Modification of Optical Band-Gap of Si Films After Ion Irradiation

Amorphous silicon (a-Si),nanocrystalline silicon (nc-Si) and hydrogenated nanocrys-talline silicon (nc-Si:H) films were fabricated by using chemical vapor deposition (CVD) system.The a-Si and nc-Si thin films were irradiated with 94 MeV Xe-ions at fluences of 1.0×10 11 ions/cm-2,1.0×10 12 ions/cm-2 and 1.0×10 13 ions/cm-2 at room temperature (RT).The nc-Si:H films were irradiated with 9 MeV Xe-ions at 1.0×10 12 Xe/cm-2,1.0×10 13 Xe/cm-2 and 1.0×10 14 Xe/cm-2 at RT.For comparison,mono-crystalline silicon (c-Si) samples were also irradiated at RT with 94 MeV Xe-ions.All samples were analyzed by using an UV/VIS/NIR spectrometer and an X-ray powder diffractometer.Variations of the optical band-gap (E g) and grain size (D) versus the irradiation fluence were investigated systematically.The obtained results showed that the optical band-gaps and grain size of the thin films changed dramatically whereas no observable change was found in c-Si samples after Xe-ion irradiation.Possible mechanism underlying the modification of silicon thin films was briefly discussed.     

MgAl2O4掺杂对ZTA-MgAl2O4复相陶瓷力学及热学性能的影响

以Al_2O_3、Zr O_2、MgO为初始粉末,采用放电等离子体烧结(SPS)制备ZTA-MgAl_2O_4复相陶瓷,研究MgAl_2O_4掺杂对ZTA-MgAl_2O_4复相陶瓷微观结构,力学及热学性能的影响。结果表明:ZTA-MgAl_2O_4复相陶瓷物相包括α-Al_2O_3、t-Zr O_2和MgAl_2O_4,烧结过程中MgO与Al_2O_3完全反应生成MgAl_2O_4;随MgAl_2O_4添加量增加,复相陶瓷Vickers硬度由21 GPa逐渐降低至17.5 GPa;而断裂韧性及抗弯强度呈现先增大后减小的趋势,当MgAl_2O_4添加量为15%(体积分数)时,断裂韧性和弯曲强度达到最大值,分别为8.55 MPa·m~(1/2)和1 056 MPa;此外,相同测试温度下复相陶瓷热导率随MgAl_2O_4添加量的增加逐渐减小,如温度为50℃时复相陶瓷热导率由18.5 W/(m·K)逐渐降低到14.3 W/(m·K)。     

氦离子辐照烧结碳化硅损伤效应研究

利用中国科学院近代物理研究所320 kV高压平台提供的氦离子辐照烧结碳化硅,辐照温度从室温到1 000 ℃,辐照注量为1015~1017 cm-2。辐照完成后,进行退火处理,然后开展透射电子显微镜、拉曼光谱、纳米硬度和热导率测试。研究发现,烧结碳化硅中氦泡形核阈值注量低于单晶碳化硅。同时,氦泡形貌和尺寸与辐照温度、退火温度有关。另外,对辐照产生的晶格缺陷、元素偏析进行了研究。结果表明,辐照产生了大量的缺陷团簇,同时氦泡生长也会发射间隙子,在氦泡周围形成间隙型位错环。在晶界处,容易发生碳原子聚集。辐照导致材料先发生硬化而后发生软化,且热导率降低。