Table of Content

15 September 2021, Volume 50 Issue 9

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Invited

Single-Crystal Fiber Growth and Single-Crystal Fiber High-Temperature Sensors: Review and Perspective

WANG Tao, JIA Zhitai, LI Yang, ZHANG Jian, TAO Xutang

2021, 50(9):  1603-1624. 

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Single-crystal fiber (SCF) is a fibrous crystalline material, which possesses broad application prospects in the fields of national defense and people's livelihood due to its excellent physical and chemical properties and large aspect ratio. With the maturity and development of the edge-defined film-fed growth technique, laser-heated pedestal growth technique and micro-pulling down technique, SCF ushers in a boom period with various materials and diversified applications. Among them, high melting point oxide SCF for high-temperature sensing has shown great potential for application in harsh environments such as strong oxidation, strong radiation, strong corrosion and strong electromagnetic interference by virtue of its high temperature resistance, oxidation resistance and compact structure. In recent years, researchers have combined optical and acoustic sensing technologies with SCF to broaden the operating temperature of conventional glass fiber sensors while maintaining the structural flexibility, and to compensate for the low lifetime of traditional contact temperature sensing tecniques such as thermocouples in harsh environments. Here, following the development process of the single crystal fiber, the technical characteristics and the research status of the growth techniques as well as the temperature sensing techniques are summarized in detail.

Research Articles

Electronic Structure and Optical Properties of K and Ti Doped Mg₂Si by First-Principles Study

ZHANG Qin, XIE Quan, YANG Wensheng, HUANG Sili

2021, 50(9):  1625-1632. 

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The geometric structure, electronic structure and optical properties of intrinsic and K, Ti doped Mg₂Si were studied by the first-principles calculation method. The calculation results indicate that the intrinsic Mg₂Si is an indirect semiconductor material with a gap of 0.290 eV. After Mg₂Si doped with K, the electronic transition mode changes from indirect transition to direct transition and the overall conduction type is p-type semiconductor. The band gap type of Mg₂Si doped with Ti has not changed, which is still an indirect band gap, and it is n-type semiconductor. The static permittivity ε₁(0) of the K and Ti doped Mg₂Si increases from 20.52 to 53.55 and 69.25, respectively, which enhances the binding ability of the doped system to charges. After doping, both the absorption spectrum and the photoconductivity have a red shift phenomenon, which effectively expands the absorption range of visible light. Besides, doping significantly decrease the absorption coefficient, reflection coefficient and photoconductivity in the visible region, which leads to an increase transmission ability, and significantly improves the optical properties of Mg₂Si.

Mechanical Properties and Thermoelectric Transport Performance of Mg₂Sn from First-Principle Calculations

CHEN Song, MAO Wenwei, WANG Weiguo

2021, 50(9):  1633-1639. 

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The narrow-band gap semiconductor Mg₂Sn is an excellent candidate for medium and low temperature thermoelectric materials due to its high abundance, low density, non-toxicity and environmental friendliness. Based on density functional theory, the elastic coefficient, phonon vibration spectrum and electron band structure of Mg₂Sn crystal were systematically analyzed in combination with different forms of electron exchange correlation energy in this paper. The thermoelectric properties of Mg₂Sn were also calculated based on the non-equilibrium Boltzmann transport theory. The results show that GGA-PBE as the electron exchange correlation energy can well fit the mechanical properties of Mg₂Sn in cubic, when the phonon vibration spectrum has no virtual frequency, and the bulk elastic modulus of Mg₂Sn in cubic is 42.1 GPa and isotropic. Mg₂Sn has low phonon thermal conductivity due to the fact that the Debye temperature curve of Mg₂Sn tends to flat and no higher than 315 K in the test temperature region above 300 K. The electronic structure near the Fermi level of Mg₂Sn can be estimated by using B3LYP as the electron exchange correlation energy,and triple degeneracy states are found near the top of the valence band. Then, the results of the thermoelectric optimal value (ZT value) present that p-type doping Mg₂Sn is better than that of n-type doping, which can reach 1.05. The results of this study provide theoretical basis for further improving the thermoelectric properties of Mg₂Sn.

Stable Configurations of Diamond (001) Surface Covered by Cu with Various Coverages and Their Electronic Properties

WU Kongping, ZHANG Leng, WANG Danbei, XIAO Liu, CHEN Zelong, ZHANG Jingchen, ZHANG Pengzhan, LIU Fei, TANG Kun, YE Jiandong, GU Shulin

2021, 50(9):  1640-1647. 

