title: Thermal Transport in Silicon Nanowires at High Temperature up to 700 K.
abstract: Thermal transport in silicon nanowires has captured the attention of scientists for understanding phonon transport at the nanoscale, and the thermoelectric figure-of-merit (ZT) reported in rough nanowires has inspired engineers to develop cost-effective waste heat recovery systems. Thermoelectric generators composed of silicon target high-temperature applications due to improved efficiency beyond 550 K. However, there have been no studies of thermal transport in silicon nanowires beyond room temperature. High-temperature measurements also enable studies of unanswered questions regarding the impact of surface boundaries and varying mode contributions as the highest vibrational modes are activated (Debye temperature of silicon is 645 K). Here, we develop a technique to investigate thermal transport in nanowires up to 700 K. Our thermal conductivity measurements on smooth silicon nanowires show the classical diameter dependence from 40 to 120 nm. In conjunction with Boltzmann transport equation, we also probe an increasing contribution of high-frequency phonons (optical phonons) in smooth silicon nanowires as the diameter decreases and the temperature increases. Thermal conductivity of rough silicon nanowires is significantly reduced throughout the temperature range, demonstrating a potential for efficient thermoelectric generation (e.g., ZT = 1 at 700 K).
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|Department of Mechanical and Aerospace Engineering, University of California , Irvine, California 92697, United States.
authors.forename: Jaeho
authors.initials: J
authors.lastname: Lee
authors.affiliation: The Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Woochul
authors.initials: W
authors.lastname: Lee
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Jongwoo
authors.initials: J
authors.lastname: Lim
authors.forename: Yi
authors.initials: Y
authors.lastname: Yu
authors.forename: Qiao
authors.initials: Q
authors.lastname: Kong
authors.affiliation: The Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Urban
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|Kavli Energy Nanosciences Institute , Berkeley, California 94720, United States.
authors.forename: Peidong
authors.initials: P
authors.lastname: Yang
keywords: Thermal conductivity; ZT; nanomaterial; phonon transport; single nanowire; thermoelectric