Surface wettability is an important property of solid/liquid interfaces. Recently, the control of contact angle (CA) has been used to drive liquid droplets in microor nanosize channels on biochemical and environmental sensing chips, where a faster CA transition rate is desirable for the prompt control of liquid movement. We studied the CA between water droplet and zinc oxide (ZnO) nanotips grown by metalorganic chemical vapor deposition (MOCVD). ZnO was grown as epitaxial films on r-plane sapphire, or as vertically aligned nanotips on various substrates, including silicon, c-plane sapphire, and glass. It is demonstrated that by using ultraviolet (UV) illumination and oxygen annealing, the CA on ZnO nanotips can be changed between 0°and 130°, whereas the CA on the ZnO films only varies between 37°and 100°. The fast transition rates also have been observed.

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When the piezoelectric stiffening matrix is added to the mechanical stiffness matrix of a finite element model, its sparse matrix structure is destroyed. A direct consequence of this loss in sparseness is a significant rise in memory and computational time requirements for the model. For weakly coupled piezoelectric materials, the matrix sparseness can be retained by a perturbation method which separates the mechanical eigenvalue solution from its piezoelectric effects. Using this approach, a perturbation and finite element scheme for weakly coupled piezoelectric vibrations in quartz plate resonators has been developed. Finite-element matrix equations were derived specifically for third-overtone thickness-shear, SC-cut quartz plate resonators with electrode platings. High-frequency piezoelectric plate equations were employed in the formulation of the finite element matrix equation. Results from the perturbation method compared well with the direct solution of the piezoelectric finite element equations. This method will result in significant savings in the computer memory and computational time. Resonance and antiresonance frequencies of a certain mode could be calculated easily by using the same eigenpair from the purely mechanical stiffness matrix. Numerical results for straight crested waves in a third overtone SC-cut quartz strip with and without electrodes are presented. The steady-state response to an electrical excitation is calculated.

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Finite element matrix equations employing high frequency, piezoelectric plate equations are derived. The equations may be used for modeling third harmonic overtone of thickness-shear vibrations. A perturbation technique is developed to account for piezoelectric stiffening in the mechanical stiffness matrix. Results from the perturbation method compares well with the direct solution of the piezoelectric finite element equations. The technique will result in significant savings in computer memory and computational time. Numerical results for straight crested waves in a third overtone SC-cut quartz strip with and without electrodes are presented. Steady state response to an electrical excitation is calculated.