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Sintering method greatly affects the sintering behavior, microstructure and properties of the ceramic composites. In the present work, TiB 2 – h -BN composites prepared by reactive spark plasma sintering (RSPS) and conventional spark plasma sintering (CSPS) are compared. Due to the in-situ synthesized TiB 2 and h -BN particles during sintering process, the reactive sintering not only inhibits the orientation of TiB 2 grains but also prevented the formation of the Card-house structure. TiB 2 – h -BN composites obtained by RSPS (R series) exhibit higher sintering activity and finer microstructure, which results in better mechanical performance than those prepared by CSPS (C series). As the SPS temperature is 1600 °C, the relative density of the composite in R series is as high as 97.3%, much higher than that (89.3%) in C series. The composite obtained by RSPS at 1600 °C also exhibits excellent mechanical properties with a bending strength of 205.3 MPa and a Vickers hardness of 2.50 GPa, respectively, which exceeds all composites prepared by CSPS at 1600–2000 °C. When the SPS temperature is 1800 °C or above, for both series, the increase of SPS temperature greatly enhances the Vickers hardness but has litter effect on the strength and electrical resistivity, which is attributed to the comprehensive effect of the density increase and microstructure coarsening. The present work indicates that in-situ reactive sintering has obvious advantages in preparing TiB 2 – h -BN composites with excellent mechanical properties at low temperature. [ABSTRACT FROM AUTHOR]

Abstract: CeO2 thin films were prepared via a sol–gel dip-coating process, and used as supports to prepare CuO/CeO2 model catalysts. The catalytic activity of the catalysts for low-temperature CO oxidation was investigated with a micro-reactor-GC system. X-ray diffraction (XRD) patterns indicate that the CeO2 films are of random orientation with dominant (111) texture, and Cu0.2Ni0.8O phase has formed in CuO/CeO2 model catalysts. The scanning electron microscopy (SEM) and scanning tunneling microscopy (STM) images show the CeO2 film surface is uniform and CuO exists in either cluster or crystal forms. CuO/CeO2/Ni has higher catalytic activity compared to CuO/CeO2/NiO/Ni. The synergistic interaction between CuO and CeO2 is the main factor responsible for high catalytic activity of CuO/CeO2 model catalysts. [Copyright &y& Elsevier]

It has been revealed that inversion symmetry breaking in graphene could induce non-trivial Berry curvature, which leads to topologically protected valleytronic applications. Here, we propose an active controllable way of realizing the inversion symmetry breaking of single layer graphene, which is induced by the contrasted AB sub-lattice charge polarization. Our theory model indicates the split of in-plane optical phonons (iTO/iLO) at Γ point is the direct result of inversion symmetry breaking in single layer graphene. Density functional theory calculation was used to quantify the sub-lattice charge polarization and the split of iTO/iLO phonons under the external in-plane electric field, which was further confirmed by Raman spectroscopy. We believe that the method of symmetry manipulation by external in-plane electric field advances fundamental comprehension for the inner mechanism of topological phase transition of graphene. We propose a controllable method to induce topological phase transition of graphene into topological non-trivial material in the way of symmetry manipulation by inducing sub-lattice contrasted charge polarization in the shape of in-plane external electric field. With Raman spectroscopy, the difference between ITO and ILO phonon can be measured. We demonstrate the split of G-peak is proportional to in-plane electric field strength applied on graphene, which is confirmed by theoretical calculation and experiments. Image 1 [ABSTRACT FROM AUTHOR]

Graphical abstract We realize the efficient modulation of relaxation channels in MoS 2 monolayers and interfacial electron transfer by forming mixed-dimensional VdW heterostructures with graphene quantum dots (GQDs) and find that the cascaded relaxation of hot electrons in GQDs that originate from the quantum confinement effect is the ultimate reason. With femtosecond pump–probe spectroscopy, the biphasic electron injection model and modified rate equations are employed to quantitatively solve the interfacial dynamics. Abstract Van der Waals (VdW) heterostructures have emerged as promising materials for atomically thin optoelectronic and photovoltaic applications, where the efficient charge separation after photo-excitation is significant to enhance device performances. However, modulating the interfacial charge transfer is still challenging due to the weak interlayer VdW interaction. Revealing electron transfer and relaxation processes in heterostructures lays foundation to tune the interfacial dynamics and optoelectronic properties. Here, we realize the efficient modulation of relaxation channels in MoS 2 monolayers and interfacial electron transfer by forming mixed-dimensional VdW heterostructures with graphene quantum dots (GQDs). With femtosecond pump–probe spectroscopy, the biphasic electron injection model and modified rate equations are employed to quantitatively solve interfacial transfer rates of mixed-dimensional VdW heterostructures. We find that the cascaded relaxation of hot electrons in GQDs that originates from the quantum confinement effect can intensively affect the interfacial dynamics. Our established model is instructive to optimize performances of future photon-harvesting devices based on mixed low-dimensional heterostructures. [ABSTRACT FROM AUTHOR]