Introduction

In this chapter, we introduce the components of the transmission electron microscope. After a brief review of the history of the electron and the electron microscope, we will consider a cross-section of a real microscope (JEOL 120CX) and identify the various stages and components inside the column. We will discuss peripheral support systems (vacuum, compressed air, water cooling, etc.) without which the microscope could not possibly function. Then we focus our attention on the general properties of round magnetic lenses and discuss basic charged particle dynamics in magnetic fields. We will illustrate the behavior of electrons in a magnetic field by means of simplified paraxial trajectory simulations, and introduce the concept of cardinal elements of a lens. Then we will consider deviations from the paraxial behavior and introduce various lens aberrations of importance in electron microscopy. We conclude the section on magnetic lenses with a brief overview of multipole lenses, used as deflectors and correctors.

The electron gun is next, and we will introduce the basic gun types and their operational parameters, along with a discussion of beam properties (current, brightness, coherence, etc.). In the remainder of the chapter, we break the microscope column down into four regions: the illumination system, the goniometer stage and objective lens, the imaging stage, and the detector stage. For each stage, we will describe the common components, why they are present, and how the microscope operator can affect their behavior. In particular, we will relate the geometry of the goniometer stage to reciprocal space and Bragg's Law. We will conclude this chapter with a brief review of electron detection systems.