CsI:TI闪烁薄膜的工艺制备和光学特性的研究

发布时间：2018-03-14 11:40

  本文选题：X射线探测　切入点：Cs　出处：《电子科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：X射线探测器在安全检察、医学成像、空间探测等众多领域都有广泛应用。作为探测器最重要部分的转换屏,其材料的光转换效率对整个系统起着决定性的作用。在本文中,我们提出了一种新的集成化X射线探测器。我们选用CsI:Tl作为荧光转换屏材料,PIN或者CCD作X射线探测系统中的荧光接收器件,采用真空热蒸发法将CsI:Tl晶体制备成呈晶柱状结构的薄膜并直接集成在CCD或者PIN上。为了抑制荧光扩散和晶柱间发生串扰,我们在Cs I:Tl闪烁晶体膜表面镀一层Al膜来对晶柱状的薄膜进行包裹和隔离,从而起到保护作用。本文的主要内容如下:按照从简单到复杂的顺序分别建立了三种理论模型:理想连续层模型、理想晶体单元模型和具有理想晶柱结构的薄膜模型。针对Cs I:Tl闪烁晶体薄膜的荧光转换因子与薄膜各结构参数的关系我们用MATLAB软件进行了仿真计算。仿真结果表明:CsI:Tl闪烁晶体薄膜厚度在400μm处时荧光转换因子最大;具有晶柱结构的薄膜的荧光转换因子明显高于无晶柱结构的薄膜的荧光转换因子;入射X光子能量越低,CsI:Tl晶体的最佳厚度越薄,反则反之。通过理论计算,我们在实际中采用了真空热蒸发法分别在Si和玻璃基片上沉积并生长CsI:Tl薄膜,并对Cs I:Tl薄膜的表面微结构和光学特性进行了测试和分析。结果表面:采用真空热蒸发法制备的Cs I:Tl薄膜沿(200)晶面择优生长,其晶体结构择优取向生长与厚度关系密切,厚度相对较小时存在明显择优取向生长,随着膜厚增加晶体生长择优取向现象明显减弱;蒸发速率越大,CsI:Tl薄膜的相对光输出强度越小;对于不同退火处理的薄膜样品,当在250℃退火时,缺陷得到改善,薄膜样品的结晶质量达到较好的程度,相对光输出也增加;通过改变镀膜的工艺方法,有效的改善薄膜的结晶质量。通过搭建样品的成像测试平台,测试了样品的光转换率、定性地测试了样品的空间分辨率。通过选择合适的沉积速率、通过合适的退火温度退火、调节薄膜厚度和薄膜微结构、利用预沉积手段来获得光转换效率高、空间分辨率高的闪烁屏,以提高闪烁成像探测器的成像质量。
[Abstract]:X-ray detectors are widely used in many fields, such as safety inspection, medical imaging, space detection and so on. As the most important part of the detector, the optical conversion efficiency of the material plays a decisive role in the whole system. We propose a new kind of integrated X-ray detector. We choose CsI:Tl as the fluorescent conversion screen material or CCD as the fluorescence receiver in the X-ray detection system. The thin films with columnar structure of CsI:Tl crystals were prepared by vacuum thermal evaporation and directly integrated into CCD or PIN. We have coated a layer of Al film on the surface of Cs I: TL scintillator film to wrap and isolate the columnar film. The main contents of this paper are as follows: according to the order from simple to complex, three theoretical models are established: ideal continuum model. Ideal crystal unit model and thin film model with ideal crystal column structure. The relationship between the fluorescence conversion factor of Cs I: TL scintillator thin film and the structure parameters of the thin film has been simulated by MATLAB software. The simulation result table is given. When the thickness of the thin film is 400 渭 m, the maximum fluorescence conversion factor is obtained. The fluorescence conversion factor of the thin film with crystal column structure is obviously higher than that of the film with no crystal column structure, the lower the incident X photon energy is, the thinner the optimum thickness of CsI: TL crystal is. In practice, CsI:Tl thin films were deposited and grown on Si and glass substrates by vacuum thermal evaporation, respectively. The surface microstructure and optical properties of Cs I: TL thin films were measured and analyzed. Results: the surface of Cs I: TL thin films prepared by vacuum thermal evaporation method has preferential growth along the crystal plane. The preferred orientation growth of the crystal structure is closely related to the thickness of Cs I: TL thin films. With the increase of film thickness, the preferred orientation phenomenon of crystal growth is obviously weakened, the higher the evaporation rate is, the smaller the relative light output intensity of CsI: TL thin films is, and for different annealed films, the preferred orientation of CsI: TL thin films is decreased with the increase of film thickness. When annealed at 250 鈩，

本文编号：1611098