One-Dimensional Phonon State of 4He Films Adsorbed in Straight Nanopores

We have studied heat capacities of ⁴He adsorbed in straight nanopores 1.8, 2.2, and 2.8 nm in diameter. Heat capacities of the ⁴He fluid film on the solid layer at 0.08–0.4 K show power laws close to T in 1.8 nm pores, close to T ² in 2.8 nm pores, and a crossover from T to T ² with increasing temperature in 2.2 nm pores. These heat capacities are explained by a model assuming a phonon dispersion with continuous one-dimensional (1D) states in the axial direction and discrete energy levels in the azimuthal direction. By fitting experimental data to the model, the phonon velocity along the pore axis and the energy gap for propagation in the cross section are derived. At temperatures sufficiently lower than the energy gap, where the thermal wave length of phonons is much longer than the effective pore diameter, the ⁴He fluid films show a T-linear heat capacity of 1D phonons propagating only along the pore axis. At higher temperatures, a 1D-2D crossover of phonons occurs.      

Fabrication of 5.8‐in. OTFT‐driven flexible color AMOLED display using dual protection scheme for organic semiconductor patterning

Abstract— A 5.8‐in. wide‐QQVGA flexible color active‐matrix organic light‐emitting‐diode (AMOLED) display consisting of organic thin‐film transistors (OTFTs) and phosphorescent OLEDs was fabricated on a plastic film. To reduce the operating voltage of the OTFTs, Ta₂O₅ with a high dielectric constant was employed as a gate insulator. Pentacene was used for the semiconductor layer of the OTFTs. This layer was patterned by photolithography and dry‐etched using a dual protection layer of poly p‐xylylene and SiO₂ film. Uniform transistor performance was achieved in the OTFT backplane with QQVGA pixels. The RGB emission layers of the pixels were formed by vacuum deposition of phosphorescent small molecules. The resulting display could clearly show color moving images even when it was bent and operated at a low driving voltage (below 15 V).     

The interaction between a crack and a dislocation dipole

This paper presents the results of an analysis which considers the interaction between a semi-infinite crack and a dislocation dipole. Applying the operator derived by Denda [1] to the crack/dislocation interaction solution developed by Lo [2], explicit expressions are obtained for the stress intensity factors at the tip of the crack. Results are computed and discussed for a variety of geometrical configurations, with the intent of developing an understanding of the effects of position and orientation of the dislocation dipole on crack tip shielding and antishielding. The solution can be used as a Green's function in semi-empirical analyses such as the one proposed by Chudnovsky [3], where the interaction between a crack in a polymeric material and the damage (crazing) which surrounds it is solved by experimentally measuring the crack opening displacements of the crazes and calculating the amount of toughening caused by the damage.

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Résumé On présente les résultats d'une analyse prenant en compte l'interaction entre une fissure semi-infinie et une paire de dislocations. En appliquant un opérateur dû à Denda à la solution d'interaction fissure/dislocation proposée par Lo, on obtient des solutions explicites pour les facteurs d'intensité de contraintes à l'extrémité de la fissure. Les résultats sont calculés et discutés pour une gamme de configurations géométriques, dans le but de développer une intelligence des effets de la position et de l'orientation de la paire de dislocations sur l'effet de couverture ou de non-couverture à l'extrémité de la fissure. La solution peut être utilisée sous la forme d'une fonction de Green dans les analyses semi-empiriques telles que celles proposées par Chudnovsky, où l'interaction entre une fissure dans un matériau polymère et l'endommagement (criques) qui l'environne est résolue par une mesure expérimentale des COD des criques et par le calcul de l'intensité du durcissement associé à l'endommagement.

     

Determination of reaction models from experimental measurements

It is demonstrated through the use of transformation relations, function approximation and error limits that it is impossible to distinguish among rival gasification models using just a single temperature programmed reaction experiment. Two experiments at different heating rates must be used and the ratio between rates is important. These depend on the models to be distinguished.     

Carbon nanofibers decorated SiC foam monoliths as the support of anti-sintering Ni catalyst for methane dry reforming

A silicon carbide (SiC) foam monolith decorated with a carbon nanofibers (CNFs) layer was employed as the catalyst support for Ni-based catalyst preparation, used for the CO₂ dry reforming of methane (DRM) reaction. The loading amount of CNFs on the SiC foam monolith was 6.6 wt.%, which obviously increased the surface area of the pristine SiC foam from 4 m²/g to 24 m²/g. The prepared CNFs layer strongly attached to the pristine SiC surface and was considerably stable even after 100 h time on stream (TOS) DRM reaction. The CNFs decorated SiC composite support provided more anchorage sites for improving the dispersion of the Ni particles and enhanced the metal-support interaction compared to the pristine SiC support. Compared with other catalysts such as Ni/SiC and Ni/CNFs, the Ni/CNFs-SiC catalyst exhibited not only the highest activity but also remarkable stability during DRM reaction. The XPS and SEM-EDS results showed that the carbon deposition over the nickel surface of Ni/CNFs-SiC catalyst was much less than those of Ni/SiC and Ni/CNFs catalysts. In addition, the XRD analysis verified that almost no sintering of nickel particle was detected over the Ni/CNFs-SiC catalyst, which was prepared with CNFs-SiC composite as catalyst support, even after 100 h TOS DRM reaction at 750 °C.     

Slippage of 4He Films and Precursor Phenomenon of Superfluidity

We have carried out quartz crystal microbalance (QCM) experiments for ⁴He films on an exfoliated single-crystalline graphite using a 32 kHz tuning fork, and have measured the temperature dependence of the resonance frequency and the Q value for various areal densities and oscillation amplitudes. Comparing with the previous experiments for Grafoil, the decoupling of the films due to the slippage or the superfluidity was larger than that of Grafoil, and the competition between the slippage and the superfluidity was observed in three-atom thick films. Furthermore, it was found that the slippage is suppressed gradually at higher temperature than the superfluid onset T _c , and that the relaxation time decreases at low temperatures while it obeys the Arrhenius law at high temperatures. These results suggest a precursor to the superfluidity of ⁴He films.     

Quantum States of Helium Atoms Confined in Nanocage in Na-Y Zeolite

We have studied the heat capacities of heliums adsorbed in Na-Y zeolite down to 70 mK. The Y-type zeolite has void cages 1.3 nm in diameter connected through narrow apertures 0.8 nm in diameter. In the nanopores at low temperatures, the second-layer He adatoms can be confined in each cage by the first solid layer. In the quantum fluid region above the second-layer promotion, where the heat capacities show qualitative differences between ⁴He and ³He, the heat capacities of ³He adatoms and the thermal relaxation processes show large and non-monotonic changes when one ³He atom is added in each cage. These results strongly suggest that the quantum fluid formed in Na-Y zeolite is not fluid film spread over the entire substrate but quantum clusters confined in each cage.