- Email: [email protected]
X-ray nanotomography characterizations of gold foams
Accepted Manuscript X-ray nanotomography characterizations of gold foams Zhaoguo Li, Jiangshan Luo, Xiulan Tan, Qi Fang, Yong Zeng, Minjie Zhou, Weidong Wu, Jicheng Zhang PII: DOI: Reference:
S0167-577X(17)30948-5 http://dx.doi.org/10.1016/j.matlet.2017.06.056 MLBLUE 22768
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
22 March 2017 8 May 2017 10 June 2017
Please cite this article as: Z. Li, J. Luo, X. Tan, Q. Fang, Y. Zeng, M. Zhou, W. Wu, J. Zhang, X-ray nanotomography characterizations of gold foams, Materials Letters (2017), doi: http://dx.doi.org/10.1016/j.matlet.2017.06.056
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
X-ray nanotomography characterizations of gold foams Zhaoguo Li, Jiangshan Luo, Xiulan Tan, Qi Fang, Yong Zeng, Minjie Zhou, Weidong Wu, and Jicheng Zhang* Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China *E-mail: [email protected] Abstract: Observation of the three-dimensional interior microstructure of low-density gold foams is very important for the optimization of their physical and chemical properties. We report on the three-dimensional internal microstructural imaging of gold foams by using X-ray computed tomography with a resolution of 50 nm. The gold foams are synthesized by the chemical dealloying method. By using focused ion beam milling technology, a foam micro-cylinder with a diameter of approximately 55 µm is prepared. The tomographical data sets of the micro-cylinder foam are collected in the angle range of ±90° at a photon energy of 8 keV. The data sets are then used to reconstruct the three-dimensional microstructure of the gold foams. The three-dimensional reconstruction information obtained from computed tomography provides an intuitive understanding of the gold foam structure. Keywords: X-ray nanotomography; gold foams; microstructures; structure characterization.
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1. Introduction Gold foam is a typical low-density metallic material, which presents excellent performance in the fields of catalysts, sensors, actuators, supercapacitors, plasmonics and ion exchange.1-3 Optimization of the electrical, thermal, mechanical and optical properties of gold foams depends on the internal microstructures, which can be tuned in the preparation process. However, the three-dimensional (3D) interior microstructure characterization of nanoporous materials remains a challenge. A focused ion beam (FIB)–scanning electron microscopy (SEM) system can be used to observe the 3D tomographic structures by the time-consuming series sectioning of samples, but this is a destructive method.4 Transmission electron tomography is a high-resolution (~13 nm3), non-destructive method, which can be used to characterize the 3D internal structures of specimens.5, 6 Unfortunately, this method is not suitable for characterizing large-scale samples owing to the limited electron penetration depth. X-ray computed tomography (XCT) is an invaluable non-destructive tomographic method for examining the 3D interior structure of thick opaque materials.7 Benefitting from the developments of Fresnel zone plates and X-ray sources, XCT has been used for two-dimensional (2D) microstructures with a resolution of better than 15 nm for soft X-rays in the photon energy range of 0.25– 1.8 keV.8 For harder X-rays, a lateral resolution below 40 nm has been reported in the photon energy range of 7–18 keV.9 The high spatial resolution XCTis widely used in the area of porous foams,10 granular structures,11 ion batteries,12 and biological13 and geological materials.14 Specifically, XCT is a powerful tool for imaging the 3D 2/9
interior microstructure of microsized and nanosized complicated materials.15-17 Observation of the 3D interior structure of artificial microstructures provides a platform for nanoscale XCT applications. In this work, we report on the 3D interior structure characterization of gold foams by using high-resolution XCT. 2. Methods The ultra-low density gold foams are prepared by a template-dealloying method.4 First, Au and Ag nanoparticles are sequentially coated onto polystyrene (PS) microspheres. Next, the cylindrical PS/(Au-Ag) monolith is formed by filter-casting of the nanoparticle coated PS suspension. Then, the self-supported Au-Ag foams are produced by removing PS template. Finally, the Ag component is selectively dealloyed in HNO3 solution by gradually increase the concentration from 3.5 mol/L to 8.0 mol/L and eventually 12.9 mol/L, the dealloying time is 24 h for every HNO3 concentration. After several times washing, the self-supported gold foams with