Atomic-Scale Understanding of Gold Cluster Growth on Different

Subscriber access provided by UNIV OF TASMANIA

Article

Atomic-Scale Understanding of Gold Cluster Growth on Different Substrates and Adsorption-Induced Structural Change Qiang Li, Deqiang Yin, Junjie Li, and Leonard Deepak Francis J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b12037 • Publication Date (Web): 28 Dec 2017 Downloaded from http://pubs.acs.org on December 30, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Atomic-Scale Understanding of Gold Cluster Growth on Different Substrates and Adsorption-Induced Structural Change Qiang Li,† Deqiang Yin,*,‡,§ Junjie Li*,§,ǁ and Leonard Francis Deepakǁ †

School of Mechanical Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China ‡

§

College of Aerospace Engineering, Chongqing University, Chongqing 400044, China.

Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan

ǁ

International Iberian Nanotechnology Laboratory (INL), Avenida Mestre Jose Veiga Braga 4715-330, Portugal.

Corresponding Authors *E-mail:[email protected] *E-mail:[email protected]

ABSTRACT: To fully understand the properties of functional nanocatalysts including nanoclusters and nanoparticles, it is necessary to know the geometric and electronic structures of the nanostructure. The catalytic properties of noble metal nanoclusters can often be improved by the formation of heterostructures on different support, but little is known about their atomic-scale structures and their interaction with the support materials. Here, we

1

ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 31

report the size- and support-dependent structures for Au nanoclusters by combining aberration-corrected

scanning

transmission

electron

microscopy

and

density-functional-theory calculations. We demonstrate lattice induced epitaxial coherence growth for Au nanoclusters on crystalline substrate of (110) MgO, different from the chain-like or random structures on amorphous carbon support. The time sequential atomic scale observations confirm that Au clusters tend to easily migrate oncrystalline MgO support. DFT calculations based on the experiment results imply the CO adsorption on MgO supported Au clusters prefer to bind at apex sites and the adsorption can induce the 3D structural change of the supported nanoclusters resulting in the formation of linear and bridge CO species. The results should help to clarify the atomistic origin of shape-, number- and support- dependent catalytic activity in the supported Au clusters catalysts.

1. INTRODUCTION Supported noble metal clusters or nanoparticles have attracted a great deal of attention lately due to their extraordinary catalytic activities in many reactions, such as in the oxidation of CO at low temperature,1-3 low-temperature water-gas shift reaction,4,5 hydrogen evolution reaction6,7 and so on.8-10 The properties, however, strongly depend not only on the composition, size, geometric structure of the metal nanoclusters or nanoparticles, but also on their interactions with the different supports.11-14 The smaller the nanoparticle, the stronger is the dependence on the geometric structures and the strong interactions between metal nanostructures and support materials.12 To understand these properties, many theoretical works have been implemented to predict the atomic structures of the supported ultra-small nanostructures.15-17 Synchrotron-radiation experiments have been used extensively in the 2


Page 3 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


characterization of the nanocatalysts shape, distance and height.18-22 It is worthy to note that the dynamic observations can also be realized by using such methods. For example, Schwartzkopf et al. show real-time investigation of the growth and migration kinetics of metal nanostructures during magnetron sputter deposition with high spatial resolution by means of in situ microbeam grazing incidence small-angle X-ray scattering (µGISAXS)23-26 and Hejral et al. report a direct study of the catalysts under catalytic CO oxidation reaction conditions using in situ high-energy grazing incidence X-ray diffraction and inline mass spectrometry.27 However, due to the limitation of spatial resolution, it is difficult to obtain atomic scale information for the catalysts by these methods. In principle, transmission electron microscopy (TEM) is one of the most powerful tools for the atomic scale characterization

of

nanomaterials.28

In

particular,

with

the

development

of

aberration-corrected electron microscopies, the Z-contrast (Z: atomic number) high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) can provide two-dimensional (2D) information directly with single-atom sensitivity, which is suitable for the study of supported nanostructures at atomic scale.29-32 Recently, Li et al. obtained 3D atomic-scale structures of large Au clusters (309 ± 6 atoms) by electron tomography in a Cs-corrected STEM.33 Browning et al. solved the structure of supported osmium clusters based on 2D STEM images.34 Tendeloo et al. reported the atomic scale dynamics of ultrasmall germanium clusters on carbon support under electron irradiation within the microscope.35 The results highlighted the influence of composition, size, and geometric structure of nanomaterials on their properties. However, due to the rapid atomic migration and electron damage to the ultra-small structures, as well as the strong interaction between

3



the nanomaterials and supports, the clear 2D image of clusters as well as the geometric structure are still not fully understood and clearly established. Here, combining the state-of-the-art aberration-corrected STEM and density functional theory (DFT) calculations, we provide size- and support-dependent structural information at atomic scale for supported metal nanostructures on different substrates. To obtain an enhanced Z-contrast image (Z : atomic number), we adopted Au (Z = 79) as a model metal, magnesium oxide (MgO) (ZMg = 12) and amorphous carbon (Z = 6) as support materials. Our results confirm that the Au clusters tend to form lattice induced coherent structures on the crystalline support, and chain-like or random structures on the amorphous support. Interestingly, the Au clusters tend to easily migrate on the surface of MgO (110) but are stabilized by the amorphous carbon. Further DFT calculations based on the experimental results imply that the CO adsorption of MgO supported Au clusters is preferentially bound at apex sites. It can also induce the 3D structural change of the supported nanoclusters and result in bridge or linear connection between CO and Au atoms.

