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Christopher J. Welsby - One of the best experts on this subject based on the ideXlab platform.

  • A Combined XPS/STM and TPD Study of the Chemisorption and Reactions of Methyl Mercaptan at a Cu(110) Surface
    Topics in Catalysis, 2003
    Co-Authors: Albert F. Carley, Philip R. Davies, Rhys V. Jones, K.r. Harikumar, M. Wyn Roberts, Christopher J. Welsby
    Abstract:

    Despite the structural similarities between methanol and methyl mercaptan (CH3SH), replacing the oxygen atom by sulfur has a profound effect on their chemistry at copper surfaces. In a combined STM, XPS and TPD study of the reaction of methyl mercaptan with clean and partially oxidised Cu(110) surfaces we have found that unlike methanol, the scission of the SH bond (both in the presence of and in the absence of oxygen) to give adsorbed Mercaptide (CH3S(a)) results in a restructuring of the surface. Low concentrations of adsorbed Mercaptide (< 1 × 1014 cm-2) result in a severe degradation of the STM image due to the high mobility of the surface adlayer. A stable surface can be regained by increasing the concentration of Mercaptide or the presence of another adsorbate such as oxygen. The reconstructed surface is characterised by very narrow terraces (typically 10-15A wide) orientated mainly in the 〈1¯10〉 direction with a “zig-zag” structure. Higher resolution images of the terraces reveal an atomic scale structure with a c(2 × 2) unit cell, each cell containing (in total) two bright features. The XPS data confirm that Mercaptide is present and show that the concentration at which islands of Mercaptide become visible in the STM images is approximately 3 × 1014 cm-2. At a surface concentration of 5.1 × 1014 cm-2 the c(2 × 2) structure is seen to be complete, consistent with the c(2 × 2) unit cell containing two Mercaptide species. On heating to 450K the Mercaptide dissociates to give chemisorbed sulfur adatoms and methane. The latter implies that the hydrogen formed when the methyl mercaptan dissociates remains chemisorbed at the surface until removed by reaction with the methyl groups. At pre-oxidised surfaces where chemisorbed hydrogen is removed as water, Mercaptide decomposition leads to ethane desorption with minor methane and ethane components, the latter indicating that methyl dehydrogenation is possible at the copper surface. STM shows that following the decomposition of the Mercaptide adlayer the copper surface regains its original structure of broad terraces (typically 100-200A wide), although a monolayer of chemisorbed sulfur is now present.

  • A Combined XPS/STM and TPD Study of the Chemisorption and Reactions of Methyl Mercaptan at a Cu(110) Surface
    Topics in Catalysis, 2003
    Co-Authors: Albert F. Carley, Philip R. Davies, Rhys V. Jones, K.r. Harikumar, M. Wyn Roberts, Christopher J. Welsby
    Abstract:

    Despite the structural similarities between methanol and methyl mercaptan (CH_3SH), replacing the oxygen atom by sulfur has a profound effect on their chemistry at copper surfaces. In a combined STM, XPS and TPD study of the reaction of methyl mercaptan with clean and partially oxidised Cu(110) surfaces we have found that unlike methanol, the scission of the SH bond (both in the presence of and in the absence of oxygen) to give adsorbed Mercaptide (CH_3S(a)) results in a restructuring of the surface. Low concentrations of adsorbed Mercaptide (< 1 × 10^14 cm^-2) result in a severe degradation of the STM image due to the high mobility of the surface adlayer. A stable surface can be regained by increasing the concentration of Mercaptide or the presence of another adsorbate such as oxygen. The reconstructed surface is characterised by very narrow terraces (typically 10-15Å wide) orientated mainly in the 〈1¯10〉 direction with a “zig-zag” structure. Higher resolution images of the terraces reveal an atomic scale structure with a c(2 × 2) unit cell, each cell containing (in total) two bright features. The XPS data confirm that Mercaptide is present and show that the concentration at which islands of Mercaptide become visible in the STM images is approximately 3 × 10^14 cm^-2. At a surface concentration of 5.1 × 10^14 cm^-2 the c(2 × 2) structure is seen to be complete, consistent with the c(2 × 2) unit cell containing two Mercaptide species. On heating to 450K the Mercaptide dissociates to give chemisorbed sulfur adatoms and methane. The latter implies that the hydrogen formed when the methyl mercaptan dissociates remains chemisorbed at the surface until removed by reaction with the methyl groups. At pre-oxidised surfaces where chemisorbed hydrogen is removed as water, Mercaptide decomposition leads to ethane desorption with minor methane and ethane components, the latter indicating that methyl dehydrogenation is possible at the copper surface. STM shows that following the decomposition of the Mercaptide adlayer the copper surface regains its original structure of broad terraces (typically 100-200Å wide), although a monolayer of chemisorbed sulfur is now present. Oxygen chemisorption is completely inhibited by Mercaptide concentrations of 5 × 10^14 cm^-2 but occurs at lower concentrations. The STM images show that the Mercaptide and oxygen adsorbates form separate islands, in contrast to the coadsorption of hydrogen sulfide and oxygen. The influence of oxygen on the thermal desorption of Mercaptide is discussed in the light of the structural data.

