Determination of the Key Parameters Causing Unexplained Dynamic Phenomena in High-Speed Atomic Force Microscopy

Board Of Regents, Nshe, Obo University Of Nevada, Reno, Reno NV

Investigators

Abstract

The ability to accurately and rapidly measure the physical properties of materials at extremely small length scales is key to advancing scientific research and technological progress. The atomic force microscope, in which a micrometer sized cantilevered beam is used to physically probe a material of interest, is one of the primary tools for making quantitative measurements of material properties at scales on the order of one billionth of a meter. However, when conducting atomic force microscope measurements at high scanning speeds, unexplained phenomena present themselves. These unexplained phenomena impede accurate scientific measurement. There is currently a lack of experimental data to properly characterize and model these unexplained phenomena. A set of well-designed experiments and numerical simulations that test the suspected variables related to these scanning speed phenomena will be conducted. Highly quantitative and rapid measurements, such as the real-time evolution of the mechanical properties of viruses exposed to various stimuli or nano-scale corrosion processes occurring in real-time, will be enabled by this work and will allow new and cutting-edge research in areas such as medicine, biology, and materials engineering, thus, benefiting the US economy and the progress of science. In addition, the project's educational plan will develop a hands-on, interactive, and portable learning platform that will expose K-12, undergraduate, and graduate students to atomic force microscopy and the scientific principles used in its operation. The educational plan will engender further interest and retention in the Science, Technology, Engineering, and Mathematics fields. The project objective is to determine the key parameters that cause observed scan velocity related phenomena in contact mode high-speed atomic force microscopy and to develop mathematical models that will predict this behavior. The project objective will be obtained by pursuing the following specific tasks: 1) Systematically determine the primary variables causing the scan velocity phenomena via a suite of experiments that control the suspected sources of the phenomena such as relative humidity, scan speed, scan angle, sample composition, fluid environment, and AFM tip radii. The output data will also be used to determine the functional form of predictive models used to characterize the scan velocity related phenomena. 2) Perform computational fluid-structure interaction simulations to investigate the effect of scan velocity on the hydrodynamic forces acting on the bulk microcantilever. The large scan velocities used in high-speed atomic force microscopy domains will affect the hydrodynamic forces acting on the microcantilever, which to date, are calculated under the assumption that the surrounding fluid is quiescent. These fluid-structure interaction simulations will be used to determine a mathematical model to predict the hydrodynamic forces on the cantilever system due to fluid velocity effects. This research will allow for accurate contact mode high-speed atomic force microscopy measurements that extend beyond topographical imaging, across a wide range of scan velocities. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.