Modification in structural and optical properties of ZnO, CeO2 doped Al2O3-PbO-B2O3 glasses

The structural and optical analysis of glasses is carried out by XRD, FTIR, density and UV visible spectroscopic measurement techniques. XRD results have confirmed the glassy nature of the samples. The FTIR spectral analysis reveals that with the combined presence of ZnO and CeO₂ contents in Al₂O₃-PbO-B₂O₃ glasses, more BO₃ groups are transformed into BO₄. The optical analysis reveals that optical band gap energy decreases more for CeO₂-ZnO-Al₂O₃-PbO-B₂O₃ glasses (from 2.28 to 1.84 eV). The presence of CeO₂ and ZnO in the glass samples causes more compaction of the borate network due to the formation of more BO₄ groups and the presence of ZnO₄ groups, which results an increase in density, refractive index and decrease of molar volume.     

Spectroscopic study of ZnO doped CeO2-PbO-B2O3 glasses

Glass samples of compositions xZnO-xCeO₂-(30−x)PbO-(70−x)B₂O₃ with x varying from 2% to 10% mole fraction are prepared by the melt quench technique. The structural and optical analysis of glasses is carried out by XRD, FTIR, density and UV-visible spectroscopic measurement techniques. The FTIR spectral analysis indicates that with the addition of ZnO contents in glass network, structural units of BO₃ are transformed into BO₄. It has been observed in our previous work that band gap decreases from 2.89 to 2.30 eV for CeO₂-PbO-B₂O₃ glasses with cerium content varying from 0% to 10% [Gurinder Pal Singh, Davinder Paul Singh, Physica B 406(3) (2011) 640-644]. With the incorporation of zinc in CeO₂-PbO-B₂O₃ glasses, the optical band gap energy decreases further from 2.38 to 2.03 eV. This causes more compaction of the borate network, which results in an increase of density (3.39-4.02 g/cm³). Transmittance shows that ZnO in glass samples acts as a reducing agent thathelps to convert Ce⁴⁺→Ce³⁺ ions.     

Dependence of photocurrent on UV wavelength in ZnO/Pt bottom-contact Schottky diode

We fabricated the bottom-contacted ZnO/Pt Schottky diode and investigated the dependence of its photocurrent on the wavelength of illuminated ultraviolet (UV) light source. The bottom-contacted Schottky diode was devised by growing (000l) ZnO on (111) Pt, and the fabricated device showed a strong dependence on the UV wavelength for its photo-response characteristics. When longer-wavelength-UV (e.g., UV-A) was illuminated on the device, the photo-current was increased by a factor of 200, compared to that under illumination of shorter-wavelength-UV (e.g., UV-C). The behavior is attributed to the wavelength-dependent UV penetration depth for ZnO.     

UV photodetector behavior of 2D ZnO plates prepared by electrochemical deposition

Zinc oxide (ZnO) with 2D hexagonal structure was successfully prepared using electrochemical deposition (ECD) method on a quartz substrate pre-coated with indium-doped ZnO layer. The X-ray diffraction of the prepared sample confirmed that the hexagonal structure had a dominant c-axis orientation. The scanning electron microscopy revealed the 2D hexagonal structure of the prepared ZnO.     

Characteristics of SAW UV sensors based on a ZnO/Si structure using third harmonic mode

This paper describes the characteristics of surface acoustic wave (SAW) ultraviolet (UV) sensors fabricated from a ZnO thin film using the third harmonic mode. A ZnO thin film was used as an active layer for UV detection, and a piezoelectric layer was sputtered using magnetron sputtering. The X-ray diffraction (XRD) and photoluminescence (PL) spectra showed that the ZnO sputtered onto Si(100) was highly (002)-oriented and had good optical properties. The two-port SAW resonator was based on an inter-digital transducer (IDT)/ZnO/Si structure and was fabricated and exposed under UV light at a wavelength of 380 nm. As a result, under a UV intensity of 3 mW/cm², the SAW UV sensor was greatly shifted by 400 kHz at the third harmonic mode compared to a frequency shift of 10 kHz in the fundamental mode.     

