 min, i.e. as a result of the melting of the BDAC and silver shells.

Dealloying (selective dissolution) of homogeneous metallic alloys such as Ag–Au generates nanoporous metals with intriguing properties. Until now, it has not been possible routinely to prepare such materials in a form in which they would resist mechanical strains, such as might be encountered in applications as membranes, sensors or actuators. Now a threshold potential has been identified, for dealloying of Ag–Au in aqueous HClO₄, above which spontaneous transgranular fracture occurs due to the formation of a monolayer of gold hydroxide. The fracture mechanism involves a reduction in surface diffusivity, preventing relaxation of induced tension in the porous material, and possible more exotic effects. By optimizing the Au content of the alloy, staying below the threshold potential and increasing the temperature of the electrolyte, dealloyed membranes with a high degree of mechanical integrity have been prepared. When prepared in this way, the nanoporous material shows peculiar behaviours, such as grain-boundary sintering under annealing, and reversible stiffening and embrittlement when dried in air.

Mats of PVA nanofibres were successfully prepared by the electrospinning process and were developed as carriers of drugs for a transdermal drug delivery system. Four types of non-steroidal anti-inflammatory drug with varying water solubility property, i.e. sodium salicylate (freely soluble in water), diclofenac sodium (sparingly soluble in water), naproxen (NAP), and indomethacin (IND) (both insoluble in water), were selected as model drugs. The morphological appearance of the drug-loaded electrospun PVA mats depended on the nature of the model drugs. The ¹H-nuclear magnetic resonance results confirmed that the electrospinning process did not affect the chemical integrity of the drugs. Thermal properties of the drug-loaded electrospun PVA mats were analysed by differential scanning calorimetry and thermogravimetric analysis. The molecular weight of the model drugs played a major role on both the rate and the total amount of drugs released from the as-prepared drug-loaded electrospun PVA mats, with the rate and the total amount of the drugs released decreasing with increasing molecular weight of the drugs. Lastly, the drug-loaded electrospun PVA mats exhibited much better release characteristics of the model drugs than drug-loaded as-cast films.

In_1−xGa_xN nanowires were fabricated in a tube furnace by chemical vapour deposition, with Ga, In and NH₃ as the starting materials and Au as the catalyst. Scanning electron microscopy showed that a mixture of straight and helical In_1−xGa_xN nanowires was obtained. Transmission electron microscopy (TEM) revealed that both types of nanowire exhibited core–shell structures. The crystal structure of the samples was studied by high resolution TEM and x-ray diffraction, and both cubic and hexagonal phases were found. Energy dispersive x-ray spectroscopy showed that the core had a high In content and the shell had a low In content. The nanowires were also characterized by photoluminescence. The mechanism of formation for the helical nanowires and core–shell structure is discussed.

A Pt–Pb alloy nanoparticle/multi-walled carbon nanotube (Pt–Pb/MWCNT) nanocomposite was prepared by electrodepositing Pt–Pb alloy onto MWCNTs that were vertically aligned on Ta plates. The 10–40 nm diameter Pt–Pb alloy nanoparticles were mainly deposited at the tips, and sparsely dispersed on the sidewalls of the bamboo-like MWCNTs, as demonstrated by scanning electron microscopy, transmission electron microscopy (TEM), and x-ray diffraction. The high resolution TEM (HRTEM) image showed a snowflake-like morphology for the Pt–Pb nanoparticles. This Pt–Pb/MWCNT nanocomposite exhibited much stronger electrocatalytic activity toward glucose oxidation than pristine MWCNTs, Pt–Pb on glassy carbon, and Pt/MWCNT and Au/MWCNT nanocomposites, in both neutral and alkaline solutions. This Pt–Pb/MWCNT nanocomposite electrode is hence promising for development as a nonenzymatic glucose sensor.

