Mathematical model and numerical analysis method for dynamic fracture in a residual stress field.

Residual stress field is a self-equilibrium state of stress in the bulk solid material with the inhomogeneous field of the inelastic deformations. The high level of tensile residual stress often leads to dynamic fracture resulting in the instantaneous and catastrophic destruction of the materials because the cracks are fed with the strain energy initially stored in the bulk materials due to the residual stress. The dissipation of the strain energy with crack growth results in the release and the redistribution of the residual stress.

Simulation of Catastrophic Failure in a Residual Stress Field.

Residual stress has been empirically utilized for industrial applications to control material strength and shape of fragments. The interaction between the dynamically growing cracks and the residual stress field is sufficiently complicated to prevent us from building effective models. To rigorously evaluate the release and redistribution of residual stress in the dynamic fracture process, we develop a mathematical model and a numerical analysis method for the dynamic fracture in a residual stress field.

All-inorganic colloidal silicon nanocrystals-surface modification by boron and phosphorus co-doping.

Si nanocrystals (Si-NCs) with extremely heavily B- and P-doped shells are developed and their structural and optical properties are studied. Unlike conventional Si-NCs without doping, B and P co-doped Si-NCs are dispersible in alcohol and water perfectly without any surface functionalization processes. The colloidal solution of co-doped Si-NCs is very stable and no precipitates are observed for more than 5 years.

Silicon nanocrystal-noble metal hybrid nanoparticles.

We report a novel and facile self-limiting synthesis route of silicon nanocrystal (Si NC)-based colloidally stable semiconductor-metal (gold, silver and platinum) hybrid nanoparticles (NPs). For the formation of hybrid NPs, we employ ligand-free colloidal Si NCs with heavily boron (B) and phosphorus (P) doped shells. By simply mixing B and P codoped colloidal Si NCs with metal salts, hybrid NPs consisting of metal cores and Si NC shells are spontaneously formed.

Size-Dependence of Acceptor and Donor Levels of Boron and Phosphorus Codoped Colloidal Silicon Nanocrystals.

Size dependence of the boron (B) acceptor and phosphorus (P) donor levels of silicon (Si) nanocrystals (NCs) measured from the vacuum level was obtained in a very wide size range from 1 to 9 nm in diameter by photoemission yield spectroscopy and photoluminescence spectroscopy for B and P codoped Si-NCs. In relatively large Si-NCs, both levels are within the bulk Si band gap. The levels exhibited much smaller size dependence compared to the valence band and conduction band edges.