Helical twisting power of antiferroelectric chiral terphenyls in different matrices

To determine the influence of chemical structure on the Helical Twisting Power (HTP), we tested four optically active dopants having a terphenyl rigid core and the same chiral centre but differing in the length of nonchiral terminal chain and the substitution of benzene rings with fluorine atoms. The compounds were added to different achiral liquid crystalline matrices: nematic and smectic C. It was found that HTP as well as its temperature variation depends on the kind of used matrices. It gives a conclusion that information about HTP obtained in one matrix cannot be uncritically transferred to another one.     

Enhancement of Photocatalytic Activity of Sodium Bismuth Titanate by Doping with Copper,Silver, and Tin Ions

Perovskite type oxides, sodium bismuth titanate (Na_0.5Bi_0.5TiO₃), and Ag⁺, Cu²⁺, and Sn²⁺ doped Na_0.5Bi_0.5TiO₃ were prepared by pechini and ion exchange methods, respectively. Photocatalytic activities of these catalysts were tested by decomposition of methylene blue (MB) under visible light irradiation. Results showed that the photocatalytic activity of metal ion doped Na_0.5Bi_0.5TiO₃ was higher than undoped Na_0.5Bi_0.5TiO₃. Relatively high photocatalytic performance of Ag⁺‐doped Na_0.5Bi_0.5TiO₃ is mainly ascribed to the efficient separation of electron‐hole (e^–, h⁺) pairs, lower bandgap energy and the creation of active hydroxyl radicals ( ^? OH). Further, the Ag⁺‐doped Na_0.5Bi_0.5TiO₃ catalyst showed good reusability up to four cycles. A possible mechanism for the enhanced photocatalytic performance was proposed. The synthesized photocatalysts were characterized by XRD, SEM, EDS, XPS, FT‐IR, and UV/Vis DRS techniques.     

Synthesis of Anthracene Derivatives with Azaacene-Containing Iptycene Wings and the Utilization as a Dopant for Solution-Processed Organic Light-Emitting Diodes

Substituted acene derivatives are regarded as promising materials for organic electronic devices such as organic light-emitting diodes (OLEDs). In particular, anthracene derivatives are known to exhibit good fluorescence property, with the air stability and solubility in common organic solvents expected to give advantages for solution-processed device fabrication. In this study, a series of bistriisopropylsilyl(TIPS)ethynyl anthracene derivatives with azaacene-containing iptycene wings have been synthesized by using condensation reactions. Effects of size of azaacenes on optical properties and packing structures were investigated. UV/Vis absorption and fluorescence spectra indicate that the π-elongation of iptycene units has small effects on the overall π-system, which is also supported by electrochemical measurements. Secondly, single-crystal X-ray analysis implies that the molecules likely have interactions with the iptycene units of adjacent molecules, while the iptycene wings and TIPSethynyl groups can prevent the central anthracene unit from undesirable non-radiative energy loss. Finally, the most emissive derivative was used as a dopant for solution-processed OLEDs, showing obvious electroluminescence with a luminance of over 920 cd m⁻².     

Ternary MgTiX-alloys: a promising route towards low-temperature, high-capacity, hydrogen-storage materials

In the search for hydrogen-storage materials with a high gravimetric capacity, Mg(y)Ti((1-y)) alloys, which exhibit excellent kinetic properties, form the basis for more advanced compounds. The plateau pressure of the Mg--Ti--H system is very low (approximately 10(-6) bar at room temperature). A way to increase this pressure is by destabilizing the metal hydride. The foremost effect of incorporating an additional element in the binary Mg--Ti system is, therefore, to decrease the stability of the metal hydride. A model to calculate the effect on the thermodynamic stability of alloying metals was developed by Miedema and co-workers. Adopting this model offers the possibility to select promising elements beforehand. Thin films consisting of Mg and Ti with Al or Si were prepared by means of e-beam deposition. The electrochemical galvanostatic intermittent titration technique was used to obtain pressure-composition isotherms for these ternary materials and these isotherms reveal a reversible hydrogen-storage capacity of more than 6 wt. %. In line with the calculations, substitution of Mg and Ti by Al or Si indeed shifts the plateau pressure of a significant part of the isotherms to higher pressures, while remaining at room temperature. It has been proven that, by controlling the chemistry of the metal alloy, the thermodynamic properties of Mg-based hydrides can be regulated over a wide range. Hence, the possibility to increase the partial hydrogen pressure, while maintaining a high gravimetric capacity creates promising opportunities in the field of hydrogen-storage materials, which are essential for the future of the hydrogen economy.     

Thermal analysis,effect of dopants,spectral characterisation and growth aspects of KAP crystals

Potassium acid phthalate (KAP) which is also known as potassium hydrogen phthalate (KC₈H₅O₄), a semi-organic compound was grown from its aqueous solution only by slow evaporation method at room temperature. The effect of metallic salts HgCl₂ and PbCl₂ as dopants in the growth aspects, thermal properties and SHG efficiency of KAP were determined using UV-VIS, FTIR spectral studies, thermal (TG and DTA) analysis and NLO test. There is only one significant mass loss step on TG curve of pure and doped KAP crystal. DTA curve exhibit a higher peak temperature in case of doped KAP crystal compared to those of pure KAP crystals.     