bimodal porous structure are obtained. Figure 1(a) and 1(b) show the SEM images of the synthesized gold foams. The diameter of the microspherical shells is approximately 10 µm. The X-ray diffraction pattern of gold foams as shown in inset of Fig. 1(a) demonstrates that the main component in foams is Au. The chemically synthesized gold foams are macroscopical cylindrical monoliths with diameters of ~4 mm. However, the large size of the foam monoliths is far greater than the field-of-view (FOV) region (~60 3µm3) of the XCT machine. To prepare a suitable sample for XCT characterization, FIB milling technology has been used to process a microsized foam cylinder, as shown in Fig. 1(c),where the diameter of the 3/9
micro-cylinder is approximately 55 µm. The foam micro-cylinder is protrudent on the surface of the macroscopical foam monolith. The gold foam micro-cylinder was characterized by an Xradia nanoscale XCT system. Fig. 2(a) shows the measurement configuration. A laboratory X-ray source (rotating copper anode) was used to emit X-rays, and an energy filter was used to provide monochromatic X-rays with a photon energy of 8 keV. The capillary condenser lens focused the X-rays onto the sample, which was placed on a rotation stage. The X-rays transmitted through the sample were magnified by a Fresnel zone plate, and finally were recorded on a 1024×1024 charge coupled device (CCD) camera. For the large FOV measurement mode (which corresponded to a resolution of 150 nm), the pixel size of the sample at the camera screen was approximately 64 nm with a total FOV of 65.6 2 µm2. A total of 901 radiographs were automatically collected from −90° to 90° in 0.2° intervals with an exposure time of 60 s per image. Fig. 2(b) and 2(c) display two typical projection images at two rotation angles that were perpendicular to each other. The projections of hollow spherical shells can be clearly seen. These projection images were reconstructed by a standard filtered back-projection algorithm.18 3. Results Figure 3 shows the reconstructed results of the gold foams in a spatial volume of 603µm3. Fig. 3(a) displays the reconstructed slices along the axial direction of the micro-cylinder. The sharp white rings indicate the cross-sections of the gold microspherical shells. We determined that the shells’ thickness and diameter were 4/9
approximately 800 nm and 10 µm, respectively. These values were close to the values obtained from SEM (Fig. 1(d)). Moreover, we can see that some shells were fused with each other to form dumbbell-shaped shells (indicated by red arrows in Fig. 3(a)). Fig. 3(b) presents the 3D rendering of the gold foam micro-cylinder. The stack structure of the microspherical shells could be identified. The internal structure is also shown in Fig. 3(c) in an angle-cut manner. The hollow shells of the microspheres can be clearly seen. Figure 4 shows the reconstructed results of a single microspherical shell located on the top of the micro-cylinder. When we used the high-resolution measurement mode (correspondingto a resolution of 50 nm), a pixel resolution of 16 nm in the CCD screen with a total FOV of 16.3 2 µm2 was achieved. The reconstructed slices, as shown in Fig. 4(a), revealed that the thickness of the shell was around 300 nm and the diameter of the microsphere was approximately 10 µm. These values were consistent with the values obtained from SEM (Fig. 1(b)). Fig. 4(b) and 4(c) show the 3D rendered images of the gold microspherical shell from different viewing angles. The fine 3D microstructure of the microspherical shell is observed. 4. Conclusions In conclusion, a gold foam micro-cylinder with a diameter of ~55 µm has been characterized by X-ray computed nanotomography with 50-nm spatial resolution. The three-dimensional structure of the gold foam is reconstructed. The three-dimensional images of the gold foams reconstructed by computed tomography provide an intuitive understanding of the foam material structures. 5/9
Acknowledgements This work is financially supported by the National Natural Science Foundation of China (Grant Nos. 11604310, 11404304, 60908023), the National Key Scientific Instrument and Equipment Development Project of China (Grant No. 2014YQ090709) and the Key Laboratory of Ultra-Precision Machining Technology Foundation of CAEP (Grant No. ZZ15003). References 1.
J. Biener, G. W. Nyce, A. M. Hodge, M. M. Biener, A. V. Hamza and S. A. Maier, Adv. Mater. 20, 1211 (2008).
2.
Y. Ding and M. Chen, MRS Bull. 34, 569 (2009).
3.
B. C. Tappan, S. A. Steiner-III and E. P. Luther, Angew. Chem. Int. Ed. 49 (27), 4544 (2010).
4.
K. Zhang, X. Tan, J. Zhang, W. Wu and Y. Tang, RSC Adv. 4 (14), 7196 (2014).
5.
