Phonon scattering in graphene over substrate steps

Abstract

We calculate the effect on phonon transport of substrate-induced bends in graphene. We consider bending induced by an abrupt kink in the substrate, and provide results for different step-heights and substrate interaction strengths. We find that individual substrate steps reduce thermal conductance in the range between 5% and 47%. We also consider the transmission across linear kinks formed by adsorption of atomic hydrogen at the bends and find that individual kinks suppress thermal conduction substantially, especially at high temperatures. Our analysis show that substrate irregularities can be detrimental for thermal conduction even for small step heights. V C 2014 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4898066]Graphene is the material with the highest thermal conductivity reported so far, 1-3 with important prospective applications for example for thermal management of nanoelectronics. 4,5 The ultimately thin membrane adhere well to substrates and typically will ripples, wrinkles, and bubbles form when graphene is transferred onto a flat substrate. On the other hand, since graphene is known to cling to the smallest irregularities, 6 this also results in deformation and bending caused by the conformation of graphene to a irregular surface. This could, for instance, be steps in surfaces such as SiC or edges of other 2D materials such as BN. It is thus highly relevant to consider the effects of deformation on the thermal transport properties of graphene. There are several recent studies which investigate the effects of substrate induced geometrical modulations on the electronic and transport properties of graphene. [7][8][9][10] In particular, Low and coworkers 9 considered the effect on the electronic transport when graphene is deformed due to physisorption on a flat substrate presenting an abrupt step. They used a simple Lennard-Jones potential to model the substrate-graphene interaction with parameters corresponding to a step in SiC, and found that the bend itself causes an insignificant scattering of the electrons. Also, the related effect of ripples and wrinkles on electronic structure and transport in graphene on substrates has been investigated. 11-13Inspired by the study of Low et al., 9 we here consider phonon transport for a model of an abrupt step in a otherwise structureless substrate. We calculate the transport for various step-heights and interaction strengths. The effects of the substrate are two-fold. First, (i) the geometry of graphene is modulated by the irregularity of the substrate, which alters the force constants locally and therefore scatters phonons. Second, (ii) the substrate gives rise to a renormalization of the vibrational modes and increases the line widths (i.e., reduces phonon lifetimes). Here, we focus on the deformation (i) and neglect the dynamics of the structureless substrate.We find that the effect of the substrate induced bend in the graphene on the phonon transport is not negligible, and can reduce the conductance with more than 10% at room temperature. For very stro...

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Directed growth of hydrogen lines on graphene: High-throughput simulations powered by evolutionary algorithm

“…• bending we find the minimum ROC close to 10Å, which are close to the previous results [30]. We also perform single hydrogen adsorption calculations on curved graphene for 90…”

“…The lengths of the curved parts across the step are chosen so as to remove the tensile stress after hydrogenation. For different interaction strengths, which correspond to different substrates, ROC is found to be in the range between 13.5Å and 3.3Å, where the step height is kept as 10Å [28,30]. In Figs.…”

“…A straightforward way to deform graphene is to introduce steps in the underlying substrate. Such deformation also affects electronic and thermal transport properties [28][29][30].…”

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“…8,[12][13][14][15][16][17][18] Recently, it was shown that other two-dimensional materials can also be stable and that they widen the potential of two-dimensional materials for applications. [19][20][21][22] Of particular importance are graphene-like carbon allotropes, called graphyne structures composed of one-atom-thick sheets of carbon atoms but containing sp carbon bonds in addition to sp 2 hybridized bonds [23][24][25] (see Fig.…”