Ferreira and team write silver nanoparticles on phosphate glass


Christina Oehler, MechSE Communications

Tungchao Julia Lu Professor Placid Ferreira, along with PhD student Kyle Jacobs, recently wrote a research paper that was published in the September 2 issue of Advanced Functional Materials
The paper, titled “Painting and Direct Writing of Silver Nanostructures on Phosphate Glass with Electron Beam Irradiation,” gives an in-depth look into the study of using an electron beam to write patterns on a specific type of conductive substrate. The outcome of their research will benefit other scientists in furthering the development of writing with electron beam irradiation. 
In traditional electron microscopy, the substrate must be conductive to allow the charge from the beam to dissipate. In Ferreira and Jacobs’ process, however, their substrate, made of transparent AgIAgPO3, only conducts silver ions and not electrons. When an electron beam hits the surface it combines with the silver ions to produce silver metal. This allows the flow of silver ions to the surface so that the process can continue without charging. Their paper reveals that, depending on the total charge deposited from the electron beam, this process can consequentially have two distinct results. 
For one outcome, the team found that when there is a smaller charge transfer per area, silver nanoparticles within the substrate will cause the glass to reflect effervescent colors. After experimenting with different controls and variables, they found that they were able to demonstrate their ability to write reflective, multi-colored patterns with sub-micron resolution. 


A micro-sized Illinois logo written with the researchers' process.
A micro-sized Illinois logo written with the researchers' process.
A micro-sized Illinois logo written with the researchers' process.


They also found that there was an entirely different set of results when there is a larger charge transfer onto the substrate, which forces silver particles to form in bulk on the surface of the glass.
“Silver metal is electronically conductive as well as better at absorbing the electron beam, meaning that it more effectively captures the high energy beam electrons and uses their negative charge to electrochemically extract more silver from glass.” said Jacobs. 
This method is key to the development of writing silver structures on the surface of glass. 
“The ability to directly write silver particles of different sizes and shapes will be useful in investigating the properties of these interactions and their potential uses, especially due to the optical transparency of the AgIAgPO3 glass substrate,” said Jacobs.
Their discovery is also relevant for the growing field of plasmonics, where the oscillations of electrons in a metal can couple with electromagnetic fields of visible light. 
Alternative methods for in situ metal deposition exist, but they use metal-atom containing precursor gases, which are not available for silver and which have resulting metals of low purity.