Direct spectroscopic evidence for vanadium species in V-MCM-41 molecular sieve characterized by UV resonance Raman spectroscopy

Vanadium species in tetrahedral and octahedral coordination in V-MCM-41 molecular sieve are characterized by UV resonance Raman bands at 1070 and 930 cm(-1) respectively.

Characteristics and optical spectra of V : YAG crystal grown in reducing atmosphere

A V:YAG single crystal was grown by the temperature gradient technique (TGT) with graphite-heating elements. The as-grown crystal has different colorations of light green and yellow brown in different parts. Distribution of vanadium in three samples with different colorations was determined by inductively coupled plasma-mass spectrometry. From the absorption spectrum of the yellow-brown part with peaks at 370, 820 and 1320nm, we can deduce that the reducing atmosphere of carbon diffused from the heating elements can increase the concentration of tetrahedral V3+ ions and induce F color centers. All three samples exhibited light-green color after annealing in vacuum or H-2 atmospheres. In the vacuum annealing process, the V3+ ions in tetrahedral positions were enhanced through two methods: one method is the exchanging of octahedral V3+ and tetrahedral Al3+ ions in neighboring sites under thermal excitation, the other is that F color centers were thoroughly eliminated and the escaped free electrons could be captured by V ions with higher valance states to further improve the concentration of tetrahedral V3+ ions. Besides the two mechanisms, the H-2 annealing process greatly improved the V-tetra(3+) ions through the reduction effect of H-2. (c) 2006 Elsevier B.V. All rights reserved.

Electron injection assisted phase transition in a nano-Au-VO2 junction

The semiconductor-metal transition of vanadium dioxide (VO2) thin films epitaxially grown on C-plane sapphire is studied by depositing Au nanoparticles onto the thermochromic films forming a metal-semiconductor contact, namely, a nano-Au-VO2 junction. It reveals that Au nanoparticles have a marked effect on the reduction in the phase transition temperature of VO2. A process of electron injection in which electrons flow from Au to VO2 due to the lower work function of the metal is believed to be the mechanism. The result may support the Mott-Hubbard phase transition model for VO2.

新型吡咯亚胺钒烯烃聚合催化剂的研究

本文的主要工作和研究结果如下： 1. 合成与表征了一系列吡咯亚胺钒(III)配合物。在Et2AlCl的活化下，它们能高效催化乙烯聚合，活性可高达48.6 kg PE/mmolVhbar，得到高分子量且分子量分布单分散的线性聚乙烯。吡咯亚胺钒催化体系具有较好的高温耐受性，即使在70 C下聚乙烯催化活性仅比50 C时下降30-40%，并且仍然比VCl3.(THF)3活性高,且分子量分布在70 C仍能保持2.5以下，说明催化剂是单活性基的。与单配的水杨醛亚胺钒催化剂相比，吡咯亚胺钒配合物具有更高的乙烯催化活性，得到具有更窄分子量分布的聚乙烯，说明具有五元环N,N螯合的吡咯亚胺配体能更好的稳定钒活性中心，增加催化剂的活性。 2. 通过采用烷基铝预先对功能性基团进行保护的方法，我们用吡咯亚胺钒/Et2AlCl催化体系实现了乙烯与一系列功能性单体如十一烯醇、十一烯酸甲酯、烯丁醇的共聚合。与其他共聚单体相比，十一烯醇的插入率更高。在温和条件下十一烯醇的插入率可以轻松达到15.8%，活性仍能保持1.4 kg/molVh。通过控制Al/V、共聚单体浓度、聚合温度等反应参数，共聚反应的活性、功能性单体插入率、以及共聚物的分子量可在很大范围内进行调控。 3．合成并表征了一系列双吡咯亚胺钒(Ⅲ)配合物，并初步研究了其乙烯聚合行为。在Et2AlCl和三氯乙酸乙酯的存在下，这些配合物具有优异的催化乙烯聚合的能力，其聚合活性可达28.8 kg PE/mmolVh。双吡咯亚胺钒(Ⅲ)配合物比单配的吡咯亚胺钒(Ⅲ)配合物具有更好的温度耐受性，随着温度的升高，乙烯聚合活性升高，70C时活性与50C时相当或者更高。 关键词：钒催化剂，乙烯聚合，乙烯与功能性单体共聚合

Hybrid permeable metal-base transistor with large common-emitter current gain and low operational voltage

We demonstrate the suitability of N,N'-diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine (NPB), an organic semiconductor widely used in organic light-emitting diodes (OLEDs), for high-gain, low operational voltage nanostructured vertical-architecture transistors, which operate as permeable-base transistors. By introducing vanadium oxide (V2O5) between the injecting metal and NPB layer at the transistor emitter, we reduced the emitter operational voltage.

