Showing papers by "Michele Penza published in 2010"

Metal-modified and vertically aligned carbon nanotube sensors array for landfill gas monitoring applications

Abstract: Vertically aligned carbon nanotube (CNT) layers were synthesized on Fe-coated low-cost alumina substrates using radio-frequency plasma enhanced chemical vapour deposition (RF-PECVD) technology. A miniaturized CNT-based gas sensor array was developed for monitoring landfill gas (LFG) at a temperature of 150 degrees C. The sensor array was composed of 4 sensing elements with unmodified CNT, and CNT loaded with 5 nm nominally thick sputtered nanoclusters of platinum (Pt), ruthenium (Ru) and silver (Ag). Chemical analysis of multicomponent gas mixtures constituted of CO(2), CH(4), H(2), NH(3), CO and NO(2) has been performed by the array sensor responses and pattern recognition based on principal component analysis (PCA). The PCA results demonstrate that the metal-decorated and vertically aligned CNT sensor array is able to discriminate the NO(2) presence in the multicomponent mixture LFG. The NO(2) gas detection in the mixture LFG was proved to be very sensitive, e.g.: the CNT:Ru sensor shows a relative change in the resistance of 1.50% and 0.55% for NO(2) concentrations of 3.3 ppm and 330 ppb dispersed in the LFG, respectively, with a wide NO(2) gas concentration range measured from 0.33 to 3.3 ppm, at the sensor temperature of 150 degrees C. The morphology and structure of the CNT networks have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. A forest-like nanostructure of vertically aligned CNT bundles in the multi-walled form appeared with a height of about 10 microm and a single-tube diameter varying in the range of 5-35 nm. The intensity ratio of the Raman spectroscopy D-peak and G-peak indicates the presence of disorder and defects in the CNT networks. The size of the metal (Pt, Ru, Ag) nanoclusters decorating the CNT top surface varies in the range of 5-50 nm. Functional characterization based on electrical charge transfer sensing mechanisms in the metal-modified CNT-chemoresistor array demonstrates high sensitivity by providing minimal sub-ppm level detection, e.g., download up to 100 ppb NO(2), at the sensor temperature of 150 degrees C. The gas sensitivity of the CNT sensor array depends on operating temperature, showing a lower optimal temperature of maximum sensitivity for the metal-decorated CNT sensors compared to unmodified CNT sensors. Results indicate that the recovery mechanisms in the CNT chemiresistors can be altered by a rapid heating pulse from room temperature to about 110 degrees C. A comparison of the NO(2) gas sensitivity for the chemiresistors based on disorderly networked CNTs and vertically aligned CNTs is also reported. Cross-sensitivity towards relative humidity of the CNT sensors array is investigated. Finally, the sensing properties of the metal-decorated and vertically aligned CNT sensor arrays are promising to monitor gas events in the LFG for practical applications with low power consumption and moderate sensor temperature.

Metalloporphyrins-modified carbon nanotubes networked films-based chemical sensors for enhanced gas sensitivity

Abstract: In this paper the effect of the surface functionalization of the carbon nanotubes (CNT) networked films with a metalloporphyrins layer is investigated for gas sensing. Modified film exhibits an increased sensitivity of the electrical resistance towards the concentrations of common volatile compounds (alcohols, amines, aromatic and ketones), at room temperature. Furthermore, a part of the adsorption properties of the functional units is transferred to the sensor signal and, as a consequence, the selectivity of the sensor is also modified. Principal Component Analysis (PCA) demonstrates that the functionalization provides enough selectivity change to turn a triplicate of the same CNT film into an effective sensor array capable of the compounds recognition. These findings are then promising for the development of arrays of CNT-based gas nanosensors with broad selectivities for fingerprinting analysis of complex samples.

Microstructured Optical Fibers Filled with Carbon Nanotubes: Photonic Bandgap Modification and Sensing Applications

Abstract: In the recent years, a new concept is emerging in the scientific community dealing with the possibility to use optical fibers as platform to develop all-in-fiber multimaterial and multifunctional optical devices and systems (Abouraddy et al., 2007). The key feature of these new optoelectronic devices relies on the proper integration of specific materials, such as conductors, semiconductor and insulator, into the same optical fiber in order to attain advanced functionalities within a single optical fiber. A promising building block to realize these multifunctional optoelectronic devices are the Microstructured Optical Fibers (MOFs) which, being composed by a periodic distribution of micrometric air-holes running uniformly along the fiber length (Knight et al., 2003), offer an high degree of freedom in their fabrication and at the same time several opportunities of integration with specific materials. Also by manipulating the properties of the in-fiber integrated materials, the guiding features of the MOF itself can be properly changed in order to develop new tunable photonic devices (Domachuk et al. 2004; Larsen et al. 2003; Huang et al. 2004) as well as optical fiber sensors (Benabid et al. 2005; Matejec et al. 2006). Single Walled Carbon Nanotubes (SWCNTs) constitute a very promising material for multimaterial and multifunctional photonic devices in light of their unique electrical and mechanical properties (Dresselhaus et al. 2001). Furthermore, the opto-chemical sensing properties of carbon nanotubes, deposited onto singlemode standard optical fiber (SOF) configured in buffered and not buffered reflectometric configurations, have been demonstrated to be suitable (Penza et al. 2004; Penza et al. 2005 ; Consales et al. 2006; Consales et al. 2007) to perform chemical detection of volatile organic compounds (VOCs) at room temperature. 26

Metal-Functionalized and Vertically-Aligned Multiwalled Carbon Nanotube Layers for Low Temperature Gas Sensing Applications

Abstract: Vertically-aligned carbon nanotubes (CNTs) films have been grown by radiofrequency plasma-enhanced chemical vapor deposition system onto alumina substrates, coated with 2.5 nm thick Fe catalyst, for NO2, H2 and C2H5OH gas sensing applications, at sensor temperatures from room-temperature to 150°C. The CNTs appear in the form of forest-like structure. Nanoclusters of noble metals with nominal thickness of 5 nm of Pt, Ru and Ag have been sputtered on the top-surface of the vertically-aligned CNTs layers to enhance the gas sensitivity. It was demonstrated that the gas sensitivity of the metal modified CNTs-sensors significantly improved by a factor up to an order of magnitude through a spillover effect, and a broader selectivity was provided. The gas sensing properties of the CNTs-sensors, including the metal-modified CNTs, are characterized by a change of the electrical conductivity in a model of the charge transfer with a semiconducting p-type character. The metal-functionalized CNTs-sensors exhibit high sensitivity, fast response, reversibility, good repeatability, sub-ppm range detection limit. A practical application of the CNTs-sensors for monitoring landfill gas is presented.