Conformational change-modulated spin transport at single-molecule level in carbon systems

Controlling the spin transport at the single-molecule level, especially without the use of ferromagnetic contacts, becomes a focus of research in spintronics. Inspired by the progress on atomic-level molecular synthesis, through first-principles calculations, we investigate the spin-dependent electronic transport of graphene nanoflakes with side-bonded functional groups, contacted by atomic carbon chain electrodes. It is found that, by rotating the functional group, the spin polarization of the transmission at the Fermi level could be switched between completely polarized and unpolarized states. Moreover, the transition between spin-up and spin-down polarized states can also be achieved, operating as a dual-spin filter. Further analysis shows that, it is the spin-dependent shift of density of states, caused by the rotation, that triggers the shift of transmission peaks, and then results in the variation of spin polarization. Such a feature is found to be robust to the length of the nanoflake and the electrode material, showing great application potential. Those findings may throw light on the development of spintronic devices.     

改变激发环境调控Ho3+离子的上转换发光特性

稀土掺杂上转换发光材料的发光特性不仅依赖于基质材料本身,而且与其激发条件密切相关.本文主要是以Ho^3+离子为研究对象,在NaYF4和LiYF4这两种不同的基质中,研究其在不同激发条件下的上转换发光特性.通过共聚焦显微光谱测试系统,对比Ho^3+离子在NaYF4和LiYF4微米晶体中的发光特性.实验结果发现:Ho^3+离子在这两种不同基质中均展现出较强的荧光发射.然而,当激发功率增加时,在单颗粒个LiYF4微米晶体中,当激发功率增加时,Ho^3+离子则发射出较强绿光及微弱的红光,红绿比变化并不明显,其蓝光发射强度也相对较弱.当激发这两种微米粉末晶体时,结果发现:Ho^3+离子均发射较强的绿光发射并伴有微弱红光发射,两种晶体中的发射特性极其相似.由此可见,在常规测试条件下,一些特殊发光现象是很难被观测到的.同时,通过对其光谱特性的分析,对Ho^3+离子的发光机理进行了研究.     

Ru-Fe二元金属纳米粒子对氧还原的电催化性能

在1,6-己二醇溶剂中,以Ru3(CO)12和Fe3(CO)12为原料,采用低温回流方法合成了Ru-Fe纳米粒子催化剂。利用扫描电镜(SEM)、X射线衍射仪(XRD)和电化学技术表征了催化剂的物理特征和电催化性能.催化剂粉末以六方结构的Rux簇为主相,呈现出高度均匀而聚集的纳米颗粒特征.在0.5mol/L H2SO4溶液中,Ru-Fe催化剂对氧还原反应(ORR)的电催化活性高于Rux,主要归因于d电子从Ru原子到Fe原子的转移过程.     

Disappearance of Superconductivity and a Concomitant Lifshitz Transition in Heavily Overdoped Bi_2Sr_2CuO_6 Superconductor Revealed by Angle-Resolved Photoemission Spectroscopy

By partially doping Pb to effectively suppress the superstructure in single-layered cuprate Bi_2Sr_2CuO_(6+δ)(Pb-Bi2201) and annealing them in vacuum or in high pressure oxygen atmosphere, a series of high quality Pb-Bi2201 single crystals are obtained with T_c covering from 17 K to non-superconducting in the overdoped region. High resolution angle resolved photoemission spectroscopy measurements are carried out on these samples to investigate the evolution of the Fermi surface topology with doping in the normal state. Clear and complete Fermi surfaces are observed and quantitatively analyzed in all of these overdoped Pb-Bi2201 samples. A Lifshitz transition from holelike Fermi surface to electron-like Fermi surface with increasing doping is observed at a doping level of ~0.35. This transition coincides with the change that the sample undergoes superconducting-to-non-superconducting states.Our results reveal the emergence of an electron-like Fermi surface and the existence of a Lifshitz transition in heavily overdoped Bi2201 samples. This provides important information in understanding the connection between the disappearance of superconductivity and the Lifshitz transition in the overdoped region.     