Characterization and catalytic performance of pure and Li2O-doped CuO/CeO2 catalysts

Pure and Li₂O-doped CuO/CeO₂ catalysts calcined at 500 °C were prepared by impregnation method. The catalysts are characterized by DTA, TG-DTG, XRD, IR, TEM, nitrogen adsorption at −196 °C and the catalytic decomposition of hydrogen peroxide at 30 °C.The effects of molar ratio, heat treatment time and the doping on the structural, surface and catalytic properties of nanocrystalline Cu/Ce-mixed oxides system have been studied. It was found that the catalytic activity of ceria-supported copper oxide catalysts increased by increasing both the heat treatment time and dopant content. However, the pure Cu/Ce-mixed oxide solids containing 10 wt.% CuO exhibited the best performance. The characterization results indicated that the higher surface area, the formation of solid solution between copper and cerium oxides, and the high dispersion of copper species on the ceria were responsible for the high catalytic activity of the CuO/CeO₂ catalysts.     

Influence of proton irradiation on the photoluminescence spectra of zinc oxide modified by ZrO2 and ZrO2·Y2O3 nanopowders

ZnO powder photoluminescence spectra at 360-660 nm modified and unmodified by ZrO₂, ZrO₂Y₂O₃ nanopowders before and after 100 keV proton irradiation were investigated. It was found that introduction of nanoparticles led to ultraviolet band intensity decrease and to visual spectrum band intensity increase. Extinction of intensity occurs under the effect of protons in both bands of luminescence. Decomposition of spectra into elementary defects and analysis of their area change during modification and irradiation were carried out.     

Synthesis and Characterization of TiO2 Doped ZnO Microtubes

以氯化锌和硫酸钛为原料,通过湿化学法成功制备了钛掺杂氧化锌微米管. 以粉末X射线衍射仪、场发射扫描电子显微镜、光致发光系统对样品进行了表征. 结果表明,未经掺杂的氧化锌微管具有良好的六方中空结构. 在TiO₂/ZnO比率小于5%时,钛掺杂和未掺杂氧化锌管具有相近的尺度,外表光滑,近于圆柱形. 当TiO₂/ZnO比率大于5%时,生成一种由ZnO, Ti₃O₅和TiO组成的多相混合物. 钛掺杂氧化锌在光催化降解甲基橙溶液效果明显.     

Elucidating surface properties of dry-etched ZnO using H2/CH4 and H2/CH4/Ar plasma

This paper reports a study of reactive ion etching (RIE) of n-ZnO in H₂/CH₄ and H₂/CH₄/Ar gas mixtures. Variables in the experiment were gas flow ratios, radio-frequency (rf) plasma power, and total pressure. Structural and electrical parameters of the etched surfaces and films were determined. Both the highest surface roughness and highest etching rate of ZnO films were obtained with a maximum rf power of 300 W, but at different gas flow ratios and working pressures. These results were expected because increasing the rf power increased the bond-breaking efficiency of ZnO. The highest degree of surface roughness was a result of pure physical etching by H₂ gas without mixed CH₄ gas. The highest etching rate was obtained from physical etching of H₂/Ar species associated with chemical reaction of CH₄ species. Additionally, the H₂/CH₄/Ar plasma treatment drastically decreased the specific contact and sheet resistance of the ZnO films. These results indicated that etching the ZnO film had roughened the surface and reduced its resistivity to ohmic contact, supporting the application of a roughened transparent contact layer (TCL) in light-emitting diodes (LEDs).     

Influence of the physico-chemical properties of CeO2-ZrO2 mixed oxides on the catalytic oxidation of NO to NO2

Commercial and home-made Ce-Zr catalysts prepared by co-precipitation were characterised by XRD, Raman spectroscopy, N₂ adsorption at −196 °C and XPS, and were tested for NO oxidation to NO₂. Among the different physico-chemical properties characterised, the surface composition seems to be the most relevant one in order to explain the NO oxidation capacity of these Ce-Zr catalysts. As a general trend, Ce-Zr catalysts with a cerium-rich surface, that is, high XPS-measured Ce/Zr atomic surface ratios, are more active than those with a Zr-enriched surface. The decrease in catalytic activity of the Ce-Zr mixed oxided upon calcinations at 800 °C with regard to 500 °C is mainly attributed to the decrease in Ce/Zr surface ratio, that is, to the surface segregation of Zr. The phase composition (cubic or t′′ for Ce-rich compositions) seems not to be a direct effect on the catalytic activity for NO oxidation in the range of compositions tested. However, the formation of a proper solid solution prevents important surface segregation of Zr upon calcinations at high temperature. The effect of the BET surface area in the catalytic activity for NO oxidation of Ce-Zr mixed oxides is minor in comparison with the effect of the Ce/Zr surface ratio.     

