The Energy-Dispersive-X-ray-based permeation and oxidation test has been further developed by an improved theoretical analysis, in which chemical potential gradients rather than concentration gradients are employed. The developed test is able to characterize diffusion kinetics in diffusion barriers at the nanometer scale. The Cu flux coefficient in (Cu, Ni)(3)Sn intermetallic compound nanolayers was determined from the test to be 8.48 x 10(-15) mol.(m.s.J/mol)(-1) exp(-52.3 kJ.mol(-1)/RT) in a temperature range of 250 degrees C-400 degrees C. (C) 2009 Elsevier B.V. All rights reserved.