Preparation And Application Of Silicon Carbide Quantum Dots

Silicon carbide (SiC) quantum dots have strong and stable violet-green photoluminescence emission due to the quantum confinement effect. It is believed that the SiC quantum dots have promising applications in the field of optoelectronics, biology and so on. In recent years, the investigations on SiC quantum dots mainly were focused on the preparation process, the luminescence mechanism and the applications. However, in spite of all the efforts, there is no method suitable for large scale synthesis of SiC quantum dots with uniform size. And the experimental evidence of the surface structure characteristics of SiC quantum dots is in lack. This thesis mainly focuses on the two aspects. The relevant research results are as follows:1. SiC quantum dots were prepared via simple chemical etching and subsequent ultrasonic vibration from 3C-SiC powders at microscale. They were suspended in de-ionized water with various pH value, and organic solvent of methanol, ethanol, chloroform and toluene. The wavelength and intensity of the photoluminescence peak of these suspensions excited at the lines with different wavelength were recorded and analyzed. It is found that the 3C-SiC quantum dots are hydrophilic. The hydroxyl group bonding on the surface leads to a decrease of the energy gap. Also, as prepared 3C-SiC quantum dots are polarized. The 3C-SiC quantum dots are very stable in methanol, ethanol and de-ionized water.2. The 3C-SiC quantum dots suspended in de-ionized water were fabricated from the 6H-SiC polycrystalline target via the pulsed laser ablation technique. A serious of characterizations suggested that the number of quantum dots with the diameter about 2 nm is predominant. The number of the quantum dots decrease sharply with the diameter increase. The size distribution shows a clear turn point at 2.5 nm. The photoluminescence spectra revealed that the emission intensity decreases monotonously at the excitation lines with the wavelength ranging from 260 nm to 420 nm. The photoluminescence intensity drops more quickly as the excitation wavelength higher than 320 nm. The calculation confirmed that the intensity dependence on the excitations is consistent with the diameter distribution. The Fourier transform infrared spectrum implied that the surfaces of the quantum dots were passivated very well. The ultraviolet-visible absorption spectrum suggests that the band gap of as-prepared quantum dots is 2.8 eV.3. Amorphous SiC nanoparticles suspend in de-ionized water were prepared via pulsed laser ablation method from the polished 3C-SiC polycrystalline wafer in light yellow. The nanoparticles have a diameter of about 10 nm. High resolution transmission electron microscopy images and the selected area diffraction patterns confirmed that as-prepared nanoparticles are amorphous. The Fourier transform infrared spectrum suggested that the nanoparticles are of SiC and hydrophilic. The band gap calculated from the ultraviolet-visible absorption spectrum further confirmed that the nanoparticles are of SiC.As excited at 320nm, the nanoparticles have strong luminescence centered at 320 nm.