Three-dimensional atomic scale analysis of nanostructured materials

The 3-dimensional atom probe (3DAP) has been used to provide atomic-scale microcharacterisation of a number of nanostructured materials. Grain boundary segregation has been investigated in electrodeposited nanocrystalline nickel and Ni-P. In the nanocrystalline nickel, there was no observable grain boundary segregation in the as-deposited condition. After annealing, carbon and sulphur contamination was found at the boundary of an abnormally-grown grain. In the as-deposited Ni-P alloy, only limited grain boundary segregation of P is seen, but annealing produces significant segregation and the formation of Ni₃P precipitates at grain boundaries. The phase chemistry in a melt-spun amorphous Fe-Si-Cu-Nb-B-Al (FINEMET-type) alloy has also been studied, and the hetereogeneous nucleation of Fe-Si nanocrystals at Cu precipitates shown conclusively. It is found that at early stages of crystallisation, there is only limited partitioning of the Si between the nanocrystals and the amorphous matrix. Atom probe studies of thin layered films have historically been limited by specimen preparation problems, but recent advances have now yielded data on metallic multilayer films. This has allowed atomic-scale measurements of interface chemistry in these films for the first time.     

Effects of dielectric barrier discharge in air on morphological and electrical properties of graphene nanoplatelets and multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) have been functionalized by dielectric barrier discharge (DBD) in air. The extent of functionalization of MWCNTs and GNPs reaches a maximum at the delivered discharge energy of 720 and 240 J mg⁻¹, respectively. Further exposure to plasma leads to reduction of functional groups from the surface of the treated nanomaterials. It has also been demonstrated that DBD plasma does not produce dramatic structural changes in MWCNTs, while flakes of the treated GNPs become thinner and smaller in the lateral size. Conductive thin films, obtained by drop casting a solution of the treated nanomaterials in N-methyl-1-pyrrolidone on poly(methyl methacrylate) substrate, show significantly lower sheet resistance.     

Investigation of the radiative lifetime in core–shell CdSe/ZnS and CdSe/ZnSe quantum dots

Using the one band effective mass approximation model we computed the optical properties of the spherical shaped CdSe/ZnS and Cdse/ZnSe core–shell quantum dot (CSQD). For each structure we calculated the charge carrier energies and corresponding wave functions. We investigated the dependence of the carrier energies on various parameters of the CSQD, including its size. Then we calculated the radiative recombination lifetime for the two types of CSQDs nanocrystals. We found that as the size of the dot is increased the optical gap of CSQD is reduced, resulting in a reduction in electron energies and an increase in hole energies. We have shown that the radiative recombination lifetime in the CdSe/ZnS and CdSe/ZnSe CSQDs decreased by increasing the shell thickness around the core of the QD. We also showed that the radiative lifetime in the CdSe/ZnS is less than that in the CdSe/ZnSe CSQDs and is sensitive to the size and nature of shell of the semiconductor's material.     

Flower-like boehmite nanostructure formation in two-steps

Reaction between AlCl₃ and TEA (triethanolamine) gave Al(OH)₃ colloidal nanocrystals that were precursors to nucleation and growth of boehmite under hydrothermal conditions. Transition electron microscopic (TEM) observations revealed that flower-like nanostructures were produced through a binary self-assembly system. In the first stage, nanostrips organize themselves to form a bundle, because of NH₄⁺ and TEA. In the second stage, the bundles form flower-like nanostructures due to the interaction of nitrate with TEA. The size of the nanopetals (length 100–200?nm; width 100–150?nm; and thickness 20–70?nm) was measured through TEM. X-ray diffraction and Brunauer–Emmett–Teller (BET-N₂) results demonstrate that the obtained nanostructures were composed of a pure AlOOH phase with a surface area of 160?m^2?g^?1. The effect of Cl?ˉ on the growth of boehmite 3-D nanoarchitectures in the presence of NO₃ˉ was also investigated.     

