Microwave Resonant Sensors and Nanomechanical Tunable Two-Level Systems
M. Selim Hanay
Abstract: This talk will entail two technologies we develop in our lab: 1) Resonant sensors based on nanomechanical and microwave devices for sensing single molecules, nanoparticles and cells. 2) Nanomechanical buckling devices as a platform for electrically tunable two-level systems.
Nanomechanical devices can be used as exquisite sensors for mass, force and charge detection. A popular trend in recent years has been the use of multiple modes of nanomechanical sensors. When multiple modes of a resonant sensor are tracked, shape information about analytes can be obtained. In the context of micro and nano-mechanical sensors, multimode measurements provide the size and shape information —as well as the mass— of an analyte. By processing the spatial information, an image can be reconstructed . This technique, Inertial Imaging, transforms the capabilities of nanomechanical sensors to a new level: the combined knowledge of molecular mass, size and shape of the analyte can enable previously unattainable information for biomolecular analytics. These principles, originally developed for nanomechanical sensors, can be extended to electromagnetic resonant sensing as well. By embedding microfluidic channels between the signal line and ground plane of a microstripline resonator, the excess electrical volume and position of microdoplets and single cells have been measured . Sensing with higher order modes in this platform can yield further spatial properties of analytes, eventually enabling a construction of an image for cells at the microwave band.
Buckling is an important resource for bistability, sensing and shape reconfiguration at the micro- and nano-scale. Although different approaches have been developed to access buckling, such as the use of pre-stressed beams or thermal heating, very little attention was paid so far to dynamically and precisely control the critical bifurcation parameter —the compressive stress on the beam. On-demand generation of compressive stress on individually addressable microstructures is especially critical for morphologically reconfigurable devices. Here, we develop an all-electrostatic architecture to control the compressive force, as well as the direction and amount of buckling, without significant heat generation on micro/nano structures. With this architecture, we demonstrated fundamental aspects of device function and dynamics. By applying voltages at digital electronics standards, we controlled the direction of buckling readily. Lateral deflections as large as 12% of the beam length were achieved, which provides a better understanding about the dynamics of large deformation nano-buckling. By modulating the compressive stress and lateral electrostatic force acting on the beam, we tuned the potential energy barrier between the post-bifurcation stable states and characterized snap-through transitions between these states. The proposed architecture opens avenues for further studies that enable parametric oscillation applications, cell detection applications and multiplexed shape-shifting devices.