Table of contents

Electrostatic nanopatterning of poly(methylmethacrylate) (PMMA) thin films by atomic force microscopy (AFM) charge writing was investigated using Kelvin force microscopy (KFM). The lateral size of the electrostatic patterns and the amount of injected charges are closely correlated and can be controlled by the height of the voltage pulses applied to the AFM tip and the tip–sample separation during the writing process. Charge retention measurements show that PMMA has excellent charge storage properties in air under relative humidities from 1% to 60% and withstands immersion in ultra-pure water. This study thus reveals that PMMA is a very promising electret to create efficient electrostatic nanopatterns for directed self-assembly of nanoscale objects, including the broad range of colloidal particles or molecules in aqueous solutions.

Cellular iron nanocrystalline film was fabricated on carbon substrate by electron beam chemical vapor deposition (EB-CVD). The film was made up of single alpha-iron cubes with {100} facets ranging from several tens to 200 nm. The thickness and distribution of the film could be controlled by adjusting the irradiation position and duration of the electron beam. The integration of well-faceted nanocrystals enables the film to have a high ratio of free surfaces, which are essential for applications in chemical catalysis and energy absorption. The application of this film as a substrate for further nanofabrication was demonstrated.

The amorphized surface of Si(100) sputtered with low energy ions at moderate temperature was found to develop two perpendicular ripple patterns overlaying each other. The evolution of these patterns was studied over a wide range of fluence. Coarsening of both ripple modes was observed, showing a similar time dependence with a coarsening exponent of n∼0.08. In the high fluence regime, the surface enters a steady state with both ripple modes still present.

Microcantilever actuators made from carbon nanotube polymer are driven at very low pull-in voltages and the thermal bimorph effect reaches 325 µm at 26–110 °C, much greater than the values for existing devices.

We present a simple but efficient method to prepare carbon nanotube (CNT)-based flexible devices embedded in polymer substrates. In this strategy, a methyl-terminated self-assembled monolayer is first coated on a solid substrate as a release layer, and CNT-network devices fabricated on it are directly transferred into a poly(dimethylsiloxane) (PDMS) mold, resulting in flexible CNT-network devices embedded in PDMS. The embedded circuits exhibit stable operation even after significant bending. We also propose Raman spectroscopy as a powerful tool to remotely characterize the CNT-network device structures covered by a polymer layer. As a proof of concept, we demonstrate DNA sensors utilizing the fabricated CNT-network devices.

We report a straightforward method of patterning large ordered arrays of metallic nanoparticles using existing semiconductor processing technology. The topographies of contact holes created on full 200 mm wafers serve as templates to pattern Ni or Co nanoparticles. Over a large range of synthesis conditions, these patterned nanoparticles are demonstrated to successfully catalyse the growth of carbon nanotubes (CNTs) selectively in the patterned areas of the wafer. This approach to catalyst deposition is scalable and fully compatible with existing semiconductor processing technology. Thus, it can be exploited for a variety of applications where confinement of materials in nanometric domains is necessary. These results represent a further step towards the integration of CNTs into conventional Si-based technology.

We investigated the use of the focused ion-beam (FIB) technique as a nanofabrication tool for the implementation of oxide-based magnetic and magnetoelectronic functional devices. In particular, we studied the effect of using FIB lithography for the patterning of La_2/3Ca_1/3MnO₃ magnetic oxide thin films. Results obtained show that the transport properties of patterned areas were strongly degraded after the patterning process. In contrast, no degradation was detected when the patterning was performed using a less aggressive technique. The origin of this degradation correlates with Ga⁺ ion implantation, as indicated by Auger spectroscopy analysis of the patterned films.

We prepare an array of amorphous silicon nanopillars by using a modified nanosphere lithography method. The fabrication process includes three steps: (1) 70 nm thick a-Si film was deposited on a crystalline silicon substrate; (2) the substrate was coated with a monolayer of polystyrene (PS) spheres to form an ordered structure on the a-Si thin film surface; (3) the sample was etched by reactive ion etching to produce the amorphous silicon pillar array. The results of field emission measurements show a low turn-on electrical field of about 4.5 V µm⁻¹ at a current density of 10 µA cm⁻². A relatively high current density exceeding 0.2 mA cm⁻² at 9 V µm⁻¹ was also obtained. The field enhancement factor is calculated to be about 1240 according to the Fowler–Nordheim (FN) relationship. The good field emission characteristics are attributed to the geometrical morphology, crystal structure and the high density of the field emitter of the silicon nanopillar.

