Mechanics and Tribology of MEMS Materials - prod.sandia.gov ...

(Figure 7.6a), this difference is probably due to lower initial coverage of the alkylsilane on this
sample, as discussed previously.
Table 7.5. Atomic concentration of species as a function of exposure conditions for PFTS coated
Si(100)
Atomic Conc., %
Exposure Type Conditions F O C Si
as-deposited 59.1 9.9 25.8 5.3
None as-deposited, post
57.8 10.9 26.2 5.1
Co-60 radiation
XPS*
50 krad N2 59.4 9.1 26.4 5.0
50 krad air 58.8 9.8 26.2 5.1
500 krad N2 45.4 26.8 16.4 11.4
500 krad air 56.1 11.1 27.0 5.7
*The data for “post-XPS” represents a sample that was analyzed a second time by XPS after
initial XPS and contact angle measurements.
Variation in the chemical state of coating species can be highlighted by comparing the
detailed XPS spectra for each element, normalized to constant peak area. Results for ODTS after
select exposure conditions are shown in Figure 7.7.
Intensity (arb. units)
as-deposited
540 536 532 528 295 290 285 280 110 105 100 95
O1s (eV) C1s (eV) Si2p (eV)
Fig. 7.7. Detailed XPS spectra for elements present in ODTS films, normalized to constant total
intensity by element.
Comparing peak shapes, a small shoulder can be seen on the high energy side of the
carbon peak for the sample that was subjected to a second analysis by XPS, indicating the
presence of carbon in a higher binding energy configuration. Select spectra for PFTS-coated
samples are shown in Figure 7.8. In this case, the C1s spectrum is split into several peaks
representing carbon in different bonding configurations, as expected for PFTS. There are no
dramatic shifts in the relative heights of the various C1s peaks, or in the F1s spectra, with
radiation exposure or additional XPS analysis. If radiation or XPS damage caused breaking of
70
500 krad air
10 min. 13%RH air
10 min. dry air
as-dep, post XPS