Recording surface, contamination

A laser pulse strikes the surface of a specimen (a), removing material from the first layer, A. The mass spectrometer records the formation of A+ ions (b). As the laser pulses ablate more material, eventually layer B is reached, at which stage A ions begin to decrease in abundance and ions appear instead. The process is repeated when the B/C boundary is reached so that B+ ions disappear from the spectrum and C+ ions appear instead. This method is useful for depth profiling through a specimen, very little of which is needed. In (c), less power is used and the laser beam is directed at different spots across a specimen. Where there is no surface contamination, only B ions appear, but, where there is surface impurity, ions A from the impurity also appear in the spectrum (d). 

CsCl at 200°C for 14 days, is shown in Figure 4. Before this spectrum was collected, the cube was sputtered with Ar ions to remove surface contamination. Two Cs MNN transitions arise at 554 and 566 eV (6) and the larger 0 KLL peak is at 506 eV. Superimposed on Figure 4 is a spectrum of natural pollucite, recorded under the same instrument conditions and corrected for a -4 eV positional difference observed in each of the three peaks. The same charging shift was observed in the Si peaks (not shown in Figure 4), which were found at 76 eV (cube) and 72 eV (natural pollucite). Transitions from four elements, Al, Si, 0, and Cs, were observed in both spectra. Potassium was not detected in either spectrum. 

To quantify the elements deposited on the catalyst surface as a function of exposure time in the flue gas duct, their relative atomic fractions x were recorded with exposure time (Fig. 4). An increase in sulfur and arsenic contents with exposure time can be observed. Both elements were first detected after 48 h. Depending on exposure time, these elements cover increasingly large areas, 10% after 96 h, 20% after 3270 h. At the same time, all samples were observed to determine whether the detected Xjj decreases with exposure time (Fig. 5). This reduction is particularly pronounced between 24 h and 48 h. After about 400 h of exposure time, the titanium fraction has decreased to about one third of its initial value. Since it does not change after this time, it is assumed that the catalyst surface contamination process is completed. From this time on, a constant balance should be achieved between abrasion and contamination. Surprisingly, this does not hold for sulfur and arsenic. It is assumed that the modified catalyst surface involved in this abrasion/contamination balance forms a further reactive component for these elements. There is other interesting evidence that the arsenic deposited originates, at least from that point on, exclusively in the gas phase, since the arsenic entrained by the flue dust would otherwise result in an increase in Xgj. 

A small sample, about 2-5 mm long, is selected and using rubber gloves (to avoid surface contamination introduced by handling with the bare hands), an identification knot is tied in the sample and the shape of the knot recorded. Before the sample is introduced, it is thoroughly wetted out by total immersion in the liquid with the lowest density for 10 min. After the samples have been inserted in the column using tweezers, a stopper is positioned in the top of the column to prevent solvent evaporation. After a period of 2 h, the position that the sample has reached in the column is read from the calibrations. 

Various methods have been developed for measuring many of the factors that influence atmospheric corrosion. The quantity and composition of pollutants in the atmosphere, the amount collected on surfaces under a variety of conditions, and the variation of these with time have been determined. Temperature, RH, wind direction and velocity, solar radiation, and amount of rainfall are easily recorded. Not so easily determined are dwelling time of wetness (TOW), and the surface contamination by corrosive agents such as sulfur dioxide and chlorides. However, methods for these determinations have been developed and are in use at various test stations. By monitoring these factors and relating them to corrosion rates, a better understanding of atmospheric corrosion can be obtained. 

Monitoring of shipments of radioactive material. Any shipment of radioactive material that is received at or dispatched from the facility should be checked for both external surface contamination and radiation dose rates, which should conform to relevant national or international regulations (for further details see Ref. [21]). The measured results should be recorded, and... 

Monitoring of solid waste. Stored solid waste should be checked for external radiation and for possible surface contamination. In the event of the detection of external contamination, appropriate identification of the contaminating radionuclides should be performed. An appropriate record keeping system should be established and maintained to provide accountability for and traceability of solid waste. 

The u.se of well-defined reference materials is crucial with regard to chemical-state determination by XPS. However, it is very difficult to prepare well-defined surfaces for many chemical compounds due to the pre.sence of surface contaminants and multiple chemical states and to the fact that the surface compo.sition is seldom similar to the bulk composition. This point is illustrated by the use of an AgO powder sample to obtain reference BEs and peak shapes for AgO and AgO (45, 46]. The AgO was heated in vacuum in order to decompose first the contaminating carbonate and hydroxyl species and then the AgO it.self to Ag O and finally to Ag metal. The XPS Ag id spectra recorded after heating the sample to various temperatures are shown in Fig. 14. The spectral changes are complex because several Ag species are present and their BEs are separated by only a few tenths of an eV (Table 1.2). Heating at 100°C results in the loss of carbonate and hydroxyl species, at 200°C in the decomposition of AgO to Ag 0. and at 400°C in the decomposition of Ag 0 to Ag metal. Spectrum f was recorded from a clean... 

The effects of surface contamination are shown in Fig. 37, in which the O SAM image recorded from a triangle in the as-deposited condition is shown. 

It was of interest to examine effect of surface contamination on photoelectron spectra. For this purpose a polymer sample was pre-purged with SC-CO at room temperature and then was treated at 100°C. Under these conditions, double-peak stmcture in the O Is spectrum recorded at U =-IV observed after treatment at other temperatures disappeared and Hp content decreased. 

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