UCLA

Microscopic engineering of material properties is crucial to advancing the technological needs in the age when development is pushing towards the ends of the Moore’s Law. The desire to engineer materials with properties best suited for intended applications has driven development of various modulation methods. Intercalation and the use of van der Waals materials emerged as a versatile property manipulation tool due to their unique atomic structure.

In the first part of this dissertation, we developed a novel platform based on lithium ion batteries with ultrafast optical spectroscopy and electrochemical control in black phosphorus. Our investigation revealed a strong dependence in phonon-ion interactions. The thermal conductivity of black phosphorus is reversibly tunable from 2.45 to 3.86 W�m−1�K−1, 62.67 to 85.80 W�m−1�K−1, and 21.66 to 27.58 W�m−1�K−1 in the three principal directions. The phenomenon is attributed to phonon scattering introduced by intercalation. At the fully discharged state, thermal conductivity is reduced up to six times compared to the pristine crystal.

Next, we modified the intercalation system to achieve reversible complementary doping. We produce a p-type and n-type transistor through lithium ion intercalation and copper zero-valent chemical intercalation. Interestingly, we found that intercalation can suppress the neutral impurity scattering from the environment, leading to enhancement of electron mobility in the system.

We apply these findings in 2D systems to overcome ongoing challenges of multiplexable sensing in gas sensors. Due to the high noise levels in thin film sensors, alternate current analysis is seldom employed. We use bulk tin selenide crystal as sensing material in our sensors. The sensor-analyte interaction was investigated using electrochemical impedance spectroscopy coupled with an equivalent circuit model. We demonstrate that frequency-dependent phase signal signatures can detect methanol and ethanol within 10% accuracy and water vapor within 15% accuracy in gas mixtures.

In addition, we investigated the electrical transport behavior of microshutters though investigation of the electric field effects surrounding the Next-Generation Microshutter Array. We find that that design modification to a bi-electrode design can significantly improve the electrostatic torque actuation, enabling reliable actuation at a reduced voltage difference of 70 V.