Hexagonal surface

Fig. XVI-8. (a) The quasi-hexagonal surface structure of clean Pt(lOO) surface, (b) Adsorption of CO lifts this reconstruction to give the structure corresponding to the termination of (100) planes (from LEED studies). [Reprinted with permission from G. Ertl, Langmuir, 3, 4 (1987) (Ref. 56). Copyright 1987, American Chemical Society.]...

B. J. Brosilow, R. M. Ziff. Comment on NO-CO reaction on square and hexagonal surfaces A Monte Carlo simulation. J Catal 136 275-278, 1992. 

The chain arrangement of this morphology was schematically proposed as in Fig. 10. The cell of the microsphere has a hexagonal surface, and the AB diblock copolymers form a bilayer between the microspheres. From this schematic arrangement, the optimal blend ratio of the AB block copolymer in this system was calculated as 0.46. This value was very close to the blend ratio of the AB type block copolymer 0.5 at which the blend showed the hexagonal packed honeycomb-like structure. 

Fig. 11. Crystal structure of graphite. The unit cell is shaded in green, (a) Top view of the surface layer. The hexagonal surface lattice is defined by two unit vectors u and v in the xy-plane with a length of 246 pm and an angle of 120° forming a honeycomb web of hexagonal rings. The basis of the lattice consists of two carbon atoms a, (white) and /3 (red) with a distance of 142 pm. (b) Perspective view, showing the layered structure. The distance between layers is 2.36 times the next-neighbor distance of atoms within one layer, and the bond between layers is weak. The a-atoms (white) are directly above an a-atom in the layer directly underneath at a distance of 334.8 pm the /3-atoms (red) are over hollow sites (h). The unit vector w is parallel to the z-axis with a length of 669.6pm.

The top layer of the surface reconstructs to LEED/6/ form a compact hexagonal surface, with 6/5 the density of unreconstructed surface. The layer spacing expands by 14.6 5.2% from the bulk value of 1.92 A. Some top-layer atoms are buckled outward by up to an additional 0.2 0.02 A so the hexagonal layer can fit the square layer below. This is 1/2 to 2/3 of the buckling required to have top layer atoms in hard-sphere contact with all substrate atoms. 

Fig. 1 Plan view of a 50 molecule (black ring) on a hexagonal surface. In this figure, the Qo is chosen to be on top of a surface atom with a five-membered ring (black pentagon) directed towards that atom. The PES depends on their relative orientations as given by the azimuthal angle (/>a...

Fig. 7 Schematic diagram of an adsorbed water bilayer over an hexagonal surface. Large empty circles denote surface atoms and small black-filled circles represent hydrogen atoms in water molecules. The remaining circles denote oxygen atoms belonging to adsorbed water molecules. The 0° unit cell is outlined.

Fig. 24. Possible interpretation given by Morgan and Somorjai 175) for the (5 x 1) surface structure showing an hexagonal surface layer superimposed on a square substrate layer. [Redrawn from Morgan and Somorjai (175). Reproduced by permission of North-Holland Publishing Co.]...

The reactivity pattern displayed by platinum crystal surfaces for alkane isomerization reactions is completely different from that for aromatization. Studies revealed that maximum rates and selectivity (rate of desired reaction /total rate) for butane isomerization reactions are obtained on the flat crystal face with the square unit cell. Isomerization rates for this surface are four to seven times higher than those for the hexagonal surface. Isomerization rates are increased to only a small extent by surface irregularities (steps and kinks) on the platinum surfaces (Figure 7.39). 

FIG. 13.15 Hexagonal surface relief panem written on a chin film. 

Hexagonal arrays of dots and pits. The weakly nonlinear evolution of a hexagonal surface structure, h + C.C., where the wavevectors... 

Low-temperature syntheses can sometimes allow unique surface phases to be stable. Tetragonal barium ti-tanate, prepared at 700°C, has hexagonal barium titanate on the surface, which is stabilized by a higher surface free energy. Normally this hexagonal phase is not formed below 1460°C. This hexagonal surface was also found to reversibly adsorb CO2 as a surface carbonate. 

Y. Gao, T. Fujii, R. Sharma, K. Fujito, S.P. Denbaars, S. Nakamura, E.L. Hu, Roughening hexagonal surface morphology on laser hft-off (LLO) n-face GaN with simple photo-enhanced chemical wet etching, Jpn. J. Appl. Phys. 43 (2004) L637—L639. 

---