Quantum Monte Carlo study of hard-core bosons in Creutz ladder with zero flux

The quantum phase of hard-core bosons in Creutz ladder with zero flux is studied.For a specific regime of the parameters(t_x=t_p,t_y0),the exact ground-state is found analytically,which is a dimerized insulator with one electron bound in each rung of the ladder.For the case t_x,t_y,t_p0,the system is exactly studied using quantum Monte Carlo(QMC)method without a sign problem.It is found that the system is a Mott insulator for small t_p and a quantum phase transition to a superfluid phase is driven by increasing t_p.The critical t~c _pis determined precisely by a scaling analysis.Since it is possible that the Creutz ladder is realized experimentally,the theoretical results are interesting to the cold-atom experiments.     

验证辐射强度与距离平方反比率的实验

利用Nal闪烁谱仪测量了在探测器与放射源间某个距离下对应的计数率.对测量的数据分别利用等精度最小二乘法和未知参数逼近法进行了处理,观察到在某些未知参数下,最小二乘法引起的误差很大,利用未知参数逼近法得到的值能和真实值较好接近,从而验证了辐射强度与距离平方反比率.     

Enhancing visible-light photocatalytic activity of α-Bi2O3 via non-metal N and S doping

In recent years, some important research indicated that the visible-light activity of photocatalysts could be enhanced via incorporating p-block non-metal elements into the lattice. In this paper, we investigated the electronic structures of pure and different non-metal （C, N, S, F, Cl, and Br） doped α-Bi2O3 using first-principles calculations based on the density functional theory. The band structures, the electronic densities of states, and the effective masses of electrons and holes for doped α-Bi2O3 were obtained and analyzed. The N and S dopings narrowed the band gap and reduced the effective mass of the carriers, which are beneficial for the photocatalytic performance. The theoretical predication was further confirmed by the experimental results.     

The variation of Mn-dopant distribution state with x and its effect on the magnetic coupling mechanism in Znl-xMnxO nanocrystals

Zn1-xMnxO （x = 0.0005, 0.001, 0.005, 0.01, 0.02） nanocrystals are synthesized by using a wet chemical process. The coordination environment of Mn is characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, and its X-ray absorption fine structure. It is found that the solubility of substitutional Mn in a ZnO lattice is very low, which is less than 0.4%. Mn ions first dissolve into the substitutional sites in the ZnO lattice, thereby forming Mn2＋O4 tetrahedral coordination when x ≤ 0.001, then entering into the interstitial sites and forming Mn3＋O6 octahedral coordination when x ≥ 0.005. All the samples exhibit paramagnetic behaviors at room temperature, and antiferromagnetic coupling can be observed below 100 K.     

教学型椭偏仪测量各向异性单轴晶体光学参数的方法研究

椭偏仪是一种常用的现代光学测量仪器,在物理实验教学中常用于测量各向同性材料的折射率、表面薄膜厚度等光学参数。本文提出一种利用教学型椭偏仪测量各向异性单轴晶体折射率等光学参数的方法。采用多入射角的方法增加系统自由度,建立数值反演模型,获得各向异性单轴晶体光学参数,并实验测量了钒酸钇晶体的折射率等光学参数。使用教学型椭偏仪测量各向异性单轴晶体光学参数,拓展了原有教学仪器的实验范围,有助于激发学生对实验的兴趣。     

核壳结构镍的制备及催化性能

利用软化学方法制备出了聚苯乙烯(PS)/镍核壳结构和纳米镍催化剂, 并利用SEM和XRD对材料的形貌和结构进行了表征. 将上述催化剂应用于亚甲基蓝染料加氢反应, 一步实现染料褪色和硼氢化钠水解制氢. 研究表明, 核壳结构极大地提高了镍的催化能力. 在相同条件下, 核壳结构镍的加氢催化效率是纳米镍的1.42倍, 产氢效率是纳米镍的4.76倍, 这说明核壳结构在催化领域具有一定的优势.     

Ag反点阵列修饰TiO2薄膜的制备及光催化性能研究

采用胶体晶体模板技术和磁控溅射工艺,通过调制溅射功率,制备了一系列不同形貌的Ag反点阵列修饰TiO2复合薄膜．通过扫描电子显微镜（SEM）,X射线衍射（XRD）,紫外一可见分光光度计（UV-Vis）和四探针测试仪等手段对样品的结构和光催化性能进行了表征．实验结果表明：Ag反点阵列的形貌对样品光催化性能有显著影响．随着反点孔径的减小,其导电性能迅速提升,样品的光催化性能逐渐增强．孔径为710nm时,复合薄膜的光催化性能达到最高．随后,继续减小孔径,样品的光催化性能出现了一定程度的下降,这是载流子损耗增多和遮光面积增大引起的．经Ag反点阵列修饰的样品的光催化性能均明显优于TiO2薄膜,主要是由于反点阵列可有效分离光生载流子,因此使其光催化活性得到显著提高．     

利用磁谱仪研究原子核的β衰变

在原子核β衰变费米理论的基础上,利用近代物理实验中的磁谱仪测量了90Sr-90Y β放射源的动量分布,进而研究它的库里厄(Kurie)图.结合β衰变容许跃迁和禁戒跃迁的库里厄图特征,对实验数据进行了形状因子S1的改正,得到的数据能和90Sr-90Yβ放射源的跃迁性质、原子核能级自旋和宇称相吻合,有助于学生对原子核β衰变更深入的认识和进一步扩展近物实验的研究内容.     

Manipulating coupling state and magnetism of Mn-doped ZnO nanocrystals by changing the coordination environment of Mn via hydrogen annealing

Mn-doped ZnO nanocrystals are synthesized by a wet chemical route and treated in H_2/Ar atmosphere with different H_2/Ar ratios.It is found that hydrogen annealing could change the coordination environment of Mn in ZnO lattice and manipulate the magnetic properties of Mn-doped ZnO.Mn ions initially enter into interstitial sites and a Mn~(3+)O_6 octahedral coordination is produced in the prepared Mn-doped ZnO sample,in which the nearest neighbor Mn~(3+) and O~2 ions could form a Mn~(3+)-O~(2-)-Mn~(3+) complex.After H_2 annealing,interstitial Mn ions can substitute for Zn to generate the Mn~(2+)O_4tetrahedral coordination in the nanocrystals,in which neighboring Mn~(2+) ions and H atoms could form a Mn~(2+)-O~(2-)-Mn~(2+)complex and Mn-H-Mn bridge structure.The magnetic measurement of the as-prepared sample shows room temperature paramagnetic behavior due to the Mn~(3+)-O~(2-)-Mn~(3+) complex,while the annealed samples exhibit their ferromagnetism,which originates from the Mn-H-Mn bridge structure and the Mn-Mn exchange interaction in the Mn~(2+)-O~(2-)-Mn~(2+)complex.     

Evolution of Structural Defects in SiOx Films Fabricated by Electron Cyclotron Resonance Plasma Chemical Vapour Deposition upon Annealing Treatment

We study the structural defects in the SiO, film prepared by electron cyclotron resonance plasma chemical vapour deposition and annealing recovery evolution. The photoluminescence property is observed in the as-deposited and annealed samples. [-SiO3]^2- defects are the luminescence centres of the ultraviolet photoluminescence （PL） from the Fourier transform infrared spectroscopy and PL measurements. [-SiO3]^2- is observed by positron annihilation spectroscopy, and this defect can make the S parameters increase. After 1000℃ annealing, [-SiO3]^2- defects still exist in the films.