Controlling the thermal conductivity of a material independently of its electrical conductivity continues to be a goal for researchers working on thermoelectric materials for use in energy applications1, 2 and in the cooling of integrated circuits3. In principle, the thermal conductivity κ and the electrical conductivity σ may be independently optimized in semiconducting nanostructures because different length scales are associated with phonons (which carry heat) and electric charges (which carry current). Phonons are scattered at surfaces and interfaces, so κ generally decreases as the surface-to-volume ratio increases. In contrast, σ is less sensitive to a decrease in nanostructure size, although at sufficiently small sizes it will degrade through the scattering of charge carriers at interfaces4. Here, we demonstrate an approach to independently controlling κ based on altering the phonon band structure of a semiconductor thin film through the formation of a phononic nanomesh film. These films are patterned with periodic spacings that are comparable to, or shorter than, the phonon mean free path. The nanomesh structure exhibits a substantially lower thermal conductivity than an equivalently prepared array of silicon nanowires, even though this array has a significantly higher surface-to-volume ratio. Bulk-like electrical conductivity is preserved. We suggest that this development is a step towards a coherent mechanism for lowering thermal conductivity.
At a glance
- Complex thermoelectric materials. Nature Mater. 7, 105–114 (2008). &
- Thermoelectricity in semiconductor nanostructures. Science 303, 777–778 (2004).
- Cooling a microprocessor chip. Proc. IEEE 94, 1476–1486 (2006). , &
- Electronic transport in nanometre-scale silicon-on-insulator membranes. Nature 439, 703–706 (2006).
- Lower limit to the thermal conductivity of disordered crystals. Phys. Rev. B 46, 6131 (1992).
- 2006). & in Thermoelectrics Handbook: Macro to Nano (ed. Rowe, D. M.) (CRC Press,
- Quantum dot superlattice thermoelectric materials and devices. Science 297, 2229–2232 (2002). , , &
- High-thermoelectric performance of nanostructured bismuth antimony telluride bulk alloys. Science 320, 634–638 (2008).
- Cubic AgPbmSbTe2+m: bulk thermoelectric materials with high figure of merit. Science 303, 818–821 (2004).
- Significant decrease of the lattice thermal conductivity due to phonon confinement in a free-standing semiconductor quantum well. Phys. Rev. B 58, 1544–1549 (1998). &
- Silicon nanowires as efficient thermoelectric materials. Nature 451, 168–171 (2008). et al.
- Thermal conductivity of individual silicon nanowires. Appl. Phys. Lett. 83, 2934–2936 (2003). et al.
- Enhanced thermoelectric performance of rough silicon nanowires. Nature 451, 163–167 (2008). et al.
- Thin-film thermoelectric devices with high room-temperature figures of merit. Nature 413, 597–602 (2001). , , &
- Thermal conductivity of Si/SiGe superlattice nanowires. Appl. Phys. Lett. 83, 3186–3188 (2003).
, , , &
- Partially coherent phonon heat conduction in superlattices. Phys. Rev. B 67, 195311 (2003) &
- Silicon p-FETs from ultrahigh density nanowire arrays. Nano Lett. 6, 1096–1100 (2006).
- Measuring thermal and thermoelectric properties of one-dimensional nanostructures using a microfabricated device. J. Heat Transfer 125, 881–888 (2003). et al.
- Thermal conduction in ultrathin pure and doped single-crystal silicon layers at high temperatures. J. Appl. Phys. 98, 123523 (2005). &
- Marked effects of alloying on the thermal conductivity of nanoporous materials. Phys. Rev. Lett. 104, 115502 (2010).
- Minimum thermal conductivity of superlattices. Phys. Rev. Lett. 84, 927–930 (2000). &
- Phonon superlattice transport. Phys. Rev. B 56, 10754–10757 (1997). &
- Thermal-conductivity of super-lattices. Phys. Rev. B 25, 3750–3755 (1982). &
- Phonon group velocity and thermal conduction in superlattices. Phys. Rev. B 60, 2627–2630 (1999).
- Atomic-scale three-dimensional phononic crystals with a very low thermal conductivity to design crystalline thermoelectric devices. J. Heat Transfer 131, 043206 (2009).
- Nanoporous Si as an efficient thermoelectric material. Nano Lett. 8, 3750–3754 (2008).
- Lattice thermal conductivity of nanoporous Si: molecular dynamics study. Appl. Phys. Lett. 91, 223110 (2007). , , &
- Temperature dependence of the thermal conductivity of thin silicon nanowires. Nano Lett. 10, 847–851 (2010).
- Electrical properties of heavily doped silicon. J. Appl. Phys. 34, 3291–3295 (1963).
, , &
- Superlattice nanowire pattern transfer (SNAP). Acc. Chem. Res. 41, 1609–1617 (2008).
- Supplementary information (842 KB)