TY  - JOUR
A1  - Heiden, Sophia
A1  - Yue, Yanhua
A1  - Kirsch, Harald
A1  - Wirth, Jonas A.
A1  - Saalfrank, Peter
A1  - Campen, Richard Kramer
T1  - Water dissociative adsorption on α-Al2O3(112̅0) is controlled by surface site undercoordination, density, and topology
JF  - The journal of physical chemistry / publ. weekly by the American Chemical Society : C, Nanomaterials and interfaces
N2  - α-Al2O3 surfaces are common in a wide variety of applications and useful models of more complicated, environmentally abundant, alumino-silicate surfaces. While decades of work have clarified that all properties of these surfaces depend sensitively on the crystal face and the presence of even small amounts of water, quantitative insight into this dependence has proven challenging. Overcoming this challenge requires systematic study of the mechanism by which water interacts with various α-Al2O3 surfaces. Such insight is most easily gained for the interaction of small amounts of water with surfaces in ultra high vacuum. In this study, we continue our combined theoretical and experimental approach to this problem, previously applied to water interaction with the α-Al2O3 (0001) and (11̅02) surfaces, now to water interaction with the third most stable surface, that is, the (112̅0). Because we characterize all three surfaces using similar tools, it is straightforward to conclude that the (112̅0) is most reactive with water. The most important factor explaining its increased reactivity is that the high density of undercoordinated surface Al atoms on the (112̅0) surface allows the bidentate adsorption of OH fragments originating from dissociatively adsorbed water, while only monodentate adsorption is possible on the (0001) and (11̅02) surfaces: the reactivity of α-Al2O3 surfaces with water depends strongly, and nonlinearly, on the density of undercoordinated surface Al atoms.
Y1  - 2018
U6  - https://doi.org/10.1021/acs.jpcc.7b10410
SN  - 1932-7447
VL  - 122
IS  - 12
SP  - 6573
EP  - 6584
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Heiden, Sophia
A1  - Wirth, Jonas
A1  - Campen, Richard Kramer
A1  - Saalfrank, Peter
T1  - Water molecular beam scattering at alpha-Al2O3(0001)
BT  - an ab initio molecular dynamics study
JF  - The journal of physical chemistry : C, Nanomaterials and interfaces
N2  - Recent molecular beam experiments have shown that water may adsorb molecularly or dissociatively on an α-Al2O3(0001) surface, with enhanced dissociation probability compared to “pinhole dosing”, i.e., adsorption under thermal equilibrium conditions. However, precise information on the ongoing reactions and their relative probabilities is missing. In order to shed light on molecular beam scattering for this system, we perform ab initio molecular dynamics calculations to simulate water colliding with α-Al2O3(0001). We find that single water molecules hitting a cold, clean surface from the gas phase are either reflected, molecularly adsorbed, or dissociated (so-called 1–2 dissociation only). A certain minimum translational energy (above 0.1 eV) seems to be required to enforce dissociation, which may explain the higher dissociation probability in molecular beam experiments. When the surface is heated and/or when refined surface and beam models are applied (preadsorption with water or water fragments, clustering and internal preexcitation in the beam), additional channels open, among them physisorption, water clustering on the surface, and so-called 1–4 and 1–4′ dissociation.
Y1  - 2018
U6  - https://doi.org/10.1021/acs.jpcc.8b04179
SN  - 1932-7447
VL  - 122
IS  - 27
SP  - 15494
EP  - 15504
PB  - American Chemical Society
CY  - Washington
ER  -