This review focuses on the synthesis, protection, functionalization, and application of magnetic nanoparticles, as well as the magnetic properties of nanostructured systems. Substantial progress in the size and shape control of magnetic nanoparticles has been made by developing methods such as co-precipitation, thermal decomposition and/or reduction, micelle synthesis, and hydrothermal synthesis. A major challenge still is protection against corrosion, and therefore suitable protection strategies will be emphasized, for example, surfactant/polymer coating, silica coating and carbon coating of magnetic nanoparticles or embedding them in a matrix/support. Properly protected magnetic nanoparticles can be used as building blocks for the fabrication of various functional systems, and their application in catalysis and biotechnology will be briefly reviewed. Finally, some future trends and perspectives in these research areas will be outlined.

Magnetic nanoparticles: Synthesis, protection, functionalization, and application

Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.

Shape‐Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?

Semiconductor photocatalysis has received much attention as a potential solution to the worldwide energy shortage and for counteracting environmental degradation. This article reviews state-of-the-art research activities in the field, focusing on the scientific and technological possibilities offered by photocatalytic materials. We begin with a survey of efforts to explore suitable materials and to optimize their energy band configurations for specific applications. We then examine the design and fabrication of advanced photocatalytic materials in the framework of nanotechnology. Many of the most recent advances in photocatalysis have been realized by selective control of the morphology of nanomaterials or by utilizing the collective properties of nano-assembly systems. Finally, we discuss the current theoretical understanding of key aspects of photocatalytic materials. This review also highlights crucial issues that should be addressed in future research activities.

Nano‐photocatalytic Materials: Possibilities and Challenges

Core/Shell Nanoparticles: Classes, Properties, Synthesis Mechanisms, Characterization, and Applications

https://www.tcd.ie/Physics/people/Graham.Cross/SF%20Poster%202011/Schuh-ActaMater07-Mechanical%20behaviour%20of%20amorphous%20alloys.pdf

Mechanical behavior of amorphous alloys

Exchange-spring magnets are nanocomposites that are composed of magnetically hard and soft phases that interact by magnetic exchange coupling. Such systems are promising for advanced permanent magnetic applications, as they have a large energy product--the combination of permanent magnet field and magnetization--compared to traditional, single-phase materials. Conventional techniques, including melt-spinning, mechanical milling and sputtering, have been explored to prepare exchange-spring magnets. However, the requirement that both the hard and soft phases are controlled at the nanometre scale, to ensure efficient exchange coupling, has posed significant preparation challenges. Here we report the fabrication of exchange-coupled nanocomposites using nanoparticle self-assembly. In this approach, both FePt and Fe3O4 particles are incorporated as nanometre-scale building blocks into binary assemblies. Subsequent annealing converts the assembly into FePt-Fe3Pt nanocomposites, where FePt is a magnetically hard phase and Fe3Pt a soft phase. An optimum exchange coupling, and therefore an optimum energy product, can be obtained by independently tuning the size and composition of the individual building blocks. We have produced exchange-coupled isotropic FePt-Fe3Pt nanocomposites with an energy product of 20.1 MG Oe, which exceeds the theoretical limit of 13 MG Oe for non-exchange-coupled isotropic FePt by over 50 per cent.

Exchange-coupled nanocomposite magnets by nanoparticle self-assembly

Structural investigations by using high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) of silver nanodisks with different sizes are presented The disks have a face centered cubic (fcc) crystal structure and their flat surfaces are (111) Stacking faults parallel to the (111) planes are frequently observed for the nanodisks A unique (111) stacking fault model which is parallel to the flat (111) disk surface has been proposed to explain the observed 1/3{422} forbidden reflections in [111] SAED pattern and the corresponding 3×{422} supperlattice fringes in the [111] HRTEM image It is suggested that the presence of the stacking faults may be the key in the formation and growth of the disk morphology This study may provide an insight to synthetically controlling particle shape and size through defect engineering

