Preface

Metal nanoparticles and clusters constitute a remarkable set of nanomaterials that have permeated crucial fields of science and technology and are one of the most active areas of research. The interest in the chemistry and physics of these systems spans a century. Considering this rich and diverse history, it is indeed a challenge to bring a status update to the field and highlight recent important advances in the field, which makes this compilation all the more challenging. Nanotechnology promises to usher in a technological revolution due to the possibility of maximizing the properties of a material in the nanometer scale. Metal nanocrystals with dimensions above 2 nm show smoothly scaling, size-dependent properties converging to the bulk when size increases. However, what happens when the nanoparticle’s size is comparable to the Fermi wavelength of an electron? Would the properties be the expected ones? It has been observed that particles in this sub-nano regime do not follow the size-dependent behavior of nanoparticles; instead, they present totally new and fascinating properties owing to their specific geometrical and electric structures. Such species are more aptly called atomic quantum clusters (AQCs) because the origin of the new intriguing properties lies in the quantum effects that cause a splitting (band gap) of energies at the Fermi level. This band gap makes metal AQCs behave like atomic-level semiconductors. As an example, fluorescence, magnetism, circular dichroism, and high-efficiency catalysis have been seen in metal AQCs, Mn, with n 200 atoms and with sizes below 2 nm. Properties presented by small AQCs cannot be attributed to the increase of the surface area, but to the abovementioned new electronic properties displayed by these AQCs. These are some of the key points discussed in the first chapter “From Nanoto Angstrom Technology” by Arturo and coworkers. In the second chapter “Advances in Synthesis of Metal Nanocrystals,” John and coworkers discuss different schemes which yield metal nanocrystals. In this context, recent developments that have sparked new interest are highlighted. These include being able to control size, shape, and composition of particulates. The chapter reviews the contemporary synthetic advances over the past decade and provides brief perspectives on the advances responsible for this upsurge in interest.