Photoinduced second-order optical susceptibilities of Er2O3 doped TeO2-GeO2-PbO glasses

Second-order optical susceptibilities were established in the optically poled erbium doped tellurite glasses near the melting temperature. The non-linear optical susceptibility was formed by bicolor coherent optical treatment performed by two coherent laser beams originated from 50 ps Nd-YAG laser (λ = 1.32 μm) exciting the high pressure hydrogen laser cell emitting at 1907 nm. The non-centrosymmetric grating of the medium was created by coherent superposition of the fundamental laser illumination at 1907 nm and the doubled frequency one at 953.5 nm. The maximally all-optically poled SHG occurs for 2% doped Er₂O₃ (in weighting units) TeO₂-GeO₂-PbO glass. It was found that the photoinduced SHG demonstrates a saturation during the photo-treatment of 9-10 min using the two beams polarized at angle about 45° between them. During the coherent bicolor optical treatment it was achieved the value of second-order susceptibility up to 3.6 pm/V at 1907 nm. The optimal ratio between the fundamental beam with power density about 1.1 GW/cm² and writing doubled frequency seeding beam about 0.015 GW/cm² corresponds to the maximal of photoinduced SHG. For glasses with lower concentration of Er₂O₃, the relaxation of the second-order optical susceptibility is substantially longer and achieves SHG value that corresponds to 80% of the maximal ones. It is necessary to emphasize that efficient optically-poled grating exists only within the narrow temperature range near the glassing temperature. Possible physical mechanisms of the phenomenon observed are discussed. Generally the used glasses possess better parameters than early investigated germinate glasses.     

Second harmonic generation in transparent microcrystalline α-CdGa2S4-containing chalcogenide glass ceramics

Transparent glass ceramics were prepared by heat treating of the as-prepared 80GeS₂ · 10Ga₂S₃ · 10CdI₂ glass at 370 °C (T_g + 15 °C) for 72 h (labeled as GGCd10-370). The existence of α-CdGa₂S₄ crystal in GGCd10-370 glass ceramics has been testified by XRD and Raman spectroscopy. Using the typical Maker fringe technique, SHG was observed in the original transparent GGCd10-370 glass ceramics successfully, which is mainly ascribed to the α-CdGa₂S₄ nonlinear optical microcrystal. And the SH intensity is almost 0.8 times larger than that of the standard quartz reference. It can be also deduced that the thickness of crystalline layer is a little larger than the coherent length, l_c ≈ 2.7 μm.     

Scanning tunneling microscopy and spectroscopy investigations of copper phthalocyanine adsorbed on Al2O3/Ni3Al(1 1 1)

Low temperature scanning tunneling microscopy (LT-STM) and scanning tunneling spectroscopy (STS) have been used to investigate adsorbed copper phthalocyanine (C₃₂H₁₆N₈Cu) molecules on an ordered ultrathin Al₂O₃ film on the Ni₃Al(1 1 1) surface as a function of coverage and annealing temperature. For sub-monolayer coverage and a deposition temperature of 140 K two different planar molecular adsorption configurations rotated by 30° with respect to each other were observed with submolecular resolution in the STM images. The template effect of the underlying oxide film on the CuPc orientation, however, is only weak and negligible at higher coverages. For θ_CuPc ≈ 1 ML, before completion of the first layer, the growth of a second layer was already observed. The measured spacing of 3.5 Å between first and second layer corresponds to the distance between the layers in the α-modification of crystalline CuPc. The molecules deposited at 140 K are thermally stable upon prolonged annealing to temperatures up to 250 K. By the use of STS the lowest unoccupied molecular orbital (LUMO) of the adsorbed copper phthalocyanine molecules has been identified at an energy of 1.2 eV above E_F. The lateral distribution of the electronic states of the CuPc has been analyzed and mapped by STS.     

