Electrochemical imaging of contact boundary by using electron-beam addressing of a virtual cathode display

A scanning electrochemical microscope (SECM) enables surface measurements of electrical properties of various wet samples including living cells, although its probe cannot reach the interface where the samples contact a substrate. This paper reports our innovative method for electrochemical imaging of the contact boundary in wet samples in water solution. We used electron-beam (EB) addressing of a virtual cathode (VC) for an inverted electron beam lithography system, and we carried out imaging of the contact boundaries which cannot be approached by conventional scanning probe microscopes. This VC was formed on the surface of a 100-nm thick silicon nitride (SiN) membrane by low-energy EB irradiation from the lower side of the membrane. The VC appeared at the contact boundary of the wet samples and the membrane; therefore the VC virtually worked at the boundary as the scanning probe of the SECM to observe the wet contact interface. We acquired topographic and electrochemical images of micro polystyrene spheres and a DPPC/TR-DPPE supported lipid bilayer by measuring the probe current in the sample interface. The imaging results suggested spatial resolutions of-180 nm width and-90 nm depth in a topographical image could be captured using this VC-SECM system.