P. A. Midgley and R. E. Dunin-Borkowski, Nat. Mater. 8, 271 (2009).
6.
T. Fujita, L.-H. Qian, K. Inoke, J. Erlebacher and M.-W. Chen, Appl. Phys. Lett. 92, 251902 (2008).
7.
P. J. Withers, Mater. Tod. 10, 26 (2007).
8.
W. Chao, B. D. Harteneck, J. A. Liddle, E. H. Anderson and D. T. Attwood, Nature 435, 1210 (2005).
9.
Y. S. Chu, J. M. Yi, F. D. Carlo, Q. Shen, W.-K. Lee, H. J. Wu, C. L. Wang, J. Y. Wang, C. J. Liu, C. H. Wang, S. R. Wu, C. C. Chien, Y. Hwu, A. Tkachuk, W. Yun, M. Feser, K. S. Liang, C. S. Yang, J. H. Je and G. Margaritondo, Appl. Phys. Lett. 92, 103119 (2008).
10.
Y.-c. K. Chen, Y. S. Chu, J. Yi, I. McNulty, Q. Shen, P. W. Voorhees and D. C. Dunand, Appl. Phys. Lett. 96, 043122 (2010).
11.
K. M. Kareh, P. D. Lee, R. C. Atwood, T. Connolley and C. M. Gourlay, Nat. Commun. 5,
12.
J. Wang, C. Eng, Y.-c. K. Chen-Wiegart and J. Wang, Nat. Commun. 6, 7496 (2015).
13.
P. A. Midgley, E. P. W. Ward, A. B. Hungria and J. M. Thomas, Chem. Soc. Rev. 36, 1477
14.
T. Saif, Q. Lin, K. Singh, B. Bijeljic and M. J. Blunt, Geophys. Res. Lett. 43, 6799 (2016).
15.
J. Chen, C. Wu, J. Tian, W. Li, S. Yu and Y. Tian, Appl. Phys. Lett. 92, 233104 (2008).
16.
W. Li, N. Wang, J. Chen, G. Liu, Z. Pan, Y. Guan, Y. Yang, W. Wu, J. Tian, S. Wei, Z. Wu, Y.
4464 (2014).
(2007).
Tian and L. Guo, Appl. Phys. Lett. 95, 053108 (2009). 17.
C. Donnelly, M. Guizar-Sicairos, V. Scagnoli, M. Holler, T. Huthwelker, A. Menzel, I. Vartiainen, E. Muller, E. Kirk, S. Gliga, J. Raabe and L. J. Heyderman, Phys. Rev. Lett. 114, 115501 (2015).
18.
M. Soleimani and T. Pengpen, Phil. Trans. R. Soc. A 373, 20140399 (2015).
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Figure captions: Figure 1. SEM characterization of the gold foam. (a) and (b) show the SEM images of the as-prepared gold foam monoliths with different magnification. The inset in (a) shows the X-ray diffraction pattern of gold foams. The dominant diffraction peaks are labelled, which belong to the gold crystals. (c) The SEM image of the foam micro-cylinder with a diameter of ~55 µm. (d) The SEM image of gold microspherical shells near the bottom of the micro-cylinder. Figure 2. XCT characterization of the gold foam micro-cylinder. (a) A schematic diagram of the XCT measurement geometry. (b) and (c) present two typical projection images at different angles that are perpendicular to each other. Figure 3. The 3D reconstructed results of the gold foam micro-cylinder. (a) The reconstructed slices of the foam micro-cylinder, the positions of the slices are indicated in (b) as white lines. The red arrows indicate the dumbbell-shaped shells that are formed by fusing two microspherical shells. (b) The 3D rendering of the foam micro-cylinder. (c) The angle-cut cross-section view of the micro-cylinder rendering. The scale bars in (b) and (c) are 10 µm. Figure 4. The 3D reconstructed results of a single gold microspherical shell. (a) The reconstructed slices of a single gold microspherical shell, the positions of slices are indicated in (b) as white lines. (b) and (c) show the 3D rendering pictures of the gold microspherical shell from the different viewing angles. The scale bars in (b) and (c) are 3 µm.
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Figure 1.
Figure 2.
Figure 3.
Figure 4.
8/9
Highlights:
a) The ultra-low density gold foams are prepared by a template-dealloying method. b) A foam micro-cylinder with a diameter of ~55 μm is prepared by FIB milling technology. c) The 3D interior microstructure of gold foams is reconstructured by x-ray nanotomography. d) The reconstructured results provide an intuitive understanding of the gold foams.
