The effect of oxygen impurities on a caesium-covered Mo(001) surface: insights from Molecular Dynamics simulations for negative ion sources

Caesium-covered molybdenum surfaces are considered for negative ion production [1] [2]. Surface chemical-physics can help to understand the surface process influencing and determining device performances. Molecular Dynamics simulations based on ab initio calculations in the framework of DFT( Density Functional Theory) have been used to simulate the interactions occurring at the gas-surface interface [ [3] [4] [5]. In recent years, we have employed this computational tool to study the surface processes of interest in negative ion sources. The simulated processes occur on a short space/time scale but influence the complete process. Instead, the determined collisional data can be useful in the kinetic modelling of negative ion production [6] [7]. A few years ago, we started by simulating the process of the negative hydrogen ion formation [8] on a caesiated surface model [9]. Thus, we investigated and understood which formation mechanism (surface or volume) is the leading one [10]. The same investigation has been then conducted for deuterium [11]. Lately, given the non-optimal vacuum conditions in which these sources operate, we have started characterizing the interaction of oxygen (atomic and molecular) with the same surface model [12] [13]. In this contribution, after a quick overview of the previously obtained results, we will focus on those obtained for atomic and molecular oxygen interaction with the considered caesium-covered molybdenum surface. A detailed analysis of the occurring surface processes will be provided by foreseeing a possible way to attenuate the influence of the presence of oxygen on the negative ions production.