ABSTRACT
A modified method for the fabrication of a highly crystallized layer of aluminum oxide on a NiAl(110) surface is reported. The fabrication method involves the multistep selective oxidation of aluminum atoms on a NiAl(110) surface resulting from successive oxygen deposition and annealing. The surface morphology and local electronic structure of the novel aluminum oxide layer were investigated by high-resolution imaging using scanning tunneling microscopy (STM) and current imaging tunneling spectroscopy. In contrast to the standard fabrication method of aluminum oxide on a NiAl(110) surface, the proposed method produces an atomically flat surface exhibiting a hexagonal superstructure. The superstructure exhibits a slightly distorted hexagonal array of close-packed bright protrusions with a periodicity of 4.5 ± 0.2 nm. Atomically resolved STM imaging of the aluminum oxide layer reveals a hexagonal arrangement of dark contrast spots with a periodicity of 0.27 ± 0.02 nm. On the basis of the atomic structure of the fabricated layer, the formation of α-Al2O3(0001) on the NiAl(110) surface is suggested.
ABSTRACT
We developed a host-guest methodology for separation of single-walled carbon nanotubes (SWNTs) according to the handedness, diameter and metallicity by the use of diporphyrin nanotweezers and nanocalipers. Although the pyrene has been frequently used to replace porphyrin, due to a similar affinity to the surface of SWNTs and better availability, the extraction and recognition abilities of dipyrene nanotweezers were not so good as those of diporphyrin ones as we reported previously. However, introduction of a tert-butyl substituent at the 7'-position of 2-pyrene is found to enhance the extraction and recognition abilities of dipyrene nanotweezers and nanocalipers. That is, (6,5)-SWNTs were obtained in high purity by use of bis(tert-butylpyrene) nanotweezers with a phenanthrene spacer and metallic SWNTs were highly enriched by use of bis(tert-butylpyrene) nanocalipers with a carbazole-anthracene-carbazole spacer.
Subject(s)
Nanotechnology/methods , Nanotubes, Carbon/chemistry , Pyrenes/chemistry , Combinatorial Chemistry Techniques , Molecular StructureABSTRACT
We have been developing the methodology to discriminate the handedness and diameter of single-walled carbon nanotubes (SWNTs) through molecular recognition using chiral diporphyrin nanotweezers. Although relatively small diameters of SWNTs (<1.0 nm) were recognized well, nanotweezers were not able to form stable complexes with the SWNTs having the diameters >1.0 nm. In this context, we designed chiral diporphyrin with a much larger cavity, namely, "nanocalipers". The feature of the newly designed host molecule is: (1) long spacer with more than 1.4 nm consisting of three aromatic moieties; (2) nearly parallel orientation of the two porphyrins; (3) restricted conformation by biaryl linkages of the porphyrin-carbazole and carbazole-anthracene; (4) strong interaction of two porphyrins and anthracene with the surface of a SWNT through π-π stacking; and (5) stereogenic centers at the periphery of porphyrins discriminating helicity of SWNTs. As expected, we obtained optically active SWNTs with >1.0 nm in diameter and, unexpectedly, enriched metallic SWNTs over semiconducting ones. The optically active metallic SWNTs are identified for the first time, in addition to the optically active semiconducting SWNTs with such large diameters. The nanocalipers are found to recognize the diameter, handedness, and metallicity of SWNTs simultaneously.
