Fully UHV Compatible Gas Mixing System Designed for High Pressure Surface Science Applications with Ultra Pure Gases
PureGas is a modular gas handling system developed for applications such as high pressure SPM, high pressure XPS, catalysis or chemical vapor deposition, where a well defined flow of ultra pure gas is required.
The purest gases commercially available contain about 10 ppm of impurities. At 10 mbar total pressure, this corresponds to a partial pressure of contaminants of 10-4 mbar. This might (and probably will) give rise to a monolayer of contaminants in 10 ms. Hence, surface science at elevated pressures requires additional gas cleaning to at least sub ppb levels. A prerequisite to reach such low contaminant levels is that the gas system itself is UHV compatible. In addition to this requirement, the PureGas system is also designed so that all parts of the system can be leak tested with helium. The PureGas series allows the use of commercial gas cleaners for a wide range of gases. Due to the modular design, special requirements can easily be fulfilled.
Handling ultra pure gases at high pressure is a challenge when it comes to the selection of materials. At high pressure, gases will frequently react with the wall material, or with impurities on the walls, and form volatile reaction products which are then deposited onto the sample surface. Gas mixtures at elevated pressures may also undergo catalytic reactions on certain materials, forming unwanted reaction products. Therefore, the choice of materials is of utmost importance, and must be made specifically for each gas. The PureGas series has been designed with this in mind, and all materials are selected to be compatible with the particular gases in use.
The flow regulation for individual gases is carried out by standard mass flow regulators, with up to five gas channels. The Pure Gas series also allows integration of the pressure control of the gas streams. The flow rates of the individual gases and the total pressure is controlled directly by SpecsLab Prodigy, which allows the running of preprogrammed experiments. The software is highly modular and provides all functionalities, such as read out and control of flows, pressures and temperatures.