Figure 2: XPS and LEIS characterization of EDA monolayer layer and diffusion profiles of CO molecules.

(a) XPS spectra of Ni-MOF-74 with post-loaded EDA, before (orange curve) and after being sputtered at 2.5 keV for 28 min (blue curve) and 5 keV for 20 min (dark green curve). (b) LEIS spectra of Ni-MOF-74 with post-loaded EDA, after gentile sputtering with a dose of 3.2 × 10¹⁵ and 2.2 × 10¹⁶ cm⁻² Ne⁺ ions. A slight red shift of the peaks after the second sputtering (10 eV corrected in the Figure), most likely resulting from sample charging due to the ion exposure and insulating nature of the MOFs, has been corrected. (c) Energy barrier for the diffusion of a CO molecule along the 1D channel of Ni-MOF-74. Red circles: all the metal centers are saturated with CO (Supplementary Fig. 7). Black diamonds: all the metal centers are saturated with EDA molecules. The inset in c shows the relaxed atomic position of a CO molecule at the middle of the Ni-MOF-74 channel, where all the adsorption metal sites have been saturated with EDA molecules. The dashed red box shows the CO molecule. Black, red, white, grey and blue spheres represent C, O, H, N and Ni atoms, respectively.