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The electronic properties of diamond surface are easily affected by its surface covered layer, like species, concentration and structure of the surface covered layer. At present, the surface covered layer with stable configuration and excellent performance is still under study. In our work, transition metal (Cu) is used as the surface covered layer. The transition metal (Cu) studied in this paper is not only widely used in semiconductor micro-fabrication, but also has excellent performance of heat dissipation, which is very similar with diamond on this point. Moreover, ultrathin layer of Cu has recently been deposited on diamond as an epitaxy, where the thermally stable and characteristic of negative electron affinity were found. As a result, Cu-covered diamonds have become more important than ordinary electrodes, and it is very important for the Cu-diamond structure to modify and tailor electronic properties of diamond (001) surface. In this paper, the adsorption energy, stable configuration and energy band structure of diamond (001) surface covered by transition metal (Cu) with different coverage (0.25 ML, 0.5 ML and 1 ML) have been studied by density functional simulation. The results show that Cu as a surface coating can induce a negative electron affinity about -0.5 eV to -0.3 eV and a Schottky barrier height(Φ_BH) of -0.16 eV to 0.04 eV, which is in good agreement with the experimental data. At the same time, the diamond (001) surface covered by the transition metal (Cu) with various coverage has also shown the stable configurations. Therefore, all these results suggest that Cu as a surface coating have an important application in diamond-based electron emission device.

Optical and Electrical Properties of High Doping Zn/Mg LiNbO₃ Films

XIAO Jing, CHANG Shuangju, ZHAO Li, ZHU Yabin, CHEN Yunlin

2021, 50(9):  1648-1654. 

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LiNbO₃ (LN), 6% zinc-doped LiNbO₃ (LN∶ZnO) and 5% magnesia-doped LiNbO₃ (LN∶MgO) films were deposited on glass and silicon substrates at room temperature by radio frequency magnetron sputtering (RFMS) method. The deposited LN, LN∶ZnO and LN∶MgO films were annealed at 575 ℃ for improving crystallinity. The morphology, structure and optical properties of the films were investigated systematically by AFM, XRD, UV-Vis and the spectroscopic ellipsometer. XRD analysis shows that high doping Zn/Mg LN films and LN film have the same growth orientation. AFM, XRD and UV-Vis measurement results show that doping Zn/Mg will increase the grain size of LN films, and the red shift of the optical band gap is related to the grain size of the films. Moreover, the electrical properties of the deposited films were measured by Hall-effect instrument. The Hall-effect test indicates that the deposited LN, LN∶ZnO and LN∶MgO films are n-type semiconductor, and the change trend of the conductivity of LN∶MgO film is different from that of LN∶ZnO and LN films. It was found that the conductivity of LN∶MgO film is almost unchanged, LN∶ZnO and LN films gradually increases with the increase of temperature in temperature of 18 ℃ to 50 ℃.

Preparation and Strong Magneto-Optical Effect of Bi_26-x-yM_xN_yO₄₀ (M, N=Fe, Co, Gd) Sillenite Type Films

GAO Teng, XING Kun, WU Gonghui, CHEN Xin, HU Xiaolin, ZHUANG Naifeng

2021, 50(9):  1655-1661. 

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Magneto-optical materials are the indispensable and key functional materials in the field of modern optical communication. For the miniaturization of devices, high quality magneto-optical thin films have attracted much attention. The sillenite type Bi₂₅FeO₄₀ has a cubic crystal structure with high symmetry. The concentration of bismuth ions per unit volume is high, so it should have a strong magneto-optical effect in theory. However, its application is restricted due to low magnetism and difficulty in preparation. In this paper, Bi_26-x-yM_xN_yO₄₀ (M, N=Fe, Co, Gd) magneto-optical thin films with cubic sillenite type were deposited on yttrium-doped zirconium dioxide (YSZ) substrate by the magnetron sputtering method. Their morphology, magnetic properties, transmittance, and magnetic circle dichroism were discussed. Smooth surface morphology of the films was observed by atom force microscope. The thickness of the films is about 190 nm. The valence states of bismuth, iron and cobalt in the films are all +3, and other valence states are not observed, so they are meeting the charge balance. The transmittance in the near infrared region is about 60% to 70%. At room temperature, the films show superparamagnetic effect, and the magnetic properties gradually increase with the increase of doping ion concentration. And the saturation magnetization of Bi_13.6Gd_2.7Co_4.0Fe_5.7O₄₀/YSZ film reaches 29 emu/cm³. The Bi_13.6Gd_2.7Co_4.0Fe_5.7O₄₀/YSZ film exhibits a strong magneto-optical effect, the magnetic circular dichroic spectrum signal is up to 1 710 deg/cm at wavelength of 716 nm. Therefore, Bi_13.6Gd_2.7Co_4.0Fe_5.7O₄₀/YSZ film is expected to be used in integrated optical isolators and other optical communication devices.

