Pressure-Induced Phase Engineering of Gold Nanostructures

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Pressure-Induced Phase Engineering of Gold Nanostructures Qian Li, Wenxin Niu, Xingchen Liu, Ye Chen, Xiaotong Wu, XiaoDong Wen, Zhongwu Wang, Hua Zhang, and Zewei Quan J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b08647 • Publication Date (Web): 22 Oct 2018 Downloaded from http://pubs.acs.org on October 22, 2018

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Journal of the American Chemical Society

Pressure-Induced Phase Engineering of Gold Nanostructures Qian Li,† Wenxin Niu,‡ Xingchen Liu,§,⊥ Ye Chen,‡ Xiaotong Wu,† Xiaodong Wen,⊥ Zhongwu Wang,# Hua Zhang,‡,* and Zewei Quan†,* Department of Chemistry, Southern University of Science and Technology (SUSTech), Shenzhen, Guangdong 518055, P. R. China. †

Center for Programmable Materials, School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore. ‡

§ Department

of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY 14853, United

States. ⊥ State

Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, P. R. China. #Cornell

High Energy Synchrotron Source (CHESS), Cornell University, Ithaca, New York 14853, United States.

ABSTRACT: Although phase engineering of a noble metal, gold (Au), is of critical importance for both fundamental research and potential application, it still remains a big challenge in wet-chemical syntheses. In this work, we report the irreversible transformation from the hexagonal 4H to face-centered cubic (fcc) phase in Au nanoribbons (NRBs) through high pressure treatment, which has not been discovered in metals. The relative percentage of 4H and fcc phases in the recovered Au NRBs depends directly on the peak pressure applied to the original 4H Au NRBs, enabling a phase engineering of Au nanostructures. Interestingly, compared to the pure 4H Au NRBs, the crystal-phase-heterostructured 4H/fcc Au nanorods require less energy to complete the phase transition process with a lower transition pressure and in a narrower range. Finally, the atom-based transformation pathway during the 4H-to-fcc phase transition is revealed experimentally, which is supported by the first-principle calculations. This work not only demonstrates the stability of 4H Au nanostructure and the pressure-induced 4H-to-fcc transition mechanism, but also provides a strategy for the phase engineering of noble metal nanostructures.

INTRODUCTION Crystal structures of noble metals play a critical role in determining their physicochemical properties, such as chemical stability,1 optical responses2 and catalysis.3 The delicate structure modulation of noble metals has been one active subject of intensive research,4,5 but still remains a big challenge through wet-chemical syntheses.6 Typical noble metals, such as Rh, Ir, Pt, Pd, Ag and Au, crystalize in a highly symmetric and close-packed facecentered cubic (fcc) structure,7 which is a thermodynamically stable phase.8,9 However, as the size of a crystal shrinks to nanometer scale, various kinds of unusual crystal phases might emerge,10,11 showing unique properties and promising applications.6,12 The rational design and synthesis of noble metal nanostructures with unusual crystal phases is thus desired. The recent realization of Au nanoribbons (NRBs) with unusual 4H phase represents one typical example for the exploration of polytypic noble metals.2 In comparison with the characteristic stacking sequence of “ABC” along the [111]fcc direction in the fcc Au, the 4H Au possesses a stacking sequence of “ABCB” along the [001]4H direction. As is known, the ligand exchange2 and noble-metal

coating13 on the 4H Au NRBs are able to induce the 4Hto-fcc phase transformation in solutions. However, a direct observation of the transition pathway from 4H to fcc has not been achieved yet. Therefore, an in-situ investigation on the structural stability of 4H phase and transition mechanism from 4H to fcc phase is fundamentally important. Pressure, as one of three basic thermodynamic parameters, is widely used to study the solid phase transformations,14-17 especially for nanomaterials.18-21 Compared with solution methods, the high pressure technique allows us to obtain the in-situ information of structure modulation of nanomaterials under continuous compression, offering direct evidence for their structural stability and transition process. Herein, we report the systematic study on the 4H-to-fcc phase transition in the 4H Au NRBs through a combination of high pressure angle dispersive X-ray diffraction (ADXRD) and highresolution transmission electron microscope (HRTEM) characterizations as well as first-principle calculations. It is worthy to mention that our result is different from the commonly observed partial dislocations of the closepacked planes in the hexagonal close-packed (hcp)-to-fcc

