量子侷限效應對硫化鎘/雙團聯共聚合物混摻系統之影響

Quantum Confinement Effect of CdS/Block Copolymer Hybrid System

王心盈(Xing-Ying Wang)

指導教授 ： 何榮銘

國立清華大學/工學院/化學工程學系/碩士(2006年)

摘要

To study the quantum confinement effect and dipole-dipole interaction for semiconductor nanostructures templated by block copolymers, poly(4-vinylpyridine)-b-poly(caprolactone) (P4VP-PCL) diblock copolymers were used to serve as templates and combined with cadmium sulfide. Because of quantum confinement effect attributed to the size of the semiconductor below Bohr radius, a 3D confinement environment like a micellar texture is needed to prevent the aggregation of the semiconductor. Micellization was carried out due to the coordination between the nitrogen lone-pair electrons of P4VP and the cadmium ions in a PCL selective solvent (for instance, chlororbenzene). The process of the coordination between P4VP and the cadmium ions was traced by Fourier Transform Infrared (FTIR) Spectrometer. Two shoulders near the characteristic peaks of C=N (1600cm-1 and 1550cm-1) appeared and caused the decrease in the intensity of the two characteristic peaks. In order to examine dipole-dipole interaction for semiconductor nanostructures, different coupling conditions were established by controlling the packing degree of micelles which was controlled by the thickness of the Cd2+/P4VP-PCL thin-film samples. The thin-film samples were prepared by controlling spin rate and/or solution concentration; the micellar texture was formed as evidenced by transmission electron microscopy (TEM). The formation of CdS nanostructures was then achieved by using H2S(g) as reduction agent and the reduction process was traced by FTIR and ultraviolet-visible (UV) spectroscopy. As observed by TEM, the average size of Cd2+/P4VP-PCL micelles is about 25 nm and the micellar texture remains after reduction process. The FTIR results showed that the intensity of characteristic peaks of the C=N bond is increased due to the formation of cadmium sulfide nanoparticles. In addition, a significant absorption peak was observed after reduction from the UV spectrum which also proves the existing of cadmium sulfide. The average size of cadmium sulfide nanoparticles is around 2 nm as evidenced by TEM; well consistent to the estimated particle size according to the UV results. Interesting spectroscopic results were found in the UV spectrum. A significant blue shift as compared to the bulk state of cadmium sulfide was observed due to the result of quantum confinement effect. In addition, a significant red shift of absorption owing to the dipole-dipole interaction was found as the thickness of thin film increases substantially. We presume that the distance between micelles and the coupling number of micelles is the major reason to lead the change in absorption, and the micelles can be took as a dipole moment unit. Therefore, the intensity of dipole-dipole interaction increases when the distance between micelles decreases or the coupling number of micelles increases so as to cause the decrease in energy band gap of cadmium sulfide nanoparticles.

關鍵字

量子侷限效應 ； 高分子團聯共聚合物 ； 硫化鎘 ； 偶極力吸引作用

並列摘要

無資料

並列關鍵字

quantum confinement effect ； block copolymer ； cadmium sulfide ； dipole-dipole interaction

參考文獻

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