Measuring the thermal properties of anisotropic films of hybrid materials poses a challenge to existing metrology techniques. We have developed a new approach for measuring the volumetric heat capacity and anisotropic thermal conductivity of these systems using the 3ω method. While there exist many avenues for measuring the thermal properties of thin films, most carry with them difficult requirements such as smooth surfaces or advanced lithography. Here, we present measurements of a film's in-plane and cross-plane conductance and its volumetric heat capacity using relatively simple sample configurations, each requiring a single heater. For the measurement of volumetric heat capacity, we present a new model fitting method, relying on a standard film-on-substrate configuration. For the measurement of in-plane thermal conductance by 3ω, we have developed the use of an embedded micro-wire heater in suspended drop cast films, allowing for a 12 μm wide heater without the need for advanced lithography. We also expose the surprisingly significant effect of thermal radiation in the suspended film measurement and its associated error. Our measurements reveal a large anisotropy in the thermal conductivity of our test material, Te-PEDOT:PSS, of kin-plane/kcross-plane = 19, consistent with the nanoscale morphology of the material.

In this paper, we propose a lightweight wearable thermoelectric (TE) cooler with a rationally designed flexible heatsink. Heatsinks are commonly designed for use with stationary applications, and are consequently rigid and heavy. These traditional heatsinks are incompatible with wearable applications, which must be durable, mechanically flexible, and lightweight while maintaining performance. This paper presents a flexible heatsink based on a ternary composite of silicone elastomer, phase-change material, and graphite powder; this combination is needed to achieve high flexibility and durability as well as the optimum heat capacity and thermal conductivity. Those factors are key requirements for a heatsink to optimize the cooling performance of a TE cooler and maintain a longer cooling capacity. With our optimized ternary composite flexible heatsink, we achieved a cooling temperature of ∼5 K at 0.5 W input power and kept cooling for more than 5 h under ambient conditions. On-body testing of the wearable TE cooler with flexible heatsink was also performed to demonstrate potential applications in the real-world. Our work provides fundamental insights to designing wearable TE devices and paves the way for innovative solutions for on-body thermal management applications such as clothing, hats, seat cushions, and other portable devices.

Efficient control of photons is enabled by hybridizing light with matter. The resulting light-matter quasi-particles can be readily programmed by manipulating either their photonic or matter constituents. Here, we hybridized infrared photons with graphene Dirac electrons to form surface plasmon polaritons (SPPs) and uncovered a previously unexplored means to control SPPs in structures with periodically modulated carrier density. In these periodic structures, common SPPs with continuous dispersion are transformed into Bloch polaritons with attendant discrete bands separated by bandgaps. We explored directional Bloch polaritons and steered their propagation by dialing the proper gate voltage. Fourier analysis of the near-field images corroborates that this on-demand nano-optics functionality is rooted in the polaritonic band structure. Our programmable polaritonic platform paves the way for the much-sought benefits of on-the-chip photonic circuits.