Molecular tail chemistry controls thermal transport in fullerene films

Journal Article · Thu Jun 18 00:00:00 EDT 2020 · Physical Review Materials

DOI:https://doi.org/10.1103/physrevmaterials.4.065404· OSTI ID:1639072

Giri, Ashutosh ^[1]; Chou, Stanley Shihyao ^[2]; Drury, Daniel E. ^[2]; Tomko, Kathleen Q. ^[1]; Olson, David ^[1]; Gaskins, John T. ^[1]; Kaehr, Bryan James ^[2]; Hopkins, Patrick E. ^[1]

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1. Univ. of Virginia, Charlottesville, VA (United States)
2. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Herein we report on the thermal conductivities of alkyl- and indene-group functionalized fullerene derivative thin films as measured via time domain thermoreflectance and steady state thermoreflectance. The thermal conductivities vary from $0.064\pm 0.007$ W ${\mathrm{m}}^{–1}$ ${\mathrm{K}}^{–1}$ for [6,6]-phenyl ${\mathrm{C}}_{61}$ -butyric acid methyl ester (PCBM) to $0.15\pm 0.017$ W ${\mathrm{m}}^{–1}$ ${\mathrm{K}}^{–1}$ for indene- ${\mathrm{C}}_{60}$ bisadduct at room temperature and do not exhibit significant temperature dependence from 300 to 375 K. In comparison to the thermal conductivity of PCBM, increasing the length of the alkyl chain, as in the case of [6,6]-phenyl ${\mathrm{C}}_{61}$ -butyric acid butyl ester, and [6,6]-phenyl ${\mathrm{C}}_{61}$ -butyric acid octyl ester leads to higher thermal conductivities. Likewise, increasing the number of alkyl chains attached to the fullerenes as in the case of bisadduct PCBM leads to a higher thermal conductivity compared to that of PCBM. We present atomistic insights into the role of chemical functionalization on the overall heat transfer in these fullerene derivatives by conducting molecular dynamics simulations and lattice dynamics calculations. The thermal conductivities predicted via our atomistic simulations qualitatively agree with the experimental trends for our fullerene derivatives. Lattice dynamics calculations reveal that one of the main factors dictating the ultralow thermal conductivities in fullerene derivatives is the large reduction in modal diffusivities in the molecular crystals as calculated from the Allen-Feldman model, thus providing an explanation for their largely reduced thermal conductivities as compared to that of ${\mathrm{C}}_{60}$ crystals. The low diffusivities result from high degrees of localization of Einstein-like vibrations in fullerene derivatives due to the molecular side chains, providing the ability to dial-in the properties of these low thermal conductivity solids via molecular engineering.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States). Center for Integrated Nanotechnologies (CINT)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); US Department of the Navy, Office of Naval Research (ONR); USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Energy Efficiency Office. Advanced Manufacturing Office
• Grant/Contract Number: AC04-94AL85000; NA0003525
• OSTI ID: 1639072
• Report Number(s): SAND--2020-6463J; 686892
• Journal Information: Physical Review Materials, Journal Name: Physical Review Materials Journal Issue: 6 Vol. 4; ISSN 2475-9953
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
74 ATOMIC AND MOLECULAR PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY