Revealing the Phase Segregation and Evolution Dynamics in Binary Nanoalloys via Electron Beam-Assisted Ultrafast Heating and Cooling

Abstract

Gas-phase synthesized binary nanoparticles (NPs) possess ultraclean surfaces, which benefit versatile uses in sensors and catalysts. However, precise control of their configuration and properties is still a big challenge because the growth mechanism and phase evolution dynamics in these NPs are very hard to unveil. Here, we report a strategy to investigate the phase evolution dynamics in binary NPs by using e-beam assisted ultrafast local heating and cooling inside a transmission electron microscope. With this strategy, the phase segregation and corresponding shape evolution of PbBi NPs are in situ revealed. It is found that the as-prepared PbBi alloy NPs will transform into heterostructures under e-beam stimulated structural relaxation, leading to the formation of featured Janus configurations with faceted Bi polyhedron parts and intermetallic hemisphere parts. During phase segregation, Pb 1 Bi 1 and Pb 7 Bi 3 phases are captured and identified, and a model of phase and shape evolution of PbBi nanoalloys is developed and contrasted with that of their bulk counterparts. These findings benefit the understanding of the phase dynamics of binary NPs and can provide in-depth information for engineering their structures for practical applications.

Surface Chemistry-Dominated Shape and Phase Transitions in PbBi Binary Nanoparticles: Implications for the Stability of Nanomaterials in Application

“…To have NPs with ultra-clean surfaces, an in situ evaporation-and-deposition (EAD) method , was used for sample preparation. The details of the EAD method have been reported in a previous work, and the main idea of this method is to fabricate NPs directly inside the transmission electron microscope chamber (under high vacuum conditions) so as to prevent surface contamination, absorption, or oxidation.…”

“…As can be seen, the PbBi NPs have a solidsolution phase and a spherical shape, and no oxidation layer can be found on the smooth surfaces (see Supporting Information Figure S1 for more information). According to the phase diagram of the Pb−Bi alloy, 39 this solid-solution phase tends to undergo phase segregation under the thermal stimulus, and a Janus structure consisting of an ε-Pb 7 Bi 3 hemisphere and a faceted Bi polyhedron will form subsequently, 37 as shown in Figure 1b. Interestingly, when these phase-separated NPs were further subjected to oxidation in air, as shown in Figure 1c, dealloying occurred in the ε-Pb 7 Bi 3 phase together with the disappearance of the facets on the Bi parts.…”

“…Once the holey carbon film dried, it was put into the holder of the transmission electron microscope to perform the in situ EAD process. The parameters employed and details of the process can be found elsewhere. , For a short surface treatment, the obtained PbBi NPs were exposed to air at room temperature for several hours. Then, they were put back into the transmission electron microscope chamber for further characterization.…”

Controllable fabrication of hollow In2O3 nanoparticles by electron beam irradiation

“…In NPs were synthesized using electron beam irradiation inside the TEM. [22][23][24] After intense electron beam irradiation, In NPs with a wide size distribution (Fig. 1b) were formed around initial InP mircoparticles due to either electron-beam heating or electrostatic charging/discharging.…”

STEM in situ thermal wave observations for investigating thermal diffusivity in nanoscale materials and devices

“…While SThM and near-field light adopting techniques are limited to surface measurement, TDTR and other methods using a laser as a heat source have challenges in achieving a spatial resolution of sub-10 nm. To enhance local heating capability, adopting an electron beam of a transmission electron microscope (TEM) as a nanosized heat source has been reported (16)(17)(18). So far, using the electron energy loss spectroscopy (EELS) technique, temperature mappings have been obtained by detecting the shifting of the plasmon peak (19), phonon peak (20), and the ratio between the intensity of gain and loss peaks (21,22).…”