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phase transitions, especially in metals including cobalt and silver.22,23 In our study, the 4H-to-fcc transition involves the opposite movements of Au atoms in A and C layers to the face centers of their adjacent four Au atoms in (010)4H planes, resulting in the flattening of (112) planes observed with transmission electron microscope (TEM). Furthermore, the 4H-to-fcc structural transition is completed at a much lower pressure in the crystal-phaseheterostructured 4H/fcc Au nanorods (NRs).3,24 EXPERIMENTAL METHODS Sample Syntheses. The 4H Au NRBs used for the high pressure-induced phase transitions were synthesized according to the previous reports with slight modification.2 In a typical synthesis, 442 mL of hexane, 27.5 mL of oleylamine, and 31.25 mL of 1,2dichloropropane were added into a glass bottle and thoroughly mixed. Subsequently, 0.5 g of gold(III) chloride trihydrate were added to the mixture and dissolved by shaking. The glass bottle was then capped and heated in an oven at 58 °C for 16 h. The resulting products were collected by centrifugation (5,000 rpm, 3 min), washed with chloroform 4-5 times, and re-dispersed into 14 mL of chloroform for further experiments. Crystal-phase-heterostructured 4H/fcc Au NRs were synthesized according to our previous report with slight modifications.3 Briefly, after 6 mg of gold(III) chloride hydrate were dissolved in 5 mL of oleylamine, the solution was transferred into a 10 ml glass vial and heated in an oil bath at 70 °C for 17 h. The resultant products were then diluted with an equal volume of a hexane/ethanol mixture o (v/v = 10/1) and centrifuged at 4,000 rpm for 5 min, the obtained sample was dispersed into an equal volume of a hexane/ethanol mixture (v/v = 15/1), and then centrifuged at 4,000 rpm for 3 min. The obtained sample was re-dispersed into an equal volume of a hexane/ethanol mixture (v/v = 15/1) and then centrifuged at 4,000 rpm for 1 min. The final product was re-dispersed into 2 mL of hexane for further experiments. TEM characterizations. TEM images of 4H Au NRBs and 4H/fcc Au NRs before and after compression were captured using FEI Tecnai F30 transmission electron microscope with an accelerating voltage of 300 kV. High Pressure Experiments. High pressure experiments were performed in diamond anvil cells (DACs). Two gem-quality diamond anvils with a culet diameter of 0.4 mm were aligned and assembled into a DAC for pressurization of the samples. The stainless-steel gasket was pre-indented to a thickness of ~50 μm and then drilled with a 140 μm-diameter aperture at the center. The drilled hole serves as the sample chamber during compression (Figure S1). After that, the assynthesized Au nanomaterials were loaded into the compartment without any pressure transmitting media. The pressure within a DAC was calibrated by applying the standard ruby fluorescence technique.25 More experimental details are provided in the Supporting Information.