Influence of Low Heat Treatment Temperature on the Characteristics of CuAlO₂ Thin Films Prepared on SiC Substrate

HU Jichao, MENG Jiaqi, LI Dan, HE Xiaomin, WANG Xi, XU Bei, PU Hongbin

2021, 50(9):  1662-1667. 

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In order to solve the problem of low injection efficiency of p+n emitter junction caused by incomplete ionization of p-type SiC in bipolar SiC power devices at room temperature, our group proposed to use the heterojunction formed by wide bandgap p-type CuAlO₂ and n-type SiC as the emitter junction. In this work, CuAlO₂ thin films were prepared on 4H-SiC (0001) by sol-gel method. The influence of low heat treatment temperature range on the crystal structure, surface morphology and optical properties of CuAlO₂ thin films were studied. The results show that the formation of intermediate product CuO can be enhanced at higher heat treatment temperature, promoting the generation of CuAlO₂ phase in the solid phase reaction stage. The prepared CuAlO₂ thin films are mainly oriented with the (012) crystal orientation of CuAlO₂ phase with high crystal quality. In addition, the higher heat treatment in low temperature range is beneficial to obtain high quality CuAlO₂ thin films with uniform surface and lower concentration of Cu-vacancy defect. The surfaces of the films are uniform with an average crystal grain size of approximately 35 nm when the heat treatment temperature in low temperature range is 300 ℃. The CuAlO₂ thin films are highly transparent, with optical transmission exceeding 70% across the whole visible range. Meanwhile, the optical band gaps of the CuAlO₂ thin films increases slightly with the increase of heat treatment temperatures in low temperature range.

Spin Seebeck Effect of Nickel Oxide Thin Films Prepared by Reactive Magnetron Sputtering

LUO Jian, ZHANG Xiaowei, DAI Bo

2021, 50(9):  1668-1674. 

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The spin Seebeck effect is a phenomenon of spin Seebeck voltage signal caused by temperature gradient in (sub) ferromagnet, which has become one of the hot research fields of thermal spintronics. In this paper, NiO thin films were deposited on Si substrates by reactive magnetron sputtering. The effects of sputtering power, oxygen-argon ratio, sputtering pressure and substrate temperature on the microstructure and surface morphology of NiO thin films were investigated. The optimum conditions of reactive magnetron sputtering are sputtering power 110 W, oxygen-argon ratio 0.15 (O₂ 15 mL/min; Ar 100 mL/min), sputtering pressure 0.3 Pa and substrate temperature 400 ℃. The effects of temperature gradient (temperature difference), magnetic field angle, NiO thickness and Pt thickness on spin Seebeck voltage in Si/NiO/Pt structure were studied. The results show that there is a simple linear relationship between the spin Seebeck voltage and the temperature difference, the larger of the temperature difference, the higher of the spin Seebeck voltage, and the relationship between the magnetic field angle and the spin Seebeck voltage satisfies the cosine function, that is, the spin Seebeck voltage is the maximum at 0° and 180°, and zero at 90° and 270°. The greater of the thickness of the antiferromagnetic insulating layer NiO, the stronger of the measured spin Seebeck voltage signal. The thicker of the paramagnetic metal layer Pt, the weaker of the spin Seebeck voltage signal.

Effects of Sputtering Power and Sputtering Time on the Structure and Resistivity of Mg₂Si Nanocrystalline Thin Films

LIAO Yangfang, XIE Quan

2021, 50(9):  1675-1680. 

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Nanocrystalline Mg₂Si thin films were prepared on sapphire substrate by radio frequency (RF) magnetron sputtering using Mg₂Si sintered target. The effects of sputtering power (90 W to 140 W) and sputtering time (10 min to 60 min) on structure and resistivity of Mg₂Si thin films were investigated. The results show that with the increase of sputtering power, the XRD diffraction peak of the sample gradually increases. However, when the power exceeds 100 W, elemental Mg segregation appears in the samples. With the increase of sputtering time, the XRD intensity of the sample first increases and then decreases. When the sputtering time is 40 min, the XRD diffraction peak of the sample is the strongest. With the increase of sputtering time, a weak MgO diffraction peak appears in the sample. All the samples show the characteristic Raman peaks of Mg₂Si crystal, namely, the F_2g mode near 256 cm^-1 and the F_1u (LO) mode near 347 cm^-1. With the increase of sputtering power, the resistivity of the sample decreases.With the increase of sputtering time, the resistivity of the sample first decreases and then increases. When the sputtering time is 40 min, the resistivity of the sample is the minimum.

