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Surface reactivity enhancement on a Pd/Bi2Te3 heterostructure through robust topological surface states.

He QL, Lai YH, Lu Y, Law KT, Sou IK - Sci Rep (2013)

Bottom Line: We present a study of the surface reactivity of a Pd/Bi2Te3 thin film heterostructure.The topological surface states from Bi2Te3, being delocalized and robust owing to their topological natures, were found to act as an effective electron bath that significantly enhances the surface reactivity of palladium in the presence of two oxidizing agents, oxygen and tellurium respectively, which is consistent with a theoretical calculation.A partially inserted iron ferromagnetic layer at the interface of this heterostructure was found to play two competing roles arising from the higher-lying d-band center of the Pd/Fe bilayer and the interaction between the ferromagnetism and the surface spin texture of Bi2Te3 on the surface reactivity and their characteristics also demonstrate that the electron bath effect is long-lasting against accumulated thickness of adsorbates.

View Article: PubMed Central - PubMed

Affiliation: William Mong Institute of Nano Science and Technology, The Hong Kong University of Science and Technology, Hong Kong, SAR China.

ABSTRACT
We present a study of the surface reactivity of a Pd/Bi2Te3 thin film heterostructure. The topological surface states from Bi2Te3, being delocalized and robust owing to their topological natures, were found to act as an effective electron bath that significantly enhances the surface reactivity of palladium in the presence of two oxidizing agents, oxygen and tellurium respectively, which is consistent with a theoretical calculation. The surface reactivity of the adsorbed tellurium on this heterostructure is also intensified possibly benefitted from the effective transfer of the bath electrons. A partially inserted iron ferromagnetic layer at the interface of this heterostructure was found to play two competing roles arising from the higher-lying d-band center of the Pd/Fe bilayer and the interaction between the ferromagnetism and the surface spin texture of Bi2Te3 on the surface reactivity and their characteristics also demonstrate that the electron bath effect is long-lasting against accumulated thickness of adsorbates.

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Partial ToF-SIMS spectra of S#1 in negative polarity obtained from the regions W/O BT and W/BT after exposing the sample in dry air for 3 days.Only the data in the neighborhoods of Pd-, PdO− and PdO2− for each of the isotopic masses of Pd, covering 102, 104, 105, 106, 108 and 110 m/z, are displayed. The inset of (g) displays the structure of S#1. (a)–(f) and (g)–(I) show the data obtained from the region W/O BT, while (a')–(f') and (g')–(l') are those obtained from the region W/BT. The peaks marked with asterisks (*) reflect their mixed compositions with Pd-related hydrides and hydroxides. The intensities of the peaks of the spectra are on linear scale. All the Pd isotope peaks obtained from the region W/O BT and their corresponding peaks obtained from the region W/BT are normalized to the same intensity for clear comparisons.
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f1: Partial ToF-SIMS spectra of S#1 in negative polarity obtained from the regions W/O BT and W/BT after exposing the sample in dry air for 3 days.Only the data in the neighborhoods of Pd-, PdO− and PdO2− for each of the isotopic masses of Pd, covering 102, 104, 105, 106, 108 and 110 m/z, are displayed. The inset of (g) displays the structure of S#1. (a)–(f) and (g)–(I) show the data obtained from the region W/O BT, while (a')–(f') and (g')–(l') are those obtained from the region W/BT. The peaks marked with asterisks (*) reflect their mixed compositions with Pd-related hydrides and hydroxides. The intensities of the peaks of the spectra are on linear scale. All the Pd isotope peaks obtained from the region W/O BT and their corresponding peaks obtained from the region W/BT are normalized to the same intensity for clear comparisons.

