Table of Content

15 March 2021, Volume 50 Issue 3

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Research Letter

Growth of 8-Inch CaF₂ Single Crystal

XU Wusheng, PENG Minglin, YANG Chunhui

2021, 50(3):  407-409. 

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Calcium fluoride (CaF₂) crystal is a kind of excellent optical material. In this investigation, an 8-inch(20.32 cm) CaF₂ single crystal was grown by the Bridgman method. The crystal has complete appearance and no macroscopic defects such as cracking and scattering. After orientational cutting, a transparent cylindrical crystal blank with diameter of 40 mm×6 mm was obtained, the blank sample was annealed twice and then polished to obtain the final sample. The ultraviolet-visible-near infrared transmittance, optical homogeneity, and average stress birefringence were measured. The results show that the transmittance at 200 nm reaches 90%. The average stress birefringence is less than 0.5 nm/cm. The optical homogeneity reaches 2.63×10^-6.

Research Articles

Growth and Scintillation Characterization of CsI-LiCl Eutectic Material by Bridgman Method

YAN Xinlong, SHI Zhaoji, PENG Chen, WANG Rui, YANG Fan

2021, 50(3):  410-415. 

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CsI-LiCl and CsI-LiCl:Na eutectic scintillators were successfully grown in a vacuum-sealed quartz crucible by vertical Bridgman method. The periodic lamellar microstructure of the crystal was observed by SEM with the CsI phase of 5 μm thickness. The X-ray excitation luminescence spectra show that the luminescence of CsI-LiCl and CsI-LiCl:Na eutectic is mainly attributed to the oxygen induced defects luminescence. And the STE luminescence of pure CsI is observed in the CsI-LiCl eutectic. Full energy peak is observed in the α particle excited multi-channel energy spectrum of CsI-LiCl eutectic, which indicates that the eutectic has potential thermal neutron detection ability.

Epitaxial Laterally Overgrown Free-Standing GaN through HVPE by Wide-Period Mask Method

CHEN Wangyibo, XU Yu, CAO Bing, XU Ke

2021, 50(3):  416-420. 

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Gallium nitride (GaN) films are mainly obtained through heteroepitaxial growth in the traditional growth process, which often causes lattice mismatch and thermal mismatch, and therefore also brings serious dislocations and stress to GaN. At present, the most widespread method to reduce dislocations is epitaxial laterally overgrown (ELOG) technology. In this work, a layer of silicon dioxide (SiO₂) was deposited on a sapphire-based GaN substrate and it was made into wide period mask with high mask width (window width 20 μm/mask width 280 μm) by photolithography. The 325 μm thick GaN film is epitaxially grown by hydride vapor phase epitaxy (HVPE). The sample can be released by tape. At the same time, the change trend of the crystal plane during the growth of GaN is studied through the two-dimensional Wulff construction. The wide-period mask method is of great significance for the growth of peelable, low-dislocation density free-standing GaN.

Growth and Properties of Lead Zinc Niobate-Lead Titanate Single Crystals

CHEN Huiting, HE Chongjun, ZHU Jun, LI Ziqiang, GAO Huifang, LU Yuangang

2021, 50(3):  421-427. 

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Transmittance of (1-x)Pb(Zn_1/3Nb_2/3)O₃-xPbTiO₃ (PZN-PT) single crystals was systematically characterized with respect to crystallographic orientation and composition. The results show that the transmittance of tetragonal single crystal is evidently larger than that of rhombohedral and morphotropic phase boundary (MPB) single crystals. Transmittance spectrum of tetragonal PZN-12%PT single crystal poled along [001] direction ranges from 0.5 μm to 5.8 μm, its transmittance without antireflective film is roughly 65%. After poled along [011] direction, the transmittance of PZN-8%PT single crystal in MPB is much higher than that poled along [001] or [111] direction. As the PT content increases, optical band gap of single crystals decreases. Refractive indices of PZN-PT single crystals with different PT content were measured. Just as most compounds with ABO₃ perovskite structure, the refractive indices of PZN-PT single crystals are very large, which decrease rapidly with the increasing wavelength. Refractive index dispersion is obvious, and dispersion equations were fitted. Electro-optic (EO) coefficients were measured by Sénarmont compensator and two-beam interference methods. The EO coefficients of PZN-PT single crystals are very large, which reach maximum in the MPB. The effective EO coefficient of PZN-8%PT single crystal is 460 pm/V after poled along [001] direction, which is higher than 20 times that of widely used LiNbO₃. The effective EO coefficient of PZN-12%PT single crystal is 138 pm/V, which is nearly invariant from 20 ℃ to 80 ℃. Because of the excellent transmittance and outstanding EO properties, PZN-PT single crystals allow of smaller size and lower operating voltage for EO devices.