Effect of Substrate Temperature on Microstructure and Optical Properties of ZnO Thin Films

CHEN Xinghui, TANG Yinghui, WANG Jiaqiang, CHAI Hanyang, WEI Xinqi, CHEN Guangwei

2021, 50(9):  1681-1687. 

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Substrate temperature is a very important process index in the preparation of zinc oxide thin films by magnetron sputtering. Exploring the effect of substrate temperature on the microstructure and optical properties of zinc oxide thin films is of great significance for the preparation of environmental protection high quality zinc oxide ultraviolet shielding materials. A zinc oxide ceramic target with a mass fraction of 99.99% was served as a sputtering source, and a zinc oxide ultraviolet shielding film was deposited on a quartz substrate by radio frequency magnetron sputtering technology. And the effects of different substrate temperatures on the microstructure and optical properties of ZnO films were characterized and studied by X-ray diffractometer, film thickness gauge, ultraviolet-visible spectrophotometer, and fluorescence spectrophotometer instruments. The experimental results show that the as-prepared films are all hexagonal wurtzite structures, which exhibit the features of preferential growth along the (002) crystal plane, and their lattice constant, grain size, transmittance, optical energy gap, visible fluorescence, and crystal quality are closely related to the substrate temperature. When the experimental conditions satisfy that the substrate temperature is 250 ℃, the sputtering power is 160 W, the argon pressure is 0.5 Pa, the argon flow rate is 8.3 mL/min, and the deposition time is 60 min, the as-prepared zinc oxide film sample exhibits the best orientation, the largest crystal grain size, and a dense film structure, as well as good optical properties and crystal quality.

Preparation of YBCO Films by Water-Based Sol-Gel Deposition

HE Dong, XU Wenbo, HU Wenpeng, CHENG Dawei, TONG Liang

2021, 50(9):  1688-1693. 

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The effects of annealing temperature on properties of YBCO films deposited on (100) LaAlO₃ single crystal substrates derived from a water-based sol-gel process were investigated. In this paper, the in-plane texture is improved at higher temperatures but the out-of-plane texture follows an opposite trend. YBCO films annealed at 789 ℃ with homogeneous and smooth surface as well as J_c=1.7 MA/cm² at 77 K and 0 T was obtained. Particles and holes observed on the other films could result in bad connections between superconducting grains and decrease the superconducting current in the films. Strain in these films is likely to enhance the pinning force and improve the transport properties under applied field.

Synthesized and Luminescent Properties of Li(Na, K)Ba(Sr, Ca)B₉O₁₅∶Eu³⁺ Phosphor

WANG Yuhuan, CHEN Yongjie, ZHANG Wenhua, GENG Xiujuan, YANG Ying

2021, 50(9):  1694-1701. 

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A series of Eu³⁺-doped borate-based phosphors were synthesized by high temperature solid-state method in air atmosphere. The crystal phase and luminescence properties of phosphors were characterized by X-ray diffraction, fluorescence spectroscopy and chromaticity coordinates. Through the mutual substitution between alkali metals and alkaline earth metals in the LiBaB₉O₁₅, the effect of the change of the matrix composition on the luminescence properties of phosphors was investigated. In the series of Li(Na, K)Ba(Sr, Ca)B₉O₁₅∶0.07Eu³⁺phosphors, LiSrB₉O₁₅∶0.07Eu³⁺phosphor has the strongest emission intensity. The effects of calcination temperature, holding time and Eu³⁺ doping concentration on the crystal phase and luminescence properties of LiSrB₉O₁₅∶Eu³⁺ phosphor were investigated. When the calcination temperature is 750 ℃ and holding time is 1~5 h, the crystallinity of all the samples is good. When the Eu³⁺ doping concentration is 0.52, LiSrB₉O₁₅∶Eu³⁺ phosphor has the strongest luminescence intensity. When x≥0.42(x=0.42, 0.47, 0.52, 0.57), the color coordinates of LiSrB₉O₁₅∶xEu³⁺ are close to the standard red light (0.67, 0.33). The relative intensity ratio R of the emission peak at 611 nm (⁵D₀→⁷F₂) and 586 nm (⁵D₀→⁷F₁) of LiSrB₉O₁₅∶xEu³⁺(x=0.02~0.57) phosphors were compared. R value is not changed obviously, the majority of Eu³⁺ in the crystal lattice locates in inversion symmetry center sites. The luminescence properties of the LiSrB₉O₁₅∶0.52Eu³⁺ phosphor and the commercial Y₂O₃∶Eu³⁺ phosphor were compared, the luminescence intensity of LiSrB₉O₁₅∶0.52Eu³⁺phosphor is weaker than Y₂O₃∶Eu³⁺ phosphor under excitation of 260 nm wavelength, stronger than Y₂O₃∶Eu³⁺ phosphor under excitation of 362 nm and 394 nm wavelength.

