SYNTHESIS AND APPLICATION OF GRAPHENE/SILVER NANOWIRES/GOLD NANOPARTICLES HYBRID FOR AMMONIA GAS SENSING

Graphene material synthesized from chemical method (reduced Graphene Oxide – rGO) is a promising candidate for gas sensors due to their unique properties. With structure of single layer of bonded sp2 carbons in a two-dimensional (2D) lattice, rGO have large surface to volume ratio, high conductivity and electron mobility at room temperature. Meanwhile, the different oxygen-containing functional groups (contain dangling bonds) decorated on carbon networks make rGO easily respond with compatible gas molecules. However, the investigating of structure of rGO in micrometer scale shows that the chemical method often results in non-uniform film thickness on substrate due to overlap of rGO sheets. These may disrupt the conductive paths in rGO films and decrease their conductivity. Therefore, gas sensing signal of pristine rGO based sensors is tarnished and the sensors do not recover to their baseline at room temperature. In this study, silver nanowires (AgNWs) and gold nanoparticles (AuNPs) are combined with rGO material to form rGO/AgNWs/AuNPs hybrid. With one-dimensional nanostructure, the AgNWs connects effectively together many rGO islands and reduce significantly their contact resistance so that NH3 sensing signal is improved and complete recovery of the sensor is nearly achieved at room temperature. Especially, all these signals are further enhanced when the AuNPs (diameter ~ 30 nm) are added into the hybrid

Synthesis and Characterization of Ag/PEDOT:PSS Films Used for NH3_3 Selective Sensing

Nano-Ag/PEDOT-PSS films were prepared by spin-coating technique. SEM surface morphology, Raman spectra and gas sensing of methanol, humidity and NH3 were studied. The obtained results showed that the resistance of Ag/PEDOT:PSS sheets exposed to gases related to the generation of electrons from the gases adsorption that eliminated holes as the major carriers in PEDOT:PSS. For NH3 gas the largest change of the resistance of Ag/PEDOT:PSS was observed. The less sensitivity of humidity and ethanol sensing was explained due to less dedoping reaction between H2O and ethanol vapor with Ag/PEDOT:PSS, respectively. This suggests a potential application of the nano-Ag/PEDOT-PSS sensors for  the selective monitoring NH3 gas in environment

Investigation of Thermal Annealing Condition on the Optical and Electrical Properties of Hybrid Silver Nanowires/Reduced Graphene Oxide (AgNWS/rGO) Films

Herein we report a electrode in the hybrid  structure of the silver nanowires (AgNWs) with reduced graphene oxide (rGO) deposited on glass or PET substrate. The assembly and contacting in procedures of this hybrid film have been strongly affected by preparation conditions, especially annealing temperature. In this work, we have investigated the effects of thermal annealing on interconnected at nanowire junctions and between AgNWS network and rGO films via their sheet resistance and transmission. The annealing temperature was varied from 120$^{\circ}$C to 180$^{\circ}$C with 10$^{\circ}$C step to find out optimal temperature at which the wires can be joined together. The results show that at 170$^{\circ}$C, the sheet resistance and transmission of the hybrid rGO/Ag NW film are $R_{s} = 10.7\;\Omega$ sq$^{ - 1 }$ and $T = 77$% (at wavelength 550 nm) corresponding to the ratio of direct conductivity to optical conductivity $\sigma _{DC}/\sigma _{OP} = 126$ which is the best obtained value. It is expected that the hybrid AgNWS/rGO film can replace ITO film in the near future

Characterization of Ag-Doped p-Type SnO Thin Films Prepared by DC Magnetron Sputtering

Crystalline structure and optoelectrical properties of silver-doped tin monoxide thin films with different dopant concentrations prepared by DC magnetron sputtering are investigated. The X-ray diffraction patterns reveal that the tetragonal SnO phase exhibits preferred orientations along (101) and (110) planes. Our results indicate that replacing Sn2+ in the SnO lattice with Ag+ ions produces smaller-sized crystallites, which may lead to enhanced carrier scattering at grain boundaries. This causes a deterioration in the carrier mobility, even though the carrier concentration improves by two orders of magnitude due to doping. In addition, the Ag-doped SnO thin films show a p-type semiconductor behavior, with a direct optical gap and decreasing transmittance with increasing Ag dopant concentration

Observation of whispering gallery modes in InGaN/GaN multi-quantum well microdisks with Ag plasmonic nanoparticles on Si pedestals

