本論文示範了兩款過渡金屬硫化物量子點 (二硫化銀銦量子點與硫化錳量子點) 在量子點敏化太陽能電池上作為光敏化劑的應用，這也是它們在量子點敏化太陽能電池上的初次應用。 / 二硫化銀銦量子點的合成採用了一鍋合成法，合成的量子點隨後透過3-巰基丙酸連接到二氧化鈦的表面。研究發現，當量子點溶液的濃度處於較低水平的時候，量子點在二氧化鈦的吸附量會較高。另外，從不同研究小組在量子點吸附行為的報告中，觀察到量子點的吸附行為決定於實驗條件，如量子點的大小和表面活劑，納米二氧化鈦多孔膜的孔隙度和量子點的溶劑。實驗中，最高性能的二硫化銀銦量子點敏化太陽能電池的短路電流為0.49 mA/cm²，開路電壓為0.245 V，填充因子為38.26 %，光電轉換效率為0.046 %。 / 透過連續離子層沉積反應法，硫化錳量子點生長並組裝到二氧化鈦的表面上。能譜測量顯示，錳跟硫的比率在不是1:1。這現象懷疑是源於錳(2+)的小離子半徑，對錳(2+)和硫(2-)之間的化學反應產生了不良的影響，導致吸附了的錳(2+)沒有反應過來。通過優化連續離子層沉積反應法週期的數量，最高性能的硫化錳量子點敏化太陽能電池的短路電流為0.65 mA/cm²，開路電壓為0.30 V，填充因子為48.21 %，光電轉換效率為0.095 %。 / QD-SSCs sensitized with novel transition metal sulfides have been demonstrated. Both AgInS₂ QD-SSC and MnS QD-SSC presented in this thesis are new and are the first demonstrated works in the research field. / AgInS₂ QDs was synthesized by one-pot hot colloidal synthesis approach. The as-synthesized QDs were attached to the TiO₂ surface through 3-mercaptopropionic acid. Optimization process on QDs adsorption was done, and it has been observed that the amount of QDs adsorbed is higher when the concentration of the QDs solution is at low level. The variations in the behaviors in QDs adsorption between works from different research groups are considered to originate from experimental conditions such as the sizes and surfactants of QDs, porosities in the TiO₂ matrix, and the solvent for QDs dispersion. The optimized AgInS₂ QD-SSC attained a short-circuit current of 0.49 mA/cm², an open-circuit voltage of 0.245 V, a fill factor of 38.26 % and a power conversion efficiency of 0.046 %. IPCE measurements confirm the successful sensitization from AgInS₂ QDs, indicating the energetically favourable electron injection from AgInS₂ QDs to TiO₂. / By adopting the SILAR technique, MnS QDs was in-situ grown and deposited on the TiO₂ surface. EDX measurements indicated that the Mn/S ratio in the TiO₂/MnS film is not 1:1. The reason is suspected to originate from the small ionic radius of Mn²⁺ that promoted an adverse effect on the reaction between Mn²⁺ and S²₋. It is proposed that a portion of the adsorbed Mn²⁺ did not react with the S²₋., resulting an excess concentration of Mn²⁺ in the film. By optimizing the number of SILAR cycles, MnS QD-SSC was optimized to exhibit a short-circuit current of 0.65 mA/cm², an open-circuit volatge of 0.30 V, a fill factor of 48.21 % and a power conversion efficiency of 0.095 %. IPCE measurements confirm the sensitization is originated from MnS QDs, which consequently reveal an energetically favourable electron injection from the MnS QDs to TiO₂. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Cheng, Kai Chun. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese. / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Solar cells --- p.2 / Chapter 1.2.1 --- Developments --- p.2 / Chapter 1.2.2 --- Nanostructured solar cells --- p.4 / Chapter 1.2.2.1 --- Bilayer organic solar cells --- p.4 / Chapter 1.2.2.2 --- Bulk heterojunction organic solar cells --- p.5 / Chapter 1.2.2.3 --- Organic-inorganic hybrid solar cells --- p.7 / Chapter 1.2.2.4 --- Dye-sensitized solar cells --- p.8 / Chapter 1.2.2.5 --- Quantum dot-sensitized solar cells --- p.11 / Chapter 1.2.3 --- Characterization of solar cells --- p.11 / References --- p.14 / Chapter Chapter 2 --- Quantum dot-sensitized solar cells --- p.18 / Chapter 2.1 --- Quantum dots --- p.18 / Chapter 2.1.1 --- Quantum confinement --- p.18 / Chapter 2.1.2 --- Multiple exciton generation --- p.20 / Chapter 2.2 --- Quantum dot-sensitized solar cell --- p.22 / Chapter 2.2.1 --- Principles --- p.22 / Chapter 2.2.2 --- Assembly of oxide/quantum dot film --- p.25 / Chapter 2.2.3 --- Light harvesting and electron injection --- p.29 / Chapter 2.2.4 --- Titanium dioxide as electron acceptor --- p.33 / Chapter 2.2.5 --- Redox process of electrolyte --- p.37 / Chapter 2.2.6 --- Counter electrode materials --- p.39 / References --- p.41 / Chapter Chapter 3 --- Experimental Details --- p.45 / Chapter 3.1 --- Materials --- p.45 / Chapter 3.2 --- Preparation of the TiO₂ mesoporous film --- p.46 / Chapter 3.3 --- Synthesis of AgInS₂ quantum dots --- p.47 / Chapter 3.4 --- Preparation of the TiO₂/QDs film --- p.47 / Chapter 3.5 --- Configuration of the QD-sensitized solar cell --- p.49 / Chapter 3.6 --- Characterization and Photoelectrochemical Measurements --- p.51 / References --- p.52 / Chapter Chapter 4 --- Experimental Results --- p.53 / Chapter 4.1 --- AgInS₂ QD-sensitized solar cell --- p.54 / Chapter 4.1.1 --- Characterization of AgInS₂ QDs --- p.54 / Chapter 4.1.2 --- Adsorption of AgInS₂ QDs on the TiO₂ surface --- p.56 / Chapter 4.1.3 --- Photoelectrochemical measurements of the AgInS₂ QD-SSC --- p.60 / Chapter 4.2 --- MnS QD-sensitized solar cell --- p.64 / Chapter 4.2.1 --- Characterization of MnS QDs --- p.64 / Chapter 4.2.2 --- Photoelectrochemical measurements of the MnS QD-SSC --- p.69 / References --- p.74 / Chapter Chapter 5 --- Discussions and Conclusions --- p.75 / Chapter 5.1 --- Discussions --- p.76 / Chapter 5.1.1 --- AgInS₂ QD-SSC --- p.76 / Chapter 5.1.1.1 --- Adsorption of AgInS₂ QDs on the TiO₂ surface --- p.76 / Chapter 5.1.1.2 --- Electron injection --- p.80 / Chapter 5.1.1.3 --- Problems encountered and future directions --- p.83 / Chapter 5.1.2 --- MnS QD-SSC --- p.84 / Chapter 5.1.2.1 --- Growth of MnS QDs on the TiO₂ surface --- p.85 / Chapter 5.1.2.2 --- Effects of SILAR cycles on MnS QD-SSC --- p.86 / Chapter 5.1.2.3 --- Problems encountered and future directions --- p.88 / Chapter 5.1.3 --- AgInS₂ QD-SSC versus MnS QD-SSC --- p.89 / Chapter 5.2 --- Conclusions --- p.91 / References --- p.94

