Theoretical investigation on the heats of formation and the interactions among the isocyano groups in polyisocyanoprismanes C(6)H(6-n)(NC)(n) (n=1-6)

A series of polyisocyanoprismanes, C(6)H(6-n)(NC)(n) (n=1-6), has been designed computationally. We have calculated the heats of formation (HOFs) of the title compounds by using density functional theory (DFT) with 6-31G** basis set. We chose [3]prismane C(6)H(6)-D(3h) as a reference compound in the process of designing isodesmic reactions. The relationship between the HOFs and the molecular structures is discussed. The results have shown that the HOFs of the title compounds gradually increase with increasing number of isocyano groups. On average, the contribution of one isocyano group to the heat of formation is about 232.3 kJ/mol and 234.1 kJ/mol at the B3LYP and B3P86 levels, respectively. The relative stabilities of the title compounds are discussed in terms of the calculated HOFs, the energy gaps between the frontier orbitals, and the bond dissociation energies. The interactions of the isocyano groups in these polyisocyanoprismanes are also discussed. The results have not only shown that these compounds may be used as high-energy-density materials, but also provide some useful information for further syntheses.     

Density functional theory calculations for [C(2)H(4)N(2)O(6)]((n)) (n=0, +1, -1)

The structural and electronic properties of neutral and mono ionic structures of isolated ethylene glycol dinitrate (EGDN) [C(2)H(4)N(2)O(6)]((n)) (n=0, +1, -1) have been investigated by performing density functional theory calculations at B3LYP level. The optimum geometry, vibrational frequencies, electronic structure and some thermo dynamical values of the structures considered have been obtained in their ground states. The calculations reveal that as the charge develops the bond lengths and angles change. In the anionic case charge accumulation causes NO(2) elimination as a result of esteric O-N bond cleavage.     

Direct Observation of sp-d exchange interactions in colloidal Mn2+- and Co2+-doped CdSe quantum dots

The defining attribute of a diluted magnetic semiconductor (DMS) is the existence of dopant-carrier magnetic exchange interactions. In this letter, we report the first direct observation of such exchange interactions in colloidal doped CdSe nanocrystals. Doped CdSe quantum dots were synthesized by thermal decomposition of (Me4N)2[Cd4(SePh)10] in the presence of TMCl2 (TM2+ = Mn2+ or Co2+) in hexadecylamine and were characterized by several analytical and spectroscopic techniques. Using magnetic circular dichroism spectroscopy, successful doping and the existence of giant excitonic Zeeman splittings in both Mn2+- and Co2+-doped wurtzite CdSe quantum dots are demonstrated unambiguously.     

Synthesis of water-soluble CdSe quantum dots by ligand exchange with p-sulfonatocalix(n)arene (n = 4, 6) as fluorescent probes for amino acids

A simple, rapid ligand exchange route to prepare highly fluorescent, stable and water-soluble CdSe quantum dots (QDs) is reported by using p-sulfonatocalix(n)arene (SFCA(n), n = 4 or 6) instead of original trioctylphosphine oxide (TOPO) ligands. The ligands were found to have a profound effect on the luminescence response of QDs to amino acids. The SFCA(4) coated CdSe QDs were sensitive to methionine. On the other hand, SFCA(6) coated CdSe QDs turned out to be sensitive to phenylalanine. To demonstrate the detection capability of these new probes, SFCA(n) (n = 4, 6) coated CdSe QDs were used to detect methionine and phenylalanine in physiological buffer solution. Under optimal conditions, the relative fluorescence intensities of the SFCA(n) coated QDs (n = 4, 6) increased linearly with increasing concentration of amino acids. Methionine and phenylalanine enhanced the luminescence of SFCA(n) coated QDs with a concentration dependence that was best described by a Langmuir-type equation. The possible mechanism is also discussed.     

