Adsorption, Wetting, Growth, and Thermal Stability of the Protic Ionic Liquid Diethylmethylammonium Trifluoromethanesulfonate on Ag(111) and Au(111)

We have studied the adsorption, wetting, growth, and thermal evolution of the protic IL diethylmethylammonium trifluoro­methanesulfonate ([dema]­[TfO]) on Au(111) and Ag(111). Ultrathin films were deposited at room temperature (RT) and at 90 K, and were characterized in situ by angle-resolved X-ray photoelectron spectroscopy. For both surfaces, we observe that independent of temperature, initially, a closed 2D wetting layer forms. While the film thickness does not increase past this wetting layer at RT, at 200 K and below, “moderate” 3D island growth occurs on top of the wetting layer. Upon heating, on Au(111), the [dema]­[TfO] multilayers desorb at 292 K, leaving an intact [dema]­[TfO] wetting layer, which desorbs intact at 348 K. The behavior on Ag(111) is much more complex. Upon heating [dema]­[TfO] deposited at 90 K, the [dema]⁺ cations deprotonate in two steps at 185 and 305 K, yielding H­[TfO] and volatile [dema]⁰. At 355 K, the formed H­[TfO] wetting layer partly desorbs (∼50%) and partly decomposes to form an F-containing surface species, which is stable up to 570 K.