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Ongoing interest in two-dimensional (2D) layered materials has motivated extensive studies of transitional metal dichalcogenides, especially its most pronounced representative, MoS2. The few-layer MoS2exhibits distinct properties from those in bulk, which predetermine its potential usage in optoelectronics and flexible devices. Recently, it was found that the layer orientation in MoS2thin films is a key parameter for their utilization in specific devices. Thus far, the alignment of MoS2layers has been detected mostly by transmission electron microscopy (TEM). The drawback of this method is that it requires elaborate sample preparation and probes only a nanometer-scale area of the sample surface. Here we present polarized Raman spectroscopy which provides information about the MoS2layer orientation on the area a few orders larger than in TEM. We show that the depolarization ratio of the significant Raman peaks A1gand E2gshow specific values for the vertical and horizontal alignment of the MoS2layers. We also analytically calculated the depolarization ratio for a thin MoS2layer, which is in good agreement with the measured values. Polarized Raman spectroscopy thus provides a simple, reliable, and general way for specifying the layer alignment in various 2D layered materials.

Graphene oxide is a complex material whose synthesis is still incompletely understood. To study the time evolution of structural and chemical properties of oxidized graphite, samples at different temporal stages of oxidation were selected and characterized through a number of techniques: X-ray photoelectron spectroscopy for the content and bonding of oxygen, X-ray diffraction for the level of intercalation, Raman spectroscopy for the detection of structural changes, electrical resistivity measurements for probing charge localization on the macroscopic scale, and scanning transmission electron microscopy for the atomic structure of the graphene oxide flakes. We found a nonlinear behavior of oxygen uptake with time where two concentration plateaus were identified: Uptake reached 20 at % in the first 15 min, and after 1 h a second uptake started, reaching a highest oxygen concentration of >30 at % after 2 h of oxidation. At the same time, the interlayer distance expanded to more than twice the value of graphite and the electrical resistivity increased by seven orders of magnitude. After 4 days of chemical processing, the expanded structure of graphite oxide became unstable and spontaneously exfoliated; more than 2 weeks resulted in a significant decrease in the oxygen content accompanied by reaggregation of the GO sheets. These correlated measurements allow us to offer a comprehensive view into the complex oxidation process.

The paper deals with the study of optical and electrical properties of inkjet-printed graphene oxide (GO) layers, which can be used e.g. for the preparation of various types of electronic devices. To ensure stable inkjet printing conditions of GO solution, mixture was thoroughly stirred for 1 h at room temperature or sonicated in the bath for 30 min. The thicknesses of prepared layers were determined by spectroscopic ellipsometry and profilometry. An electrical conductivity of GO was increased by the multistep reduction (due to annealing) – the conductivity was changed by these processes about seven orders of magnitude (GO is an isolator and reduced GO is a conductor). For electrical and dielectric measurements, samples with GO and mixture of GO with PEDOT were prepared. All current-voltage characteristics have a diode character. From AC measurements the bulk electrical conductivity and geometric capacity of prepared layers were determined.

The Friedel–Craftstype intramolecular allylic alkylation of simple arenes is performed in the presence of a catalytic amount of MoII CO4Br222.5 mol%. The moisturetolerant protocol provided a mild and direct access to a large library of functionalized 4vinyl1,2,3,4tetrahydronaphthalenes in high yields.

The enantioselective addition of aldehydes to diethyl azodicarboxylate in ionic liquids in the presence of chiralorganocatalysts has been investigated. Of seven differentorganocatalysts tested, L-proline and L-thiazoline-2-carboxylic acid gave the highest enantioselectivities (up to 94 % ee). The best results were obtained by using [bmim]PF6 and [hmim]BF4 as ionic liquids. The scope of the methodology was probed by using various aldehydes and ketones. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Michael additions of different aldehydes and ketones to β-nitrostyrene and 2-(β-nitrovinyl)thiophene in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF6) were studied. β-Nitrostyrene was a better acceptor than 2-(β-nitrovinyl)thiophene, in terms of both reactivity and selectivity. Aldehydes proved to be better donors than ketones, which were themselves better than β-diketones. L-proline proved to be the best catalyst among seven organocatalysts tested. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Proline-catalysed asymmetric direct aldol reaction of different aromatic aldehydes with acetone and several other ketones in the room temperature ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate achieved good yields of aldolisation products with reasonable enantioselectivities, even when just 1–5% of proline was used as the catalyst; immobilisation of the catalyst in an ionic liquid phase offers simple product isolation and reuse of the catalytical system in subsequent reactions.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

For Abstract see ChemInform Abstract in Full Text.

For Abstract see ChemInform Abstract in Full Text.