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In the era of wearable electronic devices, which are quite popular nowadays, our research is focused on flexible as well as stretchable strain sensors, which are gaining humongous popularity because of recent advances in nanocomposites and their microstructures. Sensors that are stretchable and flexible based on graphene can be a prospective 'gateway' over the considerable biomedical speciality. The scientific community still faces a great problem in developing versatile and user-friendly graphene-based wearable strain sensors that satisfy the prerequisites of susceptible, ample range of sensing, and recoverable structural deformations. In this paper, we report the fabrication, development, detailed experimental analysis and electronic interfacing of a robust but simple PDMS/graphene/PDMS (PGP) multilayer strain sensor by drop casting conductive graphene ink as the sensing material onto a PDMS substrate. Electrochemical exfoliation of graphite leads to the production of abundant, fast and economical graphene. The PGP sensor selective to strain has a broad strain range of ⁓60%, with a maximum gauge factor of 850, detection of human physiological motion and personalized health monitoring, and the versatility to detect stretching with great sensitivity, recovery and repeatability. Additionally, recoverable structural deformation is demonstrated by the PGP strain sensors, and the sensor response is quite rapid for various ranges of frequency disturbances. The structural designation of graphene's overlap and crack structure is responsible for the resistance variations that give rise to the remarkable strain detection properties of this sensor. The comprehensive detection of resistance change resulting from different human body joints and physiological movements demonstrates that the PGP strain sensor is an effective choice for advanced biomedical and therapeutic electronic device utility. [ABSTRACT FROM AUTHOR]

In this work, we present a novel portable sensing device developed on a silicon chip using reduced graphene oxide (RGO) and vertically aligned silicon nanowires (SiNWs) for enhanced and selective detection of acetone. Various characterization techniques were used to confirm the successful preparation of RGO/VA-SiNWs/Si-chip hybrid nanostructure. These techniques include scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Raman spectroscopy. The prepared hybrid nanostructure was used to develop a sensor, and its gas sensing characteristics were thoroughly studied under different concentrations (0.1, 0.5 and 1 ppm) at room temperature. Compared with a pristine RGO-based sensor, the prepared hybrid nanostructure-based sensing device revealed a significantly enhanced response of approximately 40% under the exposure of 0.1 ppm concentration of acetone. The fast response/recovery time (5 s/12 s, respectively, at 0.1 ppm concentration), high reproducibility, and stability make it an ideal portable sensing device. The enhanced response at this low concentration could be attributed to the synergic effect of RGO with SiNWs and maximum adsorption of acetone due to high specific surface area, as well as strong interface adhesion at the surface of the developed hybrid nanostructure. [ABSTRACT FROM AUTHOR]

Commercially available high quality 9B pencil graphite was used for sensing of trace concentrations of nitrogen dioxide (NO2) and ammonia (NH3) at sub-ppm levels in air at ambient temperature and pressure. The pencil graphite was characterized using scanning electron microscopy (SEM), Raman spectroscopy and powder X-ray diffraction (XRD) techniques. In comparison to other sensing materials pencil graphite is very well recognized owing to its cheaper price, simplicity of fabrication, abundant over-the-counter obtainability and easy modification. The principal of operation of the chemiresistive gas sensor is based on the variation in the electrical resistance due to the selective interaction between the pencil graphite network and the specific gaseous analyte in a two-pole format. The degree of change in electrical resistance of the pencil graphite network depends on the concentration of the gaseous analyte to which it is exposed. On the basis of this fact qualitative as well as quantitative detection of the gaseous analytes can be achieved. The sensing limits of 100 parts-per-billion (ppb) and 500 ppb with sensor response times of ∼30 s and ∼50 s for NO2 and NH3, respectively is recorded using our gas detector, and are found significantly efficient in comparison to the NO2 and NH3 detectors available commercially in market. [ABSTRACT FROM AUTHOR]

