PSI - Issue 65

Svetlana V. Ustiuzhanina et al. / Procedia Structural Integrity 65 (2024) 295–301 Ustiuzhanina S.V. et al. / Structural Integrity Procedia 00 (2024) 000–000

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3. Results and Discussions

To evaluate chemical activity of Zn 2 (V,Nb,Ta)N 3 monolayers, the interaction of their surface with the most common environmental molecules, such as N 2 , CO 2 , NH 3 , NO, NO 2 H 2 O, and O 2 , is considered. The most stable atomic configurations of these molecules on the Zn 2 (V,Nb,Ta)N 3 monolayers’ surface are found. And their adsorption energy is calculated. The adsorption energy E a of a molecule on the Zn 2 (V,Nb,Ta)N 3 monolayers surface is calculated as E ads = E m+mol – E m E mol , where E m+mol , and E m are the energies of the molecule-adsorbed and the isolated Zn 2 (V,Nb,Ta)N 3 monolayers, and E mol is the energy of the molecule. Figure 2a shows the E ads of considered molecules on the Zn 2 (V,Nb,Ta)N 3 monolayers. The NH 3 molecule has the lowest E ads of -0.80 eV (Zn 2 VN 3 monolayer), -0.97 eV (Zn 2 NbN 3 monolayer), and -1.14 eV (Zn 2 TaN 3 monolayer). A moderate E ads on Zn 2 (V,Nb,Ta)N 3 monolayers is found for the NO and NO 2 molecules. Such a low E ads of the NH 3 , NO and NO 2 molecules on Zn 2 (V,Nb,Ta)N 3 monolayers can lead to hindrance of their surface by NH 3 , NO and NO 2 and a consequent change of their functionality (Kistanov (2024)). It is found that N 2 , CO 2 and O 2 molecules are unreactive with Zn 2 (V,Nb,Ta)N 3 monolayers. They possess comparably high E ads above -0.30 eV. This is important in terms of stability of Zn 2 (V,Nb,Ta)N 3 monolayers, as most of monolayers degrade due to contact with oxygen (Island et al. (2015)). Meanwhile, the H 2 O molecule has comparably low E ads on Zn 2 (V,Nb,Ta)N 3 monolayers such as -0.49 eV (Zn 2 VN 3 monolayer), -0.64 eV (Zn 2 NbN 3 monolayer), and -0.73 eV (Zn 2 TaN 3 monolayer). However, the formation of –OH groups and acids that may lead to the degradation of the Zn 2 (V,Nb,Ta)N 3 monolayers surface is not favorable without preliminary adsorption of O 2 (Liu et al (2009), Kistanov et al. (2018)). It should be noted, that E ads of studied molecules has the same trend in the case of Zn 2 (V,Nb,Ta)N 3 monolayers. The lowest E ads is attributed to the Zn 2 TaN 3 monolayer, while the highest E ads is attributed to the Zn 2 VN 3 monolayer. The adsorbed molecules can lead to the formation of local surface dipole due to the charge redistribution within the molecule and/or charge transfer between the molecule and the surface (Sun et al. (2007)). Such a local surface dipole affects chemical activity and electronic properties of materials, such as work function (WF) (Rusu and Brocks (2006)). Therefore, WF of the Zn 2 (V,Nb, Ta)N 3 monolayers adsorbed with the N 2 , CO 2 , NH 3 , NO, and NO 2 molecules is calculated. Figure 2b shows the WF of pure and molecule-adsorbed Zn 2 (V,Nb, Ta)N 3 monolayers. As can be seen, the N 2 , CO 2 , and NH 3 molecules do not significantly change the WF of Zn 2 (V,Nb, Ta)N 3 monolayers. Thus, it can be concluded that no local dipole is formed due to the adsorption of these three types of molecules. A significant decrease in the work function value of the Zn 2 (V,Nb,Ta)N 3 monolayers is found due to the adsorption of the NO molecule, while the NO 2 molecule adsorption leads to an increase in work function value of the Zn 2 (V,Nb,Ta)N 3 monolayers. This suggests that the adsorption of the NO molecule causes a local surface dipole pointing out of the surface, while the NO 2 molecule adsorption causes a local surface dipole directed towards the surface.

Fig. 2. Adsorption energy of the N 2 , CO 2 , NH 3 , NO, NO 2 H 2 O, and O 2 molecules on the Zn 2 (V,Nb,Ta)N 3 monolayers. (a) WF of pure and molecule-adsorbed the Zn 2 (V,Nb, Ta)N 3 monolayers. (b)