Fe掺杂ZnO空心微球的制备与光催化性能

ZnO是一种重要的Ⅱ-Ⅵ族半导体材料,其能带宽度约为3.37eV,在光电子学、传感、光催化、发电等诸多领域都具有巨大的应用潜力。本文采用简单的离子交换和热蒸发法成功制备了Fe掺杂ZnO空心微球,并利用扫描电镜、透射电镜、X射线粉末衍射仪对其形貌、结构以及成分等进行了详细的表征。光吸收测试证明Fe元素掺杂能够扩展ZnO的光吸收波段,实现波长375~600nm的光波吸收。另外,光催化实验证明Fe掺杂ZnO空心微球能够有效地促进罗丹明B的降解,表明合成的Fe掺杂ZnO空心微球是一种优异的光催化剂。     

Chiral Induction in Liquid Crystals with Dopants Derived from 1-Phenyl-2-Aminoalcohols

New chiral additives derived from 1-phenyl-2-aminoalcohols have been prepared and tested. Especially ephedrine and pseudoephedrine as chiral auxiliaries with two asymmetric C atoms offer functional groups of divergent reactivity. Dopants prepared by acylation with promesogenic agents can be used in various electro-optic devices. A specific utilization concerns bistable cholesteric liquid crystal displays with stacked double layer construction in order to enhance the luminance of reflected light. Further, the solubility in nematic mixtures, the long term phase behavior, the dopant's impact on textures and phase behavior, the electro-optic response and the photostability of cholesteric mixtures have been investigated.     

+3价离子掺杂钨酸铅晶体发光性能和微观缺陷的研究

通过透射光谱、x射线激发发射光谱（XSL）的测试，研究了Bridgman法生长的几种不同+3价离子掺杂钨酸铅晶体的发光性能，并利用正电子湮没寿命谱（PAT）和x光电子能谱（XPS）的实验手段，对不同钨酸铅晶体的微观缺陷进行研究.实验表明，不同的+3价离子掺杂，对钨酸铅晶体发光性能的改善不同，并使得晶体中正电子俘获中心和低价氧的浓度发生不同变化.其中掺镧晶体的正电子俘获中心和低价氧浓度均上升，而掺钇和掺铋晶体的正电子俘获中心和低价氧浓度均下降，掺锑晶体则出现了正电子俘获中心浓度上升、低价氧浓度下降的情况.提 关键词： 钨酸铅晶体 +3价离子掺杂 正电子湮没寿命谱 x光电子能谱     

Delta doping in silicon

Two-dimensional doping sheets (“δ-doping”) are integral parts of many novel semiconductor device concepts. Their practical realization in silicon (Si), however, was long delayed by the difficulty to introduce dopants into Si in a well-controlled way during epitaxial growth. Recent advances in the understanding of epitaxial growth and the incorporation of dopants in Si have overcome these difficulties and opened a new field in Si materials and device research. In this article, we review the growth, processing, and characterization of epitaxially grown 5-doped Si. Furthermore, we discuss the electronic subband states of such structures. Finally, we give an overview of device concepts that use 5-doping and analyze their properties.     

Pure and Gd-based Li,Na, Mn or Fe codoped ZnO nanoparticles: Insights into the magnetic and photocatalytic properties

The ferromagnetic and photocatalytic properties of pure ZnO, Zn_0.97Gd_0.01Li_0.02O, Zn_0.97Gd_0.01Na_0.02O, Zn_0.97Gd_0.01Mn_0.02O and Zn_0.97Gd_0.01Fe_0.02O nanoparticles prepared by sol-gel technique were investigated. The XRD, EDX, HR-TEM, FTIR and diffuse reflectance analyses confirm the formation of single phase ZnO wurtzite structure with effective incorporation of Gd/Li, Na, Mn or Fe ions into ZnO host lattice. Based on Kubelka-Munk equation, the optical band gap of pure ZnO nanoparticles was estimated to be 3.22 eV and implantation of Gd-based dual dopants induces red shifts between 0.01 and 0.29 eV. For pure ZnO nanoparticles, noticeable ferromagnetic performance was observed with saturation magnetization of 0.0133 emu/g and coercivity of 85 Oe. The binary dopants of Gd/Mn or Na induce strong enhancements in the saturation magnetization of pure ZnO nanoparticles. Where, Zn_0.97Gd_0.01Na_0.02O and Zn_0.97Gd_0.01Mn_0.02O samples exhibited perfect hysteresis loops with saturation magnetization of 0.34 and 0.717 emu/g, respectively. Higher photocatalytic activity, 97%, for methyl orange degradation was observed for Zn_0.97Gd_0.01Na_0.02O nanoparticles within 210 min under UV irradiation. The particles size and agglomeration, ionic radii of dopants and recombination centers have main effects on the photocatalytic activity performance of ZnO nanoparticles. The dual dopants of Gd/Mn efficiently trigger the room temperature ferromagnetism of the pure ZnO; but Gd/Na blend revealed the best effect in methyl orange degradation (97%).