Hetero-site nucleation for growing twisted bilayer graphene with a wide range of twist angles.

Twisted bilayer graphene (tBLG) has recently attracted growing interest due to its unique twist-angle-dependent electronic properties. The preparation of high-quality large-area bilayer graphene with rich rotation angles would be important for the investigation of angle-dependent physics and applications, which, however, is still challenging. Here, we demonstrate a chemical vapor deposition (CVD) approach for growing high-quality tBLG using a hetero-site nucleation strategy, which enables the nucleation of the second layer at a different site from that of the first layer. The fraction of tBLGs in bilayer graphene domains with twist angles ranging from 0° to 30° was found to be improved to 88%, which is significantly higher than those reported previously. The hetero-site nucleation behavior was carefully investigated using an isotope-labeling technique. Furthermore, the clear Moiré patterns and ultrahigh room-temperature carrier mobility of 68,000 cm2 V-1 s-1 confirmed the high crystalline quality of our tBLG. Our study opens an avenue for the controllable growth of tBLGs for both fundamental research and practical applications.

The Subchronic Toxic Effects of Mosla chinensis Maxim in Normal Rats.

BACKGROUND: The aim of this work was to study the toxic effects and target organs of Mosla chinensis Maxim (MCM) in rats and provide theoretical basis for clinical medication. METHODS: The subchronic toxicity study was conducted on 60 male and female SD rats using the fixed-dose method for the treatment groups and 20 male and female SD rats for the control. At the subchronic toxicity study, the water extract of MCM with fixed doses of 0.2 g/kg/day, 2 g/kg/day, and 20 g/kg/day was administered for 90 days intragastric, and the control group was given the same amount of distilled water. After 90 days, the general conditions of the rats were observed. Assessment on safety of the extract was conducted by a subchronic toxicity test which mainly examined alteration occurrence in gut flora and urine metabolism. RESULTS: There was no significant difference in physical signs, reactivity, and stool characteristics in the four groups. Compared with the control group, the number of red blood cells in the male 2 g/kg/day group and the female 0.2 g/kg/day group was significantly different (P < 0.05). The detection of serum biochemical indicators showed that MCM has an effect on liver and kidney function but has no physiological significance. The level of low-density lipoprotein in male rats was lower than that in the control group (P < 0.05). Compared with the control group, the blood glucose levels of female rats in the 0.2 g/kg/day, 2 g/kg/day, and 20 g/kg/day groups were significantly increased (P < 0.05). As far as the diversity of intestinal flora is concerned, feeding MCM for 90 days has an influence on the distribution of intestinal flora. The content of lactic acid bacteria increased, and the ratio of hard bacteria to Bacteroides (f/b) was also affected, but there was no significant difference. CONCLUSIONS: These findings showed that the long-term intragastric administration of the MCM is safe to use within its dose recommendation. But it could have a slight effect on the metabolism of uric acid by changing the composition of intestinal flora and affecting the metabolism of tryptophan.

Embryonic hematopoiesis in vertebrate somites gives rise to definitive hematopoietic stem cells.

Hematopoietic stem cells (HSCs) replenish all types of blood cells. It is debating whether HSCs in adults solely originate from the aorta-gonad-mesonephros (AGM) region, more specifically, the dorsal aorta, during embryogenesis. Here, we report that somite hematopoiesis, a previously unwitnessed hematopoiesis, can generate definitive HSCs (dHSCs) in zebrafish. By transgenic lineage tracing, we found that a subset of cells within the forming somites emigrate ventromedially and mix with lateral plate mesoderm-derived primitive hematopoietic cells before the blood circulation starts. These somite-derived hematopoietic precursors and stem cells (sHPSCs) subsequently enter the circulation and colonize the kidney of larvae and adults. RNA-seq analysis reveals that sHPSCs express hematopoietic genes with sustained expression of many muscle/skeletal genes. Embryonic sHPSCs transplanted into wild-type embryos expand during growth and survive for life time with differentiation into various hematopoietic lineages, indicating self-renewal and multipotency features. Therefore, the embryonic origin of dHSCs in adults is not restricted to the AGM.

Gas-phase dynamics in graphene growth by chemical vapour deposition.

