Thermal transport in graphene junctions and quantum dots

Yong Xu, Xiaobin Chen, Jian-Sheng Wang, Bing-Lin Gu, and Wenhui Duan

Phys. Rev. B 81, 195425 – Published 20 May 2010

Abstract

Thermal-transport properties of various graphene junctions and quantum dots with nanoscale width are systematically investigated by nonequilibrium Green’s-function method. Thermal conductance is insensitive to the detailed structure of the contact region but substantially limited by the narrowest part of the systems. Thermal-contact resistance in nanodevices carved entirely from graphene is quite low ( $\sim 10^{- 10} m^{2} K / W$ at 300 K), at least one order lower than that between graphene and other materials. Interestingly, thermal-contact resistance of double-interface junctions is just slightly higher than that of single-interface junctions, distinct from the case of electronic transport. Moreover, graphene junctions with smaller connection angles show lower thermal conductance but higher electronic conductance. The different, even opposite dependences of thermal- and electronic-transport properties on the structural characteristics may find wide applications in nanoelectronics and thermoelectricity.

Received 19 January 2010

DOI:https://doi.org/10.1103/PhysRevB.81.195425

Authors & Affiliations

Yong Xu¹, Xiaobin Chen¹, Jian-Sheng Wang², Bing-Lin Gu¹, and Wenhui Duan^1,*

¹Center for Advanced Study and Department of Physics, Tsinghua University, Beijing 100084, People’s Republic of China
²Center for Computational Science and Engineering and Department of Physics, National University of Singapore, Singapore 117542, Republic of Singapore

^*Corresponding author; dwh@phys.tsinghua.edu.cn

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Vol. 81, Iss. 19 — 15 May 2010

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Images

Figure 1
(Color online) (a) Schematics of single-interface junctions constructed by connecting 8-ZGNR to the middle (labeled by “M90,” “M60,” and “M30”) or bottom (labeled by “B90,” “B60,” and “B30”) of 18-ZGNR. The number in the label (i.e., 30, 60, and 90) represents the angle between the edge of interface and that of 8-ZGNR. The red parts of the transport systems denote semi-infinite thermal leads (this convention is followed in all the figures). (b) Thermal conductance $(σ)$ at 100 K (dark blue), 300 K (blue), and 500 K (red) for the above six junctions. All the thermal conductances throughout this paper are in units of nano-Watt per Kelvin (nW/K).Reuse & Permissions
Figure 2
(Color online) (a) Schematics of graphene junctions and quantum dots formed by $n$ -ZGNR and $m$ -ZGNR $(n < m)$ : single-interface junction $Z n -Z m$ , double-interface junction $Z m -Z n -Z m$ , and quantum dot $Z n -Z m − Z n$ . (b) Thermal conductance $(σ)$ at 300 K as a function of structure parameter $m$ for “ $Z 8 -Z m$ ” (red circle), “ $Z m -Z 8 -Z m$ ” (blue triangle), and “ $Z 8 -Z m -Z 8$ ” (cyan diamond). (c) Thermal conductance $(σ)$ , (d) thermal contact resistance $(R_{C})$ and (e) thermal conductance ratio $(σ / σ_{0})$ at 300 K as a function of structure parameter $n$ for pristine $n$ -ZGNR (black square), “ $Z n -Z 18$ ” (red circle), “ $Z 18 -Z n -Z 18$ ” (blue triangle), and “ $Z n -Z 18 − Z n$ ” (cyan diamond).Reuse & Permissions
Figure 3
(Color online) (a) Phonon transmission as a function of frequency $ω$ and (b) thermal conductance as a function of temperature $T$ for pristine 8-ZGNR (black solid line), “Z8-Z18” (red dashed line), “Z18-Z8-Z18” (blue dotted line), and “Z8-Z18-Z8” (cyan dash-dotted line). (c) Schematics showing the phonon local density of states at $ω = 900 {cm}^{- 1}$ for Z8-Z18, Z18-Z8-Z18, and Z8-Z18-Z8 structures. Red (blue) color represents the largest (smallest) value.Reuse & Permissions
Figure 4
(Color online) (a) Schematics of graphene junctions and quantum dots formed by $n$ -AGNR and $m$ -AGNR $(n < m)$ : single-interface junction “ $A n -A m$ ,” double-interface junction “ $A m -A n -A m$ ” and quantum dot “ $A n -A m -A n$ .” (b) Thermal conductance $(σ)$ at 300 K as a function of structure parameter $m$ for “ $A 15 -A m$ ” (red circle), “ $A m -A 15 -A m$ ” (blue triangle), and “ $A 15 -A m -A 15$ ” (cyan diamond). (c) Thermal conductance $(σ)$ , (d) thermal contact resistance $(R_{C})$ and (e) thermal conductance ratio $(σ / σ_{0})$ at 300 K as a function of structure parameter $n$ for pristine $n$ -AGNR (black square), “ $A n -A 31$ ” (red circle), “ $A 31 -A n -A 31$ ” (blue triangle), and “ $A n -A 31 -A n$ ” (cyan diamond).Reuse & Permissions
Figure 5
(Color online) (a) Schematics of single-interface junctions formed by connecting 10-ZGNR and 17-AGNR, which have a similar width of $\sim 2.0 nm$ . The junctions can be classified into three categories in terms of the edge shape and connection angle: (1) “ZZ120” and “ZZ60;” (2) “ZA150,” “ZA90,” and “ZA30;” and (3) “AA120” and “AA60.” (b) Thermal conductance $(σ)$ as a function of temperature. (c) Thermal conductance ratios $(σ / σ_{0})$ at 100 K (dark blue), 300 K (blue), and 500 K (red).Reuse & Permissions
Figure 6
(Color online) (a) Schematics of four graphene quantum dots carved from 18-ZGNR. The width of the narrow constrictions increases from QD1 to “QD4.” (b) Thermal conductance $(σ)$ and (c) thermal conductance ratio $(η)$ between quantum dots and pristine 18-ZGNR as a function of temperature.Reuse & Permissions

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