Quantitative comparison of closed-loop and dual harmonic Kelvin probe force microscopy techniques

Kilpatrick, Jason I.; Collins, Liam; Weber, Stefan A. L.; Rodriguez, Brian J.

doi:10.1063/1.5025432

Cited by 14 publications

(29 citation statements)

References 53 publications

(101 reference statements)

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“…Traditional KPFM is a closed-loop technique in which a bias feedback loop is used to control the DC bias until it fully compensates, or minimizes, the electrostatic force between the tip and sample. Closed-loop operation imposes some limitations on the KPFM measurement, such as the requirement for feedback loop tuning, feedback errors, − and possible bandwidth limitations . Together, these motivated the development of open-loop or feedback-free KPFM methods that eliminate the need for a DC nulling bias .…”

Section: Introductionmentioning

confidence: 99%

“…Closed-loop operation imposes some limitations on the KPFM measurement, such as the requirement for feedback loop tuning, 18 feedback errors, 19−23 and possible bandwidth limitations. 24 methods that eliminate the need for a DC nulling bias. 25 Dual harmonic KPFM (DH-KPFM) is one example of open-loop KPFM, which has been utilized to measure the surface potential in ultrahigh vacuum, 25 air, 22,26 and liquid environments.…”

Section: ■ Introductionmentioning

confidence: 99%

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Visualizing Charge Transport and Nanoscale Electrochemistry by Hyperspectral Kelvin Probe Force Microscopy

Collins

Vasudevan

Sehirlioglu

2020

ACS Appl. Mater. Interfaces

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Charge-transport and electrochemical processes are heavily influenced by the local microstructure. Kelvin probe force microscopy (KPFM) is a widely used technique to map electrochemical potentials at the nanometer scale; however, it offers little information on local charge dynamics. Here, we implement a hyperspectral KPFM approach for spatially mapping bias-dependent charge dynamics in timescales ranging from the sub-millisecond to the second regime. As a proof of principle, we investigate the role mobile surface charges play in a three-unit-cell LaAlO3/SrTiO3 oxide heterostructure. We explore machine learning approaches to assist with visualization, pattern recognition, and interpretation of the information-rich data sets. Linear unmixing methods reveal hidden bias-dependent interfacial processes, most likely water splitting, which are essentially unnoticed by functional fitting of the dynamic response alone. Hyperspectral KPFM will be beneficial for investigating nanoscale charge transport and local reactivity in systems involving a possible combination of electronic, ionic, and electrochemical phenomena.

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Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Visualizing Charge Transport and Nanoscale Electrochemistry by Hyperspectral Kelvin Probe Force Microscopy

Collins

Vasudevan

Sehirlioglu

2020

ACS Appl. Mater. Interfaces

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“…In the DH-KPFM measurement, an AC bias was applied between the tip and the sample to excite the cantilever vibration at its resonant frequency. The amplitudes of the cantilever at resonant frequency (ω) as well as twice the resonant frequency (2ω) and the phase of vibration were all recorded, and the surface potential was further calculated according to previous studies . In the DH-KPFM scanning, the scan size was 20 μm, and the lift height was set to 100 nm.…”

Section: Methodsmentioning

confidence: 99%

“…Kelvin probe force microscopy (KPFM) was proven to be a powerful tool for measuring the charge density on a solid surface in air conditions. − But unfortunately, it cannot be used in a liquid environment directly, especially in polar liquids and conductive liquids, since that direct (DC) voltage bias needs to be applied to compensate for the potential difference between the tip and the sample, which may lead to the electric double-layer (EDL) charging, migration of the ions in liquid, and even decomposition of the liquid molecules. To overcome this problem, recently dual-harmonic Kelvin probe force microscopy (DH-KPFM) was designed to measure the surface potential of the solid in a liquid environment. , As with the conventional KPFM, the vibration of the cantilever is also excited by the alternating (AC) voltage bias applied between the tip and the sample in DH-KPFM. But the difference is that the amplitudes of the cantilever at the resonant frequency (ω) and twice the resonant frequency (2ω) are both recorded for further calculating the surface potential of the solid, and the DC bias is not required in DH-KPFM.…”