Mentions: The oxidation of Pd thin films on different underlying materials was firstly studied using Sample #1 [S#1, inset of Fig. 1(g) shows its structure] in which a 78-nm-ZnSe buffer was firstly grown on a GaAs (111)B substrate followed by a deposition of 7-nm-Bi2Te3 on half of the ZnSe buffer and a 9-nm-Pd capping layer on the entire surface. S#1 was exposed to dry air for 3 days prior to the measurements of Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Fig. 1 displays the resulted ToF-SIMS spectra in the neighborhood of Pd−, PdO− and PdO2− spectra for each of the isotopic masses of Pd covering 102, 104, 105, 106, 108 and 110 m/z. Fig. 1(a)–(f) and (g)–(l) show the spectra obtained from the region without Bi2Te3 (W/O BT) while (a')–(f') and (g')–(l') are those from the region with Bi2Te3 (W/BT), respectively. The signals marked in black in Fig. 1 are contributed from organic ions. It is obvious that these organic signals resulted from the region W/BT are much higher than those from the region W/O BT. This indicates that the BT thin film plays a role in enhancing the adsorption of organics on the surface of Pd. However, since the spectra of organic ions are too complicated to be analyzed as they are resulted from numerous organic species existed in ambient air, they are excluded from further analysis. A detailed study was carried out on signals resulted from ions of elemental Pd and inorganic Pd compounds, which includes candidates of PdH−, PdH2−, PdO−, PdOH−, PdOH2−, PdO2−, PdO2H− and PdO2H2−. As can be seen in Fig. 1, signals resulted from ions of elemental Pd and inorganic Pd compounds can be well distinguished from neighboring signals contributed by organic ions, and they are highlighted with different colors. For Pd isotopes with mass of 104 and higher, their nominal Pd−, PdO− and PdO2− signals may have been superposed by hydrides and hydroxides of Pd. This is why the corresponding peaks shown in Fig. 1 are marked with asterisks (*) to reflect their mixed compositions. Fig. 1 clearly shows that the intensity ratios of PdO−*/Pd−* and PdO2−*/Pd−* in the region W/BT are consistently higher than those in the region W/O BT for each of the isotopic masses of Pd. Though these signals are superposed by hydrides and hydroxides of Pd, this observation also qualitatively implies that the underlying BT thin film enhances the oxidation of Pd through efficiently adsorbing oxygenic and hydric clusters. A stronger evidence of this enhancement comes from the signals of 102Pd−, 102PdO− and 102PdO2− as shown in Fig. 1(a), (a'), (g) and (g') since they do not suffer from isotopic superposition. These spectra clearly display that the intensity ratios of 102PdO−/102Pd− and 102PdO2−/102Pd− in the region W/BT are higher than those in the region W/O BT.


Surface reactivity enhancement on a Pd/Bi2Te3 heterostructure through robust topological surface states.

He QL, Lai YH, Lu Y, Law KT, Sou IK - Sci Rep (2013)

Partial ToF-SIMS spectra of S#1 in negative polarity obtained from the regions W/O BT and W/BT after exposing the sample in dry air for 3 days.Only the data in the neighborhoods of Pd-, PdO− and PdO2− for each of the isotopic masses of Pd, covering 102, 104, 105, 106, 108 and 110 m/z, are displayed. The inset of (g) displays the structure of S#1. (a)–(f) and (g)–(I) show the data obtained from the region W/O BT, while (a')–(f') and (g')–(l') are those obtained from the region W/BT. The peaks marked with asterisks (*) reflect their mixed compositions with Pd-related hydrides and hydroxides. The intensities of the peaks of the spectra are on linear scale. All the Pd isotope peaks obtained from the region W/O BT and their corresponding peaks obtained from the region W/BT are normalized to the same intensity for clear comparisons.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3750537&req=5

