Table of contents

Driven by capillary force, wet carbon nanotube (CNT) arrays have been found to reorganize into cellular structures upon drying. During the reorganization process, individual CNTs are firmly attached to the substrate and have to lie down on the substrate at cell bottoms, forming closed cells. Here we demonstrate that by modifying catalyst structures, the adhesion of CNTs to the substrate can be weakened. Upon drying such CNT arrays, CNTs may slide away from their original sites on the surface and self-assemble into cellular patterns with bottoms open. It is also found that the sliding distance of CNTs increases with array height, and drying millimetre tall arrays leads to the sliding of CNTs over a few hundred micrometres and the eventual self-assembly into discrete islands. By introducing regular vacancies in CNT arrays, CNTs may be manipulated into different patterns.

Flower-like ZnO nanorods with diameters less than 15 nm were synthesized by a sonochemical method. The sensors fabricated from the nanorods exhibited excellent ethanol sensing properties. At the working temperature of 300 °C, their sensitivity was 176.8–100 ppm ethanol vapour. While the working temperature was reduced to 140 °C, they were still able to detect ethanol vapour at the ppm level. The reduced working temperature may be attributed to the small sizes of the nanorods.

This paper demonstrates that carbon nanotubes (CNTs) can be synthesized on a cobalt coated silicon substrate using electron cyclotron chemical vapour deposition and without intentionally heating the substrate. With the mixed gases of C₃H₈/N₂, CNTs with a multi-walled structure and a diameter up to 70 nm have been observed. Results show that the diameter of the CNTs increases with the thickness of the cobalt catalyst film and the amount of nitrogen incorporated in the CNT films considerably influences the structures of the CNTs. Vertically aligned CNTs can be fabricated with a microwave power as low as 300 W and the flow rate ratio of C₃H₈/N₂ = 20/20 sccm. The CNTs exhibit a turn-on field of 0.2 V µm⁻¹ determined at the emission current density of 10 µA cm⁻².

Ge nanocrystallites (Ge-nc) embedded in a SiO₂ matrix are investigated using Raman spectroscopy, photoluminescence and Fourier transform infrared spectroscopy. The samples were prepared by ion implantation with different implantation doses (0.5, 0.8, 1, 2, 3 and 4) × 10¹⁶ cm⁻² using 250 keV energy. After implantation, the samples were annealed at 1000 °C in a forming gas atmosphere for 1 h. All samples show a broad Raman spectrum centred at w≈304 cm⁻¹ with a slight shift depending on the implantation doses. The Raman intensity also depends on the Ge⁷⁴⁺ dose.

A maximum photoluminescence intensity is observed for the sample implanted at room temperature with a dose of 2 × 10¹⁶ cm⁻² at 3.2 eV. Infrared spectroscopy shows that the SiO₂ films moved off stoichiometry due to Ge⁷⁴⁺ ion implantation, and Ge oxides are formed in it. This result is shown as a reduction of GeO_x at exactly the dose corresponding to the maximum blue–violet PL emission and the largest Raman emission at 304 cm⁻¹. Finally, the Raman spectra were fitted with a theoretical expression to evaluate the average size, full-width at half-maximum (FWHM) and dispersion of Ge-nc size.

FeS nanoparticles (NPs) were synthesized using ethylenediamine core poly(amidoamine) (PAMAM) dendrimers of generation 4 terminated with amino (G4·NH₂), hydroxyl (G4·NGlyOH), and carboxyl (G4·SAH) groups, respectively, as stabilizers. These dendrimer-stabilized FeS NPs (FeS DSNPs) were characterized by ultraviolet–visible (UV–vis) spectrometry, zeta-potential measurements, and transmission electron microscopy (TEM). Deposition of FeS NPs onto mesoporous silica gel microparticles was attempted using two approaches: (A) direct coating of {FeS–G4·NH₂} DSNPs onto silica particles; and (B) using G4·NH₂-coated silica particles to incorporate Fe²⁺ ions for the subsequent formation of FeS NPs. Scanning electron microscopy (SEM) studies show that approach (B) was much more efficient in the incorporation of FeS NPs than approach (A). Such preparation and manipulation of FeS DSNPs provides a unique strategy for fabricating various reactive nanoplatforms for environmental remediation applications.

