Surface, vacuum, cleaning

Instmmentation for tern is somewhat similar to that for sem however, because of the need to keep the sample surface as clean as possible throughout the analysis to avoid imaging surface contamination as opposed to the sample surface itself, ultrahigh vacuum conditions (ca 10 -10 Pa) are needed in the sample area of the microscope. Electron sources in tern are similar to those used in sem, although primary electron beam energies needed for effective tern are higher, typically on the order of ca 100 keV. 

Before 1950, it was impossible to examine the true structure of a solid surface, because, even if a surface is cleaned by flash-heating, the atmospheric molecules which constantly bombard a solid surface very quickly re-form an adsorbed monolayer, which is likely to alter the underlying structure. Assuming that all incident molecules of oxygen or nitrogen stick to the surface, a monolayer will be formed in 3 x 10 second at 1 Torr (=1 mm of mercury), that is, at 10 atmosphere a monolayer forms in 3 s at 10 Torr, or 10 atmosphere but a complete monolayer takes about an hour to form at 10 Torr. The problem was that in 1950, a vacuum of 10" Torr was not achievable lO Torr was the limit, and that only provided a few minutes grace before an experimental surface became wholly contaminated. 

To get around the difficulties involved in preparing for study an interface consisting of a monolayer of polyimide on a metal substrate, vapor-deposited components of polyimide (9-111 and model molecules for parts of the polyimide (11-121 on metals have been studied recently. Due to the limited size of these model molecules, they can be vapor-deposited in monolayers on the surface of clean metallic substrate in an ultra high vacuum system. In this way, useful information concerning the initial interface formation of (parts of) polyimide on a metal surface can be obtained. 

The development of new catalytic materials needs to be complemented with detailed studies of the surface chemistry of catalysis at the molecular level in order to better define the requirements for the catalytic active sites. The wide array of modem spectroscopies available to surface scientists today is ideally suited for this task (see Surfaces). Surface science studies on catalysis typically probe reaction intermediates on model metal samples under well controlled conditions. This kind of study is traditionally carried out in ultrahigh vacuum (UHV) systems such as that shown in Figure 10. Single crystals or other well-defined metal surfaces are cleaned and characterized in situ by physical and chemical means, and then probed using a battery of surface sensitive techniqnes snch as photoelectron (XPS and UPS), electron energy loss (ELS... 

Initially the surface was cleaned in ultra high vacuum and a saturation coverage of was deposited. TPD spectra were... 

SPILL CLEAN-UP Dry sand or earth should be spread on the leak, or spill area bulk liquid may also be absorbed with fly ash or cement powder cleanup of areas contaminated wit soot should involve dry vacuuming of surfaces with a vacuum cleaning system equipped with a high efficiency particulate (HEPA) filter after preliminary cleanup, wash surfaces with alkaline of nonionic synthetic detergents in water clean nonporous electrical and mechanical equipment with organic solvents remove all sources of ignition. 

Dust emission caused by vehicle movement should be controlled by good housekeeping practices. For example, spillages on the top of tankers should be removed at the loading point, preferably using vacuum cleaning, and roadways should be hard-surfaced and kept clean. 

Figure 6. UHV STM topographic image of an in-vacuum cleaned pyrite 100 growth surface. The mounds on the surface are between 1.5 and 4 run in height. Tuimeling conditions +1 V bias and 1 nA tuimeling current.

Careful cleaning of the surfaces to be bonded from dust and debris, by vacuum cleaning or by compressed air ... 

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