The energetics, structural, electronic and optical absorption properties of the bismuth nanowires Bi_n with n = 1, 6 have been investigated using density functional theory (DFT) in the local density approximation (LDA) including the spin–orbit coupling (SOI). The inclusion of the SOI appreciably affects all the physical properties of the wires. The stable structures form four groups: the planar structures, the caged configurations, the pyramidal structures and the helical configurations. This finding may be a guide for the construction of atomic configurations of the nanowires possessing a larger number of atoms per unit cell. The most stable wire configurations are the 5-Bi pentagonal, and the 6-Bi hexagonal and 6-Bi triple zigzag wires, which should be seen in the experiments. All the wires are metallic. The behaviour of the electron states of the second category structures is quite near to that of a linear chain where the parabolic bands cross the E_F, and the number of the channels available for the electric conduction is large. Thus, one should grow the wire structures falling into the second category for achieving high conduction. For the 5-Bi pentagonal and 6-Bi hexagonal cross-sectional wires, the number of channels available for the electric conduction are ten and twelve, respectively. The SOI drastically affects the calculated optical absorption, especially in the low energy region. The absorption peaks are different in terms of the number and the energy locations for the different wires, and may be used for the characterization of the structure of a wire. Our analysis of the calculated electronic structure and the optical data of all the studied structures supports the occurrence of the 4-Bi double and/or 6-Bi triple zigzag chains in the samples of Romanov.

RAFT agents were attached to multi-walled carbon nanotubes (MWNTs); subsequently, different kinds of aqueous soluble ionic polymer chains, such as cationic polymer (poly(2-(dimethylamino) ethylmethacrylate)), anionic polymer (poly(acrylic acid)) and zwitterionic polymer (poly{3-[N-(3- methacrylamidopropyl)-N,N-dimethyl] ammoniopropane sulfonate}) were easily to grafted onto the surface of MWNTs directly by surface reversible addition-fragmentation chain transfer (RAFT) polymerization. The produced poly{3-[N-(3-methacrylamidopropyl)-N,N-dimethyl] ammoniopropane sulfonate} functionalized MWNTs, poly(acrylic acid) functionalized MWNTs and poly(2-(dimethylamino) ethyl methacrylate) functionalized MWNTs have good solubility in aqueous solution.

Single-walled carbon nanotube (SWNT) rings with a diameter of about 100 nm have been prepared by thermally decomposing hydrocarbon in a floating catalyst system. These rings appeared to consist mostly of SWNT toroids. High resolution transmission electron microscopy showed that these rings were composed of tens of SWNTs with a tightly packed arrangement. The production of SWNT rings was improved through optimizing various growth parameters, such as growth temperature, sublimation temperature of the catalyst, different gas flows and different catalyst components. The growth mechanism of the SWNT rings is discussed. In the field emission measurements we found that field emission from a halved ring is better than that from a whole SWNT ring, which contributed to the better emission from two opened ends of the nanotubes of the halved SWNT ring.

To depress evaporation of boron oxide during the high-temperature synthesis of borates, a sol–gel route followed by calcination was used to grow various aluminium borate nanowires. The morphology and structure of Al₄B₂O₉ and Al₁₈B₄O₃₃ nanowires could be controlled by adjusting the boron oxide content in the sol–gel derived precursors and the calcined temperature. Fine Al₄B₂O₉ nanowires with an average diameter of ∼20 nm were obtained by the calcination of Al₂O₃–2B₂O₃ xerogel at 1100 °C, whereas heat treatment at the same temperature for Al₂O₃–B₂O₃ xerogel gave rise to Al₁₈B₄O₃₃ nanowires with an average diameter of ∼30 nm. The morphology and composition dependence were investigated by x-ray diffraction, thermogravimetric and Brunauer–Emmett–Teller surface area analyses, and various microscopy techniques. A possible growth mechanism was also proposed based on high-resolution transmission electron microscopy observations.

A new approach to hydroxyethylated single-walled carbon nanotubes (SWNTs) is reported. Treating SWNTs with sec-butyllithium and subsequently with epoxy ethane leads to SWNTs functionalized with both butyl and hydroxyethyl groups. The functionalized SWNTs were characterized by Raman and FT-IR spectroscopy, thermogravimetric analysis (TGA) and atomic force microscopy. The degree of hydroxylation was estimated to be at least one hydroxyl group for every 31 nanotube carbon atoms from the TGA data and the resultant SWNTs can be stably dispersed in water at a concentration of 0.5 mg ml⁻¹. It was also found that the functional groups encapsulated in the channels of SWNTs possess a high thermal stability during the TGA procedure.