A new method was developed for the fabrication of CdS–TiO₂ semiconductor nanoparticles as visible-light-excitable photocatalyst at low temperatures. Nanosized CdS acting as an effective and stable sensitizer was incorporated into TiO₂ by microemulsion-mediated solvothermal hydrolyzation followed by acidic peptization of the precipitate under 70 °C. The new method avoided the calcination or other pyrochemical treatments involved in traditional preparations, and thus eliminated the unwanted agglomeration of nanoparticles or the oxidation of CdS by oxygen. Compared to traditional methods, it was highly simplified, bypassing those miscellaneous steps like filtration, sintering, milling and redispersion in solutions. The crystal structure, configuration, element composition, as well as the light-absorption properties of the obtained CdS–TiO₂ hydrosol were characterized in detail. The hydrosol consisting of uniform and small crystalline particles of about 2 nm in diameter was thermodynamically stable and showed good dispersibility. The photocatalytic activity of the 'coupled' material was confirmed through the photocatalytic degradation of methylene blue (MB) dye under visible light irradiation, and the cooperative photocatalytic mechanism is discussed.

ZnO nanoparticles were synthesized by a simple mild solution method. Spectral sensitization of nanocrystalline ZnO was carried out with [Ru(dcbpy)₂(NCS)₂ (dcbyp = 2,2'-bipyridyl-4,4'-dicarboxylate)] (RuN3) and CuPc. The electron transfer behaviours at the surface and interface in ZnO/RuN3 and ZnO/CuPc were investigated using a surface photocurrent technique. When exposed to oxygen gas, the surface photocurrent (I_SPC) responses of ZnO/RuN3 and ZnO/CuPc decreased and increased, respectively. The results demonstrated through the adsorption of oxygen gas that there are different microscopic mechanisms for the surface charges. The microscopic processes of electron transfer between oxygen molecules and dye-sensitized ZnO are discussed in detail in this paper. Such research should be valuable for fundamental science and optoelectronic device application of ZnO nanoparticles.

We theoretically investigate cross-talk in hyperfine gate control of donor-qubit quantum computer architectures, in particular the Kane proposal. By solving the Poisson and Schrödinger equations numerically for the gated donor system, we calculate the change in hyperfine coupling and thus the error in spin-rotation for the donor nuclear-electron spin system, as the gate-donor distance is varied. We thus determine the effect of cross-talk—the inadvertent effect on non-target neighbouring qubits—which occurs due to closeness of the control gates (20–30 nm). The use of compensation protocols is investigated, whereby the extent of cross-talk is limited by the application of compensation bias to a series of gates. In the light of these factors, architectural implications are then considered.

Nanoscale capacitance imaging with attofarad resolution (∼1 aF) of a nano-structured oxide thin film, using ac current sensing atomic force microscopy, is reported. Capacitance images are shown to follow the topographic profile of the oxide closely, with nanometre vertical resolution. A comparison between experimental data and theoretical models shows that the capacitance variations observed in the measurements can be mainly associated with the capacitance probed by the tip apex and not with positional changes of stray capacitance contributions. Capacitance versus distance measurements further support this conclusion. The application of this technique to the characterization of samples with non-voltage-dependent capacitance, such as very thin dielectric films, self-assembled monolayers and biological membranes, can provide new insight into the dielectric properties at the nanoscale.

The optical response of nanocomposite thin films formed by Cu nanoparticles (NPs) embedded in amorphous aluminium oxide (Al₂O₃) prepared by pulsed laser deposition (PLD) in vacuum is studied in order to investigate the possible existence of reactive processes on the Cu NPs during their covering with Al₂O₃. The study is performed as a function of the laser fluence on the Al₂O₃ target (0.6–4.6 J cm⁻²), while the laser fluence for Cu ablation is kept constant (1.8 J cm⁻²). The structural analysis of the films shows that they are formed by a high density of NPs with average dimensions in the 4.9–5.9 nm range. The optical response of the films has been followed in situ by real-time reflectivity measurements at 633 nm and after deposition by transmission measurements as a function of wavelength around the surface plasmon resonance (SPR). For low laser fluences on the Al₂O₃ target, the absorption spectrum is dominated by a well-defined SPR absorption band at 1.9 eV. As the laser fluence is increased, the intensity of the absorption band associated with the SPR decreases and shifts to 2.1 eV. The films deposited at low fluences contain metallic Cu NPs and, as the laser fluence increases sputtering of Cu from the NPs and mixing of the species from the Al₂O₃ deposition with the Cu from the NPs surface takes place. The latter process leads to the formation of an Al–Cu oxide cover on the Cu NPs. The present results provide evidence for mixing of species from the host and Cu at the surface of the NPs, and it is shown how the degree of mixing depends on the laser fluence used to ablate the Al₂O₃ host target.

