doi: https://doi.org/10.12669/pjms.36.ICON-Suppl.1861
How to cite this:Jawaid SA. Promoting Research Culture at Indus Health Network. Pak J Med Sci. Special Supplement ICON 2020. 2020;36(1):S2. doi: ...https://doi.org/10.12669/pjms.36.ICON-Suppl.1861
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Atomically thin 2D materials, currently being at the forefront of scientific and technological interest, can be categorized as metallic, semimetallic, semiconducting, insulating, or superconducting, ...depending on their chemical composition and structural configuration. They also exhibit, in some cases, a transition from an indirect to a direct bandgap alignment when bulk materials are scaled down to monolayers. An important class of 2D materials is layered transition metal dichalcogenides (TMDs) with a tunable bandgap, because photogenerated optical excitations and subsequent excitation dynamics, which produce energy migration and photogenerated charge carrier transport, make them promising candidates for a variety of optoelectronic devices, including solar cells, photodetectors, light-emitting diodes, and phototransistors. In this work, we probe the excitation dynamics following nonlinear optical absorption/scattering in two unexplored TMDs, metallic NbS2 and semimetallic ZrTe2, using a combination of the standard optical Z-scan and photoacoustic Z-scan techniques, and compare them with semiconducting MoS2. The comparison of optical Z-scan (OZ-scan), which depends on the contributions of both nonlinear scattering and nonlinear absorption, with photoacoustic Z-scan (PAZ-scan), which depends only on nonlinear absorption due to local heating from nonradiative relaxation, allows us to separate these contributions from the total nonlinear response. In addition, these studies also allow us to look at the nature of nonlinear absorption as to whether it is due to saturable absorption (SA) of a one-photon transition, reverse saturable absorption (RSA) derived from two-photon excitation processes, or any combination thereof. In MoS2, NbS2, and ZrTe2, we observed both SA and RSA. The relevant nonlinear absorption coefficient parameters were obtained. Density functional theory modeling provides an insight onto possible underlying physical processes.
We report the second harmonic scattering experiments from acetonitrile liquid suspensions of two-dimensional metal dichalcogenide nanoflakes,: the semiconducting MoS2 and WS2, the metallic NbS2, and ...the semi-metallic ZrTe2. Because the study is directly performed in the liquid phase, no symmetry breaking can be attributed to a supporting substrate as it is often the case in the investigation of the second harmonic generation efficiency for these materials. A comparative look of the origin of the nonlinear response using polarization analysis of the hyper Rayleigh scattering intensity is performed. Retardation is clearly exhibited by all nanoflakes considering their average dimensions but remains weak. This is attributed to the non-negligible role played by the nanoflake edges or the presence of surface absorbed polyoxometalates (POMs), in all cases.
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•2D materials were prepared by redox exfoliation and characterized them.•Hyper Rayleigh Scattering intensity of 2D materials was performed.•The Hyper Rayleigh Scattering response of 2D materials exhibits retardation.•Edge contribution is confirmed with a model based on nonlinear dipoles.
Understanding the electronic structure of doped semiconductors is essential to realize advancements in electronics and in the rational design of nanoscale devices. Reported here are the results of ...time-resolved X-ray absorption studies on copper-doped cadmium sulfide nanoparticles that provide an explicit description of the electronic dynamics of the dopants. The interaction of a dopant ion and an excess charge carrier is unambiguously observed via monitoring the oxidation state. The experimental data combined with DFT calculations demonstrate that dopant bonding to the host matrix is modulated by its interaction with charge carriers. Furthermore, the transient photoluminescence and the kinetics of dopant oxidation reveal the presence of two types of surface-bound ions that create midgap states.
Monolayer Silane-Coated, Water-Soluble Quantum Dots Zhang, Xi; Shamirian, Armen; Jawaid, Ali M. ...
Small (Weinheim an der Bergstrasse, Germany),
December 2, 2015, Letnik:
11, Številka:
45
Journal Article
Recenzirano
A one‐step method to produce ≈12 nm hydrodynamic diameter water‐soluble CdSe/ZnS quantum dots (QDs), as well as CdS/ZnS, ZnSe/ZnMnS/ZnS, AgInS2/ZnS, and CuInS2/ZnS QDs, by ligand exchange with a ...near‐monolayer of organosilane caps is reported. The method cross‐links the surface‐bound silane ligands such that the samples are stable on the order of months under ambient conditions. Furthermore, the samples may retain a high quantum yield (60%) over this time. Several methods to functionalize aqueous QD dispersions with proteins and fluorescent dyes have been developed with reaction yields as high as 97%.
Cap exchanging quantum dots with minimal loss of quantum yield and high stability has been a long sought‐after goal of quantum dot chemists. A one‐pot method is presented for coating nanomaterials with a monolayer‐thin shell of cross‐linked silane. The dots retain high emission efficiencies over several months under harsh conditions. Several functionalization strategies are also detailed.
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