Doping of the lead telluride and related alloys with the group III impurities results in appearance of unique physical features of a material, such as persistent photoresponse, enhanced responsive quantum efficiency (up to 100 photoelectrons/incident photon), radiation hardness and many others. As a result, single photodetectors based on Pb1-xSnxTe(In) demonstrate extremely high performance in the Terahertz wavelength range. Furthermore, it is shown that local long-lived non-equilibrium states are generated in Pb1-xSnxTe(In) alloys at low temperatures under the action of local Terahertz excitation. This result opens a possibility for construction of a "continuous" focal-plane array for detection of Terahertz radiation. Ideas for readout of information from this array are discussed.
Methods of fabrication of the photonic band gap materials are reviewed, advantages of the combined use of templating and self-assembling methods are stressed. The envelope function approach was used to consider the light field in perfect photonic crystal as the zero-order approximation. Then distortion of the photonic structure has been introduced as perturbation. The simple model used in this paper allows consideration of the effects of short-range and long-range irregularities on transmission spectra. The examples of possible application of the suggested modeling approach and micro- and nanofabrication methods include the enhancement of target detectability, as possible functional elements in focal plane arrays of infrared detectors, controlled introduction of defects, prevention certain waves from propagating though or from photonic band gap materials, detection of direction to the light source, control of temperature distribution by thermal management of microstructure, negative permeability at visible frequencies.
The envelope function approach for the electric and magnetic fields of the light wave in photonic crystals is proposed. We used this approach to investigate the light propagation in disordered photonic crystals and its reflection/refraction at the boubdary. We showed that small long-range distortion of the crystal lattice can explain pecularities of the translittance spectrum of photonic crystals.
Thin nanocrystalline arrays constructed using shear-flow crystallization of polystyrene colloidal nanoparticles consist of two types of domains D1 and D2 which are clearly visible on scanning electron microscopy patterns. Both kinds of domains have cubic close packing (ccp) and are distinguished by their orientation with regards to substrate surface. Positions of main minima in the visible-near-IR transmittance spectrum and their angular dependence on the angle between light direction and normal to the film are interpreted in terms of coexistence of different domain types and band gap structure.
Some examples of ordering in thin inorganic nanocrystalline films, structure of dye-sensitized thin films on optically transparent nanocrystalline electrodes, inorganic epitaxial growth and first heterosupermolecules with nanoparticles as coordination center are accumulated in this short review of our results and literary data to discuss the questions of morphology and optoelectronic properties of nanocrystalline junctions in resulted assembled structures.
The x-ray structure determination of three efficient Ru complex sensitizers of TiO2 nanopowders was carried out. The coordination of Ru was analyzed in terms of asymmetric ligand surrounding of metal atom and influence of chelate (pi) -conjugated ligands on the bonding of Ru with ligands and on the intermolecular association of complexes. The layered character of all three studied crystal structures could be correlated with the peculiarities of their molecular structures (polarity, presence of (pi) -conjugated moieties), what opens the possibility of using of molecular engineering methods to influence the anchoring and ordering of sensitizer molecules on semiconductor surfaces.
The crystal structure of three efficient Ru-sensitizers of TiO2 anatase nanopowders are discussed in terms of formation of two-dimensional molecular packings on the anatase surfaces. The surface areas of sensitizer molecules on the flat semiconductor surfaces are calculated. The symmetry of the (001) and (101) surface of naturally grown TiO2 anatase has been investigated using low-energy electron diffraction (LEED) technique. The first results on the orientation of sensitizer molecules on the mostly exposed surface (101) of anatase single crystal are obtained from HRTEM data. The amount of sensitizer molecules on the mostly exposed faces of anatase nanocrystals in thin colloidal TiO2 anatase films could be estimated using crystal structure data on both sensitizers structures and anatase surface.
The further morphological investigation of nanocrystalline TiO2 films, which sensitized by suitable transition metal complexes forming a new type of molecular photovoltaic systems, the studies of new films and a new Co complexes are presented herein. Scanning electron microscopy, X-ray single crystal and powder diffraction as well as X-ray diffraction at low glancing angles using synchrotron radiation have been used. The morphology of electro- and thermodeposited Pt-layers on TCO (a), polymorphic composition of films (b), possible geometry of location of complex dye molecules on the exposed most faces of TiO2 microcrystals (c) and the crystal structure of a Co(II) complex solvated by electrolyte 4- methyl-1,3-dioxolan-2-on as a precursor of the corresponding redox-system (d) are discussed.
The structure of multilayered TiO2 films formed by nano-structured colloidal particles was studied by scanning electron microscopy, x-ray powder diffraction, and other methods. The structure of the surface and inner layers of the films are discussed in relation to the methods of preparation and subsequent treatment of the films.