AFM Potential Measurement Using Dual-Frequency Bias
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Solution Overview
Problem
Existing potential measurement devices using AFM face challenges in measuring surface potential in liquids due to ion rearrangement, electrochemical reactions, and limited frequency bias voltage, leading to inaccurate results and uncontrollable forces.
Innovation Solution
A potential measurement device that applies a bias voltage with two alternating-current voltages of different frequencies, allowing the extraction of specific frequency components to calculate surface potential, enabling higher frequency operation and suppressing unnecessary interactions in high-concentration solutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single alternating-current bias voltage is applied between the electrode and sample to measure surface potential, then the measurement can be performed, but the frequency is limited due to ion rearrangement and electrochemical reactions in liquid
Solution Approach 1:
The single alternating-current bias voltage is segmented into two alternating-current voltages with different frequencies (first and second frequencies). By applying these two voltages simultaneously and detecting the electrostatic force at the difference frequency (first frequency minus second frequency), the system achieves both accurate surface potential measurement and extended frequency range, avoiding ion rearrangement and electrochemical reactions that limit single-frequency operation
Solution Approach 2:
The measurement approach transitions from single-frequency detection to multi-frequency detection by introducing a second frequency dimension. The electrostatic force detection is performed at the difference frequency between the two applied voltages, creating a new operational dimension that enables higher frequency operation while maintaining measurement accuracy through frequency domain separation
2Measurement precision
If direct-current bias voltage is applied between probe electrode and sample, then potential distribution can be measured, but electrochemical reactions occur causing uncontrollable force and surface energy changes
Solution Approach 1:
The direct-current bias voltage is replaced with alternating-current voltages that periodically reverse direction. This periodic action prevents the accumulation of charge and avoids sustained electrochemical reactions at the electrode-sample interface, eliminating the harmful surface stress and uncontrollable forces while maintaining the ability to measure potential distribution through the time-varying electrostatic force
Solution Approach 2:
The bias voltage parameters are changed from direct-current to alternating-current with specific frequency ranges. This parameter change transforms the electrostatic interaction from a static condition causing electrochemical reactions to a dynamic condition where the rapidly alternating field prevents ion rearrangement and electrochemical processes, thereby eliminating surface stress while enabling potential measurement
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for accurate measurement of surface potential in liquids with higher frequency bias voltages, reducing electrochemical reactions and ion rearrangement, and improving measurement precision in highly concentrated solutions.
Implementation Method 1
an electrostatic force Fes working between the probe electrode and the sample is determined by Expression (2) below
Implementation Method 2
a displacement measurement unit which outputs a voltage corresponding to an electrostatic force between the electrode and the sample
Implementation Method 3
a signal detection unit which outputs a magnitude of a particular frequency component contained in the voltage outputted by the displacement measurement unit
Data Source
Figure 1
Figure 2A~2C
Figure 3
AI summary
A potential measurement device (100) according to the present invention includes: an electrode (104); a displacement measurement unit (212) which outputs a voltage corresponding to an electrostatic force between the electrode and the sample; a first alternating-current power supply (101) which applies a first alternating-current voltage between the electrode and the sample; a second alternating-current power supply (102) which adds, to the first alternating-current voltage, a second alternating-current voltage having a frequency different from a frequency of the first alternating-current voltage, and applies the added voltage; and a signal detection unit (218) which outputs a magnitude of a particular frequency component contained in the output from the displacement measurement unit, in which the signal detection unit extracts, from the output by the displacement measurement unit, and outputs, to a potential calculation unit which calculates potential, (i) a magnitude and a phase of a frequency component of a frequency identical to the frequency of the first alternating-current voltage and (ii) a magnitude of a frequency component of a frequency identical to a frequency equivalent to a difference between the frequency of the first alternating-current voltage and the frequency of the second alternating-current voltage, so that the potential measurement device measures the surface potential of the sample.