Malcolm Turnbull proposed half a century ago that the question of whether all materials could form a glass state remains unresolved to this day. The vitrification of metal into a vitreous state has been the subject of scientific inquiry since the mid-20th century. Although Turnbull and Cohen theoretically proposed the possibility of vitrifying pure metals, practical results are still limited. Most notably, FCC and HCP metals are able to resist vitrification due to rapid nucleation and crystallization.
Vitrification of gold, which is notoriously difficult to vitrify. Academician Wang Weihua and Prof. Ke Haibo of the Songshan Lake Materials Laboratory, Prof. Bai Haiyang of the Institute of Physics of the Chinese Academy of Sciences, and Prof. Zhou Jihan of Peking University jointly reported the vitrification of gold (which is notoriously difficult to vitrify) and several similar close-packed face-centered cubic and hexagonal metals using picosecond pulsed laser ablation in liquid media. Vitrification occurs by rapid cooling during laser ablation and inhibition of nucleation by liquid media. Using this method, a large number of atomic configurations can be generated simultaneously, including glassy configurations, from which stable glassy states can be sampled. Simulations show that the good stability of monoatomic metals is due to the strong topological frustration of icosahedral clusters. This work breaks the limitation of the ability to form glass states of matter, shows that vitrification is an intrinsic property of matter, and provides a strategy for the preparation and design of glass states of metal from the perspective of atomic configuration. The research results were published in the latest issue of Nature Materials under the title "Breaking the vitrification limitation of monatomic metals".
【Strategy Design】The researchers used picosecond pulsed laser to ablate bulk metal targets in ethanol, which was used as a solvent and cooling medium. The process achieves rapid cooling rates of 1010 and 1013 K/s, which promote the formation of small liquid metal clusters, which are subsequently vitrified into monoatomic metallic glasses (MMG) nanoparticles (NPs). A schematic diagram of the laser-assisted ultrafast quenching method in ethanol media is shown in Figure 1a. The unit includes a picosecond pulsed laser for melting and quenching metal clusters in a liquid environment. High-resolution transmission electron microscopy (HR-TEM) image (Figure 1b) showing fully amorphous, partially amorphous, and crystalline Au nanoparticles. Fast Fourier transform (FFT) for each NP type, confirming amorphous or crystalline properties (Figure 1c). Electron energy loss spectroscopy (EELS) spectra of Au NPs, indicating purity and minimal contamination (Figure 1d-g). HR-TEM and EELS spectra of Ru NP, confirming its amorphous and monoatomic properties (Fig. 1h-i).
Figure 1. Instructions for the preparation of laser-assisted ultrafast quenching methods in ethanol media and fcc (Au) and hcp (Ru) MMG NPs observed the transformation of the amorphous region of gold MMG into a crystal structure under electron beam irradiation, providing insight into the stability and transition mechanisms of vitrified metals (Figure 2). Figure 2a shows the transition from disordered to ordered regions in the Au MMG during electron irradiation. The crystallites grow epitaxial along the boundary, causing the amorphous region to be depleted and merge with the crystalline region. Due to the high voltage and sufficient electron dose, most of the amorphous gold (A-Au) regions (marked in red) are transformed into face-centered cubic gold crystals (marked in blue). Coalescence also indicates that the amorphous region is pure gold. Similar transitions were observed on a single Au (Figure 2b) and a Ru MM GNP (Figure 2c). These glass-to-crystal transitions confirm that single gold and ruthenium metals are vitrified by this method.
Figure 2. To demonstrate the universality of the method, the authors systematically investigated the feasibility of vitrifying more single-atom metals, including metals with BCC, HCP, and FCC crystal structures. Applying this method, the authors vitrified more than a dozen (17 in total) monoatomic metals into a vitreous state and obtained various MM GNPs (Figure 3). Figures 3a-d show the results for bcc metals iron (Fe), vanadium (V), Ta, and tungsten (W), respectively, which can also be vitrified by other methods7,11. Figure 3e-h shows MMG nanoparticles vitrified by HCP metals hafnium (Hf), cobalt (Co), zirconium (Zr), and Ru, respectively. Figure 3i-p shows more MMGs produced from fcc metals, including the main group metals (aluminum (Al) and germanium (Ge)) and transition group metals (Pd, iridium (Ir), silver (Ag), Ni, copper (Cu), and platinum (Pt)).
