Controlling the Orientation of Conductive Metal-Organic Framework (cMOF) Nanofilms for Electrical Device Applications
Key Highlights :
Researchers from the Institute of Process Engineering (IPE) of the Chinese Academy of Sciences and Kyoto University have proposed a strategy to grow "face-on" and "edge-on" conductive metal-organic frameworks (cMOF) nanofilms on substrates by controlling the "stand-up" behaviors of ligands on various surfaces to overcome the difficulty in the orientation control of such films. This study was published in Proceedings of the National Academy of Sciences on Sept. 25.
Metal-organic frameworks (MOFs) are a class of materials that have been receiving increasing attention due to their unique properties. MOFs have great potential for use in modern electrical devices due to their porous nature and the ability to conduct charges in a regular network. However, the unexplored interface chemistry of cMOFs makes the controlled synthesis and advanced characterization of high-quality thin films particularly challenging.
In order to overcome this difficulty, the researchers proposed a strategy to grow "face-on" and "edge-on" conductive metal-organic frameworks (cMOF) nanofilms on substrates by controlling the "stand-up" behaviors of ligands on various surfaces. In the Langmuir–Blodgett (LB) technique, ligands with a hydrophobic core and a hydrophilic edge can adopt an upright orientation on hydrophilic surfaces when subjected to high surface pressure.
The researchers used ultra-high concentration, together with vigorous evaporation during spraying, to create a unique local high surface pressure that can induce the 'standing up' of HHTP (HHTP = 2,3,6,7,10,11-hexahydrotriphenylene) ligands. Accordingly, the 'face-on' and 'edge-on' thin films can be fabricated. Various reliable analyses were conducted to verify the crystallinity and orientation of the films with an ultra-thin thickness ranging from a few nanometers to tens of nanometers.
The operando GIWAXS imaging and electrical monitoring revealed the anisotropic framework softness associated with electrical conductivity on the cMOF nanofilm. In addition to redox interactions, the structural softness has been confirmed to modulate the electrical conductivity in an anisotropic way.
This study is a major step forward in the development of cMOFs for use in electrical devices. By controlling the orientation of cMOF nanofilms, this strategy can help to achieve better electrical performance and higher device efficiency. The findings of this study could open up new possibilities for the development of advanced electrical devices.