Recent developments in multifunctional devices show the interest in combining different materials to obtain specific properties. Through supercritical fluid chemical deposition (SFCD), silica spheres, used as a model support, were coated with copper nanoparticles (5–17 nm) with a tuneable amount of coverage (40–80%). The coating process is based on the reduction of metal precursors with hydrogen in a supercritical CO₂/isopropanol mixture in a temperature range between 100 and 150 °C at 24 MPa. Several parameters were studied such as temperature, residence time or mass ratio of precursor/silica spheres, allowing control of the size of the copper nanoparticles and of the amount of coverage from metal nanoparticles scattered onto the surface to a metal nanoparticle thin film.

We report the design, modelling, fabrication, and testing of a photo-tunable particulate medium that comprises photo-responsible polymeric microshells covered by Au nanospheres. The microshells were formed by a layer-by-layer method. The charged Au nanospheres were coated on outer surfaces of the microshells. The polymeric shells contain azobenzene moieties and shrink upon ultraviolet irradiation; therefore, the interparticle spaces between the nanospheres are tunable by UV light. The absorption spectrum of the Au nanosphere modified microshells changed drastically after the shrinkage. A decreased absorption peak of Au nanospheres and an enhanced absorption in the near-infrared region were clearly observed. The results of theoretical modelling suggest that the overall spectral changes stem mainly from the enhanced particle interactions and also from the field enhancements in the space among the nanospheres.

Selective growth of amorphous silica nanowires on a silicon wafer deposited with Pt thin film is reported. The mechanism of nanowire growth has been established to follow the vapour liquid solid (VLS) model via the PtSi phase acting as the catalyst. Nanowires grow with diameters ranging from 50 to 500 nm. These bottom-up grown nanowires exhibit photoluminescence with a stable emission of blue light at 430 nm under excitation. The effect of varying the seed layer thickness (Pt film) from 2 to 100 nm has been studied. It is observed that, above 10 nm thickness, a continuous layer of Pt₂Si re-solidifies on the surface, inhibiting the growth of nanowires. The selectivity to the Pt thickness has been exploited to create regions of nanowires connected to conducting silicide (Pt₂Si) simultaneously in a single furnace treatment. This novel approach has opened the gateways for realizing hybrid interconnects in silicon for various nano-optical applications such as the localization of light, low-dimensional waveguides for functional microphotonics, scanning near-field microscopy, and nanoantennae.

Nanocrystalline (NC) Ni–Co/CoO functionally graded materials with excellent lubricating, high anti-corrosion and anti-wear performance were fabricated by electrodeposition and subsequent cyclic thermal oxidation and quenching. Transmission electron microscopy and energy dispersive x-ray spectroscopy investigations show that bulk Ni–Co gradient deposits with an average grain size in the range of 13–40 nm demonstrated a graded structure transition from face-centred cubic to hexagonal close packed and graded composition changes from Ni-rich to Co-rich regions with the increase in deposit thickness. X-ray diffraction and x-ray photoelectron spectroscopy analysis indicated the surface layer of NC Ni–Co graded materials to be mainly composed of dense and ultrafine CoO with a (111) preferred orientation. The NC Ni–Co/CoO functionally graded materials exhibited significantly enhanced corrosion resistance in both NaOH and NaCl solutions and remarkably improved wear resistance and dry self-lubricating performance when compared with the NC Ni and Ni–Co graded deposits under dry sliding wear conditions. The higher corrosion and tribological performance of NC Ni–Co/CoO graded materials can be attributed to the graded microstructure within the deposits, the anti-corrosion barrier of a dense oxide layer and the solid lubrication effect of CoO-rich tribo-surface films.

