Page 103 - Materials Chemistry, Second Edition
P. 103

90                                              2 Solid-State Chemistry


                           a
















                                                 20μ
                  b                            c
                                               40.0
                                         50.0 nm
                                               Height (nm)  0

                                         25.0 nm
                                              −40.0
                                                 0    0.25  0.50  0.75  1.00
                                200 nm                      mm
                                         0.0 nm
                                                 20

                   100.002  nm                  Load (mN)  15
                                                 10
                                            0.8
                                                  5
                    0.2                 0.6
                       0.4           0.4          0
                                                   0    5   10   15  20
                          0.6     0.2                   Displacement (nm)
                                mm
                              0.8
           Figure 2.58. Examples of indentation processes to determine surface hardness. Shown are (a) Vickers
           indentation on a SiC–BN composite, (b) atomic force microscope images of the nanoindentation of a
           silver nanowire, and (c) height profile and load–displacement curve for an indent on the nanowire.
           Reproduced with permission from Nano Lett. 2003, 3(11), 1495. Copyright 2003 American Chemical
           Society.


           layers, and weak interactions among molecules in neighboring layers (e.g., graph-
           ite), a cleavage plane (c.f. slip planes, discussed earlier) is created where little force
           is needed to separate the crystal into two units (Figure 2.59a, b). Since the cleavage
           planes are parallel to crystal faces, the fragments formed upon cleavage will retain
           the symmetry exhibited by the bulk crystal. Whereas cleavage describes the forma-
           tion of a smooth piece of the original crystal when subjected to an external stress,
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