Lusheng Liu

Size-controllable Ni5TiO7 nanowires as promising catalysts for CO oxidation

Ni5TiO7 nanowires with controllable sizes are synthesized using PEO method combined with impregnation and annealing at 1050oC in air, with adjustment of different concentrations of impregnating solution to control the dimension of nanowires. The resulting nanowires are characterized in details using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analysis. In addition, the CO catalytic oxidation performance of the Ni5TiO7 nanowires is investigated using a fixed-bed quartz tubular reactor and an on-line gas chromatography system, indicating that the activity of this catalytic system for CO oxidation is a strong dependency upon the nanocrystal size.When the size of the Ni5TiO7 nanowires is induced from 4 μm to 50 nm, the corresponding maximum conversion temperature is lowered by ~100 oC.

Dark-blue mirror-like perovskite dense films for efficient organic–inorganic hybrid solar cells

To date, numerous approaches have been developed for fabricating high quality organometal halide perovskite thin films, however, perovskite films obtained by such methods reveal a brown or dark-brown color, which might restrain their light absorption ability. Here we report a route to synthesize dark-blue mirror-like perovskite dense films via a two-step spin-coating process assisted by treatment of nonpolar solvent scouring. Photovoltaic cells based on such dark-blue films demonstrate a high short-circuit current density (Jsc) of ∼23 mA cm−2 and a power conversion efficiency (PCE) of 16.1%. Our method would provide a new candidate method for the fabrication of perovskite solar cells with high performance.

Defect-induced strain relaxation in 3C-SiC films grown on a (100) Si substrate at low temperature in one step

The epitaxial deposition of a 3C-SiC film on a (100) Si substrate has been achieved at low temperature in one step using the microwave plasma CVD technique. A high density of defects such as misfit dislocations, stacking faults (SF) and twin boundaries (TB) is generated in the film. Defect-induced strain distribution in the 3C-SiC film is analyzed by the geometric phase analysis (GPA) method combined with X-ray diffraction (XRD) and Raman spectroscopy. The strain analysis at an atomic level reveals that periodical misfit dislocations at the interface generate high local compressive strain (>20%) around the core of the dislocations in the SiC film, relaxing the major part of the intrinsic strain. A highly compressive interfacial layer is found to form between the SiC film and Si substrate regardless of the carbonization temperature. This interfacial layer is linked with the carbonization step of the film growth process. In addition, twins and stacking faults provide a complementary route for strain relaxation during the film growth process. It is found that more strain is accommodated at the matrix/twin interface during twin nucleation rather than that at the growth stage. The atomic understanding of the effects of crystalline defects on strain relaxation will provide important implications for the control of defects in SiC films and design of high-performance SiC devices.

Fabrication of silicon-vacancy color centers in diamond films: tetramethylsilane as a new dopant source

Color centers in diamonds hold great promise for applications in optical sensors, bio-imaging, and quantum communication. Here, we synthesize Si-doped diamond films with Si-vacancy (SiV) centers by the flow of tetramethylsilane (TMS, Si(CH3)4) gas using the microwave plasma chemical vapor deposition technique. In order to achieve high emission efficiency of the SiV centers, the effect of the TMS content on the microstructural evolution and photoluminescence (PL) of this type of color center is investigated using various spectroscopic techniques and high resolution transmission electron microscopy (HRTEM). The introduction of TMS gas in the diamond films leads to grain refinement of the diamond crystals and a weak SiV PL intensity located at 738 nm, at a growth temperature of 650 °C. For diamond films grown at 870 °C, the addition of Si atoms results in grain refinement and the transition of the diamond grains from micro-size without doping (no TMS) to nano-level at a Si/C ratio of 1/100. The SiV PL intensity exhibits a non-monotonic behavior with increasing Si/C ratios. At a Si/C ratio of 1/3100, the diamond film features a structure of nano-grains separated with (100) micro-grains, and displays a maximum in the PL intensity of the SiV centers: a very strong narrow peak at 738 nm with a FWHM of about 5.1 nm. Increasing the Si/C ratio promotes the formation of a nanocrystalline structure and the decrease of the SiV PL intensity. The combination of Raman spectral and HRTEM analysis implies that the PL quenching of the SiV center with the increasing Si/C ratios is attributed to the formation of amorphous carbon. Our results not only demonstrate that the diamond film, featuring a structure of nano-crystals with (100) micro-crystals, could be a promising material with high-efficiency SiV centers, but also highlight that this approach to balancing the concentration of Si impurities and the crystalline quality of the diamond films could advance the fabrication of high-emission SiV centers for optical applications.