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Stabilization of 4H hexagonal phase in gold nanoribbons.

Fan Z, Bosman M, Huang X, Huang D, Yu Y, Ong KP, Akimov YA, Wu L, Li B, Wu J, Huang Y, Liu Q, Png CE, Gan CL, Yang P, Zhang H - Nat Commun (2015)

Bottom Line: These gold nanoribbons undergo a phase transition from the original 4H hexagonal to face-centred cubic structure on ligand exchange under ambient conditions.Furthermore, the 4H hexagonal phases of silver, palladium and platinum can be readily stabilized through direct epitaxial growth of these metals on the 4H gold nanoribbon surface.Our findings may open up new strategies for the crystal phase-controlled synthesis of advanced noble metal nanomaterials.

View Article: PubMed Central - PubMed

Affiliation: School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.

ABSTRACT
Gold, silver, platinum and palladium typically crystallize with the face-centred cubic structure. Here we report the high-yield solution synthesis of gold nanoribbons in the 4H hexagonal polytype, a previously unreported metastable phase of gold. These gold nanoribbons undergo a phase transition from the original 4H hexagonal to face-centred cubic structure on ligand exchange under ambient conditions. Using monochromated electron energy-loss spectroscopy, the strong infrared plasmon absorption of single 4H gold nanoribbons is observed. Furthermore, the 4H hexagonal phases of silver, palladium and platinum can be readily stabilized through direct epitaxial growth of these metals on the 4H gold nanoribbon surface. Our findings may open up new strategies for the crystal phase-controlled synthesis of advanced noble metal nanomaterials.

No MeSH data available.


Related in: MedlinePlus

The ligand exchange-induced phase transformation of Au NRBs.(a) A typical TEM image of an Au NRB after the ligand exchange (scale bar, 50 nm). (b) The corresponding SAED pattern of the region inside the dashed rectangle in a, showing the fcc structure oriented along the [001]f zone axis. (c) SAED pattern of the [013]f zone axis was taken by tilting the Au NRB around the [200]f zone axis by 18.2° with respect to the [001]f zone axis. (d–f) HRTEM images taken from the centre, edge and end of the marked region in a, respectively (scale bars, 2 nm). (g) Schematic illustration of the ligand-induced phase change of Au NRB.
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f2: The ligand exchange-induced phase transformation of Au NRBs.(a) A typical TEM image of an Au NRB after the ligand exchange (scale bar, 50 nm). (b) The corresponding SAED pattern of the region inside the dashed rectangle in a, showing the fcc structure oriented along the [001]f zone axis. (c) SAED pattern of the [013]f zone axis was taken by tilting the Au NRB around the [200]f zone axis by 18.2° with respect to the [001]f zone axis. (d–f) HRTEM images taken from the centre, edge and end of the marked region in a, respectively (scale bars, 2 nm). (g) Schematic illustration of the ligand-induced phase change of Au NRB.

Mentions: The 4H structure of Au NRBs is metastable, and can be transformed to the fcc structure on the exchange of surface-capped amine molecules with thiol molecules under ambient conditions (Fig. 2). Typically, the ligand exchange was conducted by vortex-mixing the Au NRB solution and a fresh 1-dodecanethiol solution for 5 min. The thiol-treated Au NRBs were analysed using STEM-EDS, which indicated the presence of sulfur in the obtained product and thus confirmed the occurrence of the ligand exchange (Supplementary Fig. 11). The structure of thiol-treated Au NRBs is found to be fcc, which is proven by the SAED pattern taken on the highlighted area in Fig. 2a, showing the square lattice pattern along the [001]f zone axis (Fig. 2b). The (001)f-oriented fcc structure is further verified using the SAED pattern taken along the [013]f zone axis, obtained by tilting the Au NRB around the [200]f axis by 18.2°, which matches well with the theoretical angle of 18.4° between [001]f and [013]f zone axes (Fig. 2c). HRTEM images further reveal the (001)f-oriented fcc structure with lattice spacing of 2.0 Å for {200} planes (Fig. 2d–f). Figure 2g and Supplementary Fig. 12 schematically demonstrate the thiol-induced phase transformation of Au NRB from the original (110)4H-oriented 4H to the (001)f-oriented fcc structure. Different from the commonly observed hcp-to-fcc phase transformation in metals that proceeds by motion of partial dislocations on the close-packed planes and results in the formation of stacking faults/twins38, the phase transition of Au NRBs might arise from the flattening of the planes (indicated by the rectangle in the left image of Fig. 2g), which is similar to the wurtzite-to-rock salt transition occurring in some semiconductor nanocrystals under high pressure, such as GaN and CdSe (refs 4, 39). Previous studies suggested that thiols and other sulfur-containing molecules can induce surface reconstruction of metals, especially favouring the generation of overlayers with high coordination numbers, such as fcc(100) that contains a square hollow site40. In addition, spherical Pt NPs were observed to transform to Pt nanocubes enclosed by {100}f facets in the presence of H2S at 500 °C (ref. 41). Therefore, the ligand-induced phase change of Au NRBs under ambient conditions is likely driven by the particularly strong and unique interaction between Au and S (refs 40, 42).