Electrical studies on bulk Se96Sn4 semiconducting glass before and after gamma irradiation

Bulk Se₉₆Sn₄ chalcogenide glass was prepared by melt quenching technique and irradiated by different doses of 4, 8, 12, 24 and 33 kGy using ⁶⁰Co gamma emitter. I-V characteristics were obtained for this glass, before and after gamma irradiation, in the temperature range 200-300 K. Ohmic behavior was observed at low electric fields (≤1×10⁴ V/m), while at higher fields, a deviation from ohmic towards non-ohmic behavior was observed. The plots of ln(I/V) vs. V were found to be straight lines and the slopes of these lines decrease linearly with temperature indicating the presence of SCLC. In the temperature range of measurements, the dependence of DC conductivity on temperature at low electric field shows two types of conduction channels, one in high temperature range 270-300 K and the other at low temperature range 200-270 K. Analysis of the experimental data shows that the conductivity at room temperature decreases with increase in irradiation dose. This is attributed to rupturing of SnSe_4/2 structural units, upon irradiation, and rebuilt of Se atoms between Se chains. This redistribution of bonds, induced by gamma irradiation, is responsible for the corresponding increase in the activation energy. The obtained values of the activation energy indicate that the conduction occurs due to thermally assisted charge carriers movement in the band tail of localized states. However, in the low temperature range, results obtained from Mott’s variable range hopping (VRH) model reveal that the density of localized states has its maximum value at a gamma dose of 12 kGy, while the disorder parameter T_o, hopping distance R_hop and hopping energy W have their minimum value at this particular dose.     

Mössbauer spectroscopy studies of spin reorientations in amorphous and crystalline (Co0.2Fe0.8)72.5Si12.5B15 glass coated micro-wires

Thermo-gravimetric, differential scanning calorimetry and comprehensive ⁵⁷Fe Mössbauer spectroscopy studies of amorphous and crystalline ferromagnetic glass coated (Co_0.2Fe_0.8)_72.5Si_12.5B₁₅ micro-wires have been recorded. The Curie temperature of the amorphous phase is T_C(amorp) ∼730 K. The analysis of the Mössbauer spectra reveals that below 623 K the easy axis of the magnetization is axial-along the wires, and that a tangential or/and radial orientation occurs at higher temperatures. At 770 K, in the first 4 hours the Mössbauer spectrum exhibits a pure paramagnetic doublet. Crystallization and decomposition to predominantly α-Fe(Si) and Fe₂B occurs either by raising the temperature above 835 K or isothermally in time at lower temperatures. Annealing for a day at 770 K, leads to crystallization. In the crystalline material the magnetic moments have a complete random orientation. After cooling back to ambient temperature, both α-Fe(Si) and Fe₂B in the glass coated wire show pure axial magnetic orientation like in the original amorphous state. The observed spin reorientations are associated with changes in the stress induced by the glass coating.     

Eu photoluminescence enhancement due to thermal energy transfer in Eu2O3-doped SiO2-B2O3-PbO2 glasses system

In this work, Eu³⁺-doped lead borosilicate glasses (SiO₂-B₂O₃-PbO₂) synthesized by fusion method had their optical properties investigated as a function of temperature. Atomic Force Microscopy images obtained for a glass matrix annealed at 350 and 500 °C show a precipitated crystalline phase with sizes 11 and 21 nm, respectively. Besides, as the temperature increases from 350 to 300 K a strong Eu³⁺ photoluminescence (PL) enhancement takes place. This anomalous feature is attributed to the thermally activated carrier transfer process from nanocrystals and charged intrinsic defects states to Eu³⁺ energy levels. In addition, the PL peaks in this temperature range were assigned to the Eu³⁺ transitions ⁵D₀→⁷F₂, at 612 nm, ⁵D₀→⁷F₁, at 595 nm, and ⁵D₀→⁷F₀, at 585 nm. It was also observed that the ⁵D₀→⁷F₃ and ⁵D₀→⁷F₄ PL bands at 655 and 700 nm, respectively, show a continuous decrease in intensity as the temperature increases.     

Electronic structure of non-centrosymmetric AgCd2GaS4 and AgCd2GaSe4 single crystals

X-ray photoelectron core-level and valence-band spectra for pristine and Ar⁺-ion irradiated (0 0 1) surfaces of AgCd₂GaS₄ and AgCd₂GaSe₄ single crystals grown, respectively, by the Bridgman method and the method of direct crystallization have been measured in the present work. The X-ray photoelectron spectroscopy (XPS) results reveal high chemical stability of (0 0 1) surfaces of AgCd₂GaS₄ and AgCd₂GaSe₄ single crystals. Electronic structure of AgCd₂GaS₄ has been calculated employing the full potential linearized augmented plane wave method. For the AgCd₂GaS₄ compound, the X-ray emission bands representing the energy distribution of the valence Ag d-, Cd d-, Ga p- and S p-like states were recorded and compared on a common energy scale with the XPS valence-band spectrum. The theoretical and experimental data regarding the occupation of the valence band of AgCd₂GaS₄ were found to be in excellent agreement to each other. Second harmonic generation (SHG) efficiency of AgCd₂GaS₄ by using the 320 ns CO laser at 5.5 μm has been recorded within the temperature range 80–300 K. Substantial increase of the photoinduced SHG which in turn is substantially dependent on the temperature has been detected for the AgCd₂GaS₄ compound.     

