Observation and modeling of single-wall carbon nanotube bend junctions

Single-wall carbon nanotube (SWNT) bends, with diameters from similar to 1.0 to 2.5 nm and bend angles from 18 degrees to 34 degrees, are observed in catalytic decomposition of hydrocarbons at 600-1200 degrees C. An algorithm using molecular dynamics (MD) simulation techniques is developed to model these structures that are considered to be SWNT junctions formed by topological defects (i.e., pentagon-heptagon pairs). The algorithm is used to predict the; tube helicities and defect configurations for bend junctions using the observed tube diameters and bend angles. The number and arrangement of die defects at the junction interfaces are found to depend on the tube helicities and bend angle. The structural and energetic calculations using the Brenner potential show a number of stable junction configurations for each bend angle with the 34 degrees bends being more stable than the others. Tight-binding calculations for local density of state and transmission coefficients are carried out to investigate electrical properties of the bend junctions.