Dissertation
Dissertation > Industrial Technology > General industrial technology > Materials science and engineering > Special structural materials

Surface Plasmon Enhanced Photoluminescence from Carbon-based Films

Author Li
Tutor HanGaoRong; ZhangXiWen
School Zhejiang University
Course Materials Science and Engineering
Keywords amorphous carbon amorphous silicon carbide PECVD surface plasmon photoluminescence
CLC TB383
Type PhD thesis
Year 2012
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Due to the strong room-temperature light emissioin property of the hydrogenated amorphous carbon (a-C:H) and the hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films, these carbon-based films have been widely considered as promising candidates for the active layers of various light emitting devices. However, due to the current blooming development of the advanced optoelectronic devices such as light emitting diodes and flat-panel display devices, stronger luminescence intensity of the conventional carbon-based films is still needed. The structural, optical and electrical properties of these carbon-based films can be controlled by manipulation of the carbon, silicon and hydrogen composition. However, the chemical bonding configurations and microstructures of the a-C:H and a-Si1-xCx:H films are very complicated since carbon atom can be in a form of sp2 or sp3 configuration. Therefore, from the practical point of view, it is crucial to elucidate the relationship among the deposition parameters, the bonding configurations, the film microstructures, and the optical properties.In this work, several series of carbon-based films were deposited by a capacitively coupled PECVD system operating at a radio frequency of 13.56 MHz. Silane, ethylene and hydrogen were used as the reaction sources, and variable deposition parameters were applied. The dependence of film deposition rates, bonding configurations, microstructures and optical properties on the deposition conditions was systematically investigated. Ag films were deposited by DC magnetron sputtering and annealed to form various surface nanostructures. The influence of Ag sputtering time, annealing temperature and annealing time on the Ag surface morphology and surface plasmon (SP) resonance was studied. The carbon-based films were combined with the nanostructured Ag films to form sandwich nanostructure with silica substrates. The dependence of SP mediated PL enhancement on the composite film structures, Ag surface morphology, the carbon-based film thickness, the PL wavelength and the internal quantum efficiency (IQE) of the carbon-based films were investigated in detail and the SP mediated PL enhancement mechanism was discussed. The main research findings are summerized as follows:1. The carbon-based films studied in this work were amorphous. The a-C:H films were composed of hydrogenated sp3 C-C network and sp2 amorphous carbon clusters embedded in the matrix; the structure of a-Si1-χCχ:H films were similar to that of a-C:H films, the silicon atoms incorporated into the spJ C-C network to form Si-C network. Strong visible photoluminescence (PL) from the carbon-based films was observed at room temperature. It was confirmed that the PL of a-C:H film originated from the radioactive recombination of excited electron-hole pairs within sp" carbon clusters, and the PL of a-Si1-χCχ:H film was dominated by the radioactive recombination through sp2 carbon clusters, silicon atoms and network defects.2. Ag was chosen as the SP-supporting material. Ag films were deposited by DC magnetron sputtering and annealed to form various surface nanostructures. It was found that the size of Ag nanoparticles increased with the increasing sputtering time, and the Ag films became continuous as the sputtering time prolonged. The increase of annealing temperature and annealing time facilitated the formation of Ag surface nanostructure. The in-plane SP resonance modes and surface morphology of the Ag films can be tuned by controlling the Ag sputtering and annealing parameters.3. The a-Si1-χCχ:H films were combined with the nanostructured Ag films. The integrated PL enhancement factors of the composite films were found to firstly increase with the Ag nanoparticle (NP) size, subsequently reach a maximum value of 3.3 when the average Ag NP size of Ag films was 76 run. The relationship between the PL enhancement factor curves and the corresponding extinction spectra was attributed to the near-field enhancement and far-field extinction, respectively. The results indicated that the PL enhancement was dominated by the scattering of SPs in the Ag films. For the a-Si1-χCχ:H/Ag composite films with continuous Ag layers, SP coupling was particularly useful for increasing PL intensity of a a-Si1-χCχ:H film with inherently low IQE.4. The blue PL of a-C:H films was enhanced by coupling through the SPs generated at Ag films. It was found that the PL enhancement increased with Ag NP size and the surface roughness of the continuous Ag films. The PL quenching was also observed in some cases, which is potentially attributed to the absorption of small Ag NPs or the electron transfer at the a-C:H/Ag interface. A maximum PL enhancement factor of 9.5 was successfully obtained when the 43 nm-thick of a-C:H film was deposited on the Ag film with the highest surface roughness (Rq=14.9 nm).

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