Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2017 Feb 13:8:14462.
doi: 10.1038/ncomms14462.

In situ study on atomic mechanism of melting and freezing of single bismuth nanoparticles

Affiliations

In situ study on atomic mechanism of melting and freezing of single bismuth nanoparticles

Yingxuan Li et al. Nat Commun. .

Abstract

Experimental study of the atomic mechanism in melting and freezing processes remains a formidable challenge. We report herein on a unique material system that allows for in situ growth of bismuth nanoparticles from the precursor compound SrBi2Ta2O9 under an electron beam within a high-resolution transmission electron microscope (HRTEM). Simultaneously, the melting and freezing processes within the nanoparticles are triggered and imaged in real time by the HRTEM. The images show atomic-scale evidence for point defect induced melting, and a freezing mechanism mediated by crystallization of an intermediate ordered liquid. During the melting and freezing, the formation of nucleation precursors, nucleation and growth, and the relaxation of the system, are directly observed. Based on these observations, an interaction-relaxation model is developed towards understanding the microscopic mechanism of the phase transitions, highlighting the importance of cooperative multiscale processes.

PubMed Disclaimer

Conflict of interest statement

The authors declare no competing financial interests.

Figures

Figure 1
Figure 1. The metastable state and crystallization of a Bi nanodroplet.
(a,b) Sequential snapshots of HRTEM imaging showing the metastable state of the Bi nanodroplet. The blue arrows in b indicate the domains still retained in liquid phase. (c,d) Sequential snapshots of HRTEM imaging showing fast crystallization of the nanodroplet after the induction period. The insets show the corresponding FFT patterns of the nanoparticle. (e) Schematic illustration of the reversible freezing/melting of the Bi nanoparticle. The scale bar in a is 5 nm, which applies to ad. The time labels correspond to when the video snaps were taken.
Figure 2
Figure 2. Point defect induced melting of Bi nanocrystal.
(ae,kn) Sequential snapshots of HRTEM imaging showing the microscopic structural details of melting process. (fj) The enlarged images corresponding to the regions as marked by the yellow squares in ae. The lattice fringes in f,g are highlighted by red lines. The dashed blue circle in h indicates a vacancy. The blue arrow in g indicates the atomic column before transforming to the vacancy in h. The area marked in dashed blue line in i indicates the gap formed by the coalescence of the defects. The areas marked in dashed blue lines in j indicate the domains in liquid-like structure with an irregular shape. The insets of ae and kn show the corresponding FFT patterns of the nanoparticle. The scale bar in a is 5 nm, which applies to ae and kn. The scale bar in f is 1 nm, which applies to fj.
Figure 3
Figure 3. Crystallization of a Bi nanodroplet by an intermediate ordered liquid.
(ad,fh) Sequential snapshots of HRTEM imaging showing a crystallization through transformation of ordered liquid structure. The insets show the corresponding FFT patterns of the nanoparticle. The spots indicated by yellow circles in the FFT patterns in bd reflect the formation of the periodic structure. The areas marked in dashed blue lines in f,g indicate the domains in disordered structure. The enlarged images of the regions as marked by the yellow squares in d,h are shown in e,i, respectively. The part that cannot transform into the well crystallized phase is indicated by the dashed orange line. The scale bar in a is 5 nm, which applies to ad,fh. The scale bar in e is 1 nm, which applies to e,i.
Figure 4
Figure 4. Quantifying the phase transitions of the nanoparticle.
The amount of crystalline order was measured from the integrated profiles taken from the 2D FFT images. The 2D FFT images in Figs 2 and 3 were transformed to FFT spectra by the Fit2D program (see details in Supplementary Fig. 9). The distinctive peaks on the integrated profiles were produced by pixel intensities of the spots in the FFT patterns. (a,b) The intensity of the left-most peak in the integrated profile, I, corresponds to the time labels in Figs 2 and 3, respectively.

References

    1. Tabazadeh A., Djikaev Y. & Reiss H. Surface crystallization of supercooled water in clouds. Proc. Natl Acad. Sci. USA 99, 15873–15878 (2002). - PMC - PubMed
    1. Jacobson L. ,C. & Molinero V. Can amorphous nuclei grow crystalline clathrates? The size and crystallinity of critical clathrate nuclei. J. Am. Chem. Soc. 133, 6458–6463 (2011). - PubMed
    1. Vekilov P. G. Nucleation. Cryst. Growth Des. 10, 5007–5019 (2010). - PMC - PubMed
    1. Shpyrko O. et al.. Surface crystallization in a liquid AuSi alloy. Science 313, 77–80 (2006). - PubMed
    1. Samanta A., Tuckerman M. E., Yu T.-Q. & Weinan E. Microscopic mechanisms of equilibrium melting of a solid. Science 346, 729–732 (2014). - PubMed

Publication types

LinkOut - more resources