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In this report, we are going to present the development and optimization of high-performance porous alumina growth having a large surface to volume ratio for ultra-high sensitive humidity sensing. The control of the structure of pores, such as the diameter of pores, depth of porous layer, etc., has shown crucial implications for the sensitivity of sensor; and there are precisely fine-tuned with the anodization process parameters. The sensitivity of the prepared sensors reaches upto 793.02% while reported sensitivity for conventional capacitive humidity sensors is much less. Besides, the prepared sensor maintains its fair responsivity as well as sensitivity even up to 100 KHz unlike 10 KHz reported by other researchers so far; and it gives an added advantage for its applications where humidity measurement at high frequencies are required The samples are characterized by Field Emission Scanning Electron Microscopy (FESEM, FEI NNS 450) to support the results and impedance spectroscopy were employed for the electrical characterization of the sensor. An equivalent electrical circuit is obtained to represent the electrical performance at different humidity level and it is in good agreement with the observed results. [ABSTRACT FROM AUTHOR]

Alumina (Al 2 O 3 ) exists in three different phases having different physical properties. In view of this fact, a systematic study has been carried out for the first time to investigate how its various phases influence the sensing performance of a MWCNTs–alumina nanocomposite based trace level gas sensor. A series of composite sensing film were prepared by dispersing MWCNTs in alumina solution followed by a sol–gel process, where the phase of alumina is controlled by specific temperatures set for an annealing process. The analysis revealed that porosity as well as the surface area varies from phase to phase in the composite film and it is the key factor which governs the sensing performance. Brunaur, Emmet and Teller (BET) analysis showed the significant increase in specific surface area of the composite film when boehmite (β-phase) was transformed into γ-phase. X-ray diffraction (XRD) results confirmed the presence of γ-, mixed δ- θ- and α-alumina phases when the annealing temperature of the composite film raised from room temperature to 450 °C, 800 °C and 1000 °C respectively. Field emission scanning electron microscopy (FESEM), BET and Atomic force microscopy (AFM) techniques were employed to examine the resultant porous structure and surface area of the annealed composite films in various phases. The composite having γ-alumina phase (annealed at 450 °C) was found to have maximum response, where the composite having α-alumina phase (annealed at 1000 °C) had the least. [ABSTRACT FROM AUTHOR]

In this paper, we report a novel approach to study the potential use of multi-walled carbon naotubes (MWCNTs)–alumina (Al 2 O 3 ) composite for heat sensing applications. This is achieved by optimizing the temperature coefficient of resistance (TCR) and thermal hysteresis of the composite. The composites were developed by uniform dispersion of MWCNTs in alumina in different concentrations following sol‐gel route. MWCNT loading in the alumina was found to be very effective to control the TCR as well as the hysteresis loss. The room temperature TCR versus MWCNTs concentration plot first shows an increasing trend with increase of MWCNTs concentration in the composite and reaches a threshold followed by drop in TCR. The maximum value of TCR that has been achieved is −0.56%/°C for 4 wt% MWCNTs content and is found to be ~1.5 times higher than the conventional metals and semiconductors. The hysteresis loss was found to decrease gradually to almost zero from 5 wt% onwards. The TCR and hysteresis variation is correlated with MWCNTs concentration dependent Raman, FESEM, EDS studies in the composite and there is a fair agreement in support of the observations. [ABSTRACT FROM AUTHOR]

Abstract: We report another unconventional growth of carbon nanotube (CNT) growth directly on flat alumina substrate (Al2O3) where neither any metal particle is used as a catalyst nor any supporting layer to facilitate its growth. All reactions are performed in atmospheric pressure in thermal CVD chamber. The diameter distribution is found 6–8nm. The CNTs are characterized using HRTEM, HRSEM, micro-Raman and EDX analysis. The I D/I G ratio in Raman spectra and TEM picture ascertains that the CNTs contain less defects and presence of amorphous carbon and other particles are nil within the CNTs structure. [Copyright &y& Elsevier]

Many physical characteristics of semiconducting materials can be finely controlled through template-based nanostructure growth, leading to tuning their properties as well. Reproducible through-hole growth of customised semiconducting nanotubes on Al 2 O 3 (AAO) template is challenging; and therefore, their production methods are of utmost importance. An efficient approach is demonstrated here to remove the sensitive barrier layer from micron thick AAO template keeping base aluminium intact, which serves as an ohmic contact. To prove the effectiveness of this approach, high aspect ratio Cadmium telluride nanotubes (CdTe NTs) having controllable diameter were synthesized using DC electrodeposition. FE-SEM and TEM micrographs illustrate the growth of through-hole nanotubes at each stage of barrier layer etching in AAO template. CdTe nanotubes with an average diameter of 80 nm, grown under various electrolyte baths, have been studied using XRD and Raman spectroscopy. Raman study was done at 77 K to check the confinement effect on multiphonon Raman scattering of LO mode in CdTe NTs. As grown nanotubes show strong luminescence in the visible region with enhanced optical bandgap, and high purity demonstrated by X-ray photoelectron spectroscopy. Excellent specific capacitance of 332 F g-1 at scan rate 100 mV s-1 was found for CdTe-NTs in 6 mol L-1 KOH electrolyte. Efficient photoluminescence (PL) emission and the increase in specific capacitance proved to be worthy for its applications in photovoltaics and energy-storage devices. An efficient and facile method is reported to make AAO membrane through-hole on base aluminium substrate. High-aspect ratio CdTe nanotube array is grown on this electrochemically modified AAO template through DC electrodeposition to study its structural and optical properties. The synthesized nanotubes were further investigated as an energy storage electrode material through cyclic voltammetry and recorded high specific capacitance. Image 1 • Facile fabrication of high aspect ratio and through hole AAO template. • DC electrodeposition of CdTe nanotube array on AAO template. • Optical and chemical surface analysis of the grown CdTe nanotubes. • Micro-Raman scattering measurements to study phonon confinement effect. • Investigation of CdTe nanotube electrode material through CV analysis for energy storage application. [ABSTRACT FROM AUTHOR]