Propagation Band Gap Characteristics of Open Ring-Like Phononic Crystal

TANG Rongjiang, PAN Chaoyuan, ZHENG Weiguang, HE Hongbin, TANG Jingtian

2021, 50(3):  428-434. 

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In order to attenuate the mid- and low-frequency vibration noise, a non-strictly symmetrical open ring-like phononic crystal structure was designed. Based on the finite element method and elastic wave theory, its band gap characteristics and vibration attenuation performance in various directions were analyzed; Combined with the vibration mode of the system, the reasons for the opening and closing of the band gap were explained, and the influence of geometric parameters on the band gap width was analyzed. The results show that due to the non-strict symmetry of the crystal, only the transmission loss in the ΓX direction is consistent with the band gap characteristics, and the attenuation performance is better than that in the MΓ direction. The average attenuation in the band gap is 27.8 dB, which is 5.5 dB higher than that in the MΓ direction. There is almost no displacement deformation in the forbidden band, and the deformation of the pass band significantly increases due to the inability to suppress the propagation of elastic waves; the horizontal and rotational movement of the core is an obvious sign of the beginning and end of the band gap. With tungsten as the core, the starting frequency and bandwidth are 500 Hz. Increasing the material density, filling rate and lattice size of the core will help to obtain a complete band gap at lower frequencies.

Preparation and Properties of Transparent Eu:Lu₂O₃ Scintillation Ceramics

WANG Jing, GE Ye, XIE Weifeng, CHEN Haohong, LI Jiang

2021, 50(3):  435-440. 

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The 5% Eu:Lu₂O₃ ceramic precursor was synthesized by wet chemical method, and the morphologies, microstructures and phases of both Eu:Lu₂O₃ ceramic precursor and the calcined Eu:Lu₂O₃ ceramic powders were studied by SEM and XRD. The results show that the powders are spherical, well-dispersed and good crystalline. The particle size is calculated to be about 68.5 nm. Using the powders calcined at 1 100 ℃ for 4 h as raw material, the highly transparent Eu:Lu₂O₃ ceramics were successfully fabricated by vacuum sintering at 1 650 ℃ for 30 h.The grain size is calculated to be about 46 μm, and in-line transmittance of the Eu:Lu₂O₃ ceramics reaches 66.3% at 611 nm. What's more, the absorption curve, the excitation spectrum, the emission spectrum and the X-ray excited emission spectrum of the Eu:Lu₂O₃ ceramics were studied. It can be observed that the absorption curve of Eu:Lu₂O₃ ceramics is consisted of the matrical absorption and active ion absorption. It can be seen from the photo-luminescence emission spectrum and X-ray excited emission spectrum of the Eu:Lu₂O₃ ceramics that an extremely strong peak is located at 611 nm, corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺. By comparison with the BGO crystal, the light output of the Eu:Lu₂O₃ ceramics is estimated to be about 85 000 ph/MeV. Eu:Lu₂O₃ ceramics have an excellent X-ray stopping power due to its high density and effective atomic number. It is indicated that Eu:Lu₂O₃ ceramics are a potential ceramic scintillator for the application of X-ray detection imaging combined with the characteristics of high light output.

Impurities of Homoepitaxy Interface on Bulk GaN Substrate

SHAO Kaiheng, XIA Songyuan, ZHANG Yumin, WANG Jianfeng, XU Ke

2021, 50(3):  441-446. 

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Homoepitaxy on bulk GaN substrate has significant advantages. However, accumulation of impurities on the regrowth interface has always been a problem that plagues the wide application of homoepitaxial, especially for electronic devices, which will bring channel effect, and for laser applications, which will affect the light field distribution in the resonator. In this paper, the in-situ treatment of metal-organic chemical vappor deposition (MOCVD) growth has achieved effective inhibition of the accumulation of interfacial impurities. The study found that the main impurities on the interface are C, H, O and Si, of which C, H, O can be removed by in-situ thermal cleaning. The problem of interface Si accumulation is mainly caused by exposure to air during the preservation of the substrate. During the growth process, the etching of the substrate by the carrier gas will release impurity elements which will accumulate at the regrowth interface. High Si background content and unstable N face of the GaN substrate are also sources of regrowth interface impurities. This paper systematically clarified the formation mechanism of interface impurities and proposed solutions.