Localizable templated growth of cobalt and tungsten nanocrystals on carbon nanotube (CNT) substrates using an in situ low pressure chemical vapour deposition (CVD) process in a scanning electron microscope is reported. Sparsely distributed individual nanocrystals of 8 nm minimum diameter and with growth rates up to 6.0 × 10⁻⁴ µm³ min⁻¹ were obtained. The growth properties depend on the precursor decomposition temperature, CNT length, thermal conductivity, convective and radiative losses, and nanotube heating characteristics, with local Joule heating of individual CNTs additionally dependent on electrical contact resistances and thermal loading compared to global substrate heating. Growth dynamics during heating necessitate moderate local CNT temperatures in order to obtain well-dispersed individual nanocrystals along the nanotube shank and preclude extraneous growth. This process is prescribed as a repeatable and localized method for high-throughput fabrication of metallic nanocrystals and films for the electrical, mechanical and magnetic functionalization of nanotubes and nanowires. It may also be employed as a tool for direct visualization and study of CVD nucleation mechanisms on nanodimensional templates and characterization of thermomechanical properties of nanostructures including internal Joule heating and phonon propagation behaviour.

Highly aligned silver nanowire arrays are synthesized under direct current electric field (DCEF) treatment by a solid state ionics method without any template at normal temperature and pressure. The degree of alignment of the synthesized nanowires increases with increase of the DCEF strength. The mechanism of the effect of the DCEF on the nanowire alignment is discussed briefly. Moreover, the alignment of the individual nanowires in a bundle is further proved by observing the polarization dependence in the experiment of the polarized reflection measurements.

At reduced dimensionality, Coulomb interactions play a crucial role in determining device properties. While such interactions within the same carbon nanotube have been shown to have unexpected properties, device integration and multi-nanotube devices require the consideration of inter-nanotube interactions. We present calculations of the characteristics of planar carbon nanotube transistors including interactions between semiconducting nanotubes and between semiconducting and metallic nanotubes. The results indicate that inter-tube interactions affect both the channel behaviour and the contacts. For long channel devices, a separation of the order of the gate oxide thickness is necessary to eliminate inter-nanotube effects. Because of an exponential dependence of this length scale on the dielectric constant, very high device densities are possible by using high-κ dielectrics and embedded contacts.

A simple hydrothermal process is proposed for synthesizing SnO₂ quantum dots (QDs), in which hydrazine hydrate is used as the mineralizer instead of NaOH. X-ray diffraction, high-resolution transmission electron microscopy (HRTEM) and UV–vis diffuse reflectance spectroscopy (DRS) were employed to characterize the product. The HRTEM image shows that the diameters of the SnO₂ nanoparticles fall into a small range of 2.3–3.1 nm, with the majority being less than the exciton Bohr radius of SnO₂ (∼2.7 nm). Analysis of the DRS spectrum showed the band gap of the SnO₂ QDs to be 3.88 eV, exhibiting a 0.28 eV blue shift from that of the bulk SnO₂ (3.6 eV). The mechanism for hydrothermal synthesis of the SnO₂ QDs using hydrazine hydrate as the mineralizer is discussed.

A new and simple approach is reported for preparing Pd/Ag and Pd/Ag/Au nanosponges, which comprise network nanowires. This in situ strategy demonstrates for the first time how to prepare alloy nanosponges with network nanowires via self-regulated reduction of sodium dodecyl sulfate (SDS) and adding the second or third metal salt in the synthesis period, without additional reduction agent. The wire's diameter in the nanosponge depends on the type of alloy nanomaterials. As supported by linear sweep voltammetry (LSV) measurements, the newly prepared alloy nanosponges with network nanowires were found to exhibit high activity toward the reduction of oxygen.

An atomically smooth Ge(001) surface on a large scale is obtained by deposition of submonolayer Ge on a Ge(001) surface at 300 °C, which repairs the missing dimer defects produced during the enhanced energy ion bombardment and annealing of the substrate. The Ge(001) samples are characterized by scanning tunnelling microscopy (STM) before and after the submonolayer Ge deposition. The ion bombardment/subsequent annealing processing and STM tip induced defects are also investigated in detail.