Wangen Shu - One of the best experts on this subject based on the ideXlab platform.

  • Stabilization mechanism of antimony Mercaptides in poly(vinyl chloride): ab initio theory studies
    Polymer Degradation and Stability, 2002
    Co-Authors: Weiquan Tian, Wangen Shu
    Abstract:

    Ab initio quantum theory has been used to study stabilizing mechanism of antimony Mercaptides in poly(vinyl chloride) (PVC). Analysis of composition of the frontier orbitals, dipole moment of the systems, charge on Sb and its bonded atoms in antimony Mercaptides, indicates that these compounds could absorb the HCl produced during the decomposition of PVC. The mechanism of stabilization is electrophilic followed by a nucleophilic step. Also they could substitute the Cl in PVC to prevent the production of HCl, thus preventing the decomposition of PVC. This mechanism is nucleophilic followed by an electrophilic process. The results from theoretical calculation match well with the test of the stabilizing effect on a PVC product containing these stabilizers. The structures of some organoantimony compounds are also reported.

Albert F. Carley - One of the best experts on this subject based on the ideXlab platform.

  • A Combined XPS/STM and TPD Study of the Chemisorption and Reactions of Methyl Mercaptan at a Cu(110) Surface
    Topics in Catalysis, 2003
    Co-Authors: Albert F. Carley, Philip R. Davies, Rhys V. Jones, K.r. Harikumar, M. Wyn Roberts, Christopher J. Welsby
    Abstract:

    Despite the structural similarities between methanol and methyl mercaptan (CH3SH), replacing the oxygen atom by sulfur has a profound effect on their chemistry at copper surfaces. In a combined STM, XPS and TPD study of the reaction of methyl mercaptan with clean and partially oxidised Cu(110) surfaces we have found that unlike methanol, the scission of the SH bond (both in the presence of and in the absence of oxygen) to give adsorbed Mercaptide (CH3S(a)) results in a restructuring of the surface. Low concentrations of adsorbed Mercaptide (< 1 × 1014 cm-2) result in a severe degradation of the STM image due to the high mobility of the surface adlayer. A stable surface can be regained by increasing the concentration of Mercaptide or the presence of another adsorbate such as oxygen. The reconstructed surface is characterised by very narrow terraces (typically 10-15A wide) orientated mainly in the 〈1¯10〉 direction with a “zig-zag” structure. Higher resolution images of the terraces reveal an atomic scale structure with a c(2 × 2) unit cell, each cell containing (in total) two bright features. The XPS data confirm that Mercaptide is present and show that the concentration at which islands of Mercaptide become visible in the STM images is approximately 3 × 1014 cm-2. At a surface concentration of 5.1 × 1014 cm-2 the c(2 × 2) structure is seen to be complete, consistent with the c(2 × 2) unit cell containing two Mercaptide species. On heating to 450K the Mercaptide dissociates to give chemisorbed sulfur adatoms and methane. The latter implies that the hydrogen formed when the methyl mercaptan dissociates remains chemisorbed at the surface until removed by reaction with the methyl groups. At pre-oxidised surfaces where chemisorbed hydrogen is removed as water, Mercaptide decomposition leads to ethane desorption with minor methane and ethane components, the latter indicating that methyl dehydrogenation is possible at the copper surface. STM shows that following the decomposition of the Mercaptide adlayer the copper surface regains its original structure of broad terraces (typically 100-200A wide), although a monolayer of chemisorbed sulfur is now present.

