Localized Charge Storage in CeO2/Si(111) By Electrostatic Force Microscopy

In this report, the local patterning of charge into CeO2/Si structures by scanning probe microscopy is examined. An electrostatic force microscope (EFM) has been used to write and image localized dots of charge on to double barrier CeO2/Si/CeO2/Si(lll) structures. By applying a large tip bias Vtip = 6 – 10 V and reducing the tip to sample separation to z = 3 – 5 nm for write times of t = 30 – 60 s, arrays of charge dots 60 – 250 nm FWHM have been written. The dependence of dot size and total stored charge on various writing parameters such as tip writing bias, tip to sample separation, and write time is examined. The total stored charge is found to be Q = 5 – 200 e per charge dot. These dots of charge are shown to be stable over periods of time greater than 24 hrs, with an initial charge decay time constant of τ ∼ 9.5 hrs followed by a period of much slower decay with τ > 24 hrs. Charge decay time constants are found to be dependent on the thickness of the lower CeO2 tunneling barrier.