The tip and the conducting substrate in tunneling microscopy form a ca
pacitor. Similarly, in electrochemistry of polarized electrode the met
al and the electrolyte form a double layer capacitor. It is shown that
the energetics of these two capacitors, namely the surface tension of
the substrate and of the polarized electrode, respectively, are gover
ned by the same relationship, the Gibbs-Lippmann equation. The implica
tions of this finding for STM imaging are discussed.