Influence of Emitter Temperature and Ionization Potentials of Emitter Atoms on Charge of Evaporated Ions

摘要

The influence of emitter temperature and ionization potentials of emitter atoms on the process of field evaporation was studied by means of time-of flight atom probe and field emission microscopy. Ni was select for the experiments of the investigation of the influence of emitter temperature T on charge of evaporated ions. This material is enough good studied by field emission methods. For the study of the influence of ionization potentials on the evaporation process alloy NiCr (20% Cr, 80% Ni) and carbide W were selected. The alloys NiCr contain the components with the values of ionization potentials I{sub}n, which negligible differ from each other (I{sub}1 = 7.63 eV for Ni and I{sub}1 = 6.76 eV for Cr). In the case of carbide W the values I{sub}n of W and C atoms have marked difference (I{sub}1 = 8.67 eV for W and I{sub}1 = 11.36 eV). The mass-spectrums were obtained at various emitter temperatures T from 80 K to the temperatures near to melting point. The increase of the emitter T does not influence upon charge of evaporated ions. At constant evaporation field F{sub}(ev) Ni was evaporated as Ni{sup}+2 at the any T from 80 K to 1000 K. The small decrease F{sub}(ev) at room T leads to appearance of the small peak of single charged ions Ni{sup}+, at the T = 1200 K and remarkable decrease F{sub}(ev) only large peak Ni{sup}+ is observed. Consequently a reduction of ion charge occurs in consequence of corresponding to reductions of value evaporation field F{sub}(ev) necessary as a rule at increase T. If a value of evaporation field is not changed, is not changed and charge of the ions under any change the temperature. In the event of field evaporation at high T and comparatively low F{sub}(ev) energy of activation of evaporation Q{sub}n is not a zero and using the known expressions for determination F{sub}(ev) illegitimate. The new method of estimation of values F{sub}(ev) is offered. The method is founded on calculation of values Q{sub}n and determinations a cross point of graphs Q{sub}n = f(F) for ions of different charges of different elements.