The gas in a single layer of a single layer of gas in the exposed surface of the real system is essentially an infinite source of gas, which makes the vacuum pump work at full capacity. The wavelength of visible light is about 5x10-5cm, and the distance between molecules in the monolayer is 10-7cm. Understanding this can highlight the extent of the single molecule layer. When the vacuum system is assembled, it is necessary to use the liquid to clean the surface of the liquid, and it is required that the residue of the cleaning liquid is completely negligible after evaporation and drying. In addition, the vapor pressure of the liquid for the final cleaning must be high enough to evaporate and dry in a short period of time.