Contact Theory vs Bulk (Doping) Theory

The device properties are generally determined by (1) the electrode contact and (2) the bulk channel. They may compete, but in a certain situation, one is more dominant than the other. There are two theories for the gas detection mechanism using nanotubes (CNTs) or nanowires (NWs). The contact theory can explain the gas detection mechanism even when the CNT has no direct chemical interaction resulting in charge transfer. The CNT conductance will be modified significantly through the transport property change across the contact. Let's assume there is an interaction between the gas and a metallic electrode. When the circuit is open, positive charges appear in the metallic electrode, but there are no charges in the CNT. But when the circuit is closed, positive charges will appear in the CNT side, too. This is essentially a pair of charged capacitors in series. The electrostatics there will modify the Schottky barrier. According to the contact theory, the gas is detected at the CNT electrode contact. The bulk theory assumes the gas molecules remove charges, and leave the opposite charges in the CNT. In this picture, the gas-CNT chemical interaction resulting in charge transfer must exist. According to the bulk theory, the gas is detected at the CNT, and the CNT contact does not play any role. The same thing goes with the substrate, STM tip, or generally environment. Device characteristics would be significantly influenced with them.

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Related Papers

Agenda		Contact Theory	Substrate effects	Bulk Theory	Contact Theory
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CNT Tunneling at contact		APL_01
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CNT Gas detection experiment		ACS_Nano_09
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T. Yamada, "Substrate Effects on Electronic Properties of Atomic Chains," J. Vac. Sci. Technol. A 17 (4), 1463-1468 (1999).

T. Yamada, "Analysis of submicron carbon nanotube field-effect transistors," Appl. Phys. Lett. 76 (5), 628-630 (2000).

T. Yamada, "Modeling of electronic transport in scanning tunneling microscope tip carbon nanotube systems," Appl. Phys. Lett. 78 (12), 1739-1741 (2001).

T. Yamada, "Modeling of Kink-shaped Carbon-nanotube Schottky Diode with Gate Bias Modulation," Appl. Phys. Lett. 80 (21), 4027-4029 (2002).

T. Yamada, Chapter 7, "Nanoelectronics Applications" in Carbon Nanotubes: Science and Applications, ed. by M. Meyyappan, (CRC, Boca, Raton, 2004).

T. Yamada, "Modeling of Carbon Nanotube Schottky Barrier Modulation under Oxidizing Conditions," Phys. Rev. B 69 (12), 125408 (2004).

T. Yamada, "Equivalent circuit model for carbon nanotube Schottky barrier: Influence of neutral polarized gas molecules," Appl. Phys. Lett. 88 (8), 083106 (2006).

T. Yamada, T. Saito , M. Suzuki , P. Wilhite , X. Sun , N. Akhavantafti , D. Fabris , and C. Y. Yang, "Tunneling Between Carbon Nanofiber and Gold Electrodes," J. Appl. Phys. 107 (4), 044304 (2010).