When is a Polynomial Ideal Binomial After an Ambient Automorphism?

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Hydrogen sorption kinetics in MgH2 and TiH2 thin films

The diffusion mechanism of H in metals and metal hydrides is studied particularly at high H2 pressures. Thin films of Mg and Ti offer a convenient tool to quantify the atomic transport. We show how different parameters of hydrogenation affect the kinetics. At 200°C, an interface controlled reaction is predominant and a linear regime of hydrogenation is observed, whereas at 300°C a parabolic regime is detected. In Mg, the hydride forms from the surface to the substrate whereas in Ti, growth of TiH2 starts from the substrate. Linear kinetics is seen during hydrogenation of Ti films, which is due to the naturally formed oxide layer on top, measured to be about 10nm thick. In the studied high pressure regime, the hydrogenation is not pressure dependent any more. Quantitative calculation of the growth rate and the diffusion coefficient of H in the hydrides is presented.</p

The role of surface oxides on hydrogen sorption kinetics in titanium thin films

Titanium is presently discussed as a catalyst to accelerate the hydrogenation kinetics of hydrogen storage materials. It is however known that H absorption in Ti decisively depends on the surface conditions (presence or absence of the natural surface oxide). In this work, we use Ti thin films of controlled thickness (50–800 nm) as a convenient tool for quantifying the atomic transport. XRD and TEM investigations allow us to follow the hydrogenation progress inside the film. Hydrogenation of TiO2 /Ti bi-layers is studied at 300 °C, for different durations (10 s to 600 min) and at varying pressures of pure H2 atmosphere. Under these conditions, the hydrogenation is found to be linear in time. By comparing films with and without TiO2 , as well as by studying the pressure dependence of hydrogenation, it is demonstrated that hydrogen transport across the oxide represents the decisive kinetic barrier rather than the splitting of H2 molecules at the surface. Hydrogenation appears by a layer-like reaction initiated by heterogeneous nucleation at the backside interface to the substrate. The linear growth constant and the H diffusion coefficient inside the oxide are quantified, as well as a reliable lower bound to the hydrogen diffusion coefficient in Ti is derived. The pressure dependence of hydrogen absorption is quantitatively modelled. </p

Wavelength‐Selective Folding of Single Polymer Chains with Different Colors of Visible Light

Photochemistry allows chemists to exert control over chemical reactions with spatiotemporal precision. Furthermore, light holds the potential to not only gate when and where but also which reaction takes place. Herein, two photocycloaddition reactions-initiated by different colors of visible light—are utilized to control the intramolecular crosslinking of single polymer chains. Irradiation with blue light (λmax = 470 nm) triggers a [2 + 2] photocycloaddition inducing an initial intramolecular crosslinking reaction, whereas subsequent irradiation with violet light (λmax = 415 nm) induces a [4 + 4] photocycloaddition, fully compacting the dual photoreactive polymer into a single-chain nanoparticle. Importantly, both crosslinked states are accessible under ultra-mild conditions requiring nothing but two different colors of visible light. The reported strategy of wavelength-selective crosslinking degrees provides key potential to be translated into materials applications for the remote control of mechanical properties on the molecular level.</p