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S0167-577X(17)30948-5 http://dx.doi.org/10.1016/j.matlet.2017.06.056 MLBLUE 22768
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
22 March 2017 8 May 2017 10 June 2017
Please cite this article as: Z. Li, J. Luo, X. Tan, Q. Fang, Y. Zeng, M. Zhou, W. Wu, J. Zhang, X-ray nanotomography characterizations of gold foams, Materials Letters (2017), doi: http://dx.doi.org/10.1016/j.matlet.2017.06.056
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
X-ray nanotomography characterizations of gold foams Zhaoguo Li, Jiangshan Luo, Xiulan Tan, Qi Fang, Yong Zeng, Minjie Zhou, Weidong Wu, and Jicheng Zhang* Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China *E-mail: [email protected] Abstract: Observation of the three-dimensional interior microstructure of low-density gold foams is very important for the optimization of their physical and chemical properties. We report on the three-dimensional internal microstructural imaging of gold foams by using X-ray computed tomography with a resolution of 50 nm. The gold foams are synthesized by the chemical dealloying method. By using focused ion beam milling technology, a foam micro-cylinder with a diameter of approximately 55 µm is prepared. The tomographical data sets of the micro-cylinder foam are collected in the angle range of ±90° at a photon energy of 8 keV. The data sets are then used to reconstruct the three-dimensional microstructure of the gold foams. The three-dimensional reconstruction information obtained from computed tomography provides an intuitive understanding of the gold foam structure. Keywords: X-ray nanotomography; gold foams; microstructures; structure characterization.
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1. Introduction Gold foam is a typical low-density metallic material, which presents excellent performance in the fields of catalysts, sensors, actuators, supercapacitors, plasmonics and ion exchange.1-3 Optimization of the electrical, thermal, mechanical and optical properties of gold foams depends on the internal microstructures, which can be tuned in the preparation process. However, the three-dimensional (3D) interior microstructure characterization of nanoporous materials remains a challenge. A focused ion beam (FIB)–scanning electron microscopy (SEM) system can be used to observe the 3D tomographic structures by the time-consuming series sectioning of samples, but this is a destructive method.4 Transmission electron tomography is a high-resolution (~13 nm3), non-destructive method, which can be used to characterize the 3D internal structures of specimens.5, 6 Unfortunately, this method is not suitable for characterizing large-scale samples owing to the limited electron penetration depth. X-ray computed tomography (XCT) is an invaluable non-destructive tomographic method for examining the 3D interior structure of thick opaque materials.7 Benefitting from the developments of Fresnel zone plates and X-ray sources, XCT has been used for two-dimensional (2D) microstructures with a resolution of better than 15 nm for soft X-rays in the photon energy range of 0.25– 1.8 keV.8 For harder X-rays, a lateral resolution below 40 nm has been reported in the photon energy range of 7–18 keV.9 The high spatial resolution XCTis widely used in the area of porous foams,10 granular structures,11 ion batteries,12 and biological13 and geological materials.14 Specifically, XCT is a powerful tool for imaging the 3D 2/9
interior microstructure of microsized and nanosized complicated materials.15-17 Observation of the 3D interior structure of artificial microstructures provides a platform for nanoscale XCT applications. In this work, we report on the 3D interior structure characterization of gold foams by using high-resolution XCT. 2. Methods The ultra-low density gold foams are prepared by a template-dealloying method.4 First, Au and Ag nanoparticles are sequentially coated onto polystyrene (PS) microspheres. Next, the cylindrical PS/(Au-Ag) monolith is formed by filter-casting of the nanoparticle coated PS suspension. Then, the self-supported Au-Ag foams are produced by removing PS template. Finally, the Ag component is selectively dealloyed in HNO3 solution by gradually increase the concentration from 3.5 mol/L to 8.0 mol/L and eventually 12.9 mol/L, the dealloying time is 24 h for every HNO3 concentration. After several times washing, the self-supported gold foams with bimodal porous structure are obtained. Figure 1(a) and 1(b) show the SEM images of the synthesized gold foams. The diameter of the microspherical shells is approximately 10 µm. The X-ray diffraction pattern of gold foams as shown in inset of Fig. 1(a) demonstrates that the main component in foams is Au. The chemically synthesized gold foams are macroscopical cylindrical monoliths with diameters of ~4 mm. However, the large size of the foam monoliths is far greater than the field-of-view (FOV) region (~60 3µm3) of the XCT machine. To prepare a suitable sample for XCT characterization, FIB milling technology has been used to process a microsized foam cylinder, as shown in Fig. 1(c),where the diameter of the 3/9
