Apr 4, 2016
Bringing Kelvin probe force microscopy into the information age
Kelvin probe force microscopy (KPFM) is an adaptation of the century-old Kelvin probe technique that leverages the high resolution and force sensitivity of the atomic force microscope to allow mapping of electrochemical properties on nanometre and even atomic scales. KPFM was invented more than 25 years ago and is now an established technique across all fields of science including research of materials that are organic, biological, or that convert and store energy. Reporting in Nanotechnology researchers recently developed a fully digital software based approach to KPFM called General Mode or G-Mode KPFM, which moves away from analogue signal processing techniques, instead utilising the emerging power of big data capture and analytics.
Classical KPFM utilises approaches such as heterodyne detection and closed-loop-bias feedback to determine electrochemical properties of the sample under investigation. Practically, this limits the KPFM measurement in terms of channels of information available (i.e., a single surface potential channel is available) and the time resolution of the measurement (e.g. ~1-10 MHz photodetector stream is down sampled to a single readout of CPD per pixel). Despite the popularity of KPFM, the level of information available (i.e. CPD) is not sufficient for systems such as electroactive materials, devices, or solid-liquid interfaces, involving nonlinear lossy dielectrics.
A new era in KPFM
In this study, the foundations are laid for a new era in KPFM utilising big data analytics. As a first step it is demonstrated that by sampling the data at sufficiently high sampling rates and using digital software based filtering and demodulation it is possible to emulate the classical KPFM aproach. However, G-Mode KPFM has several advantages over its predecessor as it negates many of the drawbacks associated with heterodyne detection and closed- loop-bias feedback, as well as significantly simplifying the technique by avoiding cumbersome instrumentation optimisation steps (i.e. lock-in parameters, feedback gains, etc.) and is immediately implementable on all atomic force microscopy platforms.
Advantages of a fully digital approach
Additional advantages of a fully digital approach are demonstrated in this research including the simultaneous capture of numerous channels of information as well as increased flexibility in terms of data exploration across frequency, time, space, and noise domains. It is believed that G-Mode KPFM will be particularly useful for probing electrodynamics in photovoltaics, liquids, and ionic conductors.
More information about this research can be found in the journal Nanotechnology 27 105706.
About the author
Liam Collins is a Post Graduate researcher in the Centre for Nanophase Materials Sciences, a Department of Energy Office of Science User Facility at Oak Ridge National Laboratory. He develops novel scanning probe techniques for investigating structure and functionality on the nanoscale. This research was conducted at the Centre for Nanophase Materials Sciences and supported by the US DOE, Basic Energy Sciences, Materials Sciences and Engineering Division through the Office of Science Early Career Research Program.