2. EXPERIMENTAL AND COMPUTATIONAL METHODS 2.1 Sample preparation and characterization. To avoid unwanted solvent effect, the specimens for STEM imaging were prepared by directly evaporating Au onto MgO (110) TEM sample or Cu grids (with amorphous carbon layer) at room temperature using molecular beam epitaxy (MBE) in a high vacuum chamber with a base pressure of ~8.0 × 10–7 Pa. Prior to the growth, MgO (110) TEM specimen was annealed at 973 K in air for 30 min to remove the amorphous layers. High-purity Au (99.95%) was thermally evaporated from the effusion

4


Page 4 of 31

Page 5 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


cell at 1475K for ~ 1 s in order to achieve a low density of Au clusters and nanoparticles. The chamber background pressure was 2.0 × 10-5 Pa during deposition and thermal evaporation rate of Au was less than 0.01 nm/s. The deposited samples were used directly for the STEM and energy-dispersive x-ray spectroscopy (EDS) characterizations. 2.1 TEM observations. HAADF-STEM images were obtained using a double aberration-corrected Titan Cubed G2 60-300 analytical microscope operated at 200 kV (with spatial resolution of ~ 0.7 nm), which was equipped with a monochromator and an X-FEG Schottky high brightness source, offering an unprecedented opportunity to probe structures with sub-Ångström resolution. HAADF-STEM images were recorded on a charge-coupled device (CCD) camera (2k × 2k, Gatan UltraSan TM 1000), and a detector with an inner semiangle of over 60.0 mrad and a probe convergence angle of ~ 22 mrad were adopted. 2.2 DFT calculations. Calculations were implemented using Vienna Ab-initio simulation package (VASP) within the framework of DFT.36 The projector-augmented wave (PAW) method was applied for the electron-ion interactions. The generalized gradient approximation (GGA) of Perdew et al. (PW91) was employed to describe the exchange-correlation functional.37, 38 Single particle Kohn-Sham wave function was expanded using the plane wave with a cutoff energy of 400 eV. The irreducible Brillouin zone was sampled with the regular Monkhorst-Pack grid of 6 × 6 × 6 k points. Since the exact structure of amorphous carbon is not known, the carbon substrate was not taken into account in our calculations.35 The initial 3D atomic models were established based on the experimental 2D images. The MgO (110) supported Au clusters or free Au clusters were put in a sufficiently large vacuum space in order to isolate them from each other and the configurations were fully optimized. All atoms

5



in the model were fully relaxed until the magnitude of force on each atom is less than 0.005 eV/Å.

3. RESULTS AND DISCUSSION Since intensity of an atomic column in HAADF images is directly proportional to atomic number Z (~ Z1.7) as well as with the number of atoms, we adopted Au (Z = 79) as the model metal, magnesium oxide (ZMg = 12) (MgO) and amorphous carbon (Z = 6) as support materials in order to obtain an enhanced Z-contrast image. An MgO (110) single crystal TEM sample was selected for the experiment because the Mg and O columns can be separately viewed along [110] in high resolution STEM image, as shown in Figure S1. The amorphous carbon structure was also checked by high resolution TEM and diffraction before deposition, as shown in Figure S2. After deposition, the size of the deposited Au nanoparticles on both substrates were checked by low magnification STEM images and confirmed that the average size of the nanoparticles is near 2-3 nm based on statistical analysis in Figure S3 and S4. From the Z contrast HAADF-STEM images, the brighter contrast for heavier atoms in each atomic column can be seen, which means that the brighter atoms, clusters and nanoparticles in both samples represent Au, consistent with the EDS results shown in Figure S5 and S6. Figure 1a-t show atomic-resolution HAADF STEM images of the MgO (110) supported Au nanoclusters with different sizes. We can see that the Au nanoclusters show an epitaxial coherent growth on the crystalline substrate, which is similar with the lattice induced epitaxial growth mechanism of thin films.39-42 According to the atomic model in Figure S1a, the Au atom aligned on the MgO (110) plane can sit atop either Mg or O columns. From

