Transition States of Nanocrystal Thin Films during Ligand-Exchange Processes for Potential Applications in Wearable Sensors

Seung Wook Lee, Hyungmok Joh, Mingi Seong, Woo Seok Lee, Ji Hyuk Choi, Soong Ju Oh

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


Ligand exchange is an advanced technique for tuning the various properties of nanocrystal (NC) thin films, widely used in the NC thin-film device applications. Understanding how the NC thin films transform into functional thin-film devices upon ligand exchange is essential. Here, we investigated the process of structural transformation and accompanying property changes in the NC thin films, by monitoring the various characteristics of silver (Ag) NC thin films at each stage of the ligand-exchange process. A transition state was identified in which the ligands are partially exchanged, where the NC thin films showed unexpected electromechanical features with high gauge factors up to 300. A model system was established to explain the origin of the high gauge factors, supported by the observation of spontaneously formed nanocracks and metal-insulator transition from the structural analysis and charge transport study, respectively. Taking advantages of the unique electromechanical properties of the NC thin films, we fabricated flexible strain gauge sensor devices with high sensitivity, reliability, and stability. We introduce a one-step fabrication process, namely, "the time- and spatial-selective ligand-exchange process", for the design of low-cost and high-performance wearable sensors that effectively detect human motion, such as finger or neck muscle movement. This study provides a fundamental understanding of the ligand-exchange process in NCs, as well as an insight into the functionalities of the NC thin films for technological applications.

Original languageEnglish
Pages (from-to)25502-25510
Number of pages9
JournalACS Applied Materials and Interfaces
Issue number30
Publication statusPublished - 2018 Aug 1

Bibliographical note

Funding Information:
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and Future Planning (2016R1C1B2006534) and (NRF-2018R1C1B6002958). This was also supported by Korea Electric Power Corporation (grant number: 18A-002).


  • intermediate state
  • ligand exchange
  • metal-insulator transition
  • nanocrystals
  • strain gauge
  • structural transformation
  • wearable sensor

ASJC Scopus subject areas

  • General Materials Science


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