Electrical property effect of oxygen vacancies in the heterojunction of LaGaO_3/SrTiO_3

Density functional theory within the local density approximation is used to investigate the effect of the oxygen vacancy on the LaGaO_3/SrTiO_3(001) heterojunction. It is found that the energy favorable configuration is the oxygen vacancy located at the 3~(rd) layer of the STO substrate, and the antiferrodistortive distortion is induced by the oxygen vacancy introduced on the SrTiO_3 side. Compared with the heterojunction without introducing oxygen vacancy, the heterojunction with introducing the oxygen vacancy does not change the origin of the two-dimensional electron gas(2DEG), that is, the 2DEG still originates from the d_(xy) electrons, which are split from the t~(2g) states of Ti atom at interface; however the oxygen vacancy is not beneficial to the confinement of the 2DEG. The extra electrons caused by the oxygen vacancy dominantly occupy the 3d_(x~2-y~2) orbitals of the Ti atom nearest to the oxygen vacancy, thus the density of carrier is enhanced by one order of magnitude due to the introduction of oxygen vacancy compared with the density of the ideal structure heterojunction.     

基于虚拟仪器的高精度Z扫描实验系统设计

设计了一个表征样品非线性特性的基于虚拟仪器的z扫描实验系统。利用Labview控制数字示波器TDS3012采集两路光强信号，并结合对微位移平台的控制实现Z扫描。以Nd：YAG飞秒放大器产生的800nm的飞秒激光作为探测光，经透镜聚焦后通过薄介质样品；用数字示波器测量样品在透镜焦点附近的透射光强，经过数据处理得到样品的非线性折射率和非线性吸收系数。利用该实验系统，对标准非线性吸收样品Rhodamine 6B进行了测量，计算得到其双光子吸收截面为σ^2=6．8GM（GM：10^-50cm4s photon^-1 molecule^-1），该结果与其他文献利用不同测量方法得到的结果接近，证明该实验系统的测量结果是正确的，可满足非线性测量的精度要求。     

蠕虫状聚离子复合型胶束的合成、组装和胶体稳定性

采用开环聚合方法制备了嵌段共聚物聚乙二醇-聚乙烯亚胺(PEG-b-PEI), 通过静电组装方法使其与质粒DNA(pDNA)在溶液中自发构筑成蠕虫状聚离子复合型胶束(PICmicelle), 利用原子力显微镜、 动态光散射、 Zeta电势和凝胶电泳等方法研究了血液或细胞间质中各种因素对胶束稳定性的影响. 结果表明, 在蠕虫状聚离子复合型胶束中, PEI和pDNA通过静电吸引构成疏水性内核, 而亲水性的PEG分子作为保护型外壳包裹在内核的表面. 在保持PEG链段长度不变的前提下, 增加PEI链段长度可明显增强PEI与pDNA的静电结合力, 有效地防止了NaCl对胶体结构的破坏, 而且有助于抑制阴离子的取代. 但增加PEI链段长度会导致胶束表面PEG分子含量的降低, 不利于胶束抵抗蛋白质的吸附和DNA酶的降解. 因此合理地调整PEG-b-PEI分子的结构, 对于获得高效、 安全和稳定的蠕虫状聚离子胶束具有重要意义.