AFM-in-SEM
FMM image. Acquired data can be viewed in 3D, where the topography together with the mechanical properties improves insight into the sur- face structure (Figure 5b). On the
other hand,
force-distance curves (or F/z spectroscopy) provide a quan- titative
estimation of the
local mechanical property by measuring the vertical force between the AFM tip and the surface, and the sample dis- placement. It is used for many purposes
including sample
Figure 5: Mechanical properties of the two-component PS and LDPE sample. (a) Sample region showing topography, energy dissipation, and FMM (PDM) image. (b) 3D correlative view showing topography combined with PDM. (c) Differ- ence in slope of force-distance curves demonstrates differences in relative hardness of the PS and LDPE components.
stiffness analysis, detailed surface-tip force progress, and local elasticity/plasticity deter- mination. Te curves (and the slopes) in Figure 5c show a clear difference between the components of the polymer blend with the established material hardness of 2 GPa for PS and 0.3 GPa for LDPE. Te advantages of com-
bining related techniques into one tool are further demon- strated on the nanoindentation of M3 class 2 high-speed steel, which is used in the automo- tive industry [16]. In general, nanoindentation
represents
Figure 6: Mechanical properties of an M3 class 2 high speed steel. (a) SE image with circles highlighting individual indents and BSE image indicating the material composition. (b) AFM topography image with profile lines detailed in the depth profile (c) and (d) 3D AFM view of indentation in the matrix. The arrows in (c) and (d) highlight the same area.
whose topography is best measured using non-contact mode. In FMM, the AFM tip is scanned in contact with the sam- ple, and an additional driving signal is applied to vibrate the tip, which is converted to a signal used for analysis. Either change in amplitude (data not shown) or phase shiſt (called phase detection microscopy [PDM]) is used to generate the
44
an extremely versatile tech- nique to determine material mechanical properties at the nanoscale such as elastic mod- ulus, hardness values, fracture toughness, or creep and yield stress. In this case, the AFM- in-SEM approach was further extended by adding a nanoin- denter [17] to the scan head. Tis hybrid technique enables sample phase identification, precise indentation targeting, and topographical analysis all in one measurement. Figure 6 shows the etched
steel nanoindentation analysis results. Te SEM images (Fig- ure 6a) showed a wide range
of separate phases of small size (MnS grain, carbide M6C, and
martensitic matrix), that were nanoindented using a force of 15 mN. Te AFM scans in Figure 6b revealed that each phase reacted differently to the acting force. Te soſtest material is the MnS grain, followed by a matrix, and the hardest is the M6
C part
of the composite, as depicted in the height profile in Figure 6c.
www.microscopy-today.com • 2020 May
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