Room-temperature near-band-edge photoluminescence of ZnO is composed of contributions from free-exciton recombination and its longitudinal-optical phonon replica. By tracking the photoluminescence of ZnO nanowires from 4K up to room temperature, the authors show that the relative contributions of these emission lines show a strong variation for samples grown under different conditions. The varying coupling strengths of the excitons and phonons thus lead to a significant shift of the energy position of the room-temperature photoluminescence. They verify that this is not caused by laser heating or stress/strain but is most probably related to crystalline imperfections in the surface region.
Lignin represents
the largest renewable resource of aromatic moieties
on earth and harbors a huge potential as a sustainable feedstock for
the synthesis of biobased aromatic fine chemicals. Due to the complex,
heterogeneous, and robust chemical structure of the biopolymer, the
valorization is associated with significant challenges. Unfortunately,
technical lignins, which are a large side stream of the pulp and paper
industries, are mainly thermally exploited. In this study, technical
Kraft lignin was selectively electrochemically depolymerized to the
aroma chemical vanillin. Using electricity, toxic and/or expensive
oxidizers could be replaced. The electrodegradation of Kraft lignin
was performed at 160 °C in a simple undivided high-temperature
electrolysis cell and studied in respect to several reaction parameters.
At optimized electrolytic conditions vanillin could be obtained in
high selectivity with 67% efficiency compared to the common nitrobenzene
oxidation. Additionally, the established high-temperature electrolysis
indicated a reliable process and could be easily adapted to a variety
of different Kraft lignins.
Coherent anti-Stokes Raman scattering (CARS) microscopy is demonstrated to be a powerful imaging technique with chemical specificity for studying chemically amplified polymer photoresists. Samples of poly(tertbutyloxycarbonyloxystyrene) (PTBOCST) resist imprinted by interferometric lithography with a pattern of lines/spaces of 400 nm/400 nm and 200 nm/200 nm were used to test CARS imaging capabilities. Chemical contrast in the image is obtained by probing the carbonyl stretching vibration of the tert-butoxyl carbonyl group of PTBOCST. The experimental images demonstrate high spatial resolution (≈270 nm) and strong signal, which allows short acquisition times. Advantages and limitations of CARS in comparison with other imaging techniques with chemical specificity, such as infrared near field scanning optical microscopy (IR NSOM), are discussed.
Lithium ion batteries play an increasing role in everyday life, giving power to handheld devices or being used in stationary storage solutions. Especially for medium or large scale solutions, the latter application confines a huge amount of energy within a small volume; however, increasing the hazard potential far above the common level. Furthermore, as the safety hazards of lithium ion cells have been known for years, impressively shown by several burning cars or laptops, the need for a further enhancement of the safety of these systems is rising. This manuscript presents measurements of the gas emission from lithium ion batteries in case of a malfunction for different scenarios, showing a large variety of species with mostly toxic to highly toxic properties. The measurements were carried out using a combination of gas chromatography-mass spectrometry (GC-MS), quadrupole mass spectrometry (QMS), photoacoustic spectroscopy, and chemical analysis. It is shown that the inflammation of a cell can be overcome, also preventing a cascading effect to neighboring cells, but giving rise to worse toxic gas emission. Furthermore, a filtration concept is presented that decreases the concentration of the emitted components significantly and promises filtration below immediately dangerous to life or health (IDLH) equivalent levels.
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