Effects of （LiCe） co-substitution on the structural and electrical properties of CaBi2Nb209 ceramics

The piezoelectric,dielectric,and ferroelectric properties of the(LiCe) co-substituted calcium bismuth niobate(CaBi2Nb2O9,CBNO) are investigated.The piezoelectric properties of CBNO ceramics are significantly enhanced and the dielectric loss tan δ decreased.This makes poling using(LiCe) co-substitution easier.The ceramics(where represents A-site Ca2+ vacancies,possess a pure layered structure phase and no other phases can be found.The Ca0.88(LiCe)0.04 0.04Bi2Nb2O9 ceramics possess optimal piezoelectric properties,with piezoelectric coefficient(d 33) and Curie temperature(TC) found to be 13.3 pC/N and 960 C,respectively.The dielectric and piezoelectric properties of the(LiCe) co-substituted CBNO ceramics exhibit very stable temperature behaviours.This demonstrates that the CBNO ceramics are a promising candidate for ultrahigh temperature applications.     

悬空石墨烯对其表面金纳米膜形貌的影响

石墨烯与金属间的相互作用是石墨烯器件研究中的关键问题之一,其涉及石墨烯器件的电学接触、锂离子电池石墨烯电极、石墨烯金属光学等方面.本文重点研究了不同层数的悬空石墨烯表面金纳米膜退火前后的形貌演化过程,观测到两个重要的现象:1)排除基底影响后的悬空石墨烯层数可以通过金纳米膜的形貌特征进行确认,但其随层数的变化趋势与有基底支撑的石墨烯正好相反;2)退火处理后的悬空石墨烯上的金纳米膜形貌演化过程具有类似水滴在荷叶上的行为.对悬空石墨烯表面金属纳米膜在退火前后的形貌变化规律及其现象背后的物理机理进行了详细的讨论和理论解释.     

原子力显微镜与表面形貌观察

简要介绍原子力显微镜观察材料表面形貌的原理。运用原子力显微镜,观察CD,VCD,DVD和可擦写的VCD光盘的刻录划痕,分析各类光盘的刻录特征,指出原子力显微镜在观察材料表面微米至纳米尺度形貌是非常有效的。     

Universal spin-dependent variable range hopping in wide-band-gap oxide ferromagnetic semiconductors

This paper proposes a universal spin-dependent variable range hopping theoretical model to describe various experimental transport phenomena observed in wide-band-gap oxide ferromagnetic semiconductors with high transition metal concentration. The contributions of the `hard gap' energy, Coulomb interaction, correlation energy, and exchange interaction to the electrical transport are considered in the universal variable range hopping theoretical model. By fitting the temperature and magnetic field dependence of the experimental sheet resistance to the theoretical model, the spin polarization ratio of electrical carriers near the Fermi level and interactions between electrical carriers can be obtained.     

Temperature-dependent specific heat of suspended platinum nanofilms at 80-380 K

Metallic nanofilms are important components of nanoscale electronic circuits and nanoscale sensors. The accurate characterization of the thermophysical properties of nanofilms is very important for nanoscience and nanotechnology. Currently, there is very little specific heat data for metallic nanofilms, and the existing measurements indicate distinct differences according to the nanofilm size. The present work reports the specific heats of 40-nm-thick suspended platinum nanofilms at 80-380 K and ~5×10^-4 Pa using the 3ω method. Over 80-380 K, the specific heats of the Pt nanofilms range from 166-304 J/(kg·K), which are 1.65-2.60 times the bulk values, indicating significant size effects. These results are useful for both scientific research in nanoscale thermophysics and evaluating the transient thermal response of nanoscale devices.     

