Hydrogen sensing with diameter- and chirality-sorted carbon nanotubes

Area of Science:

• Materials Science
• Nanotechnology
• Chemical Sensing

Background:

• Palladium's work function is sensitive to hydrogen, enabling potential work function-based sensors.
• Schottky barriers at metal-semiconductor interfaces can be modulated by surface conditions.
• Single-walled carbon nanotubes (SWNTs) offer unique electronic properties for sensor applications.

Purpose of the Study:

• To investigate the hydrogen sensing capabilities of Schottky barrier field-effect transistors (FETs).
• To utilize diameter- and chirality-sorted semiconducting SWNTs (s-SWNTs) with palladium electrodes.
• To explore the influence of SWNT diameter and device operation on hydrogen sensitivity and stability.

Main Methods:

• Fabrication of Schottky barrier FETs using palladium electrodes and sorted s-SWNTs.
• Characterization of device response to hydrogen gas at 100 ppm in air.
• Comparison of sensing performance between s-SWNTs and few-layer graphene (FLG) devices.
• Analysis of long-term sensing stability under different gate voltage conditions.

Main Results:

• Achieved an unprecedented 100-fold increase in on-state conductance for s-SWNT devices (1-1.6 nm diameter) upon exposure to 100 ppm H2.
• Observed negligible hydrogen sensing in Pd-contacted FLG devices, consistent with the absence of a significant Schottky barrier.
• Detected a vanishing sensitivity in small-diameter SWNTs, attributed to hydrogen spillover and chemisorption altering the nanotube work function.
• Demonstrated that periodic gate voltage inversion is crucial for achieving long-term sensing stability, mitigating gate screening effects.

Conclusions:

• Schottky barrier FETs based on specific diameter s-SWNTs are highly effective for hydrogen detection.
• The sensing mechanism is linked to the modulation of the palladium-semiconductor interface and nanotube properties.
• Device stability requires careful management of gate bias to overcome charge accumulation and screening effects.