Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 6, Issue 14, Pages 11341-11347Publisher
AMER CHEMICAL SOC
DOI: 10.1021/am501876d
Keywords
silkworm silk; iridium film; gold film; electron transport; thermal conductivity; Lorenz number
Funding
- Army Research Office [W911NF-12-1-0272]
- Office of Naval Research [N000141210603]
- National Science Foundation [CMMI-1264399]
- Directorate For Engineering
- Div Of Civil, Mechanical, & Manufact Inn [1264399] Funding Source: National Science Foundation
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For ultrathin metallic films, either supported or free-standing, the inside nanocrystalline nature significantly reduces the electron and thermal transport. Quantum mechanical reflection of electrons at the grain boundary reduces the electrical conductivity further than the thermal conductivity, leading to a Lorenz number in the order of 7.0 X 10(-8) W Omega K-2, much higher than that of the bulk counterpart. We report on a finding that for ultrathin (0.6-6.3 nm) iridium films coated on degummed silkworm silk fibroin, the electron transport is around 100-200% higher than that of the same film on glass fiber, even though the grain size of Ir film on silkworm silk is smaller than that on glass fiber. At the same time, the thermal conductivity of the Ir film is smaller or close to that of the film on glass fiber. Its Lorenz number is found close to that of bulk crystalline Ir despite the nanocrystalline structure in the Ir films. This is similar to the behavior of metallic glasses. Our study of gold films on silkworm silk reveals the same trend of change as compared to that on glass fiber. Electron hopping and tunneling in silkworm silk is speculated to be responsible for the observed electron transport. The finding points out that silk could provide a better substrate for flexible electronics with significantly faster electron transport.
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