Liquid-liquid interfaces offer intriguing possibilities for nanomaterials growth. Here, fundamental interface-related mechanisms that control the growth behavior in these systems are studied for Pb halide formation at the interface between NaX + PbX2 (X = F, Cl, Br) and liquid Hg electrodes using in situ X-ray scattering and complementary electrochemical and microscopy measurements. These studies reveal a decisive role of the halide species in nucleation and growth of these compounds. In Cl- and Br-containing solution, deposition starts by rapid formation of well-defined ultrathin (∼7 Å) precursor adlayers, which provide a structural template for the subsequent quasi-epitaxial growth of c-axis oriented Pb(OH)X bulk crystals. In contrast, growth in F-containing solution proceeds by slow formation of a more disordered deposit, resulting in random bulk crystal orientations on the Hg surface. These differences can be assigned to the interface chemistry, specifically halide chemisorption, which steers the formation of these highly textured deposits at the liquid-liquid interface.
The nature of self-organized three-dimensional structured architectures with spatially modulated electrical conductivity emerging in the process of hydride vapor phase epitaxial growth of single crystalline n-GaN wafers is revealed by photoelectrochemical etching. The amplitude of the carrier concentration modulation throughout the sample is derived from photoluminescence analysis and the localized heterogeneous piezoelectric response is demonstrated. The formation of such architectures is rationalized based on the generation of V-shaped pits and their subsequent overgrowth in variable direction. Detailed structure analysis with respect to X-ray diffraction and transmission electron microscopy gives striking evidence for inelastic strain to manifest in distortions of the P6 3 mc wurtzite-type structure. The deviation from hexagonal symmetry by angular distortions of the β angle between the basal plane and c-axis is found to be of around 1°. It is concluded that the lattice distortions are generated by the misfit strains originating during crystal growth, which are slightly relaxed upon photoelectrochemical etching.
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