表面改性是提高材料和器件稳定性、耐辐照和耐高低温等性能的关键技术。本论文研究工作围绕高纯锗及反应堆压力容器材料的表面改性与机制展开。通过对高纯锗进行表面钝化，减少锗表面悬挂键和界面态密度，降低高纯锗探测器的表面漏电流；以期实现中国暗物质实验CDEX的极低能阈高纯锗探测器的制备。此外，通过开展压力容器材料铁素体不锈钢A508-3和镍基合金617的辐照后表面特性研究。表征测试其微观结构和缺陷、应变和力学性能，为压力容器材料的逆向设计和性能评估提供理论支撑。研究结果如下：

（1）采用基于密度泛函理论的第一性原理方法，系统研究了Ge表面-H、-NH₂、-OH和-SiO_x四种不同钝化体系的晶格结构、电子能带结构和态密度信息，对比不同钝化基团（100）方向锗晶胞的电子特性，精准分析不同原子配比钝化层的能带结构和界面态密度，得出H、N、O原子均能有效的降低Ge晶胞的表面态；-SiO_x基团随氧原子数增多，钝化效果更加明显。证实表面改性对选择合适的钝化基团和原子比具有重要意义，有助于深入理解钝化层形成稳定表面态的机制。

（2）以CDEX原型的点电极高纯锗探测器PCGe为基础进行器件仿真，通过改变点电极的形状参数和掺杂浓度，得到锗探测器的电场和碰撞电离过程的模拟结果，解析不同参数对PCGe自增益特性的影响，并对自增益结果进行验证。

（3）开展反应堆压力容器中广泛应用的A508-3钢的Fe离子辐照，结合纳米压痕和背散射电子衍射对应的晶粒取向探索辐照硬化与晶粒取向的关系；分析得到辐照后均出现辐照硬化现象，晶粒取向在[001]方向附近时硬度值最大；而取向距[001]的旋转角从0°增大到90°时，硬度值逐渐减小。

（4）研究617合金辐照后形成He空位团簇及其力学性能变化。低剂量下辐照硬化程度较低，高剂量20 dpa辐照条件下硬度值增加20%，微观应变增加，高温退火使应力得到缓和。氦释放温度随辐照剂量增加而降低；氦释放温度随辐照能量增加而提高；高能辐照释放量减少与样品中存在较多可以起固氦作的空洞、位错相关。

Surface modification is the key technology to improve the stability, radiation resistance, high and low temperature resistance of materials and devices. The thesis focuses on the surface modification and mechanism of high-purity germanium and reactor pressure vessel materials. By passivating the germanium surface, reducing the dangling bond and the density of interface states on germanium surface could be realized. Then the surface leakage current of high-purity germanium detector is reduced, and the ultra low energy threshold high-purity germanium detector will be applicated by China dark matter experiment. In addition, the surface characteristics after irradiationof ferritic stainless steel A508-3 and nickel base alloy 617  were studied to characterize their microstructure, vacancy defects, strain and mechanical properties, which could provide theoretical support for the reverse design and performance evaluation of pressure vessel materials. The results are as follows:

(1) The first-principles method based on density functional theory is adopted to systematically study the lattice structure, electronic energy band structure and state density information of -H、-NH₂、-OH and -SiO_x four different passivation systems of Ge surface. The electronic characteristics of germanium crystal cells in different passivation group (100) directions are compared. The energy band structure and interface density of passivation layers with different atomic ratio are precisely analyzed. It shows that H, N and O atoms can effectively reduce the surface states of Ge interfaces. The passivation effect of -SiO_x is more obvious as with the increasing O atoms. The study elucidates the modification mechanism is of great significance to the selection of appropriate passivation groups and atom ratio.

(2) Based on the device simulation of germanium detector, the shape parameters and doping concentration of the point electrode are changed, and then the electric field and collision ionization process is simulated. The influence of different parameters on the gain characteristics is analyzed and the internal amplification results are verified.

(3) The A508-3 steel, which is widely used in reactor pressure vessel, was irradiated by Fe ion, and the relationship between irradiation hardening and grain orientation was explored by nano indentation and back-scattering electron diffraction. It was found that irradiation hardening occurred after irradiation, and the hardness value was the highest when the grain orientation was near the [001] direction, while the rotation angle of orientation distance [001] increased from 0°to 90°, the hardness value decreases gradually.

(4) The He vacancy clusters and mechanical properties of 617 alloy helium irradiated  were studied. The hardness increased by 20% under 20 dpa. After high dose irradiation, the micro strain increases, and high temperature annealing makes the stress relax. The temperature of helium release decreases with the increase of irradiation dose, the temperature of helium release increases with the increase of irradiation energy. The decrease of high-energy irradiation release is related to the existence of many cavities and dislocations, which can be used as fixed helium effect