Thermoelectrical properties and optical third harmonic generation of Gd-doped PbTe

Nanocrystalline TiO₂ porous films were prepared by a sol-gel dip coating method from a solution using poly(ethylene glycol) as a template, ethanol as a solvent and terpineol as a highly viscous solvent. The thickness of films increases greatly by increasing the amount of terpineol. However, the overmuch incorporation of terpineol hinders the formation of porous structure and accelerates the crack creation. The crack-free film having a three-dimensionally extended porous structure was obtained at the ethanol/terpineol ratio of 8:1, the film thickness with three depositions being 2.5 μm. Pretreatment of the precursor at an appropriate temperature also plays an important role in pore formation. Single-phase anatase TiO₂ porous films were obtained after calcinations at 550°C for 1 h, and the crystal size increases with an increase in the amount of terpineol. The pore formation mechanism is discussed primarily in relation to the phase separation in the system and self-assembly of PEG.     

Second order optical effects in Au nanoparticle-deposited ZnO nanocrystallite films

Photoinduced second harmonic generation (SHG) in Au nanoparticle-deposited ZnO nanocrystallite (NC) films was explored by applying bicolor coherent treatment of a Nd-YAG laser with wavelength 1.06?μm and its SHG. We have established that coexistence of the ZnO and Au nanoparticles gives a substantially larger SHG output with respect to pure ZnO NC deposited on the glass substrate. It was established that the value of the second order susceptibility is about 23?pm?V(-1). Better nonlinear optical susceptibilities were obtained during phototreatment at temperatures near 30-35?°C for the Au doped samples. The samples without gold NCs are temperature independent. Generally an increasing temperature leads to a decrease of the optical SHG.     

ZnS stacking order influence on the formation of Zn-poor and Zn-rich Cu2ZnSnS4 phase

This paper reports the synthesis and characterization of Cu₂ZnSnS₄ (CZTS) absorber films, prepared by a two-step electrodeposition of a ZnS (zinc sulfide) binary and a CZT (copper, zinc and tin) ternary precursors on Mo/Ti/Si substrates. The as-electrodeposited ZnS/CZT and CZT/ZnS stacks were thermally treated in a tubular furnace in sulfur environment at 550 °C. The role of the ZnS buffer layer is to provide a zinc and sulfur reservoir, needed to complete the formation of kesterite phase. X-ray diffraction and Raman analyses revealed the formation of the CZTS phase. The surface morphology and chemical composition of the films were studied using a scanning electron microscope. The bandgap values inferred from diffuse reflectance data, are discussed with respect to the stoichiometry which is considerably affected by the order of the stacks. Room-temperature photoluminescence of the CZT/ZnS sample showed a board PL band of 1.51 eV. It was found that the film with a ZnS layer on top is preferred for the formation of a Zn-rich single CZTS phase.

     

Kinetics of picosecond laser treatment of silver nanoparticles on ITO substrate

In this work, the effect of ITO substrate on Ag NP size, morphology and photoinduced absorption depending on the time of 30 ps laser treatment were explicitly studied. Silver nanoparticles with an average diameter of ∼40 nm supported on indium tin oxide (ITO) were irradiated with a tightly focused pulsed laser (doubled frequency beam) at 532 nm. The size transformation of silver nanoparticles induced by a single pulse of Nd:YAG laser (λ = 532 nm, pulse width = 30 ps) was directly observed by an electron scanning microscopy (FE-SEM) on indium tin oxide surface. Simultaneously the change in the absorption and the corresponding derivatives are also presented. These morphological changes are accompanied by a significant change in the optical absorption properties of the array. This study demonstrates that picosecond laser irradiation is an excellent technique to operate and control the properties of nanostructured materials on solid supports.     

Nanoscale synthesis and optical features of metallic nickel nanoparticles by wet chemical approaches

Nickel nanoparticles (Ni-NPs) were successfully synthesized and attached on indium tin oxide (ITO) substrate by two different methods: from solution reduction process by using sodium borohydride (NaBH₄) as reducing agent in the presence of poly(N-vinilpyrrolidone) (PVP) as protective and stabilizing agents and by polyol process under ethylene glycol EG as a solvent. The results indicated that the samples prepared in aqueous solution show the occurrence of face-centered cubic metallic nickel nanoparticles with a medium diameter of ∼31 nm and good size dispersion compared to the preparation in EG that revealed large size ∼150 nm. The dynamics of the nanoparticle's growth in the solvents and comparison with optical absorption is presented.     

Nonlinear optical diagnostic of semimagnetic semiconductors Pb1−xYbxX (X = S, Se, Te)

Nonlinear optical measurements were performed to elucidate the influence of magnetic ions on the behavior of charge carriers in magnetic semiconductors—Pb_1−xYb_xX (X = S, Se, Te at x = 1-3%). It was shown that nonlinear optical methods could be used as sensitive tools for investigations of electron-phonon anharmonicity near low-temperature semiconductor-insulator phase transitions. There exists a difference between surface and bulk-like contributions to the nonlinear optical effects. It was shown that only low-temperature Two Photon Absorption (TPA) oscillator may be related to the number of the electron-phonon anharmonic modes responsible for the observed phase transformation. The explanation of the anomalous temperature dependences is given in accordance with dipole momentum's behaviors determined by low-temperature spin-spin interactions and by electron-phonon anharmonic interactions. We have discovered that low-temperature dependence of specific heat of Pb_1−xR_xTe (R = Yb, Pr with x = 3% and 1.6%, respectively) exhibits a non-magnetic order caused by large electron-phonon contributions and structural disorder effects.     

Photoinduced absorption of Ag nanoparticles deposited on ITO substrate

Substantial changes of absorption after illumination by 300 mW continuous wave green laser at 532 nm were observed. The effect of indium tin oxide (ITO) substrate was explored versus Ag nanoparticles (AgNPs) size, their regularity and surface plasmon resonance. The ITO substrate features play a crucial role for the formation of homogenous AgNPs. The attachments of AgNPs on ITO surface as well as their homogeneity are significantly changed under the influence of the laser treatment. We study the Ag NP deposited on the two different substrates which play a crucial role in the photoinduced absorption. The dependence of the photoinduced absorption versus the time of optical treatment is explained within a framework of the photopolarization of the particular trapping levels on the borders between the ITO substrate and the Ag NP.     

Temperature anomalies of DEA-CuCl4 and TEA-CoCl2Br2/PMMA nanocomposites

Phase transitions were studied for the new synthesized ferroic (NH₂(C₂H₅)₂CuCl₄ (DEA-CuCl₄) and (NH₂(C₂H₅)₄CoCl₂Br₂ (TEA-CoCl₂Br₂) nanocrystallites (NC) incorporated into polymer matrices. Comparison with the bulk crystals is performed. A giant temperature shift (from 305.1°C to 360.3°C) of onset temperature for TEA-CoCl₂Br₂ nanoparticles after their incorporation into the PMMA matrix was found and is substantially larger compared to the DEA-CuCl₄. The DSC analysis shows that the temperature of phase transition is crucially dependent on the thermocycling and temperature rate. The principal role of the nano-sized effects is shown.