Rapid microwave-assisted hydrothermal synthesis of Bi12TiO20 hierarchical architecture with enhanced visible-light photocatalytic activities

Flower-like Bi₁₂TiO₂₀ hierarchical nanostructures composed of numerous nanobelts were synthesized at 180 °C within 1 h by a microwave-assisted hydrothermal method in the presence of cetyltrimethylammonium bromide (CTAB) for the first time. The as-prepared products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ultraviolet–visible (UV–vis) absorption spectroscopy. Furthermore, the hierarchical Bi₁₂TiO₂₀ nanostructures exhibited higher photocatalytic activities in the degradation of Rhodamine B under visible-light irradiation than that of the samples prepared without CTAB. In addition, the role of CTAB cationic surfactant has been investigated thoroughly and a possible mechanism is proposed.     

Electronic Transport in Magnetic Domain-wall Structure

The resistivity due to the domain wall in the presence of impurities in a ferromagnetic metallic wire is calculated based on the linear response theory. Assuming the local spin distribution to be spin-spiral the modification of the band structure has been obtained exactly. With this modified band structure we calculate the conductivity of the system as a function of electronic filling and show that the domain-wall contribution to the resistance can be positive or negative depending on the dimensionality, the position of the Fermi energy on the band structure and the strength of the electron local spin interaction of the system.     

Magnetization Reversal Studies of Magnetic Wire Arrays by Polarized Neutron Scattering

Polarized neutron reflectivity has been used to investigate the peak pattern and the magnetization reversal process of laterally structured Fe- and CoFe-films. The peak pattern of the wire arrays was analyzed in the specular as well as in the off-specular regime. The intensities of the different cross-sections at the off-specular first-order peak were investigated as a function of external magnetic field. Magnetization reversals are discussed and compared to MOKE studies of the same system.     

Rigid POSS Nanofiller Regulated the Interfacial Self-assembly of Particles into 2D Monolayer Superlattice with Fixed Interparticle Spacing†

Plasmonic superlattices of nanoparticles (NPs) possess unique “surface lattice resonances” properties that facilitates their wide applications in plasmonic sensing, photocatalysis, and nanoscale light manipulation. However, it is still challenging to manufacture superlattices with precisely controllable NPs distance and break the size limitation of NPs. Herein, we provided an effective strategy to construct NPs superlattices via shape-persistent polyhedral oligosilsesquioxane (POSS) molecular nanoparticles govern interfacial assembly. As a nanoscale molecule with diameter of 1.5 nm, the POSS-SH molecule provides sufficient rigid steric hindrance and hydrophobic effect for tailoring the uniformity and controllable distance between NPs in superlattices. Interestingly, synergistically with hydrophilic ligands of polyethylene glycol (PEG-SH) with optimized ratio, the rigid POSS ligands can effectively regulate the distance between NPs in a fixed range of 2.3—2.8 nm, which is independent of ligands molecular weight and particle size. Furthermore, the effective approach can be universal to anisotropic NPs for manufacturing monolayer films with high NPs density. We believe this nanoscale molecule tailored interfacial self-assembly strategy can effectively break the size of NPs and assembly obstacles for superlattice monolayer film. Additionally, the definite distance between NPs in superlattices can minimize optical energy attenuation and facilitates the applications such as surface-enhanced Raman spectroscopy and photocatalysis.      

Precise and Controllable Assembly of Block Copolymers†

With the development of nanotechnology, the precise synthesis of nanoparticles with nicely-defined dimensions and structures has been well-developed, and the functionalization and subsequent applications of the resultant nanostructures are becoming increasingly important. Comparing to inorganic nanoparticles, the nanostructures based on soft matters, especially block copolymer assemblies, are much lower in cost, easier to fabricate and richer in morphology. However, the dimensional control over the block copolymer assemblies is not as easy. Only in recent decade, with the discovery of living Crystallization-Driven Self-Assembly (CDSA) by Manners and Winnik, researchers become able to precisely tune the sizes of block copolymer assemblies in a relatively wide range. This discovery has inspired tremendous research effort in the self-assembly field, and considerable progress has been made recently. This review summarizes the main progress in the precise and controllable self-assembly field in the past five years, and is mostly focused on four aspects, including in-depth understanding of the assembly methods, extension of this method to two-dimensional nanostructures, utilization of this method to fabricate hierarchical structures, and the potential applications of these well-defined nanostructures. We hope not only to make a periodic systematic summary of previous studies, but also to provide some useful thinking for the future development of this field.