Table of contents

Atomic force microscopy (AFM) has garnered much interest in recent years for its ability to probe the structure, function and cellular nanomechanics inherent to specific biological cells. In particular, we have used AFM to probe the important structure–function relationships of the bacterium Streptococcus mutans. S. mutans is the primary aetiological agent in human dental caries (tooth decay), and is of medical importance due to the virulence properties of these cells in biofilm initiation and formation, leading to increased tolerance to antibiotics. We have used AFM to characterize the unique surface structures of distinct mutants of S. mutans. These mutations are located in specific genes that encode surface proteins, thus using AFM we have resolved characteristic surface features for mutant strains compared to the wild type. Ultimately, our characterization of surface morphology has shown distinct differences in the local properties displayed by various S. mutans strains on the nanoscale, which is imperative for understanding the collective properties of these cells in biofilm formation.

Molecular dynamics simulations are performed on n-alkinethiol self-assembled monolayers (SAMs) and their mixture on a gold surface so that the orientations of the binding of cobra cardiotoxin and E6 protein molecules can be selected using the mixing ratio of CH3-terminated SAMs with different chain lengths. The simulations suggest that a SAM surface with different mixing ratios may provide a possible platform for aligning protein molecules with a desired orientation and for enhancing the binding energy of the protein on the designed surface.

Detection of blood cholesterol is of great clinical significance. The amperometric detection technique was used for the enzymatic assay of total cholesterol. Multiwall carbon nanotubes (MWNTs), vertically aligned on a silicon platform, promote heterogeneous electron transfer between the enzyme and the working electrode. Surface modification of the MWNT with a biocompatible polymer, polyvinyl alcohol (PVA), converted the hydrophobic nanotube surface into a highly hydrophilic one, which facilitates efficient attachment of biomolecules. The fabricated working electrodes showed a linear relationship between cholesterol concentration and the output signal. The efficacy of the multiwall carbon nanotubes in promoting heterogeneous electron transfer was evident by distinct electrochemical peaks and higher signal-to-noise ratio as compared to the Au electrode with identical enzyme immobilization protocol. The selectivity of the cholesterol sensor in the presence of common interferents present in human blood, e.g. uric acid, ascorbic acid and glucose, is also reported.

We consider three-dimensional axially symmetric quantum wires with circular cross-sections whose radius may vary along the axis of the waveguide. In the narrows, there arise barriers to the longitudinal motion of an electron. Varying the radius, one can create barriers and provide conditions for resonant tunnelling of electrons. We suggest a method for numerically studying such phenomena. The method can be applied to wires not possessing axial symmetry as well. Besides this, we discuss some possible applications.

A novel parylene-embedded carbon nanotube nanoelectrode array is presented for use as an electrochemical detector working electrode material. The fabrication process is compatible with standard microfluidic and other MEMS processing without requiring chemical mechanical polishing. Electrochemical studies of the nanoelectrodes showed that they perform comparably to platinum. Electrochemical pretreatment for short periods of time was found to further improve performance as measured by cathodic and anodic peak separation of K₃Fe(CN)₆. A lower detection limit below 0.1 µM was measured and with further fabrication improvements detection limits between 100 pM and 10 nM are possible. This makes the nanoelectrode arrays particularly suitable for trace electrochemical analysis.

A novel self-aligned method to selectively immobilize proteins on a silicon dioxide surface is developed in conjunction with a standard lift-off patterning technique of a PEG layer. The approach is designed to photolithographically pattern regions that specifically bind target proteins and particles, surrounded by regions that suppress non-specific attachment of bio-species. The physical and biological properties of the derivatized surfaces at the end of the fabrication process are characterized.

In this paper, we show that ferrofluids can be pumped very effectively in closed-channel geometries both in the macro- and micro-scales using spatially travelling, sinusoidally time-varying magnetic fields. The results from numerical modelling demonstrate that the optimum pumping frequency is the reciprocal of the Brownian relaxation time constant of the magnetic nanoparticles inside the ferrofluid. Since the Brownian time constant depends in part on the overall hydrodynamic volume of the magnetic nanoparticles, this work has been carried with a view to developing functionalized ferrofluids that can be used as sensitive pathogen detectors in the context of ferrohydrodynamic pumping via travelling magnetic fields. A micro-ferrofluidic device has been designed and fabricated in order to demonstrate the potential development of this technology for pathogen detection. A cost-effective fabrication process combining insulated metal substrate etching and soft lithography is used to realize the prototype micro-ferrofluidic device. Results show good agreement between simulation and experiment. We finally propose a ferrofluid-based pathogen detection scheme that is expected to be insensitive to temperature and viscosity differences between the ferrofluid and the sample to be tested.