We investigate the conductance through and the spectrum of ballistic chaotic quantum dots attached to two s-wave superconductors, as a function of the phase difference ϕ between the two order parameters. A combination of analytical techniques—random matrix theory, Nazarov's circuit theory and the trajectory-based semiclassical theory—allows us to explore the quantum-to-classical crossover in detail. When the superconductors are not phase-biased, ϕ = 0, we recover known results that the spectrum of the quantum dot exhibits an excitation gap, while the conductance across two normal leads carrying N_N channels and connected to the dot via tunnel contacts of transparency Γ_N is . In contrast, when ϕ = π, the excitation gap closes and the conductance becomes in the universal regime. For , we observe an order-of-magnitude enhancement of the conductance towards in the short-wavelength limit. We relate this enhancement to resonant tunnelling through a macroscopic number of levels close to the Fermi energy. Our predictions are corroborated by numerical simulations.

A solvable model is developed for electronic structure calculations of shallow hydrogenic impurities in two-dimensional quantum dots. We replace the actual Coulomb interaction (local potential) between the electron and the hydrogenic impurity by a projective operator (non-local separable potential) to determine the resulting electronic states in closed form. It is shown that non-local separable potentials may be used to accurately calculate the energy shift of the electronic levels as a function of the size of the quantum dot and the impurity position.

Using a combination of top-down lithographic techniques, isolated, individual and oriented multi-wall carbon nanotubes (MWNTs) were grown on nickel or iron nanoscaled dots. In the first step of the process, micron-sized catalytic metallic dots (either iron or nickel) were prepared using UV lithography. MWNTs were then synthesized from these catalysts using a direct current plasma-assistance and hot-filament-enhanced chemical vapor deposition (CVD) reactor. Samples were characterized by means of scanning electron microscopy. It turns out that the splitting up of the micron-sized dot is favored in the iron case and that the surface diffusion of the metal is enhanced using ammonia in the gaseous mixture during the CVD process. The results are discussed giving arguments for the understanding of the MWNT growth mechanism. In a second step, a focused ion beam (FIB) procedure is carried out in order to reduce the initial dot size down to submicronic scale and subsequently to grow one single MWNT per dot. It is found that nickel is most appropriate to control the size of the dot. Dots of size 200 nm ± 40 nm are then required to grow individual MWNTs.

In this paper we describe a fractal assembly of copper nanoparticles on different substrates by controlling the chemical replacement reaction. Through calculation, we found that the 'fractal dimensions' of copper dendrites synthesized by us were about 1.832, which agreed well with the 'fractal dimensions' of natural fern leaves (fractal dimension, 1.826), suggesting that the fern fractal model was useful to describe the self-assembly of our copper nanoparticles during the chemical replacement reaction process. These results will be beneficial for the understanding of the role that highly nonequilibrium conditions play in the formation of fractal clusters as well as the self-assembly mystique of metallic nanoparticles in nonequilibrium conditions and also helpful in the future assembly of complicated nanoarchitectures of metallic nanoparticles for potential applications.

The inexpensive combination of cryogenically milled Cu₃Ge powders sonochemically processed in a standard ultrasonic cleaner has led to the prototype of a heretofore undescribed class of material. This prototype is a nanostructured composite composed of 4.5 nm diameter Cu nanocrystals embedded in a three-dimensional (3D) amorphous CuGeO₃ polyhedron web matrix. The diameters of the wires comprising the matrix are typically 5–15 nm. Complete structural and compositional characterization is reported to provide additional insight and firm designation on the observation of this previously undescribed class of material. The large surface to volume ratio of these nanoweb composites may offer unique advantages based on altered optical or electronic and magnetic properties. For example, quantum confinement of the Cu dots in the amorphous 3D nanowebs is possible. Nanostructures in general have altered properties compared to those of bulk materials and the same is expected in nanostructured composites.

Surface passivation of nanocrystals with suitable organic or inorganic materials is key to improving the photoluminescence (PL) efficiency and stability of nanocrystals. Although the hot-injection organometallic approach is a powerful tool to achieve different kinds of core/shell structures, direct synthesis of such structures in aqueous phase, which bears many advantages such as biocompatibility, water-solubility, environment-friendliness, and cheapness, is less often reported. Herein we present a facile approach for the one-pot preparation of a water-soluble core/shell structure with CdTe cores packed in a CdS shell in aqueous phase. In comparison with plain CdTe nanocrystals, the PL efficiency of the obtained CdTe/CdS core/shell structure can approach about 75%. The stability of the core/shell structure to UV irradiation and oxidation is also improved.

