Abstract
Atomic force microscopy (AFM) is a newly developed high- resolution microscopy technique, which is capable of measuring nano-scale patterns. In addition, AFM is very useful in nanofabrication, data storage and material analysis in the field of mechanical, chemical and biological engineering. A nano-probe is the most critical component of the AFM, which consists of three parts: a sharp tip, a cantilever beam and a supporting base. The tip must be sharp enough for high resolution of the surface topography. The cantilever beam must have an appropriate spring constant and a resonant frequency for the type of operation selected. The fundamental mechanical parameters in the nano-probe for the AFM are its spring constant, its resonant frequency and the geometry of the probed object. Literature indicates that researchers in the past only considered the small deflection theory when analyzing the physical properties of the nano-probe; the small deflection theory is suitable only when the object being probed does not undergo non-linear geometrical change. However, the application of nano-probe is becoming more and more extensive. The geometric dimensions or physical properties of nano-probe are different from traditional applications, as in cases such as the measuring of the red corpuscle, which needs a probe of smaller size, and the ultra-high resolution topography, which requires higher applied force. Non-linear geometry will be involved; therefore, the small deflection theory will be no longer suitable. Simulation results indicate that the large deflection theory proposed in this investigation is more feasible than the small deflection theory. When the value of the non-dimensional load reaches 1.875, the large deflection theory will be suitable for the analysis of the nano-probe. The variation between the small deflection theory and the large deflection theory occurs when the non-dimensional load reaches 0.75. Furthermore, when we analyze the nano-probe structure by FEM, we must consider the nonlinear geometry behavior to prevent the inaccuracy of simulation results. Depending on the various applications, the nano-probe structures used in the AFM should meet the following criteria: (1) good tip sharpness with a small radius apex, (2) small spring constant and (3) high resonant frequency. The mechanical parameters of a nano-probe will change with its shape and geometry, which affect the results of measurement. At present, the nano-probe is manufactured by micromachining technology. This method has many advantages, such as mass production, uniform geometry/properties and low cost. This research proposes the design rules of three types of nano-probes, the rectangular-shaped, V-shaped and chamfer V-shaped nano-probes for the AFM using the finite element method. Simulation results indicate that the parameters of V-shaped and chamfer V-shaped nano-probes have irregular effects on their mechanical properties.