超高真空指的是低于10-7帕斯卡或100纳帕斯卡(千万分之一帕斯卡)的压力。 相比之下,大气压力为101.3千帕(kilopascals),超过10亿倍,灯泡内的压力约为1帕斯卡,保温瓶内壁的压力约为0.1帕斯卡。 甚至地球周围区域的外层空间也不是超高真空,因为它的压力约为100微帕,比超高真空大一千倍。 在超高真空中,每个气体分子的平均自由路径为40公里,因此这些分子在相互碰撞之前会与室壁碰撞多次。
超高真空主要用于表面分析技术,如奥杰电子能谱、X射线光电子能谱、二次离子质谱、热脱附能谱、角度分辨光发射能谱,以及需要高纯度的薄膜生长技术,如分子束外延和超高真空化学气相沉积。 超高真空也用于粒子加速器以创造一个空的光束路径。
Creating an ultra-high vacuum requires extraordinary measures. Special chamber designs minimize surface area, high-speed pumps, including parallel pumps, must be used, high conductance tubing is used for pumps, pits of trapped gas (as in bolt threads) must be eliminated, chamber walls must be cooled to cryogenic temperatures to avoid sublimation of gases trapped in nanoscopic pockets, all metal parts must be electropolished, low-outgassing materials such as stainless steel must be used, and the system must be baked at 250 °C to 400 °C (482 °F to 752 °F) to remove hydrocarbon or water traces. Outgassing — the slow intrusion of gas molecules through tiny cracks in the chamber — can be a major problem. Some chambers may be incapable of producing an ultra-high vacuum because of the way they were fabricated, and the hardware must be thrown out and replaced. For all these reasons, achieving ultra-high vacuum can be expensive and difficult.
虽然超高真空看起来很极端,但有些环境是更好的真空,包括月球表面和星际空间。 有些空间区域,如Boötes虚空,是如此稀薄,每立方米只有一个原子。
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