Chih-Kai Yang

Noncovalent functionalization of carbon nanotubes by aromatic organic molecules

The interaction between carbon nanotubes and organic molecules including benzene (C6H6), cyclohexane (C6H12), and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ:u2009C8N2O2Cl2) have been studied using first principles calculations. The equilibrium tube-molecule distance, adsorption energy, and charge transfer are obtained. The hybridization between the DDQ molecular level and nanotube valence bands transforms the semiconducting tube into a metallic one. Coupling of π electrons between tubes and aromatic molecules are observed. Our results show that noncovalent functionalization of carbon nanotubes by aromatic molecules is an efficient way to control the electronic properties of carbon nanotubes.

A metallic graphene layer adsorbed with lithium

We found, by density functional calculation, that lithium atoms can be bonded to a graphene layer alternately on both sides by distorting the relative positions of the carbon atoms in the honeycomb lattice. Compared to the recently synthesized graphane by hydrogenation in which each carbon is pulled out of the plane by hydrogen, the carbon is pushed off instead by the attached lithium. And, surprisingly, the counterintuitive structure is a conductor. This should give consequences to its application in lithium storage.

Exploring the interaction between the boron nitride nanotube and biological molecules

We study the interaction between boron nitride nanotubes (BNNTs) and a variety of biological molecules using density functional theory. Some amino acids and nitrogenous bases that are parts of nucleotides are inserted inside the cavity of the BNNT and the overall electronic structure calculated. We conclude that there is no bonding or chemical adsorption between the wide band-gap BNNT and the biological molecules considered. This suggests that BNNTs can be used as a smooth nanoscale channel for transporting biological molecules.

Theoretical study of the single-walled gold (5,3) nanotube

Total energy calculations based on first principles reveal that a (5,3) gold nanotube has a helical pitch of 10.05nm or a natural length of 20.1A per unit cell at the minimum total energy. The figure is about 9.5% shorter than the experimental pitch of 11nm under stress from the experimental setup. Energy bands for both pitches are similar, giving five units of quantum conductance. The calculations indicate that the single-walled gold (5,3) nanotube is a robust and stable conducting wire suitable for nanoelectronic applications.

Magnetic molecules made of nitrogen or boron-doped fullerenes

By using density functional theory, we investigate the electronic structure of a fullerene C60 molecule doped with a nitrogen atom on its surface. We find that the impurity is strongly bonded to the carbon cage and the C60N molecule has a large magnetic moment of 3.00μB. We also study the adsorption of a boron atom on the fullerene. The bonding is not as strong but still provides a fairly stable structure. Most importantly, the C60B molecule possesses a magnetic moment of 0.99μB. Both molecular magnets should be useful for the application in magnetic detection, quantum information, and spintronics.

Low-energy electronic structures of nanotube-nanoribbon hybrid systems

Abstract The electronic properties of a nanotube–nanoribbon hybrid system are investigated by the first-principles calculations. This hybrid system is constructed by a zigzag carbon nanotube and an armchair graphene nanoribbon. Its electronic structures strongly depend on the nanotube location and stacking configuration. The interactions between the two subsystems would break the state degeneracy, open subband spacings, and induce more band-edge states. The predicted results could be measured directly by the scanning tunneling spectroscopy.

TRANSITION METAL/CARBON NANOTUBE HYBRID STRUCTURES

The unique geometry of carbon nanotubes offers an ideal template for designing one-dimensional metal/nanotube hybrid structures. Through ab initio calculations we found that transition-metal/nanotube hybrid structures exhibit very interesting physical properties. The hybrid structures can have drastically different conduction properties from those of the pristine tubes and considerable magnetic moments. In some instances perfect spin polarization is achieved. The results point to a new and promising approach that uses such hybrid structures as devices for spin-polarized transport, which is expected to provide immense applications in the emerging field of spintronics.