| An ultra-high vacuum (UHV) chamber was designed which incorporates a custom built photolytic source of high energy, monoenergetic H atoms for the systematic study of the reaction of H (or D) atoms with semiconductor surfaces. Hydrogen atoms were produced through the photolysis of HI (at 266 nm) or ND3 (at 193 nm) in a molecular beam. The abstraction of hydrogen atoms from an ideally hydrogen terminated Si(111)-(1 x 1):H surface by deuterium atoms produced by the 193 nm photolysis of ND3 has been observed under low and high resolution. The low resolution measurements of HD time-of-flight (TOF) were performed at surface temperatures ranging from 273 K to 683 K. An Arrhenius type plot of these results gave an activation energy of 1.3 +/− 0.3 kcal/mol for the abstraction reaction. The high resolution TOF's cover a range of incident angles from 30° to 60° in 10° increments, and were acquired at a surface temperature of 300 K. These TOF spectra are bimodal, with a fast, narrow peak, and a slow, broad peak in the HD TOR The fast and slow peaks have been least squares fitted to supersonic and Maxwell-Boltzmann distributions respectively and then converted to kinetic energy distributions. Averaged over all seven angles, the fast peak has an average energy of 1.6 +/− 0.3 eV, while the slow peak reflects a temperature of 620 +/− 60 K. It is here proposed that the fast peak is the result of a direct mechanism commonly referred to as an Eley-Rideal (ER) mechanism, whereas the slow peak results from a Langmuir-Hinshelwood (LH) or Hot Precursor (HP) mechanism. Lastly, by knowing the energy of the incident D atoms, as well as the product HD energy and the H2 bond energy, a Si-H bond energy of 76 +/− 7 kcal/mol has been determined and is in agreement with calculated values. |