High temperature phase transition in long chain (CnH2n+1NH3)2CuCl2Br2-compounds with 10 ≤ n ≤ 18

High Temperature phase transitions in long chain (C_nH_2n+1NH₃)₂CuCl₂Br₂-compounds (n ≥ 10) were detected for the first time by means of calorimetric measurements. Although the experimental data reveal a complex phase transition sequence a first phenomenological approach is attempted.     

Uptake properties of Ni2+ by nCaO.Al2O3.2SiO2 (n=1-4) prepared from solid-state reaction of kaolinite and calcite

A series of nCaO.Al2O3.2SiO2 samples (n=1-4) were prepared by solid-state reaction of mechanochemically treated mixtures of kaolinite and calcite fired at 600-1000 degrees C for 24 h. All the samples were X-ray amorphous after firing at 600-800 degrees C but had crystallized by 900 degrees C. The main crystalline phases were anorthite (n=1), gehlenite (n=2 and 3) and larnite (n=4). The uptake of Ni2+ by nCaO.Al2O3.2SiO2 samples fired at 800 and 900 degrees C was investigated at room temperature using solutions with initial Ni2+ concentrations of 0.1-50 mmol/l. Amorphous samples (fired at 800 degrees C) showed a higher Ni2+ uptake capacity than crystalline samples (fired at 900 degrees C). Ni2+ uptake was found to increase with increasing of CaO content. Amorphous 4CaO.Al2O3.2SiO2 showed the highest Ni2+ uptake capacity (about 9 mmol/g). The Ni2+ uptake abilities of the present samples are higher than those of other materials reported in the literature. Since the sorbed Ni2+/released Ca2+ ratios of these samples are close to unity, ion replacement of Ni2+ for Ca2+ is thought to be the principal mechanism of Ni2+ uptake by the present samples.     

Single crystals of Hg-12(n−1)n and infinite layer-CaCuO2 obtained at gas pressure P=10kbar

Single crystals of Hg_l-xPb_xBa₂Ca_n-lCu_nO_2n+2+?(x=0,0.2,0.5; n=2,3,4,5) and infinite layer CaCuO₂ compounds have been grown using a high gas pressure. Resistivity measurements have been performed in fields up to 10 T. The Hg_0.8Pb_0.2-1234 single crystals of a size up to 0.5×0.5 mm² have a T _c onset of 130 K. Single crystals of CaCuO₂ of a size up to 2×1 mm² have a T _c onset between 70 and 100 K. X-ray structural refinements have been performed on the CaCuO₂ and HgPb-12(n?1)n single crystals.     

预非晶化离子注入对硅p~+n结性能的影响

用Ｓｉ＋／Ｂ＋、Ａｒ＋／Ｂ＋双注入结合快速热退火技术制备出了较浅的ｐ＋ｎ结,用四探针法、扩展电阻法、背散射沟道谱、二次离子质谱等测试分析手段研究了Ｓｉ＋或Ａｒ＋预非晶化离子注入的作用。结果表明,适当条件的Ｓｉ＋预非晶化注入能有效地抑制硼原子的沟道效应,用Ｓｉ＋／Ｂ＋双注入制备出了高硼原子电激活率的Ｐ＋薄层,且电性能优良,残留二次缺陷少,ｐ＋ｎ结二极管反偏漏电流仅２．０ｎＡ／ｃｍ２（－１．４Ｖ）;而Ａｒ＋注入虽然也能抑制硼原子注入沟道效应,但它使注入硼原子电激活率低,制得的Ｐ＋薄层性能差,残留二次缺陷较多     

Electronic transport of lateral PtSi/n/n+-Si Schottky diodes

We investigated the transport properties of a lateral PtSi/n/n(+)-Si Schottky diode prepared on an n-type silicon-on-insulator (SOI) wafer with a special attention on the bipolar transport and the surface effect. With applying a back-gate bias changing from +18 V to -18 V, the unipolar transport behavior switched over to the bipolar one, where an enhanced surface recombination rate due to a high surface-to-volume ratio produced a current density approximately 3 x 10(3) A/cm2 for 2 V bias through a 40 nm-thick and 18 microm-long nanoribbon. The recombination time was estimated to be approximately 1 micros from independent CV measurements, which is much smaller value than that of a bulk. The local Fermi energy level for electrons at the channel center was monitored by an additional voltage probe during each I(D)-V(D) measurement and it revealed the intricate nature of the bipolar transport manifested by the huge asymmetrical hysteretic behavior on a drain bias cycle which is attributed to the charge storage effect and asymmetrical junction profiles.     

