No abstract

Layered transition metal dichalcogenides have distinct physicochemical properties at their edge-terminations. The production of an abundant density of edge structures is, however, impeded by the excess surface energy of edges compared to basal planes and would benefit from insight into the atomic growth mechanisms. Here, we show that edge-terminated MoS nanostructures can form during sulfidation of MoO nanocrystals by using in situ transmission electron microscopy (TEM). Time-resolved TEM image series reveal that the MoO surface can sulfide by inward progression of MoO(20-2):MoS(002) interfaces resulting in upright-oriented and edge-exposing MoS sheets. This topotactic growth is rationalized in interplay with density functional theory calculations by successive O-S exchange and Mo sublattice restructuring steps. The analysis shows that e-MoS formation is energetically favorable at MoO(110) surfaces and provides a necessary requirement for the propensity of a specific MoO surface termination to form edge-terminated MoS. Thus, the present findings should benefit the rational development of transition metal dichalcogenide nanomaterials with abundant edge-terminations.

We describe the fabrication and characterization of a significantly improved version of a microelectromechanical system-based PZT/PZT thick film bimorph vibration energy harvester with an integrated silicon proof mass; the harvester is fabricated in a fully monolithic process. The main advantage of bimorph vibration energy harvesters is that strain energy is not lost in mechanical support materials since only Pb(Zr x Ti 1−x)O 3 (PZT) is strained; as a result, the effective system coupling coefficient is increased, and thus a potential for significantly higher output power is released. In addition, when the two layers are connected in series, the output voltage is increased, and as a result the relative power loss in the necessary rectifying circuit is reduced. We describe an improved process scheme for the energy harvester, which resulted in a robust fabrication process with a record high fabrication yield of 98%. The robust fabrication process allowed a high pressure treatment of the screen printed PZT thick films prior to sintering. The high pressure treatment improved the PZT thick film performance and increased the harvester power output to 37.1 μW at 1 g root mean square acceleration. We also characterize the harvester performance when only one of the PZT layers is used while the other is left open or short circuit.

Abstract-The conventional method of modeling CMUTs use the isotropic plate equation to calculate the deflection, leading to deviations from FEM simulations including anisotropic effects of around 10% in center deflection. In this paper, the deflection is found for square plates using the full anisotropic plate equation and the Galerkin method. Utilizing the symmetry of the silicon crystal, a compact and accurate expression for the deflection can be obtained. The deviation from FEM in center deflection is <0.1%. The deflection was measured on fabricated CMUTs using a white light interferometer. Fitting the anisotropic calculated deflection to the measurement a deviation of 0.5-1.5% is seen for the fitted values. Finally it was also measured how the device behaved under increasing bias voltage and it is observed that the model including anisotropic effects is within the uncertainty interval of the measurements.