ABSTRACT
Layered carbides are fascinating compounds due to their enormous structural and chemical diversity, as well as their potential to possess useful and tunable functional properties. Their preparation, however, is challenging and forces synthesis scientists to develop creative and innovative strategies to access high-quality materials. One unique compound among carbides is Mo2Ga2C. Its structure is related to the large and steadily growing family of 211 MAX phases that crystallize in a hexagonal structure (space group P63/mmc) with alternating layers of edge-sharing M6X octahedra and layers of the A-element. Mo2Ga2C also crystallizes in the same space group, with the difference that the A-element layer is occupied by two A-elements, here Ga, that sit right on top of each other (hence named "221" compound). Here, we propose that the Ga content in this compound is variable between 2:2, 2:1, and 2: ≤1 (and 2:0) Mo/Ga ratios. We demonstrate that one Ga layer can be selectively removed from Mo2Ga2C without jeopardizing the hexagonal P63/mmc structure. This is realized by chemical treatment of the 221 phase Mo2Ga2C with a Lewis acid, leading to the "conventional" 211 MAX phase Mo2GaC. Upon further reaction with CuCl2, more Ga is removed and replaced with Cu (instead of fully exfoliating into the Ga-free Mo2CTx MXene), leading to Mo2Ga1-xCuxC still crystallizing with space group P63/mmc, however, with a significantly larger c-lattice parameter. Furthermore, 211 Mo2GaC can be reacted with Ga to recover the initial 221 Mo2Ga2C. All three reaction pathways have not been reported previously and are supported by powder X-ray diffraction (PXRD), electron microscopy, X-ray spectroscopy, and density functional theory (DFT) calculations.
ABSTRACT
We study the photophysical stability of ensemble near-surface nitrogen vacancy (NV) centers in diamond under vacuum and air. The optically detected magnetic resonance contrast of the NV centers was measured following exposure to laser illumination, showing opposing trends in air compared to vacuum (increasing by up to 9% and dropping by up to 25%, respectively). Characterization using X-ray photoelectron spectroscopy (XPS) suggests a surface reconstruction: In air, atmospheric oxygen adsorption on a surface leads to an increase in NV- fraction, whereas in vacuum, net oxygen desorption increases the NV0 fraction. NV charge state switching is confirmed by photoluminescence spectroscopy. Deposition of â¼2 nm alumina (Al2O3) over the diamond surface was shown to stabilize the NV charge state under illumination in either environment, attributed to a more stable surface electronegativity. The use of an alumina coating on diamond is therefore a promising approach to improve the resilience of NV sensors.
ABSTRACT
OBJECTIVE: To assess the efficacy and safety of 10-day sequential therapy for Helicobacter pylori (H.pylori) eradication in children. METHODS: The databases of Cochrane Central Register of Controlled Trials (CENTRAL, 2013,N01), Medline, Embase, OVID, Chinese Biological Medicine database (CBMDisc), CNKI, Chinese VIP and WANFANG (all from 2000-2013) were searched. And manual searches were performed for the relevant journals and conference proceedings. Prospective, randomized controlled trials of 10-day sequential therapy for H.pylori eradication in children were selected. The systematic review was conducted with the method recommended by The Cochrane Collaboration. RESULTS: Fifteen trials with a total of 1348 patients were included for analysis. The meta-analysis showed: (1) H.pylori eradication rates: 10-day sequential therapy were superior to triple therapy (80.78% (521/645) vs 69.84% (491/703), OR 2.13, 95%CI: 1.62-2.80, P < 0.01). It was also superior to 7-day and 10-day standard triple therapy (86.03% (271/315) vs 73.77% (225/305), 79.04% (181/229) vs 65.19% (176/270); OR 2.23, 2.11; 95%CI:1.47-3.36, 1.37-3.24;both P < 0.01) . There were non-superior to 14-day standard triple therapy (73.97% (108/146) vs 70.31% (90/128), OR 1.87, 95%CI: 0.46-7.69, P = 0.38). (2) Adverse effect rate: adverse events were similar between sequential and standard triple therapies (P = 0.58). CONCLUSION: The 10-day sequential therapy may be a new effective and safe option in treatment of H.pylori infections in children.