High pressure ADXRD experiments were conducted at the B1 station of the Cornell High Energy Synchrotron Source (CHESS). The focused monochromatic beam with the wavelength of 0.485946 Å was used as the X-ray source, and a tube collimator with a diameter of 100 μm was used to confine the monochromatic beam. CeO2 powders were used as the standard sample to perform the calibration of geometry parameters. The X-ray diffraction images were recorded by a MAR345 large area detector, and integrated into one-dimensional patterns using Fit2D software.26 ADXRD data analysis. The simulation of ADXRD patterns of 4H and fcc Au phases was performed using commercial Materials Studio 5.0 based on the previously reported structures.2 The X-ray source was chosen as synchrotron with the wavelength of 0.486 Å. Peak profiles were fitted by pseudo-Voigt peak shape function. Other constraints were the implied terms in the program. ADXRD patterns were fitted using combination of Lorentz and Gaussian functions. The fitted results were used to distinguish different phases and determine the evolution of relative peak area ratios. High pressure unit cell information of 4H phase was calculated from the reflections of 4H signal using the UNITCELL software program.27 High Pressure Calculations. High pressure calculations were performed with the plane-wave densityfunctional theory code VASP with the projectoraugmented wave5 (PAW) method.28 The generalized gradient approximation (GGA), designed by Perdew, Burke, and Ernzerhof6 (PBE), was used as the exchangedcorrelation functional. A kinetic energy cutoff of 500 eV was chosen for the plane wave basis set. We used a Gamma centered mesh of 19×19×6 for the 4H phase unit cell and 3×5×2 for the p(1×1) (110) surface slabs. The electronic energy convergence criterion was set to 10-7 eV. Fermi smearing was used for the geometry optimization calculations and the tetrahedron method with Blochl corrections for the energy calculations. The geometry optimizations were stopped when the forces on all the atoms were less than 0.001 eV/Å. The optimized structures were analyzed by the adaptive common neighbor analysis (CNA) method.29 implemented in Ovito to obtain the way of close packing of Au atoms. Furthermore, high pressure was applied to the models using the PSTRESS method in VASP every 2 GPa up to 30 GPa. For the optimization of the slabs at 0 GPa, we used ISIF = 4 in order to maintain the thickness of the vacuum layer. For the geometry optimizations with pressures, the ISIF was set to 3 to allow the relaxation of all the cell parameters and the ionic positions. RESULTS AND DISCUSSION The crystal structure of Au NRBs was determined by the ADXRD pattern at ambient conditions (Figure S2), showing that they crystalize in a hexagonal P63/mmc symmetry (4H phase), with the lattice parameters of a = b = 2.876 Å, and c = 9.480 Å. TEM images of as-prepared 4H


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Journal of the American Chemical Society Au NRBs (Figure 1a and S3a) show their average length of up to tens of micrometers. HRTEM analysis further re-

Figure 1. 4H Au NRBs before compression and after being recovered from 14.3 GPa to 1 atm. (a) TEM and (b) HRTEM images of as-synthesized 4H Au NRBs. (c) Schematic illustration of atom arrangements in Au NRBs with single 4H phase (top) and crystal-phase-heterostructured 4H/fcc (bottom) phases. (d) TEM image of the recovered Au NRB after decompression from 14.3 GPa to 1 atm. (e,f) HRTEM images of the recovered Au NRBs with sections of single 4H (e) and fcc phases (f). Insets: The corresponding fast Fourier transformation (FFT) patterns. veals that 4H Au NRBs grow along the [001]4H direction of hcp Au atoms (Figure 1b,c). The sharp (004)4H diffraction peak of 4H Au NRBs (Figure 2a and S2) represents the preferred growth orientation of NRBs. Note that the diffraction peaks of Au with fcc structure are also detected in the ADXRD pattern (Figure 2b and S2), originating from the inevitable small amount of byproduct, i.e. spherical Au nanoparticles, during the synthesis of 4H Au NRBs (Figure S3b and S3c). These fcc Au nanoparticles adopt a cubic Fm3m structure (Figure S2 and S3b). High pressure ADXRD patterns of Au nanostructures provide direct information for the structural evolution. With continuous increase of pressure from 1 atm to 14.3 GPa, all the diffraction peaks shift to higher angle (Figure 2a and S4), indicative of a pressure-induced lattice shrinkage of both 4H and fcc structures. The obvious broadening of diffraction peaks mainly originates from the presence of large fraction of surface atoms in these 4H Au NRBs, which has been reported in nanoscale systems.18 Continuous progression of both the intensity and position of diffraction peaks is observed below 1.2 GPa, suggesting that 4H and fcc phases are stable. When the pressure goes above 1.2 GPa, the intensities of diffraction peaks of 4H Au NRBs decrease, and simultaneously the fcc Au signals are gradually enhanced (Figure 2b-d). These observations

