Scanning Electron Microscope

Contents

Introduction

S/V ratio

Quantum Confinement

Synthesis of nano materials

Ball milling method

Chemical Vapor Depositon

Sol-Gel Method

X-ray diffraction

Scanning Electron Microscope

Transmission Electron Microscope

Applications of Nano materials

1M Previous Years' Questions

The Scanning Electron Microscope (SEM) is an electron microscope that uses high energy accelerating electrons instead of light (photons) to form an image of a sample by scanning the surface with a focused beam of electrons. In SEM, a beam of electrons is produced at the top of the microscope by an electron gun. The electron beam follows a vertical path through the microscope, which is held within a vacuum. The beam travels through electromagnetic fields and lenses, which focus the beam down toward the sample shown in Fig 1.

scanning electron microscope SEM

Figure 1. Scanning Electron Microscope

Once the beam hits the sample, electrons and X-rays are ejected from the sample. Actually, the electrons-sample interaction creates signals in the form of secondary electrons, backscattered electrons and various rays that are characteristic of the sample. Detectors collect these X-rays, backscattered electrons, and secondary electrons and convert them into a signal that is sent to a screen similar to a television screen. This produces the final image. The secondary electrons are emitted from the specimen play the primary role of detecting the morphology and topography of the specimen while the backscattered electrons show contrast in the composition of the elements of the specimen.

scanning-electron-microscope SEM

Figure 2.Interaction of electrons with the sample

Applications of the SEM
  • Obtain the microstructural informatipn and surface/bulk chemical analysis
  • Determine causes of failures in wide variety of materials
  • Inspection of semiconductors
  • Eliminate backlogs with rapid analysis of drugs, trace evidence, explosives and etc.