Adsorption, Wetting, Growth and Thermal Stability of the Protic Ionic Liquid [dema][TfO] 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 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.