[Paper Review] Thermal conductivity of graphene kirigami: ultralow and strain robustness

Ning Wei, Yang Chen+4 more|arXiv (Cornell University)|Dec 15, 2015

Graphene research and applications1 references4 citations

TL;DR

This study demonstrates via nonequilibrium molecular dynamics simulations that graphene kirigami (GNR-k) exhibits ultralow thermal conductivity—reduced by two orders of magnitude to ~5.1 Wm⁻¹K⁻¹—compared to pristine graphene nanoribbons (~151.6 Wm⁻¹K⁻¹), primarily due to elongated heat flux paths, reduced effective heat transfer area, and phonon scattering at edge vacancies. The structure also shows strain robustness, maintaining low thermal conductivity under deformation, suggesting utility in nanoscale thermal management and thermoelectric applications.

ABSTRACT

Kirigami structure, from the macro- to the nanoscale, exhibits distinct and tunable properties from original 2-dimensional sheet by tailoring. In present work, the extreme reduction of the thermal conductivity by tailoring sizes in graphene nanoribbon kirigami (GNR-k) is demonstrated using nonequilibrium molecular dynamics simulations. The results show that the thermal conductivity of GNR-k (around 5.1 Wm-1K-1) is about two orders of magnitude lower than that of the pristine graphene nanoribbon (GNR) (around 151.6 Wm-1K-1), while the minimum value is expected to be approaching zero in extreme case from our theoretical model. To explore the origin of the reduction of the thermal conductivity, the micro-heat flux on each atoms of GNR-k has been further studied. The results attribute the reduction of the thermal conductivity to three main sources as: the elongation of real heat flux path, the overestimation of real heat flux area and the phonon scattering at the vacancy of the edge. Moreover, the strain engineering effect on the thermal conductivity of GNR-k and a thermal robustness property has been investigated. Our results provide physical insights into the origins of the ultralow and robust thermal conductivity of GNR-k, which also suggests that the GNR-k can be used for nanaoscale heat management and thermoelectric application.

Motivation & Objective

• To investigate the thermal transport properties of graphene nanoribbon kirigami (GNR-k) structures.
• To understand the physical origins behind the drastic reduction in thermal conductivity in GNR-k compared to pristine graphene nanoribbons.
• To evaluate the impact of strain engineering on thermal conductivity in GNR-k.
• To explore the potential of GNR-k for nanoscale thermal management and thermoelectric applications.

Proposed method

• Nonequilibrium molecular dynamics (NEMD) simulations were used to calculate thermal conductivity in GNR-k structures.
• The micro-heat flux on each atom was analyzed to identify local thermal transport behavior.
• Structural parameters such as ribbon size, edge vacancy density, and geometry were systematically varied to study their effects.
• A theoretical model was developed to predict the minimum thermal conductivity approaching zero in extreme cases.
• Strain was applied to GNR-k to assess its influence on thermal conductivity and robustness.
• Phonon scattering mechanisms at edge vacancies were evaluated to explain reduced thermal transport.

Experimental results

Research questions

• RQ1 What is the extent of thermal conductivity reduction in graphene kirigami compared to pristine graphene nanoribbons?
• RQ2 What are the dominant physical mechanisms responsible for the reduction in thermal conductivity in GNR-k?
• RQ3 How does mechanical strain affect the thermal conductivity of GNR-k structures?
• RQ4 Can GNR-k maintain ultralow thermal conductivity under mechanical deformation, indicating strain robustness?
• RQ5 What is the theoretical limit of thermal conductivity in GNR-k, and how does it scale with structural design?

Key findings

• Thermal conductivity of GNR-k is reduced to approximately 5.1 Wm⁻¹K⁻¹, representing a two-order-of-magnitude decrease from pristine graphene nanoribbons (~151.6 Wm⁻¹K⁻¹).
• The minimum thermal conductivity in GNR-k is predicted to approach zero under extreme structural tuning, according to the theoretical model.
• Three main factors contribute to the reduction: elongated real heat flux path, overestimated effective heat flux area, and phonon scattering at edge vacancies.
• GNR-k exhibits strain robustness, maintaining ultralow thermal conductivity even under applied strain, indicating stability for flexible thermal applications.
• The study identifies edge engineering and structural design as effective strategies for achieving tunable, ultralow thermal conductivity in 2D materials.
• The results suggest that GNR-k is a promising candidate for nanoscale thermoelectric devices and thermal management systems.