This work discusses measurement of thermal conductivity (k) of films using a scanning hot probe method in the 3ω mode and investigates the calibration of thermal contact parameters, specifically the thermal contact resistance (R(th)C) and thermal exchange radius (b) using reference samples with different thermal conductivities. R(th)C and b were found to have constant values (with b = 2.8 ± 0.3 μm and R(th)C = 44,927 ± 7820 K W(-1)) for samples with thermal conductivity values ranging from 0.36 W K(-1) m(-1) to 1.1 W K(-1) m(-1). An independent strategy for the calibration of contact parameters was developed and validated for samples in this range of thermal conductivity, using a reference sample with a previously measured Seebeck coefficient and thermal conductivity. The results were found to agree with the calibration performed using multiple samples of known thermal conductivity between 0.36 and 1.1 W K(-1) m(-1). However, for samples in the range between 16.2 W K(-1) m(-1) and 53.7 W K(-1) m(-1), calibration experiments showed the contact parameters to have considerably different values: R(th)C = 40,191 ± 1532 K W(-1) and b = 428 ± 24 nm. Finally, this work demonstrates that using these calibration procedures, measurements of both highly conductive and thermally insulating films on substrates can be performed, as the measured values obtained were within 1-20% (for low k) and 5-31% (for high k) of independent measurements and/or literature reports. Thermal conductivity results are presented for a SiGe film on a glass substrate, Te film on a glass substrate, polymer films (doped with Fe nano-particles and undoped) on a glass substrate, and Au film on a Si substrate.
Shape memory alloys (SMAs) have the potential to be used for a wide variety of microelectromechanical systems (MEMS) applications, providing a unique combination of large deflections and high work output. A major drawback for SMAs in many applications has been the low frequency response, which is typically on the order of 100 Hz or lower, even in microscale SMA actuators. In MEMS applications, the higher surface-to-volume ratios have enabled responses to be improved by an order or magnitude or more. By further shrinking the SMA film/device dimensions, the frequency response may be improved even further. In this paper, we present a new, simplified process for fabricating sputtered, thin film SMA MEMS actuators based on nickel-titanium alloy (NiTi or, aka, NITINOL) that consisted of only one photo step to pattern the actuators using SU8. When heated through its solid–solid phase transition from low-temperature martensite to high-temperature austenite, the NiTi alloy undergoes changes in associated physical properties, such as Young’s modulus, resistivity, and surface roughness, that are critical to controlling MEMS performance. For example, these material property changes allow for the design of active or passive microscale sensors and actuators. In the new process, we are able to fabricate ultrathin films of NiTi with nanoscale thickness, which can be thermally cycled through two stable positions very rapidly, making it an intriguing thermal sensor and actuator material for high frequency applications. Additionally, NiTi can be used as an active thermal switch through resistive (i.e. joule) heating. We demonstrated a greatly improved frequency response of up to 3000 Hz with turn on voltages as low as 0.5 V (corresponding to only 1 mW power consumption) for devices exhibiting microns of cantilever tip deflection over millions of cycles, indicating these new SMA MEMS actuators have potential application for low voltage switching, modulation and tuning.
Conjugated polymers may be used as thermoelectric materials due to their low thermal conductivity and have the advantageous characteristics of conventional polymers, such as low weight, non-toxicity and low cost. Here, a detailed investigation into the thermoelectric properties of PCDTBT films is reported.Moreover, in order to improve the thermoelectric properties of this polymer, FeCl 3 is used as a doping agent. For the most optimally doped film reported in this work, a power factor value of 24 mW m À1 K À2 is obtained at 150 C. The different films were characterized by wide-angle X-ray scattering (WAXS) experiments at different temperatures. In order to see the temperature effect, the thermoelectric power factor is measured as a function of temperature from (from RT to 150 C). Thermal conductivity at room temperature is calculated with two independent methods which give values in agreement within the margin of uncertainty. The results obtained show promise and give insight to motivate future investigation into these types of carbazole derivates.
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