Surface enrichment of biomimetic apatites with biologically-active ions Mg2+ and Sr2+: A preamble to the activation of bone repair materials

The surface activation of calcium phosphate-based biomaterials for bone repair is an emerging route for improving bone regeneration processes. One way for such activation is through the exchange of surface calcium ions with biologically-active cations such as Mg²⁺ or Sr²⁺. In this work, the interactions of non-carbonated and carbonated nanocrystalline apatites with Mg²⁺ and Sr²⁺ were investigated by means of ion exchange experiments in solution. Langmuir-type isotherms were determined. For both Sr and Mg, a greater uptake was observed on the carbonated sample, and on both types of apatites the maximum strontium uptake was greater than that of magnesium. Inverse exchanges showed that the proportion of reversibly fixed ions after surface exchange was close to 85% for Mg and 75–80% for Sr. The results are related to the presence of a surface hydrated layer on the nanocrystals and possible exchange mechanisms are discussed. Our results favor the hypothesis of hetero-ionic surface exchanges (Mg²⁺↔Ca²⁺, Sr²⁺↔Ca²⁺) within the hydrated layer, and some analogy with octacalcium phosphate (OCP) is considered. This work should prove helpful for the control and understanding of the activation of synthetic apatite-based powders or scaffolds with bioactive elements, as well as for the global understanding of biomineralization processes.     

Growth of untwinned Bi2Sr2Ca n−1Cu n O2n+4+δ thin films on Nd : YAlO3 substrates

Thin film growth of Bi₂Sr₂Ca _n?1Cu _n O_2n+4+δ by molecular beam epitaxy is performed on Nd : YAlO₃ (001) substrates. It was revealed that the orthorhombicity of the Nd:YAlO₃ substrate is quite effective to the growth of untwinned Bi₂Sr₂Ca _n?1Cu _n O_2n+4+δ thin films. In all phases withn=1～3, the incommensurate structural modulation lies parallel to the Nd : YAlO₃ [100] direction, and this relation holds even in the case of superlattices. The origin of the epitaxial relation is discussed from the viewpoint of the lattice misfit. The orthorhombicity of the substrate competes with the step edges on a vicinally polished substrate for determining the in-plane growth direction. The rotation of the modulation direction was observed when the off angles are varied.     

Etude par microscopie electronique de quelques termes de la serie (Na,Ca)n Nbn O3n+2

A regular stacking of perovskite type blocks has been observed by electron microscopy in the (NaCa)_n Nb_n O_3n+2 phases, with n = 4, 5 and 6. Observation of ordered intergrowth with n = 4.5 has shown an alternation of blocks of different thickness n = 4 and n = 5. An other ordered intergrowth with n = 4.33 has been observed.     

Structures and magnetic properties of Fe(n)B (n =1-12) clusters

The configurations, electronic structures and magnetic properties of Fe(n)B (n = 1-12) clusters have been calculated within the framework of all-electron density functional theory. The calculated results indicate that the B atom prefers a surface site for all the lowest-energy structures of Fe(n)B with n = 1-9 and 11, while for Fe10B and Fe12B, the B atom is found to occupy a center site forming a B-centered Fe(n) cage. Furthermore, relatively large HOMO-LUMO gaps are found for Fe6B and Fe7B, indicating the chemical inertness of the two isomers. For Fe4B, and Fe12B, the spin magnetic moments of the Fe atom significantly increase, but the spin moments decrease slightly for all the other Fe(n)B clusters.     

