Laser breaks H-Si bonds selectively

The ability to control the breaking of chemical bonds by using lasers to selectively excite the bonds' vibrational frequencies has been a long-standing but as-yet-unrealized goal. In most experiments, the initial vibrational excitation quickly distributes throughout molecules as thermal energy. Now, using a free-electron laser, Philip I. Cohen of the University of Minnesota and colleagues have selectively broken H-Si bonds on a silicon surface. In addition to being a scientific milestone, the work could also find utility in semiconductor research, such as nanostructure fabrication. The group bombarded a silicon surface covered with 15% H and 85% D atoms with a laser tuned to the same energy as the vibrational mode of the H−Si bond. H₂ was the primary molecule released, ruling out a thermal process, which would have generated large quantities of D₂ (Science 2006, 312, 1024). The mechanism remains unresolved, but the authors hypothesize that the bonds absorb multiple photons before breaking.