Self-assembled monolayers (SAMs) of large π-conjugated aromatic thiols, 1-mercaptopyrene (MP), 6-mercaptobenzo[a]pyrene (MBP), and 1-(11-mercaptoundecyl)pyrene (MUP), prepared on Au(111) substrate at different temperatures were investigated by scanning tunneling microscopy. At room temperature, only MP and MBP molecules formed well-ordered SAMs with and () Rect symmetry, respectively. In contrast, MUP molecules were adsorbed randomly on the surface. At elevated temperatures, all three molecules produce well-ordered SAMs. At 343 K, the structure of MBP remains unchanged, while MP and MUP molecules undergo thermally induced rearrangement to form a () Rect symmetry due to improved ordering and denser packing. The results from the systematic study of controlled self-assembly of a series of pyrene-based thiols provide insights on the molecular structure-dependent and temperature-dependent organization of large π-conjugated aromatic thiols to obtain ordered SAMs.

Conducting polyaniline 5-sulfosalicylate nanotubes and nanorods were synthesized by the template-free oxidative polymerization of aniline in aqueous solution of 5-sulfosalicylic acid, using ammonium peroxydisulfate as an oxidant. The effect of the molar ratio of 5-sulfosalicylic acid to aniline on the molecular structure, molecular weight distribution, morphology, and conductivity of polyaniline 5-sulfosalicylate was investigated. The nanotubes, which have a typical outer diameter of 100–250 nm, with an inner diameter of 10–60 nm, and a length extending from 0.4 to 1.5 µm, and the nanorods, with a diameter of 80–110 nm and a length of 0.5–0.7 µm, were observed by scanning and transmission electron microscopies. The presence of branched structures and phenazine units besides the ordinary polyaniline structural features was revealed by infrared and Raman spectroscopies. The stacking of low-molecular-weight substituted phenazines appears to play a major role in the formation of polyaniline nanorods. The precipitation–dissolution of oligoaniline templates as a key element in the formation of polyaniline nanotubes is proposed to explain the crucial influence of the initial pH of the reaction mixture and its decrease during the course of polymerization.

We report the chemistry and photophysics of atomic gold and silver particles in inorganic glasses. By synchrotron irradiation of gold-doped soda-lime silicate glasses we could create and identify unambiguously the gold dimer as a stable and bright luminescing particle embedded in the glassy matrix. The gold dimer spectra coincide perfectly with rare gas matrix spectra of Au₂. The glass matrix is, however, stable for years, and is hence perfectly suited for various applications. If the irradiated gold-doped sample is annealed at 550 °C a bright green luminescence can be recognized. Intense 337 nm excitation induces a decrease of the green luminescence and the reappearance of the 753 nm Au₂ emission, indicating a strong interrelationship between both luminescence centers. Time-dependent density functional theory (TD-DFT) calculations indicate that the green luminescence can be assigned to noble metal dimers bound to silanolate centers. These complexes are recognized as the first stages in the further cluster growth process, which has been investigated with small-angle x-ray scattering (SAXS). In silver-doped glasses, Ag⁰ atoms can be identified with electron paramagnetic resonance (EPR) spectroscopy after synchrotron activation. Annealing at 300 °C decreases the concentration of Ag₁, but induces an intense white light emission with 337 nm excitation. The white luminescence can be decomposed into bands that are attributed to small silver clusters such as Ag₂, Ag₃ and Ag₄, and an additional band matching the green emission of gold-doped glasses.

Fe₅₀Pt₅₀ nanoparticles were deposited on thermally oxidized Si substrates by electron-beam co-evaporation of Fe and Pt, at substrate temperatures T_s between 300 and 700 °C. The co-deposition led to the formation of drop-like, coalesced nanoparticles, chain-like structures or continuous films, the morphology being dependent on T_s or the nominal thickness of the layer, f. The nanoparticles have a mean diameter D_p between 3 and 45 nm, which increases with increasing f. The degree of crystallization in the ordered face centred tetragonal (fct) phase of the samples depends strongly on the growth conditions and increases with increasing T_s and f. Nanoparticles with a higher proportion of the fct phase exhibit higher coercivity, with a maximum value of ∼10.3 kOe (for the specimens prepared at 600 °C with f = 8.5 nm). Conversely, samples with a high proportion of the cubic phase are either superparamagnetic or ferromagnetically soft. The thermal annealing performed on selected samples resulted in structural transformation as well as magnetic hardening that depended on f and D_p.