High-Order Mixing Effects on EPR g-factors for Er³⁺ Doped Bi₄Ge₃O₁₂ Crystals

HAO Danhui, CHAI Ruipeng, LIANG Liang

2021, 50(3):  447-453. 

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Stark levels and EPR parameters of Er³⁺ doped in Bi₄Ge₃O₁₂ crystal were studied by diagonalizing 364×364 complete energy matrices. Simultaneously, the crystal-field and J-J mixing effects on the EPR g-factors from the higher lying manifolds were evaluated, quantitatively. The results indicate that the dominant J-J mixing contribution from manifold ²K_15/2 accounts for about 2.5% for the Er³⁺. However, the most significant high-order mixing effect is from the crystal-field admixture between the first excited manifold ⁴I_13/2 and ground manifold ⁴I_15/2, where the contribution to g_⊥ is almost twice as much as that to g_// (0.21% for g_⊥, 0.092% for g_//).The other crystal-field and J-J mixing effects from the higher lying manifolds can be neglected. Therefore, only considering the contribution of ground manifold ⁴I_15/2 to EPR g-factor is a good approximation for the complex system doped with Er³⁺ ions.

Theoretical Calculation of Optical Properties of Zn₂(OH)PO₄ and Its Experimental Verification

LUO Nannan, CAO Guowei, QIE Yuanyuan, ZHANG Ran, WANG Chunxiao, GONG Pifu, LI Zhihua, LIN Zheshuai

2021, 50(3):  454-460. 

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The crystalline structure of Zn₂(OH)PO₄ (ZPOH) belongs to orthorhombic unit cell structure, space group of P2₁2₁2, which has no center of symmetry. Based on the plane-wave pseudopotential ab initio method, the electronic structure, linear refractive indices and second harmonic generation (SHG) coefficients of Zn₂(OH)PO₄ were calculated and the Sellmeier equations were also fitted. To verify the calculated values, ZPOH was synthesized using hydrothermal method, and the measured SHG effect is in accordance with the theoretical calculation. The ultraviolet (UV) cut-off edge and thermal stability of ZPOH were also reported for the first time.

First-Principles Study on Charge Transfer and Optical Properties of Mg Doped ZnO at Different Locations

WANG Ning, SUN Wei, SU Jin, GUO Fengzhi, SONG Weili, WU Haicheng, ZHOU Guanggang, LU Guiwu

2021, 50(3):  461-468. 

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Based on density functional theory, the geometric structure, atomic orbital electron population, electrostatic potential and electronic structure properties of intrinsic zinc oxide, 6.25% Mg, and 12.5% Mg atom-doped zinc oxide crystals at the isotopic, ortho and meta positions were calculated. The effects of Mg atom doping on the energy band structure, density of states and corresponding optical and electrical properties of zinc oxide were explored. The results show that Mg doping will cause the crystal lattice volume of zinc oxide crystals to become larger, the carrier mobility decreases and the absorption edge blue shifts; the adjacent diatomic doping (ZnO+2Mg-ac, ZnO+2Mg-ad) can significantly reduce the light absorption coefficient and reflectivity of zinc oxide, and increase the transmittance to sunlight; Mg-doped zinc oxide crystals are suitable for making high-quality optical transmission films.

Quantum Chemistry Study on Gas Reactions Involved with Radicals in GaN-MOVPE Process

LIU Guofeng, ZUO Ran

2021, 50(3):  469-476. 

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The gas-phase reactions involved with radicals in the TMG/NH₃/H₂ system of MOVPE process were studied by the density functional theory (DFT) of quantum chemistry. In particular, the effects of H and NH₂radicals on the pyrolysis, hydrogenolysis and adduct paths of Ga(CH₃)₃ (denoted as TMG) were studied. By calculating of the Gibbs energies ΔG and energy barriers ΔG^*/RT of different reaction paths, the roles of radicals on the reaction paths at different temperatures were determined. The study found that when T<683 K, TMG reacts with NH₃ to generate TMG:NH₃. When T>683 K, TMG:NH₃ decomposes back into TMG and NH₃. At MOVPE condition TMG is difficult to pyrolyze directly. While with H radicals involved, TMG can be easily pyrolyzed into Ga(CH₃)₂(denoted as DMG), GaCH₃(denoted as MMG) and Ga atom. When T<800 K, the rate of amide reaction between TMG and NH₃ is greater than the rate of pyrolysis with H radicals, the reaction is dominated by amide reaction. When T>800 K, the rate of pyrolysis with H radicals is greater than the rate of amide reaction, the reaction is dominated by pyrolysis with H radicals. Since the energy barrier of hydrogenolysis is rather high, the reaction can be ignored. TMG and its pyrolysis products can react with NH₂ radicals easily to produce amide DMGNH₂. The amides can further react with H radicals and eventually generate GaNH₂ as surface reaction precursors.

