共查询到18条相似文献,搜索用时 125 毫秒
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基于密度泛函理论的广义梯度近似方法研究了中性单点缺陷γ-Si3N4的能量、电子结构和光学性质. N缺陷的结合能和形成能比Si(8)和Si(4)位的都低,显示γ-Si3N4中N缺陷更易形成. 分析了各种缺陷情况下相应的态密度. Si缺陷能形成p型半导体,N缺陷使材料形成间接带隙的n型半导体. Si缺陷情况下,物质有相对大的静态介电常数,在可见光区和红外区,吸收和反射得到显著改善,但是N缺陷却没什么影响. 相似文献
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利用密度泛函理论和非平衡格林函数方法, 本文对小尺寸团簇Tan(B3N3H6)n+1 (n ≤ 4)的磁性和量子输运性质进行了系统的研究. 计算结果表明, 此类体系采用三明治结构作为其基态并且具有较高的稳定性. 体系的磁矩随团簇尺寸的增大而线性增大. 当把Tan(B3N3H6)n+1团簇耦合到Au电极上时, 形成的Au-Tan(B3N3H6)n+1-Au体系在有限偏压下展示出了较强的自旋过滤能力, 因而可以被看做是一类新型的低维自旋过滤器. 相似文献
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基于第一性原理方法计算,通过在g-C3N4中掺杂C、B和N原子, 预测了四种元素均匀分布的B-C-N三元单层材料. 除了B4-C3N4单层材料是一个具有1.18 eV带隙的半导体, 其余三种C-B-N三元单层材料都是金属材料.其中,B3C-C3N4是铁磁金属,其净磁矩为0.57 μB/原胞,可用于构建自旋电子器件材料.计算的形成能显 相似文献
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ECR-PECVD制备Si3N4薄膜的光学特性研究 总被引:1,自引:0,他引:1
本文研究了ECR-PECVD制备的Si3N4薄膜的光学特性.得到的Si3N4薄膜具有光致发光效应,在280℃沉积制备的Si3N4薄膜的光致发光波长为400nm,具有较好的单色性.测试分析了Si3N4薄膜对可见光、红外光具有较高的透射性能,Si3N4薄膜可作为红外光的增速减反射膜. 相似文献
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研究了Si3N4层在ZrN/Si3N4纳米多层膜中的晶化现象及其对多层膜微结构与力学性能的影响. 一系列不同Si3N4层厚度的ZrN/Si3N4纳米多层膜通过反应磁控溅射法制备. 利用X射线衍射仪、高分辨透射电子显微镜和微力学探针表征了多层膜的微结构和力学性能. 结果表明,由于受到ZrN调制层晶体结构的模板作用,溅射条件下以非晶态存在的Si3N4层在其厚度小于0.9 nm时被强制晶化为NaCl结构的赝晶体,ZrN/Si3N4纳米多层膜形成共格外延生长的柱状晶,并相应地产生硬度升高的超硬效应. Si3N4随层厚的进一步增加又转变为非晶态,多层膜的共格生长结构因而受到破坏,其硬度也随之降低. 相似文献
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本文通过简单的溶剂热法制备了g-C3N4与高比表面积的TiO2复合材料,该方法操作简单且能耗低. 甲基橙降解实验结果表明,高比表面积的TiO2有效提高了光催化活性. 光电化学测试结果表明,与g-C3N4复合后,TiO2的电荷载流子迁移速率得到明显改善. g-C3N4/高比表面积-TiO2的光催化活性很强,在100分钟内,6%-g-C3N4/高比表面积-TiO2对甲基橙的降解程度可达92.44%. 6%-g-C3N4/高比表面积-TiO2不仅具有良好的光催化降解性能,还具有较高的稳定性. 本文对6%-g-C3N4/高比表面积-TiO2的光催化机理也进行了系统的研究. 相似文献
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本文应用基于二极管激光器的双路光腔衰荡光谱技术,分别对大气中NO3和N2O5浓度进行监测. 通过使用实验室标准样校正有效吸收腔长比RL和系统的总损耗系数?,并获得了NO3有效吸收截面. 该装置在时间分辨率为1 s时,对NO3的测量灵敏度达到1.1 pptv,N2O5被在线转换成NO3,从而被另一路光腔衰荡光谱装置探测. 利用该装置,对合肥市区冬季夜间大气中的NO3,N2O5浓度进行了实时监测. 通过对比一次大气快速清洁过程中氮氧化物、臭氧、PM2.5等组分的浓度变化,讨论了大气环境下可能影响NO3及N2O5浓度的因素. 相似文献
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Porous Si3N4 ceramics with photoluminescence properties were prepared by pressureless sintering using α-Si3N4 powder as raw material and Eu2O3 as sintering additive. Chemical composition, phase formation, microstructure and photoluminescence properties of porous Si3N4 ceramics were studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence measurements (PL/PLE). The results show that single Eu2O3 additive promotes α→β transformation but not significant densification. A broad band emission center at 570 nm assigned to Eu2+ is observed, Eu3+ in Eu2O3 is (partially) converted to Eu2+ by reaction with Si3N4, which results in a lower β aspect ratio and β-content compared to the other Ln (Ln=lanthanide) oxide additives. 相似文献
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Theoretical investigation on the electronic structure, elastic properties, and intrinsic hardness of Si2N2O 下载免费PDF全文
According to the density functional theory we systematically study the electronic structure, the mechanical prop- erties and the intrinsic hardness of Si2N2O polymorphs using the first-principles method. The elastic constants of four Si2N2O structures are obtained using the stress-strain method. The mechanical moduli (bulk modulus, Young’s mod- ulus, and shear modulus) are evaluated using the Voigt-Reuss-Hill approach. It is found that the tetragonal Si2N2O exhibits a larger mechanical modulus than the other phases. Some empirical methods are used to calculate the Vickers hardnesses of the Si2N2O structures. We further estimate the Vickers hardnesses of the four Si2N2O crystal structures, suggesting all Si2N2O phases are not the superhard compounds. The results imply that the tetragonal Si2N2O is the hardest phase. The hardness of tetragonal Si2N2O is 31.52 GPa which is close to values of β-Si3N4 and γ-Si3N4. 相似文献
