Boundary molecules adsorption results: a water molecule is chemisorbed to form a covalent (a) and a hydrogen (b) surface-molecule bond In this regard, it is of interest to nd these bound states that do not require pre-dissociation at the grain boundaries of polycrystalline graphene.įig. The oxygen atom thus forms a bond with the carbon atom initially having two nearest neighbors and a dangling bond. In, to simulate water adsorption onto the diamond surface with a vacancy defect, the authors found a metastable state in which the molecule, without losing its integrity, is chemisorbed onto the surface. The authors of discovered that the addition of hydrogen atoms to similar atoms leads to the maximized heat adsorption. The charges on the atoms A are distributed in a complex manner from of -0.07 to +0.10 e, and for each of the clusters, the maximum positive charge is localized on the atoms with only two nearest neighbors. The calculations in this study showed that the C-C bond lengths at the boundary with =16 vary from 1.34–1.58, wider than at the (1.0) boundary. The corresponding crystallographic directions in dierent grains were positioned symmetrically relative to the boundary. In this study, we investigated the adsorption properties of the grain boundary separating the areas with a misorientation angle =16. Statistical analysis showed that the most frequent misorientation angles included were near 0 and 30, and in the intermediate values of 13–17 degrees. The structure of grain boundaries has been studied in using a transmission electron microscopy technique. Due to this, it is interesting to research the structure and properties of grain boundaries with an arbitrary crystallographic orientation via quantum chemistry techniques. These boundaries can be rough, corrugated or protruding, and have some dangling bonds and other active adsorption sites. However, the boundaries between the grains with random orientation are most common. Adsorption of molecules on graphene containing a boundary with a misorientation angle of = 16 The ideal grain boundaries formed by pentagon-heptagon pairs have been observed in experiments. Geometric, electronic, and energy parameters of the C132 H28 graphene cluster (Figure 1) containing the (1.0) boundary with adsorbed fragments of dissociation of water, phosphine, ammonia, and methaneģ.2. The adsorption properties of polycrystalline graphene 151 Table 1. This feature can be used to identify the molecules of gases on graphene in the electronic spectra. It is noticed that the EHL value for the chemisorption of dierent fragments of the molecule dissociation take dierent values. Obviously, the total energy of the “grapheneadsorbed fragments” system increases due to the formation of dangling bonds of some carbon atoms and the tension in the graphene lattice. Thus, following the results obtained in, the heat of adsorption of hydrogen on the ordered graphene is 5 eV. For all the chemisorbed molecules, the binding energy value for the fragments calculated using formula (1) is about 1 eV, which is signicantly less than the sum of the heats of adsorption for -H and the -OH group on graphene. 0.085 e, these particles act as acceptors, while -PH2 and -CH3 fragment chemisorption does not result in the “particle-graphene” charge redistribution (Table 1). The charge transfer in the case of -OH and -NH2 radical chemisorption is -0.115 and The second molecule is held at the surface, forming a hydrogen bond with the oxygen atom of the -OH fragment chemisorbed on the (1.0) boundary. There is the second water molecule physically adsorbed on the (1.0) boundary. The minimum energy is in the system where the -H and -OH groups are chemisorbed respectively on the carbon atoms of the pentagon and the heptagon on the boundary (Figure 1c). The adsorption sites selected for the water dissociation fragments aects the system parameters.
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