Suspended Microchannel Heater-Thermometer

While numerous cantilever-based metrologies have enabled the precise measurement of structural, physical, and chemical properties by monitoring the resonant behaviors of cantilever probes (Lang et al., Nanotechnol. 13, p. R29, 2002), the application of the same metrologies in liquid solution is prohibitively challenging, mainly because liquid viscosity severely degrades the quality factor of the cantilever resonance. As an entirely different approach to eliminate viscous damping in the cantilever-based metrology in conjunction with liquid solution, suspended microchannel resonators (SMRs) have recently been developed by placing the solution in a microchannel embedded inside a resonator that is surrounded by vacuum (Burg et al., Nature, 446, p.1066, 2007), as shown in Fig. 1. Since the liquid in the resonator does not degrade its resonant behavior, SMRs can weigh single nanoparticles, single bacterial cells and sub-monolayers of adsorbed proteins in water with sub-femtogram resolution (1 Hz bandwidth). Moreover, SMRs may enable high precision size or volume, density, and mass of single nanoparticles by measuring an identical object twice in two background fluids having different mass density (Lee et al., Nano Lett., 10, p. 2537, 2010). The main objective of this research is to further advance the SMR technology. In particular, we will integrate the micro/nanoscale thermal metrology with the SMR to enable the simultaneous measurement of thermal properties, such as the thermal conductivity and specific heat, and mechanical properties of liquid, suspended nanoparticles, and bacterial cells that has not been possible to this date. To this end, the microdevice is designed to have two parallel cantilevers, i.e., a suspended microchannel resonator that is illustrated in Fig. 1(a) and a suspended microchannel heater-thermometer (SMHT) that is illustrated in Fig. 1(b). In the SMHT, the microchannel is embedded under the metallic heater section, while the bimetallic cantilever will be used to achieve the temperature resolution in the order of 10-6 K. The suspended bridge design will constrict heating in the heater section and the below microchannel, which will allow the accurate calorimetry using our device. Thus by flowing a liquid sample through the SMR and the SMHT, we can simultaneously measure mechanical and thermal properties with the unprecedented accuracy. This research will focus on (1) the design, fabrication, and characterization of heater-integrated SMR devices, (2) the development of a multiscale, multiphysical model that predicts the coupled mechanical and thermoelectrical behaviors of the SMR, and (3) the application of the developed SMR devices for fundamental researches that critically require the knowledge of local thermal and mechanical properties of liquid-based materials. Once successfully completed, the proposed research will impact diverse disciplines and industry working toward nanotechnology. In particular, thermal and mechanical properties can be real-time measured at the single particle level, which is crucial to understand fundamentals of nanomaterial synthesis and behaviors. This research is in collaboration with Prof. Jungchul Lee at Sogang University in Korea. This work has been funded from the Global Research Network Grant (MEMS-D00014), one of prestigious awards to promote international collaborations from the National Research Foundation of Korea. Figure 1: (a) Cartoon showing the operation of the optical lever setup (Burg et al., Nature, 446, p.1066, 2007) and the scanning electron micrograph of a SMR cutaway view that has a buried microchannel. (b) Schematic illustration of the heater-integrated SMR with a bimetallic cantilever. The microchannel is embedded under the metallic heater.

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