Cantilever for atomic force microscopy
A cantilever system for use in an atomic force microscope (AFM) is disclosed. The cantilever system comprises a base cantilever portion and a paddle connected to the base cantilever portion with one end free to move relative to the base cantilever portion. The base cantilever portion has an effective bending stiffness, k 1 , and the paddle has an effective bending stiffness, k 2 . The ratio of the effective bending stiffness, k 1 , to the bending stiffness, k 2 , is at least greater than 4. Such a cantilever system provides a stable, i.e., invariant contact resonant frequency, independent of the changes in the local contact stiffness.
1. A device for sensing a force, comprising:
a cantilever having:
a base cantilever portion with a first end and a second end, the first end of the base cantilever portion having a protruding tip, the second end of the base cantilever portion supporting the base cantilever portion, and
a paddle with a first end and a second end, the first end of the paddle being connected to the base cantilever portion, the second end of the paddle being free to move relative to the base cantilever portion;
a generator configured for providing an input signal to a sample surface; and
a detector configured for measuring a response signal, wherein the response signal represents a deflection of the cantilever in response to a physical change of the sample surface responsive to the input signal;
wherein the base cantilever portion has an effective bending stiffness, k 1 , and the paddle has an effective bending stiffness, k 2 , a ratio of the effective bending stiffness, k 1 , to the effective bending stiffness, k 2 , is at least 4, wherein the response signal exhibits an invariant contact resonance frequency.
2. The device of claim 1 wherein the ratio of the effective bending stiffness, k 1 , to the effective bending stiffness, k 2 , is at least equal to or greater than 10.
3. The device of claim 1 wherein the base cantilever portion has a thickness, t c , and the paddle has a thickness, t p , wherein the thickness t p is no greater than one half of t c .
4. The device of claim 3 wherein the thickness t p is no greater than one third of t c .
5. The device of claim 1 wherein the response signal exhibits the invariant contact resonance frequency for different topographical features and/or material features on the sample surface.
6. The device of claim 1 wherein the detector is further configured to analyze the response signal to determine a topographical response and a functional response, wherein topographical and functional information in the response signal are decoupled.
7. The device of claim 1 wherein the input signal is an electrical signal.
8. The device of claim 1 wherein the input signal is optical or thermal radiation.
9. The device of claim 1 wherein the base cantilever portion is a V-shaped base cantilever portion.