Multiple frequency atomic force microscopy

Claim 1

A method of operating an atomic force microscope, comprising: exciting a probe tip of a cantilever at or near a resonant frequency of the cantilever which forms a first eigenmode, while keeping the tip sufficiently far from a sample having a surface that said cantilever oscillates at a free amplitude A 10 unaffected by the proximity of the cantilever to the sample surface and without making contact with the sample surface; changing the relative distance in a Z direction between a base of the cantilever and the sample surface to an amount where a detected amplitude A 1 of the first eigenmode of the cantilever is affected by the proximity of the sample surface to the tip of the cantilever, without the tip of the cantilever making contact with the sample surface; scanning the sample by creating relative movement between the tip of the cantilever and the sample surface, while using a feedback loop to control the distance between the base of the cantilever and the sample surface so that the amplitude A 1 of the first eigenmode of the cantilever is maintained at an essentially constant value; exciting the probe tip of the cantilever at or near a second eigenmode of the cantilever, where said second eigenmode of the cantilever is a different eigenmode than said first eigenmode, said scanning being at an amplitude A 2 while keeping the first eigenmode drive and feedback loop with the same values and without using said second eigenmode in said feedback loop; adjusting the amplitude A 2 of the second eigenmode of the cantilever until said amplitude A 2 indicates the second eigenmode is interacting with the sample surface with predominantly repulsive forces; varying the amplitude A 2 of the second eigenmode of the cantilever over a range of values while not including said amplitude A 2 as an input to the feedback loop; and measuring the amplitude and phase of the first and second eigenmodes of the cantilever as measured characteristics of the sample.

Claim 2

A method of operating an atomic force microscope, comprising: exciting a probe tip of a cantilever at or near a resonant frequency of the cantilever which forms a first eigenmode, while keeping the tip sufficiently far from a sample having a surface that said cantilever oscillates at a free amplitude A 10 unaffected by the proximity of the cantilever to the sample surface and without making contact with the sample surface; changing the relative distance in a Z direction between a base of the cantilever and the sample surface to an amount where a detected amplitude A 1 of the first eigenmode of the cantilever is affected by the proximity of the sample surface to the tip of the cantilever, without the tip of the cantilever making contact with the sample surface; scanning the sample by creating relative movement between the tip of the cantilever and the sample surface, while using a feedback loop to control the distance between the base of the cantilever and the sample surface so that the amplitude A 1 of the first eigenmode of the cantilever is maintained at an essentially constant value; exciting the probe tip of the cantilever at or near a second eigenmode of the cantilever, where said second eigenmode of the cantilever is a different eigenmode than said first eigenmode, said scanning being at an amplitude A 2 while keeping the first eigenmode drive and feedback loop with the same values and without using said second eigenmode in said feedback loop; adjusting the amplitude A 2 of the second eigenmode of the cantilever until said amplitude A 2 indicates the second eigenmode is interacting with the sample surface with predominantly repulsive forces; varying the amplitude A 2 of the second eigenmode of the cantilever over a range of values while not including said amplitude A 2 as an input to the feedback loop; and measuring the amplitude and phase of the first and second eigenmodes of the cantilever as measured characteristics of the sample.

Claim 5

A method of operating an atomic force microscope comprising: generating an oscillatory drive signal for a cantilever, the drive signal including a first frequency component and a different second frequency component, both of said first and second frequency components being resonant modes of a same physical portion of the cantilever; applying the oscillatory drive signal to a first end of the cantilever opposite an interaction end of the cantilever, wherein the interaction end of the cantilever includes a probe tip; positioning the cantilever proximate to a sample surface so that the probe tip interacts with the surface of the sample; detecting information indicative of the amplitude of oscillation of the probe tip; analyzing the information indicative of the amplitude of oscillation of the probe tip to determine a first amplitude component for the first frequency and a second amplitude component for the second frequency; and using a feedback loop to control the cantilever based on the first amplitude component only and allowing the amplitude of oscillation of the second amplitude component to vary, wherein said feedback loop uses only said first amplitude component, and not said second amplitude component to control said cantilever.

Claim 6

A method of operating an atomic force microscope comprising: generating an oscillatory drive signal for a cantilever, the drive signal including a first frequency component and a different second frequency component, both of said first and second frequency components being resonant modes of a same physical portion of the cantilever; applying the oscillatory drive signal to a first end of the cantilever opposite an interaction end of the cantilever, wherein the interaction end of the cantilever includes a probe tip; positioning the cantilever proximate to a sample surface so that the probe tip interacts with the surface of the sample; detecting information indicative of the amplitude of oscillation of the probe tip; analyzing the information indicative of the amplitude of oscillation of the probe tip to determine a first amplitude component for the first frequency and a second amplitude component for the second frequency; and using a feedback loop to control the cantilever based on the first amplitude component only and allowing the amplitude of oscillation of the second amplitude component to vary, wherein said feedback loop uses only said first amplitude component, and not said second amplitude component to control said cantilever.

Claim 28

A method of operating an atomic force microscope, comprising: moving a probe tip of a cantilever at a first frequency near a resonant frequency of the cantilever while keeping the tip sufficiently distant from a sample having a surface that it said cantilever oscillates at the a first free amplitude without making contact with the sample surface; moving an item to reduce a relative distance in a Z direction between a base of the cantilever and the sample surface in a way such that a detected amplitude of a first vibrational mode of the cantilever that is a first mode associated with said first frequency, is affected by a proximity of the sample surface to the tip of the cantilever without the probe tip of the cantilever making contact with the sample surface; scanning the sample by creating relative movement between the probe tip of the cantilever and the sample surface, while using a feedback loop to control the distance between the base of the cantilever and the sample surface so that the detected amplitude A 1 of the first vibrational mode of the cantilever is controlled to be a substantially constant value; exciting the probe tip of the cantilever at or near a second vibrational mode of the cantilever at second amplitude, where said second vibrational mode is a mode that is a harmonic mode above a fundamental resonance frequency of the cantilever, while keeping the first vibrational mode drive and feedback loop with the same values; monitoring said first second amplitudes to interact with the sample surface with predominantly repulsive forces; and not including said second amplitude as an input to the feedback loop, wherein one of said vibrational modes is attractive and another of said vibrational modes is repulsive.

Claim 29

A method of operating an atomic force microscope, comprising: moving a probe tip of a cantilever at a first frequency near a resonant frequency of the cantilever while keeping the tip sufficiently distant from a sample having a surface that it said cantilever oscillates at the a first free amplitude without making contact with the sample surface; moving an item to reduce a relative distance in a Z direction between a base of the cantilever and the sample surface in a way such that a detected amplitude of a first vibrational mode of the cantilever that is a first mode associated with said first frequency, is affected by a proximity of the sample surface to the tip of the cantilever without the probe tip of the cantilever making contact with the sample surface; scanning the sample by creating relative movement between the probe tip of the cantilever and the sample surface, while using a feedback loop to control the distance between the base of the cantilever and the sample surface so that the detected amplitude A 1 of the first vibrational mode of the cantilever is controlled to be a substantially constant value; exciting the probe tip of the cantilever at or near a second vibrational mode of the cantilever at second amplitude, where said second vibrational mode is a mode that is a harmonic mode above a fundamental resonance frequency of the cantilever, while keeping the first vibrational mode drive and feedback loop with the same values; monitoring said first second amplitudes to interact with the sample surface with predominantly repulsive forces; and not including said second amplitude as an input to the feedback loop, wherein one of said vibrational modes is attractive and another of said vibrational modes is repulsive.