Al-N共掺杂ZnO的第一性原理研究

为了研究p型ZnO的掺杂改性,本文运用第一性原理密度泛函理论研究了未掺杂,Al、N单掺杂和Al-N共掺杂ZnO晶体的几何结构、能带结构、电子态密度.计算结果表明:未掺杂,Al、N单掺杂和Al-N共掺杂ZnO的超晶胞体积分别为0.2043 nm3、0.2034 nm3、0.2027 nm3、0.1990 nm3,带隙分别为0.72 eV、0.71 eV、0.60 eV、0.55 eV;N是比较理想的p型掺杂受主,若在禁带中再引入激活施主Al后,可填充的电子数由原来的19个增加到24个,N原子接受从价带跃迁的电子使价带产生非局域化空穴载流子,从而提高了晶体的导电性.与未掺杂,Al、N单掺杂相比,Al-N共掺杂ZnO具有更稳定的结构,更窄的带隙,更好的导电性,更有利于实现p型化.     

Effects of B segregation on Mo-rich phase precipitation in S31254 super-austenitic stainless steels: Experimental and first-principles study

Precipitation in super-austenitic stainless steels will significantly affect their corrosion resistance and hot workability. The effects of Cr and Mo on precipitation behaviors were mainly achieved by affecting the driving force for precipitation, especially Mo has a more substantial promotion effect on the formation of the σ phase than Cr. In the present study, B addition to the S31254 super-austenitic stainless steels shows an excellent ability to inhibit precipitation. The effect of B on the precipitation behaviors was investigated by microstructure characterization and theoretical calculations. The experimental observation shows that the small addition of B inhibits the formation of the σ phase along grain boundaries and changes from continuous to intermittent distribution. Moreover, the inhibitory effect increased obviously with the increase of B content. The influence of B addition was theoretically analyzed from the atomic level, and the calculation results demonstrate that B can inhibit the formation of σ phase precipitates by suppressing Mo migration to grain boundaries. It is found that B and Mo are inclined to segregate at Σ 5 and Σ 9 grain boundaries, with B showing the most severe grain boundary segregation tendency. While B distribution at the grain boundary before precipitation begins, the segregation of Mo and Cr will be restrained. Additionally, B's occupation will induce a high potential barrier, making it difficult for Mo to diffuse towards grain boundaries.     

Ta2O5/MgF2异质结构三维光子晶体的偏振性

为了在可见及近红外波段得到具有良好带隙结构的三维光子晶体,利用传输矩阵法分析了MgF₂、Ta₂O₅ 以及Ta₂O₅/MgF₂异质结构三维光子晶体的带隙性质.结果表明：Ta₂O₅/MgF₂异质结构三维光子晶体在820~1 020 nm的近红外波段TM模式下具有不受入射光方向影响的全方位光子带隙.该结构有望用于制作近红外光波段的偏振器件.     

大面积垂直取向介孔二氧化硅薄膜的制备及性能研究

具有大尺度无缺陷垂直孔道的介孔二氧化硅薄膜在生物材料、电化学和光学传感器中具有重要应用价值.本文采用电化学辅助自组装(EASA)工艺制备大面积(5×5 cm2)孔道垂直定向的介孔二氧化硅薄膜,利用循环伏安曲线(CV),扫描电子显微镜(SEM)、原子力显微镜(AFM)、高分辨透射电子显微镜(HRTEM)、二维掠入射小角X射线散射(2D-GISAXS)等手段对薄膜渗透性、表面宏观形貌,及介孔孔道的结构等进行了表征,并通过同步辐射反射率计测试了该薄膜在极紫外波段的光学性能.结果 表明,采用EASA法在大面积基底上成功制备出了具有垂直取向孔道且渗透性良好的介孔二氧化硅薄膜,其孔径和晶胞参数大小分别为2.83 nm和4.1 nm,且其在极紫外波段(5～11nm)的反射率最高可达75;.     