基于CdSe@ZnS量子点水溶性纳米粒子的制备及荧光性能

作为一种新型的荧光探针,量子点（QD）已经受到越来越多的重视,制备工艺也显得格外重要。水相中合成的量子点效率低,油相中的量子点经过转相以后效率也大大衰减。本论文利用再沉淀包覆的方法制备了具有良好的水溶性的掺杂绿光CdSe@ZnS的纳米颗粒G-NPs（534 nm）和掺杂红光CdSe@ZnS的纳米颗粒R-NPs（610 nm）,具有窄的半峰宽（G-NPs~29 nm,R-NPs~31 nm）,较小的粒径（45 nm）,并在此基础上通过发射光谱与荧光衰减研究了量子点之间的能量传递现象。该方法保留了量子点原来的性质,基于其优良的光学性质,对人类肝细胞肝癌细胞株（HepG2）进行了荧光标记,从共聚焦成像实验结果看出,纳米颗粒得到了良好的吞噬效果。     

Er~(3+)/Tm~(3+)共掺铋硅酸盐玻璃2.0μm光谱性质（英文）

用高温熔融法制备了Er~(3+)/Tm~(3+)共掺杂无铅铋硅酸盐玻璃.测试了玻璃的吸收光谱和荧光光谱,分析和表征了Er~(3+)、Tm~(3+)离子之间的能量传递机制和传递效率,结果表明:在800 nm和1 550 nm光源泵浦下,Er~(3+)的掺入能够增强Tm~(3+)离子1.8μm发光,相应的最大发射截面分别为6.7×10~(-21)cm~2和7.3×10~(-21)cm~2,荧光带宽达到250 nm.根据Dexter-Foster模型,得到Er~(3+):~4I_(13/2)能级到Tm~(3+):~3F_4能级的直接能量传递系数为16.8×10~(-40)cm~6/s,为1 550 nm泵浦下获得较强的1.8μm发光奠定了基础.     

Electronic Phase Separation in Iron Selenide(Li,Fe)OHFeSe Superconductor System

The phenomenon of phase separation into antiferromagnetic(AFM) and superconducting(SC) or normal-state regions has great implication for the origin of high-temperature(high-T_c) superconductivity. However, the occurrence of an intrinsic antiferromagnetism above the T_c of(Li,Fe)OHFe Se superconductor is questioned. Here we report a systematic study on a series of(Li,Fe)OHFe Se single crystal samples with T_c up to ～41 K. We observe an evident drop in the static magnetization at T_(afm) ～ 125 K, in some of the SC(T_c 38 K, cell parameter c■9.27 ?) and non-SC samples. We verify that this AFM signal is intrinsic to(Li,Fe)OHFe Se. Thus, our observations indicate mesoscopic-to-macroscopic coexistence of an AFM state with the normal(below T_(afm)) or SC(below T_c) state in(Li,Fe)OHFe Se. We explain such coexistence by electronic phase separation, similar to that in high-T_c cuprates and iron arsenides. However, such an AFM signal can be absent in some other samples of(Li,Fe)OHFe Se, particularly it is never observed in the SC samples of T_c 38 K, owing to a spatial scale of the phase separation too small for the macroscopic magnetic probe. For this case, we propose a microscopic electronic phase separation. The occurrence of two-dimensional AFM spin fluctuations below nearly the same temperature as T_(afm), reported previously for a(Li,Fe)OHFe Se(T_c ～ 42 K) single crystal, suggests that the microscopic static phase separation reaches vanishing point in high T_c(Li,Fe)OHFe Se. A complete phase diagram is thus established. Our study provides key information of the underlying physics for high-T_c superconductivity.     

非线性Jaynes-Cummings模型中原子偶极矩的高阶压缩

研究了非线性双光子Jaynes-Cummings(J-C)模型系统中原子偶极矩高阶压缩的时间演化特性及其产生条件。结果表明,在弱场条件下,原子偶极矩色散或吸收分量的二阶和六阶量子涨落可被周期性压缩,非线性修正项或失谐量以及热噪声对压缩程度有显著的影响。     

依赖强度耦合的级联三能级原子系统中双模压缩真空初态场的非经典性质

运用全量子理论研究了依赖强度耦合的级联三能级原子系统中双模压缩真空初态场的压缩及量子统计性质,并讨论了初始光场的压缩参量以及原子—光场单光子失谐量对光场非经典性质的影响.