indicate that the 4H-to-fcc phase transformation occurs in the Au NRBs under external force. To clearly illustrate the progression of this phase transformation, the area ratios of typical diffraction peaks of 4H to fcc phases as a function of pressure are provided in Figure S5. Since the significant overlapping of (004)4H and (111)fcc peaks makes it difficult to determine their peak areas, two welldistinguished peaks of (102)4H and (103)4H are chosen instead, in order to make a quantitative comparison with the (200)fcc peak during this compression process (Figure 2b). It is clearly observed that the peak area ratios of (102)4H/(200)fcc and (103)4H/(200)fcc decrease rapidly over the pressure range of 1.2 and 7.5 GPa (Figure S5), indicative of a 4H-to-fcc phase transformation within Au NRBs. Such a phase transformation turns to be much slower at pressures above 7.5 GPa, suggesting an enhanced repulsion among Au atoms in a much compact structure. The diffraction intensity of 4H phase remains detectable even at the pressure of 14.3 GPa (Figure 2d), indicative of an incomplete 4H-to-fcc phase transformation in this pressure range. Upon releasing pressure, the positions of diffraction peaks shift back to lower angle (Figure 2e), attributing to the decompression-induced volumetric expansion of both 4H and fcc phases. The ratio of the 4H and fcc phases remains almost constant during the decompression



process (blue triangles in Figure S5), indicating the irreversible 4H-to-fcc phase transformation in Au NRBs, which has not been observed in high pressure studies on

metals.30 As is known, high pressure phase transitions of metals are normally reversible, owing to the metastable na-

Figure 2. High pressure structural evolution of 4H Au NRBs. (a) Representative ADXRD patterns of 4H Au NRBs under the pressure from 1 atm to 14.3 GPa. (b-d) Peak fittings of ADXRD patterns obtained at 1 atm (b), 2.7 GPa (c), and 14.3 GPa (d). The red and blue peaks are indexed to the 4H and fcc phases, respectively. (e) Representative ADXRD patterns of 4H Au NRBs during decompression. (f) Peak fitting of ADXRD pattern of the recovered sample after decompression from 14.3 GPa to 1 atm. (g) High pressure evolution of lattice volume of 4H Au during compression. Inset: Schematic illustration of the unit cell of 4H Au (a = b) (h,i) High pressure evolution of lattice parameters, a or b axis (h) and c axis (i), of 4H Au during compression. The fitted black curves are only used for clarification. ture of high-pressure phase at ambient conditions. However, in our work, since the fcc Au structure obtained during the 4H-to-fcc phase transformation at high pressure is more stable, this transformation is irreversible during decompression, which is confirmed by TEM characterizations and corresponding fast Fourier transformation (FFT) patterns. As shown in Figure 1d, the 4H phase (Figure 1e) coexists with the newly formed fcc phase (Figure 1f) in the recovered Au NRB, indicating that the treatment with a peak pressure of 14.3 GPa only

results in partial phase transformation of Au NRBs from 4H to fcc phase (Figure 2c, 2d, and 2f). In order to investigate the stability of 4H phase and understand the 4H-to-fcc transition mechanism, the dependence of lattice parameters on external pressure was studied. Upon compression to 14.3 GPa, the lattice volume of 4H unit cell decreases and does not show an obviously abrupt change (Figure 2g), indicative of a continuous contraction of 4H phase. Fitting experimental pressure-volume (P-V) datasets into the third-order