6


Page 6 of 31

Page 7 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


previous DFT calculations it has been revealed that the Au atoms sitting atop O columns is more stable than atop Mg column in the Au nanocrystal/MgO (110) heterointerface because of a lower binding energy.43 Interestingly, all the Au atoms sit atop Mg column in our experimental results. The difference can be attributed to the existed Mg vacancies on the surface of (110) MgO support produced by irradiation damage during the fabrication of TEM samples.44-47 What’s more, under the induction effect of the lattice, most of the ultra-small nanoclusters tend to form a symmetric atomic arrangement. Figure 1a-l show the 2D structures of Au2-10 and Au12 observed in our sample, which are energetically stable based on the previous theoretical prediction. In principle, for each free AuN (N = 3-13), the DFT calculations usually provide several energy stabilized geometric structures.15 However, some of the predicted energy stabilized geometric structures for free Au clusters are missing in the MgO (110) supported Au clusters but are seen in the following amorphous carbon supported Au clusters. Figure 1m-t show the structural evolution from 2D to 3D growth, driven by minimalizing the surface energy and total energy.48-50 It is worthy to note that the images are taken at very thin regions (corresponding thick region image is also shown in Figure S7) and the intensity profiles in Figure f1, o1 and s1 reveal that the height of Au clusters varied from one to a few layers with the increase of size. To uncover the influence of lattice induced effect on the geometric structures of Au nanoclusters, an amorphous carbon thin film was used as another support to deposit Au nanoparticles. Figure 2 shows the amorphous carbon supported Au nanoclusters. We can see that some of the chain like structures are seen without the MgO supported Au nanoclusters, such as Au3, Au4, Au6, Au7 and Au8 in Figure 2b, d, j, k and p. In addition, most of the

7



nanoclusters show irregular morphologies. Even for the nanoparticles with the size of ~ 2 nm they show a disordered cluster structure (as shown in Figure 2v-w and Figure S8). In Figure 2x, the Au nanocluster with a size of ~3nm show a partially ordered structure rather than a crystal structure, which can be attributed to the size which is far from the critical crystalline size in classical heterogeneous nucleation and growth mechanism, different from the lattice induced mechanism in Figure 1. The corresponding intensity profiles in Figure s1, u1 and x1 reveal that the height of Au clusters or nanoparticles are varied from one, two to ten layers along with the increase of size. To shed further light on the migration of Au nanocluster on crystalline and amorphous substrates, we implement direct dynamic observations for the nanoclusters on both substrates under electron irradiation. The stability of Au nanocluster on substrates is important to understand the change of properties in catalytic process. Figure 3a-f show the dynamic process of the Au nanoparticles on MgO (110) support. Figure 3a-d show the migration of an Au cluster (marked as the red arrow) on the support. Figure e-f show a rapid coalescence with a big nanoparticle located on its lower right direction. In contrast, Au nanoclusters tend to be stable on amorphous carbon support (marked by the red arrow in Figure 3g-l), the reason being that the carbon films can stabilize gold clusters with a binding energy of ~0.3 eV per Au atom.51 The rapid migration of the ultra-small Au clusters on the surface of crystalline support is harmful to their catalytic properties. Recently, Dollinger et al. report that size-selected Au clusters can be created on porous TiO2 and act as a high efficient catalysts for the bromination of 1,4-dimethoxybenzene in solution in experiment.52 The results identify that the active sites of supported Au nanoclusters can be created and stabilized in porous TiO2

8


Page 8 of 31

Page 9 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


structure using gas phase methods. In the present study, our results show another possible route to stabilize the ultra-small metal clusters using amorphous supports. What’s more, although the Au cluster finds it difficult to migrate on the carbon support, the ultra-small cluster with about 30 atoms show a structural evolution from a near-square structure to an elongated structure under electron irradiation. To obtain 3D structures of the Au clusters based on the 2D STEM images, we took the MgO supported Au4, Au7, Au8 and carbon supported Au4 and Au8 as examples and conducted a series of DFT calculations. The initial atomic models were constructed based on atomic x and y coordinates in HAADF-STEM images and assumed possible z values. After full relaxation, the models keep close to initial configuration, demonstrating that they indeed corresponding to local minima and that the measured clusters are stable. If there is a considerable discrepancy between the experimental images and relaxed structure, we adjusted the initial models and conducted further optimizations. Figure 4 shows the relaxed models of MgO (110) supported Au4, Au7 and Au8 and free Au4 and Au8 (Since the exact structure of amorphous carbon is not known, the carbon support was not considered for the calculations35). It is worthy to note that for unclear images or complex systems, the statistical parameter estimation theory is usually applied to estimate the structural parameters, and then the ab initio calculations are implemented to evaluate the stability of the structure.31, 35 However, the Cs-corrected microscopy with a high spatial resolution of ~0.7 nm allows us to clearly determine the atomic columns in the ultra-small Au clusters. From the projections along different orientation, we can see that the Au clusters on MgO tend to show a 3D geometry rather than an absolutely in-plane structure like calculated free Au clusters.15 Considering the

