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Here we characterize a highly efficient approach for protein confinement and enzyme immobilization in NH₂– or HOOC– functionalized mesoporous silica (FMS) with pore sizes as large as tens of nanometres. We observed a dramatic increase of enzyme loading in both enzyme activity and protein amount when using appropriate FMS in comparison with unfunctionalized mesoporous silica and normal porous silica. With different protein loading density in NH₂–FMS, the negatively charged glucose oxidase (GOX) displayed an immobilization efficiency (I_e, the ratio of the specific activity of the immobilized enzyme to the specific activity of the free enzyme in stock solution) in a range from 30% to 160%, while the same charged glucose isomerase (GI) showed an I_e of 100% to 120%, and the positively charged organophosphorus hydrolase (OPH) exhibited I_e of more than 200% in HOOC–FMS. The enzyme–FMS composite was stained with the charged gold nanoparticles and imaged by transmission electron microscopy (TEM). Fourier transform infrared (FTIR) spectroscopy showed no major secondary structural change for the enzymes entrapped in FMS. Thanks to the large, rigid, open pore structure of FMS, the reaction rate and K_m of the entrapped enzymes in FMS were comparable to those of the free enzymes in solution. In principle, the general approach described here should be applicable to many enzymes, proteins, and protein complexes since both pore sizes and functional groups of FMS are controllable.

Magnetic nanoparticle arrays have been fabricated by combining chemically synthesized Fe₃O₄ nanoparticles with a diblock copolymer template substrate consisting of self-assembled polystyrene (PS) dots in a polymethylmethacrylate (PMMA) matrix. The influence of the volume fraction of the Fe₃O₄ suspending solution and the withdrawal speed of the template on the formation of array structures was investigated. A small volume fraction of the nanoparticles and low withdrawal speed play an important role in the fabrication of the patterned arrays of nanoparticles via template assisted self-assembly. Below a withdrawal speed of 0.5 mm s⁻¹ and a nanoparticle volume fraction below 0.05 vol% (in particular, at extremely high dilutions of less than 0.01 vol%), the selective deposition of one to several nanoparticles on every single PS dot becomes possible.

A microwave plasma chemical vapour deposition (MPCVD) system has been used to deposit nanometre-sized single-crystalline diamonds on 1 × 1 cm² Si(100) substrates. The distribution of deposited diamonds has good uniformity over the whole Si substrate surface by using a dome-shaped Mo anode which allows the application of bias-enhanced nucleation. The morphology and crystallinity of the deposits on Si were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with electron diffraction and lattice images. SEM and TEM observations show that oriented diamond nuclei as single crystals with facets can form on self-formed Si cones through epitaxial SiC within a short bias period. After a longer bias time, it has been observed that polycrystalline diamonds formed as a result of secondary nucleation.

Six-line ferrihydrite (FH) nanoparticles have been synthesized in the core of reverse micelles, used as nanoreactors to obtain average particle sizes . The blocking temperatures T_B^m extracted from magnetization data increased from ≈10 to 20 K for increasing particle size. Low-temperature Mössbauer measurements allowed us to observe the onset of differentiated contributions from the particle core and surface as the particle size increases. The magnetic properties measured in the liquid state of the original emulsion showed that the ferrihydrite phase is not present in the liquid precursor, but precipitates in the micelle cores after the free water is freeze-dried. Systematic susceptibility χ_ac(f,T) measurements showed the dependence of the effective magnetic anisotropy energies E_a with particle volume, and yielded an effective anisotropy value of K_eff = 312 ± 10 kJ m⁻³.

One-dimensional (1D) zinc oxide (ZnO) hierarchical structures have been self-assembled on amorphous carbons using thermal chemical vapour transport and condensation. Three typical micro- and nanostructures consisting of micrometre-sized rods and nanometre-sized needles were observed. Growth mechanisms were established to elucidate the growth properties of 1D ZnO hierarchical structures.

Wurtzite ZnSe nanowires were prepared on GaAs substrates in a metal-organic chemical vapour deposition system. Electron microscopy shows that they are smooth and uniform in size. Both transmission electron microscopy and x-ray diffraction reveal the wurtzite structure of the nanowires, which grows along the direction. Raman scattering studies on individual nanowires were performed in the back-scattering geometry at room temperature. Besides the commonly observed longitudinal and transverse optical phonon modes, a possible surface mode located at 233 cm⁻¹ is also observed in the Raman spectrum. A peak located at 2.841 eV was clearly observed in the photoluminescence spectra of the nanowires, which can be assigned to near band edge emissions of wurtzite ZnSe.

