Nanometre-scale surface morphology

As mentioned before and assuming the vahdity of the continuum elasticity theory at the dislocation core, F. C. Frank derived the expression for the characteristic radius of a hollow core (Frank, 1951)  

From this expression we observe that R / hc- The terrace connecting two spirals, one left-handed and the other right-handed, will grow indefinitely if the diameter of the critical 2D nucleus, 2Rc, is less than the distance between the emerging points of the two spirals (Frank, 1949). The minimum measured separation between coupled spirals is about 50 nm, so that R 25 nm (see Section 5.1). Asymmetric hollow cores can be clearly seen in Fig. 5.13 and are in fact composed of two single hollow cores of the same sign separated by about 2/ hc, as can be inferred from the figure. 

The decay of the stress field can be approximated by the following expression u nR c) 1 

At this point it is important to realize that from single crystals the full crystallographic information is usually obtained by XRD methods (space group, lattice parameters and atomic coordinates) but that for thin films this is hardly the case, because of the physical limitation imposed by the substrate, in particular when the microcrystals are oriented, in which case only a reduced number of reflections are available. Hence only partial information is obtained with conventional diffraction methods. Removing the microcrystals, e.g., by scratching, in order to perform XRD measurements from the powder is not always possible and handling such small and fragile microcrystals with the usual tools is almost impossible. 

We saw previously the example of TMTSF thin films where the lattice parameters could be obtained, and proof that the triclinic phase coincides with that found for 

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Near-field scanning techniques are relative newcomers, and the basis for their interpretation is less well established. However, AFM has opened up new perspectives for morphological studies, particularly given that excessive surface damage in soft specimens can be avoided by use of non-contact or intermittent contact modes. Its sensitivity to surface topography nevertheless makes AFM prone to artefacts when used to observe surfaces prepared by microtoming, and its effective depth of field is limited compared with SEM. On the other hand, if lamellar surfaces can be prepared such that the surface relief (or hardness, friction variations) is representative of the bulk texture, very striking detail can be recorded at the nanometre scale in deformed polyolefins [11]. 

Several research approaches are pursued in the quest for more efficient and active photocatalysts for water splitting (i) to find new single-phase materials, (ii) to tune the band-gap energy of TJV-active photocatalysts (band-gap engineering), and (iii) to modify the surface of photocatalysts by deposition of cocatalysts to reduce the activation energy for gas evolution. Obviously, the previous strategies must be combined with the control of the s)mthesis of materials to customize the crystallinity, electronic structure, and morphology of materials at nanometric scale, as these properties have a major impact on photoactivity. 

Scopelliti PE, Borgonovo A, Indrieri M, Giorgetti L, Bongiomo G, Carbone R, et al. The effect of surface nanometre-scale morphology on protein adsorption. PLoS One 2010 5 el 1862. Yang L, Li YW, Sheldon BW, Webster TJ. Altering surface energy of nanocrystalline diamond to control osteoblast responses. J Mater Chem 2012 22 205-14. 

ScopeUiti, P.E., Borgonovo, A., Indrieri, M., Giorgetti, L., Bongiorno, G., Carbone, R., Podesta, A., Milani, R, 2010.The effect of surface nanometre-scale morphology on protein adsorption. PLoS One 3. 

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