Red-Emitting Eu³⁺-Doped Sr₃Y₂TeO₉ Phosphors

YANG Yin, YANG Weibin, LUO Xin, XIE Lanchi, LIN Hongyi, XIONG Feibing

2021, 50(9):  1702-1708. 

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A series of new red-emitting Sr₃Y_2-xTeO₉∶xEu³⁺ phosphors were prepared by high temperature solid-state method, and the phase structure, luminescent performances, decay life and thermal stability of Sr₃Y_2-xTeO₉∶xEu³⁺ were studied. The results show that new red-emitting Sr₃Y_2-xTeO₉∶xEu³⁺ phosphors can emit intensive red light under near-ultraviolet or blue light excitation, and it demonstrate that the concentration quenching mechanism is attributed to the dipole-dipole interaction between Eu³⁺ ions. The color coordinates of these phosphors with different Eu³⁺ concentrations are in the red spectral region. The temperature-dependent luminescences emission spectra reveal that these phosphors show good thermal stability. The optimal doping concentration of Eu³⁺ is x=0.34 for Sr₃Y_2-xTeO₉∶xEu³⁺ phosphor, and its fluorescence decay lifetime is deduced to be 0.619 ms. These overall results show that new red-emitting Sr₃Y_2-xTeO₉∶xEu³⁺ is promising phosphor applied in phosphor-converted near UV-excited white light-emitting diodes.

Fluorescence Properties of α- and β-BiNbO₄∶Eu³⁺

LI Qiang, HUANGFU Zhanbiao, LI Haining, DONG Xingbang, ZHU Xiang, HAO Yunqi, WANG Zheng

2021, 50(9):  1709-1714. 

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Orthorhombic phase α-BiNbO₄∶Eu³⁺ and triclinic phase β-BiNbO₄∶Eu³⁺ were synthesized by solid-state reaction method. Their structure and fluorescence properties were studied by X-ray diffractometer (XRD), Raman spectra, absorption spectra and luminescence spectra. Results indicate that pure α-BiNbO₄ were successfully synthesized at 900 ℃, while triclinic phase β-BiNbO₄ obtained at 1 200 ℃. The band structure of both structure BiNbO₄ was studied using the first principle theory and absorption spectra. The optical band gap obtained for α-BiNbO₄ and β-BiNbO₄ are 2.69 eV and 2.96 eV respectively, in agreement with the theoretical result of 2.640 eV and 3.032 eV. After Eu³⁺ doping, theirs band gap blue shifts to 2.89 eV and 3.05 eV respectively, which effectively change their optical response range. The main emission peaks are from ⁵D₀→⁷F₂ transition of Eu³⁺ for both structural BiNbO₄∶Eu, centerted at 615 nm and 611 nm respectively. But the emission intensity of β-BiNbO₄∶Eu sample is much higher, and its luminescence intensity ratio between ⁵D₀→⁷F₂ and ⁵D₀→⁷F₁ transitions is much higher. For Er³⁺ doping, upconversion emission is observed for both structures excited at 980 nm. The upconversion emission intensity of β-BiNbO₄∶Er sample is almost 40 times higher than that of α-BiNbO₄∶Er sample. This results indicate that β-BiNbO₄ is more suitable as the host material of rare earth ions doping phosphor.

Preparation, Luminescence Properties and Energy Transfer of Ca₂LaTaO₆∶Dy³⁺, Tb³⁺ Phosphors with Tunable Color

YUAN Bo, QI Chaochao, ZHANG Xiangting, LUAN Guoyan

2021, 50(9):  1715-1722. 

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High-efficiency yellow-green polychromatic luminescent phosphors Ca₂LaTaO₆∶Dy³⁺, Tb³⁺were obtained by high-temperature solid-state reaction method. The main narrow emission comes from the 547 nm of Tb³⁺ and a wide excitation band is located in the region of 250~400 nm due to the sensitization of Dy³⁺. The energy transfer system was constructed by co-doping Dy³⁺ and Tb³⁺ into Ca₂LaTaO₆ (CLTO) matrix. Furthermore, the energy transfer for Dy³⁺→Tb³⁺ was confirmed by excitation/emission spectra and lifetime decay curve measurements. The energy emigration is dominated by dipole-quadrupole interaction, and the efficiency can reach 80% or even higher. Under the characteristic excitation of Dy³⁺, the luminescence color changes from yellow to green by adjusting the relative doping concentration of Dy³⁺ and Tb³⁺ based on the energy transfer. The results indicate that Ca₂LaTaO₆∶Dy³⁺, Tb³⁺ phosphor with adjustable emission color has potential applications in phosphor-converted white LEDs.

