ABSTRACT
A high sensitivity and simple ethanol sensor based on an un-cladded multimode plastic optical fiber (UCPOF) coated with carbon nanotubes (CNTs) for the detection of different concentrations of ethanol in de-ionized water is developed and demonstrated. The UCPOF probe is fabricated by chemically removing the fiber cladding and integrated with CNT as a sensing layer. The effect of surface morphology on the sensor performance is investigated by characterizing another UCPOF coated with GO nanomaterial. The developed fibers are coated with CNTs and GO using drop casting technique. Energy dispersive X-ray spectroscopy (EDX), atomic-force microscopy (AFM) and scanning electron microscope (SEM) are used to investigate the element and morphology of the synthesized nanomaterials. The experimental results indicated that the absorbance spectrum of the CNT-based UCPOF sensor increases linearly with a higher sensitivity of 0.68/vol% and magnitude change of 95.4% as compared to 0.19/vol% and 56.3%, respectively, for the GO-based sensor. The UCPOF coated with CNT exhibits faster response and recovery than that of GO. The sensor shows high selectivity to ethanol amongst a range of diluted organic VOCs. The superior sensing performance of the developed fiber sensor indicates its high efficiency for ethanol detection in various industrial applications.
ABSTRACT
The possibility to grow in zincblende (ZB) and/or wurtzite (WZ) crystal phase widens the potential applications of semiconductor nanowires (NWs). This is particularly true in technologically relevant III-V compounds, such as GaAs, InAs, and InP, for which WZ is not available in bulk form. The WZ band structure of many III-V NWs has been widely studied. Yet, transport (that is, carrier effective mass) and spin (that is, carrier g-factor) properties are almost experimentally unknown. We address these issues in a well-characterized material: WZ indium phosphide. The value and anisotropy of the reduced mass (µ exc) and g-factor (g exc) of the band gap exciton are determined by photoluminescence measurements under intense magnetic fields (B, up to 28 T) applied along different crystallographic directions. µ exc is 14% greater in WZ NWs than in a ZB bulk reference and it is 6% greater in a plane containing the WZ c axis than in a plane orthogonal to c. The Zeeman splitting is markedly anisotropic with g exc = |ge| = 1.4 for Bâ¥c (where ge is the electron g-factor) and g exc = |ge - gh,//| = 3.5 for B//c (where gh,// is the hole g-factor). A noticeable B-induced circular dichroism of the emitted photons is found only for B//c, as expected in WZ-phase materials.
ABSTRACT
InP nanowires were grown on 111B InP substrates by metal-organic chemical vapour deposition in the presence of colloidal gold particles as catalysts. Transmission electron microscopy and photoluminescence measurements were carried out to investigate the effects of V/III ratio and nanowire diameter on structural and optical properties. Results show that InP nanowires grow preferably in the wurtzite crystal structure than the zinc blende crystal structure with increasing V/III ratio or decreasing diameter. Additionally, time-resolved photoluminescence (TRPL) studies have revealed that wurtzite nanowires show longer recombination lifetimes of approximately 2500 ps with notably higher quantum efficiencies.
