Piezoresistive cantilevers for force measurements

The Atomic Force Microscope (AFM) has been used extensively for imaging surface topography with atomic resolution. It essentially detects changes in surface topography through bending of a cantilever beam. In addition to its imaging capabilities, an AFM cantilever is also an effective instrument for measuring very small forces. Force measurements can provide important information for studying various physical phenomena. These include physical forces as well as biological processes.; The deflection of an AFM cantilever can be detected using several different techniques. The piezoresistive technique, which uses cantilevers with integrated piezoresistive sensors, has become an attractive alternative to the more popular optical deflection technique because of its ease of use and scalability. This work focuses on the development of piezoresistive cantilevers as force sensors. Issues relevant to the design, optimization, fabrication, and operation of these devices are discussed.; Several design and optimization techniques are used to show that piezoresistive cantilevers can achieve resolution comparable to that of optical cantilevers. Ultra-thin n-type piezoresistive cantilevers are fabricated and characterized to show significant performance improvements over previous work. Noise characteristics of n-type piezoresistors and how they relate to sensor performance are also discussed.; Since analytical models are only available for cantilevers with simple geometry, a simplified finite element technique is used to design and optimize a two-axis cantilever structure. Using this technique, the two-axis cantilever can be optimized for specific applications,; Finally, this two-axis cantilever device is used to measure the adhesion properties of isolated gecko setae. Results from this study revealed some interesting characteristics of the setae adhesion process, and provided support to the adhesion by van der Waals hypothesis.; In addition to providing quantitative measurements on the adhesive forces of setae, experiments performed in this work also contributed to the overall understanding of how the setae work. All of this information can provide inspirations for the design of artificial adhesive structures.