This paper investigates the electromechanical coupling in single-walled carbon nanotubes. In the model system, the extra electric charge of the nanotube is assumed to be uniformly distributed on carbon atoms. The electrostatic interactions between charged carbon atoms are calculated using the Coulomb law. The deformation of the charged nanotube is obtained by using the molecular structural mechanics method and considering the electrostatic interactions as an external loading acting on carbon atoms. The axial strain is found to be a symmetric function of applied charge, and our predictions are in very good agreement with those from ab initio calculations. The present results indicate that the nanotube aspect ratio has a strong effect on the axial strain when the ratio is less than 10 and the general trend is that the strain increases with the aspect ratio. The peak axial and radial strains occur at nanotube diameters of around 1.2–1.5 nm.

Carbon nanofibres (CNFs) exhibiting bamboo-like, hollow fibril morphology were prepared from a mixture of polyethylene glycol (PEG) and iron-based compounds such as Fe₂(SO₄)₃·nH₂O, Fe(NO₃)·9H₂O or FeO(OH) by a thermal process. These materials were well mixed in distilled water prior to thermal treatment in an air/nitrogen atmosphere. With increasing temperature, the mixture underwent solvent removal, dehydrogenation, thermal decomposition, carbonization and catalytic graphitization to form CNFs. Results show that CNFs can be formed with different PEG/catalyst ratios (100/1–1000/1 by weight) at 750 °C. The catalyst effect is discussed for the formation of bamboo-like CNFs. The diameter of the CNFs was about 30–50 nm while the length was a few micrometres.

Transmission electron microscopy (TEM) is a key technique in the structural characterization of carbon nanotubes. For device applications, carbon nanotubes are typically grown by chemical vapour deposition (CVD) on silicon substrates. However, TEM requires very thin samples, which are electron transparent. Therefore, for TEM analysis, CVD grown nanotubes are typically deposited on commercial TEM grids by post-processing. However, this procedure can damage the nanotubes, and it does not work reliably if the nanotube density is too low. The ability to do TEM directly on as-grown nanotubes on the silicon substrate would solve these problems. For this purpose, we have fabricated micromachined silicon TEM grids with narrow open slits on them. Since the nanotubes grown on these substrates are suspended freely over the open slits, the micromachined substrates form a natural TEM grid for direct imaging of CVD grown nanotubes. Furthermore, the background noise is significantly reduced during micro-Raman spectroscopy, resulting in a better signal-to-noise ratio. As a result, these micromachined Si substrates provide a low cost, mass producible, efficient, and reliable platform for direct TEM, SEM, AFM, and Raman characterization of as-grown nanotubes. These grids can be used for characterizing a wide range of other nanomaterials, including peapods, nanowires, and nanofibres.

Hexagonal Al_xGa_1−xN nanorods were grown by plasma-assisted molecular beam epitaxy (PAMBE) on Si(001) substrates. The Al mole fraction was determined from x-ray diffraction (XRD) measurement and its value was varied from 0 to 15. It is found that, under group III-rich conditions, the growth rate of the Al_xGa_1−xN nanorods decreases and the diameter increases due to the possibility of incorporation of aluminium and gallium. In order to study structural and optical properties, x-ray diffraction and cathodoluminescence (CL) measurements were carried out. The Al content (x) is calculated from these measurements and their values are compared.

Large-scale synthesis of ternary Zn_xCd_1−xS zigzag nanowires was achieved in a one-step metal–organic chemical vapour deposition (MOCVD) process with co-fed single precursors of ZnS and CdS. Their morphologies, structures and optical properties were characterized and confirmed by scanning electron microscopy, high-resolution transmission electron microscopy, x-ray spectroscopy, and photoluminescence. The Zn_xCd_1−xS zigzag nanowires are single crystalline, with axis [001], by changing the growth direction from to . Regarding the formation of zigzag nanowires, we suggest that the shear strain and slight fluctuation of the reaction conditions may be the major factors that make the nanowires change growth direction. In addition, because of the lower temperature and versatility, this new fabrication method might present a new and facile way to form other ternary nanomaterials. Furthermore, the green emission of the nanowires may have potential applications in electronic/optical nanodevices.

In the present work we investigated the photoluminescence property of silicon nanocrystals in silicon nitride prepared by ammonia sputtering. Silicon nanocrystals were demonstrated to form even after thermal annealing at 700 °C. Compared with the control sample using N₂ as the reactive gas, the luminescence intensity of silicon nanocrystals in silicon nitride prepared by NH₃ sputtering was greatly increased. The improvement in photoluminescence was attributed to the introduction of hydrogen-related bonds, which could well passivate the nonradiative defects existing at the interface between silicon nanocrystals and the silicon nitride matrix.

