The objectives of this research are to examine the feasibility of real-time sensing of chemical and biological species by using the unique materials and electronic properties of carbon nanotubes, and to demonstrate the multi-agent sensing and information processing capabilities of such devices.

The current rectification property of chemical-vapor-deposited (CVD), as-grown, single-walled carbon nanotubes (SWNTs) was investigated. The long strands of SWNT bundles were used to fabricate multiple arrays of switching devices with channel lengths of 3, 5, 7, and 10um on a 15×15mm2 silicon dioxide (SiO2) on silicon (Si) substrate. The devices were fabricated by photolithographically depositing a 100-nm layer of gold (Au) on top of 10-nm-thick titanium (Ti) to serve as electrodes with varying source (S) and drain (D) separation. The dimension of each electrode pad was 250 × 250 um. The samples were then annealed at 200°C for 30 minutes in constant flow of nitrogen to eliminate possible oxide defects.

AFM topographical image (a) of as-grown CVD Nanotubes, and (b) the related height profile.
A majority of the fabricated devices, regardless of channel length, showed current rectification characteristics with high throughput of current (I) in the forward bias (V). Atomic force microscope (AFM) analysis of the device structure and surface topology of SWNTs suggests the observed rectification of current results from surface irregularities and is possibly due to change in the chirality of a single tube. Using fabricated SWNT field-effect transistors (FETs), the effects of gases, particularly O2 and N2, were demonstrated on the fabricated devices.

The present process is compatible with current industry-standard silicon electronics and could be easily transitioned for mass fabrication of the SWNT switching devices. The increase in current magnitude in the presence of oxygen and nitrogen shows that the devices composed of SWNTs can be used in sensor applications.

This work was done by Govind Mallick and Shashi P. Karna of the Army Research Laboratory. For more information, download the Technical Support Package (free white paper) at under the Materials category. ARL-0076

This Brief includes a Technical Support Package (TSP).
Real-Time Intelligent Chemical and Biological Nanosensors on a Flexible Platform

(reference ARL-0076) is currently available for download from the TSP library.

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This article first appeared in the April, 2010 issue of Defense Tech Briefs Magazine.

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