Cooperative nitrogen insertion processes: Thermal transformation of $\mathrm{N}{\mathrm{H}}_{3}$ on a Si(100) surface

Cooperative nitrogen insertion processes: Thermal transformation of $N H_{3}$ on a Si(100) surface

J. C. F. Rodríguez-Reyes and A. V. Teplyakov

Phys. Rev. B 76, 075348 – Published 30 August 2007

Abstract

The thermal behavior of an ammonia-covered Si(100) surface is investigated by infrared spectroscopy and density functional methods. Upon adsorption at room temperature, $(Si) N H_{2}$ and Si-H species are formed on the surface. Comparison of the vibrational studies with density functional calculations suggests that the $(Si) N H_{2}$ structures are preferentially located on the same side along the silicon dimer row on a $(2 \times 1)$ reconstructed Si(100) surface, although a mixture of different long-range configurations is likely formed. Decomposition of these $(Si) N H_{2}$ species is observed to start at temperatures as low as $500 K$ . Theoretical predictions of the vibrational modes indicate that at this point, the spectrum is composed of a combination of ${(Si)}_{2} N H$ and ${(Si)}_{3} N$ vibrational signatures, which result from insertion of N into Si-Si bonds. Our computational study of the formation of ${(Si)}_{2} N H$ structures indicates that subsurface insertion is more feasible if the strain imposed during the insertion in a Si dimer is attenuated by a ${(Si)}_{2} N H$ structure already inserted in the neighboring dimer along the same silicon dimer row. This cooperative reaction lowers the energetic requirements for subsurface insertion, providing a theoretical explanation for the mechanism of thermal decomposition of $N H_{3}$ on Si(100) and for other systems where subsurface migration is observed experimentally.