Electrochemical formation and microstructure of porous GaP have been investigated. Nanostructured porous GaP layers of thickness up to ≈ 20 μm were fabricated on n-type (111)-oriented crystalline c-GaP substrates. Studies of microstructure of porous GaP in dependence on electrolyte type and regimes of technological procedure have been carried out by scanning electron microscopy. The samples were characterized by spectroscopic ellipsometry in visible and near UV spectral range. The investigations have shown that the structure and optical response of porous GaP can be efficiently controlled by technological procedure of electrochemical formation. The shape and dimension of pores can be varied from nanometer-scaled cylindrical pores to GaP nanorods.
The structural, optical, and magnetic properties are studied in the (M_2Cu_2O_3)_m(CuO_2)_n-type single crystals with the surface on which the Bi-2212-type phase was indicated. The physical properties of such samples were interpreted to some extent by the contributions of two phases. When the secondary phases on the surface of the samples were removed by mechanical polishing or etching by Ar^{+}-ion plasma, the physical properties were typical of the (M_2Cu_2O_3)_m(CuO_2)_n-type crystals. The optical method was shown to be effective for indication of secondary Bi-rich phases on the surface of (M_2Cu_2O_3)_m(CuO_2)_n samples.
Ellipsometric studies of NdMnO_3 single crystals of orthorhombic symmetry were carried out in the spectral range 0.5-5.0 eV. Experimental data, which were obtained on the (001)_{pc}-type planes of pseudo-cubic system, were analyzed in the model of biaxial crystal. For the first time, three componentsε_x,ε_y,ε_z of the effective dielectric function for manganites of orthorhombic symmetry were determined. From ellipsometric data, the spectra of optical conductivity and loss function were also calculated and considered. The fine structure of the spectra and optical anisotropy was the basis for discussion of the microscopic origin of the optical transitions responsible for the optical features. The electronic excitations due to dipole-forbidden spin-allowed transitions of the d-d-type in Mn-ions, f-f-type in Nd-ions and charge-transfer 2p(O)-3d(Mn) transitions were taken into account. The data for NdMnO_3 were compared with those obtained for other related undoped and doped single crystals of perovskite-type structure, LaMnO_3, (LaBa)(MnCo)O_3 and (LaCa)CoO_3.
La_{1-x}MnO_3 films grown by metal organic chemical vapor deposition technique on r-plane cut Al_2O_3 substrates were investigated. The change of the optical response over the La_{1-x}MnO_3/Al_2O_3 sample surface was investigated along with the temperature dependence of magnetization. The mostly pronounced difference in the spectra of dielectric function occurred in the region of the d-d transitions of Mn-ions. The changes in the optical spectra and magnetic properties were correlated to the structural features of thin film.
Magnetization M(T) and M(H) data of single crystals of the S=1/2 quasi-one-dimensional system (A_{2}Cu_{2}O_{3})_{m}(CuO_{2})_{n} with various A-site constituents are compared. The studied orthorhombic, incommensurate crystals are characterized by m/n=5/7,7/10, and 9/13. The role of rare-earth ions located in A-sites is discussed.
Aqueous solution of meso-tetra(4-sulfonatophenyl)porphine was deposited on electrochemically etched n-Si wafers. The morphology of the hybrid systems was investigated by scanning electron microscope and atomic force microscope techniques. The optical response of the hybrid systems was studied by spectroscopic ellipsometry in the range of 1-5 eV. Particular features in adsorption process were revealed for meso-tetra(4-sulfonatophenyl)porphine deposited on variously chemically treated Si substrates. It was found that porphyrin J-aggregates can be intercalated into large pores formed in a bulk n-Si as well as into nanopores of luminescent oxide layer.
Iron-containing nanoparticles and clusters were formed in silica with porosity, which was predetermined by different procedures of sol-gel technology and the chemical composition of precursors. Bulk and layer-type samples of different porosity were synthesized and investigated. The morphology, magnetic, and optical properties were studied to characterize the samples and to analyze the formation of Fe-oxides. Experimental results showed that both Fe_2O_3 and Fe_3O_4 were formed in the samples and that their relative amount was dependent on preparation technology.
The results of photoemission and optical studies of icosahedral single-grain ZnMgEr quasicrystals are presented. Synchrotron radiation photoemission measurements were performed on in situ cleaved samples at 10^{-10} mbar pressure and low, 140-150 K temperature. The valence band photoemission spectra measured reveal a simple metal-type valence band of icosahedral ZnMgEr with a distinct Fermi edge cut-off and with a sharp pseudogap feature. The photoemission spectra of shallow Mg 2p and Zn 3d core levels indicate a coordination shift of Mg 2p spin-orbit doublet and an oscillating dependence of Zn 3d photoemission line components on the photon energy within the hν=20-160 eV range investigated. The optical response of icosahedral ZnMgEr, a dispersion of the dielectric function, was measured by the spectroscopic ellipsometry technique in the 0.5-5.0 eV spectral range. The optical spectra of the quasicrystal indicate the Drude-type optical response superimposed with a peak of interband optical transitions. The interband optical transitions can be modelled with the pseudogap parameters which agree with those deduced in an analysis of the photoemission valence band spectra.
The results of an optical spectroscopy study of the icosahedral fci-ZnMgHo quasicrystal are presented. The dielectric function of the quasicrystal was measured by the spectroscopic ellipsometry technique in the spectral range of 0.1-5.0 eV. The analysis of the dielectric function shows that an optical response of fci-ZnMgHo is a superposition of the free-electron Drude-type contribution and that of the interband transitions across the fci-ZnMgHo pseudogap.
Magnetic properties of Pb[Cu(SO_4)(OH)_2] (linarite) natural single crystals were studied by magnetization and specific heat measurements. The angular dependences of magnetization were revealed which correlated with the regularities of the crystal structure. At about 2.8 K this quasi-one-dimensional Heisenberg system undergoes a phase transition to the long-range antiferromagnetic order with antiparallel magnetic moments aligned probably along the b-axis. The antiferromagnetic order is evidenced by the metamagnetic transition and pronounced λ-type anomaly at T_N in the specific heat. Using phenomenological modeling based on a quantum transfer-matrix method, we argue that at higher temperatures linarite is a quasi-one-dimensional system with competing ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange interactions.
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