芳纶复合纳米纤维气凝胶的制备及其性能研究

将SiO2纳米粒子加入到由去质子化方法制备的芳纶纳米纤维分散液中,制备芳纶复合纳米纤维气凝胶。通过一系列表征测试,分析了无机纳米粒子添加的芳纶复合气凝胶的力学性能、热性能和燃烧性能。试验结果表明:制得的复合纳米气凝胶的密度为5.6 mg/cm^(3),在80%压缩应变下可承受280 kPa的应力,并且具备低导热系数[27.0 mW/(m·K)],热释放峰值仅为11.12 W/g;芳纶复合纳米纤维气凝胶属于离火自熄灭材料,具有优异的阻燃防火性能。

First-Principles Study of Two Dimensional Transition Metal Phthalocyanine-Based Metal-Organic Frameworks in Kagome Lattice

Transition metal phthalocyanines (TMPc) and relevant derivatives can act as pervasive molecules for their electronic, magnetic, and optical applications. Numerous researches based on TMPc are carried out, attempting to synthesize novel two-dimensional (2D) metal-organic frameworks. Recently, some 2D poly-TMPc frameworks including FePc [J. Am. Chem. Soc. 133, 1203 (2011)], CoPc [Chem. Commun. 51, 2836 (2015)], and Ni-NiPc [J. Mater. Chem. A 6, 1188 (2018)] frameworks have been successfully synthesized experimentally. Meanwhile, potential applications in catalysis, gas storage, and spintronics were predicted by theoretical studies. Here, we propose a new kind of 2D poly-TMPc frameworks with kagome lattice (denoted as kag-TMPc) and systematically investigate their electronic and magnetic properties by employing first-principles calculations. We have demonstrated that the 2D kag-MnPc framework displays quite stable ferromagnetic ordering with Curie temperature about 125 K as indicated by Monte Carlo simulations based on Heisenberg model and prefers out-of-plane easy-magnetization axis. The 2D kag-CrPc framework is an ideal candidate for S=2 kagome antiferromagnet with RT3 magnetic order. Particularly, the investigations on optical absorption suggest that when the TMPc molecules are self-assembled into 2D kag- TMPc frameworks, their absorption wave bands are broadened, especially in visible region.

Single-Atom Protecting Group for on-Surface Synthesis of Graphdiyne Nanowires

On-surface synthesis of semiconducting graphdiyne nanowires usually su er severe side re- actions owing to the high reactivity of the butadiynylene units at noble metal surfaces, limiting the production of isolated nanowires. In this work, we report the high-yield synthesis of branchless graphdiyne nanowires [-C≡C-Ph2-C≡C-]n via on-surface Ullmann coupling of 1,4-bis(4-bromophenyl)-1,3-butadiyne molecules with chemical vapor deposition method. Non-contact atomic force microscopy with single-bond resolution reveals that single gold adatoms act as e ective protecting groups for butadiynylene units by forming Au-π ligand bonds, preventing unwanted branched coupling reactions and enabling the synthesis of ultralong isolated graphdiyne nanowires. This study will stimulate further investigation on the role of various surface adatoms in protecting on-surface reactions.

Construction of twisted graphene–silicene heterostructures

Van der Waals stacking of two-dimensional crystals with rotation or mismatch in lattice constants gives rise to rich physical phenomena that are closely related to the strong correlations and band topology.Twisted graphene and silicene heterobilayers have been theoretically predicted to host a tunable transport gap due to the mismatch of Dirac cones in the graphene and silicene layers.However,experimental realization of such twisted structure is challenging.Here,we report the formation of twisted graphene/silicene bilayers on Ru(0001)crystal via intercalation.Different moirépatterns form as single-crystalline graphene grows over different grains of the Ru surface.After silicon intercalation,graphene/silicene bilayers are observed with different twisting angles on top of different grains of the Ru substrate.Our work provides a new pathway towards construction of graphene based twisted heterobilayers.

Epitaxial growth of highly strained antimonene on Ag（111）

The synthesis of antimonene, which is a promising group-V 2D material for both fundamental studies and technological applications, remains highly challenging. Thus far, it has been synthesized only by exfoliation or growth on a few substrates. In this study, we show that thin layers of antimonene can be grown on Ag（111） by molecular beam epitaxy. High-resolution scanning tunneling microscopy combined with theoretical calculations revealed that the submonolayer Sb deposited on a Ag（111） surface forms a layer of AgSb2 surface alloy upon annealing. Further deposition of Sb on the AgSb2 surface alloy causes an epitaxial layer of Sb to form, which is identified as antimonene with a buckled honeycomb structure. More interestingly, the lattice constant of the epitaxial antimonene （5 /-） is much larger than that of freestanding antimonene, indicating a high tensile strain of more than 20%. This kind of large strain is expected to make the antimonene a highly promising candidate for room- temperature quantum spin Hall material.

Observation of pseudogap in SnSe2 atomic layers grown on graphite

Superconducting metal dichalcogenides(MDCs)present several similarities to the other layered SI1-perconductors like cuprates.The superconductivity in atomically thin MDCs has been demonstrated by recent experiments,however,the investigation of the superconductivity intertwined with other or-ders are scarce.Investigating the pseudogap in atomic layers of MDCs may help to understand the superconducting mechanism for these true two dimensional(2D)superconducting systemns.Herein we report a pseudogap opening in the tunneling spectra of thin layers of SnSe2 epitaxially grown on highly oriented pyrolytic graphite(HOPG)with scanning tunneling microscopy/spectroscopy(STM/STS).A significant V-shaped pseudogap was observed to open near the Fermi level(Er)in the sTS.And at elevated temperatures,the gap gradually evolves to a shallow dip.Our experimental observations provide direct evidence of a pseudogap state in the electron-doped SnSe2 atomic layers on the HOPG surface,which may stimulate further exploration of the mechanism of superconductivity at 2D limit in MDCs.