Metastable phase formation in the Au-Si system via ultrafast nanocalorimetry

Zhang, M.; Wen, Jian; Efremov, Mikhail Yu.; Olson, E. A.; Zhang, Z. S.; Hu, Liusen; Rama, Lito P. de la; Kummamuru, Ravi K.; Kavanagh, K. L.; Ma, Zheng; Allen, L. H.

doi:10.1063/1.4712342

Cited by 26 publications

(13 citation statements)

References 48 publications

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“…Various metastable Au–Si phases are known to form as intermediate states during rapid quenching of Au–Si liquid . The metastable phase observed in Figure S5 in the Supporting Information is consistent with one of these phases, δ 1 (Supporting Information).…”

supporting

confidence: 57%

Surface Crystallization of Liquid Au–Si and Its Impact on Catalysis

Panciera

Tersoff²,

Gamalski

et al. 2018

Advanced Materials

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is unique in forming a 2D crystalline compound at its surface, with a fixed atomic-scale thickness, over a range of temperature. While this layer has not been imaged directly, diffraction studies have established that an ordered bilayer (the low-temperature (LT) phase) exists up to 12 °C above the eutectic temperature. [2,8] (A higher temperature phase has also been detected, although its properties are less clear. [9,10] ) At present there is no straightforward explanation for this unique behavior. Ordered surface phases have been explained by surface prefreezing, [11] a phenomenon that is analogous to the wellknown surface premelting. However, an ordered prefreezing layer is expected to be present only very near the transition temperature and to have a thickness that diverges as the temperature approaches the transition temperature, both of which are inconsistent with the behavior of Au-Si. The ordered surface phase in Au-Si also cannot be explained as a solute coming out of solution and wetting the surface, as can occur in dilute Ga solutions. [6] Here, we use in situ transmission electron microscopy (TEM) to observe directly the formation of a crystalline 2D compound at the surface of liquid Au-Si. By varying both temperature and composition we find that the 2D phase can be stable over a surprisingly large range, over 150 °C, extending above and below the eutectic temperature. We develop a simple thermodynamic model that explains the wide stability range and composition dependence. Given the persistence of the surface ordering, we explore its effects on critical aspects of the behavior of Au-Si. We find that the surface layer plays a key role in the pathway of eutectic decomposition of Au-Si into solid Au + solid Si on cooling, and also that it is the root cause of the dramatic changes observed in the catalytic properties of Au-Si on cooling. We derive a strategy for controlling the presence of the surface phase as a tool in nanostructure fabrication.Surface ordering on droplets of Au-Si of different dia meters is shown in Figure 1a,b and Movie S1 in the Supporting Information. These high spatial and temporal resolution data (see the Supporting Information) were recorded by in situ heating of Si substrates decorated with Au nanoparticles, with or without exposure to the Si source gas disilane (Si 2 H 6 ). On reaching the Au-Si eutectic temperature T E = 363 °C, [12] the Au reacts with Si to form Au-Si liquid droplets. Imaging the surfaces of these droplets in profile view (Figure 1a) shows that there are two well-defined crystalline layers at the surface. The ordering can also be detected in projection over the entire droplet area in Figure 1a. In the smaller droplet shownIn situ transmission electron microscopy reveals that an atomically thin crystalline phase at the surface of liquid Au-Si is stable over an unexpectedly wide range of conditions. By measuring the surface structure as a function of liquid temperature and composition, a simple thermodynamic model is developed to explain the stability of the or...

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supporting

confidence: 57%

Surface Crystallization of Liquid Au–Si and Its Impact on Catalysis

Panciera

Tersoff²,

Gamalski

et al. 2018

Advanced Materials

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“…As a result of that mechanism, heterogeneous nanostructures of Au containing Si phase inclusions are formed. Such nanostructures have been observed in several works describing directional solidification of Au-Si eutectics [10,13,14,28].…”

Section: Resultsmentioning

confidence: 65%

Substrate Dependence in the Formation of Au Nanoislands for Plasmonic Platform Application

et al. 2019

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In this work, the influence of the various substrates on Au nanoisland formation has been studied. Nanostructures were obtained via annealing of thin Au films. In order to determine nanoisland formation mechanisms, correlation between an initial film thickness and temperature of formation, shapes, and dimensions of nanostructures was examined. For the surface morphology studies, nanograin structure, and chemical composition analysis, SEM, HR TEM, and EDS measurements were performed, respectively. Morphology studies showed that the temperature at which nanostructures form varies for different substrates, which indicates high impact of the substrate material on the nanostructure formation. In the case of silicon substrate, besides the phenomenon of spinodal dewetting, the effect of eutectics on the nanostructures was additionally taken into consideration.

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“…During the formation of nanostructures from thin metallic films, it is necessary to take into account, in addition to dewetting, also directional solidification of eutectics [3,5,19–21]. In the gold–silicon system, an Au-rich eutectic melts at a temperature of 363 °C.…”

Section: Resultsmentioning

confidence: 99%

Au–Si plasmonic platforms: synthesis, structure and FDTD simulations

Gapska¹,

Łapiński²,

Syty³

et al. 2018

Beilstein J. Nanotechnol.

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Plasmonic platforms based on Au nanostructures have been successfully synthesized by directional solidification of a eutectic from Au and the substrate. In order to determine homogeneous shape and space distribution, the influence of annealing conditions and the initial thickness of the Au film on the nanostructures was analyzed. For the surface morphology studies, SEM and AFM measurements were performed. The structure of platforms was investigated using XRD and XPS methods. Structural investigations confirmed, that nanostructures consist of metallic Au, growing along the [111] direction. The most homogeneous seems to be the platform obtained by solidification of a 2.8 nm Au film, annealed at 550 °C for 15 min. This sample was subsequently chosen for theoretical calculations. Simulations of electromagnetic field propagation through the produced samples were performed using the finite-difference time domain (FDTD) method. The calculated absorbance, as a result of the FDTD simulation shows a quite good agreement with experimental data obtained in the UV–vis range.

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Metastable phase formation in the Au-Si system via ultrafast nanocalorimetry

Cited by 26 publications

References 48 publications

Surface Crystallization of Liquid Au–Si and Its Impact on Catalysis

Surface Crystallization of Liquid Au–Si and Its Impact on Catalysis

Substrate Dependence in the Formation of Au Nanoislands for Plasmonic Platform Application

Au–Si plasmonic platforms: synthesis, structure and FDTD simulations

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