Titanium sublimation pumps

Fig. 3. Schematic drawing of the high pressure electron spectrometer. A, Argon ion gun D, differentially pumped region EL, electron lens G, gas cell HSEA, hemispherical electron analyzer LO, two-grid LEED optics LV, leak valve M, long travel rotatable manipulator P, pirani gauge S, sample TSP titanium sublimation pump W, window X, twin anode x-ray source.

Each of the turns in the titanium sublimation pump contains approximately 1.2 g of useable titanium supply. At a heating current of 50 A the surface temperature comes to about 1850 K, the sublimation rate approximately 0.12 g/h, i.e. a turn can be operated continuously for about 10 hours. Since at pressures below 1 10 mbar sublimation is not continuous but rather only at intervals which - at low pressures (below 5 10 mbar) and low gas volumes - are already more than ten times the actual sublimation period, one may assume a pumping period of almost one month at a working pressure of 10 mbar per turn. 

The desorption peak of 16 amu around 200 K is due to methane, which is produced in the titanium sublimation pump during methanol exposure, and adsorbed on the sample holder. The main desorption products are H2 around 400 K and CO above 800 K. The H2 desorption peak is much larger than that observed upon the H2 adsorption up to saturation on the clean surface. The H2 desorption peaks seem to consist of three components two relatively small components at 350-400 K and around 500 K and a sharp peak at 410 K. For the HD desorption trace, only the peak at 350-400 K is seen. These results suggests that the methanol decomposition reaction on the clean Mo(l 12) surface proceeds as follows. 

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. 

Chapter 3 also considered those entrapment pumps that remove gas particles by sorption effects such as gettering and implantation. The operating principles of sputter ion pumps were explained (Example 3.26) and some typical calculations performed (Examples 3.27-3.29). Aspects of the use of titanium sublimation pumps were dealt with (Examples 3.30-3.33). 

Vacuum pumps are generally divided into 13 categories according to the working principle, as listed in Table 2.5. They include water jet pump, water ring pump, steam ejector, oil-sealed rotaiy pump, Roots pump, vacuum diffusion pump, oil vapom booster pump, sputtering-ion pump, radial field pump, titanium sublimation pump, sorption pump, molecular pump and cryopump [9],... 

DP refers to diffusion pumps, TP to turbomolecular pumps, SP to titanium sublimation pumps, V to Valves, and S to defining slits. 

XPS analyses were performed using a PHI 5700 spectrophotometer equipped with a concentric hemispherical analyzer in the standard configuration (Physical Electronics, Eden Prairie, MN, USA). The vacuum system consists of a turbo-molecular pump, ion pump, and a titanium sublimation pump. The base pressure before the analysis was better than 10 Pa. The X-ray source was A1K0 (1486.6 eV), run at 300 watts. The incident angle was 54.7° and the emission angle was 45° with respect to the sample surface normal. All the spectra were obtained in digital mode. A constant energy of 23.50 eV was set across the hemispheres of the electron analyzer operated in the Fixed Analyzer Transmission (FAT) mode for the detailed spectra the survey spectra have been acquired with 187.85 eV pass... 

A photograph and a schematic diagram of this system are shown in Figs. I and 2, respectively. It consists of a conventional stainless-steel UHV chamber within which an isolation cell for high-pressure studies is situated. The chamber is cylindrical in shape and has a diameter of 12 in. Ultrahigh vacuum is obtained by a mechanically backed Varian I 200 1/s diffusion pump with a liquid nitrogen trap, in combination with a water-cooled titanium sublimation pump. The background pressure of the system is lower than 1 X 10" Torr. 

The student should be aware that it takes special vacuum equipment to maintain an ultrahigh vacuum. First, a clean surface must be inside a special vacuum chamber that has no leaks—which is easier said than done. In addition, special vacuum pumps must be used to get to such high vacuums and stay there. The normal oil-filled rotary vacuum pump can only maintain a vacuum of about 10 torr or so, a full five orders of magnitude higher than what is necessary for ultrahigh vacuum. Special vacuum pumps (like turbomolecular pumps, titanium sublimation pumps, or liquid-helium-based cryopumps) are needed and can be extremely expensive. 

Entrapment pumps are self-contained units (these do not require any other pumps) capable of producing a vacuum down to 10 ° Torr. As the name suggests, entrapment pumps operate by trapping or condensing gas phase molecules into the solid state or by ionization and accelerating these molecules into a solid. Ion Pumps with Titanium sublimation pumps are more commonly included on state-of-the-art SIMS instruments. Ion pumps are operated continuously to sustain UHV conditions. Sublimation pumps, on the other hand, are operated in an intermittent maimer to allow improvement in vacuum conditions. As such pumps should not be operated at pressures greater than 10 Torr, initial pumpdown of these chambers is carried out through a combination of displacement and momentum transfer pumps. 

Further improvements in the vacuum whether resulting from increased pump-down times and/or the use of Titanium sublimation pumping... 

Sublimation pump (vacuum technology) A capture (getter) pump in which the getter material is periodically renewed by sublimation from a solid source. Example Titanium sublimation pump. See also Vacuum pump. 

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