Reversible local-modification of surface structure on clean Ge(0 0 1) by scanning tunneling microscopy below 80 K
The structure of the clean Ge(0 0 1) surface is locally and reversibly changed between c(4×2) and p(2×2) by controlling the bias voltage of a scanning tunneling microscopy (STM) below 80 K. It shows hysteresis for the direction of the sample bias voltage change. The c(4×2) structure is observed with the sample bias voltage Vb⩽-0.7 V. This structure is maintained at Vb⩽0.7 V with increasing the bias voltage from -0.7 V. When Vb is higher than 0.8 V, the structure changes to p(2×2). This structure is then maintained at Vb⩾-0.6 V with decreasing the bias voltage from +0.8 V. The area of the structure change can be confined in the single dimer row just under the STM tip using a bias voltage pulse. In particular, the minimum transformed length is four dimers along the dimer row in the transformation from p(2×2) to c(4×2). The observed local change of the reconstruction with hysteresis is attributed to the energy transfer process from the tunneling electron to the Ge lattice in the local electric field due to the STM bias voltage. A phenomenological model is proposed for the structure changes. It is based on a cascade inversion of the dimer buckling orientation along the dimer row.