Honeycombed rings

The interaction of hydrogen with preadsorbed oxygen at Pt(lll) led to hexagonal and honeycomb structures to develop at 131 K, which could be associated with OH phases with also evidence for water formation. The front (bright ring) consisted mainly of OH(a) and the area behind the front of H20(a). The mechanism suggested is that H(a) reacts first with 0(a) to form OH(a) and then H20(a) the water is mobile and reacts with O(a) to form OH(a) it is therefore an autocatalytic reaction. 

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 geometries in the six-coordinate species, 25a and 25b, are also far from regular even a severely distorted octahedral description appears inappropriate. The DMIO derivative, 25a, forms a honeycomb network due to a combination of S — Sn and O —> Sn intermolecular interactions and the rings are formed from six molecules191. 

Under certain conditions, rather well-defined ring and honeycomb patterns can be formed by solution casting of thin films. Recently Nolte described the formation of isolated rings with diameters of several micrometers formed by stacked porphyrin molecules [287], Phase segregation or eruption of gas bubbles was assumed to be responsible for the peculiar assembly of the porphyrin wheels . However, the regular shape of the solute molecules was also considered to be of crucial importance, Another example is the honeycomb pattern of star shaped poly(styrene)-block-poly(-p-phenylene) films described by Francois [288], In this case, the peculiar molecular shape was emphasized to be of crucial importance besides the proper choice of solvent and evaporation conditions [289],... 

It must be pointed out, however, that the formation of rings and honeycomb pattern is a consequence of the instability of thin films to convection, caused by the fast evaporation of the solvent [290], It does not require complex shaped molecules or even depend on some molecular recognition process. 

In addition, CNTs exhibit several Raman features whose frequencies change with changing excitation wavelength. A prominent example for this unusual behavior is the disorder-induced D band which results from a defect-induced double-resonant process [46]. In the molecular picture, the D band originates from the breathing vibrations of aromatic rings in the honeycomb lattice. A quantitative description of the D band intensity in graphene was recently derived by Sato et al. 

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