Researchers were able to develop a new amalgamation process that results in two metals producing nanocrystals, opening a new avenue for creating intermetallic nanocrystals for a variety of specialized applications. 

The new process was devised by a team from ETH Zurich, having a liquid metal penetrate the solid one during the amalgamation procedure in an impressively intuitive technique. Researchers report their findings in the Science Advances article "Size- and Composition-Controlled Intermetallic Nanocrystals via Amalgamation Seeded Growth."

Arquerite, a Natural Amalgam of Silver and Mercury
(Photo: Robert M. Lavinsky via Wikimedia Commons)
Arquerite is a very rare variety of mercurian silver amalgam containing 13% of mercury. This rarity is found in only four localities worldwide, 2 in Chile (Type Locality) and 2 in British Columbia, Canada. This flattened, rounded thumbnail is river-worn since arquerite is composed of two soft native elements, silver, and mercury.

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An 'Intuitive' Method for Producing Nanocrystals

Nanocrystals are small spheres, usually in the nanometer range, that are made up of atoms arranged in a regular crystalline arrangement. Their unique properties give them a host of benefits as materials for specialized uses. For example, cadmium and selenium nanocrystals have been extensively studied for their potential use, from LED displays to specialized equipment in medical imaging, as noted in a February 2021 study appearing in Nature Communications, examining their inherent structural defects.

Also, intermetallic nanocrystals, which are materials created from two different metals arranged in a crystalline lattice, have become materials of interest due to their applications in catalysis, data storage, electronics, and biomedicine. With the number of metals and metallic materials known to humankind, there are theoretically thousands of possible combinations that could lead to nanocrystals. However, only a few of them have been made in reality. This prompted the researchers from the Institute for Electronics at ETH Zurich.

"Our method is simple and intuitive-so intuitive, in fact, that we were surprised that no one had had this idea before us," said Maksym Yarema, a co-author of the study, in a news release from ETH Zurich. In previously available processes, nanocrystals are only made of a single metal, where metal atoms, like salts, are introduced into a solution where the atoms reform as nanocrystals. Yarema explained that while forming nanocrystals from two metals is theoretically possible, translating these theories into reality is a lot harder, if not outright impossible. It led them to turn to a centuries-old procedure for mixing metals: amalgamation.

Using Amalgamation in Forming Nanocrystals

Traditionally, amalgams are the results of alloy where mercury bonds with another metal, having been used in a variety of applications from mining to dental fillings. While mercury has been the most popular metal mixed with other materials, researchers said that it is possible to perform amalgamation with other liquid metals.

The ETH Zurich team then applied the same concept but in the context of nanoscale materials. They began by dispersing a single metal nanocrystal like silver before introducing the atoms of a second material like gallium in molecular form as the mixture is heated up to around 300 degrees.

The researchers explained that the unusually high temperature breaks the chemical bonds in the gallium-amide, releasing liquid molecular gallium that accumulates around the silver nanocrystals, setting off the amalgamation process. After some time, a new crystal lattice is formed, one that contains both silver and gallium atoms in the crystalline structure.

Additionally, the researchers said that the technique is controllable, which they demonstrated by creating various intermetallic nanocrystals like copper-gallium, palladium-zinc, and gold-gallium.


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