Enhanced spectroscopic gas sensors using in-situ grown carbon nanotubes

Abstract

In this letter we present a fully complementary-metal-oxide-semiconductor (CMOS) compatible microelectromechanical system (MEMS) thermopile infrared (IR) detector employing vertically aligned multi-walled carbon nanotubes (CNT) as an advanced nano-engineered radiation absorbing material. The detector was fabricated using a commercial silicon-on-insulator (SOI) process with tungsten metallization; comprising a silicon thermopile and a tungsten resistive micro-heater, both embedded within a dielectric membrane formed by a deep-reactive ion etch following CMOS processing. In-situ CNT growth on the device was achieved by direct thermal chemical vapour deposition (T-CVD) using the integrated micro-heater as a micro-reactor. The growth of the CNT absorption layer was verified through scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The functional effects of the nanostructured ad-layer were assessed by comparing CNT-coated thermopiles to uncoated thermopiles. Fourier transform infrared (FTIR) spectroscopy showed that the radiation absorbing properties of the CNT adlayer significantly enhanced the absorptivity, compared with the uncoated thermopile, across the IR spectrum (3 μm-15.5 μm). This led to a four-fold amplification of the detected infrared signal (4.26 µm) in a CO 2 non-dispersive-infra-red (NDIR) gas sensor system. The presence of the CNT layer was shown not to degrade the robustness of the uncoated devices; whilst the 50 % modulation depth of the detector was only marginally reduced by 1.5 Hz. Moreover, we find that the 50 % normalized absorption angular profile is

Oxidized single-walled carbon nanotubes and nanocones: a DFT study

“…Functionalization of carbon nanostructures changes their mechanical, structural and solubility properties. As a result, novel materials are obtained with improved processability, necessary for building molecular devices suitable for constitution of electronic systems, 1,2 gases sensors and storage, 3,4 heavy metal and nano-metallic particulate selective adsorption devices 5,6 and also drug delivery systems. [7][8][9][10] The functionalization is made through physical 11,12 or chemical routes, 13,14 doping with different atoms 15 and oxidation reactions [16][17][18][19][20][21][22] of the nanostructure surface.…”

A low cost MEMS based NDIR system for the monitoring of carbon dioxide in breath analysis at ppm levels

“…Fortunately, for CO2 breath analysis, the level of CO2 is in the range of 4 to 5 %, thus the CO2 concentration can be measured with relative short paths lengths. It has previously been reported path lengths of 10 mm or lower and up to 10 cm have been used for CO2 detection in the concentrations expected on breath [32,33]. Preliminary experiments, with a stable 80 mm path length (in an aluminium chamber shown in Figure 3) were performed to provide a stable benchmark standard.…”

Towards Integrated Mid-Infrared Gas Sensors

“…CMOS integrated MIR emitters, with drive and temperature control, can feature membrane diameters as small as 600 μm, and have ∼50 mW DC power consumption (∼1 mW optical output power), when operated at 550 ∘C, with good emission for λ > 8 μm (Figure 4a). We have also showed that the radiation properties of carbon nanotubes (CNTs) can significantly enhance both emissivity [95] and absorptivity [94] of MIR devices, due to their blackbody-like behaviour (nearly unity) (Figure 4b).…”