The use of arrays of chemical detectors has been realized in electronic nose applications. Recently attention has been focused on the application of e-Noses in the medical arena. These are electronic devices that typically employ non-selective gas sensitive elements for the monitoring of odours and other gaseous analytes. Currently, the lack of relative specificity to a mixture of gaseous analytes for these sensing elements makes the use of pattern recognition algorithms to process the signal and match the acquired data profile to a known pattern necessary, thus identifying the signature of the odour or gas detected. An alternative approach to chemical detection through the use of small arrays (two or three elements) of selective gas sensors made of nanostructured semiconducting films and membranes is described in this work. Sensor selectivity is defined here as higher sensitivity to a given gas or class of gases in the presence of interfering gaseous species. Transition metal oxides are key sensing elements of resistive type chemical detectors. A given oxide may be found in several polymorph phases, each having a distinct structural configuration. Gas–oxide interactions are strongly dependent on the 'structure sensitivity' of the polymorph used in sensing. This paper reviews the effect of polymorphism on the gas specificity and the importance of nanoscale processing for stabilizing the desirable oxide phases, and it introduces a gas-polymorph selection library for building the next generation of gas sensing systems with inherent selectivity to be used as non-invasive disease diagnosis tools.

A new approach to the observation and analysis of dynamic structural and functional parameters in the microcirculation is described. The new non-invasive optical system is based on cellular nonlinear networks (CNNs), highly integrated analogue processor arrays whose processing elements, the cells, interact directly within a finite local neighbourhood. CNNs, thanks to their parallel processing feature and spatially distributed structure, are widely used to solve high-speed image processing and recognition problems and in the description and modelling of biological dynamics through the solution of time continuous partial differential equations (PDEs). They are therefore considered extremely suitable for spatial–temporal dynamic characterization of fluidic phenomena at micrometric to nanometric scales, such as blood flow in microvessels and its interaction with the cells of the vessel wall. A CNN universal machine (CNN-UM) structure was used to implement, via simulation and hardware (ACE16k), the algorithms to determine the functional capillarity density (FCD) and red blood cell velocity (RBCV) in capillaries obtained by intravital microscopy during in vivo experiments on hamsters. The system exploits the moving particles to distinguish the functional capillaries from the stationary background. This information is used to reconstruct a map and to calculate the velocity of the moving objects.

This work presents a new electrolysis-based microelectromechanical systems (MEMS) diaphragm actuator. Electrolysis is a technique for converting electrical energy to pneumatic energy. Theoretically electrolysis can achieve a strain of 136 000% and is capable of generating a pressure above 200 MPa. Electrolysis actuators require modest electrical power and produce minimal heat. Due to the large volume expansion obtained via electrolysis, small actuators can create a large force. Up to 100 µm of movement was achieved by a 3 mm diaphragm. The actuator operates at room temperature and has a latching and reversing capability.

Scanning probe microscopy (SPM) has been one of the most important tools to image and, hopefully, to manipulate bio-structures at micro/nanoscales. However, the current out-of-plane cantilever design makes it very difficult to extend the spectrum of the current SPM technology to meet many new functionalities arising from bio-engineering applications. An in-plane scanning probe concept is developed to accommodate the new functional requirements. It is designed to have a single-strand multi-walled carbon nanotube (CNT) tip assembled at the end of the probe, a built-in actuator and a tip deflection sensor, all in the same plane. The coplanar design is compatible with most of the standard MEMS processes and would facilitate the assembly of a carbon nanotube tip to the micromachined probe. The in-plane design features a switchable stiffness which adapts the scanning probe's stiffness to the changing surface hardness of the sample. This paper describes how the variable stiffness is accomplished by engaging or disengaging electrostatically actuated clutches, in addition to the discussions on many possible benefits of the in-plane scanning platform.

Ribonuclease (RNase), an enzyme which degrades RNA, is ubiquitous in living organisms, can renature after autoclaving, and is difficult to inactivate. The removal of RNase is especially necessary for the reverse transcription–polymerase chain reaction (RT-PCR) and for in vitro transcription and translation. Typically, RNase inhibitors must be added to these reactions nowadays. Molecularly imprinted polymers (MIPs) could offer many advantages for removal of undesired enzymes, including high binding selectivity, stability, low cost, and facile synthesis. Surface imprinting, employing immobilized RNase, was used in this study to make the most effective use of the template molecules—clearly, inaccessible binding sites, no matter how well imprinted, are not useful for target binding. Different monomers and cross-linkers were used to synthesize RNase-templated MIPs, and the rebinding capacity of each composition was characterized. We found that using polyethylene glycol 400 dimethacrylate (PEG400DMA) gave the highest imprinting effectiveness (i.e. the highest RNase binding ratio between imprinted and non-imprinted polymers). However, including styrene monomer (50 wt%) gave polymers with the highest overall affinity for ribonuclease A (RNase A). Finally, isothermal titration calorimetry was used as an auxiliary tool to help elucidate the mechanisms of the binding of monomers to templates, and ligands to MIPs.

Arrays of MEMS fabricated flow sensors inspired by the acoustic flow-sensitive hairs found on the cerci of crickets have been designed, fabricated and characterized. The hairs consist of up to 1 mm long SU-8 structures mounted on suspended membranes with normal translational and rotational degrees of freedom. Electrodes on the membrane and on the substrate form variable capacitors, allowing for capacitive read-out. Capacitance versus voltage, frequency dependence and directional sensitivity measurements have been successfully carried out on fabricated sensor arrays, showing the viability of the concept. The sensors form a model system allowing for investigations on sensory acoustics by their arrayed nature, their adaptivity via electrostatic interaction (frequency tuning and parametric amplification) and their susceptibility to noise (stochastic resonance).