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The structural, electronic and thermodynamic properties of cubic Zn3N2 under hydrostatic pressure up to 80 GPa are investigated using the local density approximation method with pseudopotentials of the ab initio norm-conserving full separable Troullier-Martin scheme in the frame of density functional theory. The structural parameters obtained at ambient pressure are in agreement with experimental data and other theoretical results. The change of bond lengths of two different types of Zn-N bond with pressure suggests that the tetrahedral Zn-N bond is slightly less compressible than the octahedral bond. By fitting the calculated band gap, the first and second order pressure coefficients for the direct band gap ofthe Zn3N2 were determined to be 1.18×10−2 eV/GPa and −2.4×10−4 eV/(GPa)2, respectively. Based on the Mulliken population analysis, Zn3N2 was found to have a higher covalent character with increasing pressure. As temperature increases, heat capacity, enthalpy, product of temperature and entropy increase, whereas the Debye temperature and free energy decrease. The present study leads to a better understanding of how Zn3N2 materials respond to compression. 相似文献
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Predictions of pressure-induced structural transition, mechanical and thermodynamic properties of α-and β-Si3N4 ceramics: ab initio and quasi-harmonic Debye modeling 下载免费PDF全文
The plane-wave pseudo-potential method within the framework of ab initio technique is used to investigate the structural and elastic properties of α-and β-Si3N4.The ground-state parameters accord quite well with the experimental data.Our calculation reveals that α-Si3N4 can retain its stability to at least 40 GPa when compressed at 300 K.The α→β phase transformation would not occur in a pressure range of 0-40 GPa and a temperature range of 0-300 K.Actually,the α→β transition occurs at 1600 K and 7.98 GPa.For α-and β-Si3N4,the c axes are slightly more incompressible than the a axes.We conclude that β-Si3N4 is a hard material and ductile in nature.On the other hand,β-Si3N4 is also found to be an ionic material and can retain its mechanical stability in a pressure range of 0-10 GPa.Besides,the thermodynamic properties such as entropy,heat capacity,and Debye temperature of α-and β-Si3N4 are determined at various temperatures and pressures.Significant features in these properties are observed at high temperature.The calculated results are in good agreement with available experimental data and previous theoretical values.Many fundamental solid-state properties are reported at high pressure and high temperature.Therefore,our results may provide useful information for theoretical and experimental investigations of the Si3N4 polymorphs. 相似文献
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采用反应磁控溅射法制备了一系列具有不同Si3N4层厚度的AlN/Si3N4纳米多层膜,利用X射线衍射仪、高分辨透射电子显微镜和微力学探针表征了多层膜的微结构和力学性能.研究了Si3N4层在AlN/Si3N4纳米多层膜中的晶化现象及其对多层膜生长结构与力学性能的影响.结果表明,在六方纤锌矿结构的晶体AlN调制层的模板作用下,通常溅射条件下以非晶态存在的Si3N4层在其厚度小于约1nm时被强制晶化为结构与AlN相同的赝形晶体,AlN/Si3N4纳米多层膜形成共格外延生长的结构,相应地,多层膜产生硬度升高的超硬效应.Si3N4随层厚的进一步增加又转变为非晶态,多层膜的共格生长结构因而受到破坏,其硬度也随之降低.分析认为,AlN/Si3N4纳米多层膜超硬效应的产生与多层膜共格外延生长所形成的拉压交变应力场导致的两调制层模量差的增大有关.
关键词:
3N4纳米多层膜')" href="#">AlN/Si3N4纳米多层膜
外延生长
赝晶体
超硬效应 相似文献
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HfC/Si3N4 nanomultilayers with various thicknesses of Si3N4 layer have been prepared by reactive magnetron sputtering. Microstructure and mechanical properties of the multilayers have been investigated. The results show that amorphous Si3N4 is forced to crystallize and grow coherently with HfC when the Si3N4 layer thickness is less than 0.95 nm, correspondingly the multilayers exhibit strong columnar structure and achieve a significantly enhanced hardness with the maximum of 38.2 GPa. Further increasing Si3N4 layer thickness leads to the formation of amorphous Si3N4, which blocks the coherent growth of multilayer, and thus the hardness of multilayer decreases quickly. 相似文献
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The influence of hydrothermal modification of γ-Al2O3 on the properties of NiMo/γ-Al2O3 catalyst was investigated in this paper. The experimental results showed that the use of the modified γ-Al2O3 in the preparation of the NiMo/γ-Al2O3 catalyst led to the increase of the dispersion of the surface Mo and Ni oxides, favored the formation of the poly-molybdates and promoted the reduction of the active Mo oxides owing to the increase of the surface acidity of the modified γ-Al2O3. Therefore, the NiMo/γ-Al2O3 catalyst supported on the modified γ-Al2O3 exhibited a higher hydrodenitrogenation (HDN) activity than that supported on the untreated γ-Al2O3 in the temperature range of 300-340 °C. 相似文献