Vacuum system, design chambers

Photoelectron spectroscopy (PES) was performed at the Swedish National Synchrotron Radiation Laboratory, MAX lab. The beamline and the spectrometer are unique in construction since all three phases of matter (gas, liquid, and solid) can be studied ([16] and references therein). This is made possible by means of efficient differential pumping of the analysis chamber of the instrument. To the existing spectrometer we have developed an electrochemical preparation technique where the electrochemistry is performed in a specially designed preparation chamber attached to the analysis chamber of the spectrometer. Thus, all electrochemistry is performed inside the vacuum system of the spectrometer. There are several advantages with this technique. First, the electrochemistry is performed in a controlled atmosphere without any exposure to air. Second, the surface is analyzed within minutes after the electrochemical reaction. Third, the same electrode is analyzed at the same spot for the different electrochemical treatments. The device used for the electrochemical preparations is described in detail elsewhere [17]. 

Differential pumping is the term used to describe the process by which different pressures are maintained in various locations within the instrument, e.g., during the desolvation of ESI droplets and in the collision-induced dissociation cells used in MS/MS instruments. As dictated by the requirements for differential pumping, vacuum systems are designed as a series of interconnecting chambers with low conductance connections, between which ions can be moved efficiently, while the pressures necessary for the operation of the individual components are preserved. Typically, pressures of -10 to 10 Torr ( 10 ° Torr in FT instruments) are required in mass analyzers. 

The control of particulate contamination in a system is very dependent on the system design and fixturing, the ability to clean the system, and the gas source/distribution system. The use of dry lubricants decreases wear and particle generation. In particular, bolts used in the vacuum chamber should be silver-plated to prevent wear and galling. Some types of plasma... 

For low pressure pipelines that have ports open to the atmosphere, eg, sewers or closed effluent culverts, samplers are designed to sample through manholes. In a typical system, the Hquid is lifted through a suction line into the sampling chamber under vacuum. When filled, the vacuum shuts off, and the sample drains into a sample jar. A secondary float prevents any Hquid from reaching the vacuum pump. The suction line then drains by gravity back to the source. 

CVD reactions are most often produced at ambient pressure in a freely flowing system. The gas flow, mixing, and stratification in the reactor chamber can be important to the deposition process. CVD can also be performed at low pressures (LPCVD) and in ultrahigh vacuum (UHVCVD) where the gas flow is molecular. The gas flow in a CVD reactor is very sensitive to reactor design, fixturing, substrate geometry, and the number of substrates in the reactor, ie, reactor loading. Flow uniformity is a particulady important deposition parameter in VPE and MOCVD. 

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