Crystal-substrate interaction

Making use of Eqs. (2) and (3) the condition for the equilibrium form dO = 0, dV = 0 leads to Wulff s rule (Gibbs-Curie-Wulff theorem [iii-v]) generalized by - Kaischew [i] to account for the crystal-substrate interaction ... 

The Gibbs-Curie condition including the crystal-substrate interaction can be rewritten in the form... 

Crawford et al. performed an extensive systematic study of the influence of 5CB-substrate interactions on the ordering of liquid crystal molecules at the interface and on the orientational wetting of the system [21,22]. To vary the liquid crystal-substrate interaction, the chain length of the aliphatic acids (C H2n+i-COOH), attached to the walls of Anopore membranes, was varied from n = 5 to n = 20. Based on the experience with lecithine, one would... 

Liquid crystals confined into cylindrical cavities are the most suitable systems for deirteron NMR studies of the interfacial liquid crystal-substrate interactions. There are, however, other systems of confined liquid crystals, which are more important for applications (PDLC and H-PDLC materials), or have been the object of intensive theoretical studies. The latter are composite systems with a random network of pores like liquid crystals in nano-pore glasses, aerogels and aerosils. Unfortunately, in all these cases NMR spectroscopy alone cannot yield accurate information on the surface-or constraint-induced order in the high-temperature phase as no quadrupole splitting is observed. The nature of the spectral line-broadening (static or dynamic) has to be established using NMR relaxometry. Current NMR results related to these systems will be briefly discussed in Sect. 2.4. 

Other interesting thin-film studies using AES have included the growth of platinum on Ti02- and SrO-terminated (100) SrTiOs single-crystal substrates [2.154], of epitaxial niobium films on (110) T1O2 [2.155], the interaction of copper with a (0001) rhenium surface [2.156], and the characterization of radio-frequency (rf) sputtered TiN films on stainless steel [2.157]. 

Since the interaction energy /s with the finite substrate is not easy to handle due to the loss of two dimensional periodicity assumed in the derivation of Eq. 5, we simplify the substrate interaction. We considered that the substrate was a sandwich of the amorphous and the crystalline layers, and the attractive potential Uo(z) works at any point (x,y), while the translational barrier Ui(z) cos(2nx/k) only works on the crystalline substrate. The implicit assumption is that the atomic densities of the crystal and the amorphous are not so different. 

The zeolite provides the environment for shape selective chemistry and is also a high surface area support on which to disperse platinum in a relatively confined environment. The small platinum crystals within the zeolite channels and the orientation effect of the channel window are responsible for the high efficiency of the Pt-KL catalyst to convert linear paraffin to aromatics. Zeolite KL also provides an electron rich environment to enhance stronger platinum-substrate interaction via stronger platinum-support interaction. A review on the subject can be found in the article written by Meriasdeau and Naccache [85]. 

The study of cellulases has progressed considerably in the present decade. Recombinant DNA techniques have been applied and protein-chemical and structural studies have provided new insights. Crystallization of the first cellulases has succeeded recently and detailed structural information may be expected soon. It is hoped that this will give a further incentive to studying the intricate reaction mechanism of these enzymes and their substrate interactions (adsorptions). The important synergy phenomena certainly need a more systematic approach and new techniques should be applied in this area. 

The analysis of such patterns reveals that the microcrystals are preferentially oriented with their (021) planes, the contact planes, parallel to the substrate s surface. The interesting point is that, in order to satisfy such orientation, the hydrogen bonds of the dimers at the interface have to be broken and in addition some reorganization of the molecules is needed (see Fig. 5.6(g)). In conclusion, the molecule-substrate interactions are sufficiently strong (larger yuns and y nv values) to induce COO Aik bonds, where Aik represents sodium and potassium, but the growing crystals adapt their structure in order to crystallize in the known monoclinic bulk phase. 

Growth of various semiconductors onto certain single-crystal substrates has resulted in epitaxial growth in a number of cases. This epitaxy has been well studied for CdS deposition by Lincot et al. [59-63]. Although the epitaxy requires a certain degree of lattice matching between semiconductor and substrate, chemical interactions between the constituents of the deposition solution and the substrate are important as well (discussed in more detail in Chap. 4). It is a reasonable assumption that epitaxial deposition occurs via an ion-by-ion process. Indeed, it has... 

When adsorption takes place on an ordered metal-crystal surface, the adsorbed material forms ordered surface structures. The root cause of this is in mutual atomic interactions, which may be categorized into adsorbate-adsorbate and adsorbate-substrate interactions. In case of chemisorption, the former is considerably the weaker of the two. The possible long-range ordering of the overlayer formed is dominated by adsorbate-adsorbate interaction, however. Ordering of the adsorbed material is also dependent on the degree of surface coverage. Thus, for instance, at... 

This crystal structure shows that the iodide forms hydrogen bonds to all six NH of the two peptide moieties in the complex. It also demonstrates how effectively the anion is embedded between the cyclopeptides. Complex formation thus shields the guest from surrounding solvent molecules, an effect that strengthens receptor-substrate interactions this might be one reason for the anion affinity of 5 in aqueous solution. 

Supramolecular chemistry on crystalline surfaces is governed to a large extent by lateral interactions. Nevertheless, the substrate plays an important role in mediating these interactions. Intermolecular recognition on a surface, for example, can take place only if the adsorbate-substrate interaction allows the molecules to meet each other. Therefore, the choice of the substrate plays a decisive role. Too strong interactions immobilize molecules and do not leave room for 2D supramolecular chemistry or may even induce decomposition too weak adsorbate-substrate interactions cause high mobility and 2D crystallization phenomena will not occur. 

Investigating 2D self-assembly at the molecular level provides new insight into complex inter molecular interactions. These model studies are usually performed under well-defined conditions in order to have more control on complicated surface processes [13]. This includes single-crystal substrates which allow the application of diffraction techniques. 

Liquid crystals represent a transition between solid crystalline substances and isotropic liquids. On heating, mesophases are formed that have ordered structures which can be nematic, smectic or cholesteric. On further heating, the orientation is disturbed and the phases are converted into an isotropic liquid. The long structure of liquid crystals causes isomers with more drawn-out shapes to be readily dissolved in the ordered liquid crystal substrate ( mesophase ) thus yielding stronger sor-bat-sorbent interactions,... 

The effect of the support on the behavior of supported metals through electronic interactions, which becomes especially extremely important at high metal dispersions, is of course avoidable only in case of single crystal substrates. 

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