9



lattice mismatch of 1.6% between Au nanocrystal and (110) MgO, the Au-Au bond length in the Au nanocluster should be different from the value of ~ 2.88 Å in the bulk.53 Therefore, we statistically obtain the change of Au-Au bond length in MgO supported Au4 from 3.040 to 3.072 Å, Au7 from 2.918 to 3.050 Å, and Au8 from 2.613 to 2.760 Å, as shown in table S1 The results show an atom number (N) dependent Au-Au bond length in the Au nanoclusters on the support of MgO (110) substrate. The Au-Au bond length is changed from near Mg-Mg bond length of ~ 3.05 Å to the length in bulk Au accompanied with the increase of the numbers of atoms, which is in accordance with the change of morphology of Au nanoclusters from 2D to 3D transition in Figure 1. The Au/MgO system is an important catalytic system, especially for the oxidation of CO at low temperatures.43, 54 Due to the difficulty to get real atomic models for the supported systems, many calculations of CO adsorption have been focused on the free Au clusters or nanocrystals.55 To uncover the influence of CO adsorption on the structure of MgO supported Au clusters, we implement the DFT calculation of CO adsorption based on the obtained atomic models of Au7/MgO and Au4/MgO in Figure 5. Figure 5a-g show the singe CO adsorption of MgO supported Au7 from atom 1 to 7 labeled in Figure 4b1. Figure 5h-I show the singe CO adsorption of MgO supported Au7 from atom 1 to 2 marked in Figure 4c1. In both clusters, we can see that single CO adsorption can induce the structural fluctuation of the supported Au nanoclusters from one 3D structure to another 3D structure. Moreover, the different adsorption positions result in different geometric structures as well as different connections between CO and Au atoms, such as, the CO adsorption in the position 3 in Figure 4b; the carbon can form a bridge connection between two Au atoms rather than linear

10


Page 10 of 31

Page 11 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


connection in other atomic position of 1-2 and 4-7 in Figure 4b1 (Figure S9). Figure j-k show the CO saturated adsorption on MgO supported Au7 and Au4 in Figure 4a and 4c. The relaxed model show similar 3D to 3D structural fluctuations with the single CO adsorption. To further uncover the CO preferential sites, we have carried out statistical analysis of the changes in total energy and Au-C bonding length at different sites. The results show that the Au-C bond length can vary from 1.88 to 2.22 Å. The relative total energy curves for CO molecule adsorbed to an apex site (green curve) and to an edge site (red curve) of the Au7 in Figure 4b1 are shown in Figure 6. The significant energetic and bonding differences between the two types of adsorption sites imply that CO molecule prefer to bind to the apex sites rather than the edge sites of the supported small gold clusters.

4. CONCLUSIONS We present an atomic-scale observations and show a quantitative interpretation about the supported Au clusters. The results confirm that the lattice can induce an epitaxial coherence growth of metal clusters on crystal substrates, and a chain like or random growth mechanism on amorphous support. Compared to the rapid migration of Au cluster on crystalline MgO support, the amorphous carbon substrate can stabilize the Au clusters. Based on the clear 2D STEM images, we demonstrate that quantitative interpretation can uncover the 3D structures of the hetero-nanostructures. Further DFT calculations imply that the CO adsorption can induce the change of geometry of the supported Au nanoclusters and result in different connections between CO and Au atoms. Such a combined atomic-scale study provides insights into 3D structures of the ultra-small Au nanoclusters on crystalline and amorphous

11



substrates and helps to clarify the atomistic mechanism of shape-, number- and support dependent catalytic activity in the case of supported Au cluster catalysts.

12


Page 12 of 31

Page 13 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ASSOCIATED CONTENT Support Information. Support Information is available from the ACS Publications website or from the author. Atomic model and HAADF-STEM image of pure (110) MgO, HAADF-STEM image, high resolution TEM image and corresponding fast Fourier transformation (FFT) of amorphous carbon support, low magnification and atomic scale HAADF STEM images after deposition of Au clusters onto the MgO and carbon support, the size distribution of deposited Au clusters on MgO and carbon supports, EDS mapping and spectrum of Au clusters, HAADF and corresponding annular bright-field (ABF) STEM images of Au clusters on MgO (110) and amorphous carbon support, atomic models of CO adsorbed Au clusters, the atom number (N) dependent Au-Au bond length.

AUTHOR INFORMATION Corresponding Authors *E-mail:[email protected] *E-mail:[email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS J.J.L. appreciates the Chinese Scholarship Council for financial support. This work was supported in part by the National Natural Science Foundation of China (NSFC) (grant no.

13



11302141).

