Single crystals double-layer

Thus the composition of the crystals can take up two discrete values, depending on whether a single or double layer structure is present, for comparable values of L and /. This prediction was confirmed by experimental results (Lotz et al., 1966). 

Their crystal structures, which are different from those of the binary compounds, are listed in table 13. In many cases the rare earths and one of the two non-metals, X, form sheets of general formula (RX) , the second non metal Z being between these sheets in a single or double layer. Some exceptions of this general arrangement are known, however, especially in the series of polytypes RSeF with R = Y or the heavy rare earths. 

Fig. 7, View of the glycine crystal parallel to the c axis showing the single and double layers of glycine molecules held together by hydrogen bonds.

A number of theories have been put forth to explain the mechanism of polytype formation (30—36), such as the generation of steps by screw dislocations on single-crystal surfaces that could account for the large number of polytypes formed (30,35,36). The growth of crystals via the vapor phase is beheved to occur by surface nucleation and ledge movement by face specific reactions (37). The soHd-state transformation from one polytype to another is beheved to occur by a layer-displacement mechanism (38) caused by nucleation and expansion of stacking faults in close-packed double layers of Si and C. 

In situ Fourier transform infrared and in situ infrared reflection spectroscopies have been used to study the electrical double layer structure and adsorption of various species at low-index single-crystal faces of Au, Pt, and other electrodes.206"210 It has been shown that if the ions in the solution have vibrational bands, it is possible to relate their excess density to the experimentally observed surface. 

K. The electrical double-layer structure at Ag single-crystal faces has been studied extensively.6,10,i5,22,24,32,61,63,75,ss, 149-151,177a, 188,250-... 

Electrical Double-Layer Parameters of Bi Single-Crystal Faces in Various Solvents... 

Almost all that is known about the crystal face specificity of double-layer parameters has been obtained from studies with metal single-crystal faces in aqueous solutions. Studies in nonaqueous solvents would be welcome to obtain a better understanding of the influence of the crystallographic structure of metal surfaces on the orientation of solvent molecules at the interface in relation to their molecular properties. 

Hamelin, A. Double-Layer Properties at sp and sd Metal Single-Crystal Electrodes 16... 

CO adsorption on electrochemically facetted (Clavilier), 135 Hamm etal, 134 surfaces (Hamm etal), 134 Platinum group metals in aqueous solutions, 132 and Frumkin s work on the potential of zero charge thereon, 129 Iwasita and Xia, 133 and non-aqueous solutions, 137 potentials of zero charge, 132, 137 preparation of platinum single crystals (Iwasita and Xia), 133 Platinum-DMSO interfaces, double layer structure, 141 Polarization time, 328 Polarons, 310... 

Many studies at single-crystal electrodes of xp-metals were directed at the special features of double-layer stracture and the potential of zero charge at the various single-crystal faces. It was shown that rather large differences could exist between the potentials of zero charge of different faces (see Table 10.1). 

Climent V, Gomez R, Orts JM, Aldaz A, Fehu JM. 1997. The potential of zero total charge of single-crystal electrodes of platinum group metals. In Korzeniewski C, Conway BE, eds. The Electrochemical Society Proceedings (Electrochemical Double Layer). Pennington, NJ The Electrochemical Society, pp. 222-237. 

Climent V, Coles BA, Compton RG. 2002c. Laser-induced potential transients on a Au(lll) single-crystal electrode. Determination of the potential of maximum entropy of double layer formation. J Phys Chem B 106 5258-5265. 

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