Temperature-dependent thermal and electrical conduction in metallic nanostructures

dc.contributor.advisor Xinwei Wang
dc.contributor.author Cheng, Zhe
dc.contributor.department Mechanical Engineering
dc.date 2018-08-11T09:43:39.000
dc.date.accessioned 2020-06-30T02:56:04Z
dc.date.available 2020-06-30T02:56:04Z
dc.date.copyright Thu Jan 01 00:00:00 UTC 2015
dc.date.embargo 2015-10-08
dc.date.issued 2015-01-01
dc.description.abstract <p>In this work, temperature dependent electrical and thermal conduction in the bio-supported 3.2 nm-thin Ir nanofilm and individual silver nanowire are studied at reduced temperatures. For the Ir film, by studying the temperature-dependent behavior (300 K down to 43 K) of electron thermal conductivity (), we quantify the extremely confined defect-electron scatterings and isolate the intrinsic phonon-electron scattering that is shared by the bulk Ir. At low temperatures below 50 K,  of the film has almost two orders of magnitude reduction from that of bulk Ir. The film has ∂/∂T>0 while the bulk Ir has ∂/∂T <0. We introduce a unified thermal resistivity (=T/) to interpret these completely different ~T relations. It is found that the film and the bulk Ir share a very similar ~T trend while they have a different residual part (Θ0) at 0 K limit: 0~0 for the bulk Ir, and 0=5.5 mK2/W for the film. The Ir film and the bulk Ir have very close ∂Θ/∂T (75 to 290 K): 6.33×10-3 mK/W for the film and 7.62×10-3 mK/W for the bulk Ir. This strongly confirms the similar phonon-electron scattering in them. The temperature dependent behavior of the Lorenz number of the Ir film is also reported down to 10 K. Due to the strong defect-electron scattering, a very large residual electrical resistivity (1.2410-7 ·m) is observed for the film that dominates the overall electron transport (1.24~1.5510-7 ·m). The Debye temperature (221 K) of the film is found much smaller than that of bulk (308 K). This phonon softening strongly confirms the extensive surface and grain boundary electron scatterings. We find the Wiedemann-Franz Law still applies to our film even at low temperatures. The overall Lorenz number and that of imperfect structure (~2.25×10-8 W·Ω/K2) are close to the Sommerfeld value and shows little temperature dependence. This is contrast to other studied low dimensional metallic structures that have a much larger Lorenz number (3~7×10-8 W·Ω/K2). Electron tunneling and hopping in the biomaterial substrate are speculated responsible for the observed Lorenz number.</p> <p>Additionally, the thermal and electrical transport in an individual silver nanowire is characterized down to 35 K for in-depth understanding of the strong structural defect induced electron scattering. The results indicate that, at room temperature, the electrical resistivity increases by around 4 folds from that of bulk silver. The Debye temperature (151 K) of the silver nanowire is found 36% lower than that (235 K) of bulk silver, confirming strong phonon softening. At room temperature, the thermal conductivity is reduced by 55% from that of bulk silver. This reduction becomes larger as the temperature goes down. A large residual  is observed for silver nanowire while that of the bulk silver is almost zero. The same ~T trend proposes that the silver nanowire and bulk silver share the similar phonon-electron scattering mechanism for thermal transport. Due to phonon-assisted electron energy transfer across grain boundaries, the Lorenz number of the silver nanowire is found much larger than that of bulk silver and decreases with decreasing temperature.</p>
dc.format.mimetype application/pdf
dc.identifier archive/lib.dr.iastate.edu/etd/14345/
dc.identifier.articleid 5352
dc.identifier.contextkey 7896994
dc.identifier.doi https://doi.org/10.31274/etd-180810-3896
dc.identifier.s3bucket isulib-bepress-aws-west
dc.identifier.submissionpath etd/14345
dc.identifier.uri https://dr.lib.iastate.edu/handle/20.500.12876/28530
dc.language.iso en
dc.source.bitstream archive/lib.dr.iastate.edu/etd/14345/Cheng_iastate_0097M_14782.pdf|||Fri Jan 14 20:18:43 UTC 2022
dc.subject.disciplines Materials Science and Engineering
dc.subject.disciplines Mechanical Engineering
dc.subject.disciplines Mechanics of Materials
dc.subject.disciplines Nanoscience and Nanotechnology
dc.subject.keywords Mechanical Engineering
dc.subject.keywords Electrical conductivity
dc.subject.keywords low temperatures
dc.subject.keywords Metallic nanofilm
dc.subject.keywords Silver nanowire
dc.subject.keywords Thermal conductivity
dc.subject.keywords Wiedemann-Franz Law
dc.title Temperature-dependent thermal and electrical conduction in metallic nanostructures
dc.type article
dc.type.genre thesis
dspace.entity.type Publication
relation.isOrgUnitOfPublication 6d38ab0f-8cc2-4ad3-90b1-67a60c5a6f59
thesis.degree.level thesis
thesis.degree.name Master of Science
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