Pyrimidine and s-triazine as structural motifs for ordered adsorption on Si(100): a first principles study

Abstract

The chemisorption of pyrimidine and s-triazine, two aromatic molecules with N atoms in the aromatic ring, is studied by first principles calculations to examine not only the chemisorption energy, but also the reaction barriers and the cooperative effects. Among the reaction paths at low coverage, the formation of a cross-bridge structure with two N-Si dative bonds is almost barrierless and should be dominant at low temperature. At higher coverage and low temperature, these cross-row structures should produce an ordered zig-zag pattern, even though it is not the energetically most stable arrangement. Upon heating, the zig-zag pattern could be transformed into lines along dimer rows. These two molecules also provide structural motifs that could facilitate the formation of ordered adsorption structures on Si(100). By symmetry, the complexity of tight-bridge structures could be greatly reduced, while the X-C-X motif, with X being an electronegative atom, could provide the building blocks for cross-row bridges.

Effect of Heteroaromaticity on Adsorption of Pyrazine on the Ge(100)-2×1 Surface

“…Experimentally, we find that the peak at 400.7 eV increases from 66 ± 2% at room temperature to 80 ± 2% at 180 K of the total nitrogen N (1s) component. Previous studies suggest that reaction products with low or no activation barrier, such as dative bonds, are promoted by decreasing the substrate temperature. , Considering all possible adsorption products, this result suggests that at low temperature there is a higher contribution of nitrogen in its datively bonded state and confirms the assignment of the peak at 400.7 eV to datively bonded species. Product 2C which is observed at room temperature (Figure ) shows much lower abundance at 180 K.…”

“…From (c) to (h) in Figure , different cycloaddition reactions are shown: [2+2] CN (c), [2+2] CC (d), [4+2] NN (e), [4+2] CC (f), [4+2+2] CC (g), and [4+2+2] NN (h). A [4+2+2] cycloaddition refers to a surface reaction between 4π electrons from the adsorbate molecule and 2π electrons for each surface dimer (see Figure g,h); a previous work refers to these reactions as “cross-row” or “cross-bridge” reactions. ,, In all these cases, the aromaticity of the adsorbate is disrupted, as previously shown in studies of pyridine and pyrazine on Si(100) surfaces. , While this is enthalpically unfavorable, the accessibility of pathways that allow for reduction of the aromatic character can be attributed to a small increase in entropy, creating a thermal switch between aromatic and nonaromatic adsorbate configurations. , …”

Landscape of s-triazine molecule on Si(100) by a theoretical x-ray photoelectron spectroscopy and x-ray absorption near-edge structure spectra study

“…For s-triazine, the dative bond between an electronegative nitrogen atom and a silicon atom of the surface is shaped by a barrier-free process. [12] At low temperatures, it seems to be propitious to the formation of Si-N dative bonds. As suggested by the available experiment, the striazine molecule is parallel to the silicon surface when the adsorbed sample is heated to 200 K. In our work, the fully optimized geometries of both the s-triazine molecule and the five possible adsorbed derivatives are displayed in Fig.…”

“…Recently, the study on chemisorption of s-triazine molecule involving three N atoms on Si(100) surface is gradually being focused. According to previous related literature, [12] we construct five possible different adsorption configurations of s-triazine on Si(100). For the present, the landscape and identification of structures are two of the basic investigations for this kind of chemisorption systems, which could conduce to a wider range of applications as organic semiconductors.…”

Geometric and electronic structures of pyrazine molecule chemisorbed on Si(100) surface by XPS and NEXAFS spectroscopy

“…Aromatic molecule is an important organic group in organic materials, and the adsorption of aromatic compounds on the silicon surface through covalent bonds is a typical reaction between π-conjugated molecules and the Si dimer. To date, a variety of these types of adsorbed structures have been produced in both theoretical and experimental studies according to the sides, polarity, substituent groups and the types of heteroatoms in the aromatic ring [7,8]. In the aromatic family, pyrazine (C 4 H 4 N 2 ), lightly modified by inserting two para-nitrogen atoms into the six-membered aromatic ring, is isoelectronic to benzene and pyridine, and may be an ideal building block for various synthetic compounds and new functional materials [8,9].…”