研究目的
Investigating the field emission patterns from various types of carbon nanotubes (CNTs) and hydrogen terminated CNTs (H-CNTs) using time-dependent density functional theory (TD-DFT).
研究成果
The emission patterns of CNTs and H-CNTs correspond to the atoms located in the tube tip, with armchair CNTs showing focused beams and zigzag CNTs showing unfocused beams. The study highlights the importance of CNT structure in determining emission patterns and suggests further investigation into the causes of focusing features.
研究不足
The study does not explain the cause of the different focusing features observed between armchair and zigzag CNTs. The potential distributions and wave functions in the direction parallel to the tube axis were checked but did not reveal the cause.
1：Experimental Design and Method Selection:
The study employs time-dependent density functional theory (TD-DFT) method using the octopus code for calculating field emission patterns. The calculation is non-periodic, with wave function and density zero at the boundary of the simulation box. The external electric field is trapezoidal form constructed with a ramp time of 2.63 fs and constant time of 1.32 fs.
2：63 fs and constant time of 32 fs.
Sample Selection and Data Sources:
2. Sample Selection and Data Sources: Model structures include open-ended and capped armchair and zigzag CNTs and H-CNTs with diameters of 6.8 - 7.2? and lengths of 9 – 12?.
3：8 - 2? and lengths of 9 – 12?.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Simulation box is a cylinder with a 20? in diameter and 60? in length. Grid cutoff energy is 711 eV.
4：Experimental Procedures and Operational Workflow:
The tube geometry is relaxed at zero electric field. Emission patterns are analyzed on planes at different distances from the tube tip top by studying charge densities and wave functions under external electric field.
5：Data Analysis Methods:
Analysis of emission patterns, charge densities, and wave functions to determine focusing characteristics and symmetries.
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