Sufficient condition for reliability measurement of sample geometry by atomic force microscopy

Abstract

A sufficient condition for determining the reliability of geometry measurements using atomic force microscopy for relatively small cantilever tilt angles is proposed. A relationship between the basic geometric parameters of surface roughness, geometric deviations of the probe, the angles of the cantilever and the inclination of the side faces of the probe, as well as the dimensions of the nonlocal point of the probable contact of its side faces with protrusions of roughness has been established. As a sufficient condition for the reliability of geometry measurements using atomic force microscopy, an obvious requirement is accepted. It determines the smallness of the ratio of the sizes of a nonlocal point to the distance between neighboring nonlocal points. Publications in which the measurement of surface nano-geometry of the samples does not indicate the roughness of the sample surface and the probe, the angles at the tip of the probe and the tilt of the cantilever, as well as the best resolution (smallest step) at which the study is carried out, cannot be accepted as reliable, because the results obtained in them are probabilistic in nature. The surface images obtained using atomic force microscopy without proper justification for the resolution (value of the measurement step) represent only a qualitative picture, on the basis of which it makes no sense to carry out any computational manipulations. In order to increase the reliability of measurements of surface geometry using atomic force microscopy, it is necessary to radically increase the accuracy of the manufacture of probes, as well as use probes with the smallest possible angle at the apex. In addition, it is necessary to make changes in the design of the atomic force microscopy. In particular, the automatic rotation of the microscope stage should be designed. It should provide closeness the probe axis direction to the normal to the average plane of the sample. This “integral” angle of rotation of the microscope stage is easily iteratively determined at the stage of preliminary investigation of the geometry of the surface of the sample. In this case, it will be necessary to geometrically increase the length of the cantilever so that the base extends beyond the limits of the sample.