  • A Combined XPS/STM and TPD Study of the Chemisorption and Reactions of Methyl Mercaptan at a Cu(110) Surface
    Topics in Catalysis, 2003
    Co-Authors: Albert F. Carley, Philip R. Davies, Rhys V. Jones, K.r. Harikumar, M. Wyn Roberts, Christopher J. Welsby
    Abstract:

    Despite the structural similarities between methanol and methyl mercaptan (CH_3SH), replacing the oxygen atom by sulfur has a profound effect on their chemistry at copper surfaces. In a combined STM, XPS and TPD study of the reaction of methyl mercaptan with clean and partially oxidised Cu(110) surfaces we have found that unlike methanol, the scission of the SH bond (both in the presence of and in the absence of oxygen) to give adsorbed Mercaptide (CH_3S(a)) results in a restructuring of the surface. Low concentrations of adsorbed Mercaptide (< 1 × 10^14 cm^-2) result in a severe degradation of the STM image due to the high mobility of the surface adlayer. A stable surface can be regained by increasing the concentration of Mercaptide or the presence of another adsorbate such as oxygen. The reconstructed surface is characterised by very narrow terraces (typically 10-15Å wide) orientated mainly in the 〈1¯10〉 direction with a “zig-zag” structure. Higher resolution images of the terraces reveal an atomic scale structure with a c(2 × 2) unit cell, each cell containing (in total) two bright features. The XPS data confirm that Mercaptide is present and show that the concentration at which islands of Mercaptide become visible in the STM images is approximately 3 × 10^14 cm^-2. At a surface concentration of 5.1 × 10^14 cm^-2 the c(2 × 2) structure is seen to be complete, consistent with the c(2 × 2) unit cell containing two Mercaptide species. On heating to 450K the Mercaptide dissociates to give chemisorbed sulfur adatoms and methane. The latter implies that the hydrogen formed when the methyl mercaptan dissociates remains chemisorbed at the surface until removed by reaction with the methyl groups. At pre-oxidised surfaces where chemisorbed hydrogen is removed as water, Mercaptide decomposition leads to ethane desorption with minor methane and ethane components, the latter indicating that methyl dehydrogenation is possible at the copper surface. STM shows that following the decomposition of the Mercaptide adlayer the copper surface regains its original structure of broad terraces (typically 100-200Å wide), although a monolayer of chemisorbed sulfur is now present. Oxygen chemisorption is completely inhibited by Mercaptide concentrations of 5 × 10^14 cm^-2 but occurs at lower concentrations. The STM images show that the Mercaptide and oxygen adsorbates form separate islands, in contrast to the coadsorption of hydrogen sulfide and oxygen. The influence of oxygen on the thermal desorption of Mercaptide is discussed in the light of the structural data.

  • An STM and XPS study of the chemisorption of methyl mercaptan at a Cu(110) surface
    Surface Science, 2001
    Co-Authors: Albert F. Carley, Philip R. Davies, Rhys V. Jones, K.r. Harikumar, M. Wyn Roberts
    Abstract:

    XP spectra of a Cu(1 1 0) surface exposed to methyl mercaptan at 290 K show the presence of an adsorbate assigned to Mercaptide, CH3S(a). Scanning tunneling microscopic (STM) images show that the formation of the adsorbed Mercaptide (CH3S(a)) is accompanied by a restructuring of the surface. The reconstructed surface is characterized by very narrow terraces (typically 10–15 A wide) oriented mainly in the 〈110〉 direction with a `zig-zag' structure. Higher resolution images of the terraces reveal an atomic scale structure with a c(2×2) unit cell, each cell containing two bright features. The combination of STM and X-ray photoelectron spectroscopy (XPS) shows that the c(2×2) structure is complete at a surface concentration of ∼5 ×1014cm−2, consistent with the c(2×2) unit cell containing two equivalent Mercaptide species. On heating to 450 K the Mercaptide dissociates to give chemisorbed sulfur adatoms and the desorption of all of the surface carbon. The STM images show that following the decomposition of the Mercaptide adlayer the copper surface regains its original structure of broad terraces (typically 100–200 A wide), though an adlayer of chemisorbed sulfur atoms is now present.

