Narrow Results

Dithallium phthalocyanine (Tl₂Pc) was synthesized by direct reaction of Tl metal with 1,2-dicyanobenzene. A thin film of the product was prepared by vacuum deposition on KCl single-crystalline substrate and its structure and epitaxy were examined by electron microscopy. The crystal structure of the thin film was the same as the orthorhombic structure reported previously. The film grew epitaxially on KCl substrate as expected from point-on-line coincidence. The UV-vis spectrum of the film was measured and compared with that of an as-synthesized powder sample. The UV-vis spectrum of the thin film of Tl₂Pc showed some differences from that of the powder in the visible region, which may result from the difference in molecular orientation. The electrical resistance of a Tl₂Pc thin film deposited on mica was about 10¹⁰Ω in our measuring set-up, which means that the film does not show high conductivity.

Using a kinetic, Monte Carlo model influence of Schwoebel barriers on morphology of growing films was investigated. With the increase of the deposited dose, transition from 2D to 3D growth mode within Stranski–Krastanow (SK) region without changing interlayer exchange and the growth parameters, was observed. The influence of interlayer atomic exchange on 2D island density, average and maximum island sizes in different atomic layers of thin film were in question. The enlargement of island sizes with the increase of the atomic layer number was demonstrated. This effect is much more pronounced in heterosystems, where atomic hops in the upper layer dominate over hops to the lower layer. The mechanism for transition from two-dimensional to three-dimensional growth mode in one growth process was suggested.

The growth mechanisms of GaAs nanowhiskers (NWs) during molecular beam epitaxy (MBE) are studied theoretically and experimentally. A kinetic model of the diffusion-induced NW growth is presented that allows one to predict the dependence of NW length on the drop radius and on the technologically controlled MBE growth conditions. The results of scanning electron microscopy studies of GaAs NWs grown at different conditions on the GaAs(111)B surface activated by Au are presented and analyzed. It is shown that the length of NWs increases with decreasing the drop radius and with decreasing the deposition rate of GaAs, while its temperature dependence has a certain maximum. The aspect ratio of MBE-grown GaAs NWs is higher than 100. The maximum length of NWs is several times larger than the effective thickness of the deposited GaAs. The obtained results demonstrate that the NW growth is controlled by the adatom diffusion toward their tip rather than by the adsorption-induced vapor–liquid–solid mechanism. The growth conditions' influence on the NW morphology may be used for the controlled fabrication of NWs by MBE for different applications.

Formation of semiconductor quantum dots from a metastable wetting layer with the effective thickness well below the critical thickness is observed experimentally in the InAs/GaAs(100) and in the Ge/Si(100) systems. The observed effect is explained within the frame of the kinetic theory of quantum dot formation in mismatched heteroepitaxial systems.

Bi₂FeCrO₆ thin films were epitaxially grown by pulsed laser deposition on (100)-oriented LaAlO₃, (LaAlO₃)_0.3(Sr₂LaTaO₆)_0.7 and SrTiO₃ single crystalline substrates with and without epitaxial CaRuO₃ buffered layer. The in-plane compressive strain induces monoclinic distortion of the Bi₂FeCrO₆ lattice cell. The strain originates from lattice mismatch between CaRuO₃ and single crystal substrates. The similar crystal structure of the substrate and the layer lead to coherent epitaxial growth of the heterostructures and avoid strain relaxation in particular for BFCO films deposited on LaAlO₃ substrates. The ferroelectric character is demonstrated for all grown BFCO films. The residual in-plane strain weakly affects the effective piezoelectric coefficient of BFCO layers.

Pb(Zr_0.65Ti_0.35)O₃ (PZT) thin films were deposited on SrRuO₃ (SRO) buffer layer coated LaAlO₃ (LAO) substrates by RF sputtering method. X-ray diffraction analyses indicate that the PZT thin films show epitaxial orientation and the in-plane epitaxial relationship between film and substrate is deduced as (001)[010]_PZT‖(001)[010]_SRO‖(001)[010]_LAO. Despite the Zr-richcomposition, observations using transmission electron microscopy reveal that the PZT thin films exhibited tetragonal phase, which was due to the clamping effect of the substrates. The clamping effecton the electrical properties, especially on the dielectric properties, was evaluated. Ferroelectric measurements show that PZT films with LAO/SRO substrates were fatigue-free. However, the test of dielectric property dependences on temperature manifests a relatively low Curie temperature of the PZT films. The loss tangent decreasedwith increase intemperature. Owing to the release of clamping stress, the loss tangent decreased dramatically while the temperature was approaching the phase transition temperature of PZT thin films.

Colloidal inorganic nanocrystals (NCs) constitute an important class of advanced nanomaterials owing to the flexibility with which their dimensionality-dependent physical–chemical properties can be controlled by engineering their compositional, structural, and geometric features in the synthesis stage and the versatility with which they can be exploited in disparate technological fields, spanning from optoelectronics, energy conversion/production to catalysis, and biomedicine. In recent years, building upon knowledge acquired on the thermodynamic and kinetic processes that underlie NC evolution in liquid media, synthetic nanochemistry research has made tremendous advances, opening new possibilities for designing, creating, and mastering increasingly complex NC-based assemblies, in which sections of different materials are grouped together into free-standing, easily processable multifunctional nanocomposite systems. This chapter will provide an overview of this fast-growing research field by illustrating progress achieved in the wet-chemical development of last-generation breeds of so-called hybrid or heterostructured nanocrystals (HNCs) in asymmetric non-core/shell geometries, in which distinct material modules are interconnected in heterodimer, heterooligomer, and anisotropic multidomain architectures via heteroepitaxial bonding interfaces of limited extension. The focus will be on HNCs that incorporate at least one magnetic material component combined with semiconductors and/or plasmonic metals, which hold potential for generating enhanced, unconventional magnetic behavior, on one side, and diversified or even new properties and capabilities, on the other side. Various synthetic strategies, all based on the manipulation of seeded-growth techniques, will be described and rationally interpreted within the framework of the currently understood mechanisms of colloidal heteroepitaxy.