Figure 3. Extensive preparation of MMG NPs from monoatomic metals, including bcc, hcp, and fcc metals, to illustrate the effects of liquid media during the cooling phase, the authors performed MD simulations of an Au model system with two different types of substrates. A nanoparticle is located on an amorphous matrix, similar to uncontaminated conditions in a liquid medium; The other is located on a crystal substrate (fcc(100) and fcc(111)) that provide heterogeneous nucleation. The experimental results show that the glass transformation of fcc monoatomic metals can be achieved at a very similar cooling rate (1013Ks-1), which indicates an important contribution of the liquid medium to the formation of MMG, i.e., an ultra-fast cooling rate, inhibiting heteronucleation and promoting glass formation. The authors prepared a schematic diagram to compare the container-free/uncontaminated conditions with the contaminated treatment boundary conditions during rapid cooling of AuNP (Figure 4b). The simulations are consistent with the experimental observation that your FCC metals, including Au, can be vitrified in container-free/uncontaminated conditions during a rapid cooling process. In addition, reducing the sample size to generate nanoscale particles by this method can reduce the likelihood of encountering contaminants in these small volumes, thereby reducing the likelihood of heteronucleation, which promotes the formation of amorphous structures. Using this method, the authors can simultaneously obtain a large number of nanoparticles with different atomic configurations and distributed energies during a batch of preparations. Extensive studies of regenerated and ultra-stable glass have shown that the stability of glass can be significantly altered by adjusting the topological frustration of the structure. Glass stability is inherently structural. A key issue is to discover the structural basis for the stability of the control configuration. Therefore, MD simulations were performed to explore the effect of atomic configuration on the stability of glass. To better understand this problem, the authors propose that MMGNPs with different stability are located in different basins of PEL (Fig. 4c), which shows the configuration dependence of glass stability. These stable amorphous configurations may be located in local deep basins of PEL (as shown in Positions A and C in Figure 4c). As shown in Figure 4d, unstable configurations (e.g., configuration I) crystallize within 0.1 ns, while stable configurations (e.g., configuration II) remain amorphous at all times. Configurations I and II are located in two different basins of PEL (Figure 4c). When relaxed at the same temperature, configuration I can easily fall into the deep basin of the crystal as it passes through the small energy barrier, while configuration II can stabilize in a metastable basin. Configuration II exhibits a higher resistance to opacity than Configuration I, suggesting that there can be some specific atomic stacking in Configuration II to improve stability. As shown in Figure 4e, the cluster distribution of atoms shows some differences between stable and unstable configurations. The atomic structure of the two glasses is shown in Figure 4f, where icosahedral clusters are shown.
Figure 4. MD Simulations to Reveal the Influence and Stability of Liquid Media【Summary】In this paper, we propose the process of glass transformation of face-centered cubic gold (fcc AU) into glass, which also occurs on other face-centered cubic (fcc), hexagonal cubic (HCP), and face-centered cubic (BCC) single-atomic metals. The formation of Au MMG is attributed to rapid cooling and inhibition of heterogeneous nucleation. Rapid cooling can be achieved during ultrafast pulsed laser ablation in liquids, where the appropriate liquid medium is critical for the vitrification of your crystal plane cubemetal. These two advantages provide an ideal environment for amorphization and greatly inhibit the heterogeneous nucleation and growth of crystals. This strategy can generate a library of atomic configurations for obtaining MMGs with different stability, some of which may be very stable.
--Testing Services--
Source: Frontiers of Polymer Science