Controllable Fabrication of SiC@C-Fe3O4 Hybrids and Their Excellent Electromagnetic Absorption Properties

In this work, a batch of novel ternary hybrids (SiC@C-Fe3O4), characterized by SiC nanowires core, carbon shell, and adhered Fe3O4 nanoparticles were controllably synthesized via surface carbonization of SiCnw followed by hydrothermal reaction. Carbon, which was derived from SiC with nanometer thickness, possesses an amorphous structure, while Fe3O4 nanoparticles are in a crystalline state. Simultaneously, the inducement of Fe3O4 nanoparticles can provide significant magnetic loss, which is well-tuned by changing the molar content of iron precursors (FeCl3·6H2O and FeCl2·4H2O). SiC@C-Fe3O4 hybrids show great electromagnetic absorption performance owing to the synergy effect of dielectric and magnetic losses. The minimum refection loss can reach to −63.71 dB at 11.20 GHz with a thickness of 3.10 mm, while the broad effective absorption bandwidth (EAB) can reach to 7.48 GHz in range of 10.52–18.00 GHz with a thickness of 2.63 mm. Moreover, the EAB can also cover the whole X band and Ku band. The outstanding performance of the obtained material implys that it is a promising candidate as an electromagnetic absorber.

Controlled reduction of graphene oxide via hydrogen plasma for tuning sensitivity and recovery time of rGo based oxygen gas sensor

Graphene with high electronic transport, large surface-to-volume ratio and nanometer thickness is excellent for gas sensing applications. However, its sensitivity and recovery face serious limitations in practical considerations. In this study, graphene oxide (Go) sheets were synthesized and exposed to hydrogen (H2) plasma to reduced it into a reduced graphene oxide (rGo) in a controlled procedure. In this regard, Go sheets were irradiated with plasma at different times and their electrical properties were evaluated. The results showed that with increasing bombardment time from 2 to 8 min, the conductivity of the sheets increased but for a longer time no significant increase was observed compared to 8 min. Raman spectroscopy also showed that the increase in plasma radiation led to an increase in defects within the sheets. The appearance of defects in rGo improved its sensitivity to oxygen (O2) gas, but nevertheless reduced its recovery time. Therefore, by introducing the plasma bombardment process in a completely controlled way, we showed that the sensitivity and recovery time of rGo can be effectively tuned.

Structure and Dynamics of Interfacial Water on Muscovite Surface under Different Temperature Conditions (298 K to 673 K): Molecular Dynamics Investigation

We performed molecular dynamics (MD) simulations to study structure, stability, and dynamics of the water adsorption layer on muscovite mica at several temperatures (from 298 K to 673 K) and pressures (0.1 MPa, 10 MPa, and 50 MPa). We studied the structure of the adsorption layers with three characteristic peaks of density and orientation of H2O molecules in one-dimensional and two-dimensional profiles. The results show that the water adsorption layers become less structured and more mobile as the temperature increases. We also found the first and the second layers are less diffusive than the third one, and the difference of diffusivity gets unclear as the temperature increases. Finally, we discuss implications to hydration forces and wettability, which are significant interfacial properties of the multiphase fluids system such as water/gas/mineral systems, from the viewpoint of water adsorption film with nanometer thickness.

NANOMETER THICKNESS SILICON-ON-INSULATOR FILMS THERMAL STABILITY

Thermal stability of 2.2 and 4.7 nm thick silicon-oninsulator films was studied within anneal temperature range of 800-1100оС. It was found that at the higher temperatures film thickness decreases and stoichiometric composition changes with increasing the proportion of the amorphous phase. Mechanisms of structural stability dependence upon film thickness is discussed.