sentences:  By applying an alternating bias to the metal-coated probe, carriers are alternately accumulated and depleted within the semiconductor’s surface layers, changing the tip-sample capacitance.The magnitude of this change in capacitance with the applied voltage gives information about the concentration of carriers (SCM amplitude data), whereas the difference in phase between the capacitance change and the applied, alternating bias carries information about the sign of the charge carriers (SCM phase data).Because SCM functions even through an insulating layer, a finite conductivity is not required to measure the electrical properties.