Atomic image of hydrogen-terminated Si(001) surfaces after wet cleaning and its first-principles study.

Atomic arrangements of the hydrogen-terminated Si(001) surface after wet cleaning are investigated by scanning tunneling microscopy and by first-principles calculations. The hydrogen-terminated Si(001) surface after dilute HF cleaning is atomically rough with a structure of terraces and steps. In addition, it is confirmed that 1 × 1 dihydride structures are formed inside the terraces. First-principles calculations reveal that the maxima of the local density of states string parallel to the Si-H direction on the 1 × 1 dihydride structure, which makes it possible to determine the atomic arrangement of the observed atomic images. When the surface after HF cleaning is subsequently rinsed with ultrapure water, rows emerge along the 〈110〉 direction. Atomic images show that the rows are mainly formed by a 2 × 1 unit cell. To elucidate the atomic structure of the 2 × 1 unit cell, it is proposed that every other row of the ideal 1 × 1 dihydride surface is preferentially etched with ultrapure water. Total energy calculations are performed based on the first principles of quantum mechanics, which justify the proposed etching mechanism of the Si(001) surface with ultrapure water. [ABSTRACT FROM AUTHOR]