AFM Probe Tapping Mode for Subsurface Imaging
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Solution Overview
Problem
Existing subsurface atomic force microscopy methods face challenges in minimizing sample damage and effectively decoupling surface and subsurface information, as they often require high force application and suffer from shear forces and drift during measurement.
Innovation Solution
The method employs a non-resonant cantilever probe that initially measures surface topography at a defined set point force in contact or non-contact mode, followed by subsurface measurements using acoustic vibrations in the MHz range, allowing for decoupled surface and subsurface topography capture without influencing the tip-sample boundary conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If contact-mode feedback is used to obtain subsurface images, then measurement precision is improved, but sample damage increases due to high force application and shear forces
Solution Approach 1:
The patent applies periodic tapping mode where the probe intermittently contacts the sample surface rather than maintaining continuous contact. The probe taps the surface at a frequency above the cantilever's resonant frequency, allowing the system to collect subsurface information during brief contact periods while minimizing shear forces and sample damage between taps. This periodic action resolves the contradiction by providing sufficient contact for measurement precision while limiting cumulative damage.
Solution Approach 2:
The patent utilizes mechanical vibration by driving the cantilever at frequencies above its resonant frequency during tapping mode operation. The vibrational motion allows the probe to interact with the sample in a dynamic manner, reducing adhesion forces and shear stresses that would otherwise cause sample damage. The vibration enables subsurface signal detection while maintaining lower average contact forces, thus improving the ratio of measurement quality to sample damage.
2Measurement precision
If higher set point force is applied to improve signal to noise ratio, then measurement precision is improved, but sample damage and drift increase
Solution Approach 1:
By using periodic tapping mode with optimized tap duration and frequency, the system achieves high signal-to-noise ratios during brief contact periods without requiring continuously high setpoint forces. The intermittent nature of the contact allows for higher peak forces during tapping (improving signal) while maintaining lower average forces (reducing damage and drift).
Solution Approach 2:
The system dynamically adjusts the tapping amplitude and frequency to optimize the balance between signal acquisition and sample preservation. By controlling the tap depth and duration dynamically, the system achieves sufficient signal strength for high-quality imaging while limiting the mechanical stress applied to the sample, thereby reducing damage and drift.
3Productivity
If surface and subsurface measurements are performed simultaneously at the same set point force, then productivity is improved, but measurement precision deteriorates due to coupling between surface and subsurface signals
Solution Approach 1:
The patent segments the measurement process into distinct phases: surface topography measurement during retraction and subsurface measurement during approach or contact phases. By separating the measurement functions in time and space, the system maintains high productivity through automated sequencing while achieving precise decoupling of surface and subsurface signals, eliminating the trade-off between efficiency and measurement quality.
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 minimizes deformation and shear forces, enabling accurate and efficient simultaneous surface and subsurface imaging with reduced sample damage, allowing for high-throughput three-dimensional stiffness and viscoelasticity mapping.
Implementation Method 1
an acoustic vibrator in communication with the sample to provide a vibration to the sample, the vibration comprising a modulation frequency
Implementation Method 2
a detector to detect a deflection of the probe tip
Data Source
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AI summary
The present document relates to a anatomic force microscope comprising a probe comprising a probe tip configured to sense a sample disposed proximate to the probe tip, a detector to detect a deflection of the probe tip, an actuator coupled to the probe and configured to move the probe in a sense state with the sample at a predetermined force set point and a vibrator in communication with the sample to provide a vibration to the sample, the vibration comprising a modulation frequency, wherein the acoustic vibrator is configured to provide the vibration in a modulation period after an initial sense period without modulation and wherein the probe is moved during or after said modulation period to a successive sample position over said sample while moving the probe in a non-contact state.