To understand the phenomenon of fullerene growth during its synthesis, an attempt is made to model a minimum energy growth route using a semi-empirical quantum mechanics code. C₂ addition leading to C₆₀ was modelled and three main routes, i.e. cyclic ring growth, pentagon and fullerene road, were studied. The growth starts with linear chains and, at n = 10, ring structures begins to dominate. The rings continue to grow and, at some point n>30, they transform into close-cage fullerenes and the growth is shown to progress by the fullerene road until C₆₀ is formed. The computer simulations predict a transition from a C₃₈ ring to fullerene. Other growth mechanisms could also occur in the energetic environment commonly encountered in fullerene synthesis, but our purpose was to identify a minimal energy route which is the most probable structure. Our results also indicate that, at n = 20, the corannulene structure is energetically more stable than the corresponding fullerene and graphene sheet, however a ring structure has lower energy among all the structures up to n≤40. Additionally, we have also proved that the fullerene road is energetically more favoured than the pentagon road. The overall growth leading to cage closure for n = 60 may not occur by a single route but by a combination of more than one route.

Two fluorine-doped diamond-like carbon (F-DLC) stamps with sub-100 nm line patterns were fabricated using a direct etching method. These were applied successfully to ultraviolet (UV) nanoimprint lithography without requiring an anti-adhesion layer coating. Tests were performed to determine the optimum fluorine concentration for the F-DLC stamps. The ideal stamp material consisted of 25 at.% F-DLC with a contact angle of 85°, UV transmittance of 16.4–26.8%, and hardness of 4.5 GPa. The O₂ plasma etch rate of the DLC was increased considerably by the fluorine doping, making it comparable to the etch rate of polymethyl methacrylate (PMMA). Thus, only PMMA was used as the etch mask in the fabrication of the stamps.

We report the first study of argon (Ar)-plasma-enhanced intermixing of InAs/InGaAs/InP self-assembled quantum dots (QDs) in an inductively coupled plasma reactive ion etch system. The Ar-plasma exposure creates point defects, which propagate into the QD structure and enhance the intermixing between the QDs and their barrier layers, hence tuning the energy bandgap of the QDs. By optimizing the plasma exposure time and the annealing temperature, we observe (i) a blueshift of 160 nm and an increase in the photoluminescence (PL) intensity of the QD samples immediately after Ar-plasma exposure for 90 s, and (ii) a further increase in the blueshift of 330 nm, accompanied by 2.5-times increase in the PL intensity and 37 nm narrowing in the PL linewidth after subsequent rapid thermal annealing at 720 °C. The ability to generate a large blueshift without degrading the material quality shows that Ar-plasma exposure is an efficient post-growth technique for tuning the energy bandgap of QD structures.

This study examined the influence of multi-walled carbon nanotubes (MWNTs) on the growth of the unicellular protozoan Tetrahymena pyriformis. Contrary to the findings from most other investigations, our experiment indicated that MWNTs stimulated growth of the cells cultured in proteose peptone yeast extract medium (PPY). Atomic force microscopy images and thermogravimetric analysis showed the spontaneous formation of peptone–MWNT conjugates in the medium by noncovalent binding. Uptake of large amounts of the conjugates by Tetrahymena pyriformis was responsible for growth stimulation, evidenced by images with fluorescently labelled peptone. After the PPY medium was replaced by a filtrated pond water medium (FPW), however, inhibition of the growth of cells exposed to MWNTs occurred. Measurements of the level of malondialdehyde and superoxide dismutase activity demonstrated further that MWNTs might be either toxic or nontoxic, depending on the medium used to cultivate Tetrahymena pyriformis. The biological effects of the interaction of MWNTs with some composites in culture media would be helpful for understanding the mechanisms of the toxicity of carbon nanotubes to living systems.

Bacteria and viruses were encapsulated in electrospun polymer nanofibres. The bacteria and viruses were suspended in a solution of poly(vinyl alcohol) (PVA) in water and subjected to an electrostatic field of the order of 1 kV cm⁻¹. Encapsulated bacteria in this work, (Escherichia coli, Staphylococcus albus) and bacterial viruses (T7, T4, λ) managed to survive the electrospinning process while maintaining their viability at fairly high levels. Subsequently the bacteria and viruses remain viable during three months at −20 and −55 °C without a further decrease in number. The present results demonstrate the potential of the electrospinning process for the encapsulation and immobilization of living biological material.