Metal nanoparticles are interesting building blocks for realizing films for a number of applications that include bio- and chemical sensing. To date, spherical metal nanoparticles have been used to generate functional electrical coatings. In this paper we demonstrate the synthesis of electrically conductive coatings using biologically prepared gold nanotriangles as the building blocks. The gold nanotriangles are prepared by the reduction of aqueous chloroaurate ions using an extract of the lemongrass plant (Cymbopogon flexuosus) which are thereafter assembled onto a variety of substrates by simple solution casting. The conductivity of the film shows a drastic fall upon mild heat treatment, leading to the formation of electrically conductive thin films of nanoparticles. We have also investigated the possibility of using the gold nanotriangle films in vapour sensing. A large fall in film resistance is observed upon exposure to polar molecules such as methanol, while little change occurs upon exposure to weakly polar molecules such as chloroform.

We describe a procedure for fabricating sub-5 nm gap junctions with sub-100 nm electrode-width using conventional photolithography. The fabrication procedure involves two photolithographic processes followed by shadow evaporation and electromigration. After lift-off following the second metal shadow evaporation, a nanoscale wire with a diameter less than 100 nm is fabricated along a sidewall of the second patterned photo-resist. The nanowire is cut by a milliamp current flow, then a sub-5 nm gap metal junction with a sub-100 nm electrode-width is fabricated. The temperature dependence of the conductance of the molecular wires that were bridging the junctions over the ultrasmall gap indicated a hopping conduction behaviour. The results demonstrate that these junctions can be used in the study of conductance measurements through molecular wires.

The magnetic properties and microstructure of CoTb/FePt bilayer films are investigated. The magnetic anisotropy of the Co₇₀Tb₃₀/FePt(001) film is perpendicular to the film plane. The saturated magnetization (M_s) and perpendicular coercivity () of the Co₇₀Tb₃₀/FePt(001) bilayer films are higher than those of single-layered Co₇₀Tb₃₀ films. The and M_s are 5450 Oe, and 403 emu cm⁻³, respectively. As the temperature is increased to 200 °C, there is a rapid decrease in the value.

In our study we use methodology based on a wet chemistry process to fill single-wall carbon nanotubes (SWCNTs) with silver nanowires. The novelty of the study comes from long continuous silver nanowires incorporated in a SWCNT with a mean diameter of 1.22 nm. Using high resolution transmission electron microscopy and electron diffraction we evidence the formation of 100–250 nm long silver wires within SWCNTs. The electronic structure of Ag-SWCNTs is presented in comparison to the corresponding reference purified SWCNTs using electron energy-loss spectroscopy in transmission. The structural changes and the variation of the electronic properties are analysed with electron diffraction and the core-level excitations.

The I–V behaviour of a single semiconducting ZnSe nanowire with a diameter of about 20 nm has been studied by means of electric measurement under inspection with a transmission electron microscope. The experimental results showed not only an exponential relation between the current and applied bias voltage, but also the existence of a high contact resistance with characteristic features consistent with Schottky potential barriers at the gold electrodes and the semiconducting ZnSe nanowire contacts. These Schottky barriers with asymmetrical characteristics may result from different orientations of gold grains that have different work functions. The threshold bias voltages for breakdown of the Schottky barriers examined at the Au–ZnSe nanowire contacts were about −2.5 and 1.6 V respectively.

Monolayer-protected silver nanoparticles were directly synthesized in a highly concentrated organic phase (>2 M) and then printed into conductive lines on polyimide by a drop-on-demand inkjet printer. The fully organic phase system contains silver nitrate as a silver precursor, n-butylamine as a media dissolving silver salt, dodecanoic acid as a capping molecule, toluene as a solvent, and sodium borohydride as a reducing reagent. Even using only generic chemicals, monodispersed silver nanocrystals with size of 7 nm were easily synthesized at the 100 g scale in a 1 litre reactor. Hydrocarbon monolayer-protected silver nanocrystal showed excellent dispersion stability even at metal content >70 wt%. The silver ink with metal content of 33 wt% had a viscosity of 5.4 cP and surface tension of 25 dyn cm⁻¹. The silver ink was successfully inkjetted on variable substrates and then metallized at 250 °C. The metallized silver patterns exhibited very low specific electrical resistance (6 µΩ cm)