Composite Fe₃O₄–SiO₂ materials were prepared by the sol–gel method with tetraethoxysilane and aqueous-based Fe₃O₄ ferrofluids as precursors. The monoliths obtained were crack free and showed both optical and magnetic properties. The structural properties were determined by infrared spectroscopy, x-ray diffractometry and transmission electron microscopy. Fe₃O₄ particles of 20 nm size lie within the pores of the matrix without any strong Si–O–Fe bonding. The well established silica network provides effective confinement to these nanoparticles. The composites were transparent in the 600–800 nm regime and the field dependent magnetization curves suggest that the composite exhibits superparamagnetic characteristics.

Using a Si-based porous anodic alumina membrane as a mask, we demonstrate a way to pattern Si surface. After removing the SiO₂ nanoislands formed during anodization of the Al/Si interface, we obtain a Si nanotip array on the surface of a Si wafer. This array shows an excellent field emission property with a low turn-on field of 8.5 V µm⁻¹. The Fowler–Nordheim plot obtained is linearly dependent, indicating that the emission current arises from the quantum tunnelling effect. The Si nanotip array can be expected to have important applications in nanoelectronic devices.

Two- and four-probe electrical measurements on individual tin oxide (SnO₂) nanowires were performed to evaluate their conductivity and contact resistance. Electrical contacts between the nanowires and the microelectrodes were achieved with the help of an electron- and ion-beam-assisted direct-write nanolithography process. High contact resistance values and the nonlinear current–bias (I–V) characteristics of some of these devices observed in two-probe measurements can be explained by the existence of back-to-back Schottky barriers arising from the platinum–nanowire contacts. The nanoscale devices described herein were characterized using impedance spectroscopy, enabling the development of an equivalent circuit. The proposed methodology of nanocontacting and measurements can be easily applied to other nanowires and nanometre-sized materials.

The preparation and characterization of pure rare-earth-metal bulks with controllable nanostructures are reported in this paper. A novel 'oxygen-free' in situ synthesis technique that combines inert-gas condensation with spark plasma sintering (SPS) technology is proposed. Taking into account the special mechanisms of SPS consolidation and the scale effects of nanoparticles, we introduced practical procedures for preparing rare-earth bulks of amorphous, mixed amorphous and nanocrystals, and nanocrystalline microstructures, respectively. Compared with the conventional polycrystalline bulk, these nanostructured bulks exhibit substantially improved physical and mechanical properties. This technique enables comprehensive studies on the microstructures and properties of a large variety of nanostructured metallic materials that are highly reactive in the air.

Various types of tungsten oxide nanostructures, including nanowires, nanobundles, and three-dimensional nanowire networks, have been synthesized on large-area silicon substrates by simply heating an array of tungsten filaments in a vacuum chamber. The fine structure and components of as-prepared products can been controlled by changing the tungsten filament temperature. This approach is free of catalysts and templates, and provides an economical method for large-scale preparation of various types of tungsten oxide nanostructures for applications.

A new technique was developed for the deposition of colloidal metal nanoparticles on carbon nanotubes. It involves fast evaporation of a suspension containing sonochemically functionalized carbon nanotubes and colloidal nanoparticles. It was demonstrated that metallic nanoparticles with different sizes and concentrations can be deposited on the carbon nanotubes with only a few agglomerates. The technique does not seem to be limited by what the nanoparticles are, and therefore would be applicable to the deposition of other nanoparticles on carbon nanotubes. PtPd and CoPt₃ alloy nanoparticles were used to demonstrate the deposition process. It was found that the surfactants used to disperse the nanoparticles can hinder the nanoparticle deposition. When the nanoparticles were washed with ethanol, they could be well deposited on the carbon nanotubes. The obtained carbon nanotube supported metal nanoparticles were characterized by transmission electron microscopy, energy dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and cyclic voltammetry.