Section: Introductionmentioning

confidence: 99%

Detecting the Liquid–Solid Contact Electrification Charges in a Liquid Environment

2021

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Contact electrification (CE) has been known for more than 2600 years, but its mechanism remains ambiguous, especially for liquid–solid cases. In previous studies on liquid–solid CE, the charges on a dielectric surface in a liquid environment have not been discussed due to the lack of proper measurement techniques, which may be responsible for the poor understanding on the liquid–solid CE. Here, the CE between dielectrics and different liquids, including deionized (DI) water, benzene, and cyclohexane (CYH), is performed by using dual harmonic Kelvin probe force microscopy (DH-KPFM). We focus on the transferred charges on the dielectric surface when it keeps in contact with a liquid. It is observed that the CE surface charges are screened in DI water, but not in organic solutions, suggesting that the electric double layer (EDL) is responsible for the screening of the surface charges. Moreover, it is revealed that the charge transfer in liquid–solid CE occurs not only in the contact but also during the separation process. Based on the observations, a model is proposed to describe the whole process of liquid–solid CE, in which the electron transfer plays a dominant role, and the adsorption of counterions in the EDL on the dielectric surface during separation is considered.

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“…They incorporate a direct measurement of either the amplitude or frequency response of the AFM probe to an applied single-frequency bias modulation. Furthermore, multi-frequency operations of OL KPFM were introduced as band-excitation OL BE-KPFM [37][38][39], intermodulation electrostatic force microscopy [40], and dual-harmonic KPFM (DH-KPFM) [34,41,42]. In DH-KPFM, the CPD is obtained from the ratio of the amplitudes of the first two harmonics of the cantilever response to an AC bias modulation and requires a prior calibration for the gain of the cantilever's transfer function.…”

Section: Introductionmentioning

confidence: 99%

Open-loop amplitude-modulation Kelvin probe force microscopy operated in single-pass PeakForce tapping mode

Stan¹,

Namboodiri²

2021

Beilstein J. Nanotechnol.

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The open-loop (OL) variant of Kelvin probe force microscopy (KPFM) provides access to the voltage response of the electrostatic interaction between a conductive atomic force microscopy (AFM) probe and the investigated sample. The measured response can be analyzed a posteriori, modeled, and interpreted to include various contributions from the probe geometry and imaged features of the sample. In contrast to this, the currently implemented closed-loop (CL) variants of KPFM, either amplitude-modulation (AM) or frequency-modulation (FM), solely report on their final product in terms of the tip–sample contact potential difference. In ambient atmosphere, both CL AM-KPFM and CL FM-KPFM work at their best during the lift part of a two-pass scanning mode to avoid the direct contact with the surface of the sample. In this work, a new OL AM-KPFM mode was implemented in the single-pass scan of the PeakForce Tapping (PFT) mode. The topographical and electrical components were combined in a single pass by applying the electrical modulation only in between the PFT tip–sample contacts, when the AFM probe separates from the sample. In this way, any contact and tunneling discharges are avoided and, yet, the location of the measured electrical tip–sample interaction is directly affixed to the topography rendered by the mechanical PFT modulation at each tap. Furthermore, because the detailed response of the cantilever to the bias stimulation was recorded, it was possible to analyze and separate an average contribution of the cantilever to the determined local contact potential difference between the AFM probe and the imaged sample. The removal of this unwanted contribution greatly improved the accuracy of the AM-KPFM measurements to the level of the FM-KPFM counterpart.

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Quantitative comparison of closed-loop and dual harmonic Kelvin probe force microscopy techniques

Cited by 14 publications

References 53 publications

Visualizing Charge Transport and Nanoscale Electrochemistry by Hyperspectral Kelvin Probe Force Microscopy

Visualizing Charge Transport and Nanoscale Electrochemistry by Hyperspectral Kelvin Probe Force Microscopy

Detecting the Liquid–Solid Contact Electrification Charges in a Liquid Environment

Open-loop amplitude-modulation Kelvin probe force microscopy operated in single-pass PeakForce tapping mode

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