低温生长Zn1-xCoxO(x=0.33)薄膜的微结构和磁性

用电子束反应蒸镀法在低温生长了Zn1-xCoxO薄膜.Co含量x高达0.33的Zn1-xCoxO薄膜仍具有类ZnO的纤锌矿结构,没有杂质相,Co的化合价为 2.场冷和零场冷M-T及M-H曲线表明,Zn1-xCoxO(x=0.33)薄膜在低温下具有铁磁性;随着温度的升高,其剩磁和矫顽力均逐渐下降,在65 K以上趋于零,显示出超顺磁性.Zn1xCoxO薄膜的低温铁磁性起源于Co2 离子之间的双交换相互作用及载流子诱导的sP d交换耦合作用,而从低温(＜65 K)铁磁态到高温(＞65 K)超顺磁态的转变可归因于薄膜的纳米晶小尺寸效应.     

Cation-cation interactions between uranyl(VI) ions

Data on crystalline U(VI) compounds with mutual coordination of uranyl ions in their structure (cation-cation interactions, CCIs) are summarized. The topology and geometry of CCIs, including the characteristics of Voronoi-Dirichlet polyhedra of uranium atoms, are analyzed. 15 types of complexes [UO ₂ ²⁺ ] _n formed by CCIs are revealed. The influence of CCIs on the stereochemical features of U(VI) are considered, and common and distinctive features of CCIs in uranyl(VI) and neptunyl(V) compounds are discussed. Factors favoring the occurrence of CCIs in uranyl compounds are analyzed. The spectroscopic manifestations of CCIs are considered. Data on CCIs in some noncrystalline media are presented. The strength of cation-cation bonds in uranyl complexes is analyzed.     

Inhibited Ru(bpy)3 2+ electrochemiluminescence related to electrochemical oxidation activity of inhibitors

Electrochemiluminescence (ECL) has been accepted by the analytical chemist as a powerful tool for detection of many inorganic and organic compounds. Ru(bpy)3 2+ has been the most popular ECL system, and many investigations have been focused on the application based on the enhancement or inhibition of Ru(bpy)3 2+ ECL system. However, not much attention has been paid to the theoretical investigation of this ECL system, especially to the inhibiting mechanism for the Ru(bpy)3 2+ ECL system. In the present study, many of the inorganic and organic compounds with electrochemical oxidation activity were found to strongly inhibit Ru(bpy)3 2+ ECL. To explain these inhibited ECL phenomena, a new "electrochemical oxidation inhibiting" mechanism has been proposed via the establishment of a corresponding model. The effects of applied potential, uncompensated resistance, and concentration of inhibitor on the inhibited ECL derived from the model have been verified by experiments. The new ECL inhibition mechanism can be commonly used to explain many kinds of inhibited ECL presently observed, and it is envisioned to result in finding of more inhibitors of this type and establishment of new sensitive ECL detection methods for them.     

Successful synthesis of Hg0.80Re0.20Sr2Can−1CunO2n+2+δ (n = 1, 2) by the sealed quartz tube technique

Ba-free Hg,Re-1201 and -1212 were prepared by the sealed quartz tube technique. The starting materials were nominal precursor Re0.20Sr2CanCun–1Ox(n = 1, 2) and HgO. The unreacted pellets were annealed at 750 °C for 12 h for the n = 1 member and 850 °C for 12 h for the n = 2 member. Rietveld structural refinement was performed with the X-ray diffraction patterns, including impurity phases if needed. Both phases showed SG P4/mmm (nr. 123). Fitted tetragonal cell parameters were a = b = 3.7822(1) Å, c = 8.8776(5) Å and a = b = 3.8205(3) Å c = 12.0438(8) Åirc for the n = 1 and n = 2 members, respectively. DCSQUID (Superconducting Quantum Interference Device) magnetometry and AC susceptibility were used to measure the superconducting properties of the samples. We also studied the effect of post-treatments in oxygen and argon. No superconductivity was found for the n = 1 in any case. However, Tc,onset as high as 107 K was determined for the Hg,Re-1212.     

