Paper VT-TuP7
Low-carbon Steel Chamber and Double Viton O-ring Sealing for Electron Microscope

Tuesday, November 8, 2016, 6:30 pm, Room Hall D

Generally, EM(Electron Microscope) consists of an electron beam generation part, beam control part and a specimen chamber. Among them, in order to get a high imaging resolution, condition and function of electron gun are the most important. Firstly, vacuum level of electron gun chamber is maintained properly depends on the method of electron beam generation. Secondly, gun chamber should be shielded from stray magnetic field which influences the electron beam. Lastly, gun chamber had better have adjustable parts for precise alignment of gun position. In this work, we center around on a simple and cheap electron gun structure for EM. For the purpose of it, we adopt the low-carbon steel for gun chamber material and double Viton O-ring for gun chamber sealing, thereby succeeding in making adjustable gun system maintaining UHV(Ultra High Vacuum) condition.

Recently, B. Cho shows that Low-carbon steel (C≤0.2 wt. %) has a sufficiently low outgassing rate for constructing UHV chamber [1]. Low-carbon steel is a soft magnetic material that is relatively inexpensive and has a high magnetic permeability, so it block out the stray magnetic field. O-ring is usually used for motion vacuum part and also possible to align electron gun in high vacuum. Schottky emitter and cold field emitter are used for high resolution EM, however those require the UHV condition for preventing contamination of tip surface. For EM based on Schottky emitter, we designed the electron gun with low-carbon steel and double O-rings which support UHV condition by pumping out the permeated gases between double O-rings. We compared the performance of double Viton O-rings and double Kalrez O-rings experimentally after 150 ℃ baking process. The Viton material is better than Kalrez in our system and the vacuum pressure of electron gun arrived at ~10^-8 Pa at room temperature. The vacuum pressure is maintained as UHV when the electron gun chamber surface is moved at the double O-ring surface. We applied the Viton double O-ring electron gun system to commercial EM replacing original electron gun to get EM images. We observed the evaporated gold nano-particles and got the magnification up to 200K. Also, we measured the electron beam current stabilities of extractor and probe beam. We demonstrated that Low-carbon steel and double Viton O-ring can be used for EM with Schottky emitter and show highly magnified images of gold nano-particles. We anticipated that these methods could replace the existing electron gun system of EM, thereby providing a simple structure and reducing the cost of production of EM.