AFM Cantilever Design for Multimode Q Control: Arbitrary Placement of Higher Order Modes

In the fast growing field of multifrequency atomic force microscopy (AFM), the benefits of using higher order modes have been extensively reported on. However, higher modes of AFM cantilevers are difficult to instrument and Q control is challenging owing to their high-frequency nature. At these high frequencies, the latencies in the computations and analog conversions of digital signal processing platforms become significant and limit the effective bandwidth of digital feedback controller implementations. To address this issue, this article presents a novel cantilever design for which the first five modes are placed within a 200-kHz bandwidth. The proposed cantilever is designed using a structural optimization routine. The close spacing and low mechanical bandwidth of the resulting cantilever allows for the implementation of Q controllers for all five modes using a standard field programmable gate array (FPGA) development board for bimodal AFM and imaging on higher order modes.