Size effect on the SHG properties of Cu-doped CdI2 nanocrystals

Because the optically induced second harmonic generation (SHG) is prevented by symmetry in a centrosymmetric material, one needs to form noncentrosymmetric processes in order to observe the SHG. However, one of the efficient ways to enhance the noncentrosymmetricity of a material is to dope it with an appropriate impurity and amount. We grow Cu-doped CdI₂ layered nanocrystal structures from the mixture of CdI₂ and CuI using the standard Bridgman-Stockbarger method and investigate the nano-confined effects by studying the second-order optical effect via the measurements of SHG. The second-order susceptibility for the nanocrystals is calculated and the values at liquid helium temperature range from 0.38 to 0.83 pm V⁻¹ for the thicknesses of 10-0.8 nm respectively. The size dependence demonstrates the nano-sized quantum-confined effect with a clear increase in the SHG with decreasing the thickness of the nanocrystal or crystal temperature. Since the local electron-phonon anharmonicity is described by third-order rank tensors in disordered systems, the SHG is very similar to that one introduced for the third-order optical susceptibility. It has been confirmed by observing the large photoluminescent yield of the pure crystals. The Raman scattering spectra taken for thin nanocrystals confirm the phonon modes originating from interlayer phonons crucially responsible for the observed effects. The obtained results show that the Cu-doped CdI₂ layered nanocrystals are promising materials for applications in optoelectronic nano-devices.     

Bioactivity of SiO2-CaO-P2O5-Na2O glasses containing zinc-iron oxide

Glasses with composition x(ZnO,Fe₂O₃)(65 − x)SiO₂20(CaO,P₂O₅)15Na₂O (6 ≤ x ≤ 21 mol%) were prepared by melt-quenching technique. Bioactivity of the glasses was investigated in vitro by examining apatite formation on the surface of glasses treated in acellular simulated body fluid (SBF) with ion concentrations nearly equal to those in human blood plasma. Formation of bioactive apatite layer on the samples treated in SBF was confirmed by using Fourier transform infrared reflection (FTIR) spectroscopy, grazing incidence X-ray diffraction (GI-XRD) and scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer. Development of an apatite structure on the surface of the SBF treated glass samples as functions of composition and time could be established using the GI-XRD data. FTIR spectra of the glasses treated in SBF show features at characteristic vibration frequencies of apatite after 1-day of immersion in SBF. SEM observations revealed that the spherical particles formed on the glass surface were made of calcium and phosphorus with the Ca/P molar ratio being close to 1.67, corresponding to the value in crystalline apatite. Increase in bioactivity with increasing zinc-iron oxide content was observed. The results have been used to understand the evolution of the apatite surface layer as a function of glass composition and immersion time in SBF.     

Magnetic dynamics of charge ordered Nd0.80Na0.20MnO3 compound

The magnetic dynamics of charge ordered Nd_0.8Na_0.2MnO₃ compound was studied by measuring the temperature variation of magnetization for different magnetic fields up to 7 T and, the field variation of magnetization at different temperatures down to 5 K. This sample exhibits a charge-ordering transition at 180 K, followed by a weak ferromagnetic (FM) transition at around 100 K and a spin glass like transition below 40 K. Suppression of charge-ordering and spin glass like transition and increase in FM T_C were observed with an increase in magnetic field. A reversible metamagnetic transition above a threshold field (H_f) of 4.5 T was observed at 130 K, followed by a saturation magnetization of 3.2 μ_B/f.u. However at 5 K, an irreversible field induced first order phase transition from charge ordered state to FM state was observed at H_f=5 T. For comparison, the temperature and field variations of magnetization were studied on a FM compound from the same series with the composition Nd_0.90Na_0.10MnO₃. A clear FM transition with a T_C of 113 K and a saturation magnetization of 4.3 μ_B/f.u was observed.     

