Polymer and metallodielectric based photonic crystals

The bottom-up colloidal synthesis of photonic crystals has attracted interest over top-down approaches due to their relatively simplicity, the potential to produce large areas, and the low-costs with this approach in fabricating complex 3-dimensional structures. This thesis focuses on the bottom-up approach in the fabrication of polymeric colloidal photonic crystals and their subsequent modification. Poly(methyl methacrylate) sub-micron spheres were used to produce opals, inverse opals and 3D metallodielectric photonic crystal (MDPC) structures. The fabrication of MDPCs with Au nanoparticles attached to the PMMA spheres core–shell particles is described. Various alternative procedures for the fabrication of photonic crystals and MDPCs are described and preliminary results on the use of an Au-based MDPC for surface-enhanced Raman scattering (SERS) are presented. These preliminary results suggest a threefold increase of the Raman signal with the MDPC as compared to PMMA photonic crystals. The fabrication of PMMA-gold and PMMA-nickel MDPC structures via an optimised electrodeposition process is described. This process results in the formation of a continuous dielectric-metal interface throughout a 3D inverted photonic crystal structure, which are shown to possess interesting optical properties. The fabrication of a robust 3D silica inverted structure with embedded Au nanoparticles is described by a novel co-crystallisation method which is capable of creating a SiO2/Au NP composite structure in a single step process. Although this work focuses on the creation of photonic crystals, this co-crystallisation approach has potential for the creation of other functional materials. A method for the fabrication of inverted opals containing silicon nanoparticles using aerosol assisted chemical vapour deposition is described. Silicon is a high dielectric material and nanoparticles of silicon can improve the band gap and absorption properties of the resulting structure, and therefore have the potential to be exploited in photovoltaics

Colloidal co-crystallization: A new route for production of three-dimensional metallodielectric photonic crystals

Growth of three-dimensional (3D) photonic crystals is most interesting research in new and enhancing devices performance ranging from sensor, optoelectronic, photovoltaic and also surface enhance Raman scattering. Co-crystallization with bottom up technique was introduced in producing 3D photonic crystals with metal properties or so called as metallodielectric photonic crystals and also its inverse structure. In this study, poly(methyl methacrylate) (PMMA) particles, acid-hydrolyzed tetraethylorthosilicate solution and pre-formed gold nanoparticles was combined followed by the removal of PMMA template. Relatively large (10 s of mm), robust and crack-free films with thickness of approximately below 20 deposition layers was successfully produced by this simple yet effective route. Its morphology, particle size and optical properties were characterized by scanning electron microscopy (SEM), optical bench set-up

A bottom-up fabrication method for the production of visible light active photonic crystals

A method which combines polymer particle assembly, chemical infiltration and etching with an aerosol assisted deposition process is described for the fabrication of 3D inverse opal (10) structures with sub-micron periodicity and precision. This procedure not only overcomes limitations associated with slow, expensive micro-fabrication methods but also permits the tuning of refractive index contrast via the direct incorporation of photonically-active, preformed, tailored silicon nanostructures. It is demonstrated that this approach can be used to modify the photonic band gap (PBG) by effectively depositing/patterning optically active silicon nanocrystals (ncSi) onto the pore walls of a 3D inverse opal structure. This simple, yet effective method for preparing functional complex 3D structures has the potential to be used generically to fabricate a variety of functional porous 3D structures that could find application not only in new or improved photonic crystal (PC) devices but also in areas such as catalysis, separation, fuel cells technology, microelectronics and optoelectronics

A bottom-up fabrication method for the production of visible light active photonic crystals

A method which combines polymer particle assembly, chemical infiltration and etching with an aerosol assisted deposition process is described for the fabrication of 3D inverse opal (10) structures with sub-micron periodicity and precision. This procedure not only overcomes limitations associated with slow, expensive micro-fabrication methods but also permits the tuning of refractive index contrast via the direct incorporation of photonically-active, preformed, tailored silicon nanostructures. It is demonstrated that this approach can be used to modify the photonic band gap (PBG) by effectively depositing/patterning optically active silicon nanocrystals (ncSi) onto the pore walls of a 3D inverse opal structure. This simple, yet effective method for preparing functional complex 3D structures has the potential to be used generically to fabricate a variety of functional porous 3D structures that could find application not only in new or improved photonic crystal (PC) devices but also in areas such as catalysis, separation, fuel cells technology, microelectronics and optoelectronics

Passive Q-switching operation of erbium-doped fiber laser with gold nanoparticles embedded into PVA film as saturable absorber

We demonstrate a Q-switched Erbium-doped fiber laser (EDFL) using a newly developed gold nanoparticles (GNPs) based saturable absorber (SA) for the first time. The GNPs were embedded in polyvinyl alcohol (PVA) for film-forming and inserted into an Erbium-doped fiber laser (EDFL) cavity to achieve passive Q-switching. The Q-switched EDFL operates at 1560 nm with a pump power threshold of 35 mW, a pulse repetition rate tunable from 19.7 to 89.9 kHz, and the smallest pulse-width of 2.64 µs. The Q-switching pulse shows no spectral modulation with a peak-to-pedestal ratio of 69 dB indicating the high stability of the laser. The highest pulse energy of 103 nJ was obtained at 118 mW pump power. These results show that the GNPs based SA is available for pulsed operation in the 1550 nm spectral range. © 2019, S.C. Virtual Company of Phisics S.R.L. All right reserved

Synergistic effects of Pr6O11 and Co3O4 on electrical and microstructure features of ZnO-BaTiO3 varistor ceramics

This paper investigated the effects of Pr6O11 and Co3O4 on the electrical properties of ZnO-BaTiO3 varistor ceramics. The Pr6O11 doping has a notable influence on the characteristics of the nonlinear coefficient, varistor voltage, and leakage current where the values varied from 2.29 to 2.69, 12.36 to 68.36 V/mm and 599.33 to 548.16 µA/cm2, respectively. The nonlinear varistor coefficient of 5.50 to 7.15 and the varistor voltage of 7.38 to 8.10 V/mm was also influenced by the use of Co3O4 as a dopant. When the amount of Co3O4 was above 0.5 wt.%, the leakage current increased from 202.41 to 302.71 μA/cm2. The varistor ceramics with 1.5 wt.% Pr6O11 shows good nonlinear electrical performance at higher breakdown voltage and reduced the leakage current of the ceramic materials. Besides, the varistor sample that was doped with 0.5 wt.% Co3O4 was able to enhance the nonlinear electrical properties at low breakdown voltage with a smaller value of leakage current