The protein tubulin is a target for several anti-mitotic drugs, which affect microtubule dynamics, ultimately leading to cell cycle arrest and apoptosis. Many of these drugs, including the taxanes and Vinca alkaloids, are currently used clinically in the treatment of several types of cancer. Another tubulin binding drug, colchicine, although too toxic to be used as a chemotherapeutic agent, is commonly used for the treatment of gout. The main disadvantage that all of these drugs share is that they bind tubulin indiscriminately, leading to the death of both cancerous and healthy cells. However, the broad cellular distribution of several tubulin isotypes provides a platform upon which to construct novel chemotherapeutic drugs that could differentiate between different cell types, reducing the undesirable side effects associated with current chemotherapeutic treatments. Here, we report an analysis of ten human β tubulin isotypes and discuss differences within each of the previously characterized paclitaxel, colchicine and vinblastine binding sites.

Nanoimprint lithography (NIL) has stimulated great interest in both academic research and industrial development due to its high resolution, high throughput and low cost advantages. Though NIL has been demonstrated to be very successful in replicating nanoscale features, it also has its limitations as a general lithography technique. Its fundamental moulding characteristics (i.e. physically displacing polymer materials) frequently lead to pattern defects when replicating arbitrary patterns, especially patterns with broad size distribution. To solve this problem, we have developed a combined nanoimprint and photolithography technique that uses a hybrid mould to achieve good pattern definitions. In this work, we applied this technique to fabricate finger-shaped nanoelectrodes, and demonstrated nanoscale pentacene organic thin film transistors (OTFTs). Methods of the hybrid mask–mould (HMM) fabrication and results on the device electrical characteristics are provided. With combined advantages of both photolithography and NIL, and the applicability to general nanoscale device and system fabrication, this method can become a valuable choice for low cost mass production of micro- and nanoscale structures, devices and systems.

The scanner drift of the atomic force microscope (AFM) is a great disadvantage to the application of digital image correlation to micro/nano-scale deformation measurements. This paper has addressed the image distortion induced by the scanner drifts and developed a method to reconstruct AFM images for the successful use of AFM image correlation. It presents such a method, that is to generate a corrected image from two correlated AFM images scanned at the angle of 0° and 90° respectively. The proposed method has been validated by the zero-deformation test. A buckling test of a thin plate under AFM has also been demonstrated. The in-plane displacement field at the centre point of the buckling plate has been successfully characterized by the application of the image correlation technique on reconstructed AFM images.

A simple, one-step method is developed to fabricate various nanostructures such as nanoholes and nanolines based on the detachment of an organic polymer film in contact with a patterned polyurethane acrylate mould under a low physical pressure (1–2 bar) at ambient conditions. Calculation of the work of adhesion based on contact angle measurements indicates that the adhesion strength at the organic/mould interface is greater than that at the organic/substrate interface, resulting in a successful detachment without any surface modifications. 4,4^'-bis[N-1-napthyl-N-phenyl-amino]biphenyl (NPB) is used as the organic film owing to its low cohesion energy and stability in air. Nanoholes as small as 150 nm and nanolines as small as 50 nm have been fabricated using this approach. These nanostructures are used as a template for selective deposition of silver nanoparticles and a wet/dry etch resist for further pattern transfer.

Single-crystalline dandelion-like β-MnO₂ three-dimensional microstructures have been successfully prepared for the first time via a simple hydrothermal process based on the direct reaction between Mn(NO₃)₂ and H₂O₂. H₂O₂ plays an important role in the formation of the dandelion-like morphology. The formation mechanism of the dandelion-like nanostructures was investigated and discussed based on the experimental results. Magnetic measurements show that the Néel temperature of the as-obtained product is 100 K, which is about 6 K higher than that of the corresponding bulk β-MnO₂ crystals.

The growth and optical properties of GaN nanorods grown on Si(111) substrates by rf plasma assisted molecular-beam epitaxy are investigated by means of field emission scanning electron microscopy and photoluminescence measurements as a function of growth time. It is clearly demonstrated that the rate of growth of the nanorod diameter starts to increase after ∼90 min because of the coalescence of neighbouring nanorods. And the optical properties of the samples grown at a high growth rate are dramatically changed due to induced defects. The critical diameter for defect-free GaN nanorods is determined as below ∼140 nm under N-rich conditions.

We report that high quality PbS nanocrystals, synthesized in the strong quantum confinement regime, have quantum yields as high as 70% at room temperature. We use a combination of modelling and photoluminescence up-conversion to show that we obtain a nearly monodisperse size distribution. Nevertheless, the emission displays a large nonresonant Stokes shift. The magnitude of the Stokes shift is found to be directly proportional to the degree of quantum confinement, from which we establish that the emission results from the recombination of one quantum confined charge carrier with one localized or surface-trapped charge carrier. Furthermore, the surface state energy is found to lie outside the bulk bandgap so that surface-related emission only commences for strongly quantum confined nanocrystals, thus highlighting a regime where improved surface passivation becomes necessary.