CdSexS1-x quantum dots (QDs) have been grown in borosilicate glass matrix using two step annealing technique and are characterized by AFM, XRD, UV-Vis absorption, HRTEM and Raman spectroscopy measurements. AFM studies show that nearly spherical clusters of about 5-10 nanocrystals were grown. From XRD measurements, it is found that the nanocrystals are grown in hexagonal phase. From HRTEM measurements, it is observed that the size of QDs increases from 5.1 to 9.5 nm with increasing annealing duration from 3 to 10 hrs. Blue shift in absorption spectrum indicates that quantum confinement increases with decreasing annealing durations. Raman spectrum of CdSexS1-x QDs shows two mode type of behavior i.e., CdSe like longitudinal optical phonon mode (LO1) and CdS like longitudinal optical phonon mode (LO2). It has been observed that with increasing the size of QDs from 5.1 to 9.5 nm, LO1 shifts from 205 to 210 cm-1 while LO2 shifts from 278 to 291 cm-1. The shift in the LO1 and LO2 Raman peaks towards high frequencies has been interpreted due to increase in the lattice compressive strain with the increase in QDs size. The effect of phonon negative dispersion on the shift of LO1 and LO2 is found to be comparatively insignificant. It is also found that the ratio of intensity of overtones to the fundamental mode increases from 0.34 to 0.48 with decreasing QD size. This indicates that the electron-phonon coupling increases with the decrease in size of QD due to increasing overlap of electron and hole wave function in small size QDs. It is further observed that the frequency of the surface optical phonon mode remains unchanged as the size of QD changes but the intensity decreases with the increase in the size of QDs finally merging in LO mode Raman spectrum. [ABSTRACT FROM AUTHOR]

An efficient white polymer light-emitting diode (WPLED) with stable Commission Internationale de l’éclairage (CIE) coordinates is fabricated. A blue electroluminescence (EL)-emitting conducting polymer [poly(9,9-di- n-hexyl-fluorenyl-2,7-diyl)] is used as a host for red [ Bis(1-phenyl-isoquinoline)(acetylacetonate)iridium(III)] and green [iridium(III) tris(2-(4-tolyl)pyridinato- N,C2)] phosphorescent dyes. Although efficient triplet energy transfer is not possible in the green phosphorescent dye, the self-trapping mechanism is utilized for the emission of EL in the green region while an efficient triplet exciton energy transfer from the host to the red dye is utilized for EL in the red wavelength region. Concentrations of the three constituents are optimized to obtain pure white light of appropriate CIE coordinates. An efficient electron-blocking layer based on a biomaterial (salmon-DNA) is also incorporated in the WPLED to improve the device performance. The WPLED shows three distinguished peaks for the primary colors and achieved a maximum luminance and luminous efficiency of 350 cd/m2 and 0.86 cd/A, respectively. [ABSTRACT FROM AUTHOR]

Hybrid solar cells consisting of a composite of poly (3-hexylthiophene) (P3HT), single walled carbon nanotube (SWCNT), and cadmium selenide/zinc sulphide (CdSe/ZnS) coreshell quantum dots (QDs) have been fabricated in the present work. The bulk hetrojunction has been formed from the bilayer of P3HT:SWCNT composite and QDs using inter-diffusion process. Due to low percolation limit and high conductivity of SWCNT, the photo-generated electrons are collected at the electrode very fast (within few femto-seconds) enhancing the efficiency of the solar cell. The absorption measurements on the composite film show that the addition of SWCNT in the hybrid structure increases the absorption coefficient in the near infrared region and also makes the spectrum wider as compared to that of P3HT. The photoluminescence (PL) measurements show that the PL of hybrid P3HT, SWCNT, and QDs is quenched about ∼15 times as compared to that of P3HT film. This shows that a significant charge transfer of electrons occurs through SWCNT to the electrode. The morphology of P3HT:SWCNT:CdSe/ZnS was observed using atomic force microscopy. With this approach, we have been able to achieve power conversion efficiency of 5.4% using a standard solar simulator with an irradiance of 100 mW/cm2. [ABSTRACT FROM AUTHOR]