Reducing battery materials to nano-scale dimensions may improve battery performance while maintaining the use of
low-cost materials. However, we need better characterization tools with atomic to nano-scale resolution in order to
understand degradation mechanisms and the structural and mechanical changes that occur in these new materials during
battery cycling. To meet this need, we have developed a micro-electromechanical systems (MEMS)-based platform for
performing electrochemical measurements using volatile electrolytes inside a transmission electron microscope (TEM).
This platform uses flip-chip assembly with special alignment features and multiple buried electrode configurations. In
addition to this platform, we have developed an unsealed platform that permits in situ TEM electrochemistry using ionic
liquid electrolytes. As a test of these platform concepts, we have assembled MnO2 nanowires on to the platform using
dielectrophoresis and have examined their electrical and structural changes as a function of lithiation. These results
reveal a large irreversible drop in electronic conductance and the creation of a high degree of lattice disorder following
lithiation of the nanowires. From these initial results, we conclude that the future full development of in situ TEM
characterization tools will enable important mechanistic understanding of Li-ion battery materials.
We have experimentally demonstrated operation of a laterally deformable optical NEMS grating transducer. The device is fabricated in amorphous diamond on a silicon substrate with standard lithographic techniques. For small changes in the spacing of the grating elements, a large change in the optical reflection amplitude is observed. An in-plane motion detection sensitivity of 160 fm/√Hz has been measured, which agrees well with theoretical models. This sensitivity compares favorably to that of any other MEMS transducer. Calculations predict that this sensitivity could be improved by up to two orders of magnitude in future designs. As well as having applications to the field of accelerometers and other inertial sensors, this device could also be used as a modulator for optical switching.
We have developed radio frequency microelectromechanical systems (RF MEMS) capacitive switches using amorphous diamond (a-D) as a novel tunable dielectric with controlled leakage. The switch is fabricated from sputtered and electroplated metals using surface micromachining techniques. The mechanical stress and resistivity of the a-D dielectric are controlled by the parameters of a high-temperature annealing process. These initial devices exhibit a down-state capacitance of 2.6 pF, giving an isolation of better than 18 dB at 18 GHz, and a predicted static power dissipation of 10 nW. This technology is promising for the development of reliable, low power RF MEMS switches.