Properties of Zn3N2-doped ZnO films deposited by pulsed laser deposition

The optical properties of N-doped ZnO films grown by pulsed laser deposition are examined for which zinc nitride is used as the source of nitrogen. The motivation for this study is to determine if nitrogen-related acceptor state formation can be achieved in ZnO films using Zn₃N₂ doping in the ablation target. The films were deposited in oxygen or nitrogen on c-plane sapphire. Photoluminescence measurements at 20 K reveal a 3.31 eV acceptor-bound exciton emission due to nitrogen substitution on the oxygen site, donor-acceptor pair emission at 3.23 ± 1 eV and free electron-acceptor at 3.27 eV. The binding energy of the N-related acceptor is estimated to be in the range of 170-15 meV. While the as-deposited films were n-type, thermal annealing in oxygen yielded insulating behavior, consistent with compensating acceptor states.     

Synthesis and characterization of zinc oxide nanoparticles: application to textiles as UV-absorbers

We report the synthesis and characterization of nanosized zinc oxide particles and their application on cotton and wool fabrics for UV shielding. The nanoparticles were produced in different conditions of temperature (90 or 150 °C) and reacting medium (water or 1,2-ethanediol). A high temperature was necessary to obtain small monodispersed particles. Fourier transformed infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray powder diffractometry (XRD) were used to characterize the nanoparticles composition, their shape, size and crystallinity. The specific surface area of the dry powders was also determined. ZnO nanoparticles were then applied to cotton and wool samples to impart sunscreen activity to the treated textiles. The effectiveness of the treatment was assessed through UV–Vis spectrophotometry and the calculation of the ultraviolet protection factor (UPF). Physical tests (tensile strength and elongation) were performed on the fabrics before and after the treatment with ZnO nanoparticles.     

Growth of ZnO thin films on c-plane Al2O3 by molecular beam epitaxy using ozone as an oxygen source

The growth of c-axis oriented ZnO thin films on c-plane Al₂O₃ via molecular beam epitaxy (MBE) using dilute ozone (O₃) as an oxygen source was investigated. Four-circle X-ray diffraction (XRD) indicates that films grown at 350 °C are epitaxial with respect to the substrate, but with a broad in-plane and out-of-plane mosaic. The films were highly conductive and n-type. Epitaxial film growth required relatively high Zn flux and O₃/O₂ pressure. The growth rate decreased rapidly as growth temperature was increased above 350 °C. The drop in growth rate with temperature reflects the low sticking coefficient of Zn at moderately high temperatures and limited ozone flux for the oxidation of the Zn metal. Characterization of the films included atomic force microscopy (AFM), X-ray diffraction, photoluminescence, and Hall measurements. These results show that molecular beam epitaxy of ZnO using ozone is rate limited by the ozone flux for growth temperatures above 350 °C.     

Sm~(3+),Sr~(2+)共掺杂对CeO_2基电解质性能影响的密度泛函理论+U计算

Sm~(3+),Sr~(2+)共掺杂CeO_2的离子电导率被证实可高达Sm~(3+)掺杂CeO_2离子电导率的近两倍,然而,共掺杂对CeO_2电导率的作用机理尚不明确.本文利用第一性原理计算的密度泛函理论+U方法,对Sm~(3+)和Sr~(2+)共掺杂的CeO_2进行了系统的研究,对比Sm~(3+)或Sr~(2+)单掺杂的CeO_2体系,计算并分析了共掺杂体系的电子态密度、能带结构、氧空位形成能以及氧空位迁移能等微观属性.计算结果表明,Sm~(3+),Sr~(2+)的共掺杂对CeO_2基电解质性能的提高具有协同效应,二者的共掺杂不仅能协同抑制CeO_2体系的电子电导率,还能在单掺杂CeO_2的基础上进一步降低氧空位形成能,Sm~(3+)的存在还有助于降低Sr~(2+)对氧空位的俘获作用,而Sr~(2+)的加入则能够在Sm~(3+)掺杂CeO_2的基础上进一步降低最低氧空位迁移能,爬坡式弹性能带方法计算表明共掺杂体系的氧空位迁移能最低可达0.314/0.295 eV,低于Sm~(3+)掺杂CeO_2的最低氧空位迁移能.研究揭示了Sm~(3+),Sr~(2+)共掺杂对CeO_2电导率的协同作用机理,对进一步研发其他高性能的共掺杂电解质材料具有重要的指导意义.     

