Direct measurement and control of peak tapping forces in atomic force microscopy for improved height measurements

Abstract

The intermittent contact mode, also known as tapping mode, is the most popular AFM measurement technique due to limited force acting on the observed surface and the scanning tip. The tip–sample interaction detection method suffers, however, from the complexity of the forces causing the amplitude and phase change when the tip approaches the surface. In this paper we present the utilization of the time-resolved tip–sample interaction detection technique allowing imaging of the mechanical properties of the sample under the reduced influence of the force applied to the surface on its imaging. Observation of certain phenomena related to the tip–sample contact event, the so-called peak force value, allows us to notice the presence of the feature's height measurement error. Moreover, when the setpoint is changed, the distribution of the peak force map also varies, indicating the altered response of the material to the pressure caused by the tip. Eventually, when the roughness of the surface is calculated, it may vary as well. In this paper, we also propose the utilization of measurement of the maximum force the tip has on the surface during every oscillation cycle as the Z-axis feedback signal in order to improve the measurement technique and reduce the described issue. The experimental data are presented as well.