M.M. Malik

Luminescence and Morphological Kinetics of Functionalized ZnS Colloidal Nanocrystals

This paper reports functionalized zinc sulphide (ZnS) semiconductor nanocrystals (quantum dots, approx., 2.5 nm) which are an important building block in self-assembled nanostructures. ZnS is functionalized by organic stabilizer Thio glycolic acid (TGA). The samples have been synthesized by colloidal technique at relatively low temperature (below 100°C) at an atmospheric pressure of 10−3 torr. Manganese (Mn) doping ions have been incorporated (doped) in ZnS host lattice and observed its effect on growth morphology and optical properties of ZnS colloidal nanocrystals. By XRD, SEM, TEM, and PL, the obtained cubic phase nanosized TGA-capped ZnS materials were characterized. The morphology of ZnS obtained at different temperatures are analyzed by SEM. The crystallite size of the ZnS nanoparticles was estimated from the X-ray diffraction pattern by using Scherrer’s formula (approximately 2.5 nm) which is confirmed by TEM. The estimated bandgap value of ZnS NC’s by (𝛼ℎ𝜐)2 versus ℎ𝜐 plot was 4.89 eV. Gaussian fitting curve in photoluminescence (PL) spectra indicated room temperature emission wavelength range from 300 to 500 nm in undoped and Mn-doped ZnS, with different emission peak intensities, and suggested the wide band emission colours in visible and near UV region which has wider applications in optical devices.

Low cost, p-ZnO/n-Si, rectifying, nano heterojunction diode: Fabrication and electrical characterization

Summary A low cost, highly rectifying, nano heterojunction (p-ZnO/n-Si) diode was fabricated using solution-processed, p-type, ZnO nanoparticles and an n-type Si substrate. p-type ZnO nanoparticles were synthesized using a chemical synthesis route and characterized by XRD and a Hall effect measurement system. The device was fabricated by forming thin film of synthesized p-ZnO nanoparticles on an n-Si substrate using a dip coating technique. The device was then characterized by current–voltage (I–V) and capacitance–voltage (C–V) measurements. The effect of UV illumination on the I–V characteristics was also explored and indicated the formation of a highly rectifying, nano heterojunction with a rectification ratio of 101 at 3 V, which increased nearly 2.5 times (232 at 3 V) under UV illumination. However, the cut-in voltage decreases from 1.5 V to 0.9 V under UV illumination. The fabricated device could be used in switches, rectifiers, clipper and clamper circuits, BJTs, MOSFETs and other electronic circuitry.

Synthesis And Characterization Of Silver Sulfide Nanoparticles Of Various Morphologies Using Chitosan As Stabilizer

Synthesis of Silver Sulfide nanoparticles of various morphologies were successfully done through colloidal synthesis technique at relatively low temperature using Chitosan bio polymer as stabilizer. The effect of change in stabilizer concentration, reagent concentrations and reaction temperature at constant pH on morphology and optical properties of synthesized products are also studied. It was found that reagent concentration and temperature both played important role in change in morphology of synthesized product. The crystal structure studies of synthesized products were carried out by powder X‐ray diffraction technique which reveals the formation of Acanthite monoclinic Ag2S crystal structure and SAD was taken for only two samples whose analysis using XRD was difficult. The optical properties and quantum confinement effect of the products were confirmed by means of spectroscopic measurements. Morphologies obtained were characterized by SEM. Further the functionality and effectiveness of stabilization ...

Optical and Structural Investigations of Manganese Doped ZnS/SiO2 Core-Shell Nanostructure

The paper reports room temperature synthesis of wurtzite type manganese doped ZnS nanostructures via colloidal technique. The reaction procedure found to play an important role in the crystal growth of ZnS. Surface encapsulation of ZnS by silica (SiO2) provides effective approach for uniform coating, where 3-Mercaptopropyl Tri methoxysilane (MPS) has been used for silica source as a capping molecule. The obtained silica coated ZnS nanocrystals were well dispersed with hexagonal wurtzite structure of core-shell particles size of about 15 nm. Aggregation of these nanoparticles has been promoted to special shaped structures, which are crystals of 8H wurtzite with prominent pyramidal morphology with curved faces. Growth phenomena of this wurtzite polytype of homologous series 8H is based on screw dislocations and exhibited optimal photoluminescence (PL) spectra.

Effect of heavy ion irradiation on self-assembled Pr3+:ZnS/TiO2 nanocrystals

We report the modifications in the structural and optical characteristics of Pr doped ZnS/TiO2 nanocrystals under 120 MeV Au9+ ions irradiation at various fluence ranges. The structural modification of Pr doped ZnS/TiO2 under swift heavy ion irradiation (SHI) shows texturing of ZnS crystalline planes as revealed by x-ray diffraction (XRD) pattern. Scanning electron microscopy (SEM) analysis shows cubical microstructures of pristine Pr3+ doped ZnS/TiO2 which are grown by aggregated nanoparticles. The morphological modifications under SHI show the growth of nano whiskers at highest fluence 3 × 1013 ions cm−2 with simultaneous disintegration of the initial cubical morphology. Photoluminescence (PL) spectrum reveals the white emission with luminescence peak at 485 nm, 525 nm and 665 nm for corresponding transition energy levels 3P0- 3H4, 3P0- 3H5 and 3P0- 3F2 of Pr3+ ions in ZnS host matrix. Also, it shows the characteristic blue emission due to sulphur vacancies at 379 nm in ZnS. At higher irradiation fluence 3 × 1013 ions cm−2, decreased PL intensity shows production of high dislocation density or non-radiative recombination of carriers in nanocrystalline Pr3+ doped ZnS/TiO2 structure.