By Dave DeFusco

Dr. Fredy Zypman, director of the Katz School’s M.A. in Physics, and several recent graduates have developed an advanced algorithm that uses scanning force microscopy to measure electric charges on nanoscale rings, a promising innovation that enhances the precision of charge measurements and has valuable applications in nanotechnology, biosensing, quantum computing and materials science.

Their study, “Theory for Measuring Electric Charge Density of a Ring from Scanning Force Microscopy,” published in the American Institute of Physics Advances, explores how a charged ring interacts with the tip/sensor of a scanning force microscope (SFM). SFM is a spatially precise technique that records the movement of its tip as it scans microscopic structures. These movements are analyzed to identify and classify forces, including electrostatic ones.

The researchers created a method to turn the tiny forces measured by a special microscope into charge values inside a ring. These infinitesimal forces, billions of times lighter than a feather, can be detected with today's technology. Their method acts like a bridge, connecting the charge spreading on the ring with the forces that the microscope measures.

“This research has immediate use to designing smaller and more efficient devices, detecting biological molecules with unprecedented precision, and understanding and manipulating the properties of new materials,” said Moshe Gordon, a co-author of the paper who graduated this year with a master’s in physics from the Katz School.

The key breakthrough of the study is its method of breaking down an uneven charge distribution into simpler components called multipoles. By using data from electrostatic forces, the algorithm calculates these multipole values to accurately determine how the charge is spread across the ring.

“This approach is particularly useful because multipoles play a major role in electrostatic interactions at microscopic scales,” said Yonathan Magendzo, a co-author of the paper who graduated from with a B.A. in physics in 2023.

The ability to measure charge density with nanometer-scale resolution has far-reaching implications. Charged rings are found in numerous systems, including molecular pumps, biosensors and nano-optoelectronic devices. For instance: 

• Biomedicine: Electrically charged molecular rings are crucial in peptide synthesis and bio-piezo materials used for tissue engineering. 
• Quantum Computing: Charged nano-rings are promising candidates for qubit storage, where precise charge measurement is critical. 
• Advanced Materials: Understanding charge effects in nanostructures can enhance the design of nanoelectronics and biomaterials. 

“Carbon, gold and silver nano-rings synthesized through various techniques stand to benefit from this method,” said Benjamin Goykadosh, a co-author of the paper who graduated from the Katz School with an M.A. in physics in 2022. “Charge properties play a pivotal role in their applications, and this algorithm offers a new tool to explore and optimize these properties.”

Current charge measurement techniques, such as Kelvin probe force microscopy and electric force microscopy, face limitations in accuracy and spatial resolution. This study bridges the gap, offering a powerful tool to dissect electrostatic interactions at the nanoscale.

“Our work contributes to the understanding of charge-driven processes, from self-assembly in large molecules to the performance of electronic devices,” said Dr. Fredy Zypman, senior author of the paper and professor of physics. “By enabling precise charge mapping, the algorithm opens doors to new scientific discoveries and technological innovations.”