[Nb@Ge13/14]3−: New Family Members of Ge-Based Intermetalloid Clusters

During the past two decades, single-atom-centered medium-sized germanium clusters [M@Ge_n] (M=transition metals, n>12) have been extensively explored, both from theoretical perspectives and experimental gas-phase syntheses. However, the actual structural arrangements of the Ge₁₃ and Ge₁₄ endohedral cages are still ambiguous and have long remained an unresolved problem for experimental implementation. In this work, we successfully synthesize 13-/14-vertex Ge clusters [Nb@Ge₁₃]³⁻ ( 1 ) and [Nb@Ge₁₄]³⁻ ( 2 ), which are structurally characterized and exhibit unprecedented topologies, neither classical deltahedra nor 3-connected polyhedral structures. Theoretical analysis indicates that the major stabilization of the Ge backbones arises due to the substantial interaction of Ge 4p-AOs with the endohedral Nb 4d-AOs through three/four-center two-electron bonds with an enhanced electron density accumulated over the shortest Nb−Ge13 contact in 1 . Low occupancies of the direct two-center two-electron (2c–2e) Nb−Ge and Ge−Ge σ bonds point to a considerable degree of electron delocalization over the Ge cages revealing their electron deficiency.     

How the Aggregates Determine Bound Rubber Models in Silicone Rubber? A Contrast Matching Neutron Scattering Study

The correlation between aggregates and bound rubber structures in silicone rubbers(S(phr)) with various silica fractions(ΦSi) has been investigated by contrast matching small-angle neutron scattering(SANS), swelling kinetics, and low-field nuclear magnetic resonance(NMR).Mixed solvents with deuterated cyclohexane fractions of 4.9% and 53.7% were chosen to match the scattering length densities of the matrix(SMP(phr)) and the filler(SMS(phr)), respectively. All the data consistently suggest that:(i) There is a critical threshold ΦSic between 10 and 30 phr;below ΦSic, the isolated aggregates are dominant, while beyond ΦSic, some rubber fraction is trapped among the agglomerate;(ii) ΦSiindependent thicknesses around 7.5 nm(NMR) and 8.6 nm(SANS) suggest that the bound rubber formation is determined by inherent properties of the components, and the power-law around 4.2 suggests an exponential changed gradient density of the bound rubber;(iii) SMS(80) presents a bicontinuous bound rubber with three characteristic lengths of 41, 100, and 234 nm. The expanded correlation length, a 20 nm smaller aggregate sizes suggest that such existent bicontinuous network in dry samples with less ΦSi is kind of impacted by swelling. With the obtained bound rubber models, the reinforcing mechanism of filled silicone rubber is elucidated.     

Heterometallic zinc uranium oxyfluorides incorporating imidazole ligands

Two heterometallic uranium oxyfluorides with hybrid networks were hydrothermally synthesized by incorporating two imidazoles, 1-(biphenyl-4-yl)-1H-imidazole(bpi) and 1,4-di(1H-imidazol-1-yl)benzene(dib), formulated as Zn(bpi)2(UO2)2(H2O)F6(1) and Zn(dib)(UO2)F4 0.5H2O(2). Compound 1consists of chains of edge-sharing UO2F5 and UO2F4(H2O) pentagonal bipyramids, which are linked by Zn(bpi)2moieties to form the sheet structure with decorated bpi. While in compound 2, sheets of edgesharing dimers of UO2F5 pentagonal bipyramids and Zn F3N2 polyhedra are linked by dib, creating a pillared three-dimensional framework. The two compounds represent the few examples of heterometallic uranium oxyfluorides incorporating organic ligands. The syntheses, structure as well as the IR spectra, UV–vis spectra and luminescent properties of the bimetallic uranium oxyfluorides are studied.     

