A computational study of the surface structure and reactivity of calcium fluoride

Surface reconstruction of fluorites in vacuum and aqueous environment

“…for each additionally adsorbed water molecule with increasing coverage are given in Table VI. We found a mean adsorption energy of 52 kJ/mol for the (111) termination, which suggests that water molecules are physisorbed rather than chemisorbed onto the surface. Our results agree with previous ab initio calculations at the same level of theory [3] and with water contact angle measurements. The latter suggest a partial hydrophobic character of (111) fluorite terminations [30,74].…”

“…Similar conclusions were found in previous molecular dynamics simulations based on density functional theory, suggesting the preference for an associative rather than dissociative adsorption of water molecules [3,75].…”

“…Fluorite-type crystals have been extensively investigated in the past [1][2][3][4][5][6][7][8] due to their broad technological relevance, including optical applications such as litho-excimer laser optics [9,10], beam deliveries, and zoom lenses, but also as a fluxing agent in the aluminum industry, as ceramic composites in fuel cell applications [11], and as an insulator within semiconductor multilayer structures [12]. Recently, CaF 2 nanoparticles have also attracted interest for medical applications, e.g., as markers in cancer therapy [13] and for potential use in dental care [14][15][16].…”

Structure and diffusion of intrinsic defects, adsorbed hydrogen, and water molecules at the surface of alkali-earth fluorides calculated using density functional theory

“…61,62 Despite being relatively weak adsorption, this associated adsorption is overwhelmingly favored, in agreement with previous experimental studies on CaF 2 ͑111͒ and BaF 2 ͑111͒, 23 and theoretical studies on CaF 2 ͑111͒. 21 In particular, by comparing the energies of the molecularly adsorbed H 2 O with that of the dissociated ͑OH+ H͒, we see that dissociation costs over 3 eV in energy ͑see Table VI͒. We have also considered the situation where water is already dissociated on the surface, and calculated an OH group at a metal site and a H on a neighboring fluorine site on the surface.…”

“…5,6 The basic fluorite bulk and surface structures have been the subject of numerous experimental and computational studies, [7][8][9][10][11][12][13][14][15][16][17][18][19] and more recent low-energy electron diffraction studies have looked into the surface's structure in detail. 20 Studies of water on the surface have been more sparse, generally predicting that water weakly interacts with the surface in normal conditions, 21 but can dissociate or even etch the surface in the presence of surface defects or at high pH. [22][23][24][25] The development of atomic force microscopy ͑AFM͒, and its capability to study insulating surfaces in atomic resolution 26-29 offers a powerful tool for studying surface properties, and this has also been applied to investigate the surfaces of alkali-earth fluorides.…”