New Ordered Structure for the H-Saturated Si(100) Surface: The (3×1) Phase

High-resolution infrared data of Si(100) surfaces saturated with H at room temperature show that the so-called 1×1 surface is in fact a disordered phase with roughly half the H bonded in monohydride (H-Si-Si-H) and half in dihydride (Si${\mathrm{H}}_2$) configurations. Upon saturation exposure at 380 K, the surface is ordered into a newly identified 3×1 phase, as evidenced by LEED, involving repeated alternating monohydride and dihydride units.