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Since the size, shape, and microstructure of nanocrystalline materials strongly impact physical and chemical properties, the development of new synthetic routes to nanocrystals with controlled composition and morphology is a key objective of the nanomaterials community. This objective is dependent on control of the nucleation and growth mechanisms that occur during the synthetic process, which in turn requires a fundamental understanding of both classical nucleation and growth and non-classical growth processes in nanostructured materials. Recently, a novel growth process called Oriented Attachment (OA) was identified which appears to be a fundamental mechanism during the development of nanoscale materials. OA is a special case of aggregation that provides an important route by which nanocrystals grow, defects are formed, and unique—often symmetry-defying—crystal morphologies can be produced. This growth mechanism involves reversible self-assembly of primary nanocrystals followed by reorientation of the assembled nanoparticles to achieve structural accord at the particle-particle interface, the removal of adsorbates and solvent molecules, and, finally, the irreversible formation of chemical bonds to produce new single crystals, twins, and intergrowths.

Crystallization and Growth of Colloidal Nanocrystals provides a current understanding of the mechanisms related to nucleation and growth for use in controlling nanocrystal morphology and physical-chemical properties, and is essential reading for any chemist or materials scientist with an interest in using nanocrystals as building blocks for larger structures. This book provides a compendium for the expert reader as well as an excellent introduction for advanced undergraduate and graduate students seeking a gateway into this dynamic area of research.



Chapter 1. Introduction

The transmission electron microscopy image in Fig.1.1a shows well-dispersed magnetite particles with a dimension below 10nm, i.e., nanoparticles. The black arrows in this figure indicate the presence of equiaxial (almost spherical) particles and well-faceted (triangular-shaped) nanoparticles. A high-resolution transmission electron microscopy analysis (see Fig.1.1b, c) reveals that each particle is formed by a single crystalline domain; i.e., each particle is a single crystal and both particles have the same crystalline structure despite a different shape.
Edson Roberto Leite, Caue Ribeiro

Chapter 2. Basic Principles: Thermodynamics and Colloidal Chemistry

To obtain a complete understanding of the crystallization and growth process of a nanocrystal in a colloidal dispersion, knowledge of basic thermodynamics and colloidal chemistry principles is essential. For instance, the classical crystallization process is based on a Gibbs free energy (G) analysis where the free energy of the bulk crystal is considered as a surface free energy contribution. Thus, a brief introduction of thermodynamics principles is important to facilitate an analysis of the crystallization and growth process. Therefore, a revision of the basic principles related to colloidal chemistry will be presented because the main bottom-up chemical approach to synthesize nanocrystals is based on a colloidal synthesis process [1, 2].
Edson Roberto Leite, Caue Ribeiro

Chapter 3. Classical Crystallization Model: Nucleation and Growth

The nucleation and growth process is a well-accepted model to describe several processes involving the crystallization of a condensed phase. This model can be applied to describe the crystallization process of single elements such as metal, where the liquid phase and the crystalline phase present the same chemical composition, as well as the crystallization of covalent and ionic crystals processed by wet chemical route. In this case, the process is much more complicated due to the presence of different chemical composition and, consequently, a chemical potential between the solid phase and the liquid phase.
Edson Roberto Leite, Caue Ribeiro

Chapter 4. Oriented Attachment and Mesocrystals

Despite the good applicability of the Ostwald ripening model, recent studies have demonstrated that this mechanism cannot be considered responsible for the growth process in some systems or in nonequilibrium systems [1–9]. The oriented attachment mechanism was proposed as another significant process, which may occur during nanocrystal growth [10–14]. By this mechanism, nanocrystals can grow by the alignment and coalescence of neighboring particles by eliminating a common boundary. The driving force for this mechanism is the decrease in the surface and grain boundaries’ free energies.
Edson Roberto Leite, Caue Ribeiro

Chapter 5. Oriented Attachment (OA) with Solid–Solid Interface

One of the characteristics of the OA mechanism not found in the OR (Ostwald ripening) mechanism is the presence of a solid–solid interface between nanocrystals, indicating that the growth process begins only after contact is established between particles.
Edson Roberto Leite, Caue Ribeiro

Chapter 6. Trends and Perspectives in Nanoparticles Synthesis

The focus of nanostructured materials is gradually shifting from the synthesis of nanocrystals with a controlled morphology and size to the organization or assembly of those nanocrystals into larger nanostructures in a natural sequence, especially in the use of nanocrystals as fundamental building blocks for the development of functional thin films and devices. In addition, the synthesis of controlled nanocrystals is still a challenge, particularly in the synthesis of transition metal oxides. In this final chapter, the trends in the synthesis of nanocrystals with controlled shapes and exposed facets will be discussed with a focus on metal oxide nanoparticles.
Edson Roberto Leite, Caue Ribeiro


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