Size- and composition-controlled intermetallic nanocrystals via amalgamation seeded growth

Abstract

Intermetallic nanocrystals are a large family of emerging materials with extensive applications in many fields. Yet, a generalized synthetic method for intermetallic nanocrystals is lacking. Here, we report the development of a colloidal synthesis method based on amalgamation of monometallic nanocrystal seeds with low–melting point metals. We use this approach to achieve crystalline and compositionally uniform intermetallic nanocrystals of Au-Ga, Ag-Ga, Cu-Ga, Ni-Ga, Pd-Ga, Pd-In, and Pd-Zn compounds. We demonstrate both compositional tunability across the phase spaces (e.g., AuGa2, AuGa, Au7Ga2, and Ga-doped Au), size tunability (e.g., 14.0-, 7.6-, and 3.8-nm AuGa2), and size uniformity (e.g., 5.4% size deviations). This approach makes it possible to systematically achieve size- and composition-controlled intermetallic nanocrystals, opening up a multitude of possibilities for these materials.

Synthesis of PtSn4 Intermetallic Nanodisks through a Galvanic Replacement Mechanism

“…Temperature is a key factor in colloidal synthesis, especially in the intermetallic formation process. 29 As mentioned above, high temperatures (over 350 °C for the bulk PtSn 4 intermetallic phase 13 ) are usually required to overcome the energy barriers for forming atomic ordering. In the developed galvanic replacement synthetic system, the PtSn 4 intermetallic phase was formed under mild temperatures, from 60 to 120 °C.…”

Solution–Liquid–Solid Growth of One-Dimensional Metal-Oxide Nanostructures Assisted by Catalyst Design

“…Gold NPs (Figure S1) were alloyed with the metallic component of the desired metal oxide (i.e., Au-In and Au-Sn alloys; TEM images in Figure a,b, respectively). The alloy formation can be explained by either the amalgamation of gold that serves as the seed in a seeded growth mechanism or by the diffusion of the reduced metal precursor into the gold NP. The use of gold provides better chemical stability and avoids fast oxidation compared to pure low-m.p.…”

Engineering of Oxide Protected Gold Nanoparticles

“…As illustrated by Figure 1a, the first step is to synthesize Au− Ga NPs. According to our amalgamation approach, 35 we use Ga 2 (NMe 2 ) 6 as a Ga precursor and introduce it into a heated solution of Au seeds, where it undergoes thermolysis. The resulting liquid Ga accumulates on the surface of Au seed and diffuses into the particle, forming a homogeneous Au−Ga alloy.…”

“…% Ga concentration, meaning that we work with Gadoped Au NPs as well as intermetallic Au−Ga phases. 35 As an oxidizing agent, we select 4-Methylpyridine N-oxide (MPNO) and dissolve it in octadecene. 36 We then carry out a controlled oxidation of Au−Ga NPs by MPNO at elevated temperatures between 100 and 250 °C and reaction times up to 8 h, where lower temperatures require longer times for a complete oxidation.…”

“…A further increase of Ga content (>25 at. %) leads to the formation of Au 7 Ga 2 and AuGa intermetallic phases, which exhibit low symmetry crystal structures 35 and a very broad or not detectable LSPR peak (blue lines in Figure 2c). Importantly, complete oxidation of all Au−Ga NPs in solution (e.g., via MPNO at 200 °C for 8 h) yields NPs, which again show a well-defined, red-shifted LSPR peak (red lines in Figure 2c), indicating that Ga atoms dealloy from the Au−Ga core, forming a thin Ga 2 O 3 shell.…”