Everhart–Thornley detector

Everhart–Thornley Detector

The Everhart–Thornley Detector (ETD) is a secondary electron detector used primarily in Scanning Electron Microscopy (SEM) to collect low-energy secondary electrons that are emitted from the surface of a specimen when it is bombarded with a primary electron beam. This detector plays a crucial role in the imaging and analysis capabilities of SEMs, providing detailed topographical information about the specimen's surface. The ETD was invented in 1960 by Thomas Everhart and Richard F.M. Thornley.

Overview

The Everhart–Thornley Detector is designed to enhance the imaging capabilities of a Scanning Electron Microscope by detecting secondary electrons (SEs) that are ejected from the surface of a specimen due to the interaction with the primary electron beam. These secondary electrons have low energy, typically less than 50 eV, and their yield is highly dependent on the surface topography and composition of the specimen, making them ideal for high-resolution surface imaging.

Components and Function

The ETD consists of a scintillator, a light guide, and a photomultiplier tube. The scintillator is coated with a material that emits photons when struck by secondary electrons. The emitted photons are then guided through a light pipe to the photomultiplier tube, where they are converted into an electrical signal that can be processed to form an image.

Scintillator

The scintillator is typically made of a material like P47 phosphor or Yttrium Aluminum Garnet (YAG) doped with Cerium. When secondary electrons hit the scintillator, they cause it to emit photons, which are then directed towards the photomultiplier tube.

Photomultiplier Tube

The photomultiplier tube (PMT) is a highly sensitive light detector that can convert the photons it receives into an electrical signal. The sensitivity of the PMT allows the ETD to detect the very low levels of light produced by the interaction of secondary electrons with the scintillator.

Operation

In operation, the ETD is positioned to collect secondary electrons that are ejected from the specimen's surface. A positive bias is applied to the detector to attract the low-energy secondary electrons towards the scintillator. Once the secondary electrons reach the scintillator, they generate photons that are then converted into an electrical signal by the PMT. This signal is processed to create an image that reflects the topographical and compositional variations of the specimen's surface.

Applications

The Everhart–Thornley Detector is widely used in various fields such as materials science, biology, and nanotechnology for surface imaging and analysis. Its ability to provide high-resolution images makes it an essential tool for examining surface structures, defects, and compositions.

Advantages and Limitations

The main advantage of the ETD is its ability to provide high-resolution images of the specimen's surface. However, its dependence on secondary electron emission means that it is less effective for imaging non-conductive materials without a conductive coating, as these materials can accumulate charge that repels secondary electrons.

See Also

• Scanning Electron Microscopy (SEM)
• Electron Microscopy
• Secondary Electron
• Material Science
• Nanotechnology

```

This template is designed for use in marking articles as stubs related to Electron Microscopy. It categorizes articles into the "Electron microscopy stubs" category for easy tracking and improvement. The template uses the `

` template, a common approach for creating stub templates in MediaWiki, particularly in WikiMD. The image used should be relevant to electron microscopy and must be uploaded to the wiki with the correct permissions.