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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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XPS core-level spectra of S#4.(a) Fe 2p peaks. Spectra (4a-1) and (4a-2) are the Fe 2p core-levels spectra obtained from the region W/O Fe and W/Fe of S#4A, while Spectra (4a-3) and (4a-4) are the corresponding spectra obtained from S#4B, respectively. The inset displays the structure of S#4. (b) Te 3d peaks. Spectra (4b-1) and (4b-2) are Te 3d core-levels spectra obtained from the region W/Fe and W/O Fe of S#4A, while Spectra (4b-3) and (4b-4) are the corresponding spectra obtained from S#4B, respectively. (c) Pd 3d peaks. Spectra (4c-1) and (4c-2) are the Pd 3d core-levels spectra obtained from the region W/Fe and W/O Fe from S#4A. (d) Pd 3p and O 1s peaks. Spectra (4d-1) and (4d-2) are the spectra in a spectral region involving the Pd 3p and O 1s core-levels obtained from the region W/Fe and W/O Fe of S#4A, while Spectra (4d-3) and (4d-4) are the corresponding spectra obtained from S#4B, respectively. (e) Fitting results of Te 3d5/2 peaks in Spectra (4b-3) and (4b-4).
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f4: XPS core-level spectra of S#4.(a) Fe 2p peaks. Spectra (4a-1) and (4a-2) are the Fe 2p core-levels spectra obtained from the region W/O Fe and W/Fe of S#4A, while Spectra (4a-3) and (4a-4) are the corresponding spectra obtained from S#4B, respectively. The inset displays the structure of S#4. (b) Te 3d peaks. Spectra (4b-1) and (4b-2) are Te 3d core-levels spectra obtained from the region W/Fe and W/O Fe of S#4A, while Spectra (4b-3) and (4b-4) are the corresponding spectra obtained from S#4B, respectively. (c) Pd 3d peaks. Spectra (4c-1) and (4c-2) are the Pd 3d core-levels spectra obtained from the region W/Fe and W/O Fe from S#4A. (d) Pd 3p and O 1s peaks. Spectra (4d-1) and (4d-2) are the spectra in a spectral region involving the Pd 3p and O 1s core-levels obtained from the region W/Fe and W/O Fe of S#4A, while Spectra (4d-3) and (4d-4) are the corresponding spectra obtained from S#4B, respectively. (e) Fitting results of Te 3d5/2 peaks in Spectra (4b-3) and (4b-4).

Mentions: As predicted by theories1617 and proved by recent experiments181920, a deposition of ferromagnetic impurities on a TI surface will lead to an interaction between the ferromagnetism and the surface spin texture of TI, which breaks the TRS and opens up a surface band gap in the energy spectrum of TSSs. Consequently, this will lead to a transition of the Dirac electrons of TSSs from being massless and delocalized to massive and localized. Thus, by inserting an Fe thin layer at the interface between Pd and BT of a Te/Pd/BT structure, one can study the expected weakening of the enhancement in the surface reactivity of Pd and Te so as to further confirm the role of BT in providing the electron bath. Sample #4 [S#4, inset of Fig. 4(a) shows its structure] was fabricated with a 78-nm-ZnSe buffer layer and a 7-nm BT thin film on the entire surface followed by depositing 2-monolayers of Fe on half of the BT surface, and then covered the entire sample surface with a 9-nm-Pd layer then a 1.3-nm-Te layer. An as-prepared piece of this sample (S#4A) was quickly transferred to the XPS system and another piece was kept in dry air for 7 days (S#4B) prior to performing the XPS measurement. The resulted spectra in the spectral region of the Fe 2p core-levels are shown in Fig. 4(a), in which Spectra (4a-1) and (4a-2) are obtained from the region without Fe (W/O Fe) and with Fe (W/Fe) of S#4A, while the corresponding spectra of S#4B are shown as Spectra (4a-3) and (4a-4). As expected, no detectable Fe signal was resulted in Spectra (4a-1) and (4a-3), while Spectra (4a-2) and (4a-4) display the signature of the expected Fe 2p core-levels spectra. It is worth to note that Spectra (4a-2) and (4a-4) are basically identical, indicating the inserted Fe layer is quite stable.