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Journal of the American Chemical Society Birch−Murnaghan equation of state below ~4 GPa generates the bulk modulus (B0) of 106.01 GPa and pressure derivative (B0’) of 21.93 (Figure S6). In the

comparison with the bulk Au with fcc structure (B0 = 172.5 GPa, and

Figure. 3. High pressure ADXRD patterns and TEM results of crystal-phase-heterostructured 4H/fcc Au NRs. (a) Representative ADXRD patterns of 4H/fcc Au NRs at different pressures. (b-e) Peak fittings of ADXRD patterns of 4H/fcc Au NRs at 1 atm (b), 6.2 GPa (c) and 14.4 GPa (d) during compression, as well as the recovered Au NRs at 1 atm after decompression from 15.7 GPa (e). (f) Representative TEM image of as-synthesized 4H/fcc Au NR. (g) TEM image of the recovered Au NR after decompression from 15.7 GPs to 1 atm. B0’ = 5.4)31 and Au microcrystals with a body-centered orthorhombic structure (B0 = 138.3 GPa, and B0’ = 8.3)32, such smaller B0 and larger B0’ values observed in the 4H Au NRBs suggest it is more sensitive to compression. Once the pressure is greater than 1.2 GPa, the lattice parameters of a and b start to show a slight expansion of ~0.01 Å (Figure 2h). Such a discontinuous evolution behavior in these lattice axes confirms that the pressureinduced 4H-to-fcc phase transformation occurs above 1.2 GPa (Figure 2a). Therefore, the Au atomic lattices in (001)4H plane (a and b axes of 4H unit cell) require slight expansion to induce this structural transformation. Above 2.7 GPa, the lattice axes of a and b in 4H phase decrease, owing to the pressure-induced structure contraction. In contrast, the length of c axis continuously decreases until 7.5 GPa. However, a gradual increase of the c value above 7.5 GPa (Figure 2i) is expected from the enhanced repulsion between Au atoms at elevated pressures, which is consistent with the slowly decreased phase ratio of 4H to fcc in this region (Figure S5). The aforementioned

investigation demonstrates the incomplete 4H-to-fcc transformation at 14.3 GPa. Over the course of continuous pressurization to 30.0 GPa, it is observed that the 4H Au completely transforms to fcc phase at ~26.1 GPa (Figure S7a and S7b). Furthermore, when the pressure is released from 30.0 GPa to ambient conditions, the pure fcc phase is maintained, as confirmed by both the ADXRD and TEM results (Figure S7c and S8), further confirming the claim of this irreversible 4H-to-fcc phase transformation. It is different from the commonly observed phase transitions in metals.25 Different from the pure 4H Au NRBs, the crystal-phaseheterostructured 4H/fcc Au nanorods (NRs) synthesized based on our previous report3 were used to explore the effects of interfaces between 4H and fcc phases on the stabilities of metastable 4H phase and pressure-induced irreversible 4H-to-fcc phase transition (Figure S9). A typical ADXRD pattern shows that the 4H/fcc Au NRs include comparable diffraction intensities of 4H and fcc



phases (Figure 3a, 3b and S10). HRTEM image (Figure 3f) reveals that 4H and fcc phases are alternating along the longitudinal direction. Figure 3a shows the pressureinduced ADXRD evolution of 4H/fcc Au NRs up to 15.7

GPa. The 4H-to-fcc phase transition occurs at the first pressure point of 0.7 GPa, evidenced by the rapidly decreased peak

Figure 4. Proposed 4H-to-fcc phase transition mechanism based on HRTEM and calculation results. (a) HRTEM image of as-synthesized 4H Au NRB. Au atoms marked with different colors corresponding to different stacking layers in 4H phase (red: layer A, yellow: layer B, and blue: layer C). (b) HRTEM image of recovered Au NRB with fcc structure. (c) Schematic illustration of 4H unit cell with highlighted (112)4H plane. (d) Schematic illustration of the 4H-to-fcc phase transition in 4H unit cell. (e) Schematic illustration of the 4H-to-fcc phase transition viewed along the (001)4H (left) and (100)fcc planes (right). The red dashed lines represent the same set of atoms in Au NRBs before (4H phase) and after the pressure treatment (fcc phase). Note that the red Au atoms are blocked by the blue ones along this viewing direction, as shown in Figure S12. (f) Calculated high pressure structures of 4H Au at 0 GPa (left), 2 GPa (middle) and 4 GPa (right). Methylamine molecules cover the surface of 5-layer slab model of 4H Au NRBs with exposure of the (110) surface. area ratios of (102)4H/(200)fcc and (103)4H/(200)fcc (Figure S11 and 3a-3c). In addition, compared with 26.1 GPa for 4H Au NRBs, the 4H-to-fcc phase transition is completely realized at a considerably lower critical pressure of 14.4 GPa for 4H/fcc Au NRs (Figure 3d). After fully releasing

