The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

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

1. Introduction 20642. Synthesis of Magnetic Nanoparticles 20662.1. Classical Synthesis by Coprecipitation 20662.2. Reactions in Constrained Environments 20682.3. Hydrothermal and High-TemperatureReactions20692.4. Sol-Gel Reactions 20702.5. Polyol Methods 20712.6. Flow Injection Syntheses 20712.7. Electrochemical Methods 20712.8. Aerosol/Vapor Methods 20712.9. Sonolysis 20723. Stabilization of Magnetic Particles 20723.1. Monomeric Stabilizers 20723.1.1. Carboxylates 20733.1.2. Phosphates 20733.2. Inorganic Materials 20733.2.1. Silica 20733.2.2. Gold 20743.3. Polymer Stabilizers 20743.3.1. Dextran 20743.3.2. Polyethylene Glycol (PEG) 20753.3.3. Polyvinyl Alcohol (PVA) 20753.3.4. Alginate 20753.3.5. Chitosan 20753.3.6. Other Polymers 20753.4. Other Strategies for Stabilization 20764. Methods of Vectorization of the Particles 20765. Structural and Physicochemical Characterization 20785.1. Size, Polydispersity, Shape, and SurfaceCharacterization20795.2. Structure of Ferro- or FerrimagneticNanoparticles20805.2.1. Ferro- and Ferrimagnetic Nanoparticles 20805.3. Use of Nanoparticles as Contrast Agents forMRI20825.3.1. High Anisotropy Model 20845.3.2. Small Crystal and Low Anisotropy EnergyLimit20855.3.3. Practical Interests of Magnetic NuclearRelaxation for the Characterization ofSuperparamagnetic Colloid20855.3.4. Relaxation of Agglomerated Systems 20856. Applications 20866.1. MRI: Cellular Labeling, Molecular Imaging(Inﬂammation, Apoptose, etc.)20866.2.

Magnetic Iron Oxide Nanoparticles: Synthesis, Stabilization, Vectorization, Physicochemical Characterizations, and Biological Applications

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?

A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

This work presents transmission electron microscopy results relevant in the question of the origin of the anomalous light scattering which occurs near α-β transition. We analyze the spatial dependence of the order parameter and its evolution when the temperature is varied within the whole range of existence of the incommensurate state (in “EQT” and in “ELT” phases). Observation was also performed in the diffraction mode. This study shows in particular that the conclusions of Aslanyan et al [J. Phys.: Cond. Matter 10, 4565 (1998)] are erroneous.

On the evolution of texture between α and β phases in quartz: Aspects relevant with the problem of the anomalous light scattering

II–VI and II1−x Mn x VI nanocrystals were prepared by the pressure cycle method using the Paris–Edinburgh cell. The recovered samples are nanocrystals in the cubic phase zinc-blend (ZB) structure and were characterized using transmission electron microscopy, electron diffraction, X-ray diffraction and Raman scattering. Transmission electron micrographs show that these nanocrystals are nearly spherical with diameters ranging from 20 to 50 nm depending on the sample under investigation. The Raman scattering measurements confirm the existence of II–VI nanocrystals in the cubic phase (ZB). The magnetic properties of Cd0.5Mn0.5Te nanoparticles were found to vary with the particle size and were different from those observed for the Cd0.5Mn0.5Te bulk initial samples. The χ vs. T data show temperature hysteresis due to spin-glass form, which occurs at T g=21 K, for both the bulk as well as for the recovered nanoparticle samples. The zero-field cooled and field-cooled χ vs. T curves for the nanoparticles showed a ...

II-VI and II1-xMnxVI semiconductor nanocrystals formed by the pressure cycle method

Starting from a mixture of commercially available ZrO2 and Y2O3 powders, YxZr1-xO2-x/2 nanocristalline powders have been prepared by melting and vaporization under air in a solar image furnace and characterized by X-Ray Diffraction and Transmission Electron Microscopy . Depending on the starting powder mixture composition, the yttrium content in the nanophases can be controlled and the tetragonal or cubic phases can be obtained. The powders have a most probable grain radius of about 10 to 12 nm. The grains appear as isolated unstrained single crystals with polyhedral shapes.

YxZr1-xO2-x/2 Nanophase Powders Prepared by a Vaporization / Condensation Process in a Solar Furnace

Structural Characterization of Ferroelectric and Multiferroic Nanostructures by Advanced TEM Techniques

The invention relates to a method for manufacturing solid cobalt nanorods (2) epitaxied on a solid substrate (5), in which: at least one surface portion (8) of the solid substrate (5) is immersed in a metal solution including at least one compound that is a precursor of cobalt with an initial concentration in a liquid solvent medium, said surface portion (8) being made of crystalline solid platinum; during a growing step, said metal solution is maintained with the substrate (5) resting in a pressurised reaction chamber and under conditions suitable for allowing spontaneous growth by epitaxy of cobalt nanorods (2) from said platinum-free surface portion(s) (8) of said substrate (5).

Etienne Snoeck

Papers

On the evolution of texture between α and β phases in quartz: Aspects relevant with the problem of the anomalous light scattering

II-VI and II1-xMnxVI semiconductor nanocrystals formed by the pressure cycle method

YxZr1-xO2-x/2 Nanophase Powders Prepared by a Vaporization / Condensation Process in a Solar Furnace

Structural Characterization of Ferroelectric and Multiferroic Nanostructures by Advanced TEM Techniques

Method for manufacturing nanorods epitaxied on a substrate, epitaxied nanorods obtained by such a method and digital data recording medium