PHYS 22533

Solid State Physics Course Overview

• Instructor: Dr. KMDC Jayathilaka

Course References

• Key Texts:

  • Elementary Solid State Physics by M.L. Omar

  • Solid State Physics by N.W. Ashcroft & M.W. Mermin

  • Introduction to Solids by L.V. Azroff

  • Physical Properties of Materials by M.C. Lovell, A.J. Avery, M.W. Vernon

  • Additional material science and crystallography books.

Objectives

• Knowledge Acquisition:

  • Understand solid structures.

  • Learn material characterization techniques, including X-ray diffraction (XRD).

  • Explore electrical properties of materials.

Learning Outcomes

• By course end, students will:

  • Demonstrate foundational knowledge in solid-state physics and semiconductor devices.

What is Solid State Physics?

• Definition & Scope:

  • Study of properties of solid materials.

  • Examines interactions among atomic nuclei and electrons through electrostatic forces.

  • Develops fundamental laws governing solid behavior.

States of Matter

• Matter can exist in different states:

  • Solids: Definite shape and volume.

  • Liquids: Definite volume but take the shape of their container.

  • Gases: No definite shape or volume.

  • Liquid Crystals: Intermediate state, showing properties of both liquids and solids.

Classification of Solids

• Types of Solid Materials:

  • Crystalline:

    • Single Crystal: Periodic atomic structure throughout.

    • Polycrystalline: Aggregate of many small single crystals or grains.

  • Amorphous (Non-Crystalline): Randomly oriented atoms without defined patterns.

Crystalline Solids

• Characteristics:

  • Atoms exhibit a regular, repeating pattern.

  • Majority of solids are classified as crystalline, leading to clearer understanding of properties and behaviors compared to non-crystalline materials.

  • Significant impact on electrical properties is essential in modern technologies.

Types of Crystalline Structures

• Single Crystals:

  • Consist of a periodic atomic structure throughout volume.

  • Exhibit symmetry at long-range scales.

• Polycrystalline Solids:

  • Composed of many small grains with distinct boundaries.

  • High order at atomic scales, grains typically range from 100 nm to 100 microns.

  • Nanocrystalline materials possess grains smaller than 100 nm.

Amorphous Solids

• Description:

  • Composed of inattentively oriented atoms, ions, or molecules without long-range order.

  • Short-range order possible, examples include plastics, glasses, and amorphous silicon used in solar cells.

Lattice Structures

• Lattice Definition:

  • Regular, periodic arrangement of atoms, forming a three-dimensional network.

  • A lattice is an imaginary construct, the actual atomic arrangement refers to the crystal structure.

• Basis: Group of atoms associated with every lattice point to form crystal structure.

Unit Cells

• Unit Cell: Smallest geometrical unit that, when repeated, forms the entire lattice.

  • Defined by six lattice constants: a, b, c, α, β, and γ.

• Primitive Unit Cell: Contains one lattice point.

• Non-Primitive Unit Cell: Contains more than one lattice point.

Types of Unit Cells

• Seven Basic Unit Cells: Includes cubic, tetragonal, orthorhombic, hexagonal, monoclinic, triclinic, and rhombohedral.

• Cubic Lattices: Simple (SC), Body-Centered (BCC), and Face-Centered (FCC).

Atomic Parameters

• Number of Atoms in Unit Cell (Z): Calculated based on atom positions shared across multiple unit cells.

• Coordination Number (CN): Number of nearest neighbor atoms; indicates atomic packing tightness.

• Atomic Radius Relationships: Mathematical relations derived using geometry to link atomic sizes with unit cell edge length.

• Atomic Packing Fraction (APF): Ratio of total atomic volume to volume of the unit cell, critical in describing packing efficiency.

Density and Void Space in Unit Cells

• Density: Mass per unit volume, closely resembles bulk material density.

• Void Space: Unoccupied space within a unit cell calculated as a percentage of total cell volume.

Electrical Conduction in Solids

• Current Definition: Flow rate of charges, measured in Amperes (C/s).

• Drift Velocity: Average speed of electrons under an electric field, indicative of current in conductors.

• Drude Model: Simplifies electrical conduction modeling but has limitations in explaining thermal dependencies and specific heat.

Conclusion

• Solid state physics forms the basis for understanding various materials and their characteristics essential for applications in technology, electronics, and material science.