Relationships between phase morphology and mechanical deformation processes in various electrospun polymer nanocomposite nanofibres (PNCNFs) containing different types of one-, two- and three-dimensional nanofiller have been investigated by transmission electron microscopy using in situ tensile techniques. From the study of the phase structure of electrospun PNCNFs, two morphological standard types are classified for the analysis of deformation mechanisms: the binary system (polymer matrix and nanofillers), and the ternary system (polymer matrix, nanofillers and nanopores on the fibres surface). According to these categories, deformation processes have been characterized, and different schematic models for these processes are proposed. The finding of importance in the present work is a brittle-to-ductile transition in polymer nanocomposite fibres during in situ tensile deformation processes. This unique feature in the deformation behaviour of electrospun PNCNFs provides an optimal balance of stiffness, strength and toughness for use as reinforcing elements in a polymer based composite of a new kind.

The effects of Mg addition on the emission of green photons from ZnO nanoparticles were studied. Energy dispersive x-ray spectroscopy (EDS) and Auger electron spectroscopy (AES) data demonstrated that ZnO nanoparticles with surface segregation of MgO (ZnO:MgO) were precipitated from colloidal reactions between Zn²⁺,Mg²⁺ and OH⁻ ions suspended in ethanol. The photoluminescence emission spectra showed stronger green emission from suspended ZnO:MgO versus ZnO nanoparticles. ZnO:MgO also exhibited a stable green emission colour, which was slightly red-shifted from 495 to 520 nm with 168 days of ageing. It was postulated that the presence of MgO on the surface of ZnO prevented both the aggregation of ZnO nanoparticles via electrostatic stabilization of the suspension, and the formation of non-radiative recombination states on the surface, resulting in more intense, stable photoemission from ZnO. The red shift of the green emission from suspended ZnO nanoparticles with extended ageing was attributed to filling of radiative surface trap states in the bandgap.

Nickel oxide (NiO) nanorings were synthesized by controllable thermal decomposition of precursor Ni(OH)₂ nanoplates obtained via the reaction between Ni(NO₃)·6H₂O and NaOH under hydrothermal conditions. The process of their formation was investigated and an unexpected catalytic property of this novel-shaped material is reported for CO oxidation.

The influence of ultrathin Au cluster films on the growth of para-hexaphenyl (p-6P) fibres is investigated. Whereas p-6P at elevated temperatures forms long, mutually parallel fibres on plain mica, these fibres become shorter but taller on Au covered mica, up to a Au film thickness of approximately 8 nm. The degree to which fibres are mutually parallel decreases with increasing Au thickness. For thicker Au films the length of the fibres increases again, and their morphology changes from flat to faceted; for Au film thicknesses above 20 nm, fibre networks are formed. The spectroscopic properties of the fibres are not modified by the Au layer, enabling independent control of the fibre morphology by means of the intermediate metallic layer.

Mechanical properties of suspended quasi-one-dimensional polymer nanostructures were investigated using atomic force microscopy (AFM). A recently developed new acid-free etch method combined with electron beam lithography was used to fabricate suspended polypyrrole (PPy) nanotubes and helical polyacetylene (HPA) nanofibres. The elastic modulus of each suspended structure was obtained by AFM force–distance measurements. The estimated modulus value of the PPy nanotube (HPA nanofibre) was 0.96 GPa (0.5 GPa). Using this acid-free method, all-organic flexible NEMS devices can be fabricated in the future.

The iron-incorporated mesoporous silica material Fe-HMS was successfully synthesized at ambient temperature by using dodecylamine as the template agent, and it was characterized by XRD, SEM, FT–IR, UV–vis, ESR and N₂ adsorption measurements. Its catalytic performance was studied for phenol hydroxylation with H₂O₂ in a fixed-bed reactor. The results show that Fe³⁺ ions have been successfully incorporated into the framework of HMS, and Fe-HMS has a uniform mesoporous structure with about 2.7 nm pore diameter. After Fe-HMS is calcined, most of the Fe³⁺ ions remain in the tetrahedral coordinated framework, and only a small part of Fe species migrate to the extraframework. Fe-HMS has high catalytic activity and very high selectivity to dihydroxybenzene for the hydroxylation of phenol. Over the Fe-HMS catalyst, the product distribution of phenol hydroxylation is different from that over the microporous TS-1 zeolite. The solvents have great influence on the catalytic activity of Fe-HMS, and water is the best solvent.

A new structural mechanics model is developed to closely duplicate the atomic configuration and behaviours of single-walled carbon nanotubes (SWCNTs). The SWCNTs are effectively represented by a space frame, where primary and secondary beams are used to bridge the nearest and next-nearest carbon atoms, to mimic energies associated with bond stretching and angle variation, respectively. The elastic properties of the frame components are generalized from molecular dynamics (MD) simulation based on an accurate ab initio force field, and numerical analyses of tension, bending, and torsion are carried out on nine different SWCNTs. The space-frame model also closely duplicates the buckling behaviours of SWCNTs in torsion and bending. In addition, by repeating the same process with continuum shell and beam models, new elastic and section parameters are fitted from the MD benchmark experiments. As an application, all three models are employed to study the thermal vibration behaviours of SWCNTs, and excellent agreements with MD analyses are found. The present analysis is a systematic structural mechanics attempt to fit SWCNT properties for several basic deformation modes and applicable to a variety of SWCNTs. The continuum models and fitted parameters may be used to effectively simulate the overall deformation behaviours of SWCNTs at much larger length- and timescales than pure MD analysis.

