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ABSTRACT: 3-Chloro-1-propanol (HO−CH2−CH2−CH2−Cl) covalently binds onto Si(100)-2×1 through the thermal dissociation of the OH group to form Si−O−CH2−CH2−CH2−Cl surface intermediates, evidenced by the appearance of the Si−H stretching mode (2110 cm−1) and the retention of C−Cl stretching mode (654 cm−1) in the high-resolution electron energy loss spectroscopy (HREELS) spectrum of chemisorbed 3-chloro-1-propanol molecules and the chemical downshift of O1s binding energy (BE) in the X-ray photoelectron spectroscopy (XPS) study. The C−Cl bonds in the chemisorbed 3-chloro-1-propanol can be cleaved upon 193 nm irradiation, resulting in Si−O−CH2CH2CH2−CH2CH2CH2−O−Si through lateral diradical coupling. Upon covering the chemisorbed 3-chloro-1-propanol with physisorbed molecules, photoinduced diradical coupling between physisorbed and chemisorbed molecules was also evidenced, achieving the secondary attachment of 3-chloro-1-propanol on the Si surface and forming Si−O−CH2CH2CH2−CH2CH2CH2−OH.
09/2010;
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ABSTRACT: We previously demonstrated that acetonitrile (N[triple bond]C-CH(3)) binds to the adjacent adatom-rest atom pair of Si(111)-7x7 through a [2+2]-like cycloaddition reaction, forming a (Si)N=C(Si)-CH(3)-like surface species [Tao et al., J. Phys. Chem. B 106, 3890 (2002)]. Current investigation clearly showed that chloroacetonitrile (N[triple bond]C-CH(2)Cl), propargyl chloride (HC[triple bond]C-CH(2)Cl), and 3-chloropropionitrile (N[triple bond]C-CH(2)-CH(2)Cl) react with the surface via enelike reactions, concurrently involving N[triple bond]C/C[triple bond]C as well as the breakage of the C-Cl/C-H bond. Further separation of the unsaturated bond (C[triple bond]C) from the C-Cl bond using CH(2) spacers in 5-chloro-1-pentyne (CH[triple bond]C-CH(2)CH(2)CH(2)Cl) would direct the reaction to a [2+2]-like cycloaddition. These experimental results clearly suggest the possibility of controlling the surface reaction pathways by tuning the organic molecular structures. This strategy can be useful in designing and fabricating functional molecular templates on Si(111)-7x7.
The Journal of chemical physics 06/2010; 132(21):214710. · 3.09 Impact Factor
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ABSTRACT: The Covalent binding of p-benzoquinone (O═C6H4═O) and the formation of an aromatic ring (−O—C6H4—O−) on Si(111)-7×7 have been investigated by using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. For chemisorbed p-benzoquinone, the absence of v(C═O) at 1659 cm−1, the retention of sp2-v(C−H) at 3050 cm−1, the appearance of v(Si−O) at 824 cm−1, and aromatic v(C═C)/δip(C−H) at 1600/1505 cm−1 demonstrate that the molecule reacts with the surface in a [6+2]-like cycloaddition mode, which is further confirmed by XPS and density functional theory (DFT) vibrational calculations. DFT calculations indicate that the [6+2]-like cycloadduct (−O—C6H4—O−) bridging two nearest adatoms in neighboring half-unit cells is the most stable. This binding scheme may prove useful for chemical and electronic modification of the semiconductor surfaces.
05/2010;
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ABSTRACT: The adsorption of halogenated acetonitrile (X−CH2C≡N, X = F, Cl, Br) on Si(100)-2×1 has been studied using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculation. Fluoroacetonitrile chemisorbs on the Si(100)-2×1 surface via a C≡N [2 + 2] cycloaddition-like reaction, while chloroacetonitrile is chemically bound to the Si surface through both C≡N [2 + 2] cycloaddition-like and ene-like reactions. However, bromoacetonitrile was found to attach onto the surface exclusively through the ene-like reaction. The different reaction pathways of these halogenated compounds on the Si(100)-2×1 surface demonstrate that the halogen substitution groups play an important role in manipulating the reaction channels of bifunctional molecules, offering a great flexibility in surface reaction of silicon surfaces.
