SYNTHESIS AND CHARACTERIZATION OF ZNO : MN DOPED NANOPARTICLES, NANORODS AND NANOBELTS Abhijeet Ojha1,*, Basant Choudhary *, Manoj Jangid *, Prof. Kanan Bala Sharma** * Centre
for Converging Technologies, University of Rajasthan, jaipur-302004, Rajasthan, India. **Department of Physics , University of Rajasthan, Jaipur.-302004,India. Corresponding Author : ojha.abhijeet@gmail.com
Flow Chart of ZnO NP’s & Nanorodes
Abstract Zinc oxide (ZnO) is a transparent wide bandgap semiconductor compound (Eg = 3.37 eV) with a direct electronic transition and has a large exciton binding energy (60 meV) that ensures high luminescence efficiency at room temperature. Similar to GaN , ZnO is considered as a promising material for photonic devices working in the ultraviolet and blue spectral regions.Recent studies have shown that ZnO exhibits many novel nanoscale structures, such as nanorods, nanowires,nanotubes, nanoneedles, nanocombs and so forth,which open up new prospects for applications in micro-optoelectronic devices. In addition, theoretical calculations have predicted that transition-metal-doped ZnO materials may exhibit room-temperature ferromagnetism.This offers opportunities for developing spintronic devices combining standard microelectronics with spin-dependent effects. Such spin-based devices are multifunctional and have very high integration density, ultra-fast data processing speed and low electrical power consumption. However, to realize this idea, a thorough knowledge of the role of impurities and interaction mechanisms taking place in doped ZnO materials is essential. Experimental Zinc oxide nanostructures are of huge scientific and technical interests because of their large excitonic binding energy (EB) 60 meV and better thermal stabilities .
Sample Preparation & Exprimentation :
Synthesis of long length Mn doped ZnO nanoparticle, nanobelts & nanorodes were carried out using chemicals zinc acetate, manganese acetate and absolute ethanol. The synthesis method was initially based on the experimental procedure . Alcohols are commonly used because the solvent also act as a reagent. However, the solvent does not participate in the reaction forming ZnO from zinc acetate .
Synthesis of ZnO nanoparticles Colloidal solution was prepared from Zinc acetate and absolute ethanol. 0.1M Zn2+,prepared from Zinc acetate in absolute ethanol; was refluxed under distillation and stirred for 3hours at 80 0C. Desired proportion of manganese impurity obtained from 0.1M Mn2+ , prepared from Mn acetate, in 100 ml of ethanol,0.1 gm of poly (N-vinyl 2pyrroledone)(PVP) were also added in the reaction during the synthesis process. The concentration of PVP, the capping agent was kept at 0.1 gm per 10 ml of ethanol. The remaining hygroscopic product was mixed with 0.1M LiOH prepared in 100 ml deionized water in which precipitates started forming then precipitates were separated out using centrifugal machine at 5000 rpm and then sample were dried in vacuum oven at 800C. TEMPLATE DESIGN © 2008
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Experimental Procedure Cont … .
Synthesis of ZnO nanobelts : The precursor was prepared from Zinc acetates and absolute ethanol was refluxed at 80 0 C for 3hours . The remaining hygroscopic product is mixed with Mn impurity obtained from 0.1M Mn2+ were separated out and mixed with 0.14M LiOH prepared in 100ml deionized water. The precipitates were separated out using centrifugal machine at 3500rpm. Samples were then dried in the oven at 80oC for 4 hours. We increase the concentration of LiOH from 0.1 M to 0.14 M by doping so that the near neutral clusters are formed and pH =8. This will helps to form long length Nanobelts . helps to form long length nanobelts.
