氢离子辐照诱导的钨表面周期性刻蚀研究

The periodic etching of tungsten surface induced by hydrogen ion irradiation

采用扫描电镜(Scanning Electron Microscope,SEM)、导电原子力显微镜(Conductive Atomic Force Microscope,CAFM)、能谱仪(Energy Dispersive Spectrometer,EDS)和纳米压痕等表征技术和方法,综合分析了130 eV氢(H)离子辐照诱导的多晶钨(W)材料的辐照损伤行为。研究表明:H离子辐照剂量从1.0×10^(24) ions·m^(−2)增加到1.5×10^(25) ions·m^(−2)时,W材料表面经历了H聚集成泡、在晶界处长大,并逐渐扩散至晶粒表面,直至H泡破裂导致的W表面层脱落的周期性演变过程,一个周期的演变过程所需的H离子辐照剂量约为(6.0~8.0)×10^(24) ions·m^(−2)。纳米压痕的分析表明辐照后W材料的表面硬度降低,EDS也未检测到W材料表面含有C、O等杂质,这进一步验证了低能H离子辐照后W表面不稳定损伤层的演变是导致W材料刻蚀的主要原因。该工作对于进一步理解在低于溅射阈值能条件下H离子辐照诱导W材料表面刻蚀机制上具有重要参考价值。

[Background]Metal tungsten(W)has a high melting point,low hydrogen solubility and high thermal conductivity.Therefore,it has been selected as one of the most promising plasma-facing materials for the future international thermonuclear experimental reactor(ITER).[Purpose]This study aims to investigate the etching process of polycrystalline W induced by low energy hydrogen ion irradiation.[Methods]Polycrystalline W materials were irradiated with 130 eV hydrogen ions.The irradiation damage behavior of W was researched by scanning electron microscopy(SEM),conductive atomic force microscopy(CAFM),Energy Dispersive Spectrometer(EDS)and nano indentation.[Results]The investigates show that when the irradiation dose of H ions increases from 1.0×10^(24) ions·m^(-2) to 1.5×10^(25) ions·m^(-2),the surface of W material experiences a periodic evolution process from forming bubbles with H aggregation,the bubbles becoming bigger at grain boundaries,and gradually diffusing to the grain surface,until the W surface layer falls off due to the rupture of H bubbles.The irradiation dose required for one period of evolution is about(6.0~8.0)×10^(24) ions·m^(-2).Nano indentation measurements show that the surface hardness of W material decreases after H ion irradiation.No impurities,especially elements of C and O,are detected on the W surface by EDS.[Conclusions]It is verified that the evolution of the unstable damage layer on the W surface induced by irradiations of low energy H ion is the main reason for the etching of W material.This work is very important for further understanding of the etching mechanism of W surface induced by H ion irradiation under the condition that the energy of irradiated H ion is lower than the sputtering threshold energy.