Environmental monitoring of low-ppb ammonia concentrations based on single-wall carbon nanotube chemiresistor gas sensors: Detection limits, response dynamics, and moisture effects

EUROSENSORS 2014, the XXVIII edition of the conference series.Under a Creative Commons license.We present single-wall carbon nanotube (SWCNT) chemiresistor gas sensor (CGS) operating at room temperature, displaying an enhanced sensitivity to NH3. Ammonia concentrations in the full range of the average [NH3] in a urban environment have been measured, and a detection limit of 3 ppb is demonstrated, which is well below the sensitivities so far reported for non- functionalized SWCNTs operating at room temperature. Different materials were tested as substrates, including cheap plastic flexible substrates. In addition to a careful preparation of the SWCNT layers, the low-ppb limit is also attained by revealing and properly tracking a fast dynamics during the desorption process. On the basis of these results a model of the CGS response vs time is proposed. When functionalized with indium-tin oxide nanoparticles, a sensitivity increase is detected, along with a remarkable selectivity towards moisture.Peer Reviewe

Growth and microstructural analysis of nanosized Y2O3 doped with rare-earths

Nanosized cubic Y2O3 samples, undoped and doped with 10 mol% Nd2O3, Eu2O3, Gd2O3, Tb2O3, Ho2O3 and Er2O3 (Y(1.8)Ln(0.2)O(3), where Ln=Nd, Eu, Gd, Tb, Ho or Er), were prepared by means of a controlled hydrolysis method in an aqueous solution containing ammonia, Y(NO3)(3) and Ln(NO3)(3) as precursors, and a surface modifier. The microstrain and the average size of the diffraction domains have been calculated from the XRD patterns and the results have been compared with those obtained by a combustion synthesis. It is shown that the cell parameter of the C-M2O3 (bcc structure related to the CaF2 structure; the M atom is 6-coordinated) structure of doped Y2O3 is correlated to the ion size of the dopant. The shape of the crystallites appears to be needle-like in all cases, while the microstrains depend on the dopant and are probably due to surface effect. XRD and Raman analysis show that, despite the heavy doping, only one phase in the Y2O3 powders is present. (C) 2000 Elsevier Science S.A. All rights reserved

Detection of a coherent excitonic state in the layered semiconductor BiI3_{3}

The measurement and manipulation of the coherent dynamics of excitonic states constitute a forefront research challenge in semiconductor optics and in quantum coherence-based protocols for optoelectronic technologies. Layered semiconductors have emerged as an ideal platform for the study of exciton dynamics with accessible and technologically relevant energy and time scales. Here, we investigate the sub-picosecond exciton dynamics in a van-der-Waals semiconductor upon quasi-resonant excitation, and achieve to single out an incipient coherent excitonic state. Combining broadband transient reflectance spectroscopy and simulations based on many-body perturbation theory, we reveal a transient enhancement of the excitonic line intensity that originates from the photoinduced coherent polarization that is phase-locked with the interacting electromagnetic field. This finding allows us to define the spectral signature of a coherent excitonic state and to experimentally track the dynamical crossover from coherent to incoherent exciton, unlocking the prospective optical control of an exciton population on the intrinsic quantum-coherence timescale

Spectroscopic evidence of in-gap states at the SrTiO3/LaAlO3 ultrathin interfaces

Experimental evidence of differences in the electronic properties of an insulating and a conducting SrTiO3/LaAlO3 interface is provided by soft x-ray spectroscopies. While core level photoemission measurements show that only at the conducting interface Ti ions with 3+ ionization state are present, by using resonant photoemission and x-ray absorption spectroscopies, it is shown that in both samples in-gap states with a Ti 3d character are present, but their density is higher at the conducting interface

Trends in the Development of Electronic Noses Based on Carbon Nanotubes Chemiresistors for Breathomics

The remarkable potential of breath analysis in medical care and diagnosis, and the consequent development of electronic noses, is currently attracting the interest of the research community. This is mainly due to the possibility of applying the technique for early diagnosis, screening campaigns, or tracking the effectiveness of treatment. Carbon nanotubes (CNTs) are known to be good candidates for gas sensing, and they have been recently considered for the development of electronic noses. The present work has the aim of reviewing the available literature on the development of CNTs-based electronic noses for breath analysis applications, detailing the functionalization procedure used to prepare the sensors, the breath sampling techniques, the statistical analysis methods, the diseases under investigation, and the population studied. The review is divided in two main sections: one focusing on the e-noses completely based on CNTs and one reporting on the e-noses that feature sensors based on CNTs, along with sensors based on other materials. Finally, a classification is presented among studies that report on the e-nose capability to discriminate biomarkers, simulated breath, and animal or human breath

A Chemiresistor Sensor Array Based on Graphene Nanostructures: From the Detection of Ammonia and Possible Interfering VOCs to Chemometric Analysis

Sensor arrays are currently attracting the interest of researchers due to their potential of overcoming the limitations of single sensors regarding selectivity, required by specific applications. Among the materials used to develop sensor arrays, graphene has not been so far extensively exploited, despite its remarkable sensing capability. Here we present the development of a graphene-based sensor array prepared by dropcasting nanostructure and nanocomposite graphene solution on interdigitated substrates, with the aim to investigate the capability of the array to discriminate several gases related to specific applications, including environmental monitoring, food quality tracking, and breathomics. This goal is achieved in two steps: at first the sensing properties of the array have been assessed through ammonia exposures, drawing the calibration curves, estimating the limit of detection, which has been found in the ppb range for all sensors, and investigating stability and sensitivity; then, after performing exposures to acetone, ethanol, 2-propanol, sodium hypochlorite, and water vapour, chemometric tools have been exploited to investigate the discrimination capability of the array, including principal component analysis (PCA), linear discriminant analysis (LDA), and Mahalanobis distance. PCA shows that the array was able to discriminate all the tested gases with an explained variance around 95%, while with an LDA approach the array can be trained to accurately recognize unknown gas contribution, with an accuracy higher than 94%