## 2 Materials and Methods  
The activation process of the NEG films was investigated by in situ SRPES, performed at the photoelectron spectroscopy station (4B9B beamline) in the Beijing Synchrotron Radiation Facility, equipped with a SCIENTA R4000 analyzer. The synchrotron radiation light is monochromated by four high-resolution gratings and equipped with a hemispherical energy analyzer. The light source covers photon energies in the range from 10 eV to 1100 eV. During measurements, the base pressure was better than \(3\times 10^{-8}\) Pa. The photon energy was calibrated by measuring the 4f XPS peak of a clean sheet of polycrystalline gold foil that was electrically connected to the sample. The samples were heated in a heating treatment chamber and transferred to a SRPES analysis chamber through a transfer chamber under vacuum. The background vacuum of all chambers was around \(3\times 10^{-8}\) Pa.  
The Zr, ZrVHf and TiZrV films were deposited on oxygen-free electrolytic (OFE) copper substrates by direct current (DC) magnetron sputtering. The cathode voltage and current were approximately 300 V and 0.25 A, respectively. The working gas (Krypton) pressure was approximately 1.5 Pa. The magnetic field was kept at approximately 200 Gauss. The duration of deposition was about 11 h. After deposition, the NEG films were intentionally exposed in the air before mounting into the load lock chamber. The NEG films were annealed in the heating treatment chamber at a pre-set temperature measured by an infrared thermometer. After annealing, the NEG films were transferred to the in situ SRPES analysis chamber. The SRPES spectra were acquired at a photon energy of 700 eV. A series of core level SRPES spectra (O 1s, C 1s, Ti 2p, V 2p, Zr 3d and Hf 4f) were acquired at room temperature after degassing the NEG films at 80 \({}^{\circ}\)C for 6 h, and heating at 120 \({}^{\circ}\)C, 180 \({}^{\circ}\)C, 200 \({}^{\circ}\)C, 250 \({}^{\circ}\)C and 300 \({}^{\circ}\)C for 0.5 h, respectively, under UHV conditions. The spectra fitting was done using a Gaussian-Lorentzian line shape with XPSPEAKS developed by [PERSON] after having performed the Shirley background corrections.  
Rutherford back-scattering (RBS)/channeling measurements were performed on a collimated 2.0-MeV He\({}^{+}\) beam produced by 5 SDH-2 Pelletron at Peking University. The accelerator provides a He\({}^{+}\) beam. The sample was mounted on a high precision (0.01\({}^{\circ}\)) three-axis goniometer in a vacuum chamber, so that the orientation of this sample relative to the He\({}^{+}\) beam could be precisely controlled. A detector coupled to a multichannel analyzer was located about 7.5 cm from the sample. The backscattered particles were accepted by an Au-Si barrier detector. The detection angle was 160\({}^{\circ}\) and its energy resolution was about 18 keV. The size of the crystallites was investigated by X-ray diffraction (XRD) (Bruker D8 Advance) on the NEG films. The X-ray source was a copper anode with a wavelength of 0.1540 nm. A diffractometer was used in a \(\theta-20\) mode, 20 varying from 20\({}^{\circ}\) to 100\({}^{\circ}\) in steps of 0.02\({}^{\circ}\)/sec. Under the assumption of a homogeneous single phase and of roughly equiaxed crystal grains, the Scherrer formula \(\Delta(20)=0.88\lambda/(\omega\cos\theta)\) was applied to determine the average dimension \(\omega\) of the crystallites, where \(\lambda\) is the source wavelength 0.154 nm, 20 is the measured angle in radians and \(\Delta(20)\) is the full width at half-maximum in radians.