超高效液相色谱-串联质谱法测定卷烟中果糖、葡萄糖、蔗糖、麦芽糖

建立超高效液相色谱–串联质谱法测定卷烟中果糖、葡萄糖、蔗糖、麦芽糖4种水溶性糖的含量。样品用水超声提取,稀释过滤后直接进样,以Acquity BEH Amide色谱柱为分析柱,乙腈和水为流动相,梯度洗脱,采用负离子多反应监测模式分析。果糖和葡萄糖的线性范围为2.5～30μg/mL,蔗糖和麦芽糖的线性范围为0.25～3μg/mL,线性相关系数均大于0.997,方法检出限均为0.03 mg/g。加标样品的平均回收率为93.6%～101.0%,测定结果的相对标准偏差为0.7%～2.9%(n=6)。该方法简便、快速,可用于卷烟样品中果糖、葡萄糖、蔗糖、麦芽糖的测定。     

构建核壳结构增强Ho~(3+)离子在镥基纳米晶中的红光上转换发射

本文主要以具有六方相结构的NaLuF_4:Yb~(3+)/Ho~(3+)/Ce~(3+)纳米晶体为核,采用外延生长法构建具有同质结构的NaLuF_4:Yb~(3+)/Ho~(3+)/Ce~(3+)@NaLuF_4:Yb~(3+)核壳纳米晶体.借助X-射线衍射仪及透射电子显微镜对样品的晶体结构、形貌及尺寸进行表征.在近红外光980nm激光激发下,通过构建核壳结构及有效调控外壳中敏化离子Yb~(3+)离子的掺杂浓度,实现Ho~(3+)离子在NaLuF_4纳米晶体中的红光发射增强.实验结果表明:在相同的激发条件下,具有核壳结构的NaLuF_4:Yb~(3+)/Ho~(3+)/Ce~(3+)@NaLuF_4:Yb~(3+)纳米晶体的红光发射均得到了增强,同时,当外壳中Yb~(3+)离子的掺杂浓度为10.0%时,其上转换红光发射强度最强,为NaLuF_4:Yb~(3+)/Ho~(3+)/Ce~(3+)晶体核红光发射强度的5.8倍.根据其光谱特性及发光动力学过程,讨论了同质壳及壳中敏化离子掺杂浓度变化对其发光特性的影响规律.这种具有较强红光发射的核壳结构纳米晶体在生物医学、防伪编码、多色显示等领域具有较大的应用前景.     

Ce掺杂6H-SiC电子结构和光学性质的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法,对未掺杂及Ce掺杂6H-SiC的电子结构和光学性质进行理论计算.计算结果表明,未掺杂6H-SiC是间接带隙半导体,其禁带宽度为2.045 eV,掺杂Ce元素,带隙宽度下降为0.812 eV.未掺杂6H-SiC在价带的低能区,Si-3s、C-2s电子轨道对态密度的贡献较大,在价带的高能区,主要是由Si-3p、Si-3s、C-2p态组成.掺杂后Ce原子的4f轨道主要贡献在导带部分,掺杂后电导率提高.未掺杂时,只有一个介电峰,是价带电子跃迁到导带电子所致,掺杂后有两个介电峰,第一个介电峰是由于导带电子跃迁到Ce原子4f轨道上产生,第二个峰是价带电子向导带电子跃迁产生.未掺杂6H-SiC,在能量为10.31 eV处吸收系数达到最大值,掺杂后在能量为6.57 eV处,吸收系数达到最大值.     

石英晶体板非线性高频振动的拓展伽辽金法分析

针对考虑几何和材料非线性的石英晶体板厚度剪切振动和弯曲振动的方程组,利用扩展伽辽金法对该方程组进行转化和求解,分别获得了强烈耦合的厚度剪切振动模态和弯曲振动模态的频率响应关系,绘制了不同振幅比和不同驱动电压影响下的频率响应曲线图。数值计算结果表明可以选取石英晶片的最佳长厚比尺寸来避免两种模态的强烈耦合。驱动电压的变化将引起石英晶体谐振器厚度剪切振动频率的明显改变,必须将振动频率的漂移值控制在常用压电声波器件的允许值之内。扩展伽辽金法对石英晶体板非线性振动方程组的求解为非线性有限元分析和偏场效应分析奠定了基础。