Oct 4, 2013
Improving contact quality in AFM-based electrical measurements
Conductive Atomic Force Microscopy (CAFM) has become a very powerful tool to examine the electrical properties of nanosurfaces. In this work, researchers from the University of Pennsylvania in the US and the Grenoble Institute of Technology in France used a conductive AFM tip as an electrode to measure electron transport across a metal nanoparticle-oxide interface. They found that contact quality between the tip and the nanoparticles can be improved by optimizing the tip loading force.
The team has shown that the tip loading force can affect electrical measurements of gold nanoparticle-strontium titanate (STO) interfaces. The conductive tip contacts the nanoparticles and closes the electrical circuit thanks to a built-in module. In this study, the voltage was applied through the particle/oxide interface, and current simultaneously measured.
The current response is very sensitive to the contact quality between the tip and the nanoparticle and can be improved by increasing the loading force. Interestingly, the researchers found negligible nanoparticle deformation for loading forces in the nN–µN range because the induced stress in this range is still lower than the yield stress of gold nanoparticles.
As mentioned in a recent publication by the same group, improving the current-voltage response requires a sufficiently high loading force for good contact in nanoscale electrical measurements. A larger loading force is believed to effectively "tear off" any contaminated layers of the commercial conductive tips, and thus improves intimate contact between the two surfaces. On the other hand, the applied stress should be lower than the yield stress of the metal particles to protect the nanoparticle and the tip. Therefore, tip loads on the order of tens to hundreds of nN are high enough to investigate local electrical properties.
In conclusion, this work could help improve electrical measurements on the nanoscale in the future.
More detailed information can be found in the journal Nanotechnology 24 395703.
About the author
This research was conducted by the Bonnell Group. This group is interested in studying materials properties using scanning probe microscopy (SPM) and is led by Prof. Dawn A Bonnell. She has been studying surface science for more than 20 years. Jiechang Hou is a PhD student in this group and her main area of research lies in the electrical and plasmonic properties of nanoscale metal-oxide interfaces. Baptiste Rouxel is a masters student in the Department of Materials Science and Engineering, INP Grenoble, France. He joined the group as a summer exchange student. Prof. Stephen S Nonnenmann, the previous postdoctoral fellow in the group, is now assistant professor at the University of Massachusetts Amherst. Wei Qin is now a PhD student at the University of California, Davies, and he mainly works on TEM characterization.