Ultra-low thermal conductivity in TiO2:C superlattices

Abstract

TiO₂:C superlattices are fabricated from atomic/molecular layer deposited (ALD/MLD) inorganic–organic [(TiO₂)_m(Ti–O–C₆H₄–O–)_k=1]_n thin films via a post-deposition annealing treatment that converts the as-deposited monomolecular organic layers into sub-nanometer-thick graphitic interface layers confined within the TiO₂ matrix. The internal graphitic layers act as effective phonon-scattering boundaries that bring about a ten-fold reduction in the thermal conductivity of the films with a decreasing superlattice period down to an ultra-low value of 0.66 ± 0.04 W m⁻¹ K⁻¹ – a finding that makes inorganic-C superlattices fabricated by the present method promising structures for e.g. high-temperature thermal barriers and thermoelectric applications.