Sample Data with Mn++ doping Concentrations The notation and detailed description of the samples names of inthe people who studied our work. --------------------------------------------------------------------------------No. Sample Descript. Diffusion Diffusion Dopant time(min) temperature conc (◦C) (at %) --------------------------------------------------------------------------------1.ZnO Pure ZnO --850 ----2.ZMO1 Mn-doped ZnO 20 850 0.46 3 ZMO2 Mn-doped ZnO 40 850 1.15 4 ZMCO (Mn)-co-doped ZnO 20 (Mn) 850 0.72 (Mn) .Morphological characterizations : X-ray Diffraction (XRD) data for structural characterization of the various prepared samples of ZnO were collected on an X-ray diffractometer (PW1710) using Cu-Kradiation (1.541).reveal long length nanobelts ranging to a few micrometers in length and XRD pattern reveal their high crystallinity. Wurtzite geometry of ZnO was confirmed as planes <100>,<002> and <101> were obtained. Refluxing of precursor containing zinc acetate and ethanol for long time results in long nanobelts of ZnO. Addition of a catalyst stops isotropic agglomeration of particles instead anisotropic agglomeration occurs resulting in nanowires or nanobelts . 0.1M LiOH give positively charged nanobelts (pH = 6.5) whereas 0.14M LiOH gives nearly neutral nanobelts (pH = 8.0)12. It is very much clear from the SEM images obtained from two methods that positively charged clusters results in deformation of nanobelts and nearly neutral charged clusters results in long length nano belts.
X-ray Diffraction Pattern (XRD) pattern of ZnO nanobelts
Cont …
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The precursor prepared from Zinc acetates and absolute ethanol was refluxed at 80o C for 1hour under oxygen atmosphere. The remaining hygroscopic product is mixed with Mn impurity obtained from 0.1M Mn2+ was separated out and mixed with 0.14 M LiOH prepared in 100 ml deionized water. The precipitates were separated out using centrifugal machine at 4500rpm. Samples were then dried in the oven at 80o C for 4 hours. PL Spectra that is found that the presence of impurities in nanorods influences their PL spectra. For Mn-doped samples (ZMO1 and ZMO2), their PL spectra are similar to the spectrum of pure ZnO. There are two peaks at about 387 and 530–540 nm, corresponding to UV and visible emissions, respectively. The former is attributed to exciton-related near-band-edge luminescence while the latter is commonly referred to as a deep-level/trapstate emission . With increasing Mn doping concentration (for ZMO2), the UV peak shifts to a shorter wavelength (∼382 nm), but its intensity is still very strong. At wavelengths around 660 nm, there is a hump in the PL spectra of ZMO1 and ZMO2,(assigned to an intrinsicdefect-induced emission.) Synthesis of ZnO nanorods
PL spectra of ZnO at different concentration
Results and discussion
TEM Image of ZnO : Mn nanorod.
TEM of ZnO:Mn nanoparticles
SEM Image of ZnO : Mn nanobelt
Conclusion… Mn doped ZnO nanocrystals were synthesized using wet chemical synthesis technique.ZnO nanophosphordoped with variable concentration of Mn have been synthesized in the lab and characterized using TEM and SEM. Figs shows the fabricated ZnO nanostructures. Scanning Electron Microscope(SEM) image shows the nanobelt which have a size around one millimeter. Transmission Electron Microscope(TEM) studies shows that the average diameter of the particles is in between 25-100 nm and the diameter of the rod is around 66 nm. It is clear from the results that Zn:Mn nanostructures are very sensitive to the preparation conditions and we can fabricate any desired nanostructure. High purity nanobelts of ZnO having lengths in the range of several hundreds of micrometers to a few millimeters have been synthesized in the laboratory. SEM gives beautiful results of the synthesized doped nanobelts. Length of the nanobelts varies from a few micrometers to a few millimeters. XRD patterns confirm the wurtzite crystal structure and high crystallanity.
Applications & References… Mn doped ZnO nanobelts have several applications and can be employed as best suit materials for spintronics, gas sensors, better insulation materials, high energy density batteries etc. References :-[ 1] B. B. Lakshmi, C. J. Patrissi, C. R. Martin, Chem.Mater. 9, 2544 (1997). [2] L. Vayssieres, K. Keis, A. Hagfeldt, S. E. Lindquist, Chem. Mater. 13, 4395 (2001). [3] C. Pacholski, A. Kornowski, H. Weller, Angew. Chem. Int. Edn. Engl. 41, 1188 (2002). [4] L. Vayssieres, Adv. Mater. 15, 464 (2003).