FIGURE 4-38 Left: The frictional coefficient is defined as the frictional force divided by the normal force. Right: A frictional loop is measured by monitoring the lateral signal as it goes from left to right and right to left.

The frictional coefficient of a probe moving over a surface is defined as the loading force divided by the horizontal force:

Because an AFM can measure the vertical and horizontal force (see Section 4.3.1), it is possible to measure frictional coeffi cients at the nanoscale. A frictional loop curve is first measured (see Figure 4-39); then the coefficients of friction which is proportional to W may be calculated¹³. Calculation of the frictional coefficient from a frictional loop requires detailed knowledge of the parameters associated with the geometry of the AFM scanner from which the measurements are derived.

FIGURE 4-39 Left: The frictional coefficient is defined as the frictional force divided by the normal force. Right: A frictional loop is measured by monitoring the lateral signal as it goes from left to right and right to left.

By placing a small temperature sensing device at the end of an AFM probe it is possible to make a number of thermal measurements of a surface. Th e two primary types of probes used in an AFM for making thermal measurements are the thermocouple and the resistive probe, shown in Figure 4-40.