14


Page 14 of 31

Page 15 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


REFERENCES (1) Saavedra, J.; Whittaker, T.; Chen, Z.; Pursell, C. J.; Rioux, R. M. Controlling Activity and Selectivity Using Water in the Au-Catalysed Preferential Oxidation of CO in H2. Nat. Chem. 2016, 8, 584-589. (2) Margitfalvi, J. L.; Fási, A.; Hegedűs, M.; Lónyi, F.; Gőbölös, S.; Bogdanchikova. N. Au/MgO Catalysts Modified with Ascorbic Acid for Low Temperature CO Oxidation. Cataly. Today. 2002, 72, 157-169. (3) Valden, M.,; Lai, X.; Goodman, D. W.; Onset of Catalytic Activity of Gold Clusters on Titania with the Appearance of Nonmetallic Properties. Science 1998, 281, 1647-1650. (4) Magadzu, T.; Yang, J. H.; Henao, J. D.; Kung, M. C.; Kung, H. H.; Scurrell, M. S. Low-Temperature Water-Gas Shift Reaction Over Au Supported on Anatase in the Presence of Copper: EXAFS/XANES Analysis of Gold–Copper Ion Mixtures on TiO2. J. Phys. Chem. C. 2017, 121, 8812-8823. (5) Yao, S.; Zhang, X.; Zhou, W.; Gao, R.; Xu, W.; Ye, Y.; Lin, L.; Wen, X.; Liu, P.; Chen, B., et al. Atomic-Layered Au Clusters on α-MoC as Catalysts for the Low-Temperature Water-Gas Shift Reaction. Science 2017, 357, 389-393. (6) Lin, L.; Zhou, W.; Gao, R.; Yao, S.; Zhang , X.; Xu, W.; Zheng, S.; Jiang, Z.; Yu, Q.; Li, Y. W., et al. Low-Temperature Hydrogen Production from Water and Methanol Using Pt/α-MoC Catalysts. Nature 2017, 544, 80-83. (7) Shi, Y.; Zhang, B. Recent Advances in Transition Metal Phosphide Nanomaterials: Synthesis and Applications in Hydrogen Evolution Reaction. Chem. Soc. Rev. 2016, 45, 1529-1541.

15



(8) Daniel, M. C.; Astruc, D. Gold Nanoparticles: Assembly, Supramolecular Chemistry, Quantum-Size-Related Properties, and Applications toward Biology, Catalysis, and Nanotechnology. Chem. Rev. 2004, 104, 293-346. (9) Nesselberger, M.; Roefzaad, M.; Hamou, R. F.; Biedermann, P. U.; Schweinberger, F. F.; Kunz, S.; Schloegl, K.; Wiberg, G. K.; Ashton, S.; Heiz, U., et al. The Effect of Particle Proximity on the Oxygen Reduction Rate of Size-Selected Platinum Clusters. Nat. Mater. 2013, 12, 919-924. (10) Han, X.; Cheng, F.; Zhang, T.; Yang, J.; Hu, Y.; Chen, J. Hydrogenated Uniform Pt Clusters Supported on Porous CaMnO3 as a Bifunctional Electrocatalyst for Enhanced Oxygen Reduction and Evolution. Adv. Mater. 2014, 26, 2047-2051. (11) Ortalan, V.; Uzun, A.; Gates, B. C. Browning, N. D. Towards Full-Structure Determination of Bimetallic Nanoparticles with an Aberration-Corrected Electron Microscope. Nat. Nanotechnol. 2010, 5, 843-847. (12) Tyo, E. C.; Vajda, S. Catalysis by Clusters with Precise Numbers of Atoms, Nat. Nanotechnol. 2015, 10, 577-588. (13) Imaoka, T.; Akanuma, Y.; Haruta, N.; Tsuchiya, S.; Ishihara, K.; Okayasu, T.; Chun, W. J.; Takahashi, M.; Yamamoto, K. Platinum Clusters with Precise Numbers of Atoms for Preparative-Scale Catalysis. Nat. Commun. 2017, 8, 688. (14) Mondal, S.; Thattarathody, R.; Dhar, B. B.; Snellman, M.; Li, J.; Francis, L. D.; Devi, R. N. Understanding Alloy Structure and Composition in Sinter-Resistant AgPd@SiO2 Encapsulated Catalysts and Their Effect on Catalytic Properties. New J. Chem. 2017, 41， 14652.

16


Page 16 of 31

Page 17 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(15) Deka, A.; Deka, R. C. Structural and Electronic Properties of Stable Aun (n = 2-13) Clusters: A Density Functional Study. J. Mol. Struc-Theochem. 2008, 870, 83-93. (16) Kuang, X. J.; Wang, X. Q.; Liu, G. B. A Density Functional Study on the AunAg (n = 1-12) Alloy Clusters. J. Alloy. Compd. 2013, 570, 46-56. (17) Abraham, J.; Strunskus, T.; Faupel, F.; Bonitz, M. Molecular Dynamics Simulation of Gold Cluster Growth during Sputter Deposition. J. Appl. Phys. 2016, 119, 185301. (18) Toshima, N.; Harada, M.; Yonezawa, T.; Kushihashi, K.; Asakura, K. Structural Analysis of Polymer-Protected Palladium/Platinum Bimetallic Clusters as Ddispersed Catalysts by Using Extended X-Ray Absorption Fine Structure Spectroscopy. J. Phys. Chem. 1991, 95, 7448-7453. (19) Reifsnyder, S. N.; Otten, M. M.; Sayers, D. E.; Lamb, H. H. Hydrogen Chemisorption on Silica-Supported Pt Clusters: In Situ X-Ray Absorption Spectroscopy. J. Phys. Chem. B 1997, 101, 4972-4977. (20) Shivhare, A.; Chevrier, D. M.; Purves, R. W.; Scott, R. W. J. Following the Thermal Activation of Au25SR)18 Clusters for Catalysis by X-Ray Absorption Spectroscopy. J. Phys. Chem. C. 2017, 117, 20007-20016. (21) Schwartzkopf, M.; Hinz, A.; Polonskyi, O.; Strunskus, T.; Löhrer, F. C.; Körstgens, V.; Müller-Buschbaum, P.; Faupel, F.; Roth, S. V. Role of Sputter Deposition Rate in Tailoring Nanogranular Gold Structures on Polymer Surfaces. ACS Appl. Mater. Inter. 2017, 9, 5629-5637.

