A first-principles study of transition metal surfaces

Date
2022-12
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Abstract

The effect an adsorbate species on copper (Cu) and tungsten (W) is examined in two parts using first-principles density functional theory calculations; for both studies the (100), (110), and (111) surfaces were studied. An oxygen monolayer was adsorbed onto the surface of Cu and the electronic properties were examined. The existence of an oxygen monolayer on the surface of Cu was verified by calculating the adsorption energy. The total density of states revealed little changes upon adsorption of the oxygen monolayer. However, when an external electric field was applied to the clean and oxidized surfaces it was shown that the clean surface was greatly impacted while the O/Cu surface was not. The O/Cu surface was not effected because of the presence of strong directional bonding and the O-Cu bond being strong enough to overcome the effects of the electric field. A first-principle approach was used to study the effects of an alkali metal iodide \emph{X}I (X= Li, Na, K, Rb, and Cs) on the work function of the (100), (110), and (111) surfaces of W. The adsorption of the alkali iodides revealed three distinct trends: (1) for all systems the most energetically (lowest formation energy) stable XI/W (111) surface had the smallest work function reduction while the least energetically stable (highest formation energy) XI/W (110) surface had the largest work function reduction. Using the total density of states (TDOS), it was determined that XI/W (111) surfaces had the strongest bonds resulting in the highest work functions. (2) For all surface orientations, from LiI/W to CsI/W, the formation energies are increasing while the work functions are decreasing, and (3) the calculated work function reduction was largest for the XI/W (110) surface despite having the largest clean surface work function (up a 3:51 eV reduction for CsI/W (110)). Additionally, it was previously suggested that the electrostatic energy is responsible for the dipole orientation and work function reduction. Contrary to the suggested model, the dipole orientation and work function reduction is dependent on the elastic strain (size-effects) caused by the alkali metals.


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Keywords
density functional theory, work function, surfaces, transition metals
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