No abstract

No abstract

Dehydrative cyclocondensation processes for semiconductor surface modification can be generally suggested on the basis of well-known condensation schemes; however, in practice this approach for organic functionalization of semiconductors has never been investigated. Here we report the modification of hydrogen-terminated silicon surfaces by cyclocondensation. The cyclocondensation reactions of nitrobenzene with hydrogen-terminated Si(100) and Si(111) surfaces are investigated and paralleled with selected cycloaddition reactions of nitro- and nitrosobenzene with Si(100)-2x1. Infrared spectroscopy is used to confirm the reactions and verify an intact phenyl ring and C-N bond in the reaction products as well as the depletion of surface hydrogen. High resolution N 1s X-ray photoelectron spectroscopy (XPS) suggests that the major product for both cyclocondensation reactions investigated is a nitrosobenzene adduct that can only be formed following water elimination. Both IR and XPS are augmented by density functional theory (DFT) calculations that are also used to investigate the feasibility of several surface reaction pathways, which are insightful in understanding the relative distribution of products found experimentally. This novel surface modification approach will be generally applicable for semiconductor functionalization in a highly selective and easily controlled manner.

Chemical control of interfaces formed on silicon surfaces is important for many practical applications. In this work, the reaction of nitrosobenzene with a clean Si(100)-2 × 1 surface by [2 + 2] cycloaddition at room temperature is investigated. This reaction is compared to the 1,3-dipolar cycloaddition reaction of nitrobenzene on the same surface and to the cyclocondensation reaction of nitrobenzene with hydrogen-terminated Si(100) surfaces. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) methods were used for this study. For both nitrosobenzene and nitrobenzene on Si(100)-2 × 1, oxygen migrates subsurface, despite substantial kinetic barriers. The effects of oxygen migration are addressed by combining DFT cluster modeling and XPS in the N 1s region. The reaction pathways of these nitrogen-containing bifunctional molecules on a clean Si(100)-2 × 1 surface lead to the phenylnitrene adduct as the dominant surface species, while the nitrosoadduct is the primary product for the cyclocondensation reaction of nitrobenzene on hydrogen-terminated Si(100). After the formation of nitrosoadducts following adsorption, thermal annealing drives oxygen subsurface leaving the phenylnitrene adduct as the main species. This serves as a solid evidence that a specific surface adduct can be obtained from these bifunctional molecules without decomposition of the phenyl ring.