pressure to ambient conditions, Au NRs with a single fcc phase can be obtained (Figure 3e and 3g). Such results demonstrate that the 4H/fcc Au NRs require less energy for the accomplishment of irreversible 4H-to-fcc transition under compression. As is known, for solid-solid


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Journal of the American Chemical Society phase transitions, the interface between different structures can act as an initiation site to facilitate the occurrence of phase transition under external force, which has been reported in other heterostructures.33 Therefore, the high pressure instability of 4H/fcc Au NRs may arise from the presence of abundant 4H/fcc phase interfaces as the initiation sites, thus facilitating the 4Hto-fcc phase transition. Experimentally, the 4H-to-fcc phase transformation can be achieved on Au NRBs to engineer the phases of Au nanostructures. In order to understand the underlying mechanism of the 4H-to-fcc phase transformation and fully uncover the microscopic transition pathway, HRTEM characterizations are performed on staring 4H Au NRBs (Figure 4a) and recovered fcc Au NRBs (Figure 4b). The orientations of Au NRBs shown in Figures 4a and 4b are adjusted to be identical to directly correlate their atomic arrangements in 4H and fcc phases. It is worth mentioning that the recovered Au NRBs and NRs exhibit puckered surface planes, which possibly introduce deviated TEM projections of these Au nanostructures. Therefore, there is a slight distortion in the high pressure recovered fcc lattice in TEM image. The Au atoms with “ABCB” stacking in 4H NRBs are marked with different colors (red for layer A, yellow for layer B, and blue for layer C), corresponding to the ones in 4H unit cell (Figure 4a and 4c). As shown in Figure 4b, the close-packed (111)fcc planes with a different stacking sequence of “ABC” along [111] axis dominate in the recovered fcc Au NRBs. Such changes are illustrated by the atomic variations on (112)4H planes, as highlighted in Figure 4a. In a 4H unit cell, two Au atoms in A and C layers are located on the opposite side of (112)4H plane at ambient conditions (Figure 4c). The lattice planes of (112)4H in 4H structure are converted into the (111)fcc plane in fcc structure (Figure 4b). It can be deduced that the compression drives these two atoms in A and C layers to gradually approach the face centers of adjacent ac planes (Figure 4d and 4e), resulting in slight expansion of a and b axes between 1.2 and 2.7 GPa (Figure 2h). Meanwhile, with continuous structural contraction, the persistent insertion of Au atoms in A and C layers also calls for more space between adjacent B layers, leading to a little enlargement of the c value above 7.5 GPa (Figure 2i). As illustrated in Figure 4e, such atomic movements are also accompanied by a simultaneous change of the 4H unit cell parameters (axes angles and lengths), resulting in the final structural transformation of 4H into fcc structure (Figure 4e and SX Movie 1 in Supporting Information). These direct observations demonstrate that the pressure-induced 4H-to-fcc phase transformation in Au NRBs involves variation of the close-packed plane from (001)4H to (111)fcc, similar to the wurtzite-to-rock salt phase transformations observed in semiconductor nanocrystals.34 Moreover, this observation is quite different from the well-known hcp-to-fcc transition in metals, such as Co22 and Ag23, which normally proceeds through the motion of partial dislocations on the closepacked planes.

