AFM Manipulation of EGaIn Microdroplets to Generate Controlled, On-Demand Contacts on Molecular Self-Assembled Monolayers

Eugene Jia Hao Soh, Hippolyte P.A.G. Astier, Dan Daniel*, Jia Qing Isaiah Chua, Ali Miserez, Zian Jia, Ling Li, Sean J. O'Shea, Harish Bhaskaran*, Nikodem Tomczak*, Christian A. Nijhuis*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


Liquid metal droplets, such as eutectic gallium-indium (EGaIn), are important in many research areas, such as soft electronics, catalysis, and energy storage. Droplet contact on solid surfaces is typically achieved without control over the applied force and without optimizing the wetting properties in different environments (e.g., in air or liquid), resulting in poorly defined contact areas. In this work, we demonstrate the direct manipulation of EGaIn microdroplets using an atomic force microscope (AFM) to generate repeated, on-demand making and breaking of contact on self-assembled monolayers (SAMs) of alkanethiols. The nanoscale positional control and feedback loop in an AFM allow us to control the contact force at the nanonewton level and, consequently, tune the droplet contact areas at the micrometer length scale in both air and ethanol. When submerged in ethanol, the droplets are highly nonwetting, resulting in hysteresis-free contact forces and minimal adhesion; as a result, we are able to create reproducible geometric contact areas of 0.8-4.5 μm2with the alkanethiolate SAMs in ethanol. In contrast, there is a larger hysteresis in the contact forces and larger adhesion for the same EGaIn droplet in air, which reduced the control over the contact area (4-12 μm2). We demonstrate the usefulness of the technique and of the gained insights in EGaIn contact mechanics by making well-defined molecular tunneling junctions based on alkanethiolate SAMs with small geometric contact areas of between 4 and 12 μm2in air, 1 to 2 orders of magnitude smaller than previously achieved.

Original languageEnglish (US)
Pages (from-to)14370-14378
Number of pages9
JournalACS Nano
Issue number9
StatePublished - Sep 27 2022

Bibliographical note

Funding Information:
D.D. acknowledges funding from A*STAR Competitive Research Fund (project number SC25/21-110411). N.T. is grateful to the Agency for Science, Technology and Research (A*STAR) for providing financial support under the Pharos Advanced Surfaces Programme (grant number 1523700101, project number SC25/16-2P1203).

Publisher Copyright:
© 2022 American Chemical Society. All rights reserved.


  • atomic force microscopy
  • EGaIn
  • liquid metal
  • micromanipulation
  • molecular electronics

ASJC Scopus subject areas

  • General Materials Science
  • General Engineering
  • General Physics and Astronomy


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