Low Voltage Electron Microscopy: Principles and Applications

Chapter 1

Introduction to the Theory and Advantages of Low Voltage Electron Microscopy

David C. Bell¹ and Natasha Erdman²

¹School of Engineering and Applied Sciences, Harvard University, USA

²JEOL USA Inc., USA

1.1 Introduction

The fundamental aspects of electron microscopy all relate directly to the physics of the interactions between the electron beam and sample. These interactions have been studied extensively since the discovery of the electron by J.J. Thompson in 1897. Energetic electrons are described as “ionizing radiation”—the general term used to describe radiation that is able to ionize or remove the tightly bound inner shell electrons from a material. This is obviously an advantage for electron microscopy in that it produces a wide range of secondary signals such as secondary electrons and X-rays, but is also a disadvantage from the perspective that the sample is “ionized” by the electron beam and possibly structurally damaged, which depending on the accelerating voltage happens in a number of different ways. The advantages of using a lower accelerating voltage for the electron beam are that the energy is reduced and hence the momentum that can be transferred to sample from the electron is also reduced. This, however, has the unwanted effect of reducing the possible emitted signal; although, with recent improvements in detectors, cameras and the use of aberration correctors, the signal to noise and the resolution to produce a final image can not only be maintained but ...