In this study, plasmonic freestanding InGaN/GaN multi-quantum well (MQW) microdisks were fabricated on Si (111) pedestals using wet chemical undercut etching, followed by decorating of Ag nanoparticles on microdisks to improve whispering gallery mode (WGM) resonance emission. The enhancement resulted from the plasmonic coupling effect between excitons in MQWs and localized surface plasmons of Ag. The radial resonance of WGMs from optically pumped microdisk cavities were observed in the photoluminescence spectra at a threshold optical pumping power density of 4.7 kW/cm2 with a WGM mode spacing of Δλ = 1.3 nm

Effect of Silver Nanowire Dimension to Ammonia Adsorption of Graphene-silver Nanowires Hybrid

In this report, we study the effect of silver nanowires (AgNws) dimension to electrical properties of rGO/AgNws hybrid. The alteration of these electrical properties leads the difference of ammonia sensibility of the rGO/AgNws hybrid based sensing devices. When the rGO is accompanied by AgNws of different sizes from \sim 500$~\text{nm to } 10\;\mum, the ammonia sensitivity of these hybrids change from 60% to 340% alteration compared with the bare rGO material

Safety and efficacy of fluoxetine on functional outcome after acute stroke (AFFINITY): a randomised, double-blind, placebo-controlled trial

Background Trials of fluoxetine for recovery after stroke report conflicting results. The Assessment oF FluoxetINe In sTroke recoverY (AFFINITY) trial aimed to show if daily oral fluoxetine for 6 months after stroke improves functional outcome in an ethnically diverse population. Methods AFFINITY was a randomised, parallel-group, double-blind, placebo-controlled trial done in 43 hospital stroke units in Australia (n=29), New Zealand (four), and Vietnam (ten). Eligible patients were adults (aged ≥18 years) with a clinical diagnosis of acute stroke in the previous 2–15 days, brain imaging consistent with ischaemic or haemorrhagic stroke, and a persisting neurological deficit that produced a modified Rankin Scale (mRS) score of 1 or more. Patients were randomly assigned 1:1 via a web-based system using a minimisation algorithm to once daily, oral fluoxetine 20 mg capsules or matching placebo for 6 months. Patients, carers, investigators, and outcome assessors were masked to the treatment allocation. The primary outcome was functional status, measured by the mRS, at 6 months. The primary analysis was an ordinal logistic regression of the mRS at 6 months, adjusted for minimisation variables. Primary and safety analyses were done according to the patient's treatment allocation. The trial is registered with the Australian New Zealand Clinical Trials Registry, ACTRN12611000774921. Findings Between Jan 11, 2013, and June 30, 2019, 1280 patients were recruited in Australia (n=532), New Zealand (n=42), and Vietnam (n=706), of whom 642 were randomly assigned to fluoxetine and 638 were randomly assigned to placebo. Mean duration of trial treatment was 167 days (SD 48·1). At 6 months, mRS data were available in 624 (97%) patients in the fluoxetine group and 632 (99%) in the placebo group. The distribution of mRS categories was similar in the fluoxetine and placebo groups (adjusted common odds ratio 0·94, 95% CI 0·76–1·15; p=0·53). Compared with patients in the placebo group, patients in the fluoxetine group had more falls (20 [3%] vs seven [1%]; p=0·018), bone fractures (19 [3%] vs six [1%]; p=0·014), and epileptic seizures (ten [2%] vs two [<1%]; p=0·038) at 6 months. Interpretation Oral fluoxetine 20 mg daily for 6 months after acute stroke did not improve functional outcome and increased the risk of falls, bone fractures, and epileptic seizures. These results do not support the use of fluoxetine to improve functional outcome after stroke

Ammonia Gas Sensing Behavior of Hybridization between Reduced Graphene Oxide and Gold Nanoparticles

Stack and composite are the two ways of hybridization between gold nanoparticles (AuNPs) and reduced graphene oxide (rGO) which have been fabricated and tested the ability to detect NH3 gas at room temperature. The device based on the rGO-AuNP composite structure exhibited the highest response and the fastest response and recovery time compared to stack and bare rGO. The red shift of a resonant peak in the absorption spectra and the negative shift in the binding energy of 4f5/2 peak indicated that the remarkable NH3 gas-sensing properties of this composite are mainly attributed to a chemical bonding formed between AuNPs and rGO at the defective sites. This type of interaction facilitates the electron transfer from the defect states to the AuNP surface wherein it easily reacts with the oxygen molecules in the atmosphere to create oxygen absorbents. Consequently, NH3 not only reacts with sp3-hybridized atoms but also reacts primarily with oxygen absorbents on the surface of AuNPs, resulting in a better sensing behavior of composite samples