Cantilevers and tips for atomic force microscopy

The key component of the atomic force microscope (AFM) is a cantilever with a tip. The tip must be sharp enough to record with high lateral resolution the topography. The cantilever must also have the appropriate compliance and resonant frequency for the type of operation selected, which can be either a contact or a noncontact mode of operation. The requirement for a low spring constant (less than 1 N/m) and a high resonant frequency (greater than 10 kHz) led to silicon micromachining techniques early on in the development of the AFM. Silicon micromachining is a technology by which a silicon wafer is processed through a series of deposition, photolithography, and etching steps to produce a mechanical structure with dimensional tolerances in the order of 1 μm. The use of silicon micromachining techniques has benefited the AFM in several aspects: (1) sharper tips can be manufactured with micromachining techniques than with alternative electrochemical etching techniques, as used for scanning tunneling microscopy tips; (2) batch fabrication simultaneously of thousands of cantilevers guarantees a high degree of reproducibility in the mechanical properties of the cantilevers; and (3) micromachined cantilevers are inexpensive.