Integrated polysilicon thermistors for microfluidic sensing

This thesis documents results related to the design, fabrication, and testing of integrated polysilicon thermistors for microfluidic sensing in experimental investigations of micro impinging jet cooling and microchannel flow. Such experimental study has yielded fundamental understanding and practical design guidelines of these two microfluidic applications. Novel MEMS devices fabricated include temperature imagers, MEMS nozzles and nozzle arrays, and micro fluidic couplers. A technology for suspended microchannels with integrated polysilicon thermistors has been developed and used for microchannel flow study and flow-rate sensing. Theoretical models have been developed to analyze such micro thermal and fluidic phenomena. In the micro impinging jet cooling study, a MEMS-based heat transfer measurement paradigm has been successfully developed for the first time. This includes technology for MEMS device fabrication, an experimental setup well suited for microscale thermal study, and accurate and efficient data processing techniques. Sensing and heating are integrated into a single thermal imager chip, which allows temperature measurement over a large area at very high spatial resolution. The heat transfer data demonstrate the excellent promise of micro-impinging-jet heat transfer, and provide useful rules for designing impinging-jet-based micro heat exchangers for IC packages. In the investigation of micro channel flow, suspended microchannels with integrated thermistors have successfully been designed and fabricated to study the basic science of micro-scale channel flow. Considerable discrepancies between existing theory and experimental data have been observed, and an improved flow model that accounts for the effects of compressibility, boundary slip, fluid acceleration, non-parabolic fluid velocity profile and channel-wall bulging has been proposed to address such discrepancies. In addition, micro fluidic couplers have been designed and fabricated as the fluidic interface connection between micro fluidic systems and the external macro environment. The experiments show that MEMS couplers are capable of handling pressures as high as 1200 psig. Finally, this thesis presents the development of liquid flow sensors. Resolution of 0.4 nL/min and a capability of bubble detecting have been demonstrated. A numerical model is developed to understand device operation and to guide the design process. Excellent agreement has been found between numerical and experimental results

Design, fabrication, and testing of silicon microgimbals for super-compact rigid disk drives

This paper documents results related to design optimization, fabrication process refinement, and micron-level static/dynamic testing of silicon micromachined microgimbals that have applications in super-compact computer disk drives as well as many other engineering applications of microstructures and microactuators requiring significant out-of-plane motions. The objective of the optimization effort is to increase the in-plane to out-of-plane stiffness ratio in order to maximize compliance and servo bandwidth and to increase the displacement to strain ratio to maximize the shock resistance of the microgimbals, while that of the process modification effort is to simplify in order to reduce manufacturing cost. The testing effort is to characterize both the static and dynamic performance using precision instrumentation in order to compare various prototype designs

The Effect of Ultrafine Magnesium Hydroxide on the Tensile Properties and Flame Retardancy of Wood Plastic Composites

The effect of ultrafine magnesium hydroxide (UMH) and ordinary magnesium hydroxide (OMH) on the tensile properties and flame retardancy of wood plastic composites (WPC) were investigated by tensile test, oxygen index tester, cone calorimeter test, and thermogravimetric analysis. The results showed that ultrafine magnesium hydroxide possesses strengthening and toughening effect of WPC. Scanning electron micrograph (SEM) of fracture section of samples provided the positive evidence that the tensile properties of UMH/WPC are superior to that of WPC and OMH/WPC. The limited oxygen index (LOI) and cone calorimeter test illustrated that ultrafine magnesium hydroxide has stronger flame retardancy and smoke suppression effect of WPC compared to that of ordinary magnesium hydroxide. The results of thermogravimetric analysis implied that ultrafine magnesium hydroxide can improve the char structure which plays an important role in reducing the degradation speed of the inner matrix during combustion process and increases the char residue at high temperature

Experimental Progress on Layered Topological Semimetals

We review recent experimental progresses on layered topological materials, mainly focusing on transitional metal dichalcogenides with various lattice types including 1T, Td and 1T' structural phases. Their electronic quantum states are interestingly rich, and many appear to be topological nontrivial, such as Dirac/Weyl semimetallic phase in multilayers and quantum spin hall insulator phase in monolayers. The content covers recent major advances from material synthesis, basic characterizations, angle-resolved photoemission spectroscopy measurements, transport and optical responses. Following those, we outlook the exciting future possibilities enabled by the marriage of topological physics and two dimensional van der Waals layered heterostructures.Comment: 2D Materials (2019

Evidence for quasi-one-dimensional charge density wave in CuTe by angle-resolved photoemission spectroscopy

We report the electronic structure of CuTe with a high charge density wave (CDW) transition temperature Tc = 335 K by angle-resolved photoemission spectroscopy (ARPES). An anisotropic charge density wave gap with a maximum value of 190 meV is observed in the quasi-one-dimensional band formed by Te px orbitals. The CDW gap can be filled by increasing temperature or electron doping through in situ potassium deposition. Combining the experimental results with calculated electron scattering susceptibility and phonon dispersion, we suggest that both Fermi surface nesting and electron-phonon coupling play important roles in the emergence of the CDW