Photocatalytic Mechanism of Rare Earth Metal Ce³⁺ Doped ZnO Materials

LI Peixin, XIN Lang, SONG Jia, YANG Aiyun, CUI Juan, YIN Chunhao

2021, 50(9):  1723-1728. 

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The photocatalytic materials of Ce∶ZnO composite powder with higher photocatalytic activity was prepared by sol-gel method. The crystal type and structure, free radical type and content, and photocatalytic efficiency of the prepared powder samples were characterized by X-ray diffraction, electron paramagnetic resonance and ultraviolet visible spectroscopy. X-ray diffraction test results of the composite samples show that with the increase of doping concentration, the characteristic peaks of (111) and (200) crystal plane of CeO₂ are detected successively, and the intensity of the diffraction peaks gradually increases. In addition, appropriate doping (c(Ce³⁺)=2%) can reduce the grain size of ZnO crystal. The results of electron paramagnetic resonance test show that there are three kinds of free radicals in Ce∶ZnO composite photocatalytic material, which are Zn-H complex, positive monovalent oxygen vacancy and superoxide ions adsorbed on the surface of CeO₂. Ultraviolet visible test shows that appropriate doping (c(Ce³⁺)=2%) could effectively improve the photocatalytic activity of ZnO catalyst. Based on the analysis of electron paramagnetic resonance and ultraviolet visible test results, the doping of Ce³⁺ provides more electrons for O₂ when it is converted to Ce⁴⁺, on the other hand, the generated CeO₂ has a strong oxygen absorption capacity. The photocatalytic activity of ZnO is improved by increasing the utilization rate of O₂ and generating more active free radicals. In the experiment, the influence process of Ce³⁺ doping on the synthesis of free radicals in ZnO materials was successfully characterized by electron paramagnetic resonance and X-ray diffraction techniques, and the electron transfer process in the photocatalytic degradation of methyl orange by Ce∶ZnO composites was reasonably explained by ultraviolet visible technology.

Synthesis of ZnMoO₄ Powder by Coprecipitation Method and Its Antibacterial Performance

LIU Xin, TANG Yanchao, LIU Fang, LI Jiake

2021, 50(9):  1729-1734. 

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ZnMoO₄ powder was synthesized by coprecipitation method using Zn(NO₃)₂·6H₂O and (NH₄)₆Mo₇O₂₄·4H₂O as main materials. Phase composition, microstructure of the synthesized samples were characterized by XRD, SEM, and so on. Antibacterial performance of the synthesized samples with different treatment temperatures were studied through Escherichia coli as the killing object. The results show that precursor mainly consists of non-crystalline with a small amount of ZnMoO₄, Zn₂Mo₃O₈, Zn(OH)₂ and MoO₃; the precursor is transferred into ZnMoO₄ when heat treated at 400 ℃ to 600 ℃ for 30 min. With the increase of heat treatment temperature, the crystal structure of ZnMoO₄ is gradually improved, so antibacterial performance of ZnMoO₄ is increased. When the heat treatment temperature is 600 ℃, ZnMoO₄ with good crystallization can be obtained, and particle size of ZnMoO₄ is granular and flake-like with average size of 1.5 μm. The as-synthesized ZnMoO₄ owns better antibacterial performance. Among them, antibacterial performance of ZnMoO₄ synthesized by heat treatment of 600 ℃ is the best, and its antibacterial rate arrives at 99.2% after 24 h antibacterial test. When 5% ZnMoO₄ powder is added into commercial coating slurry, antibacterial rate of the coating reaches 95.7%, which has good application prospects.

In-Situ Preparation of Bi₃O₄Br/Bi₁₂O₁₇Br₂ Photocatalyst and Their Degradation Performances of Sulfamethoxazole

LI Rui, ZHANG Xiao, ZHANG Lulu, XIE Fangxia, ZHANG Xiaochao, WANG Yawen, FAN Caimei

2021, 50(9):  1735-1744. 