We report a scanning focused laser technique for pixel-by-pixel activation of the screen-printed carbon nanotube cathodes for field emission flat panel displays. The turn-on and working field of the cathodes became as low as 1.96 V µm⁻¹ and 2.70 V µm⁻¹, respectively, after 57 kW cm⁻² laser irradiation. The current density even reached 4.00 mA cm⁻² at 2.90 V µm⁻¹, which was 1285 times larger than the untreated one. This dramatic enhancement is due to the fact that the focused laser can remove not only the surface contamination, but can change the geometric structure of the treated pixel as well. More importantly, these laser activated carbon nanotube cathodes show much more uniform field emission performances, as required by flat panel displays.

Ordered arrays of FePt nanoparticles were prepared using a diblock polymer micellar method combined with plasma treatment. Rutherford backscattering spectroscopy analyses reveal that the molar ratios of Fe to Pt in metal-salt-loaded micelles deviate from those when metal precursors are added, and that the plasma treatment processes have little influence upon the compositions of the resulting FePt nanoparticles. The results from Fourier transform infrared spectroscopy show that the maximum loadings of FeCl₃ and H₂PtCl₆ inside poly(styrene)–poly(4-vinylpyridine) micelles are different. The composition deviation of FePt nanoparticles is attributed to the fact that one FeCl₃ molecule coordinates with a single 4-vinylpyridine (4VP) unit, while two neighboring and uncomplexed 4VP units are required for one H₂PtCl₆ molecule. Additionally, we demonstrate that the center-to-center distances of the neighboring FePt nanoparticles can also be tuned by varying the drawing velocity.

We report on the investigation of correlated spectral properties of two different surface-related photoluminescence bands in ZnO nanowires. We show that the spectral position and the temperature-dependent intensity of the surface-related emission band A are directly correlated with the emission of the surface-exciton band SX. We measure the thermal activation energies of both emission bands and present time-resolved photoluminescence data to deduce the photoluminescence decay time of the A emission band. We propose a model to explain the experimental observations and assign the A emission band to excitons bound to structural defects in the surface layer of the nanowires.

We study the structural, electronic and optical properties of the (n,n)/(2n,0);n = 3 and 6 superlattices of carbon nanotubes (CNs) by employing the first principles pseudo-potential method within density functional theory (DFT) in the generalized gradient approximation (GGA). There occur pentagon–heptagon defects along the circumference of the heterojunction of these superlattices. The role of the length of the superlattice unit cell on the electronic and optical properties has been investigated. The curvature effects on the various properties are also discussed. The heterojunctions of the small diameter n(3,3)/n(6,0) superlattices which possess a threefold rotational symmetry exhibit an oscillatory behaviour in terms of the fundamental energy bandgaps which vanish whenever the integer n is a multiple of 3. These results indicate that a similar oscillatory behaviour in the fundamental gap energy having a periodicity of 6 may be observed in the case of the large diameter n(6,6)/n(12,0) superlattices whose heterojunctions reveal a sixfold symmetry. The system energy of the 3(6,6)/3(12,0) superlattice shows a minimum. The electronic structure and optical absorption of a superlattice are quite different from those of its constituent carbon nanotubes. The present results obtained after employing all the s-, p- and d-orbitals of the atoms (although the d-orbital contributions are quite small) are quite different from the findings of earlier workers who have employed a phenomenological tight-binding formulation considering only one π orbital or four orbitals. We find that most of the states are extended resonance states and are quite delocalized in contrast to the earlier finding of the occurrence of the completely localized states in sections of the constituent nanotubes. The metallic superlattices exhibit a high density of states (DOS) at the Fermi level (E_F). For the large diameter n(6,6)/n(12,0) superlattices, the electron energy gap vanishes for n = 1 and 2 but increases up to a maximum value of 0.344 eV for n = 3 and decreases thereafter for larger n, a result which is in disagreement with earlier workers. These new facts have not been reported in the literature so far.

In this paper, palladium (Pd) nanoparticles have been successfully encapsulated into the channels of modified SBA-15 in situ via a facile, ethylene glycol (EG)-assisted sonochemical method. The products were confirmed by x-ray diffraction, transmission electron microscopy (TEM) and nitrogen adsorption analysis. The Pd/SBA-15 composite was used for the realization of direct electron transfer of hemoglobin (Hb). Electrochemical results showed that the Pd nanoparticles in the channels of SBA-15 could enhance the direct electron transfer between Hb and the electrode surface. The composite modified electrode displayed excellent electrochemical behavior. The sensor fabricated by the composite showed an excellent response to the reduction of hydrogen peroxide (H₂O₂), and the linear range for the determination of H₂O₂ was from 1.8 to 119.3 µM with a detection limit of 0.8 µM.