质子与金属布线层核反应对微纳级静态随机存储器单粒子效应的影响分析

金属布线层对微纳级静态随机存储器(static random access memory, SRAM) 质子单粒子效应敏感性的影响值得关注. 利用Geant4针对不同能量(30 MeV, 100 MeV, 200 MeV和500 MeV)的质子与微纳级SRAM器件的核反应过程开展计算, 研究了核反应次级粒子的种类、线性能量传输值(linear energy transfer, LET)及射程情况, 尤其对高LET 值的核反应次级粒子及其射程开展了详细分析. 研究表明, 金属布线层的存在和质子能量的增大为原子序数大于或等于30的重核次级粒子的产生创造了条件, 器件体硅区中原子序数大于60的重核离子来源于质子与钨材料的核反应, 核反应过程中的特殊作用机理会生成原子序数在30至50之间的次级粒子, 且质子能量的增大有助于这种作用机理的发生, 原子序数在30至50之间的次级粒子在器件体硅区的LET值最大约为37 MeV·cm²/mg, 相应射程可达到几微米, 对于阱深在微米量级的微纳级SRAM器件而言, 有引发单粒子闩锁的可能. 研究结果为空间辐射环境中宇航器件的质子单粒子效应研究提供理论支撑.     

稳恒磁场下水热法制备钡铁氧体

利用XRD,SEM,TEM和振动样品磁强计(VSM)等检测手段对不同磁场强度下水热法制备的钡铁氧体粉末进行了分析.实验结果表明,无磁场下,150℃时得到的产物为BaFe2O4颗粒,而180℃时产物为片状BaFe12O19施加磁场后,150和180℃下水热反应产物都为棒状BaFe12O19随着磁感应强度的增加,水热反应产...     

σ-Aromaticity-Induced Stabilization of Heterometallic Supertetrahedral Clusters [Zn6Ge16]4− and [Cd6Ge16]4−

In this work, the largest heterometallic supertetrahedral clusters, [Zn₆Ge₁₆]⁴⁻ and [Cd₆Ge₁₆]⁴⁻, were directly self-assembled through highly-charged [Ge₄]⁴⁻ units and transition metal cations, in which 3-center–2-electron σ bonding in Ge₂Zn or Ge₂Cd triangles plays a vital role in the stabilization of the whole structure. The cluster structures have an open framework with a large central cavity of diameter 4.6 Å for Zn and 5.0 Å for Cd, respectively. Time-dependent HRESI-MS spectra show that the larger clusters grow from smaller components with a single [Ge₄]⁴⁻ and ZnMes₂ units. Calculations performed at the DFT level indicate a very large HOMO–LUMO energy gap in [M₆Ge₁₆]⁴⁻ (2.22 eV), suggesting high kinetic stability that may offer opportunities in materials science. These observations offer a new strategy for the assembly of heterometallic clusters with high symmetry.     

晶粒尺寸对气相沉积薄膜磁取向生长的影响研究

为了研究强磁场下薄膜取向生长规律,采用真空蒸发气相沉积法分别制备了不同磁场方向生长的Zn和Bi薄膜.XRD结果发现磁化率差异较小的Zn薄膜在4T时产生了明显的取向生长,而磁化率差异较大的Bi薄膜在5T磁场强度还没有发生取向生长.SEM结果显示Zn薄膜和Bi薄膜晶粒尺寸上有明显的差别,利用Zn薄膜在4T磁场下的取向建立晶粒尺寸和取向生长的对应关系,提出薄膜发生取向时晶粒的磁化能须大于热能kT的420倍.薄膜是否发生取向生长取决于三个因素:薄膜单个晶粒的大小V,材料不同晶向的磁化率差异Δ关键词： 强磁场 磁取向 薄膜生长 材料电磁加工     

Insight into the Excellent Tribological Performance of Highly Oriented Poly(phenylene sulfide)

Achieving low friction and wear of poly(phenylene sulfide)(PPS) without using fillers or blending is a challenging task, but one of considerable practical importance. Here we describe how neat PPS with high tribological performance is achieved by manipulating processing parameters(pressure, flow and temperature). The key to achieving high tribological performance is comparatively high molecular chain orientation, realized in neat PPS, at high shear rates and low pressure. The friction coefficient and wear rate are as low as ~0.3 and~10^-6 mm³·N^-1·m^-1, respectively, which break the record for neat PPS. These values are even better than those for PPS-based blends and comparable to PPS composites. Further studies show, for the first time, that wear rate decreases exponentially with increasing molecular chain orientation, prompting us to revise the classical Archard's law by including the effect of molecular chain orientation. These findings open the possibility of using neat PPS in highly demanding tribological applications.