Abstract
Objective: The objective of this study is to synthesize CdO nanoparticle and nanoflakes both in a single way. Also the purpose of removing defects from semiconductor nanoparticles has been considered. Methods: Very small sized Cadmium oxide nanoparticles (11 – 29 nm) and nanoflakes of average size 70 nm were prepared by sol-gel process. Two solutions of 0.2M CdCl2 and 0.2M NaOH were used with a mixture of 1:2 ethylene glycol and methanol. Two different heating method of dried precipitate was adopted to observe the morphology and defect characteristics. Half of the precipitate was annealed in furnace and rest half in domestic microwave. Findings: The fcc (NaCl-type) structure has been found in the nanostructures with lattice constant varying with annealing temperature. We propose a linear relation for the change in lattice constant. HRTEM pictures show nanoflakes and hexagonal nanoparticles. The ratio curve of coincidence Doppler broadening spectroscopy (CDBS) found defect concentration reduction and agglomeration effect on microwave irradiation in place of furnace annealing. It indicated reduction of defects inside the nanoparticles. The S and W parameter revealed the chemical surroundings and momentum distribution of the vacancy clusters varying with crystallite size. Novelty: Furnace annealing and microwave irradiation showed different effect of surface strain on lattice. Microwave irradiation has been used to reduce defects inside CdO nanocrystals for potential application and coincidence Doppler broadening spectroscopy showed potential to be a very effective tool of defect characterization and electron momentum comparison. Also, this work presents how microwave radiation can be used to prepare nanoflakes and nanoparticles from same reactants without any substrate. Keywords: Domestic microwave; nanocrystals; positron annihilation; solgel processes
Highlights
Nowadays the nanomaterials have drawn much attention for its wide application and increase of basic knowledge in materials[1] research
The lattice constant of bulk Cadmium oxide (CdO) is 4.6900Å [14] whereas those of the samples synthesised in this work differed from this value on account of their nanocrystalline structure
Nanocrystallite size of microwave synthesized samples are in the range 18 – 70 nm
Summary
Nowadays the nanomaterials have drawn much attention for its wide application and increase of basic knowledge in materials[1] research. Point defects can decrease the desired level of doping that can be achieved while fabricating a semiconductor device. To overcome these difficulties defect concentration should be reduced. Many researchers have reported their work on characterization[9], and electrical, optical, [10] magnetic [11] studies on CdO and other metal oxide nanomaterials. In this report sol – gel method followed by annealing and microwave irradiation has been utilized to synthesize six different CdO nanosamples to obtain various crystallite sizes and nanoflakes. Microwave irradiation method provided simple and fast routes to the synthesis of pure nanomaterials with narrow distribution of size and no high temperature or high pressure was needed. Its need to observe if any change occurs in dimensionality of nanomaterials on alteration of microwave power
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