Simulation of MoS₂/SnS Heterojunction Solar Cells

ZHAO Hanghang, YUAN Jiren, DENG Xinhua, HUANG Haibin

2021, 50(3):  477-483. 

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Stannous sulfide (SnS) is a class Ⅳ-Ⅵ layered compound semiconductor material. It's band gap is very close to the optimal band gap of 1.5 eV for solar cells, and the light absorption coefficient is very large (α>10⁴ cm^-1) in the visible light range, so it is a promising material for application. The MoS₂/SnS heterojunction solar cells were simulated by using the solar cell simulation software wxAMPS. The influence of SnS absorption layer thickness, doping concentration and defect states on the performance of solar cells were mainly studied. The results show that the optimal thickness of SnS absorption layer is 2 μm, the optimal doping concentration is 1.0×10¹⁵ cm^-3, and when the concentration of Gaussian defect states is more than 1.0×10¹⁵ cm^-3, the performance parameters of the cell decrease with the increase of concentration. However, when the concentration of tail defect states exceeds 1.0×10¹⁹ cm^-3·eV^-1, the performance of solar cell decreases. The interface defect states have obvious influence on the solar cell performance, when the concentration exceeds 1.0×10¹² cm^-2, the open circuit voltage, short circuit current, filling factor and conversion efficiency decrease rapidly. In addition, the optimal conversion efficiency is 24.87%, the open circuit voltage is 0.88 V, and the short circuit current is 33.4 mA/cm². It can be concluded that MoS₂/SnS heterojunction solar cell is a promising photovoltaic device structure.

Preparation and Electrical Properties of n-In_0.35Ga_0.65N/p-Si Heterojunction

WANG Ting, ZHAO Hongli, GUO Shiwei, YAO Juan, LI Shuang, FU Yuechun, SHEN Xiaoming, HE Huan

2021, 50(3):  484-490. 

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InGaN film was deposited on p-Si substrate using a self-refited pulsed laser deposition (PLD) system with double laser light paths and two-component target. The microstructure of InGaN film and the electrical properties of n-InGaN/p-Si heterojunction were investigated. The results show that InGaN film exhibits a single crystal structure with [0001] preferred orientation.The surface of the film is smooth and dense, and the atomic content of In is 35%. The Hall effect measurements show that In_0.35Ga_0.65N film exhibits n-type characteristics with high carrier concentration, high mobility and low resistivity. The current-voltage (I-V) analysis shows that n-In_0.35Ga_0.65N/p-Si heterojunction has good rectification characteristics with the rectification ratio of 25 at ±4 V, and the open circuit voltage is 1.32 V. There exists two current transport mechanisms in n-In_0.35Ga_0.65N/p-Si heterojunction: thermally assisted carrier tunneling and recombination-tunneling mechanism. In addition, the reverse saturation current, barrier height and ideality factor of the heterojunction are 1.05×10^-8A, 0.86 eV, and 6.87, respectively.

Preparation and Characterization of WS₂-MoS₂ Vertical Heterostructure by One-Step CVD

QIAN Yezheng, DING Kaixuan, YU Jiajun, XIAO Shaoqing

2021, 50(3):  491-496. 

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The preparation and optoelectronic properties of WS₂-MoS₂ vertical heterostructure were mainly studied. Molybdenum oxide (MoO₃), tungsten oxide (WO₃) and sulfur powder (S) were employed as reactants, and then high quality WS₂-MoS₂ vertical heterostructures were prepared by using an improved one-step chemical vapor deposition method (CVD). Raman spectroscopy (Raman), photoluminescence spectroscopy (PL), optical microscope (OM), atomic force microscope (AFM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and other related devices were used to characterize the morphology and element composition of the heterostructures. At last, the photodetector based on WS₂-MoS₂ vertical heterostructure was produced, and the photoelectric characteristics of the fabricated device including the output characteristic curve, transfer characteristic curve and photocurrent curve were measured. The test results show that the photodetector based on WS₂-MoS₂ vertical heterostructure exhibits wonderful photoresponse characteristics under the 532 nm laser mode. It obviously means that the photodetector based on WS₂-MoS₂ vertical heterostructure can be applied to the preparation of high-efficiency optoelectronic devices and have broad application prospects in the field of microelectronics.