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Bi_xO_yBr_z photocatalysts exhibit great potential in the application of organic pharmaceutical wastewater treatment and air purification. However, the catalysis activity and application of photocatalyst is greatly limited by its intrinsic high recombination rate of photo-generated charge carriers. In this work, a novel Bi₃O₄Br/Bi₁₂O₁₇Br₂composite photocatalyst was prepared via a facile in-situ hydrolysis-calcination route and its photocatalytic performance was evaluated by the sulfamethoxazole (SMX) degradation efficiency via simulated solar light irradiation. The structure and property were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), nitrogen adsorption and desorption, UV-Vis diffuse reflectance spectra (UV-Vis DRS), electrochemical impedance spectroscopy (EIS), Steady photoluminescence and Mott-Schottky curves. Results reveal that Bi₃O₄Br/Bi₁₂O₁₇Br₂ composite photocatalyst display the optimum photocatalytic performance, and its removal efficiency of SMX reaches 87% under 30 min simulated solar light irradiation, which is improved approximately 30% and 24% than that of pure Bi₃O₄Br and pure Bi₁₂O₁₇Br₂, respectively. Based on characterization analysis, the superior performance is attributed to higher electron-hole separation rate and lower charge transfer resistance. Finally, the underlying photocatalytic mechanism was elucidated based on the band structure and radical scavenging experiments. This findings provide novel ideas and methods of the construction of the composite photocatalysts system for strong organics pharmaceutical wastewater treatment.

Effect of Preparation Methods on Physicochemical Properties of Al₂O₃-CeO₂ and Its Catalytic Performance of CO₂ Hydrogenation to Methanol

FAN Xingqi, YAO Mengqin, LIU Fei, WANG Xiaodan, CAO Jianxin

2021, 50(9):  1745-1755. 

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The interfacial properties of the composite oxides have a significant relationship with the catalytic performance of CO₂ hydrogenation to methanol. Accordingly, the effects of various preparation methods including physical blending, impregnation, traditional co-precipitation and microfluidic continuous co-precipitation on the interfacial property and catalytic performance of Al₂O₃-CeO₂ composite oxides were investigated. Although the impregnation effect can moderately tune the interface properties of Al₂O₃/CeO₂, the insufficient oxygen vacancy defects resulted in inferior catalytic performance. The solid solution structure of co-precipitation sample enhanced the interfacial interaction of Al₂O₃/CeO₂ and the binding energy of the electron, forming sufficient oxygen vacancy defects to activate CO₂. The sample prepared by the microfluidic continuous co-precipitation has the excellent catalytic performance due to its smaller grain size, uniform composite structure and sufficient oxygen vacancy defects. Under the conditions of V(H₂)∶V(CO₂)∶V(N₂)=72∶24∶4, reaction temperature 320 ℃, reaction pressure 3 MPa and space velocity 9 000 mL·g^-1·h^-1, the CO₂ conversion, methanol selectivity and methanol space-time yield of the Al₂O₃-CeO₂ composite oxide can reach 15.3%, 86.4%, and 0.076 g·mL^-1·h^-1, respectively.

Carbon Dioxide Adsorption Property of Kaolinite-Based Mesoporous Composites

CHEN Xinyi, CHENG Hongfei, ZHAO Bingxin, HU Mianshu, JIA Xiaohui

2021, 50(9):  1756-1764. 

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The problem of global warming caused by the rapid growth of carbon emissions has attracted more and more attention in all countries, so it is of great importance to develop feasible CO₂ capture materials. In this paper, kaolinite is used as raw material, to prepare mesoporous silica carrier (KNH) with the method of calcination-alkali activation-acid etching. Then the pentaethylenehexaamine (PEHA) functionalized mesoporous silica (KNH-PEHA) was synthesized via impregnation. The prepared samples were characterized by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and N₂ adsorption-desorption isotherms treated by BET (Brunauer-Emmett-Teller) analysis. And the solid adsorbent is also used to study the adsorption property of carbon dioxide (CO₂). The results indicate that the structure of PEHA-loaded KNH is not changed, but its carbon dioxide adsorption capacity is improved. When the adsorption temperature is 25 ℃, the CO₂ adsorption capacity of KNH is 147.39 cm³/g, and the CO₂ adsorption capacity of KNH (KNH-P-30) with a mass percentage of PEHA of 30% reaches 389 cm³/g, which is much higher than that without PEHA modified KNH adsorption. At the same time, it express the adsorption mechanism of the solid adsorbent for CO₂, which provides a new idea for the application of kaolinite in the field of gas adsorption.

Magnetic Field Design and Simulation of Cylindrical Magnetron Sputtering Target

YANG Xinlei, MI Qian, GONG Lirong, ZHOU Fenglin

2021, 50(9):  1765-1773. 

