An atomic beam diffraction study of a rare gas monolayer of square symmetry: Kr on (100) NaCl

Properties of a Suggested Commensurate Monolayer Solid of Kr/NaCl(001)

“…The calculations evaluate the static potential energy for lattices of Kr in the presence of the NaCl(001) surface. The Kr pair potentials are the HFD-B2 semiempirical potential fitted to 3D data supplemented by the McLachlan substrate-mediated dispersion energy with coefficients C s1 = 39.2 au and C s2 = 13.5 au, estimated using the approximation of Rauber et al, and an effective distance z ov = 1.8 Å to the image plane, based on an estimated Kr−NaCl distance . For the bilayer calculations, the van der Waals coefficient for second layer Kr atoms is C 3 = 0.256 au, again evaluated using the Rauber approximation.…”

“…DeKieviet et al 7 observed a square monolayer lattice of Kr with nearest-neighbor distance L nn = 4.02 ( 0.04 Å at 30 K using helium atom diffraction. This is about 1.6% larger than the lattice constant of NaCl and about 0.5% larger than the nearestneighbor spacing 5 in 3D Kr at 30 K. They also reported a bilayer solid with a square lattice.…”

“…The Kr pair potentials are the HFD-B2 semiempirical potential fitted to 3D data 16 supplemented by the McLachlan substrate-mediated dispersion energy 1 with coefficients C s1 = 39.2 au and C s2 = 13.5 au, estimated using the approximation of Rauber et al, and an effective distance z ov = 1.8 Å to the image plane, based on an estimated KrÀNaCl distance. 7 For the bilayer calculations, the van der Waals coefficient for second layer Kr atoms is C 3 = 0.256 au, again evaluated using the Rauber approximation. The potential energy and forces arising from 36 neighboring Kr atoms are calculated; this treats five shells of neighbors in the triangular lattice (L 5 = 3L nn ) and seven shells in the square lattice (L 7 = (10) 1/2 L nn ).…”

“…In this context, the monolayer solid of krypton on the (001) face of NaCl might be relatively simple because the 3D nearest-neighbor spacing of Kr at low temperature is L nn = 3.99 Å, and the low-temperature lattice constant of the square surface lattice of NaCl(001) is scriptl = 3.96 Å. Experiments − on Kr/NaCl(001) show a remarkable degree of contradiction, although there is agreement that the basic spatial arrangement of the monolayer Kr is a square lattice. Further, as will be shown here, modeling of the Kr/NaCl(001) monolayer solid depends on corrugation energy terms that are poorly known and that admit complex structures.…”

“…There are several remarkable features of the Kr/NaCl(001) experiments that become evident when the observations are compared against other physisorbed krypton layers. Besides the occurrence of the square lattice, − there is the quite narrow chemical potential range of stability of the monolayer solid before the bilayer is formed . There also is the question of stability relative to the 2D triangular lattice and to uniaxial compression from the square lattice.…”