Inverse Volcano: A New Molecule-Surface Interaction Phenomenon

Explosive desorption of guest molecules embedded in amorphous solid water upon its crystallization is known as the "molecular volcano."Here, we describe an abrupt ejection of NH3 guest molecules from various molecular host films toward a Ru(0001) substrate upon heating, utilizing both temperature programmed contact potential difference and temperature programmed desorption measurements. NH3 molecules abruptly migrate toward the substrate due to either crystallization or desorption of the host molecules, following an "inverse volcano"process considered a highly probable phenomenon for dipolar guest molecules that strongly interact with the substrate.