A 2,2′-bipyridyl-containing
poly(arylene-ethynylene)-alt-poly(arylene-vinylene)
polymer, acting as a light-harvesting
ligand system, was synthesized and coupled to an organometallic rhodium
complex designed for photocatalytic NAD+/NADH reduction.
The material, which absorbs over a wide spectral range, was characterized
by using various analytical techniques, confirming its chemical structure
and properties. The dielectric function of the material was determined
from spectroscopic ellipsometry measurements. Photocatalytic reduction
of nucleotide redox cofactors under visible light irradiation (390–650
nm) was performed and is discussed in detail. The new metal-containing
polymer can be used to cover large surface areas (e.g. glass beads)
and, due to this immobilization step, can be easily separated from
the reaction solution after photolysis. Because of its high stability,
the polymer-based catalyst system can be repeatedly used under different
reaction conditions for (photo)chemical reduction of NAD+. With this concept, enzymatic, photo-biocatalytic systems for solar
energy conversion can be facilitated, and the precious metal catalyst
can be recycled.
Anodic HfO2 memristors grown in phosphate, borate, or citrate electrolytes and formed on sputtered Hf with Pt top electrodes are characterized at fundamental and device levels. The incorporation of electrolyte species deep into anodic memristors concomitant with HfO2 crystalline structure conservation is demonstrated by elemental analysis and atomic scale imaging. Upon electroforming, retention and endurance tests are performed on memristors. The use of borate results in the weakest memristive performance while the citrate demonstrates clear superior memristive properties with multilevel switching capabilities and high read/write cycling in the range of 106. Low temperature heating applied to memristors shows a direct influence on their behavior mainly due to surface release of water. Citrate-based memristors show remarkable properties independent on device operation temperatures up to 100 °C. The switching dynamic of anodic HfO2 memristors is discussed by analyzing high resolution transmission electron microscope images. Full and partial conductive filaments are visualized, and apart from their modeling, a concurrency of filaments is additionally observed. This is responsible for the multilevel switching mechanism in HfO2 and is related to device failure mechanisms.
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