title: Spectral phonon scattering from sub-10 nm surface roughness wavelengths in metal-assisted chemically etched Si nanowires.
abstract: Frequency dependence in phonon surface scattering is a debated topic in fundamental phonon physics. Recent experiments and theory suggest such a phenomenon, but an independent agreement between the two remains elusive. We report low-temperature dependence of thermal conductivity in silicon nanowires fabricated using a two-step, metal-assisted chemical etch. By reducing etch rates down to 0.5 nm/s from the typical >100 nm/s, we report controllable roughening of nanowire surfaces and selectively focus on moderate roughness scales rather than the extreme scales investigated previously. This critically enables direct comparison with perturbation-based spectral scattering theory. Using experimentally characterized surface roughness, we show that a multiple scattering theory provides excellent agreement and explanation of the observed low-temperature dependence of rough surface nanowires. The theory does not employ any fitting parameters. A 5-10 nm roughness correlation length is typical in metal-assisted chemical etching and resonantly scatters dominant phonons in silicon, leading to the observed ~T(1.6-2.4) behavior. Our work provides fundamental and quantitative insight into spectral phonon scattering from rough surfaces. This advances applications of nanowires in thermoelectric energy conversion.
authors: Department of Mechanical Science & Engineering, University of Illinois, Urbana, Illinois 61801, United States.
authors: M G
authors: MG
authors: Ghossoub
authors: K V
authors: KV
authors: Valavala
authors: M
authors: M
authors: Seong
authors: B
authors: B
authors: Azeredo
authors: K
authors: K
authors: Hsu
authors: J S
authors: JS
authors: Sadhu
authors: P K
authors: PK
authors: Singh
authors: S
authors: S
authors: Sinha
mesh_terms: D008670:Metals / Q000737:chemistry; D053770:Nanowires / Q000737:chemistry*; D010316:Particle Size; D060739:Phonons; D012825:Silicon / Q000737:chemistry*; D013499:Surface Properties; D013814:Thermal Conductivity
chemical_list: D008670:Metals; D012825:Silicon