Fast nanoscale modification of Ag(111) using a scanning tunneling microscope

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Abstract
Epitaxial Ag(111) films have been grown on mica. They exhibit flat terraces of a few 100 nm diameter, suitable for nanoscale modification with the scanning tunneling microscope(STM). Under ambient conditions, surface modifications of a few nanometers diameter were produced by raising the bias from below 1 V to a bias between 3 and 7 V for less than 50 ns. The steady‐state current could be limited to 2 pA. This means that the modification is initiated while only a few electrons pass the tunneling junction, indicating that it is not a current effect. At positive sample bias, usually holes are formed, while at negative bias hillocks occur. In the case of hole formation, the current does not change significantly on a time scale of 10 μs. When hillocks are formed, the current may rise after the application of the voltage pulse. It was limited to 4 nA by the external circuitry and remains saturated until the tip is withdrawn on a time scale of milliseconds, i.e., the characteristic for the feedback loop control. Also in this case the modification is not caused by a current effect, since the limiting current would still allow nondestructive STM imaging. It is concluded that the modifications are caused by field evaporation of sample and tip material, respectively.