Moisture absorption characteristics of a SiO2 film from 2 to 3 μm

We prepare SiO2 coatings on different substrates by either electron-beam evaporation or dual ion-beam sputtering. The relative transmittances of the Si O2 coatings are measured during the heating process. The Si O2 coating microstructures are studied. Results indicate that the intensity and peak position of moisture absorption are closely related to the microstructures of the coatings. The formation of microstructures depends not only on the preparation process of the coatings but also on the substrate characteristics.     

Surface reconstruction on stishovite SiO2,HfO2 and rutile TiO2 （001）

This paper systematically investigates the surface reconstruction processes and patterns on stishovite SiO 2,HfO 2 and rutile TiO 2 (001) by using classical molecular dynamics.It is found that these three surfaces relax instead of reconstruction at 0 K,and have little possibility to reconstruct below 40 K.Above 40 K,surface reconstructions take place as collective atomic motion which can be speeded by higher temperature or compressed strain.Several reconstruction patterns with approximate surface energies are found,and electrostatic potentials on them are also provided in comparison with possible microscopic results.     

Adsorption of methyl orange on mesoporous γ-Fe2O3/SiO2 nanocomposites

Mesoporous γ-Fe₂O₃/SiO₂ nanocomposite containing 30 mol% of γ-Fe₂O₃ was prepared by a template-free sol-gel method, and its removal ability for methyl orange (MO) was investigated. The nanocomposite was characterized using X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), Fourier transform infrared (FTIR) absorption measurements, nitrogen adsorption-desorption measurements, and magnetic measurements. The synthesized γ-Fe₂O₃/SiO₂ nanocomposite has a mesoporous structure with an average pore size of 3.5 nm and a specific surface area of 245 m²/g, and it exhibits ferrimagnetic characteristics with the maximum saturation magnetization of 20.9 emu/g. The adsorption of MO on the nanocomposite reaches the maximum adsorbed percentage of ca. 80% within a few minutes, showing that most of MO can be removed in a short time. The MO adsorption data fit well with both Langmuir and Freundlich adsorption isotherms. The maximum adsorption capacity of MO is estimated to be 476 mg/g.     

Transformation from β-Ga2O3 to GaN Nanowires via Nitridation

Element doping is an important way to modify the properties of semiconductor materials. In our previous work, it was found that nitrogen-doping in β-Ga2O3 nanowires can induce a novel luminescence emission （around 740 nm） caused by generation of acceptor levels at the middle of the band gap of the β-Ga2O3 nanowires. Here we report that further heavy doping of nitrogen can transform the β-Ga2O3 nanowires completely into wurtzite structured GaN nanowires. Transmission electron microscopy （TEM）, x-ray diffraction （XRD） and Raman spectrum are used to evaluate the transition process. Both XRD and Raman analysis reveal that the monoclinic β-Ga2O3 nanowires start phase transformation at a temperature around 850℃ towards wurtzite structured GaN. Our results will be very helpful to profound our understanding of the doping induced effects and phase transformation in semiconductor compounds.     

The hybrid photocatalyst of TiO2–SiO2 thin film prepared from rice husk silica

The TiO₂–SiO₂ thin film was prepared by self-assembly method by mixing SiO₂ precursor with titanium precursor solution and aged to obtain a co-precipitation of silica and titanium crystals. Dip coating method was applied for thin film preparation on glass slide. The X-ray diffraction (XRD) of the self-assembly thin film had no characteristic property of SiO₂ and even anatase TiO₂ but indicated new crystal structure which was determined from the Fourier Transform Infrared Spectrophotometer (FTIR) as a hybridized Ti–O–Si bonding. The surface area and surface volume of the self-assembly sample were increased when SiO₂ was incorporated into the film. The self-assembly TiO₂–SiO₂ thin film exhibited the enhanced photocatalytic decolorization of methylene blue (MB) dye. The advantages of SiO₂ are; (1) to increase the adsorbability of the film and (2) to provide the hydroxyl radical to promote the photocatalytic reaction. The self-assembly thin film with the optimum molar ratio (SiO₂:TiO₂) as 20:80 gave the best performance for photocatalytic decolorization of MB dye with the overall efficiency of 81%.     

