Introduction to Scanning Electron Microscopy
Introduction To Scanning Electron Microscopy
At the completion of the prac, the practical experience of operating a scanning electron microscope is sufficient to operate the particular machine in the future. During the experiment, two different gold plated samples are analysed under the SEM and compositional and topographic information is identified and analysed. Both the information is derived by changing the working distance, accelerating voltage, aperture size, probe current, resolution and magnification.
AIM
To analyse samples and obtain micrographs of the surface, using a scanning electron microscope. The experimental images are compared against the different material structures and defects between the various samples at different magnifications and resolutions.
INTRODUCTION
A schematic of a scanning electron microscope is shown below. The instrument can be separated into three major sections including electron-optical column', vacuum system and electronics and display system.
Figure 1: Layout off scanning Electron Microscope.
In the optical part of instrument, the first thing we notice is the need for a source of illumination. No visible photons of light are produced within the SEM but an invisible beam of electrons. The beam is produced from an electron gun' and a cross-section through a simplified electron gun is shown below.
Figure 2: Cross-section through an electron gun
A V-shaped tungsten filament (I) is heated electrically to about 2700Kand the high temperature causes many of the electrons in the tungsten to become sufficiently excited for them to escape. This process is called "thermionic emission".
Once freed the electrons would be quickly recaptured by the filament, because in losing them, it will have become positively charged. Applying a high negative voltage (typically 2-25 kV) between the filament and a nearby earthed anode disc, accelerates the electrons away from the filament and their velocity depends on the
At the completion of the prac, the practical experience of operating a scanning electron microscope is sufficient to operate the particular machine in the future. During the experiment, two different gold plated samples are analysed under the SEM and compositional and topographic information is identified and analysed. Both the information is derived by changing the working distance, accelerating voltage, aperture size, probe current, resolution and magnification.
AIM
To analyse samples and obtain micrographs of the surface, using a scanning electron microscope. The experimental images are compared against the different material structures and defects between the various samples at different magnifications and resolutions.
INTRODUCTION
A schematic of a scanning electron microscope is shown below. The instrument can be separated into three major sections including electron-optical column', vacuum system and electronics and display system.
Figure 1: Layout off scanning Electron Microscope.
In the optical part of instrument, the first thing we notice is the need for a source of illumination. No visible photons of light are produced within the SEM but an invisible beam of electrons. The beam is produced from an electron gun' and a cross-section through a simplified electron gun is shown below.
Figure 2: Cross-section through an electron gun
A V-shaped tungsten filament (I) is heated electrically to about 2700Kand the high temperature causes many of the electrons in the tungsten to become sufficiently excited for them to escape. This process is called "thermionic emission".
Once freed the electrons would be quickly recaptured by the filament, because in losing them, it will have become positively charged. Applying a high negative voltage (typically 2-25 kV) between the filament and a nearby earthed anode disc, accelerates the electrons away from the filament and their velocity depends on the