ionized aggregates of a few hundred to a few thousand atoms rather than individual atoms or molecules. These clusters are formed by the condensation of evaporated atoms during adiabatic expansion through a narrow aperture into a high vacuum region. They are then ionized by electron impact and uniformly accelerated in an electric field between source and substrate surface. A single charge on the cluster is thus used to accelerate many hundreds of atoms. A cluster consisting of 500 atoms has a diameter of the order of 30 A. The size, charge, and acceleration voltage of the clusters are intimately related with the film formation process.
The author of this book is considered to be the pioneer of the ionized-cluster beam technique. He started the research in this field at Kyoto University (Japan) in 1972. The various activities of the author to promote the spreading of this method throughout the world largely determine also the character of this book. In 60 of the 100 references 7: Takagi is one of the authors. This unbalanced selection of the material implies that a critical comparison of the ionized-cluster beam deposition with both conventional evaporation and sputter deposition as well as low-energy ion deposition is unfortunately not given. Throughout the entire text the author emphasizes the advantages of "his" technique. In the case of crystalline semiconducting materials, like e.g. Si or GaAs, this point of view is totally misleading, because the quality of thin films prepared by ionized-cluster deposition is far inferior to that of films prepared by either chemical vapor deposition or by molecular beam epitaxy. Unfortunately, most aspects of ionized-cluster beam deposition discussed in this book are treated only qualitatively. A number of misprints and errors should be eliminated in a following edition.
Due to the partiality and the lack of an in-depth treatment of the subject this book is of limited use only. It can, however, serve as an introduction to the field.
Klaus Ploog Max-Planck-Institut fur Festkorperforschung, Stuttgart (FRG)