Passivation effect of allylamine molecule on the electronic structure of a Si(001)−(2×1) surface (original) (raw)
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Surface Science, 2010
The room-temperature adsorption and thermal evolution of allylamine on Si(100)2 × 1 have been investigated by using temperature-dependent X-ray photoelectron spectroscopy (XPS) and thermal desorption spectrometry (TDS). The presence of a broad N 1 s feature at 398.9 eV, attributed to a N-Si bond, indicates N-H dissociative adsorption. On the other hand, the presence of C 1 s features at 284.6 eV and 286.2 eV, corresponding to C=C and C-N, respectively, and the absence of the Si-C feature expected at 283.2 eV shows that [2 + 2] C=C cycloaddition does not occur at room temperature. These XPS data are consistent with the unidentate staggered and eclipsed allylamine conformer adstructures arising from N-H dissociation and not [2 + 2] C=C cycloaddition. The apparent conversion of the N 1 s feature for Si-N(H)-C at 398.9 eV to that for Si-N(H) at 397.7 eV and the total depletion of C 1 s feature for C-N at 286.2 eV near 740 K indicates cleavage of the C-N bond, leaving behind a Si-N(H)• radical. Furthermore, the C=C C 1 s feature at 284.6 eV undergoes steep intensity reduction between 740 K and 825 K, above which a new C 1 s feature at 283.2 eV corresponding to SiC is found to emerge. These spectral changes suggest total dissociation of the ethenyl fragment and the formation of SiC. Moreover, while the total N 1 s intensity undergoes a minor reduction (24%) upon annealing up to 1090 K, a considerable reduction (43%) is found in the overall C 1 s intensity. This observation is consistent with our TDS data, which shows the desorption of C-containing molecules including propene and ethylene at 580 K and of acetylene at 700 K. The lack of N-containing desorbates suggests that the dissociated N species are likely bonded to multiple surface Si atoms or diffused into the bulk. Interestingly, both the staggered and eclipsed N-H dissociative adstructures are found to have a less negative adsorption energy than the [N, C, C] tridentate or the [2 + 2] C=C cycloaddition adstructures by our DFT calculations, which suggests that the observed formation of N-H dissociative adstructures is kinetically favored on the Si(100)2 × 1 surface.
Physical Review B, 2003
The structural and bonding properties of adsorbed trimethylamine and dimethylamine on the Si͑001͒ surface are investigated by first-principles density-functional calculations. We find that trimethylamine dissociation is not kinetically feasible because of the existence of a high-energy barrier for the NuCH 3 bond cleavage, but dimethylamine dissociation accompanying the NuH bond cleavage takes place at room temperature. Our initial-state theory calculation for the N ͑C͒ 1s core level of adsorbed trimethylamine obtains 2.77 ͑0.67͒ eV greater binding energy than that of dissociated dimethylamine. The final-state effect due to screening of the N ͑C͒ core hole yields 2.90 ͑0.78͒ eV. These N and C 1s core-level shifts of adsorbed trimethylamine are attributed to rehybridization between the lone-pair state of the N atom and the empty dangling-bond state of the down atom of the Si dimer. In addition, unlike dimethylamine adsorption which attains full coverage with one molecule per surface dimer, we find significant repulsive interactions between adsorbed trimethylamine molecules, disfavoring adsorption at every Si dimer. This result accounts for a relatively lower saturation coverage in trimethylamine adsorption, which was observed from multiple internal reflection Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy.
Silicon Surfaces as Electron Acceptors: Dative Bonding of Amines with Si(001) and Si(111) Surfaces
Journal of the American Chemical Society, 2001
The bonding of the trimethylamine (TMA) and dimethylamine (DMA) with crystalline silicon surfaces has been investigated using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, and density-functional computational methods. XPS spectra show that TMA forms stable dative-bonded adducts on both Si(001) and Si(111) surfaces that are characterized by very high N(1s) binding energies of 402.2 eV on Si(001) and 402.4 eV on Si(111). The highly ionic nature of these adducts is further evidenced by comparison with other charge-transfer complexes and through computational chemistry studies. The ability to form these highly ionic charge-transfer complexes between TMA and silicon surfaces stems from the ability to delocalize the donated electron density between different types of chemically distinct atoms within the surface unit cells. Corresponding studies of DMA on Si(001) show only dissociative adsorption via cleavage of the N-H bond. These results show that the unique geometric structures present on silicon surfaces permit silicon atoms to act as excellent electron acceptors.
