Isotopic and spin selectivity of H_2 adsorbed in bundles of carbon nanotubes

Due to its large surface area and strongly attractive potential, a bundle of carbon nanotubes is an ideal substrate material for gas storage. In addition, adsorption in nanotubes can be exploited in order to separate the components of a mixture. In this paper, we investigate the preferential adsorption of D_2 versus H_2(isotope selectivity) and of ortho versus para(spin selectivity) molecules confined in the one-dimensional grooves and interstitial channels of carbon nanotube bundles. We perform selectivity calculations in the low coverage regime, neglecting interactions between adsorbate molecules. We find substantial spin selectivity for a range of temperatures up to 100 K, and even greater isotope selectivity for an extended range of temperatures,up to 300 K. This isotope selectivity is consistent with recent experimental data, which exhibit a large difference between the isosteric heats of D_2 and H_2 adsorbed in these bundles.Comment: Paper submitted to Phys.Rev. B; 17 pages, 2 tables, 6 figure

Stable and metastable reconstructions at the C60/Au(110) interface

The geometric structure of C60 monolayers on Au(110) has been investigated by scanning tunneling microscopy. C60 rearranges the (11̄0) rows of surface Au atoms into several unique new reconstruction patterns, i.e. (1 7 5), (1 7 6) and stepped (1 7 2). The latter two reconstructions are merely metastable. The stable (1 7 5) reconstruction is characterized by only two adsorption sites, in which each C60 molecule has two ridge Au atoms as nearest neighbours. The changes in the Au reconstruction and the tendency to bind to the most reactive surface atoms indicate strong chemical bonding between the substrate and C60

Observation of a new Au ( 111 ) reconstruction at the interface of an adsorbed C60 overlayer

Scanning tunneling microscope studies of monolayer films of C60 sublimed onto Au ( 111 ) facets reveal a new Au reconstruction at the C60-Au ( 111 ) interface after annealing to a temperature of 700 K. C60 forms two well-ordered hexagonal phases upon which is superimposed a striped texturing with a long-range height modulation of 48 1 \uc5. and a periodicity of 90\u2013160 \uc5. This texturing is shown to arise from a modification of the reconstruction of clean Au ( 111 ) present at the C60-Au interface. The observations indicate that the C60-Au interaction reduces energetic factors favoring compression of the first Au layer resulting in a substantial increase in the unit cell of the Au reconstruction along \u3008110\u3009 directions. This decompression of the first Au layer also favors the formation of a commensurate C60 layer