臺灣博碩士論文加值系統

本研究擬製備異質結構薄膜期能提高材料的光電化學響應，文獻生成BaTiO3/TiO2異質結構的方法多為水熱法或空氣燒結，其中並未有以水熱化學法並以還原氣氛熱處理製備者。本研究利用水熱-化學電池法，於溶液中添加Ba(CH3COO)2或與C6H12N4 (HMT)製備鈦酸鋇薄膜，未添加HMT所製備的以BTO稱之，有添加HMT所製備則以nBTO稱之。透過不同氧分壓之空氣、Ar、N2、Ar/5%H2、N2/5%H2與NH3氣氛，於不同溫度與不同持溫時間熱處理製備BaTiO3/TiO2異質結構薄膜。另以第一原理計算氮摻雜或形成氧空位對鈦酸鋇晶體、能帶結構與態密度的影響，本研究以兩種方法計算，取代型摻雜與虛擬晶體近似法(VCA)。
根據XRD分析結果，以較高氧分壓之空氣、Ar與N2於900℃~930℃持溫5小時熱處理鈦酸鋇薄膜，因底材TiN皆被氧化成TiO2，因此光電流密度極低。以NH3於700℃持溫5小時熱處理鈦酸鋇薄膜，底材TiN未氧化，維持BaTiO3/TiN薄膜，因此光電流密度也低。而經低氧分壓氣氛Ar/5%H2與N2/5%H2於不同溫度持溫5小時熱處理後的薄膜含有TiN、TiO2與Ba1.12(Ti8O16)/BaTiO3，經由FE-TEM選區繞射結果，成功製備出BaTiO3/Ba1.12(Ti8O16)/TiO2/TiN異質結構，因此光電流密度皆較熱處理前高，其中830℃~1000℃熱處理之薄膜光電流密度達1000 µA/cm2以上，皆較650℃~710℃熱處理之薄膜的光電流密度高出許多，可能是因為氧空位需要足夠的熱處理溫度與時間以形成所致，而氧空位的存在可提升光電化學反應。此外以Ar/5%H2與N2/5%H2於930℃持溫5小時熱處理nBTO薄膜皆具有大於2000 µA/cm2光電流密度，經由XPS分析知N2/5%H2熱處理後薄膜未有氮摻雜，因此可確定光電流提升原因非為含氮氣氛熱處理所致。
綜合以上實驗結果知本研究成功製備出BaTiO3/TiO2/TiN異質結構薄膜，在N2/5%H2於950℃持溫3小時熱處理nBTO，可得本研究最高的光電流密度6059±141 µA/cm2。
另由電腦模擬計算結果知，無論以取代型或VCA計算氮摻雜鈦酸鋇於低濃度氮摻雜(0 at%~5at%)時，能隙皆有隨氮摻雜量上升而下降的趨勢，其中以取代型氮摻雜計算與文獻較相似。鈦酸鋇晶體中形成氧空位，晶體體積隨氧空位濃度上升而變大；而能隙隨氧空位濃度上升而上升的趨勢與文獻相符合。

This research aims to prepare the heterostructure thin films to enhance the photoelectrochemical response of the material. Previous literature has primarily utilized hydrothermal or air sintering methods to create BaTiO3/TiO2 heterostructures, without any instances of employing a hydrothermal-galvanic couple method approach followed by a reducing atmosphere heat treatment. In this study, a hydrothermal-galvanic couple method was employed to fabricate BaTiO3 thin films in a solution by adding either Ba(CH3COOH)2 alone or together with C6H12N4 (HMT). The films prepared without HMT are referred to as BTO, while those prepared with HMT are labeled as nBTO. BaTiO3/TiO2 heterostructure thin films were fabricated through heat treatment at different temperatures and with varying holding times under various oxygen partial pressure atmospheres, including air, Ar, N2, Ar/5%H2, N2/5%H2, and NH3. Additionally, the influence of nitrogen doping or the formation of oxygen vacancies on the BaTiO3 crystal, band structure, and density of states was simulated using first-principles calculations. Two simulation methods were employed: substitutional doping and the virtual crystal approximation (VCA).
Based on the XRD analysis results, the BaTiO3 film underwent heat treatment within a temperature range of 900°C to 930°C for a duration of 5 h, under air, Ar, and N2 atmospheres characterized by relatively high oxygen partial pressures. During this process, the TiN underlayer was entirely oxidized to form TiO2, resulting in an extremely low photocurrent density. On the other hand, when the BaTiO3 film was heat-treated at 700°C for 5 h within an atmosphere characterized by an extremely low oxygen partial pressure of NH3, the substrate TiN remained unoxidized and did not transform into TiO2. This resulted in the formation of a BaTiO3/TiN film, which exhibited a low photocurrent density. Thin films contained TiN, TiO2, and Ba1.12(Ti8O16)/BaTiO3 after undergoing heat treatment under low oxygen partial pressure conditions (Ar/5%H2 and N2/5%H2) at various temperatures for 5 h. According to the FE-TEM selected area diffraction outcomes, a BaTiO3/Ba1.12(Ti8O16)/TiO2/TiN heterostructure was successfully synthesized. Consequently, the resulting photocurrent density was higher than that observed prior to heat treatment. Notably, the photocurrent density for films subjected to heat treatment between 830°C and 1000°C exceeded 1000 µA/cm2, significantly surpassing the values recorded for films treated at 650°C to 710°C. The reason behind this improvement may lie in the requirement for sufficient heat treatment temperature and duration to facilitate the formation of oxygen vacancies. The presence of oxygen vacancies further amplifies the photoelectrochemical reaction. Furthermore, nBTO thin films subjected to heat treatment using Ar/5%H2 and N2/5%H2 at 930°C for 5 h exhibited a photocurrent density exceeding 2000 µA/cm2. XPS analysis revealed the absence of nitrogen doping in films after N2/5%H2 heat treatment. Consequently, it can be confidently established that the augmented photocurrent density is not attributed to the nitrogen-rich atmosphere during heat treatment.
By integrating the aforementioned experimental findings, this study successfully synthesized heterostructured thin films of BaTiO3/TiO2/TiN. The application of heat treatment to nBTO at 950°C for 3 h under an N2/5%H2 atmosphere yielded the highest photocurrent density of 6059±141 µA/cm2 in this research.
Additionally, according to the results obtained from computer simulations, regardless of whether substitutional or VCA methods were employed to calculate nitrogen-doped BaTiO3 at low nitrogen doping concentrations (ranging from 0 at% to 5 at%), a consistent trend was observed: the bandgap decreased as the nitrogen doping level increased. Notably, the calculations involving substitutional nitrogen doping closely aligned with the literature findings. Within the BaTiO3 crystal, the formation of oxygen vacancies was observed. The crystal volume expanded as the concentration of oxygen vacancies increased. Simultaneously, the bandgap exhibited a trend of increasing as the concentration of oxygen vacancies rose, which is in accordance with existing literature.

