Temperature dependence of mechanical stiffness and dissipation in ultrananocrystalline diamond resonators

We have studied the mechanical softening and dissipation of ultrananocrystalline diamond (UNCD) resonators with temperature. Resonant excitation and ring down measurements were conducted under ultra high vacuum (UHV) conditions in a decoupled UHV atomic force microscope (AFM) to determine the Young's Modulus and quality factor (Q) in UNCD cantilever structures. The temperature dependence of Young's modulus revealed the characteristic Wachtman's empirical relation. From this measurement the Debye temperature was estimated to be $\sim $ 1460\r{ }K, significantly lower than Debye temperature of 1860\r{ }K for single crystal diamond. The quality factors of different resonators increased as the cantilevers were cooled from 300\r{ }K to 30\r{ }K and with the hydrogen termination of the cantilever surface. The results indicate that surface and bulk defects significantly contribute to the observed dissipation as well as the mechanical softening in UNCD resonators.