单层型氧化铁催化剂的制备及其前体的表征:Ⅱ.催化剂前体的表征

用三种方法，即草酸络铁（Ⅱ）酸铵的过量水溶液含浸，三乙酰丙酮铁的甲苯溶液热吸附和硝酸铁溶液饱和浸渍法制备了种载体上氧化铁的负载样品，对用不同方法制备的催化剂前体中表面铁物种的存在形式，结构和分散度等进行了细致的表征和详细的讨论，并与焙烧后样品中Ｆｅ＾３＋的最终形态进行了关联。     

光纤位移传感演示实验

光纤位移传感演示实验刘丽敏，苑立波（哈尔滨船舶工程学院物理部１５０００１）一、光纤传感技术简介光纤传感技术是伴随着光导纤维及光通信技术的发展而逐步形成的．在光通信系统中，光纤从作远距离传输光波信号的媒质，但是，在实际光传输过程中，光纤易受外界环境因素...     

Spin-flip process through double quantum dots coupled to two half-metallic ferromagnetic leads

We investigate the spin-flip process through double quantum dots coupled to two half-metallic ferromagnetic leads in series. By means of the slave-boson mean-field approximation, we calculate the density of states in the Kondo regime for two different configurations of the leads. It is found that the transport shows some remarkable properties depending on the spin-flip strength. These effects may be useful in exploiting the role of electronic correlation in spintronics.     

变化的电流产生的热量不能用平均值计算

对2009年北京市某区的一道关于电磁感应的模拟题产生质疑,师生共同讨论、分析、整理,认为题目用电流的平均值算出的变化电流产生的热量值存在错误.     

效应代数的表示

本文讨论了抽象效应代数的表示问题. 对于一个抽象效应代数(E,⊕, 0, 1), 如果存在一个Hilbert 空间 H 和一个单态射 φ:E →ε(H), 那么称 E 为可表示的且称(φ,H) 是E 的一个表示, 其中ε(H) 表示 H 上所有正压缩算子构成的效应代数. 给出了一些可表示的和不可表示的效应代数的例子, 证 明了非空集 X 上的任一模糊集系统 F 和Boolean 代数B_X 都是可表示的效应代数.     

Transient electromagnetically induced transparency spectroscopy of 87Rb atoms in buffer gas

We study the transient response dynamics of ⁸⁷Rb atomic vapor buffered in 8 torr Ne gas through an electromagnetically induced transparency configured in $\varLambda$-scheme. Experimentally, the temporal transmission spectra versus probe detuning by switching on and off the coupling one show complex structures. The transmitted probe light intensity drops to a minimum value when the coupling light turns off, showing a strong absorption. Even at the moment of turning on the coupling light at a subsequent delayed time, the atomic medium shows a fast transient response. To account for the transient switching feature, in the time-dependent optical Bloch equation, we must take the transverse relaxation dephasing process of atomic vapor into account, as well as the fluorescence relaxation along with the optical absorption. This work supplies a technique to quantify the transverse relaxation time scale and to sensitively monitor its variation along the environment by observing the transient dynamics of coherent medium, which is helpful in characterizing the coherent feature of the atomic medium.     

Experimental observation of pseudogap in a modulation-doped Mott insulator: Sn/Si(111)-(√30×√30)R30°

Unusual quantum phenomena usually emerge upon doping Mott insulators. Using a molecular beam epitaxy system integrated with cryogenic scanning tunneling microscope, we investigate the electronic structure of a modulation-doped Mott insulator Sn/Si(111)-($\sqrt{3}\times \sqrt{3})R$30$^\circ$. In underdoped regions, we observe a universal pseudogap opening around the Fermi level, which changes little with the applied magnetic field and the occurrence of Sn vacancies. The pseudogap gets smeared out at elevated temperatures and alters in size with the spatial confinement of the Mott insulating phase. Our findings, along with the previously observed superconductivity at a higher doping level, are highly reminiscent of the electronic phase diagram in the doped copper oxide compounds.     

平面靶直流溅射制备YBCO高温超导薄膜研究

开展了平面靶溅射法制备YBa2Cu3O7-δ(YBCO)高温超导薄膜工艺研究,以达到提高沉积速率的目的。通过增加工作气体总压(Pt),采用基片旋转达到离轴溅射模式,有效地克服了传统平面靶直流溅射法中高能粒子轰击和负离子反溅射现象。在两英寸LaA lO3(LAO)基片上成功外延生长得到了微观结构良好、电学性能优越(临界电流密度Jc=2.3/2.0mA/cm2)的双面YBCO高温超导薄膜。     

微波法制备纳米碳点反应机制与发光机理

为探讨微波法制备纳米碳点发光性质的影响规律与本质,采用微波加热法通过控制微波功率、反应时间以及pH值合成了一系列纳米碳点,并利用荧光激发光谱与发射光谱测试对纳米碳点的发光性质进行了表征,结合紫外吸收光谱与傅立叶红外光谱对反应产物官能团变化分析,最终揭示了微波加热过程中葡萄糖向纳米碳点转变的机制与发光机理。结果表明,采用微波法制备纳米碳点,当微波功率为560 W,反应时间为2.5 min时,获得纳米碳点发光性能最佳。当采用波长370 nm紫外光激发时,对应451 nm的蓝光发射强度最高。伴随纳米碳点溶液pH值从酸性变为碱性,纳米碳点最强发光峰的激发光波长由350 nm显著向高波长方向移动,且发光峰强度显著升高。紫外吸收光谱与傅立叶红外光谱显示反应过程中形成了多环芳香族碳氢化合物,表明微波加热过程中是葡萄糖单糖向多糖聚合并最终发生碳化的过程。不同pH值下纳米碳点发光性质的差异,源于对纳米碳点中C=C键与C=O键比例的调整,从而实现对纳米碳点的光学带隙宽度及激子束缚能等的综合调控。     

单层FeSe薄膜/氧化物界面高温超导

单层FeSe/SrTiO₃界面增强超导的发现为理解高温超导机理提供了一个新的途径,也为实现新的高温超导体开拓了新思路.本文通过在SrTiO₃（001）表面高温沉积Mg进而沉积单层FeSe薄膜,制备出了FeSe/MgO双层/SrTiO₃异质结.利用扫描隧道显微镜研究了异质结的电学及超导特性,观测到约14–15 meV的超导能隙,比体相FeSe超导能隙值增大了5–6倍,与K掺杂双层FeSe/SrTiO₃的超导能隙值相当.这一结果可理解为能带弯曲造成的界面电荷转移和界面处电声耦合共同作用导致的超导增强.FeSe/MgO界面是继FeSe/TiO₂之后的一个新界面超导体系,为研究界面高温超导机理提供了新载体.