Weiquan Tian - One of the best experts on this subject based on the ideXlab platform.

  • Stabilization mechanism of antimony Mercaptides in poly(vinyl chloride): ab initio theory studies
    Polymer Degradation and Stability, 2002
    Co-Authors: Weiquan Tian, Wangen Shu
    Abstract:

    Ab initio quantum theory has been used to study stabilizing mechanism of antimony Mercaptides in poly(vinyl chloride) (PVC). Analysis of composition of the frontier orbitals, dipole moment of the systems, charge on Sb and its bonded atoms in antimony Mercaptides, indicates that these compounds could absorb the HCl produced during the decomposition of PVC. The mechanism of stabilization is electrophilic followed by a nucleophilic step. Also they could substitute the Cl in PVC to prevent the production of HCl, thus preventing the decomposition of PVC. This mechanism is nucleophilic followed by an electrophilic process. The results from theoretical calculation match well with the test of the stabilizing effect on a PVC product containing these stabilizers. The structures of some organoantimony compounds are also reported.

M. Wyn Roberts - One of the best experts on this subject based on the ideXlab platform.

  • A Combined XPS/STM and TPD Study of the Chemisorption and Reactions of Methyl Mercaptan at a Cu(110) Surface
    Topics in Catalysis, 2003
    Co-Authors: Albert F. Carley, Philip R. Davies, Rhys V. Jones, K.r. Harikumar, M. Wyn Roberts, Christopher J. Welsby
    Abstract:

    Despite the structural similarities between methanol and methyl mercaptan (CH3SH), replacing the oxygen atom by sulfur has a profound effect on their chemistry at copper surfaces. In a combined STM, XPS and TPD study of the reaction of methyl mercaptan with clean and partially oxidised Cu(110) surfaces we have found that unlike methanol, the scission of the SH bond (both in the presence of and in the absence of oxygen) to give adsorbed Mercaptide (CH3S(a)) results in a restructuring of the surface. Low concentrations of adsorbed Mercaptide (< 1 × 1014 cm-2) result in a severe degradation of the STM image due to the high mobility of the surface adlayer. A stable surface can be regained by increasing the concentration of Mercaptide or the presence of another adsorbate such as oxygen. The reconstructed surface is characterised by very narrow terraces (typically 10-15A wide) orientated mainly in the 〈1¯10〉 direction with a “zig-zag” structure. Higher resolution images of the terraces reveal an atomic scale structure with a c(2 × 2) unit cell, each cell containing (in total) two bright features. The XPS data confirm that Mercaptide is present and show that the concentration at which islands of Mercaptide become visible in the STM images is approximately 3 × 1014 cm-2. At a surface concentration of 5.1 × 1014 cm-2 the c(2 × 2) structure is seen to be complete, consistent with the c(2 × 2) unit cell containing two Mercaptide species. On heating to 450K the Mercaptide dissociates to give chemisorbed sulfur adatoms and methane. The latter implies that the hydrogen formed when the methyl mercaptan dissociates remains chemisorbed at the surface until removed by reaction with the methyl groups. At pre-oxidised surfaces where chemisorbed hydrogen is removed as water, Mercaptide decomposition leads to ethane desorption with minor methane and ethane components, the latter indicating that methyl dehydrogenation is possible at the copper surface. STM shows that following the decomposition of the Mercaptide adlayer the copper surface regains its original structure of broad terraces (typically 100-200A wide), although a monolayer of chemisorbed sulfur is now present.