This paper introduces a process to synthesize well aligned carbon nanotubes (CNTs) from ethanol flames by using a uniform electric field generated from a DC power supply. It has been found that (1) comparing with the other processes a small electric field is enough to align CNTs; (2) the synthesis process becomes more controllable and repeatable; (3) the electric field also improves the diameter uniformity and the crystallinity of graphite sheets. It is thought that the alignment mechanism is due to the electrostatic force acting upon the catalyst particles at the tips of CNTs. The present process has advantages such as convenience of applying electric field, simple experiment set-up, and large area synthesis of well aligned CNTs.

Large area, aligned amorphous silica nanowires grow on the inner wall of bubble-like silica film, which is prepared by thermal evaporation of a molten gallium–silicon alloy in a flow of ammonia. These nanowires are 10–20 nm in diameter and 0.5–1.5 µm in length. The bubble-like silica film functions as a substrate, guiding the growth of silica nanowires by a vapour–solid process. This work helps us to clearly elucidate the growth mechanism of aligned amorphous silica nanowires, ruling out the possibility of liquid gallium acting as a nucleation substrate for the growth of the aligned silica nanowires. A broad emission band from 290 to 600 nm is observed in the photoluminescence (PL) spectrum of these nanowires. There are seven PL peaks: two blue emission peaks at 430 nm (2.88 eV) and 475 nm (2.61 eV); and five ultraviolet emission peaks at 325 nm (3.82 eV), 350 nm (3.54 eV), 365 nm (3.40 eV), 385 nm (3.22 eV) and 390 nm (3.18 eV), which may be related to various oxygen defects.

We have recently fabricated dye-sensitized solar cells (DSSCs) comprising nanofibrous TiO₂ membranes as electrode materials. A thin TiO₂ film was pre-deposited on fluorine doped tin oxide (FTO) coated conducting glass substrate by immersion in TiF₄ aqueous solution to reduce the electron back-transfer from FTO to the electrolyte. The composite polyvinyl acetate (PVac)/titania nanofibrous membranes can be deposited on the pre-deposited thin TiO₂ film coated FTO by electrospinning of a mixture of PVac and titanium isopropoxide in N,N-dimethylformamide (DMF). The nanofibrous TiO₂ membranes were obtained by calcining the electrospun composite nanofibres of PVac/titania as the precursor. Spectral sensitization of the nanofibrous TiO₂ membranes was carried out with a ruthenium (II) complex, cis-dithiocyanate-N,N^'-bis(2,2^'-bipyridyl-4,4^'-dicarboxylic acid) ruthenium (II) dihydrate. The results indicated that the photocurrent and conversion efficiency of electrodes can be increased with the addition of the pre-deposited TiO₂ film and the adhesion treatment using DMF. Additionally, the dye loading, photocurrent, and efficiency of the electrodes were gradually increased by increasing the average thickness of the nanofibrous TiO₂ membranes. The efficiency of the fibrous TiO₂ photoelectrode with the average membrane thickness of 3.9 µm has a maximum value of 4.14%.

Energy exchanges between orderly intertube axial motion and vibrational modes are studied for isolated systems of two coaxial carbon nanotubes at temperatures ranging from 300 to 500 K. It is found that the excess intertube van der Waals energy, depleted from the intertube axial motion, is primarily stored in low-frequency mechanical modes of the oscillator for an extended period of time. This constitutes the first computer simulation of a nanomechanical device that exhibits negative friction.

Single-crystal ZnO nanowires were successfully grown on modified well-aligned carbon nanotube (CNT) arrays by a hydrothermal process. The pre-deposited ZnO grains on the CNTs served as the nucleation sites for the growth of ZnO nanowires. The attached growth of ZnO nanowires on the well-aligned CNT arrays formed a 3D configuration. The 3D hybrid nanostructured material could find application in sensors and other electronic or optoelectronic devices.

Uniform and step-shaped Bi nanowire (NW) arrays have been synthesized by electrochemical deposition inside the uniform and step-shaped nanochannels of an anodic aluminium oxide template. These Bi NWs are highly oriented and single crystalline. The current–voltage characteristics of the parallel uniform Bi nanowires show that the contacts between Bi NWs and gold film do not make significant contributions to the I–V characteristics of the step-shaped Bi NWs. The diameters of the thick segment and the thin segment of the step-shaped Bi NWs are about 70 and 40 nm, respectively. Their current–voltage characteristics show conventional metal–semiconductor junction behaviour. The approach can be exploited to produce one-dimensional metal–semiconductor junctions using step-shaped NWs consisting of other semi-metals without any external doping, which may find various applications in nanotechnology.