SnO₂/Sn nanocables have been grown on single-crystal Si substrates by metal catalyst assisted thermal evaporation of SnO powders. The morphologies and structures of the prepared nanocables were determined on the basis of field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD), Raman and photoluminescence (PL) spectra analyses. The microstructures and compositions of the top and bottom regions of the SnO₂/Sn nanocables were identified by HRTEM in detail, which revealed some basic physical and chemical processes involved in the formation of the nanocables. A growth model was proposed to address the formation of SnO₂/Sn nanocables on the basis of the vapour–liquid–solid (VLS) process.

A novel and facile chemical synthesis of highly faceted multiply twinned gold nanocrystals is reported. The gold nanocrystals are hexagonal in transmission electron microscopy and icosahedral in scanning electron microscopy. Phosphotungstic acid (PTA), which was previously reduced, serves as a reductant and stabilizer for the synthesis of gold nanocrystals. The PTA–gold nanocomposites are quite stable in aqueous solutions, and electrochemically active towards the hydrogen evolution reaction.

A TiO₂ nanotube array with a large surface area is fabricated on a glass substrate using a ZnO nanorod array and sol–gel process, and the structural characteristics of the TiO₂ nanotube array are investigated. The well-aligned ZnO nanorod array, which is deposited on ZnO seed layer coated glass substrates by the wet-chemical route, is used as a template to synthesize TiO₂/ZnO composite nanostructures through the sol–gel process. Then, by selectively removing the ZnO template, a TiO₂ nanotube with contours of the ZnO nanorods is fabricated on the ZnO seed layer coated glass. The resultant TiO₂ nanotubes are 1.5 µm long and 100–120 nm in inner diameter, with a wall thickness of ∼10 nm. In addition, by adjusting the experimental parameters, such as the dip-coating cycle number or heating rate, porous TiO₂ thick films can also be obtained.

We present self-consistent, non-equilibrium Green's function calculations of the characteristics of short channel carbon nanotube transistors, focusing on the regime of ballistic transport with ohmic contacts. We first establish that the band line-up at the contacts is renormalized by charge transfer, leading to Schottky contacts for small diameter nanotubes and ohmic contacts for large diameter nanotubes, in agreement with recent experiments. For short channel ohmic contact devices, source–drain tunnelling and drain-induced barrier lowering significantly impact the current–voltage characteristics. Furthermore, the ON state conductance shows a temperature dependence, even in the absence of phonon scattering or Schottky barriers. This last result also agrees with recently reported experimental measurements.

A method for analysing systems of isolated single-walled carbon nanotubes is of paramount importance if their structural characteristics are to be fully understood and utilized. Here we offer a simple technique for analysing such systems, with unprecedented contrast, using transmission electron microscope imaging of carbon nanotubes suspended over large holes in a silicon nitride grid. The nanotubes are grown directly on the viewing grids, using the chemical vapour deposition process, thus avoiding the use of chemicals or aggressive treatments. This method is simultaneously non-invasive, reusable, allows the analysis of multiple structures based on carbon nanotubes and is quickly implemented.

A convenient preparation is reported for subnanometre size uncapped ZnO quantum dots, which permits the previously inaccessible live observation of the growth of the clusters in the molecular size regime. The preparation method utilizes electric field-induced transient pore formation (electroporation) in synthetic unilamellar vesicles. This condition allows for facile monitoring of the time-dependent UV spectra associated with the growth of the clusters which are found to initially exhibit novel, oscillating red and blue shifts of the characteristic absorption band, ultimately followed by a monotonic red shift—the latter reflecting cluster growth beyond a size of ∼10 Å. Through a comparison of the observed oscillating transition energies with the corresponding trends found theoretically by others, the wavelengths of the sequential spectral peaks can be assigned to the (ZnO)₁ monomer (5.66 eV), dimer (ZnO)₂ (5.19 eV), (ZnO)₅ (6.21 eV), (ZnO)₁₂ (5.76 eV), and (ZnO)₁₅ (6.01 eV). Growth beyond (ZnO)₁₅ is associated with the customary monotonic red shift of the absorption band (5.59 and 4.95 eV). The reason for oscillation of red and blue shift of the HOMO–LUMO gaps was explained by the structural differences of Zn_iO_i (i = 1–15). Under the experimental conditions used, a stable system is reached after 12 days. This solution is estimated to contain 1.4 × 10¹⁷ (ZnO)₁₅ particles, each with a greatest dimension of ∼10 Å.

