Using a familiar tool in a way that was never meant to be used opens up a whole new method of material exploration, a UConn Researchers report in Notifications of the National Academy of SciencesTheir specific findings may someday create more energy-efficient computer chips, but the new technique itself can open new discoveries across a wide range of products.
Atomic Force Microscopes (ASM) move ultra-sharp tops in the materials so close, but never touch the surface. The tip can be felt when the surface is to detect electrical and magnetic forces produced by the material. Methodically going back and forth, the researcher can plot the surface properties of the material in the same way that the surveyor methodically passes through a piece of land to map the territory. ASMs can give a map of the holes, protuberances, and material properties on a scale that is thousands of times less than a grain.
ACM are designed for surface testing. Most of the time, the user is trying very hard not to pick up the material with the tip, as this may damage the surface of the material. But sometimes it happens. Several years ago, aspirant Yassin Koutes and Justin Luria, a postdoctoral student, are studying solar cells in Brian Hugh's Laboratory of Materials Science and Engineering Professor, accidentally penetrating their sample. Initially, they thought it was an irritating mistake, they noticed that the properties of the material looked different when Kyute clutched the top of the ASM deep into the ditch she had accidentally dug.
Coutes and Luria did not pursue him. But another graduate, James Stefs, was inspired to take a closer look at the idea. What would happen if you intentionally used the top of the ASM like a chisel and dug into material, he asked? Will it be able to plot the electrical and magnetic properties layer by layer, constructing a 3-D picture of the properties of the material in the same way it is applied to the surface in 2-D? And whether the properties look different in the material?
The answers, Steffes, Huey and their colleagues report PNAS, yes and yes. They are buried in a sample of bismuth ferrite (BiFeO3), which is multiferrous at room temperature. Multi-ferroids are materials that can have multiple electrical or magnetic properties simultaneously. For example, bismuth ferrite is an antiferromagnet – reacts to magnetic fields, but generally does not show a north or south magnetic pole – and a ferroelectric, which means there is a switchable electric polarization. Such ferroelectric materials usually consist of small plots called domains. Each domain is like a cluster of batteries, all of their positive terminals are aligned in the same direction. Clusters on both sides of this area will be directed in a different direction. They are very valuable to computer memory because the computer can reverse the domain by "writing" the material using magnetic or electric fields.
When a material scientist reads or writes information about a piece of bismuth ferrite, they can usually only see what is happening on the surface. But they would like to know what is happening below the surface – if it is understood, it may be possible to inject the material into more efficient computer chips that work faster and use less energy than those available today. This could lead to a big difference in overall energy consumption in society – already 5% of all US electricity consumption is routed to working computers.
To understand, Steffes, Huey, and the rest of the team used the AFM tip to dig carefully through a bismuth ferrite film and spot the interior piece by piece. They have found that they can make a map of the individual areas all the way down, exposing patterns and properties that have not always been apparent on the surface. Sometimes the domain is narrowed down until it disappears or is divided into y-form or merged with another domain. No one has ever seen inside the material that way. It was a revelation similar to looking at 3-D tomographic bone scan when you were only able to read 2-D X-rays before.
"About 30,000 AFMs are already installed worldwide, with a great deal of them trying [3-D mapping with] AFM in 2019 as our community realizes that they have just scratched the surface all the time, "Huey predicts, and he believes that more laboratories will buy AFM now if it turns out that 3-D mapping works for their materials, and some microscope makers will start designing AFMs specifically for 3D scanning.
Stephan subsequently graduated from UConn with a Ph.D. degree. and now works at GlobalFoundries, a computer chip maker. Researchers from Intel, muRata and elsewhere are also intrigued by what the group has found for bismuth ferment because they are looking for new materials to make the next generation of computer chips. Huey's team, meanwhile, is now using AFMs to digest all types of materials from concrete to bone to a host of computer components.
"By working with academic and corporate partners, we can use our new insight to understand how to better design these materials to use less energy, optimize their performance, and improve their reliability and durability – these are examples of what materials scientists are looking for every day, "says Hugh.
Ratio between the structure and the magnetic properties of ceramics
James J. Steffes et al., Ferroelectric thickness scaling in BiFeO3 by atomic force tomography microscopy, Notifications of the National Academy of Sciences (2019). DOI: 10.1073 / pnas.1806074116