In this study, we present a novel method for preparing multi-walled carbon nanotubes (MWCNTs) grafted with a poly(2-methacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester) (GMA-IDA)-cadmium sulfide complex (CNTs-G-ICdS complex) through plasma-induced grafting polymerization. The characteristics of the MWCNTs after being grafted with the GMA-IDA polymer were monitored by a Fourier transform infrared (FT-IR) spectroscope. Scanning electronic microscopy (SEM) shows that the amount of GMA-IDA grafted onto the MWCNTs increases with the concentration of GMA-IDA monomer. The complex resulting from GMA-IDA polymer grafting onto the MWCNTs, CNTs-G-I (15%), shows excellent dispersion properties in aqueous solution and has high Zeta potential values over a wide range of pH values, from 2 to 12. Moreover, Raman spectroscopy was used to confirm the successful chemical modification of MWCNTs through the plasma treatment. The chelating groups, −N(CH₂COO⁻)₂ in the GMA-IDA polymer grafted on the surface of the CNTs-G-I, are the coordination sites for chelating cadmium ions, and are further used as nano-templates for the growth of CdS nanocrystals (quantum dots). Moreover, TEM microscopy reveals that the size of the CdS nanocrystals on the CNT surfaces increases with increasing S²⁻ concentration. In addition, high resolution x-ray photoelectron (XPS) spectroscopy was used to characterize the functional groups on the surface of the MWCNTs after chemical modification by the plasma treatment and grafting with GMA-IDA polymer.

Sulfur is used to promote the formation of germanium nanocrystals from the robust organometallic precursor, triphenylgermanium chloride, at elevated temperatures (300 °C) in the surfactant/solvent hexadecylamine. Transmission electron microscopy shows that 8 nm germanium nanocrystals are produced that self-assemble into uniform-sized 60 nm germanium nanoclusters after purification. Electron diffraction studies show that the germanium nanoclusters have a diamond germanium crystal structure and energy dispersive x-ray spectroscopy shows that the nanoclusters are primarily composed of pure germanium.

Helical amorphous nanosprings have attracted particular interest due to their special mechanical properties. In this work we present a simple model, within the framework of the Kirchhoff rod model, for investigating the structural properties of nanosprings having asymmetric cross section. We have derived expressions that can be used to obtain the Young's modulus and Poisson's ratio of the nanospring material composite. We also address the importance of the presence of a catalyst in the growth process of amorphous nanosprings in terms of the stability of helical rods.

Self-assembled GaInNAs/GaAsN single-layer quantum dot (QD) lasers, grown using solid source molecular beam epitaxy, have been fabricated and characterized. A high output power of 40.76 mW/facet was obtained from a GaInNAs QD laser with dimensions of 50 × 700 µm² at 10 °C. Temperature-dependent measurements were carried out on the GaInNAs QD lasers of different cavity lengths. For comparison, temperature-dependent measurements were also performed on GaInNAs single quantum well (SQW) and triple QW (TQW) lasers. Unlike the relationship between cavity length and T₀ in GaInNAs SQW/TQW lasers, longer-cavity GaInNAs QD lasers (50 × 1700 µm²) showed a lower T₀ of 65.1 K, which is believed to be due to non-uniformity of the GaInNAs QD layer. Furthermore, compared to GaInNAs SQW lasers, a significant improvement in temperature sensitivity was observed in the TQW GaInNAs lasers. This is attributed to a reduction in the relative contribution of the Auger recombination current and suppression of heavy-hole leakage in the TQW laser structures.

The electronic and transport properties of carbon nanotubes subject to the influences of a transverse electric field and an arbitrary magnetic field are studied by the tight-binding model. The external fields would modify the energy dispersions, destroy the state degeneracy, change the symmetry characteristics, alter the energy gap, modulate the electron effective mass, and create extra band-edge states. The energy gap and the electron effective mass exhibit a rich dependence on the field strength, the magnetic field direction, and the types of carbon nanotubes. A semiconductor–metal transition would be allowed for certain field strengths and magnetic field directions. The variations of energy dispersions with the external fields will also be reflected in the conductance. Special features of the conductance, such as single-shoulder, multi-shoulder, and spike structures, are predicted.

Gold nanoparticles were synthesized through a continuous UV irradiation method using citric acid as a reducer and protective agent. After a period of continuous UV irradiation, the nanoparticles transformed into two-dimensional (2D) nanonetworks, porous nanoplates and compact nanoplates with hexagonal, triangular or truncated triangular pores through a self-assembly process which was dependent on the citric acid concentration. Selected area electron diffraction (SAED) patterns indicated that both the nanonetworks and the porous nanoplates were single crystalline. The influence of citric acid concentration and irradiation time on the morphological transition of Au nanostructures was investigated. The process of morphological transition was presumably discussed.