Lysine adsorption on the silanized SiO2-surface for immobilization of the estrogen receptor hERα

We investigated the adsorption of the l-lysine (200 mmol) molecule to a silanized SiO₂ surface as a function of the pH value. The SSC (Spraying Spin Coating) method [Cherkouk et al., J. Colloid Interf. Sci. 337 (2009) 375-380] was applied to functionalize the SiO₂ surface by using the (3-aminopropyl)trimethoxysilane (APMS) as coupling agent with a NH₂ functional group. We adsorbed lysine molecules to the silane film for pH-values of 2.5, 7.5, 8.7, 9.5 and 13, which correspond to the di-cationic, cationic, zwitterinonic (pH 8.7 and 9.5) and the anionic charge state of lysine, respectively. The infrared spectroscopy is not suitable to investigate the system because the NH³⁺ signal at 1600 cm⁻¹ originating from the silane film overlaps with the infrared signal of the deprotonated carboxyl group of the lysine molecule. X-ray photoelectron spectroscopy (XPS) was used to measure the binding energies C 1s and N 1s as function of the pH value. This pH change affects the charge state which was fitted in the XPS spectra to obtain the optimal adsorption conditions at pH 7.5 of the lysine to the functionalized SiO₂ surface.     

Influence of annealing on microstructure and magnetic-transport of FeCo–SiO2 nanogranular films

A series of FeCo–SiO₂ nanogranular films were prepared using magnetron controlled sputtering method. The microstructure, tunneling giant magnetoresistance (TMR) and magnetic properties of FeCo–SiO₂ films deposited at room temperature and then annealed at various temperatures were investigated using transmission electron microscopy (TEM), conventional four probes method and vibrated sample magnetometer (VSM) under room temperature, respectively. The results showed that all FeCo–SiO₂ films consisted of FeCo granules with equiaxial shape uniformly dispersed in the SiO₂ matrix and formed body-centered cubic (bcc) structure. With increasing the annealing temperature, FeCo granule size increased monotonically. For film with 30.5 vol% FeCo, the size distribution satisfied the log-normal function at lower annealing temperature. While with increasing annealing temperature, the size distribution deviated gradually from the log-normal function. Meanwhile, upon varying the annealing temperature, the TMR of films with lower volume fraction reached a peak value at higher annealing temperature and the TMR of films with higher volume fraction reached a peak value at lower annealing temperature. In addition, the results also indicated that the sensitivity of TMR changed non-monotonically with the increment of the annealing temperature and both the saturation magnetization and the susceptibility of FeCo (30.5 vol%)–SiO₂ films increased with increasing the annealing temperature.     

Study on the n-β-FeSi2/p-Si solar cells under different illuminated directions

The n-β-FeSi₂/p-Si heterojunction solar cells can be used under illumination of β-FeSi₂ side or Si side. In this work, the effects of illuminated direction on the photovoltaic properties of n-β-FeSi₂/p-Si heterojunction solar cells were analyzed by numerical methods. The calculated results show that the n-β-FeSi₂/p-Si heterojunction solar cell under illumination of β-FeSi₂ side has superior photovoltaic properties, which is consisting with the experimental reports. For the illumination of Si side, the photo-generated carriers in the back surface of Si substrate are far from the built-in electric field, resulting in the reduced conversion efficiency. The calculated results indicate that we should choose the illumination of β-FeSi₂ side for n-β-FeSi₂/p-Si heterojunction solar cell application.     

High-frequency FeCoNiNbB–SiO2 nano-granular films with high resistivity and adjustable resonance frequency from 1.3 to 7.8?GHz

A series of (FeCoNiNbB) _x –(SiO₂)_1−x nano-granular thin films were fabricated by magnetron sputtering with different oblique incidence angles θ. High-resolution transmission electron micrographs show that the films consist of amorphous CoFeM (M = Ni, Nb, B) alloy particles with diameter about 2 nm surrounded by amorphous SiO₂ matrix. Excellent soft magnetic properties have been achieved with a variable in-plane uniaxial magnetic anisotropy field H _k0, which increases monotonically with θ and x, and decreases with the composition of B in FeCoM. For one typical sample of x=0.63 with θ=30°, H _ch and H _ce are 4.2 Oe and 5.4 Oe, respectively, ρ reaches 12.5 mΩ cm and 4π M _s and H _k0 are 5.70 kG s and 92 Oe, respectively, which lead to a high ferromagnetic resonance frequency f _r of 2.2 GHz. Based on the analysis of experimental results, two sources for the origin of the magnetic anisotropy, namely anisotropic magnetic coupling and orientation order of atomic pairs, are suggested.     

