Ultrahigh vacuum scanning force scanning tunneling microscope: Application to high-resolution imaging of Si(111)7x7

We present a combined scanning force/scanning tunneling microscope (SFM/STM) operating in ultrahigh vacuum using a fiber-optic laser interferometer to detect the lever deflection. As force microscope it operates in ac and de mode with commercial (Si, Si3N4) or individually made (W) cantilevers. Samples and cantilevers can be inserted without breaking the vacuum using a load-lock system. The force sensor includes a novel three-dimensional micropositioner based on the piezoelectric slider principle. The system includes standard surface analytical techniques (low-energy electron diffraction/Auger, prepared for x-ray photoelectron spectroscopy) and is equipped for mass spectroscopic detection of reaction products from catalytic surfaces at elevated temperature. Tips are cleaned in situ using electron bombardment. By using tungsten cantilevers with a high spring constant (k=100-200 N/m), it is possible to switch directly between STM and SFM operation. As reference surface we have used the Si(111)7X7 reconstruction, prepared by in situ flashing to 1150 degrees C, which is imaged at atomic resolution using STM as well as ac-mode SFM. (C) 1996 American Institute of Physics.