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The cylindrical magnetron sputtering cathode target, playing a key role in many application fields, could be controbally tuned by structure and magnetic field distribution. Otherwise, up to now, it is inadequate for the structure research of this type of target. Herein, this structure was calculated by AC/DC interface in COMSOL Multiphysics, including constructing 3D model, dividing mesh and results analysis. In addition, the distribution law of magnetic field on target surface is determined by the structural parameters of magnets, the shape of the magnetic yoke, and the structural arrangement in the target. The results show that the magnetic filed of the target surface is directly affected by the cross-sectional area of the magnetic ring, the thickness and height of the magnetic yoke. Also, the uniform area of the magnetic field on the target surface is determined by the magnetic yoke gap in the magnetic circuit structure and the shape of the extension arm of the magnetic yoke. Herein, a novel cylindrical magnetron sputtering target is presented, which has a uniformly distributed magnetic field on the target surface and the magnetic induction intensity is 20 mT to 35 mT. In addition, the uniform magnetic field area on the parallel target surface reaches about 35% to 40%. This work pave a way to deeply apply cylindrical magnetron sputtering cathode target into coating process.

Eccentric Balance of Improved Single Crystal Furnace Lifting System

WANG Wei, HUANG Ming, CHANG Xiaoyu, ZHANG Hao, WU Qi, LONG Lianchun

2021, 50(9):  1774-1779. 

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With the rapid development of photovoltaic industry, the quality requirement of silicon single crystal is increasing. Czochralski is the main method to produce single crystal silicon. The production scale of single crystal silicon can be enlarged by increasing the height of the sub-chamber in the single crystal furnace. Due to the large increase in the height of the sub-chamber and the distance between the centroid of the single crystal furnace lifting head and the rotating axis of the single crystal furnace, the overall stability of the single crystal furnace is greatly affected and the production quality of the single crystal silicon is reduced. In order to solve this problem, a reliable mechanical analysis model of single crystal furnace was established, and the dynamic response of the whole single crystal furnace was analyzed by numerical simulation method. The law of motion and the maximum swing amplitude of the bottom end of tungsten wire rope were calculated when the height of the sub-chamber was increased, which provides a basis for improving the design. The numerical simulation analysis shows that the large eccentricity of the lifting head is the main reason for the shaking of the single crystal furnace lifting system. For this reason, it is proposed to add a centroid adjustment device to the lifting head, and the control system is adjusted to ensure that the mass center of the lifting head is on the rotation axis to reduce the swing of the lifting system.

Reviews

Epitaxy of Wide Bandgap Semiconductors on Silicon Carbide Substrate

KAI Cuihong, WANG Rong, YANG Deren, PI Xiaodong

2021, 50(9):  1780-1795. 

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Wide bandgap semiconductors are ideal materials for the application of high power density, high frequency and low-loss power electronic devices, owning to the advantages of wide bandgap, high electron saturation velocity, and high breakdown field. Attributed to the high thermal conductivity, high chemical stability and high heat resistance of silicon carbide (SiC), epitaxy of wide bandgap semiconductors on SiC is promising to exploit the advantages of wide bandgap semiconductors and improve the performance of wide bandgap semiconductor devices. Benefiting from the continuous quality-improvement and cost-reduction of SiC substrates, wide bandgap semiconductors grown on SiC substrates are ushering in an explosive growth. Epitaxy of high quality wide bandgap semiconductors on SiC substrates is critical to the performance and reliability of wide bandgap semiconductor devices. This paper summarizes the recent progress obtained on epitaxial growth of SiC, gallium nitride (GaN) and gallium oxide (Ga₂O₃) on SiC substrates. In addition, the prospective of wide bandgap semiconductors grown on SiC substrates for high-performance electronics are prospected.

Research Progress of Cu₂ZnSn(S,Se)₄ Thin Film Solar Cells

ZHANG Daoyong, WANG Shurong

2021, 50(9):  1796-1809. 

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Low cost thin film solar cells have great development space and application prospects in the photovoltaic field. Copper-zinc-tin-sulfur-selenium (Cu₂ZnSn(S, Se)₄, CZTSSe) thin film solar cells have many advantages, such as high abundance, non-toxic, high light absorption coefficient, a suitable optical band gap, high theory optoelectronic conversion efficiency and stable characteristic. So it is a kind of novel thin film photovoltaic cells with great scale application potential. The development history, preparation methods and research status of CZTSSe thin film solar cells are introduced in this paper. By comparative analyzing the reported CZTSSe thin film solar cells, the current achievements and status of CZTSSe thin film solar cells are summarized. Finally, the current problems about CZTSSe thin film solar cells are demonstrated and their future perspectives are presented.