Matthew Yao

Electronic structure and contact resistance at an open-end carbon nanotube and copper interface

We report a quantum mechanics study on the electronic structure and contact resistance at an open-end carbon nanotube and copper interface. The local density of states near the carbon nanotube (CNT)/Cu interface are computed using density functional theory (DFT), and the transmission coefficient is calculated using a nonequilibrium Green’s function method in conjunction with DFT. The current-voltage relation of the simulating cell is obtained by using the Landauer–Buttiker formula, from which the contact resistance can be determined. Our results indicate that the contact resistance of the Cu/CNT/Cu system is comparable to that of solder/Cu interface in electronic packaging.

Interfacial thermal resistance between metallic carbon nanotube and Cu substrate

A comprehensive model was developed to calculate the interfacial thermal resistance between a metallic carbon nanotube (CNT) and a Cu substrate. The new model accounts for both phonon-mediated and electron-mediated thermal transfer at the interface, as well as the effect of electron-phonon coupling within CNT and Cu. The phonon-mediated thermal transfer was simulated using the non-equilibrium molecular dynamics, while the electron-mediated thermal transfer was computed by the non-equilibrium Green’s function method in conjunction with the density function theory. The effect of electron-phonon coupling within Cu and CNT was investigated by using the kinetic theory. Our results show that (1) electron-phonon coupling within Cu and CNT contributes significantly to the overall thermal transfer across the CNT/Cu interface, and (2) contributions to the overall thermal conductance at the CNT/Cu interface from the electron-mediated thermal transfer are comparable to that from the phonon-mediated thermal transfer.

Effects of local structural defects on the electron transport in a carbon nanotube between Cu electrodes

Using the first-principles approach with the Landauer formalism, we studied the effects of monovacancy and Stone–Wales defects on the electrical conductance of carbon nanotube (CNT) itself and its junction with copper electrodes. We found that the Stone–Wales defect has almost negligible impact on the electrical performance of the CNT(5,5) and its junction with copper at the Fermi level, while the monovacancy can reduce the electrical conductance of the CNT(5,5) significantly and that of the Cu/CNT(5,5)/Cu junction by more than 30%.

Electrical Contact Resistance at the Carbon Nanotube/Pd and Carbon Nanotube/Al Interfaces in End-Contact by First-Principles Calculations

Reported in this paper is a quantum mechanics study on the electronic structure and contact resistance at the interfaces formed when an open-end single-walled carbon nanotube (CNT) is in end-contact with aluminum (Al) and palladium (Pd), respectively. The electronic structures are computed using a density functional theory (DFT), and the transmission coefficient is calculated using a nonequilibrium Green’s function (NEGF) in conjunction with the DFT. The current–voltage relation of the simulating cell is obtained by using the Landauer–Buttiker formula, from which the contact resistance can be determined. Our results show that the electronic structure and electron transport behavior are strongly dependent on the electrode. It is found that the CNT/Pd interface has a weaker bond than the CNT/Al interface. However, the CNT/Pd interface shows a lower electrical contact resistance.

Effects of interwall interaction on the electrical conductance at the junction between a double-walled carbon nanotube and copper electrodes

Considered in this letter are the effects of interwall interaction on the electrical conductance at the junction of a double-walled carbon nanotube (DWCNT) between two copper electrodes. In the end-contact configuration, the effect of interwall interaction on the electrical conductance is rather weak, and both walls of DWCNT contribute to the electronic transport almost as if they are parallel connectors. In the side-contact configuration, not only the inner tube does not contribute to the overall electrical conductance, its presence hinders the electronic transport of the outer wall by causing significant localization of density of states near the Fermi level.

Atomistic simulations of heat transfer at carbon nanotube/Si interfaces

Molecular dynamics simulations are used to compute the thermal conductance at the interface between an open-end single-wall carbon nanotube and a Si substrate for different CNT lengths and temperature. It is found that the thermal conductance at the CNT/Si interface increases with increasing temperature up to 1200K. The enhanced phonon transfer at higher temperatures is mainly due to the anharmonicity at the interfaces. Strong thermal and mechanical coupling is also observed, i.e., the thermal conductance at the CNT/Si interface is dependent on the contact pressure at the interface.

Conducting Properties of a Contact Between Open-End Carbon Nanotube and Various Electrodes

The carbon nanotube (CNT) is becoming a promising candidate as electrical interconnects in nanoscale electronics. This paper reports the electronic structure and the electrical conducting properties at the interface between an open-end single wall CNT (SWCNT) and various metal electrodes, such as Al, Au, Cu, and Pd. A simulation cell consisting of an SWCNT with each end connected to the metal electrode was constructed. A voltage bias is prescribed between the left- and right-electrodes to compute the electronic conductance. Due to the electronic structure, the electron density and local density of states (LDOS) are calculated to reveal the interaction behavior at the interfaces. The first-principle quantum mechanical density functional and non-equilibrium Green’s function (NEGF) approaches are adopted to compute the transport coefficient. After that, the voltage-current relation is calculated using the Landauer-Buttiker formalism. The results show that electrons are conducted through the electrode/CNT/electrode two-probe system. The contact electronic resistance is calculated by averaging the values in the low voltage bias regime (0.0–0.1 V), in which the voltage–current relationship is found to be linear. And the electrical contact conductance of electrode/CNT/electrode system show the electrode-type dependent, however, the amplitude for different electrodes is of the same order.Copyright