17



(22) Schwartzkopf, M.; Buffet, A.; Körstgens, V.; Metwalli, E.; Schlage, K.; Benecke, G.; Perlich, J.; Rawolle, M.; Rothkirch, A.; Heidmann, B. From Atoms to Layers: In Situ Gold Cluster Growth Kinetics during Sputter Deposition. Nanoscale 2013, 5, 5053-5062. (23) Schwartzkopf, M.; Santoro, G.; Brett, C. J.; Rothkirch, A.; Polonskyi, O.; Hinz, A.; Metwalli, E.; Yao, Y.; Strunskus, T.; Faupel, F. Real-Time Monitoring of Morphology and Optical Properties during Sputter Deposition for Tailoring Metal-Polymer Interfaces. ACS Appl. Mater. Inter.

2015, 7, 13547-13556.

(24) Roth, S. V.; Santoro, G.; Risch, J. F.; Yu, S.; Schwartzkopf, M.; Boese, T.; Döhrmann, R.; Zhang, P.; Besner, B.; Bremer, P. Patterned Diblock Co-Polymer Thin Films as Templates for Advanced Anisotropic Metal Nanostructures. ACS Appl. Mater. Inter. 2015, 7, 12470-12477. (25) Santoro, G.; Yu, S.; Schwartzkopf, M.; Zhang, P.; Koyiloth Vayalil, S.; Risch, J. F.; Rübhausen, M. A.; Hernández, M.; Domingo, C.; Roth, S. V. Silver Substrates for Surface Enhanced Raman Scattering: Correlation Between Nanostructure and Raman Scattering Enhancement. Appl. Phys. Lett. 2014, 104, 243107. (26) Schwartzkopf, M.;Roth, S. V. Investigating Polymer–Metal Interfaces by Grazing Incidence Small-Angle X-Ray Scattering from Gradients to Real-Time Studies. Nanomaterials 2016, 6, 239. (27) Hejral, U.; Müller, P.; Balmes, O.; Pontoni, D.; Stierle, A. Tracking the Shape-Dependent Sintering of Platinum-Rhodium Model Catalysts under Operando Conditions. Nat. Commun. 2016, 7, 10964.

18


Page 18 of 31

Page 19 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(28) Cargnello, M.; Doan-Nguyen, V. V.; Gordon, T. R.; Diaz, R. E.; Stach, E. A.; Gorte, R. J.; Fornasiero, P.; Murray, C. B. Control of Metal Nanocrystal Size Reveals Metal-Support Interface Role for Ceria Catalysts. Science 2013, 341, 771-773. (29) Browning, N. D.; Aydin, C.; Lu, J.; Kulkarni, A.; Okamoto, N. L.; Ortalan, V.; Reed, B. W.; Uzun, A.; Gates, B. C. Quantitative Z-Contrast Imaging of Supported Metal Complexes and Clusters-A Gateway to Understanding Catalysis on the Atomic Scale. ChemCatChem. 2013, 5, 2673-2683. (30) Kesavan, R. S. L.; Jensen, M. M.; Tiruvalam, R.; He, Q.; Dimitratos, N.; Wendt, S.; Glasius, M.; Kiely, C. J.; Hut chings, G. J.; Besenbacher, F. Selective Photocatalytic Oxidation of Benzene for the Synthesis of Phenol Using Engineered Au-Pd Alloy Nanoparticles Supported on Titanium Dioxide. Chem. Commun. 2014, 50, 12612-12614. (31) Li, J.; Yin, D.; Chen, C.; Li, Q.; Lin, L.; Sun, R.; Huang, S.; Wang, Z. Atomic-Scale Observation of Dynamical Fluctuation and Three-Dimensional Structure of Gold Clusters. J. Appl. Phys. 2015, 117, 085303. (32) . Chen, G.; Zhao, Y.; Fu, G.; Duchesne, P. N.; Gu, L.; Zheng, Y.; Weng, X.; Chen, M.; Zhang, P.; Pao, C. W., et al. Interfacial Effects in Iron-Nickel Hydroxide-Platinum Nanoparticles Enhance Catalytic Oxidation. Science 2014, 344, 495-499. (33) Li, Z. Y.; Young, N. P.; Vece, M. D.; Palomba, S.; Palmer, R. E.; Bleloch, A. L.; Curley, B. C.; Johnston, R. L.; Jiang, J.; Yuan, J. Three-Dimensional Atomic-Scale Structure of Size-Selected Gold Nanoclusters. Nature 2008, 451, 46-48. (34) Aydin, C.; Kulkarni, A.; Chi, M.; Browning, N. D.; Gates, B. C. Three-Dimensional Structural Analysis of MgO-Supported Osmium Clusters by Electron Microscopy with