The encapsulation of individual nanoparticles has gained great attention as a method for both stabilizing nanoparticles and tailoring their surface properties. In particular, the encapsulation of nanoparticles with silica shells is advantageous for bioconjugation and applications to (nano)biotechnology. Herein we report a method for constructing gold nanoparticle (AuNP)/silica core/shell hybrid structures by biomimetic silicification of silicic acids. The procedure consists of surface-initiated, atom transfer radical polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) from AuNPs and biomimetic polycondensation of silicic acids by using poly(DMAEMA) as a synthetic counterpart for silaffins that are found in diatoms. The resulting AuNP/silica hybrids were characterized by Fourier transform infrared spectroscopy, energy dispersive x-ray spectroscopy, UV–vis spectroscopy and transmission electron microscopy. In addition, the immobilization of biological ligands onto the hybrids was investigated for potential applications to biotechnology. As a model ligand, biotin was attached onto the AuNP/silica hybrids through substitution reaction and Michael addition reaction, and the attachment was confirmed by fluorescence microscopy after complexation with fluorescein-conjugated streptavidin.

The encapsulated copper atoms inside a defected single-walled carbon nanotube escape from the tube through the defect hole as the temperature increases. This causes the partially confined copper nanowires (CNWs) to undergo special structural transformations from a solid to a distinguishable helical layered structure and finally to the liquid state. The defect has a vital function in automatically adjusting the internal pressure and copper atom density. The critical structural transformation temperature of the CNW is significantly influenced by the confinement conditions of the carbon nanotube.

ZnS nanostructures with different morphologies of submicrospheres, nanosheets and nanorods were synthesized by solution precipitation of thiourea with Zn(NO₃)₂ in the presence of block copolymer at low temperature. The sizes and morphologies of ZnS can be controlled simply by changing the processing parameters. The results show that the ZnS submicrospheres are of 250–500 nm in diameter, nanosheets are 2.5 µm × 5.5 µm with an estimated thickness of 20–30 nm, and nanorods are 2–5 nm in diameter and 10–30 nm in length. Keeping the precursor system in an autoclave at 105 °C results in the formation of ZnS submicrospheres; ultrasonication and keeping the system at room temperature leads to the formation of ZnS nanosheets; and long-time continuous ultrasonication and keeping the system in an autoclave at 105 °C induces the formation of uniform ZnS nanorods. We argue that the reaction temperature and P123 may play crucial roles in the formation of three ZnS structures in this work. The morphologically controllable synthesis strategies may be extended to the shape-controlled production of nanostructures of other inorganic materials.

Oleic acid (OA) modified zinc-blende cadmium selenium nanocrystals (NCs) with different diameters, 3–5 nm, have been prepared. We find that the morphology and fluorescent properties of the samples are related to the preparation conditions such as the chain-length and concentration of the cadmium precursor as well as the concentration of OA. The hybrid solar cells based on the obtained spherical CdSe NCs as an acceptor and Poly(2-methoxy-5-(2'-ethylhexoxy)-p-phenylenevinylene) (MEH-PPV) as a donor show an energy conversion efficiency (ECE) as high as 0.85%, three times higher than that reported before for spherical CdSe NCs/conjugated polymer hybrid solar cells. When poly(3-hexylthiophene) (P3HT) is used as the donor phase instead of MEH-PPV, the energy conversion efficiency increases up to 1.08%. The solar cell based on CdSe NCs/conjugated polymer has the potential to open up new production technologies for hybrid solar cells based on semiconductor NCs.

The effect of Ge deposition rate on the morphology and structural properties of self-assembled Ge/Si(001) islands was studied. Ge/Si(001) layers were grown by solid-source molecular-beam epitaxy at 500 °C. We adjusted the Ge coverage, 6 monolayers (ML), and varied the Ge growth rate by a factor of 100, R = 0.02–2 ML s⁻¹, to produce films consisting of hut-shaped Ge islands. The samples were characterized by scanning tunnelling microscopy, Raman spectroscopy, and Rutherford backscattering measurements. The mean lateral size of Ge nanoclusters decreases from 14.1 nm at R = 0.02 ML s⁻¹ to 9.8 nm at R = 2 ML s⁻¹. The normalized width of the size distribution shows non-monotonic behaviour as a function of R and has a minimum value of 19% at R = 2 ML s⁻¹. Ge nanoclusters fabricated at the highest deposition rate demonstrate the best structural quality and the highest Ge content (∼0.9).

