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Tham khảo tài liệu 'new tribological ways part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 404 New Tribological Ways Flateral 2 klat X Slat Fig. 1. A typical force-distance curve obtained by AFM. Fig. 2. Scanning angle selection for AFM tip a The cantilever torsion at a scanning mode of contact and scanning angle of 90o b reproduced from Leggett et al. 2005 A typicaly friction loop c Friction versus applied load curves acquired by AFM reproduced from Song et al. 2008. where klat is the lateral spring constant Slat is the lateral sensitivity of the photodiode AV is the torsion signal. However the calibration of klat is still a challenge and therefore the friction force obtained from the friction loops Fig. 2c is generally expressed in a raw voltage form in the current studies. By acquiring friction at different applied loads the friction Ff -applied load Fn curves can be plotted which is described by equation Schwarz et al. 1995 Ff aFn C2Fn C3 3 where C1-C3 are the material-dependent constants and the index m 0 m 1 depends on the asperity geometry Li et al 1999 . However plenty of studies show that a linear dependence is often observed equation 3 is therefore simplified to the following form by assuming C1 0. Ff ụFn Fo 4 where ụ is friction coefficient and Fo is assumed to be related with the adhesive force between AFM tip and the surface Brewer et al. 2001 Foster et al. 2006 Li et al 1999 Ou et al. 2009 Song et al. 2006 Song et al. 2008 Zhao et al. 2009 . Construction of Various Self-assembled Films and Their Application as Lubricant Coatings 405 The CFM is distinguished from the usual AFM technique by its probe tip which is chemically immobilized with certain functional molecules Fig. 3a . This new SFM technique has been used to probe adhesion and friction forces between distinct chemical groups in organic and aqueous solvents. As shown in Fig. 3b covalent modification of the Si3N4 tip with thiols and reactive silanes can be realized by different approaches Noy et al. 1997 . Fig. 3. Schematic drawing of the CFM setup. The inset illustrates the .