19



Single-Atom Sensitivity. Angew. Chem. Int. Edit. 2013, 52, 5262-5265. (35) Bals, S.; Aert, S. V.; Romero, C. P.; Lauwaet, K.; Van Bael, M. J.; Schoeters, B.; Partoens, B.; Yücelen, E.; Lievens, P.; Van Tendeloo, G. Atomic Scale Dynamics of Ultrasmall Germanium Clusters. Nat. Commun. 2012, 3, 897. (36) Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for ab initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B 1996, 54, 11169. (37) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865-3868. (38) Wang, X.; Li, J.; Zhao, Z.; Huang, S.; Xie, W. Crystal Structure and Electronic Structure of Quaternary Semiconductors Cu2ZnTiSe4 and Cu2ZnTiS4 for Solar Cell Absorber. J. Appl. Phys. 2013, 112, 023701. (39) Li, J.; Lv, S.; Chen, C.; Huang, S.; Wang, Z. Interfacial Defect Complex at the MgO/SrTiO3 Heterojunction and Its Electronic Impact. RSC Adv. 2014, 4, 51002-51007. (40) Chen, C.; Lv, S.; Li, J.; Wang, Z.; Liang, X.; Li, Y.; Viehland, D.; Nakajima, K.; Ikuhara, Y. Two-Dimensional Electron Gas at the Ti-Diffused BiFeO3/SrTiO3 Interface. Appl. Phys. Lett. 2015, 107, 031601. (41) Yao, T.; Chen, R.; Li, J.; Han, J.; Qin, W.; Wang, H.; Shi, J.; Fan, F.; Li, C. Manipulating the Interfacial Energetics of n-type Silicon Photoanode for Efficient Water Oxidation. J. Am. Chem. Soc. 2016, 138, 13664-13672. (42) Li, J.; Yin, D.; Li, Q.; Sun, R.; Huang, S.; Meng, F.; Interfacial Defects Induced Electronic Property Transformation at Perovskite SrVO3/SrTiO3 and LaCrO3/SrTiO3 Heterointerfaces. Phys. Chem. Chem. Phys. 2017, 19, 6945-6951.

20


Page 20 of 31

Page 21 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(43) Duan, Z.; Henkelman, G. O2 Activation at the Au/MgO (001) Interface Boundary Facilitates CO Oxidation. Phys. Chem. Chem. Phys. 2016, 18, 5486-5490. (44) Van Bokhoven J. A.; Lamberti C.; Eds., X-Ray Absorption and X-Ray Emission Spectroscopy: Theory and Applications. Wiley Press: Chichester, U.K., 2016. (45) Aydin, C. ; Kulkarni, A.; Chi, M.; Browning, N. D.; Gates, B.C. Atomically Resolved Site-Isolated Catalyst on MgO: Mononuclear Osmium Dicarbonyls Formed from Os3(CO)12. J. Phys. Chem. Lett. 2012, 3, 1865–1871. (46) Shibata, N.; Goto, A.; Matsunaga, K.; Mizoguchi, T.; Findlay, S. D.; Yamamoto, T.; Ikuhara, Y. Interface Structures of Gold Nanoparticles on TiO2 (110). Phys. Rev. Lett. 2009, 102, 136105. (47) Li, J.; Wang, Z.; Chen, C.; Huang, S. Atomic-Scale Observation of Migration and Coalescence of Au Nanoclusters on YSZ Surface by Aberration-Corrected STEM. Sci. Rep. 2014, 4, 5521. (48) Li, J.; Wang, Z.; Deepak, F. L. In-Situ Atomic-Scale Observation of Droplet Coalescence Driven Nucleation and Growth at Liquid/Solid Interfaces. ACS Nano 2017, 11, 5590-5597. (49) Barnard, A. S.; Lin, X. M.; Curtiss, L. A. Equilibrium Morphology of Face-Centered Cubic Gold Nanoparticles > 3 nm and the Shape Changes Induced by Temperature. J. Phys. Chem. B 2005, 109, 24465-24472. (50) Li, J.; Li, Q.; Wang, Z.; Deepak, F. L. Real-Time Dynamical Observation of Lattice Induced Nucleation and Growth in Interfacial Solid-Solid Phase Transitions. Cryst. Growth. Des. 2016, 16, 7256-7262.

21



(51) Maiti, A.; Ricca, A. Metal–Nanotube Interactions-Binding Energies and Wetting Properties. Chem. Phys. Lett. 2004, 395, 7-11. (52) Dollinger, A.; Stolch, L.; Luo, Y.; Beck, M.; Strobel, C. H.; Hagner, M.; Dilger, S.; Bein, M.; Polarz, S.; Gantefoer, G. F. Size-Selected Gold Clusters on Porous Titania as the Most “Gold-Efficient” Heterogeneous Catalysts. Phys. Chem. Chem. Phys. 2014, 16, 11017-11023. (53) Zeng, C.; Chen, Y.; Liu, C.; Nobusada, K.; Rosi, N. L.; Jin, R. Gold Tetrahedra Coil up: Kekulé-Like and Double Helical Superstructures. Sci. Adv. 2015, 1, e1500425. (54) Grisel, R. J. H.; Nieuwenhuys, B. E. Selective Oxidation of CO, Over Supported Au Catalysts. J. Cataly. 2001, 199, 48-59. (55) Molina, L.; Hammer, B. Active Role of Oxide Support during CO Oxidation at Au/MgO. Phys. Rev. Lett. 2003, 90, 206102.