Ru掺杂SnO2半导体固溶体的电子结构研究

运用基于密度泛函理论的第一性原理方法,建立了SnO₂以及不同比例Ru掺杂的SnO₂超胞模型,在对其进行几何优化后计算了Sn_1-xRu_xO₂(x=0,1/16,1/12,1/8,1/6,1/4,1/2)半导体的电子结构,并讨论了其晶格参数、电荷密度、能带结构和态密度(包括分态密度)等性质。结果表明,掺杂后,晶格参数随掺杂量的增加线性减小,与实验值的偏差在4%以内;掺杂后,在费米能级处可以提供更多的填充电子,使得电子跃迁至导带更容易,固溶体的导电性增强。为Sn_1-xRu_xO₂固溶体电极材料的发展和应用提供了理论基础。     

MgF2表面结构稳定性及电子特性的密度泛函理论研究

用密度泛函理论(DFT)研究了MgF₂(010)、MgF₂(001)、MgF₂(011)及MgF₂(110)四种表面10种构型的稳定性和电子特性. 结果表明: 四种表面的邻近表面几层原子均出现了明显的驰豫现象, 终止于单层F原子的表面相对稳定; 进一步对比分析四种表面(终止于单层F原子的稳定构型)的表面能发现, 稳定性依次减弱排列为MgF₂(110)、MgF₂(011)、MgF₂(010)、MgF₂(001); 最稳定的MgF₂(110)表面的态密度显示在费米能级以下较多的成键电子处于低能级区, 同时由于表面的影响, 导致表面F原子电荷聚集显负电性, 促使表面活性增加.     

R面、C面蓝宝石上生长的InGaN多层量子点的发光性质研究

采用表面钝化和MOCVD低温生长在蓝宝石(0001)面(即C面)和蓝宝石(1102)面(即R面)上形成了InGaN量子点,并构成了该量子点的多层结构.原子力显微镜测试的结果表明单层InGaN量子点平均宽约40nm,高约15nm;而多层量子点上层的量子点则比单层的InGaN量子点大.R面蓝宝石衬底上生长的InGaN量子点和C面蓝宝石衬底上生长的InGaN量子点相比,其PL谱不仅强度高,而且没有多峰结构.这是由于在C面蓝宝石衬底上生长的InGaN/GaN多层量子点沿生长方向[0001]存在较强的内建电场,而在R面蓝宝石衬底上得到的多层量子点沿着生长方向[1120]没有内建电场.InGaN量子点变温光致发光(PL)谱研究发现量子点相关的峰有快速红移现象,这是量子点系统所特有的PL谱特征.用在R面蓝宝石上生长的InGaN量子点作有源层有望避免内建电场的影响,得到高量子效率且发光波长稳定的发光器件.     

内包碳化铁洋葱状富勒烯的合成和表征

自从Kr（ae）tschmer等发现宏观量制备富勒烯的方法以来,这种新型的球形碳质材料已经引起材料科学家愈来愈多的关注．特别是以洋葱状形态和包裹外来物质进入洋葱状富勒烯内部的碳质材料更是展现了这种新型碳材料的应用前景．     

Detection of finger interruptions in silicon solar cells using photoluminescence imaging

Finger interruptions are common problems in screen printed solar cells, resulting in poor performance in efficiency because of high effective series resistance. Electroluminescence(EL) imaging is typically used to identify interrupted fingers. In this paper, we demonstrate an alternative method based on photoluminescence(PL) imaging to identify local series resistance defects, with a particular focus on finger interruptions. Ability to detect finger interruptions by using PL imaging under current extraction is analyzed and verified. The influences of external bias control and illumination intensity on PL images are then studied in detail. Finally, in comparison with EL imaging, the using of PL imaging to identify finger interruptions possesses the prominent advantages: in PL images, regions affected by interrupted fingers show higher luminescence intensity, while regions affected by recombination defects show lower luminescence intensity. This inverse signal contrast allows PL imaging to more accurately identify the defect types.