Tuning the electron-phonon interaction via exploring the interrelation between Urbach energy and fano-type asymmetric raman line shape in GO-hBN nanocomposites.

Hexagonal boron nitride (hBN), having an in-plane hexagonal structure in the sp2arrangement of atoms, proclaims structural similarity with graphene with only a small lattice mismatch. Despite having nearly identical atomic arrangements and exhibiting almost identical properties, the electronic structures of the two materials are fundamentally different. Considering the aforementioned condition, a new hybrid material with enhanced properties can be evolved by combining both materials. This experiment involves liquid phase exfoliation of hBN and two-dimensional nanocomposites of GO-hBN with varying hBN and graphene oxide (GO) ratios. The optical and vibrational studies conducted using UV-vis absorption and Raman spectroscopic analysis report the tuning of electron-phonon interaction (EPI) in the GO-hBN nanocomposite as a function of GO content (%). This interaction depends on disorder-induced electronic and vibrational modifications addressed by Urbach energy (Eu) and asymmetry parameter (q), respectively. The EPI contribution to the induced disorders estimated from UV-vis absorption spectra is represented as EPI strength (Ee-p) and its impact observed in Raman phonon modes is quantified as an asymmetry parameter (q). The inverse of the asymmetry parameter is related toEe-p, asEe-p∼ 1/|q|. Here in this article, a linear relationship has been established betweenEuand the proportional parameter (k), wherekis determined as the ratio of the intensity of specific Raman mode (I) andq2, explaining the disorders' effect on Raman line shape. Thus a correlation between Urbach energy and the asymmetry parameter of Raman mode confirms the tuning of EPI with GO content (%) in GO-hBN nanocomposite.

Chemically synthesized graphene for electrochemical biosensing.

We report a new chemical method for synthesis of graphene with good yield. Graphene obtained by this chemical route was subjected to electrochemical characterization using two different redox materials for their suitability in electrochemical biosensing applications. The synthesized graphene was used for the detection of neurotransmitters like dopamine and serotonin. The electrodes exhibited 20% +/- 5% (N = 5) decrease in their signal after forty five days storage in the laboratory atmosphere. High stability of chemically synthesized graphene as electrochemical biosensor is presented in this work.

Work Function Modulation of Few-Layer Graphene by Swift Heavy Ion Irradiation.

Here, we report the structural and electronic modification induced in chemical vapor deposited graphene by using swift heavy ions (70 MeV Ni6+).Raman spectroscopy was used to quantify the irradiation-induced modification in vibrational properties. The increase in defect density with fluence causes an increase in the intensity ratio of its characteristic Raman D and G band. The increase in defect density also results in a decrease in crystallite size. The changes in the crystal structure are observed from X-rays diffraction measurement. Swift heavy ion irradiation induced defect, modified the surface roughness and surface potential of graphene thin film as measured from atomic force microscopy and scanning Kelvin probe microscopy respectively. The increase in the work function, surface roughness as well as defect concentration with fluence, indicate the possibility of linear correlation between them. Presence of defects in graphene sheets strongly affects surface electronic and optical properties of the material that can be used to tailor the optoelectronics device performance.

Evolution of Raman Spectra in Ion Irradiated MoS2 Atomic Layers: Computational and Experimental Studies.

Herein we report the existence of biaxial strain in swift heavy ion irradiated Molybdenum disulfide (Mos2) as confirmed from Raman spectroscopic measurement and computational study. Defect induced external strain modifies the electronic structure and phonon frequency of the material. In this work, chemically exfoliated Mos2 nanosheets have been exposed to 70 MeV Ni+7 ion irradiation from varying fluence. The Raman spectra reveal that the defect induced LA(M) peak (longitudinal acoustic mode of Phonon at M point) evolves linearly with ion fluence, besides that several other new peaks appear and become visible in Raman spectra thus relaxing Raman fundamental selection rule. Theoretically, simulated Phonon dispersion also supports the fact that tensile strain results in the red shifting of the Raman peak position. The increment of the defect induced LA(M) peak intensity with increasing ion fluence could be a measure of defect quantitatively. This study will be beneficial in the application of external strain to engineer properties of Mos2 as well as understanding the degree of strain inside it quantitatively.

Work Function Modulation of Molybdenum Disulfide Nanosheets by Introducing Systematic Lattice Strain.

Tuning the surface electronic properties of 2D transition metal dichalcogenides such as Molebdenum disulfide (MoS2) nanosheets is worth exploring for their potential applications in strain sensitive flexible electronic devices. Here in, the correlation between tensile strain developed in MoS2 nanosheets during swift heavy ion irradiation and corresponding modifications in their surface electronic properties is investigated. With prior structural characterization by transmission electron microscopy, chemically exfoliated MoS2 nanosheets were exposed to 100 MeV Ag ion irradiation at varying fluence for creation of controlled defects. The presence of defect induced systematic tensile strain was verified by Raman spectroscopy and X-ray Diffraction analysis. The effect of ion irradiation on in-plane mode is observed to be significantly higher than that on out-of-plane mode. The contribution of irradiation induced in-plane strain on modification of the surface electronic properties of nanosheets was analyzed by work function measurement using scanning Kelvin probe microscopy. The work function value is observed to be linearly proportional to tensile strain along the basal plane indicating a systematic shifting of Fermi surface with fluence towards the valence band.