11:15 AM - CH03.01.03
Theoretical Models for KPFM with Flexible Tip Apices
Ondrej Krejci1,Adam Foster1,2,3
Aalto University1,Kanazawa University2,Graduate School Materials Science in Mainz,3
Show Abstract
More than 10 years ago two types of Scanning Probe Microscopy (SPM) – Scanning Tunneling Microscopy (STM) [1] and non-contact Atomic Force Microscopy (nc-AFM) [2] – showed a possibility to reveal positions of atoms on small flat organic molecules in real space without any damage to the sample. These two works noticeably enhanced the field of molecular, 1 and 2D material studies in surface science (i.e. [3]). The sub-molecular resolution was achieved by usage of non-reactive and flexible tip-apices like CO-molecule [4]. Kelvin Probe Force Microscopy (KPFM)[5] is a technique proceeded with combined nc-AFM/STM instrument, which basically measures the effect of applied voltage between the microscope tip and sample on the measured force. It has possibility to measure the changes of work-function on the microscale and electric field above the sample on the nanoscale. However, the physics behind KPFM signal with flexible-tip apices showing the sub-molecular resolution, which could help with elemental recognition, remain unknown.
In this work, we will summarize up-to-date knowledge about KPFM [5,6] focusing mainly on measurements with simultaneous frequency modulation - Atomic Force Microscopy / Scanning Tunneling Microcopy instruments. Based upon this, we will present a new model for electrostatic field, which is describing the experiments with CO-metal tips [7] and metal substrates. This new electrostatic model is applied in a Density Functional Theory (DFT) calculations simulating the full tip-sample system. The results of the DFT calculations will be compared with simple mechanistic models capturing various sources of achieved signal. All these models and simulations have aim to recover the physics behind KPFM with flexible tip apices. This knowledge can help to get more information about the sample with SPM and is possibly a further step towards reliable chemical resolution in SPM.
References:
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