INTRODUCTION

In this text we will discuss a variety of physical properties, which form the basis for intelligent devices. These properties are closely linked to the physical structure of the materials. The arrangements of the atoms/molecules determine important symmetries in the system that, in turn, influence the electronic and optical properties. For example, the presence or absence of inversion symmetry determines properties such as the piezoelectric effect used for sensors and ultrasonic applications. Ferroelectric materials depend upon special crystalline properties of ionic crystals. Valence band properties in semiconductors are determined by the cubic symmetry in the crystals.

In addition to the arrangement of atoms in crystals, it is also important to understand the nature of surfaces and interfaces. Many devices are based on phenomena that are unique to surfaces or interfaces. Finally, we have to realize that most materials are far from perfect crystals. Poly crystalline materials, amorphous materials, and materials with defects are also used in making smart devices.

In this chapter we will examine the structural properties of a variety of materials used for smart device applications. We will start with perfect crystals.

CRYSTALLINE MATERIALS

Almost all high-performance devices are based on crystalline materials. Although, as we will see later in the chapter, there are some devices that use low-cost amorphous or poly crystalline semiconductors, their performance is quite poor. Crystals are made up of identical building blocks, the block being an atom or a group of atoms.