Geok Bee Teh

Colloidal Synthesis of Silicon Nanocrystals Via Inverse Micelles Microemulsion

Abstract We describe here the synthesis and characterization of silicon nanocrystals prepared by using microemulsion technique which involved the formation of inverse micelles. Colloidal systems employing TOAB as the surfactant molecules were used to synthesise nanosized silicon nanocrystals. The initial reaction of silicon tetrachloride, SiCl4 with a strong reducing agent, NaBH4 produced Si nanocrystals with hydrogen terminated surfaces. The surfaces of the nanocrystals were then capped with 1-heptene which protected the silicon nanocrystals from oxidation. The resultant surface passivated silicon nanocrystals suspended in organic solvent were characterized by Fourier transform infrared spectroscopy, photoluminescence spectroscopy and high resolution transmission electron microscopy. This study provided direct evidence of ageing, stability of different surface passivation and the quantum confinement effect in nanosized silicon nanocrystals.

Effect of Sol-Gel Synthesis on the Structural and Photoluminescence Properties of Magnetoplumbite-Type Strontium Ferrite

Magnetoplumbite-type (M-type) strontium ferrite particles with two stoichiometric ratios (SrFexO19; x = 9.2 and 11.6) have been synthesized via the sol-gel technique employing ethylene glycol as the gel precursor. The prepared samples were characterized using x-ray diffractometry (XRD), thermogravimetric analysis (TGA), photoluminescence (PL) spectrophotometry, field emission scanning electron microscopy (FESEM), energy dispersive x-ray spectrometry (EDS) and superconductivity quantum interference device magnetometry (SQUID). X-ray powder diffraction patterns showed that the samples were single-phase with the space group of P63/mmc and cell parameter values of a = 5.88 Ǻ and c = 23.03 – 23.04 Ǻ. EDS results confirmed the composition being mainly of M-type SrFe12O19. The photoluminescence property of strontium ferrite was examined at excitation wavelength of 260 - 290 nm and significant PL emission peaks centered at 334 nm were detected. Both as-prepared strontium ferrites exhibited significant oxygen vacancies which were detectable via TGA where the sample with the Sr/Fe ratio of 1:11.6 exhibited the highest oxygen vacancies in its structure.

Synthesis and Characterization of Highly Crystalline Zinc Phosphide Nanoparticles

Nanoscale alpha zinc phosphide (α-Zn3P2) particles are a class of promising opto-electronic materials which have attracted worldwide attention. The synthetic protocols pertaining to α-Zn3P2 nanoparticles have been largely based on the use of costly, pyrophoric and toxic phosphines precursors. We reported here the results of our investigation into the viability of fabricating crystalline α-Zn3P2 nanoparticles using phosphorous pentabromide (PBr5) as precursor via an air-stable solid hydrogen phosphide (PH)x intermediate. HRTEM analysis revealed the best sample as spherical crystalline α-Zn3P2 nanoparticles with diameter found to be 5.8±2.1 nm. These particles exhibited photoluminescence centered at 470 nm (2.6 eV), blue-shifted by 1.2 eV from the 1.4 eV of bulk α-Zn3P2.