22


Page 22 of 31

Page 23 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure captions Figure 1 Typical HAADF STEM images of Au clusters on (110) MgO substrate and intensity profiles. a-l, showing the atomic scale structures of Au2-10 and Au12 observed in the sample. m-t, showing the structural evolution from 2D to 3D growth under the drive of minimalizing the surface energy. f1, o1 and s1 showing the corresponding intensity profiles in Figure 1f, 1o and 11. Figure 2 Typical HAADF STEM images of Au clusters on amorphous carbon support and intensity profiles. a-r, show the atomic scale structures of Au1-10 observed in the sample. s-x, show the structural evolution from 2D to 3D growth under the drive of minimalizing the surface energy. s1, u1 and x1 show the corresponding intensity profiles in Figure 2s, 2u and 2x.

Figure 3 A sequence of atomic scale HAADF STEM images for small Au nanoclusters on different support. a-f, show the rapid migration and coalescence of Au clusters on MgO (110) substrate. g-l, show amorphous carbon stabilized Au clusters.

Figure 4 Relaxed 3D geometries viewed from different directions. The atomistic models are constructed based on the experimental images shown in Fig. 1i (a), 1g (b), 1h (c), 1c (d), 2f (e) and 2o (f), and a full structural relaxation is conducted.

Figure 5 CO adsorption induced structural changes on MgO (110) supported Au clusters viewed from different directions. a-g, show single CO adsorption of MgO supported Au7

23



from atom 1 to 7 labeled in Figure 4b1. h-i, show the single CO adsorption of MgO supported Au7 from atom 1 to 2 marked in Figure 4c1. j-k, show the CO saturated adsorption on MgO supported Au7 and Au4 in Figure 4a1 and 4b1.

Figure 6 The relative total energy curves for adsorption of a CO molecule to an apex (atom 1, 3, 5 and 7 in Figure 4b1) and to an edge site (atom 2, 4 and 6 in Figure 4b1) of the Au7 cluster in Figure 4b1.

24


Page 24 of 31

Page 25 of 31

Figure 1

a

b

c

d

e

f

g

h

i

j

k

l

m

n

o

p

q

r

s

t

f1

250

o1

240

s1

200

Intensity

140

150

120 100

160

Intensity

160

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


100

80

80

50

60 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 Position (nm)

0.5

1.0 1.5 Position (nm)

2.0

2.5

0

25


1

2 3 Position (nm)

4


Figure 2 a

b

c

d

e

f

g

h

i

j

k

l

m

n

o

p

q

r

s

t

u

v

w

x

3.4x106

s1

4x106

3.3x10

Intensity

3.3x106 6

u1

3.8x106

x1

3.6x106

3x106

Intensity

3.4x106

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 31

3x106

3.4x106

3.2x106

3x106

3.1x106 0.2

0.4

0.6 0.8 Position (nm)

1.0

3.2x106

0.2

0.4 0.6 0.8 Position (nm)

1.0

26


0.5

1.0 1.5 2.0 Position (nm)

2.5

3.0

Page 27 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3

a

0sb

1.0 s c

2.0 s

d

3.0 s e

4.0 s f

5.0 s

g

0s h

4.0 s i

28.0 s

j

44.0 s k

60.0 s l

100.0 s

27



Figure 4 a1

b1

c1

23 4 1 6 5 1 7 1 2

d1

a2

a3

a4

b2

b3

b4

c2

c3

c4

d2

d3

d4

e1

e2

e3

e4

f1

f2

f3

f4

28


Page 28 of 31

Page 29 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5 a1

a2

a3

a4

b1

b2

b3

b4

c1

c2

c3

c4

d1

d2

d3

d4

e1

e2

e3

e4

f1

f2

f3

f4

g1

g2

g3

g4

h1

h2

h3

h4

i1

i2

i3

i4

j1

j2

j3

j4

k1

k2

k3

k4

29



Relative Total Energy (eV)

Figure 6

0.25

edge sites

0.20 0.15 apex sites

0.10 0.05 0.00 1.90

1.95 2.00 2.05 Bonding Length ( )

Å

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 31

30


2.10

Page 31 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC Graphic Coherent structures on (110) MgO Au3

Au4

Au5

Au6

Au9 Au8 Au10 Au7 Chain-like structures on carbon Au3

Au4

Au5

Au6

Au7

Au8

Au8

Au9

31


Atomic-Scale Understanding of Gold Cluster Growth on Different

Recommend Documents