Stacking Faults in Formation of Silver Nanodisks

Nanobelts, Nanocombs, and Nanowindmills of Wurtzite ZnS

ZnS, an important wide-bandgap semiconductor, is a photo-luminescence material. [1] Due to its wide bandgap of 3.8 eV, doping of ZnS with elements such as Tb and Eu, [2] can produce a wide range of exciting optical properties. Quantum dots of core±shell structured CdSe/ZnS have been found to exhibit a lasing effect and can be used for fluoro-immunoas-says, biological imaging, and biosensors. [3,4] Quantum confinement induced lasing has been observed in CdSe/ZnS. Semiconducting ZnO is one of the most important functional oxides for smart devices and optoelectronics. Recently, ultra-long nanobelt structures of ZnO, SnO 2 , In 2 O 3 , CdO, Ga 2 O 3 , and PbO 2 have been synthesized by simply evaporating the desired commercial metal oxide powders at high temperatures. [6,7] The as-synthesized oxide nanobelts are pure, structurally uniform, single crystalline, and most of them are free from dislocations. They have a rectangular cross section with typical widths of 100±300 nm, width-to-thickness ratios of 5±10 nm, and lengths of up to a few millimeters. The nano-belts are an ideal system for fully understanding dimensionally confined transport phenomena in functional oxides and for building functional devices along individual nanobelts. Nanosize sensors and field-effect transistors based on individual nanobelts have been fabricated. Colloid based methods are likely the most popular techniques for synthesis of semiconductor quantum dots. In this paper, using as-synthesized ZnO nanobelts as a template , nanostructured ZnS nanocables and nanotubes have been synthesized by chemical reaction. The structure of the ZnS has been analyzed and the corresponding photolumines-cence properties have been measured. A small blue shift is observed for the ZnO±ZnS cable structures, suggesting a small quantum-confinement effect. The template-assisted method is demonstrated to be a unique technique for producing ZnS nanostructures with controlled morphology. We first present the structural change of the ZnO nanobelt pre-and post-reaction with H 2 S. Figure 1a shows a scanning electron microscope (SEM) image of the as-synthesized ZnO nanobelts, which are pure and structurally uniform. A transmission electron microscope (TEM) image of the nanobelts is given in Figure 2a, clearly showing its uniformity in shape. The ZnO nanobelts have two fast growth directions, [0001] and [1010]. [6] For the [0001] ZnO nanobelts, the top surfaces are ± (21 10), and the side surfaces are ± (0110). The contrast observed on the nanobelts is due to bending induced strain, which is the so-called bending contour in electron diffrac-tion. Based …

Rectangular Porous ZnO–ZnS Nanocables and ZnS Nanotubes

Bulk metallic glasses subjected to quasistatic uniaxial compression at room temperature typically display large elastic strains but limited plastic flow of 0--2% before failure. We have developed an amorphous alloy, ${\mathrm{Zr}}_{59}{\mathrm{Ta}}_{5}{\mathrm{Cu}}_{18}{\mathrm{Ni}}_{8}{\mathrm{Al}}_{10},$ which experiences an average macroscopic plastic strain of 4.5% before failure. The as-cast alloy shows no evidence for the presence of crystalline phases, and displays a distinct glass transition temperature and a wide supercooled liquid region. Upon compression beyond the yield point, the alloy develops shear bands which show a pronounced tendency for branching. We propose that this shear band branching distributes the plastic strain on the shear band, thereby suppressing crack initiation and allowing the material to experience a large macroscopic plastic strain before failure.

Jing Li

Papers

Exchange-coupled nanocomposite magnets by nanoparticle self-assembly

Stacking Faults in Formation of Silver Nanodisks

Nanobelts, Nanocombs, and Nanowindmills of Wurtzite ZnS

Rectangular Porous ZnO–ZnS Nanocables and ZnS Nanotubes

Enhanced plastic strain in Zr-based bulk amorphous alloys