Stabilization of 4H hexagonal phase in gold nanoribbons.

Fan Z, Bosman M, Huang X, Huang D, Yu Y, Ong KP, Akimov YA, Wu L, Li B, Wu J, Huang Y, Liu Q, Png CE, Gan CL, Yang P, Zhang H - Nat Commun (2015)

The ligand exchange-induced phase transformation of Au NRBs.(a) A typical TEM image of an Au NRB after the ligand exchange (scale bar, 50 nm). (b) The corresponding SAED pattern of the region inside the dashed rectangle in a, showing the fcc structure oriented along the [001]f zone axis. (c) SAED pattern of the [013]f zone axis was taken by tilting the Au NRB around the [200]f zone axis by 18.2° with respect to the [001]f zone axis. (d–f) HRTEM images taken from the centre, edge and end of the marked region in a, respectively (scale bars, 2 nm). (g) Schematic illustration of the ligand-induced phase change of Au NRB.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4525209&req=5

f2: The ligand exchange-induced phase transformation of Au NRBs.(a) A typical TEM image of an Au NRB after the ligand exchange (scale bar, 50 nm). (b) The corresponding SAED pattern of the region inside the dashed rectangle in a, showing the fcc structure oriented along the [001]f zone axis. (c) SAED pattern of the [013]f zone axis was taken by tilting the Au NRB around the [200]f zone axis by 18.2° with respect to the [001]f zone axis. (d–f) HRTEM images taken from the centre, edge and end of the marked region in a, respectively (scale bars, 2 nm). (g) Schematic illustration of the ligand-induced phase change of Au NRB.
Mentions: The 4H structure of Au NRBs is metastable, and can be transformed to the fcc structure on the exchange of surface-capped amine molecules with thiol molecules under ambient conditions (Fig. 2). Typically, the ligand exchange was conducted by vortex-mixing the Au NRB solution and a fresh 1-dodecanethiol solution for 5 min. The thiol-treated Au NRBs were analysed using STEM-EDS, which indicated the presence of sulfur in the obtained product and thus confirmed the occurrence of the ligand exchange (Supplementary Fig. 11). The structure of thiol-treated Au NRBs is found to be fcc, which is proven by the SAED pattern taken on the highlighted area in Fig. 2a, showing the square lattice pattern along the [001]f zone axis (Fig. 2b). The (001)f-oriented fcc structure is further verified using the SAED pattern taken along the [013]f zone axis, obtained by tilting the Au NRB around the [200]f axis by 18.2°, which matches well with the theoretical angle of 18.4° between [001]f and [013]f zone axes (Fig. 2c). HRTEM images further reveal the (001)f-oriented fcc structure with lattice spacing of 2.0 Å for {200} planes (Fig. 2d–f). Figure 2g and Supplementary Fig. 12 schematically demonstrate the thiol-induced phase transformation of Au NRB from the original (110)4H-oriented 4H to the (001)f-oriented fcc structure. Different from the commonly observed hcp-to-fcc phase transformation in metals that proceeds by motion of partial dislocations on the close-packed planes and results in the formation of stacking faults/twins38, the phase transition of Au NRBs might arise from the flattening of the planes (indicated by the rectangle in the left image of Fig. 2g), which is similar to the wurtzite-to-rock salt transition occurring in some semiconductor nanocrystals under high pressure, such as GaN and CdSe (refs 4, 39). Previous studies suggested that thiols and other sulfur-containing molecules can induce surface reconstruction of metals, especially favouring the generation of overlayers with high coordination numbers, such as fcc(100) that contains a square hollow site40. In addition, spherical Pt NPs were observed to transform to Pt nanocubes enclosed by {100}f facets in the presence of H2S at 500 °C (ref. 41). Therefore, the ligand-induced phase change of Au NRBs under ambient conditions is likely driven by the particularly strong and unique interaction between Au and S (refs 40, 42).

Bottom Line: These gold nanoribbons undergo a phase transition from the original 4H hexagonal to face-centred cubic structure on ligand exchange under ambient conditions.Furthermore, the 4H hexagonal phases of silver, palladium and platinum can be readily stabilized through direct epitaxial growth of these metals on the 4H gold nanoribbon surface.Our findings may open up new strategies for the crystal phase-controlled synthesis of advanced noble metal nanomaterials.

View Article: PubMed Central - PubMed

Affiliation: School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.

ABSTRACT
Gold, silver, platinum and palladium typically crystallize with the face-centred cubic structure. Here we report the high-yield solution synthesis of gold nanoribbons in the 4H hexagonal polytype, a previously unreported metastable phase of gold. These gold nanoribbons undergo a phase transition from the original 4H hexagonal to face-centred cubic structure on ligand exchange under ambient conditions. Using monochromated electron energy-loss spectroscopy, the strong infrared plasmon absorption of single 4H gold nanoribbons is observed. Furthermore, the 4H hexagonal phases of silver, palladium and platinum can be readily stabilized through direct epitaxial growth of these metals on the 4H gold nanoribbon surface. Our findings may open up new strategies for the crystal phase-controlled synthesis of advanced noble metal nanomaterials.

No MeSH data available.


Related in: MedlinePlus