  • A Combined XPS/STM and TPD Study of the Chemisorption and Reactions of Methyl Mercaptan at a Cu(110) Surface
    Topics in Catalysis, 2003
    Co-Authors: Albert F. Carley, Philip R. Davies, Rhys V. Jones, K.r. Harikumar, M. Wyn Roberts, Christopher J. Welsby
    Abstract:

    Despite the structural similarities between methanol and methyl mercaptan (CH_3SH), replacing the oxygen atom by sulfur has a profound effect on their chemistry at copper surfaces. In a combined STM, XPS and TPD study of the reaction of methyl mercaptan with clean and partially oxidised Cu(110) surfaces we have found that unlike methanol, the scission of the SH bond (both in the presence of and in the absence of oxygen) to give adsorbed Mercaptide (CH_3S(a)) results in a restructuring of the surface. Low concentrations of adsorbed Mercaptide (< 1 × 10^14 cm^-2) result in a severe degradation of the STM image due to the high mobility of the surface adlayer. A stable surface can be regained by increasing the concentration of Mercaptide or the presence of another adsorbate such as oxygen. The reconstructed surface is characterised by very narrow terraces (typically 10-15Å wide) orientated mainly in the 〈1¯10〉 direction with a “zig-zag” structure. Higher resolution images of the terraces reveal an atomic scale structure with a c(2 × 2) unit cell, each cell containing (in total) two bright features. The XPS data confirm that Mercaptide is present and show that the concentration at which islands of Mercaptide become visible in the STM images is approximately 3 × 10^14 cm^-2. At a surface concentration of 5.1 × 10^14 cm^-2 the c(2 × 2) structure is seen to be complete, consistent with the c(2 × 2) unit cell containing two Mercaptide species. On heating to 450K the Mercaptide dissociates to give chemisorbed sulfur adatoms and methane. The latter implies that the hydrogen formed when the methyl mercaptan dissociates remains chemisorbed at the surface until removed by reaction with the methyl groups. At pre-oxidised surfaces where chemisorbed hydrogen is removed as water, Mercaptide decomposition leads to ethane desorption with minor methane and ethane components, the latter indicating that methyl dehydrogenation is possible at the copper surface. STM shows that following the decomposition of the Mercaptide adlayer the copper surface regains its original structure of broad terraces (typically 100-200Å wide), although a monolayer of chemisorbed sulfur is now present. Oxygen chemisorption is completely inhibited by Mercaptide concentrations of 5 × 10^14 cm^-2 but occurs at lower concentrations. The STM images show that the Mercaptide and oxygen adsorbates form separate islands, in contrast to the coadsorption of hydrogen sulfide and oxygen. The influence of oxygen on the thermal desorption of Mercaptide is discussed in the light of the structural data.

  • An STM and XPS study of the chemisorption of methyl mercaptan at a Cu(110) surface
    Surface Science, 2001
    Co-Authors: Albert F. Carley, Philip R. Davies, Rhys V. Jones, K.r. Harikumar, M. Wyn Roberts
    Abstract:

    XP spectra of a Cu(1 1 0) surface exposed to methyl mercaptan at 290 K show the presence of an adsorbate assigned to Mercaptide, CH3S(a). Scanning tunneling microscopic (STM) images show that the formation of the adsorbed Mercaptide (CH3S(a)) is accompanied by a restructuring of the surface. The reconstructed surface is characterized by very narrow terraces (typically 10–15 A wide) oriented mainly in the 〈110〉 direction with a `zig-zag' structure. Higher resolution images of the terraces reveal an atomic scale structure with a c(2×2) unit cell, each cell containing two bright features. The combination of STM and X-ray photoelectron spectroscopy (XPS) shows that the c(2×2) structure is complete at a surface concentration of ∼5 ×1014cm−2, consistent with the c(2×2) unit cell containing two equivalent Mercaptide species. On heating to 450 K the Mercaptide dissociates to give chemisorbed sulfur adatoms and the desorption of all of the surface carbon. The STM images show that following the decomposition of the Mercaptide adlayer the copper surface regains its original structure of broad terraces (typically 100–200 A wide), though an adlayer of chemisorbed sulfur atoms is now present.