NMR analysis of poly(ethylene naphthalate) + poly(butylene terephthalate) blends

Melt blends of poly (butylene terephthalate) (PBT) and poly (ethylene naphthalate) (PEN) with 30, 40, 50, 60 and 70 wt% PEN were prepared using a single screw extruder and injection moulding machine. ¹³C and ¹H nuclear magnetic resonance (NMR) spectra were obtained with a Bruker DRX-400 instrument, on solutions prepared by dissolving samples of the homopolymers and each blend in deuterated trifluoroacetic acid + chloroform mixtures (1:1 by volume). The absence of new signals in ¹H and ¹³C spectra, that would be expected to result from transesterification reactions in the PBT + PEN blend system, provides convincing evidence that such reactions do not occur in these blends under the melt processing conditions that were used. In the light of published work on solid-state NMR studies of these and related blend systems, and our observations of partial miscibility with a very small domain size, together with substantial enhancement of the mechanical properties of PBT by blending with PEN, we conclude that the improvement in mechanical properties arises from molecular scale mixing of the homopolymers and strong but non-covalent bonding interactions over the very large interfacial area between the PBT-rich and PEN-rich phases.     

Effective lattice stabilization of gadolinium aluminate garnet (GdAG) via Lu3+ doping and development of highly efficient (Gd,Lu)AG:Eu3+ red phosphors

Abstract

The metastable garnet lattice of Gd₃Al₅O₁₂ is stabilized by doping with smaller Lu³⁺, which then allows an effective incorporation of larger Eu³⁺ activators. The [(Gd_1?xLu_x)_1?yEu_y]₃Al₅O₁₂ (x = 0.1–0.5, y = 0.01–0.09) garnet solid solutions, calcined from their precursors synthesized via carbonate coprecipitation, exhibit strong luminescence at 591 nm (the ⁵D₀ → ⁷F₁ magnetic dipole transition of Eu³⁺) upon UV excitation into the charge transfer band (CTB) at ～239 nm, with CIE chromaticity coordinates of x = 0.620 and y = 0.380 (orange-red). The quenching concentration of Eu³⁺ was estimated at ～5 at.% (y = 0.05), and the quenching was attributed to exchange interactions. Partial replacement of Gd³⁺ with Lu³⁺ up to 50 at.% (x = 0.5) while keeping Eu³⁺ at the optimal content of 5 at.% does not significantly alter the peak positions of the CTB and ⁵D₀ → ⁷F₁ emission bands but slightly weakens both bands owing to the higher electronegativity of Lu³⁺. The effects of processing temperature (1000–1500 °C) and Lu/Eu contents on the intensity, quantum efficiency, lifetime and asymmetry factor of luminescence were thoroughly investigated. The [(Gd_0.7Lu_0.3)_0.95Eu_0.05]₃Al₅O₁₂ phosphor processed at 1500 °C exhibits a high internal quantum efficiency of ～83.2% under 239 nm excitation, which, in combination with the high theoretical density, favors its use as a new type of photoluminescent and scintillation material.     

The stability and optical gap of zinc oxide clusters (ZnO)n (n = 2-18)

The stability and the optical band gap of the Zinc Oxide clusters (ZnO)n (n = 2-18) are investigated by using density functional theory (DFT) and the time-dependent density functional theory (TD-DFT), respectively. The differences between the HOMO-LUMO gap (delta(h-l)) and the optical gap (delta(opt)) are dramatic for small clusters (2 < or = n < or = 5). As the increasing of the cluster size, the differences become small. The results indicate that the stability and the optical gap are related to the sizes and symmetries of the clusters. Further, it is shown that the structures have much greater impact on the optical gap, there is the dipole-forbidden transition in the optical gap for high symmetric structures.