01/2010;
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ABSTRACT: The covalent attachment of 4-chloroaniline on the Si(111)-7×7 surface was investigated by using a combination of X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS), and density functional theory (DFT) calculations. The HREELS spectra suggest that one of the N−H bonds dissociates to form Si−N and Si−H bonds with the phenyl ring and the C−Cl bond unperturbed upon chemisorption. The XPS results confirm that only the NH2 group participates in the surface binding. This binding mode and surface reaction pathway are further supported by the DFT calculation. The resulting chlorobenene-like structure on Si(111)-7×7 can be employed for further photochemical modification and functionalization.
03/2009;
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Journal of the American Chemical Society 08/2007; 129(27):8404-5. · 9.91 Impact Factor
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ABSTRACT: The adsorption of glycine and l-cysteine on Si(111)-7 x 7 was investigated using high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). The observation of the characteristic vibrational modes and electronic structures of NH3+ and COO- groups for physisorbed glycine (l-cysteine) demonstrates the formation of zwitterionic species in multilayers. For chemisorbed molecules, the appearance of nu(Si-H), nu(Si-O), and nu(C=Omicron) and the absence of nu(O-H) clearly indicate that glycine and l-cysteine dissociate to produce monodentate carboxylate adducts on Si(111)-7 x 7. XPS results further verified the coexistence of two chemisorption states for each amino acid, corresponding to a Si-NH-CH2-COO-Si [Si-NHCH(CH2SH)COO-Si] species with new sigma-linkages of Si-N and Si-O, and a NH2-CH2-COO-Si [NH2CH(CH2SH)COO-Si] product through the cleavage of the O-H bond, respectively. Glycine/Si(111)-7 x 7 and l-cysteine/Si(111)-7 x 7 can be viewed as model systems for further modification of Si surfaces with biological molecules.
Langmuir 06/2007; 23(11):6218-26. · 4.19 Impact Factor
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ABSTRACT: The adsorption of glycine and l-cysteine on Si(111)-7×7 was investigated using high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). The observation of the characteristic vibrational modes and electronic structures of NH3+ and COO- groups for physisorbed glycine (l-cysteine) demonstrates the formation of zwitterionic species in multilayers. For chemisorbed molecules, the appearance of ν(Si−H), ν(Si−O), and ν(CΟ) and the absence of ν(O−H) clearly indicate that glycine and l-cysteine dissociate to produce monodentate carboxylate adducts on Si(111)-7×7. XPS results further verified the coexistence of two chemisorption states for each amino acid, corresponding to a Si−NH−CH2−COO−Si [Si−NHCH(CH2SH)COO−Si] species with new σ-linkages of Si−N and Si−O, and a NH2−CH2−COO−Si [NH2CH(CH2SH)COO−Si] product through the cleavage of the O−H bond, respectively. Glycine/Si(111)-7×7 and l-cysteine/Si(111)-7×7 can be viewed as model systems for further modification of Si surfaces with biological molecules.
04/2007;
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ABSTRACT: The covalent attachment of N-methylallylamine (MAA) and N,N-dimethylallylamine (DMAA) on Si(111)-7×7 was investigated with high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). Experimental results showed that MAA chemisorbs dissociatively on Si(111)-7×7 through the cleavage of its N−H bond, while DMAA is covalently bonded to the silicon surface via a [2+2]-like cycloaddition between its CC group and the adjacent adatom−rest atom pair. This study demonstrates that the selective organic functionalization of silicon surfaces can be achieved by fine-tuning molecular structures.
04/2007;
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ABSTRACT: The interaction of methacrylic acid and methyl methacrylate with Si(111)-7 x 7 has been investigated using high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). While methacrylic acid chemisorbs dissociatively through O-H bond cleavage, methyl methacrylate is covalently attached to the silicon surface via a [4+2] cycloaddition. The different reaction pathways of these two compounds on Si(111)-7 x 7 demonstrate that the substitution groups play an important role in determining the reaction channels for multifunctional molecules, leading to the desired flexibility in the organic modification of silicon surfaces.
The Journal of Physical Chemistry B 11/2005; 109(42):19831-8. · 3.70 Impact Factor
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ABSTRACT: The interaction of methacrylic acid and methyl methacrylate with Si(111)-7×7 has been investigated using high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). While methacrylic acid chemisorbs dissociatively through O−H bond cleavage, methyl methacrylate is covalently attached to the silicon surface via a [4+2] cycloaddition. The different reaction pathways of these two compounds on Si(111)-7×7 demonstrate that the substitution groups play an important role in determining the reaction channels for multifunctional molecules, leading to the desired flexibility in the organic modification of silicon surfaces.
09/2005;
