Operando STM study of the interaction of imidazolium-based ionic liquid with graphite

Understanding interactions at the interfaces of carbon with ionic liquids (ILs) is crucially beneficial for the diagnostics and performance improvement of electrochemical devices containing carbon as active materials or conductive additives in electrodes and ILs as solvents or additives in electrolytes. The interfacial interactions of three typical imidazolium-based ILs, 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (AMImTFSI) ILs having ethyl (C2), butyl (C4) and octyl (C8) chains in their cations, with highly oriented pyrolytic graphite (HOPG) were studied in-situ by electrochemical scanning tunneling microscopy (EC-STM). The etching of HOPG surface and the exfoliation of graphite/graphene flakes as well as cation intercalation were observed at the HOPG/C2MImTFSI interface. The etching also takes place in C4MImTFSI at −1.5 V vs Pt but only at step edges with a much slower rate, whereas C8MIm+ cations adsorbs strongly on the HOPG surface under similar conditions with no observable etching or intercalation. The EC-STM observations can be explained by the increase in van der Waals interaction between the cations and the graphite surface with increasing length of alkyl chains

Determination of organic acids evolution during apple cider fermentation using an improved HPLC analysis method

An efficient method for analyzing ten organic acids in food, namely citric, pyruvic, malic, lactic, succinic, formic, acetic, adipic, propionic and butyric acids, using HPLC was developed. Boric acid was added into the mobile phase to separate lactic and succinic acids, and a post-column buffer solution [5 mmol/L p-toluensulfonic acid (p-TSA) + 20 mmol/L bis (2-hydroxyethyl) iminotris (hydroxymethyl) methane (bis¿tris) + 100 ¿mol/L sodium ethylenediaminetetraacetic (EDTA-2Na)] was used to improve the sensitivity of detection. The average spiked recoveries for the ten organic acids ranged from 82.9 to 127.9% with relative standard deviations of 1.44¿4.71%. The linear ranges of determination were from 15 to 1,000 mg/L with correlation coefficients of 0.9995¿0.9999. The metabolism of organic acids in cider, and the effect of nutrients including diammonium phosphate (DAP), thiamine, biotin, niacinamide and pantothenic acid on their metabolism, were studied using this method of analysis. We found that before cider brewing, additions of 200 mg/L DAP and 0.3 mg/L thiamine to apple juice concentrate results in a high quality cider

Spectroscopic Observations of Planetary Nebulae in the Northern Spur of M31

We present spectroscopy of three planetary nebulae (PNe) in the Northern Spur of the Andromeda Galaxy (M31) obtained with the Double Spectrograph on the 5.1 m Hale Telescope at the Palomar Observatory. The samples are selected from the observations of Merrett et al. Our purpose is to investigate formation of the substructures of M31 using PNe as a tracer of chemical abundances. The [O III] 4363 auroral line is detected in the spectra of two objects, enabling temperature determinations. Ionic abundances are derived from the observed collisionally excited lines, and elemental abundances of nitrogen, oxygen, and neon as well as sulphur and argon are estimated. Correlations between oxygen and the alpha-element abundance ratios are studied, using our sample and the M31 disk and bulge PNe from the literature. In one of the three PNe, we observed relatively higher oxygen abundance compared to the disk sample in M31 at similar galactocentric distances. The results of at least one of the three Northern Spur PNe might be in line with the proposed possible origin of the Northern Spur substructure of M31, i.e. the Northern Spur is connected to the Southern Stream and both substructures comprise the tidal debris of the satellite galaxies of M31.Comment: 5 tables, 17 figures; accepted for publication in Ap

Optical properties of TlNi2Se2: Observation of pseudogap formation

The quasi-two-dimensional nickel chalcogenides $TlNi_2Se_2$ is a newly discovered superconductor. We have performed optical spectroscopy study on $TlNi_2Se_2$ single crystals over a broad frequency range at various temperatures. The overall optical reflectance spectra are similar to those observed in its isostructure $BaNi_2As_2$. Both the suppression in $R(\omega)$ and the peaklike feature in $\sigma_1(\omega)$ suggest the progressive formation of a pseudogap feature in the midinfrared range with decreasing temperatures, which might be originated from the dynamic local fluctuation of charge-density-wave (CDW) instability. We propose that the CDW instability in $TlNi_2Se_2$ is driven by the saddle points mechanism, due to the existence of van Hove singularity very close to the Fermi energy.Comment: 5 pages, 4 figure

Intrinsic Percolative Superconductivity in KxFe2-ySe2 Single Crystals

Magnetic field penetration and magnetization hysteresis loops (MHLs) have been measured in KxFe2-ySe2 single crystals. The magnetic field penetration shows a two-step feature with a very small full-magnetic-penetration field (Hp1= 300 Oe at 2 K), and accordingly the MHL exhibits an abnormal vanishing of the central peak near zero field below 13 K. The width of the MHL in KxFe2-ySe2 at the same temperature is in general much smaller than that measured in the relatives Ba0.6K0.4Fe2As2 and Ba(Fe0.92Co0.08)2As2, and the MHLs in the latter two samples show the normal central peak near zero field. All these anomalies found in KxFe2-ySe2 can be understood in the picture that the sample is percolative with weakly coupled superconducting islands.Comment: 5 page, 4 figure