[en] Experimental devices have been developed for examining the work function (WF) change - by means of Kelvin probe (KP) - of metallic and ceramic materials due to ion irradiation in low energy (500 eV) or high energy (MeV) ranges. The charging effect on the performance of the KP was efficiently reduced using appropriate shielding. An error deduction method has been suggested to effectively eliminate the influence due to charging by introducing a reference sample. Polycrystalline Ni samples, each of 99.95% purity, were used in the research. The experiments were performed using He⁺ and H⁺ ion beams of 1 MeV, 2 x 10¹⁶ ions/m²/s under a pressure of 1 x 10^-4 Pa, and a He⁺ beam of 500 eV, 2 x 10¹⁷ ions/m²/s under a pressure of about 1 x 10^-2 Pa. The results indicated that the irradiation of 500 eV He⁺ resulted in a WF decrease, then an increase until saturation, while 1 MeV ions only induced a WF decrease, then saturation. A surface model of a loosely bound adsorbed layer plus a native oxide layer on metals is presented to explain the observed phenomena. The nuclear stopping is responsible for the results in the case of 500 eV He⁺ irradiation that is powerful enough to sputter away the whole overlayer from the bulk surface. In the MeV case, the electronic stopping plays a decisive role, which allows the topmost adsorbed layer to be partially removed by He⁺ and H⁺ of 1 MeV. The application of this technique to monitoring/characterisation of material surfaces in the field of nuclear engineering is to be discussed. (authors)