Crystalline surface reconstruction

Potential excursions provoking surface oxidations and surface reconstructions of crystalline surfaces. These phenomena can be monitored on noble metal surfaces over a wide range of potentials. With the unique atomic resolution of in situ STM/AFM, it is possible to follow corrosion processes in real time at the atomic level. 

For reconstructed, crystalline surfaces the position vectors of the atoms have to be de-... 

Crystalline surfaces can be classified using the five two-dimensional Bravais lattices and a basis. Depending on the surfaces structure, the basis may include more than just the first surface layer. The substrate structure of a surface is given by the bulk structure of the material and the cutting plane. The surface structure may differ from the substrate structure due to surface relaxation or surface reconstruction. Adsorbates often form superlattices on top of the surface lattice. 

The Cu(100) surface shows in 0.1 M NaOH a similar anodic and cathodic peak both at E = —0.8 V [137] however, no reconstruction of the surface could be found. This is presumably not necessary because the Cu(100) surface is less densely packed in comparison with Cu(lll) and matches already the cuprite structure. Similarly, the close match of the anodic and cathodic peaks without a hysteresis is an additional indication for a faster adsorption process, whereas the surface reconstruction of Cu(lll) with the dilfusion of the Cu atoms to the step edges slows the adsorption process. The anodic film forms at first also a granular structure and a final crystalline film. First STM studies suggest an orientation of Cu(100) parallel to Cu2O(100) with a distance parameter of 0.3 nm which corresponds again to the Cu Cu distance within the cuprite structure. 

In this paper, we only focus on the properties of hydrogen-terminated silicon clusters and the surface reconstructions are ignored. All the cluster models, we used in the present work, were cut out of crystalline silicon and the surfaces were terminated with hydrogen atoms. 

In Section 14 we considered crystalline solids and approximated their structures as if the materials were infinite and periodic in all three dimensions. This may be a good approximation when studying the bulk properties of the material, but for some properties the fact that the material is finite is of ultimate importance. Among these are those properties that are related to the existence of surfaces. The fact that the atoms at the surfaces have a lower coordination than those in the interior and accordingly have dangling bonds leads to the existence of surface-specific properties. These include surface reconstructions for which the surface atoms adopt a structure different from that of the interior, as well as a higher reactivity of the surface atoms. The latter is the topic of the present section. 

The crystallographic structure of interphases can be investigated with various methods. In situ, the application of X-ray diffraction D4SEX is possible. Because of the depth of penetration of X-ray beams both in the transmission and the external reflection arrangement, the sample has to be made very thin in order to minimize unwanted contributions from the bulk of the electrode. Crystalline products of corrosion processes [47,48], surface films [49], surface reconstruction [50] and catalyst systems [51] have been investigated. 

Titanium dioxide (in rutile and anatase structures) is the most investigated crystalline system in the surface science of metal oxides. The review article [783] summarizes the results of experimental and theoretical studies of titanium dioxide (bulk and surface) made up to 2002 inclusive. The information about calculations of the surface reconstruction, surface defects and growth of metals on Ti02 is also included. The results of the later theoretical studies of rntHe surfaces can be found in [784-795] and references therein. In the majority of the calculations the slab model was used for the study of periodic surface structures. 

For Sb and A1 on HOPG, and for Si and Ge on crystalline SiNx/Si(lll), most grown-up crystallites have definite polar (also azimuthal for some) orientation alignment with the substrate. In contrast, for Ge on graphite, and Si and Ge on amorphous SiNx/Si(001), the orientation of the nanocrystals seems completely random, and high-index facets are observed quite often. Surface reconstructions not formed on bulk crystals are observed on some facets. These observations reflect the unique capacity of nanoscale facets to accommodate certain surface superstructures that are not observable on a macroscopic scale. 

The three-dimensional synnnetry that is present in the bulk of a crystalline solid is abruptly lost at the surface. In order to minimize the surface energy, the themiodynamically stable surface atomic structures of many materials differ considerably from the structure of the bulk. These materials are still crystalline at the surface, in that one can define a two-dimensional surface unit cell parallel to the surface, but the atomic positions in the unit cell differ from those of the bulk structure. Such a change in the local structure at the surface is called a reconstruction. 

Anionic surfactants are present in surface water, resulting in serious environmental pollution. Therefore, adsorption of surfactants, such as sodium dodecylsulfate [155,156], on Mg/Al LDHs has received considerable attention. Ulibarri et al. also published the results of sorption of an anionic surfactant (sodium dodecylbenzenesulfonate) from water by LDHs and calcined samples (773 K), focusing both on their potential application as a sorbent and on the possibility of their recycling [154,157]. They found that anionic exchange was complete when the interlayer anion in the LDH precursor was Cl", reaching 100 % of AEG, and calcined LDH-carbonates were better adsorbents than those derived from LDH-chloride samples, however. It was also claimed that an increase in the crystallinity of the LDH samples probably leads to better ordered calcined mixed oxides, facilitating reconstruction of the layers and enlarging the absorption capacity. 

FIGURE 3.2. (a) Chemical structure of octanethiol. (b) A constant current STM image of octanethiol SAM on Au(l 11). Au reconstruction is lifted and alkanethiols adopt commensurate crystalline lattice characteriized by a c(4 x 2) superlattice of a (a/3 x V3)R30°. (c) Model of commensuration condition between alkanethiol monolayer (large circles) and bulk-terminated Au surface (small circles). Diagonal slash in large circles represents azimuthal orientation of plane defined by all-trans hydrocarbon chain. (Reprint with permission from Ref.25 G. E. Poirier, Chem. Rev., 97, 1117-1127 (1997). Copyright 1997 American Chemical Society.)... 

---