Visualization of Thermal Transport Properties of Self-Assembled Monolayers on Au(111) by Contact and Noncontact Scanning Thermal Microscopy

Abstract

Thermal transport properties of patterned binary self-assembled monolayers (SAMs) on Au(111) were examined using scanning thermal microscopy (SThM) with both contact and noncontact methods. We fabricated two-dimensional (2D) patterns with two separate domains of n-hexadecanethiol/benzenethiol, benzenethiol/n-butanethiol, or n-hexadecanethiol/n-butanethiol. In the experimental setup, the efficiency of thermal transport from a SThM tip to the SAM surface can be evaluated in terms of the temperature change at the SThM tip. In the contact regime, where a SThM tip physically contacts the SAM surface, direct thermal transport through the SAM and radiation-based thermal transport through the space where SAMs exist may contribute to a drop in temperature at the tip. In the noncontact regime, thermal transport relies on radiation-based heat dissipation from the heated tip to the SAMs. 2D mapping of the spatial temperature distribution on SAMs reflects the difference in thermal transport properties of the two SAM domains. We found that the contact method is effective for visualizing the temperature contrast, which reflects the thermal transport properties of the constituent molecules when the domains of the SAMs have a similar height, while the noncontact method allows visualization of the temperature distribution, which is related to the height of each domain of the SAMs, rather than the chemical structures of the constituent molecules. Combination of contact and noncontact SThM enables 2D imaging of thermal transport properties and topographic imaging simultaneously and represents a new technique for investigating the thermal properties of materials surfaces, which is essential for nanoscale thermal management.

Self-Assembled Monolayers for Interfacial Engineering in Solution-Processed Thin-Film Electronic Devices: Design, Fabrication, and Applications

“…SAMs can play the role of a "phonon bridge" to connect the phonon densityof-states of adjacent layers, which leads to the increase in interfacial thermal conductance at the interface. 74,75 SAMs with an ordered monolayer structure are usually regarded as a quasi-2D material. 76 The major difference between 2D materials and SAMs comes from the variation in the bonding modes with the substrate and the connecting strength between adjacent constitutional units in films.…”

“…The thermal effects induced by light and electricity will also create huge impacts on the device stability. 74,75 Though thermal conduction can be facilitated by direct contact with SAMs at the heterogeneous interface, internal and external mechanical stresses might still stem from a mismatch in the thermal expansion coefficients of different layers. SAMs can alleviate compressive and tensile stresses with the molecular flexibility because of their versatility in possessing different functional groups and act as a molecular glue that strengthens the interface to prevent delamination.…”

Quantitative Characterization of Local Thermal Properties in Thermoelectric Ceramics Using “Jumping‐Mode” Scanning Thermal Microscopy

“…Two types of SThM probes are usually used for local measurements of thermal conductivity: thermocouple-based probes [11,22] and resistive probes. [4,23] The resistive probes are commercially available, while thermocouple-based probes are usually custommade.…”

“…The measurements can be performed in quasistatic (heating by a DC, Direct Current) [5] and dynamic (heating by an AC, Alternating Current) modes. [4,6,7] Despite many efforts to quantitatively map thermal conductivity, realistic quantitative SThM has been shown mostly for topographically very smooth materials, such as thin-film hafnium oxide, [8] graphene-based nanomaterials, [5,9] van der Waals 2D materials, [10] self-assembled monolayers, [11] etc., while there is a lack of studies in conventional bulk materials. One of the reasons is probe durability, [12] which significantly limits the range of the materials that can be studied by scanning in the contact mode.…”

Insights into Thermal Transport through Molecular π-Stacking

“…An increased understanding of charge-carrier transport in organic materials has resulted in great advances in the molecular design of organic semiconductors, and organic electronics have been established, , which inspire new concepts and uses for electronic devices developed conventionally using silicon technology. − Following this excellent precedent, a deeper understanding of thermal transport through molecules in organic materials, , which have classically been considered to be poor thermal conductors, could allow for the development of new thermal-management technologies . However, major difficulties still exist, since organic materials consist of molecules assembled together through weak intermolecular forces, and further, organic compounds are quite diverse, with unique structural anisotropies and properties.…”