| 题名 | 氟掺杂及铋过量BiFeO3薄膜的制备与光、电性能研究 |
| 作者 | 徐方龙 |
| 学位类别 | 硕士 |
| 答辩日期 | 2014-05-28 |
| 授予单位 | 中国科学院大学 |
| 授予地点 | 北京 |
| 导师 | 徐金宝 |
| 关键词 | 铁酸铋 电学性能 掺杂 光学性能 溶胶-凝胶 |
| 学位专业 | 材料物理与化学 |
| 中文摘要 | 近年来，多铁材料作为新型的多功能材料受到了广泛的关注。铁酸铋（BiFeO3）是其中一个典型代表。BiFeO3是一种单相多铁材料，也是少数在室温下同时具有铁电性(居里温度TC〜850℃)和(反)铁磁性(尼尔温度TN〜370℃)的材料之一。在一定温度范围内共存的铁电性和铁磁性使BiFeO3存在磁电耦合的特性，使其在信息存储、自旋电子设备以及传感器等方面都具有很大的应用前景。然而，BiFeO3材料的漏电流较大，这在很大程度上限制了它的应用，降低漏电流是需要解决的一个关键问题。同时，BiFeO3作为一种窄带隙半导体，加上它的自发极化特性，使该材料很有可能突破传统太阳能电池带隙电压的限制并为未来高效稳定的太阳能电池以及相应光电器件的发展，提供一个崭新的途径。薄膜的折射率和消光系数是薄膜的重要参数，在一定程度上决定了薄膜的力学特性、光电特性以及光学特性等。因此，准确地测量薄膜的厚度和光学常数在薄膜的制备和应用中起着关键的作用。 本文以BiFeO3薄膜材料作为主要研究对象，针对BiFeO3薄膜的电学性能和光学性能展开研究。同时详细讨论了制备的BiFeO3薄膜的微观结构和性能参数。本文主要研究内容分为以下几点： 1、利用溶胶-凝胶工艺在ITO/玻璃衬底上制备了F掺杂的BiFeO3-xFx (x＝0, 0.02, 0.04, 0.06, 0.08)薄膜。X射线衍射分析表明，制备出的样品结晶程度良好，为单一钙钛矿结构，空间群为R3c。随着F-离子掺杂量的增加，介电常数相应增加。样品均呈出较强的介电色散。随着F-离子掺杂量的增加，BiFeO3薄膜的漏电流密度逐渐降低。 2、采用溶胶-凝胶法于Si衬底上，在550℃温度下退火制备出了BiFeO3薄膜并初步探索了样品的光学性质。X射线衍射分析表明样品为纯相，通过原子力显微镜对样品的表面形貌进行表征，结果表明：所得样品表面光滑且无裂纹，均方根粗糙度为4.87 nm。薄膜的折射率随着波长的增加而逐渐降低。在短波段，BiFeO3薄膜的消光系数非常小，表明样品在该波段几乎呈现透明状态。随着波长的增加，消光系数逐渐降低。通过溶胶-凝胶法，以Fe(NO)3·9H2O 和Bi(NO)3·5H2O为原材料，乙二醇甲醚为溶剂，冰乙酸为脱水剂和催化剂，于FTO衬底上制备Bi过量不同摩尔分数的BiFeO3薄膜。研究了Bi过量对薄膜物相，表面形貌，禁带宽度及光伏性能的影响。结果表明：薄膜呈现自由取向。Bi过量不同摩尔分数时，体系并未出现明显的相转变，为R3c空间群。晶粒尺寸随着Bi含量的增加总体呈现先下降后上升的趋势。薄膜的禁带宽度及光伏性能均可由Bi过量不同摩尔分数得以调控，当Bi过量10 mol%时，禁带宽度最小，为2.31 eV。 |
| 英文摘要 | In recent years, multiferroic material has received extensive attention as a new multifunctional material and BiFeO3 is a typical representative of that. BiFeO3 is a single phase multiferroic material, and is also one of the materials that exhibit both ferroelectricity (TC～850℃) and (anti) ferromagnetic (TN～370℃). At a certain temperature range, the coexisting ferroelctricity and ferromagnetism of multiferroic materials BiFeO3 induce the magnetic-electric effect, which makes BiFeO3 have potential application in multifunctional devices, such as the data storage, spintronics, and sensors. However, BiFeO3 has a large leakage current, which limits its application. Reducing the leakage current is one of the key issues we need to solve. Meanwhile, as a kind of narrow band-gap semiconductor and the unique spontaneous polarization of BiFeO3 may make it overcome the restriction of band gap voltage in conventional solar cell and provide a new approach to the development of efficient stable solar cell in future as well as the relevant photoelectric device. The refractive index and extinction coefficient are important parameters of thin films and determine the mechanical, photoelectric and optical properties of thin films to a certain extent. Therefore, measuring the thickness and optical constants of thin films accurately plays a key role in the preparation and application of thin films. In this paper, BiFeO3 thin film material is the main research object and we focus on the electrical and optical properties of BiFeO3 thin film. At the same time, we discussed the microstructure and properties parameters of BiFeO3 thin film in detail. This article main research content is divided into the following: 1. F doped BiFeO3-xFx (x＝0, 0.02, 0.04, 0.06, 0.08) thin films have been synthesized on ITO/glass substrates using a sol-gel method. X-ray diffraction analysis showed that the obtained samples were highly crystallized and exhibited a single-phase perovskite structure with the space group R3c. The dielectric constants increased with F- ions doping amount increasing. All the films showed an intense dielectric dispersion. The leakage current density decreased with F- ions doping amount increasing. 2. BiFeO3 thin film was prepared on Si substrate annealed at 550℃ via a sol-gel method and we preliminary explored the optical properties of the sample. X-ray diffraction analysis showed that the sample adopted a pure phase. The surface morphology of the sample was characterized by atomic force microscope and the results showed that the surface was smooth and without cracks. The root mean square roughness was 4.87 nm. The refractive index decreased with the increase of wavelength. At short wavelength, the extinction coefficient of the BiFeO3 thin films is very small, so the thin films are nearly transparent nearby this wavelength region. As wavelength increasing, the extinction coefficient increased. BiFeO3 thin films with different Bi excess content were prepared on FTO substrates via sol-gel method taking Fe(NO)3?9H2O and Bi(NO)3?5H2O as starting materials. 2-methoxyethanol is solvent and ice acetic acid is dehydrating agent and catalyst. We studied the effect of excess Bi contents on the microstructure, optical and photovoltaic properties of BiFeO3 thin films. The results showed that, BiFeO3 thin films adopted random orientation. No obvious phase transition was observed with different Bi excess content and the space group was R3c.The grain size of the samples decreased at first and then increased with Bi content increasing. Both of the optical and photovoltaic properties can be tuned by adding different Bi content. BiFeO3 thin film with Bi excess 10 mol% showed the narrowest band gap Eg＝2.31eV. |
| 公开日期 | 2014-08-05 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.xjipc.cas.cn/handle/365002/3435]  |
| 专题 | 新疆理化技术研究所_材料物理与化学研究室 |
| 作者单位 | 中国科学院新疆理化技术研究所 |
| 推荐引用方式 GB/T 7714 | 徐方龙. 氟掺杂及铋过量BiFeO3薄膜的制备与光、电性能研究[D]. 北京. 中国科学院大学. 2014. |
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