Photogalvanic Effect of Doped Monolayer WS₂ Based on First-Principles

YUAN Qiuming, CHEN Yan, XU Zhonghui, LUO Bing, CHEN Zhen

2021, 50(3):  497-503. 

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Based on the non-equilibrium Green function-density functional theory, the photoelectric effect of doped monolayer WS₂ with VA group elements (N, P, As or Sb) was calculated by first-principles, and the microcosmic mechanism of doping to improve the photogalvanic effect was explained. The results show that photocurrent can be generated in the monolayer WS₂ under linearly polarized light. Since the doping reduces the spatial inversion symmetry of the monolayer WS₂, the photocurrent generated by the illuminated central area of the monolayer WS₂ doped with N, P, As, or Sb significantly increases, and the photocurrent and the polarization angle show a perfect sinusoidal relationship, which conforms to the phenomenological theory. Among them, the effect of N doping is the best. The doped monolayer WS₂ obtains the maximum photocurrent (1.75) when the photon energy is 3.1 eV, and the polarization sensitivity reaches the maximum (18.1). The monolayer WS₂ doped with P, As and Sb achieves a larger photocurrent when the photon energy is 3.9 eV, and has a higher polarization sensitivity. The research results show that the doping can effectively enhance the photogalvanic effect and obtain higher polarization sensitivity, revealing the potential application prospects of doped monolayer.

Theoretical Study on the Photogalvanic Effect of Monolayer 2H-MoTe₂

LUO Bing, CHEN Yan, XU Zhonghui

2021, 50(3):  504-508. 

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The band gap of the material is an important factor affecting the detection ranges of the photodetector. The monolayer 2H-MoTe₂ has attracted a wide range of research interests due to its suitable band gap. In this paper, based on the non-equilibrium Green's function-density functional theory, using first-principles methods, the photogalvanic effect(PGE) of the monolayer 2H-MoTe₂ was studied. The results show that under linearly polarized light, the photocurrent function produced by MoTe₂ is consistent with the phenomenological theory. It can generate a larger photocurrent in the photon energies range of 1.6 eV to 1.8 eV (690 nm to 770 nm). The reason for obtaining the higher photocurrent is the electron stimulated transition at the S point in the first Brillouin zone which analyzed using the band structure and density of states. Meanwhile, in the zigzag direction, when the bias voltage is 0.8 V, the photocurrent reaches its peak, but in the armchair direction, when the bias voltage is 0.4 V, the max photocurrent can be reached. The calculation results in this paper can be used to guide the design of photodetectors based on MoTe₂, especially the design of infrared photodetectors.

Effect of Deposition Temperature on Microstructure of Silicon Oxide Film Prepared by Plasma Enhanced Chemical Vapor Deposition

YOU Jiachuan, ZHAO Lei, DIAO Hongwei, WANG Wenjing

2021, 50(3):  509-515. 

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Hydrogenated silicon oxide (SiO_x:H) films were prepared by 13.56 MHz radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). The effect of the deposition temperature (T) variation (from 50 ℃ to 400 ℃) on the film performance and microstructure were investigated. The T increases could induce the decreases of oxygen content (C_O) in the SiO_x:H film and at the same time make the film transform from nanocrystalline state to amorphous state gradually, which resulted in the film crystallinity (X_C) decreases and the film refractive index (n) increases. Further, it was found that the microstructure factor (R) decreases and the hydrogen content (C_H) in the SiO_x:H film increases first and then decreases with the T increases. A maximum of C_H could be obtained with an intermediate T. Based on the above results, the low-temperature formed film is considered as a typical composite with hydrogenated nanocrystalline silicon (nc-Si:H) inserted in the hydrogenated amorphous silicon oxide (a-SiO_x:H) matrix, however, the high-temperature deposited film consists of hydrogenated amorphous silicon (a-Si:H) matrix with nc-Si:H and a-SiO_x:H phases less and less diluted inside. The results show that excellent hydrogenated nanocrystalline silicon oxide (nc-SiO_x:H) film with high X_C and C_O for solar cell application should be deposited at a relatively low temperature.

Controllable Preparation and Photoelectrochemical Performance of TiO₂ Thin Film with Different Morphology

WANG Xinwei, CHE Zhiyuan, ZHANG Xing, LI Lingwei, ZHANG Wei, SU Shi, MA Jinwen

2021, 50(3):  516-522. 

