Electronic states and shapes of silicon quantum dots

A curviform surface breaks the symmetrical shape of silicon quantum dots on which some bonds can produce localized electronic states in the bandgap. The calculation results show that the bonding energy and electronic states of silicon quantum dots are different on various curved surfaces, for example, a Si-O-Si bridge bond on curved surface provides localized levels in bandgap and its bonding energy is shallower than that on the facet. The red-shifting ofthe photoluminescence spectrum on smaller silicon quantum dots can be explained by the curved surface effect. Experiments demonstrate that silicon quantum dots are activated for emission due to the localized levels provided by the curved surface effect.     

韧性氧化铝-氧化锆纳米复合渗透陶瓷的制备

采用包裹共沉淀法制备了韧性氧化铝-氧化锆纳米复合渗透陶瓷(AlZrx),其中AlZr30的平均三点弯曲强度(σ3P)高达(621.30±40.15)MPa,平均断裂韧性(KIC)高达(6.72±1.45)MPa.m0.5。并讨论了w(ZrO2)对AlZrx力学性能和微观结构的影响。XRD确定AlZrx的主晶相为α-Al2O3,四方相ZrO2和单斜相ZrO2。     

Activation of silicon quantum dots and coupling between the active centre and the defect state of the photonic crystal in a nanolaser

A new nanolaser concept using silicon quantum dots (QDs) is proposed. The conduction band opened by the quantum confinement effect gives the pumping levels. Localized states in the gap due to some surface bonds on Si QDs can be formed for the activation of emission. An inversion of population can be generated between the localized states and the valence band in a QD fabricated by using a nanosecond pulse laser. Coupling between the active centres formed by localized states and the defect states of the two-dimensional (2D) photonic crystal can be used to select the model in the nanolaser.     

共沉淀分离富集偏最小二乘法在茶叶重金属测定中的应用

以铜试剂为共沉淀剂,在pH值为10.0的条件下,共沉淀分离富集茶叶中痕量金属离子Ni^(2+)、Pb^(2+)、Cd^(2+)和Cu^(2+),并分析了铜试剂与金属离子形成配合物的最佳沉淀条件.用4-(2-吡啶偶氮)间苯二酚(PAR)作为这4种重金属离子的显色剂进行分光光度测定,采用偏最小二乘-紫外可见光度法同时测定了四组分金属离子的模拟混合试样,并在茶叶中进行上述金属离子含量的测定.方法操作简便、结果可靠,对茶叶中重金属测定有一定实用价值.     

硅量子点的形状及其弯曲表面效应

硅量子点的弯曲表面引起系统的对称性破缺, 致使某些表面键合在能带的带隙中形成局域电子态.计算结果表明:硅量子点的表面曲率不同形成的表面键合结合能和电子态分布明显不同. 例如, Si–O–Si桥键在曲率较大的表面键合能够在带隙中形成局域能级, 而在硅量子点曲率较小的近平台表面上键合不会形成任何局域态, 但此时的键合结合能较低. 用弯曲表面效应(CS)可以解释较小硅量子点的光致荧光光谱的红移现象. CS效应揭示了纳米物理中又一奇妙的特性. 实验证实, CS效应在带隙中形成的局域能级可以激活硅量子点发光. 关键词： 硅量子点 弯曲表面效应 表面键合 局域能级     

Curved surface effect and emission on silicon nanostructures

The curved surface （CS） effect on nanosilicon plays a main role in the activation for emission and photonic manipulation. The CS effect breaks the symmetrical shape of nanosilicon on which some bonds can produce localized electron states in the band gap. The investigation in calculation and experiment demonstrates that the different curvatures can form the characteristic electron states for some special bonding on the nanosilicon surface, which are related to a series of peaks in photoluminecience （PL）, such as LN, LNO, Lo1, and Lo2 lines in PL spectra due to Si-N, Si-NO, Si=O, and Si-O-Si bonds on curved surface, respectively. Si-Yb bond on curved surface of Si nanostructures can provide the localized states in the band gap deeply and manipulate the emission wavelength into the window of optical communication by the CS effect, which is marked as the Lyb line of electroluminescence （EL） emission.