Very low hysteresis organic thin-film transistors

Very low hysteresis vanadyl-phthalocyanine/para-sexiphenyl thin-film transistors (TFTs) have been fabricated using benzocyclobutenone (BCBO) derivatives/tantalum pentoxide (Ta2O5)/BCBO triple gate dielectrics. The field effect mobility, on/off current ratio and threshold voltage of organic TFTs are 0.45 cm(2) V-1 s(-1), 3.5 x 10(4) and -6.8 V, respectively. To clarify the mechanism of hysteresis, devices with different dielectrics have been studied. It is found that the bottom BCBO derivatives (contact with a gate electrode) block the electron injection from a gate electrode to dielectrics.

Effect of the work function of gate electrode on hysteresis characteristics of organic thin-film transistors with Ta2O5/polymer as gate insulator

Organic thin-film transistors (OTFTs) using high dielectric constant material tantalum pentoxide (Ta2O5) and benzocyclobutenone (BCBO) derivatives as double-layer insulator were fabricated. Three metals with different work function, including Al (4.3 eV), Cr (4.5 eV) and Au (5.1 eV), were employed as gate electrodes to study the correlation between work function of gate metals and hysteresis characteristics of OTFTs. The devices with low work function metal Al or Cr as gate electrode exhibited high hysteresis (about 2.5 V threshold voltage shift). However, low hysteresis (about 0.7 V threshold voltage shift) OTFTs were attained based on high work function metal Au as gate electrode.

Polymerization of 1,3-butadiene with VO(P-204)(2) and VO(P-507)(2) activated by alkylaluminum

The oxovanadium phosphonates (VO(P-204)(2) and VO(P-507)(2)) activated by various alkylaluminums (AlR3, R = Et, i-Bu, n-Oct; HAIR(2), R = Et, i-Bu) were examined in butadiene (Bd) polymerization. Both VO(P-204)(2) and VO(P-507)(2) showed higher activity than those of classical vanadium-based catalysts (e.g. VOCl3, V(acac)(3)). Among the examined catalysts, the VO(P-204)(2)/Al(Oct)(3) system (I) revealed the highest catalytic activity, giving the poly(Bd) bearing M-n of 3.76 x 10(4) g/mol, and M-w/M-n ratio of 2.9, when the [Al]/[V] molar ratio was 4.0 at 40 degrees C. The polymerization rate for I is of the first order with respect to the concentration of monomer. High thermal stability of I was found, since a fairly good catalytic activity was achieved even at 70 degrees C (polymer yield > 33%); the M-n value and M-w/M-n, ratio were independent of polymerization temperature in the range of 40-70 degrees C. By IR and DSC, the poly(Bd)s obtained had high 1,2-unit content (> 65%) with atactic configuration. The 1,2-unit content of the polymers obtained by I was nearly unchanged, regardless of variation of reaction conditions, i.e. [Al]/[V], ageing time, and reaction temperature, indicating the high stability of stereospecificity of the active sites.

Nanotubes of mixed-valence, transition metal compounds synthesized by solution phase approach

A solution-phase approach to synthesize four kinds of mixed-valence, transition metal compounds nanotube is described. The approach is based on the self-assembly of siloxane sol. The resulted production of mixed-valence, transition metal compounds share a common structural characteristic of tubular geometrical morphology, at least for the ones we studied. The results demonstrate that the synthesis strategy can be a general route for preparation of compound nanotubes. In addition, the size control of nanotubular materials can be easily achieved through varying the ionic strength of solution. Based on the strategy, the diameters of ultrathin Ru-Fe nanotubes can be easily tuned between 100 nm and 800 nm.