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Anatase TiO₂ thin films with different morphology were prepared on FTO substrates by hydrothermal method. With the increasing of hydrochloric acid concentration in the precursor, TiO₂ thin films gradually evolved from spherical particle films into TiO₂ nanosheet array films with a large percentage of high-energy exposed (001) planes. By analyzing the evolution rule of morphology and X-ray diffraction patterns, a reasonable growth and evolution mechanism of TiO₂ thin film with different morphology was proposed, and the role of hydrochloric acid was explained. In order to further improve the performance of TiO₂ thin films, CdS quantum dots (QDs) sensitization was performed on different TiO₂ thin films by the successive ionic layer adsorption and reaction method. The optical absorption performance and photoelectrochemical (PEC) properties of composite films were studied by ultraviolet visible absorption spectroscopy and three-electrode electrochemistry system. The optical absorption data and PEC performance data show that the properties of CdS/TiO₂ composite films are better than those of pure TiO₂ thin films, and the properties of nanosheet array films are obviously better than other morphologies, which illustrates the performance superiority of TiO₂ nanosheet array films with large area high-energy (001) planes exposed. The excellent PEC properties also suggest that the QDs sensitized TiO₂ nanosheet array films with a large percentage of high-energy surfaces have potential applications in PEC solar cells.

Crystal Structure and Density Functional Theory of 3-Tert-Butyl-1-(3-Hydroxyphenyl)Urea

CHEN Dongmei, CHEN Yumei, WU Qingmei, ZHOU Zhixu

2021, 50(3):  523-529. 

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Urea and its derivatives have a long history of applications in chemistry, agriculture and medicine. The aryl urea derivative, which plays a crucial role in medicinal fields and chemistry as intermediates. The title compound, 3-tert-butyl-1-(3-hydroxyphenyl)urea was synthesized by amidation and oxygenation two-step reaction, and it's single crystal was obtained by solvent evaporation at room temperature. The crystal stacking and the mode of intermolecular interaction were analyzed and the structure was confirmed by ¹H NMR, FT-IR, ¹³C NMR, MS and X-ray single crystal diffraction. In addition, the optimal structure and frontier orbital energy were calculated through the density functional theory (DFT) by using B3LYP method with the 6-311+G(2d, p) basis set and the molecular structure of the crystal was compared with the theoretical calculation. The result indicates that the crystal structure by the X-ray diffraction is very close to the molecular structure optimized by DFT. What's more, the crystal structure of 1 shows that the intermolecular packing is stabilized by hydrogen bondings and the vander Waals forces, and hydrogen bonding is one of the vital factors in the crystal stability. The crystals of 3-tert-butyl-1-(3-hydroxyphenyl)urea belong to the monorhombic system with space group is P2₁/n and the cell parameters are a=1.181 42(6) nm, b=1.762 00(8) nm, c=1.179 02(5) nm, Z=8.

Construction of Three-Dimensional Hydrogen-Bonding Network in the Inclusion Compound with Double Betaine as Guest

YANG Yuan, SHEN Jing, QIN Haoli

2021, 50(3):  530-535. 

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A novel inclusion compound [^-OOCCH₂N⁺(CH₃)₂]₂(CH₂)₃·4(NH₂)₂CS has been prepared with thiourea and double betaine, and the crystal structure was characterized by single crystal X-ray diffraction. Crystal structural analysis shows that the complex is triclinic, with space group P1¯, a=0.884 5(2) nm, b=0.936 7(2) nm, c=0.946 4(3) nm, α=91.591(2)°, β=91.591(2)°, γ=91.591(2)°, Z=1, R₁=0.039 9, wR₂=0.100 6(I>2σ(I)). In the crystal structure of the title compound, thiourea molecules are connected side by side through N-H…S hydrogen bonds to form a tetramer. The hydrogen bond layer is formed by carboxyl groups of the guest molecules and the thiourea tetramer through N-H…O hydrogen bonds. And the guest dications are sandwiched between adjacent hydrogen bonding layers to form a sandwich crystal structure.

Synthesis of Ultrafine ZnO Nanowire Arrays and Its Electrochemical Performance

ZHOU Yangyang, ZHANG Ziying, WENG Ying

2021, 50(3):  536-541. 

