X-ray Damage to CF ₃ CO ₂ -Terminated Organic Monolayers on Si/Au: Principal Effect of Electrons

Abstract

The relative importance of x-rays alone and of x-ray-generated primary and secondary electrons in damaging organic materials was explored by use of self-assembled monolayers (SAMs) on multilayer thin-film supports. The substrates were prepared by the deposit of thin films of silicon (0, 50, 100, and 200 angstroms) on thick layers of gold (2000 angstroms). These systems were supported on chromium-primed silicon wafers. Trifluoroacetoxy-terminated SAMs were assembled on these substrates, and the samples were irradiated with common fluxes of monochromatic aluminum K(alpha) x-rays. The fluxes and energy distributions of the electrons generated by interactions of the x-rays with the various substrates, however, differed. The substrates that emitted a lower flux of electrons exhibited a slower loss of fluorine from the SAMs. This observation indicated that the electrons-and not the x-rays themselves-were largely responsible for the damage to the organic monolayer.

Modification of biphenylselenolate monolayers by low‐energy electrons

“…Note that the results obtained for low-energy electrons are valid for X-rays as well, since the major impact of X-ray irradiation results from photoelectrons and inelastic and secondary electrons [12,19]. As for the system of this study, these films differ from the respective, well-studied thiol-derived films by the headgroup [33].…”

“…Of these three parameters the packing density and -closely related -perfection of the crystallographic structure directly influence the quenching probability of the primary excitation, diminishing the effective radiation load for densely packed films and SAMs with better crystallinity [18]. The substrate material determines the strength of the headgroup-substrate bond (see below) and the secondary electron yield [19], which adds to the primary X-ray or electron flux, giving the total irradiation load [20]. However, the biggest influence on the extent and course of irradiation-induced reactions has the molecular architecture [12].…”

An in situ temperature‐programmed XPS study of the surface chemical reactions of thiophene with Ag/titania

“…Therefore, we have used the Ti 2p 3/2 and S 2p lines to determine the surface products of any interaction of the Ag/titania sorbent with thiophene at 25 Ž C. We have observed a fast darkening of the adsorption complex of Ag/titania with thiophene under the XPS measurements at 25 Ž C. This observation is indicative of the XPS-induced sample damage in the presence of the adsorbed thiophene. Indeed, it is known that XPS can impose a significant electron-induced, [45] as well as photon-induced, damage [46] of the organic monolayers adsorbed on a variety of substrates, both metals and insulators. The BE of the S 2p line at 25 Ž C of 162.1 eV is close to the BE of 161.9 eV for sulfur in silver sulfide (Ag 2 S).…”

Degradation of poly(vinyl chloride) and nitrocellulose in XPS

“…Measurements were recorded using the 5 mA x-ray source setting with a 14°angle of emission and with electron beam currents of 0, 6, 30 and 300 nA, bracketing the 30 nA expected from Eqn. (8). From the decay curves of the Cl 2p peak area we obtain the decay rate k(PVC).…”