Epitaxy tilted

In this chapter we discuss the measurement and analysis of simple epitaxial stractures. After showing how to select the experimental conditions we show how to derive the basic layer parameters the composition of ternaries, mismatch of quaternaries, misorientation, layer thickness, tilt, relaxation, indications of strain, curvature and stress, and area homogeneity. We then discuss the hmitations of the simple interpretation. 

If one makes use of the rather limited information available and given above one may infer that a tilt of between 20° and 30° is normal for straight chain azobenzene derivatives when deposited as LB films, even when a homeotropic phase exists. Such a structure can only be produced in a rather loosely packed film. At the moment it is an open question whether monolayers of these materials exist in the hexatic phase as is the case for fatty acids or whether the structure more nearly corresponds to the smectic-A phase. In the case of the birefringent phase described by Jones et al. [151] it was shown that, once this phase was established, further layers deposited by the LB technique go down in an epitaxial manner. 

Table 7.4 summarizes the out-of-plane and in-plane epitaxial relationships of ZnO films and sapphire substrates, the c-axis and a-axis lattice constants of ZnO, the ZnO full peak widths at half maximum (FWHM) of 20-to and uj scans, and the tilt of the ZnO structure along surface normal [47]. Because of the low intensity of the asymmetric (10l4) reflection, the a-lattice constant has larger uncertainty compared to the c-axis lattice constant. The epitaxial relationships correspond to the results of Ohtomo (see Table 1 in [22]). 

Figure 11.16. Optimum biasing time for different bias voltage. The circles mark hetero-epitaxial films, while the triangles correspond to specimens without significant azimuthal alignment. The biasing times fopt of the HOD films with minimum FWHM for the azimuthal tilt angle are connected by straight lines. The vertical extension of the bright area defines the width of the BEN process time window [293].

Gnki is the modulus of the vector of the reciprocal lattice associated to the (hkl) rehection, A9 is the tilt angle from the Bragg condition, and 0 is the angle between the lateral facets and the basal plane (if re-entrant angles are present, the width of the fringes is smaller [110]). If the epitaxial relationships are known, the nature of the facets is directly deduced from the 0 angles [115]. The structure of individual... 

Fig. 9 (A) Schematic illustration of the VLSE process. (B) Tilted SEM image of vertical Si nanowire array grown on a (111) Si wafer. (C) Tilted SEM image of Si nanowire array grown on Si(l 0 0). (From Ref. f) Three of the four equivalent (111) directions are indicated by the white arrows. (D) Cross-sectional SEM images of a 4 im-wide, anisotropically etched trench in a Si(l 1 0) wafer. (E) Au-catalyzed, lateral epitaxial nanowire growth across an 8 tm-wide trench, connecting to opposing sidewall. (From Ref.P f)...

Apart from the (disordered and ordered) monolayer phases of tetraeene/ Ag(l 11), a second ordered phase is observed at higher coverage. This so-called (3-phase [69] is a bilayer with an extremely complex structure which is discussed elsewhere [49]. There are two notable facts about this phase. Firstly, the first layer of the bilayer is not the flat lying monolayer phase (a-phase). Rather, under the influence of the attractive intermolecular interactions with molecules in the seeond layer, the first layer re-orders and (partly) tilts up. This behaviour is markedly different from PTCDA, where the first layer forces the second layer into its epitaxial structure. This disparity indicates once more that for the two systems the weighting between intermolecular and interfacial interactions is different. Seeondly, a detailed analysis of single-molecule spectra in the (3-phase shows that the moleeular environment has a very strong influence on the electronic properties of individual molecules, even for molecules far away from the metal. 

T. S. Kuan, C. K. Inoki, R. Zhang, S. Gu, and T. F. Kuech, Origin of the c-axis tilt occurring during the lateral epitaxial overgrowth of GaN, presented at the 2001 APS March Meeting, unpublished results. 

N. Gmeinwieser, K. Engl, U. T. Schwarz, J. Zweck, W. Wegscheider, S. Miller, A. Leber, A. Weimar, A. Lell, and V. Harle, Strain, wing tilt and photoluminescence in epitaxial lateral overgrown GaN on SiC substrates, Phys. Status Solidi A 201, 2760-2763 (2004). 

Compared to the normal sample preparation method, this method takes much less time, and it is not necessary to check whether the sample is ready or not. By using this technique, one can obtain more or less the same quality cross-section samples as with the conventional method even for HREM studies. However, one can not tilt the sample so much. Fortunately, it is still suitable for an epitaxially grown thin film. 

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