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 (U HV) NC-AFM, the atomic resolution images can be obtained, as the capil lary forces between the cantilever tip and the sample are eliminated. A UHV NC-AFM with a unique frequency modulation (FM) technique has bee n developed. We have obtained atomic resolution images of the Si(111) 7x7, Si(100) 2x1 structures and oxygen adsorption Si(111)7x7 surface a long with the scanning tunneling microscope (STM) images. Using a simi lar technology, a UHV scanning Kelvin probe microscope (SKPM) utilizin g the gradient of electrostatic force has also been developed. In the SKPM it is possible to simultaneously observe the contact potential di fference (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.