Competing Pathways in N -Allylurea Adsorption on Si(111)-(7 × 7)
The Journal of Physical Chemistry C, 2012
Functionalization of silicon surfaces with Nallylurea (CH 2 CH−CNH−CO−NH 2) represents a valuable strategy to obtain covalently bonded Si−C interfaces with amino and/or carbonyl termination. In this work, we studied N-allylurea adsorption on the Si(111)-(7 × 7) surface by combining X-ray and ultraviolet photoemission spectroscopy (XPS and UPS) with high resolution energy loss spectroscopy (HREELS) measurements. XPS core level analysis provides information on the molecular attachment process. Si−C covalent bonding is evidenced by the presence of a C 1s component at 284.8 eV, while interaction through N−Si bonding is proved by the presence of a N 1s component at 397.8 eV. Three different adsorption mechanisms are envisaged: (I) [2 + 2]-like cycloaddition occurring at the rest atom−adatom dimer through cleavage of the vinyl group, (II) Si−N bonding at adatom sites upon cleavage of NH 2 and rearrangement of the ureic group to form an imidol species (−NC−OH), with release of a H atom, and (III) hydrosilylation at adatom sites, through cleavage of the vinyl group and involvement of H atoms provided by reaction II.
Chemical Physics Letters, 2004
The reaction of the bifunctional organic molecule 1-dimethylamino-2-propyne (DMAP) on the Si(100) surface has been investigated by density functional calculations on a one-dimer cluster model. We found that, once in the physisorbed dative bonded well (À22.1 kcal mol À1), DMAP can proceed to react via a number of pathways. We first considered the cycloaddition of the C"C triple bond, leading to Si-C di-r bonded product (À58.6 kcal mol À1), computing an energy barrier of 33.1 kcal mol À1. We considered also possible dissociative pathways of dative bonded DMAP, i.e., methylene C-H, methyl C-H or N-CH 3 bond cleavage.
Molecular and dissociative bonding of amines with the Si-(7×7) surface
Surface Science, 2003
The interaction of trimethylamine (TMA) and dimethylamine (DMA) with the Si(1 1 1)-(7 Â 7) surface has been studied by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS). STM data for TMA at low coverage show molecular features exhibiting a strong preference for bonding at the center adatom sites. XPS data show that at low coverage the majority of molecules form a highly ionic dative-bonded molecular adduct in which the N atom donates electron density to the surface, leading to a very high N(1s) binding energy of 402.4 eV. UPS data show that the interaction of TMA with the Si(1 1 1)-(7 Â 7) surface also involves the restatom, suggesting that formation of dative bonds may also alter the restatom state. At very high exposures, a new, dissociative pathway becomes important, leading to dissociation and the appearance of new fragments with lower N(1s) binding energies of 399.1 eV. Corresponding studies for DMA only show dissociative bonding on Si(1 1 1), forming H atoms and N(CH 3) 2 species. While the N(CH 3) 2 species bonds primarily to the adatoms, the H atoms can bond to either adatoms or restatoms. Possible reaction mechanism and the reactivity of the different types of surface silicon atoms are discussed.
Surface Science, 2009
Competition between the C dbnd C functional group with the OH group in allyl alcohol and with the C dbnd O group in allyl aldehyde in the adsorption and thermal chemistry on Si(1 0 0)2×1 has been studied by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD), as well as density-functional theory (DFT) calculations. The similarities found in the C 1s and O 1s spectra for both molecules indicate that the O-H dissociation product for allyl alcohol and [2 + 2] C dbnd O cycloaddition product for allyl aldehyde are preferred over the corresponding [2 + 2] C dbnd C cycloaddition products. Temperature-dependent XPS and TPD studies further show that thermal evolution of these molecules gives rise to the formation of ethylene, acetylene, and propene on Si(1 0 0)2×1, with additional CO evolution only from allyl alcohol. The formation of these desorption products also supports that the [2 + 2] C dbnd C cycloaddition reaction does not occur. In addition, the formation of SiC at 1090 K is observed for both allyl alcohol and allyl aldehyde. We propose plausible surface-mediated reaction pathways for the formation of these thermal evolution products. The present work illustrates the crucial role of the Si(1 0 0)2×1 surface in selective reactions of the Si dimers with the O-H group in allyl alcohol and with the C dbnd O group in allyl aldehyde over the C dbnd C functional group common to both molecules.
Journal of molecular modeling, 2018
Using density functional theory, we explored the termination process of Si (100)-2 × 1 reconstructed surface mechanistically through the dehydrogenation of small molecules, considering methyl amine and methanol as terminating reagents. At first, both the terminating reagents form two types of adduct through adsorption on the Si (100)-2 × 1 surface, one in chemisorption mode and the other via physisorption, from which the dehydrogenation process is initiated. By analyzing the activation barriers, it was observed that termination of the Si-surface through the dehydrogenation is kinetically almost equally feasible using either reagent. We further examined in detail the mechanism for each termination process by analyzing geometrical parameters and natural population analysis charges. From bonding evaluation, it is evident that hydrogen abstraction from adsorbates on the Si-surface is asymmetric in nature, where one hydrogen is abstracted as hydride by the electrophilic surface Si and th...