This study shows a detailed report on the morphological, structural and optical properties of CdSe QDs synthesised by the hot injection method. Cadmium acetate dihydrate and Se powder were used as cadmium and selenide precursors, respectively. Various QD sizes were achieved by synthesizing in temperature range of 150ºC, 175ºC, 200ºC, 225ºC, 250ºC, 275ºC and 300ºC, respectively. The as synthesized QDs by the hot injection method were cross-examined for their morphological, structural and optical using HRTEM, FTIR, XRD, RS, and UV-Vis spectroscopy techniques respectively. FTIR analysis has revealed vibrations at 738, 738, 738, 738, 735, 735 and 733 cm-1 for the QDs synthesized at various temperatures of 150, 175, 200, 225, 250, 275, and 300℃, respectively. The presence of the above mentioned peaks confirms the presence of Cd-Se bond in our samples. XRD analysis of CdSe QDs revealed diffraction peaks at 2 angles of 16.66 , 25.20 , 34.77 , 40.9 , 45.39 and 49.1 for 150 17.4 , 25.22 , 34.85 , 41.7 , 44.45 and 47.5 for the QDs synthesized at various temperatures of 175 17.07 , 25.19 , 34.85 , 41.34 , 44.41 and 48.86 for 200 ; 16.34 , 25.20 , 34.76 , 40.6 , 44.74 and 49.48 for 225 ; 17.44 , 25.17 , 34.19 , 41.7 , 44.45 , 49.24 for 250 ; 16.70 , 25.16 , 34.85 , 40.32 , 45.1 and 49.1 7 for 275 ;and 17.35 , 25.18 , 35.13 , 41.63 , 45.7 , 49.48 for 300 . These XRD peaks relate to crystal planes of (100), (002), (102), (220), (103) and (112) which belong to hexagonal Wurtzite CdSe crystal structure. Additionally XRD analysis has revealed a general peak shift to higher 2 values was observed for CdSe QDs. HRTEM analysis showed that the synthesised CdSe QDs have a spherical shape and are monodispersed. Moreover, HRTEM analysis has revealed CdSe QDs modal crystallite size of 1.79 nm, 1.81 nm, 2.06 nm, 2.08 nm, 2.11 nm, 3.10 nm and 3.12 nm for the QDs synthesized at various temperatures of 150ºC, 175ºC, 200ºC, 225ºC, 250ºC, 275ºC and 300ºC, respectively. HRTEM results were in mutual agreement with XRD results. Additionally, the SAED images showed intense electron diffraction rings, which confirmed that the as-synthesised CdSe QDs have a Wurtzite crystal structure. RS analysis showed that CdSe QDs have LO and 2LO vibrational modes which are characteristic peaks for CdSe. The presence of these peaks in Raman spectra further supports our previous observation from XRD analysis and HRTEM analysis that the synthesized CdSe QDs have a Wurtzite crystal structure. The effect of synthesis temperature Raman peak shift, FHWH and peak intensity has been cross examined in this work, Moreover, the effect of increasing temperature on the peak shift, FWHM and peak intensity is discussed in detail below. UV-Vis analysis revealed an absorbance of CdSe QDs in higher wavelengths as temperature was increased. Furthermore, the Yu et al 2003 relation was used to calculate QD size and band gap energy of CdSe QDs. The results showed that QD size increases with increasing synthesis temperature, which is in agreement with HRTEM and XRD results.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufh/vital:29466 |
| Date | January 2017 |
| Creators | Makinana, Sinovuyo |
| Publisher | University of Fort Hare, Faculty of Science and Agriculture |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis, Masters, MSc |
| Format | 116 leaves, pdf |
| Rights | University of Fort Hare |
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