Frequency Response of Carbon Nanotube Probes during Tapping Mode of Atomic Force Microscopy

The dynamic behaviors of carbon nanotube probes applied in Atomic Force Microscope measurement are of interest in advanced nanoscalar topography. In this paper, we developed the characteristic equations and applied the model analysis to solve the eigenvalues of the microcantilever and the carbon nanotube. The eigenvalues were then used in the tapping mode system to predict the frequency responses against the tip-sample separations. It was found that the frequency drop steeply if the separation was less than certain distances. This instability of frequency is deduced from the jump of microcantilever or the jump of the carbon nanotube. Various lengths and binding angles of the carbon nanotube were considered, and the results indicated that the binding angle dominated the frequency responses and jumps.

Thermal Transport Properties of Various Thin Films for MEMS Applications

The thermal properties of thin films, such as thermal conductivity and diffusivity, are important in design and analysis of MEMS (micro electro mechanical systems), particularly in microscale thermal systems and high-power electronic/optoelectronic devices. In the present study, the thermal conductivity and diffusivity of a variety of thin film materials, which are commonly used in MEMS applications, are measured. The samples include Au, Sn, Mo, Al/Ti alloy, AlN, and SiC. The Au sample is deposited by the e-beam evaporation technique while the rest of the metallic samples are deposited by sputtering processes. The AlN and SiC films are also prepared by sputtering processes. In the experiment, the thermal diffusivities of metallic thin films are measured by two independent methods — the AC calorimetric method and photothermal mirage technique. The thermal conductivities of dielectric thin films are measured by the 3 omega technique. The results show that the thermal transport properties of some of the films are significantly smaller than those of the same material in bulk form. Especially, the AlN and SiC thin films exhibit pronounced thermal conductivity reduction because of the size effect. The electrical conductivities of the metallic thin films are measured as well. The results for Au and Sn are consistent with the thermal conductivity, confirming the Wiedmann-Franz law. However, Al/Ti and Mo thin films show considerable deviation from the law. The results are analyzed based on the XRD (X-Ray diffraction) and AFM (Atomic Force Microscope) measurement.