The forces between two molecularly smooth mica surfaces are measured in monovalent and divalent cations electrolyte solutions by a surface force apparatus （SFA）. The properties of K＋, Na＋, and Mg2＋ between molecularly smooth mica surfaces are investigated. The Derjagui-Landau- Verwey-Overbeek （DLVO） force and the hydration force are detected in the experiment. The results show that in lower concentrations of a monovalent electrolyte solution （about 10-4 mol/L）, the force curves are completely in good agreement with those computed by the DLVO theory. However, additional short-range repulsive forces which deviate from the DLVO theory are observed when the concentrations of cations are above the critical bulk concentration, which is different for each electrolyte. The results show the properties of these cations on both the screening effect adsorbed on the mica surface and the hydration in solution. From the results, the interaction energy between two hydrated ions of potassium or sodium can also be estimated.
In order to improve the measurement precision and increase the reliability of the femtosecond laser transient thermoreflectance system, the relative optical path difference between pump and probe beams is prolonged, which can improve the fitting accuracy of the experimental data to the theoretical model. A modified experimental setup is devised with the pump path intercalated a moving stage identical to the one in the probe path, which extends the optical path difference of the probe beam relative to the pump beam from 4 to 8 ns. The measured results indicate that the uncertainty from the misalignment and divergence of both beams can be ignored when the last 4 ns experimental data are connected with those of the first 4 ns smoothly. The as-obtained thermal conductance of AI/Si and Cr/Si interfaces agrees well with the reported experimental values, which verifies the reliability of this modified version of this measurement.
