Adsorption of Phosphorus on a Ru(0001) surface
A density functional theory study
T.I. Beeker (TU Delft - Mechanical Engineering)
M.H.F. Sluiter – Mentor
J. Meyer – Mentor (Universiteit Leiden)
S. Hariharan – Graduation committee member (Universiteit Leiden)
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Abstract
Interest in transition metal surfaces has grown in fields such as catalysts and semiconductors. Models of initial adsorption and growth of adsorbates are used to verify if certain structures are formed. Structural complexity and diversity of overlayers often determines this growth. Understanding the difference between a clean single crystal transition metal surface and adsorbate covered surfaces at the atomic scale are a first step. Characterization at atomic scale however can be challenging and help can come from electronic structure theory. Much is known about the overlayers of oxygen on a Ru(0001) surface, yet little research has been conducted in understanding the interaction between phosphorus and Ru(0001). In this work the adsorption mechanism of phosphorus on a ruthenium (0001) is studied. Density functional theory (DFT) calculations were performed to find optimal adsorption sites on a Ru(0001) surface for P. The four high coordination positions were then used to form distinct combinations upon stacking layers. There it became evident that in the regime of first layers, the adhesion and stacking of adsorbate layers is governed by the Ru(0001) stacking order and highest probable coordination sites on the surface. Upon stacking more layers, the adsorbate layer follows a pattern of ’on top’ stacking with alternating layer heights. The bond distances and lack of electron transfer show a tendency to form P-P bi-layers. Binding enegies within the P-P bilayer (intra-bilayer) are stronger than binding energies between successive bi-layers (inter-bilayers). Latter one being dominated by VanderWaals forces. A minimal analytical sum of binding interactions is proposed to the surface and bilayer energies showing an accurate description of the DFT results. Bilayer formation and weak inter-bilayer interactions indicate the possibility of formation of two-dimensional phosphorene structures. At last as a point for future work possible supercells are constructed an tabulated that could accommodate adhesion of phosphorene (oxide) structures with minimal strain.