We demonstrate the deterministic shape-selective synthesis and growth of CdSe nanowires, nanosaws and nanoribbons by a simple vapour-transport process in a tube furnace. The key step, in order to achieve reproducible shape selectivity for a given set of deposition parameters, is to exclude any effects of the temperature ramping. We prove that an efficient precursor-flow shutter is achieved just by varying the total furnace pressure. We then present a shape-diagram linking the different nanocrystals morphologies to only two parameters: powder and substrate temperature. These are varied in the 550–700 °C and 400–600 °C range, respectively. A model explaining the shape control is discussed.

The voltage margin of a resistor-logic demultiplexer can be improved significantly by basing its connection pattern on a constant-weight code. Each distinct code determines a unique demultiplexer, and therefore a large family of circuits is defined. We consider using these demultiplexers for building nanoscale crossbar memories, and determine the voltage margin of the memory system based on a particular code. We determine a purely code-theoretic criterion for selecting codes that will yield memories with large voltage margins, which is to minimize the ratio of the maximum to the minimum Hamming distance between distinct codewords. For the specific example of a 64 × 64 crossbar, we discuss what codes provide optimal performance for a memory.

We report a novel approach to grow highly oriented, freestanding and structured carbon nanotubes (CNTs) between two substrates, using microwave plasma chemical vapour deposition. Sandwiched, multi-layered catalyst structures are employed to generate such structures. The as-grown CNTs adhere well to both the substrate and the top contact, and provide a low-resistance electric contact between the two. High-resolution scanning electron microscope (SEM) images show that the CNTs grow perpendicular to these surfaces. This presents a simple way to grow CNTs in different, predetermined directions in a single growth step. The overall resistance of a CNT bundle and two CNT-terminal contacts is measured to be about 14.7 k Ω. The corresponding conductance is close to the quantum limit conductance G₀. This illustrates that our new approach is promising for the direct assembly of CNT-based interconnects in integrated circuits (ICs) or other micro-electronic devices.

Details of the vapour–liquid–solid Au droplet catalysed growth of ZnS nanobelts are elucidated in this work. The inclination of the Au droplet after solidification shows that it is indeed in the liquid state during nanobelt growth. Numerous stacking faults are observed when (0001) wurtzite is the side surface of the nanobelt. Compressive stress at the droplet–nanobelt–atmosphere triple interface is the cause of the stacking faults. Sawteeth-like structures are observed on the Zn-terminated polar (0001) side surface only. These surfaces are chemically active, while S-terminated surfaces and non-polar surfaces are not. On these active surfaces, autocatalysed vapour–solid growth leads to the formation of the observed sawteeth.

Monodispersed, highly crystalline dendrimer-stabilized gold nanoparticles (Au DSNPs) were synthesized via hydrazine reduction chemistry and stabilized using primary amine-terminated poly(amidoamine) (PAMAM) dendrimers of different generations (generations 2–6) with the same molar ratios of dendrimer terminal nitrogen ligands/gold atoms. The sizes of the synthesized Au DSNPs decrease with the increase of the number of dendrimer generations. These Au DSNPs are fluorescent and display strong blue emission intensity at 458 nm. Polyacrylamide gel electrophoresis (PAGE) analysis indicates that all Au DSNPs are stable and both metal NPs and dendrimer stabilizers do not separate from each other during the electrophoresis process. The synthesized inorganic/organic hybrid Au DSNPs provide new nanoplatforms that will be further modified with various biological ligands for the application of biosensing and targeted cancer therapeutics.

Hexagonal wurtzite structure Tb(OH)₃ nanowires with a uniform diameter of about 70–80 nm and lengths of up to several micrometres have been synthesized on a large scale via a hydrothermal treatment based on the use of an anodic aluminium membrane as the template. Aligned Tb(OH)₃ nanowire arrays can be obtained by dissolving the template. Field emission scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, selected area electron diffraction, x-ray diffraction, and photoluminescence (PL) spectra have been employed to characterize the as-prepared samples. The PL spectrum of Tb(OH)₃ under 350 nm excitation consists of four main peaks at 489.9, 543, 584 and 621 nm, among which that for the electric dipole transition ⁵D₄ to ⁷F₅ (at 543 nm) is the strongest. Furthermore, a preliminary suggestion for the mechanism of growth of the Tb(OH)₃ nanowires using the hydrothermal–template synthesis technique has been proposed.

Ternary alloy CdSSe nanowires and nanoribbons were successfully grown through a one-step thermal evaporation route using Au as a catalyst. The nanostructures obtained are uniform in diameter, and have smooth surfaces. High-resolution transmission electron microscopy, energy dispersive x-ray spectra and x-ray diffraction showed that both the nanowires and the nanoribbons have high-quality single-crystalline nature, and their compositions can be determined as CdS_0.6Se_0.4 and CdS_0.3Se_0.7, respectively. The mechanisms of formation of these two different nanostructures were discussed. The photoluminescence measurements showed very strong band-edge emission for both samples, which further demonstrates the single-crystal nature of the as-obtained CdSSe alloys. This finding may be extended for fabricating other composition-tunable 1D ternary alloy nanostructures.

