8—9.5 keV正电子致Ti的K壳层电离截面的实验研究

低能正电子碰撞原子内壳层电离截面的实验数据目前还很缺乏,从而影响了对近年来发展的各相关理论模型的检验,限制了慢正电子束流技术在诸多领域中的应用.本文采用慢正电子束流装置产生的8—9.5 keV正电子束碰撞纯厚Ti靶,利用硅漂移探测器(SDD)收集正电子碰撞Ti靶产生的X射线,同时采用高纯锗探测器在线获得与靶碰撞的入射正电子数,从而得到Ti的K壳层实验产额,并基于蒙特卡罗模拟程序PENELOPE获得模拟产额.将实验产额分别与内壳层电离截面数据库采用经典光学数据模型(ODM)和扭曲波玻恩近似理论模型(DWBA)的蒙特卡罗模拟产额进行对比,发现基于ODM理论模型的模拟产额与实验值有较大的偏差,基于DWBA理论模型的模拟产额与实验结果符合较好.根据实验产额和基于DWBA理论模型的模拟产额的比较结果,对蒙特卡罗模拟程序使用的DWBA理论模型数据库进行修正后再进行模拟和比较,从而得到可靠的8—9.5 keV正电子致Ti原子K壳层电离截面数据.     

铁冷轧形变以及热处理对形变缺陷的影响

采用常用冷轧设备对铁进行冷轧引入形变缺陷。研究形变量和温度对形变缺陷的影响。形变样品中的微观缺陷、物相结构和形貌分别使用正电子湮没技术（PAT）、X射线衍射仪（XRD）和透射电子显微镜（TEM）进行表征分析。对经过673 K热处理的形变样品前后进行XRD测试,结果显示,随着形变量的增加,样品中晶面方向（200）具有择优生长趋势,673 K热处理后,择优趋势更加明显,同时晶粒的尺寸也增大。利用正电子湮没寿命谱和多普勒展宽能谱对样品中形变缺陷的热力学稳定性进行研究,发现形变引入的空位型缺陷约在673 K回复完毕,723 K后位错缺陷开始回复。The pure iron was cold rolled with the thickness reduction from 0% to 75%. The microstructure defects, crystallographic structure and morphology of deformed specimens were characterized by positron annihilation technique (PAT), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD results show that the intensity of (200) increased with increasing deformation, 673 K heat-treatment promote the preference of (200) and the grain size of (200) was increased. The PAT results show that the vacancy type defect was annihilated at 673 K and the dislocation type defects start to annihilate at 723 K.     

不同硫压退火对溅射沉积ZnS薄膜性能的影响

ZnS作为一种宽带隙半导体,以其优异的光电性能近年来受到广泛关注,在太阳能电池、光催化剂以及传感器方面有着广阔的应用前景.本文首先以射频磁控溅射方法沉积了ZnS薄膜,然后在600℃温度和不同硫压下进行退火,通过X射线衍射、扫描电子显微镜、能量散射X射线谱、紫外-可见透射光谱以及慢正电子多普勒展宽谱对ZnS薄膜的晶体结构、表面形貌、晶粒尺寸、成分、透光率以及缺陷进行分析.结果表明:硫气氛后退火能够改善ZnS薄膜结晶性,退火后ZnS薄膜光学带隙为3.43—3.58 eV.当硫压高于0.49 atm(1 atm=1.01×10⁵ Pa)时,ZnS内部硫间隙原子以及表面单质硫降低了薄膜在可见光区的透光率.慢正电子多普勒展宽谱结果还表明,ZnS薄膜的缺陷浓度由表层到内层逐渐降低,薄膜缺陷随着硫压增加而降低.同时,3γ湮没证明了薄膜内部较为致密,硫化会导致薄膜开孔率增加.吸附硫通过内扩散占据了晶体中硫空位缺陷的位置,导致缺陷浓度降低,进而改善了薄膜质量.     

硫化温度对ZnS薄膜生长质量的影响

采用热反应法对玻璃衬底上以磁控溅射制备的Zn薄膜进行硫化,制备出ZnS薄膜。薄膜的微观结构、物相结构和表面形貌分别采用正电子湮没技术（PAT）、X射线衍射仪（XRD）、扫描电子显微镜（SEM）进行分析和表征。利用慢正电子湮没多普勒展宽对四个不同硫化温度下得到的ZnS薄膜样品中膜层结构缺陷进行研究,测量了薄膜中的空位型微观缺陷的相对浓度,指出445℃硫化样品中正电子注入能量在1.5~4.5 keV后S参数最小,说明该硫化温度下反应生成的ZnS薄膜结构缺陷浓度最小,膜的致密度最高。XRD结果显示薄膜在445℃以上硫化后,呈（111）择优生长趋势。从扫描电镜的结果也可以看出,在445℃硫化后,薄膜的晶粒明显地变得更大、更致密,这是因为ZnS晶胞比Zn晶胞大以及硫化过程中ZnS固相再结晶的缘故。ZnS thin films have been prepared by sulfurizing zinc thin films deposited on glass substrate by magnetron sputtering for two hours. The microstructure defects, crystallizations and surface morphology of zinc films sulfurized at different temperature were analyzed by PAT (positron annihilation technique), XRD(X-ray diffraction) and SEM (Scanning electron microscopy), respectively. For analyzing the structure defect of four samples with different sulfurization temperature, PAT has been used to obtain the relative concentration of defects. With the positron energy range of 1.5~4.5 keV, the S parameter of ZnS films is minimum. It demonstrates that ZnS films produced at 445℃ have the minimum structural defect concentration and the highest density. XRD results show that films are blende structure with the preference of (111) orientation above 445℃. And from the result of SEM, because of ZnS films recrystallization, the crystal grains obviously become large and dense at 445℃.     

Tunable monoenergy positron annihilation spectroscopy of polyethylene glycol thin films

Doppler broadening and coincidence Doppler broadening of annihilation radiation experiments have been performed in three kinds of polyethylene glycol(PEG) membrane formed with different average molecular weight using the tunable monoenergy slow positron probe as a function of implantion energy. The obtained positron annihilation parameters are interpreted from two aspects: surface effect and differences in micro-structure or chemical environment of positron annihilation. The experimental results show that the regulation of densification of PEG molecular packing and distribution uniformity from the near surface layer to the bulk region in the film forming process can be well realized by changing its molecular weight. Combining a variable monoenergetic slow positron beam and these two positron annihilation spectroscopy methods is a powerful tool to study positron annihilation characteristics and for polymeric thin-film fine structure analysis.