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)

XPS core-level spectra of S#4.(a) Fe 2p peaks. Spectra (4a-1) and (4a-2) are the Fe 2p core-levels spectra obtained from the region W/O Fe and W/Fe of S#4A, while Spectra (4a-3) and (4a-4) are the corresponding spectra obtained from S#4B, respectively. The inset displays the structure of S#4. (b) Te 3d peaks. Spectra (4b-1) and (4b-2) are Te 3d core-levels spectra obtained from the region W/Fe and W/O Fe of S#4A, while Spectra (4b-3) and (4b-4) are the corresponding spectra obtained from S#4B, respectively. (c) Pd 3d peaks. Spectra (4c-1) and (4c-2) are the Pd 3d core-levels spectra obtained from the region W/Fe and W/O Fe from S#4A. (d) Pd 3p and O 1s peaks. Spectra (4d-1) and (4d-2) are the spectra in a spectral region involving the Pd 3p and O 1s core-levels obtained from the region W/Fe and W/O Fe of S#4A, while Spectra (4d-3) and (4d-4) are the corresponding spectra obtained from S#4B, respectively. (e) Fitting results of Te 3d5/2 peaks in Spectra (4b-3) and (4b-4).
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f4: XPS core-level spectra of S#4.(a) Fe 2p peaks. Spectra (4a-1) and (4a-2) are the Fe 2p core-levels spectra obtained from the region W/O Fe and W/Fe of S#4A, while Spectra (4a-3) and (4a-4) are the corresponding spectra obtained from S#4B, respectively. The inset displays the structure of S#4. (b) Te 3d peaks. Spectra (4b-1) and (4b-2) are Te 3d core-levels spectra obtained from the region W/Fe and W/O Fe of S#4A, while Spectra (4b-3) and (4b-4) are the corresponding spectra obtained from S#4B, respectively. (c) Pd 3d peaks. Spectra (4c-1) and (4c-2) are the Pd 3d core-levels spectra obtained from the region W/Fe and W/O Fe from S#4A. (d) Pd 3p and O 1s peaks. Spectra (4d-1) and (4d-2) are the spectra in a spectral region involving the Pd 3p and O 1s core-levels obtained from the region W/Fe and W/O Fe of S#4A, while Spectra (4d-3) and (4d-4) are the corresponding spectra obtained from S#4B, respectively. (e) Fitting results of Te 3d5/2 peaks in Spectra (4b-3) and (4b-4).
Mentions: As predicted by theories1617 and proved by recent experiments181920, a deposition of ferromagnetic impurities on a TI surface will lead to an interaction between the ferromagnetism and the surface spin texture of TI, which breaks the TRS and opens up a surface band gap in the energy spectrum of TSSs. Consequently, this will lead to a transition of the Dirac electrons of TSSs from being massless and delocalized to massive and localized. Thus, by inserting an Fe thin layer at the interface between Pd and BT of a Te/Pd/BT structure, one can study the expected weakening of the enhancement in the surface reactivity of Pd and Te so as to further confirm the role of BT in providing the electron bath. Sample #4 [S#4, inset of Fig. 4(a) shows its structure] was fabricated with a 78-nm-ZnSe buffer layer and a 7-nm BT thin film on the entire surface followed by depositing 2-monolayers of Fe on half of the BT surface, and then covered the entire sample surface with a 9-nm-Pd layer then a 1.3-nm-Te layer. An as-prepared piece of this sample (S#4A) was quickly transferred to the XPS system and another piece was kept in dry air for 7 days (S#4B) prior to performing the XPS measurement. The resulted spectra in the spectral region of the Fe 2p core-levels are shown in Fig. 4(a), in which Spectra (4a-1) and (4a-2) are obtained from the region without Fe (W/O Fe) and with Fe (W/Fe) of S#4A, while the corresponding spectra of S#4B are shown as Spectra (4a-3) and (4a-4). As expected, no detectable Fe signal was resulted in Spectra (4a-1) and (4a-3), while Spectra (4a-2) and (4a-4) display the signature of the expected Fe 2p core-levels spectra. It is worth to note that Spectra (4a-2) and (4a-4) are basically identical, indicating the inserted Fe layer is quite stable.

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