Multi-walled carbon nanotubes (CNTs), either on an SiO₂ substrate or suspended above the substrate, were contacted to W, Au and Pt tips using a nanoprobe system, and current–voltage (I–V) characteristics were measured inside a scanning electron microscope. Linear I–V curves were obtained when Ohmic contacts were established to metallic CNTs. Methods for establishing Ohmic contacts on a CNT have been developed using the Joule heating effect when the tips are clean and e-beam exposing the contacting area of the tip when the tips are covered by a very thin contamination layer. When the contact is not good, non-linear I–V curves are obtained even though the CNTs that have been contacted are metallic. The resistance measured from the metal tip–CNT–metal tip system ranges from 14 to 200 k Ω. When the CNT was contacted via with Ohmic contacts the total resistance of the CNT was found to change roughly linearly with the length of the CNTs between the two tips. Field effect measurements were also carried out using a third probe as the gate, and field effects were found on certain CNTs with non-linear I–V characteristics.

CuO is the prototype compound of cuprate superconductors, so understanding its electronic structures will facilitate the study of the pairing mechanism and miscellaneous states of high-temperature superconductors. We prepared uniform CuO nanocrystals (7–100 nm) and studied their size-dependent Raman scattering spectra. The relative variation between the two-phonon scattering band (2B_g) and the one-phonon band (B_g) indicates a decreasing electron–phonon coupling with reducing size, which unveils the dominant Fröhlich electron–phonon coupling, as indicated by Devreese, but not the small polaron in CuO. Moreover, the anomalous enhancement of the multi-phonon band at a critical size and 1D structure at room temperature is attributable to an enhanced electron–phonon coupling accompanied by phonon–plasmon coupling, i.e., the 'plasphon' proposed by Alexandrov et al in 1981.

The elastic contact of non-ideal conical and Berkovich indenters with bi-layer half-spaces is investigated. Blunted tips are simulated as smooth surfaces. The boundary element method is employed to carry out the numerical simulations of nanoindentation.

An analytical analysis of the influence of the coating thickness and the tip bluntness magnitude on the nanoindentation loading curve is realized. The dimensionless compression force is introduced in order to describe the nanoindentation at different approaches between the indenter and the coated half-space. A practical technique for determining the Young's modulus of coatings is proposed. The technique is based on the modelling of indentation of the blunted indenter tip into the coating/substrate composite. This technique is applied to the nanoindentation study of nanocrystalline Cr coatings on silicon and glass substrates being tested by a diamond Berkovich indenter with a blunted tip.

A detailed elaboration of the transformations of iron species, present in natural and Fe(NO₃)₃ loaded montmorillonite, during carbon deposition and carbon nanotube growth is described. According to transmission electron microscopy results, deposited carbon atoms form fibres in the case of pristine montmorillonite and multiwalled carbon nanotubes in the case of Fe(III) loaded montmorillonite. Mössbauer and x-ray diffraction analysis results point to an extensive reduction of structural and intercalated Fe(III) cations to Fe(II) with the latter migrating from the interlayer space to the vacant octahedral sites of the mineral's lattice. Such migration of the non-structural iron catalyst prohibits extensive contamination of the final composite with various metal catalyst impurities. The crucial role of the active catalytic centres in the formation of carbon nanotubes is ascribed to a minor quantity of iron, found entrapped in the carbon nanostructures, which, at the end of the reaction, is identified as iron carbide. The interesting formation of a nanometric γ-iron precipitate is also detected, which is probably stabilized through strong interactions with the lattice of montmorillonite. Finally, it is demonstrated that iron-rich natural clay minerals can serve as direct catalysts for carbon nanotube growth.

Mechanical behaviour analysis plays an important role in the design of micro/nano-electromechanical system (MEMS/NEMS) devices for reliability. In this paper, the size-dependent mechanical properties of nanostructures are numerically studied with the finite element method (FEM) by developing a kind of surface element to take into account the surface elastic effect. This method is then applied to the investigation of the interaction between two pressurized nanovoids and the effective moduli of two-dimensional nanoporous material. The numerical results indicate that surface elasticity can significantly alter the nature of interaction forms and the effective moduli by inducing a strong size dependence in conventional results.

A novel method for the electrospinning of multiple polymer jets into nanofibres is presented. In this work, 20 wt% nylon 6 solution was electrified and pushed by air pressure through the walls of a porous polyethylene tube. Multiple jets formed on the porous surface and electrospun into nanoscale fibres. The length weighted fibre diameters have a similar mean diameter to those from a single jet but broader in distribution. The mass production rate from the porous tube is 250 times greater than from a typical single jet.

An experimental and numerical investigation of the effect of material anisotropy on the self-positioning of epitaxial nanostructures has been performed. The self-positioning occurs due to a lattice mismatch between two epitaxial material layers (GaAs and In_0.2Ga_0.8As) of a hinge. Both materials have cubic crystal symmetry and possess anisotropic mechanical properties. The dependence of the hinge curvature radius on the material orientation angle was obtained experimentally by creating self-positioning hinges with different angles between the hinge axis and material crystallographic axes. The same self-positioning structures were modelled by solving geometrically nonlinear problems with the help of the finite element method. Experimental and numerical values of the hinge curvature radius are in qualitative agreement. It is found that material anisotropy significantly affects the shape of self-positioning structures.

