Palladium/Single-Walled Carbon Nanotube Back-to-Back Schottky Contact-Based Hydrogen Sensors and Their Sensing Mechanism

Abstract

A Schottky contact-based hydrogen (H2) gas sensor operable at room temperature was constructed by assembling single-walled carbon nanotubes (SWNTs) on a Si/SiO2 substrate bridged by Pd microelectrodes in a chemiresistive/chemical field effect transistor (chemFET) configuration. The Schottky barrier (SB) is formed by exposing the Pd-SWNT interfacial contacts to H2 gas, the analyte it was designed to detect. Because a Schottky barrier height (SBH) acts as an exponential bottleneck to current flow, the electrical response of the sensor can be particularly sensitive to small changes in SBH, yielding an enhanced response to H2 gas. The sensing mechanism was analyzed by I-V and FET properties before and during H2 exposure. I-Vsd characteristics clearly displayed an equivalent back-to-back Schottky diode configuration and demonstrated the formation of a SB during H2 exposure. The I-Vg characteristics revealed a decrease in the carrier mobility without a change in carrier concentration; thus, it corroborates that modulation of a SB via H2 adsorption at the Pd-SWNT interface is the main sensing mechanism.

Enhanced sensing of gas molecules by a 99.9% semiconducting carbon nanotube-based field-effect transistor sensor

“…6,[18][19][20][21] If the Pd contacts the semiconducting CNTs, a Schottky barrier (SB) can be formed at the interface between the Pd electrode and semiconductor CNTs; hence, the Schottky barrier height (SBH) can be modulated, resulting from the change in the Pd work function caused by the adsorption of H 2 molecules. 6,[18][19][20][21][22][23] This SBH modulation could be a useful sensing element for the detection of H 2 because the electric current over and through the SB arising from thermionic emission and tunneling is exponentially dependent on the change in the SBH. Furthermore, the "nanoscale" SB contact comprising the semiconducting CNTs and electrodes has its own advantage, as the open contact geometry allows unhindered diffusion of gas molecules to the barrier and leads to a beneficial effect on the response dynamics, compared to a "macroscopic" SB contact.…”

Optical properties of C-Pd films prepared on silica substrate studied by UV-VIS-NIR spectroscopy

“…It is seen that an absorption coefficient of fullerene increases in the short wavelength, this phenomenon is attenuated in the visible region and completely disappears in the UV region. Therefore, the optical parameters could only be determined for the wavelength λ > ~ 700 nm equations (1)(2)(3)(4)(5). More precise estimation of the value of energy corresponding to particular positions was facilitated after removing the DC component from transmittance function using the high-pass filtering.…”

“…This material can be useful for gas detection, in particular hydrogen detection [1][2][3][4]. One of the simple technology to produce such nanocomposites is Physical Vapour Deposition method (PVD), where C 60 fullerene and palladium acetate are used as a carbon and palladium sources respectively [5][6].…”

Transparent carbon nanotube film as sensitive material for surface plasmon resonance based optical sensors

“…The high ratio surface/volume, the strong sensitivity of the electrical properties to the external ambient [3] make them ideal material for many kind of sensors such strain sensors [4], FET sensors [5], electrochemical biosensors [6] and gas sensors [7]. Moreover SWCNTs are also interesting since they conserve their electrical properties also in thin transparent films [8], suggesting the possible application for optically sensitive transparent films.…”