排序方式: 共有35条查询结果,搜索用时 15 毫秒
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A. Borgschulte R. Gremaud S. de Man R.J. Westerwaal J.H. Rector B. Dam R. Griessen 《Applied Surface Science》2006,253(3):1417-1423
The optical properties, the switching kinetics and the lifetime of hydrogen switchable mirrors based on Mg-Ni alloys are determined with particular regard to the composition of the optically active metal-hydride layer in combination with the thickness of the catalytic capping layer. For this, a high-throughput experiment is introduced. The switching kinetics and the reversibility of switchable mirrors are strongly thickness dependent, though the details hinge on the fine structure of the clustered capping layer. Therefore, the kinetics is correlated with the surface structures of Pd on MgyNi1−y as investigated by scanning tunneling microscopy. The results are explained by the so-called strong metal-support interaction (SMSI) state, characterized by a complete encapsulation of the capping layer clusters by oxidized species originating from the support. The SMSI-effect is less important with increasing Pd-layer thickness, and is suppressed by a good wetting of the Pd-clusters on the optically active film. This explains the critical thickness for the catalyzed hydrogen uptake observed in many switchable mirror systems. Moreover, the degradation of the kinetics during cycling is found to depend on the Pd-layer thickness and on the gas environment. Only films, covered with at least 15 nm Pd, show small degradation caused by the SMSI-effect. The SMSI-effect is partly reversible: after changing the gas environment from hydrogen to oxygen, the oxide on the Pd-clusters can be partly removed. 相似文献
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Prof. Dr. Ronald Griessen Dr. Christiaan Boelsma Herman Schreuders Prof. Dr. Chase P. Broedersz Dr. Robin Gremaud Prof. Dr. Bernard Dam 《Chemphyschem》2020,21(15):1632-1643
Enthalpy-entropy compensation (EEC) is very often encountered in chemistry, biology and physics. Its origin is widely discussed since it would allow, for example, a very accurate tuning of the thermodynamic properties as a function of the reactants. However, EEC is often discarded as a statistical artefact, especially when only a limited temperature range is considered. We show that the likeliness of a statistical origin of an EEC can be established with a compensation quality factor (CQF) that depends only on the measured enthalpies and entropies and the experimental temperature range. This is directly derived from a comparison of the CQF with threshold values obtained from a large number of simulations with randomly generated Van ‘t Hoff plots. The value of CQF is furthermore a direct measure of the existence of a genuine isoequilibrium or isokinetic relationship. 相似文献
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Lohstroh W Westerwaal RJ Noheda B Enache S Giebels IA Dam B Griessen R 《Physical review letters》2004,93(19):197404
In addition to a mirrorlike (Mg2Ni) and a transparent (Mg2NiH4) state, thin films of Mg2NiHx exhibit a remarkable black state with low reflection over the entire visible spectrum, essentially zero transmission and a low electrical resistivity. Such a black state is not explicable for a homogeneous layer since a large absorption coefficient always yields substantial reflection. We show that it results from a self-organized and reversible double layering of metallic Mg2NiH0.3 and semiconducting Mg2NiH4. 相似文献
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A. J. J. van Dalen M. R. Koblischka R. Griessen M. Jirsa G. Ravi Kumar 《Physica C: Superconductivity and its Applications》1995,250(3-4):265-274
Superconducting current densities js and dynamic relaxation rates Q d ln js/d In(dBe/dt), where dBe/dt is the sweep rate of the external magnetic field Be, were measured as a function of temperature (5 K < T < 65 K) in magnetic fields up to 7 T on a twin-free DyBa2Cu3O7−δ single crystal by means of a high-sensitivity capacitance torque magnetometer. Above 15 K, we observe a “fishtail” effect, i.e. a pronounced minimum in the js(Be) curve at fields around Be = 1 T. The relaxation rate Q shows an anomalous increase at low fields which is correlated to the minimum in the js(Be) curve. Both the js versus Be and Q versus Be data are used as input parameters into the generalized inversion scheme developed by Schnack et al. [Phys. Rev. B 48 (1993) 13178] to calculate the true critical current density jc which is by definition independent of relaxation effects. Interestingly, the jc(Be, T) curves derived in this way do not show a minimum. This points clearly to a dynamic contribution to the fishtail effect. The true critical current density jc(Be, T) decreases weakly with increasing Be over the entire measured temperature and field range, as expected for single-vortex pinning. This indicates that the observed fishtail effect is not caused by a crossover from single-vortex pinning to pinning of flux bundles. The temperature dependence of jc is in good agreement with the predictions of a model based on single-vortex pinning caused by spatial fluctuations in the charge-carrier mean free path. 相似文献
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Par G. Brändli R. Griessen 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1971,22(4):737-741
Summary The deformation of an ellipsoid under the influence of the non-uniform form effect has been obtained from an exact solution of the elastic equations using the boundary conditions arising from an appropriate approximation of the surface stresses. In the special case of the sphere our results agree with the exact calculation of Brown and Gersdorf. 相似文献
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