Interaction of hydrogen with a nickel surface in the low-temperature field evaporation

The process of field evaporation of nickel in hydrogen atmosphere under pressure 10−6 Pa at 20 K was investigated using a high resolution pulsed-laser time-of-flight atom-probe field ion microscope. Under these conditions, the ions of H+, H2+ and H3+ were detected as well as those of Ni2+, Ni+ and NiHx+ (x=1 -3). On the basis of both: experimentally determined energy distribution of ions and ab initio calculations in the density-functional theory (DFT) for Ni-H, including external homogeneous electrostatic fields, we can state that hydrogen atoms are bound to the nickel surface in the presence of the electrostatic field of strength about 30 V/nm. These complex ions are formed within two topmost layers at the nickel surface in the high electric field applied.