中空硫化鎘奈米粒子之電鍍沈積製備及研究

Preparation of Hollow CdS Nanoparticles via Electrodeposition

張晉豪(Jin-Hao Jhang)

指導教授 ： 洪偉修

國立臺灣師範大學/理學院/化學系/碩士(2009年)

摘要

在本篇論文，我們利用氬電漿（argon plasma）轟擊高定向熱解石墨(HOPG)表面而產生一均勻的表面缺陷。而這些均勻的缺陷會有較高的表面能（surface energy），使得鎘奈米粒子（Cadmium nanoparticles）較能夠均勻的沉積於石墨基材上；而無經過氬電漿轟擊的石墨表面，其本身因具有自然的斷面缺陷(edge)，所以在沉積奈米粒子時容易對石墨表面具有選擇性，而傾向於沉積在斷面缺陷上。由實驗中發現，利用氬電漿轟擊石墨表面最佳的氣體壓力在8-20 mtorr之間；若氣體壓力過高，則會造成石墨表面的缺陷不緻密均勻，反而造成奈米粒子在石墨表面上的聚集。在電化學沉積過程中，我們發現溶解在電解液中的氧分子會在電極表面被還原成氫氧根離子(Hydroxide anions)而與鎘離子(cadmium cations)產生不溶性的氫氧化鎘(Cd(OH)2)奈米粒子；這個過程將會有效地增加石墨表面奈米粒子的密度。爾後，我們利用硫化氫氣體(H2S)與石墨表面上的氫氧化鎘或鎘奈米粒子在高溫(300℃)條件下進行取代反應生成硫化鎘奈米粒子(CdS nanoparticles)；再利用X光光電子能譜儀(X-ray photoelectron spectroscopy)研究其表面化學組成之變化。其中我們觀察鎘元素束縛能之變化以及硫元素XPS強度的改變來證明硫化鎘奈米粒子反應在300℃下於10-15分鐘完成。此外，我們利用高解析度穿透式電子顯微鏡(High-resolution transmission microscopy)觀察硫化鎘奈米粒子之結晶性與其晶格影像。在穿透式電子顯微影像上可得知此硫化鎘奈米粒子為立方堆積(cubic-phase)而且是明顯的中空結構奈米粒子。中空結構之硫化鎘奈米粒子在先前文獻中已經被證實以及研究過，造成中空結構之原因被稱為Kirkendall effect。最後，我們利用低溫光子激發光光譜儀測量硫化鎘奈米粒子之光學性質。在實驗中可得到此硫化鎘奈米粒子之放光光譜於486 nm (2.55 eV)有一明顯的放光波峰，此放光波峰可解釋為能隙所造成的放光。而我們在相對較長波長498 nm (2.49 eV)之位置有發現一不明顯的放光波峰，而此可被解釋為奈米粒子表面缺陷所造成之放光。

關鍵字

hollow CdS ； Ar plasma treatment ； electrodeposition

並列摘要

In this thesis, we used the argon plasma to treat a fresh graphite surface for generating the homogeneous defects. The defects have the higher surface energy which is similar to the edge on the native graphite surface; hence, the distribution of cadmium (Cd) nanoparticles on the graphite can be more homogeneous. In our experiments, we found that the flowing pressure in the range of 8-20 mtorr during the plasma treatment is the optimal condition. The plasma treatment at an excessive pressure results in the undesired aggregation of nanoparticles. In the electrodeposition process, the reduction of molecular oxygen in aqueous solution generates the hydroxide anion (OH-) and facilitates the cadmium cation (Cd2+) to form the solid cadmium hydroxide (Cd(OH)2(s)) on the graphite surface; and it can increase the higher particle density on the graphite surface than the case in absence of molecular oxygen. Subsequently, we synthesized CdS nanoparticles from Cd(OH)2/Cd0 nanoparticles with the exposure to H2S(g) (600 mtorr) at 300oC. The variation in the surface chemical composition of nanoparticles after the treatment of H2S was investigated with X-ray photoelectron spectroscopy (XPS). The formation of CdS from Cd(OH)2/Cd0 was completed in 10-15 min at 300oC. Based on the measurement of high-resolution transmission microscopy, it was concluded that the CdS nanostructure has a cubic crystal lattice and exhibits the hollow structure which is caused by the Kirkendall effect. Finally, the low-temperature Macro-photoluminescence spectra of the CdS nanoparticle shows an emission peak at 2.55 eV (486 nm) with a shoulder at 2.49 eV (498 nm), which are attributed to the direct band-gap transition and the transition at the surface-defect, respectively.

並列關鍵字

中空硫化鎘奈米粒子 ； 氬電漿處理 ； 電化學沉積

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