Source: Dissertation Abstracts International, Volume: 69-06, Section: B, page: 3789.

Adviser: Udo D. Schwarz.

In this thesis, the ability of atomic force microscopy to achieve virtually drift-free three-dimensional (3D) force mapping with atomic resolution is demonstrated for the first time. This new measurement mode is illustrated with graphite, which has been chosen due to its remarkable qualities as a solid lubricant.

To obtain the level of stability and control necessary to establish this measurement mode, a new home-built low-temperature scanning probe microscope was setup first. The microscope, whose design is presented in the Chaps. 2-4, enables high-resolution experimentation in both scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) modes. A tuning-fork-based Q-plus style sensor is used to allow for flexibility in choosing probe tip materials. The system comprises three vacuum chambers and an on-top helium cryostat with the microscope enclosed in a double set of thermal shields for stability. To keep turn-around times low, tip as well as sample can be exchanged in-situ at low temperatures.

Various examples for the microscope performance are given in Chap. 5. Among other images, STM micrographs of copper(III) at 5 K are shown that feature the atomic lattice superimposed with electronic surface charge waves. Generally, atomic corrugations as low as 1 pm have been routinely resolved. To demonstrate low-temperature NC-AFM operation, atomic-resolution data with a corrugation of 4-5 pm and a noise of below 1 pm is presented for graphite.

The new 3D force mapping mode is discussed and illustrated in Chap. 6. From the recorded 3D data, not only the complete force field over the surface, but also the entire 3D energy landscape were extracted. Subsequently, the lateral forces acting on an atomically sharp tip were derived with picometer resolution showing large areas of very low lateral force on the surface of graphite. These large areas of low lateral force might be the fundamental reason for the very low frictional resistance observed on this material. In addition, the data allowed to determine the exact location of the carbon atoms in NC-AFM images of graphite, a question that is widely being discussed in the literature.