Item

Abstract

The preferred adsorption sites of xenon in the recently synthesized metal-organic framework MFU-4l(arge) possessing a bimodal pore structure (with pore sizes of 12 angstrom and 18.6 angstrom) were studied via the combination of low temperature thermal desorption spectroscopy and in situ X-ray powder diffraction. The diffraction patterns were collected at 110 K and 150 K according to the temperature of the desorption maxima. The maximum entropy method was used to reconstruct the electron density distribution of the structure and to localize the adsorbed xenon using refined data of the Xe-filled and empty sample. First principles calculations revealed that Xe atoms exclusively occupy the Wyckoff 32f position at approximately 2/3 2/3 2/3 along the body diagonal of the cubic crystal structure. At 110 K, Xe atoms occupy all 32 f positions (8 atoms per pore) while at 150 K the occupancy descends to 25% (2 atoms per pore). No Xe occupation of the small pores is observed by neither experimental measurements nor theoretical studies. Large scale, homogeneous quasi-free standing monolayer graphene is obtained on a (111) oriented cubic SiC bulk crystal. The free standing monolayer was prepared on the 3C-SiC(111) surface by hydrogen intercalation of a (6 root 3 x 6 root 3)R30 degrees-reconstnicted carbon monolayer, so-called zerolayer graphene, which had been grown in Ar atmosphere. The regular morphology of the surface, the complete chemical and structural decoupling of the graphene layer from the SiC substrate as well as the development of sharp monolayer pi-bands are demonstrated. On the resulting sample, homogeneous graphene monolayer domains extend over areas of hundreds of square-micrometers.