Self-assembly of nanomaterials over macroscopic dimensions and development of novel nano-electromechanical systems (NEMS) hold great promise for numerous nanotech applications. However, it has always been a great challenge to find a general route for controlled self-assembly of nanomaterials and generating electromechanical response at the nanoscale level. This work indicates that self-organized anisotropic nematic liquid crystals (LC) can be exploited for nanotemplating purposes to pattern carbon nanotubes (CNTs) and Quantum dots (QDs) over a macroscopic dimension. The pattern formed by the CNTs or QDs can be controlled by applying external electric and magnetic fields, developing novel nano-electromechanical and nano-magnetomechanical systems. Self-organizing nematic liquid crystals (LC) impart their orientational order onto dispersed carbon nanotubes (CNTs) and obtain CNT-self-assembly on a macroscopic dimension. The nanotubes-long axis, being coupled to the nematic director, enables orientational manipulation via the LC nematic reorientation. Electric field induced director rotation of a nematic LC+CNT system is of potential interest due to its possible application as a nano-electromechanical system. Electric field and temperature dependence of dielectric properties of an LC+CNT composite system have been investigated to understand the principles governing CNT-assembly mediated by the LC. In the LC+CNT nematic phase, the dielectric relaxation on removing the applied field follows a single exponential decay, exhibiting a faster decay response than the pure LC above a threshold field. Due to a strong LC-CNT anchoring energy and structural symmetry matching, CNT long axis follows the director field, possessing enhanced dielectric anisotropy of the LC media. This strong anchoring energy stabilizes local pseudo-nematic domains, resulting in nonzero dielectric anisotropy in the isotropic LC phase. These anisotropic domains respond to external electric fields and show intrinsic frequency response. The presence of these domains makes the isotropic phase electric field-responsive, giving rise to a large dielectric hysteresis effect. These polarized domains maintain local directors, and do not relax back to the original state on switching the field off, showing non-volatile electromechanical memory effect. Assembling quantum dots (QDs) into nanoscale configurations over macroscopic dimensions is an important goal to realizing their electro-optical potential. In this work, we present a detailed study of a pentylcyanobiphenyl liquid crystal (LC) and a CdS QD colloidal dispersion by probing the dielectric property  and relaxation as a function of an applied ac-electric field Eac. In principle, dispersing QDs in a nematic LC medium can direct the dots to align in nearly one-dimensional chain-like structures along the nematic director and these assemblies of QDs can be directed by external electric fields. In a uniform planar aligned cell, the Fréedericksz switching of the LC+QDs appears as a two-step process with the same initial switching field as the bulk but with the final value larger than that for an aligned bulk LC. The relaxation of  immediately following the removal of Eac follows a single-exponential decay to its original value that is slower than the bulk but becomes progressively faster with increasing Eac, eventually saturating. These results suggest that the arrangement of the QDs is mediated by the LC.