Chemical vapour deposition on a Cu substrate is becoming a very important approach to obtain high quality graphene samples. Previous studies of graphene growth on Cu mainly focus on surface processes. However, recent experiments suggest that gas-phase dynamics also plays an important role in graphene growth. In this article, gas-phase processes are systematically studied using computational fluid dynamics. Our simulations clearly show that graphene growth is limited by mass transport under ambient pressures while it is limited by surface reactions under low pressures. The carbon deposition rate at different positions in the tube furnace and the concentration of different gas phase species are calculated. Our results confirm that the previously realized graphene thickness control by changing the position of the Cu foil is a result of gas-phase methane decomposition reactions.

Slope efficiency over 30% single-frequency ytterbium-doped fiber laser based on Sagnac loop mirror filter.

A high-slope-efficiency single-frequency (SF) ytterbium-doped fiber laser, based on a Sagnac loop mirror filter (LMF), was demonstrated. It combined a simple linear cavity with a Sagnac LMF that acted as a narrow-bandwidth filter to select the longitudinal modes. And we introduced a polarization controller to restrain the spatial hole burning effect in the linear cavity. The system could operate at a stable SF oscillating at 1064 nm with the obtained maximum output power of 32 mW. The slope efficiency was found to be primarily dependent on the reflectivity of the fiber Bragg grating. The slope efficiency of multi-longitudinal modes was higher than 45%, and the highest slope efficiency of the single longitudinal mode we achieved was 33.8%. The power stability and spectrum stability were <2% and <0.1%, respectively, and the signal-to-noise ratio measured was around 60 dB.

Growth mode and defect evaluation of GaSb on GaAs substrate: a transmission electron microscopy study.

We use transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) techniques to confirm and analyze the interfacial misfit (IMF) and non-IMF growth modes for GaSb epilayers on GaAs substrates. Under optimized IMF growth conditions, only pure 90 degrees dislocations are generated along both [110] and [1-10] directions and located exactly at the epi-substrate interface, which leads to very low density of misfit dislocations propagating from the GaSb/GaAs interface along the growth direction, compared to the non-IMF growth condition. The mechanism of defect annihilation indicates that this IMF mergence process happens without formation of threading dislocations into the GaSb epilayer, which is a completely relaxed growth mode with extremely low defect density. Based on scanning several sets of wafer surfaces, plan-view TEM confirms that the misfit defect densities are estimated to be approximately 5 x 10(5) cm(-2) for IMF growth mode and approximately 10(9) cm(-2) for non-IMF growth mode.

784-nm amplified spontaneous emission from Tm3+-doped fluoride glass fiber pumped by an 1120-nm fiber laser.

We report 784-nm (1G4 --> 3H5 transition) amplified spontaneous emission (ASE) from Tm3+-doped fluoride (ZrF4-BaF2-LaF3-AlF3-NaF) glass fiber pumped by an 1120-nm fiber laser. To our best knowledge, this is the first report of 784-nm (1G4 --> 3H5 transition) ASE in a Tm3+-doped fluoride fiber laser. Its effects on a 480-nm (1G4 --> 3H6 transition) blue laser were also discussed.

Random microchip laser.

A microchip-type laser with multiple scattering from powder as necessary feedback is demonstrated. The laser consists of a transparent ceramic Nd:YAG microchip and a Nd:YAG powder tablet, operates at quasi-continuous- wave regime pumped by a laser diode array.

Single frequency 1083nm ytterbium doped fiber master oscillator power amplifier laser.

Single frequency 1083nm ytterbium fiber master oscillator power amplifier system was demonstrated. The oscillator was a linear fiber cavity with loop mirror filter and polarization controller. The loop mirror with unpumped ytterbium fiber as a narrow bandwidth filter discriminated and selected laser longitudinal modes efficiently. Spatial hole burning effect was restrained by adjusting polarization controller appropriately in the linear cavity. The amplifier was 5 m ytterbium doped fiber pumped by 976nm pigtail coupled laser diode. The linewidth of the single frequency laser was about 2 KHz. Output power up to 177 mW was produced under the launched pump power of 332 mW.

Multiple-color cw visible lasers by frequency sum-mixing in a cascading Raman fiber laser.

Multiple cw visible lasers at wavelengths ranging from 550nm to 625nm were generated by intracavity frequency sum-mixing of a cascading Raman fiber laser in a type-I noncritically phase-matched lithium triborate crystal. The phase matching conditions for individual wavelengths were realized by tuning the temperature of the lithium triborate crystal.