The critical power to maintain thermally stable molecular junctions

Abstract

With the rise of atomic-scale devices such as molecular electronics and scanning probe microscopies, energy transport processes through molecular junctions have attracted notable research interest recently. In this work, heat dissipation and transport across diamond/ benzene/diamond molecular junctions are explored by performing atomistic simulations. We identify the critical power P cr to maintain thermal stability of the junction through efficient dissipation of local heat. We also find that the molecule-probe contact features a powerdependent interfacial thermal resistance R K in the order of 10 9 kW À 1 . Moreover, both P cr and R K display explicit dependence on atomic structures of the junction, force and temperature. For instance, P cr can be elevated in multiple-molecule junctions, and streching the junction enhances R K by a factor of 2. The applications of these findings in molecular electronics and scanning probing measurements are discussed, providing practical guidelines in their rational design.

Assessment of Self‐Assembled Monolayers as High‐Performance Thermal Interface Materials

“…We first calculate vibrational spectra of diamond–SAM–diamond systems through equilibrium MD (EMD) simulations at 300 K, which include both ballistic and diffusive processes of heat transport. The spectral overlap between SAM and diamond is obtained by integrating the spectra over frequency, that is, I = ∫ f c (ω) f d (ω)dω, where f (ω) is the spectral function of the phonon mode frequency ω. The increase in spectral overlap indicates the activation of more channels between vibration modes with the same frequency, resulting in the increase of ITC .…”

“…To understand this mechanical effect, we find that as the SAM is stretched, covalent CC bonds at the chain‐substrate contact and those within the chain are elongated along the direction of thermal transport. Consequently, the stiffness of the alkane chains and group velocities of propagating modes decrease, and this softening effect reduces the thermal conductance . In contrast, as the SAM is compressed, the flexible chains collapse, leading to negligible changes in the bond lengths but significant distortion of the linear conformation through bond angle bending.…”

“…Nanostructures and nanoscale interfaces are fundamental units for materials and devices in nanoelectronics, thermoelectric energy conversion, and electrochemical energy storage, and thus thermal transport through interfaces with nanoscale gaps is of critical importance for their performance. Interfacial thermal resistance arises from the mismatch between vibrational modes in the contact materials and weak interactions between them at the interface . The resistance could be reduced by introducing thermal interface materials (TIMs), which fill the gap between materials and enhance the interfacial thermal coupling.…”

“…Thermal and mechanical properties of SAMs have been explored both experimentally and theoretically as potential TIMs . Zheng et al showed that silane‐based SAMs with varying end groups enhance the ITC between sapphire and polystyrene by a factor of 7, through functionalizing the sapphire surface with SAM.…”

Probing Thermal Conductivity of Fullerene C60 Hosting a Single Water Molecule

“…In higher frequencies (>40THz), the magnitude of each phonon mode for H 2 O@C 60 and empty C 60 is close, but there are obvious shifts of modes to low frequencies when the water molecule is encapsulated in the empty C 60 . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For instance, the modes at the frequency 59.3THz and 57.5 THz in the empty C 60 have shifted to 56.0 THz and 54.2 THz in the H 2 O@C 60 , respectively. The shifting phenomenon of the phonon modes to low frequencies usually is referred to as the red shift and corresponds to the reduction of group velocity of phonon groups.…”