PREFACE

Functionalization of semiconductor surfaces through direct molecule attachment is an important approach to tailoring the chemical, physical, and electronic properties of semiconductor surfaces. Incorporating the functions of organic molecules into semiconductor-based materials and devices can serve various technological applications, as in the development of microelectronic computing, micro- and optoelectronic devices, microelectromechanical machines, three-dimensional memory chips, silicon-based nano- or biological sensors, and nanopatterned organic and biomaterial surfaces. Dry organic reactions in vacuum and wet organic chemistry in solution are two major categories of strategies for functionalization of these surfaces, which is the focus of this book. The growth of molecular multilayer architectures on the formed organic monolayers is described. The immobilization of biomolecules such as DNA on organic layers chemically attached to semiconductor surfaces is also introduced. The patterning of complex structures of organic layers and metallic nanoclusters on surfaces for application in sensing technologies is discussed. This book covers both advances in fundamental science and the latest achievements and applications in this rapidly growing field over the past decade.

Surface analytical techniques are used to characterize the organic functionalized interface. Chapter 2 briefly introduces the main surface analytic techniques used in this field. The functionalization of semiconductor surfaces involves the chemical binding of organic molecules on active sites of the semiconductor surface. The creation of a reactive site comprising one to several atoms is the prerequisite for the functionalization of semiconductor surfaces. Chapter 3 describes the surface structures of semiconductors and the methods used to prepare them for the attachment of organic molecules. Early studies of the chemical attachment of organic molecules on semiconductor surfaces focused on the mechanistic understanding of pericyclic reactions of the simplest unsaturated organic molecules, acetylene and ethylene. Chapter 4 describes these early studies of pericyclic reactions and other small molecules with a single functional group. Later, efforts were made to attach aromatic molecules, as these five- or six-membered aromatic molecules are the building blocks for polymers or other functional materials. Chapter 5 summarizes the chemical binding of small aromatic molecules and the reaction mechanisms for this functionalization.

Selectivity of products in the functionalization of semiconductor surfaces is an important issue, since a homogeneous organic layer on the semiconductor surface is required for high-performance molecular and semiconductor devices. However, most organic materials are actually bifunctional or multifunctional molecules. Understanding the competition and selectivity of different functional groups on the semiconductor surfaces is fundamentally important. Chapter 6 focuses on the influence of functional groups in substituted aromatic molecules on the selection of a reaction channel. Polycyclic aromatic hydrocarbons are comprised of multiple fused benzene rings. They are promising materials for the development of new semiconductor devices using organic materials as the active layer. The chemical binding of these large aromatic systems is thus very important for the field of organic electronic devices and nanodevices. Chapter 7 summarizes the covalent binding of polycyclic aromatic hydrocarbon systems on semiconductor surfaces.

In addition to chemical binding through the formation of strong covalent bonds at the semiconductor–organic interface, organic molecules may transfer electrons to or accept electrons from semiconductor surfaces, resulting in dative bonding. This bonding mode results from the availability of electron-rich and electron-deficient sites on semiconductor surfaces. Chapter 8 describes studies of dative bonding of organic molecules on semiconductor surfaces.

Theoretical simulation has been a very important component in the developing understanding of organic functionalization of semiconductor surfaces. It is widely used to mechanistically understand the binding configuration of organic molecules, particularly multifunctional organic molecules through the point of view of kinetics and thermodynamics. Chapter 9 exemplifies the integration of this theoretical component into fundamental studies of mechanism in the field of functionalization of semiconductor surfaces.

Besides the identification of the structure of surfaces and adsorbates atom by atom in real space, scanning tunneling microscopy (STM) has another important function in breaking chemical bonds of an adsorbate to create a reactive site or radical that can then act as a precursor for a subsequent new reaction on the elemental semiconductor surface. This is a promising approach to modification and functionalization of semiconductor surfaces at the atomic level. This approach is clearly described in Chapter 10.

In parallel with the early studies of the reaction mechanisms of organic molecules on semiconductor surfaces in vacuum, studies of the functionalization of semiconductor surfaces through solution phase (wet) chemistry have been carried out. The formation of organic layers through solution chemistry is described in Chapter 11. The chemical stability of organic thin films formed in this manner is reviewed in Chapter 12. On the basis of our fundamental understanding of the functionalization of semiconductor surfaces with small organic molecules, the functionalization of semiconductors with larger, biologically relevant molecules has developed recently. Application of these systems in biosensing is developing as a very exciting field. The progress made in this area is reviewed in Chapter 13.

In summary, this book reviews many of the important research areas in the field of functionalization of semiconductor surfaces from the past two decades. These reviews are provided by leading researchers across this exciting field of surface and materials chemistry. We hope that this volume will prove to be useful to active researchers in this field, as well as students and research scientists new to the field of semiconductor surface functionalization.

We thank the contributors to this collection of reviews for the elegant research that makes up the subject of this book. We also thank them for providing the critical reviews and commentaries on the field that comprise the individual chapters here. Finally, we acknowledge the support of the Chemistry Division of the National Science Foundation that supported the work of our laboratory described here, the Chemistry Department of the National University of Singapore for ongoing support of collaborative work in this area, and the support from Department of Chemistry and Biochemistry of University of Notre Dame.

FRANKLIN (FENG)TAO

STEVEN L. BERNASEK