Silicon quantum dots (QDs) in SiO2 superlattices were fabricated by alternate deposition of silicon oxide (SiO2) and silicon-rich oxide (SRO), i.e. SiOx (x<2), and followed by high temperature annealing. A deposited SRO film is thermodynamically unstable below 1173oC and phase separation and diffusion of Si atoms in the amorphous SiO2 matrix creates nano-scaled Si quantum dots. The quantum-confined energy gap was measured by static photoluminescence (PL) using an Argon ion laser operating at 514.5 nm. The measured energy band gaps of crystalline Si QDs in SiO2 matrix at room temperature (300 K) show that the emission energies from 1.32 eV to 1.65 eV originating Si dot sizes from 6.0 nm to 3.4 nm, respectively. There is a strong blue-shift of the PL energy peak position with decreasing the quantum dot size and this shows the evidence of quantum confinement of our fabricated Si QDs in SiO2 matrix. The PL results indicate that the fabricated Si QDs in SiO2 matrix could be suitable for the device application such as top cell material for all-silicon tandem solar cells. Silicon QD superlattices in nitride matrix were fabricated by alternate deposition of silicon nitride (Si3N4) and silicon-rich nitride (SRN) by PECVD or co-sputtering of Si and Si3N4 targets. High temperature furnace annealing under a nitrogen atmosphere was required to form nano-scaled silicon quantum dots in the nitride matrix. The band gap of silicon QD superlattice in nitride matrix (3.6- 7.0 nm sized dots) is observed in the energy range of 1.35- 1.98 eV. It is about 0.3- 0.4 eV blue-shifted from the band gap of the same sized quantum dots in silicon oxide. It is believed that the increased band gap is caused by a silicon nitride passivation effect. Silicon-rich carbide (SRC, i.e. Si1-xCx) thin films with varying atomic ratio of the Si to C were fabricated by using magnetron co-sputtering from a combined Si and C or SiC targets. Off-stoichiometric Si1-xCx is of interest as a precursor to realize Si QDs in SiC matrix, because it is thermodynamically metastable when the composition fraction is in the range 0 < x < 0.5. Si nanocrystals are therefore able to precipitate during a post-annealing process. SiC quantum dot superlattices in SiC matrix were fabricated by alternate deposition of thin layers of carbon-rich silicon carbide (CRC) and SRC using a layer by layer deposition technique. CRC layers were deposited by reactive co-sputtering of Si and SiC targets with CH4. The PL energy band gap (2.0 eV at 620 nm) from 5.0 nm SRC layers could be from the nanocrystalline ??-SiC with Si-O bonds and the PL energy band gap (1.86 eV at 665 nm) from 6.0 nm SRC layers could be from the nanocrystalline ??-SiC with amorphous SiC clusters, respectively. The dielectric material for an all-silicon tandem cell is preferably silicon oxide, silicon nitride or silicon carbide. It is found that for carrier mobility, dot spacing for a given Bloch mobility is in the order: SiC > Si3N4 > SiO2. By ab-initio simulation and PL results, the band gap for a given dot size is in the order: SiC > Si3N4 > SiO2. However, the PL intensity for a given dot size is in the order: SiC < Si3N4 < SiO2.

