报告题目：In Situ Characterization of Active and Inactive Catalysts Nanoparticles for Carbon Nanotube Growth

报 告 人：Renu Sharma，Center for Nanoscale Science and Technology，National Institute of Science and Technology, Gaithersburg, MD 20899-6203

报告时间：6月8日（周五）15:00

报告地点：清华—富士康纳米科技研究中心四楼报告厅

报告摘要：Catalytic chemical vapor deposition (C-CVD), using a transition metal catalyst (Ni, Fe, Co, etc.) on SiO2or Al2O3support and a carbon-containing precursor (C2H2, C2H4, CH4, CO, etc.), is commonly employed for large scale synthesis of carbon nanotubes (CNTs). However, controlling the synthesis conditions to obtain CNTs with the desired structure and morphology for a specific application has still not been demonstrated. Recently, the effect of synthesis conditions on the structure and morphology of CNTs has been revealed by dynamic observations using environmental scanning-transmission electron microscopy (ESTEM). In situ observations show that the catalyst remains crystalline during the growth, while both in situ and ex situ observations have confirmed that not all catalyst particles are active for CNT growth. Previous reports have shown that the Fe3C structure is formed during CNT growth from Fe catalyst particles, but not much has been reported about the inactive nanoparticles (NPs). We have measured spacings and angles between the lattice planes for both active and inactive nanoparticles using high resolution images, extracted from the same video sequence. Our measurements confirm that the structure of the particles active for CNT nucleation and growth is Fe3C. However lattice plane spacings and angles measured for inactive particles correspond to those of the Fe5C2structure. This structure was commonly seen in particles that remained inactive during observation as well as in nanoparticles that were enclosed in a graphitic shell. Moreover, we also observed the structure of an active particle change from Fe3C to Fe5C2upon deactivation. These results show that both the structure and orientation of the catalyst NPs are important for CNT growth: carbon atoms may be bound by surfaces that do not provide easy diffusion paths or a nucleation plane for graphite layers. Complete analysis and models explaining the role of orientation and the formation of carbon coatings on the catalytic activity of such NPs will be presented. A detailed structural analysis of active and inactive particles, subjected to same experimental conditions during dynamic observations will be presented.