Observation of silicon surfaces using ultrahigh vacuum noncontact atomic force microscope

The advantage of noncontact atomic force microscope (NC-AFM) is, that the interaction between the tip and the sample is reduced as compared with the other AFM techniques. Furthermore, in the ultrahigh vacuum (UHV) NC-AFM, the atomic resolution images can be obtained, as the capillary forces between the cantilever tip and the sample are eliminated. A UHV NC-AFM with a unique frequency modulation (FM) technique has been developed. We have obtained atomic resolution images of the Si(111) 7x7, Si(100) 2x1 structures and oxygen adsorption Si(111)7x7 surface along with the scanning tunneling microscope (STM) images. Using a similar technology, a UHV scanning Kelvin probe microscope (SKPM) utilizing the gradient of electrostatic force has also been developed. In the SKPM it is possible to simultaneously observe the contact potential difference (CPD) and the NC-AFM topographic images. The CPD image of Si(111) surface with deposited Au clearly shows the potential difference between the 7x7 and the 5x2 phases. A high resolution image of the Ag-deposited Si(111) 7x7 surface is obtained by simultaneous observation of the CPD and the NC-AFM topographic images.