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Using Zn(NO₃)₂·6H₂O and C₆H₁₂N₄ as raw materials, ZnO nanowire arrays with uniform morphology and size were synthesized by conventional two-step hydrothermal method on carbon fiber cloth. Their crystal structure and morphologies were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and their electrochemical performance was tested by constant current charge-discharge test. The results show that these materials have excellent electrochemical performance. After 150 cycles at the current density of 200 mA/g, the specific capacity of ZnO nanowire arrays is still about 730 mAh/g, and the Coulomb efficiency remains above 95%. At a high rate of 1 200 mA/g, the charge-discharge capacity of the products is still about 481 mAh/g, showing good cycle stability and reversibility. The ultrafine ZnO nanowire arrays are a promising anode material for lithium-ion batteries.

Preparation of Carbon Nanotubes Loaded RuO₂ Nanoparticles and the Performance of Li-CO₂ Battery

GU Yang, WANG Zhen, LI Xue, XIAO Jie, ZENG Xiaoyuan

2021, 50(3):  542-547. 

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The Li-CO₂ battery captures CO₂ gas and converts it into electricity, which can not only alleviate the greenhouse effect, but also provide a higher theoretical energy density, which has attracted wide attention from researchers. However, Li-CO₂ batteries still face some thorny problems, such as high overpotential and poor cycle life. Electrocatalysts that efficiently promote the reduction of CO₂ and the decomposition of discharge products play a key role in Li-CO₂. Using hydrated ruthenium trichloride solution as the precursor, ruthenium dioxide (RuO₂) nanoparticles were uniformly loaded on the carbon nanotube (CNT) substrate by a simple hydrothermal method, and the ruthenium dioxide nanoparticles were successfully prepared with uniform dispersion and RuO₂-CNT catalytic cathode with three-dimensional porous structure. Under the dual action of the three-dimensional porous structure formed by cross-linked carbon nanotubes and the high-efficiency catalytic activity of RuO₂ nanoparticles, the discharge capacity and cycle performance of the Li-CO₂ battery are significantly improved. At a current density of 100 mA·g^-1, the first discharge specific capacity can reach 1 912 mAh·g^-1. In addition, under the conditions of a current density of 100 mA·g^-1 and a constant capacity of 500 mAh·g^-1, it can be cycled stably for 120 cycles. It provides a new idea for the design and preparation of Li-CO₂ battery catalytic cathode.

Preparation of High Performance Brush-Like Zinc Oxide Mesocrystals and Its Reinforcing Effect on Properties of Resin Composites

QIN Yang, ZHANG Qinghong, WANG Ruili, LIU Mei

2021, 50(3):  548-557. 

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The inorganic filler is the main component of dental resin composite, which is very important for the properties of resin composite. In this paper, ZnO mesocrystals with porous and hierarchical structure were achieved by a thermal hydrolysis method using gum arabic as structure-directing agent. The thickness and diameter of the synthesized ZnO mesocrystals were about 1.2 μm and 1.0 μm. The amorphous silica in a thickness of 4~6 nm was uniformly coated on the surface of ZnO mesocrystals via the microfluidc process. ZnO mesocrystals were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The ZnO@SiO₂ was firstly modified with 3-methacryloxypropyl trimethoxysilane (γ-MPS), and mixed with modified SiO₂ nanoparticles as co-filler. Subsequently modified inorganic particles were added into Bis-GMA/TEGDMA to prepare dental composite resin by light-curing. The mechanical testing show that the mass fraction of ZnO@SiO₂ (≤5%) could improve the mechanical properties of composite resin effectively. The silica matrix composite resin filled with 3% ZnO@SiO₂ demonstrates the best mechanical properties, among which the flexural strength, flexural modulus and compression strength increase by 12.9%, 6.6% and 3.7%, respectively, in comparison with the composite using of only SiO₂ filler. This optimal composite also exhibits superior antimicrobial activity, with antibacterial rate up to 98.7% to Streptococcus mutans. In addition, the composite resin with ZnO@SiO₂ also has better wear resistance.

Precision Cutting Mechanism of Monocrystalline Silicon Based on Single Abrasive Micro-Scratch

WANG Long, WANG Liuying, LIU Gu, TANG Xiujian, YANG Nengjun, YOU Yinfeng, LIU Guohao

2021, 50(3):  558-564. 

