AFM with Suppressed Parasitic Signals

A method for determining information about a sample based on a lateral signal, comprising:

• varying a distance between the sample and a probe tip along a direction approximately perpendicular to a plane of the sample in an intermittent contact mode, wherein the probe tip is included in a cantilever and is offset along a lateral direction from a longitudinal axis of torsion of the cantilever, and wherein the variation of the distance has a lowest fundamental frequency that is significantly less than a lowest flexural resonance frequency of the cantilever;
• measuring the lateral signal associated with a torsional mode of the cantilever during atomic force microscopy (AFM) measurements, the lateral signal corresponding to a force between the sample and the probe tip;
• maintaining, using a feedback circuit in the AFM and relative to a threshold value, one of:
• the force between the sample and the probe tip, and a deflection of the cantilever corresponding to the force, wherein maintaining the force involves changing the distance between the sample and the probe tip along the direction, and
• determining the information about the sample based on the lateral signal.

A non-transitory computer-readable storage medium for use in conjunction with an atomic force microscope (AFM), the computer-readable storage medium configured to store a program module that, when executed by the AFM, causes the AFM to:

• vary a distance between a sample and a probe tip along a direction approximately perpendicular to a plane of the sample in an intermittent contact mode, wherein the probe tip is included in a cantilever and is offset along a lateral direction from a longitudinal axis of torsion of the cantilever, and wherein the variation of the distance has a fundamental frequency that is significantly less than a lowest flexural resonance frequency of the cantilever;
• measure a lateral signal associated with a torsional mode of the cantilever during atomic force microscopy (AFM) measurements, the lateral signal corresponding to a force between the sample and the probe tip;
• maintain, using a feedback circuit in the AFM and relative to a threshold value, one of:
• the force between the sample and the probe tip, and a deflection of the cantilever corresponding to the force, wherein maintaining the force involves changing the distance between the sample and the probe tip along the direction, and
• determine information about the sample based on the lateral signal.

An atomic force microscope (AFM), comprising:

• a sample stage configured to hold a sample;
• a cantilever with a probe tip, the probe tip being offset along a lateral direction from a longitudinal axis of torsion of the cantilever;
• an actuator, coupled to at least one of the sample stage and the cantilever, configured vary a distance between the sample and the probe tip along a direction approximately perpendicular to a plane of the sample stage in an intermittent contact mode;
• a measurement circuit configured to measure a lateral signal associated with a torsional mode of the cantilever during the AFM measurements, and configured to measure a vertical signal associated with relative displacement, along the direction, of the probe tip and the sample, wherein the lateral signal corresponding to a force between the sample and the probe tip, and wherein, during the AFM measurements, the variation of the distance has a fundamental frequency that is significantly less than a lowest flexural resonance frequency of the cantilever;
• and
• wherein the AFM is configured to determine information about the sample based on the lateral signal and the vertical signal.

A method for determining information about a sample, comprising:

• varying a distance between the sample and a probe tip along a direction approximately perpendicular to a plane of the sample in an intermittent contact mode, wherein the probe tip is included in a cantilever and is offset along a lateral direction from a longitudinal axis of torsion of the cantilever, and wherein the variation of the distance has a fundamental frequency that is significantly less than a lowest flexural resonance frequency of the cantilever;
• measuring a lateral signal associated with a torsional mode of the cantilever during atomic force microscopy (AFM) measurements and measuring a vertical signal associated with relative displacement, along the direction, of the probe tip and the sample, wherein the lateral signal corresponding to a force between the sample and the probe tip;
• and
• determining the information about the sample based on the lateral signal and the vertical signal.

A non-transitory computer-readable storage medium for use in conjunction with an atomic force microscope (AFM), the computer-readable storage medium configured to store a program module that, when executed by the AFM, causes the AFM to:

• vary a distance between a sample and a probe tip along a direction approximately perpendicular to a plane of the sample in an intermittent contact mode, wherein the probe tip is included in a cantilever and is offset along a lateral direction from a longitudinal axis of torsion of the cantilever, and wherein the variation of the distance has a fundamental frequency that is significantly less than a lowest flexural resonance frequency of the cantilever;
• measure a lateral signal associated with a torsional mode of the cantilever during atomic force microscopy (AFM) measurements and measure a vertical signal associated with relative displacement, along the direction, of the probe tip and the sample, wherein the lateral signal corresponding to a force between the sample and the probe tip;
• and
• determine information about the sample based on the lateral signal and the vertical signal.