Probability Distributions.- Linear Models for Regression.- Linear Models for Classification.- Neural Networks.- Kernel Methods.- Sparse Kernel Machines.- Graphical Models.- Mixture Models and EM.- Approximate Inference.- Sampling Methods.- Continuous Latent Variables.- Sequential Data.- Combining Models.

Pattern Recognition and Machine Learning

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American Society for Testing and Materials

Thermal conductivity of carbon nanotubes and their polymer nanocomposites: A review

The unique and tunable properties of carbon-based nanomaterials enable new technologies for identifying and addressing environmental challenges. This review critically assesses the contributions of carbon-based nanomaterials to a broad range of environmental applications: sorbents, high-flux membranes, depth filters, antimicrobial agents, environmental sensors, renewable energy technologies, and pollution prevention strategies. In linking technological advance back to the physical, chemical, and electronic properties of carbonaceous nanomaterials, this article also outlines future opportunities for nanomaterial application in environmental systems.

Environmental applications of carbon-based nanomaterials.

The analysis of various parameters of metal oxides and the search of criteria, which could be used during material selection for solid-state gas sensor applications, were the main objectives of this review. For these purposes the correlation between electro-physical (band gap, electroconductivity, type of conductivity, oxygen diffusion), thermodynamic, surface, electronic, structural properties, catalytic activity and gas-sensing characteristics of metal oxides designed for solid-state sensors was established. It has been discussed the role of metal oxide manufacturability, chemical activity, and parameter's stability in sensing material choice as well.

Metal oxides for solid-state gas sensors: What determines our choice?

Multiwalled carbon nanotube (MWCNT) films have been fabricated by using plasma-enhanced chemical vapor deposition system onto Cr–Au patterned alumina substrates, provided with 3nm thick Fe growth catalyst, for NO2 and NH3 gas sensing applications, at sensor temperature in the range of 100–250°C. Nanoclusters of noble metal surface catalysts (Au and Pt) have been sputtered on the surface of MWCNTs to enhance the gas sensitivity with respect to unfunctionalized carbon nanotube films. It was found that the gas sensitivity of Pt- and Au-functionalized MWCNT gas sensors significantly improved by a factor up to an order of magnitude through a spillover effect for NH3 and NO2 gas detections, respectively. The metal-functionalized MWCNT sensors exhibit very high gas sensitivity, fast response, reversibility, good repeatability, and sub-ppm range detection limit with the sensing properties of the MWCNT films tailored by surface catalyst used to functionalize the MWCNT sensors.

Enhancement of sensitivity in gas chemiresistors based on carbon nanotube surface functionalized with noble metal (Au, Pt) nanoclusters

We demonstrate the integration of single-walled carbon nanotubes (SWCNTs) onto quartz crystal microbalance (QCM) and standard silica optical fiber (SOF) sensor for alcohol detection at room temperature. Different transducing mechanisms have been used in order to outline the sensing properties of this class of nanomaterials, in particular the attention has been focused on two key parameters in sensing applications: mass and refractive index changes due to gas absorption. Here, Langmuir–Blodgett (LB) films consisting of tangled bundles of SWCNTs without surfactant molecules have been successfully transferred onto QCM and SOF. Mass-sensitive 10MHz QCM SWCNTs sensor exhibited a resonant frequency decreasing upon tested alcohols exposure; also the normalized optoelectronic signal (λ=1310nm) of the refractive index-sensitive SOF SWCNTs sensor was found to decrease upon alcohols ambient. Highly sensitive, repeatable and reversible responses of the QCM and SOF SWCNTs sensors indicate that the detection, at room t...

