Structural and Electrical Studies on ZnS Nanoparticles Prepared Without Using Capping Agent (original) (raw)

In this work, zinc sulfide (ZnS) nanoparticles have been synthesized by simple chemical precipitation method without using any capping agent. The synthesized nanoparticles were characterized using XRD, optical microscopy, UV-Vis, FTIR, and impedance spectroscopy. The X-ray diffraction shows that ZnS particles have cubic sphalerite structure with the crystallite size of 10-20 nm. SEM images of nanopowder samples reveal the presence of nanoflakes and agglomerated nanoparticles. Formation of ZnS has been confirmed through the appearance of 714 cm -1 absorption peak. The thermal stability of synthesized nanoparticles has been checked by annealing the material at different temperatures. Transformation of ZnS into ZnO subsequent to annealing has been evidenced from XRD and FTIR studies. UV-Vis spectra exhibited a red shift in the optical absorption on increase in annealing temperature. Variation in electrical conductivity obtained from impedance measurements at different temperatures has been suitably correlated to Davis-Mott model Keywords: zinc sulfide nanoparticles; II-VI semiconductors; chemical precipitation method; optical band gap; annealing 1 Introduction Currently there is a great deal of interest in optical and structural properties of nanometer sized semiconductor particles . Additionally, such nanoparticles have exhibited applicability as zero-dimensional quantum confinement material besides application in optoelectronics and photonics . Nano semiconductors, including II-VI group semiconductors show significant departures from bulk properties when the scale of confinement approaches to excitonic Bohr radius which sets the length scale for optical process. The photo-emission wavelengths, the band gap and lattice parameter are strongly dependent on the grain size rendering tailorability of these properties as a function of grain size. However, the biggest hurdle in nanotechnology seems to be the control of grain size in a few nanometer range . As a consequence, the development of semiconductor nanocrystals of controlled shape and size possessing desired optoelectronic properties has been the subject of intense research. Within the family of nano-semiconductors, Zinc Sulfide has been extensively investigated due to its wide ranging applications in Photoluminescence (PL), Electroluminescence (EL), Cathodoluminescence (CL) devices, Light Emitting Diodes, reflectors and dielectric filters. It has a wide band gap of 3.5-3.8 eV at room temperature and better chemical stability compared to other chalcogenides. Its band can be tuned in the UV region. [9-13]. Annealing treatment is very common in semiconductor processing. It can be used to remove the defects and to test the stability of the crystals at a given temperature under the given ambient conditions, which is important for device purposes. To the best of our knowledge, there are only few reports on the annealing effects on ZnS . Keeping in view the above, an effort has been made here to study the effect of annealing on the optical, structural and electrical properties of ZnS particles.