title: Thermal conductivity reduction of crystalline silicon by high-pressure torsion.
abstract: We report a dramatic and irreversible reduction in the lattice thermal conductivity of bulk crystalline silicon when subjected to intense plastic strain under a pressure of 24 GPa using high-pressure torsion (HPT). Thermal conductivity of the HPT-processed samples were measured using picosecond time domain thermoreflectance. Thermal conductivity measurements show that the HPT-processed samples have a lattice thermal conductivity reduction by a factor of approximately 20 (from intrinsic single crystalline value of 142 Wm(-1) K(-1) to approximately 7.6 Wm(-1) K(-1)). Thermal conductivity reduction in HPT-processed silicon is attributed to the formation of nanograin boundaries and metastable Si-III/XII phases which act as phonon scattering sites, and because of a large density of lattice defects introduced by HPT processing. Annealing the samples at 873 K increases the thermal conductivity due to the reduction in the density of secondary phases and lattice defects.
authors.affiliation: Department of Mechanical Engineering, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan.
authors.forename: Sivasankaran
authors.initials: S
authors.lastname: Harish
authors.affiliation: Department of Mechanical Engineering, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan.
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Tabara
authors.affiliation: Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan.
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Ikoma
authors.affiliation: Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan ; International Institute of Carbon-Neutral Energy Research (WPI - I2CNER), Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan.
authors.forename: Zenji
authors.initials: Z
authors.lastname: Horita
authors.affiliation: Department of Mechanical Engineering, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan ; International Institute of Carbon-Neutral Energy Research (WPI - I2CNER), Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Takata
authors.affiliation: International Institute of Carbon-Neutral Energy Research (WPI - I2CNER), Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan ; Department of Materials Science and Engineering and Materials Research Laboratory, University of Illinois, Urbana, IL 61801, USA.
authors.forename: David G
authors.initials: DG
authors.lastname: Cahill
authors.affiliation: Department of Mechanical Engineering, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan ; International Institute of Carbon-Neutral Energy Research (WPI - I2CNER), Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan.
authors.forename: Masamichi
authors.initials: M
authors.lastname: Kohno
keywords: High-pressure torsion; Silicon thermal conductivity; Thermoelectrics; Time domain thermoreflectance