A field emission gun is a device utilized in electron microscopy, specifically in scanning electron microscopes (SEM) and transmission electron microscopes (TEM). It is designed to generate a focused beam of electrons for imaging and analyzing samples at high magnification levels.
The field emission gun consists of a cathode, an anode, and a high-voltage power supply. The cathode is typically made of a metallic material, such as tungsten or lanthanum hexaboride, which possesses a sharp tip. When a high voltage is applied between the cathode and anode, a strong electric field is created at the cathode tip, causing electrons to be emitted through a process called field emission.
These emitted electrons form a coherent beam due to their high energy and narrow distribution. The electric field applied between the tip and the anode controls the intensity and focusing of the electron beam, enabling fine-tuning of the imaging and analysis in the microscope. Additionally, magnetic lenses are often implemented to further focus the beam and increase the resolution.
Field emission guns offer several advantages over traditional thermionic emission electron sources, including better brightness, higher coherence, and reduced space-charge effects. These features enhance the resolution and imaging capabilities of electron microscopes, allowing for detailed examination of samples in various scientific disciplines, such as materials science, nanotechnology, biology, and semiconductor research.