第一章 緒論 1
1.1 前言 1
1.2 研究動機 2
1.3 研究目的 2
第二章 理論背景與文獻回顧 3
2.1 理論背景 3
2.1.1 水熱-化學電池法 3
2.1.2 異質結構 4
2.2 文獻回顧 5
2.2.1 本實驗室以水熱-化學電池法製備鈣鈦礦薄膜 5
2.2.2 本實驗室製備鈣鈦礦薄膜並量測其光電流密度特性 10
2.2.3 鈦酸鋇/二氧化鈦異質結構 13
2.2.4 氮摻雜鈣鈦礦氧化物/金屬氧化物異質結構文獻 15
2.2.5 鈦酸鋇第一原理計算 16
第三章 研究方法 19
3.1 實驗流程 19
3.2 TiN薄膜製程 20
3.3 水熱-化學電池法製備鈦酸鋇薄膜 20
3.4 不同氣氛熱處理鈦酸鋇薄膜 21
3.5 分析儀器 22
3.5.1 場發射掃描式電子顯微鏡 22
3.5.2 X光繞射儀 22
3.5.3 紫外光/可見光/紅外光光譜儀 22
3.5.4 電化學分析儀 22
3.5.5 X光光電子能譜儀 23
3.5.6 多功能聚焦離子束與場發射穿透式電子顯微鏡 23
3.6 第一原理計算 24
第四章 結果 25
4.1 以水熱-化學電池法製備鈦酸鋇薄膜 25
4.1.1 電流-時間曲線與外觀 25
4.1.2 結晶相與顯微結構分析 26
4.1.3 成分分析 28
4.1.4 能隙 28
4.1.5 光電流密度 29
4.2 不同氣氛熱處理鈦酸鋇以製備鈦酸鋇/二氧化鈦異質結構 32
4.2.1 各氣氛氧分壓分析與外觀 32
4.2.2 結晶相分析 35
4.2.3 成分分析 42
4.2.4 能隙 45
4.2.5 光電流密度 46
4.3 第一原理計算氮摻雜與氧空位對鈦酸鋇晶體、能帶結構與態密度影響 46
4.3.1 鈦酸鋇收斂性測試 46
4.3.2 鈦酸鋇的晶體結構與能帶結構計算 49
4.3.2.1 氮摻雜鈦酸鋇之計算結果 50
4.3.2.2 形成氧空位對鈦酸鋇晶體之計算結果 55
4.3.2.3 氮摻雜與氧空位形成以符合電中性條件之計算結果符合電中性條件之計算結果 58
4.3.3 以VCA計算缺陷對鈦酸鋇的影響 63
第五章 討論 66
5.1 高光電流密度的確認 66
5.2 高光電流密度表現的因素 67
5.2.1 異質結構 67
5.2.2 還原氣氛處理 71
5.2.2.1 TiN不可完全氧化 75
5.2.2.2 氧空位的生成 77
5.2.3 優化光電流密度方法 79
5.3 第一原理計算 82
5.3.1 氮摻雜鈦酸鋇 82
5.3.2 添加氧空位於鈦酸鋇晶體 84
5.3.3 計算與計算的文獻以及實驗結果相比較 85
第六章 結論 89
參考文獻 91

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