Here we present a method to synthesize single-walled carbon nanotubes (SWNTs) selectively suspended on tips of silicon-based nanostructure (Si-ns) templates. The Si-ns templates vertically aligned to the substrates are fabricated via an anisotropic etch process using reactive hydrogen plasmas, in which the etch-resistive nanomasks are the nanosized particles formed by thermal annealing of multi-layered catalytic thin films. After plasma etching, the nanosized self-masks remaining at the tips of the Si-ns directly serve as the catalysts for SWNT growth by thermal chemical vapour deposition. Consequently, the synthesized SWNTs are selectively suspended on the tips of the Si-ns, as revealed by characterizations using scanning electron microscopy and resonance Raman spectroscopy. This methodology provides a simple and straightforward approach to assemble two different nanomaterials, i.e., Si-ns and suspended SWNTs, together as a building block for constructing nanodevices for possible applications.

The compositional distribution in a self-assembled InAs(P) quantum wire grown by molecular beam epitaxy on an InP(001) substrate has been determined by electron energy loss spectrum imaging. We have determined the strain and stress fields generated in and around this wire capped with a 5 nm InP layer by finite element calculations using as input the compositional map experimentally obtained. Preferential sites for nucleation of wires grown on the surface of this InP capping layer are predicted, based on chemical potential minimization, from the determined strain and stress fields on this surface. The determined preferential sites for wire nucleation agree with their experimentally measured locations. The method used in this paper, which combines electron energy loss spectroscopy, high-resolution Z contrast imaging, and elastic theory finite element calculations, is believed to be a valuable technique of wide applicability for predicting the preferential nucleation sites of epitaxial self-assembled nano-objects.

Rapid and selective molecular exchange across a barrier is essential for emulating the properties of biological membranes. Vertically-aligned carbon nanofibre (VACNF) forests have shown great promise as membrane mimics, owing to their mechanical stability, their ease of integration with microfabrication technologies and the ability to tailor their morphology and surface properties. However, quantifying transport through synthetic membranes having micro- and nanoscale features is challenging. Here, fluorescence recovery after photobleaching (FRAP) is coupled with finite difference and Monte Carlo simulations to quantify diffusive transport in microfluidic structures containing VACNF forests. Anomalous subdiffusion was observed for FITC (hydrodynamic radius of 0.54 nm) diffusion through both VACNFs and SiO₂-coated VACNFS (oxVACNFs). Anomalous subdiffusion can be attributed to multiple FITC–nanofibre interactions for the case of diffusion through the VACNF forest. Volume crowding was identified as the cause of anomalous subdiffusion in the oxVACNF forest. In both cases the diffusion mode changes to a time-independent, Fickian mode of transport that can be defined by a crossover length (R_CR). By identifying the space-and time-dependent transport characteristics of the VACNF forest, the dimensional features of membranes can be tailored to achieve predictable molecular exchange.

In recent years, several researchers have reported the occurrence of reversible resistance switching effects in simple metal nanogap junctions. A large negative resistance is observed in the I–V characteristics of such a junction when high-bias voltages are applied. This phenomenon is characteristic behaviour on the nanometre scale; it only occurs for gap widths slightly under 13 nm. Furthermore, such a junction exhibits a non-volatile resistance hysteresis when the bias voltage is reduced very rapidly from a high level to around 0 V, and when the bias voltage is reduced slowly. This non-volatile resistance change occurs as a result of changes in the gap width between the metal electrodes, brought about by the applied bias voltage.

The effect of high-energy proton irradiation on the physical properties of carbon nanotubes (CNTs) was investigated. The focus of the study was on the electrical properties of single-walled carbon nanotube (SWNT) network devices exposed to proton beams. Field-effect transistors (FETs) of network type were fabricated using SWNTs and were then irradiated by high-energy proton beams of 10–35 MeV with a fluence of 4 × 10¹⁰–4 × 10¹² cm⁻² that are comparable to the aerospace radiation environment. The electrical properties of both metallic and semiconducting CNT network FET devices underwent no significant change after the high-energy proton irradiation, indicating that the CNT network devices are very tolerant in proton beams. Raman spectra confirm the proton-radiation hardness of CNT network FET devices. The radiation hardness of CNT network FET devices promises therefore the potential usefulness of CNT-based electronics for future space application.

