Effect of grain size and orientation degree on thermal shock resistance of BN-matrix textured ceramics under cyclic thermal shock

Hexagonal boron nitride (h-BN) has a typical two-dimensional flake structure, so the anisotropy of h-BN grains caused by directional arrangement cannot be ignored when studying the thermal vibration resistance of materials under thermal cycling. In this paper, h-BN-matrix textured ceramics prepared with different holding time were selected, and the effects of thermal vibration temperature difference and thermal cycles on the phase and thermal vibration resistance of h-BN-matrix textured ceramics were studied. The results show that under the condition of high-frequency thermal cycling, the residual strength ratio (RSR) of BN-based textured ceramics is closely related to the holding time and showing obvious anisotropy. At the same time, there is a thermal vibration temperature range in which the internal stress will change from relief to re-accumulation.     

Work Function Optimization Technology of Indium Tin Oxide Films

氧化铟锡薄膜的功函数优化技术

张博¹,张智博²,郭新涛¹,杨亚楠²,刘滢¹,杨磊³,朱嘉琦²

（1. 中国航空制造技术研究所 材料研究部,北京100024;

2. 哈尔滨工业大学 特种环境复合材料技术国家级重点实验室,哈尔滨150080;3. 哈尔滨工业大学 分析测试中心,哈尔滨150080）

创新点说明：

1.通过等离子轰击技术辅助磁控溅射制备了高功函数的In2O3:Sn薄膜,实现了室温下透明导电薄膜的简易制备。

2.分析了In2O3:Sn薄膜功函数的变化机制。测试结果表明,In2O3:Sn薄膜功函数的增加是由于低氧化态Sn²⁺向高氧化态Sn⁴⁺转变,在高轰击能的作用下,表面结合Sn-O键增多提高了In2O3:Sn薄膜的功函数。

研究目的：

In2O3:Sn薄膜作为一种透明导电材料,有着广阔的发展前景。但是未经处理的In2O3:Sn薄膜具有较低的功函数,在应用中受到了很大的限制。此外,In2O3:Sn功函数的变化机理还存在诸多争议。为了解决In2O3:Sn薄膜功函数低的问题,本文使用无老化效应的等离子体轰击辅助磁控溅射的方法,改进In2O3:Sn薄膜功函数,进一步阐明In2O3:Sn薄膜功函数的变化机制。

研究方法：

采用等离子体轰击辅助磁控溅射制备优先取向的In2O3:Sn薄膜来提升功函数,实现了室温下透明导电薄膜的简易制备。此外,我们利用X射线衍射(XRD),X射线光电子能谱(XPS）和紫外荧光光谱法(UPS)等测试手段,通过改变Ar⁺等离子体轰击的沉积条件,阐明In2O3:Sn薄膜功函数的变化机制。

研究结果：

1） In2O3:Sn薄膜的XRD图显示,负偏压较低时（|Vp|<|-500 V|）,In2O3:Sn薄膜的晶体结构为非晶态。当|-500 V|<|Vp|<|-700 V|时,带正电的氩离子受到负偏压的作用加速对薄膜表面进行撞击,动能转化成部分内能和表面原子运动的能量,从而加速了表面原子迁移率,使得In2O3:Sn表面晶化,显现(222)晶面。

2）In2O3:Sn薄膜XPS测试结果显示,随着负偏压的增大,ISn²⁺/ISn⁴⁺的比例从1.75逐渐降到0.35。与此同时,Sn⁴⁺峰的半高宽也发生了相应的变窄,从~1.2减少到~1.0左右。这也可以证明,等离子体轰击过程有助于低价的Sn²⁺向高价Sn⁴⁺的转变。

3）从不同负偏压下制备In2O3薄膜的UPS光谱可以看出,随着负偏压的增加,虽然In2O3:Sn薄膜氧空位的含量有所减少,但是并不会降低In2O3:Sn薄膜中载流子浓度。最大功函数WF=5.1 eV在(EF-EVBM)=2.69时产生。

结论：通过等离子轰击技术辅助磁控溅射制备了高功函数的In2O3:Sn薄膜。In2O3:Sn薄膜的功函数受到直流脉冲电压施加的Ar⁺等离子体轰击的显著影响。具有|Vp|=|-500V|的In2O3:Sn薄膜,增强的吸附原子迁移率消除了缺陷,改善了表面微晶的形成。低价态Sn²⁺的氧化态逐渐向高价态Sn⁴⁺的氧化态转变,引起In2O3:Sn表面的氧增多,提高了In2O3:Sn薄膜的功函数。

关键词：功函数,氧化铟锡,低温结晶,等离子体轰击纳米片;锂离子电池;比容量;液氮

     

Ablation behaviors of SiC nanowire-reinforced ZrC-SiC coating-matrix integrated C/C composites with different ratios of precursors

A novel method to prepare a coating on the C/C composite is discussed. The precursor infiltration pyrolysis method is usually applied to prepare interior ceramic matrix, thus SiC nanowires that can absorb the surficial precursor are added to prepare surficial ceramics. The method accomplishes the integration of the coating and the matrix so that no coating peels off after ablation. Moreover, the material with a ZrC/SiC precursor ratio of 5:1 (Z5S1), whose mass and linear rates are 0.47 mg/s and 0.95 µm/s, exhibits the highest overall resistance to ablation. The results demonstrate that higher ZrC content and more uniform phase distribution are beneficial to keep ZrO₂ in solid and form a denser and firmer oxide layer, which is more effective in improving the ablation resistance of the C/C composite.     

Effect of polarization on photoexcited carrier dynamics in ferroelectric thin films

Ferroelectric materials are considered as a promising candidate for photovoltaic devices owing to spontaneous polarization which may affect the photocarrier dynamics and raise photovoltaic effect. However, the interaction mechanism between the ferroelectric polarization and the photocarrier dynamics is still unclear, which limits the practical applications of this kind of materials. Here, we used femtosecond time-resolved reflectance measurements to monitor the photocarrier dynamics of PbTi_1-xNi_xO₃ (PTNO) films with different Ni doping concentrations, therefore the samples have different ferroelectric polarizations. We found that in the PTNO films with larger polarizations, the photocurrents are higher and the photocarriers recombined slower. We deduce that the depolarization fields are stronger in films with larger polarizations, and the photogenerated electrons and holes are separated more effectively. The recombination of photocarriers is retarded and the photocurrent is improved. Our study supplies a novel way for the enhancement of photovoltaic performances of ferroelectric material.     

SiCf/SiC复合材料表面Si/Yb2Si2O7双层涂层结合强度分析

目的 通过选择合适的复合材料拉伸方向和涂层制备工艺,在SiCf/SiC复材上获得高结合强度的Si/Yb2Si2O7双层涂层.方法 采用真空等离子喷涂技术在2.5D编织的SiCf/SiC复合材料表面制备Si涂层、Si/Yb2Si2O7双层涂层.采用金相、XRD、SEM和EDS对试样进行表征,采用拉伸试验测试涂层的结合强度...