Pumps ultra-high vacuum

Since that time, the method is widely developed experimental setups are improved and adjusted to many different purposes (e.g. for the investigations of oxidation and reduction reactions). Today, two main types of equipment are available those operating under ultrahigh vacuum and so-called flow systems. WeU-defined surfaces of single-crystalline samples are investigated in a continuously pumped ultra-high vacuum (UHV) chamber (this technique is often referred to as thermal desorption spectroscopy—TDS [5]). The equipment that is constructed to allow adsorption-desorption in the gas flow are most often used for the investigation of porous materials (catalysts, for example). Vacuum setups are customarily used for surface science studies, but they can be also useful for the characterization of porous materials. 

Vacimm Technique. There is a growing literature on ultra high vacuum technique by conventional methods (22). It will suffice to say that vacua of the order of 10 to 10 mm. Hg can be obtained readily with the use of either oil or mercury diffusion pumps. The crucial points are ... 

Of course, everything except the electronics and data system associated with the SIMS experiment must be In a vacuum system, with the experimental results desired dictating the degree of vacuum required. This can range from ultra-high vacuum to pressures achievable with a simple diffusion pump. 

A UHV chamber for LEED studies is evacuated to ultra-high vacuum with a combination of pumps consisting of a turbomolecular pump (backed with an oil-sealed rotary vane pump) and a titanium sublimation pump (TSP). When the chamber is evacuated by both pumps, a total pressure of 4 x 10 9mbar is achieved and residual gas analysis shows that this consists of 50% Ar + 50% H2. 

OTHER HIGH/ULTRA-HIGH VACUUM PUMPS... 

Ultra-High Vacuum Levels Without Ultra-High Vacuum Pumps... 

G.F. Weston, Pumps for Ultra-high Vacuum, Vacuum, 28, 209-233 (1978). 

To achieve ultra-high vacuums (0.1-0.001 Pa, corresponding to 10-3-10-s Torr) it is necessary to couple a diffusion pump to the rotary oil pump. 

The magnetic coil shown in figs. 2.15 and 2.16 was used to orient the electron polarisation vector P parallel to the axis of the analysing target—Mott detector system. The deflection system is part of the differential pumping stage which is necessary for the maintenance of the required ultra-high vacuum in the source chamber. 

A systematic view of the relevant elements is depicted in Figure 17.10. The deposited clusters can be exposed to different reactant gases by two kinds of valves. First, they can be exposed isotropically to e.g. O2 by a commercial, ultra-high vacuum (UHV) compatible, variable leak valve. Second, reactant molecules (e.g. CO) can be introduced via a pulsed molecular beam produced by a piezo-electric driven, pulsed valve. This pulsed valve has a high pulse-to-pulse stability (time profile), and allows the study of catalytic processes on supported clusters at relatively high pressures (up to 10 mbar). Furthermore, a stainless steel tube is attached to the pulsed nozzle in order to collimate the molecular beam and to expose the reactant molecules to the substrate only. The pulse duration at the position of the sample can, in principle, be varied from 1 ms up to continuous operation. For the experiments described below a constant pulse duration of about 100 ms was used. The repetition rate of the pulsed valve can be up to 100 Hz. The experiments were carried out at 0.1 Hz the 10 s interlude allows the reactant gas to be pumped completely. 

The ultra-high vacuum chamber is commonly made from stainless steel, and joints of chamber parts are made from crushed copper gaskets. Ultra-high vacuum pressure can be achieved using diffusion pumps, sputter ion pumps or turbomolecular pumps. Currently, sputter ion pumps and turbomolecular pumps are more commonly used than diffusion pumps that may contaminate the chamber by leaking oil gas molecules. 

SIMS requires an ultra-high vacuum environment, similar to AES and XPS. The ultra-high vacuum environment ensures that trajectories of ions remain undisturbed during SIMS surface analysis. The SIMS vacuum chamber and pumping system is not much different from that for AES and XPS. Figure 8.5 illustrates common SIMS structure in a vacuum chamber in which there are two main components a primary ion system and a mass analyzer system. The primary ion system includes a primary ion source, a Wien filter and ion beam deflector. The mass analysis system includes a secondary ion extractor filter, mass analyzer and ion detector. 

To lubricate high and ultra-high vacuum pumps special lubricants with low vapour pressures at the working temperature are used, produced from naphthenic or paraffinic mineral oils by molecular distillation with good oxidative and thermal stability. Synthetic esters are another group of lubricants for vacuum pumps, the most widely used are di-n-butyl and di-n-octyl phthalates. 

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