Ag and Ag₂S nanocrystals (NCs) were synthesized by a simple 'one-step' process. Dodecanethiol played three important roles in the synthesis: as the capping reagent, reducer (for the synthesis of Ag) and S²⁻ source (for the synthesis of Ag₂S). Due to the multifunctional characteristic of dodecanethiol, only two reactants (silver nitrate and dodecanethiol) are needed in the synthesis, avoiding the use of toxic organic solvents and a complex reaction procedure. X-ray powder diffraction and transmission electron microscopy studies indicated that both the phase (Ag or Ag₂S) and the particle size were controlled by reaction parameters. The infrared spectra studies indicated that the nanoparticles were stabilized by dodecanethiol. As a result, the particles were stable (no irreversible conglomeration) in the solid state and in solution for several months. In addition, a large quantity of Ag and Ag₂S NCs could be readily obtained. A possible formation and size evolution mechanism for Ag and Ag₂S NCs was proposed.

Nanobelts of nickel hydroxyl sulfate have been prepared on a large scale via a simple template-free hydrothermal reaction on the basis of a complex [Ni(NH₃)₆]²⁺ formed with Ni²⁺ and ammonia in an ethanol–water solution. The as-synthesized nanobelts were single crystals, with several tens of microns in length and 50–150 nm in width. The nanobelts were enclosed by top surfaces (100) and side surfaces (001) and their growth direction was parallel to [010]. The function of aqueous ammonia and ethanol was discussed. Furthermore, nanostructures of a mixture of crystralline NiO and amorphous nickel sulfate with various morphologies, such as nanobelts, porous nanobelts, and nanoparticles, were obtained by the thermal treatment of the as-synthesized Ni(SO₄)_0.3(OH)_1.4 nanobelts at different temperatures.

We investigate a new generation of fullerene nano-oscillators: a single-walled carbon nanotube with one buckyball inside with an operating frequency in the tens-of-gigahertz range. A quantitative characterization of energy dissipation channels in the peapod pair has been performed via molecular dynamics simulation. Edge effects are found to be the dominant cause of dynamic friction in the carbon-peapod oscillators. A comparative study on the energy dissipation also reveals the significant impact of temperature and impulse velocity on the frictional force.

Single-walled carbon nanotube (CNT) arrays have been assembled on various substrates over mm-scale surface areas by combining fluidic alignment with soft lithography (micropatterning in capillaries) techniques. The feature size of the nanotube patterns reaches down to submicrometre scale. To this end, tailored substrate surface modification and pre-alignment of chopped CNTs in suspension are highly critical.

Large-scale long continuous FeS₂ nanowire filled carbon nanotubes (CNTs) were one-step synthesized in the presence of NaN₃ in supercritical CS₂ at 500 °C using ferrocene as the iron source. The CNTs have outer diameters in the range of 15–25 nm and the core FeS₂ nanowires inside CNTs are characterized as single crystals, with an average diameter of 8 nm and up to several micrometres in length. The band gap of FeS₂ nanowire filled CNTs was determined as 5.69 eV from the ultraviolet and visible light absorption spectrum, showing its promise for application in reversible conversion between solar energy and electrical or chemical energy.

Following the recent low temperature synthesis of high quality and single crystal CdSe quantum nanowires, we have used a thermodynamic model to investigate the plausibility of axial-growth and oriented-attachment formation mechanisms. Using surface energies for clean and alkylamine-passivated CdSe surfaces reported elsewhere by Manna et al (2005 J. Phys. Chem. B 109 6183), we have compared equilibrium and metastable shapes of CdSe nanowires as a function of aspect ratio and axial orientation for different degrees of surface passivation. In general, the theoretical results support the oriented-attachment of low aspect quantum dots or nanorods, followed by coalescence to form high aspect quantum wires.

The authors regret that the data in table 1 contained some errors. The correct table 1 is shown below.

Table 1. Corrosion potential (E_corr), corrosion current (i_corr) and polarization resistance (R_p) of nancorystalline Ni–Co graded deposits measured in different solutions.

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