Discussion
A surface of Li metal (sample X) was suspected to be completely coated with a thin layer of Li2O (sample Y). When X and Y are analysed by X-ray photoelectron spectroscopy :
Answer: A
The kinetic energy of the photoelectrons from X (Li metal) will be higher than from Y (Li2O).
In XPS the measured kinetic energy is
\[ KE = h\nu - BE - \phi \]
In Li2O lithium is present as Li+. The loss of electron density makes the remaining 1s electrons more tightly held, so the Li 1s binding energy is higher in the oxide than in the metal (a chemical shift). For the same X-ray energy, a higher binding energy means a lower kinetic energy.
So Y gives photoelectrons of lower kinetic energy, ruling out D, and the binding energy for Y is higher, not lower, ruling out C. Option B compares Y with itself.
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