Concepts for chemical state analysis at constant probing depth by lab-based XPS/HAXPES combining soft and hard X-ray sources

The greater information depth provided in hard X-ray photoelectron spectroscopy (HAXPES) enables nondestructive analyses of the chemistry and electronic structure of buried interfaces. Moreover, for industrially relevant elements like Al, Si, and Ti, the combined access to the Al 1s, Si 1s, or Ti 1s photoelectron line and its associated Al KLL, Si KLL, or Ti KLL Auger transition, as required for local chemical state analysis on the basis of the Auger parameter, is only possible with hard X-rays. Until now, such photoemission studies were only possible at synchrotron facilities. Recently, however, the first commercial XPS/HAXPES systems, equipped with both soft and hard X-ray sources, have entered the market, providing unique opportunities for monitoring the local chemical state of all constituent ions in functional oxides at different probing depths, in a routine laboratory environment. Bulk-sensitive shallow core levels can be excited using either the hard or soft X-ray source, whereas more surface-sensitive deep core-level photoelectron lines and associated Auger transitions can be measured using the hard X-ray source. As demonstrated for thin Al₂O₃, SiO₂, and TiO₂ films, the local chemical state of the constituting ions in the oxide may even be probed at near-constant probing depth by careful selection of sets of photoelectron and Auger lines, as excited with the combined soft and hard X-ray sources. We highlight the potential of lab-based HAXPES for the research on functional oxides and also discuss relevant technical details regarding the calibration of the kinetic binding energy scale.     

Exploring the Subtle Effect of Aliphatic Ring Size on Minor Actinide-Extraction Properties and Metal Ion Speciation in Bis-1,2,4-Triazine Ligands

The synthesis and evaluation of three novel bis-1,2,4-triazine ligands containing five-membered aliphatic rings are reported. Compared to the more hydrophobic ligands 1 – 3 containing six-membered aliphatic rings, the distribution ratios for relevant f-block metal ions were approximately one order of magnitude lower in each case. Ligand 10 showed an efficient, selective and rapid separation of Am^III and Cm^III from nitric acid. The speciation of the ligands with trivalent f-block metal ions was probed using NMR titrations and competition experiments, time-resolved laser fluorescence spectroscopy and X-ray crystallography. While the tetradentate ligands 8 and 10 formed Ln^III complexes of the same stoichiometry as their more hydrophobic analogues 2 and 3 , significant differences in speciation were observed between the two classes of ligand, with a lower percentage of the extracted 1:2 complexes being formed for ligands 8 and 10 . The structures of the solid state 1:1 and 1:2 complexes formed by 8 and 10 with Y^III, Lu^III and Pr^III are very similar to those formed by 2 and 3 with Ln^III. Ligand 10 forms Cm^III and Eu^III 1:2 complexes that are thermodynamically less stable than those formed by ligand 3 , suggesting that less hydrophobic ligands form less stable An^III complexes. Thus, it has been shown for the first time how tuning the cyclic aliphatic part of these ligands leads to subtle changes in their metal ion speciation, complex stability and metal extraction affinity.     

Numerical experiments with LP formulations of the maximum clique problem

Central European Journal of Operations Research - The maximum clique problems calls for determining the size of the largest clique in a given graph. This graph problem affords a number of zero-one...     

Kinetics and isotope patterns of ethanol and acetaldehyde emissions from yeast fermentations of glucose and glucose-6,6-d2 using selected ion flow tube mass spectrometry: a case study.

As a prelude to investigations of the emission of metabolites from human cell lines in vitro, we have conducted a study using selected ion flow tube mass spectrometry (SIFT-MS) of the acetaldehyde and ethanol that appear in the headspace above a fermenting yeast/glucose/water mixture in sealed glass bottles at a temperature of 30 degrees C. A fixed quantity of yeast (10 mg) and varying amounts (2, 4, 8 and 16 mg) of both non-deuterated glucose and glucose-6,6-d2 in 5 mL of water were used and the emission of the acetaldehyde and the ethanol were observed as a function of time. The ethanol and acetaldehyde concentrations in the headspace were obtained from the magnitudes of their characteristic ions on the accumulated SIFT mass spectra and, when the deuterated glucose was used, characteristic singly and doubly deuterated ions were obvious. This study indicates, as expected, that ethanol is the major species generated and that acetaldehyde is a relatively minor component of the headspace and a very minor component of the liquid phase. We estimate that about 10(8) ethanol molecules are produced per minute per cell in this yeast fermentation process. The distribution of the non-deuterated and partially deuterated ethanol under these fermentation conditions is observed to be C2H5OH (66 +/- 4)%, C2H4DOH(6 +/- 1)%, C2H3D2OH(28 +/- 4)%, and the analogous distribution for the acetaldehyde is the same, within error. These results indicate that the D atoms in the glucose-6,6-d2 are mostly retained by the 6-C atom, but the appearance of the singly deuterated ethanol and acetaldehyde indicates that some D/H mixing must be occurring in the enzymatic reactions. The results of this study illustrate the potential and power of on-line SIFT-MS analysis in this area of research.     

TiO2 Nanotubes: Nitrogen‐Ion Implantation at Low Dose Provides Noble‐Metal‐Free Photocatalytic H2‐Evolution Activity

Low‐dose nitrogen implantation induces an ion and damage profile in TiO₂ nanotubes that leads to “co‐catalytic” activity for photocatalytic H₂‐evolution (without the use of any noble metal). Ion implantation with adequate parameters creates this active zone limited to the top part of the tubes. The coupling of this top layer and the underlying non‐implanted part of the nanotubes additionally contributes to an efficient carrier separation and thus to a significantly enhanced H₂ generation.     

Methanol Mitigation during Manufacturing of Fruit Spirits with Special Consideration of Novel Coffee Cherry Spirits

Methanol is a natural ingredient with major occurrence in fruit spirits, such as apple, pear, plum or cherry spirits, but also in spirits made from coffee pulp. The compound is formed during fermentation and the following mash storage by enzymatic hydrolysis of naturally present pectins. Methanol is toxic above certain threshold levels and legal limits have been set in most jurisdictions. Therefore, the methanol content needs to be mitigated and its level must be controlled. This article will review the several factors that influence the methanol content including the pH value of the mash, the addition of various yeast and enzyme preparations, fermentation temperature, mash storage, and most importantly the raw material quality and hygiene. From all these mitigation possibilities, lowering the pH value and the use of cultured yeasts when mashing fruit substances is already common as best practice today. Also a controlled yeast fermentation at acidic pH facilitates not only reduced methanol formation, but ultimately also leads to quality benefits of the distillate. Special care has to be observed in the case of spirits made from coffee by-products which are prone to spoilage with very high methanol contents reported in past studies.