2 research outputs found
Thermal Conductivity of Mechanically Joined Semiconducting/Metal Nanomembrane Superlattices
The decrease of thermal conductivity
is crucial for the development
of efficient thermal energy converters. Systems composed of a periodic
set of very thin layers show among the smallest thermal conductivities
reported to-date. Here, we fabricate in an unconventional but straightforward
way hybrid superlattices consisting of a large number of nanomembranes
mechanically stacked on top of each other. The superlattices can consist
of an arbitrary composition of n- or p-type doped single-crystalline
semiconductors and a polycrystalline metal layer. These hybrid multilayered
systems are fabricated by taking advantage of the self-rolling technique.
First, differentially strained nanomembranes are rolled into three-dimensional
microtubes with multiple windings. By applying vertical pressure,
the tubes are then compressed and converted into a planar hybrid superlattice.
The thermal measurements show a substantial reduction of the cross-sectional
heat transport through the nanomembrane superlattice compared to a
single nanomembrane layer. Time-domain thermoreflectance measurements
yield thermal conductivity values below 2 W m<sup>–1</sup> K<sup>–1</sup>. Compared to bulk values, this represents a reduction
of 2 orders of magnitude by the incorporation of the mechanically
joined interfaces. The scanning thermal atomic force microscopy measurements
support the observation of reduced thermal transport on top of the
superlattices. In addition, small defects with a spatial resolution
of ∼100 nm can be resolved in the thermal maps. The low thermal
conductivity reveals the potential of this approach to fabricate miniaturized
on-chip solutions for energy harvesters in, e.g., microautonomous
systems