At the ionic liquid|metal interface: structure formation and temperature dependent behavior of an ionic liquid
Benedikt Uhl1, Till Cremer, Michael Roos
1Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm, Germany. juergen.behm@uni-ulm.de.
Physical Chemistry Chemical Physics : PCCP
|September 11, 2013
Summary
Researchers studied ionic liquid films of 1-butyl-1-methylpyrrolidinium-bis(trifluoromethylsulfonyl)imide ([BMP][TFSA]) on gold surfaces. They observed 2D liquid, glass, and crystalline states depending on temperature, with crystalline phases being more stable.
Area of Science:
- Surface Science
- Materials Science
- Physical Chemistry
Background:
- Ionic liquids (ILs) exhibit unique properties due to their tunable structures.
- Understanding IL film formation on surfaces is crucial for applications in nanotechnology and catalysis.
- Investigating the phase behavior of ILs at the nanoscale provides fundamental insights into their interactions with substrates.
Purpose of the Study:
- To investigate the growth, structure, and thermal disordering of [BMP][TFSA] films on Au(111).
- To characterize the different phases (liquid, glass, crystalline) formed by the IL adlayer.
- To determine the thermal stability and substrate influence on the IL film structure.
Main Methods:
- Ultrahigh vacuum (UHV) conditions were employed for film preparation and analysis.
- Scanning tunneling microscopy (STM) was used to visualize surface morphology and structure.
- Angle-resolved X-ray photoelectron spectroscopy (ARXPS) determined film composition and interfacial interactions.
Main Results:
- Two-dimensional film growth of [BMP][TFSA] occurred up to one monolayer on Au(111) at room temperature, forming a 2D liquid state.
- At lower temperatures, the adlayer transitioned into a disordered 2D glass or an ordered 2D crystalline phase.
- The crystalline phase structure was influenced by the Au(111) substrate reconstruction, and it exhibited greater thermal stability than the glass state.
Conclusions:
- The phase behavior of [BMP][TFSA] films on Au(111) is highly temperature-dependent, forming distinct liquid, glass, and crystalline states.
- The underlying substrate reconstruction plays a role in templating the ordered crystalline phase.
- The crystalline phase offers enhanced thermal stability compared to the glassy phase, with stability influenced by adsorbate coverage.
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