Successive magnetic transitions and low temperature magnetocaloric effect in RE2Ni7 (RE=Dy, Ho)

Magnetic properties of rare-earth intermetallics RE₂Ni₇ (RE=Dy, Ho) are reported. Both the samples undergo two successive magnetic transitions at T_h (paramagnetic to ferromagnetic) and T_l (spin reorientation) below 100 K. The transitions are found to be second order in nature as evident from the Arrot plot analysis. Large reversible magnetocaloric effect (MCE) was observed at low temperature in the studied samples. The maximum value of the magnetic entropy change in Ho₂Ni₇ is found to be −12.5 J/kg K (for 0 to 50 kOe of field change) around 25 K with a high relative cooling power (RCP) of 534 J/kg. The Dy counterpart also shows moderately large values of MCE (−7.3 J/kg K) and RCP (475 J/kg) around the magnetic transition region for similar change in the magnetic field. RE₂Ni₇ compounds can be promising materials for magnetic refrigeration in the temperature range of helium and hydrogen liquefaction.     

Enhanced antibacterial performance of hybrid semiconductor nanomaterials: ZnO/SnO2 nanocomposite thin films

The nano-sized coupled oxides ZnO/SnO₂ thin films in a molar ratio of 2:1 (Z2S), 1:1 (ZS) and 1:2 (ZS2) were prepared using sol-gel dip coating method and characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-vis spectroscopy. Escherichia coli (E. coli, ATCC 25922) was selected as a model for the Gram-negative bacteria to evaluate antibacterial property of composite samples compared with single ZnO (Z) and single SnO₂ (S) films. The antibacterial activity has been studied applying the so-called antibacterial drop test under UV illumination. The bactericidal activity was estimated by relative number of bacteria survived calculated from the number of viable cells which form colonies on the nutrient agar plates. The influence of the SnO₂-ZnO nanocomposite composition on the structural features and on the antibacterial properties of the thin films are reported and discussed. It is found that all coatings exhibited a high antibacterial activity. The coupled oxide photocatalyst Z2S has better photocatalytic activity to bacteria inactivation than ZS, ZS2, Z and S films. Furthermore, nanostructured films were active even in the absence of irradiation.     

The gas response enhancement from ZnO film for H2 gas detection

ZnO thin films were prepared by thermal oxidation of Zn metal at 400 °C for 30 and 60 min. The XRD results showed that the Zn metal was completely converted to ZnO with a polycrystalline structure. The sensors had a maximum response to H₂ at 400 °C and showed stable behavior for detecting H₂ gases in the range of 40 to 160 ppm. The film oxidized for 60 min in oxygen flow exhibited higher response than that of the 30 min oxidation which was approximately 4000 for 160 ppm H₂ gas concentration. The sensing mechanism was modeled according to the oxygen-vacancy model.     

Broad yellow orange emission from SrAl2O4:Pr phosphor with blue excitation for application to white LEDs

Photoluminescence excitation to intermediate atomic levels of rare earth activator ion (praseodymium) situated intragap in alkaline earth aluminate (AEA) SrAl₂O₄ has been tailored. This lead to blue excitation (2.7 eV) of large band gap AEA possible. Photoluminescence (PL) emission in the visible region extends from 525 to 650 nm corresponding to transition from ³P₀ and ¹D₂ excited states to different ³H_J and ³F_J states of Pr³⁺, broadened by crystal field effect of SrAl₂O₄. Thus SrAl₂O₄:Pr³⁺ promise to be a good candidate for solid state lighting in conjunction with blue LED.     

Study of structural, optical and electrical properties of ZnO and SnO2 thin films

The investigation of structure, optical and electrical properties of tin and zinc oxide films on glass substrates by using magnetron sputtering are carried out. X-ray data show the formation of textured tin oxides film during deposition and its transformation to SnO₂ polycrystalline film at low temperature (200 C) if the concentration of oxygen in the chamber is high (O₂ — 100%, Ar — 0%). Optimal conditions of SnO₂ polycrystalline film deposition (pressure of Ar–O₂ mixture in chamber — 2.7 Pa, concentration of O₂ — 10%) are determined. Low resistivity of as-deposited ZnO film and increasing ZnO crystallite sizes and phase volume at temperatures higher than the melting point of Zn (419.5 C) are explained by formation of conductive Zn and ZnO particle chains and their destruction, respectively.     

Enhancing the crystallinity and surface roughness of sputtered TiO2 thin film by ZnO underlayer

TiO₂ and TiO₂/ZnO double layer films were sputtered on glass substrates. It was found that a thin ZnO underlayer is helpful for tailoring the microstructure and surface morphology of the TiO₂ film. By applying a 70-nm-thick ZnO underlayer, a TiO₂ thin film of 100 nm in thickness with well crystallized anatase phase and rough surface was successfully fabricated without heating the substrate. Relatively high photo-catalytic activity and good hydrophilic properties were observed in such TiO₂/ZnO double layer films.