High selectivity and sensitivity through nanoparticle sensors for cleanroom CO2detection.

Clean room facilities are becoming more popular in both academic and industry settings, including low-and middle-income countries. This has led to an increased demand for cost-effective gas sensors to monitor air quality. Here we have developed a gas sensor using CoNiO2nanoparticles through combustion method. The sensitivity and selectivity of the sensor towards CO2were influenced by the structure of the nanoparticles, which were affected by the reducing agent (biofuels) used during synthesis. Among all reducing agents, urea found to yield highly crystalline and uniformly distributed CoNiO2nanoparticles, which when developed into sensors showed high sensitivity and selectivity for the detection of CO2gas in the presence of common interfering volatile organic compounds observed in cleanroom facilities including ammonia, formaldehyde, acetone, toluene, ethanol, isopropanol and methanol. In addition, the urea-mediated nanoparticle-based sensors exhibited room temperature operation, high stability, prompt response and recovery rates, and excellent reproducibility. Consequently, the synthesis approach to nanoparticle-based, energy efficient and affordable sensors represent a benchmark for CO2sensing in cleanroom settings.

Surface Structure-Dependent Low Turn-On Electron Field Emission from Polypyrrole/Tin Oxide Hybrid Cathodes.

We present a new surface structure-dependent cold cathode material capable of sustaining high electron emission current suitable for next-generation low turn-on field-emission devices. The low turn-on electric field for electron emission in the cathode materials is critical, which facilitates the low-power room-temperature operation, a key factor required by the industrial sector. We demonstrate the facile synthesis of polypyrrole (PPy)/tin oxide (SnO2)-based core-shell hybrid cold cathode materials for large area applications. The technique used here is based on a simple and economical method of surfactant-mediated polymerization. The coupled investigation of X-ray diffraction along with electron microscopy reveals the formation of rutile phase SnO2 nanoparticles of size ∼15 nm. These SnO2 nanoparticles act as nucleation sites for the growth of PPy nanofibers, resulting in encapsulated SnO2 nanoparticles in the PPy amorphous matrix. The coupling of spherical-shaped core-shell structures of PPy/SnO2 resulted into the particle train-like nanostructured form of the hybrid material. These core-shell structures formed the local p-n junction between the n-type SnO2 (core) and p-type PPy (shell). The long chains of these p-n junctions in nanofibers result in the modification of the electronic band structure of PPy, leading to a reduction in the work function of the electrons. The significant surface structural modification in PPy/SnO2 causes a prominent reduction in the turn-on electric field for electron emission in PPy/SnO2 nanocomposite (∼1.5 V/µm) as compared to the pure PPy (∼3.3 V/µm) without significant loss in current density (∼1 mA/cm2). The mechanism of improved field-emission behavior and advantages of using such hybrid nanomaterials as compared to other composite nanomaterials have also been discussed in detail.

Structural, nanomechanical, field emission and ammonia gas sensing properties of nitrogenated amorphous carbon films deposited by filtered anodic jet carbon arc technique.

This paper reports the effect of substrate bias on the structural, nanomechanical, field emission and ammonia gas sensing properties of nitrogenated amorphous carbon films embedded with nanocrystallites (a-C: N: nc) deposited by a filtered anodic jet carbon arc (FAJCA) technique. The films are characterized by X-ray diffraction, high resolution transmission electron microscopy, energy dispersive X-ray spectroscopic analysis, Raman spectroscopy, nanoindentation, field emission and ammonia gas sensing measurements. The properties of the films obtained are found to depend on the substrate bias. The maximum hardness (H)=42.7 GPa, elastic modulus (E)=330.4 GPa, plastic index parameter (H/E)=0.129 and elastic recovery (% ER)=74.4% have been obtained in a-C: N: nc films deposited at -60 V substrate bias which show the lowest ID/IG=0.43, emission threshold (ET)=4.9 V/µm accompanied with the largest emission current density (Jmax)=1 mA/cm(2) and field enhancement factor (ß)=1805.6. The gas sensing behavior of the a-C: N: nc film has been tested by measuring the change in electrical resistance of the sample in ammonia environment at room temperature with the fast response and recovery time as 29 and 66.9s, respectively.