Metallic Au nanowires were electrochemically synthesized in 20 µm thick ion track etched polycarbonate membranes with the nominal pore diameter of 200 nm. Scanning and transmission electron microscopy analysis and x-ray diffraction of samples revealed that the nanowires are dense with a fcc texturing. The I–V characteristics of a single Au nanowire were investigated using a four-point microprobe set-up. The Au nanowire was placed in electrical contact with electrodes patterned on planar substrates using a dual-beam focused ion beam technique. The resistivity of the Au nanowires was found to be 2.8 × 10⁻⁴ Ω cm.

Morphology evolution of high-index GaAs(331)A surfaces during molecular beam epitaxy (MBE) growth has been investigated in order to achieve regularly distributed step-array templates and fabricate spatially ordered low-dimensional nano-structures. Atomic force microscope (AFM) measurements have shown that the step height and terrace width of GaAs layers increase monotonically with increasing substrate temperature. By using the step arrays formed on GaAs(331)A surfaces as the templates, we have fabricated highly ordered InGaAs nanowires. The improved homogeneity and the increased density of the InGaAs nanowires are attributed to the modulated strain field caused by vertical multi-stacking, as well as the effect of corrugated surface of the template. Photoluminescence (PL) tests confirmed remarkable polarization anisotropy.

A simple, productive and low-cost route has been developed to synthesize multi-armed CdTe nanorods using myristic acid (MA) as a complex agent. The yield of this approach can reach 75%. The dimension of the multi-armed nanorods can be controlled by tuning the molar ratios of Cd/Te and Cd/MA; the diameter can be changed from 2 to 7 nm while the length from 15 to 60 nm. The hexagonal structure was confirmed in x-ray diffraction analysis. However, it was assumed that one crystal is composed of the dominant hexagonal structure along with a cubic structure in the core.

We report strong visible photoluminescence (PL) from thermally treated tetra-ethyl-ortho-silicate (TEOS) thin films at room temperature. High-resolution transmission electron microscope (HRTEM) studies showed that the PL originated from nanocrystalline-Si (nc-Si). HRTEM images showed that as-grown TEOS thin films had quasi-static amorphous (QSA) SiO₂ phases instead of the typical amorphous (TA) SiO₂ phases, and that they divided into small pieces of nc-Si after thermal treatment. In addition, Fourier transform infrared (FTIR) investigations showed that the QSA-SiO₂ phases were composed of three types of bonding modes (i.e., Si–O–Si bending, Si–O bending, and Si–O–Si stretching), which play important roles in the formation of the nc-Si at relatively lower annealing temperatures.

In this work a theoretical study of Ti monomers and wires interacting with an (8, 0) semiconductor single-wall carbon nanotube (SWNT), by inside as well as outside faces, is presented. Spin-polarized total-energy ab initio calculations, based on the density functional theory, are used to describe the structural, electronic and magnetic properties of the studied systems. The most stable configurations for monomers are found to be over the centre of a C–C bond for inside and over the midpoint of the centre of the hexagonal site for outside. Considering that the Ti atoms on the tube surface tend to form continuous wires, to allow a comprehensive view of the interaction of the Ti wires with the SWNT surface, we present a complete understanding, both from inside and outside the nanotube. Our calculations have shown that the most stable configuration is with the wire inside the tube, with the resulting electronic structures showing a metallic system with high hybridization between the Ti and C atoms and a large charge transfer from Ti to C atoms. For Ti wire adsorbed inside the tube the low spin configuration is shown to be more stable than high spin configuration and the opposite behaviour is observed for the corresponding outside case. These novel results are relevant for the understanding of Ti atoms covering and filling SWNTs, demonstrating the high stability of these systems and suggesting that they can be useful for future use in nanodevices, in particular for spintronics and nanosensors.

We report on the fabrication of chemically nanopatterned gold surfaces by combining electron-beam lithography with gas and liquid phase thiolization. The line-edge roughness of the patterns is ∼4 nm, corresponding to a limiting feature size in the range of 15 nm. Indications for a lower packing density of the self-assembled monolayers grown in the nanofeatures are given, and evidences for the bleeding of thiols along the grain boundaries of the gold substrate are displayed. A comparison is provided between nanopatterned thiol and silane monolayers on gold and on silicon wafers, respectively. The line-edge roughnesses are shown to be close to each other for these two systems, indicating that the limiting step is currently the lithography step, suggesting possible improvement of the resolution. The advantages and drawbacks of thiol versus silane monolayers are finally discussed with respect to the formation of chemically nanopatterned surfaces.

Iron structures with dimensions of the order of the minimum domain size (∼50 nm at room temperature) may provide us with a new high-density data storage method. Limitations have been observed in existing depositional atom lithography schemes for producing these structures. We present a proof-in-principle experiment using an alternative scheme based upon direct exposure metastable neon-atom lithography. Iron structures with dimensions of the order of 7.5 µm are produced by this method. Extension of this work to the application of standing-wave atom lithography and laser cooling flux enhancement techniques is discussed as a method for reducing dimensions to a size equating to a dot array density of around 0.1 Gbit mm⁻².