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Novel compositional mode

Novel compositional mode: Ringing Mode TM

Ringing Mode is a new AFM imaging mode that provides previously inaccessible information regarding the composition of samples. As an extension of sub-resonance tapping, it allows the collection of 8 new physical sample properties in addition to standard sub-resonance imaging modes. Ringing Mode utilizes portions of a signal received from an AFM cantilever that have hitherto been regarded as noise and, typically, filtered out or ignored.

A typical unfiltered signal of an AFM cantilever position (deflection) as a function of time is shown in the figure above. Positive values of the deflection correspond to the cantilever deflection due to forces of repulsion, and vice versa; negative d stands for the attraction between the AFM probe and sample surface.

Overview 

Ringing ModeTM is a combination of the oscillatory non-resonant mode and a resonant one. It operates with the non-resonant feedback, but utilizes the signal information from the ringing of the AFM cantilever (free resonance oscillations of the cantilever which occur after detaching the AFM probe from a sample surface). The analysis of the amplitude of the ringing signal provides novel information about the sample surface.

Ringing Mode works with standard AFM probes used in sub-resonant modes. NSS has demonstrated the application of this mode for various polymers and bio-materials. Ringing ModeTM works with any non-resonant mode, including ScanAssystTM, PeakForce Tapping®, HybriDTM, Pulsed Force Mode, and other commercial modes. It works while scanning  in air and in liquids. 

 

Advantages of Ringing ModeTM:

 

Provides up to eight additional novel information channels.

 Ringing ModeTM produces a quantitative level of imaging. It gives new information about surfaces including:

– Restored (averaged) adhesion.

– Adhesion height.

– Disconnection height.

– Pull-off neck height.

– Disconnection distance.

– Disconnection energy loss.

– Dynamic creep phase shift.

– Zero-force height (this channel, though, is available in some commercial AFMs).

 

 A schematic of the signal exploited by Ringing ModeTM

One full cycle of 1 kHz vertical oscillation of the Z scanner is presented. A typical unfiltered signal of the cantilever deflection d (or force=kd, where k is the spring constant of the cantilever) as a function of time is shown. The dash-envelope lines show the decrease of the oscillating amplitude of the AFM cantilever due to dissipation.

> Restored (averaged) adhesion. After the pull-off (point D in the figure above ), the AFM cantilever jumps away from the surface, and the ringing starts. Each oscillation has smaller and smaller amplitude due to dissipation. When the quality factor is known (can be measured separately), one can extrapolate the value of the adhesion force to the moment of pull-off or, more precisely, to the time when the extrapolation curve crosses the deflection curve. This is shown in the above figure as point E. We call this restored adhesion (note, not yet averaged). Because the measured values of the cantilever deflection have an intrinsic noise, it is advantageous to calculate restored adhesion using multiple points of the ringing signal, and, subsequently, to average the obtained values to decrease the noise in the measured value of the restored adhesion. We call this restored averaged adhesion.

> Zero-force height (available in some commercial AFMs). The position of the sample when the load force (the cantilever deflection) is zero, points (B, B*) in the figure above.

> Adhesion height. The position of the sample at the maximum negative deflection of the cantilever (force is equal to the force of adhesion),  point (D).

> Disconnection height. The position of the sample when the force is equal to the force of restored adhesion,  point (E).

> Pull-off neck height. The height of the neck between the AFM probe and sample surface created by the adhesive action of the probe at the moment of pull-off, parameter Δ in the figure above.

> Disconnection distance. The height of the molecular asperities/molecules stretched by the AFM probe, parameter δ in the figure above.

> Disconnection energy loss. Energy losses due to disipative disconnection of the AFM probe from the sample surface. This energy loss comes from the energy of the viscoelastic pull of the sample material under the probe and from rapturing the molecular contacts between the probe and sample. The latter can include the breakage of water meniscus if the scanning is done in air.

> Dynamic creep phase shift. The phase difference between oscillation of the sample and AFM cantilever.

 

Example of the new data channels.

A principally new imaging channel of the Ringing ModeTM - disconnection distance. The cell height is shown as reference (simultaneously recorded in PeakForce Tapping® mode). The scan rate is 0.5 Hz. An example of a human melanoma cell is shown.

 

Human skin flake sample imaged at 1 Hz (1 sec per line). The disconnection energy loss (the energy loss during separation of the AFM probe from the sample surface) and the dissipation energy (imaged using PeakForce Tapping®) are shown.

 

 

For AFMs lacking a sub-resonance tapping mode, Ringing ModeTM can provide four standard channels for sub-resonance tapping.
 

– Adhesion.

– Load Force (error).

– DMT modulus.

– Viscoelastic losses.

 

Ringing Mode delivers a dramatic increase in imaging speed, up to 20x as demonstrated using polymers.

This is 20x faster compared to the fastest existing non-resonant modes. The same two-polymer blend is imaged in PeakForce Tapping® and Ringing ModeTM below. The scanning speed ranges from 0.5Hz to 5Hz. One can see a clear artifacts/degradation of the PeakForce® images while the Ringing ModeTM images remain artifact-free.


 

Ringing Mode delivers up to 5x better resolution.

 

Below are height images of a human melanoma cell surface. The image on the left displays adhesion height recorded with the Ringing ModeTM and the image on the right shows regular height recorded with the PeakForce Tapping® mode. The radii of the curvature of the adhesion and regular heights demonstrate the most frequent values observed in both height images.

 

Ringing Mode delivers less imaging artifacts.
 

Our proprietary algorithm identifies and removes interference artifacts. It is important to note that our algorithm does not alter the values of measured physical parameters (a typical problem of existing filters). The ringing physically happens around zero deflection of the cantilever. Therefore, the shift of the background (the reason for the artifact due to interference) is easily identified and subsequently, corrected.

Ringing Mode delivers less noise due to multiple averaging of the recorded signal.
 

Because the ringing curve contains multiple measurements/information, it can be averaged. This typically results in a substantial decrease of noise in defining this adhesion. We call this parameter “averaged restored adhesion”, or just “restored adhesion”. 

AFM maps of human skin flake surfaces simultaneously imaged in the new NSS’ Ringing ModeTM and existing PeakForce Tapping® modes. The scan rate is 1 Hz (1 sec per line). Averaged restored adhesion and regular adhesion maps are shown. 

The image above (Disconnection energy loss) shows an example of the imaging of a human skin cornea layer simultaneously imaged with the Ringing ModeTM and PeakForce Tapping®. One can clearly see less noise (and consequently, higher resolution) in the Ringing ModeTM.

Ringing Mode works in air and in liquids.
 

 A few examples:

LDPE/PS blend in water:

 

Surface of a treated polystyrene surface in water:

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