Electronic Evolution from the Parent Mott Insulator to a Superconductor in Lightly Hole-Doped Bi2Sr2CaCu2O8+σ

High temperature superconductivity in cuprates is realized by doping the Mott insulator with charge carriers. A central issue is how such an insulating state can evolve into a conducting or superconducting state when charge carriers are introduced. Here, by in situ vacuum annealing and Rb deposition on the Bi₂Sr₂Ca_0.6Dy_0.4Cu₂O_8+σ(Bi2212) sample surface to push its doping level continuously from deeply underdoped(T_c = 25...     

Structure and photoluminescence properties of epitaxial SnO2 films grown on α-Al2O3 (0 1 2) by MOCVD

SnO₂ thin films have been successfully deposited on α-Al₂O₃ (0 1 2) substrates by metalorganic chemical vapor deposition (MOCVD) in the temperature range 500-700 °C. The films were epitaxially grown in the tetragonal SnO₂ phase and were (1 0 1) oriented. In-plane orientation relationship [0 1 0]SnO₂||[1 0 0]Al₂O₃ and [1 0 1?]SnO₂||[1? 2? 1]Al₂O₃ was determined between the film and substrate. Photoluminescence (PL) spectra measured at room temperature revealed that the film grown at 700 °C showed an intense ultra-violet (UV) PL peak at 333 nm, which was a band-edge emission peak in SnO₂ films. At a temperature of 13 K, a new broad PL band centered at about 480 nm was observed. The corresponding PL mechanisms are discussed in detail.     

Rotational analysis of 6ν3 and 6ν3+ν2−ν2 bands of N2O from ICLAS spectra between 12,760 and 12,900 cm

The absorption spectrum of nitrous oxide (N₂O) has been recorded by Intracavity Laser Absorption Spectroscopy between 12,760 and 12,900 cm⁻¹. The rotational analysis led to an improved determination of rovibrational parameters of the 6ν₃ and 6ν₃+ν₂-ν₂ bands of ¹⁴N₂¹⁶O. The high J rotational levels of the (0 0 ⁰6) and (0 1 ¹6) upper states were found perturbed by an anharmonic interaction. Line intensity values of the 6ν₃ band are provided and the main effective dipole moment parameter has been determined.     

Postprocessing treatments to improve the laser damage resistance of fused silica optical surfaces and SiO2 coatings

The combination of deep wet etching and a magneto-rheological finishing(MRF) process is investigated to simultaneously improve laser damage resistance of a fused-silica surface at 355 nm. The subsequently deposited SiO2 coatings are researched to clarify the impact of substrate finishing technology on the coatings. It is revealed that a deep removal proceeding from the single side or double side had a significant impact on the laser-induced damage threshold(LIDT) of the fused silica, especially for the rear surface. After the deep etching, the MRF process that followed does not actually increase the LIDT, but it does ameliorate the surface qualities without additional LIDT degradation. The combination guarantee both the integrity of the surface’s finish and the laser damage resistance of the fused silica and subsequent SiO2 coatings.     

Switching from unusual to usual ferromagnetism in “112” LnBaCo2O5.50±δ: By calcium doping

The effect of calcium doping on the magnetic and transport properties of the intermediate size lanthanide cobaltites of the type Ln_1−xCa_xBaCo₂O_5.50±δ (Ln=Y, Gd, Eu and Sm) has been investigated for 0?x?0.2. The substitution of Ln by calcium induces a large expansion of the ferromagnetic state in the whole temperature range below T_C. The unusual trend of the decrease in T_C with the increase in Ln size in the undoped parent oxides becomes opposite in the calcium doped samples. Such an unusual behavior of the ferromagnetic T_C in the parent compounds is explained on the basis of thermally activated hole-mediated ferromagnetic coupling between the high-spin cobalt ions. The ferromagnetic state of the Ca-doped samples originates from the Co³⁺–O–Co⁴⁺ superexchange interaction, where Co⁴⁺ emerges from the disproportionation mechanism of the cobalt Co³⁺ into Co²⁺ and Co⁴⁺. However, the Ca-doping does not significantly affect the metal–insulator transition, which is associated with the structural change and not related to the spin state transition.     

