Variation of Electron Level Enables Semiconducting-to-Metallic Transition in Single Phenalenyl-Based Molecules
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graphene layers, which eventually form the nanofibers, were assisted by dynamic formation of monoatomic step ledges on the graphene–Ni interface. The researchers performed density functional theory calculations to understand the origins of the interfacial process and the transport of C and Ni atoms along the graphene–Ni interface. The surface transport of the C atoms was shown to be the rate-limiting step for the nanofiber growth. The experimental results and theoretical calculations indicate that the step edges on the Ni surface act as growth centers for graphene growth because C binds more strongly to such sites. This mechanism is likely to be of broad significance for any metal-catalyzed nanofiber growth, according to the researchers. They said that this study reveals the first direct glimpses of the initial stages of nanofiber growth using nanoscale real-time growth observations. Metallic step-edges acting as spatio-temporal dynamic growth sites may be important for understanding other types of catalytic reactions and nanomaterial syntheses. GOPAL RAO
Variation of Electron Level Enables Semiconducting-to-Metallic Transition in Single PhenalenylBased Molecules Quantum transport properties of singlemolecule electronic devices are affected not only by the choice of molecules but also by the interface structures used. K. Tagami and M. Tsukada from the University of Tokyo and L. Wang from Southern Yangtze University in China studied theoretically the conductive properties of single boron- and nitrogensubstituted phenalenyl molecules (C13H9) and found that they can tune the properties of the molecules from semiconducting to metallic depending on the type of central atom used. The researchers reported in the February issue of Nano Letters that by changing the type of central atom from carbon to nitrogen or boron, they can dramatically alter the transport properties of the system. The researchers calculated the atomic coordinates (i.e., the size) of each molecule, and connected it to electrodes by bonding a mercapto-vinyl group to the α or β site, which is the second- and thirdnearest to the central atom site, respectively. Molecules connected through β sites demonstrate a conduction channel that is energetically very close to the Fermi energy of the gold electrodes. In contrast, with the connection through the β site, nitrogen- and carbon-containing phenalenyl molecules become semiconMRS BULLETIN/MARCH 2004
ducting, while the boron-type displays metallic properties. The researchers also found that when the electrodes are connected to the β sites, the conductance through the carbon-containing phenalenyl molecule is spin-dependent. The researchers said that the change in the transport features originates from the spatial distribution of the nonbonding molecular orbital, which has amplitude only on the α sites. These features do not change when the researchers substitute the central atom of phenalenyl with the nitrogen; however, if they substitute it with the boron atom, then the quantum transport occurs through the or
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