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High efficiency and precision grinding of monocrystalline silicon plays an important role in the field of microelectronics and optoelectronics manufacturing. To explore the cutting characteristics and mechanism of precision grinding of silicon wafer devices, diamond grain with triangular pyramid shape was used to scratch the surface of monocrystalline silicon under different loading pressures to simulate the grinding process. The evolution law of scratch morphology, cutting force and cutting depth were analyzed, and the micro cutting mechanism of monocrystalline silicon was explained. The critical value of microcracking removal is normal cutting force of 80 mN and critical cutting depth of 2.03 μm. The critical condition of spalling removal is normal cutting force of 800 mN and cutting depth of 5.65 μm. Cutting depth and grinding force ratio have distinct differentiation characteristics under different cutting mechanism conditions. The variation law of average cutting depth with loading pressure shows self similarity characteristics. In addition, the cutting force equations of plastic removal, micro crushing removal and spalling removal are constructed respectively, which can more accurately describe the close relationship between cutting force and cutting depth. These works are of great significance to further improve the cutting theory of monocrystalline silicon materials, and improve the manufacturing ability of semiconductor.

Structure and Electrical Properties of Sb₂O₃-Doped BiFeO₃-BaTiO₃ Piezoelectric Ceramics

HUANG Zhiqiang, HE Xiujiang, HE Xinhua, FU Xiaoyi, WANG Xin, LU Zhenya

2021, 50(3):  565-571. 

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0.7BiFeO₃-0.3BaTiO₃+x%Sb₂O₃ (mass fraction) ceramics (BFO-BTO+xSb, x=0.00~0.20) were synthesized by the conventional solid state reaction method, and the effect of Sb₂O₃ doping on the crystalline phase structure, dielectric, conductive, piezoelectric and ferroelectric properties of BFO-BTO ceramics was investigated, along with doping mechanism. The results indicate that Sb doping change the crystal structure from a pesodocubic lattice to a rhombohedral lattice. Sb substitution for B site increases ferroelectric relaxation, decreases dielectric loss at high temperature, and also lowers the Curie temperature. The conductive characteristics demonstrate that Sb doping changes the concentration of $V_O^×$ and Fe²⁺, and decreases the conductivity, without changing the conductive mechanism with oxygen vacancy as the dominant carrier. BFO-BTO+xSb ceramics exhibit optimum electric properties at x=0.05: d₃₃=213 pC/N, k_p=28.8%, Q_m=38, T_c=520 ℃, P_r=24.7 μC/cm².

Preparation and Characterization of Boron Carbide Ceramics Enhanced by Reduced GO

XU Sen, FANG Ningxiang, ZHANG Shanwei, ZHANG Hong, LIN Wensong

2021, 50(3):  572-577. 

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GO/Boron carbide (GO/B₄C) composite powders were prepared by ball-milling and atomizing granulation. Reduced GO/Boron carbide (rGO/B₄C) composites were obtained by vacuum hot pressing at 2 100 ℃ under the pressure of 30 MPa. The surface phase and mechanical properties of the composites were analyzed by SEM, TG and XRD, three-point bending method and drainage method. The effect of GO dosage on the bending strength and fracture toughness of rGO/B₄C composites was studied. The results show that the uniformly mixed GO/B₄C composite powder can be obtained by gradually adding the stable and dispersed GO/water suspension to the B₄C slurry during the ball milling process. The bending strength and fracture toughness of rGO/B₄C composites, in which the GO content is 1.5%, are 535 MPa and 5.2 MPa · m^1/2, respectively, 72.6% and 136% higher than those of B₄C ceramics. It is beneficial to the application of boron carbide ceramics in military protection field. The toughening mechanism of rGO/B₄C composites was explained from the aspects of graphene pulling, crack deflection and bridging. This will allow future researchers to further investigate the toughening effect of GO and it is also conducive to its large-scale industrial production.

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Research Progress of Low-Dimensional Group-VA Nanomaterials:from Structural Properties to Preparation Applications

LIU Qichao, ZHANG Hui

2021, 50(3):  578-586. 

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The zero band gap of graphene and low carrier mobility of molybdenum disulfide hinder their applications in electronic device. The successful preparation of single-layer black phosphorous and the direct band gap, higher carrier mobility and negative poisson's ratio of phosphene make up for the shortcomings of graphene and molybdenum disulfide, which has triggered great research interests on the low-dimensional group-VA nanomaterials. It enables the rapid development of low-dimensional group-VA nanomaterials in the fields of materials science and optoelectronics. Recent research results on the low-dimensional group-VA nanomaterials are summarized in this paper. Combining theoretical calculations and experimental synthesis, relationship between the structure and performance of the materials is analyzed. Finally, the preparation methods and applications of the above materials are summarized. The low-dimensional group-VA nanomaterials exhibit a variety of crystal structures, high dynamic stability, versatile electronic structures and higher carrier mobility and other characteristics. Such properties make low-dimensional group-VA nanomaterials have a wide range of applications in low-dimensional optoelectronic devices.