Tham khảo tài liệu 'modern tribology handbook 2010 part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | FIGURE a Topography and b lateral force map of an AgBr thin film deposited on NaCl 001 at room temperature image size pm X pm . The AgBr islands are 1 to 6 monolayers high and partially cover the NaCl substrate. In the lateral force map the AgBr islands are revealed as areas with about ten times higher friction than the corresponding friction observed on the NaCl surface. From Meyer E. Luthi R. Howald L. and Guntherodt . 1995. Friction force microscopy in Forces in Scanning Probe Methods Guntherodt . Ansel-metti D. and E. Meyer Eds. Kluwer Academic Publishers Dordrecht The Netherlands 285. With permission. are still unanswered. Since we focus in this chapter on the analysis of wearless friction on atomically flat surfaces without defects it is reasonable to expect that the origin for the different friction observed on the different materials can be found in the local arrangement of the atoms at the tip-sample contact area. If this expectation holds it should be possible to distinguish areas of different chemical composition by lateral force microscopy. This ability is sometimes called chemical imaging examples for such investigations will be discussed in Section . Another interesting consequence of the above expectation is that the friction should depend on the direction with which the tip profiles the sample surface. This frictional anisotropy is especially easy to verify experimentally if a material exhibiting an asymmetric surface potential is used as a sample as presented in Section . Finally we will see in Section that even small conformational . purely geometrical changes within a surface unit cell give rise to different friction in lateral force maps. Frictional Contrast Caused by Local Changes in the Chemical Composition The ability of the FFM to provide a contrast between surfaces of different chemical composition is not only important for tribologists but also of considerable general interest for users .