Molecular dynamics simulations are used to investigate the microstructures of Cu–Ni nanoparticles with different concentrations of oversized atoms added to them. A many body second moment tight binding approximation potential is adopted to model the interatomic interactions. The Honeycutt–Anderson (HA) pair analysis technique is adopted to analyse in detail the transformation between local structures at different temperatures. From the simulation results, at temperatures higher than the melting point, the nanoparticles are in a liquid state and an icosahedral local structure is most frequently found inside the nanoparticles. At temperatures beneath the melting point, the fraction of FCC local structure increases with decreasing concentrations of the larger size atoms, whereas a larger fraction of amorphous structure still remains in the solid state for higher concentrations of oversized atoms. This is because the effects of distortion and misfit are more significant for a nanoparticle having a higher concentration of oversized atoms.

We report an easy synthesis of highly branched gold particles through a seed-mediated growth approach in the presence of citrate. The addition of citrate in the growth solution is found to be crucial for the formation of these branched gold particles. Their size can be varied from 47 to 185 nm. The length of the thumb-like branch is estimated to be between about 5 and 20 nm, and changes slightly as the particle size increases. Owing to these obtuse and short branches, their surface plasmon resonance displays a marked red-shift with respect to the normal spherical particles. These branched gold particles exhibit stronger SERS activity than the non-branched ones, which is most likely related to these unique branching features.

Nanoparticles are of immense importance both from the fundamental and application points of view. They exhibit quantum size effects which are manifested in their improved magnetic and electric properties. Mechanical attrition by high energy ball milling (HEBM) is a top down process for producing fine particles. However, fineness is associated with high surface area and hence is prone to oxidation which has a detrimental effect on the useful properties of these materials. Passivation of nanoparticles is known to inhibit surface oxidation. At the same time, coating polymer film on inorganic materials modifies the surface properties drastically. In this work a modified set-up consisting of an RF plasma polymerization technique is employed to coat a thin layer of a polymer film on Fe nanoparticles produced by HEBM. Ball-milled particles having different particle size ranges are coated with polyaniline. Their electrical properties are investigated by measuring the dc conductivity in the temperature range 10–300 K. The low temperature dc conductivity (I–V) exhibited nonlinearity. This nonlinearity observed is explained on the basis of the critical path model. There is clear-cut evidence for the occurrence of intergranular tunnelling. The results are presented here in this paper.

Densely packed and well-aligned coaxial (core–shell) CdS–CdO and ZnS–ZnO nanorod arrays were prepared with a one-step, non-catalytic, template-free metalorganic chemical vapour deposition (MOCVD) process by using single-source molecular precursors Cd(O-EtXan)₂ and Zn(O-EtXan)₂, respectively (O-EtXan = S₂COCH₂CH₃). Data from pyrolysis gas chromatography/mass spectrometry of the precursors revealed the sequence of formation, namely sulfide core first and oxide shell later, with the first formed sulfide nanorods serving as the template for subsequent in situ oxide shell coating. The coaxial CdS–CdO and ZnS–ZnO nanorod arrays were formed at collection temperatures of 180 and 200 °C, respectively. At a slightly higher collection temperature of 250 °C, coaxial ZnS–ZnO nanowires were also obtained. The coaxial nanostructure was characterized and confirmed with high-resolution transmission electron microscopy. In a photoluminescence study, near band edge emissions at around 530 nm, a composite emission of the two near band edge emissions of 524 nm of CdS and 551 nm of CdO, were observed for the coaxial CdS–CdO nanorod sample, while defect-induced emissions at around 470 nm were observed for both coaxial ZnS–ZnO nanorod and nanowire samples. A more stable oxide shell not only protects the sulfide core but also provides possible surface passivation beneficial to enhanced photoluminescence. The present work demonstrates the feasibility of growth of coaxial one-dimensional nanostructures from single-source precursors that contain all the necessary constituent elements in one compound.