Structural and optical properties of Ga2(1−x)In2xO3 films prepared on α-Al2O3 (0 0 0 1) by MOCVD

Ga_2(1−x)In_2xO₃ thin films with different indium content x [In/(Ga + In) atomic ratio] were prepared on α-Al₂O₃ (0 0 0 1) substrates by the metal organic chemical vapor deposition (MOCVD). The structural and optical properties of the Ga_2(1−x)In_2xO₃ films were investigated in detail. Microstructure analysis revealed that the film deposited with composition x = 0.2 was polycrystalline structure and the sample prepared with x up to 0.8 exhibited single crystalline structure of In₂O₃. The optical band gap of the films varied with increasing Ga content from 3.72 to 4.58 eV. The average transmittance for the films in the visible range was over 90%.     

Luminescence of LiTb(PO3)4:Sm3+ and energy transfer from Tb3+ to Sm3+ under vacuum ultraviolet–ultraviolet excitation

The photoluminescence (PL) of LiTb(PO₃)₄, LiGd_0.97Sm_0.03(PO₃)₄, and LiTb_0.97Sm_0.03(PO₃)₄ under vacuum ultraviolet (VUV)/ultraviolet (UV) excitation were studied. We observed the VUV–UV sensitization of Sm³⁺ emission (561 nm, 601 nm, 649 nm, and 710 nm) by Tb³⁺ in LiTb(PO₃)₄:Sm³⁺, which leads to the yellow light emission (486 nm, 546 nm, 561 nm, 587 nm, 601 nm, 621 nm, 649 nm, and 710 nm) of LiTb(PO₃)₄:Sm³⁺ phosphor under UV and VUV excitation. The emission is a result of partial energy transfer from Tb³⁺ to Sm³⁺, which is discussed in detail in terms of the excitation and emission spectra and decay curves.     

Highly thermal stable transparent conducting SnO2:Sb epitaxial films prepared on α-Al2O3 (0 0 0 1) by MOCVD

Antimony-doped tin oxide (SnO₂:Sb) single crystalline films have been prepared on α-Al₂O₃ (0 0 0 1) substrates by metal organic chemical vapor deposition (MOCVD). The antimony doping was varied from 2% to 7% (atomic ratio). Post-deposition annealing of the SnO₂:Sb films was carried out at 700-1100 °C for 30 min in atmosphere ambient. The effect of annealing on the structural, electrical and optical properties of the films was investigated in detail. All the SnO₂:Sb films had good thermal stability under 900 °C, and the 5% Sb-doped SnO₂ film exhibited the best opto-electrical properties. Annealed above 900 °C, the 7% Sb-doped SnO₂ film still kept high thermal stability and showed good electrical and optical properties even at 1100 °C.     

Structural and photoluminescence properties of SnO2:Ga films deposited on α-Al2O3 (0 0 0 1) by MOCVD

Gallium-doped tin oxide (SnO₂:Ga) films have been prepared on α-Al₂O₃ (0 0 0 1) substrates at 500 °C by the pulse mode metalorganic chemical vapor deposition (MOCVD) method. The relative amount of Ga (Ga/(Ga+Sn) atomic ratio) varied from 3% to 15%. Post-deposition annealing of the films was carried out at different temperatures for 1.5 h in ambient atmosphere . The structural, electrical, optical and photoluminescence (PL) properties of the films have been investigated as a function of annealing temperature. All the films have the rutile structure of pure SnO₂ with a strong (2 0 0) preferred orientation. A single ultraviolet (UV) PL peak near 337.83 nm was observed at room temperature for the 3% Ga-doped as-grown film and near 336 nm for the 15%-doped film, which can be ascribed to electron transition from the oxygen vacancy and interstitial Ga³⁺ donor levels to the acceptor level formed by the substitution of Ga³⁺ for the Sn site. After annealing, the luminescence spectra have changed a little bit, which is being discussed in detail.