Point defects at cleavedSrn+1RunO3n+1(001) surfaces

The (001) surfaces of cleaved ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ and ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ samples were investigated using low-temperature scanning tunneling microscopy and density functional theory calculations. Intrinsic defects are not created during cleaving. This experimental observation is consistent with calculations, where the formation energy for a Sr and O vacancy, 4.19 eV and 3.81 eV, respectively, is significantly larger than that required to cleave the crystal, 1.11 eV/(1 \ifmmode\times\else\texttimes\fi{} 1) unit cell. Surface oxygen vacancies can be created through electron bombardment, however, and their appearance is shown to vary strongly with the imaging conditions. Point defects observed on as-cleaved surfaces result from bulk impurities and adsorption from the residual gas.