Insights into Chemical Bonding Modes and Heat Transport\nat the Molecular Level

Despite the demand\nfor nanoscale thermal management technologies\nof material surfaces and interfaces using organic molecules, heat\ntransport properties at the single molecular level remain elusive\ndue to the experimental difficulty of measuring temperature at the\nnanoscopic scale. Here we show how chemical bonding modes can affect\nthe heat transport properties of single molecules. We focused on four\nmolecular systems: benzylthiol linked to another phenyl group by either\na triple (compound <b>1</b>), double (<b>3</b>), or amide\n(<b>4</b>) bond and a common linear alkanethiol (<b>2</b>), all of which are nearly identical in molecular length. We prepared\nbinary self-assembled monolayers (SAMs) using <b>1</b> as a\ncommon reference in combination with <b>2</b>–<b>4</b> and investigated their relative heat transport properties using\nscanning thermal microscopy (SThM). Two-dimensional temperature mapping\nof the binary SAMs showed that C≡C and C=C bonds provide more\neffective pathways for heat transport compared to C–C bonds.\nSince the amide molecule has resonance structures with C=N double\nbond character, we expected that its heat transport properties would\nbe comparable to those of the thiols containing triple or double bonds.\nHowever, the heat transport properties of this molecule prevailed\nover the others, most likely due to the formation of additional heat\ntransport pathways caused by intermolecular hydrogen bonding. These\nfindings may provide important guidelines for the design of organic\nmaterials for nanoscale thermal management.