Wet thermal oxidations of polycrystalline Si₀.₅₄Ge₀.₄₆ films at 600°C for 30 and 50 min were carried out. A stable mixed oxide was obtained for films that were oxidized for 50 min. For film oxidized for 30 min, however, a mixed oxide with Ge nanocrystallites embedded in the oxide matrix was obtained. A trilayer gate stack structure that consisted of tunnel oxide/oxidized polycrystalline Si₀.₅₄Ge₀.₄₆/rf sputtered SiO₂ layers was fabricated. We found that with a 30 min oxidized middle layer, annealing the structure in N₂ ambient results in the formation of germanium nanocrystals and the annealed structure exhibits memory effect. For a trilayer structure with middle layer oxidized for 50 min, annealing in N₂ showed no nanocrystal formation and also no memory effect. Annealing the structures with 30 or 50 min oxidized middle layer in forming gas ambient resulted in nanocrystals embedded in the oxide matrix but no memory effect. This suggests that the charge storage mechanism for the trilayer structure is closely related to the interfacial traps of the nanocrystals. / Singapore-MIT Alliance (SMA)

Thesis (Ph. D.)--University of Texas at Dallas, 2006. / Includes bibliographical references (leaves 109-116).

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 126-135). Also available in electronic version.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 163-175).

It is very interesting to probe the rotational symmetry of semiconductor quantum dots for quantum information and quantum computation applications. We studied the effects of rotational symmetry in semiconductor quantum dots using configuration interaction calculation. Moreover, to compare with the experimental data, we studied the effects of hidden symmetry. The 2D single-band model and the 3D single-band model were used to generate the single-particle states. How the spectra affected by the breaking of hidden symmetry and rotational symmetry are discussed. The breaking of hidden symmetry splits the degeneracy of electron-hole single-triplet and triplet-singlet states, which can be clearly seen from the spectra. The breaking of rotational symmetry redistributes the weight percentage, due to the splitting of px and py states, and gives a small brightness to the dark transition, giving rise to asymmetry peaks. The asymmetry peaks of 4X, 5X, and 6X were analyzed numerically. In addition, Auger-like satellites of biexciton recombination were found in the calculation. There is an asymmetry peak of the biexciton Auger-like satellite for the 2D single-band model while no such asymmetry peak occurs for the 3D single-band model. Few-particle effects are needed in order to determine the energy separation of the biexciton main peak and the Auger-like satellite. From the experiments, it was confirmed that the lower emission energy peak of X2-spectrum is split. The competed splitting of the X2- spectra were revealed when temperature dependence was implemented. However, since the splitting is small, we suggest the X2- peaks are broadened in comparison with other configurations according to single-band models. Furthermore, the calculated excitonic emission patterns were compared with experiments. The 2D single-band model fails to give the correct energy order of the peaks for the few-particle spectra; on the other hand the peaks order from 3D single-band model consistent with experimental data.

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In this study, we develop self-assembled nano-metal-dots etching mask techniques to fabricate quantum dots (QDs) nano-pillars. We explain the self-assembled nano-metal-dots formation processes by using Dewetting model. Two important experimental factors including (1) interaction force between film and vapor during annealing (£^FV),¡]2¡^interaction force between film and substrate (£^FS) are study to investigate the self-assembled processes. A 200nm thick SiO2 buffer layer is first deposited on the GaAs substrate to congregate thermal energy during the RTA process. In our group, the QDs optimum grown temperature condition is 570¢J, so we develop Au-Ge nano-dots process especially for GaAs based QDs samples. The 8nm thick Au-Ge is annealed at lower 500oC for 60sec under the pressure of 5 E6 Torr to format the nano-dots on QDs samples. The Au-Ge nano-dots have a size and density of 250 ¡Ó 50 nm and 4 E8 cm-2,respectively. We use the Au-Ge nano-dots as mask and dry etching process to fabricate the 9-layer vertical coupled QDs nano-pillars. The diameter and height of the QDs nano-pillar are 250, and 800nm, respectively. According to the QDs density, each nano-pillar contains 1600 QDs in it. The QDs nano-pillar resonance signals are observed by the low temperature cryogenic cathode-luminescence measurement. A strong nano-pillar resonance signal in 1050 nm matched to our simulation results is observed.