micro-cylinder is approximately 55 µm. The foam micro-cylinder is protrudent on the surface of the macroscopical foam monolith. The gold foam micro-cylinder was characterized by an Xradia nanoscale XCT system. Fig. 2(a) shows the measurement configuration. A laboratory X-ray source (rotating copper anode) was used to emit X-rays, and an energy filter was used to provide monochromatic X-rays with a photon energy of 8 keV. The capillary condenser lens focused the X-rays onto the sample, which was placed on a rotation stage. The X-rays transmitted through the sample were magnified by a Fresnel zone plate, and finally were recorded on a 1024×1024 charge coupled device (CCD) camera. For the large FOV measurement mode (which corresponded to a resolution of 150 nm), the pixel size of the sample at the camera screen was approximately 64 nm with a total FOV of 65.6 2 µm2. A total of 901 radiographs were automatically collected from −90° to 90° in 0.2° intervals with an exposure time of 60 s per image. Fig. 2(b) and 2(c) display two typical projection images at two rotation angles that were perpendicular to each other. The projections of hollow spherical shells can be clearly seen. These projection images were reconstructed by a standard filtered back-projection algorithm.18 3. Results Figure 3 shows the reconstructed results of the gold foams in a spatial volume of 603µm3. Fig. 3(a) displays the reconstructed slices along the axial direction of the micro-cylinder. The sharp white rings indicate the cross-sections of the gold microspherical shells. We determined that the shells’ thickness and diameter were 4/9
approximately 800 nm and 10 µm, respectively. These values were close to the values obtained from SEM (Fig. 1(d)). Moreover, we can see that some shells were fused with each other to form dumbbell-shaped shells (indicated by red arrows in Fig. 3(a)). Fig. 3(b) presents the 3D rendering of the gold foam micro-cylinder. The stack structure of the microspherical shells could be identified. The internal structure is also shown in Fig. 3(c) in an angle-cut manner. The hollow shells of the microspheres can be clearly seen. Figure 4 shows the reconstructed results of a single microspherical shell located on the top of the micro-cylinder. When we used the high-resolution measurement mode (correspondingto a resolution of 50 nm), a pixel resolution of 16 nm in the CCD screen with a total FOV of 16.3 2 µm2 was achieved. The reconstructed slices, as shown in Fig. 4(a), revealed that the thickness of the shell was around 300 nm and the diameter of the microsphere was approximately 10 µm. These values were consistent with the values obtained from SEM (Fig. 1(b)). Fig. 4(b) and 4(c) show the 3D rendered images of the gold microspherical shell from different viewing angles. The fine 3D microstructure of the microspherical shell is observed. 4. Conclusions In conclusion, a gold foam micro-cylinder with a diameter of ~55 µm has been characterized by X-ray computed nanotomography with 50-nm spatial resolution. The three-dimensional structure of the gold foam is reconstructed. The three-dimensional images of the gold foams reconstructed by computed tomography provide an intuitive understanding of the foam material structures. 5/9
Acknowledgements This work is financially supported by the National Natural Science Foundation of China (Grant Nos. 11604310, 11404304, 60908023), the National Key Scientific Instrument and Equipment Development Project of China (Grant No. 2014YQ090709) and the Key Laboratory of Ultra-Precision Machining Technology Foundation of CAEP (Grant No. ZZ15003). References 1.
J. Biener, G. W. Nyce, A. M. Hodge, M. M. Biener, A. V. Hamza and S. A. Maier, Adv. Mater. 20, 1211 (2008).
2.
Y. Ding and M. Chen, MRS Bull. 34, 569 (2009).
3.
B. C. Tappan, S. A. Steiner-III and E. P. Luther, Angew. Chem. Int. Ed. 49 (27), 4544 (2010).
4.
K. Zhang, X. Tan, J. Zhang, W. Wu and Y. Tang, RSC Adv. 4 (14), 7196 (2014).
5.
P. A. Midgley and R. E. Dunin-Borkowski, Nat. Mater. 8, 271 (2009).
6.
