Mesomorphic bipyridine building blocks bearing an sp3 carbon and a hydroxy function

The synthesis of novel symmetrical liquid crystalline compounds based on 5-methyl-5-[2-(4-alkyloxyphenyl)-2-hydroxyethyl]-2,2-bipyridines is reported, together with some physical properties. Although the chelating head-groups are connected via a chiral sp³ carbon atom, all the materials are mesomorphic. Intermolecular hydrogen bonding between pyridino and hydroxy fragments in the mesophases is made apparent by FTIR spectroscopy.     

Anisotropic energy distribution of sputtered atoms induced by low energy heavy ion bombardment

The theory of anisotropic sputtering published in Phys. Rev. B 71(2), 026101 (2005) and Radiat. Effects Defects Solids 159(5), 301 (2004) has been modified and used to calculate the sputtering yield energy distributions for copper, tungsten, and aluminum targets bombarded by low-energy argon ion. As usual, the electronic stopping is ignored in the analysis. The present theory (modified Sigmund’s theory) has been shown to fit the corresponding experimental results of sputtering yield energy distributions well, except for the cases where the larger ion incident angle and larger sputtering emission angles were considered. The larger discrepancy between the present theory and the experimental result in the latter cases is probably due to the influence of direct recoil atoms on the energy spectrum. Compared with Falcone’s analytical theory, the present theory can reproduce much better experimental results of sputtering phenomena. The fact clearly demonstrates the intrinsic relation between the ion–energy dependence of the total sputtering yield and the sputtering yield energy distribution and suggests the great importance of momentum deposited on the target surface in the physical sputtering     

Experimental investigation on bit-rate-adaptive software synchronous optical sampling

A tunable optical rail is embedded into the cavity of a nonlinear-polarization-rotation(NPR) mode-locked fiber laser to generate a sampling pulse with different repetition frequencies and realize bit-rate-adaptive software synchronous optical sampling.Two ultrashort pulses(20.26677 and 20.22900 MHz) are derived,and a 100-MHz data signal is sampled twice with these pulses based on sum-frequency generation(SFG) in periodically poled lithium niobate(PPLN).The eye diagram is successfully recovered,and an estimated bit rate of 102.22 MHz is derived.This method is feasible for bit rates ranging from 200 MHz to 1 GHz,with <3% relative error.     

(Ni0.81Fe0.19)1-xCrx作为种子层对NiFe/FeMn交换偏置的影响

采用一种新的种子层材料:(Ni081Fe019)1-xCrx,通过改变种子层中Cr原子的含量,使得在其上生长的NiFeFeMn双层膜的织构和晶粒尺寸产生极大的差异,系统研究了NiFeFeMn双层膜中FeMn晶粒尺寸和织构对交换偏置的影响.实验结果表明,在FeMn的γ相(111)织构较好的前提下,交换偏置场的大小与织构的差异没有关系;FeMn的晶粒尺寸对交换偏置场有很大影响,较小的反铁磁层晶粒对交换偏置场有利,过大的反铁磁层晶粒不利于交换偏置场.将(Ni081Fe019)05Cr05与传统的种子层材料Ta进 关键词： 交换偏置 晶粒尺寸 织构 种子层     

成分和厚度的依赖

通过调整Mn的成分，系统地研究了Ni81Fe19/Ni100-xMnx双层膜的磁学性质，特别是交换偏置场(Hex)的变化.当Ni100-xMnx中Mn的原子百分比在534%到600%之间时，对于150nm的Ni81Fe19，得到了最大的交换偏置场175kA/m，同时由于Mn对Ni81Fe19层的扩散所造成的磁矩的降低小于20%；高角x射线衍射证明Ni100-xMnx的晶格常数随着Mn成分的改变而变化，Mn含量越多，其晶格常数越大；制备态Ni100-xMnx膜晶格常数与θ相NiMn膜晶格常数的接近程度与NiMn膜θ相形成的容易程度相对应.也研究了交换偏置场随着Ni１００-xMnx厚度的变化，第一次得到了当Ni100-xMnx中Mn的原子百分比为706%时，Ni81Fe19(150nm)/Ni100-xMnx(90nm)双层膜在经过240℃，5h退火后，可以有80kA/m的交换偏置场，此时铁磁层磁矩的大小几乎不变. 关键词： Ni81Fe19/Ni100-xMnx 交换偏置场     

