A complete procedure for the preparation of clean surfaces of especially hard ionic crystals by ultrahigh vacuum (UHV) cleavage is given and exemplified by the preparation of the (001) surface of single MgO crystals. All important tools that are needed for the preparation are explained in detail. We present a device that allows precise cleavages in UHV and show how it can be easily integrated into an existing UHV system equipped with a linear manipulator. Cleaving ionic crystals produces charges on and below the fresh surface, which strongly hamper experiments like dynamic scanning force microscopy. In the case of MgO imaging is mostly impossible right after cleavage. We show that it is sufficient to anneal MgO crystals at temperatures higher than in order to reduce a large part of the charges. For the annealing, an UHV oven is used that can be annealed up to without leaving the upper pressure region. Our techniques can be used in principle also for softer ionic crystals such as KBr, KCl, NaCl, and for other hard materials such as semiconducting ZnO.
REFERENCES
In preparation for Proceedings of NC-AFM 2005 in Nanotechnology.
We noticed that voltages of less than must be frequently applied in order to minimize electrostatic forces, however, sometimes also voltages of more than . During scanning of the MgO(001) surface, it happens very often that the tip picks up charges while contacting the surface. If the tip changes the sign of its potential, the sign of the bias voltage for minimization electrostatic forces is also changed. However, we believe that the tip is not the dominant contributor to the large electrostatic forces, as already noticed in Ref. 11.