Magnetism and thermal induced characteristics of Fe2O3 content bioceramics

Magnetic properties of Li₂O–MnO₂–CaO–P₂O₅–SiO₂ (LMCPS) glasses doped with various amounts of Fe₂O₃ were investigated. There is a dramatic change in the magnetic property of pristine LMCPS after the addition of Fe₂O₃ and crystallized at 850 °C for 4 h. Both the electron paramagnetic resonance and magnetic susceptibility measurements showed that the glass ceramic with 4 at% Fe₂O₃ exhibited the coexistence of superparamagnetism and ferromagnetism at room temperature. When the Fe₂O₃ content was higher than 8 at%, the LMCPS glasses showed ferromagnetism behavior. The complex magnetic behavior is due to the distribution of (Li, Mn)ferrite particle sizes driven by the Fe₂O₃ content. The thermal induced hysteresis loss of the crystallized LMCPS glass ceramics was characterized under an alternating magnetic field. The energy dissipations of the crystallized LMCPS glass ceramics were determined by the concentration and Mn/Fe ratios of Li(Mn, Fe)ferrite phase formed in the glass ceramics.     

Electrical properties vs. microstructure of nanocrystallized V2O5-P2O5 glasses — An extended temperature range study

An electronically conducting nanomaterial was synthesized by nanocrystallization of a 90V₂O₅·10P₂O₅ glass and its electrical properties were studied in an extended temperature range from − 170 to + 400 °C. The conductivity of the prepared nanomaterial reaches 2 ? 10^− 1 S cm^− 1 at 400 °C and 2 ? 10^− 3 S cm^− 1 at room temperature. It is higher than that of the original glass by a factor of 25 at room temperature and more than 100 below − 80 °C. A key role in the conductivity enhancement was ascribed to the material's microstructure, and in particular to the presence of the large number of small (ca. 20 nm) grains of crystalline V₂O₅. The observed conductivity dependencies are discussed in terms of the Mott's theory of the electronic hopping transport in disordered systems. Since V₂O₅ is known for its ability to intercalate lithium, the presented results might be helpful in the development of cathode materials for Li-ion batteries.     

Increased temperature bandwidth of second harmonic generator using two KTiOPO4 crystals cut at different angles

We report a second harmonic generator (SHG), whose temperature full-width of half-maximum (FWHM) bandwidth is significantly increased by replacing a single long type-II phase-matched KTiOPO₄ (KTP) crystal with two shorter crystals, which are cut at slightly different phase-matching angles. The total length of the two crystals is the same as that of the longer ones. The experimental results show that the measured temperature FWHM bandwidth of the SHG is significantly increased from 11.8 °C in the single 7 × 7 × 10 mm³ KTP crystal to 60.2 °C when the single KTP is replaced with two of 7 × 7 × 5 mm³ KTP crystals whose phase-matching angle are 1.0° apart. Such a SHG allows stable output when it is operated in the environment of very rough temperature condition.     

Ultrafast nonlinear optical properties of Bi2O3-B2O3-SiO2 oxide glass

The ultrafast nonlinear optical properties of Bi₂O₃-B₂O₃-SiO₂ oxide glass were investigated using a femtosecond optical Kerr shutter (OKS) at wavelength of 800 nm. The nonlinear response time of this Bi₂O₃-doped glass was measured to be <90 fs. The nonlinear refractive-index n₂ was estimated to be 1.6 × 10⁻¹⁴ cm²/W. Measurements for the dependence of Kerr signals on the polarization angle between the pump and probe beams showed that the Kerr signals induced by 30-fs pulse laser arose mainly from the photoinduced birefringence effect.     

An XPS study and electrical properties of Pb1.1Zr0.53Ti0.47O3/PbO/Si (MFIS) structures according to the substrate temperature of the PbO buffer layer

PbO and PZT thin films were deposited on the p-type (1 0 0) Si substrate by the rf magnetron sputtering method with PbO and Pb_1.1Zr_0.53Ti_0.47O₃ targets for the application of the metal-ferroelectric-insulator-semiconductor (MFIS) structure. The MFIS structures with the PbO buffer layer show the good electric properties including a high memory window and a low leakage current density. The maximum value of the memory window is 2.0 V under the applied voltage of 9 V for the Pt/PZT (200 nm, 400 °C)/PbO (80 nm)/Si structures with the PbO buffer layer deposited at the substrate temperature of 300 °C. From the X-ray photoelectron spectroscopy (XPS) results, we could confirm that the substrate temperature of PbO affects the chemical states of the interface between the PbO buffer layer and Si substrate, which results in the inter-diffusion of Pb and the formation of the intermediate phases (PbSiO₃). And the existence of the undesired SiO₂ layer, which is the low dielectric layer, was confirmed at the surface region of the Si substrate by the XPS depth profile analysis.     

