semiconductor physics and Devices

Week 5: Bonding in Solids (Part 1)

Lecture Topics:

1. Introduction to Bonding in Solids

   • Overview of the types of bonding found in solids and how they influence the material’s properties.

   • The role of bonding in determining electrical, thermal, mechanical, and optical properties of solids.

   • Types of bonds in solids: ionic, covalent, metallic, van der Waals, and hydrogen bonding.

2. Ionic Bonding

   • Occurs between atoms with large differences in electronegativity (e.g., NaCl).

   • Transfer of electrons from one atom (typically a metal) to another (typically a non-metal), resulting in positive and negative ions.

   • Characteristics: High melting points, electrical conductivity in molten state, brittleness, and solubility in water.

   • Madelung constant: The sum of electrostatic interactions between ions in a crystal lattice.

     • Example calculation of Madelung constant for a simple cubic lattice.

3. Covalent Bonding

   • Occurs when atoms share electrons (e.g., in diamond or Si).

   • Strong directionality in covalent bonds due to sharing of electrons between specific atoms.

   • Characteristics: High melting points, hardness, poor electrical conductivity in pure form, and strong directional bonds.

   • Covalent bonding in semiconductors like silicon (Si) and its influence on electronic properties.

4. Metallic Bonding

   • Occurs between metal atoms, where electrons are free to move throughout the lattice (electron sea model).

   • Characteristics: Good electrical and thermal conductivity, malleability, ductility, and luster.

   • The role of free electrons (delocalized electrons) in conducting electricity and heat.

   • Explanation of metallic bonding in metals like copper (Cu) and aluminum (Al).

Examples:

• Comparison of the bonding types in NaCl (ionic) and diamond (covalent).

• Explanation of why ionic solids are brittle and metallic solids are malleable.

• Calculation of the Madelung constant for an ionic crystal.

Homework/Exercises:

1. Explain the differences between ionic, covalent, and metallic bonding and how each affects the properties of materials.

2. Calculate the Madelung constant for a one-dimensional chain of alternating positive and negative ions.

3. Explain why metals are good conductors of electricity while covalent solids like diamond are insulators.

Suggested Reading:

• Charles Kittel, Introduction to Solid State Physics, Chapter 3: Crystal Binding.

Key Takeaways:

• Bonding in solids determines a material's properties, such as conductivity, hardness, melting point, and ductility.

• Ionic bonds involve the transfer of electrons, covalent bonds involve sharing electrons, and metallic bonds involve a sea of delocalized electrons.

• Understanding bonding is crucial for predicting and explaining the behavior of different types of solids.

This week provides an introduction to the different types of bonding in solids, focusing on ionic, covalent, and metallic bonds, with an emphasis on their influence on material properties.