title: Quasi-ballistic Electronic Thermal Conduction in Metal Inverse Opals.
abstract: Porous metals are used in interfacial transport applications that leverage the combination of electrical and/or thermal conductivity and the large available surface area. As nanomaterials push toward smaller pore sizes to increase the total surface area and reduce diffusion length scales, electron conduction within the metal scaffold becomes suppressed due to increased surface scattering. Here we observe the transition from diffusive to quasi-ballistic thermal conduction using metal inverse opals (IOs), which are metal films that contain a periodic arrangement of interconnected spherical pores. As the material dimensions are reduced from ∼230 nm to ∼23 nm, the thermal conductivity of copper IOs is reduced by more than 57% due to the increase in surface scattering. In contrast, nickel IOs exhibit diffusive-like conduction and have a constant thermal conductivity over this size regime. The quasi-ballistic nature of electron transport at these length scales is modeled considering the inverse opal geometry, surface scattering, and grain boundaries. Understanding the characteristics of electron conduction at the nanoscale is essential to minimizing the total resistance of porous metals for interfacial transport applications, such as the total electrical resistance of battery electrodes and the total thermal resistance of microscale heat exchangers.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Barako
authors.forename: Aditya
authors.initials: A
authors.lastname: Sood
authors.forename: Chi
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
authors.forename: Junjie
authors.initials: J
authors.lastname: Wang
authors.forename: Takashi
authors.initials: T
authors.lastname: Kodama
authors.forename: Mehdi
authors.initials: M
authors.lastname: Asheghi
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Zheng
authors.affiliation: Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
authors.forename: Paul V
authors.initials: PV
authors.lastname: Braun
authors.forename: Kenneth E
authors.initials: KE
authors.lastname: Goodson
keywords: Inverse opal; electron scattering; porous metal; surface scattering; thermal conductivity