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  • 學位論文

The Synthesis of Copper Sulfides Nanowires and Their Applications in Energy Devices

硫化銅奈米線的製備與能源元件之應用

指導教授 : 陳力俊

摘要


本論文主要探討p型半導體-硫化銅奈米線於能源元件(可變式電阻記憶體以及光催化產氫)方面的應用與探討。 第一部分為硫化銅奈米線陣列之合成以及其電阻轉換效應表現的研究。我們以一個低成本、低溫、避免使用毒性化合物的方法,直接合成大面積均勻單晶奈米線於銅片上,此樣品可直接製作成可變電阻式記憶體,我們可以得到相當優異的元件表現(啟動電壓 < 0.2 V,重置電壓 < -0.1 V,元件循環 > 103 次,高低電阻比 > 105),接著在以原子層沉積系統製作與氧化鋅結合的自整流p-n介面,作為附帶有選擇器的1D1R結構,此結構亦有良好的電性表現與淺力(啟動電壓 < 1.3 V,重置電壓 < -0.6 V,高低電阻比 > 105)。 第二部份我們延續第一部分可變式電阻式記憶體的研究,我們利用臨場掃描式電子顯微鏡觀察單根硫化銅奈米線電阻轉換的機制,跳開電化學金屬化(ECM)的機制框架,我們以兩根鈍性金屬做為導電電極,發現硫化銅奈米線可以自身存在的銅原子以及銅缺陷使電阻作可變轉換,且於高低限制電流下,其個別表現出由銅離子或銅缺陷主導電阻轉換的情形,除了兩者在電性曲線以及穿透式電子顯微鏡結構分析下的不同,金屬性或離子性的差異亦可以由低阻態電阻值隨溫度變化的趨勢所觀察出。且藉由改變限制電流,使的單根硫化銅奈米線有多狀態的儲存方式(multi-state storage),可增加可變式電阻記憶體的記憶密度。 第三部分是利用調變銅缺陷量使的硫化銅帶有局部表面電漿共振效應,進而對光催化效益之提升。我們以陽離子交換法合成可調變銅含量的硫化銅奈米線,樣品成分組成如Cu2S、Cu7S4、CuS等等。除了結構成分的鑑定外,可見光-近紅外光光譜的吸收曲線亦呈現出其隨著銅缺陷含量變化的表面電漿共振吸收鋒,我們將樣品投入可見光光催化分解胺硼烷產氫的量測中,可以得到相當高效率的催化特性,其中,成分分布主要由Cu7S4組成的樣品三更是達到最高的效率值(25.54 mmol/g.h)。緊接著將鈀奈米顆粒附著於各樣品的表面上,大幅提升實驗樣品光催化效益(鈀-樣品三: 157.04 mmol/g.h)。

並列摘要


The p-type copper sulfides system with unique properties and the corresponding applications have been investigated in the thesis. In first part, Cu2S nanowire arrays have been fabricated via a facile hydrothermal method on copper substrate. The copper substrate could be served as electrode in ReRAM devices, in which the excellent resistive switching (RS) performance (Vset < 0.2 V, Vreset < -0.1 V, retention > 103, on-off ration > 105) could be demonstrated. Then ZnO branched structure has been deposited on Cu2S for the self-rectifying p-n junction, as the selector of 1D1R structure to prevent the leakage issue. The 1D1R structure also exhibited promising performance (Vset < 1.3 V, Vreset < -0.6 V, on-off ration > 105). In the second part, multilevel resistance has been demonstrated for devices based on individual Cu2S nanowire with two inert (W) electrodes. Up to five levels can be achieved by varying the compliance current (C.C.), significantly enhancing the data storage density. Compared to previous works on multilevel memory, the present devices exhibit outstanding performances with lower operating voltage (Vset < 0.6 V at IC.C.= 1 μA), higher on-off ratio (>105) and longer retention time (> 103 min). From in-situ SEM and TEM analysis, the RS behavior of Cu2S nanowires under high C.C. (> 1 μA) has been found to be dominated by Cu ion diffusion inside the Cu2S nanowire. On the other hand, holes and vacant Cu lattice sites control the RS under low C.C. (< 800 nA). The results of temperature-dependent measurements of resistivity also strongly support the proposed mechanisms. The facile fabrication of Cu2S nanowires with the capability of multilevel switching shall facilitate the realization of high density memristor applications. In the third part, localized surface plasmon resonances (LSPR) in near-infrared (NIR) region have been extensively studied for copper chalcogenide nanostructures, not only for the absorption enhancement but also tunable LSPR characteristics with their free carrier concentrations or defects. In the present work, one-step cation exchange method has been used to synthesize Cu2-xS nanowires with x varied between 0 and 1, including Cu2S, Cu7S4 and CuS and so forth. The plasmonic band of Cu2-xS nanowires shifts to a shorter wavelength with the increase in x, as observed in VIS-NIR spectra, which is attributed to the increase in density of copper vacancies. The Cu2-xS nanowires have been used as catalysts towards the photocatalytic generation of H2 from ammonia borane (AB). Among samples with different Cu-S compositions, Sample 3 which is mainly composed by Cu7S4 exhibited the highest activity in terms of H2 evolution rate (25.54 mmol/g.h). Moreover, a marked enhancement of the H2 evolution rate (157.04 mmol/g.h) could be achieved after decorating the Cu2-xS nanowires with Pd nanoparticles to form the hybrid structures. The results of the present investigation may lead to an effective strategy for the design and development of LSPR materials for photocatalytic applications.

參考文獻


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