Alcohol detection using carbon nanotubes acoustic and optical sensors

A highly sensitive Surface Acoustic Wave (SAW) sensor system for relative humidity (RH) detection using chemically interactive polyvinyl-alcohol (PVA) film with implemented electronic module is described. The system configured as a dual resonator SAW oscillator consists of two SAW resonators, two RF amplifiers, and a mixer. The mixed frequency has been considered as output of the SAW sensor. The SAW response toward 60% RH has been measured as a frequency change of about −11.5 MHz, at room temperature. A cross-sensitivity of the PVA film toward organic vapours with bonded OH groups has been also detected. The RH sensing characteristics, at room temperature, of the PVA-based dual SAW sensor have been analyzed in terms of sensitivity, calibration curve, detection limit, noise, water-resistance, short–medium term repeatability, aging, and sensing performances comparison.

Relative humidity sensing by PVA-coated dual resonator SAW oscillator

We investigate the impact of the tailored load of gold (Au) nanoclusters functionalizing the sidewalls of the carbon nanotubes (CNTs) networks on gas sensing performance of a chemiresistor, operating at a working temperature in the range of 20–250 °C. CNTs networked films have been grown by radiofrequency plasma enhanced chemical vapour deposition (RF-PECVD) technology onto low-cost alumina substrate, provided with 6 nm nominally thick cobalt (Co) growth-catalyst. Nanoclusters of Au have been deposited by sputtering onto CNTs networks with a controlled loading of equivalent thickness of 2.5, 5 and 10 nm. Microstructure and morphology of the CNTs have been characterized by FE-SEM and TEM with diameter of the bundles of nanotubules of 10–40 nm. CNTs and Au-modified CNTs exhibit a p-type response with a decrease in electrical resistance upon exposure to oxidizing NO 2 gas and an increase in resistance upon exposure to reducing gases (NH 3 , CO, N 2 O, H 2 S, SO 2 ). Negligible response has been found for CNTs and Au-modified CNTs sensors exposed to CO, N 2 O, SO 2 . In the contrast, significantly enhanced gas response of NO 2 , H 2 S and NH 3 , up to a low limit of sub-ppm level, has been measured for Au-functionalized CNTs-chemiresistors. Highest gas sensitivity to NO 2 , H 2 S and NH 3 has been found by CNTs functionalized with Au loading of 5 nm, at 200 °C. An optimal operating temperature for each Au-modified CNTs-sensor exposed to NO 2 gas has been recorded. Good repeatability of the electrical response to 200 ppb NO 2 is also reported, at 200 °C. These results demonstrate the efficiency of the CNTs-chemiresistors functionalized with Au nanoclusters for selective air-pollutants environmental monitoring applications.

Functional characterization of carbon nanotube networked films functionalized with tuned loading of Au nanoclusters for gas sensing applications

A gas chemiresistor, fabricated onto alumina using multi-walled carbon nanotubes (MWCNTs) networked films grown by radiofrequency plasma enhanced chemical vapor deposition (RF-PECVD) technology, is described for high-performance gas detection, at an operating temperature of 200 °C. Functionalizations of MWCNTs tangled bundle-films with nominally 5-nm thick Pt- and Pd-nanoclusters, prepared by magnetron sputtering, provide higher sensitivity for significantly enhanced gas detection of NO2, H2S, NH3, CO, up to a low limit of sub-ppm level. The measured electrical conductance of the functionalized MWCNTs upon gas exposures is modulated by charge transfer with p-type semiconducting characteristics. Pt- and Pd-nanoclusters functionalized MWCNTs gas sensors exhibited better performances compared to unfunctionalized MWCNTs, making them promising candidates for air-pollutants environmental monitoring. Simple electronic interface for the chemiresistor has been developed with a voltage output of the sensor signal.

Michele Penza

Papers

Enhancement of sensitivity in gas chemiresistors based on carbon nanotube surface functionalized with noble metal (Au, Pt) nanoclusters

Alcohol detection using carbon nanotubes acoustic and optical sensors

Relative humidity sensing by PVA-coated dual resonator SAW oscillator

Functional characterization of carbon nanotube networked films functionalized with tuned loading of Au nanoclusters for gas sensing applications

Pt- and Pd-nanoclusters functionalized carbon nanotubes networked films for sub-ppm gas sensors