基于PSD评价及伪随机轨迹的单晶碳化硅表面粗糙度研究

随着新能源、特高压需求爆发，以单晶碳化硅为代表的第三代半导体技术近几年得到了飞速发展，大口径单晶碳化硅材料制备已经成为现实，相比于目前已成熟应用的RB-SiC材料，单晶碳化硅不需要通过CVD或PVD改性就可以获得1 nm甚至更优的表面粗糙度，在光学元件领域的应用具有广阔前景，但同时加工难度高是亟待解决的问题。为了解决单晶碳化硅材料在光学加工过程中的粗糙度问题，提出了一种基于PSD评价及熵增理论的伪随机轨迹加工改善粗糙度的方法。相较于传统单一的Ra值评价方法，通过引入PSD曲线丰富了粗糙度评价的维度；利用对熵增理论的分析，从理论上讨论了确定性抛光轨迹和伪随机轨迹对粗糙度尺度下累计误差影响的区别。通过对6 in (1 in=2.54 cm)单晶碳化硅进行多轮抛光实验，结果表明：在相同初始粗糙度情况下，确定性轨迹与伪随机轨迹虽均得到了Ra约1 nm的粗糙度值，但PSD曲线可以明显看出确定性轨迹出现了尖峰，而伪随机轨迹则更为平滑。验证了特定采样区间下的PSD曲线作为粗糙度评价手段的有效性，同时论证了伪随机轨迹相较于确定性轨迹在单晶碳化硅材料抛光上的优势。     

Corrosion related properties of iron(100) surface in liquid lead and bismuth environments:A first-principles study

The corrosion of steels in liquid metal lead （Pb） and bismuth （Bi） is a critical challenge in the development of accel-erator driven systems （ADS）. Using a first-principles method with a slab model, we theoretically investigate the interaction between the Pb （Bi） atom and the iron （Fe） （100） surface to assess the fundamental corrosion properties. Our investigation demonstrates that both Pb and Bi atoms favorably adsorb on the （100） surface. Such an adsorption decreases the energy required for the dissociation of an Fe atom from the surface, enhancing the dissolution tendency significantly. The seg- regation of six common alloying elements （Cr, A1, Mn, Ni, Nb, and Si） to the surface and their impacts on the corrosion properties are also considered. The present results reveal that Si seems to have a relatively good performance to stabilize the surface and alleviate the dissolving trend caused by Pb and Bi.