Papers by Author: Rong Fuh Louh

Abstract: Fabrication of high sphericity, monodispersed microspheres (100~600 nm) of various oxides (SiO₂, TiO₂, ZnO, In₂O₃, SnO₂) via sol-gel process and polystyrene (PS) microspheres (200~400 nm) via emulsion polymerization is presented. A high colloidal stability suspension was obtained by adjusting the zeta potential of such spheres and pH of the colloid. The 3-D photonic crystal (PhC) templates of opaline structure on ITO-coated glasses and silicon wafers were easily formed under electrophoretic self-assembly (EPSA) of microspheres under the influence of exerting electrical forces. Different setups of counter-electrode were attempted to establish an electrical field. The lattice constant of an ordered opal structure by EPSA can also be tuned by the electrical field gradient. Interestingly various self-assembled 3-D structures of silica microspheres in either symmetrical curvilinear profile or triangular ridges can be produced through EPSA route using specific counter-electrode setups. The measured optic properties of such 3-D PhC templates manifest photonic bandgap (PBG) based on planar-wave expansion (PWE) simulation to verify the existence of real PBG in PhC samples with tunable nanostructures. The PS PhC templates are currently used to easily transform into inverse opal structure (IOS) by infiltrating sol of other oxides with high dielectric constant (e.g. ZnO or TiO₂) and filled with metallic nanoparticles (Ni or Cu) by electrochemical deposition or chemical bath deposition (CBD).

Abstract: The chalcogenide CdSe quantum dots (QDs) were obtained by wet chemical synthesis route, using cadmium oxide and pure selenium as precursors, hexadecylamine (HDA), tetradecylphosphine oxide (TDPO) and tri-n-octylphosphine oxide (TOPO) as complexing agents in tri-n-butylphosphine (TBP) solvent in the reactor with an argon protection atmosphere. This study aims at manipulating the size of QDs for the potential in vivo medical applications. The CdSe nanoparticles were analyzed by particle size analyzer, photoluminescence (PL) spectroscopy, FE-SEM, TEM, and XPS. The desired particle size and photoluminescence response of CdSe QDs can be achieved by adjusting proper molar ratios of HDA/TOPO and CdO/Se, along with the synthesis temperature and reaction time. Our results show that the obtained CdSe quantum dots have the average particle size of 1~10 nm within a size variation of 1.5 nm. The resultant CdSe QDs provide stable PL responses as excited by light sources of 388~550 nm wavelengths.

Abstract: Chemical bath deposition (CBD) is a fairly simple synthetic route to prepare II-VI semicondutive zinc sulfide thin films, which can be prepared on the flat surface of glass or silicon wafer substrates in the solution containing the precursors of zinc and sulfur ions in terms of ambient conditions of varying acidity. This study particularly aims at the growth dependence and optical property of ZnS thin films in the CBD process by different experiment parameters, whereas we intend to choose suitable types of zinc ionic precursors to be coupled with various CBD parameters such as reaction temperature and time, precursor concentration, types and complexing agents as well as post-deposition heat treatment conditions. Addition of different concentration of ethylenediamine, ammonium sulfate, sodium citrate and hydrazine in the CBD reaction process was used to control the adequate growth rate of ZnS thin films. As a consequence, the rapid thermal annealing was employed to enhance the film uniformity and thickness evenness, transmittance and the energy gap of ZnS samples. The results would lead to a potential application of buffer layer for the Cu (In,Ga)Se2 based thin film solar cells. The analytic instrument including SEM, AFM, UV-VIS were used to examine the CBD-derived nanosized ZnS buffer layers for the thin film solar cells. The ZnS thin films prepared by the chemical bath deposition in this study results in film thickness of 80 ~ 100 nm, high transmittance of 80~85% and the energy gap of 3.89 ~ 3.98 eV.

Abstract: Monosized silica microspheres (100−500 nm) were prepared by a sol-gel process by using tetraethyl orthosilicate precursor. A well-dispersed suspension was obtained by adjusting suspension to be weakly basic for a better yield of electrophoretic self-assembly (EPSA). A perfect EPSA behavior of silica microspheres into the layered pattern with the FCC structure was created. EPSA technique has been demonstrated as a simple and effective route to make numerous templates, which are associated with 3-D structures of silica microspheres in asymmetric geometries, for design of photonic crystals.