AFM Modes

Ringing Mode

A PeakForce Tapping add-on for compositional mapping

Ringing Mode is a powerful extension of PeakForce Tapping that  provides new insights through multidimensional imaging; it simultaneously records up to 8 new quantitative compositional imaging channels in a single scan, extending PeakForce QNM studies with rich and complementary data. This sub-resonant mode:

  • Enables nanoscale mapping of previously inaccessible information on surface adhesion properties of materials;
  • Provides exclusive access to new data channels through unique utilization of the ringing portion of peak force feedback signal; and
  • Integrates seamlessly on Bruker AFM systems.

Integrated as a single AFM operational mode, Ringing Mode and PeakForce QNM together provide a more comprehensive solution for nanoscale characterization.

Demo the new Ringing Mode for AFM nanomechanical property imaging of soft sample materials such as polymers, biological cells, tissue, and biopolymers (video credit: NanoScience Solutions Inc.)

Enabling Enhanced Surface Adhesion Property Mapping

The ringing signal resulting from surface detachment of the AFM probe has previously had limited emphasis. Unlike any other existing AFM mode, Ringing Mode utilizes this rich signal to provide new insights into the often-complex unbinding process of surface molecules.

As a result, Ringing Mode delivers 8 new quantitative compositional imaging channels. This extends the available data in PeakForce QNM to provide up to 14 available different data types, including the standard nanomechanical property channels. Ringing Mode expands on the unique strengths of PeakForce QNM to provide enhanced adhesion property information that is complementary to existing mechanical and structural data.

Ringing Mode's unique compositional imaging channels include:

  • Restored Adhesion
  • Adhesion Height
  • Zero-force Height
  • Disconnection Height
  • Pull-off Neck Size
  • Disconnection Distance
  • Disconnection Energy Loss
  • Dynamic Creep Phase Shift

Providing New & Complementary Surface Property Information for Materials

Neck Formation in Soft Matter

Measuring the maximum height of the neck pulled from a sample surface during probe retraction, Pull-Off Neck Size provides insights into processes, such as polymer necking or membrane tubule formation in cells. This extends PeakForce QNM mechanical property information to provide information on tensile deformation of surface layers at the nanoscale.

Ringing Mode + PeakForce QNM images simultaneously obtained on a human melanoma cell. Bright areas in the Pull-off Neck Height image indicate areas of the cell membrane that form a longer, more stable neck between the sample and AFM tip during pull-off. All four data channels provide independent information demonstrating the richness of the data available. (Dokukin & Sokolov, Nat. Sci. Rep. (2017) 7: 11828.)

Extension Length of Surface Molecules

Disconnection Distance measures the length of molecules stretched from the surface by the AFM probe, such as those found in polymer coatings or cell membranes. These nanoscale maps can provide key information as to the surface distribution and organization of soft, flexible molecules that are not easily imaged by other techniques.

Ringing Mode + PeakForce QNM images simultaneously obtained on PS/LDPE polymer sample showing difference between Pull-off Neck Size and Disconnection Distance data channels (diagrams and cross sections). The Disconnection Distance includes the length of both the neck and any remaining surface molecules. (Dokukin & Sokolov, Nat. Sci. Rep. (2017) 7: 11828.)

High-Resolution Imaging of Surface Molecules

Ringing Mode enables highly accurate nanoscale compositional mapping of sample surfaces, including the distribution of surface coating molecules, with nanometer spatial resolution. This is due to minimization of tip-sample contact size that happens at the disconnection point.

High-resolution Ringing Mode + PeakForce QNM images obtained on the surface of a surface-coated nanoparticle. Heterogeneity of distribution of the surface molecules indicated by the Neck Size of ~10nm is clearly observed in the Neck Size data channel. The distribution of the height of the molecular coat (Disconnection Distance) is substantially different from that of the Neck Size, indicating the high complexity of molecular coat formation. (Makarova et al., Micros. Microanal. (2020) 26(S2): 1-3.)

Energy Dissipation During Tip-Sample Interaction

During interaction of the AFM probe with the sample surface, energy is dissipated due to (1) adhesion energy, (2) energy due to the viscous response of the sample material during the contact deformation, and finally, (3) disconnection energy loss. PeakForce QNM Dissipation Energy provides the sum of all energy contributions. Ringing Mode separately measures Disconnection Energy Loss, which is most closely associated with the surface layer or surface molecules rather than distortion of the bulk sample material.

Images of Ringing Mode Disconnection Energy Loss and PeakForce QNM Dissipation Energy simultaneously collected on corneocytes. Disconnection Energy Loss is a measurement of energy dissipation most closely associated with the surface layer of surface molecules. Dissipation Energy represents energy losses from multiple contributions and includes Disconnection Energy Loss. (Dokukin & Sokolov, Nat. Sci. Rep. (2017) 7: 11828.)

Enriched Adhesion Information

AFM adhesion measurements typically consider overall tip-sample detachment (pull-off force). Restored Adhesion focuses only on the adhesive forces involved in detachment of residual surface molecules or molecular tails after the AFM tip has lost adhesive contact with the sample surface.

Ringing Mode + PeakForce QNM images simultaneously acquired on PS/LDPE polymer sample. Adhesion data clearly identifies LPDE as having stronger adhesive interactions with the AFM tip than PS. Restored Adhesion data shows that surface layer of LDPE is also more heterogeneous and disconnection of the residual surface molecules from the tip is more dissipative. (Dokukin & Sokolov, Nat. Sci. Rep. (2017) 7: 11828.)

Extending Your PeakForce Tapping Studies

With seamless hardware and software integration, use of Bruker’s exclusive probes, and ‘one-click’ calibration, Ringing Mode easily expands your PeakForce QNM experiments and, for the first time, unlocks new possibilities for investigating the adhesive properties of materials at the nanoscale.

Ringing Mode is fully compatible with Bruker’s Performance Line of SPM systems.

A schematic of the signal exploited in ringing mode. 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.

Developed by Prof. Igor Sokolov and Dr. Maxim Dokukin (Tufts University) and presented to the market by Nanoscience Solutions Inc., Ringing Mode utilizes the same sub-resonant peak force feedback signal as PeakForce QNM to take advantage of the precise force control and separately measured adhesion but focuses on the ringing portion of the signal resulting from surface detachment of the AFM cantilever to extract key information regarding adhesion and unbinding events. Click here to read more about Ringing Mode on the Nanoscience Solutions, Inc. site.

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