To further confirm the aforementioned phase transition mechanism, high pressure calculations of 4H Au NRBs are performed based on the density functional theory (DFT). As 4H Au NRBs mainly expose the (110) surfaces (Figure 1), a 5-layer p(1×1) (110) slab model is used to simulate these 4H Au NRBs.35 The slabs are replicated in the c direction with a vacuum distance of 15 Å to avoid interaction between slabs. Meanwhile, methylamine molecules with 1/4 surface coverage are brought to the surface, to simulate the long-chain oleylamine molecules capped on the 4H Au NRBs (Figure S13). The calculated relation of enthalpy as a function of pressure (Figure S14) reveals an apparent discontinuity at the enthalpic energy of 2.68 eV in the range of 2 - 4 GPa, implying the possible occurrence of the 4H-to-fcc phase transformation. This calculated pressure range is in good agreement with that observed in our experiments (Figure 1a). In addition, the computational simulations reveal that compression causes flattening of (112)4H planes, which turns into the (111)fcc planes of Au at 4 GPa (Figure 4f). This atomic sliding pathway is also consistent with the TEM observations (Figure 4a and 4b). Further calculation between the energy of high pressure and ambient ligand for the 4H-to-fcc phase transition should be performed in the future. CONCLUSIONS In summary, the 4H-to-fcc phase transformation of Au nanostructures has been achieved via the application of high pressure, enabling the phase engineering of Au nanostructures. Both experimental and computational results reveal the atomic movement pathway in the pressure-induced 4H-to-fcc phase transition, which is distinct from the well-known hcp-to-fcc phase transition in other metals. Our work illustrates an opposite shift of Au atoms in A and C stacking layers to the face centers of nearest four Au atoms in the ac plane. In addition, the phase interfaces in the crystal-phase-heterostructured 4H/fcc Au NRs can facilitate the sluggish 4H-to-fcc phase transformation. This work not only provides insights into the structural stability and phase transformation of Au nanostructures, but also offers a new strategy for using pressure to engineer the crystal phase content of noble metal nanomaterials, which could be used for crystal phase-based promising applications in catalysis, surface enhanced Raman scattering, waveguide, photothermal therapy, sensing, clean energy, etc.13,36-39

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: Supporting figures and movie. (PDF, avi)

AUTHOR INFORMATION Corresponding Author *[email protected] (ZQ)



Y.; Fan, Z.; Wu, X.-J.; Chen, J.; Luo, J.; Li, S.; Gu, L.; Zhang, H. Nat. Chem. 2018, 10, 456.

*[email protected] (HZ)

Notes The authors declare no competing financial interests.

ACKNOWLEDGMENT

(15) Mao, W. L. Nat. Mater. 2015, 14, 466.

This work was supported by the National Natural Science Foundation of China (NSFC) (No. 51772142, 11604141), Shenzhen Science and Technology Innovation Committee including fundamental research projects (No. JCYJ20170412152528921) and peacock technology innovation project (No. KQJSCX20170328155428476), Development and Reform Commission of Shenzhen Municipality (Novel Nanomaterial Discipline Construction Plan), and start-up fund and Presidential fund from SUSTech. CHESS at Cornell University is supported by the NSF award DMR-0936384. It was also supported MOE under AcRF Tier 2 (MOE2015-T2-2057; MOE2016-T2-2-103; MOE2017-T2-1-162) and AcRF Tier 1 (2016-T1-001-147; 2016-T1-002-051; 2017-T1-001-150; 2017-T1002-119), and NTU under Start-Up Grant (M4081296.070.500000) in Singapore. We would like to acknowledge the Facility for Analysis, Characterization, Testing and Simulation, Nanyang Technological University, Singapore, for use of their electron microscopy (and/or Xray) facilities. We appreciate Prof. Ronald Hoffmann in Cornell University for his invaluable suggestions and comments on this work.

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Pressure-Induced Phase Engineering of Gold Nanostructures

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