Pt/C催化剂颗粒体系SEM成像的计算机模拟

Pt纳米颗粒/C基底体系是典型的纳米催化剂应用体系，本文采用蒙特卡罗方法模拟了该体系的扫描电子显微镜成像。给出了不同尺度的Pt纳米颗粒在C基底中不同深度下二次电子和背散射电子成像的衬度。计算结果显示：(1)在PI／C衬度的形成中，材料的原子序数衬度而不是形貌衬度起了主要作用：(2)只有分布在C基底表面或者表面以下很浅深度内(大约三倍颗粒直径)的Pt颗粒才可以在二次电子信号中被观察到，而背散射信号中则可以观察到更深的Pt颗粒(大约五倍颗粒直径)；(3)当颗粒尺度小于几十纳米时。其二次电子信号衬度与通常微米尺度的情形有很大不同，最亮处位于颗粒的中央而不是边缘，且随着颗粒尺度的降低。二次电子产额绝对值也相应降低。

Computer simulation of SEM images for Pt/C catalyst systems

Carbon-matrix-Pt-particles system is a typical nano-catalyst system.In this work,a comprehensive and accurate Monte Carlo simulation model was applied to investigate the SEM imaging for such system,resulting in the secondary electron(SE)and backscattered electron(BSE)contrast of Pt nanoparticles with different sizes and at different depths in glassy carbon matrix.The results showed that:(1)The imaging contrast of such system was mainly due to material contrast rather than topographical contrast;(2)Only those particles located on,or quite close to,the matrix surface can be clearly revealed in a SE image.The maximum visible depth in SE observation for a Pt particle embedded in carbon matrix is about 3 times of the particle size,and is about 5 times for BSE observation;(3)Different from the usual case for observation of large particles in micrometer scale,the maximum SE emission yield of Pt particles appeared at the center of,instead at the side of,the particle when the size falls down to nanometer region.