Physisorption of CO on the MgO(100) Surface

Abstract

The ability to grow thin MgO(100) films of quality approaching that of vacuum-cleaved MgO(100) is demonstrated using low-energy electron diffraction and temperature-programmed desorption (TPD) of CO. Highly ordered MgO(100) surfaces are used to study the adsorption and desorption of CO. A linearly increasing sticking coefficient from 0.47 ( 0.03 to 0.90 is observed for relative CO coverages, θ, less than 0.8 monolayer (ML). For this coverage range, the total sticking coefficient is given by S MgO (1 -P CO ) + S CO P CO , where S MgO (S CO ) is the sticking on the bare (CO-covered) MgO and P CO is the probability of striking the CO-covered surface. In TPD, the desorption of CO is dominated at very low coverages by desorption from sites influenced by defects. At intermediate coverages (0.25-0.8 ML) the CO desorbs via first-order desorption. At 0.8 ML where the monolayer peak saturates, the desorption energy is 17 ( 2 kJ/mol and the preexponential factor is 1 × 10 15(2 s -1 . The desorption energy increases linearly as coverage decreases due to repulsive interactions between adsorbed CO molecules. Above θ ) 0.8 ML the adsorption occurs on fully-CO-covered MgO(100) surfaces, and further increases in θ are achieved by compression of the CO layer. The compression results in a sharp decrease in desorption energy, which, upon saturation of the first CO layer (θ ) 1 ML) and the formation of a c(4×2) ordered phase, has a value of ∼9 kJ/mol. † Part of the special issue "John T. Yates, Jr. Festschrift".

CO adsorption on the surface of MgO(001) thin films

“…Both thermal desorption spectra exhibit two desorption peaks at 52 and 68 K, respectively. The peak at 52 K corresponds to desorption of CO molecules adsorbed on regular terrace sites, in agreement with similar studies on MgO single crystals and thin films [13,14]. From these TDS data, a desorption energy of 15 kJ/mol was extracted.…”

“…However, CO-TDS data from vacuum-cleaved MgO single crystals resolved this discrepancy in favor of the theoretical predictions [13]. These results were recently confirmed for appropriately prepared MgO thin films [14].…”

Differential adsorption of complex organic molecules isomers at interstellar ice surfaces

“…By approximating the pre-exponential factor to be independent of both the coverage and the energy, one can invert this equation, giving the adsorption energy as a function of the amount of remaining molecules (DeJong & Niemantsverdriet 1990;Dohnalek et al 2001)…”

Deposition and crystallization studies of thin amorphous solid water films on Ru(0001) and on CO-precovered Ru(0001)

“…16 The deposition and crystallization of ASW and the ice surface morphology have therefore been investigated extensively to further our understanding of chemical reactions on ice surfaces. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] In this work, we have investigated the deposition, crystallization mechanism, crystallization kinetics, and morphological change of ASW thin films on both bare Ru͑0001͒ and CO-precovered Ru͑0001͒ surfaces ͑referred to as CO / Ru͑0001͒, hereafter͒, particularly focusing on interfacial effects induced by the preadsorption of CO. It is well known [29][30][31][32][33][34][35][36][37] that ASW layers can exhibit different morphologies and different interactions with the substrate, depending on the precise deposition conditions.…”