f1: Partial ToF-SIMS spectra of S#1 in negative polarity obtained from the regions W/O BT and W/BT after exposing the sample in dry air for 3 days.Only the data in the neighborhoods of Pd-, PdO− and PdO2− for each of the isotopic masses of Pd, covering 102, 104, 105, 106, 108 and 110 m/z, are displayed. The inset of (g) displays the structure of S#1. (a)–(f) and (g)–(I) show the data obtained from the region W/O BT, while (a')–(f') and (g')–(l') are those obtained from the region W/BT. The peaks marked with asterisks (*) reflect their mixed compositions with Pd-related hydrides and hydroxides. The intensities of the peaks of the spectra are on linear scale. All the Pd isotope peaks obtained from the region W/O BT and their corresponding peaks obtained from the region W/BT are normalized to the same intensity for clear comparisons.
Mentions: The oxidation of Pd thin films on different underlying materials was firstly studied using Sample #1 [S#1, inset of Fig. 1(g) shows its structure] in which a 78-nm-ZnSe buffer was firstly grown on a GaAs (111)B substrate followed by a deposition of 7-nm-Bi2Te3 on half of the ZnSe buffer and a 9-nm-Pd capping layer on the entire surface. S#1 was exposed to dry air for 3 days prior to the measurements of Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Fig. 1 displays the resulted ToF-SIMS spectra in the neighborhood of Pd−, PdO− and PdO2− spectra for each of the isotopic masses of Pd covering 102, 104, 105, 106, 108 and 110 m/z. Fig. 1(a)–(f) and (g)–(l) show the spectra obtained from the region without Bi2Te3 (W/O BT) while (a')–(f') and (g')–(l') are those from the region with Bi2Te3 (W/BT), respectively. The signals marked in black in Fig. 1 are contributed from organic ions. It is obvious that these organic signals resulted from the region W/BT are much higher than those from the region W/O BT. This indicates that the BT thin film plays a role in enhancing the adsorption of organics on the surface of Pd. However, since the spectra of organic ions are too complicated to be analyzed as they are resulted from numerous organic species existed in ambient air, they are excluded from further analysis. A detailed study was carried out on signals resulted from ions of elemental Pd and inorganic Pd compounds, which includes candidates of PdH−, PdH2−, PdO−, PdOH−, PdOH2−, PdO2−, PdO2H− and PdO2H2−. As can be seen in Fig. 1, signals resulted from ions of elemental Pd and inorganic Pd compounds can be well distinguished from neighboring signals contributed by organic ions, and they are highlighted with different colors. For Pd isotopes with mass of 104 and higher, their nominal Pd−, PdO− and PdO2− signals may have been superposed by hydrides and hydroxides of Pd. This is why the corresponding peaks shown in Fig. 1 are marked with asterisks (*) to reflect their mixed compositions. Fig. 1 clearly shows that the intensity ratios of PdO−*/Pd−* and PdO2−*/Pd−* in the region W/BT are consistently higher than those in the region W/O BT for each of the isotopic masses of Pd. Though these signals are superposed by hydrides and hydroxides of Pd, this observation also qualitatively implies that the underlying BT thin film enhances the oxidation of Pd through efficiently adsorbing oxygenic and hydric clusters. A stronger evidence of this enhancement comes from the signals of 102Pd−, 102PdO− and 102PdO2− as shown in Fig. 1(a), (a'), (g) and (g') since they do not suffer from isotopic superposition. These spectra clearly display that the intensity ratios of 102PdO−/102Pd− and 102PdO2−/102Pd− in the region W/BT are higher than those in the region W/O BT.

Bottom Line: We present a study of the surface reactivity of a Pd/Bi2Te3 thin film heterostructure.The topological surface states from Bi2Te3, being delocalized and robust owing to their topological natures, were found to act as an effective electron bath that significantly enhances the surface reactivity of palladium in the presence of two oxidizing agents, oxygen and tellurium respectively, which is consistent with a theoretical calculation.A partially inserted iron ferromagnetic layer at the interface of this heterostructure was found to play two competing roles arising from the higher-lying d-band center of the Pd/Fe bilayer and the interaction between the ferromagnetism and the surface spin texture of Bi2Te3 on the surface reactivity and their characteristics also demonstrate that the electron bath effect is long-lasting against accumulated thickness of adsorbates.

View Article: PubMed Central - PubMed

Affiliation: William Mong Institute of Nano Science and Technology, The Hong Kong University of Science and Technology, Hong Kong, SAR China.

ABSTRACT
We present a study of the surface reactivity of a Pd/Bi2Te3 thin film heterostructure. The topological surface states from Bi2Te3, being delocalized and robust owing to their topological natures, were found to act as an effective electron bath that significantly enhances the surface reactivity of palladium in the presence of two oxidizing agents, oxygen and tellurium respectively, which is consistent with a theoretical calculation. The surface reactivity of the adsorbed tellurium on this heterostructure is also intensified possibly benefitted from the effective transfer of the bath electrons. A partially inserted iron ferromagnetic layer at the interface of this heterostructure was found to play two competing roles arising from the higher-lying d-band center of the Pd/Fe bilayer and the interaction between the ferromagnetism and the surface spin texture of Bi2Te3 on the surface reactivity and their characteristics also demonstrate that the electron bath effect is long-lasting against accumulated thickness of adsorbates.

Show MeSH