In vitro evaluation of bioactivity of CaO-SiO2-P2O5-Na2O-Fe2O3 glasses

Glasses with compositions 41CaO(52 − x)SiO₂4P₂O₅·xFe₂O₃3Na₂O (2 ≤ x ≤ 10 mol.%) were prepared by melt quenching method. Bioactivity of the different glass compositions was studied in vitro by treating them with simulated body fluid (SBF). The glasses treated for various time periods in SBF were evaluated by examining apatite formation on their surface using grazing incidence X-ray diffraction, Fourier transform infrared reflection spectroscopy, scanning electron microscopy and energy dispersive spectroscopy techniques. Increase in bioactivity with increasing iron oxide content was observed. The results have been used to understand the evolution of the apatite surface layer as a function of immersion time in SBF and glass composition.     

Characterization of hybrid electrolytes prepared from the Li2S-P2S5 glasses and alkanediols

Inorganic-organic hybrid electrolytes were prepared by the mechanochemical method using the Li⁺ ion conductive 70Li₂S·30P₂S₅ glass and various alkanediols. Local structure of the prepared electrolytes was analyzed by FT-IR and Raman spectroscopy. The effects of the proportion and chain length of alkanediols on conductivity of the hybrid electrolytes were investigated. The hybrid electrolyte with 2 mol.% of 1,4-butanediol exhibited the conductivity of 9.7 × 10^− 5 S cm^− 1 at room temperature and the unity of lithium ion transference number. The use of alkanediols with shorter chain length was effective in increasing conductivity of hybrid electrolytes. The electrolyte using ethyleneglycol showed the highest conductivity of 1.1 × 10^− 4 S cm^− 1 at room temperature. Lowering glass transition temperature by incorporation of alkanediols is responsible for the enhancement of conductivity of hybrid electrolytes.     

Spray pyrolytic deposition of solid electrolyte Bi2V0.9Cu0.1O5.35 films

Copper substituted bismuth vanadate films have been successfully deposited first time by spray pyrolysis technique on glass substrates suitable for low temperature solid oxide fuel cells. Desired phase formation of polycrystalline Bi₂V_0.9Cu_0.1O_5.35 (BICUVOX.10) was confirmed by X-ray diffraction technique. These films were further studied with EDAX and SEM techniques for their compositional and morphological characterization. Electrical conductivity of BICUVOX.10 is found to be 5.7 × 10⁻² (Ω cm)⁻¹ at 698 K, predicts the onset temperature for ionic contribution suitable for low temperature SOFC applications. Room temperature complex impedance plot reveals that electrical process arises due to contribution from the grain interior.     

Structure and magnetic entropy change of suck-cast Gd60Co26Al6Ge8 alloy

The Gd₆₀Co₂₆Al₆Ge₈ alloy has been prepared by the copper-mold suck-casting and its phase component has been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). It is shown that this alloy consists of primary crystalline Gd₅Ge₃ phase and amorphous matrix. The glass transition temperature (T_g) and crystallization temperatures (T_x) occur at 292 and 320 °C, respectively. The maximal magnetic entropy change (ΔS_M) under 0-5 T field is about 7.6 J (kg⁻¹ K⁻¹) at 155 K and the refrigeration capacity (RC) is about 768 J kg⁻¹, which makes Gd₆₀Co₂₆Al₆Ge₈ bulk metallic glass matrix composite a promising candidate for magnetic refrigerant.     

Laser-induced forward transfer technique for maskless patterning of amorphous V2O5 thin film

A laser-induced forward transfer technique has been applied for the maskless patterning of amorphous V₂O₅ thin films. A sheet beam of a frequency doubled (SHG) Q-switched Nd:YAG laser was irradiated on a transparent glass substrate (donor), the rear surface of which was pre-coated with a vacuum-deposited V₂O₅ 180 nm thick film was either in direct contact with a second glass substrate (receiver) or a 0.14 mm air-gap was maintained between the donor film and the receiving substrate. Clear, regular stripe pattern of the laser-induced transferred film was obtained on the receiver. The pattern was characterized using X-ray diffraction (XRD), optical absorption spectroscopy, scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), atomic force microscopy (AFM), etc.