Structure and Nonequilibrium Heat‐Transfer of a Physisorbed Molecular Layer on Graphene

Abstract

The structure of a physisorbed sub-monolayer of 1,2-bis(4-pyridyl)ethylene (bpe) on epitaxial graphene is investigated by Low-Energy Electron Diffraction and Scanning Tunneling Microscopy. Additionally, non-equilibrium heat-transfer between bpe and the surface is studied by Ultrafast Low-Energy Electron Diffraction. Bpe arranges in an oblique unit cell which is not commensurate with the substrate. Six different rotational and/or mirror domains, in which the molecular unit cell is rotated by 28±0.1 with respect to the graphene surface, are identified. The molecules are weakly physisorbed, as evidenced by the fact that they readily desorb at room temperature. At liquid nitrogen temperature, however, the layers are stable and time-resolved experiments can be performed. The temperature changes of the molecules and the surface can be measured independently through the Debye-Waller factor of their individual diffraction features. Thus, the heat flow between bpe and the surface can be monitored on a picosecond timescale. The time-resolved measurements, in combination with model simulations, show the existence of three relevant thermal barriers between the different layers. The thermal boundary resistance between the molecular layer and graphene was found to be 2±1•10-8 K m 2 W-1. Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff))

Impact of Atomic Coating on Thermal Conductivity of Nano Materials

“…Wit et al explored the impact of coated organic monolayer (1,2-bis(4-pyridyl)ethylene, bpe) on thermal property of epitaxial graphene by ultrafast low-energy electron diffraction [97]. This organic layer is weakly interacted with graphene.…”

Gigahertz streaking and compression of low-energy electron pulses

“…1 , blue curve), this low-energy regime is highly relevant for structural dynamics studies of surface reconstructions, adsorbates, as well as mono- and bilayers. 51 Recently, our group developed ultrafast low-energy electron diffraction (ULEED) in transmission 26 and reflection, 11 with first applications in the observation of adsorbate dynamics, 52 phase-ordering kinetics, 11,53 lattice thermalization, 54 and the coherent control of structural phase transformations. 55,56 In order to achieve pulse durations down to , miniaturized electron guns 27 were developed that reduce total propagation distances to the order of a few .…”

Ultrafast Probing and Coherent Vibrational Control of a Surface Structural Phase Transition

“…The advantages of nanotips as electron sources has been harnessed by a variety of fascinating experiments, including ultrafast low-energy electron diffraction in transmission [17] and reflection [18,55,219], ultrafast point-projection microscopy [220][221][222], ultrafast TEM [23,223,224], or as sources for novel types of electron accelerators [225]. They are typically prepared by electrochemical etching of polyor single-crystalline wires [226,227] or focused ion beam milling [112].…”

“…The following chapter gives an overview of the capabilities of ULEED. From proofof-principle experiments [217] to the observation and control of surface-specific structural dynamics [53], the technique has demonstrated its potential in various fields of surface science, including polymer and molecular dynamics at surfaces [217,219], surface reconstructions on the µm scale [231], as well as ultrafast structural transitions and phase ordering kinetics in CDW systems [18,53,55]. Of crucial importance for all these experiments is the high temporal and momentum resolution of the two ultrafast electron guns, which will be reviewed first for this reason.…”