Zhonghua Li

Molecular dynamics (MD) simulations have been performed to investigate the mechanical properties of hydrogen functionalized graphene allotropes (GAs) for H-coverage spanning the entire range (0-100%). Four allotropes (graphyne, cyclic graphene, octagonal graphene, and biphenylene) with larger unit lattice size than graphene are considered. The effect of the degree of functionalization and molecular structure on the Young's modulus and strength are investigated, and the failure processes of some new GAs are reported for the first time. We show that the mechanical properties of the hydrogenated GAs deteriorate drastically with increasing H-coverage within the sensitive threshold, beyond which the mechanical properties remain insensitive to the increase in H-coverage. This drastic deterioration arises both from the conversion of sp2 to sp3 bonding and easy rotation of unsupported sp3 bonds. Allotropes with different lattice structures correspond to different sensitive thresholds. The Young's moduli deterioration of fully hydrogenated allotropes can be up to 70% smaller than that of the corresponding pristine structure. Moreover the tensile strength shows an even larger drop of about 90% and higher sensitivity to H-coverage even if it is small. Our results suggest that the unique coverage-dependent deterioration of the mechanical properties must be taken into account when analyzing the performance characteristics of nanodevices fabricated from functionalized GAs.

An analytical expression is developed to predict the thermal residual stress redistribution in a passivated bamboo interconnect based on the coupling of the grain boundary diffusion with the interconnect-passivation interface diffusion. Quantitative results show that the thermal stress redistribution in the interconnect depends strongly on the microstructure of the interconnect, the initial state of the thermal residual stress and the diffusivity ratio of the grain boundary to the interface.

An analytic expression is developed to predict grain boundary void growth in bamboo interconnect under thermal residual stress field. The rate process is controlled by grain boundary and interconnect/passivation interface diffusions. The thermal residual stress field relaxes during void growth. Based on the present analysis, the behaviors of the void growth and the stress redistribution are characterized as a function of the microstructure of the interconnect, the state of the thermal residual stress, the initial size of the void, as well as the diffusivity ratio between the interface and the grain boundary.