CdTe量子点-铜酞菁复合体系荧光共振能量转移的研究

以波长为780 nm、重复频率为76 MHz、脉宽为130 fs的飞秒激光作为激发光源, 采用超快时间分辨光谱技术研究了CdTe量子点-铜酞菁复合体系的荧光共振能量转移. 实验结果表明, 在780 nm的双光子激发条件下, 复合体系中CdTe量子点的荧光寿命随着铜酞菁溶液浓度的增加而减少, 荧光共振能量转移效率增加. 同时也研究了激发功率对荧光共振能量转移效率的影响. 结果表明, 随着激发光功率的增加, 复合体系溶液中CdTe量子点的荧光寿命增加, 荧光共振能量转移效率减小, 其物理机理是因为高激发功率下的热效应和由双光子诱导的高阶激发态的跃迁. 当激发光功率为200 mW时, 双光子荧光共振能量转移效率为43.8%. 研究表明CdTe量子点-铜酞菁复合体系是非常有潜力的第三代光敏剂.     

Mie理论在生物组织散射特性分析中的应用

根据等效颗粒散射模型，运用经典的Mie理论，对生物组织的散射相函数、各向异性因子及散射系数进行了数值计算.计算结果表明：可见光照射生物组织时，各向异性因子、散射系数随等效颗粒直径增大而增大；等效颗粒直径较小时，各向异性因子、散射系数随入射光波长增大而单调减小；随着等效颗粒直径增大，各向异性因子、散射系数随入射光波长变化不再具有单调性.上述计算结果可合理解释公布的实验结果. 关键词： 生物组织 散射 Mie理论 等效颗粒     

Ge2Sb2Te5非晶薄膜中超快载流子动力学的飞秒分辨反射光谱研究

利用飞秒时间分辨抽运-探测反射光谱技术研究了室温下Ge₂Sb₂Te₅非晶薄膜中载流子超快动力学及其激发能量密度依赖性.发现光激发后05 ps时间内,反射变化率降到最小值,然后开始迅速增加,在几个皮秒时间内达到大于初始反射率的新的最大值.反射率的减小量、增加量和增加速率均随激发能量密度的增大而增加.利用高密度等离子体的Auger复合及其感应的晶格加热模型较好地定量解释了反射率由最小到最大的快速变化过程,表明高密度等离子体的Auger复合加热 关键词： 抽运-探测光谱 2Sb₂Te₅非晶薄膜')" href="#">Ge₂Sb₂Te₅非晶薄膜 Auger复合 载流子动力学     

Triphenylamine derivatized phenylacetylene macrocycle with large two-photon absorption cross-section

A phenylacetylene macrocycle (PAM) derivative containing triphenylamine as the framework was synthesized in one-step Sonogashira coupling. The photophysical and electrochemical properties were investigated in details. This hexamer shows significant enhancement in two-photon absorption cross-section relative to reported PAM derivatives.     

Spontaneous generation of chirality and chiroptical spectra of N-nitroso-2,4-diaryl-3-azabicyclo[3.3.1]nonanes

The crystal structures of several bicyclic N-nitrosamines indicate that they crystallize in the chiral (Sohncke) space group P2₁2₁2₁ as conglomerates. This allows the resolution of these compounds by manual picking of the enantiomorphous crystals. The optical activity of the single crystals was confirmed by their CD spectra taken in KBr disks. The absolute configurations of the title nitrosamines were assigned by crystallographic measurements and by a comparison of their CD spectra with those of a reference compound resolved by classical methods. The observed Cotton effect signs, corresponding to the n–π¹ transition, were correlated with the helicity of the inherently chiral nitrosamine chromophore.