Absolute atomic-scale measurements of the Gibbsian interfacial excess of solute at internal interfaces

A method consistent with the Gibbs' formalism is presented for measuring the Gibbsian interfacial excess of solute ({Γ}) at an internal interface using atom-probe field-ion microscopy (APFIM). The values of {Γ} are measured directly, that is, without deconvolution procedures. The relationships between {Γ} and the thermodynamic-state variables of an internal interface are studied using the techniques of APFIM and transmission electron microscopy (TEM). Examples are given of the application of APFIM-TEM to the measurement of {Γ} at grain boundaries in an Fe(Si) alloy.