A complete description of CD-AFM principles and operation is outside the scope of this paper. However, the basic distinction between CD-AFM and conventional AFM is that CD-AFMs use two-axis (lateral and vertical) sensing of the tip–sample interaction and position control. In conventional AFM, the sensing of the tip–sample interaction is essentially limited to the vertical axis. When the two-axis tip control algorithm is combined with flared tips, it is possible to scan near-vertical and even re-entrant sidewalls.