T. Fujita, L.-H. Qian, K. Inoke, J. Erlebacher and M.-W. Chen, Appl. Phys. Lett. 92, 251902 (2008).
7.
P. J. Withers, Mater. Tod. 10, 26 (2007).
8.
W. Chao, B. D. Harteneck, J. A. Liddle, E. H. Anderson and D. T. Attwood, Nature 435, 1210 (2005).
9.
Y. S. Chu, J. M. Yi, F. D. Carlo, Q. Shen, W.-K. Lee, H. J. Wu, C. L. Wang, J. Y. Wang, C. J. Liu, C. H. Wang, S. R. Wu, C. C. Chien, Y. Hwu, A. Tkachuk, W. Yun, M. Feser, K. S. Liang, C. S. Yang, J. H. Je and G. Margaritondo, Appl. Phys. Lett. 92, 103119 (2008).
10.
Y.-c. K. Chen, Y. S. Chu, J. Yi, I. McNulty, Q. Shen, P. W. Voorhees and D. C. Dunand, Appl. Phys. Lett. 96, 043122 (2010).
11.
K. M. Kareh, P. D. Lee, R. C. Atwood, T. Connolley and C. M. Gourlay, Nat. Commun. 5,
12.
J. Wang, C. Eng, Y.-c. K. Chen-Wiegart and J. Wang, Nat. Commun. 6, 7496 (2015).
13.
P. A. Midgley, E. P. W. Ward, A. B. Hungria and J. M. Thomas, Chem. Soc. Rev. 36, 1477
14.
T. Saif, Q. Lin, K. Singh, B. Bijeljic and M. J. Blunt, Geophys. Res. Lett. 43, 6799 (2016).
15.
J. Chen, C. Wu, J. Tian, W. Li, S. Yu and Y. Tian, Appl. Phys. Lett. 92, 233104 (2008).
16.
W. Li, N. Wang, J. Chen, G. Liu, Z. Pan, Y. Guan, Y. Yang, W. Wu, J. Tian, S. Wei, Z. Wu, Y.
4464 (2014).
(2007).
Tian and L. Guo, Appl. Phys. Lett. 95, 053108 (2009). 17.
C. Donnelly, M. Guizar-Sicairos, V. Scagnoli, M. Holler, T. Huthwelker, A. Menzel, I. Vartiainen, E. Muller, E. Kirk, S. Gliga, J. Raabe and L. J. Heyderman, Phys. Rev. Lett. 114, 115501 (2015).
18.
M. Soleimani and T. Pengpen, Phil. Trans. R. Soc. A 373, 20140399 (2015).
6/9
Figure captions: Figure 1. SEM characterization of the gold foam. (a) and (b) show the SEM images of the as-prepared gold foam monoliths with different magnification. The inset in (a) shows the X-ray diffraction pattern of gold foams. The dominant diffraction peaks are labelled, which belong to the gold crystals. (c) The SEM image of the foam micro-cylinder with a diameter of ~55 µm. (d) The SEM image of gold microspherical shells near the bottom of the micro-cylinder. Figure 2. XCT characterization of the gold foam micro-cylinder. (a) A schematic diagram of the XCT measurement geometry. (b) and (c) present two typical projection images at different angles that are perpendicular to each other. Figure 3. The 3D reconstructed results of the gold foam micro-cylinder. (a) The reconstructed slices of the foam micro-cylinder, the positions of the slices are indicated in (b) as white lines. The red arrows indicate the dumbbell-shaped shells that are formed by fusing two microspherical shells. (b) The 3D rendering of the foam micro-cylinder. (c) The angle-cut cross-section view of the micro-cylinder rendering. The scale bars in (b) and (c) are 10 µm. Figure 4. The 3D reconstructed results of a single gold microspherical shell. (a) The reconstructed slices of a single gold microspherical shell, the positions of slices are indicated in (b) as white lines. (b) and (c) show the 3D rendering pictures of the gold microspherical shell from the different viewing angles. The scale bars in (b) and (c) are 3 µm.
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Figure 1.
Figure 2.
Figure 3.
Figure 4.
8/9
Highlights:
a) The ultra-low density gold foams are prepared by a template-dealloying method. b) A foam micro-cylinder with a diameter of ~55 μm is prepared by FIB milling technology. c) The 3D interior microstructure of gold foams is reconstructured by x-ray nanotomography. d) The reconstructured results provide an intuitive understanding of the gold foams.
9/9